Absence of Dp71 in mdx3cv mouse spermatozoa alters flagellar morphology and the distribution of ion channels and nNOS

Signaling through the dystrophin glycoprotein complex affects the stress-dependent transcriptome in Drosophila

Deficiencies in the human dystrophin glycoprotein complex (DGC), which links the extracellular matrix with the intracellular cytoskeleton, cause muscular dystrophies, a group of incurable disorders associated with heterogeneous muscle, brain and eye abnormalities. Stresses such as nutrient deprivation and aging cause muscle wasting, which can be exacerbated by reduced levels of the DGC in membranes, the integrity of which is vital for muscle health and function. Moreover, the DGC operates in multiple signaling pathways, demonstrating an important function in gene expression regulation. To advance disease diagnostics and treatment strategies, we strive to understand the genetic pathways that are perturbed by DGC mutations. Here, we utilized a Drosophila model to investigate the transcriptomic changes in mutants of four DGC components under temperature and metabolic stress. We identified DGC-dependent genes, stress-dependent genes and genes dependent on the DGC for a proper stress response, confirming a novel function of the DGC in stress-response signaling. This perspective yields new insights into the etiology of muscular dystrophy symptoms, possible treatment directions and a better understanding of DGC signaling and regulation under normal and stress conditions.

Kcnj16 (Kir5.1) Gene Ablation Causes Subfertility and Increases the Prevalence of Morphologically Abnormal Spermatozoa

The ability of spermatozoa to swim towards an oocyte and fertilize it depends on precise K+ permeability changes. Kir5.1 is an inwardly-rectifying potassium (Kir) channel with high sensitivity to intracellular H+ (pHi) and extracellular K+ concentration [K+]o, and hence provides a link between pHi and [K+]o changes and membrane potential. The intrinsic pHi sensitivity of Kir5.1 suggests a possible role for this channel in the pHi-dependent processes that take place during fertilization. However, despite the localization of Kir5.1 in murine spermatozoa, and its increased expression with age and sexual maturity, the role of the channel in sperm morphology, maturity, motility, and fertility is unknown. Here, we confirmed the presence of Kir5.1 in spermatozoa and showed strong expression of Kir4.1 channels in smooth muscle and epithelial cells lining the epididymal ducts. In contrast, Kir4.2 expression was not detected in testes. To examine the possible role of Kir5.1 in sperm physiology, we bred mice with a deletion of the Kcnj16 (Kir5.1) gene and observed that 20% of Kir5.1 knock-out male mice were infertile. Furthermore, 50% of knock-out mice older than 3 months were unable to breed. By contrast, 100% of wild-type (WT) mice were fertile. The genetic inactivation of Kcnj16 also resulted in smaller testes and a greater percentage of sperm with folded flagellum compared to WT littermates. Nevertheless, the abnormal sperm from mutant animals displayed increased progressive motility. Thus, ablation of the Kcnj16 gene identifies Kir5.1 channel as an important element contributing to testis development, sperm flagellar morphology, motility, and fertility. These findings are potentially relevant to the understanding of the complex pHi- and [K+]o-dependent interplay between different sperm ion channels, and provide insight into their role in fertilization and infertility.

Single-Molecule Localization of the Cardiac Voltage-Gated Sodium Channel Reveals Different Modes of Reorganization at Cardiomyocyte Membrane Domains

BACKGROUND

Mutations in the gene encoding the cardiac voltage-gated sodium channel Na_v1.5 cause various cardiac arrhythmias. This variety may arise from different determinants of Na_v1.5 expression between cardiomyocyte domains. At the lateral membrane and T-tubules, Na_v1.5 localization and function remain insufficiently characterized.

METHODS

We used novel single-molecule localization microscopy and computational modeling to define nanoscale features of Na_v1.5 localization and distribution at the lateral membrane, the lateral membrane groove, and T-tubules in cardiomyocytes from wild-type (N=3), dystrophin-deficient (mdx; N=3) mice, and mice expressing C-terminally truncated Na_v1.5 (ΔSIV; N=3). We moreover assessed T-tubules sodium current by recording whole-cell sodium currents in control (N=5) and detubulated (N=5) wild-type cardiomyocytes.

