Feeding low density lipoprotein receptor null (Ldlr-/-) mice a Western Diet (WD) not only causes dyslipidemia and atherosclerosis, it also causes vascular inflammation of brain, kidneys, and the small intestine mesentery. The intestine contains more immune cells than any other organ in the body. The number and activation state of these immune cells is in part governed by bacterial and viral products that get past the enterocytes, but they are also governed by lipid signaling molecules such as lysophosphatidic acid 18:1 (LPA 18:1). A major precursor to LPA 18:1 is lysophosphatidylcholine 18:1 (LysoPC 18:1). LysoPC 18:1 is formed in enterocytes preferentially using oleic acid synthesized in the enterocytes by Stearoyl Co-A desaturase-1 (Scd1). Enterocyte LysoPC 18:1 is converted to LPA 18:1 by the action of enterocyte lysophospholipase D (autotaxin). Dietary fat alters the microbiome and increases intestinal permeability via signaling pathways dually controlled by the levels of bacterial lipopolysaccharide (LPS), and enterocyte generated lipid signaling molecules such as LPA 18:1. We hypothesize that the levels of LPS and molecules such as LPA 18:1 in the small intestine determine the systemic response to dietary fat challenge.
Aim 1 will determine the role and mechanism(s) of enterocyte Scd1 in diet-induced dyslipidemia and vascular inflammation. Administering LPA 18:1 or LysoPC 18:1 to Ldlr-/- mice on a chow diet mimicked feeding these mice WD. We generated Ldlr-/- mice with enterocyte knockdown of Scd1, which on WD lowered enterocyte levels of LysoPC 18:1 and LPA 18:1. We will determine if enterocyte knockdown of Scd1 favorably alters: 1) aortic atherosclerosis; 2) cholesterol and lipid absorption; 3) composition of the microbiome; 4) microbiome-host interactions; 5) intestinal permeability and serum endotoxin levels; 6) lipids secreted from enterocytes (determined using a lipidomics approach); and 7) Notch pathway to ameliorate diet-induced vascular inflammation.
Aim 2 will determine the role and mechanism(s) of enterocyte lysophospholipase D (autotaxin). We generated Ldlr-/- mice with enterocyte knockdown of Enpp2, the gene for autotaxin. Enterocyte knockdown of Enpp2 reduced levels of LPA 18:1 in enterocytes and plasma, and decreased WD-induced dyslipidemia and systemic inflammation. We will determine if enterocyte knockdown of Enpp2 reduces aortic atherosclerosis. We hypothesize that increased levels of enterocyte unsaturated LPA species such as LPA 18:1 lead to the oxidation of chylomicrons secreted from enterocytes, which leads to vascular inflammation. We will determine if enterocyte knockdown of Enpp2 favorably alters these events.
Aim 3 will determine the mechanism(s) of action of a concentrate of tomatoes expressing the apoA-I mimetic peptide 6F from a transgene (Tg6F) in ameliorating diet-induced dyslipidemia and vascular inflammation. We will determine if Tg6F mimics enterocyte knockdown of Scd1 and Enpp2. We will determine the lipids removed from mouse jejunum by Tg6F. We will determine if Tg6F preserves the Notch pathway and prevents vascular inflammation in mice fed chow supplemented with LysoPC 18:1, or LPA 18:1 or fed WD.
We discovered that lipid signaling molecules produced in small intestine absorptive cells amplify the ability of dietary fat to cause dyslipidemia, atherosclerosis and vascular inflammation. We developed an oral concentrate of tomatoes containing a mimetic of the main protein in HDL that decreases the levels of these signaling molecules, and ameliorates dyslipidemia, atherosclerosis and vascular inflammation in mice fed a high-fat high-cholesterol diet. The proposed studies are aimed at understanding the mechanisms by which the lipid signaling molecules amplify the effects of dietary fat, and the mechanisms by which the oral concentrate ameliorates the effects of these lipid signaling molecules.