Inhibition of retinoic acid biosynthesis by the bisdichloroacetyldiamine WIN 18,446 markedly suppresses spermatogenesis and alters retinoid metabolism in mice

Recent Progress of Induced Spermatogenesis In Vitro

Sperm, a crucial gamete for reproduction in sexual reproduction, is generated through the proliferation, differentiation, and morphological transformations of spermatogonial stem cells within the specialized microenvironment of the testes. Replicating this environment artificially presents challenges. However, interdisciplinary advancements in physics, materials science, and cell engineering have facilitated the utilization of innovative materials, technologies, and structures for inducing in vitro sperm production. This article offers a comprehensive overview of research progress on inducing in vitro sperm production by categorizing techniques into two major systems based on matrix-based and non-matrix-based approaches, respectively. Detailed discussions are provided for both types of technology systems through comparisons of their similarities and differences, as well as research advancements. The aim is to provide researchers in this field with a comprehensive panoramic view while presenting our own perspectives and prospects.

The Role of Retinoic Acid in Spermatogenesis and Its Application in Male Reproduction

Spermatogenesis in mammalian testes is essential for male fertility, ensuring a continuous supply of mature sperm. The testicular microenvironment finely tunes this process, with retinoic acid, an active metabolite of vitamin A, serving a pivotal role. Retinoic acid is critical for various stages, including the differentiation of spermatogonia, meiosis in spermatogenic cells, and the production of mature spermatozoa. Vitamin A deficiency halts spermatogenesis, leading to the degeneration of numerous germ cells, a condition reversible with retinoic acid supplementation. Although retinoic acid can restore fertility in some males with reproductive disorders, it does not work universally. Furthermore, high doses may adversely affect reproduction. The inconsistent outcomes of retinoid treatments in addressing infertility are linked to the incomplete understanding of the molecular mechanisms through which retinoid signaling governs spermatogenesis. In addition to the treatment of male reproductive disorders, the role of retinoic acid in spermatogenesis also provides new ideas for the development of male non-hormone contraceptives. This paper will explore three facets: the synthesis and breakdown of retinoic acid in the testes, its role in spermatogenesis, and its application in male reproduction. Our discussion aims to provide a comprehensive reference for studying the regulatory effects of retinoic acid signaling on spermatogenesis and offer insights into its use in treating male reproductive issues.

Reversible Contraception in Males: An Obtainable Target?

The last few decades have brought contraception to the forefront of research, with great strides made in effectively targeting and optimizing the physiology, pharmacology, and delivery processes that prevent pregnancy. However, these advances still predominantly target female contraceptives for the prevention of contraception, whereas targeting the male sex has lagged far behind. This has led to a marked deficiency in safe and effective male contraceptive agents, resulting in a heavy dependence on female contraceptives to prevent unwanted and unplanned pregnancies. Current research in the veterinary field and in rodents highlights several promising avenues whereby novel, safe, and effective male contraceptive alternatives are being developed-with an emphasis on reduced side effects and reversibility potential. This review aims to discuss current and novel male contraceptives (both human and veterinary formulations) while highlighting their efficacy, advantages, and disadvantages.

Restoration of fertility in nonablated recipient mice after spermatogonial stem cell transplantation

Spermatogonial stem cell (SSC) transplantation is a valuable tool for studying stem cell-niche interaction. However, the conventional approach requires the removal of endogenous SSCs, causing damage to the niche. Here we introduce WIN18,446, an ALDH1A2 inhibitor, to enhance SSC colonization in nonablated recipients. Pre-transplantation treatment with WIN18,446 induced abnormal claudin protein expression, which comprises the blood-testis barrier and impedes SSC colonization. Consequently, WIN18,446 increased colonization efficiency by 4.6-fold compared with untreated host. WIN18,446-treated testes remained small despite the cessation of WIN18,446, suggesting its irreversible effect. Offspring were born by microinsemination using donor-derived sperm. While WIN18,446 was lethal to busulfan-treated mice, cyclophosphamide- or radiation-treated animals survived after WIN18,446 treatment. Although WIN18,446 is not applicable to humans due to toxicity, similar ALDH1A2 inhibitors may be useful for SSC transplantation into nonablated testes, shedding light on the role of retinoid metabolism on SSC-niche interactions and advancing SSC research in animal models and humans.

Targeting nuclear receptor corepressors for reversible male contraception

Despite numerous female contraceptive options, nearly half of all pregnancies are unintended. Family planning choices for men are currently limited to unreliable condoms and invasive vasectomies with questionable reversibility. Here, we report the development of an oral contraceptive approach based on transcriptional disruption of cyclical gene expression patterns during spermatogenesis. Spermatogenesis involves a continuous series of self-renewal and differentiation programs of spermatogonial stem cells (SSCs) that is regulated by retinoic acid (RA)-dependent activation of receptors (RARs), which control target gene expression through association with corepressor proteins. We have found that the interaction between RAR and the corepressor silencing mediator of retinoid and thyroid hormone receptors (SMRT) is essential for spermatogenesis. In a genetically engineered mouse model that negates SMRT-RAR binding (SMRTmRID mice), the synchronized, cyclic expression of RAR-dependent genes along the seminiferous tubules is disrupted. Notably, the presence of an RA-resistant SSC population that survives RAR de-repression suggests that the infertility attributed to the loss of SMRT-mediated repression is reversible. Supporting this notion, we show that inhibiting the action of the SMRT complex with chronic, low-dose oral administration of a histone deacetylase inhibitor reversibly blocks spermatogenesis and fertility without affecting libido. This demonstration validates pharmacologic targeting of the SMRT repressor complex for non-hormonal male contraception.

Determination of pharmacological inhibition of ALDH2 by ethanol clearance in mice

OBJECTIVES

Retinoic acid plays diverse physiological and pathophysiological roles in reproduction, immune function, energy metabolism and carcinogenesis. Because of the potential benefits of inhibiting retinoic acid biosynthesis in certain disease states, efforts are underway to develop inhibitors of retinoic acid biosynthesis via inhibition of the aldehyde dehydrogenase-1 A (ALDH1A) family of enzymes. However, many potential ALDH1A inhibitors also inhibit the related ALDH2 enzyme that plays a role in the metabolism of ethanol. Accurate in vitro assessment of ALDH2 inhibition is problematic, and to date, there are no published in vivo assays to determine inhibition of ALDH2 by candidate ALDH1A inhibitors.

STUDY DESIGN

To address this, we developed a novel gas-chromatography-mass-spectrometry ethanol clearance assay in mice using orally administered ethanol and serial measurement of ethanol over time. We then used this assay to determine pharmacological inhibition of ALDH2 by candidate ALDH1A inhibitors.

RESULTS

Ethanol clearance in untreated male mice occurs within sixty minutes. Male mice treated with WIN 18,446, a known ALDH1A inhibitor that also inhibits ALDH2, demonstrated significant inhibition of ethanol clearance compared to untreated controls. Novel pyrazole and piperazine ALDH1A inhibitors were then tested with the piperazine inhibitor demonstrating ALDH2 inhibition via impaired ethanol clearance while the pyrazole inhibitor did not interfere with ethanol metabolism, suggesting a lack of ALDH2 inhibition.

CONCLUSIONS

Inhibition of ethanol clearance is a useful in vivo method of inferring pharmacologic inhibition of hepatic ALDH2. This assay may be useful in the development of novel ALDH1A specific inhibitors for a variety of therapeutic indications.

Return to fertility, toxicology, and transgenerational impact of treatment with WIN 18,446, a potential male contraceptive, in mice

OBJECTIVES

We examined the return to fertility and transgenerational impact of treatment with WIN 18,446, an experimental male contraceptive, in mice.

STUDY DESIGN

We paired male mice treated with WIN 18,446 for 4 weeks to suppress spermatogenesis, followed by a 9-week recovery, and mated them with normal females to assess fertility. F1 generation mice were subsequently mated to ascertain any transgenerational impact of treatment on fertility. Testes were examined histologically.

