Mediation of sperm-egg fusion: evidence that mouse egg alpha6beta1 integrin is the receptor for sperm fertilinbeta

The metalloprotease ADM-4/ADAM17 promotes axonal repair

Axonal fusion is an efficient means of repair following axonal transection, whereby the regenerating axon fuses with its own separated axonal fragment to restore neuronal function. Despite being described over 50 years ago, its molecular mechanisms remain poorly understood. Here, we demonstrate that the Caenorhabditis elegans metalloprotease ADM-4, an ortholog of human ADAM17, is essential for axonal fusion. We reveal that animals lacking ADM-4 cannot repair their axons by fusion, and that ADM-4 has a cell-autonomous function within injured neurons, localizing at the tip of regrowing axon and fusion sites. We demonstrate that ADM-4 overexpression enhances fusion to levels higher than wild type, and that the metalloprotease and phosphatidylserine-binding domains are essential for its function. Last, we show that ADM-4 interacts with and stabilizes the fusogen EFF-1 to allow membranes to merge. Our results uncover a key role for ADM-4 in axonal fusion, exposing a molecular target for axonal repair.

Role of Integrins in Sperm Activation and Fertilization

In mammals, integrins are heterodimeric transmembrane glycoproteins that represent a large group of cell adhesion receptors involved in cell-cell, cell-extracellular matrix, and cell-pathogen interactions. Integrin receptors are an important part of signalization pathways and have an ability to transmit signals into and out of cells and participate in cell activation. In addition to somatic cells, integrins have also been detected on germ cells and are known to play a crucial role in complex gamete-specific physiological events, resulting in sperm-oocyte fusion. The main aim of this review is to summarize the current knowledge on integrins in reproduction and deliver novel perspectives and graphical interpretations presenting integrin subunits localization and their dynamic relocation during sperm maturation in comparison to the oocyte. A significant part of this review is devoted to discussing the existing view of the role of integrins during sperm migration through the female reproductive tract; oviductal reservoir formation; sperm maturation processes ensuing capacitation and the acrosome reaction, and their direct and indirect involvement in gamete membrane adhesion and fusion leading to fertilization.

Cyclic FEE Peptide Improves Human Sperm Movement Parameters without Modification of Their Energy Metabolism

Cyclic fertilin peptide (cFEE: phenylalanine, glutamic acid; glutamic acid) improves gamete interaction in humans. We investigate whether it could be via improvement of sperm movement parameters and their mitochondrial ATP production. Sperm movement parameters were studied using computer-assisted sperm analysis (CASA) in sperm samples from 38 patients with normal sperm in medium supplemented with cyclic fertilin against a control group. Sperm mitochondrial functions were studied using donor’s sperm, incubated or not with cFEE. It was evaluated by the measurement of their ATP production using bioluminescence, their respiration by high resolution oxygraphy, and of mitochondrial membrane potential (MMP) using potentiometric dyes and flow cytometry. cFEE significantly improved sperm movement parameters and percentage of hyperactivated sperm. Impact of inhibitors showed OXPHOS as the predominant energy source for sperm movement. However, cFEE had no significant impact on any of the analyzed mitochondrial bioenergetic parameters, suggesting that it could act via a more efficient use of its energy resources.

Adhesion molecules in gamete transport, fertilization, early embryonic development, and implantation-role in establishing a pregnancy in cattle: A review

Cell-cell adhesion molecules have critically important roles in the early events of reproduction including gamete transport, sperm-oocyte interaction, embryonic development, and implantation. Major adhesion molecules involved in reproduction include cadherins, integrins, and disintegrin and metalloprotease domain-containing (ADAM) proteins. ADAMs on the surface of sperm adhere to integrins on the oocyte in the initial stages of sperm-oocyte interaction and fusion. Cadherins act in early embryos to organize the inner cell mass and trophectoderm. The trophoblast and uterine endometrial epithelium variously express cadherins, integrins, trophinin, and selectin, which achieve apposition and attachment between the elongating conceptus and uterine epithelium before implantation. An overview of the major cell-cell adhesion molecules is presented and this is followed by examples of how adhesion molecules help shape early reproductive events. The argument is made that a deeper understanding of adhesion molecules and reproduction will inform new strategies that improve embryo survival and increase the efficiency of natural mating and assisted breeding in cattle.

Enhancer RNA and NFκB-dependent P300 regulation of ADAMDEC1

We observed increased expression of ADAMDEC1 RNA in monocytes from patients with systemic lupus erythematosus. The precise role of ADAMDEC1 is uncertain and uniquely among metalloproteinases it utilizes a zinc-coordinating aspartic acid residue which allows it to escape inhibition by tissue inhibitor of metalloprotease-3 (TIMP-3). A closely related gene encodes the protein ADAM28, which is not up-regulated in lupus. We leveraged the ability to look at both gene's promoters and enhancers simultaneously. ADAMDEC1 was up-regulated by LPS while ADAM28 was not upregulated in the short term. We identified MAP kinases and NFκB as critical cell pathways regulating the expression of ADAMDEC1. These same pathways were implicated in driving the expression of the ADAMDEC1 upstream enhancer RNAs. We demonstrated that binding of the enhancer RNAs produced from the upstream enhancer were critically important and that p300 bound to both the RNA from the enhancer and the DNA at the enhancer. P300 binding to the enhancer was dependent on NFκB. These data define the critical pathways regulating the expression of ADAMDEC1 and extend our knowledge of the roles of enhancer RNAs and mechanistically links p300 and enhancer RNAs.

The molecular basis of fertilization (Review)

Fertilization is the fusion of the male and female gamete. The process involves the fusion of an oocyte with a sperm, creating a single diploid cell, the zygote, from which a new individual organism will develop. The elucidation of the molecular mechanisms of fertilization has fascinated researchers for many years. In this review, we focus on this intriguing process at the molecular level. Several molecules have been identified to play a key role in each step of this intriguing process (the sperm attraction from the oocyte, the sperm maturation, the sperm and oocyte fusion and the two gamete pronuclei fusion leading to the zygote). Understanding the molecular mechanisms of the cell-cell interactions will provide a better understanding of the causes of fertility issues due to fertilization defects.

