Regulating the fate of stem cells for regenerating the intervertebral disc degeneration

Table 1 Modifying genes essential for the development of intervertebral disc

Ref.	Protein (Gene)	Key findings
Choi et al[14], 2012	Sonic Hedgehog (SHH)	Sclerotome tissue formation, annulus fibrosus formation, chondrogenesis of sclerotome cells
Wijgerde et al[15], 2005	Noggin (NOG)	Antagonist of the BMP pathway, promotes Shh intracellular signaling cascade and Pax1 gene activation
Murtaugh et al[16], 1999	Bone Morphogenetic Protein (BMP) family	In the presence of Shh, promotes chondrocyte differentiation of somite-derived IVD progenitors
Peters et al[21], 1999	Paired Box 1 (PAX1)	Chondrogenic commitment of sclerotome cells
Sugimoto et al[27], 2013	SRY-Box 9 (SOX)	Regulates IVD tissue growth and development
Sohn et al[30], 2010	Transforming growth factor-β (TGF-β)	Development of vertebral bodies
Pearson et al[31], 2005	Homeodomain Protein (HOX)	Somite Patterning

IVD: Intervertebral disc.

Table 2 Variation in properties of different sources of stem cell types

Properties	MSCs	ESCs	iPSCs
Sources	Perinatal and adult tissues	Embryo at blastocyst stage	Genetically reprogrammed specialized cells
Plasticity	Multipotent	Pluripotent	Pluripotent
Teratoma formation	No	Yes	Yes
Growth	Limited	High	High
Ethical concerns	No	Yes	No
Immune rejection	No	Yes	No
Cell transplantation	Autologous and allogenic	Allogenic	Autologous
Clinical trials in human patients	Ongoing	Limited	In vitro/in vivo only
Use in genetic disorder	Deficient (Carry mutated gene)	Superior	Deficient (Carry mutated gene)
Ease of isolation	Yes	No	No

MSCs: Mesenchymal stem cells; ESCs: Embryonic stem cells; iPSCs: Induced pluripotent stem cells.

Table 3 Human umbilical cord-derived mesenchymal stem cells compared with other stem cells sources

Properties	Perinatal	Adult	Embryonic
Ability to differentiate into various cell type	√	√	√
Plastic adherence	√	√
High in vitro proliferation ability	√		√
Low risk of tumorigenicity	√	√
Ethical issues			√
Lower risk of viral contamination	√		√
Capacity for autologous transplantation	√	√
Established/proven treatment in human patients	√	√
Ease of collection	√	√
Less need for stringent antigen typing	√	√

Table 4 Summary of studies on cellular therapeutic approaches for regenerative potential of the degenerated disc

