Anti-EMR1 monoclonal antibody, clone Cl:A3-1 [Biotin]

Non-alcoholic fatty liver disease (NAFLD) is gaining in importance and is linked to obesity. Especially, the development of fibrosis and portal hypertension in NAFLD patients requires treatment. Transgenic TGR(mREN2)27 rats overexpressing mouse renin spontaneously develop NAFLD with portal hypertension but without obesity. This study investigated the additional role of obesity in this model on the development of portal hypertension and fibrosis. Obesity was induced in twelve-week old TGR(mREN2)27 rats after receiving Western diet (WD) for two or four weeks. Liver fibrosis was assessed using standard techniques. Hepatic expression of transforming growth factor-beta 1 (TGF-beta 1), collagen type I alpha 1, alpha-smooth muscle actin, and the macrophage markers Emr1, as well as the chemoattractant Ccl2, interleukin-1 beta (IL1 beta) and tumor necrosis factor-alpha (TNF alpha) were analyzed. Assessment of portal and systemic hemodynamics was performed using the colored microsphere technique. As expected, WD induced obesity and liver fibrosis as confirmed by Sirius Red and Oil Red O staining. The expression of the monocyte-macrophage markers, Emr1, Ccl2, IL1 beta and TNF alpha were increased during feeding of WD, indicating infiltration of macrophages into the liver, even though this increase was statistically not significant for the EGF module-containing mucin-like receptor (Emr1) mRNA expression levels. Of note, portal pressure increased with the duration of WD compared to animals that received a normal chow. Besides obesity, WD feeding increased systemic vascular resistance reflecting systemic endothelial and splanchnic vascular dysfunction. We conclude that transgenic TGR(mREN2)27 rats are a suitable model to investigate NAFLD development with liver fibrosis and portal hypertension. Tendency towards elevated expression of Emr1 is associated with macrophage activity point to a significant role of macrophages in NAFLD pathogenesis, probably due to a shift of the renin-angiotensin system towards a higher activation of the classical pathway. The hepatic injury induced by WD in TGR(mREN2)27 rats is suitable to evaluate different stages of fibrosis and portal hypertension in NAFLD with obesity.

A novel member of the EGF-TM7 family, mEMR4, was identified and characterized. The full-length mouse EMR4 cDNA encodes a predicted 689-amino acid protein containing two epidermal growth factor (EGF)-like modules, a mucin-like spacer domain, and a seven-transmembrane domain with a cytoplasmic tail. Genetic mapping established that mEMR4 is localized in the distal region of mouse chromosome 17 in close proximity to another EGF-TM7 gene, F4/80 (Emr1). Similar to F4/80, mEMR4 is predominantly expressed on resident macrophages. However, a much lower expression level was also detected in thioglycollate-elicited peritoneal neutrophils and bone marrow-derived dendritic cells. The expression of mEMR4 is up-regulated following macrophage activation in Biogel and thioglycollate-elicited peritoneal macrophages. Similarly, mEMR4 is over-expressed in TNF-alpha-treated resident peritoneal macrophages, whereas interleukin-4 and -10 dramatically reduce the expression. mEMR4 was found to undergo proteolytic processing within the extracellular stalk region resulting in two protein subunits associated noncovalently as a heterodimer. The proteolytic cleavage site was identified by N-terminal amino acid sequencing and located at the conserved GPCR (G protein-coupled receptor) proteolytic site in the extracellular region. Using multivalent biotinylated mEMR4-mFc fusion proteins as a probe, a putative cell surface ligand was identified on a B lymphoma cell line, A20, in a cell-binding assay. The mEMR4-ligand interaction is Ca2+-independent and is mediated predominantly by the second EGF-like module. mEMR4 is the first EGF-TM7 receptor known to mediate the cellular interaction between myeloid cells and B cells.