Molecular Mechanisms Elicited by d-Aspartate in Leydig Cells and Spermatogonia

Microenvironment of spermatogonial stem cells: a key factor in the regulation of spermatogenesis

Spermatogonial stem cells (SSCs) play a crucial role in the male reproductive system, responsible for maintaining continuous spermatogenesis. The microenvironment or niche of SSCs is a key factor in regulating their self-renewal, differentiation and spermatogenesis. This microenvironment consists of multiple cell types, extracellular matrix, growth factors, hormones and other molecular signals that interact to form a complex regulatory network. This review aims to provide an overview of the main components of the SSCs microenvironment, explore how they regulate the fate decisions of SSCs, and discuss the potential impact of microenvironmental abnormalities on male reproductive health.

New Insights into D-Aspartate Signaling in Testicular Activity

D-aspartate (D-Asp) is an amino acid found in high concentrations in the testis and pituitary gland. Increasing evidence suggests that D-Asp promotes spermatogenesis by activating testosterone production in the Leydig cells via LH release from the pituitary gland. In vitro studies indicate that D-Asp may also influence steroidogenesis and spermatogenesis through autocrine and paracrine signals. D-Asp enhances StAR and steroidogenic enzyme expressions, facilitating testicular cell proliferation via the GluR/ERK1/2 pathway. Moreover, it supports spermatogenesis by enhancing the mitochondrial function in spermatocytes, aiding in the metabolic shift during meiosis. Enhanced mitochondrial function, along with improved MAM stability and reduced ER stress, has been observed in Leydig and Sertoli cells treated with D-Asp, indicating potential benefits in steroidogenesis and spermatogenesis efficiency. Conversely, D-Asp exerts a notable anti-apoptotic effect in the testis via the AMPAR/AKT pathway, potentially mediated by antioxidant enzyme modulation to mitigate testicular oxidative stress. This review lays the groundwork for future investigations into the molecules promoting spermatogenesis by stimulating endogenous testosterone biosynthesis, with D-amino acids emerging as promising candidates.

Potential role of mitochondria and endoplasmic reticulum in the response elicited by D-aspartate in TM4 Sertoli cells

D-Aspartic Acid (D-Asp) affects spermatogenesis by enhancing the biosynthesis of the sex steroid hormones acting either through the hypothalamus-pituitary-testis axis or directly on Leydig cells. Recently, in vitro studies have also demonstrated the direct effects of D-Asp on the proliferation and/or activity of germ cells. However, although D-Asp is present in Sertoli cells (SC), the specific role of the amino acid in these cells remains unknown. This study investigated the effects of D-Asp on the proliferation and activity of TM4 SC, focusing on the mitochondrial compartment and its association with the endoplasmic reticulum (ER). We found that D-Asp enhanced the proliferation and activity of TM4 cells as evidenced by the activation of ERK/Akt/PCNA pathway and the increase in the protein levels of the androgen receptor. Furthermore, D-Asp reduced both the oxidative stress and apoptotic process. An increase in mitochondrial functionality and dynamics, as well as a reduction in ER stress, were also found in D-Asp-treated TM4 cells. It is known that mitochondria are closely associated with ER to form the Mitochondrial-Associated Endoplasmic Reticulum Membranes (MAM), the site of calcium ions and lipid transfer from ER to the mitochondria, and vice versa. The data demonstrated that D-Asp induced stabilization of MAM in TM4 cells. In conclusion, this study is the first to demonstrate a direct effect of D-Asp on SC activity and to clarify the cellular/molecular mechanism underlying these effects, suggesting that D-Asp could stimulate spermatogenesis by improving the efficiency of SC.

Barley sprouts and D-Aspartic acid supplementation improves fertility, hatchability, and semen quality in aging male broiler breeders by up-regulating StAR and P450SCC gene expressions

At 50 wk of age, broiler breeder roosters exhibit a significant decline of fertility. Therefore, the aim of this study was to assess the impact of incorporating barley sprout (BS) powder, D-aspartic acid (DA), or their combination into the diet on fertility, hatchability, semen quality, and the relative expression of StAR and P450SCC genes in aging broiler roosters. Aging (50 wk) male broiler breeders (n=32) were randomly assigned to one of four dietary treatments (2 × 2 factorial) with 2 levels of BS (0 or 2% basal diet) and DA (0 or 200 mg/kg/BW) for 12 wk. Roosters were individually housed under a 14-h light and 10-h dark cycle, with 150 g/d feed allocation and free access to fresh water, then euthanized. Throughout the study, the body weight of the broiler breeders was measured, along with various parameters related to semen quality, on a weekly basis. Additionally, artificial insemination was performed during the last 2 wk to evaluate reproductive endpoints. The results revealed that both BS and DA decreased (P < 0.01) body weight. Interestingly, the inclusion of BS, either alone or in combination with DA, resulted in a significant increase in total and forward sperm motility. Furthermore, it was demonstrated that the seminal concentration of malondialdehyde, a marker of oxidative stress, was significantly decreased by more than 20% in all groups compared to the control. The combination of both BS and DA led to the highest levels of circulating testosterone, as well as the functionality and membrane integrity of sperms. Additionally, it resulted in increased sperm concentrations, production, and penetration, ultimately leading to improved fertility rate and hatchability percentage. Moreover, a positive association between total motility and fertility was observed (P < 0.01). Furthermore, the combined supplementation of BS and DA up-regulated the relative mRNA expression of P450scc and StAR (P < 0.01). To summarize, dietary inclusion of BS, DA, or their combination have a potential to improve various aspects of reproductive performance in aging roosters.

Steroidogenesis Upregulation through Mitochondria-Associated Endoplasmic Reticulum Membranes and Mitochondrial Dynamics in Rat Testes: The Role of D-Aspartate

Mitochondria-Associated Endoplasmic Reticulum Membranes (MAMs) mediate the communication between the Endoplasmic Reticulum (ER) and the mitochondria, playing a fundamental role in steroidogenesis. This study aimed to understand how D-aspartate (D-Asp), a well-known stimulator of testosterone biosynthesis and spermatogenesis, affects the mechanism of steroidogenesis in rat testes. Our results suggested that D-Asp exerts this function through MAMs, affecting lipid trafficking, calcium signaling, ER stress, and mitochondrial dynamics. After 15 days of oral administration of D-Asp to rats, there was an increase in both antioxidant enzymes (SOD and Catalase) and in the protein expression levels of ATAD3A, FACL4, and SOAT1, which are markers of lipid transfer, as well as VDAC and GRP75, which are markers of calcium signaling. Additionally, there was a decrease in protein expression levels of GRP78, a marker of aging that counteracts ER stress. The effects of D-Asp on mitochondrial dynamics strongly suggested its active role as well. It induced the expression levels of proteins involved in fusion (MFN1, MFN2, and OPA1) and in biogenesis (NRF1 and TFAM), as well as in mitochondrial mass (TOMM20), and decreased the expression level of DRP1, a crucial mitochondrial fission marker. These findings suggested D-Asp involvement in the functional improvement of mitochondria during steroidogenesis. Immunofluorescent signals of ATAD3A, MFN1/2, TFAM, and TOMM20 confirmed their localization in Leydig cells showing an intensity upgrade in D-Asp-treated rat testes. Taken together, our results demonstrate the involvement of D-Asp in the steroidogenesis of rat testes, acting at multiple stages of both MAMs and mitochondrial dynamics, opening new opportunities for future investigation in other steroidogenic tissues.

