Palmitic acid and lipopolysaccharide induce macrophage TNFα secretion, suppressing browning regulators and mitochondrial respiration in adipocytes

Obesity and its associated pro-inflammatory activity contribute significantly to metabolic dysfunction. In contrast, browning of white adipose tissue (WAT) generally improves metabolic health. Our prior research suggested that macrophage-derived pro-inflammatory cytokines suppress key regulators of browning-adrenergic receptor β3 (Adrb3) and peroxisome proliferator-activated receptor γ (Pparg)-as well as energy metabolism mediators-insulin receptor substrate 1 (Irs1) and hormone-sensitive lipase (Lipe)-in diet-induced obese mice. To explore this mechanism, we developed an in vitro model using RAW264.7 macrophages and 3T3-L1 adipocytes exposed to palmitic acid (PA) and/or lipopolysaccharide (LPS). PA (200 microM) and LPS (1.0 microg/ml) synergistically promoted M1 polarization of macrophages and secretion of pro-inflammatory cytokines, with tumor necrosis factor-α (TNFα), C-C motif chemokine ligand 2 (CCL2), CCL5, and interleukin-6 (IL-6) being predominant. Conditioned media from both control and PA-treated macrophages, when exposed to LPS ≥0.01 microg/ml, significantly downregulated Adrb3, Pparg, Irs1, and Lipe in adipocytes. At physiologically relevant LPS levels (≤0.001 microg/ml), PA-treated macrophage media exerted greater suppression of these genes than controls. Among the cytokines, TNFα emerged as the primary mediator, significantly reducing expression of the four key regulators. Furthermore, adipocytes treated with TNFα exhibited significant reductions in both uncoupling protein 1 (Ucp1) expression and mitochondrial respiration. These findings demonstrate that exposure to obesity-associated factors (PA and LPS) induces macrophage-derived TNFα, which suppresses browning and mitochondrial function in adipocytes. This mechanism may inform new therapeutic strategies targeting TNFα to alleviate obesity-related metabolic disorders.