Regulation of peroxisome proliferator-activated receptor-γ in liver fibrosis

Abstract

The peroxisome proliferator-activated receptors (PPARs) impart diverse cellular effects in biological systems. Because stellate cell activation during liver injury is associated with declining PPARgamma expression, we hypothesized that its expression is critical in stellate cell-mediated fibrogenesis. We therefore modulated its expression during liver injury in vivo. PPARgamma was depleted in rat livers by using an adenovirus-Cre recombinase system. PPARgamma was overexpressed by using an additional adenoviral vector (AdPPARgamma). Bile duct ligation was utilized to induce stellate cell activation and liver fibrosis in vivo; phenotypic effects (collagen I, smooth muscle alpha-actin, hydroxyproline content, etc.) were measured. PPARgamma mRNA levels decreased fivefold and PPARgamma protein was undetectable in stellate cells after culture-induced activation. During activation in vivo, collagen accumulation, assessed histomorphometrically and by hydroxyproline content, was significantly increased after PPARgamma depletion compared with controls (1.28 +/- 0.14 vs. 1.89 +/- 0.21 mg/g liver tissue, P < 0.03). In isolated stellate cells, AdPPARgamma overexpression resulted in significantly increased adiponectin mRNA expression and decreased collagen I and smooth muscle alpha-actin mRNA expression compared with controls. During in vivo fibrogenesis, rat livers exposed to AdPPARgamma had significantly less fibrosis than controls. Collagen I and smooth muscle alpha-actin mRNA expression were significantly reduced in AdPPARgamma-infected rats compared with controls (P < 0.05, n = 10). PPARgamma-deficient mice exhibited enhanced fibrogenesis after liver injury, whereas PPARgamma receptor overexpression in vivo attenuated stellate cell activation and fibrosis. The data highlight a critical role for PPARgamma during in vivo fibrogenesis and emphasize the importance of the PPARgamma pathway in stellate cells during liver injury.

Sonic hedgehog is an autocrine viability factor for myofibroblastic hepatic stellate cells

“…Amplification reactions were performed using a SYBR Green PCR Master Mix (Applied Biosystems). cDNA samples (1 to 5 dilution) were used for quantitative two-step PCR as described [36]. Each sample was analyzed in triplicate.…”

Adiponectin Regulation of Stellate Cell Activation via PPARγ-Dependent and -Independent Mechanisms

“…Next, we found that exposure of Activation of hepatic stellate cells is associated with enhanced expression of the nuclear receptor PPAR␤/␦, recognized for its role in energy homeostasis, particularly lipid oxidation, 26 and with reduced expression of PPAR␥, known for its role in regulation of adipocyte differentiation. 6,27 We next examined whether adiponectin overexpression modulated the expression of specific members of the adipogenic program in stellate cells. PPAR␥, SREBP1c, and CEBP␣ were all up-regulated after overexpression of adiponectin in stellate cells ( Figure 6, C-E).…”

“…Given that stellate cell activation is associated with significant decline in PPAR␥ and that forced expression of PPAR␥ leads to reversal of stellate cell activation, 27,28 we asked whether the effect of PPAR␥ is dependent on adiponectin. Primary stellate cells from adiponectin-deficient animals and controls were exposed to the PPAR␥ ligand troglitazone (5 g/mL) for 5 days.…”

“…PPAR␥ ligands are known to prevent stellate cell activation 27 (Figure 7, A and B). Furthermore, our data suggest that the effect of PPAR␥ ligands on stellate cells is adiponectin dependent.…”

Aquaporin-1 Promotes Angiogenesis, Fibrosis, and Portal Hypertension Through Mechanisms Dependent on Osmotically Sensitive MicroRNAs

“…24 Briefly, frozen tissue was weighed and processed using hydrochloric acid hydrolysis and chloramine-T-dimethylaminobenzaldehyde incubation, and absorbance at 561 nm was recorded and compared with a standard prepared from commercial hydroxyproline (Sigma).…”