Blood-testis barrier and spermatogenesis： lessons From genetically-modified mice

The blood-testis barrier （BTB） is found between adjacent Sertoli cells in the testis where it creates a unique microenvironment for the development and maturation of meiotic and postmeiotic germ cells in seminiferous tubes. It is a compound proteinous structure, composed of several types of cell junctions including tight junctions （TJs）, adhesion junctions and gap junctions （GJs）. Some of the junctional proteins function as structural proteins of BTB and some have regulatory roles. The deletion or functional silencing of genes encoding these proteins may disrupt the BTB, which may cause immunological or other damages to meiotic and postmeiotic cells and ultimately lead to spermatogenic arrest and infertility. In this review, we will summarize the findings on the BTB structure and function from genetically-modified mouse models and discuss the future perspectives.

Super Antibiotics, Part II. Hyperforin, Mass Spectroscopy (MS) and Gas Chromatography-Mass Spectrometry (GC-MS), Evidence of Permeability of the Blood-Testis Barrier (BTB) and the Blood-Brain Barrier (BBB) to Hyperforin

In the first article of this series, we presented some evidence of hyperforin as an antibiotic, antiprotozoal, antiviral, anticancer, and immunomodulatory substance. In the present article, evidence of the permeability of the blood-testis barrier (BTB) and blood-brain barrier (BBB) to hyperforin and its distribution in other organs of the domestic pig (Sus scrofa domesticus) are revealed. Seven-month-old male boars with a body mass of 100 kg were fed a diet containing hyperforin. Organs were surgically removed under anesthesia. Organs were suitable prepared and extracted, and then analyzed using gas chromatography-mass spectrometry with supersonic molecular beams (GC-MS with SMB). The presence of hyperforin was recorded in all organs and body fluids. Special attention was paid to the evaluation of the presence of hyperforin in the brain and testes of experimental animals. The presence of hyperforin in the brain and testes of experimental animals was established by GC-MS with SMB. The results are of interest because penicillin and numerous other antibiotics cannot pass through the BTB or BBB if healthy or non-inflamed, which limits their use in patients with meningitis and gonorrhea. The findings are also of interest in cases of penicillin- and multi-antibiotic-resistant bacterial infections.

Regulation of blood-testis barrier dynamics by the mT0RCl/rpS6 signaling complex:an in vitro study

During spermatogenesis, developi ng germ cells that lack the cellular ultrastructures of filopodia and lamellipodia gen erally found in migrating cells, such as macrophages and fibroblasts, rely on Sertoli cells to support their transport across the seminiferous epithelium. These in elude the transport of preleptote ne spermatocytes across the blood-testis barrier (BTB), but also the transport of germ cells, in particular developing haploid spermatids, across the seminiferous epithelium, that is to and away from the tubule lumen, depending on the stages of the epithelial cycle. On the other hand, cell junctions at the Sertoli cell-cell and Sertoli-germ cell in terface also un dergo rapid remodeli ng, invo Iving disassembly and reassembly of cell j un ctions, which, in turn, are supported by actin- and microtubule-based cytoskeletal remodeling. Interestingly, the underlying mechanism(s) and the invoIving biomolecule(s) that regulate or support cytoskeletal remodeling remain largely unknown. Herein, we used an in vitro model of primary Sertoli cell cultures that mimicked the Sertoli BTB in vivo overexpressed with the ribosomal protei n S6 (rpS6, the down stream signali ng protein of mammalian target of rapamycin complex 1 [mTORCl]) cloned into the mammalian expression vector pCI-neo, namely, quadruple phosphomimetic and constitutively active mutant of rpS6 (pCI-neo/p-rpS6-MT) versus pCI-neo/rpS6-WT (wild-type) and empty vector (pCI-neo/Ctrl) for studies. These findings provide compelling evidence that the mT0RCl/rpS6 signal pathway exerted its effects to promote Sertoli cell BTB remodeling. This was mediated through changes in the organization of actin- and microtubulebased cytoskeletons, involving changes in the distribution and/or spatial expression of actin- and microtubule-regulatory proteins.

