Association of dystrophin-related protein 2 (DRP2) with postsynaptic densities in rat brain

Autophagy and apoptosis cascade: which is more prominent in neuronal death?

Autophagy and apoptosis are two crucial self-destructive processes that maintain cellular homeostasis, which are characterized by their morphology and regulated through signal transduction mechanisms. These pathways determine the fate of cellular organelle and protein involved in human health and disease such as neurodegeneration, cancer, and cardiovascular disease. Cell death pathways share common molecular mechanisms, such as mitochondrial dysfunction, oxidative stress, calcium ion concentration, reactive oxygen species, and endoplasmic reticulum stress. Some key signaling molecules such as p53 and VEGF mediated angiogenic pathway exhibit cellular and molecular responses resulting in the triggering of apoptotic and autophagic pathways. Herein, based on previous studies, we describe the intricate relation between cell death pathways through their common genes and the role of various stress-causing agents. Further, extensive research on autophagy and apoptotic machinery excavates the implementation of selective biomarkers, for instance, mTOR, Bcl-2, BH3 family members, caspases, AMPK, PI3K/Akt/GSK3β, and p38/JNK/MAPK, in the pathogenesis and progression of neurodegenerative diseases. This molecular phenomenon will lead to the discovery of possible therapeutic biomolecules as a pharmacological intervention that are involved in the modulation of apoptosis and autophagy pathways. Moreover, we describe the potential role of micro-RNAs, long non-coding RNAs, and biomolecules as therapeutic agents that regulate cell death machinery to treat neurodegenerative diseases. Mounting evidence demonstrated that under stress conditions, such as calcium efflux, endoplasmic reticulum stress, the ubiquitin-proteasome system, and oxidative stress intermediate molecules, namely p53 and VEGF, activate and cause cell death. Further, activation of p53 and VEGF cause alteration in gene expression and dysregulated signaling pathways through the involvement of signaling molecules, namely mTOR, Bcl-2, BH3, AMPK, MAPK, JNK, and PI3K/Akt, and caspases. Alteration in gene expression and signaling cascades cause neurotoxicity and misfolded protein aggregates, which are characteristics features of neurodegenerative diseases. Excessive neurotoxicity and misfolded protein aggregates lead to neuronal cell death by activating death pathways like autophagy and apoptosis. However, autophagy has a dual role in the apoptosis pathways, i.e., activation and inhibition of the apoptosis signaling. Further, micro-RNAs and LncRNAs act as pharmacological regulators of autophagy and apoptosis cascade, whereas, natural compounds and chemical compounds act as pharmacological inhibitors that rescue neuronal cell death through inhibition of apoptosis and autophagic cell death.

Whole exome sequencing revealed a novel dystrophin-related protein-2 (DRP2) deletion in an Iranian family with symptoms of polyneuropathy

Objective(s):

Charcot-Marie Tooth disease (CMT) is one of the main inherited causes of motor and sensory neuropathies with variable expressivity and age-of onset. Although more than 70 genes have been identified for CMT, more studies are needed to discover other genes involved in CMT. Introduction of whole exome sequencing (WES) to capture all the exons may help to find these genes.

Materials and Methods:

Here, we tried to find the genetic cause of the neuropathy in two Iranian brothers using WES. Blood sample was collected from probands and their family members to extract the genomic DNA. The extracted DNA from one of the affected case was subjected for WES. The variant calls were filtered to reveal the pathogenic variant. Presence of the candidate mutation was confirmed using Sanger sequencing. The pathogenic potential of the variant was examined using in silico software. Using ClustalW multiple alignment, the presence of variant in conserved domain of protein was investigated. The parent and another affected boy were also checked for presence of the variant using PCR-sequencing.

Results:

The obtained data presented a novel TTC del mutation in CDS 738 of dystrophin related protein 2 (DRP2) gene, which was validated by sequencing. The variant was located in a conserved domain of DRP2 protein and predicted as pathogenic. Two affected boys were hemizygous for the mutation and received the mutation from mother.

