Age-related alterations in the expression of prohormone convertase messenger ribonucleic acid (mRNA) levels in hypothalamic proopiomelanocortin mRNA neurons in the female C57BL/6J mouse.

POMC processing is mediated by the prohormone convertases (PC1 and PC2). The cleavage of beta-endorphin-(1-31) is mediated by PC2. PC2 can also further cleave beta-endorphin-(1-31) to beta-endorphin-(1-27). We previously reported a significant increase in the proportion of beta-endorphin-(1-27) and -(1-27) forms in the arcuate nucleus (ARC) of the hypothalamus in middle-aged females with irregular estrous cycles (5-7 days) compared to young female C57BL/6J mice with regular cycles (4-5 days). Changes in processing enzymes may be a mechanism underlying this change. We compared ARC messenger RNA (mRNA) levels of PC1, PC2, and furin by Northern blot and in situ hybridization analyses in young, middle-aged, and old mice. Antisense complementary RNA probes to mouse PC1, PC2, and furin were radiolabeled and used in single label studies, alone or in combination with a mouse POMC digoxigenin-labeled complementary RNA probe for double label studies. For Northern blot analysis, young (4- to 5-month-old) normally cycling (4-5 days) mice at diestrus were compared to middle-aged (12- to 13-month-old) irregularly cycling (5-7 days) mice at diestrus. By Northern blot analysis, a significant increase (P < 0.05) in ARC PC2 mRNA levels was detected in middle-aged compared to young mice, but ARC PC1 and furin mRNA levels were unaltered. Single label in situ hybridization analysis confirmed these findings in the general neuron population. We also observed a significant reduction in ARC furin mRNA levels in old mice compared to either young or middle-aged mice. Double labeling in situ hybridization histochemistry demonstrated that PC2 mRNA levels were significantly increased (at least 2-fold) in POMC mRNA-containing neurons of middle-aged compared to young mice. Selective changes in PC2 mRNA levels in ARC POMC neurons are correlated with changes in beta-endorphin-(1-31) processing to beta-endorphin-(1-27)/(1-26) in middle-aged animals. Our data suggest that the natural age-related shift in beta-endorphin peptide processing is mediated by PC2.