F5-peptide induces aspermatogenesis by disrupting organization of actin- and microtubule-based cytoskeletons in the testis

The blood-testis barrier disruption is a prerequisite for toxicant-induced peritubular macrophage increases in the testis of peripubertal rats

Peritubular macrophages (PTMφ) are predominantly localized near spermatogonial stem cells in the testis. We previously revealed that exposure of peripubertal male Fischer rats to mono-(2-ethylhexyl) phthalate (MEHP) leads to increased PTMφs in the testis. The mechanisms that trigger increases in PTMφs in the testis are poorly understood. However, MEHP exposure is known to both induce spermatocyte apoptosis and to perturb the blood-testis barrier (BTB). This study aims to elucidate the association between the disruption of BTB and the increases of PTMφs in the testis by comparing the effects observed with MEHP to 2 other testicular toxicants with variable effects on the BTB and subtype of germ cell undergoing apoptosis. Methoxyacetic acid (MAA) acts directly on spermatocytes and does not affect BTB function, whereas cadmium chloride (CdCl2) induces profound injury to BTB. The results indicated that MAA exposure significantly increased spermatocyte apoptosis, whereas no significant changes in the numbers of PTMφs in the testis occurred. In contrast, CdCl2 exposure disrupted BTB function and increased the abundance of PTMφs in the testis. To further investigate whether MEHP-induced changes in BTB integrity accounted for the increase in PTMφs, a plasmid for LG3/4/5, the functional component of laminin-alpha 2, was overexpressed in the testis to stabilize BTB integrity before MEHP exposure. The results showed that LG3/4/5 overexpression substantially reduced the ability of MEHP to compromise BTB integrity and prevented the increase in PTMφ numbers after MEHP exposure. These results indicate that BTB disruption is necessary to increase PTMφs in the testis induced by toxicants.

Blood-testis barrier: a review on regulators in maintaining cell junction integrity between Sertoli cells

The blood-testis barrier (BTB) is formed adjacent to the seminiferous basement membrane. It is a distinct ultrastructure, partitioning testicular seminiferous epithelium into apical (adluminal) and basal compartments. It plays a vital role in developing and maturing spermatocytes into spermatozoa via reorganizing its structure. This enables the transportation of preleptotene spermatocytes across the BTB, from basal to adluminal compartments in the seminiferous tubules. Several bioactive peptides and biomolecules secreted by testicular cells regulate the BTB function and support spermatogenesis. These peptides activate various downstream signaling proteins and can also be the target themself, which could improve the diffusion of drugs across the BTB. The gap junction (GJ) and its coexisting junctions at the BTB maintain the immunological barrier integrity and can be the "gateway" during spermatocyte transition. These junctions are the possible route for toxicant entry, causing male reproductive dysfunction. Herein, we summarize the detailed mechanism of all the regulators playing an essential role in the maintenance of the BTB, which will help researchers to understand and find targets for drug delivery inside the testis.

Autophagy regulation and protein kinase activity of PIK3C3 controls sertoli cell polarity through its negative regulation on SCIN (scinderin)

Sertoli cells are highly polarized testicular cells that provide a nurturing environment for germ cell development and maturation during spermatogenesis. The class III phosphatidylinositol 3-kinase (PtdIns3K) plays core roles in macroautophagy in various cell types; however, its role in Sertoli cells remains unclear. Here, we generated a mouse line in which the gene encoding the catalytic subunit, Pik3c3, was specifically deleted in Sertoli cells (cKO) and found that after one round of normal spermatogenesis, the cKO mice quickly became infertile and showed disruption of Sertoli cell polarity and impaired spermiogenesis. Subsequent proteomics and phosphoproteomics analyses enriched the F-actin cytoskeleton network involved in the disorganized Sertoli-cell structure in cKO testis which we identified a significant increase of the F-actin negative regulator SCIN (scinderin) and the reduced phosphorylation of HDAC6, an α-tubulin deacetylase. Our results further demonstrated that the accumulation of SCIN in cKO Sertoli cells caused the disorder and disassembly of the F-actin cytoskeleton, which was related to the failure of SCIN degradation through the autophagy-lysosome pathway. Additionally, we found that the phosphorylation of HDAC6 at site S59 by PIK3C3 was essential for its degradation through the ubiquitin-proteasome pathway. As a result, the HDAC6 that accumulated in cKO Sertoli cells deacetylated SCIN at site K189 and led to a disorganized F-actin cytoskeleton. Taken together, our findings elucidate a new mechanism for PIK3C3 in maintaining the polarity of Sertoli cells, in which both its autophagy regulation or protein kinase activities are required for the stabilization of the actin cytoskeleton.Abbreviations: ACTB: actin, beta; AR: androgen receptor; ATG14: autophagy related 14; BafA1: bafilomycin A1; BECN1: beclin 1, autophagy related; BTB: blood-testis barrier; CASP3: caspase 3; CDC42: cell division cycle 42; CDH2: cadherin 2; CHX: cycloheximide; CTNNA1: catenin (cadherin associated protein), alpha 1; CYP11A1: cytochrome P450, family 11, subfamily A, polypeptide 1; EBSS: Earle's balanced salt solution; ES: ectoplasmic specialization; FITC: fluorescein isothiocyanate; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GCNA: germ cell nuclear acidic protein; GJA1: gap junction protein, alpha 1; H2AX: H2A.X variant histone; HDAC6: histone deacetylase 6; KIT: KIT proto-oncogene, receptor tyrosine kinase; LAMP1: lysosomal associated membrane protein 1; MAP3K5: mitogen-activated protein kinase kinase kinase 5; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; OCLN: occludin; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; PIK3R4: phosphoinositide-3-kinase regulatory subunit 4; PNA: arachis hypogaea lectin; RAC1: Rac family small GTPase 1; SCIN: scinderin; SQSTM1/p62: sequestosome 1; SSC: spermatogonia stem cell; STK11: serine/threonine kinase 11; TJP1: tight junction protein 1; TubA: tubastatin A; TUBB3: tubulin beta 3 class III; TUNEL: TdT-mediated dUTP nick-end labeling; UB: ubiquitin; UVRAG: UV radiation resistance associated gene; VIM: vimentin; WT1: WT1 transcription factor; ZBTB16: zinc finger and BTB domain containing 16.

Deoxynivalenol Induces Blood-Testis Barrier Dysfunction through Disrupting p38 Signaling Pathway-Mediated Tight Junction Protein Expression and Distribution in Mice

Deoxynivalenol (DON) is widely present in cereals and processed grains. It can disrupt the blood-testicular barrier (BTB), leading to sterility in males; however, the mechanism is unknown. In this study, 30 Kunming mice and TM4 cells were exposed to 0 or 4.8 mg/kg (28 d) and 0-2.4 μM (24 h) of DON, respectively. Histopathological findings showed that DON increased BTB permeability in mice, leading to tight junction (TJ) structural damage. Immunofluorescence results indicated that DON disrupted the localization of zonula occludens (ZO)-1. The results of protein and mRNA expression showed that the expression of ZO-1, occludin, and claudin-11 was reduced, and that the p38/GSK-3β/snail and p38/ATF-2/MLCK signaling pathways were activated in mouse testes and TM4 cells. Pretreatment with the p38 inhibitor SB203580 maintained TJ integrity in TM4 cells after exposure to DON. Thus, DON induced BTB dysfunction in mice by disrupting p38 pathway-mediated TJ expression and distribution.

Embelin alleviates weaned piglets intestinal inflammation and barrier dysfunction via PCAF/NF-κB signaling pathway in intestinal epithelial cells

BACKGROUND

Intestinal barrier plays key roles in maintaining intestinal homeostasis. Inflammation damage can severely destroy the intestinal integrity of mammals. This study was conducted to investigate the protective effects of embelin and its molecular mechanisms on intestinal inflammation in a porcine model. One hundred sixty 21-day-old castrated weaned pigs (Duroc × Landrace × Yorkshire, average initial body weight was 7.05 ± 0.28 kg, equal numbers of castrated males and females) were allotted to four groups and fed with a basal diet or a basal diet containing 200, 400, or 600 mg embelin/kg for 28 d. The growth performance, intestinal inflammatory cytokines, morphology of jejunum and ileum, tight junctions in the intestinal mucosa of piglets were tested. IPEC-1 cells with overexpression of P300/CBP associating factor (PCAF) were treated with embelin, the activity of PCAF and acetylation of nuclear factor-κB (NF-κB) were analyzed to determine the effect of embelin on PCAF/NF-κB pathway in vitro.

