ABSTRACTDelivery of insulin to the surface of myocytes is required for skeletal muscle (SkM) insulin action. Previous studies have shown that SkM insulin delivery is reduced in the setting of obesity and insulin resistance (IR). The key variables that control SkM insulin delivery are 1) microvascular perfusion and 2) the rate at which insulin moves across the continuous endothelium of SkM capillaries. Obesity and IR are associated with reduced insulin-stimulated SkM perfusion. Whether an impairment in trans-endothelial insulin transport (EIT) contributes to SkM IR, however, is unknown. We hypothesized that EIT would be delayed in a mouse model of diet-induced obesity (DIO) and IR. Using intravital insulin imaging, we found that DIO male mice have a ~15% reduction in EIT compared to their lean counterparts. This impairment in EIT is associated with a 45% reduction in the density of endothelial vesicles. Despite impaired EIT, hyperinsulinemia sustained delivery of insulin to the interstitial space in DIO male mice. Even with maintained interstitial insulin delivery DIO male mice still showed SkM IR, indicating severe myocyellular IR in this model. Interestingly, there was no difference in EIT, endothelial ultrastructure or SkM insulin sensitivity between lean and high fat diet-fed female mice. These results suggest that, in male mice, obesity results in damage to the capillary endothelium which limits the capacity for EIT.
Endothelial Transcytosis of Insulin: Does It Contribute to Insulin Resistance?
