Inhibition of phosphatidylinositol 3-kinase signaling in hepatic stellate cells blocks the progression of hepatic fibrosis #

Abstract

The hepatic stellate cell (HSC) is the primary cell type in the liver responsible for excess collagen deposition during fibrosis. Following a fibrogenic stimulus the cell changes from a quiescent vitamin A-storing cell to an activated cell type associated with increased extracellular matrix synthesis and increased cell proliferation. The phosphatidylinositol 3-kinase (PI3K) signaling pathway has been shown to regulate several aspects of HSC activation in vitro, including collagen synthesis and cell proliferation. Using a targeted approach to inhibit PI3K signaling specifically in HSCs, we investigated the role of PI3K in HSCs using a rodent model of hepatic fibrosis. An adenovirus expressing a dominant negative form of PI3K under control of the smooth muscle ␣-actin (␣SMA) promoter was generated (AdSMAdnPI3K). Transducing HSCs with Ad-SMAdnPI3K resulted in decreased proliferation, migration, collagen expression, and several additional profibrogenic genes, while also promoting cell death. Inhibition of PI3K signaling was also associated with reduced activation of Akt, p70 S6 kinase, and extracellular regulated kinase signaling as well as reduced cyclin D1 expression. Administering Ad-SMAdnPI3K to mice following bile duct ligation resulted in reduced HSC activation and decreased extracellular matrix deposition, including collagen expression. A reduction in profibrogenic mediators, including transforming growth factor beta, tissue inhibitor of metalloproteinase 1, and connective tissue growth factor was also noted. However, liver damage, assessed by alanine aminotransferase levels, was not reduced. Conclusion: Inhibition of PI3K signaling in HSCs during active fibrogenesis inhibits extracellular matrix deposition, including synthesis of type I collagen, and reduces expression of profibrogenic factors. These data suggest that targeting PI3K signaling in HSCs may represent an effective therapeutic target for hepatic fibrosis. (HEPATOLOGY 2009;50:1512-1523

HOTAIR Epigenetically Modulates PTEN Expression via MicroRNA-29b: A Novel Mechanism in Regulation of Liver Fibrosis

“…For targeting HSCs, the a-SMA promoter was amplified from the pSMP8 plasmid and the PCR product cloned into the pTOPO plasmid (Invitrogen) as described previously. 41 Then, the a-SMA promoter was excised from the pTOPO plasmid using EcoRI and cloned into the EcoRI site in pDNR plasmid (BD Bioscience) upstream of the shHOTAIR insert. Sequencing confirmed orientation and integrity of the insert.…”

Transforming Growth Factor-β (TGF-β)-mediated Connective Tissue Growth Factor (CTGF) Expression in Hepatic Stellate Cells Requires Stat3 Signaling Activation

“…In addition to the canonical Smad pathway, TGF-␤ can also activate other signaling molecules such as Erk1/2, JNK, p38 MAPK, PKC, and PI3K/Akt, which is largely cell type-dependent (25). Previous studies have demonstrated that selective inhibition of those signaling pathways resulted in a potent reduction of CTGF mRNA expression in activated HSCs (26,27). The underlying mechanisms, however, have not been clarified yet.…”

Hepatic Stellate Cells in Inflammation‐Fibrosis‐Carcinoma Axis

“…Studies showed that a potent tyrosine kinase inhibitor, PTK/ZK blocks both the PDGF and TGF-ß-signaling pathways in HSCs . HSCs transducted with an adenovirus expressing a dominant negative form of PI3K under control of a-SMA promoter resulted in decreased proliferation, migration, collagen expression, and several additional profibrogenic genes, while also promoting cell death (Son et al, 2009). These results indicated that intervention with TGF-ß and PDGF signaling and their crosstalk signaling pathways is highly promising on preventing and destroying the inflammation-fibrosis-carcinoma axis.…”