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Frontiers in Neurology 2019Myofibrillar myopathies (MFM) are a clinically and genetically heterogenous group of inherited myopathies characterized by aggregation of Z-disc proteins. Mutations in...
Myofibrillar myopathies (MFM) are a clinically and genetically heterogenous group of inherited myopathies characterized by aggregation of Z-disc proteins. Mutations in desmin account for ~7% of MFM. We report here a Hmong family with an autosomal dominant MFM caused by a novel variant in the desmin gene. The proband presented with lower limb followed by upper limb weakness starting in the 5th decade. On examination, there was distal more than proximal muscle weakness. One sibling was similarly affected, while another had an asymptomatic elevation of creatine kinase. Genetic testing revealed a novel p.Ser13Tyr variant, which was predicted by algorithms to alter protein function. Muscle biopsy revealed a MFM. Muscle MRI demonstrated selective involvement of the tensor fasciae latae, semitendinosus, sartorius, gracilis, gastrocnemius, soleus, and peroneus longus muscles. In this family, the histological and MRI findings assisted in the interpretation of genetic testing results.
PubMed: 31998224
DOI: 10.3389/fneur.2019.01375 -
PloS One 2011Mutations in the skeletal muscle α-actin gene (ACTA1) cause congenital myopathies including nemaline myopathy, actin aggregate myopathy and rod-core disease. The...
Mutations in the skeletal muscle α-actin gene (ACTA1) cause congenital myopathies including nemaline myopathy, actin aggregate myopathy and rod-core disease. The majority of patients with ACTA1 mutations have severe hypotonia and do not survive beyond the age of one. A transgenic mouse model was generated expressing an autosomal dominant mutant (D286G) of ACTA1 (identified in a severe nemaline myopathy patient) fused with EGFP. Nemaline bodies were observed in multiple skeletal muscles, with serial sections showing these correlated to aggregates of the mutant skeletal muscle α-actin-EGFP. Isolated extensor digitorum longus and soleus muscles were significantly weaker than wild-type (WT) muscle at 4 weeks of age, coinciding with the peak in structural lesions. These 4 week-old mice were ~30% less active on voluntary running wheels than WT mice. The α-actin-EGFP protein clearly demonstrated that the transgene was expressed equally in all myosin heavy chain (MHC) fibre types during the early postnatal period, but subsequently became largely confined to MHCIIB fibres. Ringbinden fibres, internal nuclei and myofibrillar myopathy pathologies, not typical features in nemaline myopathy or patients with ACTA1 mutations, were frequently observed. Ringbinden were found in fast fibre predominant muscles of adult mice and were exclusively MHCIIB-positive fibres. Thus, this mouse model presents a reliable model for the investigation of the pathobiology of nemaline body formation and muscle weakness and for evaluation of potential therapeutic interventions. The occurrence of core-like regions, internal nuclei and ringbinden will allow analysis of the mechanisms underlying these lesions. The occurrence of ringbinden and features of myofibrillar myopathy in this mouse model of ACTA1 disease suggests that patients with these pathologies and no genetic explanation should be screened for ACTA1 mutations.
Topics: Actins; Animals; Behavior, Animal; Disease Models, Animal; Gene Expression; Green Fluorescent Proteins; Mice; Mice, Inbred C57BL; Mice, Transgenic; Muscle Contraction; Muscle Fibers, Skeletal; Muscle, Skeletal; Myopathies, Nemaline; Myosin Heavy Chains; Phenotype; Recombinant Fusion Proteins; Transgenes
PubMed: 22174871
DOI: 10.1371/journal.pone.0028699 -
Molecular Genetics and Metabolism... Jun 2018
PubMed: 30023292
DOI: 10.1016/j.ymgmr.2018.02.002 -
International Journal of Molecular... Dec 2023Small heat shock proteins (sHsps) are a family of ATP-independent molecular chaperones that function as "holdases" and prevent protein aggregation due to changes in...
