Topical Area: Obesity
Objectives : Metabolic endotoxemia is known to induce systemic inflammation and adipose tissue dysfunction during obesity. Pentraxin 3 (PTX3), a member of the pentraxin family can be induced by inflammatory stimuli in adipocytes. However, how PTX3 regulates inflammation in adipocytes is not fully understood. MicroRNAs (miRNAs) are key regulators of inflammatory gene expression. Specifically, miR-21 plays a role in the resolution of inflammation through inhibiting Toll-like receptor 4 (TLR4) signaling pathway. This study aimed to investigate how PTX3 regulates inflammatory homeostasis involving miR-21 during lipopolysaccharide (LPS) stimulation in brown adipocytes.
Methods : Using PTX3 knockout (KO) mouse and primary stromal-vascular (SV) cell culture models, we determined the effect of PTX3 deficiency on miR-21 expression, secretion, and inflammatory response in brown adipocytes, as well as the rescue effect of recombinant PTX3 on LPS-induced inflammation.
Results : Brown adipose tissue (BAT) had significantly higher levels of Dicer protein expression than inguinal and epididymal adipose depots; fully differentiated brown adipocytes expressed higher levels of Dicer than SV cells. These results suggest that BAT is the major site of miRNA production, and brown adipocyte is the main cell type that produces miRNAs. Moreover, we found brown adipocytes but not SV cells are the LPS responsive cells in miR-21 expression and secretion. In WT brown adipocytes, LPS stimulation significantly up-regulated cellular levels of miR-21. Interestingly, PTX3 deficiency led to a significant increase in the basal levels of both cellular and secreted miR21 compared to WT cells. Unlike in WT cells, LPS treatment suppressed cellular expression as well as secretion of miR-21 in PTX3 KO brown adipocytes. Treatment of recombinant PTX3 slightly up-regulated cellular expression of miR-21, but significantly increased the secretion of miR-21 in PTX3 KO brown adipocytes. Moreover, Treatment of recombinant PTX3 significantly attenuated LPS-stimulated increase in the expression of TNFα and MCP1 genes in PTX3 KO adipocytes.
Conclusions : We conclude that PTX3 plays an anti-inflammatory role in part via regulating the expression and secretion of miR-21.
Funding Sources : American Diabetes Association