Myosin Heavy Chain IIa Gene Research Articles

Association between polymorphism rs2032487 in the non-muscle myosin heavy chain IIA gene (MHY9) and chronic kidney disease secondary to type 2 diabetes mellitus in a population of the Canary Islands

IntroductionCertain polymorphisms in the non-muscle myosin IIA (MYH9) and apolipoprotein L1 (APOL1) genes have been associated to chronic kidney disease (CKD) in different populations. This study examined the association between the MHY9 rs2032487 and APOL1 rs73885319 polymorphisms and advanced CKD related to type 2 diabetes mellitus (T2DM) in a population of Gran Canaria (Canary Islands, Spain). Patients and methodsPolymorphisms were genotyped in 152 patients with advanced CKD (estimated glomerular filtration rate [eGFR] <30ml/min/1.73m2) secondary to T2DM, 110 patients with T2DM onset ≥20 years before without advanced CKD (eGFR ≥45ml/min/1.73m2 and no proteinuria), and 292 healthy blood donors over 50 years of age without CKD or diabetes. ResultsThe frequency of the risk allele for rs2032487 was 10.7% in patients with diabetes and advanced CKD, 7.1% in those with diabetes but without advanced CKD, and 6.1% in healthy subjects, with significant differences between the first and third groups (p=0.015). Among subjects with advanced CKD, 78.5% were homozygous for the protective allele, as compared to 87.9% in the other two groups (p=0.015 and p=0.016 respectively). The frequency of the risk allele for the rs73885319 polymorphism did not exceed 0.5% in any of the three groups. ConclusionsThese data suggest that polymorphism rs2032487 is associated to advanced CKD related to T2DM in the population of Gran Canaria.

Expression of the inclusion body myopathy 3 mutation in Drosophila depresses myosin function and stability and recapitulates muscle inclusions and weakness

Hereditary myosin myopathies are characterized by variable clinical features. Inclusion body myopathy 3 (IBM-3) is an autosomal dominant disease associated with a missense mutation (E706K) in the myosin heavy chain IIa gene. Adult patients experience progressive muscle weakness. Biopsies reveal dystrophic changes, rimmed vacuoles with cytoplasmic inclusions, and focal disorganization of myofilaments. We constructed a transgene encoding E706K myosin and expressed it in Drosophila (E701K) indirect flight and jump muscles to establish a novel homozygous organism with homogeneous populations of fast IBM-3 myosin and muscle fibers. Flight and jump abilities were severely reduced in homozygotes. ATPase and actin sliding velocity of the mutant myosin were depressed >80% compared with wild-type myosin. Light scattering experiments and electron microscopy revealed that mutant myosin heads bear a dramatic propensity to collapse and aggregate. Thus E706K (E701K) myosin appears far more labile than wild-type myosin. Furthermore, mutant fly fibers exhibit ultrastructural hallmarks seen in patients, including cytoplasmic inclusions containing aberrant proteinaceous structures and disorganized muscle filaments. Our Drosophila model reveals the unambiguous consequences of the IBM-3 lesion on fast muscle myosin and fibers. The abnormalities observed in myosin function and muscle ultrastructure likely contribute to muscle weakness observed in our flies and patients.

The E706K IBM3 Myosin Mutation Depresses the Chemomechanical Properties and Increases the Lability of the Molecular Motor

Hereditary myosin myopathies are muscle diseases with variable clinical features and age of onset. Inclusion body myopathy 3 (IBM3) is an autosomal dominant myopathy associated with a missense mutation (E706K) in the myosin heavy chain IIa gene (MYH2). The disease is mild in childhood but appears progressive in adulthood, with proximal muscle weakness affecting movement. Biopsies from adult patients reveal dystrophic alterations and rimmed vacuoles consistent with an increased expression of the mutant motor with advanced age. We constructed a transgene encoding E706K myosin and expressed it in Drosophila (E699K) indirect flight and jump muscles. Flight and jump abilities were reduced in heterozygous flies and were nearly absent in homozygotes consistent with the possible age-related dose-dependent response observed in patients. The mutant myosin displayed 80% lower actin sliding velocity and 74 and 83% reductions in basal and actin stimulated ATPase activities compared to wild-type myosin. Electron microscopy revealed E706K (E699K) myosin heads bear a dramatic propensity to collapse and to aggregate relative to wildtype heads. At 23°C, 77.5% (n=1146) of control molecules exhibited two well-resolved independent heads compared to only 22.5% (n=1014) of mutant myosin molecules. A five minute, 37°C incubation induced 80.9% (n=1181) of the control molecules’ heads to form intra- or intermolecular aggregates versus 95.3% (n=1192) of the mutant myosin heads. This test directly assessed motor integrity and suggests E706K (E699K) myosin is far more labile than wildtype myosin. We are imaging mutant myocytes to determine if the ultrastructural hallmarks seen in adult patients also appear in our fly model. The depressed motor properties and the propensity for the mutant myosin to collapse and aggregate likely contribute to the muscle weakness observed in our fly model and possibly in senescent patients.

