Cellular colocalization and coregulation between hypothalamic pro-TRH and prohormone convertases in hypothyroidism

Area of Science:

• Neuroendocrinology
• Molecular Endocrinology
• Cell Biology

Background:

• Prohormone convertases (PCs), specifically PC1/3 and PC2, are crucial for post-translational processing of hormones in the secretory pathway.
• Pro-thyrotropin-releasing hormone (pro-TRH) is processed by PC1/3 and PC2 in both brain regions regulating thyroid-stimulating hormone secretion and other brain areas.
• Thyroid hormone's impact on pro-TRH processing via PC1/3 and PC2 expression in specific brain nuclei remains largely unexplored.

Purpose of the Study:

• To investigate the hypothesis that thyroid hormone status alters pro-TRH processing by modulating PC1/3 and PC2 expression in specific rat brain nuclei.
• To examine the coexpression and coregulation of pro-TRH, PC1/3, and PC2 in the paraventricular nucleus (PVN), lateral hypothalamus (LH), and ventromedial nucleus (VMN) under hypothyroid and euthyroid conditions.

Main Methods:

• Induction of hypothyroidism in rats using 6-n-propyl-2-thiouracil (PTU) treatment.
• Quantitative analysis of pro-TRH, PC1/3, and PC2 expression in the PVN, LH, and VMN.
• Confocal microscopy to assess the colocalization of processing enzymes (PC1/3, PC2) with pro-TRH.

Main Results:

• PTU-induced hypothyroidism significantly increased the expression of PC1/3, PC2, and pro-TRH in the PVN and LH, but not the VMN.
• Confocal analysis revealed increased colocalization of PC1/3 or PC2 with pro-TRH in the PVN, particularly in ventral and medial regions.
• No significant regulation of colocalization was observed in the ventromedial hypothalamus (VMH) or LH.

Conclusions:

• Thyroid hormone status dynamically regulates pro-TRH processing enzyme expression and their colocalization with pro-TRH in specific brain nuclei.
• The observed increase in PC1/3 and PC2 colocalization with pro-TRH in the PVN suggests a novel mechanism for altering hormonal biosynthesis in response to thyroid hormone levels.
• These findings highlight a previously unrecognized regulatory pathway for neuroendocrine hormone processing influenced by thyroid hormone status.