A Disintegrin and Metalloprotease (ADAM): Historical Overview of Their Functions

Since the discovery of the first disintegrin protein from snake venom and the following identification of a mammalian membrane-anchored metalloprotease-disintegrin implicated in fertilization, almost three decades of studies have identified additional members of these families and several biochemical mechanisms regulating their expression and activity in the cell. Most importantly, new in vivo functions have been recognized for these proteins including cell partitioning during development, modulation of inflammatory reactions, and development of cancers. In this review, we will overview the a disintegrin and metalloprotease (ADAM) family of proteases highlighting some of the major research achievements in the analysis of ADAMs' function that have underscored the importance of these proteins in physiological and pathological processes over the years.

Sperm-egg fusion: a molecular enigma of mammalian reproduction

The mechanism of gamete fusion remains largely unknown on a molecular level despite its indisputable significance. Only a few of the molecules required for membrane interaction are known, among them IZUMO1, which is present on sperm, tetraspanin CD9, which is present on the egg, and the newly found oolema protein named Juno. A concept of a large multiprotein complex on both membranes forming fusion machinery has recently emerged. The Juno and IZUMO1, up to present, is the only known extracellular receptor pair in the process of fertilization, thus, facilitating the essential binding of gametes. However, neither IZUMO1 nor Juno appears to be the fusogenic protein. At the same time, the tetraspanin is expected to play a role in organizing the egg membrane order and to interact laterally with other factors. This review summarizes, to present, the known molecules involved in the process of sperm-egg fusion. The complexity and expected redundancy of the involved factors makes the process an intricate and still poorly understood mechanism, which is difficult to comprehend in its full distinction.

Critical role of exosomes in sperm-egg fusion and virus-induced cell-cell fusion

In mammals, two integral membrane proteins, sperm IZUMO1 and egg CD9, regulate sperm-egg fusion, and their roles are critical, but yet unclear. Recent studies, however, indicate interesting connections between the sperm-egg fusion and virus-induced cell-cell fusion. First, CD9-containing exosome-like vesicles, which are released from wild-type eggs, can induce the fusion between sperm and CD9-deficient egg, even though CD9-deficient eggs are highly refractory to the fusion with sperm. This finding provides strong evidence for the involvement of CD9-containing, fusion-facilitating vesicles in the sperm-egg fusion. Secondly, there are similarities between the generation of retroviruses in the host cells and the formation of small cellular vesicles, termed exosomes, in mammalian cells. The exosomes are involved in intercellular communication through transfer of proteins and ribonucleic acids (RNAs) including mRNAs and microRNAs. These collective studies provide an insight into the molecular mechanism of membrane fusion events.

Angiotensin converting enzyme (ACE) and ACE2 bind integrins and ACE2 regulates integrin signalling

The angiotensin converting enzymes (ACEs) are the key catalytic components of the renin-angiotensin system, mediating precise regulation of blood pressure by counterbalancing the effects of each other. Inhibition of ACE has been shown to improve pathology in cardiovascular disease, whilst ACE2 is cardioprotective in the failing heart. However, the mechanisms by which ACE2 mediates its cardioprotective functions have yet to be fully elucidated. Here we demonstrate that both ACE and ACE2 bind integrin subunits, in an RGD-independent manner, and that they can act as cell adhesion substrates. We show that cellular expression of ACE2 enhanced cell adhesion. Furthermore, we present evidence that soluble ACE2 (sACE2) is capable of suppressing integrin signalling mediated by FAK. In addition, sACE2 increases the expression of Akt, thereby lowering the proportion of the signalling molecule phosphorylated Akt. These results suggest that ACE2 plays a role in cell-cell interactions, possibly acting to fine-tune integrin signalling. Hence the expression and cleavage of ACE2 at the plasma membrane may influence cell-extracellular matrix interactions and the signalling that mediates cell survival and proliferation. As such, ectodomain shedding of ACE2 may play a role in the process of pathological cardiac remodelling.

The biology and dynamics of mammalian cortical granules

Cortical granules are membrane bound organelles located in the cortex of unfertilized oocytes. Following fertilization, cortical granules undergo exocytosis to release their contents into the perivitelline space. This secretory process, which is calcium dependent and SNARE protein-mediated pathway, is known as the cortical reaction. After exocytosis, the released cortical granule proteins are responsible for blocking polyspermy by modifying the oocytes' extracellular matrices, such as the zona pellucida in mammals. Mammalian cortical granules range in size from 0.2 um to 0.6 um in diameter and different from most other regulatory secretory organelles in that they are not renewed once released. These granules are only synthesized in female germ cells and transform an egg upon sperm entry; therefore, this unique cellular structure has inherent interest for our understanding of the biology of fertilization. Cortical granules are long thought to be static and awaiting in the cortex of unfertilized oocytes to be stimulated undergoing exocytosis upon gamete fusion. Not till recently, the dynamic nature of cortical granules is appreciated and understood. The latest studies of mammalian cortical granules document that this organelle is not only biochemically heterogeneous, but also displays complex distribution during oocyte development. Interestingly, some cortical granules undergo exocytosis prior to fertilization; and a number of granule components function beyond the time of fertilization in regulating embryonic cleavage and preimplantation development, demonstrating their functional significance in fertilization as well as early embryonic development. The following review will present studies that investigate the biology of cortical granules and will also discuss new findings that uncover the dynamic aspect of this organelle in mammals.

Zona pellucida glycoprotein 3 (pZP3) and integrin β2 (ITGB2) mRNA and protein expression in porcine oocytes after single and double exposure to brilliant cresyl blue test