Small heat shock proteins (sHsps) are a family of ATP-independent molecular chaperones that function as "holdases" and prevent protein aggregation due to changes in temperature, pH, or oxidation state. sHsps have a conserved α-crystallin domain (ACD), which forms the dimer building block, flanked by variable N- and C-terminal regions. sHsps populate various oligomeric states as a function of their sequestrase activity, and these dynamic structural features allow the proteins to interact with a plethora of cellular substrates. However, the molecular mechanisms of their dynamic conformational assembly and the interactions with various substrates remains unclear. Therefore, it is important to gain insight into the underlying physicochemical properties that influence sHsp structure in an effort to understand their mechanism(s) of action. We evaluated several disease-relevant mutations, D109A, F113Y, R116C, R120G, and R120C, in the ACD of HspB5 for changes to in vitro chaperone activity relative to that of wildtype. Structural characteristics were also evaluated by ANS fluorescence and CD spectroscopy. Our results indicated that mutation Y113F is an efficient holdase, while D109A and R120G, which are found in patients with myofibrillar myopathy and cataracts, respectively, exhibit a large reduction in holdase activity in a chaperone-like light-scattering assay, which indicated alterations in substrate-sHsp interactions. The extent of the reductions in chaperone activities are different among the mutants and specific to the substrate protein, suggesting that while sHsps are able to interact with many substrates, specific interactions provide selectivity for some substrates compared to others. This work is consistent with a model for chaperone activity where key electrostatic interactions in the sHsp dimer provide structural stability and influence both higher-order sHsp interactions and facilitate interactions with substrate proteins that define chaperone holdase activity.
Topics: Humans; alpha-Crystallins; Biological Assay; Heat-Shock Proteins, Small; Molecular Chaperones; Protein Folding
PubMed: 38203641
DOI: 10.3390/ijms25010471 -
Muscle & Nerve Jul 2009The nucleic acid binding protein TDP-43 was recently identified in normal myonuclei and in the sarcoplasm of inclusion body myositis (IBM) muscle. Here we found TDP-43...
The nucleic acid binding protein TDP-43 was recently identified in normal myonuclei and in the sarcoplasm of inclusion body myositis (IBM) muscle. Here we found TDP-43 sarcoplasmic immunoreactivity in 23% of IBM myofibers, while other reported IBM biomarkers were less frequent, with rimmed vacuoles in 2.8%, fluorescent Congo red material in 0.57%, SMI-31 immunoreactivity in 0.83%, and focal R1282 beta-amyloid immunoreactivity in 0.00% of myofibers. The presence of as little as >1% of myofibers with nonnuclear sarcoplasmic TDP-43 was highly sensitive (91%) and specific (100%) to IBM among 50 inflammatory myopathy patient samples, although some patients with hereditary inclusion body myopathies and myofibrillar myopathy also had sarcoplasmic TDP-43. TDP-43 mutations were sought, and none were identified. TDP-43 could be one of many nucleic acid binding proteins that are abnormally present in IBM sarcoplasm. They could potentially interfere with the normal function of extranuclear RNAs that maintain myofiber protein production.
Topics: Amyloid beta-Peptides; Congo Red; DNA-Binding Proteins; Humans; Indoles; Muscle Fibers, Skeletal; Myositis, Inclusion Body; Neurofilament Proteins; Oligonucleotide Array Sequence Analysis; Sarcoplasmic Reticulum
PubMed: 19533646
DOI: 10.1002/mus.21386 -
The Journal of Biological Chemistry Jul 2016Mutations of HSPB5 (also known as CRYAB or αB-crystallin), a bona fide heat shock protein and molecular chaperone encoded by the HSPB5 (crystallin, alpha B) gene, are...