RESULTS

WIN 18,446-treated mice and their progeny produced normally sized litters (6.5 pups per litter after treatment and 7.3 pups per litter from the progeny). However, testes histology revealed rare residual intratesticular foci of mineralization after treatment.

CONCLUSIONS

Fertility normalizes after WIN 18,446 treatment, and progeny also have normal fertility.

WIN18,446 enhances spermatogonial stem cell homing and fertility after germ cell transplantation by increasing blood-testis barrier permeability

Spermatogonial stem cells (SSCs) possess a unique ability to recolonize the seminiferous tubules. Upon microinjection into the adluminal compartment of the seminiferous tubules, SSCs transmigrate through the blood-testis barrier (BTB) to the basal compartment of the tubule and reinitiate spermatogenesis. It was recently discovered that inhibiting retinoic acid signaling with WIN18,446 enhances SSC colonization by transiently suppressing spermatogonia differentiation, thereby promoting fertility restoration. In this study, we report that WIN18,446 increases SSC colonization by disrupting the BTB. WIN18,446 altered the expression patterns of tight junction proteins (TJPs) and disrupted the BTB in busulfan-treated mice. WIN18,446 upregulated the expression of FGF2, one of the self-renewal factors for SSCs. While WIN18,446 enhanced SSC colonization in busulfan-treated wild-type mice, it did not increase colonization levels in busulfan-treated Cldn11-deficient mice, which lack the BTB, indicating that the enhancement of SSC colonization in wild-type testes depended on the loss of the BTB. Serial transplantation analysis revealed impaired self-renewal caused by WIN18,446, indicating that WIN18,446-mediated inhibition of retinoic acid signaling impaired SSC self-renewal. Strikingly, WIN18,446 administration resulted in the death of 45% of busulfan-treated recipient mice. These findings suggest that TJP modulation is the primary mechanism behind enhanced SSC homing by WIN18,446 and raise concerns regarding the use of WIN18,446 for human SSC transplantation.

Male Contraception

Approximately 40 to 50% of pregnancies are unintended. Contraceptive use significantly reduces the risk of unintended pregnancy. Approximately 70% of couples' contraceptive use is female and 30% is male, attributable to the reliance on condoms and vasectomies. Unfortunately, many women cannot use currently available contraceptives due to medical contraindications or side effects. At the same time, men want additional safe and effective contraceptive methods. Because of this, work to develop novel, safe, and effective male contraceptives is underway. This review will briefly discuss the pros and cons of condoms and vasectomies, and then describe research into the development of novel methods of male contraception, by the mechanism of action of the contraceptive. First, we will discuss male contraceptives that block sperm transmission. Next, we will discuss male contraceptives that impair sperm production. Lastly, we will discuss male contraceptives that impair sperm function.

Practice and development of male contraception: European Academy of Andrology and American Society of Andrology guidelines

BACKGROUNDS

Despite a wide spectrum of contraceptive methods for women, the unintended pregnancy rate remains high (45% in the US), with 50% resulting in abortion. Currently, 20% of global contraceptive use is male-directed, with a wide variation among countries due to limited availability and lack of efficacy. Worldwide studies indicate that >50% of men would opt to use a reversible method, and 90% of women would rely on their partner to use a contraceptive. Additional reasons for novel male contraceptive methods to be available include the increased life expectancy, sharing the reproductive risks among partners, social issues, the lack of pharma industry involvement and the lack of opinion makers advocating for male contraception.

AIM

The present guidelines aim to review the status regarding male contraception, the current state of the art to support the clinical practice, recommend minimal requirements for new male contraceptive development and provide and grade updated, evidence-based recommendations from the European Society of Andrology (EAA) and the American Society of Andrology (ASA).

METHODS

An expert panel of academicians appointed by the EAA and the ASA generated a consensus guideline according to the GRADE (Grading of Recommendations, Assessment, Development and Evaluation) system.

RESULTS

Sixty evidence-based and graded recommendations were produced on couple-centered communication, behaviors, barrier methods, semen analysis and contraceptive efficacy, physical agents, surgical methods, actions before initiating male contraception, hormonal methods, non-hormonal methods, vaccines, and social and ethical considerations.

CONCLUSION

As gender roles transform and gender equity is established in relationships, the male contribution to family planning must be facilitated. Efficient and safe male-directed methods must be evaluated and introduced into clinical practice, preferably reversible, either hormonal or non-hormonal. From a future perspective, identifying new hormonal combinations, suitable testicular targets, and emerging vas occlusion methods will produce novel molecules and products for male contraception.

ALDH1A Inhibition Suppresses Colitis and Alters α4β7 Integrin Expression on Activated T Cells in Mdr1a-/- Mice

There are limited pharmacological treatment options for inflammatory bowel disease (IBD), and some of these options are expensive and administered by injection or infusion. Thus, new cheaper and easier (oral) treatment options are needed. ALDH1A enzymes produce retinoic acid that can affect intestinal diseases such as IBD by regulating immune cells in the gut. We previously demonstrated that an orally deliverable ALDH1A inhibitor, WIN 18,466, can suppress colitis in an acute mouse model of IBD. Here, we tested the efficacy of ALDH1A inhibition in a chronic mouse model of IBD. Mdr1a-/- mice were treated with a diet containing WIN 18,446 starting 1 week prior to inducing colitis by H. bilis inoculation. Treatment was continued until the study end point and colitis was monitored based on clinical symptoms and confirmed by histological analysis. Immune cell phenotypes in colon-draining lymph nodes (cMLN) were analyzed. WIN 18,446 treatment reduced clinical symptoms and improved histopathologic colitis scores. This was associated with decreased expression of the gut homing integrin, α4β7, on T cells in cMLN; increased expression of CD103, a protein associated with tissue-resident memory T cells; and changes in dendritic cells, plasmacytoid dendritic cells and B cells in inhibitor-treated mice. ALDH1A inhibition broadly influences immune cells during colitis and is a potential new target for IBD treatment. Future studies will be needed to determine the efficacy of ALDH1A inhibition on active colitis and to evaluate its relative efficacy in comparison to approved drugs.

Retinoic Acid Influences connexin43 Expression During Joint Formation in the Regenerating Zebrafish Fin

Background

The regenerating zebrafish fin skeleton is comprised of multiple bony fin rays, each made of alternating bony segments and fin ray joints. This pattern is regulated by the gap junction protein Connexin43 (Cx43), which provides instructional cues to skeletal precursor cells (SPCs). Elevated Cx43 favors osteoblast differentiation and disfavors joint forming cell differentiation. The goal of this article is to test if retinoic acid (RA) contributes to the regulation of cx43 expression.

Materials and Methods

Functional studies inhibiting the RA-synthesizing enzyme Adh1a2 were evaluated using in situ hybridization to monitor gene expression and with measurements of the length of fin ray segments to monitor impacts on SPC differentiation and joint formation.

Results

Aldh1a2-knockdown leads to reduced expression of cx43 and increased expression of evx1, a gene required for joint formation. Additionally, inhibition of Aldh1a2 function leads to short fin ray segments. We also find evidence for synergy between aldh1a2 and cx43, suggesting that these genes function in a common molecular pathway to regulate joint formation.

Conclusions

The role of RA is to promote cx43 expression in the regenerating fin to regulate joint formation and the length of bony fin ray segments. We suggest that RA signaling must coordinate with additional pathways that also regulate cx43 transcription.