Brilliant cresyl blues (BCB) staining test is a useful tool in assessing the competence of cumulus-oocyte-complexes (COCs) in several mammalian species. It is mostly used to select gametes after they are recovered from the ovary or before and after IVM to isolate those oocytes that reach developmental competency. However, there is evidence that double exposure to BCB test may lead to impaired fertilization or even have a toxic effect on cells. The aim of the present study was to investigate the expression pattern of sperm-egg interaction molecules in oocytes after single and double exposure to BCB test. Follicles were dissected from porcine ovaries after slaughter and aspirated COCs were cultured in standard porcine IVM culture medium (TCM 199) for 44 h. The BCB test was applied to COCs before and after IVM. In developmentally competent oocytes, assessed by determining the activity of glucose-6-phosphate dehydrogenase (G6PDH; BCB test), real-time quantitative PCR reaction methods, western blot and confocal microscopy analysis were applied to determine the transcript levels of porcine zona pellucida glycoprotein 3 (pZP3), and integrin beta 2 (ITGB2), as well as the levels of pZP3 and ITGB2 proteins. In the control group, assessment of the expression of the investigated genes was performed before and after IVM without BCB test. We observed a significantly higher level of pZP3 mRNA in oocytes after single exposure to BCB test compared to control before and after IVM (P < 0.001), and to double staining (P < 0.05). The level of ITGB2 mRNA was also increased in gametes after single exposure to BCB test as compared to control before and after IVM (P < 0.001, P < 0.01, respectively), and double staining (P < 0.05). Western blot analysis demonstrated a higher level of pZP3 protein in oocytes after single staining with BCB as compared to control both before and after IVM (P < 0.001, P < 0.05, respectively) and double staining (P < 0.05). Confocal microscopic observations have revealed the same pattern of increased level of pZP3 and ITGB2 expression after single exposure to BCB test. In both cases we detected specific cytoplasmic localization of both proteins. The ITGB2 protein has zona pellucida and membrane localization in control oocytes before IVM. After IVM and after single exposure to BCB, ITGB2 was also strongly detected in the cytoplasm. In both cases, after double exposure to BCB both proteins were detected only partially in the cytoplasm. Our results suggest that (i) single exposure to BCB increased the expression of sperm-oocyte interaction genes, (ii) double exposure to BCB leads to only partial expression of pZP3 and ITGB2 in oocyte cytoplasm, (iii) the BCB staining test itself may be a cause of specific pZP3 translocation from the zona pellucida to the cytoplasm, and that (iv) in vitro maturation of oocytes may increase ITGB2 expression and translocation from the zona pellucida to the cytoplasm.

Fusion as the result of sperm–somatic cell interaction

The research has been designed to investigate whether acrosome-reacted spermatozoa can fuse with somatic cells and to check whether this event may involve the molecular machinery implicated in the sperm–egg fusion. Boar spermatozoa were capacitatedin vitroand then treated with A23187 to induce acrosome reaction and activate their fusogenic potential. Reacted spermatozoa, loaded with the membrane-permeant fluorescent dye calcein AM, were incubated with plated granulosa cells or cells derived from stable cell lines: CRFK, VERO, and ESK4. The fusion between spermatozoa and somatic cells was revealed by the diffusion of the fluorescent dye from the sperm to the cell as membrane fusion and cytoplasmic continuity between the two cells were established. The involvement of integrin α6 and tetraspanin CD9 in the process of fusion was assessed by carrying out the experiment in the presence of antibodies against these molecules. Moreover, the incidence of fusion displayed by the different cell types used was analyzed in relation to their content in the above molecules assessed by western blot and immunostaining. The role of CD9 was additionally investigated by using CD9-negative cells. The data presented demonstrate that boar spermatozoa can fuse with different somatic cell types derived from different species and the process requires the combined presence of both integrin and tetraspanin molecules on the cell plasma membrane.

Integrins as "functional hubs" in the regulation of pathological angiogenesis

It is well accepted that complex biological processes such as angiogenesis are not controlled by a single family of molecules or individually isolated signaling pathways. In this regard, new insight into the interconnected mechanisms that regulate angiogenesis might be gained by examining this process from a more global network perspective. The coordination of signaling cues from both outside and inside many different cell types is required for the successful completion of angiogenesis. Evidence is accumulating that the multifunctional integrin family of cell adhesion receptors represent an important group of molecules that play active roles in sensing, integrating, and distributing a diverse set of signals that regulate many cellular events required for angiogenesis. Given the ability of integrins to bind numerous extracellular ligands and transmit signals in a bi-directional fashion, we will discuss the multiple ways by which integrins may serve as a functional hub during pathological angiogenesis. In addition, we will highlight potential imaging and therapeutic strategies based on the expanding new insight into integrin function.

Egg integrins: back in the game of mammalian fertilization

Recent data provide insights into the function of egg integrins in mammalian fertilization and address some of the controversies regarding the involvement of these molecules in sperm-egg interaction.

Beta1 integrin is an adhesion protein for sperm binding to eggs

We investigated the role of beta(1) integrin in mammalian fertilization and the mode of inhibition of fertilinbeta-derived polymers. We determined that polymers displaying the Glu-Cys-Asp peptide from the fertilinbeta disintegrin domain mediate inhibition of mammalian fertilization through a beta(1) integrin receptor on the egg surface. Inhibition of fertilization is a consequence of competition with sperm binding to the cell surface, not activation of an egg-signaling pathway. The presence of the beta(1) integrin on the egg surface increases the rate of sperm attachment but does not alter the total number of sperm that can attach or fuse to the egg. We conclude that the presence of beta(1) integrin enhances the initial adhesion of sperm to the egg plasma membrane and that subsequent attachment and fusion are mediated by additional egg and sperm proteins present in the beta(1) integrin complex. Therefore, the mechanisms by which sperm fertilize wild-type and beta(1) knockout eggs are different.

Polymeric ADAM protein mimics interrogate mammalian sperm-egg binding

The sperm proteins ADAM2 and ADAM3, members of the ADAM family of proteins, have been implicated in mammalian sperm-egg binding. However, elucidating their roles is complex because of the interdependence of ADAM protein expression in the testis. Hence, multivalent probes containing the three-amino acid binding sequence of ADAM2, glutamate-cysteine-aspartate (ECD), and ADAM3, glutamine-cysteine-aspartate (QCD), were designed, synthesized, and tested to investigate gamete interactions. In this work, ECD polymer mimics were synthesized by ring-opening metathesis polymerization with a faster initiating ruthenium catalyst than previously used. Polymers containing 100 copies of the ECD peptide mimic were found to be the best inhibitors of fertilization. The multivalent QCD polymers were also tested as inhibitors of fertilization. The structure-activity profile was the same as ECD polymers, but the overall potency was lower. Both ECD and QCD polymers require the presence of beta(1) integrin to inhibit fertilization. Next, triblock ABA and ABC copolymers containing both ECD and QCD ligands were synthesized with 96 monomer spacers as their B blocks. Although these polymers had lower densities of ECD and QCD peptides, their potencies correlated with the potencies of their corresponding homopolymers. In addition, no synergy between ECD and QCD mimics was observed. All the data suggest that QCD and ECD bind to the same complex of proteins that includes beta(1) integrin.