Conclusion:

Here, we provided the evidence for the contribution of DRP2 in CMT. Also, the symptoms shed light on molecular aspect of this genetically heterogeneous disease.

Proteomic change by Korean Red Ginseng in the substantia nigra of a Parkinson's disease mouse model

Background

Recent studies have shown that Korean Red Ginseng (KRG) successfully protects against dopaminergic neuronal death in the nigrostriatal pathway of a Parkinson's disease (PD) mouse model induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration; however, the mechanism has yet to be identified. Therefore, in this study we used two-dimensional electrophoresis to investigate the effects of KRG on the changes in protein expression in the substantia nigra (SN) of MPTP-treated mice.

Methods

Male C57BL/6 mice (9 wk old) were intraperitoneally administered MPTP (20 mg/kg) four times at 2-h intervals, after which KRG (100 mg/kg) was orally administered once a day for 5 d. Two hours after the fifth KRG administration, a pole test was conducted to evaluate motor function, after which the brains were immediately collected. Survival of dopaminergic neurons was measured by immunohistochemistry, and protein expression was measured by two-dimensional electrophoresis and Western blotting.

Results

KRG alleviated MPTP-induced behavioral dysfunction and neuronal toxicity in the SN. Additionally, the expression of eight proteins related to neuronal formation and energy metabolism for survival were shown to have changed significantly in response to MPTP treatment or KRG administration. KRG alleviated the downregulated protein expression following MPTP administration, indicating that it may enhance neuronal development and survival in the SN of MPTP-treated mice.

Conclusion

These findings indicate that KRG may have therapeutic potential for the treatment of patients with PD.

Candidate gene prioritization based on spatially mapped gene expression: an application to XLMR

Motivation: The identification of genes involved in specific phenotypes, such as human hereditary diseases, often requires the time-consuming and expensive examination of a large number of positional candidates selected by genome-wide techniques such as linkage analysis and association studies. Even considering the positive impact of next-generation sequencing technologies, the prioritization of these positional candidates may be an important step for disease-gene identification.

Results: Here, we report a large-scale analysis of spatial, i.e. 3D, gene-expression data from an entire organ (the mouse brain) for the purpose of evaluating and ranking positional candidate genes, showing that the spatial gene-expression patterns can be successfully exploited for the prediction of gene–phenotype associations not only for mouse phenotypes, but also for human central nervous system-related Mendelian disorders. We apply our method to the case of X-linked mental retardation, compare the predictions to the results obtained from a previous large-scale resequencing study of chromosome X and discuss some promising novel candidates.

Contact:rosario.piro@unito.it

Supplementary information:Supplementary data are available at Bioinformatics online.

Dystrophins, utrophins, and associated scaffolding complexes: role in mammalian brain and implications for therapeutic strategies

Two decades of molecular, cellular, and functional studies considerably increased our understanding of dystrophins function and unveiled the complex etiology of the cognitive deficits in Duchenne muscular dystrophy (DMD), which involves altered expression of several dystrophin-gene products in brain. Dystrophins are normally part of critical cytoskeleton-associated membrane-bound molecular scaffolds involved in the clustering of receptors, ion channels, and signaling proteins that contribute to synapse physiology and blood-brain barrier function. The utrophin gene also drives brain expression of several paralogs proteins, which cellular expression and biological roles remain to be elucidated. Here we review the structural and functional properties of dystrophins and utrophins in brain, the consequences of dystrophins loss-of-function as revealed by numerous studies in mouse models of DMD, and we discuss future challenges and putative therapeutic strategies that may compensate for the cognitive impairment in DMD based on experimental manipulation of dystrophins and/or utrophins brain expression.

