Low concentration of HgCl₂ drives rat hepatocytes to autophagy/apoptosis/necroptosis in a time-dependent manner

Abstract

Mercury (Hg) is known to produce hepatotoxicity driving cells towards apoptosis. It was recently reported that low concentrations of Hg (5 μM) initiate autophagy in vitro within 30 min of incubation modulated by several autophagy-related gene proteins, and co-regulators through ubiquitination. The present study aimed to elucidate in vitro mode of cytotoxic responses including programed cell death in 5-μM Hg-treated rat hepatocytes. Autophagy proceeded from 30 min to 4 hr mediated by crosstalk between specific regulating factors of cell-death-signaling mechanisms. It was noted that after 4-hr incubation with 5 μM HgCl₂, cells were driven towards apoptosis followed by necroptosis within 6.5 hr. Receptor-interacting serine-threonine protein 3 (RIP3) and caspase-8 played a significant role in interlinking function. The positive role of caspase-8 with RIP3 significantly triggered caspase-3 via extrinsic apoptotic pathway. A shift from apoptosis to necroptosis occurred after 6 hr via tumor necrosis factor α-RIP3-caspase-8 pathway. No alteration in caspase-3 expression and presence of high-mobility group box 1 protein in nucleus indicated absence of apoptosis and necrosis in rat hepatocytes between 6.5 and 8 hr. Data indicated that cellular homeostasis is regulated by modulating different proteins and driving hepatocytes through autophagy to apoptosis to necroptosis in a time-dependent manner.

Keywords:

• mercury
• apoptosis
• necroptosis
• RIP3
• hepatocytes

Acknowledgments

S. Chatterjee is grateful to the National Academy of Sciences, India (NASI) for a Senior Research Fellowship, P.P. Banerjee is grateful to the University Grants Commission (UGC) for a BSR Fellowship and S. Bhattacharya acknowledges NASI for the award of a Senior Scientist Platinum Jubilee Fellowship. Authors are grateful to Prof. Samir Bhattacharya for extending his laboratory facilities and to UGC for the Center for Advanced Studies grants which enabled the present study.