NOD1 Mediates Insulin Resistance in Response to Circulating Free Fatty Acids

Abstract

Insulin resistance (IR) in type 2 diabetes (T2D) is associated with chronic low-grade inflammation. We have shown that nucleotide binding oligomerization domain (NOD)1, an intracellular pattern recognition receptor for bacterial wall peptidoglycans, is a factor linking the innate immune system to the development of high fat diet-induced IR. Although high fat diet may result in NOD1 activation via increased intestinal absorption of bacterial products, NOD1 has also been shown to be activated by saturated fatty acids in intestinal cells and adipocytes. We hypothesize that NOD1 plays a role in IR caused by chronic high levels of circulating free fatty acids (FFA) as found in obesity and T2D. Wild type (WT) and NOD1-/- mice were infused with ethylpalmitate (resulting in raised circulating palmitate) or ethanol vehicle as a control, for 48 hours to model prolonged elevation of circulating FFA in vivo. Hyperinsulinemic-euglycemic clamp with tracer methodology was then used to assess peripheral and hepatic insulin sensitivity. WT mice treated with ethylpalmitate had decreased peripheral and hepatic insulin sensitivity expressed as stimulation of glucose utilization (Control= 123%±30 and Ethylpalmitate= 25%±25, p<.05) and suppression of glucose production (Control= 51%±10 and Ethylpamitate= 22%±2, p<.05). NOD1-/- mice were protected from palmitate induced IR, showing no difference in stimulation of glucose utilization (Control= 289%±27 and Ethylpalmitate= 352%±64) and suppression of glucose production (Control= 63%±16 and Ethylpalmitate= 95%±25) with or without palmitate. Thus, our data provide compelling evidence that NOD1 activation via elevated plasma FFA contributes to the development of peripheral and hepatic IR. Disclosure S.L. Rivers: None. L. Yeung: None. K.L. Chan: None. Y. Mori: None. D. Philpott: None. A. Klip: None. A. Giacca: None.