Tyrosine hydroxylase deletion in Ntsr1 neurons confers resistance to diet-induced weight gain: an energy-balance analysis

Abstract

High-fat diet (HFD) disrupts circadian feeding rhythms and promotes diet-induced obesity (DIO), but the neural mechanisms linking diet to energy balance remain unclear. Previously, we demonstrated that dopamine production in neurotensin receptor 1 (Ntsr1)-expressing neurons was required for HFD-induced daytime overfeeding and DIO. Here, we tested whether DIO resistance in Ntsr1Cre;Thflox conditional knockout (cKO) mice was explained by altered energy expenditure. We replicated resistance to HFD-induced weight gain and assessed food intake, indirect calorimetry, activity, body temperature, fecal energy, fecal nonesterified fatty acids, and the gut microbiome. Indirect calorimetry on standard chow diet (SCD) was confounded by reduced intake and body weight loss, whereas HFD-fed cKO mice consumed food readily and resisted weight gain. Unlike our previous study, daytime feeding was not suppressed; instead, cKO mice were slightly and variably hypophagic on HFD but not SCD. DIO resistance was not accompanied by increased energy expenditure, activity, or body temperature. Rather, cKO mice showed reduced energy expenditure and activity and lower body temperature on both diets. In the replication cohort, HFD fecal output was lower in cKO mice, whereas the independent bomb-calorimetry cohort showed no genotype difference in fecal mass; fecal energy density and nonesterified fatty acid concentration were unchanged. Preliminary analysis of the microbiome was consistent with an obesity-resistant gut profile. Together, these findings indicate that the feeding phenotype is diet- and experiment-dependent and that DIO resistance is not explained by increased energy expenditure, activity, thermogenesis, or detectable changes in fecal energy or fat content.