*2.4. KLF15 Knock Down or Overexpression*

In rat cardiomyocytes treated with KLF15 siRNAs, there were significant increases in cardiomyocyte size and ANP mRNA expression [15]. The loss of KLF15 alone was sufficient to induce cell hypertrophy [13]. Two studies explored overexpression of KLF15 in cardiomyocytes [13,15]. In contrast to the gene knock down study, overexpression of KLF15 reduced cardiomyocyte ANP and BNP mRNA [13,15] and led to reduced cardiomyocyte size in one study [13] but not the other [15].

Two studies examined KLF15 levels in cardiac fibroblasts. KLF15 inhibited the expression of CTGF in cardiac fibroblasts [12,17]. Adenoviral overexpression of KLF15 in neonatal rat ventricular fibroblasts (NRVF) inhibited both basal and TGFβ induced CTGF expression. Similar to TGFβ treatment in cardiomyocytes [15], TGFβ reduced KLF15 gene expression and induced CTGF in NRVF [12]. Co-immunoprecipitation and mobility shift experiments showed KLF15 inhibited recruitment of a co-activator P/CAF (a potent transcriptional co-activator of Smad3 target genes) to the CTGF promoter with no effect on Smad3 binding. KLF15 mediated repression of CTGF promoter was rescued by overexpressing P/CAF [12].

In primary neonate rat cardiac fibroblasts in which hypertrophy was also induced with TGFβ, silencing of the KLF15 gene with KLF15-shRNA significantly decreased KLF15 protein. In contrast, KLF15 overexpression with a recombinant adenovirus increased KLF15 protein expression. Fibroblasts stimulated with TGFβ alone showed increased collagen mRNA. TGFβ stimulated fibroblasts with KLF15 overexpression had less fibrosis and hypertrophy, reduced CTGF and myocardin related transcription factor A (MRFT-A) mRNA, all of which were increased in KLF15-shRNA infected fibroblasts [17].









mRNA, messenger ribonucleic acid; NRVF, neonatal rat ventricular fibroblasts; NRVM, neonatal rat ventricular myocytes; TGFβ, transforming

 growth factor beta.
