Treatment of
type 2 diabetes mellitus continues to pose an important clinical challenge, with most existing
therapies lacking demonstrable ability to improve cardiovascular outcomes. The atheroprotective
peptide apelin (APLN) enhances
glucose utilization and improves
insulin sensitivity. However, the mechanism of these effects remains poorly defined. We demonstrate that the expression of
APLNR (APJ/AGTRL1), the only known receptor for
apelin, is predominantly restricted to the endothelial cells (ECs) of multiple adult metabolic organs, including skeletal muscle and adipose tissue. Conditional endothelial-specific deletion of
Aplnr (AplnrECKO ) resulted in markedly impaired
glucose utilization and abrogation of
apelin-induced
glucose lowering. Furthermore, we identified inactivation of
Forkhead box protein O1 (FOXO1) and inhibition of endothelial expression of
fatty acid (FA)
binding protein 4 (FABP4) as key downstream signaling targets of
apelin/
APLNR signaling. Both the Apln-/- and AplnrECKO mice demonstrated increased endothelial FABP4 expression and excess tissue FA accumulation, whereas concurrent endothelial Foxo1 deletion or pharmacologic FABP4 inhibition rescued the excess FA accumulation phenotype of the Apln-/- mice. The impaired
glucose utilization in the AplnrECKO mice was associated with excess FA accumulation in the skeletal muscle. Treatment of these mice with an FABP4 inhibitor abrogated these metabolic phenotypes. These findings provide mechanistic insights that could greatly expand the therapeutic repertoire for
type 2 diabetes and related metabolic disorders.