Since the last submission, we reported that feeding a Western diet (WD) to LDLR null mice increased small intestine levels of unsaturated (but not saturated) lysophosphatidic acid (LPA). Adding unsaturated LPA to low- fat mouse chow resulted in i) levels of unsaturated LPA in the small intestine and plasma similar to that achieved on WD; ii) mimicked WD in causing dyslipidemia and systemic inflammation; and iii) in unpublished studies produced similar levels of aortic atherosclerosis. Adding transgenic tomatoes expressing the apoA-I mimetic peptide 6F (Tg6F) to mouse chow supplemented with unsaturated LPA or adding Tg6F to WD decreased unsaturated LPA levels in the small intestine ameliorating dyslipidemia and aortic atherosclerosis. We propose to determine the mechanisms by which unsaturated LPA and WD act in the small intestine to cause dyslipidemia and inflammation, and the mechanisms by which Tg6F ameliorates dyslipidemia and inflammation. Adding unsaturated (but not saturated) lysophosphatidylcholine (LysoPC) to low-fat mouse chow produced dyslipidemia similar to adding unsaturated LPA or feeding WD. A specific oral inhibitor of autotaxin reduced LysoPC-mediated dyslipidemia. We hypothesize that LysoPC produced by the action of Group 1B phospholipase A2 on dietary phosphatidylcholine is acted upon by autotaxin in the small intestine to produce LPA. Based on preliminary data, we hypothesize that intestinally-derived unsaturated LPA decreases inositol- requiring enzyme 1 (Ire1 ) mRNA and protein levels and increases microsomal triglyceride transfer protein (Mtp) mRNA levels and activity in the small intestine, which results in increased secretion of lipoproteins from the small intestine. WD also caused induction of enzymes (Lpcat3; Scd1) in the small intestine that promote the formation of unsaturated phospholipids. Together with Project 5 we hypothesize that intestine-specific knockdown of Lpcat3 will lead to increased levels of unsaturated LPA in the small intestine in response to WD, and intestine-specific knockdown of Scd1 will lead to decreased unsaturated LPA levels in the small intestine. Preliminary data demonstrate that the inflammatory response to intestinally-derived LPA is genetically determined. Together with Project 4 we will identify the genetic factors controlling the response to intestinally- derived LPA using the Hybrid Mouse Diversity Panel. Preliminary data indicate that Tg6F prevents the WD- mediated increase in Mtp mRNA levels in the small intestine. We hypothesize that Tg6F decreases WD- mediated dyslipidemia by increasing Ire1 mRNA and protein levels and decreasing Mtp mRNA and activity in the small intestine leading to decreased secretion of lipoproteins from the small intestine. Based on other preliminary data showing that i) unsaturated LPA induces Cd36 expression in the small intestine similar to WD; ii) Tg6F inhibits the WD-mediated increase in Cd36 expression in the small intestine; and iii) enterocytes from the small intestine of mice on WD supplemented with Tg6F absorb less cholesterol, we hypothesize that Tg6F decreases cholesterol absorption by decreasing expression of enterocyte Cd36 in the proximal small intestine.
This project will determine novel mechanisms by which the small intestine contributes to diet-induced dyslipidemia and atherosclerosis. Additionally, this project will determine the mechanisms by which tomatoes transgenic for an apolipoprotein mimetic peptide act in the small intestine to ameliorate diet-induced dyslipidemia and atherosclerosis.
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