RESULTS

The results showed that embelin decreased (P < 0.05) serum D-lactate and diamine oxidase (DAO) levels, and enhanced the expression of ZO-1, occludin and claudin-1 protein in jejunum and ileum. Moreover, the expression levels of critical inflammation molecules (interleukin-1β, interleukin-6, tumor necrosis factor-α, and NF-κB) were down-regulated (P < 0.05) by embelin in jejunal and ileal mucosa. Meanwhile, the activity of PCAF were down-regulated (P < 0.05) by embelin. Importantly, transfection of PCAF siRNAs to IPEC-1 cell decreased NF-κB activities; embelin treatment downregulated (P < 0.05) the acetylation and activities of NF-κB by 31.7%-74.6% in IPEC-1 cells with overexpression of PCAF.

CONCLUSIONS

These results suggested that embelin ameliorates intestinal inflammation in weaned pigs, which might be mediated by suppressing the PCAF/NF-κB signaling pathway.

Drug transport across the blood-testis barrier

The blood-testis barrier transfers nutrients to spermatogenic tubules to ensure the normal physiological function of the testes. It also restricts the "entry and exit" of biological macromolecules in the testicular lumen and provides a unique microenvironment for spermatogenesis. This makes the testes a safe place for some viruses and tumors, as immune factors cannot function and drugs fail to reach therapeutic concentrations in the testes. This review aimed to describe the factors regulating the structure and physiological function of the blood-testis barrier. By understanding therapeutic mechanisms of action, drugs can be developed to function in the testicles.

HIV-1 Establishes a Sanctuary Site in the Testis by Permeating the BTB Through Changes in Cytoskeletal Organization

Studies suggest that HIV-1 invades the testis through initial permeation of the blood-testis barrier (BTB). The selectivity of the BTB to antiretroviral drugs makes this site a sanctuary for the virus. Little is known about how HIV-1 crosses the BTB and invades the testis. Herein, we used 2 approaches to examine the underlying mechanism(s) by which HIV-1 permeates the BTB and gains entry into the seminiferous epithelium. First, we examined if recombinant Tat protein was capable of perturbing the BTB and making the barrier leaky, using the primary rat Sertoli cell in vitro model that mimics the BTB in vivo. Second, we used HIV-1-infected Sup-T1 cells to investigate the activity of HIV-1 infection on cocultured Sertoli cells. Using both approaches, we found that the Sertoli cell tight junction permeability barrier was considerably perturbed and that HIV-1 effectively permeates the BTB by inducing actin-, microtubule-, vimentin-, and septin-based cytoskeletal changes in Sertoli cells. These studies suggest that HIV-1 directly perturbs BTB function, potentially through the activity of the Tat protein.

Busulfan impairs blood-testis barrier and spermatogenesis by increasing noncollagenous 1 domain peptide via matrix metalloproteinase 9

BACKGROUNDS

Sterility induced by anti-cancer treatments has caused significant concern, yet the mechanism and treatment exploration are little for male infertility after cancer therapy. Busulfan, the antineoplastic that was widely applied before bone marrow transplantation, was known to induce male reproductive disorder.

OBJECTIVES

To investigate the effect of busulfan on blood-testis barrier function in adult rats and determine whether noncollagenous 1 domain peptide, the biologically active fragment proteolyzed from the collagen α3 chain (IV) by matrix metalloproteinase 9, was involved during this process.

MATERIALS AND METHODS

Adult male rats were treated with one-dose or double-dose of busulfan (10 mg/kg) before euthanized at day 35. Blood-testis barrier integrity assay, HE staining, immunofluorescence, and Western blot were used to validate the effect of busulfan on blood-testis barrier permeability and spermatogenesis. JNJ0966 was applied to specifically inhibit the matrix metalloproteinase 9 activity. The polymerization activity of F-actin/G-actin and microtubule/tubulin in the testis were assessed by using commercial kits.

RESULTS

A noteworthy blood-testis barrier injury and significant up-regulation of matrix metalloproteinase 9 activity and noncollagenous 1 level after a single-dose busulfan (10 mg/kg) treatment in adult rat testis were revealed. The application of JNJ0966 was found to decrease noncollagenous 1 level and rescue the busulfan-induced blood-testis barrier injury including the mis-localization of junction proteins across the seminiferous epithelium, by recovering the organization and polymerization of both F-actin and microtubule. The busulfan-induced spermatogenesis impairment was also improved by JNJ0966.

CONCLUSION

These findings thus demonstrate that the elevation in matrix metalloproteinase 9 and noncollagenous 1 might participate in busulfan-induced blood-testis barrier disruption in adult male rats. As such, busulfan-induced male infertility could possibly be managed through interventions on noncollagenous 1 production.

Role of laminin and collagen chains in human spermatogenesis - Insights from studies in rodents and scRNA-Seq transcriptome profiling

Studies have demonstrated that biologically active fragments are generated from the basement membrane and the Sertoli cell-spermatid adhesion site known as apical ectoplasmic specialization (apical ES, a testis-specific actin-based anchoring junction) in the rat testis. These bioactive fragments or peptides are produced locally across the seminiferous epithelium through proteolytic cleavage of constituent proteins at the basement membrane and the apical ES. Studies have shown that they are being used to modulate and coordinate cellular functions across the seminiferous epithelium during different stages of the epithelial cycle of spermatogenesis. In this review, we briefly summarize recent findings based on studies using rat testes as a study model regarding the role of these bioactive peptides that serve as a local regulatory network to support spermatogenesis. We also used scRNA-Seq transcriptome datasets in the public domain for OA (obstructive azoospermia) and NAO (non-obstructive azoospermia) human testes versus testes from normal men for analysis in this review. It was shown that there are differential expression of different collagen chains and laminin chains in these testes, suggesting the possibility of a similar local regulatory network in the human testis to support spermatogenesis, and the possible disruption of such network in men is associated with OA and/or NOA.

Bioactive fragments of laminin and collagen chains: lesson from the testis

Recent studies have shown that the testis is producing several biologically active peptides, namely the F5- and the NC1-peptides from laminin-γ3 and collagen α3 (IV) chain, respectively, that promotes blood-testis barrier (BTB) remodeling and also elongated spermatid release at spermiation. Also the LG3/4/5 peptide from laminin-α2 chain promotes BTB integrity which is likely being used for the assembly of a 'new' BTB behind preleptotene spermatocytes under transport at the immunological barrier. These findings thus provide a new opportunity for investigators to better understand the biology of spermatogenesis. Herein, we briefly summarize the recent findings and provide a critical update. We also present a hypothetical model which could serve as the framework for studies in the years to come.

A laminin-based local regulatory network in the testis that supports spermatogenesis

In adult rat testes, the basement membrane is structurally constituted by laminin and collagen chains that lay adjacent to the blood-testis barrier (BTB). It plays a crucial scaffolding role to support spermatogenesis. On the other hand, laminin-333 comprised of laminin-α3/ß3/γ3 at the apical ES (ectoplasmic specialization, a testis-specific cell-cell adherens junction at the Sertoli cell-step 8-19 spermatid interface) expressed by spermatids serves as a unique cell adhesion protein that forms an adhesion complex with α6ß1-integrin expressed by Sertoli cells to support spermiogenesis. Emerging evidence has shown that biologically active fragments are derived from basement membrane and apical ES laminin chains through proteolytic cleavage mediated by matrix metalloproteinase 9 (MMP9) and MMP2, respectively. Two of these laminin bioactive fragments: one from the basement membrane laminin-α2 chain called LG3/4/5-peptide, and one from the apical ES laminin-γ3 chain known as F5-peptide, are potent regulators that modify cell adhesion function at the Sertoli-spermatid interface (i.e., apical ES) but also at the Sertoli cell-cell interface designated basal ES at the blood-testis barrier (BTB) with contrasting effects. These findings not only highlight the physiological significance of these bioactive peptides that create a local regulatory network to support spermatogenesis, they also open a unique area of research. For instance, it is likely that several other bioactive peptides remain to be identified. These bioactive peptides including their downstream signaling proteins and cascades should be studied collectively in future investigations to elucidate the underlying mechanism(s) by which they coordinate with each other to maintain spermatogenesis. This is the goal of this review.

