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The deleterious effects of statins on skeletal muscle are well known, but the mechanism associated with these effects remains unresolved. Statins are associated with mitochondrial damage, which may contribute to muscle myopathy. Here we demonstrate that simvastatin induces mitophagy in skeletal muscle cells and hypothesized that attenuating this process by silencing the mitophagy adapter p62/sequestosome-1 (SQSTM1) might mitigate myotoxicity. Surprisingly, silencing p62/SQSTM1 in differentiated C2C12 muscle cells exacerbated rather than attenuated myotoxicity. This inhibition of mitophagy in the face of statin challenge correlated with increased release of cytochrome c to the cytosol, activation of caspase-3, and lactate dehydrogenase (LDH) release. Correspondingly, targeted knockdown of Parkin, a canonical E3 ubiquitin ligase important for mitophagy, mirrored the effects of p62/SQSTM1 silencing. To corroborate these findings in vivo, we treated Parkin knockout mice with simvastatin for 2 wk. In line with our findings in vitro, these mitophagy-compromised mice displayed reduced spontaneous activity, loss of grip strength, and increased circulating levels of muscle damage marker LDH. Our findings demonstrate that mitophagy is an important mechanism to resist statin-induced skeletal muscle damage.—Ramesh, M., Campos, J. C., Lee, P., Song, Y., Hernandez, G., Sin, J., Tucker, K. C., Saadaeijahromi, H., Gurney, M., Ferreira, J. C. B., Andres, A. M. Mitophagy protects against statin-mediated skeletal muscle toxicity.

Mitophagy plays a major role in heart physiology. Impairment of Parkin-dependent mitophagy in heart is known to be deleterious. Obesity is a known cardiovascular risk factor. Impaired autophagy has been reported in models of obesity or hyperlipidemia/hypercholesterolemia; however less is known regarding obesity and mitophagy. The aim of this study was to evaluate the regulation of Parkin expression in hearts of mice fed a high fat diet. Interestingly, we found a significant decrease in Parkin protein in hearts of HFD mice compared those fed a low-fat diet. This was associated with mitochondrial dysfunction in the context of ischemia/reperfusion (I/R). This downregulation was not associated with a decrease in Parkin mRNA expression. We did not detect any change in the degradation rate of Parkin and only a slight decrease in its translation. The reduction of Parkin protein abundance in HFD hearts remains a mystery and will need further studies. However, Parkin depletion in the setting of obesity may contribute to cardiovascular risk.

Pioglitazone (PIO) and GLP-1R receptor agonist (GLP1Ra) have been shown to be cardioprotective against ischemic cardiac injury. Much less is known about the effects of these agents on adverse post-MI LV remodeling. Based on our earlier findings that PIO and a GLP1Ra stimulate mitochondrial turnover, we evaluated the effects of these agents on post-MI remodeling. Lean mice underwent permanent coronary artery ligation (PCAL) to ensure that remodeling would be independent of changes in infarct size. Vehicle, PIO and GLP1Ra (Sigma) were administered i.p. 2h after the infarct and then every other day for a total of 6 doses. Echo and histology (Masson’s trichrome) were used to assess LV remodeling 30 days post-MI (late phase); immune cell infiltration was assessed 7 days after PCAL (early phase) via hematoxylin and eosin (H&E) staining. Both PIO and GLP1Ra were associated with significant improvements in ejection fraction and fractional shortening (A); however, at the dose used, neither drug restored function to that of the sham-operated mice (EF 60% and FS 30%, data not shown). GLP1Ra-treated mice exhibited a marked reduction in immune cell infiltration at 7d after PCAL (B), and fibrosis at 30d (C) compared to vehicle or PIO. While PIO had no effect on immune-cell infiltration and fibrosis, it was effective in attenuating post-MI remodeling. While sharing a common endpoint of attenuating adverse remodeling, the finding that PIO stimulates mitochondrial biogenesis and GLP1Ra induces mitophagy may help explain their disparate findings with respect to early phase remodeling.

