Autophagy, a dynamic intracellular degradation system, is critical for cellular renovation and maintaining equilibrium. By eliminating damaged components and recycling essential molecules, autophagy safeguards cellular integrity and function. The versatility of the autophagy process across various biological functions enable cells to adapt and maintain homeostasis under unfavourable conditions. Disruptions in autophagy can shift a cell from a healthy state to a disease state or, conversely, support a return to health. This review delves into the multifaceted role of autophagy during aging and age-related diseases such as cancer, highlighting its significance as a unifying target with promising therapeutic implications. Cancer development is a dynamic process characterized by the acquisition of diverse survival capabilities for proliferating at different stages. This progression unfolds over time, with cancer cells exploiting autophagy to overcome encountered stress conditions during tumor development. Notably, there are several common pathways that utilize the autophagy process during aging and cancer development. This highlights the importance of autophagy as a crucial therapeutic target, holding the potential to not only impede the growth of tumor but also enhance the patient's longevity. This review aims to simplify the intricate relationship between cancer and aging, with a particular focus on the role of autophagy.

Sirtuin 6 (SIRT6), a member of the class III histone deacetylase (HDAC) family, is crucial for the maintenance of general health and is associated with increased life expectancy and resistance to age-related diseases such as cancer and metabolic disorders. A comparative analysis of the SIRT6 gene in Ashkenazi Jewish (AJ) centenarians and noncentenarian controls found a distinct allele, centSIRT6, enriched in the centenarian group. This allele features 2 linked substitutions, N308K and A313S, and exhibits enhanced functions, including more efficient suppression of LINE1 retrotransposons, improved repair of DNA double-strand breaks, and increased efficiency in cancer cell killing. Notably, centSIRT6 shows lower deacetylase activity but higher mono-adenosine diphosphate (ADP) ribosyl transferase activity compared with the wild-type enzyme. This study used several bioinformatics tools to explore the structural changes caused by the N308K and A313S substitutions in centSIRT6 and to elucidate how these alterations contribute to changes in the enzymatic activities of SIRT6. The results indicate that these mutations reduce the structural flexibility of centSIRT6, thus weakening its interactions with acetyl-lysine but strengthening its interactions with ADP-ribose. This research provides useful information for future experimental studies to further investigate the molecular mechanisms of centSIRT6.

Senescence is a cellular state induced by various stressors or extracellular signals, but a universal pathway that triggers this process irrespective of the initial stressor has yet to be identified. Recent data indicate that chromatin opening, particularly in the noncoding genome, is a hallmark of cellular senescence. We propose a model in which this increased chromatin accessibility mediated by transcription factors downstream of the senescence-inducing stressors acts as a decisive factor to commit cells toward the senescence fate. Engagement toward senescence is then determined by the balance between mechanisms that increase or decrease chromatin accessibility and can be influenced by modulating the activity of specific histone-modifying complexes. Traits of senescent cells, such as increased nuclear and nucleolar size, the secretion of pro-inflammatory cytokines, reduced rRNA biogenesis, telomere dysfunction, expression of retrotransposons and endogenous retroviruses, as well as DNA damage, can all be attributed to increased chromatin accessibility. This concept suggests potential targets to tilt the balance toward the senescence response in the context of future therapies against cancer and age-related diseases.

Silent information regulator 5 (SIRT5) is the fifth member of the sirtuin family, which is mainly expressed in mitochondrial matrix. SIRT5 plays a key role in metabolism and antioxidant responses, and is an important regulator for maintaining intracellular homeostasis. Given its involvement in multiple cellular processes, dysregulation of SIRT5 activity is associated with a variety of diseases. This review explores the structural characteristics of SIRT5 that influence its substrate specificity, highlights recent research advances, and summarizes its four key enzymatic activities along with their corresponding substrates in disease contexts. We also discuss the natural products that modulate SIRT5 activity and identify potential targets of SIRT5 through virtual docking, which may provide new therapeutic avenues. Although the mechanism of SIRT5 in diseases needs to be further elucidated and deglutathionylation activities are still at an early stage, targeting SIRT5 and its substrates holds significant promise for the development of novel therapeutics.

Cellular senescence is characterized by proliferation arrest and a senescence-associated secretory phenotype (SASP), that plays a role in aging and the progression of various age-related diseases. Although various metabolic alterations have been reported, no consensus exists regarding mitochondrial bioenergetics. Here we compared mitochondrial metabolism of human fibroblasts after inducing senescence with different stimuli: the oxidant hydrogen peroxide (H2O2), the genotoxic doxorubicin, serial passage, or expression of the H-RASG12V oncogene (RAS). In senescence induced by H2O2, doxorubicin or serial passage a decrease in respiratory control ratio (RCR) and coupling efficiency was noted, in relation to control cells. On the contrary, oncogene-induced senescent cells had an overall increase in respiration rates, RCR, spare respiratory capacity and coupling efficiency. In oncogene-induced senescence (OIS) the increase in respiration rates was accompanied by an increase in fatty acid catabolism, AMPK activation, and a persistent DNA damage response (DDR), that were not present in senescent cells induced by either H2O2 or doxorubicin. Inhibition of AMPK reduced mitochondrial oxygen consumption and secretion of proinflammatory cytokines in OIS. Assessment of enzymes involved in acetyl-CoA metabolism in OIS showed a 3- to 7.5-fold increase in pyruvate dehydrogenase complex (PDH), a 40% inhibition of mitochondrial aconitase, increased phosphorylation and activation of ATP-citrate lyase (ACLY), and inhibition of acetyl-CoA carboxylase (ACC). There was also a significant increase in expression and nuclear levels of the deacetylase sirtuin 6 (SIRT6). These changes can influence the sub-cellular distribution of acetyl-CoA and modulate protein acetylation reactions in the cytoplasm and nuclei. In fact, ACLY inhibition reduced histone 3 acetylation (H3K9Ac) in OIS and secretion of SASP components. In summary, our data show marked heterogeneity in mitochondrial energy metabolism of senescent cells, depending on the inducing stimulus, reveal new metabolic features of oncogene-induced senescent cells and identify AMPK and ACLY as potential targets for SASP modulation.

