TPH2 and obesity due to melanocortin 4 receptor deficiency: To further investigate whether a HFD itself or obesity-associated changes result in dramatic upregulation in adipocyte Tph2 expression, we analyzed Tph2 mRNA levels in age-matched chow-fed C57BL/6J and ob/ob mice or C57BL/6J mice fed a HFD for 6 weeks.