Date of Award

3-30-2007

Document Type

Open Access Thesis

Degree Name

Medical Doctor (MD)

First Advisor

Gerald I Shulman MD

Abstract

It is well known that metabolites resulting from the accumulation of fat in tissue results in fatty liver, obesity, and insulin resistance. Because triglyceride synthesis is essential for this process, inhibition of the final step of TG synthesis has been considered as a new therapeutic target for hepatosteatosis and insulin resistance. In this study, we investigated the metabolic impact of acyl CoA: diacylglycerol acyltransferase 1 (DGAT1) and 2 (DGAT2) suppression. We used antisense oligonucleotides (ASOs) to reduce the expression of these enzymes in liver and fat in Sprague Dawley rats fed a 27% safflower oil high fat diet (HFD) for 4 weeks. Rats were injected with one of the following: saline, control ASO, DGAT1 ASO or DGAT2 ASO subcutaneously twice a week for 4 weeks. DGAT1 and DGAT2 ASO treatment reduced DGAT1 and DGAT2 mRNA levels in liver by 95% and 57% respectively but only DGAT2 ASO treatment significantly reduced TG content when compared to the saline group. We determined the effects of ASO treatment on insulin action in vivo during a 135 min hyperinsulinemic(4mU/kg/min)-euglycemic clamp. Glucose turnover and uptake were assessed using [3-3H]glucose infusion and [1-14C]2-deoxyglucose injection during clamps. DGAT2 ASO treated rats were protected from HFD induced insulin resistance as demonstrated by an 80% increase in glucose infusion rate (24.0±0.9 vs. 13.4±1.1 mg/kg/min, p<0.001). This was accounted for by significant suppression of hepatic glucose production (82±6 vs. 53±11% p<0.05) and a 54% increase in insulin-stimulated whole body glucose uptake (25.3±1.1 vs. 16.3±0.7 mg/kg/min, p<0.001) when compared to the control ASO group. Insulin-stimulated glucose uptake in skeletal muscle and suppression of plasma free fatty acid levels during the clamp were also significantly increased in DGAT2 ASO treated rats when compared to controls (2DG uptake: 329±31 vs. 263±28 nmol/g/min, p=0.03, suppression of FFA: 64±4 vs. 48±5%, p=0.015). Of note, the DGAT2 ASO group showed less weight gain than controls despite the same food consumption over the treatment period. The ratio of weight gain versus food consumption, efficiency of weight gain, was significantly lower in the DGAT2 group when compared to other groups, suggesting an increase in energy expenditure in the DGAT2 ASO group. In summary, this study demonstrates that the reduction of DGAT2 using an ASO protects against insulin resistance in liver and peripheral tissue.

Comments

This is an Open Access Thesis.

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