A multi-omics analysis of viral nucleic acid poly(I:C) responses to mammalian testicular stimulation

The male reproductive system has a standard immune response regulatory mechanism, However, a variety of external stimuli, including viruses, bacteria, heat, and medications can damage the testicles and cause orchitis and epididymitis. It has been shown that various RNA viruses are more likely to infect the testis than DNA viruses, inducing orchitis and impairing testicular function. It was found that local injection of the viral RNA analog poly(I:C) into the testes markedly disrupted the structure of the seminiferous tubules, accompanied by apoptosis and inflammation. Poly(I:C) mainly inhibited the expression of testosterone synthesis-associated proteins, STAR and MGARP, and affected the synthesis and metabolism of amino acids and lipids in the testis. This led to the disruption of the metabolite levels in the testis of mice, thus affecting the normal spermatogenesis process. The present study analyzed the acute inflammatory response of the testis to viral infection using a multi-omics approach. It provides insights into how RNA virus infection impairs testicular function and offers a theoretical basis for future studies on immune homeostasis and responses under stress conditions in male reproduction.

Exposure to PM2.5, seminal plasma metabolome, and semen quality among Chinese adult men: Association and potential mediation analyses

Exposure to ambient fine particulate matter (PM2.5) has been linked to a decline in semen quality, but the underlying mechanisms for this association remain unclear. We aimed to examine whether specific metabolites act as mediators in the association between PM2.5 exposure and changes in semen quality. We conducted untargeted metabolomics analysis using LC-MS/MS platforms to identified seminal plasma metabolites associated with various semen quality parameters among 200 Chinese adult men. Additionally, we performed mediation analyses to examine the effects of the seminal plasma metabolites on the association between PM2.5 exposure and semen quality. We identified 140 differential metabolites between the normal and abnormal semen groups, involving two metabolic pathways: Alanine, aspartate and glutamate metabolism, and Aminoacyl-tRNA biosynthesis. We additionally identified 7 specific seminal plasma metabolites that were associated with discrepant metabolic networks related to semen quality. The mediation analysis revealed that D-Aspartate might play a mediating role in the adverse effects of ambient PM2.5 exposure on both total and progressive motility during spermatogenesis period (70-90 days before ejaculation), with a proportion of mediation up to 16% and 17%, respectively. Exposure to PM2.5 was associated with alterations in D-Aspartate levels, which might partially mediate the association between PM2.5 and reduced sperm motility.

Comparative genomic survey and functional analysis of DKKL1 during spermatogenesis in the Chinese soft-shelled turtle (Pelodiscus sinensis)

A feature of the Chinese soft-shelled turtle (Pelodiscus sinensis) is seasonal spermatogenesis; however, the underlying molecular mechanism is not well clarified. Here, we firstly cloned and characterized P. sinensis DKKL1, and then performed comparative genomic studies, expression analysis, and functional validation. P. sinensis DKKL1 had 2 putative N-glycosylation sites and 16 phosphorylation sites. DKKL1 also had classic transmembrane structures that were extracellularly localized. DKKL1's genetic distance was close to turtles, followed by amphibians and mammals, but its genetic distance was far from fishes. DKKL1 genes from different species shared distinct genomic characteristics. Meanwhile, they were also relatively conserved among themselves, at least from the perspective of classes. Notably, the transcription factors associated with spermatogenesis were also identified, containing CTCF, EWSR1, and FOXL2. DKKL1 exhibited sexually dimorphic expression only in adult gonads, which was significantly higher than that in other somatic tissues (P < 0.001), and was barely expressed in embryonic gonads. DKKL1 transcripts showed a strong signal in sperm, while faint signals were detected in other male germ cells. DKKL1 in adult testes progressively increased per month (P < 0.05), displaying a seasonal expression trait. DKKL1 was significantly downregulated in testes cells after the sex hormones (17β-estradiol and 17α-methyltestosterone) and Wnt/β-catenin inhibitor treatment (P < 0.05). Likewise, the Wnt/β-catenin inhibitor treatment dramatically repressed CTCF, EWSR1, and FOXL2 expression. Conversely, they were markedly upregulated after the 17β-estradiol and 17α-methyltestosterone treatment, suggesting that the three transcription factors might bind to different promoter regions, thereby negatively regulating DKKL1 transcription in response to the changes in the estrogen and androgen pathways, and positively controlling DKKL1 transcription in answer to the alterations in the Wnt/β-catenin pathway. Knockdown of DKKL1 significantly reduced the relative expression of HMGB2 and SPATS1 (P < 0.01), suggesting that it may be involved in seasonal spermatogenesis of P. sinensis through a positive regulatory interaction with these two genes. Overall, our findings provide novel insights into the genome evolution and potential functions of seasonal spermatogenesis of P. sinensis DKKL1.

Separation and Identification of Isoleucine Enantiomers and Diastereomers Using an Original Chiral Resolution Labeling Reagent

D-Amino acids, which are present in small amounts in living organisms, are responsible for a variety of physiological functions. Some bioactive/biomolecular peptides also contain D-amino acids in their sequences; such peptides express different functions than peptides composed only of L-form amino acids. Among the 20 amino acids that make up proteins, threonine (Thr) and isoleucine (Ile) have two chiral carbons and thus have two enantiomers and diastereomers. These stereoisomers have been previously analyzed through HPLC using chiral columns or chiral resolution labeling reagents. However, the separation and identification of these stereoisomers are highly laborious and complicated. Herein, we propose an analytical method for the separation and identification of Ile stereoisomers through LC-MS using our original chiral resolution labeling reagent, 1-fluoro-2,4-dinitrophenyl-5-L-valine-N,N-dimethylethylenediamine-amide (L-FDVDA) and a PBr column packed with pentabromobenzyl-modified silica gel. Twenty DL-amino acids including Thr stereoisomers (41 amino acids including glycine) were separated and identified using C18 column. Ile stereoisomers could be separated using not a C18 column but a PBr column. Additionally, we showed that peptides containing Thr and Ile stereoisomers can be accurately detected through labeling with L-FDVDA.