Aldehyde Dehydrogenase 2 as a Therapeutic Target in Oxidative Stress-Related Diseases: Post-Translational Modifications Deserve More Attention

Aldehyde dehydrogenase 2 (ALDH2) has both dehydrogenase and esterase activity; its dehydrogenase activity is closely related to the metabolism of aldehydes produced under oxidative stress (OS). In this review, we recapitulate the enzyme activity of ALDH2 in combination with its protein structure, summarize and show the main mechanisms of ALDH2 participating in metabolism of aldehydes in vivo as comprehensively as possible; we also integrate the key regulatory mechanisms of ALDH2 participating in a variety of physiological and pathological processes related to OS, including tissue and organ fibrosis, apoptosis, aging, and nerve injury-related diseases. On this basis, the regulatory effects and application prospects of activators, inhibitors, and protein post-translational modifications (PTMs, such as phosphorylation, acetylation, S-nitrosylation, nitration, ubiquitination, and glycosylation) on ALDH2 are discussed and prospected. Herein, we aimed to lay a foundation for further research into the mechanism of ALDH2 in oxidative stress-related disease and provide a basis for better use of the ALDH2 function in research and the clinic.

Commensal segmented filamentous bacteria-derived retinoic acid primes host defense to intestinal infection

Interactions between the microbiota and mammalian host are essential for defense against infection, but the microbial-derived cues that mediate this relationship remain unclear. Here, we find that intestinal epithelial cell (IEC)-associated commensal bacteria, segmented filamentous bacteria (SFB), promote early protection against the pathogen Citrobacter rodentium, independent of CD4⁺ T cells. SFB induced histone modifications in IECs at sites enriched for retinoic acid receptor motifs, suggesting that SFB may enhance defense through retinoic acid (RA). Consistent with this, inhibiting RA signaling suppressed SFB-induced protection. Intestinal RA levels were elevated in SFB mice, despite the inhibition of mammalian RA production, indicating that SFB directly modulate RA. Interestingly, RA was produced by intestinal bacteria, and the loss of bacterial-intrinsic aldehyde dehydrogenase activity decreased the RA levels and increased infection. These data reveal RA as an unexpected microbiota-derived metabolite that primes innate defense and suggests that pre- and probiotic approaches to elevate RA could prevent or combat infections.

A chemoproteomics approach to determine the mechanism of testicular toxicity for the Bruton's tyrosine kinase inhibitor CC-292

During drug development, potential safety issues can occur at any time. Understanding the cause of a toxicity can help with deciding on how to advance the drug development program. Chemoproteomics provides a way to help understand the cause of a toxicity where the affected tissue is accessible and can be probed with a covalently binding compound that is analogous to the offending drug. In this case, CC-292, a covalently binding Bruton's Tyrosine Kinase (BTK) inhibitor, had produced testicular toxicity in rodents. Experiments were conducted using a CC-292 analogue that could be chemically modified with biotin to probe rodent testes homogenates for potential binding sites that were subsequently recovered with avidin beads. These biotin-tagged proteins undergo trypsin digest on the avidin beads to yield peptides that are identified using mass spectrometry. Two proteins were identified from the testicular homogenates of both rats and mice, namely retinal dehydrogenase 1 and 2 (ALDH1A1 and 1A2). Literature confirmed a link between inhibition of these enzymes and testicular toxicity. Subsequently, molecular modelling was used to demonstrate that CC-292 can be docked into both the NAD and retinal binding pockets of the analogous human ALDH1A2 enzyme. These data suggest that the off-target binding site for CC-292 on ALDH enzymes may provide a mechanistic explanation to the testicular toxicity observed in rodents and that there may be a potential concern for human male fertility. Significance Statement Biotinylated covalently binding drug analogues are used to enrich bound proteins from tissue homogenates where toxicity was observed in rodents. Bound proteins were subsequently identified by mass spectroscopy. Competition of the analogue binding with the parent inhibitor itself and 3D molecular modeling were used to establish a likely link between the off-targets of CC-292, ALDH1A1 and 1A2, with potential testicular toxicity.

Oncorequisite role of an aldehyde dehydrogenase in the pathogenesis of T-cell acute lymphoblastic leukemia

Aldehyde dehydrogenases (ALDH) are overexpressed in various types of cancers. One of the ALDH family genes, ALDH1A2, is aberrantly expressed in more than 50% of cases of T-cell acute lymphoblastic leukemia (T-ALL). However, its molecular function and role in the pathogenesis of T-ALL are largely unknown. Chromatin immunoprecipitation-sequencing and RNA-sequencing analyses showed that the oncogenic transcription factor TAL1 and its regulatory partners bind to the intronic regulatory element of the ALDH1A2 gene, directly inducing a T-ALL-specific isoform with enzymatic activity. ALDH1A2 was preferentially expressed in the TAL1-positive T-ALL subgroup. In TALL cell lines, depletion of ALDH1A2 inhibited cell viability and induced apoptosis. Interestingly, gene expression and metabolomic profiling revealed that ALDH1A2 supported glycolysis and the tricarboxylic acid cycle, accompanied by NADH production, by affecting multiple metabolic enzymes to promote ATP production. Depletion of ALDH1A2 increased the levels of reactive oxygen species, while the levels were reduced by ALDH1A2 overexpression both in vitro and in vivo. Overexpression of ALDH1A2 accelerated tumor onset and increased tumor penetrance in a zebrafish model of T-ALL. Taken together, our results indicate that ALDH1A2 protects against intracellular stress and promotes T-ALL cell metabolism and survival. ALDH1A2 overexpression enables leukemic clones to sustain a hyper-proliferative state driven by oncogenes.

Evaluation of spice and herb as phyto-derived selective modulators of human retinaldehyde dehydrogenases using a simple in vitro method

Selective modulation of retinaldehyde dehydrogenases (RALDHs)-the main aldehyde dehydrogenase (ALDH) enzymes converting retinal into retinoic acid (RA), is very important not only in the RA signaling pathway but also for the potential regulatory effects on RALDH isozyme-specific processes and RALDH-related cancers. However, very few selective modulators for RALDHs have been identified, partly due to variable overexpression protocols of RALDHs and insensitive activity assay that needs to be addressed. In the present study, deletion of the N-terminal disordered regions is found to enable simple preparation of all RALDHs and their closest paralog ALDH2 using a single protocol. Fluorescence-based activity assay was employed for enzymatic activity investigation and screening for RALDH-specific modulators from extracts of various spices and herbs that are well-known for containing many phyto-derived anti-cancer constituents. Under the established conditions, spice and herb extracts exhibited differential regulatory effects on RALDHs/ALDH2 with several extracts showing potential selective inhibition of the activity of RALDHs. In addition, the presence of magnesium ions was shown to significantly increase the activity for the natural substrate retinal of RALDH3 but not the others, while His-tag cleavage considerably increased the activity of ALDH2 for the non-specific substrate retinal. Altogether we propose a readily reproducible workflow to find selective modulators for RALDHs and suggest potential sources of selective modulators from spices and herbs.

Investigation of an ALDH1A1-specific inhibitor for suppression of weight gain in a diet-induced mouse model of obesity

BACKGROUND

Retinoic acid (RA) controls diverse physiological functions including weight regulation and energy metabolism. It has been reported that mice lacking ALDH1A1, one of the aldehyde dehydrogenases (ALDH) that synthesize RA, are healthy and resistant to weight gain, raising the possibility that inhibiting this enzyme might treat obesity. We previously demonstrated that treatment with a pan-ALDH1A enzyme inhibitor, WIN18446, suppressed weight gain in mice fed a high-fat diet (HFD), but caused increased hepatic lipidosis and reversible male infertility.

METHODS

A series of piperazine compounds that inhibited ALDH1A1 were identified and their inhibitory activity was characterized in vitro using purified recombinant enzymes and cell-based assay systems. One potent compound, FSI-TN42 (N42) was examined for its oral bioavailability and pharmacodynamic effects. In addition, its effect on weight gain was investigated by daily oral administration to C57BL/6 male mice receiving a HFD, and compared with mice receiving WIN18446 or vehicle alone (n = 6/group, 200 mg compound/kg body weight) for 5 weeks. Body weights were measured weekly, and a glucose tolerance test was performed after 4 weeks of treatment. Tissues were collected to determine changes in adipose weight, hepatic lipidosis, retinoid metabolism, and expression of genes associated with RA and lipid metabolism.