Mutations of HSPB5 (also known as CRYAB or αB-crystallin), a bona fide heat shock protein and molecular chaperone encoded by the HSPB5 (crystallin, alpha B) gene, are linked to multisystem disorders featuring variable combinations of cataracts, cardiomyopathy, and skeletal myopathy. This study aimed to investigate the pathological mechanisms involved in an early-onset myofibrillar myopathy manifesting in a child harboring a homozygous recessive mutation in HSPB5, 343delT. To study HSPB5 343delT protein dynamics, we utilize model cell culture systems including induced pluripotent stem cells derived from the 343delT patient (343delT/343delT) along with isogenic, heterozygous, gene-corrected control cells (WT KI/343delT) and BHK21 cells, a cell line lacking endogenous HSPB5 expression. 343delT/343delT and WT KI/343delT-induced pluripotent stem cell-derived skeletal myotubes and cardiomyocytes did not express detectable levels of 343delT protein, contributable to the extreme insolubility of the mutant protein. Overexpression of HSPB5 343delT resulted in insoluble mutant protein aggregates and induction of a cellular stress response. Co-expression of 343delT with WT prevented visible aggregation of 343delT and improved its solubility. Additionally, in vitro refolding of 343delT in the presence of WT rescued its solubility. We demonstrate an interaction between WT and 343delT both in vitro and within cells. These data support a loss-of-function model for the myopathy observed in the patient because the insoluble mutant would be unavailable to perform normal functions of HSPB5, although additional gain-of-function effects of the mutant protein cannot be excluded. Additionally, our data highlight the solubilization of 343delT by WT, concordant with the recessive inheritance of the disease and absence of symptoms in carrier individuals.
Topics: Cardiomyopathies; Cataract; Female; Homozygote; Humans; Induced Pluripotent Stem Cells; Male; Models, Biological; Muscle Fibers, Skeletal; Muscular Diseases; Mutant Proteins; Myocytes, Cardiac; Pedigree; Protein Aggregation, Pathological; RNA, Messenger; Recombinant Proteins; Sequence Deletion; Solubility; alpha-Crystallin B Chain
PubMed: 27226619
DOI: 10.1074/jbc.M116.730481 -
The Journal of Clinical Investigation Mar 2014The ubiquitously expressed multifunctional cytolinker protein plectin is essential for muscle fiber integrity and myofiber cytoarchitecture. Patients suffering from...
The ubiquitously expressed multifunctional cytolinker protein plectin is essential for muscle fiber integrity and myofiber cytoarchitecture. Patients suffering from plectinopathy-associated epidermolysis bullosa simplex with muscular dystrophy (EBS-MD) and mice lacking plectin in skeletal muscle display pathological desmin-positive protein aggregation and misalignment of Z-disks, which are hallmarks of myofibrillar myopathies (MFMs). Here, we developed immortalized murine myoblast cell lines to examine the pathogenesis of plectinopathies at the molecular and single cell level. Plectin-deficient myotubes, derived from myoblasts, were fully functional and mirrored the pathological features of EBS-MD myofibers, including the presence of desmin-positive protein aggregates and a concurrent disarrangement of the myofibrillar apparatus. Using this cell model, we demonstrated that plectin deficiency leads to increased intermediate filament network and sarcomere dynamics, marked upregulation of HSPs, and reduced myotube resilience following mechanical stretch. Currently, no specific therapy or treatment is available to improve plectin-related or other forms of MFMs; therefore, we assessed the therapeutic potential of chemical chaperones to relieve plectinopathies. Treatment with 4-phenylbutyrate resulted in remarkable amelioration of the pathological phenotypes in plectin-deficient myotubes as well as in plectin-deficient mice. Together, these data demonstrate the biological relevance of the MFM cell model and suggest that this model has potential use for the development of therapeutic approaches for EBS-MD.
Topics: Animals; Cell Differentiation; Cells, Cultured; Desmin; Drug Evaluation, Preclinical; Heat-Shock Proteins; Intermediate Filaments; Mice; Mice, Inbred C57BL; Mice, Knockout; Muscle Fibers, Skeletal; Muscle Strength; Muscle, Skeletal; Myoblasts; Myopathies, Structural, Congenital; Phenylbutyrates; Plectin; Protein Stability; Sarcomeres; Up-Regulation
PubMed: 24487589
DOI: 10.1172/JCI71919 -
Stem Cell Research Oct 2023Here we introduce the human induced pluripotent stem cell (hiPSC) line HIMRi001-A generated from cultured dermal fibroblasts of a 60-year-old male patient with a...
