Abstract
The role of kisspeptin in stimulating hypothalamic GnRH is undisputed. However, the role of kisspeptin signaling in testicular function is less clear. The testes are essential for male reproduction through their functions of spermatogenesis and steroidogenesis. Our review focused on the current literature investigating the distribution, regulation and effects of kisspeptin and its receptor (KISS1/KISS1R) within the testes of species studied to date. There is substantial evidence of localised KISS1/KISS1R expression and peptide distribution in the testes. However, variability is observed in the testicular cell types expressing KISS1/KISS1R. Evidence is presented for modulation of steroidogenesis and sperm function by kisspeptin signaling. However, the physiological importance of such effects, and whether these are paracrine or endocrine manifestations, remain unclear.
Highlights
Kisspeptin is an established regulator of puberty onset [1,2], sexual maturation and adult reproductive activity [3]
In contrast to Mei et al [12], strong kisspeptin immunoreactivity was noted in both Leydig cells and in elongated spermatids; whereas, KISS1R was expressed in the acrosomal region of spermatids and mature spermatozoa but not in spermatogonial cells or spermatocytes of adult mice
KISS1R was observed in mice spermatozoa, and KISS1 was observed in Leydig cells, which have a major role in testicular steroidogenesis. These results suggest a possible paracrine signaling pathway between sperm and Leydig cells
Summary
Kisspeptin is an established regulator of puberty onset [1,2], sexual maturation and adult reproductive activity [3]. Multiple studies have observed the distribution, expression and activity of both KISS1/KISS1R in the testes [11,12,13,14]. Re-expression of KISS1R in GnRH neurons is insufficient to normalise testicular function, suggesting a potential direct role of KISS1/KISS1R in testis physiology [15]. Studies in primates [16,17,18], rodents [19,20,21], amphibians [22,23,24] and fish [25,26] have observed potential regulatory roles of kisspeptin in germ cell progression, modulation of sperm function and testicular steroidogenesis. We discuss evidence of local expression of KISS1/KISS1R system in the testes and its role in direct testicular functions
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