Sirtuins are the NAD+-dependent class III lysine deacylases (KDACs). Members of this family have been linked to longevity and a wide array of different diseases, motivating the pursuit of sirtuin modulator compounds. Sirtuin 6 (SIRT6) is a primarily nuclear KDAC that deacetylates histones to facilitate gene repression. In addition to this canonical posttranslational modification "eraser" function, SIRT6 can use NAD+ instead to "write" mono-ADP-ribosylation (mARylation) on target proteins. This enzymatic function has been primarily associated with SIRT6's role in the DNA damage response. This modification has been challenging to study because it is not clear under what precise cellular contexts it occurs, only a few substrates are known, and potential interference from other ADP-ribosyltransferases in cells, among other reasons. In this work, we used commercially available ADP-ribosylation detection reagents to investigate the mARylation activity of SIRT6 in a reconstituted system. We observed that SIRT6 is activated in its mARylation activity by binding to dsDNA ends. We further identified a surprising target motif within biochemical substrates of SIRT6, polyhistidine repeat tracts, which are present in several previously identified SIRT6 mARylation substrates. This work provides important context for SIRT6 mARylation activity, in contrast to its KDAC activity, and generates a list of new potential SIRT6 mARylation substrates based on the polyhistidine motif.

Cisplatin is a widely used DNA-targeting anticancer drug. Histone deacetylase inhibitors (HDACi) cause histone hyperacetylation, changing chromatin structure and accessibility of genomic DNA by the genotoxic drug. As a consequence, HDACi could promote cisplatin cytotoxicity. Hence, the underlying mechanisms by which HDACi alter the action pathways of cisplatin to promote its anticancer activity have attracted increasing attention during the past decades. It has been commonly accepted that HDACi elevate the acetylation level of histones to release genomic DNA to cisplatin attack, increasing the level of cisplatin-induced DNA lesions to promote cisplatin cytotoxicity. However, how the HDACi-enhanced cisplatin lesion on DNA impacts the downstream biological processes, and whether the promotion of HDACi to cisplatin activity is attributed to their inherent anticancer activity or to their induced elevation of histone acetylation, have been in debate. Several studies showed that HDACi-enhanced DNA lesion could promote cisplatin-induced apoptosis, cell cycle arrest, and reactive oxygen species (ROS) generation, subsequently promoting cisplatin efficiency. In contrast, HDACi-induced elimination of ROS and inhibition of ferroptosis were thought to be the main ways by which HDACi protect kidneys from acute injury caused by cisplatin. Based on our recent research, we herein review and discuss the advances in research on the mechanisms of HDACi-induced enhancement in cisplatin cytotoxicity. Given that histone acetyltransferase (HAT) inhibitors also show an effect enhancing cisplatin cytotoxicity, we will discuss the diverse roles of histone acetylation in cancer therapy in addition to the synergistic anticancer effect and potential of HDACi with genotoxic drugs and radiotherapy.

Brown and beige adipocytes dissipate energy to generate heat through uncoupled respiration, and the hormone norepinephrine plays an important role in stimulating brown fat thermogenesis and beige adipocyte development in white adipose depots. Increasing energy expenditure by promoting the function and development of brown and beige fat is a potential approach to treat obesity and diabetes. Here, we investigated the effects of macrophage sirtuin 6 (SIRT6) on the regulation of the norepinephrine content of brown adipose tissue (BAT) and on obesity in mice. Myeloid SIRT6 deficiency impaired the thermogenic function of BAT, thereby decreasing core body temperatures because of reduced norepinephrine concentrations in BAT and subsequently leading to cold sensitivity. In addition, the oxygen consumption rate was reduced, resulting in severe insulin resistance and obesity. Furthermore, macrophage SIRT6 deficiency inhibited BAT thermogenesis after cold exposure or norepinephrine treatment and cold exposure-induced increases in markers of lipid metabolism and thermogenesis in white adipose tissue. Myeloid-specific SIRT6 deficiency promoted H3K9 acetylation in the promoter regions and the expression of genes encoding the norepinephrine-degrading enzyme MAOA and the norepinephrine transporter SLC6A2 in macrophages in BAT, leading to norepinephrine degradation and obesity. Our findings indicate that SIRT6 in macrophages is essential for maintaining norepinephrine concentrations in BAT in mice.

The sirtuin family comprises seven NAD+-dependent enzymes which catalyze protein lysine deacylation and mono ADP-ribosylation. Sirtuins act as central regulators of genomic stability and gene expression and control key processes, including energetic metabolism, cell cycle, differentiation, apoptosis, and aging. As a result, all sirtuins play critical roles in cellular homeostasis and organism wellness, and their dysregulation has been linked to metabolic, cardiovascular, and neurological diseases. Furthermore, sirtuins have shown dichotomous roles in cancer, acting as context-dependent tumor suppressors or promoters. Given their central role in different cellular processes, sirtuins have attracted increasing research interest aimed at developing both activators and inhibitors. Indeed, sirtuin modulation may have therapeutic effects in many age-related diseases, including diabetes, cardiovascular and neurodegenerative disorders, and cancer. Moreover, isoform selective modulators may increase our knowledge of sirtuin biology and aid to develop better therapies. Through this review, we provide critical insights into sirtuin pharmacology and illustrate their enzymatic activities and biological functions. Furthermore, we outline the most relevant sirtuin modulators in terms of their modes of action, structure-activity relationships, pharmacological effects, and clinical applications.