mTORC1/rpS6 and p-FAK-Y407 signaling regulate spermatogenesis: Insights from studies of the adjudin pharmaceutical/toxicant model

In rodents and humans, the major cellular events at spermatogenesis include self-renewal of spermatogonial stem cells and undifferentiated spermatogonia via mitosis, commitment of spermatogonia to differentiation and transformation to spermatocytes, meiosis, spermiogenesis, and the release of spermatozoa at spermiation. While details of the morphological changes during these cellular events have been delineated, knowledge gap exists between the morphological changes in the seminiferous epithelium and the underlying molecular mechanism(s) that regulate these cellular events. Even though many of the regulatory proteins and biomolecules that modulate spermatogenesis are known based on studies using genetic models, the underlying regulatory mechanism(s), in particular signaling pathways/proteins, remain unexplored since much of the information regarding the signaling regulation is unknown. Studies in the past decade, however, have unequivocally demonstrated that the testis is using several signaling proteins and/or pathways to regulate multiple cellular events to modulate spermatogenesis. These include mTORC1/rpS6/Akt1/2 and p-FAK-Y407. While selective inhibitors and/or agonists and antagonists are available to examine some of these signaling proteins, their use have limitations due to their specificities and also potential systemic cytotoxicity. On the other hand, the use of genetic models has had profound implications for our understanding of the molecular regulation of spermatogenesis, and these knockout (null) models have also revealed the factors that are critical for spermatogenesis. Nonetheless, additional studies using in vitro and in vivo models are necessary to unravel the signaling pathways involved in regulating seminiferous epithelial cycle. Emerging data from studies, such as the use of the adjudin pharmaceutical/toxicant model, have illustrated that this non-hormonal male contraceptive drug is utilizing specific signaling pathways/proteins to induce specific defects in spermatogenesis, yielding mechanistic insights on the regulation of spermatogenesis. We sought to review these recent data in this article, highlighting an interesting approach that can be considered for future studies.

A local regulatory network in the testis mediated by laminin and collagen fragments that supports spermatogenesis

It is almost five decades since the discovery of the hypothalamic-pituitary-testicular axis. This refers to the hormonal axis that connects the hypothalamus, pituitary gland and testes, which in turn, regulates the production of spermatozoa through spermatogenesis in the seminiferous tubules, and testosterone through steroidogenesis by Leydig cells in the interstitium, of the testes. Emerging evidence has demonstrated the presence of a regulatory network across the seminiferous epithelium utilizing bioactive molecules produced locally at specific domains of the epithelium. Studies have shown that biologically active fragments are produced from structural laminin and collagen chains in the basement membrane. Additionally, bioactive peptides are also produced locally in non-basement membrane laminin chains at the Sertoli-spermatid interface known as apical ectoplasmic specialization (apical ES, a testis-specific actin-based anchoring junction type). These bioactive peptides are derived from structural laminins and/or collagens at the corresponding sites through proteolytic cleavage by matrix metalloproteinases (MMPs). They in turn serve as autocrine and/or paracrine factors to modulate and coordinate cellular events across the epithelium by linking the apical and basal compartments, the apical and basal ES, the blood-testis barrier (BTB), and the basement membrane of the tunica propria. The cellular events supported by these bioactive peptides/fragments include the release of spermatozoa at spermiation, remodeling of the immunological barrier to facilitate the transport of preleptotene spermatocytes across the BTB, and the transport of haploid spermatids across the epithelium to support spermiogenesis. In this review, we critically evaluate these findings. Our goal is to identify research areas that deserve attentions in future years. The proposed research also provides the much needed understanding on the biology of spermatogenesis supported by a local network of regulatory biomolecules.

The Non-hormonal Male Contraceptive Adjudin Exerts its Effects via MAPs and Signaling Proteins mTORC1/rpS6 and FAK-Y407

Adjudin, 1-(2,4-dichlorobenzyl)-1H-indazole-3-carbohydrazide (formerly called AF-2364), is a nonhormonal male contraceptive, since it effectively induces reversible male infertility without perturbing the serum concentrations of follicle stimulating hormone (FSH), testosterone, and inhibin B based on studies in rats and rabbits. Adjudin was shown to exert its effects preferentially by perturbing the testis-specific actin-rich adherens junction (AJ) at the Sertoli-spermatid interface known as apical ectoplasmic specialization (apical ES), thereby effectively inducing spermatid exfoliation. Adjudin did not perturb germ cell development nor germ cell function. Also, it had no effects on Sertoli cell-cell AJ called basal ectoplasmic specialization (basal ES), which, together with tight junction constitute the blood-testis barrier (BTB), unless an acute dose of adjudin was used. Adjudin also did not perturb the population of spermatogonial stem cells nor Sertoli cells in the testis. However, the downstream signaling protein(s) utilized by adjudin to induce transient male infertility remains unexplored. Herein, using adult rats treated with adjudin and monitored changes in the phenotypes across the seminiferous epithelium between 6 and 96 h in parallel with the steady-state protein levels of an array of signaling and cytoskeletal regulatory proteins, recently shown to be involved in apical ES, basal ES and BTB function. It was shown that adjudin exerts its contraceptive effects through changes in microtubule associated proteins (MAPs) and signaling proteins mTORC1/rpS6 and p-FAK-Y407. These findings are important to not only study adjudin-mediated male infertility but also the biology of spermatogenesis.

NC1-Peptide From Collagen α3 (IV) Chains in the Basement Membrane of Testes Regulates Spermatogenesis via p-FAK-Y407

The blood-testis barrier (BTB) in the testis is an important ultrastructure to support spermatogenesis. This blood-tissue barrier undergoes remodeling at late stage VII to early stage IX of the epithelial cycle to support the transport of preleptotene spermatocytes across the BTB to prepare for meiosis I/II at the apical compartment through a mechanism that remains to be delineated. Studies have shown that NC1-peptide-derived collagen α3 (IV) chain in the basement membrane is a bioactive peptide that induces BTB remodeling. It also promotes the release of fully developed spermatids into the tubule lumen. Thus, this endogenously produced peptide coordinates these 2 cellular events across the seminiferous epithelium. Using an NC1-peptide complementary deoxyribonucleic acid (cDNA) construct to transfect adult rat testes for overexpression, NC1-peptide was found to effectively induce germ cell exfoliation and BTB remodeling, which was associated with a surge and activation of p-rpS6, the downstream signaling protein of mTORC1 and the concomitant downregulation of p-FAK-Y407 in the testis. In order to define the functional relationship between p-rpS6 and p-FAK-Y407 signaling to confer the ability of NC1-peptide to regulate testis function, a phosphomimetic (and thus constitutively active) mutant of p-FAK-Y407 (p-FAK-Y407E-MT) was used for its co-transfection, utilizing Sertoli cells cultured in vitro with a functional tight junction (TJ) barrier that mimicked the BTB in vivo. Overexpression of p-FAK-Y407E-MT blocked the effects of NC1-peptide to perturb Sertoli cell BTB function by promoting F-actin and microtubule cytoskeleton function, and downregulated the NC1-peptide-mediated induction of p-rpS6 activation. In brief, NC1-peptide is an important endogenously produced biomolecule that regulates BTB dynamics.

Endogenously produced LG3/4/5-peptide protects testes against toxicant-induced injury

Laminin-α2 chain is one of the major constituent proteins of the basement membrane in the mammalian testis. The laminin-type globular (LG) domains of LG3, 4 and 5 (LG3/4/5, an 80 kDa fragment) can be cleaved from laminin-α2 chain at the C-terminus via the action of matrix metalloproteinase 9 (MMP-9). This LG3/4/5 is a biologically active fragment, capable of modulating the Sertoli cell blood–testis barrier (BTB) function by tightening the barrier both in vitro and in vivo. Overexpression of LG3/4/5 cloned into a mammalian expression vector pCI-neo in Sertoli cells in a Sertoli cell in vitro model with a functional BTB also protected Sertoli cells from cadmium chloride (CdCl₂, an environmental toxicant) mediated cell injury. Importantly, overexpression of LG3/4/5 in the testis in vivo was found to block or rescue cadmium-induced BTB disruption and testis injury. LG3/4/5 was found to exert its BTB and spermatogenesis promoting effects through corrective spatiotemporal expression of actin- and MT-based regulatory proteins by maintaining the cytoskeletons in the testis, illustrating the therapeutic implication of this novel bioactive fragment.