RESULTS

N42 irreversibly binds and inhibits ALDH1A1 in vitro with a low nM IC₅₀ and 800-fold specificity for ALDH1A1 compared to ALDH1A2. Daily oral administration of N42 significantly suppressed weight gain (P < 0.05) and reduced visceral adiposity (p < 0.05) in mice fed a HFD without the hepatic lipidosis observed with WIN18446 treatment.

CONCLUSIONS

We developed a potent and specific inhibitor of ALDH1A1 that suppressed weight gain in mice fed a HFD. These findings demonstrate that inhibition of ALDH1A1 is a feasible target for drug development to treat and/or prevent obesity.

Emerging approaches to male contraception

Despite significant interests in contraception by men, effective methods of male contraception are limited to vasectomy and condoms. Recently, there have been several promising advances in male contraceptive research. This review will update readers on recent research in both hormonal and nonhormonal approaches to male contraception. Hormonal approaches to male contraception have been stymied by adverse effects, formulations requiring injections or implants, a 5% to10% nonresponse rate, as well as poor understanding of user acceptability. In the last several years, research has focused on novel, orally bioavailable androgens such as dimethandrolone undecanoate and 11β-methyl-19-nor-testosterone. Additionally, combinations of a topical testosterone gel combined with a gel containing segesterone acetate, a potent progestin, have shown promise in clinical trials recently. Simultaneously, significant preclinical progress has been made in several approaches to nonhormonal male contraceptives, including compounds that inhibit sperm motility such as eppin, compounds that inhibit retinoic acid binding or biosynthesis, and reversible approaches to obstruction of the vas deferens. It is imperative for these areas of research to continue making strides so that there is a gamut of contraceptive options for couples to choose from. Some of these approaches will hopefully reach clinical utility soon, greatly improving contraceptive choice for couples.

Transient suppression of transplanted spermatogonial stem cell differentiation restores fertility in mice

A remarkable feature of tissue stem cells is their ability to regenerate the structure and function of host tissue following transplantation. However, the dynamics of donor stem cells during regeneration remains largely unknown. Here we conducted quantitative clonal fate studies of transplanted mouse spermatogonial stem cells in host seminiferous tubules. We found that, after a large population of donor spermatogonia settle in host testes, through stochastic fate choice, only a small fraction persist and regenerate over the long term, and the rest are lost through differentiation and cell death. Further, based on these insights, we showed how repopulation efficiency can be increased to a level where the fertility of infertile hosts is restored by transiently suppressing differentiation using a chemical inhibitor of retinoic acid synthesis. These findings unlock a range of potential applications of spermatogonial transplantation, from fertility restoration in individuals with cancer to conservation of biological diversity.

Targeting NAD-dependent dehydrogenases in drug discovery against infectious diseases and cancer

Dehydrogenases are oxidoreductase enzymes that play a variety of fundamental functions in the living organisms and have primary roles in pathogen survival and infection processes as well as in cancer development. We review here a sub-set of NAD-dependent dehydrogenases involved in human diseases and the recent advancements in drug development targeting pathogen-associated NAD-dependent dehydrogenases. We focus also on the molecular aspects of the inhibition process listing the structures of the most relevant molecules targeting this enzyme family. Our aim is to review the most impacting findings regarding the discovery of novel inhibitory compounds targeting the selected NAD-dependent dehydrogenases involved in cancer and infectious diseases.

Modulation of Gut Microbiota and Oxidative Status by β-Carotene in Late Pregnant Sows

Recent evidences suggest that gut microbiota plays an important role in regulating physiological and metabolic activities of pregnant sows, and β-carotene has a potentially positive effect on reproduction, but the impact of β-carotene on gut microbiota in pregnant sows remains unknown. This study aimed to explore the effect and mechanisms of β-carotene on the reproductive performance of sows from the aspect of gut microbiota. A total of 48 hybrid pregnant sows (Landrace × Yorkshire) with similar parity were randomly allocated into three groups (n = 16) and fed with a basal diet or a diet containing 30 or 90 mg/kg of β-carotene from day 90 of gestation until parturition. Dietary supplementation of 30 or 90 mg/kg β-carotene increased the number of live birth to 11.82 ± 1.54 and 12.29 ± 2.09, respectively, while the control group was 11.00 ± 1.41 (P = 0.201). Moreover, β-carotene increased significantly the serum nitric oxide (NO) level and glutathione peroxidase (GSH-Px) activity (P < 0.05). Characterization of fecal microbiota revealed that 90 mg/kg β-carotene increased the diversity of the gut flora (P < 0.05). In particular, β-carotene decreased the relative abundance of Firmicutes including Lachnospiraceae AC2044 group, Lachnospiraceae NK4B4 group and Ruminococcaceae UCG-008, but enriched Proteobacteria including Bilophila and Sutterella, and Actinobacteria including Corynebacterium and Corynebacterium 1 which are related to NO synthesis. These data demonstrated that dietary supplementation of β-carotene may increase antioxidant enzyme activity and NO, an important vasodilator to promote the neonatal blood circulation, through regulating gut microbiota in sows.

Biparental contributions of the H2A.B histone variant control embryonic development in mice

Histone variants expand chromatin functions in eukaryote genomes. H2A.B genes are testis-expressed short histone H2A variants that arose in placental mammals. Their biological functions remain largely unknown. To investigate their function, we generated a knockout (KO) model that disrupts all 3 H2A.B genes in mice. We show that H2A.B KO males have globally altered chromatin structure in postmeiotic germ cells. Yet, they do not show impaired spermatogenesis or testis function. Instead, we find that H2A.B plays a crucial role postfertilization. Crosses between H2A.B KO males and females yield embryos with lower viability and reduced size. Using a series of genetic crosses that separate parental and zygotic contributions, we show that the H2A.B status of both the father and mother, but not of the zygote, affects embryonic viability and growth during gestation. We conclude that H2A.B is a novel parental-effect gene, establishing a role for short H2A histone variants in mammalian development. We posit that parental antagonism over embryonic growth drove the origin and ongoing diversification of short histone H2A variants in placental mammals.

Protective Effects of ALDH1A Enzyme Inhibition on Helicobacter-Induced Colitis in Smad3-/- Mice are Associated with Altered α4ß7 Integrin Expression on Activated T Cells

Many inflammatory bowel disease (IBD) patients require surgical intervention due to limited pharmacological treatment options. Antibodies targeting α4ß7, a gut-homing integrin, are one of the most promising IBD treatments. As retinoic acid (RA) regulates expression of gut-homing proteins including α4ß7 integrin, we tested if ALDH1A enzymes in the RA synthesis pathway could be targeted for IBD treatment using a potent inhibitor, WIN 18,446. Age- and sex-matched Smad3^-/- mice were fed a diet with and without WIN 18,446 for 3 weeks before triggering inflammation with Helicobacter bilis infection. Colitis was evaluated by histopathology one week following the IBD trigger, and T cell subsets were evaluated before and after the IBD trigger. WIN 18,446 treatment significantly reduced IBD severity in Smad3^-/- mice and reduced expression of α4ß7 integrin on multiple activated CD4⁺ T cell subsets. This change was associated with increased ratios of induced regulatory T cells to Th17 cells during the inflammatory response in the draining lymph nodes. These studies indicate that RA reduction via ALDH1A enzyme inhibition is a potential new target for IBD treatment. Further studies are needed to examine its effects on other types of immune cells, to evaluate the efficacy window for this target, and to determine its efficacy in other animal models of IBD.