Genomes are blueprints of life essential for an organism's survival, propagation, and evolutionary adaptation. Eukaryotic genomes comprise of DNA, core histones, and several other nonhistone proteins, packaged into chromatin in the tiny confines of nucleus. Chromatin structural organization restricts transcription factors to access DNA, permitting binding only after specific chromatin remodeling events. The fundamental processes in living cells, including transcription, replication, repair, and recombination, are thus regulated by chromatin structure through ATP-dependent remodeling, histone variant incorporation, and various covalent histone modifications including phosphorylation, acetylation, and ubiquitination. These modifications, particularly involving histone variant H2AX, furthermore play crucial roles in DNA damage responses by enabling repair protein's access to damaged DNA. Chromatin also stabilizes the genome by regulating DNA repair mechanisms while suppressing damage from endogenous and exogenous sources. Environmental factors such as ionizing radiations induce DNA damage, and if repair is compromised, can lead to chromosomal abnormalities and gene amplifications as observed in several tumor types. Consequently, chromatin architecture controls the genome fidelity and activity: it orchestrates correct gene expression, genomic integrity, DNA repair, transcription, replication, and recombination. This review considers connecting chromatin organization to functional outcomes impacting transcription, DNA repair and genomic integrity as an emerging grand challenge for predictive molecular cell biology.

Cardiovascular disease (CVD) is the leading cause of mortality and morbidity, accounting for major public health concerns worldwide. CVD poses an immense burden on the global healthcare system and economy. Ischemic heart disease, stroke, heart failure, atherosclerosis, and hypertension are the major diseases belonging to CVDs and ischemic heart diseases and stroke contribute to most CVD-induced deaths. Previously published review articles focused on the role of SIRT6 in CVDs but did not focus on the important role of SIRT6 in modulating the signaling pathways involved in CVDs and targeting them to treat CVDs. Thus, this review aims to identify and delineate the major signaling pathways that are involved in CVDs and whether SIRT6 can modulate those pathways to improve and treat CVDs. Alongside possible applications of small molecule modulators of SIRT6 in cardiovascular disease treatment have been comprehensively analyzed.

Grap2 and CyclinD1 interacting protein (GCIP) has been suggested to function as a tumor suppressor and acts as a transcriptional regulator that negatively controls cancer cell growth, invasion, and migration. Knockdown of GCIP reportedly enhances cancer cell migration and invasion, but no previous study has examined the mechanism(s) by which GCIP suppresses migration/invasion in cancer cells. Here, we report that cDNA microarray-based expression profiling of A549 cells without and with knockdown of GCIP reveals that the expression levels of ITGAV and ICAM-1 are negatively regulated by GCIP. In vitro co-immunoprecipitation and in vivo proximity ligation assays reveal that GCIP interacts with c-Myc. Sequence analyses reveal the presence of two c-Myc regulatory motifs (E-boxes) within the ITGAV promoter. Luciferase reporter and ChIP assays indicate that GCIP represses ITGAV transcription by interacting with c-Myc on the E-box binding sites of the ITGAV promoter region. Furthermore, GCIP interacts with SIRT6 in vitro and in vivo and cooperates with SIRT6, thereby linking its activity, to negatively regulate transcription at the E-box by modulating c-Myc transcription ability. Taken together, these findings contribute to our understanding of GCIP in tumorigenesis and identify a previously unrecognized function of GCIP: It can interact with c-Myc and SIRT6 at E-box binding sites of the ITGAV promoter region. Our data collectively reveal a regulatory network involving GCIP, SIRT6, c-Myc, and ITGAV, and suggest that the SIRT6-GCIP complex negatively regulates the oncogenic function of c-Myc in cell proliferation and migration.

Plp1-lineage Schwann cells (SCs) of peripheral nerve play a critical role in vascular remodeling and osteogenic differentiation during the early stage of bone healing, and the abnormal plasticity of SCs would jeopardize the bone regeneration. However, how Plp1-lineage cells respond to injury and initiate the vascularized osteogenesis remains incompletely understood. Here, by employing single-cell transcriptional profiling combined with lineage-specific tracing models, we uncover that Plp1-lineage cells undergoing injury-induced glia-to-MSCs transition contributed to osteogenesis and revascularization in the initial stage of bone injury. Importantly, our data demonstrated that the Sonic hedgehog (Shh) signaling was responsible for the transition process initiation, which was strongly activated by c-Jun/SIRT6/BAF170 complex-driven Shh enhancers. Collectively, these findings depict an injury-specific niche signal-mediated Plp1-lineage cells transition towards Gli1+ MSCs and may be instructive for approaches to promote bone regeneration during aging or other bone diseases.

The intricate mechanisms underlying transcription-dependent genome instability involve G-quadruplexes (G4) and R-loops. This perspective elucidates the potential link between these structures and genome instability in aging. The co-occurrence of G4 DNA and RNA-DNA hybrid structures (G-loop) underscores a complex interplay in genome regulation and instability. Here, we hypothesize that the age-related decline of sirtuin function leads to an increase in acetylated helicases that bind to G4 DNA and RNA-DNA hybrid structures, but are less efficient in resolving them. We propose that acetylated, less active, helicases induce persistent G-loop structures, promoting transcription-dependent genome instability in aging.

Lithocholic acid (LCA) is accumulated in mammals during calorie restriction and it can activate AMP-activated protein kinase (AMPK) to slow down ageing1. However, the molecular details of how LCA activates AMPK and induces these biological effects are unclear. Here we show that LCA enhances the activity of sirtuins to deacetylate and subsequently inhibit vacuolar H+-ATPase (v-ATPase), which leads to AMPK activation through the lysosomal glucose-sensing pathway. Proteomics analyses of proteins that co-immunoprecipitated with sirtuin 1 (SIRT1) identified TUB-like protein 3 (TULP3), a sirtuin-interacting protein2, as a LCA receptor. In detail, LCA-bound TULP3 allosterically activates sirtuins, which then deacetylate the V1E1 subunit of v-ATPase on residues K52, K99 and K191. Muscle-specific expression of a V1E1 mutant (3KR), which mimics the deacetylated state, strongly activates AMPK and rejuvenates muscles in aged mice. In nematodes and flies, LCA depends on the TULP3 homologues tub-1 and ktub, respectively, to activate AMPK and extend lifespan and healthspan. Our study demonstrates that activation of the TULP3-sirtuin-v-ATPase-AMPK pathway by LCA reproduces the benefits of calorie restriction.

