Acylated ghrelin treatment normalizes skeletal muscle mitochondrial oxidative capacity and AKT phosphorylation in rat chronic heart failure

Abstract

Background: Chronic heart failure (CHF) is associated with skeletal muscle abnormalities contributing to exercise intolerance, muscle loss, and negative impact on patient prognosis. A primary role has been proposed for mitochondrial dysfunction, which may be induced by systemic and tissue inflammation and further contribute to low insulin signalling. The acylated form of the gastric hormone ghrelin (AG) may improve mitochondrial oxidative capacity and insulin signalling in both healthy and diseased rodent models.

Methods: We investigated the impact of AG continuous subcutaneous administration (AG) by osmotic minipump (50 nmol/kg/day for 28 days) compared with placebo (P) on skeletal muscle mitochondrial enzyme activities, mitochondrial biogenesis regulators transcriptional expression and insulin signalling in a rodent post-myocardial infarction CHF model.

Results: No statistically significant differences (NS) were observed among the three group in cumulative food intake. Compared with sham-operated, P had low mitochondrial enzyme activities, mitochondrial biogenesis regulators transcripts, and insulin signalling activation at AKT level (P < 0.05), associated with activating nuclear translocation of pro-inflammatory transcription factor nuclear factor-κB. AG completely normalized all alterations (P < 0.05 vs P, P = NS vs sham-operated). Direct AG activities were strongly supported by in vitro C2C12 myotubes experiments showing AG-dependent stimulation of mitochondrial enzyme activities. No changes in mitochondrial parameters and insulin signalling were observed in the liver in any group.

Conclusions: Sustained peripheral AG treatment with preserved food intake normalizes a CHF-induced tissue-specific cluster of skeletal muscle mitochondrial dysfunction, pro-inflammatory changes, and reduced insulin signalling. AG is therefore a potential treatment for CHF-associated muscle catabolic alterations, with potential positive impact on patient outcome.

Keywords: Ghrelin; Insulin signalling; Mitochondria; Skeletal muscle.

Figure 1

Skeletal muscle mitochondrial enzyme activities and mitochondrial biogenesis transcript levels. Effects of continuous subcutaneous administration of gastric hormone acylated ghrelin (50 nmol/kg/day for 28 days) by osmotic minipump in a rodent post‐myocardial infarction chronic heart failure model on citrate synthase (A) and cytochrome c oxidase (B) activity and on PGC1α (C) and PPARγ (D) gene expression in skeletal muscle. a.u., arbitrary units, *P < 0.05 versus other groups, mean ± SEM, n = 14–18/group. IMA‐P, myocardial infarction with placebo; IMA‐AG, myocardial infarction with gastric hormone acylated ghrelin.

Figure 2

Skeletal muscle nuclear factor‐κB (NFκB) nuclear content and AKT phosphorylation. Effects of continuous subcutaneous administration of AG (50 nmol/kg/day for 28 days) by osmotic minipump in a rodent post‐myocardial infarction chronic heart failure model on nuclear NF‐κB (A), tissue triglycerides (B), and pAKT (C) levels in skeletal muscle. *P < 0.05 vs. other groups, mean ± SEM, n = 14–18/group. IMA‐P, myocardial infarction with placebo; IMA‐AG, myocardial infarction with gastric hormone acylated ghrelin.

Figure 3

Gastric hormone acylated ghrelin (AG) activities in vitro in C2C12 myotubes. Effects of the incubation with increasing concentrations of AG or unacylated ghrelin versus control (Ct) on citrate synthase (A) and cytochrome c oxidase (B) activity and adenosine triphosphate (ATP) synthesis rate (C) in C2C12 myotubes. PPKM, pyruvate + palmitoyl‐L‐carnintine + α‐ketoglutarate + malate; PCM, palmitoyl‐L‐carnintine + malate; GM, glutamate + malate; SR, succinate + rotenone. *P < 0.05 versus Ctrl, ^$ P < 0.05 versus AG 0.1 μM, mean ± SEM, n = 14–18/group.

Figure 4

Liver mitochondrial enzyme activities and mitochondrial biogenesis transcript levels. Effects of continuous subcutaneous administration of gastric hormone acylated ghrelin (50 nmol/kg/day for 28 days) by osmotic minipump in a rodent post‐myocardial infarction chronic heart failure model on citrate synthase activity (A), on PGC1α (B), and PPARγ (C) gene expression and on tissue triglycerides (D) and pAKT (E) levels in the liver. Mean ± SEM, n = 14–18/group. IMA‐P, myocardial infarction with placebo; IMA‐AG, myocardial infarction with gastric hormone acylated ghrelin.