Ventromedial hypothalamic NPY Y2 receptor in the maintenance of body weight in diet-induced obesity in mice
This study examined changes in neuropeptide Y (NPY) Y2 receptor binding in the brains of C57BL/6 mice in response to different levels of high-fat diets via three dietary intervention methods: high-fat diet, switching from high- to low-fat diet and finally, energy restricted high-fat diet. Forty-five C57Bl/6 male mice were fed a high-fat diet for 8 weeks and then classified as diet-induced obese (DIO) or diet-resistant (DR) mice according to the highest and lowest body weight gainers, respectively. The DIO and DR mice were then randomly divided into three groups each and either continued on their high-fat diet ad libitum (DIO-H and DR-H), changed to a low-fat diet (DIO-L and DR-L) or pair-fed via energy restricted high-fat diet (DIO-P and DR-P) for a further 6 weeks. During the course of this study, body weight, energy intake and plasma peptide YY (PYY) were measured. The study revealed that the replacement of a high-fat diet with a low-fat diet was associated with a significant lowering of ventromedial hypothalamic (VMH) Y2 receptor binding in both the DIO-L and DR-L mice (-37%, -36%), and also a lowered plasma PYY level in the DIO-L mice (-25%). Despite a continued consumption of the high-fat diet, energy restricted pair feeding caused a lower VMH Y2 receptor binding in the obese mice (DIO-P) following weight loss compared to the DR-P mice (-14%). In conclusion, this study showed that changing diets from high- to low-fat can significantly lower the VMH Y2 receptor binding irrespective to the obesity phenotype. Energy restriction, even while on high-fat feeding, can cause a lower VMH Y2 receptor binding compared to DR mice even after body weight loss to similar levels. This suggests either a possible intrinsic nature of the DIO mice or a body weight set-point re-establishment to drive body weight regain.