Critical role of arginase 2 in obesity‐induced metabolic dysregulation in female mice: Implication of macrophage inflammatory response

Abstract

We have previously shown that deletion of the mitochondrial isoform of the ureahydrolase enzyme (A2) protected against obesity‐induced metabolic dysregulation in “male” mice fed high fat high sucrose diet (HFHS) for 16 weeks. Additionally, A2 expression was upregulated 1.5‐fold in visceral adipose tissue (VAT) of WT "male" mice fed HFHS vs WT fed normal chow diet (ND). Interestingly, A2 expression was elevated 3‐fold in VAT of WT HFHS "female" mice vs WT ND. In the current study, we determined the consequences of global A2 deletion in “female” mice on the same diet protocol. Body weight was measured weekly, adiposity was measured using nuclear magnetic resonance and metabolic activity was assessed using indirect calorimetry. Increases in body weight in WT HFHS female mice, VAT weight and total adiposity were abrogated in A2−/− HFHS mice by 24, 84 and 54%, respectively (p<0.05). Glucose tolerance tests showed a significantly reduced area under the curve in A2−/− HFHS mice vs WT (p<0.05). The leaner phenotype observed in A2−/− mice was in line with the improved metabolic activity as evidenced by increased energy expenditure, volume of O2 consumed and CO2 produced in A2−/− mice fed HFHS vs WT HFHS. Obesity‐induced VAT inflammation and vascular rarefaction contribute to unhealthy expansion of adipose tissue resulting in disrupted metabolic and endocrine functions. VAT sections from WT HFHS stained with isolectin B4 revealed reduced vascular density which was preserved in A2−/− HFHS. Flowcytometry analysis of stromal vascular fraction isolated from VAT of WT HFHS mice showed an increase in proinflammatory M1 macrophages (F4/80+CD11c+) (p=0.06) and a significant decrease in antiinflammatory M2 macrophages (F4/80+CD206+) (p<0.05), the latter was not affected in male mice. These effects were blunted in A2−/− HFHS female mice, reducing the M1/M2 ratio towards a favorable, less inflammatory state. Given the role of A2 in polarizing macrophages to an inflammatory state in vivo, we wished to determine the specific effect of macrophage A2 on inflammatory responses. Peritoneal macrophages from WT and A2−/− female mice were isolated, cultured in vitro and treated with 100 ng/ml lipopolysaccharide (LPS) or vehicle for 24 hr. WT macrophages exposed to LPS showed an activated inflammasome pathway (increased expressions of NLRP3 and pro‐IL‐1β) compared to control group (p<0.05). These effects of LPS were blunted in isolated A2−/− macrophages, indicating that A2 promotes inflammatory macrophage responses in female mice. Collectively, our data show that A2 is a critical mediator of obesity‐induced metabolic dysregulation, VAT vascular rarefaction and increased macrophage inflammatory responses in female mice.Support or Funding InformationR01 HL070215, R01 EY01176 & AHA17PRE33660321