Myh9Q1443L Is a Novel Mouse Model of MYH9-Related Disorders

AbstractAbstract 2527May-Hegglin Anomaly was originally defined as patients with macrothrombocytopenia. It is now recognized that the phenotypes of May-Hegglin Anomaly and the related syndromes described by Epstein, Fechtner and Sebastian overlap comprising macrothrombocytopenia, neutrophil inclusions, deafness, cataract formation and nephritis. These disorders are defined by mutations in the non-muscle myosin heavy chain IIA gene, MYH9 and have been termed MYH9-Related Disorders.Myh9 is required during murine embryogenesis as Myh9-null embryos die of patterning defects. Megakaryocyte-specific deletion of Myh9 has been performed by the Gachet group and Shivdasani and colleagues examined megakaryocyte function in Myh9-deficient embryonic stem cells induced to differentiate in vitro. The phenotypes of these mice include increased bleeding times, absence of clot retraction and defective Integrin β3 phosphorylation coupling to impaired activation of downstream Rho-Rock signalling and lamellipodia formation. To date, no knock-in MYH9 alleles corresponding to MYH9-related Disorder mutations have been reported. MYH9-related Disorders frequently are misdiagnosed as Chronic Immune Thrombocytopenia, so having enhanced knowledge of the molecular etiology of mutant MYH9 alleles is a priority.Our group has been interested in utilizing random mutagenesis to identify novel alleles of human hematopoietic disorders. We performed a dominant screen in which 129 male mice were mutagenized with ENU and back-crossing was performed on the C57BL/6 background. We identified a heritable line (7238) with macrothrombocytopenia that mapped to a 4.25 Mb region on mouse Chromosome 15. Due to our inability to further refine the interval through back-crossing, we performed high throughput sequencing by comparing SNPs between 129, C57BL/6, 7238/+ and 7238/7238 mice. We identified 18 novel variations, including 1 that corresponded to a coding change - Myh9 Q1443L. Subsequent Sanger sequencing and back-crossing eliminated the remaining 17 variations, confirming our assignment of the 7238 phenotype to a mutation of Myh9. The Myh9 Q1443L allele is within proximity of the MYH9 D1424Y/N/H mutations found within clinical specimens.Myh9Q1443L/Q1443L mice are viable allowing us to examine the effect of mutation of one or both alleles of Myh9. Myh9Q1443L/Q1443L mice had increased bleeding times, whereas Myh9Q1443L/+ mice were identical to wild type mice. Platelet aggregation experiments were performed after ADP or thrombin stimulation. Decreased aggregation was observed in a dosage-dependent manner, with Myh9Q1443L/+ mice displaying intermediate levels when compared with Myh9Q1443L/Q1443L co-hort. Adherence and aggregation of Myh9Q1443L/Q1443L platelets to a collagen matrix was decreased at shear rates of 350/s and 1800/s. Staining of Myh9Q1443L/+ and Myh9Q1443L/Q1443L neutrophils also revealed neutrophil inclusions.In addition to the hematopoietic phenotypes, we have observed increased cataract formation with a frequency of 36% in wild type animals, 60% in Myh9Q1443L/+ and 92% in Myh9Q1443L/Q1443L mice. Sporadic hematuria and proteinuria is found in Myh9Q1443L mice. We are currently performing albumen loading and lipopolysaccharide activation experiments to determine whether 7238 mice have altered response to nephric stress. We are crossing 7238 mice to the DBA genetic background, which is more sensitive to subtle kidney phenotypes. We performed auditory brain response measurements on aged wild type, Myh9Q1443L/+ and Myh9Q1443L/Q1443L mice and observed no differences in frequency responses ranging from 2 to 24kHz. Myh9Q1443L/+ mice displayed hypertrophy of the preputial gland whereas Myh9Q1443L/Q1443L males showed atrophy of this gland and Myh9Q1443L/Q1443L male mice have reduced fertility. No differences in fertility have been described to date in MYH9 related disorders.In conclusion, Myh9Q1443L/Q1443L mice display macrothrombocytopenia, neutrophil inclusions and cataract formation described in MYH9-related disorders and represent the first animal model of May-Hegglin Anomaly. Disclosures:No relevant conflicts of interest to declare.