Evidence of the protective role of D-Aspartate in counteracting/preventing cadmium-induced oxidative stress in the rat testis

Cadmium (Cd), by producing oxidative stress and acting as an endocrine disruptor, is known to cause severe testicular injury, documented by histological and biomolecular alterations, such as decreased serum testosterone (T) level and impairment of spermatogenesis. This is the first report on the potential counteractive/preventive action of D-Aspartate (D-Asp), a well-known stimulator of T biosynthesis and spermatogenesis progression by affecting hypothalamic-pituitary-gonadal axis, in alleviating Cd effects in the rat testis. Our results confirmed that Cd affects testicular activity, as documented by the reduction of serum T concentration and of the protein levels of steroidogenesis (StAR, 3β-HSD, and 17β-HSD) and spermatogenesis (PCNA, p-H3, and SYCP3) markers. Moreover, higher protein levels of cytochrome C and caspase 3, together with the number of cells positive to TUNEL assay, indicated the intensification of the apoptotic process. D-Asp administered either simultaneously to Cd, or for 15 days before the Cd-treatment, reduced the oxidative stress induced by the metal, alleviating the consequent harmful effects. Interestingly, the preventive action of D-Asp was more effective than its counteractive effect. A possible explanation is that giving D-Asp for 15 days induces its significant uptake in the testes, reaching the concentrations necessary for optimum function. In summary, this report highlights, for the first time, the beneficial role played by D-Asp in both counteracting/preventing the adverse Cd effects in the rat testis, strongly encouraging further investigations to consider the potential value of D-Asp also in improving human testicular health and male fertility.

D-Aspartate Depletion Perturbs Steroidogenesis and Spermatogenesis in Mice

High levels of free D-aspartate (D-Asp) are present in vertebrate testis during post-natal development, coinciding with the onset of testosterone production, which suggests that this atypical amino acid might participate in the regulation of hormone biosynthesis. To elucidate the unknown role of D-Asp on testicular function, we investigated steroidogenesis and spermatogenesis in a one-month-old knockin mouse model with the constitutive depletion of D-Asp levels due to the targeted overexpression of D-aspartate oxidase (DDO), which catalyzes the deaminative oxidation of D-Asp to generate the corresponding α-keto acid, oxaloacetate, hydrogen peroxide, and ammonium ions. In the Ddo knockin mice, we found a dramatic reduction in testicular D-Asp levels, accompanied by a significant decrease in the serum testosterone levels and testicular 17β-HSD, the enzyme involved in testosterone biosynthesis. Additionally, in the testes of these Ddo knockin mice, the expression of PCNA and SYCP3 proteins decreased, suggesting alterations in spermatogenesis-related processes, as well as an increase in the cytosolic cytochrome c protein levels and TUNEL-positive cell number, which indicate an increase in apoptosis. To further investigate the histological and morphometric testicular alterations in Ddo knockin mice, we analyzed the expression and localization of prolyl endopeptidase (PREP) and disheveled-associated activator of morphogenesis 1 (DAAM1), two proteins involved in cytoskeletal organization. Our results showed that the testicular levels of DAAM1 and PREP in Ddo knockin mice were different from those in wild-type animals, suggesting that the deficiency of D-Asp is associated with overall cytoskeletal disorganization. Our findings confirmed that physiological D-Asp influences testosterone biosynthesis and plays a crucial role in germ cell proliferation and differentiation, which are required for successful reproduction.

Determination of d- and l-Amino Acids in Garlic Foodstuffs by Liquid Chromatography-Tandem Mass Spectrometry

Black garlic is currently attracting interest as a health food and constituent of commercial supplements; however, no data regarding the d-amino acids within black garlic have been reported. Therefore, the amino acid compositions of methanol extracts from fresh and black garlic were compared herein. We investigated the contents of the d- and l-forms of amino acids in commercial fresh, black, and freeze-dried garlic foodstuffs by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using a pre-column chiral derivatization reagent, succinimidyl 2-(3-((benzyloxy)carbonyl)-1-methyl-5-oxoimidazolidin-4-yl) acetate. Several d-amino acids, namely, the d-forms of Asn, Ala, Ser, Thr, Glu, Asp, Pro, Arg, Phe, Orn, Lys, and Tyr, were observed in the methanol extract of black garlic, whereas only d-Ala was detected in that of fresh garlic foodstuffs. These data suggest that several d-amino acids can be produced during fermentation for preparing black garlic.

Differentiation of neonate mouse spermatogonia on two-dimensional and three-dimensional culture systems supplemented with d-Serine and Dizocilpine (MK-801)

N-methyl-d-aspartate (NMDA) modulates the spermatogenesis process through stimulating the steroid hormone biosynthesis. The aim of this study was to evaluate the effects of NMDA receptors agonists (d-Serine) and antagonists (MK801) on spermatogonia differentiation on decellularization testicular matrix (DTM) hydrogel scaffold. Four treatment groups were planned: 2D + D-Serine, 3D + D-Serine, 2D + MK801, and 3D + MK801. Results showed that cell viability was significantly decreased after 48 h in the 3D + D-Serine group and after 24 and 48 h in the 3D + MK801 group compared to the controls. The spermatogonia proliferation after two, four, and eight weeks was significantly increased in the 3D + D-Serine culture, while it was significantly reduced in the 2D + MK801 and 3D + MK801 groups after four and eight weeks. Real-time PCR results demonstrated that pre-meiotic gene (Plzf) expression was significantly increased only in the 3D + D-Serine culture compared to the control groups after four weeks of culture. The meiotic gene (Sycp3) expression was significantly increased in the 2D + D-Serine and 3D + D-Serine compared to the 2D controls after four and eight weeks. The post-meiotic gene (Tnp1) level in the 3D + D-Serine was significantly higher than the other groups. Flow-cytometry results indicated that the protein expression of Plzf (after four and eight weeks), Sycp3 (after eight weeks), and Tnp1 (after eight weeks) in the d-Serine-treated groups was significantly increased compared with the 2D control groups. There were not any significant changes in the gene expression of spermatogenic-related markers in MK801 culture media. However, a significant decrease in the protein levels of Plzf after eight weeks and Sycp3 after four and eight weeks was observed. In conclusion, the addition of NMDARs agonists (d-Serine) could be used to regulate the differentiation of spermatogonia in the 3D culture system.

Promising Application of D-Amino Acids toward Clinical Therapy

The versatile roles of D-amino acids (D-AAs) in foods, diseases, and organisms, etc., have been widely reported. They have been regarded, not only as biomarkers of diseases but also as regulators of the physiological function of organisms. Over the past few decades, increasing data has revealed that D-AAs have great potential in treating disease. D-AAs also showed overwhelming success in disengaging biofilm, which might provide promise to inhibit microbial infection. Moreover, it can effectively restrain the growth of cancer cells. Herein, we reviewed recent reports on the potential of D-AAs as therapeutic agents for treating neurological disease or tissue/organ injury, ameliorating reproduction function, preventing biofilm infection, and inhibiting cancer cell growth. Additionally, we also reviewed the potential application of D-AAs in drug modification, such as improving biostability and efficiency, which has a better effect on therapy or diagnosis.

The PI3K/AKT signaling pathway: How does it regulate development of Sertoli cells and spermatogenic cells?

The PI3K/AKT signaling pathway is one of the most crucial regulatory mechanisms in animal cells, which can mainly regulate proliferation, survival and anti-apoptosis in cell lines. In the seminiferous epithelium, most studies were concentrated on the role of PI3K/AKT signaling in immature Sertoli cells (SCs) and spermatogonia stem cells (SSCs). PI3K/AKT signaling can facilitate the proliferation and anti-apoptosis of immature Sertoli cells and spermatogenic cells. Besides, in mature Sertoli cells, this pathway can disintegrate the structure of the blood-testis barrier (BTB) via regulatory protein synthesis and the cytoskeleton of Sertoli cells. All of these effects can directly and indirectly maintain and promote spermatogenesis in male testis.