Comprehensive analysis of reproductive ADAMs: relationship of ADAM4 and ADAM6 with an ADAM complex required for fertilization in mice

A Disintegrin And Metalloprotease (ADAM) family members expressed in male reproductive tissues are divided phylogenetically into three major groups. In the present study, we analyzed six ADAMs in one of the groups (ADAMs 4, 6, 24, 26, 29, and 30) of which function is largely unknown. Our results showed that most of the ADAMs undergo unique processing during sperm maturation and are located at the surface of sperm head. We found that the levels of ADAM4 and ADAM6 are dramatically reduced in Adam2 and Adam3 knockout sperm defective in various fertilization processes. We observed premature processing of ADAM4 in the Adam3-null mice. Furthermore, we obtained a result showing complex formation of ADAM6 with ADAM2 and ADAM3 in testis. Taken together, these results disclose involvement of ADAM4 and ADAM6 in a reproductive ADAM system that functions in fertilization.

Importance of the porcine ADAM3 disintegrin domain in sperm-egg interaction

In the mouse, ADAM3, a well-characterized testis-specific protein of the A disintegrin and metalloprotease (ADAM) family, has a crucial role in fertilization by mediating sperm binding to the egg zona pellucida. However, little is known about ADAM3 in other species, such as domestic pigs. We have identified porcine ADAM3 and analyzed the protein. RT-PCR and trypsinization of sperm surface proteins revealed that porcine ADAM3 is expressed at high levels in the testis and on the sperm surface. Furthermore, an IVF inhibition assay with a recombinant porcine ADAM3 disintegrin domain showed that treatment of the disintegrin domain effectively prevented pig sperm-egg interactions. In the present study, we demonstrated the presence of ADAM3a and ADAM3b molecules in the pig and examined their roles in fertilization.

Presence, processing, and localization of mouse ADAM15 during sperm maturation and the role of its disintegrin domain during sperm–egg binding

Successful fertilization requires gametes to complete several stages, beginning with maturation and transport along the male and female reproductive tracts and ending with the interaction between the sperm and the egg. This last step involves sperm–egg adhesion and membrane fusion. ADAMs (disintegrin and metalloprotease domain proteins) are a family of membrane-anchored glycoproteins that are thought to play diverse roles in cell–cell adhesion through their interaction with integrins. This study analyzes the presence, location, processing, and possible role of ADAM15 in mouse sperm. The presence of ADAM15 in mouse spermatozoa was detected by Western blotting, which revealed that ADAM15 is post-translationally processed, during epididymal sperm maturation and the acrosome reaction. The 35 kDa antigen present in the acrosome-reacted sperm is the last proteolytic product of the 110/75 kDa ADAM15 found in non-capacitated sperm. This 35 kDa protein contains the disintegrin domain. By indirect immunofluorescence, ADAM15 was identified in the acrosomal region and along the flagellum of mouse spermatozoa. In acrosome-reacted sperm, ADAM15 was lost from the acrosomal region, but remained diffusely distributed throughout the head and flagellum. Furthermore, the ADAM15 disintegrin domain (RPPTDDCDLPEF) partially inhibited fusion and almost completely inhibited sperm–oolemma adhesion. In conclusion, our data indicate that ADAM15 is present in the testis and in spermatozoa from the caput, corpus, and cauda epididymis, as well as in non-capacitated and acrosome-reacted gametes. Results also indicate that ADAM15 is processed during epididymal maturation and acrosome reaction and that it may play a role during sperm–egg binding.

Protein kinase C activity in mouse eggs regulates gamete membrane interaction

Gamete membrane interaction is critical to initiate the development of a new organism. The signaling pathways governing this event, however, are poorly understood. In this report, we provide the first evidence that protein kinase C activity in mouse eggs plays a crucial role in the regulation of this process. Stimulating PKC activity in mouse eggs by phorbol 12-myristate 13-acetate (PMA) drastically inhibited the egg's membrane ability to bind and fuse with sperm. Surprisingly, this significant reduction of gamete membrane interaction was also observed in eggs treated with the PKC inhibitors staurosporine and calphostin c. In further analysis, we found that while no change of egg actin cytoskeleton was detected after either PMA or calphostin c treatment, the structural morphology of egg surface microvilli was severely altered in the PMA-treated eggs, but not in the calphostin c-treated eggs. Moreover, sperm, which bound but did not fuse with the eggs treated with the anti-CD9 antibody KMC8, were liberated from the egg membrane after PMA, but not calphostin c, treatment. Taken together, these results suggest that egg PKC may be precisely balanced to regulate gamete membrane interaction in a biphasic mode, and this biphasic regulation is executed through two different mechanisms.

Alpha6beta1 integrin expressed by sperm is determinant in mouse fertilization

Background

Based on inhibition tests, the alpha6beta1 integrin was suggested to be a sperm receptor, but further experiments using gene deletion techniques have shown that neither oocyte alpha6, nor beta1 integrin subunits were essential for mouse fertilization.

Results

Using Western blot analysis and immunofluorescence, we showed that the mouse sperm expresses the alpha6beta1 integrin. As for oocyte, binding of GoH3 anti-alpha6 antibody to sperm induces a specific inhibition of sperm fertilizing ability. Comparing zona-intact and zona-free eggs in fusion tests, we showed that the removal of the zona pellucida by acid treatment bypasses fertilizing oocyte alpha6beta1 integrin's function in the adhesion/fusion process.

Conclusion

These findings show that alpha6beta1 integrin is expressed by both gametes and is functional in their membranes interaction. These results and previous reports, about fertilization of alpha6 or beta1 integrin subunits deleted oocytes by wild type sperm, suggest that the presence of alpha6beta1 integrin on one of the two gamete membranes can rescue the fertilization process. This hypothesis is further supported by the exchange of membrane fragments occurring between gametes prior to fusion that we recently reported.

