[Show abstract][Hide abstract] ABSTRACT: The anorexigenic neuromodulator alpha-melanocyte-stimulating hormone (alpha-MSH; referred to here as alpha-MSH1-13) undergoes extensive posttranslational processing, and its in vivo activity is short lived due to rapid inactivation. The enzymatic control of alpha-MSH1-13 maturation and inactivation is incompletely understood. Here we have provided insight into alpha-MSH1-13 inactivation through the generation and analysis of a subcongenic mouse strain with reduced body fat compared with controls. Using positional cloning, we identified a maximum of 6 coding genes, including that encoding prolylcarboxypeptidase (PRCP), in the donor region. Real-time PCR revealed a marked genotype effect on Prcp mRNA expression in brain tissue. Biochemical studies using recombinant PRCP demonstrated that PRCP removes the C-terminal amino acid of alpha-MSH1-13, producing alpha-MSH1-12, which is not neuroactive. We found that Prcp was expressed in the hypothalamus in neuronal populations that send efferents to areas where alpha-MSH1-13 is released from axon terminals. The inhibition of PRCP activity by small molecule protease inhibitors administered peripherally or centrally decreased food intake in both wild-type and obese mice. Furthermore, Prcp-null mice had elevated levels of alpha-MSH1-13 in the hypothalamus and were leaner and shorter than the wild-type controls on a regular chow diet; they were also resistant to high-fat diet-induced obesity. Our results suggest that PRCP is an important component of melanocortin signaling and weight maintenance via control of active alpha-MSH1-13 levels.
The Journal of clinical investigation 09/2009; 119(8):2291-303. DOI:10.1172/JCI37209 · 13.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Leptin regulates synaptic plasticity in the hypothalamic NPY/AgRP and POMC neurons of the arcuate nucleus. In addition, negative energy balance such as fasting is associated with changes in mitochondrial function and density in the NPY/AgRP neurons that are uncoupling protein 2 (UCP2)-mediated. In his study we investigated whether leptin affects hypothalamic mitochondrial function and if so, does it involve UCP2 activation. We found that leptin deficient mice (Lepob/ob) displayed elevated UCP2 mRNA levels compared to wild type controls (wt). Leptin replacement for 48 hours restored UCP2 mRNA to the levels of wt animals. Mitochondrial density was increased in NPY/AgRP neurons of the Lepob/ob mice. However, a decrease in mitochondrial density was also observed in pro-opiomelanocortin (POMC) neurons. In both neuronal populations leptin replacement restored the mitochondrial density to the levels of wt controls. Measurements of mitochondrial respiratory states showed that state 2, state 4 and free fatty acid-induced uncoupling activity were all significantly increased in Lepob/ob mice compared to wt and 48 hr leptin-treated Lepob/ob mice. Accordingly, resting mitochondrial membrane potential was significantly lower in Lepob/ob mice than wt and 48 hr leptin-treated Lepob/ob mice. Finally, analysis of reactive oxygen species showed a significant increase of ROS production in Lepob/ob mice. We conclude that leptin plays a significant role in regulating mitochondrial denisity, respiration, membrane potential and ROS production of both NPY/AgRP and POMC neurons in the arcuate nucleus and this role is strongly correlated with the mitochondrial UCP2 levels.
Keystone 2009 - Obesity: Novel Aspects of the Regulation of Body Weight; 01/2008