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Unsaturated Fatty Acids Regulate Gene Expression of Cellular Retinol-Binding Protein, Type II in Rat Jejunum^1,2,

School of Food and Nutritional Sciences, The University of Shizuoka, Shizuoka 422, Japan

We have shown that cellular retinolbinding 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 explored which types of fatty acids modulate CRBP II gene expression. Rats previously fed a low fat, high starch diet were force-fed a basal fat-free diet or the diet supplemented with 0.21 mol/L of various fatty acids (i.e., caprylic, palmitic, stearic, oleic, linoleic and -linolenic acids). Force-feeding a diet containing linoleic acid produced 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 -linolenic acids) were able to enhance CRBP II mRNA levels by 54–63% within 6 h, whereas a medium-chain fatty acid (caprylic acid) and a saturated fatty acid (stearic acid) elicited little effect on the CRBP II mRNA levels; palmitic acid produced only a small elevation (16%) of the CRBP II mRNA level. Transcripts of both retinoid X receptor and 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 jejunum. These results suggest that the levels of CRBP II mRNA might be modulated by long-chain and unsaturated fatty acids or their metabolites, presumably through the action of PPAR or other orphan receptors.

KEY WORDS: • fatty acids • retinol • rats • cellular retinol-binding protein II

¹ Supported by a grant-in-aid (01570088, 04670097) for scientific research from the Ministry of Education, Science and Culture of Japan.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ To whom correspondence and reprint requests should be addressed.

Manuscript received 10 October 1994. Revision accepted 14 February 1995.