Cell-surface association between matrix metalloproteinases and integrins: role of the complexes in leukocyte migration and cancer progression

Leukocyte motility is known to be dependent on both β2-integrins and matrix metalloproteinases MMP-2/-9 or gelatinases, which mediate leukocyte adhesion and the proteolysis needed for invasion, respectively. Gelatinases not only play an important role in cell migration, tissue remodeling, and angiogenesis during development, but are also involved in the progression and invasiveness of many cancers, including leukemias. The concept that MMPs associate with integrins, as well as their importance in some physiologic and pathologic conditions, has been advanced previously but has not been examined on leukocytes. This review will examine mainly the function of the MMP-integrin complexes in normal leukocyte migration and the effect of integrin and broad-spectrum MMP inhibitors in tumor progression.

Multivalent fertilinbeta oligopeptides: the dependence of fertilization inhibition on length and density

The sperm protein fertilinbeta, a member of the ADAM family of proteins, is implicated in sperm-egg binding in all mammals studied to date. Multivalent inhibitors containing the three amino acid binding sequence of fertilinbeta, ECD, have been shown previously to be more effective inhibitors of fertilization than their monovalent counterparts. Here, we probed sperm-egg interactions with ruthenium-catalyzed ring-opening metathesis polymers that contained from 3 to 70 ECD pharmacophores in densities ranging from 10% to 100%. Evaluation of the polymer potencies, and synthesis of a triblock copolymer from two building blocks, revealed that two multivalent contacts are sufficient for maximal inhibition, and that the distance between ECD pharmacophores required is 7-9 monomers spanning 4-5 nm. We conclude that inhibition requires recruitment of two receptors on the egg surface into an inhibitory complex.

CD9 controls the formation of clusters that contain tetraspanins and the integrin α6β1, which are involved in human and mouse gamete fusion

The process of gamete fusion has been largely studied in the mouse and has revealed the crucial role of the tetraspanin CD9. By contrast, human gamete fusion remains largely unknown. We now show that an anti-α6 integrin mAb (GoH3) strongly inhibited human sperm-egg fusion in human zona-free eggs. Furthermore, a mAb directed against CD151, a tetraspanin known to associate with α6β1, partially inhibited sperm-egg fusion. By contrast, the addition of an anti-CD9 mAb to zona free eggs had no effect. The integrin α6β1, CD151 and CD9 tetraspanins were evenly distributed on human zona-intact oocytes. On zona-free eggs, the integrin α6β1 and tetraspanin CD151 patched and co-localized but the tetraspanin CD9 remained unchanged. CD9 mAb prevented α6β1 integrin clustering and gamete fusion when added prior to, but not after, zona removal. Antibody-mediated aggregation of integrin α6β1 yielded patches that were bigger and more heterogeneous in mouse oocytes lacking CD9. Moreover, a strong labelling of α6β1 could be observed at the sperm entry point. Altogether, these data show that CD9 controls the redistribution of some membrane proteins including the α6β1 integrin into clusters that may be necessary for gamete fusion.

Role of integrins, tetraspanins, and ADAM proteins during the development of apoptotic bodies by spermatogenic cells

We have previously reported that Sertoli cell geometric changes induced by a Fas (CD95) agonist or by restricting Sertoli cell spreading can trigger spermatogenic cell detachment from Sertoli cell surfaces and initiate a programmed cell death sequence. Here, we have focused on ADAM proteins, tetraspanins CD9 and CD81, and the integrin beta1 subunit, which is co-expressed in testis with integrin alpha3 and integrin alpha6 subunits, to understand how these molecules may stabilize spermatogenic cell attachment to Sertoli cell surfaces. Like ADAM proteins, integrin beta1, alpha3, and alpha6 subunits, and CD9 and CD81 transcripts are expressed in the fetal testis and throughout testicular maturation, as well as, in Sertoli-spermatogenic cell co-cultures. Prespermatogonia (gonocytes) display CD9 and CD81 immunoreactive sites. Integrin alpha6 subunit transcripts have unusual developmental characteristics: fetal testis expresses the integrin alpha6B isoform exclusively. In contrast, the integrin alpha6B isoform co-exists with the integrin alpha6A isoform in prepubertal testes and Sertoli-spermatogenic cell co-cultures. A blocking anti body targeting the extracellular domain (N-terminal) of the integrin beta1 subunit causes rapid contraction of Sertoli cells leading to the gradual detachment of associated spermatogenic cells. In contrast, predicted active site peptides targeting the disintegrin domain of ADAM 1, ADAM 2, ADAM 3 (cyritestin), ADAM 4, ADAM 5, ADAM 6, and ADAM 15 (metragidin) do not disturb significantly the attachment of spermatogenic cells to Sertoli cell surfaces. Spermatogenic cells dislodged from their attachment sites by the integrin beta1 subunit blocking antibody display annexin V immunoreactivity, a sign of early apoptosis. Time-lapse videomicroscopy demonstrates that the removal by apoptosis of a single member of a spermatogenic cell cohort inter-connected by cytoplasmic bridges does not affect the remaining members of the cohort. During spermatogenic cell apoptosis, integrin beta1, alpha3, and alpha6 subunits, and tetraspanins CD9 and C81 become displaced away from the developing apoptotic bodies. In contrast, the intermediate filament protein Sak57, a keratin 5 ortholog, concentrates in the developing apoptotic bodies. We propose that the redistribution of integrin-tetraspanin complexes during spermatogenic cell apoptosis may be evidence of a signaling cascade initiated by Sertoli cell geometric changes. As a result, Sertoli cell reduction in surface area may be a limiting factor of spermatogenic cell survival and in the developmental regulation of spermatogenic cell progenies in the intact seminiferous epithelium.

