O efeito de mediadores químicos e vesículas extracelulares secretados pelo tecido adiposo de pacientes obesos sobre a função e diferenciação de osteoblastos humanos

Abstract

Obesity is a multifactorial disease characterized by excessive body fat accumulation. During obesity development, white adipose tissue undergoes a pathological expansion in which hypertrophied adipocytes modify their secretory profile contributing to low-grade chronic inflammation establishment. Obesity-derived pro-inflammatory mediators interfere with the functions of various organs and tissues, and those obese-adipose tissue products can also affect bone tissue. Many works have demonstrated that pro-inflammatory cytokines induce an inhibition of osteoblasts activity, cells that produce bone extracellular matrix (BECM); while activating the differentiation and activity of osteoclasts, which promotes bone resorption; resulting in bone loss. However, the increase in mechanical load is a factor that stimulates bone formation. Because of this, the effect of obesity on bone remodeling is still a topic that generates disagreements. Additionally, the role of extracellular vesicles released by obese adipose tissue on osteoblast activity is poorly explored, justifying the investigation. In this work, the cells SAOS-2 human osteoblast lineage were treated with conditioned media of the cultures of subcutaneous adipose tissue from obese (OCM) and eutrophic (ECM) patients during the maturation of these cells in vitro. Furthermore, we isolated the extracellular vesicles in adipose tissue conditioned media of obese (EVO) and eutrophic (EVE) subjects to assess their interference in the osteoblast differentiation process. It was observed that OCM increased cell proliferation, promoted a morphological modification to a spindle-shaped form, decreased BECM calcification, and reduced the expression of osteogenic markers. OCM also increased mesenchymal markers, promoting β-Catenin degradation, reducing integrin β1 expression, and decreasing FAK activation. These alterations were not observed after treatment with isolated extracellular vesicles. Because OCM has higher concentrations of TGF-β1, the role of this factor in its effects on osteoblasts was further investigated. Treatment with TGF-β1 produced similar results as OCM treatment. Blockade of TGF-β in OCM reversed the morphological modification and altered proliferation but did not reestablish calcification. The data indicate that mediators released by the adipose tissue during obesity can induce cellular regression of mature osteoblast phenotype towards an osteoprogenitor-like profile, partly caused by increased release of TGF-β1 produced by obese-adipose tissue