Dysregulation of lncRNA and circRNA Expression in Mouse Testes after Exposure to Triptolide

BACKGROUND

Triptolide has been shown to exert various pharmacological effects on systemic autoimmune diseases and cancers. However, its severe toxicity, especially reproductive toxicity, prevents its widespread clinical use for people with fertility needs. Noncoding RNAs including lncRNAs and circRNAs are novel regulatory molecules that mediate a wide variety of physiological activities; they are crucial for spermatogenesis and their dysregulation might cause male infertility. However, whether they are involved in triptolide-induced reproductive toxicity is completely unknown.

METHODS

After exposure of mice to triptolide, the total RNAs were used to investigate lncRNA/circRNA/mRNA expression profiles by strand-specific RNA sequencing at the transcriptome level to help uncover RNA-related mechanisms in triptolide-induced toxicity.

RESULTS

Triptolide significantly decreased testicular weight, damaged testis and sperm morphology, and reduced sperm motility and density. Remarkable deformities in sperm head and tail were also found in triptolide-exposed mice. At the transcriptome level, the triptolide-treated mice exhibited aberrant expression profiles of lncRNAs/circRNAs/mRNAs. Gene Ontology and pathway analyses revealed that the functions of the differentially expressed lncRNA targets, circRNA cognate genes, and mRNAs were closely linked to many processes involved in spermatogenesis. In addition, some lncRNAs/circRNAs were greatly upregulated or inducibly expressed, implying their potential value as candidate markers for triptolide-induced male reproductive toxicity.

CONCLUSION

This study provides a preliminary database of triptolide-induced transcriptome, promotes understanding of the reproductive toxicity of triptolide, and highlights the need for research on increasing the medical efficacy of triptolide and decreasing its toxicity.

NC1-peptide regulates spermatogenesis through changes in cytoskeletal organization mediated by EB1

During the epithelial cycle of spermatogenesis, different sets of cellular events take place across the seminiferous epithelium in the testis. For instance, remodeling of the blood-testis barrier (BTB) that facilitates the transport of preleptotene spermatocytes across the immunological barrier and the release of sperms at spermiation take place at the opposite ends of the epithelium simultaneously at stage VIII of the epithelial cycle. These cellular events are tightly coordinated via locally produced regulatory biomolecules. Studies have shown that collagen α3 (IV) chains, a major constituent component of the basement membrane, release the non-collagenous (NC) 1 domain, a 28-kDa peptide, designated NC1-peptide, from the C-terminal region, via the action of MMP-9 (matrix metalloproteinase 9). NC1-peptide was found to be capable of inducing BTB remodeling and spermatid release across the epithelium. As such, the NC1-peptide is an endogenously produced biologically active peptide which coordinates these cellular events across the epithelium in stage VIII tubules. Herein, we used an animal model, wherein NC1-peptide cloned into the pCI-neo mammalian expression vector was overexpressed in the testis, to better understanding the molecular mechanism by which NC1-peptide regulated spermatogenic function. It was shown that NC1-peptide induced considerable downregulation on a number of cell polarity and planar cell polarity (PCP) proteins, and studies have shown these polarity and PCP proteins modulate spermatid polarity and adhesion via their effects on microtubule (MT) and F-actin cytoskeletal organization across the epithelium. More important, NC1-peptide exerted its effects by downregulating the expression of microtubule (MT) plus-end tracking protein (+TIP) called EB1 (end-binding protein 1). We cloned the full-length EB1 cDNA for its overexpression in the testis, which was found to block the NC1-peptide-mediated disruptive effects on cytoskeletal organization in Sertoli cell epithelium and pertinent Sertoli cell functions. These findings thus illustrate that NC1-peptide is working in concert with EB1 to support spermatogenesis.

Cdc42 is involved in NC1 peptide-regulated BTB dynamics through actin and microtubule cytoskeletal reorganization

Noncollagenous domain 1 (NC1)-peptide is a biologically active peptide derived from the C-terminal region of collagen α3(IV) chain, a structural constituent protein at the basement membrane in the rat testis, likely via proteolytic cleavage of matrix metalloproteinase 9. Studies have shown that this NC1 peptide regulates testis function by inducing Sertoli cell blood-testis barrier (BTB) remodeling and is also capable of inducing elongate spermatid exfoliation through its disruptive effects on the organization of actin- and microtubule (MT)-based cytoskeletons at these cell adhesion sites. However, the underlying molecular mechanism remains unknown. NC1 peptide was found to exert its biologic effects through an activation of small GTPase cell division control protein 42 homolog (Cdc42) because cooverexpression of the dominant negative mutant of Cdc42 [namely, Cdc42-T17N (via a single mutation of amino acid residue 17 from the N terminus from Thr to Asn by site-directed mutagenesis, making it constitutively inactive)] and NC1 peptide was able to block the NC1 peptide-induced Sertoli cell tight junction-permeability barrier disruption. Their cooverexpression also blocked the NC1 peptide-induced misdistribution of BTB-associated proteins at the cell-cell interface and also disruptive cytoskeletal organization of F-actin and MTs through changes in spatial expression of the corresponding actin and MT regulatory proteins. Interestingly, NC1 peptide was also found to induce an up-regulation of phosphorylated (p)-ribosomal protein S6 (rpS6) (namely, p-rpS6-S235/S236) and a concomitant down-regulation of p-Akt1/2 (namely, p-Akt1-S473 and p-Akt2-S474), but these changes could not be blocked by overexpression of Cdc42-T17N. More importantly, NC1 peptide-induced Cdc42 activation was effectively blocked by treatment of Sertoli cell epithelium with a p-Akt1/2 activator SC79, which is also capable of blocking NC1 peptide-induced down-regulation of p-Akt1-S473 and p-Akt2/S474, but not p-rpS6-S235/S236 up-regulation. In summary, these findings illustrate that Cdc42 is working downstream of the mammalian target of rapamycin complex 1/rpS6/Akt1/2 signaling pathway to support NC1 peptide-mediated effects on Sertoli cell function in the testis using the rat as an animal model.-Su, W., Cheng, C. Y. Cdc42 is involved in NC1 peptide-regulated BTB dynamics through actin and microtubule cytoskeletal reorganization.

Crosstalk between Sertoli and Germ Cells in Male Fertility

Spermatogenesis is supported by intricate crosstalk between Sertoli cells and germ cells including spermatogonia, spermatocytes, haploid spermatids, and spermatozoa, which takes place in the epithelium of seminiferous tubules. Sertoli cells, also known as 'mother' or 'nurse' cells, provide nutrients, paracrine factors, cytokines, and other biomolecules to support germ cell development. Sertoli cells facilitate the generation of several biologically active peptides, which include F5-, noncollagenous 1 (NC1)-, and laminin globular (LG)3/4/5-peptide, to modulate cellular events across the epithelium. Here, we critically evaluate the involvement of these peptides in facilitating crosstalk between Sertoli and germ cells to support spermatogenesis and thus fertility. Modulating or mimicking the activity of F5-, NC1-, and LG3/4/5-peptide could be used to enhance the transport across the blood-testis barrier (BTB) of contraceptive drugs or to treat male infertility.

Regulation of BTB dynamics in spermatogenesis - insights from the adjudin toxicant model

During spermatogenesis, cell organelles and germ cells, most notably haploid spermatids, are transported across the seminiferous epithelium so that fully developed spermatids line-up at the edge of the tubule lumen to undergo spermiation at stage VIII of the cycle. Studies have suggested that the microtubule (MT)-based cytoskeleton is necessary to support these cellular events. However, the regulatory molecule(s) and underlying mechanism(s) remain poorly understood. Herein, we sought to better understand this event by using an adjudin-based animal model. Adult rats were treated with adjudin at low-dose (10 mg/kg b.w.) which by itself had no notable effects on spermatogenesis. Rats were also treated with low-dose adjudin combined with overexpression of two endogenously produced blood-testis barrier (BTB) modifiers, namely rpS6 [ribosomal protein S6, the downstream signaling protein of mammalian target of rapamycin complex 1 (mTORC1)] and F5-peptide (a biological active peptide released from laminin-γ3 chain at the Sertoli-spermatid interface) versus the two BTB modifiers alone. Overexpression of these two BTB modifiers in the testis was shown to enhance delivery of adjudin to the testis, effectively inducing disruptive changes in MT cytoskeletons, causing truncation of MT conferred tracks that led to their collapse across the epithelium. The net result was massive germ cell exfoliation in the tubules, disrupting germ cell transport and cell adhesion across the seminiferous epithelium that led to aspermatogenesis. These changes were the result of disruptive spatial expression of several MT-based regulatory proteins. In summary, MT cytoskeleton supported by the network of MT regulatory proteins is crucial to maintain spermatogenesis.