RESULTS

We show that Na_v1.5 organizes as distinct clusters in the groove and T-tubules which density, distribution, and organization partially depend on SIV and dystrophin. We found that overall reduction in Na_v1.5 expression in mdx and ΔSIV cells results in a nonuniform redistribution with Na_v1.5 being specifically reduced at the groove of ΔSIV and increased in T-tubules of mdx cardiomyocytes. A T-tubules sodium current could, however, not be demonstrated.

CONCLUSIONS

Na_v1.5 mutations may site-specifically affect Na_v1.5 localization and distribution at the lateral membrane and T-tubules, depending on site-specific interacting proteins. Future research efforts should elucidate the functional consequences of this redistribution.

Dietary Biotin Supplementation Impairs Testis Morphology and Sperm Quality

Supplements containing pharmacological concentrations of biotin are commercially available over the counter. Classical toxicity studies have considered biotin administration as harmless; however, recent investigations have shown that biotin supplementation modifies tissue morphology without changes in toxicity markers, raising concerns about the consequences of morphological changes on tissues' functions and the safety of pharmacological concentrations of the vitamin. Testes are very sensitive to toxicants, and testicular histology is a reliable method to study its function. In this work, we investigated the effects of dietary biotin supplementation on testis morphology and spermatogenesis function using an experimental model, in which we have not observed unfavorable effects on other tissue functions or toxicity markers. Male BALB/cAnNHsd mice were fed a control or a biotin-supplemented diet (1.76 or 97.7 mg biotin/kg diet) for 8 weeks. Compared to the control group, the biotin-supplemented mice presented remarkable testis morphology changes, including increased spermatogonia layers; the cellular mechanism involved is related to increased proliferation. Sperm count and serum testosterone levels were not affected, but spermatozoa motility and morphology were significantly impaired in the biotin-supplemented mice. These results caution against the use of supplements with high concentrations of biotin and indicate that biotin's pharmacological effects on morphology need to be considered in toxicological studies.

Effect of Dp71 deficiency on the oxytocin hypothalamic axis in osmoregulation function in mice

Dp71 is the major form of dystrophins (Dp) in the supraoptic nucleus (SON) and in the neural lobe of hypophysis (NL/HP). Dp71-null mice exhibit a hypo-osmolar status attributed to an altered osmosensitivity of the SON and to a perturbed vasopressinergic axis. Because oxytocin (OT) is implicated in osmoregulation via natriuresis, this study explored the oxytocinergic axis in Dp71-null mice after salt-loading (SL). Under normosmolar conditions, OT-mRNA expression was higher in the Dp71-null SON compared to wild-type (wt) and the OT peptide level has not changed. Dp-immunostaining was localized in astrocytes end-feet surrounding vessels in wt SON. This distribution changed in Dp71-null SON, Dp being detected in OT-soma of MCNs. nNOS and NADPH-diaphorase levels increased in the OT area of the Dp71-null SON compared to wt. In the NL/HP, OT level reduced in Dp71-null mice and Dp localization changed from pituicytes end-feet in wt SON to OT terminals in Dp71-null SON. Salt-Loading resulted in an increase of OT-mRNA and peptide levels in wt SON but had no effect in Dp71-null SON. In the NL/HP, OT content was reduced after SL. For Dp71-null mice, OT level, already low in control, was not modified by SL. Dp level was not affected by SL in the SON nor in the NL/HP. Our data confirmed the importance of Dp71 for the SON functionality in osmoregulation. The localization of Dp71 at the glial-vascular interface could be associated with SON osmosensitivity, leading to an adequate OT synthesis in the SON and release from the NL/HP upon plasmatic hyperosmolality.