Synthesis of 2-phenyl-5,6,7,8-tetrahydroquinoxaline derivatives and screening for P2X1-purinoceptor antagonist activity in isolated preparations of rat vas deferens, for translation into a male contraceptive†

Sympathetically mediated contractions of smooth muscle cells in the vasa deferentia are mediated by neuronally released adenosine 5′-triphosphate (ATP) and noradrenaline, which stimulate P2X1-purinoceptors and α_1A-adrenoceptors, respectively. This process is crucial for sperm transport, as demonstrated in knockout mouse studies where simultaneous genetic deletion of P2X1-purinoceptors and α_1A-adrenoceptors resulted in male infertility. We hypothesize that dual pharmacological antagonism of these two receptors could inhibit sperm transport sufficiently to provide a novel nonhormonal method of male contraception. To generate a suitable P2X1-purinoceptor antagonist, substituents were introduced on the phenyl moiety of 2-phenyl-5,6,7,8-tetrahydroquinoxaline to create a series of analogues that were tested for P2X1-purinoceptor antagonism in isolated preparations of rat vas deferens. Novel compounds were initially screened for their ability to attenuate contractile responses to electrical field stimulation (EFS: 60 V, 0.5 ms, 0.2 Hz). The addition of polar substituents to the meta, but not ortho, position markedly increased the inhibition of contractions, as did the addition of both polar and aliphatic substituents to the para position. Di-substituted compounds were also synthesized and tested, resulting in a compound 31 (2-hydroxy, 4-fluoro), which exhibited the greatest potency, with an IC₅₀ of 14 μM (95% confidence limits: 12–16 μM). Additionally, compound 31 noncompetitively antagonized contractions mediated by exogenously administered αß-methylene ATP (10 nM–30 μM) but had no inhibitory effect on contractions mediated by exogenously administered noradrenaline (30 nM–100 μM) or acetylcholine (30 nM–100 μM). These results have contributed to a structure–activity relationship profile for the P2X1-purinoceptor that will inform future designs of more potent antagonists.

Retinoic acid receptor antagonists for male contraception: current status†

Retinoic acid receptor alpha (RARA), a nuclear receptor protein, has been validated as a target for male contraception by gene knockout studies and also pharmacologically using a pan-retinoic acid receptor antagonist. Retinoic acid receptor alpha activity is indispensable for the spermatogenic process, and therefore its antagonists have potential as male contraceptive agents. This review discusses the effects of systematic dosing regimen modifications of the orally bioavailable and reversible pan-antagonist BMS-189453 as well as studies with the alpha-selective antagonists BMS-189532 and BMS-189614 in a murine model. We also provide an overview of structure-activity studies of retinoic acid receptor alpha antagonists that provide insight for the design of novel alpha-selective ligands.

In-vitro differentiation of early pig spermatogenic cells to haploid germ cells

Spermatogonial stem cells (SSCs) self-renew and contribute genetic information to the next generation. Pig is wildly used as a model animal for understanding reproduction mechanisms of human being. Inducing directional differentiation of porcine SSCs may be an important strategy in exploring the mechanisms of spermatogenesis and developing better treatment methods for male infertility. Here, we established an in-vitro culture model for porcine small seminiferous tubule segments, to induce SSCs to differentiate into single-tail haploid spermatozoa. The culture model subsequently enabled spermatozoa to express the sperm-specific protein acrosin and oocytes to develop to blastocyst stage after round spermatid injection. The addition of retinoic acid (RA) to the differentiation media promoted the efficiency of haploid differentiation. RT-PCR analysis indicated that RA stimulated the expression of Stra8 but reduced the expression of NANOS2 in spermatogonia. Genes involved in post-meiotic development, transition protein 1 (Tnp1) and protamine 1 (Prm1) were upregulated in the presence of RA. The addition of an RA receptor (RAR) inhibitor, BMS439, showed that RA enhanced the expression of cAMP responsive-element binding protein through RAR and promoted the formation of round spermatids. We established an efficient culture system for in-vitro differentiation of pig SSCs. Our study represents a model for human testis disease and toxicology screening. Molecular regulators of SSC differentiation revealed in this study might provide a therapeutic strategy for male infertility.

A cell-based high-content screen identifies isocotoin as a small molecule inhibitor of the meiosis-specific MEIOB-SPATA22 complex†

MEIOB and SPATA22 are meiosis-specific proteins, interact with each other, and are essential for meiotic recombination and fertility. Aspartic acid 383 (D383) in MEIOB is critical for its interaction with SPATA22 in biochemical studies. Here we report that genetic studies validate the requirement of D383 for the function of MEIOB in mice. The Meiob^D383A/D383A mice display meiotic arrest due to depletion of both MEIOB and SPATA22 proteins in the testes. We developed a cell-based bimolecular fluorescence complementation (BiFC) assay, in which MEIOB and SPATA22 are fused to split YFP moieties and their co-expression in cultured cells leads to the MEIOB–SPATA22 dimerization and reconstitution of the fluorophore. As expected, the interaction-disrupting D383A substitution results in the absence of YFP fluorescence in the BiFC assay. A high-throughput screen of small molecule libraries identified candidate hit compounds at a rate of 0.7%. Isocotoin, a hit compound from the natural product library, inhibits the MEIOB–SPATA22 interaction and promotes their degradation in HEK293 cells in a dose-dependent manner. Therefore, the BiFC assay can be employed to screen for small molecule inhibitors that disrupt protein–protein interactions or promote degradation of meiosis-specific proteins.

Sources of all-trans retinal oxidation independent of the aldehyde dehydrogenase 1A isozymes exist in the postnatal testis†

Despite the essential role of the active metabolite of vitamin A, all-trans retinoic acid (atRA) in spermatogenesis, the enzymes, and cellular populations responsible for its synthesis in the postnatal testis remain largely unknown. The aldehyde dehydrogenase 1A (ALDH1A) family of enzymes residing within Sertoli cells is responsible for the synthesis of atRA, driving the first round of spermatogenesis. Those studies also revealed that the atRA required to drive subsequent rounds of spermatogenesis is possibly derived from the ALDH1A enzymes residing within the meiotic and post-meiotic germ cells. Three ALDH1A isozymes (ALDH1A1, ALDH1A2, and ALDH1A3) are present in the testis. Although, ALDH1A1 is expressed in adult Sertoli cells and is suggested to contribute to the atRA required for the pre-meiotic transitions, ALDH1A2 is proposed to be the essential isomer involved in testicular atRA biosynthesis. In this report, we first examine the requirement for ALDH1A2 via the generation and analysis of a conditional Aldh1a2 germ cell knockout and a tamoxifen-induced Aldh1a2 knockout model. We then utilized the pan-ALDH1A inhibitor (WIN 18446) to test the collective contribution of the ALDH1A enzymes to atRA biosynthesis following the first round of spermatogenesis. Collectively, our data provide the first in vivo evidence demonstrating that animals severely deficient in ALDH1A2 postnatally proceed normally through spermatogenesis. Our studies with a pan-ALDH1A inhibitor (WIN 18446) also suggest that an alternative source of atRA biosynthesis independent of the ALDH1A enzymes becomes available to maintain atRA levels for several spermatogenic cycles following an initial atRA injection.

Development of Novel Male Contraceptives

Unintended pregnancy is surprisingly common, accounting for 40-50% of pregnancies worldwide. Contraception is the most effective means of preventing unintended pregnancy. Seventy percent of all contraceptives are used by women; however, some women are unable to use contraceptives due to health conditions or side effects. Many men wish to take a more active role family planning, but currently have only two effective male contraceptive options, condoms and vasectomy. Therefore, work to develop novel male contraceptives analogous to popular female methods, such as daily pills or long-acting shots and implants, is underway. This paper will briefly discuss the pros and cons of condoms and vasectomies, and then review the research into novel methods of male contraception.

