Alterations in the testis and epididymis associated with loss of function of the cystatin-related epididymal spermatogenic (CRES) protein

Host defense amyloids: Biosensors of the immune system?

There is considerable evidence showing that highly ordered aggregate structures known as amyloids carry out essential biological roles in species ranging from bacteria to humans. Indeed, many antimicrobial peptides/proteins form amyloids to carry out their host defense functions and many amyloids are antimicrobial. The similarity of host defense amyloids from bacterial biofilms to the mammalian epididymal amyloid matrix implies highly conserved host defense structures/functions. With an emphasis on the epididymal amyloid matrix, here we review the common properties of host defense amyloids including unique traits that would allow them to function as powerful biosensors of the immune system.

Type 2 Cystatins and Their Roles in the Regulation of Human Immune Response and Cancer Progression

Cystatins are a family of intracellular and extracellular protease inhibitors that inhibit cysteine cathepsins-a group of lysosomal cysteine proteases that participate in multiple biological processes, including protein degradation and post-translational cleavage. Cysteine cathepsins are associated with the development of autoimmune diseases, tumor progression, and metastasis. Cystatins are categorized into three subfamilies: type 1, type 2, and type 3. The type 2 cystatin subfamily is the largest, containing 10 members, and consists entirely of small secreted proteins. Although type 2 cystatins have many shared biological roles, each member differs in structure, post-translational modifications (e.g., glycosylation), and expression in different cell types. These distinctions allow the type 2 cystatins to have unique biological functions and properties. This review provides an overview of type 2 cystatins, including their biological similarities and differences, their regulatory effect on human immune responses, and their roles in tumor progression, immune evasion, and metastasis.

Effects of Heparan sulfate acetyl-CoA: Alpha-glucosaminide N-acetyltransferase (HGSNAT) inactivation on the structure and function of epithelial and immune cells of the testis and epididymis and sperm parameters in adult mice

Heparan sulfate (HS), an abundant component of the apical cell surface and basement membrane, belongs to the glycosaminoglycan family of carbohydrates covalently linked to proteins called heparan sulfate proteoglycans. After endocytosis, HS is degraded in the lysosome by several enzymes, including heparan-alpha-glucosaminide N-acetyltransferase (HGSNAT), and in its absence causes Mucopolysaccharidosis III type C (Sanfilippo type C). Since endocytosis occurs in epithelial cells of the testis and epididymis, we examined the morphological effects of Hgsnat inactivation in these organs. In the testis, Hgsnat knockout (Hgsnat-Geo) mice revealed statistically significant decrease in tubule and epithelial profile area of seminiferous tubules. Electron microscopy (EM) analysis revealed cross-sectional tubule profiles with normal and moderately to severely altered appearances. Abnormalities in Sertoli cells and blood-testis barrier and the absence of germ cells in some tubules were noted along with altered morphology of sperm, sperm motility parameters and a reduction in fertilization rates in vitro. Along with quantitatively increased epithelial and tubular profile areas in the epididymis, EM demonstrated significant accumulations of electrolucent lysosomes in the caput-cauda regions that were reactive for cathepsin D and prosaposin antibodies. Lysosomes with similar storage materials were also found in basal, clear and myoid cells. In the mid/basal region of the epithelium of caput-cauda regions of KO mice, large vacuolated cells, unreactive for cytokeratin 5, a basal cell marker, were identified morphologically as epididymal mononuclear phagocytes (eMPs). The cytoplasm of the eMPs was occupied by a gigantic lysosome suggesting an active role of these cells in removing debris from the epithelium. Some eMPs were found in proximity to T-lymphocytes, a feature of dendritic cells. Taken together, our results reveal that upon Hgsnat inactivation, morphological alterations occur to the testis affecting sperm morphology and motility parameters and abnormal lysosomes in epididymal epithelial cells, indicative of a lysosomal storage disease.

