46 Inhibition of Lipolysis with Acipimox Targets Post-burn White Adipose Browning by Altering Macrophage Polarity Journal Articles uri icon

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abstract

  • Abstract Introduction Severe burns are accompanied by a detrimental hypermetabolic stress response that can persist for years post-injury. Our previous work revealed that, under prolonged stress, white adipose tissue (WAT) adopts brown adipose-like traits in a process termed ‘browning’. This switch, characterized by the presence of uncoupling protein 1 (UCP1), is driven by the polarization of macrophages towards an M2 phenotype. Recently, we demonstrated that inhibiting lipolysis with the clinically approved drug, Acipimox, represses the burn-induced thermogenic activation of WAT. These findings raise the possibility that elevated rates of lipolysis may play a role in regulating the macrophage polarization state after major burn. However, the interconnection between post-burn lipolysis and inflammation remains unclear. In the present study, we investigated the mechanism underlying Acipimox’s inhibitory effects on burn-induced browning. Using a mouse model of thermal injury, we determine the metabolic effects of reducing WAT lipolysis on burn-induced macrophage recruitment and M2-polarization. Methods Adult C57BL/6 mice received a 30% total body surface area scald burn. Mice were then given daily intraperitoneal injections of APX (50 mg/Kg). On day 7 post-burn, the inguinal adipose tissue depot (iWAT) was harvested for histological analyses. Flow cytometry and F4/80 staining were used to assess adipose macrophage distribution and profile, and gene expression was analyzed via qPCR. Results APX administration significantly increased mitochondrial coupling, reflected by the decrease in UCP-1 (p< 0.05) and PGC-1a (p< 0.01) levels relative to the iWAT of untreated burn mice. F4/80 immunostaining of iWAT demonstrated decreased macrophage recruitment in Acipimox treated mice (p< 0.05). Flow cytometric analysis indicated decreased macrophage infiltration at 7 days in Acipimox treated mice (p< 0.05). Furthermore, iWAT from Acipimox treated mice demonstrated a pro-inflammatory profile, indicated by a greater distribution of TLR4 positive macrophages (p< 0.05). Conclusions Previously, we showed that the administration of Acipimox effectively suppressed PKA-mediated lipolysis and improved mitochondrial coupling in adipose tissue post-burn. Here, we elucidate the mechanism underlying these metabolic changes. Importantly, we show Acipimox exerts its inhibitory effects on burn-induced WAT browning by directly modulating macrophage recruitment and the M2-polarization state. Applicability of Research to Practice Our study highlights the critical role of lipolysis in mediating the key post-burn metabolic phenomena browning and inflammation. The data presented herein validate the pharmacological inhibition of lipolysis as a potentially powerful therapeutic strategy to counteract the detrimental metabolic effects induced by burn.

publication date

  • March 3, 2020