Oxidative stress-dependent contribution of HMGB1 to the interplay between apoptosis and autophagy in diabetic rat liver

Abstract

The progression of oxidative stress, resulting cell damage, and cell death underlies the etiology of liver damage/dysfunction as a complication of diabetes. High-mobility group box 1 (HMGB1) protein, a chromatin-binding nuclear protein and damage-associated molecular pattern molecule, is integral to oxidative stress and signaling pathways regulating cell death and cell survival. We previously found that in streptozotocin (STZ)-induced diabetic rats, reduction of oxidative stress after melatonin administration lowered necrotic cell death and increased expression of HMGB1 and hepatocellular damage. In the present study, we examined whether alleviation of diabetes-attendant oxidative stress and ensuing change in HMGB1 expression influence the dynamic equilibrium between apoptosis/autophagy and liver damage. We observed that elevated HMGB1 protein levels in diabetic rat liver accompanied increased interactions of HMGB1 with TLR4 and RAGE, and activation of the intrinsic apoptotic pathway and Beclin 1-dependent autophagy. The absence of p62 degradation in diabetic rat liver pointed to defective autophagy which was responsible for lower autophagosome/autophagolysosome formation and an increased apoptosis/autophagy ratio. Compared to diabetic rats, in melatonin-treated diabetic rats, the structure of liver cells was preserved, HMGB1/TLR4 interaction and downstream apoptotic signaling were significantly reduced, HMGB1/Beclin 1 colocalization and interactions were augmented and Beclin 1-mediated autophagy, mithophagy in particular, were increased. We concluded that in mild oxidative stress, HMGB1 is cytoprotective, whereas in intense oxidative stress, HMGB1 actions promote cell death and liver damage. Since reduced HMGB1 binds to RAGE but not to TLR4, redox modification of HMGB1 as a mechanism regulating the cross-talk between apoptosis and autophagy in diabetes is discussed.

Modulation of diabetes-related liver injury by the HMGB1/TLR4 inflammatory pathway

“…Immunoprecipitation Immunoprecipitation was performed as previously described [33]. The whole liver homogenate (500 μg) was precleared by incubation with control IgG and protein A/G agarose (Santa Cruz Biotechnology) and the precleared supernatant was incubated overnight at 4°C with 2 μg of anti-HMGB1 antibody (ab18256) in TEG buffer (10 mM TrisHCl, pH 7.6, 4 mM EDTA, 10% glycerol, 50 mM NaCl).…”

“…Depending on its concentration, TNF-α can either have protective or damaging effects. This has been demonstrated in acute liver injury [11] where its elevated presence triggers a series of intracellular events that result in the activation of apoptosis, a type of cell death which is increased in diabetic rat liver [33]. Since inflammation is one of the main etiological factors in the development and progression of diabetes-related tissue injury, it is important to investigate diabetes-induced signaling pathways that maintain the inflammatory environment and to identify endogenous participants that would be suitable therapeutic targets for controlling inflammation.…”

“…Increased expression of TLR4 was reported in liver injury models, such as partial hepatectomy and ischemia-reperfusion, where it is involved in the clearance of endotoxins, in the production of pro-inflammatory and antiinflammatory cytokines, and the generation of reactive oxidative species (ROS) [14,36]. In our previous study, we described the involvement of TLR4 in the induction of the intrinsic apoptotic cell death pathway in diabetic rat liver through interaction with exogenous high mobility group box 1 (HMGB1) protein [33].…”

Beneficial effects of the novel marine oxygen carrier M101 during cold preservation of rat and human pancreas

“…Radical production leads to an exponential chain reaction and damages related to oxidative stress can lead to necrosis, which can be observed with specific markers such as HMGB1. HMGB1 is known to be released by oxidative stress‐induced necrotic cells . To break this chain reaction and prevent spreading of oxidative stress, ROS must be converted to harmless molecules by antioxidant enzymes or scavenger receptors.…”

“…HMGB1 is known to be released by oxidative stress-induced necrotic cells. 27,52,53 To break this chain reaction and prevent spreading of oxidative stress, ROS must be converted to harmless molecules by antioxidant enzymes or scavenger receptors. We observed this M101, when present in both the preservation and perfusion solutions, also improved islet function and led to an increase in insulin secretion in response to glucose stimulation (data not shown for an increase in GLUT2 expression) concomitantly with a decrease in p38-MAPK pathway activity.…”