Structural and kinetic features of aldehyde dehydrogenase 1A (ALDH1A) subfamily members, cancer stem cell markers active in retinoic acid biosynthesis

Aldehyde dehydrogenases catalyze the NAD(P)⁺-dependent oxidation of aldehydes to their corresponding carboxylic acids. The three-dimensional structures of the human ALDH1A enzymes were recently obtained, while a complete kinetic characterization of them, under the same experimental conditions, is lacking. We show that the three enzymes, ALDH1A1, ALDH1A2 and ALDH1A3, have similar topologies, although with decreasing volumes in their substrate-binding pockets. The activity with aliphatic and retinoid aldehydes was characterized side-by-side, using an improved HPLC-based method for retinaldehyde. Hexanal was the most efficient substrate. ALDH1A1 displayed lower K_m values with hexanal, trans-2-hexenal and citral, compared to ALDH1A2 and ALDH1A3. ALDH1A2 was the best enzyme for the lipid peroxidation product, 4-hydroxy-2-nonenal, in terms of k_cat/K_m. The catalytic efficiency towards all-trans and 9-cis-retinaldehyde was in general lower than for alkanals and alkenals. ALDH1A2 and ALDH1A3 showed higher catalytic efficiency for all-trans-retinaldehyde. The lower specificity of ALDH1A3 for 9-cis-retinaldehyde against the all-trans- isomer might be related to the smaller volume of its substrate-binding pocket. Magnesium inhibited ALDH1A1 and ALDH1A2, while it activated ALDH1A3, which is consistent with cofactor dissociation being the rate-limiting step for ALDH1A1 and ALDH1A2, and deacylation for ALDH1A3, with hexanal as a substrate. We mutated both ALDH1A1 (L114P) and ALDH1A2 (N475G, A476V, L477V, N478S) to mimic their counterpart substrate-binding pockets. ALDH1A1 specificity for citral was traced to residue 114 and to residues 458 to 461. Regarding retinaldehyde, the mutants did not show significant differences with their respective wild-type forms, suggesting that the mutated residues are not critical for retinoid specificity.

Biochemical and physiological importance of the CYP26 retinoic acid hydroxylases

The Cytochrome P450 (CYP) family 26 enzymes contribute to retinoic acid (RA) metabolism and homeostasis in humans, mammals and other chordates. The three CYP26 family enzymes, CYP26A1, CYP26B1 and CYP26C1 have all been shown to metabolize all-trans-retinoic acid (atRA) it's 9-cisRA and 13-cisRA isomers and primary metabolites 4-OH-RA and 4-oxo-RA with high efficiency. While no crystal structures of CYP26 enzymes are available, the binding of various ligands has been extensively explored via homology modeling. All three CYP26 enzymes are inducible by treatment with atRA in various prenatal and postnatal tissues and cell types. However, current literature shows that in addition to regulation by atRA, CYP26 enzyme expression is also regulated by other endogenous processes and inflammatory cytokines. In humans and in animal models the expression patterns of CYP26 enzymes have been shown to be tissue and cell type specific, and the expression of the CYP26 enzymes is believed to regulate the formation of critical atRA concentration gradients in various tissue types. Yet, very little data exists on direct disease associations of altered CYP26 expression or activity. Nevertheless, data is emerging describing a variety of human genetic variations in the CYP26 enzymes that are associated with different pathologies. Interestingly, some of these genetic variants result in increased activity of the CYP26 enzymes potentially leading to complex gene-environment interactions due to variability in dietary intake of retinoids. This review highlights the current knowledge of structure-function of CYP26 enzymes and focuses on their role in human retinoid metabolism in different tissues.

Leydig cell genes change their expression and association with polysomes in a stage-specific manner in the adult mouse testis

Spermatogenesis in mammals occurs in a very highly organized manner within the seminiferous epithelium regulated by different cell types in the testis. Testosterone produced by Leydig cells regulates blood-testis barrier formation, meiosis, spermiogenesis, and spermiation. However, it is unknown whether Leydig cell function changes with the different stages of the seminiferous epithelium. This study utilized the WIN 18,446 and retinoic acid (RA) treatment regime combined with the RiboTag mouse methodology to synchronize male germ cell development and allow for the in vivo mapping of the Leydig cell translatome across the different stages of one cycle of the seminiferous epithelium. Using microarrays analysis, we identified 11 Leydig cell-enriched genes that were expressed in stage-specific manner such as the glucocorticoid synthesis and transport genes, Cyp21a1 and Serpina6. In addition, there were nine Leydig cell transcripts that change their association with polysomes in correlation with the different stages of the spermatogenic cycle including Egr1. Interestingly, the signal intensity of EGR1 and CYP21 varied among Leydig cells in the adult asynchronous testis. However, testosterone levels across the different stages of germ cell development did not cycle. These data show, for the first time, that Leydig cell gene expression changes in a stage-specific manner during the cycle of the seminiferous epithelium and indicate that a heterogeneous Leydig cell population exists in the adult mouse testis.

Recent insights on the role and regulation of retinoic acid signaling during epicardial development

The vitamin A metabolite, retinoic acid, carries out essential and conserved roles in vertebrate heart development. Retinoic acid signals via retinoic acid receptors (RAR)/retinoid X receptors (RXRs) heterodimers to induce the expression of genes that control cell fate specification, proliferation, and differentiation. Alterations in retinoic acid levels are often associated with congenital heart defects. Therefore, embryonic levels of retinoic acid need to be carefully regulated through the activity of enzymes, binding proteins and transporters involved in vitamin A metabolism. Here, we review evidence of the complex mechanisms that control the fetal uptake and synthesis of retinoic acid from vitamin A precursors. Next, we highlight recent evidence of the role of retinoic acid in orchestrating myocardial compact zone growth and coronary vascular development.

Comparative Metabonomic Investigations of Schistosoma japonicum From SCID Mice and BALB/c Mice: Clues to Developmental Abnormality of Schistosome in the Immunodeficient Host

The growth and development of schistosome has been affected in the immunodeficient hosts. But it remains unresolved about the molecular mechanisms involved in the development and reproduction regulation of schistosomes. This study tested and compared the metabolic profiles of the male and female Schistosoma japonicum worms collected from SCID mice and BALB/c mice at 5 weeks post infection using liquid chromatography tandem mass spectrometry (LC-MS/MS) platform, in which the worms from SCID mice were the investigated organisms and the worms from BALB/c mice were used as the controls. There were 1015 ion features in ESI+ mode and 342 ion features in ESI- mode were identified after filtration by false discovery rate. Distinct metabolic profiles were found to clearly differentiate both male and female worms in SCID mice from those in BALB/c mice using multivariate modeling methods including the Principal Component Analysis (PCA), Partial Least Squares Discriminant Analysis (PLS-DA), and Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA). There were more differential metabolites in female worms than in male worms between SCID mice and BALB/c mice. And common and uniquely perturbed metabolites and pathways were identified among male and female worms from SCID mice when compared with BALB/c mice. The enriched metabolite sets of the differential metabolites in male worms between SCID mice and BALB/c mice included bile acid biosynthesis, taurine and hypotaurine metabolism, sphingolipid metabolism, retinol metabolism, purine metabolism, etc. And the enriched metabolite sets of differential metabolites in female worms included retinol metabolism, alpha linolenic acid and linoleic acid metabolism, purine metabolism, sphingolipid metabolism, glutamate metabolism, etc. Further detection and comparison in transcript abundance of genes of the perturbed retinol metabolism and its associated meiosis process in worms identified clues suggesting accumulated retinyl ester and perturbed meiotic process. These findings suggested an association between the schistosome with retarded growth and development in SCID mice and their perturbed metabolites and metabolic pathways, and provided a new insight into the growth and development regulation of S. japonicum worms from the metabolic level, which indicated great clues for discovery of drugs or vaccines against the parasites and disease with more researches.

Two functionally redundant sources of retinoic acid secure spermatogonia differentiation in the seminiferous epithelium

In mammals, all-trans retinoic acid (ATRA) is instrumental to spermatogenesis. It is synthesized by two retinaldehyde dehydrogenases (RALDH) present in both Sertoli cells (SCs) and germ cells (GCs). In order to determine the relative contributions of each source of ATRA, we have generated mice lacking all RALDH activities in the seminiferous epithelium (SE). We show that both the SC- and GC-derived sources of ATRA cooperate to initiate and propagate spermatogenetic waves at puberty. In adults, they exert redundant functions and, against all expectations, the GC-derived source does not perform any specific roles despite contributing to two-thirds of the total amount of ATRA present in the testis. The production from SCs is sufficient to maintain the periodic expression of genes in SCs, as well and the cycle and wave of the SE, which account for the steady production of spermatozoa. The production from SCs is also specifically required for spermiation. Importantly, our study shows that spermatogonia differentiation depends upon the ATRA synthesized by RALDH inside the SE, whereas initiation of meiosis and expression of STRA8 by spermatocytes can occur without ATRA.