Expression and localization of dystrophins and β-dystroglycan in the hypothalamic supraoptic nuclei of rat from birth to adulthood

Dystrophins (Dps) are the sub-membranous proteins that work via the dystrophin-associated proteins complex, which comprises β-dystroglycan (β-DG), a cell surface receptor for extracellular matrix. Recently, we have revealed β-DG decrease and central function impairment of supraoptic nucleus (SON) in Dp71 deficient adult mice, opening the question on the profiles of Dps and β-DG during SON development. At birth and the age of 10, 20 and 60 days, we examined the expression by RT-PCR and Western-blotting, and the distribution by immunohistochemistry of Dps and β-DG. Also, we analyzed, by immunohistochemistry and Western-blotting, the neuropeptide, arginine vasopressin (AVP), in the SON at the different ages. At birth, Dp71 and to a lesser extends, Dp140 and Dp427, and also β-DG are revealed in the SON. They are localized in the magnocellular neurons (MCNs), astrocytes and vessels. From birth to adulthood, the AVP raise in the SON coincides with the progressive increase of Dp71 level while the level of Dp140 and Dp427 increased only at D20, D10 post-natal development, respectively, and β-DG expression did not change. Moreover, the location of Dps or/and β-DG in the cell compartments was modified during development: at D10, Dps appeared in the astrocytes end-feet surrounding MCNs, and at D20, Dps and β-DG codistributed in the astrocytes end-feet, surrounding MCNs and vessels. Such a distribution marks the first steps of post-natal SON development and may be considered essential in the establishment of structural plasticity mechanisms in SON, where astrocyte end-feet, vessels, magnocellular neurons, are physiologically associated. The disappearance of β-DG in the MCNs nucleus marks the adulthood SON and suggests that the complex of Dps associating β-DG is required for the nucleoskeleton function in the post-natal development.

Utrophin Compensates dystrophin Loss during Mouse Spermatogenesis

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder resulting from mutations in the dystrophin gene. The mdx/utrn^−/− mouse, lacking in both dystrophin and its autosomal homologue utrophin, is commonly used to model the clinical symptoms of DMD. Interestingly, these mice are infertile but the mechanisms underlying this phenomenon remain unclear. Using dystrophin deficient mdx mouse and utrophin haplodeficient mdx/utrn^+/− mouse models, we demonstrate the contribution of Dp427 (full-length dystrophin) and utrophin to testis and epididymis development, as well as spermatogenesis. We show that Dp427 deficiency disturbed the balance between proliferation and apoptosis of germ cells during spermatogenesis, which was further disrupted with utrophin haplodeficiency, deciphering a compensatory role of utrophin for dystrophin in the male reproductive system. In the spermatozoa, we have found a compensatory response of utrophin to dystrophin deficiency - namely the upregulation and relocation of utrophin to the flagellar midpiece. This study demonstrates the contribution of Dp427 and utrophin in male fertility, suggesting a potential pathology in DMD patients.

Transcription factors YY1, Sp1 and Sp3 modulate dystrophin Dp71 gene expression in hepatic cells

Dystrophin Dp71, the smallest product encoded by the Duchenne muscular dystrophy gene, is ubiquitously expressed in all non-muscle cells. Although Dp71 is involved in various cellular processes, the mechanisms underlying its expression have been little studied. In hepatic cells, Dp71 expression is down-regulated by the xenobiotic β-naphthoflavone. However, the effectors of this regulation remain unknown. In the present study we aimed at identifying DNA elements and transcription factors involved in Dp71 expression in hepatic cells. Relevant DNA elements on the Dp71 promoter were identified by comparing Dp71 5'-end flanking regions between species. The functionality of these elements was demonstrated by site-directed mutagenesis. Using EMSAs and ChIP, we showed that the Sp1 (specificity protein 1), Sp3 (specificity protein 3) and YY1 (Yin and Yang 1) transcription factors bind to the Dp71 promoter region. Knockdown of Sp1, Sp3 and YY1 in hepatic cells increased endogenous Dp71 expression, but reduced Dp71 promoter activity. In summary, Dp71 expression in hepatic cells is carried out, in part, by YY1-, Sp1- and Sp3-mediated transcription from the Dp71 promoter.

