HSP72 Is a Mitochondrial Stress Sensor Critical for Parkin Action, Oxidative Metabolism, and Insulin Sensitivity in Skeletal Muscle

Abstract

Increased heat shock protein (HSP) 72 expression in skeletal muscle prevents obesity and glucose intolerance in mice, although the underlying mechanisms of this observation are largely unresolved. Herein we show that HSP72 is a critical regulator of stress-induced mitochondrial triage signaling since Parkin, an E3 ubiquitin ligase known to regulate mitophagy, was unable to ubiquitinate and control its own protein expression or that of its central target mitofusin (Mfn) in the absence of HSP72. In wild-type cells, we show that HSP72 rapidly translocates to depolarized mitochondria prior to Parkin recruitment and immunoprecipitates with both Parkin and Mfn2 only after specific mitochondrial insult. In HSP72 knockout mice, impaired Parkin action was associated with retention of enlarged, dysmorphic mitochondria and paralleled by reduced muscle respiratory capacity, lipid accumulation, and muscle insulin resistance. Reduced oxygen consumption and impaired insulin action were recapitulated in Parkin-null myotubes, confirming a role for the HSP72-Parkin axis in the regulation of muscle insulin sensitivity. These data suggest that strategies to maintain HSP72 may provide therapeutic benefit to enhance mitochondrial quality and insulin action to ameliorate complications associated with metabolic diseases, including type 2 diabetes.

Genetic manipulation of cardiac Hsp72 levels does not alter substrate metabolism but reveals insights into high-fat feeding-induced cardiac insulin resistance

“…Body composition analysis revealed an increase in body weight, fat mass, and body fat percentage (Fig. 5a-d) with high-fat feeding, but in line with previous analysis of these mice at 20 weeks of age (Drew et al 2014), no difference in weight was detected with the deletion of Hsp72. Consistent with what was observed with the Hsp72 Tg mice, no difference in heart mass was detected ( Fig.…”

“…Despite the documented alterations in metabolic processes in the skeletal muscle of Hsp72 gain of function (Hsp72 Tg) or Hsp72 loss of function models (Hsp72 KO) (Chung et al 2008;Drew et al 2014;Henstridge et al 2014), our study finds little evidence that these changes also occur in cardiac tissue. This suggests that Hsp72 may play an organ-specific role in modulating metabolic processes.…”

“…The Hsp72 KO mice were purchased from the Mutant Mouse Regional Resource Centers (MMRRC) and crossed with C57BL/6J mice to create heterozygous mice. This line has the two genes responsible for induction of Hsp72 (Hspa1a and Hspa1b) deleted (whole body) (Drew et al 2014). The colony was then maintained with heterozygous x heterozygous breeding to allow for comparison with wild-type littermates.…”

“…7a, b). As it has been noted that Hsp72 KO mice have a disrupted skeletal muscle mitochondrial morphology (Drew et al 2014), we isolated fresh mitochondria from the hearts of these mice and analyzed their ability to consume oxygen in the basal state and in response to the addition of ADP and the oxidative phosphorylation uncoupling agent FCCP. There was no difference between the groups in relation to high-fat feeding or the deletion of Hsp72 in the basal state.…”

Heat stress induces mitochondrial adaptations in skeletal muscle

“…HSP60, mtHSP70, and TNF receptor-associated protein 1 [TRAP-1]) were dramatically increased by heat stress treatment 20,43,48) . Furthermore, an interesting observation was recently reported that HSP72, conventionally considered as cytosolic HSP, translocates to mitochnodria from cytosol and interacts with Parkin in response to increased mitochondrial stress 50) . Therefore, in addition to an assay of protein, analyzing properties of HSPs at the post-translational level (e.g.…”