Loss of CEACAM1 in endothelial cells causes hepatic fibrosis.

OBJECTIVES: Hepatocytic CEACAM1 plays a critical role in NASH pathogenesis, as bolstered by the development of insulin resistance, visceral obesity, steatohepatitis and fibrosis in mice with global Ceacam1 (Cc1) deletion. In contrast, VECadCre+Cc1fl/fl mice with endothelial loss of Cc1 manifested insulin sensitivity with no visceral obesity despite elevated NF-κB signaling and increased systemic inflammation. We herein investigated whether VECadCre+Cc1fl/fl male mice develop hepatic fibrosis and whether this is mediated by increased production of endothelin1 (ET1), a transcriptional NF-κB target. METHODS: VECadCre+Et1.Cc1fl/fl mice with combined endothelial loss of Cc1/Et1 genes were generated. Histological and immunohistochemical analyses were conducted on their livers and on liver tissue biopsies from adult patients undergoing bariatric surgery or from patients with NASH diagnosis receiving liver transplant. RESULTS: Hepatic fibrosis and inflammatory infiltration developed in VECadCre+Cc1fl/fl liver parenchyma. This was preceded by increased ET1 production and reversed with combined endothelial loss of Et1. Conditioned media from VECadCre+Cc1fl/fl, but not VECadCre+Et1.Cc1fl/fl primary liver endothelial cells activated wild-type hepatic stellate cells; a process inhibited by bosentan, an ETAR/ETBR dual antagonist. Consistently, immunohistochemical analysis of liver biopsies from patients with NASH showed a decline in endothelial CEACAM1 in parallel with increased plasma endothelin1 levels and progression of hepatic fibrosis stage. CONCLUSIONS: The data demonstrated that endothelial CEACAM1 plays a key role in preventing hepatic fibrogenesis by reducing autocrine endothelin1 production.

Aortic Fibrosis in Insulin-Sensitive Mice with Endothelial Cell-Specific Deletion of Ceacam1 Gene.

(1) Background: Mice with global Ceacam1 deletion developed plaque-like aortic lesions even on C57BL/6J background in the presence of increased endothelial cell permeability and insulin resistance. Loss of endothelial Ceacam1 gene caused endothelial dysfunction and reduced vascular integrity without affecting systemic insulin sensitivity. Because endothelial cell injury precedes atherosclerosis, we herein investigated whether the loss of endothelial Ceacam1 initiates atheroma formation in the absence of insulin resistance. (2) Methods: Endothelial cell-specific Ceacam1 null mice on C57BL/6J.Ldlr-/- background (Ldlr-/-VECadCre+Cc1fl/fl) were fed an atherogenic diet for 3-5 months before metabolic, histopathological, and en-face analysis of aortae were compared to their control littermates. Sirius Red stain was also performed on liver sections to analyze hepatic fibrosis. (3) Results: These mice displayed insulin sensitivity without significant fat deposition on aortic walls despite hypercholesterolemia. They also displayed increased inflammation and fibrosis. Deleting Ceacam1 in endothelial cells caused hyperactivation of VEGFR2/Shc/NF-κB pathway with resultant transcriptional induction of NF-κB targets. These include IL-6 that activates STAT3 inflammatory pathways, in addition to endothelin-1 and PDGF-B profibrogenic effectors. It also induced the association between SHP2 phosphatase and VEGFR2, downregulating the Akt/eNOS pathway and reducing nitric oxide production, a characteristic feature of endothelial dysfunction. Similarly, hepatic inflammation and fibrosis developed in Ldlr-/-VECadCre+Cc1fl/fl mice without an increase in hepatic steatosis. (4) Conclusions: Deleting endothelial cell Ceacam1 caused hepatic and aortic inflammation and fibrosis with increased endothelial dysfunction and oxidative stress in the presence of hypercholesterolemia. However, this did not progress into frank atheroma formation. Because these mice remained insulin sensitive, the study provides an in vivo demonstration that insulin resistance plays a critical role in the pathogenesis of frank atherosclerosis.

Insulin Sensitivity Is Retained in Mice with Endothelial Loss of Carcinoembryonic Antigen Cell Adhesion Molecule 1.