Functional significance of the sex chromosomes during spermatogenesis

Mammalian sex chromosomes arose from an ordinary pair of autosomes. Over hundreds of millions of years, they have evolved into highly divergent X and Y chromosomes and have become increasingly specialized for male reproduction. Both sex chromosomes have acquired and amplified testis-specific genes, suggestive of roles in spermatogenesis. To understand how the sex chromosome genes participate in the regulation of spermatogenesis, we review genes, including single-copy, multi-copy, and ampliconic genes, whose spermatogenic functions have been demonstrated in mouse genetic studies. Sex chromosomes are subject to chromosome-wide transcriptional silencing in meiotic and postmeiotic stages of spermatogenesis. We also discuss particular sex-linked genes that escape postmeiotic silencing and their evolutionary implications. The unique gene contents and genomic structures of the sex chromosomes reflect their strategies to express genes at various stages of spermatogenesis and reveal the driving forces that shape their evolution.Free Chinese abstract: A Chinese translation of this abstract is freely available at http://www.reproduction-online.org/content/149/6/R265/suppl/DC1.Free Japanese abstract: A Japanese translation of this abstract is freely available at http://www.reproduction-online.org/content/149/6/R265/suppl/DC2.

Lack of dystrophin protein Dp71 results in progressive cataract formation due to loss of fiber cell organization

PURPOSE

Dp71 is the main product of the Duchenne muscular dystrophy (DMD) gene in the central nervous system. While studying the impact of its absence on retinal functions, we discovered that mice lacking Dp71 also developed a progressive opacification of the crystalline lens. The purpose of this study was to perform a detailed characterization of the cataract formation in Dp71 knockout (KO-Dp71) mice.

METHODS

Cataract formations in KO-Dp71 mice and wild-type (wt) littermates were assessed in vivo by slit-lamp examination and ex vivo by histological analysis as a function of aging. The expression and cellular localization of the DMD gene products were monitored by western blot and immunohistochemical analysis. Fiber cell integrity was assessed by analyzing the actin cytoskeleton as well as the expression of aquaporin-0 (AQP0).

RESULTS

As expected, a slit-lamp examination revealed that only one of the 20 tested wt animals presented with a mild opacification of the lens and only at the most advanced age. However, a lack of Dp71 was associated with a 40% incidence of cataracts as early as 2 months of age, which progressively increased to full penetrance by 7 months. A subsequent histological analysis revealed an alteration in the structures of the lenses of KO-Dp71 mice that correlated with the severity of the lens opacity. An analysis of the expression of the different dystrophin gene products revealed that Dp71 was the major DMD gene product expressed in the lens, especially in fiber cells. The role of Dp71 in fiber cells was also suggested by the progressive disorganization of the lens fibers, which was observed in the absence of Dp71 and demonstrated by irregular staining of the actin network and the aqueous channel AQP0.

CONCLUSIONS

While its role in the retina has been well characterized, this study demonstrates for the first time the role played by Dp71 in a different ocular tissue: the crystalline lens. It primarily demonstrates the role that Dp71 plays in the maintenance of the integrity of the secondary lens fibers.

Subcellular localization of dystrophin isoforms in cardiomyocytes and phenotypic analysis of dystrophin-deficient mice reveal cardiac myopathy is predominantly caused by a deficiency in full-length dystrophin

Duchenne muscular dystrophy (DMD) is an X-linked recessive progressive muscle degenerative disorder that causes dilated cardiomyopathy in the second decade of life in affected males. Dystrophin, the gene responsible for DMD, encodes full-length dystrophin and various short dystrophin isoforms. In the mouse heart, full-length dystrophin Dp427 and a short dystrophin isoform, Dp71, are expressed. In this study, we intended to clarify the functions of these dystrophin isoforms in DMD-related cardiomyopathy. We used two strains of mice: mdx mice, in which Dp427 was absent but Dp71 was present, and DMD-null mice, in which both were absent. By immunohistochemical staining and density-gradient centrifugation, we found that Dp427 was located in the cardiac sarcolemma and also at the T-tubules, whereas Dp71 was specifically located at the T-tubules. In order to determine whether T tubule-associated Dp71 was involved in DMD-related cardiac disruption, we compared the cardiac phenotypes between DMD-null mice and mdx mice. Both DMD-null mice and mdx mice exhibited severe necrosis, which was followed by fibrosis in cardiac muscle. However, we could not detect a significant difference in myocardial fibrosis between mdx mice and DMD-null mice. Based on the present results, we have shown that cardiac myopathy is caused predominantly by a deficiency of full-length dystrophin Dp427.

