Decreased DMPK transcript levels in myotonic dystrophy 1 type IIA muscle fibers

DNA methylation changes and increased mRNA expression of coagulation proteins, factor V and thrombomodulin in Fuchs endothelial corneal dystrophy

Late-onset Fuchs endothelial corneal dystrophy (FECD) is a disease affecting the corneal endothelium (CE), associated with a cytosine-thymine-guanine repeat expansion at the CTG18.1 locus in the transcription factor 4 (TCF4) gene. It is unknown whether CTG18.1 expansions affect global methylation including TCF4 gene in CE or whether global CE methylation changes at advanced age. Using genome-wide DNA methylation array, we investigated methylation in CE from FECD patients with CTG18.1 expansions and studied the methylation in healthy CE at different ages. The most revealing DNA methylation findings were analyzed by gene expression and protein analysis. 3488 CpGs had significantly altered methylation pattern in FECD though no substantial changes were found in TCF4. The most hypermethylated site was in a predicted promoter of aquaporin 1 (AQP1) gene, and the most hypomethylated site was in a predicted promoter of coagulation factor V (F5 for gene, FV for protein). In FECD, AQP1 mRNA expression was variable, while F5 gene expression showed a ~ 23-fold increase. FV protein was present in both healthy and affected CE. Further gene expression analysis of coagulation factors interacting with FV revealed a ~ 34-fold increase of thrombomodulin (THBD). THBD protein was detected only in CE from FECD patients. Additionally, we observed an age-dependent hypomethylation in elderly healthy CE.Thus, tissue-specific genome-wide and gene-specific methylation changes associated with altered gene expression were discovered in FECD. TCF4 pathological methylation in FECD because of CTG18.1 expansion was ruled out.

Myotonic dystrophy type 1 embryonic stem cells show decreased myogenic potential, increased CpG methylation at the DMPK locus and RNA mis-splicing

Skeletal muscle tissue is severely affected in myotonic dystrophy type 1 (DM1) patients, characterised by muscle weakness, myotonia and muscle immaturity in the most severe congenital form of the disease. Previously, it was not known at what stage during myogenesis the DM1 phenotype appears. In this study we differentiated healthy and DM1 human embryonic stem cells to myoblasts and myotubes and compared their differentiation potential using a comprehensive multi-omics approach. We found myogenesis in DM1 cells to be abnormal with altered myotube generation compared to healthy cells. We did not find differentially expressed genes between DM1 and non-DM1 cell lines within the same developmental stage. However, during differentiation we observed an aberrant inflammatory response and increased CpG methylation upstream of the CTG repeat at the myoblast level and RNA mis-splicing at the myotube stage. We show that early myogenesis modelled in hESC reiterates the early developmental manifestation of DM1.

Summary: Early developmental abnormalities in myotonic dystrophy type 1 are reiterated in vitro in myotubes differentiated from human embryonic stem cells that carry the mutation.

The dystrophia myotonica WD repeat-containing protein DMWD and WDR20 differentially regulate USP12 deubiquitinase

Despite its potential clinical relevance, the product of the DMWD (dystrophia myotonica, WD repeat containing) gene is a largely uncharacterized protein. The DMWD amino acid sequence is similar to that of WDR20, a known regulator of the USP12 and USP46 deubiquitinases (DUBs). Here, we apply a combination of in silico and experimental methods to investigate several aspects of DMWD biology. Molecular evolution and phylogenetic analyses reveal that WDR20 and DMWD, similar to USP12 and USP46, arose by duplication of a common ancestor during the whole genome duplication event in the vertebrate ancestor lineage. The analysis of public human gene expression datasets suggests that DMWD expression is positively correlated with USP12 expression in normal tissues and negatively correlated with WDR20 expression in tumors. Strikingly, a survey of the annotated interactome for DMWD and WDR20 reveals a largely nonoverlapping set of interactors for these proteins. Experimentally, we first confirmed that DMWD binds both USP12 and USP46 through direct coimmunoprecipitation of epitope-tagged proteins. We found that DMWD and WDR20 share the same binding interface in USP12, suggesting that their interaction with the DUB may be mutually exclusive. Finally, we show that both DMWD and WDR20 promote USP12 enzymatic activity, but they differentially modulate the subcellular localization of the DUB. Altogether, our findings suggest a model whereby mutually exclusive binding of DMWD and WDR20 to USP12 may lead to formation of deubiquitinase complexes with distinct subcellular localization, potentially targeting different substrate repertoires.

