217-OR: Depalmitoylation Inhibition Improves Glucose Tolerance by Promoting Endothelial Insulin Transcytosis

Mechanisms underlying insulin resistance are obscure, but insulin transport across endothelial cells is rate-limiting for insulin delivery to peripheral tissues. Protein palmitoylation regulates trafficking of endothelial organelles. Many acyltransferases mark proteins with palmitate, while acyl protein thioesterase 1 (APT1) is the dominant palmitate eraser, allowing protein cycling. We tested the hypothesis that APT1 affects glucose metabolism by mediating insulin access to target tissues. In two endothelium-specific knockout mouse models (Tie2-Cre and VE-cadherin-CreERT2), APT1 deficiency was associated with enhanced glucose clearance and increased insulin sensitivity on high-fat diet (HFD). HFD endothelial APT1 knockout mice had increased muscle phospho-Akt with similar body weight, body composition, and adipose inflammatory markers as compared to control mice. To assess insulin transcytosis across the endothelium, we used an immune-microneedle patch technique (employing 600-micron length microneedles coated with insulin antibody that penetrate the dermal layer of the skin) to measure insulin content of interstitial fluid (ISF). When the microneedle patch was applied to abdominal skin 10 min after administration of human insulin, ISF insulin in HFD endothelial knockout APT1 mice was ~60% higher (p=0.022) than in HFD control mice. When skin ISF was isolated by centrifugation, insulin determined by ELISA was ~50% higher (p=0.001) in HFD endothelial knockout APT1 mice than in HFD control mice. APT1 deficiency did not affect muscle endothelial morphology by electron microscopy. In human adipose microvascular endothelial cells, APT1 deficiency induced chemically or genetically promoted insulin transcytosis while APT1 overexpression decreased insulin transcytosis. These findings suggest that endothelial palmitoylation affects insulin transport from the blood to target tissues to mediate insulin sensitivity and glucose tolerance in mice.