During the development of metabolic disease, dysfunction in insulin receptor (IR) signaling occurs within AgRP neurons of the arcuate nucleus of the hypothalamus (ARC). However, the timeline of IR dysfunction and its relative contribution to disease progression remains unclear.
Using in vivo fiber photometry, we found insulin resistance in response to a high-fat fed (HFF) diet occurs over the progression of disease, with significantly impaired AgRP sensitivity to insulin within 4 weeks of HFF. To explore the functional contribution of AgRP insulin resistance to metabolic disease, we developed a novel CRISPR-Cas9 mediated technique to ablate the expression of IRs specifically within AgRP neurons in adult mice (AgRP-Cas9+AAVgIR). Chow-fed AgRP-Cas9+AAVgIR mice showed extreme body-weight increase within 4 weeks following IR deletion - comparable to wild-type animals on a HFF - which was reversible upon re-expression of a CRISPR insensitive version of the IR. AgRP-Cas9+AAVgIR mice also showed severely impaired whole body insulin sensitivity as assessed by the hyperinsulinemic-euglycemic clamp.
To assess the relative contribution of AgRP IR on the development of obesity, we assessed the effects of a HF diet in AgRP-Cas9+AAVgIR mice. AgRP-Cas9+AAVgIR HFF mice showed a significantly higher: weight increase, fasting blood glucose levels, and adiposity, as well as significantly impaired insulin response compared to controls. Reverting to a calorie-restricted diet ameliorated some of these impairments only in the presence of a functional IR. Finally, we propose that AgRP IR signalling causes significant changes to adiposity through alterations in peripheral tissue innervation we observe following modulation of AgRP neurons.
Taken together, our findings identify AgRP neurons of the ARC as critical regulators of whole-body metabolism. We establish that insulin signaling within AgRP neurons is crucial in regulating energy homeostasis and glyceamic control and that insulin resistance within this neuronal population is a key component in accelerating development of obesity.