Abnormalities in Skeletal Muscle Myogenesis, Growth, and Regeneration in Myotonic Dystrophy

Myotonic dystrophy type 1 (DM1) and 2 (DM2) are autosomal dominant degenerative neuromuscular disorders characterized by progressive skeletal muscle weakness, atrophy, and myotonia with progeroid features. Although both DM1 and DM2 are characterized by skeletal muscle dysfunction and also share other clinical features, the diseases differ in the muscle groups that are affected. In DM1, distal muscles are mainly affected, whereas in DM2 problems are mostly found in proximal muscles. In addition, manifestation in DM1 is generally more severe, with possible congenital or childhood-onset of disease and prominent CNS involvement. DM1 and DM2 are caused by expansion of (CTG•CAG)n and (CCTG•CAGG)n repeats in the 3' non-coding region of DMPK and in intron 1 of CNBP, respectively, and in overlapping antisense genes. This critical review will focus on the pleiotropic problems that occur during development, growth, regeneration, and aging of skeletal muscle in patients who inherited these expansions. The current best-accepted idea is that most muscle symptoms can be explained by pathomechanistic effects of repeat expansion on RNA-mediated pathways. However, aberrations in DNA replication and transcription of the DM loci or in protein translation and proteome homeostasis could also affect the control of proliferation and differentiation of muscle progenitor cells or the maintenance and physiological integrity of muscle fibers during a patient's lifetime. Here, we will discuss these molecular and cellular processes and summarize current knowledge about the role of embryonic and adult muscle-resident stem cells in growth, homeostasis, regeneration, and premature aging of healthy and diseased muscle tissue. Of particular interest is that also progenitor cells from extramuscular sources, such as pericytes and mesoangioblasts, can participate in myogenic differentiation. We will examine the potential of all these types of cells in the application of regenerative medicine for muscular dystrophies and evaluate new possibilities for their use in future therapy of DM.

Expanded CTG repeat demarcates a boundary for abnormal CpG methylation in myotonic dystrophy patient tissues

Myotonic dystrophy (DM1) affects multiple organs, shows age-dependent progression and is caused by CTG expansions at the DM1 locus. We determined the DM1 CpG methylation profile and CTG length in tissues from DM1 foetuses, DM1 adults, non-affected individuals and transgenic DM1 mice. Analysis included CTCF binding sites upstream and downstream of the CTG tract, as methylation-sensitive CTCF binding affects chromatinization and transcription of the DM1 locus. In humans, in a given foetus, expansions were largest in heart and smallest in liver, differing by 40-400 repeats; in adults, the largest expansions were in heart and cerebral cortex and smallest in cerebellum, differing by up to 5770 repeats in the same individual. Abnormal methylation was specific to the mutant allele. In DM1 adults, heart, liver and cortex showed high-to-moderate methylation levels, whereas cerebellum, kidney and skeletal muscle were devoid of methylation. Methylation decreased between foetuses and adults. Contrary to previous findings, methylation was not restricted to individuals with congenital DM1. The expanded repeat demarcates an abrupt boundary of methylation. Upstream sequences, including the CTCF site, were methylated, whereas the repeat itself and downstream sequences were not. In DM1 mice, expansion-, tissue- and age-specific methylation patterns were similar but not identical to those in DM1 individuals; notably in mice, methylation was present up- and downstream of the repeat, but greater upstream. Thus, in humans, the CpG-free expanded CTG repeat appears to maintain a highly polarized pattern of CpG methylation at the DM1 locus, which varies markedly with age and tissues.