Summary: All-trans retinoic acid made by Sertoli cells is instrumental to spermatogenesis and is specifically required for spermatid release.

Design, synthesis, and ex vivo evaluation of a selective inhibitor for retinaldehyde dehydrogenase enzymes

The retinaldehyde dehydrogenase (RALDH) enzymes, RALDH1, RALDH2, and RALDH3, catalyze the irreversible oxidation of retinaldehyde to all-trans-retinoic acid (ATRA). Despite the importance of the RALDH enzymes in embryonic development, postnatal growth and differentiation, and in several disease states, there are no commercially available inhibitors that specifically target these isozymes. We report here the development and characterization of a small molecule inhibitor dichloro-all-trans-retinone (DAR) (Summers et al., 2017) that is an irreversible inhibitor of RALDH1, 2, and 3 that effectively inhibits RALDH1, 2, and 3 in the nanomolar range but has no inhibitory activity against mitochondrial ALDH2. These results provide support for the development of DAR as a specific ATRA synthesis inhibitor for a variety of experimental and clinical applications.

Can inhibition of retinoic acid biosynthesis function as a non-hormonal female contraceptive?

OBJECTIVE

Vitamin A deficient females have reduced fertility due to decreased retinoic acid production. WIN 18,446 inhibits retinoic acid biosynthesis and functions as a contraceptive in males. We tested whether WIN 18,446 treatment would suppress fertility in female mice.

STUDY DESIGN

Female mice were treated with WIN 18,446 and mated. Pregnancy rates were compared using Fisher's exact test.

RESULTS

WIN 18,446 reduced pregnancy compared with control (p=.03). However, one animal became pregnant with malformed embryos.

CONCLUSIONS

WIN 18,446 treatment significantly reduces fecundity, but teratogenicity in the setting of contraceptive failure limits the appeal of this approach to female contraception.

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

Enzymes of the ALDH1A subfamily of aldehyde dehydrogenases are crucial in regulating retinoic acid (RA) signaling and have received attention as potential drug targets. ALDH1A2 is the primary RA-synthesizing enzyme in mammalian spermatogenesis and is therefore considered a viable drug target for male contraceptive development. However, only a small number of ALDH1A2 inhibitors have been reported, and information on the structure of ALDH1A2 was limited to the NAD-liganded enzyme void of substrate or inhibitors. Herein, we describe the mechanism of action of structurally unrelated reversible and irreversible inhibitors of human ALDH1A2 using direct binding studies and X-ray crystallography. All inhibitors bind to the active sites of tetrameric ALDH1A2. Compound WIN18,446 covalently reacts with the side chain of the catalytic residue Cys320, resulting in a chiral adduct in ( R) configuration. The covalent adduct directly affects the neighboring NAD molecule, which assumes a contracted conformation suboptimal for the dehydrogenase reaction. The reversible inhibitors interact predominantly through direct hydrogen bonding interactions with residues in the vicinity of Cys320 without affecting NAD. Upon interaction with inhibitors, a large flexible loop assumes regular structure, thereby shielding the active site from solvent. The precise knowledge of the binding modes provides a new framework for the rational design of novel inhibitors of ALDH1A2 with improved potency and selectivity profiles.

Retinoic acid signaling promotes the cytoskeletal rearrangement of embryonic epicardial cells

All- trans-retinoic acid (RA), a vitamin A metabolite, is an important signaling molecule required for the proper development of the heart. The epicardium is the main source of RA in the embryonic heart, yet the cardiogenic functions of epicardial-produced RA are not fully understood. Here, we investigated the roles of RA signaling in the embryonic epicardium using in vivo and in vitro models of excess or deficiency of RA. Our results suggested that RA signaling facilitates the cytoskeletal rearrangement required for the epicardial-to-mesenchymal transition of epicardial cells. In vivo treatment with an inhibitor of RA synthesis delayed the migration of epicardial-derived precursor cells (EPDCs) into the myocardium; the opposite was seen in the case of dehydrogenase/reductase superfamily (DHRS)3-deficient embryos, a mouse model of RA excess. Analysis of the behavior of epicardial cells exposed to RA receptor agonists or inhibitors of RA synthesis in vitro revealed that appropriate levels of RA are important in orchestrating the platelet-derived growth factor-induced loss of epithelial character, cytoskeletal remodeling, and migration, necessary for the infiltration of the myocardium by EPDCs. To understand the molecular mechanisms by which RA regulates epicardial cytoskeletal rearrangement, we used a whole transcriptome profiling approach, which in combination with pull-down and inhibition assays, demonstrated that the Ras homolog gene family, member A (RhoA) pathway is required for the morphologic changes induced by RA in epicardial cells. Collectively, these data demonstrate that RA regulates the cytoskeletal rearrangement of epicardial cells via a signaling cascade that involves the RhoA pathway.-Wang, S., Yu, J., Jones, J. W., Pierzchalski, K., Kane, M. A., Trainor, P. A., Xavier-Neto, J., Moise, A. R. Retinoic acid signaling promotes the cytoskeletal rearrangement of embryonic epicardial cells.

Pharmacological inhibition of ALDH1A enzymes suppresses weight gain in a mouse model of diet-induced obesity

BACKGROUND

Retinoic acid (RA) is known to play a role in weight regulation. Because mice without ALDH1A1, a major RA synthesizing enzyme, are resistant to diet-induced obesity, we tested a hypothesis that pharmacological inhibition of RA synthesis can suppress weight gain in a murine model of diet-induced obesity.

METHODS

C57BL/6J male mice were fed a high fat diet (HFD) for 8 weeks to induce obesity and then randomized to a HFD with or without WIN 18,446, an RA synthesis inhibitor, for an additional 9 weeks. Body weight, body composition, energy expenditure, activity, and food intake were measured. Levels of retinoids, lipids, and genes involved in the metabolism of retinoid and lipids were also determined.

RESULT

s Mice treated with WIN 18,446 gained significantly less weight and had decreased adipose tissue weight, adipocyte size, and macrophage infiltration in adipose tissue. In addition, we observed higher UCP1 expression in adipose tissues and decreased expression of RA responsive genes and genes involved in fatty acid synthesis in the livers and lungs of mice treated with WIN 18,446.

CONCLUSIONS

Pharmacological suppression of RA synthesis via inhibition of ALDH1A1 may be a potential target for treatment of obesity.

Isotretinoin administration improves sperm production in men with infertility from oligoasthenozoospermia: a pilot study

There is currently no effective medical therapy for men with infertility due to oligoasthenozoospermia. As men with abnormal sperm production have lower concentrations of 13-cis-retinoic acid in their testes, we hypothesized that men with infertility from oligoasthenozoospermia might have improved sperm counts when treated with isotretinoin (13-cis-retinoic acid). We conducted a single-site, single-arm, pilot study to determine the effect of therapy with isotretinoin on sperm indices in 19 infertile men with oligoasthenozoospermia. Subjects were men between 21 and 60 years of age with infertility for longer than 12 months associated with sperm concentrations below 15 million sperm/mL. All men received isotretinoin 20 mg by mouth twice daily for 20 weeks. Subjects had semen analyses, physical examinations, and laboratory tests every 4 weeks during treatment. Nineteen men enrolled in the study. Median (25th, 75th) sperm concentration increased from 2.5 (0.1, 5.9) million/mL at baseline to 3.8 (2.1, 13.0) million/mL at the end of treatment (p = 0.006). No significant changes in sperm motility were observed. There was a trend toward improved sperm morphology (p = 0.056). Six pregnancies (three spontaneous and three from intracytoplasmic sperm injection) and five births occurred during the study. Four of the births, including all three of the spontaneous pregnancies, were observed in men with improvements in sperm counts with isotretinoin therapy. Treatment was well tolerated. Isotretinoin therapy improves sperm production in some men with oligoasthenozoospermia. Additional studies of isotretinoin in men with infertility from oligoasthenozoospermia are warranted.