Mesenchymal stem/stromal cells (MSCs) are involved in the maintenance and regeneration of a large variety of tissues due to their stemness and multi-lineage differentiation capability. Harnessing these advantageous features, a flurry of clinical trials have focused on MSCs to treat different pathologies, but only few protocols have received regulatory approval so far. Among the various causes hindering MSCs' efficacy is the emergence of cellular senescence, which has been correlated with specific characteristics, such as morphological and epigenetic alterations, DNA damage, ROS production, mitochondrial dysfunction, telomere shortening, non-coding RNAs, loss of proteostasis, and a peculiar senescence-associated secretory phenotype. Several strategies have been investigated for delaying or even hopefully reverting the onset of senescence, as assessed by the senescent phenotype of MSCs. Here, the authors reviewed the most updated literature on the potential causes of senescence, with a particular emphasis on the current and future therapeutic approaches aimed at reverting senescence and/or extending the functional lifespan of stem cells.

Alzheimer's disease (AD) is an aging-related neurodegenerative disorder that results in progressively impaired memory and is often associated with amyloid plaques. Previous studies implicate the deacetylases SIRT1 and SIRT2 in regulating the processing of amyloid precursor protein (APP). Here, we investigated whether APP is regulated by the related deacetylase SIRT6, which shows aging-associated decreases in activity. We found that the abundance of SIRT6 was reduced in the cortex and hippocampus of aged and AD model mice and negatively correlated with that of APP. In mouse hippocampal neurons and transfected human cells, SIRT6 interacted with and deacetylated APP at three consecutive Lys residues (Lys649, Lys650, and Lys651). This deacetylation, in turn, increased the ubiquitylation of APP, leading to its proteasomal degradation. SIRT6 abundance in neurons was reduced by oxidative stress and DNA damage, both of which are implicated in neurodegenerative pathology. Systemic pharmacological activation of SIRT6 ameliorated both amyloid pathology and cognitive deficits in APP/PS1 mice, a mouse model of AD. The findings demonstrate that the activity of SIRT6 destabilizes APP and suggest that activating SIRT6 has therapeutic potential to reduce amyloid-associated pathology in patients with AD.

Cardiomyopathy constitutes a global health burden. It refers to myocardial injury that causes alterations in cardiac structure and function, ultimately leading to heart failure. Currently, there is no definitive treatment for cardiomyopathy. This is because existing treatments primarily focus on drug interventions to attenuate symptoms rather than addressing the underlying causes of the disease. Notably, the cardiomyocyte loss is one of the key risk factors for cardiomyopathy. This loss can occur through various mechanisms such as metabolic disturbances, cardiac stress (e.g., oxidative stress), apoptosis as well as cell death resulting from disorders in autophagic flux, etc. Sirtuins (SIRTs) are categorized as class III histone deacetylases, with their enzyme activity primarily reliant on the substrate nicotinamide adenine dinucleotide (NAD (+)). Among them, Sirtuin 1 (SIRT1) is the most intensively studied in the cardiovascular system. Forkhead O transcription factors (FOXOs) are the downstream effectors of SIRT1. Several reports have shown that SIRT1 can form a signaling pathway with FOXOs in myocardial tissue, and this pathway plays a key regulatory role in cell loss. Thus, this review describes the basic mechanism of SIRT1-FOXOs in inhibiting cardiomyocyte loss and its favorable role in cardiomyopathy. Additionally, we summarized the SIRT1-FOXOs related regulation factor and prospects the SIRT1-FOXOs potential clinical application, which provide reference for the development of cardiomyopathy treatment.

Extracellular vesicles, also known as exosomes, influence numerous cellular functions by regulating different signaling pathways. However, their role in animal reproduction remains understudied. This study aimed to evaluate the effects of porcine follicular fluid-derived exosomes (pff-Exos) on porcine oocyte in vitro maturation and parthenogenetic embryo development. We obtained pff-Exos through mixed-method ultracentrifugation and size-exclusion chromatography. Transmission electron microscopy revealed an increase in the expression of exosome markers in the first four of thirteen fractions. The number of pff-Exo was 2.2 × 106 particles per microliter. The highest maturation rate of porcine oocytes treated with pff-Exo was observed with 1.1 × 107 particles of pff-Exo in the absence of porcine follicular fluid (pFF) culture conditions. Moreover, increased expression of Gdf9 and Bmp15 was observed. The developmental rate was the highest upon treatment with 1.1 × 107 particles of pff-Exo, which increased the total cell number in blastocysts. Embryonic development to the 2-cell stage was similar between the control and pff-Exo groups; however, development to the 4-cell stage and blastocyst was significantly increased in the pff-Exo group (61.6 ± 6.08 % and 29.72 ± 1.41 %, respectively; P < 0.05) compared with that in the control group (42.0 ± 5.19 % and 18.14 ± 1.78 %, respectively). The expression levels of Oct4, Sox2, Bcl2, Elf4, and Gcn5 significantly increased at the pff-Exo 2-cell stage, whereas those of Bax, Hdac1, Hdac6, and Sirt6 decreased. Specifically, the Oct4, Sox2, Elf4, Gcn5, and Hdac6 levels remained stable in pff-Exo 4-cell embryos, whereas those of p53 and Hat1 were reduced and increased, respectively. Treatment with pffExos significantly increased H3K9 and H3K14 acetylation levels. These results demonstrate that pff-Exo affects the in vitro maturation of porcine oocytes and early embryonic development by regulating gene expression.