The age of single-gene neurological disorders is not dead

This edition of Brain sees the first of a series of articles describing new genes responsible for inherited neurological disease, thus expanding the clinical neurogenetics portfolio. Sebahattin Cirak from the Institute of Child Health in London led a transcontinental consortium of clinical and basic science researchers who map the locus for a gene responsible for an autosomal dominant distal myopathy (Cirak et al. , 2010). Their work casts new light on the disease mechanisms of these poorly understood disorders; but at the same time, they broaden concepts on the potential mechanisms involved. Distal myopathies provide a classical example of the way that molecular genetics has revolutionized classifications in clinical neurology (Table 1). First described in the early part of the last century (Gowers, 1902), they were the focus of that old neurological chestnut ‘is the distal weakness due to muscle or nerve dysfunction?’ and were latterly subdivided into discrete entities based on astute clinical examination (reviewed in Barohn et al. , 1998). Early gene mapping studies identified several loci, highlighted the likely aetiological heterogeneity and led to the further delineation of different clinical groups (Udd, 2009). A major subgroup was associated with pathological myofibrils (myfibrillar myopathies) (Udd, 2009), overlapping with inherited limb girdle syndromes. Positional cloning and candidate gene analysis led to the rounding-up of some obvious culprits [ MYO7 , the myosin heavy chain 7 gene (Meredith et al. , 2004) and fast IIa myosin as recently published in Brain (Tajsharghi et al. , 2010)] and provided a satisfying explanation for the muscle group specificity of some distal myopathies [including the ophthalmoplegia in inclusion body myopathy-3, due to mutations in the myosin heavy chain IIa gene (Martinsson et al. , 2000)], but the real power of these ‘reverse genetic studies’ was in revealing new proteins required for intact muscle …

Human disease caused by loss of fast IIa myosin heavy chain due to recessive MYH2 mutations

Striated muscle myosin heavy chain is a molecular motor protein that converts chemical energy into mechanical force. It is a major determinant of the physiological properties of each of the three muscle fibre types that make up the skeletal muscles. Heterozygous dominant missense mutations in myosin heavy chain genes cause various types of cardiomyopathy and skeletal myopathy, but the effects of myosin heavy chain null mutations in humans have not previously been reported. We have identified the first patients lacking fast type 2A muscle fibres, caused by total absence of fast myosin heavy chain IIa protein due to truncating mutations of the corresponding gene MYH2. Five adult patients, two males and three females, from three unrelated families in UK and Finland were clinically assessed and muscle biopsy was performed in one patient from each family. MYH2 was sequenced and the expression of the corresponding transcripts and protein was analysed in muscle tissue. The patients had early-onset symptoms characterized by mild generalized muscle weakness, extraocular muscle involvement and relatively favourable prognosis. Muscle biopsy revealed myopathic changes including variability of fibre size, internalized nuclei, and increased interstitial connective and adipose tissue. No muscle fibres expressing type IIa myosin heavy chain were identified and the MYH2 transcripts were markedly reduced. All patients were compound heterozygous for truncating mutations in MYH2. The parents were unaffected, consistent with recessive mutations. Our findings show that null mutations in the fast myosin heavy chain IIa gene cause early onset myopathy and demonstrate that this isoform is necessary for normal muscle development and function. The relatively mild phenotype is interesting in relation to the more severe phenotypes generally seen in relation to recessive null mutations in sarcomeric proteins.