Effect of NMDA receptor agonist and antagonist on spermatogonial stem cells proliferation in 2- and 3- dimensional culture systems

BACKGROUND

The main purpose of this study was to investigate the effect of D-serine (DS) and Dizocilpine (MK-801) on the proliferation of spermatogonial stem cells (SSCs) in two-dimensional (2D) and three-dimensional (3D) culture systems.

METHODS AND RESULTS

The SSCs of male NMRI mice were isolated by enzymatic digestion and cultured for two weeks. Then, the identity of SSCs was validated by anti-Plzf and anti-GFR-α1 antibodies via immunocytochemistry (ICC). The proliferation capacity of SSCs was evaluated by their culture on a layer of the decellularized testicular matrix (DTM) prepared from mouse testis, as well as two-dimensional (2D) with different mediums. After two weeks of the initiation of proliferation culture on 3D and 2D medium, the pre-meiotic at the mRNA and protein levels were evaluated via qRT-PCR and flow cytometry methods, respectively. The results showed that the proliferation rate of SSCs in 3D culture with 50 mM glutamic acid and 20 mM D-serine was significantly different from other groups after 14 days treatment. mRNA expression levels of promyelocytic leukemia zinc finger (Plzf) in 3D cultures supplemented by 20 mM D-serine and 50 mM glutamic acid were considerably higher than the 3D control group (p < 0.001). The flow cytometry analysis revealed that the amount of Plzf in the 2D-culture groups of SSCs with 20 mM MK-801 was considerably lower compared to the 2D-culture control group (p < 0.001).

CONCLUSIONS

This study indicated that decellularized testicular matrix supplemented with D-serine and glutamic acid could be considered a promising vehicle to support cells and provide an appropriate niche for the proliferation of SSCs.

d-aspartate and N-methyl-d-aspartate promote proliferative activity in mouse spermatocyte GC-2 cells

D-Aspartate (D-Asp) and its methylated form N-methyl-d-aspartate (NMDA) promote spermatogenesis by stimulating the biosynthesis of sex steroid hormones. d-Asp also induces spermatogonia proliferation directly by activating the ERK/Aurora B pathway. In the present study, a mouse spermatocyte-derived cell line (GC-2) which represents a stage between preleptotene spermatocyte and round spermatids was exposed to 200 μM d-Asp or 50 μM NMDA for 30 min, 2 h, and 4 h to explore the influence of these amino acids on cell proliferation and mitochondrial activities occurring during this process. By Western blotting analyses, the expressions of AMPAR (GluA1-GluA2/3 subunits), cell proliferation as well as mitochondria functionality markers were determined at different incubation times. The results revealed that d-Asp or NMDA stimulate proliferation and meiosis in the GC-2 cells via the AMPAR/ERK/Akt pathway, which led to increased levels of the PCNA, p-H3, and SYCP3 proteins. The effects of d-Asp and NMDA on the mitochondrial functionality of the GC-2 cells strongly suggested an active role of these amino acids in germ cell maturation. In both d-Asp- and NMDA-treated GC-2 cells mitochondrial biogenesis as well as mitochondrial fusion are increased while mitochondria fission is inhibited. Finally, the findings showed that NMDA significantly increased the expressions of the CII, CIII, CIV, and CV complexes of oxidative phosphorylation system (OXPHOS), whereas d-Asp induced a significant increase in the expressions only of the CIV and CV complexes. The present study provides novel insights into the mechanisms underlying the role of d-Asp and NMDA in promoting spermatogenesis.

N-Methyl-d-aspartic Acid (NMDA) Receptor Is Involved in the Inhibitory Effect of Ketamine on Human Sperm Functions

Ketamine, which used to be widely applied in human and animal medicine as a dissociative anesthetic, has become a popular recreational drug because of its hallucinogenic effect. Our previous study preliminarily proved that ketamine could inhibit human sperm function by affecting intracellular calcium concentration ([Ca²⁺]_i). However, the specific signaling pathway of [Ca²⁺]_i induced by ketamine in human sperm is still not clear yet. Here, the N-methyl-d-aspartic acid (NMDA) receptor was detected in the tail region of human sperm. Its physiological ligand, NMDA (50 μM), could reverse ketamine's inhibitory effect on human sperm function, and its antagonist, MK801 (100 μM), could restrain the effect of NMDA. The inhibitory effect caused by 4 mM ketamine or 100 μM MK801 on [Ca²⁺]_i, which is a central factor in the regulation of human sperm function, could also be recovered by 50 μM NMDA. The results suggest that the NMDA receptor is probably involved in the inhibitory effect of ketamine on human sperm functions.

Transcriptome analysis revealed differences in the microenvironment of spermatogonial stem cells in seminiferous tubules between pre-pubertal and adult buffaloes

The microenvironment in the seminiferous tubules of buffalo changes with age, which affects the self-renewal and growth of spermatogonial stem cells (SSCs) and the process of spermatogenesis, but the mechanism remains to be elucidated. RNA-seq was performed to compare the transcript profiles of pre-pubertal buffalo (PUB) and adult buffalo (ADU) seminiferous tubules. In total, 17,299 genes from PUB and ADU seminiferous tubules identified through RNA-seq, among which 12,271 were expressed in PUB and ADU seminiferous tubules, 4,027 were expressed in only ADU seminiferous tubules, and 956 were expressed in only PUB seminiferous tubules. Of the 17,299 genes, we identified 13,714 genes that had significant differences in expression levels between PUB and ADU through GO enrichment analysis. Among these genes, 5,342 were significantly upregulated and possibly related to the formation or identity of the surface antigen on SSCs during self-renewal; 7,832 genes were significantly downregulated, indicating that genes in PUB seminiferous tubules do not participate in the biological processes of sperm differentiation or formation in this phase compared with those in ADU seminiferous tubules. Subsequently, through the combination with KEGG analysis, we detected enrichment in a number of genes related to the development of spermatogonial stem cells, providing a reference for study of the development mechanism of buffalo spermatogonial stem cells in the future. In conclusion, our data provide detailed information on the mRNA transcriptomes in PUB and ADU seminiferous tubules, revealing the crucial factors involved in maintaining the microenvironment and providing a reference for further in vitro cultivation of SSCs.