Roles of the sirtuins in aging and longevity appear related to their evolutionarily conserved functions as retroviral-restriction factors. Retrotransposons also promote the aging process, which can be reversed by the inhibition of their activity. SIRT6 can functionally limit the mutation activity of LINE-1 (L1), a retrotransposon causing cancerogenesis-linked mutations accumulating during aging. Here, an overview of the molecular mechanisms of the controlling effects was created by the pathway enrichment and gene function prediction analysis of a protein interaction network of SIRT6 and L1 retrotransposon proteins L1 ORF1p, and L1 ORF2p. The L1-SIRT6 interaction network is enriched in pathways and nodes associated with RNA quality control, DNA damage response, tumor-related and retrotransposon activity-suppressing functions. The analysis also highlighted sumoylation, which controls protein-protein interactions, subcellular localization, and other post-translational modifications; DNA IR Damage and Cellular Response via ATR, and Hallmark Myc Targets V1, which scores are a measure of tumor aggressiveness. The protein node prioritization analysis emphasized the functions of tumor suppressors p53, PARP1, BRCA1, and BRCA2 having L1 retrotransposon limiting activity; tumor promoters EIF4A3, HNRNPA1, HNRNPH1, DDX5; and antiviral innate immunity regulators DDX39A and DDX23. The outline of the regulatory mechanisms involved in L1 retrotransposition with a focus on the prioritized nodes is here demonstrated in detail. Furthermore, a model establishing functional links between HIV infection, L1 retrotransposition, SIRT6, and cancer development is also presented. Finally, L1-SIRT6 subnetwork SIRT6-PARP1-BRCA1/BRCA2-TRIM28-PIN1-p53 was constructed, where all nodes possess L1 retrotransposon activity-limiting activity and together represent candidates for multitarget control.

The circadian clock is an autonomous timekeeping system evolved by organisms to adapt to external changes, regulating a variety of important physiological and behavioral processes. Recent studies have shown that the sirtuin family of histone deacetylases is involved in regulating the expression of clock genes and plays an important role in maintaining the normal rhythm of clock gene expression and behavior. Moreover, sirtuins are regulated directly or indirectly by the circadian clock system. The mutual regulation between the circadian clock and sirtuins is likely involved in a variety of signal transduction and metabolism processes. In this review, we discuss the molecular mechanisms and research progress on the intertwined relationship between the circadian clock and sirtuins, mainly in mammals, highlighting sirtuins as molecular links between metabolic control and circadian rhythms and offering our perspectives on future developments in the field.

Poly(ADP-ribose) polymerase 1 (PARP1) is an abundant nuclear protein involved in DNA repair, chromatin structure, and transcription. However, the regulation of its different functions remains poorly understood. Here, we report the role of PARP1 acetylation status in modulating its DNA repair and transactivation functions. We demonstrate that histone deacetylase 5 (HDAC5) determines PARP1 acetylation at Lys498 and Lys521 sites. HDAC5-mediated deacetylation at Lys498 site regulates PARP1 DNA damage response and facilitates efficient recruitment of DNA repair factors at damaged sites, thereby promoting cell survival. Additionally, HDAC5-mediated deacetylation at Lys521 site promotes PARP1 coactivator function, resulting in induction of proliferative and metabolic genes in an activating transcription factor 4-dependent manner. Thus, PARP1 induces metabolic adaptation to spur malignant phenotype. Our studies in mouse tumor models suggest that pharmacological inhibition of PARP1 enzymatic activity does not block tumor progression robustly as transactivation function remains unperturbed. These findings provide key mechanistic insights into PARP1 regulation and expand its role in tumor development.

SIRT6 owns versatile types of enzymatic activities as a multitasking protein, including ribosyltransferase and deacetylase. To investigate the epigenetic regulations of SIRT6 on MSC fate determination via histone deacetylation, we used allosteric small molecules specifically controlling its histone 3 deacetylation activities. Results showed that enhanced deacetylation of SIRT6 promoted the ossific lineage commitment of MSC and finally achieved anabolic effects on hard tissues. Mechanistically, H3K9ac and H3K56ac, governed by SIRT6, in MSC orchestrated the transcriptions of crucial metabolic genes, mediating MSC fate determination. Most importantly, our data evidenced that modulating the epigenetic regulations of SIRT6, specifically via enhancing its deacetylation of H3K9ac and H3K56ac, was a promising choice to treat bone loss diseases and promote dentin regeneration. In this study, we revealed the specific roles of SIRT6's histone modification in MSC fate determination. These findings endow us with insights on SIRT6 and the promising therapeutic choices through SIRT6's epigenetic functions for hard tissues regeneration.

SIRT6, an evolutionarily conserved histone deacetylase, has been identified as a novel direct downstream target of Akt/FoxO3a and a tumor suppressor in colon cancer in our previous research. Nevertheless, the precise mechanisms through which SIRT6 hinders tumor development remain unclear. To ascertain whether SIRT6 directly impacts Survivin transcription, a ChIP assay was conducted using an anti-SIRT6 antibody to isolate DNA. YM155 was synthesized to explore Survivin's role in mitochondrial apoptosis, autophagy and tumor progression. Our investigation into the regulation of Survivin involved real-time fluorescence imaging in living cells, real-time PCR, immunohistochemistry, flow cytometry, and xenograft mouse assays. In this current study, we delved into the role of SIRT6 in colon cancer and established that activated SIRT6 triggers mitochondrial apoptosis by reducing Survivin expression. Subsequent examinations revealed that SIRT6 directly binds to the Survivin promoter, impeding its transcription. Notably, direct inhibition of Survivin significantly impeded colon cancer proliferation by inducing mitochondrial apoptosis and autophagy both in vitro and in vivo. More interestingly, Survivin inhibition reactivated the Akt/FoxO3a pathway and elevated SIRT6 levels, establishing a positive feedback loop. Our results identify Survivin as a novel downstream transcriptional target of SIRT6 that fosters tumor growth and holds promise as a prospective target for colon cancer therapy.

