To date, increasing evidence indicates that the thiazolidinediones (TZDs) have benefits in certain conditions of chronic liver disease, including nonalcoholic steatohepatitis.1, 2 TZDs are selective agonists for the nuclear transcription factor peroxisome proliferator-activated receptor-γ (PPARγ) that have potent anti-inflammatory effects on hepatic stellate cells (HSCs). For instance, exposing HSCs to TZDs resulted in reversion of most features of the activated phenotype of HSCs, reduction in the expression of matrix proteins, and blocking of the secretion of proinflammatory chemokines.2
We offer an additional important mechanism for the development of a molecular target of PPARγ, i.e., PPARγ agonist-induced hepatocyte growth factor (HGF) may have an essential part in the protection from chronic liver injury. HGF has been shown to suppress liver cirrhosis, hepatocyte apoptosis, and production of transforming growth factor-β.3 Previously, Li et al. clearly demonstrated that PPARγ agonists strongly stimulate HGF promoter and subsequent gene/protein expression in mesangial cells.4 Indeed, we observed that peripheral blood mononuclear cells produce a significant amount of HGF in the supernatants by stimulation with TZDs, which are blocked by a selective PPARγ antagonist (Fig. 1). This evidence suggests that, in the presence of a PPARγ agonist, both tissue and immune cells could produce HGF at an inflammatory locus and probably in blood circulation. In this context, we read with interest the article by Aoyama et al.,5 which showed that pioglitazone treatment augumented the hepatic proliferative response in KK-Ay mice in response to partial hepatectomy. Future studies are needed to explore the connection between PPARγ and HGF, and such investigations would contribute to progress in understanding the mechanisms of the efficacy of TZDs in chronic liver disease.