F5-Peptide and mTORC1/rpS6 Effectively Enhance BTB Transport Function in the Testis-Lesson From the Adjudin Model

During spermatogenesis, the blood-testis barrier (BTB) undergoes cyclic remodeling that is crucial to support the transport of preleptotene spermatocytes across the immunological barrier at stage VIII to IX of the epithelial cycle. Studies have shown that this timely remodeling of the BTB is supported by several endogenously produced barrier modifiers across the seminiferous epithelium, which include the F5-peptide and the ribosomal protein S6 [rpS6; a downstream signaling molecule of the mammalian target of rapamycin complex 1 (mTORC1)] signaling protein. Herein, F5-peptide and a quadruple phosphomimetic (and constitutively active) mutant of rpS6 [i.e., phosphorylated (p-)rpS6-MT] that are capable of inducing reversible immunological barrier remodeling, by making the barrier "leaky" transiently, were used for their overexpression in the testis to induce BTB opening. We sought to examine whether this facilitated the crossing of the nonhormonal male contraceptive adjudin at the BTB when administered by oral gavage, thereby effectively improving its BTB transport to induce germ cell adhesion and aspermatogenesis. Indeed, it was shown that combined overexpression of F5-peptide and p-rpS6-MT and a low dose of adjudin, which by itself had no noticeable effects on spermatogenesis, was capable of perturbing the organization of actin- and microtubule (MT)-based cytoskeletons through changes in the spatial expression of actin- and MT-binding/regulatory proteins to the corresponding cytoskeleton. These findings thus illustrate the possibility of delivering drugs to any target organ behind a blood-tissue barrier by modifying the tight junction permeability barrier using endogenously produced barrier modifiers based on findings from this adjudin animal model.

mTORC1/rpS6 and spermatogenic function in the testis-insights from the adjudin model

mTORC1/rpS6 signaling complex promoted Sertoli blood-testis barrier (BTB) remodeling by perturbing Sertoli cell-cell adhesion site known as the basal ectoplasmic specialization (ES). mTORC1/rpS6 complex also promoted disruption of spermatid adhesion at the Sertoli-spermatid interface called the apical ES. Herein, we performed analyses using the adjudin (a non-hormonal male contraceptive drug under development) model, wherein adjudin was known to perturb apical and basal ES function when used at high dose. Through direct administration of adjudin to the testis, adjudin at doses that failed to perturb BTB integrity per se, overexpression of an rpS6 phosphomimetic (i.e., constitutively active) mutant (i.e., p-rpS6-MT) that modified BTB function considerably potentiated adjudin efficacy. This led to disorderly spatial expression of proteins necessary to maintain the proper cytoskeletal organization of F-actin and microtubules (MTs) across the seminiferous epithelium, leading to germ cell exfoliation and aspermatogenesis. These findings yielded important insights regarding the role of mTORC1/rpS6 signaling complex in regulating BTB homeostasis.

mTORC1/rpS6 signaling complex modifies BTB transport function: an in vivo study using the adjudin model

Studies have shown that the mTORC1/rpS6 signaling cascade regulates Sertoli cell blood-testis barrier (BTB) dynamics. For instance, specific inhibition of mTORC1 by treating Sertoli cells with rapamycin promotes the Sertoli cell barrier, making it "tighter." However, activation of mTORC1 by overexpressing a full-length rpS6 cDNA clone (i.e., rpS6-WT, wild type) in Sertoli cells promotes BTB remodeling, making the barrier "leaky." Also, there is an increase in rpS6 and p-rpS6 (phosphorylated and activated rpS6) expression at the BTB in testes at stages VIII-IX of the epithelial cycle, and it coincides with BTB remodeling to support the transport of preleptotene spermatocytes across the barrier, illustrating that rpS6 is a BTB-modifying signaling protein. Herein, we used a constitutively active, quadruple phosphomimetic mutant of rpS6, namely p-rpS6-MT of p-rpS6-S235E/S236E/S240E/S244E, wherein Ser (S) was converted to Glu (E) at amino acid residues 235, 236, 240, and 244 from the NH2 terminus by site-directed mutagenesis, for its overexpression in rat testes in vivo using the Polyplus in vivo jet-PEI transfection reagent with high transfection efficiency. Overexpression of this p-rpS6-MT was capable of inducing BTB remodeling, making the barrier "leaky." This thus promoted the entry of the nonhormonal male contraceptive adjudin into the adluminal compartment in the seminiferous epithelium to induce germ cell exfoliation. Combined overexpression of p-rpS6-MT with a male contraceptive (e.g., adjudin) potentiated the drug bioavailability by modifying the BTB. This approach thus lowers intrinsic drug toxicity due to a reduced drug dose, further characterizing the biology of BTB transport function.

Planar cell polarity protein Dishevelled 3 (Dvl3) regulates ectoplasmic specialization (ES) dynamics in the testis through changes in cytoskeletal organization

In the mammalian testes, such as in rats, the directional alignment of polarized elongating/elongated spermatids, in particular step 17–19 spermatids, across the plane of seminiferous epithelium resembles planar cell polarity (PCP) found in hair cells of the cochlea. It is obvious that spermatid PCP is necessary to support the simultaneous development of maximal number of elongating/elongated spermatids to sustain the daily production of > 50 million sperm per adult rat. Studies have shown that the testis indeed expresses multiple PCP proteins necessary to support spermatid PCP. Herein, using physiological and biochemical assays, and morphological analysis, and with the technique of RNA interference (RNAi) to knockdown PCP protein Dishevelled (Dvl) 1 (Dvl1), Dvl2, Dvl3, or Dvl1/2/3, Dvl proteins, in particular Dvl3, it was shown that Dvl3 played a crucial role of support Sertoli cell tight junction (TJ)-permeability barrier function through changes in the organization of actin- and microtubule (MT)-based cytoskeletons. More important, an in vivo knockdown of Dvl1/2/3 in the testis, defects of spermatid polarity were remarkably noted across the seminiferous epithelium, concomitant with defects of spermatid adhesion and spermatid transport, leading to considerably defects in spermatogenesis. More important, Dvl1/2/3 triple knockdown in the testis also impeded the organization of actin- and MT-based cytoskeletons owing to disruptive spatial expression of actin- and MT-regulatory proteins. In summary, PCP Dishevelled proteins, in particular, Dvl3 is a regulator of Sertoli cell blood–testis barrier (BTB)  and also spermatid PCP function through its effects on the actin- and MT-based cytoskeletons in Sertoli cells.

F5-peptide enhances the efficacy of the non-hormonal male contraceptive adjudin

OBJECTIVE

The bioavailability of the non-hormonal male contraceptive adjudin is low in rats due to the blood-testis barrier (BTB). This study was designed to examine if F5-peptide, an endogenously produced reversible BTB modifier, could enhance the bioavailability of adjudin to affect spermatogenesis and provide a contraceptive effect in rats while reducing systemic toxicity.

STUDY DESIGN

We overexpressed F5-peptide in adult male rats (n=10 rats; with 3 or 4 rats for each of the three different experiments noted in the three regimens) by intratesticular injection of a mammalian expression vector pCI-neo (pCI-neo/F5-peptide) vs. empty vector alone (pCI-neo/Ctrl) to be followed by treatment with adjudin by oral gavage at a dose of 10 or 20 mg/kg. The status of spermatogenesis was assessed by histological analysis and dual-labeled immunofluorescence analysis on Day 16. To assess fertility, we allowed treated males (n=3-4 rats) to mate with mature female rats (n=3-4) individually, and assessed the number of pups on Days 23, 36 and 82 to assess fertility and reversibility.

RESULTS

All 4 treated rats overexpressed with F5-peptide and low-dose adjudin were infertile by Day 36, and half of these rats were fertile by Day 82, illustrating reversibility. However, overexpression of F5-peptide alone (or low-dose adjudin alone) had no effects on fertility in n=3 rats. These findings were consistent with the histology data that illustrated the BTB modifier F5-peptide promoted the action of adjudin to induce germ cell exfoliation, mediated by changes in cytoskeletal organization of F-actin and microtubules across the epithelium, thereby reducing the systemic toxicity of adjudin.

