The effect of PPARγ inhibition on bone marrow adipose tissue and bone in C3H/HeJ mice

Abstract

Bone marrow adipose tissue (BMAT) increases after menopause, and increased BMAT is associated with osteoporosis and prevalent vertebral fractures. Peroxisome proliferator-activated receptor-γ (PPARγ) activation promotes adipogenesis and inhibits osteoblastogenesis; therefore, PPARγ is a potential contributor to the postmenopausal increase in BMAT and decrease in bone mass. The aim of this study is to determine if PPARγ inhibition can prevent ovariectomy-induced BMAT increase and bone loss in C3H/HeJ mice. Fourteen-week-old female C3H/HeJ mice ( n = 40) were allocated to four intervention groups: sham surgery (Sham) or ovariectomy (OVX; isoflurane anesthesia) with either vehicle (Veh) or PPARγ antagonist administration (GW9662; 1 mg·kg−1·day−1, daily intraperitoneal injections) for 3 wk. We measured BMAT volume, adipocyte size, adipocyte number. and bone structural parameters in the proximal metaphysis of the tibia using polyoxometalate-based contrast enhanced-nanocomputed topogaphy. Bone turnover was measured in the contralateral tibia using histomorphometry. The effects of surgery and treatment were analyzed by two-way ANOVA. OVX increased the BMAT volume fraction (Sham + Veh: 2.9 ± 2.7% vs. OVX + Veh: 8.1 ± 5.0%: P < 0.001), average adipocyte diameter (Sham + Veh: 19.3 ± 2.6 μm vs. OVX + Veh: 23.1 ± 3.4 μm: P = 0.001), and adipocyte number (Sham + Veh: 584 ± 337cells/μm3 vs. OVX + Veh: 824 ± 113cells/μm3: P = 0.03), while OVX decreased bone volume fraction (Sham + Veh: 15.5 ± 2.8% vs. OVX + Veh: 7.7 ± 1.9%; P < 0.001). GW9662 had no effect on BMAT, bone structural parameters, or bone turnover. In conclusion, ovariectomy increased BMAT and decreased bone volume in C3H/HeJ mice. The PPARγ antagonist GW9662 had no effect on BMAT or bone volume in C3H/HeJ mice, suggesting that BMAT accumulation is regulated independently of PPARγ in C3H/HeJ mice.