Racemization in Post-Translational Modifications Relevance to Protein Aging, Aggregation and Neurodegeneration: Tip of the Iceberg

Homochirality of DNA and prevalent chirality of free and protein-bound amino acids in a living organism represents the challenge for modern biochemistry and neuroscience. The idea of an association between age-related disease, neurodegeneration, and racemization originated from the studies of fossils and cataract disease. Under the pressure of new results, this concept has a broader significance linking protein folding, aggregation, and disfunction to an organism's cognitive and behavioral functions. The integrity of cognitive function is provided by a delicate balance between the evolutionarily imposed molecular homo-chirality and the epigenetic/developmental impact of spontaneous and enzymatic racemization. The chirality of amino acids is the crucial player in the modulation the structure and function of proteins, lipids, and DNA. The collapse of homochirality by racemization is the result of the conformational phase transition. The racemization of protein-bound amino acids (spontaneous and enzymatic) occurs through thermal activation over the energy barrier or by the tunnel transfer effect under the energy barrier. The phase transition is achieved through the intermediate state, where the chirality of alpha carbon vanished. From a thermodynamic consideration, the system in the homo-chiral (single enantiomeric) state is characterized by a decreased level of entropy. The oscillating protein chirality is suggesting its distinct significance in the neurotransmission and flow of perceptual information, adaptive associative learning, and cognitive laterality. The common pathological hallmarks of neurodegenerative disorders include protein misfolding, aging, and the deposition of protease-resistant protein aggregates. Each of the landmarks is influenced by racemization. The brain region, cell type, and age-dependent racemization critically influence the functions of many intracellular, membrane-bound, and extracellular proteins including amyloid precursor protein (APP), TAU, PrP, Huntingtin, α-synuclein, myelin basic protein (MBP), and collagen. The amyloid cascade hypothesis in Alzheimer's disease (AD) coexists with the failure of amyloid beta (Aβ) targeting drug therapy. According to our view, racemization should be considered as a critical factor of protein conformation with the potential for inducing order, disorder, misfolding, aggregation, toxicity, and malfunctions.

Preliminary Investigation on the Ameliorative Role Exerted by D-Aspartic Acid in Counteracting Ethane Dimethane Sulfonate (EDS) Toxicity in the Rat Testis

Simple Summary

For proper fertility, the production of good-quality spermatozoa is essential. Nowadays, many environmental pollutants affect the spermatogenetic process, at different levels. For this reason, new approaches are needed to prevent/counteract these toxic effects. Here, we showed that the excitatory amino acid D-aspartic acid (D-Asp) prevents the deadly action of ethane dimethane sulfonate (EDS) on the testosterone-secreting Leydig cells in rat testis. We found that EDS, probably via the reduced testosterone level, alters the normal histology of the seminiferous epithelium, leading to germ cells death and to the decreased protein level of two Leydig cell “markers”: steroidogenic acute regulatory and prolyl endopeptidase. In addition, the same analysis performed on rats that were pre-treated with D-Asp revealed a protective role of this compound, since all the above parameters were quite normal. Moreover, we found that the protective mechanism of action involved in this scenario may be due to the ability of D-Asp to reduce the oxidative stress induced by EDS. Based on these findings, we could affirm that D-Asp may be an encouraging candidate to be used to alleviate the harmful action due to environmental pollutants exposure, in order to maintain appropriate fertility.

Abstract

Herein is reported the first evidence of the protective role of D-aspartic acid (D-Asp) in preventing the toxic effect exerted by the alkylating agent ethane dimethane sulfonate (EDS) in the rat testis. We confirmed that EDS treatment specifically destroyed Leydig cells (LC), resulting in the drastic decrease of the serum testosterone level and producing morphological changes in the germinal tubules, i.e., altered organization of the epithelium, loss of cell contacts and the consequent presence of empty spaces between them, and a reduce number of spermatozoa. Moreover, an increase of TUNEL-positive germ cells, other than alteration in the protein level and localization of two LC “markers”, StAR and PREP, were observed. Interestingly, results obtained from rats pre-treated with D-Asp for 15 days before EDS-injection showed that all the considered parameters were quite normal. To explore the probable mechanism(s) involved in the protection exerted by D-Asp, we considered the increased oxidative stress induced by EDS and the D-Asp antioxidant effects. Thiobarbiturc acid-reactive species (TBARS) levels increased following EDS-injection, while no change was observed in the D-Asp + EDS treated rats. Our results showed that D-Asp may be used as a strategy to mitigate the toxic effects exerted by environmental pollutants, as endocrine disrupters, in order to preserve the reproductive function.

A Proteomics Signature of Mild Hypospadias: A Pilot Study

Background and Objective: Mild hypospadias is a birth congenital condition characterized by the relocation of the male urethral meatus from its typical anatomical position near the tip of the glans penis, to a lower ventral position up to the brim of the glans corona, which can also be accompanied by foreskin ventral deficiency. For the most part, a limited number of cases have known etiology. We have followed a high-throughput proteomics approach to study the proteome in mild hypospadias patients. Methods: Foreskin samples from patients with mild hypospadias were collected during urethroplasty, while control samples were collected during elective circumcision (n = 5/group). A high-throughput, quantitative proteomics approach based on multiplexed peptide stable isotope labeling (SIL) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was used to ascertain protein abundance changes in hypospadias patients when compared to control samples. Results: A total of 4,815 proteins were quantitated (2,522 with at least two unique peptides). One hundred and thirty-three proteins from patients with mild hypospadias showed significant abundance changes with respect to control samples, where 38 proteins were increased, and 95 proteins were decreased. Unbiased functional biological analysis revealed that both mitochondrial energy production and apoptotic signaling pathways were enriched in mild hypospadias. Conclusions: This first comprehensive proteomics characterization of mild hypospadias shows molecular changes associated with essential cellular processes related to energy production and apoptosis. Further evaluation of the proteome may expand the search of novel candidates in the etiology of mild hypospadias and could also lead to the identification of biomarkers for this congenital urogenital condition.

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

The endogenous amino acids serine and aspartate occur at high concentrations in free D-form in mammalian organs, including the central nervous system and endocrine glands. D-serine (D-Ser) is largely localized in the forebrain structures throughout pre and postnatal life. Pharmacologically, D-Ser plays a functional role by acting as an endogenous coagonist at N-methyl-D-aspartate receptors (NMDARs). Less is known about the role of free D-aspartate (D-Asp) in mammals. Notably, D-Asp has a specific temporal pattern of occurrence. In fact, free D-Asp is abundant during prenatal life and decreases greatly after birth in concomitance with the postnatal onset of D-Asp oxidase expression, which is the only enzyme known to control endogenous levels of this molecule. Conversely, in the endocrine system, D-Asp concentrations enhance after birth during its functional development, thereby suggesting an involvement of the amino acid in the regulation of hormone biosynthesis. The substantial binding affinity for the NMDAR glutamate site has led us to investigate the in vivo implications of D-Asp on NMDAR-mediated responses. Herein we review the physiological function of free D-Asp and of its metabolizing enzyme in regulating the functions of the brain and of the neuroendocrine system based on recent genetic and pharmacological human and animal studies.

Spermatogenesis and regulatory factors in the wall lizard Podarcis sicula

Spermatogenesis is an extraordinarily complex process, regulated by several factors, which leads to the differentiation of spermatogonia into spermatozoa. Among vertebrates, several reports have been focused on the lizard Podarcis sicula, a seasonal breeder and a good model for the study of reproductive processes. The goal of this review is to resume all the available data about systemic and above all local control factors involved in the control of P. sicula testicular activity. During the seasonal reproductive cycle, the variation of the expression levels of these factors determines significant variations that induce the activation or blocking of spermatogenesis. The data supplied in this review, in addition to analyze the current literature regarding the main actors of Podarcis sicula spermatogenesis, will hopefully provide a basic model that can be used for further studies on the intratesticular interaction between molecular factors that control spermatogenesis.

