Expression of retinoic acid‐metabolizing enzymes, ALDH1A1, ALDH1A2, ALDH1A3, CYP26A1, CYP26B1 and CYP26C1 in canine testis during post‐natal development

Abstract

Mammalian spermatogenesis involves highly regulated temporal and spatial dynamics, carefully controlled by several signalling processes. Retinoic acid (RA) signalling could have a critical role in spermatogenesis by promoting spermatogonia differentiation, adhesion of germ cells to Sertoli cells, and release of mature spermatids. An optimal testicular RA concentration is maintained by retinaldehyde dehydrogenases (ALDHs), which oxidize RA precursors to produce RA, whereas the CYP26 class of enzymes catabolizes (oxidize) RA into inactive metabolites. The objective was to elucidate gene expression of these RA-metabolizing enzymes (ALDH1A1, ALDH1A2, ALDH1A3, CYP26A1, CYP26B1 and CYP26C1) and their protein presence in testes of young, peripubertal and adult dogs. Genes encoding RA-synthesizing isozymes ALDH1A1, ALDH1A2 and ALDH1A3 and RA-catabolizing isomers CYP26A1, CYP26B1 and CYP26C1 were expressed in testis at varying levels during testicular development from birth to adulthood in dogs. Based on detailed analyses of mRNA expression patterns, ALDH1A2 was regarded as a primary RA-synthesizing enzyme and CYP26B1 as a critical RA-hydrolysing enzyme; presumably, these genes have vital roles in maintaining RA homeostasis, which is imperative to spermatogenesis and other testicular functions in post-natal canine testis.

Sources ofall-transretinal oxidation independent of the aldehyde dehydrogenase 1A isozymes exist in the postnatal testis†

“…However, investigations of how and where atRA is produced to drive these processes have been complicated by gaps in our knowledge of the enzymes responsible for atRA biosynthesis. Although the expression of ALDH1A1 residing within adult Sertoli cells may contribute to the biosynthesis of atRA driving the premeiotic transitions, several groups have provided evidence to suggest that ALDH1A2 residing within the meiotic and postmeiotic germ cells is the major isomer involved [31,32,38,45]. In this report, we have examined for the first time the in vivo contribution of ALDH1A2 to postnatal testicular atRA levels using two complementary genetic approaches.…”

“…We utilized a previously published WIN7D + RA synchrony protocol with minor modifications [44,45]. Briefly, 2 dpp 129/B6 male mice were pipette fed 100 mg/kg/bw (body weight) WIN (gift from Dr John Amory) daily for 7 days, given an atRA injection on day 9 and maintained on one of the following treatment regimens during the injection recovery: (1) 1% gum tragacanth (WIN7D + RA), (2) 150 mg/kg/bw WIN (WIN7D + RA + WIN), (3) 25 mg/kg/bw of HYD (Sigma-Aldrich, H1753) (WIN7D + RA + HYD), or (4) 150 mg/kg/bw WIN and 25 mg/kg/bw HYD (WIN7D + RA + WIN/HYD) (Supplemental Figure S2).…”

“…Specifically, it has been shown that the atRA required to drive the first round of spermatogenesis is derived from the ALDH1A enzymes residing within Sertoli cells [31]. The enzymatic and cellular sources of atRA biosynthesis driving the subsequent rounds of spermatogonial differentiation remain to be identified; however, it is widely hypothesized that the ALDH1A enzymes, specifically ALDH1A2, residing within the meiotic and postmeiotic germ cells are involved [31,32,38,45]. The in vivo role that Aldh1a2 plays within germ cells has yet to be determined, as global Aldh1a2-null mice die early in embryonic development (E9.5-10.5) [39,40,46].…”

Structural Basis of ALDH1A2 Inhibition by Irreversible and Reversible Small Molecule Inhibitors

“…11–13 ALDH1A1 is expressed in sertoli cells while ALDH1A2 is found in spermatogonia, spermatids, and spermatocytes. 12,14 ALDH1A2 is regarded as the primary RA-synthesizing enzyme in mammalian spermatogenesis, 15 and ALDH1A2 levels are significantly reduced in the testicular tissue of infertile men. 16 Therefore, ALDH1A2 is considered as a promising target for the development of nonhormonal male contraceptives.…”

ITRAQ-based proteomic analysis reveals possible target-related proteins in human adrenocortical adenomas

“…ALDH1A2 as substrates can recognize free retinal and cellular retinol-binding protein-bound retinal. It mainly metabolizes octanal and decanal but does not metabolize citral, benzaldehyde, acetaldehyde, and propanal efficiently [36, 37]. Shou S et al [38] revealed that defects in IPCD and digit separation in Hoxa13 mutant mice may be partly caused by reduced levels of RA signaling stemming from a loss in the direct regulation of Aldh1a2.…”