Regulation of de novo ceramide synthesis: the role of dihydroceramide desaturase and transcriptional factors NFATC and Hand2 in the hypoxic mouse heart.

We have previously shown that ceramide, a proapoptotic molecule decreases in the mouse heart as it adapts to hypoxia. We have also shown that its precursor, dihydroceramide, accumulates with hypoxia. This implicates the enzyme dihydroceramide desaturase (DHC-DS), which converts dihydroceramide to ceramide, in a potential regulatory checkpoint in cardiomyocytes. We hypothesised that the regulation of de novo ceramide synthesis plays an important role in the cardiomyocyte adaptation to hypoxia. We used an established mouse model to induce acute and chronic hypoxia. Cardiac tissues were extracted and quantitative real-time polymerase chain reaction (qRT-PCR) was used to evaluate the expression levels of DHC-DS. Electrophoretic Mobility Shift Assays (EMSAs) and qRT-PCR were used to evaluate the activity and expression levels of an array of transcription factors that might regulate DEGS1 gene expression. We demonstrated that DEGS1 mRNA levels decrease with time in hypoxic mice concurrent with the decrease in HAND2 transcripts. Interestingly, the DEGS1 promoter harbors overlapping sites for Hand2 and Nuclear Factor of Activated T-cells (NFATC) transcription factors. We have demonstrated a physical interaction between NFATC1 and the E-Box proteins with EMSA and coimmunoprecipitation assays. The regulation of de novo ceramide synthesis in response to hypoxia and this newly described interaction between E-box and NFATC transcription factors will pave the way to identify new pathways in the adaptation of the cardiomyocyte to stress. The elucidation of these pathways will in the long-term provide insights into potential targets for novel therapeutic regimens.