Evidence on Invasion of Blood,Adipose Tissues,Nervous System and Reproductive System of Mice After a Single Oral Exposure:Nanoplastics versus Microplastics

Objective This study was designed to provide the evidences on the toxicokinetics of microplastics(MPs)and nanoplastics(NPs)in the bodies of mammals.Methods 100 nm,3μm,and 10μm fluorescent polystyrene(PS)beads were administered to mice once by gavage at a dose of 200 mg/kg body weight.The levels and change of fluorescence intensity in samples of blood,subcutaneous fat,perirenal fat,peritesticular fat,cerebrum,cerebellum,testis,and epididymis were measured at 0.5,1,2,and 4 h after administration using an IVIS Spectrum small-animal imaging system.Histological examination,confocal laser scanning,and transmission electron microscope were performed to corroborate the findings.Results After confirming fluorescent dye leaching and impact of pH value,increased levels of fluorescence intensity in blood,all adipose tissues examined,cerebrum,cerebellum,and testis were measured in the 100 nm group,but not in the 3 and 10μm groups except in the cerebellum and testis at 4 h for the 3μm PS beads.The presence of PS beads was further corroborated.Conclusion After a single oral exposure,NPs are absorbed rapidly in the blood,accumulate in adipose tissues,and penetrate the blood-brain/testis barriers.As expected,the toxicokinetics of MPs is significantly size-dependent in mammals.

Molecular basis of cryptorchidism-induced infertility

Artificial cryptorchidism or local testicular heat treatment can induce reversible oligospermia or azoospermia in monkeys and rats via germ cell apoptosis. Local warming of monkey testes in water at 43°C for 2 consecutive days (30 min per day) decreased the number of sperm in the semen by up to 80% on d 28, and the effect was completely reversed on d 144. Germ cells rely heavily on Sertoli cells for structural and nutritional support. Specialized junctions that play a pivotal role in spermatogenesis occur at sites of Sertoli-Sertoli and Sertoli-germ cell contact in the seminiferous epithelium. We demonstrated that expression of tight junction (TJ)-associated molecules, such as occludin and zonula occludens-1 (ZO-1), were greatly reduced 24–48 h after heat treatment, while the permeability of the blood-testis barrier (BTB) was simultaneously increased, but recovered 10 d later. These results indicate a reversible disruption of the BTB associated with transient inductions of transforming growth factor (TGF) β2 and β3 expression, p38 mitogen-activated protein kinase and extracellular signal-regulated kinase activation, and concomitant loss of occludin and ZO-1. This suggests that expression of TJ-associated molecules and the BTB was reversibly perturbed by mild testicular hyperthermia, and that the heat-induced induction of TGF-β might be involved in downregulating TJ-associated proteins, leading to cell junction reduction. This review discusses the changes in total gene expression patterns after experimental cryptorchidism in adult mouse testes, and the cloning of several novel, physiologically significant spermatogenesis-specific genes.

Claudin-11 and occludin are major contributors to Sertoli cell tight junction function, in vitro

The Sertoli cell tight junction （T J） is the key component of the blood-testis barrier, where it sequesters developing germ cells undergoing spermatogenesis within the seminiferous tubules. Hormonally regulated claudin-11 is a critical transmembrane protein involved in barrier function and its murine knockout results in infertility. We aimed to assess quantitatively the significance of the contribution of claudin-11 to TJ function, in vitro, using siRNA-mediated gene silencing. We also conducted an analysis of the contribution of occludin, another intrinsic transmembrane protein of the TJ. Silencing of claudin-11 and/or occludin was conducted using siRNA in an immature rat Sertoli cell culture model. Transepithelial electrical resistance was used to assess quantitatively TJ function throughout the culture. Two days after siRNA treatment, cells were fixed for immunocytochemical localization of junction proteins or lyzed for RT-PCR assessment of mRNA expression. Silencing of claudin-11, occludin, or both resulted in significant decreases in TJ function of 55% （P 〈 0.01）, 51% （P 〈 0.01）, and 62% （P 〈 0.01）, respectively. Data were concomitant with significant decreases in mRNA expression and marked reductions in the localization of targeted proteins to the Sertoli cell TJ. We provide quantitative evidence that claudin-11 contributes significantly （P 〈 0.01） to Sertoli cell TJ function in vitro. Interestingly, occludin, which is hormonally regulated but not implicated in infertility until late adulthood, is also a significant （P 〈 0.01） contributor to barrier function. Our data are consistent with in vivo studies that clearly demonstrate a role for these proteins in maintaining normal TJ barrier structure and function.

