Liver X Receptor Signaling Is a Determinant of Stellate Cell Activation and Susceptibility to Fibrotic Liver Disease

doi:10.1053/j.gastro.2010.11.053

Gastroenterology

Volume 140, Issue 3, March 2011, Pages 1052-1062

https://doi.org/10.1053/j.gastro.2010.11.053 Get rights and content

Background & Aims

Liver X receptors (LXRs) are lipid-activated nuclear receptors with important roles in cholesterol transport, lipogenesis, and anti-inflammatory signaling. Hepatic stellate cells activate during chronic liver injury and mediate the fibrotic response. These cells are also major repositories for lipids, but the role of lipid metabolism during stellate cell activation remains unclear. We investigated the role of LXR signaling stellate cell activation and susceptibility to fibrotic liver disease.

Methods

Immortalized and primary stellate cells purified from mice were treated with highly specific LXR ligands. Carbon tetrachloride and methionine/choline deficiency were used as chronic liver injury models. Reciprocal bone marrow transplants were performed to test the importance of hematopoietically derived cells to the fibrotic response.

Results

LXR ligands suppressed markers of fibrosis and stellate cell activation in primary mouse stellate cells. Lxrαβ^−/− stellate cells produce increased levels of inflammatory mediators, and conditioned media from Lxrαβ^−/− cells increases the fibrogenic program of wild-type cells. Furthermore, Lxrαβ^−/− stellate cells exhibit altered lipid morphology and increased expression of fibrogenic genes, suggesting they are primed for activation. In vivo, Lxrαβ^−/− mice have marked susceptibility to fibrosis in 2 injury models. Bone marrow transplants point to altered stellate cell function, rather than hematopoietic cell inflammation, as the primary basis for the Lxrαβ^−/− phenotype.

Conclusions

These results reveal an unexpected role for LXR signaling and lipid metabolism in the modulation of hepatic stellate cell function.

Section snippets

Mice and Liver Injury Models

Male Lxrαβ^−/− mice (12–24 weeks old) were obtained by backcrossing ≥10 generations on a pure C57/Bl6 background. Animal housing was temperature controlled with a 12-hour light/dark cycle, pathogen-free conditions, and ad libitum access to water and standard chow. The following specialized diets (Research Diets, New Brunswick, NJ) were used (see Figure 6): control diet, A02082003B; methionine/choline-deficient (MCD) diet, A02082002B. These diets differ only in the presence or absence of dl

LXRs Have Reciprocal Anti-inflammatory and Lipid Metabolic Effects in Activated Stellate Cells

To characterize nuclear receptor expression in hepatic stellate cells, we performed quantitative real-time polymerase chain reaction on 2 immortalized, fully activated stellate cell lines: rat HSC-T6 cells²⁴ and human LX-2 cells.²⁵ These lines are supposed to model stellate cells in their fully activated, myofibroblast-like state. Supplementary Table 1 lists the relative abundance of RXR heterodimers found in LX-2 cells, with LXRβ, vitamin D, thyroid, retinoic acid (RARα), and retinoid X (RXRα)

Discussion

LXRs are key regulators of cholesterol homeostasis and hepatic lipogenesis,¹⁶ but they also transrepress inflammatory genes in macrophages¹⁷ and mediate antiproliferative effects in T cells during the adaptive immune response.²⁰ We have shown here that LXRs are among the most highly expressed nuclear receptors in stellate cells and that LXR signaling regulates the expression of genes linked to metabolism, inflammation, and fibrogenesis in primary cells. Consistent with the ability of LXRs to

Acknowledgments

The authors thank David Mangelsdorf for LXR-null mice, Tim Willson for GW3965, Scott Friedman for the HSC-T6 and LX-2 cell lines, Sam French Sr for assistance with α–smooth muscle actin immunohistochemistry, Clara Magyar for digital quantification of fibrosis, and Jon Salazar for assistance with mouse husbandry.

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: Conflicts of interest The authors disclose no conflicts.

: Funding Supported by National Institutes of Health training grant T32 DK07180-30, UCLA Center for Ulcer Research and Education (CURE) Pilot and Feasibility Study grant 441349-BB-39108 (to S.W.B.), and grants HL66088, HL30568, and DK063491 (to P.T.). Additional support for cell isolation (H.T.) was from R24AA12885 (Non-Parenchymal Liver Cell Core) and P50AA11999 (Southern California Research Center for ALPD & Cirrhosis). P.T. is an investigator of the Howard Hughes Medical Institute.

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Basic—Liver, Pancreas, and Biliary TractLiver X Receptor Signaling Is a Determinant of Stellate Cell Activation and Susceptibility to Fibrotic Liver Disease

Background & Aims

Methods

Results

Conclusions

Section snippets

Mice and Liver Injury Models

LXRs Have Reciprocal Anti-inflammatory and Lipid Metabolic Effects in Activated Stellate Cells

Discussion

Acknowledgments

Biochim Biophys Acta

Gastroenterology

J Invest Dermatol

Cell

J Biol Chem

Gastroenterology

J Biol Chem

J Lipid Res

Hepatology

Mol Cell

Hepatic stellate cells: protean, multifunctional, and enigmatic cells of the liver

Physiol Rev

Liver fibrosis

J Clin Invest

Fat-storing cells (lipocytes) in human liver

Arch Pathol

“Sternzellen” in the liver: perisinusoidal cells with special reference to storage of vitamin A

Am J Anat

Hepatic lipocytes: the principal collagen-producing cells of normal rat liver

Proc Natl Acad Sci U S A

Cellular sources of noncollagenous matrix proteins: role of fat-storing cells in fibrogenesis

Semin Liver Dis

Stimulation of hepatic lipocyte collagen production by Kupffer cell-derived transforming growth factor beta: implication for a pathogenetic role in alcoholic liver fibrogenesis

Hepatology

Rat hepatic lipocytes express smooth muscle actin upon activation in vivo and in culture

J Submicrosc Cytol Pathol

Basic—Liver, Pancreas, and Biliary Tract
Liver X Receptor Signaling Is a Determinant of Stellate Cell Activation and Susceptibility to Fibrotic Liver Disease