Glial dystrophin-associated proteins, laminin and agrin, are downregulated in the brain of mdx mouse

Dystrophin 71 deficiency causes impaired aquaporin-4 polarization contributing to glymphatic dysfunction and brain edema in cerebral ischemia

OBJECTIVE

The glymphatic system serves as a perivascular pathway that aids in clearing liquid and solute waste from the brain, thereby enhancing neurological function. Disorders in glymphatic drainage contribute to the development of vasogenic edema following cerebral ischemia, although the molecular mechanisms involved remain poorly understood. This study aims to determine whether a deficiency in dystrophin 71 (DP71) leads to aquaporin-4 (AQP4) depolarization, contributing to glymphatic dysfunction in cerebral ischemia and resulting in brain edema.

METHODS

A mice model of middle cerebral artery occlusion and reperfusion was used. A fluorescence tracer was injected into the cortex and evaluated glymphatic clearance. To investigate the role of DP71 in maintaining AQP4 polarization, an adeno-associated virus with the astrocyte promoter was used to overexpress Dp71. The expression and distribution of DP71 and AQP4 were analyzed using immunoblotting, immunofluorescence, and co-immunoprecipitation techniques. The behavior ability of mice was evaluated by open field test. Open-access transcriptome sequencing data were used to analyze the functional changes of astrocytes after cerebral ischemia. MG132 was used to inhibit the ubiquitin-proteasome system. The ubiquitination of DP71 was detected by immunoblotting and co-immunoprecipitation.

RESULTS

During the vasogenic edema stage following cerebral ischemia, a decline in the efflux of interstitial fluid tracer was observed. DP71 and AQP4 were co-localized and interacted with each other in the perivascular astrocyte endfeet. After cerebral ischemia, there was a notable reduction in DP71 protein expression, accompanied by AQP4 depolarization and proliferation of reactive astrocytes. Increased DP71 expression restored glymphatic drainage and reduced brain edema. AQP4 depolarization, reactive astrocyte proliferation, and the behavior of mice were improved. After cerebral ischemia, DP71 was degraded by ubiquitination, and MG132 inhibited the decrease of DP71 protein level.

CONCLUSION

AQP4 depolarization after cerebral ischemia leads to glymphatic clearance disorder and aggravates cerebral edema. DP71 plays a pivotal role in regulating AQP4 polarization and consequently influences glymphatic function. Changes in DP71 expression are associated with the ubiquitin-proteasome system. This study offers a novel perspective on the pathogenesis of brain edema following cerebral ischemia.

A Protocol for Simultaneous In Vivo Imaging of Cardiac and Neuroinflammation in Dystrophin-Deficient MDX Mice Using [18F]FEPPA PET

Duchenne muscular dystrophy (DMD) is a neuromuscular disorder caused by dystrophin loss-notably within muscles and the central neurons system. DMD presents as cognitive weakness, progressive skeletal and cardiac muscle degeneration until pre-mature death from cardiac or respiratory failure. Innovative therapies have improved life expectancy; however, this is accompanied by increased late-onset heart failure and emergent cognitive degeneration. Thus, better assessment of dystrophic heart and brain pathophysiology is needed. Chronic inflammation is strongly associated with skeletal and cardiac muscle degeneration; however, neuroinflammation's role is largely unknown in DMD despite being prevalent in other neurodegenerative diseases. Here, we present an inflammatory marker translocator protein (TSPO) positron emission tomography (PET) protocol for in vivo concomitant assessment of immune cell response in hearts and brains of a dystrophin-deficient mouse model [mdx:utrn(+/-)]. Preliminary analysis of whole-body PET imaging using the TSPO radiotracer, [¹⁸F]FEPPA in four mdx:utrn(+/-) and six wildtype mice are presented with ex vivo TSPO-immunofluorescence tissue staining. The mdx:utrn(+/-) mice showed significant elevations in heart and brain [¹⁸F]FEPPA activity, which correlated with increased ex vivo fluorescence intensity, highlighting the potential of TSPO-PET to simultaneously assess presence of cardiac and neuroinflammation in dystrophic heart and brain, as well as in several organs within a DMD model.