D-Amino acids in mammalian endocrine tissues

D-Aspartate, D-serine and D-alanine are a regular occurrence in mammalian endocrine tissues, though in amounts varying with the type of gland. The pituitary gland, pineal gland, thyroid, adrenal glands and testis contain relatively large amounts of D-aspartate in all species examined. D-alanine is relatively abundant in the pituitary gland and pancreas. High levels of D-serine characterize the hypothalamus. D-leucine, D-proline and D-glutamate are generally low. The current knowledge of physiological roles of D-amino acids in endocrine tissues is far from exhaustive, yet the topic is attracting increasing interest because of its potential in pharmacological application. D-aspartate is known to act at all levels of the hypothalamus-pituitary-testis axis, playing a key role in reproductive biology in several vertebrate classes. An involvement of D-amino acids in the endocrine function of the pancreas is emerging. D-Aspartate has been immunolocalized in insulin-containing secretory granules in INS-1 E clonal β cells and is co-secreted with insulin by exocytosis. Specific immunolocalization of D-alanine in pituitary ACTH-secreting cells and pancreatic β-cells suggests that this amino acid participates in blood glucose regulation in mammals. By modulating insulin secretion, D-serine probably participates in the control of systemic glucose metabolism by modulating insulin secretion. We anticipate that future investigation will significantly increase the functional repertoire of D-amino acids in homeostatic control.

Agonist and antagonist NMDA receptor effect on cell fate during germ cell differentiation and regulate apoptotic process in 3D organ culture

In this work, agonist and antagonist N-methyl-D-aspartate (NMDA) receptor activation effect on cell fate during germ cell differentiation and regulate apoptotic process in 3D organ culture were studied. Afterwards, the effect of D-serine, retinoic acid (RA) and MK801 on spermatogenesis development was investigated. The animals were injected a single dose (40 mg/kg, intraperitoneal) of busulfan. After confirming the model, ten 5-day-old NMRI mice were used as spermatogonial stem cells (SSCs) transplantation donors. The SSCs were confirmed by detecting the promyelocytic leukaemia zinc finger (PLZF) protein. Then, tissue culture of the azoospermia model which had received SSCs was performed in various conditions (seven groups). The apoptosis markers levels of cells were significantly decreased in differentiation media containing RA and serine. In contrast, the expression of apoptotic markers including caspase 3, caspase 9 and Bax was increased in the presence of MK801. In conclusion, a new in vitro system capable of producing mature spermatozoa was developed that would be useful for investigating the medicinal effects of agents on the male reproductive system. Also, a comparison of spermatogenesis development in different media revealed that the presence of D-serine and RA (retinoic acid) in the culture medium has a positive effect on spermatogenesis.

New insights on the influence of free d-aspartate metabolism in the mammalian brain during prenatal and postnatal life

Free d-aspartate is abundant in the mammalian embryonic brain. However, following the postnatal onset of the catabolic d-aspartate oxidase (DDO) activity, cerebral d-aspartate levels drastically decrease, remaining constantly low throughout life. d-Aspartate stimulates both glutamatergic NMDA receptors (NMDARs) and metabotropic Glu5 receptors. In rodents, short-term d-aspartate exposure increases spine density and synaptic plasticity, and improves cognition. Conversely, persistently high d-Asp levels produce NMDAR-dependent neurotoxic effects, leading to precocious neuroinflammation and cell death. These pieces of evidence highlight the dichotomous impact of d-aspartate signaling on NMDAR-dependent processes and, in turn, unveil a neuroprotective role for DDO in preventing the detrimental effects of excessive d-aspartate stimulation during aging. Here, we will focus on the in vivo influence of altered d-aspartate metabolism on the modulation of glutamatergic functions and its involvement in translational studies. Finally, preliminary data on the role of embryonic d-aspartate in the mouse brain will also be reviewed.

D-Aspartate Upregulates DAAM1 Protein Levels in the Rat Testis and Induces Its Localization in Spermatogonia Nucleus

Cell differentiation during spermatogenesis requires a proper actin dynamic, regulated by several proteins, including formins. Disheveled-Associated-Activator of Morphogenesis1 (DAAM1) belongs to the formins and promotes actin polymerization. Our results showed that oral D-Aspartate (D-Asp) administration, an excitatory amino acid, increased DAAM1 protein levels in germ cells cytoplasm of rat testis. Interestingly, after the treatment, DAAM1 also localized in rat spermatogonia (SPG) and mouse GC-1 cells nuclei. We provided bioinformatic evidence that DAAM1 sequence has two predicted NLS, supporting its nuclear localization. The data also suggested a role of D-Asp in promoting DAAM1 shuttling to the nuclear compartment of those proliferative cells. In addition, the proliferative action induced by D-Asp is confirmed by the increased levels of PCNA, a protein expressed in the nucleus of cells in the S phase and p-H3, a histone crucial for chromatin condensation during mitosis and meiosis. In conclusion, we demonstrated, for the first time, an increased DAAM1 protein levels following D-Asp treatment in rat testis and also its localization in the nucleus of rat SPG and in mouse GC-1 cells. Our results suggest an assumed role for this formin as a regulator of actin dynamics in both cytoplasm and nuclei of the germ cells.

Aspartate racemase and d-aspartate in starfish; possible involvement in testicular maturation

d-Aspartate, aspartate racemase activity, and d-aspartate oxidase activity were detected in tissues from several types of starfish. Aspartate racemase activity in male testes of Patiria pectinifera was significantly elevated in the summer months of the breeding season compared with spring months. We also compared aspartate racemase activity with the gonad index and found that activity in individuals with a gonad index ≥6% was four-fold higher than that of individuals with a gonad index &lt;6%. The ratio of the D-form of aspartate to total aspartate was approximately 25% in testes with a gonad index &lt;6% and this increased to approximately 40% in testes with a gonad index ≥6%. However, such changes were not observed in female ovaries. Administration of d-aspartate into male starfish caused testicular growth. These results indicate the possible involvement of aspartate racemase and d-aspartate in testicular maturation in echinoderm starfish.

D-Aspartic Acid in Vertebrate Reproduction: Animal Models and Experimental Designs‡

This article reviews the animal models and experimental designs that have been used during the past twenty years to demonstrate the prominent role played by d-aspartate (d-Asp) in the reproduction of vertebrates, from amphibians to humans. We have tabulated the findings of in vivo and in vitro experiments that demonstrate the effects of d-Asp uptake on hormone production and gametogenesis in vertebrate animal models. The contribution of each animal model to the existing knowledge on the role of d-Asp in reproductive processes has been discussed. A critical analysis of experimental designs has also been carried out. Experiments performed on wild animal species suggest a role of d-Asp in the mechanisms that regulate the reproductive cycle. Several in vivo and in vitro studies carried out on mouse and rat models have facilitated an understanding of the molecular pathways activated by D-Asp in both steroidogenesis and spermatogenesis, with particular emphasis on testosterone biosynthesis. Some attempts using d-Asp for the improvement of reproductive activity in animals of commercial interest have yielded mixed results. The increased transcriptome activity of enzymes and receptors involved in the reproductive activity in d-Asp-treated broiler roosters revealed further details on the mechanism of action of d-Asp on the reproductive processes. The close relationship between d-Asp and reproductive activity has emerged, particularly in relation to its effects exerted on semen quality, proposing therapeutic applications of this amino acid in andrology and in medically-assisted procreation techniques.