CEACAM1 regulates endothelial barrier integrity. Because insulin signaling in extrahepatic target tissues is regulated by insulin transport through the endothelium, we aimed at investigating the metabolic role of endothelial CEACAM1. To this end, we generated endothelial cell-specific Ceacam1 null mice (VECadCre+Cc1fl/fl) and carried out their metabolic phenotyping and mechanistic analysis by comparison to littermate controls. Hyperinsulinemic-euglycemic clamp analysis showed intact insulin sensitivity in VECadCre+Cc1fl/fl mice. This was associated with the absence of visceral obesity and lipolysis and normal levels of circulating non-esterified fatty acids, leptin, and adiponectin. Whereas the loss of endothelial Ceacam1 did not affect insulin-stimulated receptor phosphorylation, it reduced IRS-1/Akt/eNOS activation to lower nitric oxide production resulting from limited SHP2 sequestration. It also reduced Shc sequestration to activate NF-κB and increase the transcription of matrix metalloproteases, ultimately inducing plasma IL-6 and TNFα levels. Loss of endothelial Ceacam1 also induced the expression of the anti-inflammatory CEACAM1-4L variant in M2 macrophages in white adipose tissue. Together, this could cause endothelial barrier dysfunction and facilitate insulin transport, sustaining normal glucose homeostasis and retaining fat accumulation in adipocytes. The data assign a significant role for endothelial cell CEACAM1 in maintaining insulin sensitivity in peripheral extrahepatic target tissues.

Regulation of hepatic fibrosis by carcinoembryonic antigen-related cell adhesion molecule 1.

OBJECTIVE: NAFLD is a complex disease marked by cellular abnormalities leading to NASH. NAFLD patients manifest low hepatic levels of CEACAM1, a promoter of insulin clearance. Consistently, Cc1-/- null mice displayed spontaneous hyperinsulinemia/insulin resistance and steatohepatitis. Liver-specific reconstitution of Ceacam1 reversed these metabolic anomalies in 8-month-old Cc1-/-xliver+ mice fed a regular chow diet. The current study examined whether it would also reverse progressive hepatic fibrosis in mice fed a high-fat (HF) diet. METHODS: 3-Month-old mice were fed a high-fat diet for 3-5 months, and metabolic and histopathological analysis were conducted to evaluate their NASH phenotype. RESULTS: Reconstituting CEACAM1 to Cc1-/- livers curbed diet-induced liver dysfunction and NASH, including macrovesicular steatosis, lobular inflammation, apoptosis, oxidative stress, and chicken-wire bridging fibrosis. Persistence of hepatic fibrosis in HF-fed Cc1-/- treated with nicotinic acid demonstrated a limited role for lipolysis and adipokine release in hepatic fibrosis caused by Ceacam1 deletion. CONCLUSIONS: Restored metabolic and histopathological phenotype of HF-fed Cc1-/-xliver+xliver+ assigned a critical role for hepatic CEACAM1 in preventing NAFLD/NASH including progressive hepatic fibrosis.

Forced Hepatic Overexpression of CEACAM1 Curtails Diet-Induced Insulin Resistance.

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) regulates insulin sensitivity by promoting hepatic insulin clearance. Liver-specific inactivation or global null-mutation of Ceacam1 impairs hepatic insulin extraction to cause chronic hyperinsulinemia, resulting in insulin resistance and visceral obesity. In this study we investigated whether diet-induced insulin resistance implicates changes in hepatic CEACAM1. We report that feeding C57/BL6J mice a high-fat diet reduced hepatic CEACAM1 levels by >50% beginning at 21 days, causing hyperinsulinemia, insulin resistance, and elevation in hepatic triacylglycerol content. Conversely, liver-specific inducible CEACAM1 expression prevented hyperinsulinemia and markedly limited insulin resistance and hepatic lipid accumulation that were induced by prolonged high-fat intake. This was partly mediated by increased hepatic ß-fatty acid oxidation and energy expenditure. The data demonstrate that the high-fat diet reduced hepatic CEACAM1 expression and that overexpressing CEACAM1 in liver curtailed diet-induced metabolic abnormalities by protecting hepatic insulin clearance.

Caloric restriction reverses hepatic insulin resistance and steatosis in rats with low aerobic capacity.

Rats selectively bred for low aerobic running capacity exhibit the metabolic syndrome, including hyperinsulinemia, insulin resistance, visceral obesity, and dyslipidemia. They also exhibit features of nonalcoholic steatohepatitis, including chicken-wire fibrosis, inflammation, and oxidative stress. Hyperinsulinemia in these rats is associated with impaired hepatic insulin clearance. The current studies aimed to determine whether these metabolic abnormalities could be reversed by caloric restriction (CR). CR by 30% over a period of 2-3 months improved insulin clearance in parallel to inducing the protein content and activation of the carcinoembryonic antigen-related cell adhesion molecule 1, a main player in hepatic insulin extraction. It also reduced glucose and insulin intolerance and serum and tissue (liver and muscle) triglyceride levels. Additionally, CR reversed inflammation, oxidative stress, and fibrosis in liver. The data support a significant role of CR in the normalization of insulin and lipid metabolism in liver.

