Conditional deletion of CEACAM1 causes hepatic stellate cell activation.

Objectives: Hepatic CEACAM1 expression declines with advanced hepatic fibrosis stage in patients with MASH. Global and hepatocyte-specific deletions of Ceacam1 impair insulin clearance to cause hepatic insulin resistance and steatosis. They also cause hepatic inflammation and fibrosis, a condition characterized by excessive collagen production from activated hepatic stellate cells (HSCs). Given the positive effect of PPARγ on CEACAM1 transcriptoin and on HSCs quiescence, the current studies investigated whether CEACAM1 loss from HSCs causes their activation. Methods: We examined whether lentiviral shRNA-mediated CEACAM1 donwregulation (KD-LX2) activates cultured human LX2 stellate cells. We also generated LratCre+Cc1 fl/fl mutants with conditional Ceacam1 deletion in HSCs and characterized their MASH phenotype. Media transfer experiments were employed to examine whether media from mutant human and murine HSCs activate their wild-type counterparts. Results: LratCre+Cc1 fl/fl mutants displayed hepatic inflammation and fibrosis but without insulin resistance or hepatic steatosis. Their HSCs, like KD-LX2 cells, underwent myofibroblastic transformation and their media activated wild-type HDCs. This was inhibited by nicotinic acid treatment which stemmed the release of IL-6 and fatty acids, both of which activate the epidermal growth factor receptor (EGFR) tyrosine kinase. Gefitinib inhibition of EGFR and its downstream NF-κB/IL-6/STAT3 inflammatory and MAPK-proliferation pathways also blunted HSCs activation in the absence of CEACAM1. Conclusions: Loss of CEACAM1 in HSCs provoked their myofibroblastic transformation in the absence of insulin resistance and hepatic steatosis. This response is mediated by autocrine HSCs activation of the EGFR pathway that amplifies inflammation and proliferation.

Increased Glucose-induced Secretion of Glucagon-like Peptide-1 in Mice Lacking the Carcinoembryonic Antigen-related Cell Adhesion Molecule 2 (CEACAM2).

Carcinoembryonic antigen-related cell adhesion molecule 2 (CEACAM2) regulates food intake as demonstrated by hyperphagia in mice with the Ceacam2 null mutation (Cc2(-/-)). This study investigated whether CEACAM2 also regulates insulin secretion. Ceacam2 deletion caused an increase in ß-cell secretory function, as assessed by hyperglycemic clamp analysis, without affecting insulin response. Although CEACAM2 is expressed in pancreatic islets predominantly in non-ß-cells, basal plasma levels of insulin, glucagon and somatostatin, islet areas, and glucose-induced insulin secretion in pooled Cc2(-/-) islets were all normal. Consistent with immunofluorescence analysis showing CEACAM2 expression in distal intestinal villi, Cc2(-/-) mice exhibited a higher release of oral glucose-mediated GLP-1, an incretin that potentiates insulin secretion in response to glucose. Compared with wild type, Cc2(-/-) mice also showed a higher insulin excursion during the oral glucose tolerance test. Pretreating with exendin(9-39), a GLP-1 receptor antagonist, suppressed the effect of Ceacam2 deletion on glucose-induced insulin secretion. Moreover, GLP-1 release into the medium of GLUTag enteroendocrine cells was increased with siRNA-mediated Ceacam2 down-regulation in parallel to an increase in Ca(2+) entry through L-type voltage-dependent Ca(2+) channels. Thus, CEACAM2 regulates insulin secretion, at least in part, by a GLP-1-mediated mechanism, independent of confounding metabolic factors.

Hepatic CEACAM1 Over-Expression Protects Against Diet-Induced Fibrosis and Inflammation in White Adipose Tissue.

CEACAM1 promotes insulin extraction, an event that occurs mainly in liver. Phenocopying global Ceacam1 null mice (Cc1(-/-) ), C57/BL6J mice fed a high-fat (HF) diet exhibited reduced hepatic CEACAM1 levels and impaired insulin clearance, followed by hyperinsulinemia, insulin resistance, and visceral obesity. Conversely, forced liver-specific expression of CEACAM1 protected insulin sensitivity and energy expenditure, and limited gain in total fat mass by HF diet in L-CC1 mice. Because CEACAM1 protein is barely detectable in white adipose tissue (WAT), we herein investigated whether hepatic CEACAM1-dependent insulin clearance pathways regulate adipose tissue biology in response to dietary fat. While HF diet caused a similar body weight gain in L-CC1, this effect was delayed and less intense relative to wild-type (WT) mice. Histological examination revealed less expansion of adipocytes in L-CC1 than WT by HF intake. Immunofluorescence analysis demonstrated a more limited recruitment of crown-like structures, and qRT-PCR analysis showed no significant rise in TNFα mRNA levels in response to HF intake in L-CC1 than WT mice. Unlike WT, HF diet did not activate TGF-ß in WAT of L-CC1 mice, as assessed by Western analysis of Smad2/3 phosphorylation. Consistently, HF diet caused relatively less collagen deposition in L-CC1 than WT mice, as shown by Trichrome staining. Coupled with reduced lipid redistribution from liver to visceral fat, lower inflammation and fibrosis could contribute to protected energy expenditure against HF diet in L-CC1 mice. The data underscore the important role of hepatic insulin clearance in the regulation of adipose tissue inflammation and fibrosis.