For metabolic cage studies, weight-matched 12-week-old WT (30.10 ± 1.11 g) and IFT88-KOSF-1 (31.30 ± 1.33 g) male littermates fed NC were used and 16-week-old WT (46.63.10 ± 1.78 g) and IFT88-KOSF-1 (53.40 ± 2.21 g) male littermates fed HFD were used. Metabolic rates were assessed with an indirect calorimetry system (CaloSys Calorimetry System, TSE Systems Inc.), as previously described (20, 24). For environmental acclimation, first, the experimental mice were housed 5 days in metabolic cages individually and maintained in the same room where the metabolic analyses were performed. Then the mice were individually housed in the metabolic chambers and acclimated for 48 hours. After acclimation in the chamber, food intake, oxygen consumption (VO2), carbon dioxide production (VCO2), heat generation, and movement were measured and the relationship between metabolic rate and body mass was normalized using lean body mass. Diet (NC or HFD) and water were available ad libitum unless otherwise indicated.

To measure leptin sensitivity using metabolic cages, body weight matched (28.54 ± 1.39 g for WT and 29.33 ± 1.10 g for IFT88-KOSF-1) 12-week old mice were used. After 3 days of regular cage studies, chow was removed at 6:00 pm, and mice were fasted for 1 day. The following day, experimental mice were given leptin (i.p., 5 mg/kg of body weight) with food; then metabolic parameters, including food intake, VO2, VCO2, heat generation, and movement, were monitored during the experimental period.

To assess the metabolic effects of ISO (I6504, MilliporeSigma), an adrenoreceptor agonist, 16-week old WT and IFT88-KOSF-1 mice were used and were given ISO (15 mg/kg of body weight, daily i.p. injection) for 2 weeks.