Abstract 16541: HMGB1 on Microvesicles Mediates Macrophage-Adipocyte Crosstalk and Impairs Insulin Signaling in Adipocytes

Abstract

BACKGROUND Over a billion people smoke worldwide, and more are exposed to secondhand smoke. Despite lower BMI, smokers exhibit visceral fat accumulation, insulin resistance for glucose, and increased type 2 diabetes mellitus in epidemiological studies. The underlying mechanisms remain poorly understood. We previously reported that exposure of human macrophages to tobacco smoke extract (TSE) provokes the release of membrane microvesicles (TSE-MVs) with procoagulant and proteolytic activities. - GOAL Here, we sought to investigate a potential role for TSE-MVs in metabolically harmful crosstalk between macrophages and adipocytes.

- METHODS TSE-MVs, isolated by ultracentrifugation from conditioned medium of TSE-exposed human macrophages, were added to cultured 3T3-L1 adipocytes overnight, followed by assays of chemoattraction of monocytes across a Boyden chamber and signaling responses to insulin.

- RESULTS Adipocytes exposed to TSE-MVs significantly induced monocyte transmigration and adherence, compared to unexposed control adipocytes (doubled, P<0.01). By immunoblot, we found that TSE-MVs carry high mobility group box 1 (HMGB1), a damage-associated molecular pattern (DAMP) previously shown to be released as a soluble form from activated or dying macrophages. Both TSE-MVs and recombinant HMGB1 (rHMGB1) induced adipocytes to secrete MCP1. Pretreatment of TSE-MVs with glycyrrhizin, which binds the active sites of HMGB1, attenuated the ability of these vesicles to induce MCP-1 secretion and chemoattraction. Anti-MCP-1 neutralizing antibody or the CCR2 antagonist RS504393 significantly inhibited monocyte transmigration and adherence to TSE-MV-exposed adipocytes. Importantly, treatment of adipocytes with either TSE-MVs or rHMGB1 inhibited insulin-induced Akt phosphorylation at Ser473. - CONCLUSIONS Our results indicate that HMGB1, a key DAMP, can be transported by microvesicles. Its presence on TSE-MVs released from smoke-exposed human macrophages mediates crucial, harmful crosstalk with adipocytes - namely, the induction of adipocyte secretion of MCP1, recruitment of monocytes, and impaired insulin signaling. These effects may contribute to significant metabolic derangements in individuals exposed to tobacco smoke.