The Effects of D-aspartate on Neurosteroids, Neurosteroid Receptors, and Inflammatory Mediators in Experimental Autoimmune Encephalomyelitis

OBJECTIVE

Experimental autoimmune encephalomyelitis (EAE) is a widely used model for multiple sclerosis. The present study has been designed to compare the efficiencies of oral and intraperitoneal (IP) administration of D-aspartate (D-Asp) on the onset and severity of EAE, the production of neurosteroids, and the expression of neurosteroid receptors and inflammatory mediators in the brain of EAE mice.

METHODS

In this study, EAE was induced in C57BL/6 mice treated with D-Asp orally (D-Asp-Oral) or by IP injection (D-Asp-IP). On the 20th day, brains (cerebrums) and cerebellums of mice were evaluated by histological analyses. The brains of mice were analyzed for: 1) Neurosteroid (Progesterone, Testosterone, 17β-estradiol) concentrations; 2) gene expressions of cytokines and neurosteroid receptors by reverse transcription polymerase chain reaction, and 3) quantitative determination of D-Asp using liquid chromatography-tandem mass spectrometry. Further, some inflammatory cytokines and matrix metalloproteinase-2 (MMP-2) were identified in the mouse serum using enzyme-linked immunosorbent assay kits.

RESULTS

Our findings demonstrated that after D-Asp was administered, it was taken up and accumulated within the brain. Further, IP injection of D-Asp had more beneficial effects on EAE severity than oral gavage. The concentration of the testosterone and 17β-estradiol in D-Asp-IP group was significantly higher than that of the control group. There were no significant differences in the gene expression of cytokine and neurosteroid receptors between control, D-Asp-IP, and D-Asp-Oral groups. However, IP treatment with D-Asp significantly reduced C-C motif chemokine ligand 2 and MMP-2 serum levels compared to control mice.

CONCLUSION

IP injection of D-Asp had more beneficial effects on EAE severity, neurosteroid induction and reduction of inflammatory mediators than oral gavage.

Seasonal expression and cellular distribution of star and steroidogenic enzymes in quail testis

The quail Coturnix coturnix is a seasonal breeder with a physiological switch on/off of gonadic activity. Photoperiod and temperature are the major environmental factors regulating the spermatogenesis. To more thoroughly comprehend the steroidogenic pathways that govern the seasonal reproductive cycle, we have investigated the localization of StAR protein and steroidogenic enzymes (3β-HSD, 17β-HSD, P450 aromatase, and 5α-Red) as well as androgen and estrogen levels, in the testis of reproductive and nonreproductive quails. We demonstrated that StAR, 3β-HSD, 17β-HSD, P450 aromatase, and 5α-Red were always present in the somatic (Leydig and Sertoli cells) and germ cells (spermatogonia, spermatocytes I and II, spermatids, and spermatozoa). In addition, by western blot analysis, we demonstrated that 17β-HSD, P450 aromatase, and 5α-Red showed the highest expression levels during the reproductive testis compared with nonreproductive one. Accordingly, we also found that during the reproductive phase the highest titres of testosterone, 17β-estradiol, and 5α-dihydrotestosterone are recorded. In conclusion, our findings demonstrated that in C. coturnix: (a) both somatic and germ cells are involved in the local synthesis of sex hormones; (b) 17β-HSD, P450 aromatase, and 5α-Red expressions, as well as testicular androgens and estrogens, increased in reproductive quail testis. This study strongly indicates that the steroidogenic process in quail testis exhibits seasonal changes with the promotion of both androgenic and estrogenic pathways in the reproductive period, suggesting their synergic mechanism in the spermatogenesis regulation.

Pathological Findings in Male Patients With Anti-N-methyl-d-Aspartate Receptor Encephalitis

Anti-N-methyl-d-aspartate receptor (anti-NMDAR) encephalitis is the most common type of autoimmune encephalitis. The disease predominantly affects women (1:5-1:10), with only 3 reports of autopsy findings in women being published to date. The present study reports findings from the first autopsy performed on a man with anti-NMDAR encephalitis. The patient had some scattered lesions in the limbic system with neuronal loss, gliosis, and microglial activation. The temporal and frontal cortices showed additional patchy demyelination. T-lymphocyte infiltration was detectable in the fusiform gyrus lesion. These findings were partly similar to those reported in female patients. Although clinical differences based on the sex of the patient are reported for this disease, the observed pathological similarities potentially help to establish common therapeutic strategies for all patients. Severe testicular damage was additionally observed in the male patient in this study. Biopsy-proven severe testicular damage was also confirmed in another, previously fertile man who became azoospermic. Moreover, serum follicle-stimulating hormone levels, which often increased in response to disturbed spermatogenesis, were elevated, and testosterone/luteinizing hormone ratio reflecting Leydig cell function was low in all 5 male patients in this study. Overall, these findings suggest similar brain pathology in patients of both sexes and severe testicular damage in male patients.

AMPA receptor expression in mouse testis and spermatogonial GC-1 cells: A study on its regulation by excitatory amino acids

Excitatory amino acids (EAAs) are found present in the nervous and reproductive systems of animals. Numerous studies have demonstrated a regulatory role for Glutamate (Glu), d-aspartate ( d-Asp) and N-methyl- d-aspartate (NMDA) in the control of spermatogenesis. EAAs are able to stimulate the Glutamate receptors, including the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR). Here in, we assess expression of the main AMPAR subunits, GluA1 and GluA2/3, in the mouse testis and in spermatogonial GC-1 cells. The results showed that both GluA1 and GluA2/3 were localized in mouse testis prevalently in spermatogonia. The subunit GluA2/3 was more highly expressed compared with GluA1 in both the testis and the GC-1 cells. Subsequently, GC-1 cells were incubated with medium containing l-Glu, d-Glu, d-Asp or NMDA to determine GluA1 and GluA2/3 expressions. At 30 minutes and 2 hours of incubation, EAA-treated GC-1 cells showed significantly higher expression levels of both GluA1 and GluA2/3. Furthermore, p-extracellular signal-regulated kinase (ERK), p-Akt, proliferating cell nuclear antigen (PCNA), and Aurora B expressions were assayed in l-Glu-, d-Glu-, and NMDA-treated GC-1 cells. At 30 minutes and 2 hours of incubation, treated GC-1 cells showed significantly higher expression levels of p-ERK and p-Akt. A consequent increase of PCNA and Aurora B expressions was induced by l-Glu and NMDA, but not by d-Glu. Our study demonstrates a direct effect of the EAAs on spermatogonial activity. In addition, the increased protein expression levels of GluA1 and GluA2/3 in EAA-treated GC-1 cells suggest that EAAs could activate ERK and Akt pathways through the AMPAR. Finally, the increased PCNA and Aurora B levels may imply an enhanced proliferative activity.

d- andl-Aspartate regulates growth performance, inflammation and intestinal microbial community in young pigs

Dietary 1%d-Asp andl-Asp affect the growth performance and inflammation in young pigs, which might be associated with gut microbiota.