CONCLUSION

In this proof-of-concept study, it was shown that overexpression of the F5-peptide prior to administration of adjudin to rats at a low (and ineffective dose by itself) was found to induce reversible male infertility.

IMPLICATIONS

Overexpression of F5-peptide, an endogenously produced biomolecule in the testis known to induce BTB remodeling, enhanced the contraceptive effect of adjudin in rats, supporting proof of concept studies of BTB disrupters in men.

Regulation of Blood-Testis Barrier (BTB) Dynamics, Role of Actin-, and Microtubule-Based Cytoskeletons

The blood-testis barrier (BTB) is an important ultrastructure in the testis that supports meiosis and postmeiotic spermatid development since a delay in the establishment of a functional Sertoli cell barrier during postnatal development in rats or mice by 17-20 day postpartum (dpp) would lead to a delay of the first wave of meiosis. Furthermore, irreversible disruption of the BTB by toxicants also induces infertility in rodents. Herein, we summarize recent findings that BTB dynamics (i.e., disassembly, reassembly, and stabilization) are supported by the concerted efforts of the actin- and microtubule (MT)-based cytoskeletons. We focus on the role of two actin nucleation protein complexes, namely, the Arp2/3 (actin-related protein 2/3) complex and formin 1 (or the formin 1/spire 1 complex) known to induce actin nucleation, respectively, by conferring plasticity to actin cytoskeleton. We also focus on the MT plus (+)-end tracking protein (+TIP) EB1 (end-binding protein 1) which is known to confer MT stabilization. Furthermore, we discuss in particular how the interactions of these proteins modulate BTB dynamics during spermatogenesis. These findings also yield a novel hypothetical concept regarding the molecular mechanism that modulates BTB function.

An increase of estrogen receptor α protein level regulates BDE-209-mediated blood-testis barrier disruption during spermatogenesis in F1 mice

Deca-bromodiphenyl ether (BDE-209) regulates various aspects of spermatogenesis and male fertility through its effect on estrogen receptor α (ERα), but the underlying mechanism remains unclear. Because molecular mechanisms such as remodeling of the blood-testis barrier (BTB) play crucial roles in spermatogenesis, we investigated the disruptive effects of ERα agonists on the BTB in spermatogenesis. In this study, 0, 300, and 500 mg/kg/day of BDE-209 were administered to pregnant adult mice by oral gavage from gestation day 7 to postnatal day 21. SerW3 cells were treated with methylpiperidino pyrazole (MPP) for 30 min before being treated with 50 μg/mL of BDE-209. BDE-209 increases ERα in time- and dose-dependent manners and decreases formin 1 and BTB-associated protein in F1 male mice. Furthermore, BDE-209 impairs the structure and function of the BTB. Activation of ERα signaling could disrupt the BTB, leading to spermatogenesis dysfunction. The results identified the role of ERα in BTB disruption during spermatogenesis and suggested that BTB disruption occurs because of exposure to BDE-209, which could potentially affect spermatogenesis. In conclusion, Sertoli cells seem to be the primary target of BDE-209 in the perinatal period, and this period constitutes a critical window of susceptibility to BDE-209. Also, the SerW3 cell model may not be a particularly useful cell model for studying the function of the cytoskeleton.

Dynein 1 supports spermatid transport and spermiation during spermatogenesis in the rat testis

In the mammalian testis, spermatogenesis is dependent on the microtubule (MT)-specific motor proteins, such as dynein 1, that serve as the engine to support germ cell and organelle transport across the seminiferous epithelium at different stages of the epithelial cycle. Yet the underlying molecular mechanism(s) that support this series of cellular events remain unknown. Herein, we used RNAi to knockdown cytoplasmic dynein 1 heavy chain (Dync1h1) and an inhibitor ciliobrevin D to inactivate dynein in Sertoli cells in vitro and the testis in vivo, thereby probing the role of dynein 1 in spermatogenesis. Both treatments were shown to extensively induce disruption of MT organization across Sertoli cells in vitro and the testis in vivo. These changes also perturbed the transport of spermatids and other organelles (such as phagosomes) across the epithelium. These changes thus led to disruption of spermatogenesis. Interestingly, the knockdown of dynein 1 or its inactivation by ciliobrevin D also perturbed gross disruption of F-actin across the Sertoli cells in vitro and the seminiferous epithelium in vivo, illustrating there are cross talks between the two cytoskeletons in the testis. In summary, these findings confirm the role of cytoplasmic dynein 1 to support the transport of spermatids and organelles across the seminiferous epithelium during the epithelial cycle of spermatogenesis.

The organophosphate pesticide methamidophos opens the blood-testis barrier and covalently binds to ZO-2 in mice

Methamidophos (MET) is an organophosphate (OP) pesticide widely used in agriculture in developing countries. MET causes adverse effects in male reproductive function in humans and experimental animals, but the underlying mechanisms remain largely unknown. We explored the effect of MET on mice testes (5 mg/kg/day/4 days), finding that this pesticide opens the blood-testis barrier and perturbs spermatogenesis, generating the appearance of immature germ cells in the epididymis. In the seminiferous tubules, MET treatment changed the level of expression or modified the stage-specific localization of tight junction (TJ) proteins ZO-1, ZO-2, occludin, and claudin-3. In contrast, claudin-11 was barely altered. MET also modified the shape of claudin-11, and ZO-2 at the cell border, from a zigzag to a more linear pattern. In addition, MET diminished the expression of ZO-2 in spermatids present in seminiferous tubules, induced the phosphorylation of ZO-2 and occludin in testes and reduced the interaction between these proteins assessed by co-immunoprecipitation. MET formed covalent bonds with ZO-2 in serine, tyrosine and lysine residues. The covalent modifications formed on ZO-2 at putative phosphorylation sites might interfere with ZO-2 interaction with regulatory molecules and other TJ proteins. MET bonds formed at ZO-2 ubiquitination sites likely interfere with ZO-2 degradation and TJ sealing, based on results obtained in cultured epithelial cells transfected with ZO-2 mutated at a MET target lysine residue. Our results shed light on MET male reproductive toxicity and are important to improve regulations regarding the use of OP pesticides and to protect the health of agricultural workers.

Cell polarity and cytoskeletons-Lesson from the testis

Cell polarity in the adult mammalian testis refers to the polarized alignment of developing spermatids during spermiogenesis and the polarized organization of organelles (e.g., phagosomes, endocytic vesicles, Sertoli cell nuclei, Golgi apparatus) in Sertoli cells and germ cells to support spermatogenesis. Without these distinctive features of cell polarity in the seminiferous epithelium, it is not possible to support the daily production of millions of sperm in the limited space provided by the seminiferous tubules in either rodent or human males through the adulthood. In short, cell polarity provides a novel mean to align spermatids and the supporting organelles (e.g., phagosomes, Golgi apparatus, endocytic vesicles) in a highly organized fashion spatially in the seminiferous epithelium during the epithelial cycle of spermatogenesis. This is analogous to different assembling units in a manufacturing plant such that as developing spermatids move along the "assembly line" conferred by Sertoli cells, different structural/functional components can be added to (or removed from) the developing spermatids during spermiogenesis, so that functional spermatozoa are produced at the end of the assembly line. Herein, we briefly review findings regarding the regulation of cell polarity in the testis with specific emphasis on developing spermatids, supported by an intriguing network of regulatory proteins along a local functional axis. Emerging evidence has suggested that cell cytoskeletons provide the tracks which in turn confer the unique assembly lines in the seminiferous epithelium. We also provide some thought-provoking concepts based on which functional experiments can be designed in future studies.

Vangl2 regulates spermatid planar cell polarity through microtubule (MT)-based cytoskeleton in the rat testis

During spermatogenesis, developing elongating/elongated spermatids are highly polarized cells, displaying unique apico-basal polarity. For instance, the heads of spermatids align perpendicular to the basement membrane with their tails pointing to the tubule lumen. Thus, the maximal number of spermatids are packed within the limited space of the seminiferous epithelium to support spermatogenesis.  Herein, we reported findings that  elongating/elongated spermatids displayed planar cell polarity (PCP) in adult rat testes in which the proximal end of polarized spermatid heads were aligned uniformly across the plane of the seminiferous epithelium based on studies  using confocal microscopy and 3-dimensional (D) reconstruction of the seminiferous tubules.  We also discovered  that spermatid PCP was regulated by PCP protein Vangl2 (Van Gogh-like protein 2) since Vangl2 knockdown by RNAi was found to perturb spermatid PCP. More important, Vangl2 exerted its regulatory effects through changes in the organization of the microtubule (MT)-based cytoskeleton in the seminiferous epithelium. These changes were mediated via the downstream signaling proteins atypical protein kinase C ξ (PKCζ) and MT-associated protein (MAP)/microtubule affinity-regulating kinase 2 (MARK2). These findings thus provide new insights regarding the biology of spermatid PCP during spermiogenesis.