Ezrin： a regulator of actin microfilaments in ce unctions of the rat testis

Ezrin, radixin, moesin and merlin （ERM） proteins are highly homologous actin-binding proteins that share extensive sequence similarity with each other. These proteins tether integral membrane proteins and their cytoplasmic peripheral proteins （e.g., adaptors, nonreceptor protein kinases and phosphatases） to the microfilaments of actin-based cytoskeleton. Thus, these proteins are crucial to confer integrity of the apical membrane domain and its associated junctional complex, namely the tight junction and the adherens junction. Since ectoplasmic specialization （ES） is an F-actin-rich testis-specific anchoring junction-a highly dynamic ultrastructure in the seminiferous epithelium due to continuous transport of germ cells, in particular spermatids, across the epithelium during the epithelial cycle-it is conceivable that ERM proteins are playing an active role in these events. Although these proteins were first reported almost 25 years and have since been extensively studied in multiple epithelia/endothelia, few reports are found in the literature to examine their role in the actin filament bundles at the ES. Studies have shown that ezrin is also a constituent protein of the actin-based tunneling nanotubes （TNT） also known as intercellular bridges, which are transient cytoplasmic tubular ultrastructures that transport signals, molecules and even organelles between adjacent and distant cells in an epithelium to coordinate cell events that occur across an epithelium. Herein, we critically evaluate recent data on ERM in light of recent findings in the field in particular ezrin regarding its role in actin dynamics at the ES in the testis, illustrating additional studies are warranted to examine its physiological significance in spermatogenesis.

Rearrangement of Actin Cytoskeleton by Zika Virus Infection Facilitates Blood–Testis Barrier Hyperpermeability

In recent years,various serious diseases caused by Zika virus(ZIKV)have made it impossible to be ignored.Confirmed existence of ZIKV in semen and sexually transmission of ZIKV suggested that it can break the blood–testis barrier(BTB),or Sertoli cell barrier(SCB).However,little is known about the underlying mechanism.In this study,interaction between actin,an important component of the SCB,and ZIKV envelope(E)protein domainⅢ(EDⅢ)was inferred from coimmunoprecipitation(Co-IP)liquid chromatography–tandem mass spectrometry(LC–MS/MS)analysis.Confocal microscopy confirmed the role of actin filaments(F-actin)in ZIKV infection,during which part of the stress fibers,the bundles that constituted by paralleled actin filaments,were disrupted and presented in the cell periphery.Colocalization of E and reorganized actin filaments in the cell periphery of transfected Sertoli cells suggests a participation of ZIKV E protein in ZIKV-induced F-actin rearrangement.Perturbation of F-actin by cytochalasin D(CytoD)or Jasplakinolide(Jas)enhanced the infection of ZIKV.More importantly,the transepithelial electrical resistance(TEER)of an in vitro mouse SCB(mSCB)model declined with the progression of ZIKV infection or overexpression of E protein.Co-IP and confocal microscopy analyses revealed that the interaction between F-actin and tight junction protein ZO-1 was reduced after ZIKV infection or E protein overexpression,highlighting the role of E protein in ZIKV-induced disruption of the BTB.We conclude that the interaction between ZIKV E and F-actin leads to the reorganization of F-actin network,thereby compromising BTB integrity.