Physiological Roles of Cellular Retinol-binding Protein, Type II and Regulation of Its Gene Expression in Small Intestine

TAKASE Sachiko, GODA Toshinao

doi:10.20632/vso.71.7_273

Cellular retinol-binding protein, type II (CRBP(II)) is present in large quantities in small intestine, and may play an important role in absorption and metabolism of retinol and β-carotene. The involvement of CRBP (II) in retinol absorption and its esterification in enterocytes have been proven in our several studies. The CRBP (II) levels in the small intestine were very low in embryonic chicks and then increased rapidly around hatching. Retinol bound to CRBP (II) is esterified by lecithin : retinol acyltransferase (LRAT) which activity was also extremely low in the embryos, but rose rapidly around hatching in parallel with the induction of intestinal CRBP (II). Also CRBP (II) was evidenced its role in preventing the toxic effect of unbound retinol n the rat small intestine, suggesting that consumption of excess vitamin A in amounts below 10 times the NRC'c requirement may not cause toxic disturbance. W found that the jejunum-bypass operation led to increases in the amounts of both CRBP (II) and lipoprotein Apo-B in the residual jejunal segment, suggesting that CRBP (II) might be enhanced by high fat absorption. Indeed, we discovered that rat CRBP (II) mRNA was enhanced by high fat (corn oil) diet. This increase was due to unsaturated fatty acids, but its mRNA levels were not directly related to the expression of RXRα and peroxisome proliferator-activated receptor (PPARα). We concluded that dietary fatty acids modify the CRBP (II) gene expression.

Physiological Roles of Cellular Retinol-binding Protein, Type II and Regulation of Its Gene Expression in Small Intestine

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