Actin nucleator Spire 1 is a regulator of ectoplasmic specialization in the testis

Germ cell differentiation during the epithelial cycle of spermatogenesis is accompanied by extensive remodeling at the Sertoli cell-cell and Sertoli cell-spermatid interface to accommodate the transport of preleptotene spermatocytes and developing spermatids across the blood-testis barrier (BTB) and the adluminal compartment of the seminiferous epithelium, respectively. The unique cell junction in the testis is the actin-rich ectoplasmic specialization (ES) designated basal ES at the Sertoli cell-cell interface, and the apical ES at the Sertoli-spermatid interface. Since ES dynamics (i.e., disassembly, reassembly and stabilization) are supported by actin microfilaments, which rapidly converts between their bundled and unbundled/branched configuration to confer plasticity to the ES, it is logical to speculate that actin nucleation proteins play a crucial role to ES dynamics. Herein, we reported findings that Spire 1, an actin nucleator known to polymerize actins into long stretches of linear microfilaments in cells, is an important regulator of ES dynamics. Its knockdown by RNAi in Sertoli cells cultured in vitro was found to impede the Sertoli cell tight junction (TJ)-permeability barrier through changes in the organization of F-actin across Sertoli cell cytosol. Unexpectedly, Spire 1 knockdown also perturbed microtubule (MT) organization in Sertoli cells cultured in vitro. Biochemical studies using cultured Sertoli cells and specific F-actin vs. MT polymerization assays supported the notion that a transient loss of Spire 1 by RNAi disrupted Sertoli cell actin and MT polymerization and bundling activities. These findings in vitro were reproduced in studies in vivo by RNAi using Spire 1-specific siRNA duplexes to transfect testes with Polyplus in vivo-jetPEI as a transfection medium with high transfection efficiency. Spire 1 knockdown in the testis led to gross disruption of F-actin and MT organization across the seminiferous epithelium, thereby impeding the transport of spermatids and phagosomes across the epithelium and perturbing spermatogenesis. In summary, Spire 1 is an ES regulator to support germ cell development during spermatogenesis.

mTORC1/rpS6 regulates blood-testis barrier dynamics and spermatogenetic function in the testis in vivo

The blood-testis barrier (BTB), conferred by Sertoli cells in the mammalian testis, is an important ultrastructure that supports spermatogenesis. Studies using animal models have shown that a disruption of the BTB leads to meiotic arrest, causing defects in spermatogenesis and male infertility. To better understand the regulation of BTB dynamics, we report findings herein to understand the role of ribosomal protein S6 (rpS6), a downstream signaling protein of mammalian target of rapamycin complex 1 (mTORC1), in promoting BTB disruption in the testis in vivo, making the barrier "leaky." Overexpression of wild-type rpS6 (rpS6-WT, the full-length cDNA cloned into the mammalian expression vector pCI-neo) and a constitutively active quadruple phosphomimetic mutant cloned into pCI-neo (p-rpS6-MT) vs. control (empty pCI-neo vector) was achieved by transfecting adult rat testes with the corresponding plasmid DNA using a Polyplus in vivo-jetPEI transfection reagent. On the basis of an in vivo functional BTB integrity assay, p-rpS6-MT was found to induce BTB disruption better than rpS6-WT did (and no effects in empty vector control), leading to defects in spermatogenesis, including loss of spermatid polarity and failure in the transport of cells (e.g., spermatids) and organelles (e.g., phagosomes), to be followed by germ exfoliation. More important, rpS6-WT and p-rpS6-MT exert their disruptive effects through changes in the organization of actin- and microtubule (MT)-based cytoskeletons, which are mediated by changes in the spatiotemporal expression of actin- and MT-based binding and regulatory proteins. In short, mTORC1/rpS6 signaling complex is a regulator of spermatogenesis and BTB by modulating the organization of the actin- and MT-based cytoskeletons.

Cell polarity, cell adhesion, and spermatogenesis: role of cytoskeletons

In the rat testis, studies have shown that cell polarity, in particular spermatid polarity, to support spermatogenesis is conferred by the coordinated efforts of the Par-, Crumbs-, and Scribble-based polarity complexes in the seminiferous epithelium. Furthermore, planar cell polarity (PCP) is conferred by PCP proteins such as Van Gogh-like 2 (Vangl2) in the testis. On the other hand, cell junctions at the Sertoli cell–spermatid (steps 8–19) interface are exclusively supported by adhesion protein complexes (for example, α6β1-integrin-laminin-α3,β3,γ3 and nectin-3-afadin) at the actin-rich apical ectoplasmic specialization (ES) since the apical ES is the only anchoring device in step 8–19 spermatids. For cell junctions at the Sertoli cell–cell interface, they are supported by adhesion complexes at the actin-based basal ES (for example, N-cadherin-β-catenin and nectin-2-afadin), tight junction (occludin-ZO-1 and claudin 11-ZO-1), and gap junction (connexin 43-plakophilin-2) and also intermediate filament-based desmosome (for example, desmoglein-2-desmocollin-2). In short, the testis-specific actin-rich anchoring device known as ES is crucial to support spermatid and Sertoli cell adhesion. Accumulating evidence has shown that the Par-, Crumbs-, and Scribble-based polarity complexes and the PCP Vangl2 are working in concert with actin- or microtubule-based cytoskeletons (or both) and these polarity (or PCP) protein complexes exert their effects through changes in the organization of the cytoskeletal elements across the seminiferous epithelium of adult rat testes. As such, there is an intimate relationship between cell polarity, cell adhesion, and cytoskeletal function in the testis. Herein, we critically evaluate these recent findings based on studies on different animal models. We also suggest some crucial future studies to be performed.

Regulation of spermatogenesis by a local functional axis in the testis: role of the basement membrane-derived noncollagenous 1 domain peptide

Spermatogenesis takes place in the epithelium of the seminiferous tubules of the testes, producing millions of spermatozoa per day in an adult male in rodents and humans. Thus, multiple cellular events that are regulated by an array of signaling molecules and pathways are tightly coordinated to support spermatogenesis. Here, we report findings of a local regulatory axis between the basement membrane (BM), the blood-testis barrier (BTB), and the apical ectoplasmic specialization (apical ES; a testis-specific, actin-rich adherens junction at the Sertoli cell-spermatid interface) to coordinate cellular events across the seminiferous epithelium during the epithelial cycle. In short, a biologically active fragment, noncollagenous 1 (NC1) domain that is derived from collagen chains in the BM, was found to modulate cell junction dynamics at the BTB and apical ES. NC1 domain from the collagen α3(IV) chain was cloned into a mammalian expression vector, pCI-neo, with and without a collagen signal peptide. We also prepared a specific Ab against the purified recombinant NC1 domain peptide. These reagents were used to examine whether overexpression of NC1 domain with high transfection efficacy would perturb spermatogenesis, in particular, spermatid adhesion (i.e., inducing apical ES degeneration) and BTB function (i.e., basal ES and tight junction disruption, making the barrier leaky), in the testis in vivo We report our findings that NC1 domain derived from collagen α3(IV) chain-a major structural component of the BM-was capable of inducing BTB remodeling, making the BTB leaky in studies in vivo Furthermore, NC1 domain peptide was transported across the epithelium via a microtubule-dependent mechanism and is capable of inducing apical ES degeneration, which leads to germ cell exfoliation from the seminiferous epithelium. Of more importance, we show that NC1 domain peptide exerted its regulatory effect by disorganizing actin microfilaments and microtubules in Sertoli cells so that they failed to support cell adhesion and transport of germ cells and organelles (e.g., residual bodies, phagosomes) across the seminiferous epithelium. This local regulatory axis between the BM, BTB, and the apical ES thus coordinates cellular events that take place across the seminiferous epithelium during the epithelial cycle of spermatogenesis.-Chen, H., Mruk, D. D., Lee, W. M., Cheng, C. Y. Regulation of spermatogenesis by a local functional axis in the testis: role of the basement membrane-derived noncollagenous 1 domain peptide.