Randomized clinical trials have demonstrated that pioglitazone (PIO), a thiazolidinedione, and liraglutide and semaglutide, glucagon-like peptide-1 receptor agonists (GLP1Ra), are effective in treating Type 2 diabetes mellitus. Of considerable interest is the additional observation that they may also be effective in reducing the incidence of major adverse cardiovascular events (MACE) independent of glycemic control. The mechanism underlying this protection is unknown. To test the hypothesis that enhanced mitochondrial turnover (mitophagy and mitochondrial biogenesis) might play a role, obese mice with insulin resistance were subjected to permanent coronary artery ligation (PCAL). Two hours later they were administered an i.p. bolus of vehicle (50μL DMSO), PIO (10mg/kg), or a GLP1Ra (10nmoles/25g) (Sigma). This was repeated every other day for 2 weeks. Hearts were probed by western blot for markers of mitochondrial biogenesis and mitophagy. As shown, PIO was a strong inducer of mitochondrial biogenesis evidenced by increased mitochondrial markers in the whole lysate (mitochondrial biogenesis) whereas GLP1Ra stimulated mitophagy, indicated by Parkin, p62 and optineurin translocation to the mitochondrial fraction. These findings suggest that enhanced mitochondrial biogenesis and mitophagy may be important therapeutic targets for the prevention of adverse cardiovascular outcomes. If confirmed, enhanced mitochondrial turnover may be one of the mechanisms underlying the reduced incidence of MACE that was observed in the PROactive (PIO) and the LEADER and SUSTAIN-6 (GLP1Ra) clinical trials.

Introduction: Premenopausal women, as well as females in animal studies, have a reduced risk of cardiovascular diseases and a reduced myocardial susceptibility to ischemia/reperfusion (I/R) injury. However, with constantly increasing prevalence of obesity, the impact of diet-induced obesity on females remains unclear. Mechanisms of autophagy and mitophagy, differentially regulated between males and females, have been shown to be cardioprotective and impacted under nutritional overload. Hypothesis: Autophagy and mitophagy pathways can be involved in both female cardio protection and deleterious effect of obesity. Methods: Male and female C57Bl/6J mice (n =20 per group) of 8 weeks old were fed a low-fat (LFD, 10% fat) or high-fat (HFD, 60% fat) diet for 12 weeks. At 12 weeks, hearts from mice were studied under basal conditions and after global no-flow ischemia and reperfusion on a Langendorff perfusion system. Results: In both males and females, HFD significantly increases body weight (31.4g vs 48.3g and 22.1g vs 39.9g respectively), fat mass (+200% in males and +300% in females) and blood glucose (+79mg/dl and + 54mg/dl, respectively) (all p Conclusion: All together, these results suggest an impairment of autophagy and mitophagy pathways under HFD. A more drastic change occurs in female mice and may imply a more important response of female mice to HFD, although further studies are needed. However, this result suggests that cardiovascular disease may be more deleterious in women despite their lower cardiovascular risk; additional studies examining sex differences in the response to metabolic syndrome and ischemic heart disease are warranted.

Mitophagy occurs during ischemia/reperfusion (I/R) and limits oxidative stress and injury. Mitochondrial turnover was assessed in patients undergoing cardiac surgery involving cardiopulmonary bypass (CPB). Paired biopsies of right atrial appendage before initiation and after weaning from CPB were processed for protein analysis, mitochondrial DNA/nuclear DNA ratio (mtDNA:nucDNA ratio), mtDNA damage, mRNA, and polysome profiling. Mitophagy in the post-CPB samples was evidenced by decreased levels of mitophagy adapters NDP52 and optineurin in whole tissue lysate, decreased Opa1 long form, and translocation of Parkin to the mitochondrial fraction. PCR analysis of mtDNA comparing amplification of short vs. long segments of mtDNA revealed increased damage following cardiac surgery. Surprisingly, a marked increase in several mitochondria-specific protein markers and mtDNA:nucDNA ratio was observed, consistent with increased mitochondrial biogenesis. mRNA analysis suggested that mitochondrial biogenesis was traniscription independent and likely driven by increased translation of existing mRNAs. These findings demonstrate in humans that both mitophagy and mitochondrial biogenesis occur during cardiac surgery involving CPB. We suggest that mitophagy is balanced by mitochondrial biogenesis during I/R stress experienced during surgery. Mitigating mtDNA damage and elucidating mechanisms regulating mitochondrial turnover will lead to interventions to improve outcome after I/R in the setting of heart disease.

