Thyrotropin-releasing hormone (TRH) receptors, Gq/11-protein-coupled receptors, most of them in spinal cord should derive from supraspinal sources, especially medullary raphe region, projecting to the ventral horn at varicose fibers in close association with motoneurons and in the dorsal horn into both cell bodies and fibers. Some reports provide evidence that TRH has a neurotransmitter-like action, and plays an important role in motor system function.
An Overview of Thyrotropin-releasing hormone (TRH) receptors
Thyrotropin-releasing hormone (TRH) receptor is a G-protein coupled receptor that binds to the tripeptide thyroid stimulating hormone releasing hormone. TRH is the first pituitary hormone found in the hypothalamus. Its main function is to maintain the thyroid hormone homeostasis by regulating the secretion of thyroid stimulating hormone in the pituitary, and also regulate the release of other pituitary hormones. More than two-thirds of the brain's thyrotropin-releasing hormone receptors are distributed outside the hypothalamus, such as the nucleus accumbens, cerebellum, and medulla. Thyrotropin-releasing hormone receptors are also present in many non-neural tissues such as the gastrointestinal tract, pancreas, testes, seminal vesicles, epididymis, prostate, ovary, placenta, immune system, retina and skin.
Major type of Thyrotropin-releasing hormone (TRH) receptors
Two TRH receptors have been found in species such as rats and mice: TRH-R1 and TRH-R2. However, only TRH-R1 has been found in humans so far.
TRH receptors and diseases
In 2008, researchers found that TRH-R1 and TRH-R2 were expressed in Leydig cells of rats. TRH may regulate the development of Leydig cells and the secretion of testosterone. Therefore, TRH receptors appeared in the prostate, which may be related to male fertility. Besides, small intestinal epithelial cells express TRH receptors and produce TSH, while TRH receptors are expressed in intestinal T cells. This suggests a hormone-mediated association between intestinal lymphocytes and non-hematopoietic cells, and intestinal T cell function in TRH receptors mutant mice is impaired. Therefore, TRH receptors may play an immunomodulatory role in the intestine. In addition, TRH receptors may also be used in the treatment of neurological diseases such as cerebrospinal injury, schizophrenia, Alzheimer's disease, epilepsy, Parkinson's disease and depression. Gáspár et al. found that epithelial cells of human scalp hair follicles express both TRH and TRH receptors. Stimulation of hair follicles with TRH promotes elongation of the hair shaft and prolongs hair growth, and promotes proliferation and inhibition of apoptosis of hair basal keratinocytes. Therefore, TRH receptors also has the effect of promoting hair growth and stimulating the production of melanin in the hair.
Knuever, J., Poeggeler, B., Gáspár, E., et al. (2012) Thyrotropin-releasing hormone controls mitochondrial biology in human epidermis. J Clin Endocrinol Metab, 97(3): 978-986.