Signaling pathways regulating blood-tissue barriers - Lesson from the testis

Signaling pathways that regulate blood-tissue barriers are important for studying the biology of various blood-tissue barriers. This information, if deciphered and better understood, will provide better therapeutic management of diseases particularly in organs that are sealed by the corresponding blood-tissue barriers from systemic circulation, such as the brain and the testis. These barriers block the access of antibiotics and/or chemotherapeutical agents across the corresponding barriers. Studies in the last decade using the blood-testis barrier (BTB) in rats have demonstrated the presence of several signaling pathways that are crucial to modulate BTB function. Herein, we critically evaluate these findings and provide hypothetical models regarding the underlying mechanisms by which these signaling molecules/pathways modulate BTB dynamics. This information should be carefully evaluated to examine their applicability in other tissue barriers which shall benefit future functional studies in the field. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.

Perfluorooctanesulfonate (PFOS)-induced Sertoli cell injury through a disruption of F-actin and microtubule organization is mediated by Akt1/2

PFOS (perfluorooctanesulfonate, or perfluorooctane sulfonic acid) is an anthropogenic fluorosurfactant widely used in consumer products. While its use in Europe, Canada and the U.S. has been banned due to its human toxicity, it continues to be used in China and other developing countries as a global pollutant. Herein, using an in vitro model of Sertoli cell blood-testis barrier (BTB), PFOS was found to induce Sertoli cell injury by perturbing actin cytoskeleton through changes in the spatial expression of actin regulatory proteins. Specifically, PFOS caused mis-localization of Arp3 (actin-related protein 3, a branched actin polymerization protein) and palladin (an actin bundling protein). These disruptive changes thus led to a dis-organization of F-actin across Sertoli cell cytosol, causing truncation of actin microfilament, thereby failing to support the Sertoli cell morphology and adhesion protein complexes (e.g., occludin-ZO-1, CAR-ZO-1, and N-cadherin-ß-catenin), through a down-regulation of p-Akt1-S473 and p-Akt2-S474. The use of SC79, an Akt1/2 activator, was found to block the PFOS-induced Sertoli cell injury by rescuing the PFOS-induced F-actin dis-organization. These findings thus illustrate PFOS exerts its disruptive effects on Sertoli cell function downstream through Akt1/2. As such, PFOS-induced male reproductive dysfunction can possibly be managed through an intervention on Akt1/2 expression.

Basement Membrane Laminin α2 Regulation of BTB Dynamics via Its Effects on F-Actin and Microtubule Cytoskeletons Is Mediated Through mTORC1 Signaling

A local axis connects the apical ectoplasmic specialization (ES) at the Sertoli-spermatid interface, the basal ES at the blood-testis barrier (BTB), and the basement membrane across the seminiferous epithelium functionally in rat testes. As such, cellular events that take place simultaneously across the epithelium such as spermiation and BTB remodeling that occur at the apical ES and the basal ES, respectively, at stage VIII of the cycle are coordinated. Herein, laminin α2, a structural component of the basement membrane, was found to regulate BTB dynamics. Sertoli cells were cultured in vitro to allow the establishment of a tight junction (TJ) barrier that mimicked the BTB in vivo. Knockdown of laminin α2 by transfecting Sertoli cells with laminin α2-specific short hairpin RNA vs the nontargeting negative control was shown to perturb the Sertoli cell TJ barrier, illustrating laminin α2 was involved in regulating BTB dynamics. This regulatory effect was mediated through mammalian target of rapamycin complex 1 (mTORC1) signaling because the two mTORC1 downstream signaling molecules ribosomal protein S6 and Akt1/2 were activated and inactivated, respectively, consistent with earlier findings that mTORC1 is involved in promoting BTB remodeling. Also, laminin α2 knockdown induced F-actin and microtubule (MT) disorganization through changes in the spatial expression of F-actin regulators actin-related protein 3 and epidermal growth factor receptor pathway substrate 8 vs end-binding protein 1 (a MT plus-end tracking protein, +TIP). These laminin α2 knockdown-mediated effects on F-actin and MT organization was blocked by exposing Sertoli cells to rapamycin, an inhibitor of mTORC1 signaling, and also SC79, an activator of Akt. In summary, laminin α2-mediated regulation on Sertoli cell BTB dynamics is through mTORC1 signaling.

Regulation of the blood-testis barrier by a local axis in the testis: role of laminin α2 in the basement membrane

Laminin α2 is one of the constituent components of the basement membrane (BM) in adult rat testes. Earlier studies that used a mouse genetic model have shown that a deletion of laminin α2 impedes male fertility by disrupting ectoplasmic specialization (ES; a testis-specific, actin-rich anchoring junction) function along the length of Sertoli cell in the testis. This includes ES at the Sertoli cell-elongating/elongated spermatid interface, which is known as apical ES and possibly the Sertoli-Sertoli cell interface, known as basal ES, at the blood-testis barrier (BTB). Studies have also illustrated that there is a local regulatory axis that functionally links cellular events of spermiation that occur near the luminal edge of tubule lumen at the apical ES and the basal ES/BTB remodeling near the BM at opposite ends of the seminiferous epithelium during the epithelial cycle, known as the apical ES-BTB-BM axis. However, the precise role of BM in this axis remains unknown. Here, we show that laminin α2 in the BM serves as the crucial regulator in this axis as laminin α2, likely its 80-kDa fragment from the C terminus, was found to be transported across the seminiferous epithelium at stages VIII-IX of the epithelial cycle, from the BM to the luminal edge of the tubule, possibly being used to modulate apical ES restructuring at these stages. Of more importance, a knockdown of laminin α2 in Sertoli cells was shown to induce the Sertoli cell tight junction permeability barrier disruption via changes in localization of adhesion proteins at the tight junction and basal ES at the Sertoli cell BTB. These changes were found to be mediated by a disruption of F-actin organization that was induced by changes in the spatiotemporal expression of actin binding/regulatory proteins. Furthermore, laminin α2 knockdown also perturbed microtubule (MT) organization by considerable down-regulation of MT polymerization via changes in the spatiotemporal expression of EB1 (end-binding protein 1), a +TIP (MT plus-end tracking protein). In short, laminin α2 in the BM seems to play a crucial role in the BTB-BM axis by modulating BTB dynamics during spermatogenesis.-Gao, Y., Mruk, D., Chen, H., Lui, W.-Y., Lee, W. M., Cheng, C. Y. Regulation of the blood-testis barrier by a local axis in the testis: role of laminin α2 in the basement membrane.

Transport of germ cells across the seminiferous epithelium during spermatogenesis-the involvement of both actin- and microtubule-based cytoskeletons

The transport of germ cells from the base of the seminiferous epithelium toward the luminal edge of the tubule lumen in the adluminal compartment during the epithelial cycle is an essential cellular event to support spermatogenesis. Thus, fully developed elongated spermatids (i.e., spermatozoa) can be released at spermiation in late stage VIII in rodents versus late stage II in humans. Earlier studies to examine the molecular mechanism(s) that support germ cell transport, most notably the transport of preleptotene spermatocytes across the blood-testis barrier (BTB), and the transport of elongating spermatids across the adluminal compartment during spermiogenesis, is focused on the adhesion protein complexes at the cell-cell interface. It is generally accepted that cell junctions at the Sertoli cell-cell interface at the BTB, including the actin-based tight junction (TJ), basal ectoplasmic specialization (basal ES, a testis-specific adherens junction) and gap junction (GJ), as well as the intermediate filament-based desmosome undergo constant remodeling to accommodate the transport of preleptotene spermatocytes across the barrier. On the other hand, similar junction dynamics (i.e., disassembly, reassembly and stabilization/maintenance) take place at the Sertoli-spermatid interface. Emerging evidence has shown that junction dynamics at the Sertoli cell-cell vs. Sertoli-germ cell interface are supported by the 2 intriguingly coordinated cytoskeletons, namely the F-actin- and microtubule (MT)-based cytoskeletons. Herein, we provide a brief summary and critically evaluate the recent findings. We also provide an updated hypothetical concept regarding germ cell transport in the testis utilizing the MT-conferred tracks and the MT-specific motor proteins. Furthermore, this cellular event is also supported by the F-actin-based cytoskeleton.