Type of stem cells	Gene	Preconditioning outcomes	Ref.
In vitro human cultured NP cells and MSCs	TGF-β1	TGF-β1 stimulates collagen-1 expression in cultured NP cells and in MSCs, increased collagen-1 and sox-9 expression. Co-cultured MSCs with NP cells showed high expression of collagen-1, aggrecan and sox-9 expression via TGF-β-dependent effect	[126]
Chick periosteum-derived MSCs Rabbit bone marrow-derived MSCs Rat MSCs	TGF-β1	Stimulate chondrogenesis and inhibits osteogenesis. Facilitates in vitro chondrogenic differentiation of rabbit BM-MSCs. Increased MAPK activity and upregulation of mRNA expression of sox-9, aggrecan, and collagen type II	[190,122,123]
Human adipose-derived MSCs and bone marrow-derived MSCs	TGF-β3, GDF-5, or GDF-6	In the presence of GDF-6, AD-MSCs leads to differentiation into an NP-like phenotype and results in a richer proteoglycan matrix with low rigidity	[158]
Human bone marrow-derived MSCs	TGF-β1, and GDF-5	Hypoxic TGF-β1 and GDF-5 both increased aggrecan and collagen II mRNA levels and GAGs accumulation	[159]
In vitro human bone marrow-derived MSCs	TGF-β3, dexamethasone, and ascorbate	Preconditioned BM-MSCs expressed higher level of chondrocytes differentiation markers than culture-expanded human IVD cells and articular chondrocytes	[193]
In vivo murine IVD cells	TGF-β3, GDF-5, FGF, or IGF-1	After four weeks of GDF-5 treatment, showed significantly increase in IVD height	[72]
Human adipose-derived MSCs	TGF-β1 and GDF-5	Both distinctly efficient in promoting an NP cell phenotype	[160]
Human cultured NP cells	TGF-β1, and IL-1β	TGF-β1 improved NP cell proliferation, downregulation of mRNA expression of ADAMTS-4 and -5, upregulation expression of TIMP-3. IL-1β inhibited NP cells proliferation, increase of ADAMTS-4 and -5	[161]
Canine cultured NP cells	TGF-β, and IL-10	Suppressed IL1-β and TNF-α expression inhibiting inflammatory reaction	[200]
In vitro human cultured NP cells. E19 rat cultured AF cell	TGF-β1, and IGF-1	Stimulation of human NP cells in a dose and time-dependent manner. TGF-β1 pushed AF cells to fibrocartilaginous phenotype. IGF-1 showed an upregulation of ECM	[79,162]
Murine ESCs	TGF-β, IGF, ascorbic acid, and cis-retinoic acid	All promotes differentiation toward chondrogenic lineage	[175]
Human bone marrow-derived stromal cells	TGF-β1, rhGDF-5, or bovine NPCs	Stimulates cytokeratin-19 and aggrecan/type II collagen ratio distinguish chondrogenic from IVD cell phenotype	[163]
Human bone marrow-derived MSCs	TGF-β3, and dexamethasone	Notochordal cell conditioned medium expressed higher level of NP-like phenotype markers and GAGs deposition than chondrogenic medium or TGF-β groups	[194]
Human cultured NP cells	TGF-β3, and dexamethasone	Enhanced NP proliferation, cell metabolism and reduce catabolism	[195]
Rabbit cultured NP cells	TGF-β1, and BMP-2	Robust restoration of ECM. Increased mRNA expression of aggrecan, type I and type II collagen	[133]
In vitro porcine cultured AF cells	BMP-2, and TGF-β1	Decrease in MMP-1 and increase in aggrecan synthesis	[73]
Mouse MSCs	BMP-2, 7, 13	Proliferate and differentiate into osteoblastic and chondrogenic lineages and no adverse effects on proliferation on undifferentiated MSCs	[164]
Human bone marrow-derived MSCs	BMP-7	Promotes both chondrogenic and osteogenic differentiation of MSCs	[165]
In vitro rat cultured AF cells	BMP-2	Increased mRNA expression of aggrecan and type II collagen. Also, up-regulates BMP-7 and TGFβ-3 mRNA expression	[166]
Mouse embryonic-derived MSCs	BMP-4, Insulin, triiodothyronine, or TGF-β3	All BMP-4, Insulin, and triiodothyronine suppressed adipogenesis and develop osteogenic phenotype. TGFβ-3 promotes chondrogenesis	[128]
In vitro human bone marrow-derived MSC cocultured with human cultured NP cells	BMP2, BMP4, BMP6, and BMP7	BMP4 showed a high potential for IVDs regeneration. Although, BMP2 and BMP7 showed no potent inducer for degenerated human NP cell’s regeneration	[167]
Human bone marrow-derived MSCs	BMP-13	Inhibited osteogenic differentiation of human BM-MSCs and increased proteoglycan synthesis	[168]
Human adult MSCs	BMP-3, and TGFβ-1	Enhanced cell proliferation, GAGs content and differentiation into NP-like phenotype. Upregulated smad-3 signaling pathway	[126]
Human adipose tissue-derived MSCs	BMP-2, BMP-6, BMP-7, and TGF-β2	Both TGFβ-2 and BMP-7 induces chondrogenic potential	[76]
Human cultured NP and AF IVD cells	rhBMP-2, rhBMP-12, and adenoviralBMP-12	Both rhBMP-2 and rhBMP-12 increased NP collagen and proteoglycan but least effects on AF. Though, adenoviral BMP-12 increased ECM protein formation in equally NP and AF	[99]
Human and bovine cultured NP cells	BMP-7/OP-1 with BMP-2	Enhanced GAGs production and NP cells proliferation	[77]
Human cultured NP cells	rhBMP-7	Inhibited apoptotic effects, decreased caspase-3 activity and maintained ECM production	[169]
