HL-1 cardiomyocytes cells were cultured on a gelatin (0.02 % [w/v])/fibronectin [10 μg/ml]) matrix and maintained in dedicated Claycomb Medium that was enriched with 10 % inactivated fetal bovine serum (v/v), antibiotics (100 IU/ml penicillin and 100 μg/ml streptomycin), 2 mM l-glutamine, and 0.1 mM norepinephrine. The cells were incubated at 37 °C under normoxic (21 % O2 and 5 % CO2) and hypoxic (1 % O2 and 5 % CO2) conditions. To inhibit SCD1 activity, HL-1 cells were incubated with 2 μM of the SCD1 inhibitor A939572 in Claycomb medium with 1 % (v/v) fetal bovine serum for 24 h. To induce SCD1 overexpression, HL-1 cardiomyocytes were transfected with 4 μg of empty pcDNA3 vector or pcDNA3 that encoded human SCD1 (hSCD1) plasmid using jetOPTIMUS according to Polyplus recommendation. To inhibit ATGL activity, HL-1 cells were incubated with 50 μM of the ATGL inhibitor Atglistatin in dimethylsulfoxide with 1 % (v/v) fetal bovine serum for 4 h. For the simultaneous inhSCD1 or hSCD1 and inhATGL condition, HL-1 cells were first incubated for 24 h to inhibit SCD1 activity or hSCD1 was overexpressed in normoxia or hypoxia, and then the cells were incubated with inhATGL for an additional 4 h in normoxia or hypoxia. Appropriate control cells were incubated for the same period of time in Claycomb medium that was supplemented with 1 % (v/v) fetal bovine serum and a corresponding concentration of dimethylsulfoxide.

Stearoyl-CoA desaturase 1 (SCD1) is an enzyme that is involved in the regulation of lipolysis in the heart. SCD1 also affects epigenetic mechanisms, such as DNA and histone modifications, in various tissues. Both epigenetic modifications and changes in lipid metabolism are involved in the heart's response to hypoxia. The present study tested the hypothesis that SCD1 and epigenetic modifications interact to control lipolysis in cardiomyocytes under normoxic and hypoxic conditions. We found that the inhibition of SCD1 activity and loss of SCD1 expression reduced global DNA methylation levels, DNA methyltransferase (DNMT) activity, and DNMT1 expression in HL-1 cardiomyocytes and the mouse heart. We also found that the inhibition of adipose triglyceride lipase is involved in the control of global DNA methylation levels in cardiomyocytes in an SCD1-independent manner. Additionally, SCD1 inhibition reduced expression of the hormone-sensitive lipase (Lipe) gene through an increase in methylation of the Lipe gene promoter. Under hypoxic conditions, SCD1 inhibition abolished hypoxia-inducible transcription factor 1α, likely through decreases in histone deacetylase, protein kinase A, and abhydrolase domain containing 5 protein levels, leading to the attenuation of DNA hypomethylation by DNMT1. Hypoxia led to demethylation of the Lipe promoter in cardiomyocytes with SCD1 inhibition, which increased Lipe expression. These results indicate that SCD1 is involved in the control of epigenetic mechanisms in the heart and may affect Lipe expression through changes in methylation in its promoter region. Therefore, SCD1 may be considered a key player in the epigenetic response to normoxia and hypoxia in cardiomyocytes.