AMPK involvement in endoplasmic reticulum stress and autophagy modulation after fatty liver graft preservation: a role for melatonin and trimetazidine cocktail

Abstract

Ischemia/reperfusion injury (IRI) associated with liver transplantation plays an important role in the induction of graft injury. Prolonged cold storage remains a risk factor for liver graft outcome, especially when steatosis is present. Steatotic livers exhibit exacerbated endoplasmic reticulum (ER) stress that occurs in response to cold IRI. In addition, a defective liver autophagy correlates well with liver damage. Here, we evaluated the combined effect of melatonin and trimetazidine as additives to IGL‐1 solution in the modulation of ER stress and autophagy in steatotic liver grafts through activation of AMPK. Steatotic livers were preserved for 24 hr (4°C) in UW or IGL‐1 solutions with or without MEL + TMZ and subjected to 2‐hr reperfusion (37°C). We assessed hepatic injury (ALT and AST) and function (bile production). We evaluated ER stress (GRP78, PERK, and CHOP) and autophagy (beclin‐1, ATG7, LC3B, and P62). Steatotic livers preserved in IGL‐1 + MEL + TMZ showed lower injury and better function as compared to those preserved in IGL‐1 alone. IGL‐1 + MEL + TMZ induced a significant decrease in GRP78, pPERK, and CHOP activation after reperfusion. This was consistent with a major activation of autophagic parameters (beclin‐1, ATG7, and LC3B) and AMPK phosphorylation. The inhibition of AMPK induced an increase in ER stress and a significant reduction in autophagy. These data confirm the close relationship between AMPK activation and ER stress and autophagy after cold IRI. The addition of melatonin and TMZ to IGL‐1 solution improved steatotic liver graft preservation through AMPK activation, which reduces ER stress and increases autophagy.

Melatonin Inhibits mTOR-Dependent Autophagy during Liver Ischemia/Reperfusion

“…However, Zaouali et al [16] reported that autophagy is impaired during cold I/R injury and that a cocktail of MLT and trimetazidine improves steatotic liver graft preservation through activation of autophagy. These differences in results may be due to the different I/R models (warm vs. cold) and liver types (normal vs. steatotic) employed in the two studies.…”

“…We previously showed that MLT inhibits necrotic and apoptotic cell death in a rat model of liver I/R by alleviating levels of oxidative stress [15]. Recently, a protective role of MLT has been reported in cold liver I/R through suppression of endoplasmic reticulum (ER) stress and enhanced autophagy [16]. Although the effects of MLT on autophagy have been actively studied, the precise mechanism by which MLT regulates autophagy in liver I/R remains unclear.…”

Ghrelin Attenuated Lipotoxicity via Autophagy Induction and Nuclear Factor-κB Inhibition

“…AMPK is involved in the regulation of autophagy by inhibiting mTOR phosphorylation [28]. AMPK is inhibited by endoplasmic reticulum stress [29], oxidative stress and fat accumulation in NAFLD [14]. Furthermore, the effect of AMPK activation is stimulation of hepatic fatty acid oxidation and ketogenesis, inhibition of cholesterol synthesis, lipogenesis, and triglyceride synthesis [30], exerting an therapeutic effect on NAFLD.…”

Potential benefits of melatonin in organ transplantation: a review

“…The activation of this enzyme produces the accumulation of α-subunit of hypoxia-inducible factor-1 (HIF1α, a transcription factor that functions as a master regulator of adaptive responses to reduced O 2 availability) (Fisslthaler & Fleming 2009) and induces NO· generation, which impairs the normoxic degradation of HIF1α (Zaouali et al 2010c). In fatty livers, the combined effect of melatonin and trimetazidine (TMZ at 10 −3 μM + melatonin 100 μM) as additives to IGL1 was observed to induce AMPK activation and enhance eNOS induction; as a consequence, HIF1α was stabilized (Zaouali et al 2013b). The combination of drugs caused the activation of protective genes including Hsp70, Bcl2, erythropoietin, Vegf, and heme oxygenase-1 (Ho1) (Zaouali et al 2013a).…”