SIRT3 PREVENTS DOXORUBICIN INDUCED DILATED CARDIOMYOPATHY VIA REGULATION OF MITOCHONDRIAL PROTEIN ACETYLATION: INVESTIGATING METABOLIC DYSFUNCTION AS A RESULT OF ALTERATIONS TO CARDIAC LIPIDS

Doxorubicin (DOX) is a chemotherapeutic used in the treatment cancer, however it has dose-dependent cardiotoxic side effects such as the development of dilated cardiomyopathy. Previously, we showed that DOX treatment decreases the expression of mitochondrial lysine deacetylase, sirtuin 3 (SIRT3) and alters mitochondrial protein acetylation of enzymes involved in cardiac energy production and oxidative stress in wild-type mice. Cardiac expression of full length mitochondrial localized M1-SIRT3 prevented cardiac remodelling and dysfunction characteristic of dilated cardiomyopathy in female mice. Here, we hypothesize that M1-SIRT3 expression could attenuate DOX-induced cardiac dysfunction by regulating the acetylation of enzymes involved in lipid remodelling and metabolic processes.

DOX (8mg/kg body weight for 4 weeks) was administered to mice with cardiac restricted expression of full length M1-SIRT3 (mitochondrial localized) and short form M3-SIRT3 (lacking the mitochondrial localization sequence) or non-transgenic (Non-Tg) littermates (control groups received saline). Transthoracic echocardiography was performed in male mice from all groups (n=8-13). Cardiac mitochondria were isolated, and a pan acetylated lysine antibody was used to enrich for peptides containing acetylation modifications in M3-SIRT3 and M1-SIRT3 transgenic animals by QTRP LC-MS/MS (n=6). Global lipidomic analysis of cardiac tissue was performed by QTRAP LC-MS/MS (n=6) in all groups. Expression of genes involved in metabolic processes was performed by quantitative PCR (n=6). Radio-labeled 18F-Fluorodeoxyglucose (18F-FDG) was used to examine glucose uptake by PET/MRI imaging (n=6). DOX treatment in Non-Tg male mice caused cardiac dysfunction, whereas expression of M3-SIRT3 and M1-SIRT3 attenuated cardiac remodeling and reduced ejection fraction (p < 0.05). Analysis of acetylated peptides revealed that DOX increased the acetylation of several proteins involved in cardiac energy production (e.g. ACO2 and ATP5PB) and lipid metabolism (e.g., HADHA) while M1-SIRT3 expression mitigated these effects. Lipidomic analysis of cardiac tissue identified an increase in proapoptotic lipid markers including gangliosides and phosphatidylserine species and a large decrease in triglyceride lipid species in DOX treated mice. Quantitative PCR identified increases in Cpt1a (p < 0.05) and Lipe (p=0.0518) in DOX treated Non-Tg mice, but not in M3-SIRT3 and M1-SIRT3 mice. DOX decreased the expression of Fapb3 and Hadha (p < 0.05) in all groups. 18F-FDG PET showed increased cardiac glucose uptake in Non-Tg, and M3-SIRT3 DOX treated mice (p < 0.05) but remined unchanged in M1-SIRT3 mice.

Our data show that increased M1-SIRT3 expression in the heart prevents DOX induced dilated cardiomyopathy. M1-SIRT3 expression altered mitochondrial protein acetylation while DOX decreased cardiac triglycerides and increased glucose uptake indicative of metabolic dysfunction.