Pregnancy-specific Adaptations in Leptin and Melanocortin Neuropeptides in Early Human Gestation

INTRODUCTION

Pregnancy is characterized by increased appetitive drive beginning early in gestation, yet the central mechanisms underlying this adaptation are poorly understood in humans. To elucidate central mechanisms underlying appetite regulation in early pregnancy, we examine plasma and cerebrospinal fluid (CSF) leptin and Agouti-related peptide (AgRP) as well as CSF proopiomelanocortin (POMC) as surrogates for brain melanocortin activity.

METHODS

Plasma leptin, soluble leptin receptor, AgRP, and CSF leptin, POMC, and AgRP were collected from pregnant women before cerclage placement (16.6 ± 1.1 weeks; N = 24), scheduled cesarean section (39.2 ± 0.2 weeks; N = 24), and from nonpregnant controls (N = 24), matched for age and body mass index.

RESULTS

Plasma leptin was 1.5 times higher in pregnancy vs controls (P = 0.01), but CSF leptin did not differ. CSF/plasma leptin percentage was lower in early pregnancy vs controls (0.8 ± 0.1 vs 1.7 ± 0.2; P < 0.0001) and remained unchanged at term (0.9 ± 0.1), supporting a decrease in leptin transport into CSF in pregnancy. Plasma AgRP, a peripheral biomarker of the orexigenic hypothalamic neuropeptide, was higher in early pregnancy vs controls (95.0 ± 7.8 vs 67.5 ± 5.3; P = 0.005). In early gestation, CSF AgRP did not differ from controls, but CSF POMC was 25% lower (P = 0.006). In contrast, at term, CSF AgRP was 42% higher vs controls (P = 0.0001), but CSF POMC no longer differed. Overall, the CSF AgRP/POMC ratio was 1.5-fold higher in early pregnancy vs controls, reflecting a decrease in melanocortin tone favoring appetitive drive.

CONCLUSIONS

Pregnancy-specific adaptions in the central regulation of energy balance occur early in human gestation and are consistent with decreased leptin transport into brain and resistance to the effects of leptin on target melanocortin neuropeptides.

Proopiomelanocortin (POMC), the ACTH/melanocortin precursor, is secreted by human epidermal keratinocytes and melanocytes and stimulates melanogenesis

Proopiomelanocortin (POMC) can be processed to ACTH and melanocortin peptides. However, processing is incomplete in some tissues, leading to POMC precursor release from cells. This study examined POMC processing in human skin and the effect of POMC on the melanocortin-1 receptor (MC-1R) and melanocyte regulation. POMC was secreted by both human epidermal keratinocytes (from 5 healthy donors) and matched epidermal melanocytes in culture. Much lower levels of alpha-MSH were secreted and only by the keratinocytes. Neither cell type released ACTH. Cell extracts contained significantly more ACTH than POMC, and alpha-MSH was detected only in keratinocytes. Nevertheless, the POMC processing components, prohormone convertases 1, 2 and regulatory protein 7B2, were detected in melanocytes and keratinocytes. In contrast, hair follicle melanocytes secreted both POMC and alpha-MSH, and this was enhanced in response to corticotrophin-releasing hormone (CRH) acting primarily through the CRH receptor 1. In cells stably transfected with the MC-1R, POMC stimulated cAMP, albeit with a lower potency than ACTH, alpha-MSH, and beta-MSH. POMC also increased melanogenesis and dendricity in human pigment cells. This release of POMC from skin cells and its functional activity at the MC-1R highlight the importance of POMC processing as a key regulatory event in the skin.