The mechanisms underlying the actions of Xuefu Zhuyu decoction pretreatment against neurological deficits after ischemic stroke in mice: The mediation of glymphatic function by aquaporin-4 and its anchoring proteins

Ischemic stroke (IS) has been associated with an impairment in glymphatic function. Xuefu Zhuyu Decoction (XFZYD) is widely used in the prevention and treatment of ischemic stroke. We hypothesized that Xuefu Zhuyu decoction pretreatment could attenuate early neurological deficits after ischemic stroke by enhancing the function of the glymphatic system. To prove our hypothesis, we carried out temporary middle cerebral artery occlusion and reperfusion surgery on C57BL/6 mice and then measured neurological score, infarct size and performed hematoxylin-eosin staining to assess stroke outcomes after 24 h of reperfusion. Subsequently, we injected fluorescent tracers in to the cisterna magna and evaluated tracer distribution in coronal brain sections. The polarization of aquaporin-4 (AQP4), colocalization of aquaporin-4, α-dystroglycan, β-dystroglycan and agrin were determined by immunofluorescence. Our research showed that pretreatment with Xuefu Zhuyu decoction significantly alleviated neurological scores, neurological deficits and pathological abnormalities in a mouse model of ischemic stroke. Importantly, Xuefu Zhuyu decoction pretreatment enhanced cerebrospinal fluid influx, protected aquaporin-4 depolarization and promoted the colocalization of aquaporin-4 with its anchoring proteins in the brain. Our findings highlight novel mechanisms underlying the neuroprotective effect of Xuefu Zhuyu decoction pretreatment on ischemic stroke-induced brain damage through the glymphatic system. Xuefu Zhuyu decoction pretreatment may offer a promising approach to slow the onset and progression of ischemic stroke.

Analysis of Brain Structure and Neural Organization in Dystrophin-Deficient Model Mice with Magnetic Resonance Imaging at 7 T

Background:

Dystrophin strengthens muscle cells; however, in muscular dystrophy, dystrophin is deficient due to an abnormal sugar chain. This abnormality occurs in skeletal muscle and in brain tissue.

Objective:

This study aimed to non-invasively analyze the neural organization of the brain in muscular dystrophy. We used a mouse model of muscular dystrophy to study whether changes in brain structure and neurodegeneration following dystrophin deficiency can be assessed by 7T magnetic resonance imaging.

Methods:

C57BL/10-mdx (X chromosome-linked muscular dystrophy) mice were used as the dystrophic mouse model and healthy mice were used as controls. Ventricular enlargement is one of the most common brain malformations in dystrophin-deficient patients. Therefore, we examined whether ventricular enlargement was observed in C57BL/10-mdx using transverse-relaxation weighted images. Brain parenchyma analysis was performed using diffusion MRI with diffusion tensor images and neurite orientation dispersion and density imaging. Parenchymal degeneration was assessed in terms of directional diffusion, nerve fiber diffusion, and dendritic scattering density.

Results:

For the volume of brain ventricles analyzed by T2WI, the average size was 1.5 times larger in mdx mice compared to control mice. In the brain parenchyma, a significant difference (p < 0.05) was observed in parameters indicating disturbances in the direction of nerve fibers and dendritic scattering density in the white matter region.

Conclusion:

Our results show that changes in brain structure due to dystrophin deficiency can be assessed in detail without tissue destruction by combining diffusion tensor images and neurite orientation dispersion and density imaging analyses.

Mild Traumatic Brain Injury/Concussion Initiates an Atypical Astrocyte Response Caused by Blood-Brain Barrier Dysfunction

Mild traumatic brain injury/concussion (mTBI) accounts for 70-90% of all reported TBI cases and causes long-lasting neurological consequences in 10-40% of patients. Recent clinical studies revealed increased blood-brain barrier (BBB) permeability in mTBI patients, which correlated with secondary damage after mTBI. However, the cascade of cellular events initiated by exposure to blood-borne factors resulting in sustained damage is not fully understood. We previously reported that astrocytes respond atypically to mTBI, rapidly losing many proteins essential to their homeostatic function, while classic scar formation does not occur. Here, we tested the hypothesis that mTBI-induced BBB damage causes atypical astrocytes through exposure to blood-borne factors. Using an mTBI mouse model, two-photon imaging, an endothelial cell-specific genetic ablation approach, and serum-free primary astrocyte cultures, we demonstrated that areas with atypical astrocytes coincide with BBB damage and that exposure of astrocytes to plasma proteins is sufficient to initiate loss of astrocyte homeostatic proteins. Although mTBI resulted in frequent impairment of both physical and metabolic BBB properties and leakage of small-sized blood-borne factors, deposition of the coagulation factor fibrinogen or vessel rupture were rare. Surprisingly, even months after mTBI, BBB repair did not occur in areas with atypical astrocytes. Together, these findings implicate that even relatively small BBB disturbances are sustained long term, and render nearby astrocytes dysfunctional, likely at the cost of neuronal health and function.