CEP128 is involved in spermatogenesis in humans and mice

Centrosomal proteins are necessary components of the centrosome, a conserved eukaryotic organelle essential to the reproductive process. However, few centrosomal proteins have been genetically linked to fertility. Herein we identify a homozygous missense variant of CEP128 (c.665 G > A [p.R222Q]) in two infertile males. Remarkably, male homozygous knock-in mice harboring the orthologous CEP128^R222Q variant show anomalies in sperm morphology, count, and motility. Moreover, Cep128 knock-out mice manifest male infertility associated with disrupted sperm quality. We observe defective sperm flagella in both homozygous Cep128 KO and KI mice; the cilia development in other organs is normal—suggesting that CEP128 variants predominantly affected the ciliogenesis in the testes. Mechanistically, CEP128 is involved in male reproduction via regulating the expression of genes and/or the phosphorylation of TGF-β/BMP-signalling members during spermatogenesis. Altogether, our findings unveil a crucial role for CEP128 in male fertility and provide important insights into the functions of centrosomal proteins in reproductive biology.

CEP128 is a centrosomal protein important for the organization of centriolar microtubules. Here, the authors show that a CEP128 variant observed in human male siblings causes reduced sperm counts and morphologically abnormal sperm when modeled in mice, suggesting a role for CEP128 in male fertility.

Cloning, Expression, Characterization, and Tissue Distribution of Cystatin C from Silver Carp (Hypophthalmichthys molitrix)

Cystatins are proteins, which inhibit cysteine proteases, such as papain. In this study, the 336-bp cystatin C gene (family II, HmCysC) of silver carp (Hypophthalmichthys molitrix) was cloned and expressed in Escherichia coli BL21 (DE3). HmCysC encodes the mature peptide of cystatin C (HmCystatin C), with 111 amino acids. A typical QXXXG motif was found in HmCystatin C and it formed a cluster with Cyprinus carpio and Danio rerio cystatin C in the phylogenetic tree. Quantitative real-time polymerase chain reaction analysis indicated that HmCysC was transcribed at different levels in five tested tissues of silver carp. Following purification with Ni²⁺- nitrilotriacetic acid agarose affinity chromatography, HmCystatin C displayed a molecular weight of 20 kDa in sodium dodecyl sulfate polyacrylamide gel electrophoresis. Purified HmCystatin C had strong inhibitory effects toward the proteolytic activity of papain. Immunochemical staining with anti-HmCystatin C antibody showed that HmCystatin C was widely distributed in silver carp tissues. These results collectively demonstrated the properties of HmCystatin C, providing information for further studies of cystatins from fish organisms.

Functional Mammalian Amyloids and Amyloid-Like Proteins

Amyloids are highly ordered fibrous cross-β protein aggregates that are notorious primarily because of association with a variety of incurable human and animal diseases (termed amyloidoses), including Alzheimer’s disease (AD), Parkinson’s disease (PD), type 2 diabetes (T2D), and prion diseases. Some amyloid-associated diseases, in particular T2D and AD, are widespread and affect hundreds of millions of people all over the world. However, recently it has become evident that many amyloids, termed “functional amyloids,” are involved in various activities that are beneficial to organisms. Functional amyloids were discovered in diverse taxa, ranging from bacteria to mammals. These amyloids are involved in vital biological functions such as long-term memory, storage of peptide hormones and scaffolding melanin polymerization in animals, substrate attachment, and biofilm formation in bacteria and fungi, etc. Thus, amyloids undoubtedly are playing important roles in biological and pathological processes. This review is focused on functional amyloids in mammals and summarizes approaches used for identifying new potentially amyloidogenic proteins and domains.

Deficiency of the onco-miRNA cluster, miR-106b∼25, causes oligozoospermia and the cooperative action of miR-106b∼25 and miR-17∼92 is required to maintain male fertility

