Regulation of hypothalamic prohormone convertases 1 and 2 and effects on processing of prothyrotropin-releasing hormone
Vanesa C. Sanchez, Jorge Goldstein, Ronald C. Stuart, Virginia Hovanesian, Lihong Huo, Heike Munzberg, Theodore C. Friedman, Christian Bjorbaek, Eduardo A. Nillni
Vanesa C. Sanchez, Jorge Goldstein, Ronald C. Stuart, Virginia Hovanesian, Lihong Huo, Heike Munzberg, Theodore C. Friedman, Christian Bjorbaek, Eduardo A. Nillni
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Article Metabolism

Regulation of hypothalamic prohormone convertases 1 and 2 and effects on processing of prothyrotropin-releasing hormone

Abstract

Regulation of energy balance by leptin involves regulation of several neuropeptides, including thyrotropin-releasing hormone (TRH). Synthesized from a larger inactive precursor, its maturation requires proteolytic cleavage by prohormone convertases 1 and 2 (PC1 and PC2). Since this maturation in response to leptin requires prohormone processing, we hypothesized that leptin might regulate hypothalamic PC1 and PC2 expression, ultimately leading to coordinated processing of prohormones into mature peptides. Using hypothalamic neurons, we found that leptin stimulated PC1 and PC2 mRNA and protein expression and also increased PC1 and PC2 promoter activities in transfected 293T cells. Starvation of rats, leading to low serum leptin levels, decreased PC1 and PC2 gene and protein expression in the paraventricular nucleus (PVN) of the hypothalamus. Exogenous administration of leptin to fasted animals restored PC1 levels in the median eminence (ME) and the PVN to approximately the level found in fed control animals. Consistent with this regulation of PCs in the PVN, concentrations of TRH in the PVN and ME were substantially reduced in the fasted animals relative to the fed animals, and leptin reversed this decrease. Further analysis showed that proteolytic cleavage of pro–thyrotropin-releasing hormone (proTRH) at known PC cleavage sites was reduced by fasting and increased in animals given leptin. Combined, these findings suggest that leptin-dependent stimulation of hypothalamic TRH expression involves both activation of trh transcription and stimulation of PC1 and PC2 expression, which lead to enhanced processing of proTRH into mature TRH.

Authors

Vanesa C. Sanchez, Jorge Goldstein, Ronald C. Stuart, Virginia Hovanesian, Lihong Huo, Heike Munzberg, Theodore C. Friedman, Christian Bjorbaek, Eduardo A. Nillni

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Immunolocalization of PC2 in hypophysiotropic areas of the hypothalamus ...
Immunolocalization of PC2 in hypophysiotropic areas of the hypothalamus during fed versus fasted states. (A and B) Typical photomicrographs showing the immunodistribution of PC2 in the PaLMs and the PaMPs. (C and D) The ME. (E and F) The CC. A significant decrease in PC2 immunoreactivity is shown in the PaMPs (the location of hypophysiotropic TRH neurons) from fasted animals (B) as compared with fed controls (A). See also the high-magnification images at the left of A and the right of B. In the same brain section, the PaLM subdivision, which also expresses PC2, showed a decrease during fasting (A and B; see also the high-magnification images). A and B show low magnification (×10, scale bar: 200 μm). High-magnification images are indicated by arrows (×40, scale bar: 50 μm). The ME region (C and D) shows a weak, unchanged immunostaining in the internal zone and less intense staining in the external zone of the medial portion of the ME in fed as compared with fasted animals. No changes were observed in the anterior and posterior ME (not shown). The immunoreactivity for PC2 in the CC (E and F) did not show differences between fed and fasted animals (see also insets). Magnification in E and F, ×20; scale bar: 50 μm.