Disrupted Calcium Homeostasis in Duchenne Muscular Dystrophy: A Common Mechanism behind Diverse Consequences

Duchenne muscular dystrophy (DMD) leads to disability and death in young men. This disease is caused by mutations in the DMD gene encoding diverse isoforms of dystrophin. Loss of full-length dystrophins is both necessary and sufficient for causing degeneration and wasting of striated muscles, neuropsychological impairment, and bone deformities. Among this spectrum of defects, abnormalities of calcium homeostasis are the common dystrophic feature. Given the fundamental role of Ca2+ in all cells, this biochemical alteration might be underlying all the DMD abnormalities. However, its mechanism is not completely understood. While abnormally elevated resting cytosolic Ca2+ concentration is found in all dystrophic cells, the aberrant mechanisms leading to that outcome have cell-specific components. We probe the diverse aspects of calcium response in various affected tissues. In skeletal muscles, cardiomyocytes, and neurons, dystrophin appears to serve as a scaffold for proteins engaged in calcium homeostasis, while its interactions with actin cytoskeleton influence endoplasmic reticulum organisation and motility. However, in myoblasts, lymphocytes, endotheliocytes, and mesenchymal and myogenic cells, calcium abnormalities cannot be clearly attributed to the loss of interaction between dystrophin and the calcium toolbox proteins. Nevertheless, DMD gene mutations in these cells lead to significant defects and the calcium anomalies are a symptom of the early developmental phase of this pathology. As the impaired calcium homeostasis appears to underpin multiple DMD abnormalities, understanding this alteration may lead to the development of new therapies. In fact, it appears possible to mitigate the impact of the abnormal calcium homeostasis and the dystrophic phenotype in the total absence of dystrophin. This opens new treatment avenues for this incurable disease.

Complexity of skeletal muscle degeneration: multi-systems pathophysiology and organ crosstalk in dystrophinopathy

Duchenne muscular dystrophy is a highly progressive muscle wasting disorder due to primary abnormalities in one of the largest genes in the human genome, the DMD gene, which encodes various tissue-specific isoforms of the protein dystrophin. Although dystrophinopathies are classified as primary neuromuscular disorders, the body-wide abnormalities that are associated with this disorder and the occurrence of organ crosstalk suggest that a multi-systems pathophysiological view should be taken for a better overall understanding of the complex aetiology of X-linked muscular dystrophy. This article reviews the molecular and cellular effects of deficiency in dystrophin isoforms in relation to voluntary striated muscles, the cardio-respiratory system, the kidney, the liver, the gastrointestinal tract, the nervous system and the immune system. Based on the establishment of comprehensive biomarker signatures of X-linked muscular dystrophy using large-scale screening of both patient specimens and genetic animal models, this article also discusses the potential usefulness of novel disease markers for more inclusive approaches to differential diagnosis, prognosis and therapy monitoring that also take into account multi-systems aspects of dystrophinopathy. Current therapeutic approaches to combat muscular dystrophy are summarised.

microRNA-320a prevent Müller cells from hypoxia injury by targeting aquaporin-4

Müller cells are closely related to diabetic retinopathy (DR). Aquaporin-4 (AQP4) can effectively promote the diffusion of water across cellular membranes. However, the dynamic balance of water plays key role in many diseases, such as cerebral edema. Meanwhile, the unusual expression and distribution of AQP4 in the retina are the significant causes of ocular hypertension and reperfusion injury. To explore the functional significance between microRNA-320a (miR-320a) and AQP4 in pathological hypoxia-induced DR related retinal edema, we hypothesized that miR-320a regulates AQP4 expression and internalization to relieve the edema of Müller cells under the pathological retinal hypoxia stress by targeting AQP4, thereby attenuate the damage of Müller cells. Results demonstrated that miR-320a mimics inhibited the expressions of AQP4 in Müller cells. Furthermore, overexpression miR-320a protected Müller cells by suppressing superoxide anion. In addition, overexpression miR-320a markedly attenuated hypoxia-induced injury, significantly increased the cell viability, and promoted the internalization of AQP4. Furthermore, miR-320a can also regulate the stable anchoring of AQP4 on the cell membrane. Our study indicated that miR-320a may be a potential modulator which can mediate AQP4 expression and attenuate the hypoxia damage of Müller cells. In conclusion, miR-320a may be a potential target for DR therapy by targeting AQP4.

