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

Abstract

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.

Loss of CEACAM1 in endothelial cells causes hepatic fibrosis

“…Consistent with the role of endothelial cell CEACAM1 in promoting cell differentiation [15] and regulating barrier function [16], Cc1 − /− mice develop endothelial and vascular dysfunction [12,16]. Similarly, mice with endothelial loss of Ceacam1 (VECadCre+Cc1 fl/fl ) exhibit disturbed endothelial cell junctions and endothelial dysfunction (characterized by reduced eNOSdependent NO production) together with increased circulating cytokine levels driven by hyperactivated NF-κB pathways in endothelial cells [17].…”

“…1A, panel d), and their hepatic and plasma triacylglycerol levels were normal (Table 1). Consistent with normal plasma insulin and NEFA [17], their livers manifested unchanged mRNA levels of lipogenic genes [Srebp-1c and fatty acid synthase (Fasn)] and of Cd36 fatty acid translocase (Table S4).…”

“…As previously detailed [17], VECadCre+Cc1 fl/fl (hereafter VECad+Cc1 fl/fl ) were generated by crossing Ceacam1(Cc1) loxp/loxp with mice expressing Cre under the transcriptional control of VECadherin promoter (Jackson Laboratories, Bar Harbor, ME). Mice were backcrossed with C57BL/6J.Endothelin1loxp/loxp(Et1 loxp/loxp ) mice, generated by Prof. M. Yanagisawa (University of Tsukuba, Japan) [18] and generously provided by Dr. D. E. Kohan (University of Utah).…”

Conditional deletion of CEACAM1 causes hepatic stellate cell activation

“…Bone marrow-derived macrophages [11] were obtained by flashing femurs and tibias with sterile Roswell Park Memorial Institute (RPMI)-1640 medium from Gibco supplemented with 10% horse serum, 1% L-glutamine, 1% Penicilin/Streptomycin and 10ng/ml Recombinant Mouse factor macrophage colony-stimulating factor [M-CSF] R&D Systems, Minneapolis, MN). Primary endothelial cells [13; 14] isolated from livers and hearts were maintained in DMEM-F12 (Gibco) supplemented with 20% FBS, 1% glutamine, and 1% penicillin/streptomycin (Gibco), 100 ug/ml Heparin (Sigma-Aldrich) and 100ug/ml Endothelial Cell Growth supplement [ECGS) (EMD Millipore Corporation Burlington MA).…”

Regulation of Insulin Clearance by Non-Esterified Fatty Acids

“…Additionally, CEACAM1 directly regulates insulin signaling. The insulin–insulin receptor complex formation and internalization are rapidly followed by binding of CEACAM1 to SHP2 phosphatase to sequester it and sustain persistent phosphorylation of insulin receptor substrate-1 and -2 (IRS-1 and IRS-2), key insulin signaling molecules [ 1 , 11 ]. IRS-1/2 signals through the PI3 kinase to maintain insulin action as vesicular insulin degradation occurs.…”