Profound human/mouse differences in alpha-dystrobrevin isoforms: a novel syntrophin-binding site and promoter missing in mouse and rat

Background

The dystrophin glycoprotein complex is disrupted in Duchenne muscular dystrophy and many other neuromuscular diseases. The principal heterodimeric partner of dystrophin at the heart of the dystrophin glycoprotein complex in the main clinically affected tissues (skeletal muscle, heart and brain) is its distant relative, α-dystrobrevin. The α-dystrobrevin gene is subject to complex transcriptional and post-transcriptional regulation, generating a substantial range of isoforms by alternative promoter use, alternative polyadenylation and alternative splicing. The choice of isoform is understood, amongst other things, to determine the stoichiometry of syntrophins (and their ligands) in the dystrophin glycoprotein complex.

Results

We show here that, contrary to the literature, most α-dystrobrevin genes, including that of humans, encode three distinct syntrophin-binding sites, rather than two, resulting in a greatly enhanced isoform repertoire. We compare in detail the quantitative tissue-specific expression pattern of human and mouse α-dystrobrevin isoforms, and show that two major gene features (the novel syntrophin-binding site-encoding exon and the internal promoter and first exon of brain-specific isoforms α-dystrobrevin-4 and -5) are present in most mammals but specifically ablated in mouse and rat.

Conclusion

Lineage-specific mutations in the murids mean that the mouse brain has fewer than half of the α-dystrobrevin isoforms found in the human brain. Our finding that there are likely to be fundamental functional differences between the α-dystrobrevins (and therefore the dystrophin glycoprotein complexes) of mice and humans raises questions about the current use of the mouse as the principal model animal for studying Duchenne muscular dystrophy and other related disorders, especially the neurological aspects thereof.

The dystrotelin, dystrophin and dystrobrevin superfamily: new paralogues and old isoforms

BACKGROUND

Dystrophins and dystrobrevins are distantly related proteins with important but poorly understood roles in the function of metazoan muscular and neuronal tissues. Defects in them and their associated proteins cause a range of neuromuscular disorders. Members of this superfamily have been discovered in a relatively serendipitous way; we set out to compile a comprehensive description of dystrophin- and dystrobrevin-related sequences from available metazoan genome sequences, validated in representative organisms by RT-PCR, or acquired de novo from key species.

RESULTS

Features of the superfamily revealed by our survey include: a) Dystrotelin, an entirely novel branch of the superfamily, present in most vertebrates examined. Dystrotelin is expressed in the central nervous system, and is a possible orthologue of Drosophila DAH. We describe the preliminary characterisation of its function, evolution and expression. b) A novel vertebrate member of the dystrobrevin family, gamma-dystrobrevin, an ancient branch now extant only in fish, but probably present in our own ancestors. Like dystrophin, zebrafish gamma-dystrobrevin mRNA is localised to myosepta. c) The extent of conservation of alternative splicing and alternative promoter use in the dystrophin and dystrobrevin genes; alternative splicing of dystrophin exons 73 and 78 and alpha-dystrobrevin exon 13 are conserved across vertebrates, as are the use of the Dp116, Dp71 and G-utrophin promoters; the Dp260 and Dp140 promoters are tetrapod innovations. d) The evolution of the unique N-terminus of DRP2 and its relationship to Dp116 and G-utrophin. e) A C-terminally truncated common ancestor of dystrophin and utrophin in cyclostomes. f) A severely restricted repertoire of dystrophin complex components in ascidians.

CONCLUSION

We have refined our understanding of the evolutionary history and isoform diversity of the five previously reported vertebrate superfamily members and describe two novel members, dystrotelin and gamma-dystrobrevin. Dystrotelins, dystrophins and dystrobrevins are roughly equally related to each other. Vertebrates therefore have a repertoire of seven superfamily members (three dystrophins, three dystrobevins, and one dystrotelin), with one lost in tetrapods. Most invertebrates studied have one member from each branch. Although the basic shared function which is implied by the common architecture of these distantly related proteins remains unclear, it clearly permeates metazoan biology.

