Reduced Hepatic Carcinoembryonic Antigen-Related Cell Adhesion Molecule 1 Level in Obesity

Abstract

Impairment of insulin clearance is being increasingly recognized as a critical step in the development of insulin resistance and metabolic disease. The carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) promotes insulin clearance. Null deletion or liver-specific inactivation of Ceacam1 in mice causes a defect in insulin clearance, insulin resistance, steatohepatitis, and visceral obesity. Immunohistological analysis revealed reduction of hepatic CEACAM1 in obese subjects with fatty liver disease. Thus, we aimed to determine whether this occurs at the hepatocyte level in response to systemic extrahepatic factors and whether this holds across species. Northern and Western blot analyses demonstrate that CEACAM1 mRNA and protein levels are reduced in liver tissues of obese individuals compared to their lean age-matched counterparts. Furthermore, Western analysis reveals a comparable reduction of CEACAM1 protein in primary hepatocytes derived from the same obese subjects. Similar to humans, Ceacam1 mRNA level, assessed by quantitative RT-PCR analysis, is significantly reduced in the livers of obese Zucker (fa/fa, ZDF) and Koletsky (f/f) rats relative to their age-matched lean counterparts. These studies demonstrate that the reduction of hepatic CEACAM1 in obesity occurs at the level of hepatocytes and identify the reduction of hepatic CEACAM1 as a common denominator of obesity across multiple species.

Keywords: carcinoembryonic antigen-related cell adhesion molecule 1; fatty liver disease; hyperinsulinemia; insulin clearance; insulin resistance; obesity.

Figure 1

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) level in human livers. Livers derived from anonymous obese (body mass index >30 kg/m²) 45- to 50-year-old male subjects and age-, sex-, and race-matched lean subjects. (A) CEACAM1 mRNA (CC1) was analyzed by Northern blot analysis of total liver mRNA and sequentially probed with cDNAs for CEACAM1 (CC1) followed by GAPDH for normalization. (B) Liver lysates from obese and lean subjects were analyzed by 4–12% SDS-PAGE followed by immunoblotting (Ib) with polyclonal antibody against CEACAM1 (CC1) and normalization against GAPDH. For simplicity, only two samples of each group are shown as representatives of three independent experiments. The graph on the right represents densitometry analysis of CEACAM1 bands relative to those of GAPDH in all tissues. Values shown as mean ± SEM with *P < 0.05 being statistically significant.

Figure 2

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) level in human primary hepatocytes. Primary cells were derived from the livers of the same anonymous donors and analyzed by Western analysis as in Figure 1, immunoblotting (Ib) with polyclonal antibody against CEACAM1 (CC1) and normalizing against GAPDH. For simplicity, only two samples of each group are shown as representatives of three independent experiments. The graph on the right represents densitometry analysis of CEACAM1 bands relative to those of GAPDH in all cells. Values shown as mean ± SEM with *P < 0.05 being statistically significant.

Figure 3

Hepatic carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) level in obese rodents. Ceacam1 mRNA was analyzed by qRT-PCR analysis of total liver RNA, normalized to β-Actin, from livers derived from obese fa/fa, ZDF, and Koletsky f/f rats and age-matched lean controls (n = 10/lean or obese/each strain). Values shown as mean ± SEM with *P < 0.05 being statistically significant.