Here we introduce the human induced pluripotent stem cell (hiPSC) line HIMRi001-A generated from cultured dermal fibroblasts of a 60-year-old male patient with a myofibrillar myopathy, carrying a heterozygous c.4984C > T [p.Q1662X] mutation in the filamin C (FLNC)-gene, via lentiviral expression of OCT4, SOX2, KLF4 and c-MYC. HIMRi001-A displays typical embryonic stem cell-like morphology, carries the c.4984C > T FLNC gene mutation, expressed several pluripotent stem cell makers, retained normal karyotype (46, XY) and holds the potential to differentiate in all three germ layers. We postulate that HIMRi001-A can be used for the elucidation of FLNC-associated pathomechanisms and for developing new therapeutic options.
Topics: Male; Humans; Middle Aged; Induced Pluripotent Stem Cells; Kruppel-Like Factor 4; Pluripotent Stem Cells; Fibroblasts; Mutation; Cell Differentiation
PubMed: 37748332
DOI: 10.1016/j.scr.2023.103210 -
BBA Clinical Jun 2017Myofibrillar myopathy (MFM) is a group of inherited muscular disorders characterized by myofibrils dissolution and abnormal accumulation of degradation products. So far...
Myofibrillar myopathy (MFM) is a group of inherited muscular disorders characterized by myofibrils dissolution and abnormal accumulation of degradation products. So far causative mutations have been identified in nine genes encoding Z-disk proteins, including αB-crystallin (CRYAB), a small heat shock protein (also called HSPB5). Here, we report a case study of a 63-year-old Polish female with a progressive lower limb weakness and muscle biopsy suggesting a myofibrillar myopathy, and extra-muscular multisystemic involvement, including cataract and cardiomiopathy. Five members of the proband's family presented similar symptoms. Whole exome sequencing followed by bioinformatic analysis revealed a novel D109A mutation in associated with the disease. Molecular modeling in accordance with muscle biopsy microscopic analyses predicted that D109A mutation influence both structure and function of CRYAB due to decreased stability of oligomers leading to aggregate formation. In consequence disrupted sarcomere cytoskeleton organization might lead to muscle pathology. We also suggest that mutated RQDE sequence of CRYAB could impair CRYAB chaperone-like activity and promote aggregation of lens crystallins.
PubMed: 27904835
DOI: 10.1016/j.bbacli.2016.11.004 -
Journal of Muscle Research and Cell... Jun 2016Myofibrillar myopathies (MFMs) are genetically heterogeneous dystrophies characterized by the disintegration of Z-disks and myofibrils and are associated with mutations...
Myofibrillar myopathies (MFMs) are genetically heterogeneous dystrophies characterized by the disintegration of Z-disks and myofibrils and are associated with mutations in genes encoding Z-disk or Z-disk-related proteins. The c.626 C > T (p.P209L) mutation in the BAG3 gene has been described as causative of a subtype of MFM. We report a sporadic case of a 26-year-old Italian woman, affected by MFM with axonal neuropathy, cardiomyopathy, rigid spine, who carries the c.626 C > T mutation in the BAG3 gene. The patient and her non-consanguineous healthy parents and brother were studied with whole exome sequencing (WES) to further investigate the genetic basis of this complex phenotype. In the patient, we found that the BAG3 mutation is associated with variants in the NRAP and FHL1 genes that encode muscle-specific, LIM domain containing proteins. Quantitative real time PCR, immunohistochemistry and Western blot analysis of the patient's muscular biopsy showed the absence of NRAP expression and FHL1 accumulation in aggregates in the affected skeletal muscle tissue. Molecular dynamic analysis of the mutated FHL1 domain showed a modification in its surface charge, which could affect its capability to bind its target proteins. To our knowledge this is the first study reporting, in a BAG3 MFM, the simultaneous presence of genetic variants in the BAG3 and FHL1 genes (previously described as independently associated with MFMs) and linking the NRAP gene to MFM for the first time.
Topics: Adaptor Proteins, Signal Transducing; Adult; Apoptosis Regulatory Proteins; Exome; Female; Humans; Intracellular Signaling Peptides and Proteins; Italy; LIM Domain Proteins; Muscle Proteins; Myopathies, Structural, Congenital; Transfection
PubMed: 27443559
DOI: 10.1007/s10974-016-9451-7