Carcinoembryonic antigen-related cell adhesion molecule 2 controls energy balance and peripheral insulin action in mice.

BACKGROUND & AIMS: The carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is a transmembrane glycoprotein with pleotropic functions, including clearance of hepatic insulin. We investigated the functions of the related protein CEACAM2, which has tissue-specific distribution (kidney, uterus, and crypt epithelia of intestinal tissues), in genetically modified mice. METHODS: Ceacam2-null mice (Cc2-/-) were generated from a 129/SvxC57BL/6J background. Female mice were assessed by hyperinsulinemic-euglycemic clamp analysis and indirect calorimetry and body fat composition was measured. Cc2-/- mice and controls were fed as pairs, given insulin tolerance tests, and phenotypically characterized. RESULTS: Female, but not male Cc2-/- mice exhibited obesity that resulted from hyperphagia and reduced energy expenditure. Pair feeding experiments showed that hyperphagia led to peripheral insulin resistance. Insulin action was normal in liver but compromised in skeletal muscle of female Cc2-/- mice; the mice had incomplete fatty acid oxidation and impaired glucose uptake and disposal. The mechanism of hyperphagia in Cc2-/- mice is not clear, but appears to result partly from increased hyperinsulinemia-induced hypothalamic fatty acid synthase levels and activity. Hyperinsulinemia was caused by increased insulin secretion. CONCLUSIONS: In mice, CEACAM2 is expressed by the hypothalamus. Cc2-/- mice develop obesity from hyperphagia and reduced energy expenditure, indicating its role in regulating energy balance and insulin sensitivity.

Test of the principle of initial value in rat genetic models of exercise capacity.

An inverse relationship between initial level of physical capacity and the magnitude of response to training is termed the principle of initial value. We tested the operation of this principle under experimental conditions of minimal genetic and environmental variation. Inbred rat strains previously identified as genetic models of low [Copenhagen (COP)] and high [Dark Agouti (DA)] intrinsic (untrained) exercise capacity were trained for 8 wk on a treadmill using two disparate protocols: 1) a relative mode where each rat exercised daily according to its initial capacity, and 2) an absolute mode where both strains received the same amount of training independent of initial capacity. Response to exercise was the change in running capacity as estimated by meters run to exhaustion before and after training. When trained with the relative mode, COP rats gained 88 m (+21%; NS) whereas DA rats increased distance run by 228 m (+36%; P < 0.001). When each strain trained with the same absolute amount of training, the COP strain showed essentially no change (-6 m, -2%) and the DA strain gained 325 m (+49%; P < 0.009). Differences in response to exercise between the COP and DA could not be explained by body mass differences, oxidative enzyme activity (citrate synthase or ATP), or spontaneous behavioral activity. Our data demonstrate that genetic factors causative of high response to exercise are not uniquely associated with genetic factors for low intrinsic capacity and thus are not in accord with the principle of initial value.

Interaction between altered insulin and lipid metabolism in CEACAM1-inactive transgenic mice.

Inactivation of CEACAM1 in L-SACC1 mice by a dominant-negative transgene in liver impairs insulin clearance and increases serum free fatty acid (FFA) levels, resulting in insulin resistance. The contribution of elevated FFAs in the pathogenesis of insulin resistance is herein investigated. Treatment of L-SACC1 female mice with carnitine restored plasma FFA content. Concomitantly, it normalized insulin levels without directly regulating receptor-mediated insulin internalization and prevented glucose tolerance in these mice. Similarly, treatment with nicotinic acid, a lipolysis inhibitor, restored insulin-stimulated receptor uptake in L-SACC1 mice. Taken together, these data suggest that chronic elevation in plasma FFAs levels contributes to the regulation of insulin metabolism and action in L-SACC1 mice.

CEACAM1 regulates insulin clearance in liver.

We hypothesized that insulin stimulates phosphorylation of CEACAM1 which in turn leads to upregulation of receptor-mediated insulin endocytosis and degradation in the hepatocyte. We have generated transgenic mice over-expressing in liver a dominant-negative, phosphorylation-defective S503A-CEACAM1 mutant. Supporting our hypothesis, we found that S503A-CEACAM1 transgenic mice developed hyperinsulinemia resulting from impaired insulin clearance. The hyperinsulinemia caused secondary insulin resistance with impaired glucose tolerance and random, but not fasting, hyperglycemia. Transgenic mice developed visceral adiposity with increased amounts of plasma free fatty acids and plasma and hepatic triglycerides. These findings suggest a mechanism through which insulin signaling regulates insulin sensitivity by modulating hepatic insulin clearance.