Dysregulation of Kupffer Cells/Macrophages and Natural Killer T Cells in Steatohepatitis in LXRα Knockout Male Mice

Abstract

Liver X receptor (LXR) α expression is mainly localized to metabolic tissues, such as the liver, whereas LXRβ is ubiquitously expressed. LXRα is activated by oxysterols and plays an important role in the regulation of lipid metabolism in metabolic tissues. In macrophages, LXRs stimulate reverse cholesterol transport and regulate immune responses. Although a high-cholesterol diet induces severe steatohepatitis in LXRα-knockout (KO) mice, the underlying mechanisms linking lipid metabolism and immune responses remain largely unknown. In this study, we investigated the role of LXRα in the pathogenesis of steatohepatitis by assessing the effects of a high-fat and high-cholesterol diet (HFCD) on hepatic immune cell proportion and function as well as lipid metabolism in wild-type (WT) and LXRα-KO mice. HFCD feeding induced severe steatohepatitis in LXRα-KO mice compared with WT mice. These mice had higher cholesterol levels in the plasma and the liver and dysregulated expression of LXR target and proinflammatory genes in both whole liver samples and isolated hepatic mononuclear cells. Flow cytometry showed an increase in CD68+CD11b+ Kupffer cells/macrophages and a decrease in invariant natural killer T cells in the liver of HFCD-fed LXRα-KO mice. These mice were more susceptible to lipopolysaccharide-induced liver injury and resistant to inflammatory responses against α-galactosylceramide or concanavalin-A treatment. The findings provide evidence for activation of bone marrow-derived Kupffer cells/macrophages and dysfunction of invariant natural killer T cells in LXRα-KO mouse liver. These findings indicate that LXRα regulates hepatic immune function along with lipid metabolism and protects against the pathogenesis of nonalcoholic steatohepatitis.

PNPLA3 I148M Variant Impairs Liver X Receptor Signaling and Cholesterol Homeostasis in Human Hepatic Stellate Cells

“…Dysregulation of hepatic triglyceride metabolism and impaired cholesterol homeostasis are widely recognized as active players in the development of NAFLD. Notably, increased intracellular FC accumulation positively correlates with the transition from simple steatosis toward NASH and with exacerbated HSC‐mediated liver fibrogenesis in mice fed a high‐cholesterol diet in two different models of hepatic fibrosis . At baseline, HSCs isolated from these mice already show increased FC accumulation, which sensitizes HSCs to TLR4 signaling, leading to down‐regulation of BAMBI and a faster response to profibrogenic actions of TGF‐β .…”

“…Considering the capacity of LXRs to repress release of inflammatory mediators in macrophages, the role of these nuclear receptors strongly leads to a link between hepatic metabolism and immune response. Liver resident macrophages lacking LXRs underline that the latter control the differentiation of the Kupffer cell population and regulate immune and inflammatory responses in mice . The activation and overexpression of LXRα following ROSI stimulation provides a direct anti‐inflammatory effect on cytokine expression in HSCs carrying the WT along with no detectable improvement in cells with the PNPLA3 variant (Fig.…”

Frontline Science: Concanavalin A-induced acute hepatitis is attenuated in vitamin D receptor knockout mice with decreased immune cell function

“…For analysis of ligand‐dependent VDR target gene expression, mice were treated with vehicle control or 1,25(OH) 2 D 3 (25 nmol/kg of body weight; Wako Pure Chemical Industries, Osaka, Japan) intraperitoneally 20 h and 2 h before euthanization with carbon dioxide. For immune cell activation by Con‐A or α‐galactosylceramide (α‐GalCer), mice were treated with Con‐A (12.5 mg/kg of body weight; Vector Laboratories, Burlingame, CA, USA) or α‐GalCer (0.1 mg/kg of body weight; Funakoshi Co., Tokyo, Japan) as reported previously . The experimental protocols adhered to the Nihon University Rules concerning animal care and use and were approved by Nihon University Animal Care and Use Committee (AP14M067, AP15M028, AP16M038, and AP17M019).…”

“…Hepatic MNCs were as previously described . To isolate hepatic MNCs, including resident Kupffer cells (F4/80 hi CD11b − cells), bone marrow‐derived macrophages (F4/80 lo CD11b + cells) and neutrophils (F4/80 − CD11b + cells), the liver tissues were minced with scissors and incubated with collagenase (Wako Pure Chemical Industries) in HBSS solution for 20 min at 37°C.…”

“…cDNAs were synthesized from total RNA samples with the ImProm‐II reverse transcription system (Promega Corporation, Madison, WI, USA), and subjected to real‐time polymerase chain reaction with the ABI PRISM 7000 sequence detection system or the StepOnePlus Real‐time PCR system (Thermo Fisher Scientific) using Power SYBR Green PCR Master Mix (Thermo Fisher Scientific). All primer sequences were reported previously . The calculated RNA values were normalized with the Cyclophilin B (gene symbol Ppib ) or glyceraldehyde‐3‐phosphate dehydrogenase ( Gapdh ) mRNA levels.…”