ADAM-9 (MDC-9/meltrin-gamma), a member of the a disintegrin and metalloproteinase family, regulates myeloma-cell-induced interleukin-6 production in osteoblasts by direct interaction with the alpha(v)beta5 integrin

ADAM-9, a member of the a disintegrin and metalloproteinase family, contains both metalloproteinase and disintegrin domains. Myeloma cell lines express ADAM-9; however, its function and role in the pathophysiology of multiple myeloma is unknown. The aim of this study was to establish whether primary myeloma cells express ADAM-9, whether ADAM-9 regulates IL-6 production in human osteoblasts (hOBs), whether ADAM-9 interacts with specific integrin heterodimers, and the identity of downstream signaling pathways. Primary myeloma cells demonstrated increased expression of ADAM-9 (P < .01). ADAM-9 promoted a 5-fold increase in IL-6, but not IL-1beta mRNA, and a dose- and time-dependent increase in IL-6 production by hOBs (P < .01). IL-6 induction was inhibited by an antibody to the alpha(v)beta5 integrin (P < .01) but not by antibodies to other integrin heterodimers. ADAM-9 was shown to bind directly to the alpha(v)beta5 integrin on hOBs. Antibodies to ADAM-9 and alpha(v)beta5 integrin inhibited myeloma cell-induced IL-6 production by hOBs (P < .01). Furthermore, inhibitors of p38 MAPK and cPLA2, but not NF-kappaB and JAK2, signaling pathways inhibited ADAM-9-induced IL-6 production by hOBs (P < .01). These data demonstrate that ADAM-9, expressed by myeloma cells, stimulates IL-6 production in hOBs by binding the alpha(v)beta5 integrin. This may have important consequences for the growth and survival of myeloma cells in bone.

Cyclic FEE peptide increases human gamete fusion and potentiates its RGD-induced inhibition

BACKGROUND

Alpha6beta1 integrin has been proposed to act as a sperm receptor on the mouse oocyte by interacting with spermatozoon fertilin beta. We investigated, in humans, whether oocyte integrins could act similarly in gamete fusion, using a cyclic peptide containing the putative disintegrin-binding domain of human fertilin beta [cyclic FEE (cFEE)] and RGD peptide.

METHODS

Zona-free eggs were inseminated in the absence or presence of peptides. To maintain the membrane protein pattern, the zona pellucida was removed by microdissection. Immunofluorescence and confocal microscopy were used to detect integrin subunits on the oocyte.

RESULTS

Unexpectedly, cFEE alone increased human gamete fusion by 94% instead of inhibiting fertilization. Furthermore, cFEE together with RGD potentiated the RGD-induced inhibition of fertilization in a dose-dependent manner. The data suggested the hypothesis of integrin cross-talk, further supported by the co-localization of alpha6beta1 and alphavbeta3 integrins, the putative receptors of cFEE and RGD peptides, respectively.

CONCLUSIONS

RGD-sensitive and -insensitive integrins may be associated in a multimolecular complex working as a sperm receptor on the human oocyte membrane. Supplementation of human IVF culture medium with cFEE peptide might improve fertilization rates in ART.

A secreted form of ADAM9 promotes carcinoma invasion through tumor-stromal interactions

Tumor cell invasion is a process regulated by integrins, matrix-degrading enzymes, and interactions with host tissue stromal cells. The ADAM family of proteins plays an important role in modulating various cellular responses. Here, we show that an alternatively spliced variant of ADAM9 is secreted by hepatic stellate cells and promotes carcinoma invasion. ADAM9-S induced a highly invasive phenotype in several human tumor cell lines in Matrigel assays, and the protease activity of ADAM9-S was required for invasion. ADAM9-S binds directly to alpha6beta4 and alpha2beta1 integrins on the surface of colon carcinoma cells through the disintegrin domain. ADAM9-S was also able to cleave laminin and promote invasion. Analysis of human liver metastases revealed that ADAM9 is expressed by stromal liver myofibroblasts, particularly those that are localized within the tumor stroma at the invasive front. These results emphasize the importance of tumor-stromal interactions in invasion and suggest that ADAM9-S can be an important determinant in the ability of cancer cells to invade and colonize the liver.

Synthesis, processing, and subcellular localization of mouse ADAM3 during spermatogenesis and epididymal sperm transport

To elucidate synthesis, processing, and subcellular localization of mouse ADAM3 (cyritestin) during spermatogenesis and epididymal sperm transport, we carried out immunoblotting and immunohistochemical analysis of testicular germ cells, and epididymal and vas deferens sperm, using affinity-purified anti-ADAM3 antibody. ADAM3 was initially synthesized as a 110-kDa precursor in round spermatids, and the precursor was then processed into a 42-kDa mature protein during the sperm transport into and/or once in the epididymis. The mature ADAM3 was localized on the anterior part of capacitated sperm heads and was rapidly removed from the head region during the calcium ionophore A23187-induced acrosome reaction. These results demonstrate that the mature form of ADAM3 is involved in the binding of sperm to the egg zona pellucida, not in the membrane fusion between sperm and egg.

Sperm-egg fusion: events at the plasma membrane

Sperm-egg fusion is a cell-cell membrane fusion event essential for the propagation of sexually reproducing organisms. In gamete fusion, as in other fusion events, such as virus-cell and intracellular vesicle fusion, membrane fusion is a two-step process. Attachment of two membranes through cell-surface molecules is followed by the physical merger of the plasma membrane lipids. Recent progress has demonstrated an essential role for an oocyte tetraspanin, CD9, in mouse sperm-egg fusion, and a specific molecular site crucial for CD9 function has been identified. Absence of glycosylphosphatidylinositol-anchored proteins on the oocyte surface also results in loss of oocyte fusion competence in this gamete. These discoveries provide a strong starting point for the identification of additional proteins that have roles in sperm-egg fusion.

Fertilin beta peptidic liposomes inhibit fertilization by steric blockage

Liposomes presenting fertilinbeta peptides are inhibitors of mouse in vitro fertilization. We undertook a study of the relationship between IC(50) and mole fraction of fertilinbeta in the liposome, and the size dependence of inhibition of fertilization to understand the mechanism of their inhibition. Our results indicate that a small number of multivalent contacts are required for efficient attachment of inhibitor to receptor on the target membrane, and that, as designed, the liposomes target the egg membrane but not the sperm membrane. The size dependence of the liposome inhibition demonstrates that the liposomes physically block access of the sperm to the egg membrane thereby preventing sperm binding to all egg receptors not just the fertilinbeta receptor.

