Interestingly, a similar regulation was detected in primary murine hepatocytes (Supporting Fig.
S3C). Next we tested learn more whether miR-29 members are able to modulate the expression of extracellular matrix genes during hepatic fibrogenesis. Possible miR-29 target genes were identified by three different miRNA target prediction algorithms (see Materials and Methods). We identified a high number of fibrosis-related mRNAs, including collagens, integrins, and metallopeptidases as possible targets for the miR-29 family (Supporting Table S3B). Expression of exemplary insilico identified targets was analyzed in liver samples from CCl4-treated and oil-treated Balb/c mice (Fig. 4A), which confirmed up-regulation of the potential target genes Col1a1, Col1a2, Col4a5, and Col5a3 on CCl4 treatment. We next transfected miR-29b at different concentrations into immortalized murine HSC. As shown in Fig. 4B and Fig. 4C, overexpression of miR-29b resulted in a dose-dependent and significant decrease in expression of Col1a1, Col4a5, and Col5a3, whereas down-regulation of Col1a2 failed statistical significance. Transfected scrambled miRNA had no effect on the expression of the respective genes (Fig. 4B, C, and Supporting Fig. S4). Moreover, expression of other fibrosis-related genes (Ctgf, Timp-1, and αSma) was not affected by transfection
of miR-29 (Fig. 4D and Supporting Fig. SB203580 nmr S4). Collectively, these experiments suggest a direct link between the Carbohydrate TGF-β–dependent miR-29 down-regulation and collagen up-regulation in HSC during liver fibrosis. Micro RNAs normally do not act in linear signaling cascades but are able to integrate signals from distinct upstream signaling pathways,10 suggesting that regulation of miR-29 during liver fibrosis is not only regulated by TGF-β. Recently, it was shown that miR-29 can be regulated by the transcription factor NF-κB during myogenic cancer via recruitment of histone deacetylase 1 to the miR-29 promoter region.11 We therefore examined a possible role of this pathway in the regulation of miR-29 in HSCs. Indeed, intraperitoneal injection of LPS into mice resulted in significant down-regulation
of all miR-29 members in whole liver RNA extracts (Fig. 5A). Moreover, stimulation of primary HSC as well as primary hepatocytes with LPS resulted in down-regulation of miR-29a/b/c (Fig. 5B,C). However, LPS stimulation did not significantly enhance collagen expression in these cells (Fig. 5B). Stimulation with tumor necrosis factor (TNF) but not interleukin-1 led to a strong decrease in miR-29b expression (Fig. 5D). Finally, we treated GRX-HSCs and primary HSCs with a chemical inhibitor of NF-κB activation, pyrrolidine dithiocarbamate.12 Although this treatment resulted in early cytotoxicity in primary HSCs (data not shown), GRX-HSCs—which were probably more resistant to NF-κB inhibition—showed a significantly higher expression of miR-29 compared with untreated cells (Fig. 5E).