Macrophage infiltration into adipose tissue (AT) is a hallmark of the chronic inflammatory response in obesity and is supported by an intense monocyte migration towards AT. Although it has been detected an increased proportion of circulating CD16+ monocyte subsets in obese subjects, the mechanisms underlying this effect and the contribution of these cells to the inflamed profile of obese AT are still poorly understood. We investigated whether factors secreted by human obese omental AT could polarize monocytes to CD16+ enriched phenotype, and how these changes could modify their migratory capacity towards adipose tissue itself. We show that explants of human obese omental AT, obtained during bariatric surgery, released higher levels of MIP1-α, TNFα, leptin and also VEGF, together with increasing amounts of microparticles (MP), when compared to explants of lean subcutaneous AT. A higher content of circulating MP derived from preadipocytes and leukocytes was also detected in plasma of obese subjects. Conditioned media or MP released from obese omental AT increased CD16 and CCR5 expression on CD14+CD16- monocytes and augmented their migratory capacity towards the conditioned media from obese omental AT, itself. This effect was inhibited when MIP1-α was neutralized. Additionally, we demonstrate that MP derived from obese omental AT carry and transfer TLR8 to monocytes, thus triggering an increase in CD16 expression in those cells. Our data shows a positive feedback loop between blood monocytes and obese omental AT, which releases chemotactic mediators and TLR8-enriched MP, thus inducing an up-regulation of CD16+ monocytes, favoring leukocyte infiltration in the obese omental AT.
Keywords: CCR5; CD16(+) monocytes; MIP-1α; Obesity; TLR8; adipose tissue.
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