Dystrophin Dp71 and the Neuropathophysiology of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is caused by frameshift mutations in the DMD gene that prevent the body-wide translation of its protein product, dystrophin. Besides a severe muscle phenotype, cognitive impairment and neuropsychiatric symptoms are prevalent. Dystrophin protein 71 (Dp71) is the major DMD gene product expressed in the brain and mutations affecting its expression are associated with the DMD neuropsychiatric syndrome. As with dystrophin in muscle, Dp71 localises to dystrophin-associated protein complexes in the brain. However, unlike in skeletal muscle; in the brain, Dp71 is alternatively spliced to produce many isoforms with differential subcellular localisations and diverse cellular functions. These include neuronal differentiation, adhesion, cell division and excitatory synapse organisation as well as nuclear functions such as nuclear scaffolding and DNA repair. In this review, we first describe brain involvement in DMD and the abnormalities observed in the DMD brain. We then review the gene expression, RNA processing and functions of Dp71. We review genotype-phenotype correlations and discuss emerging cellular/tissue evidence for the involvement of Dp71 in the neuropathophysiology of DMD. The literature suggests changes observed in the DMD brain are neurodevelopmental in origin and that their risk and severity is associated with a cumulative loss of distal DMD gene products such as Dp71. The high risk of neuropsychiatric syndromes in Duchenne patients warrants early intervention to achieve the best possible quality of life. Unravelling the function and pathophysiological significance of dystrophin in the brain has become a high research priority to inform the development of brain-targeting treatments for Duchenne.

Organisation of extracellular matrix proteins laminin and agrin in pericapillary basal laminae in mouse brain

Evidence suggests that extracellular matrix molecules of perivascular basal laminae help orchestrate the molecular assemblies at the gliovascular interface. Specifically, laminin and agrin are thought to tether the dystrophin-associated protein (DAP) complex to the astrocytic basal lamina. This complex includes α-syntrophin (α-Syn), which is believed to anchor aquaporin-4 (AQP4) to astrocytic endfoot membrane domains. We have previously shown that the size of the perivascular AQP4 pool differs considerably between brain regions in an α-Syn-dependent manner. Also, both AQP4 and α-Syn occur at higher densities in endfoot membrane domains facing pericytes than in endfoot membrane domains facing endothelial cells. The heterogeneous distribution of AQP4 at the regional and capillary level has been attributed to a direct interaction between AQP4 and α-Syn. This would be challenged (1) if the microdistributions of laminin and agrin fail to align with those of DAP and AQP4 and (2) if targeted deletion of α-Syn leads to a loss of laminin and/or agrin. Here, we provide the first detailed and quantitative analysis of laminin and agrin in brain basal laminae of mice. We show that the microdistributions of these molecules vary in a fashion that is well aligned with the previously reported microdistribution of AQP4. We also demonstrate that the expression patterns of laminin and agrin are insensitive to targeted deletion of α-Syn, suggesting that α-Syn deletion affects AQP4 directly and not indirectly via laminin or agrin. These data fill remaining voids in the current model of how key molecules are assembled and tethered at the gliovascular interface.

The dystroglycan receptor maintains glioma stem cells in the vascular niche

Glioblastomas (GBMs) are malignant central nervous system (CNS) neoplasms with a very poor prognosis. They display cellular hierarchies containing self-renewing tumourigenic glioma stem cells (GSCs) in a complex heterogeneous microenvironment. One proposed GSC niche is the extracellular matrix (ECM)-rich perivascular bed of the tumour. Here, we report that the ECM binding dystroglycan (DG) receptor is expressed and functionally glycosylated on GSCs residing in the perivascular niche. Glycosylated αDG is highly expressed and functional on the most aggressive mesenchymal-like (MES-like) GBM tumour compartment. Furthermore, we found that DG acts to maintain an MES-like state via tight control of MAPK activation. Antibody-based blockade of αDG induces robust ERK-mediated differentiation leading to reduced GSC potential. DG was shown to be required for tumour initiation in MES-like GBM, with constitutive loss significantly delaying or preventing tumourigenic potential in-vivo. These findings reveal a central role of the DG receptor, not only as a structural element, but also as a critical factor promoting MES-like GBM and the maintenance of GSCs residing in the perivascular niche.