Bovine cultured NP cells	BMP-7, and IGF-1	Both BMP-7 and IGF-1 induces Smad signaling pathways and suppresses noggin expression via PI3-kinase/Akt pathways	[170]
Human cultured NP and AF IVD cells	BMP-2	Improved newly synthesized proteoglycan and increased mRNA expression of aggrecan, type I and type II collagen	[171]
In vitro cultured NP cells	IGF-1	Increase of matrix synthesis in well-nourished regions	[180]
In vitro canine cultured IVD cells	IGF-1, FGF, EGF, or TGF-β3	TGF-β3 and EGF both produced higher proliferative responses than FGF. Also, IGF-1 showed a slightly significant responses in NP but no contribution in AF and transition zone	[74]
Horse cultured articular cartilage cells. Bovine cultured NP cells	IGF-1	Maintained differentiated chondrocyte morphology and enhanced synthesis of ECM molecules. Increased proteoglycan synthesis	[178,191]
Bovine cultured AF and NP cells	IGF-1, bFGF, and PDGF	Strengthened cell proliferation	[81]
Human cultured AF cells	IGF-1, and PDGF	Significant reduced in apoptotic cell level	[182]
Chondroitinase ABC injection rabbit model	OP-1	Increase in disk height and matrix synthesis	[172]
Rabbit cultured NP and AF IVD cells	OP-1	Restored collagens and upregulated proteoglycan synthesis	[173]
Human cultured NP and AF cells	OP-1	Improved in the proteoglycan contents, total DNA, and collagen	[174]
Human cultured NP cells	OP-1	Partially repaired GAGs content, depends on a very high doses	[175]
Gene therapy, in vitro human IVD cells. Gene therapy, in vivo rabbit IVD	TIMP-1	Increased proteoglycan synthesis. Less MRI and histologic evidence of degeneration	[102,103]
In vitro cultured AF cells and chondrocytes	LMP-1	Increased proteoglycan synthesis, upregulation of mRNA expression of aggrecan, collagen types I and II, BMP-2 and -7	[105]
Human synovium derived stem cells	FGF-2, and FGF-10	FGF-2 stimulates chondrogenic gene expression, GAGs deposition and promotes both chondrogenic and osteogenic lineages	[176]
Ovine bone marrow-derived MSCs	FGF-2, and FGF-18	Promotes both chondrogenic and osteogenic lineages of MSCs	[177]
In vitro cultured human NP cells	FGF2	Increased proliferative potential, redifferentiation gene expression and GAGs deposition	[178]
Bone marrow-derived MSCs	bFGF, TGFβ-1 and TCH gel	Greater survival and repair effect on the degenerated IVDs	[179]
In vitro rat cultured NP cells	rGDF-5	Dose-dependency high expression of aggrecan and collagen type II genes was induced by rGDF-5 disc cells from GDF-5-deficient mouse	[82]
In vitro bovine cultured. NP and AF cells, in vivo rabbit IVD model	rhGDF-5	Increased DNA and proteoglycan level in vitro. In vivo, rhGDF-5 injection improved IVD height, MRI and histological grade score	[183]
In vivo mice and rabbit model	GDF-5	Structural and functional maintenance of IVD	[184]
Canine BM peri-adipocyte cells (BM-PACs)	GDF-5, TGFβ-1, BMP-2, and IGF-1	GDF-5 promoted GAGs production and collagen type II without increasing collagen-10 mRNA expression	[199]
Adult bone marrow-derived MSCs	EGF	In the presence of EGF, promotes osteogenic differentiation and enhance paracrine secretion of BM-MSCs both in vitro and in vivo	[80]
In vivo rat bone marrow-derived MSCs	rhGCSF	Increase of end plates cell proliferation but no contribution in IVD regeneration or maintenance	[185]
Human synovium-derived MSCs	IL-1β, and TNF-α	Enhanced synovial MSCs proliferation and chondrogenic ability	[205,206]
Human bone marrow-derived MSCs. In vitro cultured porcine AF cells	IL-1β, and TNF-α	Both IL-1β and TNF-α suppressed chondrogenesis in a dose-selective manner. Increased expression of MMP-1	[73,207]
Gene therapy, in vitro cultured NP cells	IL-1 and IL-1Ra	IL-1Ra decreased extracellular matrix degradation	[101]
Mouse bone marrow-derived MSCs	SOX-9	Stimulate chondrogenesis	[95]
Gene therapy, in vivo in rabbit IVD	SOX-9	Chondrocyte phenotype of IVD, restored architecture of NP	[96]
Gene therapy, in vitro bovine AF cells	Sox-9, and BMP	Increased proteoglycan and/or collagen type II synthesis	[97]
Gene therapy, in vitro human NP cells	WNT-3A, WNT-5A, and WNT-11	Increased expression of redifferentiation NP genes and GAGs accumulation	[100]
Human bone marrow-derived MSCs	WNT-3A and FGF2	Synergistically both promoted MSC proliferation, chondrogenesis and cartilage formation	[186]
VEGFR-1 and VEGFR-2 lacZ/+ NP cells	VEGF	Raise NP survival	[208]
Rhesus monkey cultured NP cells	CTGF	Stimulation of collagen type II and proteoglycan synthesis	[187]
Human cultured NP cells	PRP	Enhanced NP proliferation and differentiation into chondrogenic lineage	[134]
Porcine cultured NP and AF cells; Porcine IVDD organ	PRP	Stimulation of IVDD cells proliferation. Increased mRNA expression levels of chondrogenesis and matrix formation	[83,84]
Bovine cultured AF cells	PRP	Upregulation of cell numbers and matrix synthesis	[85]
In vitro porcine cultured AF cells	PRP and other cytokines	Decreased enzymes expression causing degradation and increased matrix proteins synthesis	[86]

