Cardiomyocytic FoxP3 Attenuates Expression of β Isoform of Myosin Heavy Chain During Cardiac Hypertrophy and Effects of Triptolide.

Cardiac hypertrophy, a maladaptive response to chronic stress, progresses to heart failure through mechanisms requiring deeper exploration. While forkhead helix transcription factor P3 (FoxP3) is well-known as a key regulator in CD4+ T cells, its role in cardiomyocytes remains unclear. Here, by using isoproterenol (ISO)-induced cardiac hypertrophy models (40 mg/kg daily for in vivo study and 10 μmol/L for in vitro study), we revealed the protective role of FoxP3 in cardiac hypertrophy. Though modulating FoxP3 expression using siRNA or plasmid in cardiomyocytes, we found that FoxP3 knockdown exacerbated ISO-induced hypertrophic responses, while overexpression of FoxP3 attenuated hypertrophic effects. The protective function of cardiomyocytic FoxP3 in vivo was further confirmed by infection of adeno-associated virus. Mechanically, the cardiomyocytic FoxP3 decreased the expression of nuclear factor of activated T cells c3 (NFATc3), a key regulator of hypertrophy-related genes, to suppress hypertrophy-related genes, including atrial natriuretic peptide, brain natriuretic peptide and β-myosin heavy chain (β-MHC), and thus ameliorate hypertrophic responses. Besides, the immunoprecipitation and immunofluorescence determination showed that FoxP3 could interact with NFATc3 in the nucleus to form a transcription complex, thereby regulating the transcription activity of NFATc3. Chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift assays (EMSAs) revealed the specific binding sequences of FoxP3 in the β-MHC promoter region, with binding occupancy reduced by ISO, suggesting that FoxP3 could interact with NFATc3 to down-regulate the β-MHC expression. Importantly, we identified triptolide (TP), a bioactive natural product, as a potent inducer of FoxP3 expression. Both in vivo (10 μg/kg daily) and in vitro (10 μmol/L) studies demonstrated that TP significantly reversed cardiac hypertrophy by upregulating FoxP3 expression, thereby inhibiting NFATc3-mediated β-MHC transcription. These findings highlight cardiomyocytic FoxP3 as a novel protective factor, elucidating its underlying mechanisms and demonstrating the therapeutic potential of TP in this process.