Prolyl Carboxypeptidase Regulates Energy Expenditure and the Thyroid Axis

Abstract

Hypothalamic α-melanocyte-stimulating hormone (α-MSH) plays a central role in regulating energy uptake and expenditure. Prolyl carboxypeptidase (PRCP), a protease expressed in the hypothalamus, is responsible for the degradation of α-MSH. PRCP null animals (PRCP(gt/gt) mice) display elevated α-MSH in the hypothalamus, lower body weight, and are protected from diet induced obesity. Here, we report that PRCP(gt/gt) mice have a significant decrease in fat mass, although an increase in lean mass was also observed. In agreement with low fat accumulation, reduced leptin levels were found. Consistent with the effect of α-MSH on energy metabolism, PRCP(gt/gt) mice had increased energy expenditure with elevated circulating thyroid hormone levels and brown adipose tissue uncoupling protein 1 mRNA levels compared with control mice when exposed to regular diet. TRH mRNA levels in the PVN were significantly higher in fed PRCP(gt/gt) animals compared with fed wild-type controls. Fasting significantly decreased TRH mRNA levels in both PRCP(gt/gt) and wild-type (WT) mice. However, TRH mRNA levels in fasted PRCP(gt/gt) animals were significantly higher than those of fasted WT mice. Refeeding analysis after fasting showed a reduced food intake in PRCP(gt/gt) compared with WT mice. Finally, TRH mRNA levels in T(3)-treated hypothyroid PRCP(gt/gt) mice showed a non significant reduction compared with those of hypothyroid PRCP(gt/gt) mice, supporting the impairment of the hypothalamo-pituitary-thyroid axis in PRCP(gt/gt) mice. All together, these data confirm that PRCP plays a role in the regulation of energy metabolism.

Hypothalamic prolyl endopeptidase (PREP) regulates pancreatic insulin and glucagon secretion in mice

“…Adult male mice for Prep gt/gt and WT were acclimated in metabolic chambers (TSE System) for 4 d before the start of the recordings as previously published (27,28). For body composition, adult males were scanned in an EchoMRI machine (Echo Medical Systems), and their body composition was calculated according to body weight.…”

“…Glucose tolerance tests were performed in 16-h fasted animals as previously reported (27,28). Each animal received an i.p.…”

“…Blood glucose and insulin levels were measured after 15, 30, 60, and 120 min. An ITT was performed in ad-libitum-fed mice (27,28). Each animal received an i.p.…”

“…In situ hybridization was based on our previously published protocol (27,28). A 500-bp sequence between 1531 and 2030 was selected from the mouse PREP (GenBank accession no.…”

“…A 500-bp sequence between 1531 and 2030 was selected from the mouse PREP (GenBank accession no. NM_011156), synthesized (Biomatik), incorporated into pBluescript vector, and used as template (27,28). 35 S-labeled riboprobes were then purified using sephadex columns (ProbeQuant G-50 Micro Columns, Pharmacia Biotech) following the manufacturer's protocol, and 5 × 10 5 cpm per section was used for the hybridization (27,28).…”