Transposable elements (TEs) are essential components of eukaryotic genomes and subject to stringent regulatory mechanisms to avoid their potentially deleterious effects. However, numerous studies have verified the resurrection of TEs, particularly long interspersed nuclear element-1 (LINE-1), during preimplantation development, aging, cancer, and other age-related diseases. The LINE-1 family has also been implicated in several aging-related processes, including genomic instability, loss of heterochromatin, DNA methylation, and the senescence-associated secretory phenotype (SASP). Additionally, the role of the LINE-1 family in cancer development has also been substantiated. Research in this field has offered valuable insights into the functional mechanisms underlying LINE-1 activity, enhancing our understanding of aging regulation. This review provides a comprehensive summary of current findings on LINE-1 and their roles in aging and age-related diseases.

The aging process has been one of the most necessary research fields in the current century, and knowing different theories of aging and the role of different genetic, epigenetic, molecular, and environmental modulating factors in increasing the knowledge of aging mechanisms and developing appropriate diagnostic, therapeutic, and preventive ways would be helpful. One of the most conserved signs of aging is epigenetic changes, including DNA methylation, histone modifications, chromatin remodeling, noncoding RNAs, and extracellular RNAs. Numerous biological processes and hallmarks are vital in aging development, but epigenomic alterations are especially notable because of their importance in gene regulation and cellular identity. The mounting evidence points to a possible interaction between age-related epigenomic alterations and other aging hallmarks, like genome instability. To extend a healthy lifespan and possibly reverse some facets of aging and aging-related diseases, it will be crucial to comprehend global and locus-specific epigenomic modifications and recognize corresponding regulators of health and longevity. In the current study, we will aim to discuss the role of epigenomic mechanisms in aging and the most recent developments in epigenetic diagnostic biomarkers, which have the potential to focus efforts on reversing the destructive signs of aging and extending the lifespan.

Access to DNA is the first level of control in regulating gene transcription, a control that is also critical for maintaining DNA integrity. Cellular senescence is characterized by profound transcriptional rearrangements and accumulation of DNA lesions. Here, we discovered an epigenetic complex between HDAC4 and HDAC1/HDAC2 that is involved in the erase of H2BK120 acetylation. The HDAC4/HDAC1/HDAC2 complex modulates the efficiency of DNA repair by homologous recombination, through dynamic deacetylation of H2BK120. Deficiency of HDAC4 leads to accumulation of H2BK120ac, impaired recruitment of BRCA1 and CtIP to the site of lesions, accumulation of damaged DNA and senescence. In senescent cells this complex is disassembled because of increased proteasomal degradation of HDAC4. Forced expression of HDAC4 during RAS-induced senescence reduces the genomic spread of γH2AX. It also affects H2BK120ac levels, which are increased in DNA-damaged regions that accumulate during RAS-induced senescence. In summary, degradation of HDAC4 during senescence causes the accumulation of damaged DNA and contributes to the activation of the transcriptional program controlled by super-enhancers that maintains senescence.

This review focuses on the vital function that SIRT1 and other sirtuins play in promoting cellular senescence in vascular smooth muscle cells, which is a key element in the pathogenesis of vascular aging and associated cardiovascular diseases. Vascular aging is a gradual process caused by the accumulation of senescent cells, which results in increased vascular remodeling, stiffness, and diminished angiogenic ability. Such physiological alterations are characterized by a complex interplay of environmental and genetic variables, including oxidative stress and telomere attrition, which affect gene expression patterns and trigger cell growth arrest. SIRT1 has been highlighted for its potential to reduce cellular senescence through modulation of multiple signaling cascades, particularly the endothelial nitric oxide (eNOS)/NO signaling pathway. It also modulates cell cycle through p53 inactivation and suppresses NF-κB mediated expression of adhesive molecules at the vascular level. The study also examines the therapeutic potential of sirtuin modulation in vascular health, identifying SIRT1 and its sirtuin counterparts as potential targets for reducing vascular aging. This study sheds light on the molecular basis of vascular aging and the beneficial effects of sirtuins, paving the way for the development of tailored therapies aimed at enhancing vascular health and prolonging life.

Sirtuins are the NAD + -dependent class III lysine deacylases (KDACs). Members of this family have been linked to longevity and a wide array of different diseases, motivating the pursuit of sirtuin modulator compounds. Sirtuin 6 (SIRT6) is a primarily nuclear KDAC that deacetylates histones to facilitate gene repression. In addition to this canonical post-translational modification (PTM) "eraser" function, SIRT6 can use NAD + instead to "write" mono-ADP-ribosylation (mARylation) on target proteins. This enzymatic function has been primarily associated with SIRT6's role in the DNA damage response. This modification has been challenging to study because it is not clear under what precise cellular contexts it occurs, only a few substrates are known, and potential interference from other ADP-ribosyltransferases in cells, among other reasons. In this work, we used commercially available ADP-ribosylation detection reagents to investigate the mARylation activity of SIRT6 in a reconstituted system. We observed that SIRT6 is activated in its mARylation activity by binding to dsDNA ends. We further identified a surprising target motif within biochemical substrates of SIRT6, polyhistidine (polyHis) repeat tracts, that are present in several previously identified SIRT6 mARylation substrates and binding partners. This work provides important context for SIRT6 mARylation activity, in contrast to its KDAC activity, and proposes that SIRT6 is a histidine mARyltransferase enzyme.