Localization of CD9 in pig oocytes and its effects on sperm-egg interaction

CD9 is a cell surface protein that participates in many cellular processes, such as cell adhesion. Fertilization involves sperm and oocyte interactions including sperm binding to oocytes and sperm-oocyte fusion. Thus CD9 may play an essential role during fertilization in mammals. The present study was conducted to examine whether CD9 is present in porcine gametes and whether it participates in the regulation of sperm-oocyte interactions. The presence of CD9 in ovarian tissues, oocytes and spermatozoa was examined by immunohistochemistry, immunofluorescence and immunoblotting. Sperm binding and penetration of oocytes treated with CD9 antibody were examined by in vitro fertilization. The results showed that CD9 was present on the plasma membrane of oocytes at different developmental stages. A 24 kDa protein was found in oocytes during in vitro maturation by immunoblotting and its quantity was significantly (P < 0.001) increased as oocytes underwent maturation and reached the highest level after the oocytes had been cultured for 44 h. No positive CD9 staining was found in the spermatozoa. Both sperm binding to ooplasma and sperm penetration into oocytes were significantly (P < 0.01) reduced in anti-CD9 antibody-treated oocytes (1.2 +/- 0.2 per oocyte and 16.6% respectively) as compared with oocytes in the controls (2.5 +/- 0.4 per oocyte and 70.3% respectively). These results indicated that CD9 is expressed in pig oocytes during early growth and meiotic maturation and that it participates in sperm-oocyte interactions during fertilization.

The mechanism of sperm-oocyte fusion in mammals

Sperm-oocyte fusion is one of the most impressive events in sexual reproduction, and the elucidation of its molecular mechanism has fascinated researchers for a long time. Because of the limitation of materials and difficulties in analyzing membrane protein-protein interactions, many attempts have failed to reach this goal. Recent studies involving gene targeting have clearly demonstrated the various molecules that are involved in sperm-oocyte binding and fusion. Sperm ADAMs (family of proteins with a disintegrin and metalloprotease domain), including fertilin alpha, fertilin beta and cyritestin, have been investigated and found to be important for binding rather than for fusion and painstaking studies have raised suspicions that their putative receptors, oocyte integrins, are necessary for the sperm-oocyte interaction. Recently, several studies have focused the spotlight on CD9 and glycosylphosphatidylinositol (GPI)-anchored proteins on oocytes, and epididymal protein DE on sperm, as candidate molecules involved in sperm-oocyte fusion. Lack of, or interference with the function of, these proteins can disrupt the sperm-oocyte fusion without changing the binding. In this review we highlight the candidate molecules involved in the sperm-oocyte interaction suggested from the recent progress in this research field.

Possible function of the ADAM1a/ADAM2 Fertilin complex in the appearance of ADAM3 on the sperm surface

In mouse, two different isoforms of ADAM1 (fertilin alpha), ADAM1a and ADAM1b, are produced in the testis. ADAM1a is localized within the endoplasmic reticulum of testicular germ cells, whereas epididymal sperm contain only ADAM1b on the plasma membrane. In this study, we show that the loss of ADAM1a results in the male infertility because of the severely impaired ability of sperm to migrate from the uterus into the oviduct through the uterotubal junction. However, epididymal sperm of ADAM1a-deficient mice were capable of fertilizing cumulus-intact, zona pellucida-intact eggs in vitro despite the delayed dispersal of cumulus cells and the reduced adhesion/binding to the zona pellucida. Among testis (sperm)-specific proteins examined, only the level of ADAM3 (cyritestin) was strongly reduced in ADAM1a-deficient mouse sperm. Moreover, the appearance of ADAM3 on the sperm surface was dependent on the formation of a fertilin protein complex between ADAM1a and ADAM2 (fertilin beta) in testicular germ cells, although no direct interaction between the fertilin complex and ADAM3 was found. These results suggest that ADAM1a/ADAM2 fertilin may be implicated in the selective transport of specific sperm proteins including ADAM3 from the endoplasmic reticulum of testicular germ cells onto the cell surface. These proteins then can participate in sperm migration into the oviduct, the dispersal of cumulus cells, and sperm binding to the zona pellucida.

ADAMs: modulators of cell-cell and cell-matrix interactions

ADAMs contain adhesive and metalloprotease domains. As major ectodomain sheddases, they release a variety of cell-surface proteins, including growth factors, cytokines, cell adhesion molecules and receptors. ADAMs can also cleave and remodel components of the extracellular matrix. Hence, ADAMs are emerging as key modulators of cell-cell and cell-matrix interactions. Important questions, including if and how ADAM adhesive domains promote ADAM protease function, are currently being addressed.

Role of multiple beta1 integrins in cell adhesion to the disintegrin domains of ADAMs 2 and 3

ADAM disintegrin domains can support integrin-mediated cell adhesion. However, the profile of which integrins are employed for adhesion to a given disintegrin domain remains unclear. For example, we suggested that the disintegrin domains of mouse sperm ADAMs 2 and 3 can interact with the alpha6beta1 integrin on mouse eggs. Others concluded that these disintegrin domains interact instead with the alpha9beta1 integrin. To address these differing results, we first studied adhesion of mouse F9 embryonal carcinoma cells and human G361 melanoma cells to the disintegrin domains of mouse ADAMs 2 and 3. Both cell lines express alpha6beta1 and alpha9beta1 integrins at their surfaces. Antibodies to the alpha6 integrin subunit inhibited adhesion of both cell lines. An antibody that recognizes human alpha9 integrin inhibited adhesion of G361 cells. VLO5, a snake disintegrin that antagonizes alpha4beta1 and alpha9beta1 integrins, potently inhibited adhesion of both cell lines. We next explored expression of the alpha9 integrin subunit in mouse eggs. In contrast to our ability to detect alpha6beta1, we were unable to convincingly detect alpha9beta1 integrin on the surface of mouse eggs. Moreover, treatment of mouse eggs with 250 nm VLO5, which is 250 fold over its approximately IC(50) for inhibition of somatic cell adhesion, had minimal effect on sperm-egg binding or fusion. We did detect alpha9 integrin protein on epithelial cells of the oviduct. Additional studies showed that antibodies to the alpha6 and alpha7 integrins additively inhibited adhesion of mouse trophoblast stem cells and that an antibody to the alpha4 integrin inhibited adhesion of MOLT-3 cells to these disintegrin domains: Our data suggest that multiple integrins (on the same cell) can participate in adhesion to a given ADAM disintegrin domain and that interactions between ADAMs and integrins may be important for sperm transit through the oviduct.

