Enhanced autophagy ameliorates cardiac proteinopathy

Abstract

Basal autophagy is a crucial mechanism in cellular homeostasis, underlying both normal cellular recycling and the clearance of damaged or misfolded proteins, organelles and aggregates. We showed here that enhanced levels of autophagy induced by either autophagic gene overexpression or voluntary exercise ameliorated desmin-related cardiomyopathy (DRC). To increase levels of basal autophagy, we generated an inducible Tg mouse expressing autophagy-related 7 (Atg7), a critical and rate-limiting autophagy protein. Hearts from these mice had enhanced autophagy, but normal morphology and function. We crossed these mice with CryAB R120G mice, a model of DRC in which autophagy is significantly attenuated in the heart, to test the functional significance of autophagy activation in a proteotoxic model of heart failure. Sustained Atg7-induced autophagy in the CryAB R120G hearts decreased interstitial fibrosis, ameliorated ventricular dysfunction, decreased cardiac hypertrophy, reduced intracellular aggregates and prolonged survival. To determine whether different methods of autophagy upregulation have additive or even synergistic benefits, we subjected the autophagy-deficient CryAB R120G mice and the Atg7-crossed CryAB R120G mice to voluntary exercise, which also upregulates autophagy. The entire exercised Atg7-crossed CryAB R120G cohort survived to 7 months. These findings suggest that activating autophagy may be a viable therapeutic strategy for improving cardiac performance under proteotoxic conditions.

Aberrant Mitochondrial Fission Is Maladaptive in Desmin Mutation–Induced Cardiac Proteotoxicity

“…Echocardiograms were performed on isoflurane‐anesthetized mice with a VisualSonics Vevo 2100 Imaging System (Toronto, Ontario, Canada) using a 40‐MHz transducer to assess cardiac functional parameters 20, 21. Briefly, 2‐dimensional directed M‐mode echocardiographic images along the parasternal short axis were recorded by investigators blinded to genotype to determine left ventricular (LV) size and systolic function.…”

“…For electron microscopic examination, D7 Des Tg and non‐transgenic (Ntg) hearts were perfused with 1% paraformaldehyde/2% glutaraldehyde in the cardioplegic buffer, then with 1% paraformaldehyde/2% glutaraldehyde in 0.1 mol/L cacodylate buffer, pH 7.2, postfixed in 1% OsO 4 and processed for thin sectioning as described previously 20, 21…”

“…Hearts were collected, fixed in 10% buffered formalin, and embedded in paraffin as described previously 20, 21. Serial 5‐μm heart sections from each group were stained with Masson's trichrome21 and Sirius Red 25.…”

“…Serial 5‐μm heart sections from each group were stained with Masson's trichrome21 and Sirius Red 25. Fibrosis and collagen deposition within sections were quantitated using ImageJ software (NIH) as described previously.…”

“…Briefly, isolated NRCs were plated on Lab‐Tek II chamber slides (Thermo Scientific, 154461) at a density of 1×10 5  cells/well. Immunocytochemistry was then performed according to the procedures reported previously 17, 20, 21. Plated cells were first washed with 0.1 mol/L PBS followed by fixation and permeabilization in 4% paraformaldehyde with 0.5% Triton‐X 100 in PBS for 15 minutes.…”