Marginal level dystrophin expression improves clinical outcome in a strain of dystrophin/utrophin double knockout mice

Inactivation of all utrophin isoforms in dystrophin-deficient mdx mice results in a strain of utrophin knockout mdx (uko/mdx) mice. Uko/mdx mice display severe clinical symptoms and die prematurely as in Duchenne muscular dystrophy (DMD) patients. Here we tested the hypothesis that marginal level dystrophin expression may improve the clinical outcome of uko/mdx mice. It is well established that mdx3cv (3cv) mice express a near-full length dystrophin protein at ∼5% of the normal level. We crossed utrophin-null mutation to the 3cv background. The resulting uko/3cv mice expressed the same level of dystrophin as 3cv mice but utrophin expression was completely eliminated. Surprisingly, uko/3cv mice showed a much milder phenotype. Compared to uko/mdx mice, uko/3cv mice had significantly higher body weight and stronger specific muscle force. Most importantly, uko/3cv outlived uko/mdx mice by several folds. Our results suggest that a threshold level dystrophin expression may provide vital clinical support in a severely affected DMD mouse model. This finding may hold clinical implications in developing novel DMD therapies.

Calpain modulates capacitation and acrosome reaction through cleavage of the spectrin cytoskeleton

Research on fertilization in mammalian species has revealed that Ca(2+) is an important player in biochemical and physiological events enabling the sperm to penetrate the oocyte. Ca(2+) is a signal transducer that particularly mediates capacitation and acrosome reaction (AR). Before becoming fertilization competent, sperm must experience several molecular, biochemical, and physiological changes where Ca(2+) plays a pivotal role. Calpain-1 and calpain-2 are Ca(2+)-dependent proteases widely studied in mammalian sperm; they have been involved in capacitation and AR but little is known about their mechanism. In this work, we establish the association of calpastatin with calpain-1 and the changes undergone by this complex during capacitation in guinea pig sperm. We found that calpain-1 is relocated and translocated from cytoplasm to plasma membrane (PM) during capacitation, where it could cleave spectrin, one of the proteins of the PM-associated cytoskeleton, and facilitates AR. The aforementioned results were dependent on the calpastatin phosphorylation and the presence of extracellular Ca(2+). Our findings underline the contribution of the sperm cytoskeleton in the regulation of both capacitation and AR. In addition, our findings also reveal one of the mechanisms by which calpain and calcium exert its function in sperm.

Dp71ab/DAPs complex composition changes during the differentiation process in PC12 cells

PC12 cells express different Dp71 isoforms originated from alternative splicing; one of them, Dp71ab lacks exons 71 and 78. To gain insight into the function of Dp71 isoforms we identified dystrophin associated proteins (DAPs) that associate in vivo with Dp71ab during nerve growth factor (NGF) induced differentiation of PC12 cells. DAPs expression was analyzed by RT-PCR, Western blot and indirect immunofluorescence, showing the presence of each mRNA and protein corresponding to alpha-, beta-, gamma-, delta-, and epsilon-sarcoglycans as well as zeta-sarcoglycan mRNA. Western blot analysis also revealed the expression of beta-dystroglycan, alpha1-syntrophin, alpha1-, and beta-dystrobrevins. We have established that Dp71ab forms a complex with beta-dystroglycan, alpha1-syntrophin, beta-dystrobrevin, and alpha-, beta- and gamma-sarcoglycans in undifferentiated PC12 cells. In differentiated PC12 cells, the complex composition changes since Dp71ab associates only with beta-dystroglycan, alpha1-syntrophin, beta-dystrobrevin, and delta-sarcoglycan. Interestingly, neuronal nitric oxide synthase associates with the Dp71ab/DAPs complex during NGF treatment, raising the possibility that Dp71ab may be involved in signal transduction events during neuronal differentiation.

