New mechanism of lipotoxicity in diabetic cardiomyopathy: Deficiency of Endogenous H2S Production and ER stress

Abstract

Objective: To investigate the roles and mechanisms of endogenous hydrogen sulfide (H₂S) and endoplasmic reticulum (ER) stress in the development of diabetic cardiomyopathy (DCM).

Methods: Blood of DCM patients included in the study were collected. The model of DCM rats was established using streptozotocin (STZ) injection. Cardiac lipotoxicity in vitro models were established using 500μM palmitic acid (PA) treatment for 24h in AC16 cardiomyocytes. Endogenous H₂S production in plasma, culture supernatant and heart was measured by sulphur ion-selective electrode assay. Cell viability was tested by using the cell counting kit-8 (CCK-8) kit. Glucose regulated protein (GRP78), CCAAT/enhancer binding protein homologous transcription factor (C/EBP) homologous protein (CHOP), caspase-3 and caspase-12 expressions were measured using western blot analysis. Lipid droplet was evaluated by Oil Red O staining. Apoptosis in hearts of DCM rats was analyzed using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining.

Results: H₂S levels in serum of DCM patients and DCM rats were significant lower, H₂S contents and cystathionine-γ-lyase (CSE) expression in heart tissues of DCM rats were also markedly lower. H₂S levels in supernatants of PA-treated AC16 cardiac cells were decreased. Cardiac lipotoxicity demonstrated by increase in TUNEL positive cells and lipid deposit in vivo and in vitro accompanied by a decrease of H₂S levels. Pretreatment AC16 cells with 100μmol/L of NaHS (a donor of H₂S) could suppress the PA-induced myocardial injury similar to the effects of 4-phenylbutyric acid (4-PBA, an endoplasmic reticulum (ER) stress inhibitor), leading to an increase in cell viability and preventing lipid deposit. Meanwhile, administration diabetic rats with NaHS or 4-PBA alleviated cardiac lipotoxicity, as evidenced by decrease in TUNEL positive cells, cleaved caspase-3 expression and lipid accumulation.

Conclusion: Deficiency of endogenous H₂S was involved in lipotoxicity-induced myocardial injury. Exogenous H₂S attenuates PA-induced myocardial injury though inhibition of ER stress.

Keywords: Diabetic cardiomyopathy; Endoplasmic reticulum stress; Hydrogen sulfide; Lipotoxicity.