The identification of new genes involved in sexual development and gonadal function as potential candidates causing male infertility is important for both diagnostic and therapeutic purposes. Deficiency of the onco-miRNA cluster miR-17∼92 has been shown to disrupt spermatogenesis, whereas mutations in its paralog cluster, miR-106b∼25, that is expressed in the same cells, were reported to have no effect on testis development and function. The aim of this work is to determine the role of these two miRNA clusters in spermatogenesis and male fertility. For this, we analyzed miR-106b∼25 and miR-17∼92 single and double mouse mutants and compared them to control mice. We found that miR-106b∼25 knock out testes show reduced size, oligozoospermia and altered spermatogenesis. Transcriptomic analysis showed that multiple molecular pathways are deregulated in these mutant testes. Nevertheless, mutant males conserved normal fertility even when early spermatogenesis and other functions were disrupted. In contrast, miR-17∼92+/-; miR-106b∼25-/- double mutants showed severely disrupted testicular histology and significantly reduced fertility. Our results indicate that miR-106b∼25 and miR-17∼92 ensure accurate gene expression levels in the adult testis, keeping them within the required thresholds. They play a crucial role in testis homeostasis and are required to maintain male fertility. Hence, we have identified new candidate genetic factors to be screened in the molecular diagnosis of human males with reproductive disorders. Finally, considering the well-known oncogenic nature of these two clusters and the fact that patients with reduced fertility are more prone to testicular cancer, our results might also help to elucidate the molecular mechanisms linking both pathologies.

The Functional Mammalian CRES (Cystatin-Related Epididymal Spermatogenic) Amyloid is Antiparallel β-Sheet Rich and Forms a Metastable Oligomer During Assembly

An amyloid matrix composed of several family 2 cystatins, including the reproductive cystatin CRES, is an integral structure in the mouse epididymal lumen and has proposed functions in sperm maturation and protection. Understanding how CRES amyloid assembles in vitro may provide clues on how the epididymal amyloid matrix forms in vivo. We therefore purified full-length CRES under nondenaturing conditions and followed its aggregation from monomer to amyloid under conditions that may approximate those in the epididymal lumen. CRES transitioned into a metastable oligomer that was resistant to aggregation and only over extended time formed higher-ordered amyloids. High protein concentrations facilitated oligomer assembly and also were required to maintain the metastable state since following dilution the oligomer was no longer detected. Similar to other amyloid precursors, the formation of CRES amyloids correlated with a loss of α-helix and a gain of β-sheet content. However, CRES is unique in that its amyloids are rich in antiparallel β-sheets instead of the more common parallel β-sheets. Taken together, our studies suggest that early metastable oligomers may serve as building blocks for functional amyloid assembly and further reveal that antiparallel β-sheet-rich amyloids can be functional forms.

Characterization of fertility associated sperm proteins in Aseel and Rhode Island Red chicken breeds

This study focused on characterization of fertility associated proteins in Aseel and RIR roosters and was conducted on two generations of birds. Roosters were divided into high (>50%) and low fertility groups (<50%) based on sperm function tests and fertility rate in both the generations. Polyclonal antibodies were raised in rabbits against sperm proteins of first generation highly fertile roosters and tested for characterization of fertility associated sperm proteins in the second generation of same roosters. IgG-fraction against proteins (Anti-SP-IgG) was reacted with sperm proteins of both high and low fertile roosters of second generation on immunoblots. Sperm proteins present in highly fertile roosters were further characterized by Mass Spectrometry (MS). Use of SDS-PAGE for evaluation of sperm extracts of Aseel and RIR breeds resulted in resolution of 16 and 10 proteins on 12% acrylamide gels. Anti-SP-IgG reacted with eight and ten sperm proteins of Aseel and RIR roosters on immunoblots. The SDS-PAGE and immunoblotting analysis also indicated a variation in sperm proteins among two breeds and high/low fertile roosters. The MS analysis indicated matching of 20, 30, and 20, 25 kDa proteins (associated with high fertility rate) of Aseel and RIR roosters with immunoglobulin kappa chain variable, phospholipase A₂ (PLA2), hypothetical N332-08551 partial and cystatin like partial proteins with a top score of 41, 46, 52 and 43, respectively. Considering the function and importance of matching proteins in male reproduction, these proteins may be further explored as potential markers for fertility evaluation of Aseel and RIR roosters.

The epididymal amyloid matrix: structure and putative functions

BACKGROUND

We previously demonstrated the normal mouse epididymal lumen contains a non-pathological amyloid matrix that surrounds spermatozoa and plays important roles in sperm maturation and protection.

OBJECTIVE

The objective herein was to present a review of this work, including studies showing the amyloid structures of four members of the CRES (cystatin-related epididymal spermatogenic) subgroup are integral and essential components of the amyloid matrix.

