Published online Jul 14, 2022. doi: 10.3748/wjg.v28.i26.3201
Peer-review started: January 13, 2022
First decision: March 8, 2022
Revised: March 22, 2022
Accepted: May 13, 2022
Article in press: May 13, 2022
Published online: July 14, 2022
Processing time: 180 Days and 23.7 Hours
Endoplasmic reticulum (ER) stress contributes to the pathogenesis of chronic liver diseases, but how hepatocytes respond to ER stress has not been clarified. Alpha-fetoprotein (AFP) is secreted by hepatoma cells and elevated levels of serum AFP are associated with development of liver malignancies.
To investigate whether and how AFP could regulate ER stress and hepatocyte injury.
The distribution of AFP and the degrees of ER stress in liver tissues and liver injury were characterized by histology, immunohistochemistry, and Western blot in biopsied human liver specimens, two mouse models of liver injury and a cellular model. The levels of AFP in sera and the supernatants of cultured cells were quantified by chemiluminescence.
High levels of intracellular AFP were detected in liver tissues, particularly in the necrotic areas, from patients with chronic liver diseases and mice after carbon tetrachloride (CCl4) administration or induction of ER stress, but not from the controls. The induced intracellular AFP was accompanied by elevated activating transcription factor-6 (ATF6) expression and protein kinase R-like ER kinase (PERK) phosphorylation in mouse livers. ER stress induced AFP expression in LO2 cells and decreased their viability. ATF6, but not PERK, silencing mitigated the ER-stress-induced AFP expression in LO2 cells. Conversely, AFP silencing deteriorated the ER stress-mediated LO2 cell injury and CCl4 administration-induced liver damages by increasing levels of cleaved caspase-3, the C/enhancer binding protein homologous protein expression, mixed lineage kinase domain-like pseudokinase and PERK phosphorylation, but decreasing ATF6 expression.
ER stress upregulated intra-hepatocyte AFP expression by activating ATF6 during the process of liver injury and intracellular AFP attenuated hepatocyte apoptosis and necroptosis by alleviating ER stress.
Core Tip: During the process of liver injury, alpha-fetoprotein (AFP) expression was up-regulated in hepatocytes, especially in the necrotic areas, but it did not increase the serum AFP level. Endoplasmic reticulum (ER) stress induced intracellular AFP expression through activating activating transcription factor-6 and the up-regulated intracellular AFP expression attenuated hepatocyte apoptosis and necroptosis by feedback-down-regulating ER stress.