PKCδ as a Regulator for TGFβ1-Induced α-SMA Production in a Murine Nonalcoholic Steatohepatitis Model

The precise mechanism of TGF beta 1 signaling in the progression of non-alcoholic steatohepatitis (NASH) has remained unclear. In particular, a potential regulatory mechanism by which PKC delta affects profibrogenic gene expression had never been explored. In this study, therefore, the role of PKC delta in TGF beta 1 mediated alpha-SMA expression was investigated using NASH model mice. In preparation of the NASH model, male C57BL6/J mice were fed a methionine-choline-deficient (MCD) diet for 3 weeks, after which time they were intraperitoneally injected with lipopolysaccharide (LPS). In addition, Tlr4(Lps-d) (CH3/HeJ) mice were used to demonstrate the TGF beta 1 signaling's dependency on TLR4 induction. Liver histology and hepatic hepatitis markers were investigated, and hepatic gene expression levels were determined by real-time PCR. Acute liver injury by LPS injection specifically elevated not only alpha-SMA expression but also phospho-PKC delta in this model. In contrast, Tlr4(Lps-d) (CH3/HeJ) and blockade of TGF beta 1 receptor by SB431542 resulted in a significant reduction of PKC delta activation and alpha-SMA expression. Moreover, the TGF beta 1-induced alpha-SMA production was significantly reduced by a specific PKC delta inhibitor. These findings suggested that PKC delta plays a critical role in TGF beta 1-induced alpha-SMA production in a NASH model. Thus, this was the first demonstration of the involvement of PKC delta in the regulation of alpha-SMA expression in NASH liver tissues, and the impaired induction of PKC delta phosphorylation by LPS in a steatohepatitis condition. Interestingly, treatment by PKC delta inhibitor caused dramatic reduction of myofibroblast activation, indicating that PKC delta represents a promising target for treating NASH.