Obesity is a major health burden. Preadipocytes proliferate and differentiate in mature adipocytes in the adipogenic process, which could be a potential therapeutic approach for obesity. Deficiency of SIRT6, a stress-responsive protein deacetylase and mono-ADP ribosyltransferase enzyme, blocks adipogenesis. Mutants of SIRT6 (N308K/A313S) were recently linked to the in the long lifespan Ashkenazi Jews. In this study, we aimed to clarify how these new centenarian-associated SIRT6 genetic variants affect adipogenesis at the transcriptional and epigenetic level.

We analyzed the role of SIRT6 wild-type (WT) or SIRT6 centenarian-associated mutant (N308K/A313S) overexpression in adipogenesis, by creating stably transduced preadipocyte cell lines using lentivirus on the 3T3-L1 model. Histone post-translational modifications (PTM: acetylation, methylation) and transcriptomic changes were analyzed by mass spectrometry (LC-MS/MS) and RNA-Seq, respectively, in 3T3-L1 adipocytes. In addition, the adipogenic process and related signaling pathways were investigated by bioinformatics and biochemical approaches.

Overexpression of centenarian-associated SIRT6 mutant increased adipogenic differentiation to a similar extent compared to the WT form. However, it triggered distinct histone PTM profiles in mature adipocytes, with significantly higher acetylation levels, and activated divergent transcriptional programs, including those dependent on signaling related to the sympathetic innervation and to PI3K pathway. 3T3-L1 mature adipocytes overexpressing SIRT6 N308K/A313S displayed increased insulin sensitivity in a neuropeptide Y (NPY)-dependent manner.

SIRT6 N308K/A313S overexpression in mature adipocytes ameliorated glucose sensitivity and impacted sympathetic innervation signaling. These findings highlight the importance of targeting SIRT6 enzymatic activities to regulate the co-morbidities associated with obesity.

Aging is an inevitable physiological process, often accompanied by age-related bone loss and subsequent bone-related diseases that pose serious health risks. Research on skeletal diseases caused by aging in humans is challenging due to lengthy study durations, difficulties in sampling, regional variability, and substantial investment. Consequently, mice are preferred for such studies due to their similar motor system structure and function to humans, ease of handling and care, low cost, and short generation time. In this review, we present a comprehensive overview of the characteristics, limitations, applicability, bone phenotypes, and treatment methods in naturally aging mice and prematurely aging mouse models (including SAMP6, POLG mutant, LMNA, SIRT6, ZMPSTE24, TFAM, ERCC1, WERNER, and KL/KL-deficient mice). We also summarize the molecular mechanisms of these aging mouse models, including cellular DNA damage response, senescence-related secretory phenotype, telomere shortening, oxidative stress, bone marrow mesenchymal stem cell (BMSC) abnormalities, and mitochondrial dysfunction. Overall, this review aims to enhance our understanding of the pathogenesis of aging-related bone diseases.

SIRT6 is of interest for its promising effect in the treatment of aging-related diseases. Studies have shown quercetin (QUE) and its derivatives have varying degrees of effect on the catalytic effect of SIRT6. In the research, the effect of QUE on the protein-substrate interaction in the SIRT6-mediated mono-ADP ribosylation system was investigated by conventional molecular dynamics (MD) simulations combined with MM/PBSA binding free energy calculations. The results show that QUE can bind stably to SIRT6 with the binding energy of -22.8 kcal/mol and further affect the atomic interaction between SIRT6 and NAD+ (or H3K9), resulting in an increased affinity between SIRT6-NAD+ and decreased SIRT6-H3K9 binding capacity. At the same time, the binding of QUE can also alter some structural characteristics of the protein, with large shifts occurring in the residue regions involving the N-terminal (residues 1-27), Rossmann fold regions (residues 55-92), and ZBD (residues 164-179). Thus, QUE shows great potential as a scaffold for the design of novel potent SIRT6 modulators.

In eukaryotes, the Suv39 family of proteins tri-methylate lysine 9 of histone H3 (H3K9me) to form constitutive heterochromatin. However, how Suv39 proteins are nucleated at heterochromatin is not fully described. In the fission yeast, current models posit that Argonaute1-associated small RNAs (sRNAs) nucleate the sole H3K9 methyltransferase, Clr4/SUV39H, to centromeres. Here, we show that in the absence of all sRNAs and H3K9me, the Mtl1 and Red1 core (MTREC)/PAXT complex nucleates Clr4/SUV39H at a heterochromatic long noncoding RNA (lncRNA) at which the two H3K9 deacetylases, Sir2 and Clr3, also accumulate by distinct mechanisms. Iterative cycles of H3K9 deacetylation and methylation spread Clr4/SUV39H from the nucleation center in an sRNA-independent manner, generating a basal H3K9me state. This is acted upon by the RNAi machinery to augment and amplify the Clr4/H3K9me signal at centromeres to establish heterochromatin. Overall, our data reveal that lncRNAs and RNA quality control factors can nucleate heterochromatin and function as epigenetic silencers in eukaryotes.

Cardiovascular diseases (CVDs) can be described as a global health emergency imploring possible prevention strategies. Although the pathogenesis of CVDs has been extensively studied, the role of mitochondrial dysfunction in CVD development has yet to be investigated. Diabetic cardiomyopathy, ischemic-reperfusion injury, and heart failure are some of the CVDs resulting from mitochondrial dysfunction Recent evidence from the research states that any dysfunction of mitochondria has an impact on metabolic alteration, eventually causes the death of a healthy cell and therefore, progressively directing to the predisposition of disease. Cardiovascular research investigating the targets that both protect and treat mitochondrial damage will help reduce the risk and increase the quality of life of patients suffering from various CVDs. One such target, i.e., nuclear sirtuin SIRT6 is strongly associated with cardiac function. However, the link between mitochondrial dysfunction and SIRT6 concerning cardiovascular pathologies remains poorly understood. Although the Role of SIRT6 in skeletal muscles and cardiomyocytes through mitochondrial regulation has been well understood, its specific role in mitochondrial maintenance in cardiomyocytes is poorly determined. The review aims to explore the domain-specific function of SIRT6 in cardiomyocytes and is an effort to know how SIRT6, mitochondria, and CVDs are related.