Brain Capillary Ultrastructure in Idiopathic Normal Pressure Hydrocephalus: Relationship With Static and Pulsatile Intracranial Pressure

Idiopathic normal pressure hydrocephalus (iNPH) is a neurodegenerative disease of unknown cause. We investigated the morphology of capillaries in frontal cortex biopsies from iNPH patients and related the observations to overnight intracranial pressure (ICP) scores. A biopsy (0.9×10 mm) was taken from where the ICP sensor subsequently was inserted. Brain capillaries were investigated by electron microscopy of biopsies from 27 iNPH patients and 10 reference subjects, i.e. patients (not healthy individuals) without cerebrospinal fluid circulation disturbances, in whom normal brain tissue was removed as part of necessary neurosurgical treatment. Degenerating and degenerated pericyte processes were identified in 23/27 (85%) iNPH and 6/10 (60%) of reference specimens. Extensive disintegration of pericyte processes were recognized in 11/27 (41%) iNPH and 1/10 (10%) reference specimens. There were no differences in basement membrane (BM) thickness or pericyte coverage between iNPH and reference subjects. The pulsatile or static ICP scores did neither correlate with the BM thickness nor with pericyte coverage. We found increased prevalence of degenerating pericytes in iNPH while the BM thickness and pericyte coverage did not differ from the reference individuals. Observations in iNPH may to some extent be age-related since the iNPH patients were significantly older than the reference individuals.

Dp71 is regulated by phosphorylation and ubiquitin-proteasome system in neuronal cells

The Dystrophin (Dp) gene is responsible for Duchenne muscular dystrophy (DMD), which is characterized by progressive muscular degeneration and variable degrees of cognitive impairment. Although Dp71 is the most abundant among the Dp isoforms in the brain, the regulatory mechanisms of the related expression levels have not been elucidated. In this study, we found that the constitutive expression levels of Dp71 in PC12 cells were sensitive to proteasomal inhibition. The ectopic expression of FLAG-tagged ubiquitin revealed that Dp71 was ubiquitinated intracellularly. Interestingly, proteasomal inhibition was accompanied by a posttranslational accumulation of modified Dp71, which was restored by protein phosphatase treatment in vitro, indicating that phosphorylation is responsible for the modification and affects the proteasome-dependent degradation of Dp71. Proteasomal activity-sensitive phosphorylated Dp71 is closely associated with syntrophin, a well-known binding partner of Dp71, and syntrophin is also regulated by proteasomal activity in a similar way to Dp71, suggesting that the posttranslational regulatory machinery for Dp71 level is coupled with Dp71-syntrophin molecular complex. Taken together, our results indicated that the expression levels of Dp71 are posttranslationally regulated by the phosphorylation-ubiquitin-proteasomal pathway, which may indicate the presence of regulatory mechanisms underlying the proteostasis of both Dp and its molecular complex, which may lead to better therapeutic approaches for the treatment of Dp-related diseases.

Abnormal distribution of GABAA receptors in brain of duchenne muscular dystrophy patients

INTRODUCTION

In this study we sought to: (1) determine the distribution of GABA_A receptors (GABA_A -Rs) in the brain of Duchenne muscular dystrophy (DMD) patients; and (2) ascertain if the distribution pattern correlates with cognitive dysfunction.

METHODS

Fourteen DMD patients [young adult (n = 7, 18-25 years old) and older adult (n = 7, 30-37 years old) groups] and 16 age-matched normal volunteers participated. GABA_A -R distribution was assessed using ¹²³ I-IMZ-SPECT. Neuropsychological assessments were performed using 3 different test batteries, the WAIS-III, WMS-R, and Wisconsin Card Sorting Test (WCST).

RESULTS

All DMD patients showed significant decline in ¹²³ I-IMZ uptake in the prefrontal cortex (P < 0.05). Although no differences were detected in the WAIS-III and WMS-R, the WCST scores of DMD patients (2.8 ± 1.9) were significantly lower (P < 0.01) than those of normal volunteers (5.4 ± 0.7). Both abnormalities were more pronounced in older adult patients.

CONCLUSION

The findings demonstrate that DMD is accompanied by a reduction in the prefrontal cortex distribution of GABA_A -Rs. Muscle Nerve 55: 591-595, 2017.

