Modulation of mouse Leydig cell steroidogenesis through a specific arginine-vasopressin receptor

Characterizing the reproductive transcriptomic correlates of acute dehydration in males in the desert-adapted rodent, Peromyscus eremicus

BACKGROUND

The understanding of genomic and physiological mechanisms related to how organisms living in extreme environments survive and reproduce is an outstanding question facing evolutionary and organismal biologists. One interesting example of adaptation is related to the survival of mammals in deserts, where extreme water limitation is common. Research on desert rodent adaptations has focused predominantly on adaptations related to surviving dehydration, while potential reproductive physiology adaptations for acute and chronic dehydration have been relatively neglected. This study aims to explore the reproductive consequences of acute dehydration by utilizing RNAseq data in the desert-specialized cactus mouse (Peromyscus eremicus).

RESULTS

We exposed 22 male cactus mice to either acute dehydration or control (fully hydrated) treatment conditions, quasimapped testes-derived reads to a cactus mouse testes transcriptome, and then evaluated patterns of differential transcript and gene expression. Following statistical evaluation with multiple analytical pipelines, nine genes were consistently differentially expressed between the hydrated and dehydrated mice. We hypothesized that male cactus mice would exhibit minimal reproductive responses to dehydration; therefore, this low number of differentially expressed genes between treatments aligns with current perceptions of this species' extreme desert specialization. However, these differentially expressed genes include Insulin-like 3 (Insl3), a regulator of male fertility and testes descent, as well as the solute carriers Slc45a3 and Slc38a5, which are membrane transport proteins that may facilitate osmoregulation.

CONCLUSIONS

These results suggest that in male cactus mice, acute dehydration may be linked to reproductive modulation via Insl3, but not through gene expression differences in the subset of other a priori tested reproductive hormones. Although water availability is a reproductive cue in desert-rodents exposed to chronic drought, potential reproductive modification via Insl3 in response to acute water-limitation is a result which is unexpected in an animal capable of surviving and successfully reproducing year-round without available external water sources. Indeed, this work highlights the critical need for integrative research that examines every facet of organismal adaptation, particularly in light of global climate change, which is predicted, amongst other things, to increase climate variability, thereby exposing desert animals more frequently to the acute drought conditions explored here.

In vitro effects of substance P and arginine-vasopressin on testosterone production in Leydig cells of short and long photoperiodic hamsters

The aim of the present study was to determine the interaction between substance P (SP) and arginine-vasopressin (AVP) on basal and LH-stimulated testosterone production by Leydig cells isolated from hamsters kept under long or short days (LD-hamsters, SD-hamsters, respectively). SP inhibited the testosterone production of Leydig cells, its effect being more pronounced in the case of LH-stimulated steroidogenesis in LD-hamsters. Similarly, the addition of AVP to the culture medium resulted in a diminution of basal, as well as LH-stimulated testosterone secretions. When Leydig cells were co-incubated with SP (10(-7) M) and AVP (10(-7) M), a strong inhibition of the testosterone production by 50-60% was established in LD-animals. However, even within the experimental circumstances in SD-hamsters, the modulation of testosterone production by SP and AVP was evident. The reported results suggest that there is an interference of two regulatory pathways, namely photoperiodic dependence and paracrine control of testicular steroidogenesis in hamsters.

Substance P modulating effect on the binding capacity of hamster Leydig cell LH receptors

The influence of Substance P was studied on the binding characteristics of LH receptors in purified Leydig cells collected from golden hamsters kept under natural long or short days. Substance P exerted a differential effect on the binding capacity of LH receptors. A significant increase in Bmax was estimated in Leydig cells obtained from young hamsters living under long days. In contrast, Substance P reduced the number of the LH binding sites in Leydig cell cultures prepared from adult hamsters housed under short-day conditions.

Presence in mouse Sertoli cell-conditioned medium of a factor that expresses AVP-like inhibition of steroidogenesis by mouse Leydig cells in long-term culture

The influence of spent medium from immature mouse Sertoli cells (SCM) on testosterone production by purified Leydig cells was investigated and compared to that of AVP, a potent local modulator of Leydig cell steroidogenesis. SCM inhibited in a dose-dependent manner the hCG-stimulated testosterone production, but was ineffective in basal conditions. As is known for AVP, (i) a lag period of 72 h was prerequisite for SCM to inhibit Leydig cell function; (ii) the main effect of SCM was located at a step beyond the receptor-adenylate cyclase system, since the hCG- and 8-bromo-cAMP-stimulated testosterone productions were similarly affected. The possibility that the effect of SCM may be related to AVP-like molecule(s) is also supported by the observations that at maximal concentrations the inhibitory effects of AVP and SCM were not additive and that the inhibition of testosterone production was largely (65%) reversed by the presence of [(beta-mercapto-beta, beta-cyclopentamethylenepropionyl, O-Me-Tyr2,Arg8)-vasopressin], a selective vasopressor antagonist. These data indicate that Sertoli cells produce in vitro potent inhibitory factors of Leydig cell steroidogenesis. They provide additional evidence that one of these bioactive factors has an effect on Leydig cell function similar to that of AVP.