IVD: Intervertebral disc; BMP: Bone morphogenetic protein; EGF: Epidermal growth factor; FGF: Fibroblast growth factor; IGF-1: Insulin-like growth factor-1; OP-1: Osteogenic protein-1; PDGF: Platelet-derived growth factor; TGF-β1: Transforming growth factor-β1; ADAMTS: A disintegrin and metalloproteinase with thrombospondin motifs; TIMP: Tissue inhibitor of metalloproteinases; TNF-α: Tumor necrosis factor-α; MMP: Matrix metalloproteinase; IL-1β: Interleukin-1 beta; IL-1Ra: IL-1 receptor antagonist; SOX-9: SRY-box transcription factor-9; rhGDF-5: Recombinant human growth and differentiation factor-5; LMP-1: LIM mineralization protein-1; WNTs: Wingless-related integration site; VEGFR: Vascular endothelial growth factor receptor; LacZ: β-galactosidase; CTGF: Connective tissue growth factor; GCSF: Granulocyte colony-stimulating factor; PRP: Platelet-rich plasma; AF: Annulus fibrosus; GAGs: Glycosaminoglycans; NP: Nucleus pulposus; ECM: Extracellular matrix; IVDD: Intervertebral disc degeneration; MSCs: Mesenchymal stem cells; BM: Bone marrow; AD: Adipose tissue; ESCs: Embryonic stem cells; NPCs: Nucleus pulposus cells; MRI: Magnetic resonance imaging; DNA: Deoxyribonucleic acid; mRNA: Messenger ribonucleic acid; TCH: Temperature-responsive chitosan hydrogel; MAPK: Mitogen-activated protein kinase; PI3: Phosphatidylinositol 3; Akt: Protein kinase B.