Decreased cerebral perfusion in Duchenne muscular dystrophy patients

Duchenne muscular dystrophy is caused by dystrophin gene mutations which lead to the absence of the protein dystrophin. A significant proportion of patients suffer from learning and behavioural disabilities, in addition to muscle weakness. We have previously shown that these patients have a smaller total brain and grey matter volume, and altered white matter microstructure compared to healthy controls. Patients with more distal gene mutations, predicted to affect dystrophin isoforms Dp140 and Dp427, showed greater grey matter reduction. Now, we studied if cerebral blood flow in Duchenne muscular dystrophy patients is altered, since cerebral expression of dystrophin also occurs in vascular endothelial cells and astrocytes associated with cerebral vasculature. T1-weighted anatomical and pseudo-continuous arterial spin labeling cerebral blood flow images were obtained from 26 patients and 19 age-matched controls (ages 8-18 years) on a 3 tesla MRI scanner. Group comparisons of cerebral blood flow were made with and without correcting for grey matter volume using partial volume correction. Results showed that patients had a lower cerebral blood flow than controls (40.0 ± 6.4 and 47.8 ± 6.3 mL/100 g/min respectively, p = 0.0002). This reduction was independent of grey matter volume, suggesting that they are two different aspects of the pathophysiology. Cerebral blood flow was lowest in patients lacking Dp140. There was no difference in CBF between ambulant and non-ambulant patients. Only three patients showed a reduced left ventricular ejection fraction. No correlation between cerebral blood flow and age was found. Our results indicate that cerebral perfusion is reduced in Duchenne muscular dystrophy patients independent of the reduced grey matter volume.

Decreased inward rectifier potassium current IK1 in dystrophin-deficient ventricular cardiomyocytes

Kir2.x channels in ventricular cardiomyocytes (most prominently Kir2.1) account for the inward rectifier potassium current I_K1, which controls the resting membrane potential and the final phase of action potential repolarization. Recently it was hypothesized that the dystrophin-associated protein complex (DAPC) is important in the regulation of Kir2.x channels. To test this hypothesis, we investigated potential I_K1 abnormalities in dystrophin-deficient ventricular cardiomyocytes derived from the hearts of Duchenne muscular dystrophy mouse models. We found that I_K1 was substantially diminished in dystrophin-deficient cardiomyocytes when compared to wild type myocytes. This finding represents the first functional evidence for a significant role of the DAPC in the regulation of Kir2.x channels.

Dystroglycan Suppresses Notch to Regulate Stem Cell Niche Structure and Function in the Developing Postnatal Subventricular Zone

While the extracellular matrix (ECM) is known to regulate neural stem cell quiescence in the adult subventricular zone (SVZ), the function of ECM in the developing SVZ remains unknown. Here, we report that the ECM receptor dystroglycan regulates a unique developmental restructuring of ECM in the early postnatal SVZ. Dystroglycan is furthermore required for ependymal cell differentiation and assembly of niche pinwheel structures, at least in part by suppressing Notch activation in radial glial cells, which leads to the increased expression of MCI, Myb, and FoxJ1, transcriptional regulators necessary for acquisition of the multiciliated phenotype. Dystroglycan also regulates perinatal radial glial cell proliferation and transition into intermediate gliogenic progenitors, such that either acute or constitutive loss of function in dystroglycan results in increased oligodendrogenesis. These findings reveal a role for dystroglycan in orchestrating both the assembly and function of the SVZ neural stem cell niche.

Label-free mass spectrometric analysis reveals complex changes in the brain proteome from the mdx-4cv mouse model of Duchenne muscular dystrophy

BACKGROUND

X-linked muscular dystrophy is a primary disease of the neuromuscular system. Primary abnormalities in the Dmd gene result in the absence of the full-length isoform of the membrane cytoskeletal protein dystrophin. Besides progressive skeletal muscle wasting and cardio-respiratory complications, developmental cognitive deficits and behavioural abnormalities are clinical features of Duchenne muscular dystrophy. In order to better understand the mechanisms that underlie impaired brain functions in Duchenne patients, we have carried out a proteomic analysis of total brain extracts from the mdx-4cv mouse model of dystrophinopathy.

RESULTS

The comparative proteomic profiling of the mdx-4cv brain revealed a significant increase in 39 proteins and a decrease in 7 proteins. Interesting brain tissue-associated proteins with an increased concentration in the mdx-4cv animal model were represented by the glial fibrillary acidic protein GFAP, the neuronal Ca(2+)-binding protein calretinin, annexin AnxA5, vimentin, the neuron-specific enzyme ubiquitin carboxyl-terminal hydrolase isozyme L1, the dendritic spine protein drebrin, the cytomatrix protein bassoon of the nerve terminal active zone, and the synapse-associated protein SAP97. Decreased proteins were identified as the nervous system-specific proteins syntaxin-1B and syntaxin-binding protein 1, as well as the plasma membrane Ca(2+)-transporting ATPase PMCA2 that is mostly found in the brain cortex. The differential expression patterns of GFAP, vimentin, PMCA2 and AnxA5 were confirmed by immunoblotting. Increased GFAP levels were also verified by immunofluorescence microscopy.

