Regulation of prohormone convertases in hypothalamic neurons: implications for prothyrotropin-releasing hormone and proopiomelanocortin.

Recent evidence demonstrated that posttranslational processing of neuropeptides is critical in the pathogenesis of obesity. Leptin or other physiological changes affects the biosynthesis and processing of many peptides hormones as well as the regulation of the family of prohormone convertases responsible for the maturation of these hormones. Regulation of energy balance by leptin involves regulation of several proneuropeptides such as proTRH and proopiomelanocortin. These proneuropeptide precursors require for their maturation proteolytic cleavage by the prohormone convertases 1 and 2 (PC1/3 and PC2). Because biosynthesis of mature peptides in response to leptin requires prohormone processing, it is hypothesized that leptin might regulate hypothalamic PC1/3 and PC2 expression, ultimately leading to coordinated processing of prohormones into mature peptides. Leptin has been shown to increase PC1/3 and PC2 promoter activities, and starvation of rats, leading to low serum leptin levels, resulted in a decrease in PC1/3 and PC2 gene and protein expression in the paraventricular and arcuate nucleus of the hypothalamus. Changes in nutritional status also changes proopiomelanocortin processing in the nucleus of the solitary tract, but this is not reversed by leptin. The PCs are also physiologically regulated by states of hyperthyroidism, hyperglycemia, inflammation, and suckling, and a recently discovered nescient helix-loop-helix-2 transcription factor is the first one to show an ability to regulate the transcription of PC1/3 and PC2. Therefore, the coupled regulation of proneuropeptide/processing enzymes may be a common process, by which cells generate more effective processing of prohormones into mature peptides.