METHODS

We used conformation-dependent reagents that recognize the cross-β-sheet structure characteristic of amyloid, including thioflavin S (ThS), thioflavin T (ThT), anti-amyloid antibodies, and X-ray diffraction, as well as negative-stain transmission electron microscopy (TEM) to visualize amyloid structures in the epididymal lumen. Antibodies that specifically detect each CRES subgroup family member were also used in indirect immunofluorescence analysis.

RESULTS AND DISCUSSION

The epididymal lumen contains an amyloid matrix that surrounds maturing spermatozoa and represents a functional amyloid. Alterations in the structure of the amyloid matrix by the loss of the CRES subgroup members or the overexpression of cystatin C result in epididymal pathologies, including infertility. Preliminary data suggest the epididymal amyloid matrix is structurally and functionally similar to bacterial biofilms.

CONCLUSION

Together, these results suggest the amyloid matrix serves important roles in epididymal function including sperm maturation and protection.

Why are Functional Amyloids Non-Toxic in Humans?

Amyloids were first identified in association with amyloidoses, human diseases in which proteins and peptides misfold into amyloid fibrils. Subsequent studies have identified an array of functional amyloid fibrils that perform physiological roles in humans. Given the potential for the production of toxic species in amyloid assembly reactions, it is remarkable that cells can produce these functional amyloids without suffering any obvious ill effect. Although the precise mechanisms are unclear, there are a number of ways in which amyloid toxicity may be prevented. These include regulating the level of the amyloidogenic peptides and proteins, minimising the production of prefibrillar oligomers in amyloid assembly reactions, sequestrating amyloids within membrane bound organelles, controlling amyloid assembly by other molecules, and disassembling the fibrils under physiological conditions. Crucially, a better understanding of how toxicity is avoided in the production of functional amyloids may provide insights into the prevention of amyloid toxicity in amyloidoses.

Functional Amyloids in Reproduction

Amyloids are traditionally considered pathological protein aggregates that play causative roles in neurodegenerative disease, diabetes and prionopathies. However, increasing evidence indicates that in many biological systems nonpathological amyloids are formed for functional purposes. In this review, we will specifically describe amyloids that carry out biological roles in sexual reproduction including the processes of gametogenesis, germline specification, sperm maturation and fertilization. Several of these functional amyloids are evolutionarily conserved across several taxa, including human, emphasizing the critical role amyloids perform in reproduction. Evidence will also be presented suggesting that, if altered, some functional amyloids may become pathological.

Cystatin-related epididymal spermatogenic subgroup members are part of an amyloid matrix and associated with extracellular vesicles in the mouse epididymal lumen

STUDY QUESTION

Do the CRES (cystatin-related epididymal spermatogenic) subgroup members, including CRES2, CRES3 and cystatin E2, contribute to the formation of a nonpathological, functional amyloid matrix in the mouse epididymal lumen?

SUMMARY ANSWER

CRES2, CRES3 and cystatin E2 self-assemble with different aggregation properties into amyloids in vitro, are part of a common amyloid matrix in the mouse epididymal lumen and are present in extracellular vesicles.

WHAT IS KNOWN ALREADY

Although previously thought only to be pathological, accumulating evidence has established that amyloids, which are highly ordered protein aggregates, can also carry out functional roles in the absence of pathology. We previously demonstrated that nonpathological amyloids are present in the epididymis; specifically, that the reproductive cystatin CRES forms amyloid and is present in the mouse epididymal lumen in a film-like amyloid matrix that is intimately associated with spermatozoa. Because the related proteins CRES2, CRES3 and cystatin E2 are also expressed in the epididymis, the present studies were carried out to determine if these proteins are also amyloidogenic in vitro and in vivo and thus may coordinately function with CRES as an amyloid structure.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

The epididymides from CD1 and Cst8 (CRES)129SvEv/B6 gene knockout (KO) and wild-type mice and antibodies that specifically recognize each CRES subgroup member were used for immunohistochemical and biochemical analyzes of CRES subgroup proteins. Methods classically used to identify amyloid, including the conformation-dependent dyes thioflavin S (ThS) and thioflavin T (ThT), conformation-dependent antibodies, protein aggregation disease ligand (which binds any amyloid independent of sequence) and negative stain electron microscopy (EM) were carried out to examine the amyloidogenic properties of CRES subgroup members. Immunofluorescence analysis and confocal microscopy were used for colocalization studies.

