Circadian regulation of intestinal lipid absorption by apolipoprotein AIV involves forkhead transcription factors A2 and O1 and microsomal triglyceride transfer protein.

We have shown previously that Clock, microsomal triglyceride transfer protein (MTP), and nocturnin are involved in the circadian regulation of intestinal lipid absorption. Here, we clarified the role of apolipoprotein AIV (apoAIV) in the diurnal regulation of plasma lipids and intestinal lipid absorption in mice. Plasma triglyceride in apoAIV(-/-) mice showed diurnal variations similar to apoAIV(+/+) mice; however, the increases in plasma triglyceride at night were significantly lower in these mice. ApoAIV(-/-) mice absorbed fewer lipids at night and showed blunted response to daytime feeding. To explain reasons for these lower responses, we measured MTP expression; intestinal MTP was low at night, and its induction after food entrainment was less in apoAIV(-/-) mice. Conversely, apoAIV overexpression increased MTP mRNA in hepatoma cells, indicating transcriptional regulation. Mechanistic studies revealed that sequences between -204/-775 bp in the MTP promoter respond to apoAIV and that apoAIV enhances expression of FoxA2 and FoxO1 transcription factors and their binding to the identified cis elements in the MTP promoter at night. Knockdown of FoxA2 and FoxO1 abolished apoAIV-mediated MTP induction. Similarly, knockdown of apoAIV in differentiated Caco-2 cells reduced MTP, FoxA2, and FoxO1 mRNA levels, cellular MTP activity, and media apoB. Moreover, FoxA2 and FoxO1 expression showed diurnal variations, and their expression was significantly lower in apoAIV(-/-) mice. These data indicate that apoAIV modulates diurnal changes in lipid absorption by regulating forkhead transcription factors and MTP and that inhibition of apoAIV expression might reduce plasma lipids.

Increased intestinal lipid absorption caused by Ire1ß deficiency contributes to hyperlipidemia and atherosclerosis in apolipoprotein E-deficient mice.

RATIONALE: High fasting serum lipid levels are significant risk factors for atherosclerosis. However, the contributions of postprandial excursions in serum lipoproteins to atherogenesis are less well-characterized. OBJECTIVE: This study aims to delineate whether changes in intestinal lipid absorption associated with loss of inositol-requiring enzyme 1ß (Ire1ß) would affect the development of hyperlipidemia and atherosclerosis in Apoe(-/-) mice. METHODS AND RESULTS: We used Ire1ß-deficient mice to assess the contribution of intestinal lipid absorption to atherosclerosis. Here, we show that Ire1b(-/-)/Apoe(-/-) mice contain higher levels of intestinal microsomal triglyceride transfer protein, absorb more lipids, exhibit hyperlipidemia, and have higher levels of atherosclerotic plaques compared with Apoe(-/-) mice when fed chow and western diets. CONCLUSIONS: These studies indicate that Ire1ß regulates intestinal lipid absorption and that increased intestinal lipoprotein production contributes to atherosclerosis.

Nonalcoholic fatty liver disease in CLOCK mutant mice.

Nonalcoholic fatty liver disease (NAFLD) is becoming a major health issue as obesity increases around the world. We studied the effect of a circadian locomotor output cycles kaput (CLOCK) mutant (ClkΔ19/Δ19) protein on hepatic lipid metabolism in C57BL/6 Clkwt/wt and apolipoprotein E-deficient (Apoe-/-) mice. Both ClkΔ19/Δ19 and ClkΔ19/Δ19 Apoe-/- mice developed a full spectrum of liver diseases (steatosis, steatohepatitis, cirrhosis, and hepatocellular carcinoma) recognized in human NAFLD when challenged with a Western diet, lipopolysaccharide, or CoCl2. We identified induction of CD36 and hypoxia-inducible factor 1α (HIF1α) proteins as contributing factors for NAFLD. Mechanistic studies showed that WT CLOCK protein interacted with the E-box enhancer elements in the promoters of the proline hydroxylase domain (PHD) proteins to increase expression. In ClkΔ19/Δ19 mice, PHD levels were low, and HIF1α protein levels were increased. When its levels were high, HIF1α interacted with the Cd36 promoter to augment expression and enhance fatty acid uptake. Thus, these studies establish a regulatory link among circadian rhythms, hypoxia response, fatty acid uptake, and NAFLD. The mouse models described here may be useful for further mechanistic studies in the progression of liver diseases and in the discovery of drugs for the treatment of these disorders.

MicroRNA-30c reduces hyperlipidemia and atherosclerosis in mice by decreasing lipid synthesis and lipoprotein secretion.

Hyperlipidemia is a risk factor for various cardiovascular and metabolic disorders. Overproduction of lipoproteins, a process that is dependent on microsomal triglyceride transfer protein (MTP), can contribute to hyperlipidemia. We show that microRNA-30c (miR-30c) interacts with the 3' untranslated region of MTP mRNA and induces its degradation, leading to reductions in MTP activity and in apolipoprotein B (APOB) secretion. miR-30c also reduces lipid synthesis independently of MTP. Hepatic overexpression of miR-30c reduced hyperlipidemia in Western diet-fed mice by decreasing lipid synthesis and the secretion of triglyceride-rich ApoB-containing lipoproteins and decreased atherosclerosis in Apoe(-/-) mice. Furthermore, inhibition of hepatic miR-30c by anti-miR-30c increased hyperlipidemia and atherosclerosis. Therefore, miR-30c coordinately reduces lipid biosynthesis and lipoprotein secretion, thereby regulating hepatic and plasma lipid concentrations. Raising miR-30c levels might be useful in treating hyperlipidemias and associated disorders.