Subarachnoid hemorrhage (SAH), a specific subtype of cerebrovascular accident, is characterized by the extravasation of blood into the interstice between the brain and its enveloping delicate tissues. This pathophysiological phenomenon can precipitate an early brain injury (EBI), which is characterized by inflammation and neuronal death. Rutaecarpine (Rut), a flavonoid compound discovered in various plants, has been shown to have protective effects against SAH-induced cerebral insult in rodent models. In our study, we used a rodent SAH model to evaluate the effect of Rut on EBI and investigated the effect of Rut on the inflammatory response and its regulation of SIRT6 expression in vitro. We found that Rut exerts a protective effect on EBI in SAH rats, which is partly due to its ability to inhibit the inflammatory response. Notably, Rut up-regulated Sirtuin 6 (SIRT6) expression, leading to an increase in H3K9 deacetylation and inhibition of nuclear factor-kappa B (NF-[Formula: see text]B) transcriptional activation, thereby mediating the inflammatory response. In addition, further data showed that SIRT6 was proven to mediate the regulation of Rut on the microglial inflammatory response. These findings highlight the importance of SIRT6 in the regulation of inflammation and suggest a potential mechanism for the protective effect of Rut on EBI. In summary, Rut may have the potential to prevent and treat SAH-induced brain injury by interacting with SIRT6. Our findings may provide a new therapeutic strategy for the treatment of SAH-induced EBI.

Sunitinib (SUN) is a chemotherapeutic agent clinically approved for treatment of metastatic renal carcinoma. Despite its remarkable benefits, various renal toxicities have been reported that limit its clinical uses. Oleuropein (OLE) is the main polyphenolic constituent of olive tree and mediates the majority of its valuable pharmacological activities. The current study examined the probable renoprotective effects of OLE against SUN-induced nephrotoxicity. Adult male albino rats were co-treated by SUN (25 mg/kg, 3 times/week, PO) with either a drug vehicle or OLE (60 mg/kg/day, daily, PO) for four weeks. A control group comprising of age-matched rats was used. Four weeks later, blood specimens were collected to assess kidney functions. Kidneys were harvested for biochemical and histopathological analyses. Administration of SUN induced kidney dysfunction, along with marked rises in endothelin-1 (ET-1) and monocyte chemotactic protein-1 (MCP-1) levels in renal tissues. Histological abnormalities were also detected in kidneys of SUN-treated rats including glomerular and tubular interstitial congestion along with interstitial fibrosis. On molecular levels, there was a decline in renal SIRT6 expression along with significant up-regulation of Notch-1, NLRP-3, interleukin -1β (IL-1β) and cleaved caspsase-3. All these changes were almost alleviated by OLE co-treatment. These findings suggest the implication of SIRT6/Notch-1/NLRP3/IL-1β axis in the pathogenesis of SUN-induced nephrotoxicity and highlight OLE as a prospective renoprotective agent during SUN chemotherapy to halt its renal toxicity likely through promotion of SIRT6 and suppression of Notch-1/NLRP3/IL-1β signaling pathway.

Sirtuins are pro-longevity genes with chromatin modulation potential, but how these properties are connected is not well understood. Here, we generated a panel of isogeneic human stem cell lines with SIRT1-SIRT7 knockouts and found that any sirtuin deficiency leads to accelerated cellular senescence. Through large-scale epigenomic analyses, we show how sirtuin deficiency alters genome organization and that genomic regions sensitive to sirtuin deficiency are preferentially enriched in active enhancers, thereby promoting interactions within topologically associated domains and the formation of de novo enhancer-promoter loops. In all sirtuin-deficient human stem cell lines, we found that chromatin contacts are rewired to promote aberrant activation of the placenta-specific gene PAPPA, which controls the pro-senescence effects associated with sirtuin deficiency and serves as a potential aging biomarker. Based on our survey of the 3D chromatin architecture, we established connections between sirtuins and potential target genes, thereby informing the development of strategies for aging interventions.

Cancer-associated fibroblasts (CAFs) are abundant stromal cells in the tumor microenvironment that promote cancer progression and relapse. However, the heterogeneity and regulatory roles of CAFs underlying chemoresistance remain largely unclear. Here, we performed a single-cell analysis using high-dimensional flow cytometry analysis and identified a distinct senescence-like tetraspanin-8 (TSPAN8)+ myofibroblastic CAF (myCAF) subset, which is correlated with therapeutic resistance and poor survival in multiple cohorts of patients with breast cancer (BC). TSPAN8+ myCAFs potentiate the stemness of the surrounding BC cells through secretion of senescence-associated secretory phenotype (SASP)-related factors IL-6 and IL-8 to counteract chemotherapy. NAD-dependent protein deacetylase sirtuin 6 (SIRT6) reduction was responsible for the senescence-like phenotype and tumor-promoting role of TSPAN8+ myCAFs. Mechanistically, TSPAN8 promoted the phosphorylation of ubiquitin E3 ligase retinoblastoma binding protein 6 (RBBP6) at Ser772 by recruiting MAPK11, thereby inducing SIRT6 protein destruction. In turn, SIRT6 down-regulation up-regulated GLS1 and PYCR1, which caused TSPAN8+ myCAFs to secrete aspartate and proline, and therefore proved a nutritional niche to support BC outgrowth. By demonstrating that TSPAN8+SIRT6low myCAFs were tightly associated with unfavorable disease outcomes, we proposed that the combined regimen of anti-TSPAN8 antibody and SIRT6 activator MDL-800 is a promising approach to overcome chemoresistance. These findings highlight that senescence contributes to CAF heterogeneity and chemoresistance and suggest that targeting TSPAN8+ myCAFs is a promising approach to circumvent chemoresistance.