Classical and alternative NF-κB signaling cooperate in regulating adipocyte differentiation and function

Inflammation of adipose tissue (AT) is a central mediator of insulin resistance. However, the molecular mechanisms triggered by inflammatory cells are not fully understood. The aim of this study was to analyze the metabolic functions of lymphotoxin-β-receptor (LTβR)-mediated alternative NF-κB signaling in adipocytes and to reveal its effects on body weight and insulin sensitivity in vivo.

RelB(FatKO) mice and littermate controls were treated with LTβR agonistic antibody (α-LTβR) or a LTβR antagonist (LTβR:Ig fusion protein) after feeding a high-fat diet or standard diet. Mice were analyzed by insulin tolerance and glucose tolerance tests prior to analysis by necropsy and qRT-PCR of abdominal white adipose tissue. 3T3-L1 preadipocytes and mouse embryonic fibroblasts were used for differentiation and expression analysis after treatment with α-LTβR and differentiation to adipocytes. The molecular mechanism was elucidated by chromatin immunoprecipitation and combinatorial treatment with α-LTβR and tumor necrosis factor (TNF).

RelB(FatKO) mice showed improved insulin sensitivity despite increased adiposity and adipocyte hypertrophy. LTβR-induced activation of p52-RelB in 3T3-L1 cells attenuated adipogenesis and modulated adipocyte functions via transcriptional downregulation of peroxisome proliferator-activated receptor γ (PPARγ). This LTβR-mediated pathway was synergistically regulated via a TNF-induced increase in p100 and RelB expression and nuclear translocation.

Our data describe an anti-adipogenic action of LTβR signaling and a novel synergism of alternative and classical NF-κB signaling in the regulation of adipocytes. In conclusion, this strong synergism between the two NF-κB pathways shows a method to inhibit adipocyte differentiation and to improve insulin sensitivity and can be a potential target to treat metabolic disorders more efficiently than with other known drugs.