Local control of Leydig cell arginine vasopressin receptor by naloxone

Arginine vasopressin (AVP) and beta-endorphin are present within the testis where they could act as paracrine effectors of steroidogenesis. In this study we investigated the effect of naloxone, an opioid receptor antagonist on Leydig cell AVP receptor. Intratesticular injection of increasing doses of naloxone (0.1-100 micrograms) resulted 24 h later in a dose-dependent increase in Leydig cell AVP binding capacity. This effect occurred locally since s.c. injection of similar doses of naloxone did not alter the testicular AVP receptor content and intratesticular injection enhanced AVP receptor density only in the naloxone-treated testis but not in the contralateral vehicle-treated testis. Scatchard plot analysis of the data revealed that naloxone locally injected altered AVP binding capacity without change in affinity. These results suggest that in addition to their known paracrine effects in the testis, endogenous opioid peptides may locally control the testicular AVP system by modulating AVP receptor capacity.

Nicotine and cotinine inhibit steroidogenesis in mouse Leydig cells

Cigarette smoking alters plasma testosterone concentrations in men. The objectives of this study were to determine if nicotine and cotinine, two alkaloid products of cigarettes, affect luteinizing hormone(LH)-stimulated steroidogenesis in isolated adult mouse Leydig cells. Leydig cells from adult Swiss-Webster mice were isolated by linear density gradient and incubated (95% O2, 5% CO2) in minimum essential medium at 37 C for 3 hours with LH (10 ng) and with or without nicotine or cotinine (10(-5)-10(-7) M). Both nicotine and cotinine produced dose response inhibition (P less than 0.05) of LH-stimulated testosterone production (50-70%). The addition of 8-bromo-3',5'-cyclic monophosphate (cAMP, 500 uM) stimulated steroidogenesis comparable to LH in the absence of the alkaloids, but both nicotine and cotinine significantly (P less than 0.05) reduced testosterone production in response to cAMP, suggesting that the alkaloids inhibit testosterone production in response to LH distal to the formation of cAMP. In MEM without calcium, LH-stimulated testosterone synthesis was decreased, and neither nicotine nor cotinine significantly affected steroidogenesis. The addition of a calcium ionophore in MEM with normal calcium content enhanced (P less than 0.05) the inhibitory effects of nicotine and cotinine on LH-responsive steroidogenesis. A calcium channel blocking agent, verapamil, at 10uM significantly (P less than 0.05) reversed the inhibition of LH-stimulated testosterone production produced by both alkaloids when incubated in the medium with a normal calcium concentration. These results suggest that nicotine and cotinine either affect intracellular calcium content or block the effects of calcium on steroidogenesis in mouse Leydig cells.

AVP receptors of mouse Leydig cells are regulated by LH and E2 and influenced by experimental cryptorchidism

Exposure of pubertal mouse Leydig cells for 24 h to increasing concentrations (1-100 ng/ml) of LH elicited a dose-dependent decrease in AVP receptor content. Maximal reduction (50%) was obtained at a dose of 10 ng/ml LH. A similar treatment applied to adult Leydig cells did not influence AVP receptor density. Treatment of adult Leydig cells for 24 h by E2 (5-500 ng/ml) resulted in a dose-dependent increase in AVP receptor content. About 50% increase was achieved with 500 ng/ml E2. AVP receptor content in pubertal Leydig cells was not modified irrespective of the concentration of E2 tested. These changes in AVP receptor number were well correlated with the response of Leydig cells to AVP (10(-6) M) in terms of testosterone production. 2 weeks bilateral cryptorchidism resulted in reduction of testicular weight, circulating testosterone levels associated with a marked rise in Leydig cell AVP receptor density with no change of affinity. Testosterone production by Leydig cells from cryptorchid testes in response to AVP (10(-6) M) or hCG (100 ng/ml) stimulation was reduced compared to that of control Leydig cells. This study provides new arguments supporting the concept that AVP could be involved in local regulation of testicular steroidogenesis.