Trem2 deficiency does not worsen metabolic function in diet-induced obese mice
Triggering receptor expressed on myeloid cells 2 (Trem2) is highly expressed on myeloid cells and is involved in cellular lipid homeostasis and inflammatory processes. Trem2 deletion in mice (Trem2-/-) has been implicated in evoking adipose tissue dysfunction, but its role in worsening obesity-induced metabolic dysfunction is not resolved. Here we aimed to determine the causal role of Trem2 in regulating glucose homeostasis and insulin sensitivity in mice. Nine-week-old male and female littermate WT and Trem2-/- mice were fed low fat or high fat diet for 18 weeks and phenotyped for metabolic function. Diet-induced weight gain was similar between genotypes, irrespective of sex. Consistent with prior reports, we find that loss of Trem2 causes massive adipocyte hypertrophy and an attenuation in the lipid associated macrophage transcriptional response to obesity. In contrast to published data, we find that loss of Trem2 does not worsen metabolic function in obese mice. No differences in intraperitoneal glucose tolerance (ipGTT), oral GTT, or mixed meal substrate control, including postprandial glucose, non-esterified fatty acids, insulin, or triglycerides were found between WT and Trem2-/- animals. Similarly, no phenotypic differences existed when animals were challenged with stressors on metabolic demand (i.e., acute exercise or environmental temperature modulation) or when animals were challenged with a non-lethal dose of endotoxin. Collectively, we report a disassociation between adipose tissue remodeling caused by loss of Trem2 and whole-body metabolic homeostasis in obese mice. The complementary nature of experiments conducted gives credence to the conclusion that loss of Trem2 is unlikely to worsen glucose homeostasis in mice.