MAIN RESULTS AND THE ROLE OF CHANCE

Immunoblot and immunofluorescence analyzes showed that CRES2, CRES3 and cystatin E2 were primarily found in the initial segment and intermediate zone of the epididymis and were profoundly downregulated in epididymides from CRES KO mice, suggesting integrated functions. Except for CRES3, which was only detected in a particulate form, proteins were present in the epididymal lumen in both soluble and particulate forms including in a film-like matrix and in extracellular vesicles. The use of amyloid-specific reagents determined that all CRES subgroup members were present as amyloids and colocalized to a common amyloid matrix present in the epididymal lumen. Negative stain EM, dot blot analysis and ThT plate assays showed that recombinant CRES2, CRES3 and cystatin E2 formed amyloid in vitro, albeit with different aggregation properties. Together, our studies demonstrate that a unique amyloid matrix composed of the CRES family of reproductive-specific cystatins and cystatin C is a normal component of the mouse epididymal lumen and may play a functional role in sperm maturation by coordinating interactions between the luminal fluid and spermatozoa.

LIMITATIONS, REASONS FOR CAUTION

The structures examined in our studies were isolated from luminal fluid obtained by puncture of the epididymis and therefore we cannot rule out some contamination by epithelial cells. Although our studies show CRES family members are associated with extracellular vesicles, we have yet to determine if proteins are present on the surface or are within the vesicles. We also have not established if narrow/apical cells are the source of the CRES family extracellular vesicles. CRES and CRES2 have been previously found in the human epididymis and associated with spermatozoa; however, we have yet to determine if the human CRES subgroup proteins are amyloidogenic and if an amyloid matrix is present in the human epididymal lumen.

WIDER IMPLICATIONS OF THE FINDINGS

Understanding the regulation and biological roles of amyloids, such as the CRES subgroup amyloid matrix that functions without causing pathology, could have broad implications for understanding pathological amyloids including those associated with neurodegenerative diseases and prionopathies.

LARGE SCALE DATA

None.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by NIH grants RO1HD033903 and RO1HD056182 to G.A.C. The authors declare there are no conflicts of interest.

High-resolution helium ion microscopy of epididymal epithelial cells and their interaction with spermatozoa

We examined the rat and mouse epididymis using helium ion microscopy (HIM), a novel imaging technology that uses a scanning beam of He(+) ions to produce nanometer resolution images of uncoated biological samples. Various tissue fixation, sectioning and dehydration methods were evaluated for their ability to preserve tissue architecture. The cauda epididymidis was luminally perfused in vivo to remove most spermatozoa and the apical surface of the epithelial lining was exposed. Fixed epididymis samples were then subjected to critical point drying (CPD) and HIM. Apical stereocilia in principal cells and smaller apical membrane extensions in clear cells were clearly distinguishable in both rat and mouse epididymis using this technology. After perfusion with an activating solution containing CPT-cAMP, a permeant analog of cAMP, clear cells exhibited an increase in the number and size of membrane ruffles or microplicae. In contrast, principal cells did not exhibit detectable structural modifications. High-resolution HIM imaging clearly showed the ultrastructure of residual sperm cells, including the presence of concentric rings on the midpiece, and of cytoplasmic droplets in some spermatozoa. Close epithelium-sperm interactions were also detected. We found a number of sperm cells whose heads were anchored within the epididymal epithelium. In certain cases, the surface of the sperm cytoplasmic droplet was covered with vesicle-like structures whose size is consistent with that of epididymosomes. In conclusion, we describe here the first application of HIM technology to the study of the structure and morphology of the rodent epididymis. HIM technology represents a major imaging breakthrough that can be successfully applied to study the epididymis and spermatozoa, with the goal of advancing our understanding of their structure and function.

