Messenger RNA levels of genes involved in dysregulation of postprandial lipoproteins in type 2 diabetes: the role of Niemann–Pick C1-like 1, ATP-binding cassette, transporters G5 and G8, and of microsomal triglyceride transfer protein

Abstract

The aim of the present study was to examine the relationship between chylomicron composition and expression of genes that regulate chylomicron production in the intestine. We examined expression of the following: (1) Niemann-Pick C1-like 1 (NPC1L1), which regulates cholesterol absorption; (2) ATP-binding cassette transporters G5 and G8 (ABCG5, ABCG8), which regulate cholesterol homeostasis through their ability to excrete enterocyte cholesterol back into the lumen of the intestine; and (3) microsomal triglyceride transfer protein (MTTP), which packages the chylomicron particle by assembling cholesterol, triglyceride, phospholipids and apolipoprotein B48. Type 2 diabetic (26) and non-diabetic (21) patients were examined. Levels of NPC1L1, ABCG5 and ABCG8 and MTTP mRNA were measured in duodenal biopsies by real-time PCR. Lipoproteins were isolated by sequential ultracentrifugation. Diabetic patients had more NPC1L1 mRNA than the control subjects (p<0.02). Expression of ABCG5 and ABCG8 mRNA was lower in the diabetic patients (p<0.05) and MTTP expression was increased (p<0.05). There was a positive correlation between NPLC1L1 and MTTP mRNA (p<0.01) and a negative correlation between NPC1L1 and ABCG5 mRNA (p<0.001). Diabetic patients on statin therapy had increased ABCG5 and ABCG8 mRNA compared to those not on statin (p<0.02 and p<0.05) and less MTTP mRNA than those not on statin (p<0.05). This study demonstrates that in type 2 diabetes there are important alterations to the expression of intestinal genes that regulate cholesterol absorption and chylomicron synthesis. In diabetic patients statin therapy is associated with reduced MTTP expression and increased ABCG5 and ABCG8 mRNA. The study suggests new mechanisms to explain postprandial diabetic dyslipidaemia and the beneficial effect of statins.