Adenovirus ADP protein (E3-11.6K), which is required for efficient cell lysis and virus release, interacts with human MAD2B

The human subgroup C adenovirus (Ad) protein named adenovirus death protein (ADP) (previously named E3-11.6K) is synthesized at very late stages of infection when it mediates efficient lysis of cells and release of adenovirus to infect other cells. ADP is an integral membrane N-linked, O-linked palmitoylated glycoprotein of 101 amino acids (aa) that localizes to the nuclear membrane, endoplasmic reticulum (ER), and Golgi. It has a single membrane spanning region (roughly aa 40-60) and is oriented with aa 1-40 in the lumen and aa 61-101 in the nucleoplasm and cytoplasm. Using aa 61-101 of Ad2 ADP as bait in a yeast two-hybrid screen, we isolated a cDNA for a 211-aa protein that initially was not in the database but has now been published by others with the names human MAD2B, MAD2L2, and REV7. ADP binds strongly to human MAD2B not only in yeast but also in GST pull-down experiments and in coimmunoprecipitations of ADP and MAD2B synthesized in vitro or in vivo. ADP mutants with deletions throughout the bait region do not interact with human MAD2B, whereas a Pro69Pro70 to Ala69Ala70 mutant in the "basic-proline" domain of ADP does interact. Northern blot analyses indicate that human MAD2B is expressed ubiquitously. Human MAD2B is about 25% identical to human MAD2, a spindle assembly checkpoint protein. Two human A549 cell lines were made that constitutively overexpress MAD2B. Wild-type adenovirus lyses these cells significantly more slowly than it lyses parental A549 cells, raising the possibility that ADP and MAD2B act in opposition and suggesting that the ADP-MAD2B interaction is biologically relevant.

Differential localization of ADAM1a and ADAM1b in the endoplasmic reticulum of testicular germ cells and on the surface of epididymal sperm

Although fertilin is a heterodimeric complex between ADAM1 (A Disintegrin And Metalloprotease 1, fertilin alpha) and ADAM2 (fertilin beta) located on the sperm surface, two different ADAM1 isoforms, ADAM1a and ADAM1b, are present in the mouse testis. In this study, we have examined the localization of ADAM1a and ADAM1b in testicular germ cells and epididymal sperm. ADAM1a was restrictedly present within the endoplasmic reticulum of germ cells, whereas epididymal sperm contained only ADAM1b on the cell surface. The precursors of ADAM1a and ADAM1b formed a heterodimeric complex with that of ADAM2 in the endoplasmic reticulum of germ cells. The heterodimeric complex between the mature forms of ADAM1b and ADAM2 was also found on the sperm surface. These data imply the potential roles of ADAM1a and ADAM1b in spermatogenesis and fertilization, respectively.

None of the integrins known to be present on the mouse egg or to be ADAM receptors are essential for sperm-egg binding and fusion

Antibody inhibition and alpha6beta1 ligand binding experiments indicate that the egg integrin alpha6beta1 functions as a receptor for sperm during gamete fusion; yet, eggs null for the alpha6 integrin exhibit normal fertilization. Alternative integrins may be involved in sperm-egg binding and fusion and could compensate for the absence of alpha6beta1. Various beta1 integrins and alphav integrins are present on mouse eggs. Some of these integrins are also reported to be receptors for ADAMs, which are expressed on sperm. Using alpha3 integrin null eggs, we found that the alpha3beta1 integrin was not essential for sperm-egg binding and fusion. Oocyte-specific, beta1 integrin conditional knockout mice allowed us to obtain mature eggs lacking all beta1 integrins. We found that the beta1 integrin null eggs were fully functional in fertilization both in vivo and in vitro. Furthermore, neither anti-mouse beta3 integrin function-blocking monoclonal antibody (mAb) nor alphav integrin function-blocking mAb inhibited sperm binding to or fusion with beta1 integrin null eggs. Thus, function of beta3 or alphav integrins does not seem to be involved in compensating for the absence of beta1 integrins. These results indicate that none of the integrins known to be present on mouse eggs or to be ADAM receptors are essential for sperm-egg binding/fusion, and thus, egg integrins may not play the role in gamete fusion previously attributed to them.

Cell adhesion and fertilization: steps in oocyte transport, sperm-zona pellucida interactions, and sperm-egg fusion

Fertilization in mammals requires the successful completion of many steps, starting with the transport of gametes in the reproductive tract and ending with sperm-egg membrane fusion. In this minireview, we focus on three adhesion steps in this multistep process. The first is oocyte "pick-up," in which the degree of adhesion between the extracellular matrix of the cumulus cells and oviductal epithelial cells controls the successful pick-up of the oocyte-cumulus complex and its subsequent transfer into the oviduct. The second part of this review is concerned with the interaction between the sperm and the zona pellucida of the egg. Evidence is discussed that a plasma membrane form of galactosyltransferase on the surface of mouse sperm binds to ZP3 in the zona pellucida and initiates an acrosome reaction. Additional evidence raises the possibility that initial sperm binding to the zona pellucida is independent of ZP3. Last, we address the relationship between sperm adhesion to the egg plasma membrane and membrane fusion, especially the role of ADAM family proteins on the sperm surface and egg integrins.

Developmental regulation and neuronal expression of the cellular disintegrin ADAM11 gene in mouse nervous system

ADAM11 is the prototype member of the predominantly CNS-associated clade of the ADAM metalloprotease-disintegrins that has been implicated in neural adhesion and axon guidance. The present study describes the spatiotemporal expression pattern of the ADAM11 gene in adult and developing mouse, and identifies the cells expressing the gene. In the adult CNS, ADAM11 mRNA was present throughout the forebrain, including different cortical fields and diencephalic nuclei. In brainstem, low to moderate expression was detected in certain midbrain nuclei, while several pontine and medullary nuclei showed a very strong signal. High expression was observed in the cerebellar cortex and spinal cord. In addition, ADAM11 was expressed in ganglia of the peripheral nervous system (PNS), retinae, testes, liver, and at lower levels in epidermal and mucosal epithelia, kidney, and salivary gland. The expression was localized to neurons in all examined CNS and PNS subfields. During pre- and perinatal development, ADAM11 was differentially expressed both in the developing PNS and CNS, as well as in heart, kidney, eyes, and brown fat. The present results suggest a widespread involvement of ADAM11 in neuron-neuron or neuron-glial cell interactions during development as well as in the adult nervous system. They provide novel complementary information to recently accumulated data on CNS integrin gene expression and offer useful clues for further studies of the neural functions of ADAMs and integrins.