New Insights Into the Roles of Retinoic Acid Signaling in Nervous System Development and the Establishment of Neurotransmitter Systems

Secreted chiefly from the underlying mesoderm, the morphogen retinoic acid (RA) is well known to contribute to the specification, patterning, and differentiation of neural progenitors in the developing vertebrate nervous system. Furthermore, RA influences the subtype identity and neurotransmitter phenotype of subsets of maturing neurons, although relatively little is known about how these functions are mediated. This review provides a comprehensive overview of the roles played by RA signaling during the formation of the central and peripheral nervous systems of vertebrates and highlights its effects on the differentiation of several neurotransmitter systems. In addition, the evolutionary history of the RA signaling system is discussed, revealing both conserved properties and alternate modes of RA action. It is proposed that comparative approaches should be employed systematically to expand our knowledge of the context-dependent cellular mechanisms controlled by the multifunctional signaling molecule RA.

Male contraception

Although female contraceptives are very effective at preventing unintended pregnancy, some women can not use them because of health conditions or side-effects, leaving some couples without effective contraceptive options. In addition, many men wish to take active responsibility for family planning. Thus, there is a great need for male contraceptives to prevent unintended pregnancies, of which 80-90 million occur annually. At present, effective male contraceptive options are condoms and vasectomy, which are not ideal for all men. Therefore, efforts are under way to develop novel male contraceptives. This paper briefly reviews the advantages and disadvantages of condoms and vasectomies and then discusses the research directed toward development of novel methods of male contraception.

Vitamin A prevents round spermatid nuclear damage and promotes the production of motile sperm during in vitro maturation of vitrified pre-pubertal mouse testicular tissue

STUDY QUESTION

Does vitamin A (retinol, Rol) prevent round spermatid nuclear damage and increase the production of motile sperm during in vitro maturation of vitrified pre-pubertal mouse testicular tissue?

SUMMARY ANSWER

The supplementation of an in vitro culture of ~0.75 mm³ testicular explants from pre-pubertal mice with Rol enhances spermatogenesis progression during the first spermatogenic wave.

WHAT IS KNOWN ALREADY

The production of functional spermatozoa in vitro has only been achieved in the mouse model and remains a rare event. Establishing an efficient culture medium for vitrified pre-pubertal testicular tissue is now a crucial step to improve the spermatic yield obtained in vitro. The role of Rol in promoting the differentiation of spermatogonia and their entry into meiosis is well established; however, it has been postulated that Rol is also required to support their full development into elongated spermatids.

STUDY DESIGN, SIZE, DURATION

A total of 60 testes from 6.5 days post-partum (dpp) mice were vitrified/warmed, cut into fragments and cultured for 30 days: 20 testes were used for light microscopy and histological analyses, 20 testes for DNA fragmentation assessment in round spermatids and 20 testes for induced sperm motility assessment. Overall, 16 testes of 6.5 dpp were used as in vitro fresh tissue controls and 12 testes of 36.5 dpp mice as in vivo controls. Testes were vitrified with the optimal solid surface vitrification procedure and cultured with an in vitro organ culture system until Day 30 (D30). Histological analysis, cell death, degenerating round spermatids, DNA fragmentation in round spermatids and induced sperm motility were assessed. Testosterone levels were measured in media throughout the culture by radioimmunoassay.

MAIN RESULTS AND THE ROLE OF CHANCE

At D30, better tissue development together with higher differentiation of spermatogonial stem cells, and higher global cell division ability were observed for vitrified/warmed testicular fragments of ~0.75 mm³ with a culture medium supplemented with Rol compared to controls. During in vitro culture of vitrified pre-pubertal testicular tissue, Rol enhanced and maintained the entry of spermatogonia into meiosis and promoted a higher spermatic yield. Furthermore, decreased round spermatid nuclear alterations and DNA damage combined with induced sperm motility comparable to in vivo highlight the crucial role of Rol in the progression of spermatogenesis during the first wave.

LIMITATIONS, REASONS FOR CAUTION

Despite our promising results, the culture media will have to be further improved and adapted within the context of a human application.

WIDER IMPLICATIONS OF THE FINDINGS

The results have potential implications for the handling of human pre-pubertal testicular tissues cryopreserved for fertility preservation. However, because some alterations in round spermatids persist after in vitro culture with Rol, the procedure needs to be optimized before human application, bearing in mind that the murine and human spermatogenic processes differ in many respects.

LARGE SCALE DATA

None.

STUDY FUNDING AND COMPETING INTERESTS

This study was supported by a Ph.D. grant from the Normandy University and a financial support from 'la Ligue nationale contre le cancer' (both awarded to L.D.), funding from Rouen University Hospital, Institute for Research and Innovation in Biomedicine (IRIB) and Agence de la Biomédecine. The authors declare that there is no conflict of interest.

Analysis of the chemical toxicity effects using the enrichment of Gene Ontology terms and KEGG pathways

BACKGROUND

Chemical toxicity is one of the major barriers for designing and detecting new chemical entities during drug discovery. Unexpected toxicity of an approved drug may lead to withdrawal from the market and significant loss of the associated costs. Better understanding of the mechanisms underlying various toxicity effects can help eliminate unqualified candidate drugs in early stages, allowing researchers to focus their attention on other more viable candidates.

METHODS

In this study, we aimed to understand the mechanisms underlying several toxicity effects using Gene Ontology (GO) terms and KEGG pathways. GO term and KEGG pathway enrichment theories were adopted to encode each chemical, and the minimum redundancy maximum relevance (mRMR) was used to analyze the GO terms and the KEGG pathways. Based on the feature list obtained by the mRMR method, the most related GO terms and KEGG pathways were extracted.

RESULTS

Some important GO terms and KEGG pathways were uncovered, which were concluded to be significant for determining chemical toxicity effects.

CONCLUSIONS

Several GO terms and KEGG pathways are highly related to all investigated toxicity effects, while some are specific to a certain toxicity effect.

GENERAL SIGNIFICANCE

The findings in this study have the potential to further our understanding of different chemical toxicity mechanisms and to assist scientists in developing new chemical toxicity prediction algorithms. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

Kinetic characterization and regulation of the human retinaldehyde dehydrogenase 2 enzyme during production of retinoic acid

Retinoic acid (RA) is an important regulator of embryogenesis and tissue homoeostasis. Perturbation of RA signalling causes developmental disorders, osteoarthritis, schizophrenia and several types of tumours. RA is produced by oxidation of retinaldehyde from vitamin A. The main enzyme producing RA in the early embryo is retinaldehyde dehydrogenase 2 (RALDH2, ALDH1A2). In the present study we describe in depth the kinetic properties and regulation of the human RALDH2 (hRALDH2) enzyme. We show that this enzyme produces RA using in vivo and in vitro assays. We studied the naturally occurring all-trans-, 9-cis- and 13-cis-retinaldehyde isomers as substrates of hRALDH2. Based on the values measured for the Michaelis-Menten constant Km and the maximal rate Vmax, in vitro hRALDH2 displays the same catalytic efficiency for their oxidation. We characterized two known inhibitors of the vertebrate RALDH2 and determined their kinetic parameters on hRALDH2. In addition, RA was studied as a possible inhibitor of hRALDH2 and a regulator of its activity. We show that hRALDH2 is not inhibited by its oxidation product, all-trans-RA, suggesting the absence of a negative feedback regulatory loop. Expression of the Raldh2 gene is known to be regulated by RA itself, suggesting that the main regulation of the hRALDH2 activity level is transcriptional.