Abstract
Pigment epithelium-derived factor (PEDF) has been shown previously to prevent liver fibrosis and hepatic stellate cell (HSC) activation. By investigating the functional domains in PEDF, we identified a 34-mer peptide (residues Asp44-Asn77) that harbors the same function as the full-length PEDF protein. Not only did the 34-mer suppress the development of fibrosis in carbon tetrachloride (CCl4)-treated mouse liver but it also upregulated peroxisome proliferator-activated receptor-gamma (PPARγ) expression in HSCs in vivo. Platelet-derived growth factor (PDGF) plays a crucial role on the process of HSC activation in response to liver damage. The 34-mer suppressed PDGF-induced cell proliferation and expression of myofibroblastic marker proteins in primary rat HSC culture, increased the levels of PPARγ mRNA and protein in a dose-dependent manner and markedly reduced the level of active β-catenin protein, an HSC activating factor, in HSC-T6 cells. Similarly, IWR-1, an inhibitor of the Wnt response, displayed the same effect as the 34-mer in preventing HSC-T6 activation. The Wnt signaling-mediated PPARγ suppression was abolished by both the IWR-1 inhibitor and a small interfering RNA (siRNA) targeting β-catenin and the Wnt coreceptor, LRP6. Both PEDF and the 34-mer down-regulated PDGF receptor-α/β expression and blocked the PDGF-induced phosphorylation of Akt and ERK. Moreover, the inhibitory effect on PDGF receptor expression was abolished by PPARγ antagonists and PPARγ siRNA. Our observations indicate that the PEDF-derived 34-mer peptide can mimic PEDF in attenuating HSC activation. Investigation of this 34-mer peptide led to the identification of a signaling mechanism involving PPARγ induction, suppression of Wnt/β-catenin signaling and down-regulation of the PDGF receptor-α/β.
Highlights
Hepatic stellate cells (HSCs) have proliferative potential, they are quiescent in the healthy liver and are activated by inflammatory stimuli that lead to the manifestation of a myofibroblast-like phenotype, including the expression of the myofibroblast marker, a-smooth muscle actin (a-SMA) [1]
After CCl4 treatment twice a week for 3 weeks, relative mRNA levels of the platelet-derived growth factor (PDGF) isoforms and PDGFR-a/b in the mouse livers were evaluated by quantitative real-time room temperature (RT)-PCR and the results revealed that CCl4 treatment increased these mRNA levels by,2–4 fold compared to the untreated control (Fig. 1C)
We further examined stress fiber architecture inside HSCs, a characteristic feature of HSC activation induced by PDGF [4], by rhodamine-phalloidin staining of filamentous (F-) actin and immunofluorescence staining of a-SMA
Summary
Hepatic stellate cells (HSCs) have proliferative potential, they are quiescent in the healthy liver and are activated by inflammatory stimuli that lead to the manifestation of a myofibroblast-like phenotype, including the expression of the myofibroblast marker, a-smooth muscle actin (a-SMA) [1]. The expression of PDGF-A and -B chains increases significantly in infiltrating inflammatory cells [5] and activated HSCs [6]. Overexpressed PDGFR-a and –b in activated HSCs results in PDGF acting as a mitogen for myofibroblastic HSCs [7] and increases the number of fibrogenic cells thereby promoting the development of liver fibrosis. Development of novel agents targeting the PDGFR has been considered to be valuable in preventing hepatic fibrosis [8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
