UNSATURATED FATTY-ACIDS REGULATE GENE-EXPRESSION OF CELLULAR RETINOL-BINDING PROTEIN, TYPE-II IN RAT JEJUNUM

We have shown that cellular retinol-binding protein, type II (CRBP II) mRNA and its protein levels are elevated in the jejunum of rats fed a diet rich in long-chain triacylglycerols. In the present study, we ex plored which types of fatty acids modulate CRBP II gene expression. Ra ts previously fed a low fat, high starch diet were force-fed a basal f at-free diet or the diet supplemented with 0.21 mol/L of various fatty acids (i.e., caprylic, palmitic, stearic, oleic, linoleic and alpha-l inolenic acids). Force-feeding a diet containing linoleic acid produce d an elevation of CRBP II mRNA levels in rats in both a dose-dependent (0.053-0.21 mol/L) and time-dependent (up to 6 h) manner. Among fatty acids tested, all unsaturated fatty acids (oleic, linoleic and alpha- linolenic acids) were able to enhance CRBP II mRNA levels by 54-63% wi thin 6 h, whereas a medium-chain fatty acid (caprylic acid) and a satu rated fatty acid (stearic acid) elicited little effect on the CRBP II mRNA levels; palmitic acid produced only a small elevation (16%) of th e CRBP II mRNA level. Transcripts of both retinoid X receptor alpha an d peroxisome proliferator-activated receptor (PPAR), which are thought to interact as a heterodimer with the cis-element located in the CRBP II promoter and to be activated by 9-cis retinoic acid and long-chain fatty acids, respectively, were constitutively expressed in the rat j ejunum. These results suggest that the levels of CRBP II mRNA might be modulated by long-chain and unsaturated fatty acids or their metaboli tes, presumably through the action of PPAR or other orphan receptors.