Role of D-aspartate on biosynthesis, racemization, and potential functions: A mini-review

D-aspartate, a natural and endogenous amino acid, widely exists in animal tissues and can be synthesized through aspartate racemase and transformed by D-aspartate oxidase (DDO). D-aspartate mainly serves as a neurotransmitter and has been demonstrated to exhibit various physiological functions, including nutritional potential, regulation on reproduction and hormone biology, and neuron protection. This article mainly reviews the synthesis, racemization, and physiological functions of D-aspartate with emphasis on the potential in diseases.

D-Aspartate amends reproductive performance of aged roosters by changing gene expression and testicular histology

Male broiler breeders (n = 32) of 55 weeks of age were administered four different doses of capsulated d-aspartate (DA; 0, 100, 200 or 300 mg kg−1 day−1, p.o. (DA0, DA100, DA200 and DA300 respectively)) for 12 successive weeks to assess reproductive performance, blood testosterone, testicular histology and transcript levels of steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (P450scc), androgen receptor (AR), LH receptor (LHR), 3β-hydroxysteroid dehydrogenase (3BHSD), proliferating cell nuclear antigen (PCNA), glutamate ionotropic receptor NMDA type subunit 1 (GRIN1) and glutamate ionotropic receptor NMDA type subunit 2B (GRIN2B). Blood samples and ejaculates were collected, and bodyweight was recorded weekly for 10 weeks. AI was performed weekly for the last 2 weeks to determine the number of sperm penetration holes in the perivitelline layer, fertility and hatchability. Testes histology and transcript levels were evaluated in the 12th week. Bodyweight, numbers of Leydig cells and blood vessels, testis index and levels of sperm abnormalities were not affected (P > 0.05) by the treatment. However, sperm total and forward motility, plasma membrane integrity and functionality of sperm, ejaculate volume, testosterone concentration and fertility were higher (P < 0.05) in both the DA200 and DA300 groups compared with the other groups. In the DA100 and DA200 groups, sperm concentration, number of spermatogonia, thickness of the seminiferous epithelium and the diameter of tubules were significantly higher (P < 0.05) than the other DA-treated groups. The number of penetration holes, hatchability and malondialdehyde concentration were higher in the DA200, all DA-treated and DA300 groups respectively compared with the control and other treatment groups. Except for P450scc, AR, LHR and PCNA transcript levels in the DA300 groups, the relative expression of the genes evaluated improved significantly in the other DA-treated groups. Based on these experimental findings, it is concluded that DA improves reproductive performance of aged roosters.

Detection and quantification of d-amino acid residues in peptides and proteins using acid hydrolysis

Biomolecular homochirality refers to the assumption that amino acids in all living organisms were believed to be of the l-configuration. However, free d-amino acids are present in a wide variety of organisms and d-amino acid residues are also found in various peptides and proteins, being generated by enzymatic or non-enzymatic isomerization. In mammals, peptides and proteins containing d-amino acids have been linked to various diseases, and they act as novel disease biomarkers. Analytical methods capable of precisely detecting and quantifying d-amino acids in peptides and proteins are therefore important and useful, albeit their difficulty and complexity. Herein, we reviewed conventional analytical methods, especially 0h extrapolating method, and the problems of this method. For the solution of these problems, we furthermore described our recently developed, sensitive method, deuterium-hydrogen exchange method, to detect innate d-amino acid residues in peptides and proteins, and its applications to sample ovalbumin. This article is part of a Special Issue entitled: d-Amino acids: biology in the mirror, edited by Dr. Loredano Pollegioni, Dr. Jean-Pierre Mothet and Dr. Molla Gianluca.

Sex hormone levels in the brain of d-aspartate-treated rats

d-Aspartate (d-Asp) is an endogenous amino acid present in the central nervous system and endocrine glands of various animal taxa. d-Asp is implicated in neurotransmission, physiology of learning, and memory processes. In gonads, it plays a crucial role in sex hormone synthesis. We have investigated the effects of chronic (30 days d-Asp drinking solution) and acute (i.p. injection of 2μmol/g bw d-Asp) treatments on sex steroid synthesis in rat brain. Furthermore, to verify the direct effect of d-Asp on neurosteroidogenic enzyme activities, brain homogenates were incubated with different substrates (cholesterol, progesterone, or testosterone) with or without the addition of d-Asp. Enzyme activities were measured by evaluating the in vitro conversion rate of (i) cholesterol to progesterone, testosterone, and 17β-estradiol, (ii) progesterone to testosterone and 17β-estradiol, (iii) testosterone to 17β-estradiol. We found that d-Asp oral administration produced an increase of approximately 40% in progesterone, 110% in testosterone, and 35% in 17β-estradiol. Similarly, the results of the acute experiment showed that at 30min after d-Asp treatment, the progesterone, testosterone, and 17β-estradiol levels increased by 29-35%, and at 8h they further increased by a 100% increment. In vitro experiments demonstrate that the addition of d-Asp to brain homogenate+substrate induces a significant increase in progesterone, testosterone and 17β-estradiol suggesting that the amino acid upregulates the local activity of steroidogenic enzymes.

Olanzapine, but not clozapine, increases glutamate release in the prefrontal cortex of freely moving mice by inhibiting D-aspartate oxidase activity

D-aspartate levels in the brain are regulated by the catabolic enzyme D-aspartate oxidase (DDO). D-aspartate activates NMDA receptors, and influences brain connectivity and behaviors relevant to schizophrenia in animal models. In addition, recent evidence reported a significant reduction of D-aspartate levels in the post-mortem brain of schizophrenia-affected patients, associated to higher DDO activity. In the present work, microdialysis experiments in freely moving mice revealed that exogenously administered D-aspartate efficiently cross the blood brain barrier and stimulates L-glutamate efflux in the prefrontal cortex (PFC). Consistently, D-aspartate was able to evoke L-glutamate release in a preparation of cortical synaptosomes through presynaptic stimulation of NMDA, mGlu5 and AMPA/kainate receptors. In support of a potential therapeutic relevance of D-aspartate metabolism in schizophrenia, in vitro enzymatic assays revealed that the second-generation antipsychotic olanzapine, differently to clozapine, chlorpromazine, haloperidol, bupropion, fluoxetine and amitriptyline, inhibits the human DDO activity. In line with in vitro evidence, chronic systemic administration of olanzapine induces a significant extracellular release of D-aspartate and L-glutamate in the PFC of freely moving mice, which is suppressed in Ddo knockout animals. These results suggest that the second-generation antipsychotic olanzapine, through the inhibition of DDO activity, increases L-glutamate release in the PFC of treated mice.