Enhanced proliferation of human skeletal muscle precursor cells derived from elderly donors cultured in estimated physiological (5%) oxygen

Human skeletal muscle precursor cells (myoblasts) have significant therapeutic potential and are a valuable research tool to study muscle cell biology. Oxygen is a critical factor in the successful culture of myoblasts with low (1-6%) oxygen culture conditions enhancing the proliferation, differentiation, and/or viability of mouse, rat, and bovine myoblasts. The specific effects of low oxygen depend on the myoblast source and oxygen concentration; however, variable oxygen conditions have not been tested in the culture of human myoblasts. In this study, muscle precursor cells were isolated from vastus lateralis muscle biopsies and myoblast cultures were established in 5% oxygen, before being divided into physiological (5%) or standard (20%) oxygen conditions for experimental analysis. Five percent oxygen increased proliferating myoblast numbers, and since low oxygen had no significant effect on myoblast viability, this increase in cell number was attributed to enhanced proliferation. The proportion of cells in the S (DNA synthesis) phase of the cell cycle was increased by 50%, and p21(Cip1) gene and protein expression was decreased in 5 versus 20% oxygen. Unlike in rodent and bovine myoblasts, the increase in myoD, myogenin, creatine kinase, and myosin heavy chain IIa gene expression during differentiation was similar in 5 and 20% oxygen; as was myotube hypertrophy. These data indicate for the first time that low oxygen culture conditions stimulate proliferation, whilst maintaining (but not enhancing) the viability and the differentiation potential of human primary myoblasts and should be considered as optimum conditions for ex-vivo expansion of these cells.

Thyroid hormone receptor-β-selective agonist GC-24 spares skeletal muscle type I to II fiber shift

Triiodothyronine (T3) is known to play a key role in the function of several tissues/organs via the thyroid hormone receptor isoforms alpha (TRalpha) and beta (TRbeta). We have investigated the effects of GC-24, a novel synthetic TRbeta-selective compound, on skeletal muscle fiber-type determination, cross-sectional area, and gene expression in rat skeletal muscles. For fiber typing, cross sections of soleus and extensor digitorum longus (EDL) muscles were stained for myosin ATPase activity at various pHs. Serum T3, T4, and cholesterol levels were also determined. Analysis of highly T3-responsive genes, viz., myosin heavy chain IIa (MHCIIa) and sarcoendoplasmic reticulum adenosine triphosphatase (SERCA1), was performed by quantitative real-time polymerase chain reaction. Equimolar doses of T3 and GC-24 had a similar cholesterol-lowering effect. T3, but not GC-24, decreased fiber type I and increased fiber type II abundance in soleus and EDL muscles. Conversely, in EDL, both T3 and GC-24 decreased the mean cross-sectional area of type I fibers. MHCIIa gene expression was reduced (approximately 50%) by T3 and unchanged by GC-24. SERCA1 gene expression was strongly induced by T3 (approximately 20-fold) and mildly induced by GC-24 (approximately two-fold). These results show that GC-24 does not significantly alter the composition of skeletal muscle fiber type and further strengthens the putative use of GC compounds as therapeutic agents.

Mutations and sequence variation in the human myosin heavy chain IIa gene (MYH2)

We recently described a new autosomal dominant myopathy associated with a missense mutation in the myosin heavy chain (MyHC) IIa gene (MYH2). In this study, we performed mutation analysis of MYH2 in eight Swedish patients with familial myopathy of unknown cause. In two of the eight index cases, we identified novel heterozygous missense mutations in MYH2, one in each case: V970I and L1061V. The mutations were located in subfragment 2 of the MyHC and they changed highly conserved residues. Most family members carrying the mutations had signs and symptoms consisting mainly of mild muscle weakness and myalgia. In addition, we analyzed the extent and distribution of nucleotide variation in MYH2 in 50 blood donors, who served as controls, by the complete sequencing of all 38 exons comprising the coding region. We identified only six polymorphic sites, five of which were synonymous polymorphisms. One variant, which occurred at an allele frequency of 0.01, was identical to the L1061V that was also found in one of the families with myopathy. The results of the analysis of normal variation indicate that there is strong selective pressure against mutations in MYH2. On the basis of these results, we suggest that MyHC genes should be regarded as candidate genes in cases of hereditary myopathies of unknown etiology.