Nonpathological extracellular amyloid is present during normal epididymal sperm maturation

Amyloids are aggregated proteins characterized by a specific cross-β-sheet structure and are typically associated with neurodegenerative diseases including Alzheimer's disease. Recently, however, several nonpathological amyloids have been found in intracellular organelles of normal mammalian tissues suggesting that amyloid may also carry out biological functions. We previously have shown that the epididymal cystatin CRES (cystatin-related epididymal spermatogenic), cst8, a reproductive-specific member of the cystatin superfamily of cysteine protease inhibitors, forms amyloid in vitro suggesting that CRES amyloid may also form in vivo within the epididymal lumen. Here we show that amyloid structures containing CRES are a component of the normal mouse epididymal lumen without any apparent cytotoxic effects on spermatozoa and that these structures change along the length of the tubule. These studies suggest the presence of a functional amyloid structure that may carry out roles in sperm maturation or maintenance of the luminal milieu and which itself may undergo maturational changes along the epididymis. In contrast to previous examples of functional amyloid which were intracellular, our studies now show that nonpathological/functional amyloid can also be extracellular. The presence of an extracellular and nonpathological amyloid in the epididymis suggests that similar amyloid structures may be present in other organ systems and may carry out distinctive tissue-specific functions.

Cystatin-related epididymal spermatogenic aggregates in the epididymis

Cystatin-related epididymal spermatogenic (CRES) is the defining member of a reproductive subgroup within the family 2 cystatins of the cystatin superfamily of cysteine protease inhibitors. CRES is synthesized and secreted by the initial segment of the epididymis and is present in the sperm acrosome, suggesting roles in sperm maturation and fertilization. We have previously demonstrated that CRES is present within the epididymal lumen as monomeric (14 and N-glycosylated 19-kd forms) as well as sodium dodecyl sulfate-sensitive and sodium dodecyl sulfate-resistant high-molecular mass complexes. We have also shown that recombinant CRES protein will self-aggregate and form amyloid structures in vitro, raising the possibility that CRES might also form amyloid in vivo. Amyloid is a large protein aggregate with a specific cross-β sheet structure, and its presence is usually associated with disease. This review discusses protein aggregation in the epididymis and provides a brief overview of amyloid formation, including recent studies in other organ systems identifying examples of amyloid that are nonpathologic and carry out biologic functions (ie, functional amyloid). Studies that were carried out to determine if amyloid is present in the epididymal lumen and if CRES is associated with these structures are also described. The presence of CRES amyloid in the mouse epididymal lumen and the absence of pathology suggest either the presence of mechanisms to neutralize the cytotoxicity associated with pathologic amyloid or that CRES is a new example of a functional amyloid with roles in epididymal function.

Reduced fertility in vitro in mice lacking the cystatin CRES (cystatin-related epididymal spermatogenic): rescue by exposure of spermatozoa to dibutyryl cAMP and isobutylmethylxanthine

The cystatin CRES (cystatin-related epididymal spermatogenic; Cst8) is the defining member of a reproductive subgroup of family 2 cystatins of cysteine protease inhibitors and is present in the epididymis and spermatozoa, suggesting roles in sperm maturation and fertilization. To elucidate the role of CRES in reproduction, mice lacking the Cst8 gene were generated and their fertility examined. Although both male and female Cst8(-/-) mice generated offspring in vivo, spermatozoa from Cst8(-/-) mice exhibited a profound fertility defect in vitro. Compared to spermatozoa from Cst8(+/+) mice, spermatozoa from Cst8(-/-) mice were unable to undergo a progesterone-stimulated acrosome reaction and had decreased levels of protein tyrosine phosphorylation, suggesting a defect in the ability of Cst8(-/-) spermatozoa to capacitate. Incubation of Cst8(-/-) spermatozoa with dibutyryl cAMP and 3-isobutyl-1-methylxanthine rescued the fertility defect, including the capacity for sperm protein tyrosine phosphorylation. Both untreated Cst8(+/+) and Cst8(-/-) spermatozoa, however, exhibited similar increased total levels of cAMP and protein kinase A (PKA) activity throughout the capacitation time course compared to spermatozoa incubated under noncapacitating conditions. Taken together, these results suggest that mice lacking CRES may have altered local levels of cAMP/PKA activity, perhaps because of improper partitioning or tethering of these signaling molecules, or that the CRES defect does not directly involve cAMP/PKA but other signaling pathways that regulate protein tyrosine phosphorylation and capacitation.