Autophagy is regulated by nutrient and energy status and plays an adaptive role during nutrient deprivation and ischemic stress. Metabolic syndrome (MetS) is a hypernutritive state characterized by obesity, dyslipidemia, elevated fasting blood glucose levels, and insulin resistance. It has also been associated with impaired autophagic flux and larger-sized infarcts. We hypothesized that diet-induced obesity (DIO) affects nutrient sensing, explaining the observed cardiac impaired autophagy. We subjected male friend virus B NIH (FVBN) mice to a high-fat diet, which resulted in increased weight gain, fat deposition, hyperglycemia, insulin resistance, and larger infarcts after myocardial ischemia-reperfusion. Autophagic flux was impaired after 4 wk on a high-fat diet. To interrogate nutrient-sensing pathways, DIO mice were subjected to overnight fasting, and hearts were processed for biochemical and proteomic analysis. Obese mice failed to upregulate LC3-II or to clear p62/SQSTM1 after fasting, although mRNA for LC3B and p62/SQSTM1 were appropriately upregulated in both groups, demonstrating an intact transcriptional response to fasting. Energy- and nutrient-sensing signal transduction pathways [AMPK and mammalian target of rapamycin (mTOR)] also responded appropriately to fasting, although mTOR was more profoundly suppressed in obese mice. Proteomic quantitative analysis of the hearts under fed and fasted conditions revealed broad changes in protein networks involved in oxidative phosphorylation, autophagy, oxidative stress, protein homeostasis, and contractile machinery. In many instances, the fasting response was quite discordant between lean and DIO mice. Network analysis implicated the peroxisome proliferator-activated receptor and mTOR regulatory nodes. Hearts of obese mice exhibited impaired autophagy, altered proteome, and discordant response to nutrient deprivation.

Previous data obtained in our laboratory suggested that there may be constitutive signaling through the myeloid differentiation primary response gene 88 (Myd88)-dependent signaling cascade in murine mammary carcinoma. Here, we extended these findings by showing that, in the absence of an added Toll-like receptor (TLR) agonist, the myddosome complex was preformed in 4T1 tumor cells, and that Myd88 influenced cytoplasmic extracellular signal–regulated kinase (Erk)1/Erk2 levels, nuclear levels of nuclear factor-kappaB (NFκB) and signal transducer and activator of transcription 5 (STAT5), tumor-derived chemokine (C–C motif) ligand 2 (CCL2) expression, and in vitro and in vivo tumor growth. In addition, RNA-sequencing revealed that Myd88-dependent signaling enhanced the expression of genes that could contribute to breast cancer progression and genes previously associated with poor outcome for patients with breast cancer, in addition to suppressing the expression of genes capable of inhibiting breast cancer progression. Yet, Myd88-dependent signaling in tumor cells also suppressed expression of genes that could contribute to tumor progression. Collectively, these data revealed a multifaceted role for Myd88-dependent signaling in murine mammary carcinoma.

Previously we reported that Myd88 contributed to tumor progression. To begin to decipher what may be inducing Myd88 dependent signaling we focused on proteins that could function as damage associated molecular pattern molecules (DAMPs) since DAMPs have been reported to be secreted by tumors, and certain DAMPs mediate effects through toll-like receptors. A screen of mammary carcinoma for DAMP expression showed HMGB1 and HSP60 were significantly elevated relative to normal mammary epithelium, and targeting these DAMPs, or receptors for these DAMPs influenced growth of tumor cells. Moreover, analysis using a Myd88 inhibitory peptide suggested that HMGB1 mediated its effects in a Myd88 dependent manner, and inhibiting Myd88 function decreased HMGB1 and HSP60 gene expression. Collectively, these data suggest that HMGB1 and HSP60 contribute to growth of mammary carcinoma cells, HMGB1 accomplishes this, at least in part, through Myd88 dependent signaling, and these DAMPs are expressed in a Myd88 dependent manner.