LAUSR

As a critical regulator of the cell cycle, cyclin-dependent kinase (CDK) inhibitor p21 or p21 is involved in the development of cardiac hypertrophy and heart failure. Calcitriol, or 1,25(OH)2D3, the bioactive form of vitamin D (VD), can activate p21 expression and attenuate cardiac hypertrophy. To simulate cardiac hypertrophy in vitro and ex vivo, respectively, mice and cardiomyocytes were treated with isoproterenol (ISO). Moreover, the p21 signaling pathway was examined in ISO + VD and ISO + VD p21 inhibitor-treated cardiomyocytes. We found that calcitriol treatment led to a significant decrease in cardiac size and the mRNA levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in ISO-treated mice. Furthermore, the surface area of cardiomyocytes and the expression of ANP and BNP were decreased, and the expression of p21 was increased in the ISO + VD group compared with those in the ISO group. Furthermore, the surface area of cardiomyocytes and the expression of ANP and BNP were markedly upregulated in the ISO + VD p21 inhibitor group relative to the ISO + VD group, whereas the difference was not statistically significant compared with those of the ISO p21 inhibitor group. Therefore, our findings indicate that 1,25(OH)2D3 protects against cardiac hypertrophy in mice through upregulating p21 expression.