Loss of Hepatic Carcinoembryonic Antigen-Related Cell Adhesion Molecule 1 Links Nonalcoholic Steatohepatitis to Atherosclerosis

Regulation of lipid storage and inflammation in the liver by CEACAM1

This review focuses on a special aspect of hepatic lipid storage and inflammation that occurs during nutritional excess in obesity. Mounting evidence supports that prolonged excess fatty acid (FA) uptake in the liver is strongly associated with hepatic lipid storage and inflammation and that the two processes are closely linked by a homeostatic mechanism. There is also strong evidence that bacterial lipids may enter the gut by a common mechanism with lipid absorption and that there is a set point to determine when their uptake triggers an inflammatory response in the liver. In fact, the progression from high uptake of FAs in the liver resulting in Metabolic dysfunction-associated steatotic liver disease (MASLD) to the development of the more serious Metabolic dysfunction-associated steatohepatitis (MASH) depends on the degree of inflammation and its progression from an acute to a chronic state. Thus, MASLD/MASH implicates both excess fatty acids and progressive inflammation in the aetiology of liver disease. We start the discussion by introduction of CD36, a major player in FA and lipopolysaccharide (LPS) uptake in the duodenum, liver and adipose tissue. We will then introduce CEACAM1, a major player in the regulation of hepatic de novo lipogenesis and the inflammatory response in the liver, and its dual association with CD36 in enterocytes and hepatocytes. We conclude that CEACAM1 and CD36 together regulate lipid droplet formation and inflammation in the liver.

CEACAM1 in vascular homeostasis and inflammation

INTRODUCTION

The glycoprotein Carcinoembryonic Antigen-related Cell Adhesion Molecule 1 (CEACAM1), also known as CD66a, is a member of the immunoglobulin superfamily. It is expressed in a variety of tissues including epithelial, immune, as well as endothelial cells, and is crucial to diverse physiological and pathological mechanisms. This review aims to provide a comprehensive understanding of CEACAM1's multifaceted roles in vascular biology and inflammatory processes.

METHODS

Directed literature research was conducted using databases, such as PubMed, and relevant studies were categorized based on the physiological effects of CEACAM1.

RESULTS

CEACAM1 plays a pivotal role in vascular homeostasis, particularly influencing the formation, maturation, and aging of blood vessels, as well as the endothelial barrier function. It supports endothelium-dependent vasodilation and nitric oxide formation, thus promoting vascular integrity and regulating blood pressure. Additionally, CEACAM1 is of emerging importance to vascular inflammation and its potential clinical consequences.

CONCLUSION

CEACAM1 is a crucial regulator of vascular homeostasis and inflammation with significant implications for cardiovascular health. Despite the lack of understanding of tissue-specific modulation and isoform-dependent mechanisms, CEACAM1 could be a promising therapeutic target for the prevention of cardiovascular disease in the future.

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.

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+Cc1^fl/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+Cc1^fl/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.