Cardiac sodium channel Nav1.5 is regulated by a multiprotein complex composed of syntrophins and dystrophin

The cardiac sodium channel Na(v)1.5 plays a key role in cardiac excitability and conduction. The purpose of this study was to elucidate the role of the PDZ domain-binding motif formed by the last three residues (Ser-Ile-Val) of the Na(v)1.5 C-terminus. Pull-down experiments were performed using Na(v)1.5 C-terminus fusion proteins and human or mouse heart protein extracts, combined with mass spectrometry analysis. These experiments revealed that the C-terminus associates with dystrophin, and that this interaction was mediated by alpha- and beta-syntrophin proteins. Truncation of the PDZ domain-binding motif abolished the interaction. We used dystrophin-deficient mdx(5cv) mice to study the role of this protein complex in Na(v)1.5 function. Western blot experiments revealed a 50% decrease in the Na(v)1.5 protein levels in mdx(5cv) hearts, whereas Na(v)1.5 mRNA levels were unchanged. Patch-clamp experiments showed a 29% decrease of sodium current in isolated mdx(5cv) cardiomyocytes. Finally, ECG measurements of the mdx(5cv) mice exhibited a 19% reduction in the P wave amplitude, and an 18% increase of the QRS complex duration, compared with controls. These results indicate that the dystrophin protein complex is required for the proper expression and function of Na(v)1.5. In the absence of dystrophin, decreased sodium current may explain the alterations in cardiac conduction observed in patients with dystrophinopathies.

Role of dystrophins and utrophins in platelet adhesion process

Platelets are crucial at the site of vascular injury, adhering to the sub-endothelial matrix through receptors on their surface, leading to cell activation and aggregation to form a haemostatic plug. Platelets display focal adhesions as well as stress fibres to contract and facilitate expulsion of growth and pro-coagulant factors contained in the granules and to constrict the clot. The interaction of F-actin with different actin-binding proteins determines the properties and composition of the focal adhesions. Recently, we demonstrated the presence of dystrophin-associated protein complex corresponding to short dystrophin isoforms (Dp71d and Dp71) and the uthophin gene family (Up400 and Up71), which promote shape change, adhesion, aggregation, and granule centralisation. To elucidate participation of both complexes during the platelet adhesion process, their potential association with integrin beta-1 fraction and the focal adhesion system (alpha-actinin, vinculin and talin) was evaluated by immunofluorescence and immunoprecipitation assays. It was shown that the short dystrophin-associated protein complex participated in stress fibre assembly and in centralisation of cytoplasmic granules, while the utrophin-associated protein complex assembled and regulated focal adhesions. The simultaneous presence of dystrophin and utrophin complexes indicates complementary structural and signalling mechanisms to the actin network, improving the platelet haemostatic role.

Effect of beta-dystroglycan processing on utrophin/Dp116 anchorage in normal and mdx mouse Schwann cell membrane

In the peripheral nervous system, utrophin and the short dystrophin isoform (Dp116) are co-localized at the outermost layer of the myelin sheath of nerve fibers; together with the dystroglycan complex. Dp116 is associated with multiple glycoproteins, i.e. sarcoglycans, and alpha- and beta-dystroglycan, which anchor the cytoplasmic protein subcomplex to the extracellular basal lamina. In peripheral nerve, matrix metalloproteinase activity disrupts the dystroglycan complex by cleaving the extracellular domain of beta-dystroglycan. Metalloproteinase creates a 30 kDa fragment of beta-dystroglycan, leading to a disruption of the link between the extracellular matrix and the cell membrane. Here we asked if the processing of the beta-dystroglycan could influence the anchorage of Dp116 and/or utrophin in normal and mdx Schwann cell membrane. We showed that metalloproteinase-9 was more activated in mdx nerve than in wild-type ones. This activation leads to an accumulation of the 30 kDa beta-dystroglycan isoform and has an impact on the anchorage of Dp116 and utrophin isoforms in mdx Schwann cells membrane. Our results showed that Dp116 had greater affinity to the full length form of beta-dystroglycan than the 30 kDa form. Moreover, we showed for the first time that the short isoform of utrophin (Up71) was over-expressed in mdx Schwann cells compared with wild-type. In addition, this utrophin isoform (Up71) seems to have greater affinity to the 30 kDa beta-dystroglycan which could explain the increased stabilization of this 30 kDa form at the membrane compartment. Our results highlight the potential participation of the short utrophin isoform and the cleaved form of beta-dystroglycan in mdx Schwann cell membrane architecture. We proposed that these two proteins could be implicated in Schwann cell proliferation in response to a microenvironment stress such as mediated by accumulating macrophages in mdx mouse muscle inflammation sites.