IRF-2 Is Involved in Up-regulation of Nonmuscle Myosin Heavy Chain II-A Gene Expression during Phorbol Ester-induced Promyelocytic HL-60 Differentiation

Transcription of the nonmuscle myosin heavy chain II-A (NMHC-A) gene is regulated by various factors, including cell type, proliferation and differentiation stage, and extracellular stimuli. We have identified an intronic region (designated 32kb-150), which is located 32 kb downstream of the transcription start sites in the human NMHC-A gene, as a transcriptional regulatory region. 32kb-150 contains an interferon-stimulated response element (ISRE). By using HeLa and NIH3T3 cells, in which NMHC-A is constitutively expressed, interferon regulatory factor (IRF)-2 was found to be the only major protein, among the IRF family proteins, that bound to the ISRE in 32kb-150 both in vitro and in intact cells. IRF-2, which is known to either repress or activate target gene expression, acts as a transcriptional activator in the context of the 32kb-150 reporter gene. The carboxyl-terminal basic region of IRF-2 serves as an activation domain in this context. This is in contrast to its acting as a repressor domain in the context of the synthetic core ISRE. Furthermore, after treatment of promyelocytic HL-60 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA), which triggers differentiation into macrophages, both NMHC-A expression and IRF-2 expression were found to be up-regulated with a similar time course. TPA treatment leads to recruitment of IRF-2 to 32kb-150 of the endogenous NMHC-A gene and acetylation of the core histones surrounding this region. In addition, the ISRE in the 32kb-150 reporter gene recruits IRF-2 and mediates TPA-induced activation of a reporter gene in HL-60 cells. Together, these results indicate that IRF-2 contributes to transcriptional activation of the NMHC-A gene via 32kb-150 during TPA-induced differentiation of HL-60 cells.

Myosin heavy chain IIa gene mutation E706K is pathogenic and its expression increases with age.

The authors recently described a new autosomal dominant myopathy (OMIM 605637 inclusion body myopathy 3) associated with a missense mutation in the myosin heavy chain (MyHC) IIa gene (MyHC IIa, Human Gene Map [HGM] locus MYH2). Young patients showed minor changes in their muscle biopsies, although dystrophic alterations and rimmed vacuoles with 15- to 20-nm tubulofilaments identical to those in sporadic inclusion body myositis (s-IBM) were observed in some of the adult (especially older) patients. The current study was undertaken to investigate the relation between expression of the mutant MyHC IIa and pathologic changes in muscle. The expression of MyHC IIa in nine muscle specimens from six individuals carrying the mutation was analyzed by immunohistochemistry, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and a new reverse transcriptase--PCR method to measure the relative abundance of the various MyHC transcripts. Young patients with muscle weakness and minor pathologic changes in muscle expressed MyHC IIa at undetectable levels. MyHC IIa was expressed at high levels in adults with a progressive clinical course and dystrophic muscle changes. In these cases, a large number of muscle fibers were hybrids with expression of more than one MyHC isoform. Both MyHC IIa alleles were equally expressed. The relative level of MyHC IIa transcripts exceeded that of the corresponding protein, indicating an increased turnover of mutated protein. MyHC IIa expression was a consistent finding in muscle fibers with rimmed vacuoles. The clear correlation between pathologic changes and expression of MyHC IIa indicates that defects in MyHC may lead not only to muscle weakness but also to muscle degeneration. The consistent expression of MyHC IIa in muscle fibers with rimmed vacuoles indicates that the breakdown of sarcomeric proteins is a key element in the pathogenesis of rimmed vacuoles of s-IBM type.

Cloning of the murine non-muscle myosin heavy chain IIA gene ortholog of human MYH9 responsible for May-Hegglin, Sebastian, Fechtner, and Epstein syndromes

Mutations in the non-muscle myosin heavy chain IIA gene ( MYH9) are responsible for May-Hegglin anomaly, Sebastian, Fechtner and Epstein syndromes. These ‘ MYH9-related’ diseases are inherited as an autosomal dominant trait and are characterized by a variable expressivity of clinical features, including macrothrombocytopenia, deafness, nephrites, cataract, and Döhle-like leukocyte inclusions. To gain information of the function of the non-muscle myosin heavy chain IIA protein (NMMHC-IIA), we have identified the murine orthologue Myh9 gene. The gene is localized in a region of chromosome 15 and encodes a predicted protein of 1960 amino acids. This protein shows a high homology to the human NMMHC-IIA with 98% identity. The Myh9 exon-intron junctions were deduced from a murine genomic clone that revealed a perfect conservation of the exon structure between the human and mouse gene. Myh9 is expressed in liver, kidney, lung, and spleen. A low level of transcripts was detected also in heart and brain while no expression was revealed in skeletal muscle and testis. In vertebrates, NMMHC-IIA shows a striking degree of homology to NMMHC-IIB, which is expressed at higher level in mouse brain and testis than in other tissues, confirming the hypothesis that the two non-muscle myosins have different functional roles within cells.