D-Asp upregulates PREP and GluA2/3 expressions and induces p-ERK1/2 and p-Akt in rat testis

Abstract

D-Aspartate (D-Asp) is an endogenous amino acid that plays a central role in the development of the central nervous system (CNS) and functioning of the neuroendocrine system. In line with its functions, it is abundantly present in the CNS and reproductive systems of vertebrates and invertebrates. It has been implicated in the biosynthesis and/or secretion of hormones and factors that are involved in various reproductive functions, such as GnRH from the hypothalamus and testosterone from the testis. We conducted an in vivo study consisting of acute (i.p. injection of 2 µmol/g body weight) and chronic (15 days drinking solution) administration of D-Asp to adult rats to understand the signaling pathways elicited by D-Asp in the rat testis. We found that D-Asp upregulated the expression of prolyl endopeptidase (PREP), a serine protease having a pivotal role in the regulation of mammalian spermatogenesis and spermiogenesis. Immunofluorescence analysis revealed its overexpression in Leydig cells, Sertoli cells and spermatogonia. Moreover, PREP was found to co-localize with GluA2/3, an AMPA receptor subunit, whose protein expression also increased after D-Asp treatments. Finally, we found a significant increase in ERK and Akt activities in the testis of rats treated with D-Asp. Since PREP is known to be involved in regulating GnRH levels and in germ cell differentiation, we hypothesize D-Asp to play a pivotal role in regulating hormone homeostasis and spermatogenesis through activation of PREP, AMPAR, ERK and Akt.

Cadmium‐induced toxicity increases prolyl endopeptidase (PREP) expression in the rat testis

“…Thus, we can hypothesize that the enhanced PREP expression levels in Cd‐treated gonads, and particularly in the LC, is required for the GnRH cleavage, to regulate the physiological estrogen production and action. We corelated our previous result, demonstrating that the enhancement of PREP expression in the LC is probably required to counteract and limit the physiological level levels of GnRH, induced by the treatment with the excitatory amino acid d ‐aspartate (Santillo et al, 2019). Taken together, our results support the hypothesis that PREP plays fundamental role in reproduction, since its expression and localization is modulated in response to several endogenous and exogenous factors.…”

“…However, PREP belongs to the serine protease family, with a post proline cleavage activity in oligopeptides no longer than 30 amino acids (Szeltner & Polgár, 2008) as well as neuropeptides and peptide hormones (Mentlein, 1988; Wilk, 1983). Recently, we demonstrated the regulatory role of PREP in the reproductive functioning in mammals (Santillo et al, 2019; Venditti, Aniello, Santillo, & Minucci, 2019), both during the morphofunctional remodeling during the postnatal development of testis (Venditti & Minucci, 2019), and gametes structure and physiology (Dotolo, Kim, Pariante, Minucci, & Diano, 2016; Venditti & Minucci, 2019) in rats.…”

EH domain binding protein 1-like 1 (EHBP1L1), a protein with calponin homology domain, is expressed in the rat testis

“…Given this background, the identification and characterization of spermatogenic-related genes is an important contribution to understanding the mechanisms of both spermatogenesis and human reproduction (Guo et al, 2010;Santillo et al, 2019;Venditti et al, 2020). In this study, an attempt was made to isolate genes involved in rat spermatogenesis and to use them as new markers for true testicular activity.…”

New Evidence on the Role of D-Aspartate Metabolism in Regulating Brain and Endocrine System Physiology: From Preclinical Observations to Clinical Applications

“…Further confirmation that D-Asp plays an active role in spermatogenesis is the increase in the expression of prolyl endopeptidase (PREP) [137] and disheveled-associated activator of morphogenesis 1 (DAAM1) [138] in the testis of D-Asp-treated rats (Figure 1). These two proteins are involved in cytoskeleton remodeling, which is an integral aspect of spermatogenesis and is therefore essential for male fertility.…”