Function and genetics of dystrophin and dystrophin-related proteins in muscle

The X-linked muscle-wasting disease Duchenne muscular dystrophy is caused by mutations in the gene encoding dystrophin. There is currently no effective treatment for the disease; however, the complex molecular pathology of this disorder is now being unravelled. Dystrophin is located at the muscle sarcolemma in a membrane-spanning protein complex that connects the cytoskeleton to the basal lamina. Mutations in many components of the dystrophin protein complex cause other forms of autosomally inherited muscular dystrophy, indicating the importance of this complex in normal muscle function. Although the precise function of dystrophin is unknown, the lack of protein causes membrane destabilization and the activation of multiple pathophysiological processes, many of which converge on alterations in intracellular calcium handling. Dystrophin is also the prototype of a family of dystrophin-related proteins, many of which are found in muscle. This family includes utrophin and alpha-dystrobrevin, which are involved in the maintenance of the neuromuscular junction architecture and in muscle homeostasis. New insights into the pathophysiology of dystrophic muscle, the identification of compensating proteins, and the discovery of new binding partners are paving the way for novel therapeutic strategies to treat this fatal muscle disease. This review discusses the role of the dystrophin complex and protein family in muscle and describes the physiological processes that are affected in Duchenne muscular dystrophy.

Dystroglycan contributes to the formation of multiple dystrophin-like complexes in brain

In muscle, dystrophin anchors a complex of proteins at the cell surface which includes alpha-dystroglycan, beta-dystroglycan, syntrophins and dystrobrevins. Mutations in the dystrophin gene lead to muscular dystrophy and mental retardation. In contrast to muscle, little is known about the localization and the molecular interactions of dystrophin and dystrophin associated proteins (DAPs) in brain. In the present study, we show that alpha-dystroglycan and dystrophin are localized to large neurones in cerebral cortex, hippocampus, cerebellum and spinal cord. Furthermore, we show that dystroglycan is a member of three distinct dystrophin-containing complexes. Two of these complexes contain syntrophin and both dystrophin and syntrophin are enriched in post-synaptic densities. These data suggest that dystrophin and DAPs may have a role in the organization of CNS synapses. Interestingly, the enrichment for syntrophin in post-synaptic densities is not affected in mice mutant for all dystrophin isoforms. Thus in the brain, unlike in muscle, the association of syntrophin with dystrophin is not crucial for the DAP complex which suggests that it may be associated with other proteins.

Specific disruption of a schwann cell dystrophin-related protein complex in a demyelinating neuropathy

Dystroglycan-dystrophin complexes are believed to have structural and signaling functions by linking extracellular matrix proteins to the cytoskeleton and cortical signaling molecules. Here we characterize a dystroglycan-dystrophin-related protein 2 (DRP2) complex at the surface of myelin-forming Schwann cells. The complex is clustered by the interaction of DRP2 with L-periaxin, a homodimeric PDZ domain-containing protein. In the absence of L-periaxin, DRP2 is mislocalized and depleted, although other dystrophin family proteins are unaffected. Disruption of the DRP2-dystroglycan complex is followed by hypermyelination and destabilization of the Schwann cell-axon unit in Prx(-/-) mice. Hence, the DRP2-dystroglycan complex likely has a distinct function in the terminal stages of PNS myelinogenesis, possibly in the regulation of myelin thickness.

Dystrophins and dystrobrevins

SUMMARY

A unique arrangement of domains makes up the common region of two otherwise very different proteins - long, elegant dystrophin, and its rather dumpy distant cousin, dystrobrevin. The two work in concert, forming the core of a large membrane-bound complex in all metazoa. Like many proteins, dystrophin and dystrobrevin have diversified in the vertebrate clade, as have their binding partners, yielding specialized complexes tailored to different cellular and subcellular locations. Disruption of several components of the complex is known to result in syndromes that include progressive myopathy, sometimes combined with cognitive defects; the best known of these is Duchenne muscular dystrophy. Despite a wealth of biochemical, cell biological and genetic information, the precise role of dystrophins, dystrobrevins and their collaborators remains unclear.