CONCLUSIONS

The large number of mass spectrometrically identified proteins with an altered abundance suggests complex changes in the mdx-4cv brain proteome. Increased levels of the glial fibrillary acidic protein, an intermediate filament component that is uniquely associated with astrocytes in the central nervous system, imply neurodegeneration-associated astrogliosis. The up-regulation of annexin and vimentin probably represent compensatory mechanisms involved in membrane repair and cytoskeletal stabilization in the absence of brain dystrophin. Differential alterations in the Ca(2+)-binding protein calretinin and the Ca(2+)-pumping protein PMCA2 suggest altered Ca(2+)-handling mechanisms in the Dp427-deficient brain. In addition, the proteomic findings demonstrated metabolic adaptations and functional changes in the central nervous system from the dystrophic phenotype. Candidate proteins can now be evaluated for their suitability as proteomic biomarkers and their potential in predictive, diagnostic, prognostic and/or therapy-monitoring approaches to treat brain abnormalities in dystrophinopathies.

Perlecan is recruited by dystroglycan to nodes of Ranvier and binds the clustering molecule gliomedin

Fast neural conduction requires accumulation of Na(+) channels at nodes of Ranvier. Dedicated adhesion molecules on myelinating cells and axons govern node organization. Among those, specific laminins and dystroglycan complexes contribute to Na(+) channel clustering at peripheral nodes by unknown mechanisms. We show that in addition to facing the basal lamina, dystroglycan is found near the nodal matrix around axons, binds matrix components, and participates in initial events of nodogenesis. We identify the dystroglycan-ligand perlecan as a novel nodal component and show that dystroglycan is required for the selective accumulation of perlecan at nodes. Perlecan binds the clustering molecule gliomedin and enhances clustering of node of Ranvier components. These data show that proteoglycans have specific roles in peripheral nodes and indicate that peripheral and central axons use similar strategies but different molecules to form nodes of Ranvier. Further, our data indicate that dystroglycan binds free matrix that is not organized in a basal lamina.

Mechanisms of astrocyte-mediated cerebral edema

Cerebral edema formation stems from disruption of blood brain barrier (BBB) integrity and occurs after injury to the CNS. Due to the restrictive skull, relatively small increases in brain volume can translate into impaired tissue perfusion and brain herniation. In excess, cerebral edema can be gravely harmful. Astrocytes are key participants in cerebral edema by virtue of their relationship with the cerebral vasculature, their unique compliment of solute and water transport proteins, and their general role in brain volume homeostasis. Following the discovery of aquaporins, passive conduits of water flow, aquaporin 4 (AQP4) was identified as the predominant astrocyte water channel. Normally, AQP4 is highly enriched at perivascular endfeet, the outermost layer of the BBB, whereas after injury, AQP4 expression disseminates to the entire astrocytic plasmalemma, a phenomenon termed dysregulation. Arguably, the most important role of AQP4 is to rapidly neutralize osmotic gradients generated by ionic transporters. In pathological conditions, AQP4 is believed to be intimately involved in the formation and clearance of cerebral edema. In this review, we discuss aquaporin function and localization in the BBB during health and injury, and we examine post-injury ionic events that modulate AQP4-dependent edema formation.

Effects of prednisolone on the dystrophin-associated proteins in the blood-brain barrier and skeletal muscle of dystrophic mdx mice

The mdx mouse, the most widely used animal model of Duchenne muscular dystrophy (DMD), develops a seriously impaired blood-brain barrier (BBB). As glucocorticoids are used clinically to delay the progression of DMD, we evaluated the effects of chronic treatment with α-methyl-prednisolone (PDN) on the expression of structural proteins and markers in the brain and skeletal muscle of the mdx mouse. We analyzed the immunocytochemical and biochemical expression of four BBB markers, including endothelial ZO-1 and occludin, desmin in pericytes, and glial fibrillary acidic protein (GFAP) in glial cells, and the expression of the short dystrophin isoform Dp 71, the dystrophin-associated proteins (DAPs), and aquaporin-4 (AQP4) and α-β dystroglycan (DG) in the brain. We evaluated the BBB integrity of mdx and PDN-treated mdx mice by means of intravascular injection of horseradish peroxidase (HRP). The expression of DAPs was also assessed in gastrocnemius muscles and correlated with utrophin expression, and laminin content was measured in the muscle and brain. PDN treatment induced a significant increase in the mRNA and protein content of the BBB markers; a reduction in the phosphorylation of occludin in the brain and of AQP4/β DG in both tissues; an increase of Dp71 protein content; and an increase of both mRNA and protein levels of the AQP4/α-β DG complex. The latter was associated with enhanced laminin and utrophin in the muscle. The HRP assay demonstrated functional restoration of the BBB in the PDN-treated mdx mice. Specifically, mdx mice showed extensive perivascular labeling due to escape of the marker, while HRP was exclusively intravascular in the PDN-treated mice and the controls. These data illustrate for the first time that PDN reverses the BBB alterations in the mdx mouse and re-establishes the proper expression and phosphorylation of β-DG in both the BBB and skeletal muscle. Further, PDN partially protects against muscle damage. The reduction in AQP4 and occludin phosphorylation, coupled with their anchoring to glial and endothelial membranes in PDN-treated mice, suggests that the drug may target the glial and endothelial cells. Our results suggest a novel mechanism for PDN action on cerebral and muscular function, restoring the link between DAPs and the extracellular matrix, most likely through protein kinase inactivation.

Upregulation of brain utrophin does not rescue behavioral alterations in dystrophin-deficient mice

Dystrophin, the protein responsible for X-linked Duchenne muscular dystrophy (DMD), is normally expressed in both muscle and brain, which explains that its loss also leads to cognitive deficits. The utrophin protein, an autosomal homolog, is a natural candidate for dystrophin replacement in patients. Pharmacological upregulation of endogenous utrophin improves muscle physiology in dystrophin-deficient mdx mice, and represents a potential therapeutic tool that has the advantage of allowing delivery to various organs following peripheral injections. Whether this could alleviate cognitive deficits, however, has not been explored. Here, we first investigated basal expression of all utrophins and dystrophins in the brain of mdx mice and found no evidence for spontaneous compensation by utrophins. Then, we show that systemic chronic, spaced injections of arginine butyrate (AB) alleviate muscle alterations and upregulate utrophin expression in the adult brain of mdx mice. AB selectively upregulated brain utrophin Up395, while reducing expression of Up113 and Up71. This, however, was not associated with a significant improvement of behavioral functions typically affected in mdx mice, which include exploration, emotional reactivity, spatial and fear memories. We suggest that AB did not overcome behavioral and cognitive dysfunctions because the regional and cellular expression of utrophins did not coincide with dystrophin expression in untreated mice, nor did it in AB-treated mice. While treatments based on the modulation of utrophin may alleviate DMD phenotypes in certain organs and tissues that coexpress dystrophins and utrophins in the same cells, improvement of cognitive functions would likely require acting on specific dystrophin-dependent mechanisms.

Aquaporin-4 expression in primary human central nervous system lymphomas correlates with tumour cell proliferation and phenotypic heterogeneity of the vessel wall

No literature data are available concerning the expression of aquaporin-4 in primary central nervous system lymphomas and the relationship between aquaporin-4 expression and the morphological characteristics of blood vessels. Here, we have investigated this relationship in 24 human diffuse large B-cell primary central nervous system lymphomas by means of immunocytochemistry and confocal laser microscopy. Results have shown that: (i) a high aquaporin-4 expression correlated with a high Ki-67 index and aquaporin-4 marked tumour and endothelial cells in cytoplasm and plasma membranes, while aquaporin-4 expression was low in tumour areas with a low Ki-67 index where few tumour cells were positive to aquaporin-4, and endothelial cells showed aquaporin-4 expression on their abluminal side. (ii) Different type of cells participated in vessels formation: CD20(+) tumour cells and factor VIII(+) endothelial cells; aquaporin-4(+) tumour cells and CD31(+) endothelial cells; CD20(+) and aquaporin-4(+) tumour cells; glial fibrillary acidid protein(+) endothelial cells surrounded by glial fibrillary acidic protein(+) tumour cells. Overall, these data suggest the importance of aquaporin-4 in primary central nervous system lymphomas due to its involvement in cerebral oedema formation and resolution and tumour cell migratory activity, and have documented that tumour microvasculature in lymphomas is extremely heterogeneous, confirming the importance of neoangiogenesis in the pathogenesis of lymphomas.

Role of aquaporins in cell migration and edema formation in human brain tumors

The aquaporins (AQPs) are a family of transmembrane water channel proteins widely distributed and play a major role in transcellular and transepithelial water movement. Moreover, recent evidence indicates that AQPs may be involved in cell migration, angiogenesis, and tumor growth. This review article summarizes literature data concerning the involvement of AQP-1 and -4 in human brain tumor growth and edema formation and suggests a potential therapeutic approach by antagonizing their biological activity.