The myotonic dystrophy type 2 (DM2) gene product zinc finger protein 9 (ZNF9) is associated with sarcomeres and normally localized in DM2 patients' muscles

AIMS

Myotonic dystrophy type 2 (DM2) is caused by a [CCTG]n intronic expansion in the zinc finger protein 9 (ZNF9) gene. As for DM1, sharing with DM2 a similar phenotype, the pathogenic mutation involves a transcribed but untranslated genomic region, suggesting that RNA toxicity may have a role in the pathogenesis of these multisystem disorders by interfering with common cellular mechanisms. However, haploinsufficiency has been described in DM1 and DM2 animal models, and might contribute to pathogenesis. The aim of the present work was therefore to assess ZNF9 protein expression in rat tissues and in human muscle, and ZNF9 subcellular distribution in normal and DM2 human muscles.

METHODS

Polyclonal anti-ZNF9 antibodies were obtained in rabbit, high pressure liquid chromatography-purified, and used for Western blot, standard and confocal immunofluorescence and immunogold labelling electron microscopy on a panel of normal rat tissues and on normal and DM2 human muscles.

RESULTS

Western blot analysis showed that ZNF9 is ubiquitously expressed in mammalian tissues, and that its signal is not substantially modified in DM2 muscles. Immunofluorescence studies showed a myofibrillar distribution of ZNF9, and double staining with two non-repetitive epitopes of titin located it in the I bands. This finding was confirmed by the visualization of ZNF9 in close relation with sarcomeric thin filaments by immunogold labelling electron microscopy. ZNF9 distribution was unaltered in DM2 muscle fibres.

CONCLUSIONS

ZNF9 is abundantly expressed in human myofibres, where it is located in the sarcomeric I bands, and no modification of this pattern is observed in DM2 muscles.

Abnormal contractile activity and calcium cycling in cardiac myocytes isolated from DMPK knockout mice

Dysfunction of the gene encoding DMPK (myotonic dystrophy protein kinase) has been implicated in the human neuromuscular disease myotonic dystrophy (DM1). The cardiac features of the disease include progressive conduction defects and ventricular arrhythmias. These defects have been observed in hearts of mice deficient for DMPK function. We have investigated the role of DMPK in the function of ventricular cardiomyocytes using dmpk knockout (KO) mice. A deficit in DMPK caused enhanced basal contractility of single cardiomyocytes and an associated increase in intracellular Ca(2+), measured using fura-2. Biochemical measurements indicated hyperphosphorylation of phospholamban (PLB) in KO mice. This suggests increased Ca(2+) uptake into the sarcoplasmic reticulum (SR) as the underlying cause of enhanced contractility. This conclusion was supported by the larger amplitude of caffeine-induced Ca(2+) release from the SR in KO cardiomyocytes. Concurrent with hyperphosphorylated PLB, the response to isoprenaline was reduced. These observations suggest dmpk has a modulatory role in the control of intracellular Ca(2+) concentration in mouse ventricular cardiomyocytes, loss of which may contribute to cardiac dysfunction in DM1.

Changes in myotonic dystrophy protein kinase levels and muscle development in congenital myotonic dystrophy

Myotonic dystrophy (DM1) is caused by the expansion of a CTG repeat in the noncoding region of a protein kinase, DMPK, expressed in skeletal and cardiac muscles. The aim of the present study was to determine the effects of very large CTG expansions on DMPK expression and skeletal muscle development. In fetuses suffering from the severe congenital form of DM1 with large CTG expansions (1800 to 3700 repeats), the skeletal muscle level of DMPK was reduced to 57% of control levels and a similar reduction was observed in cultured DM1 muscle cells relative to control cultures. These results are consistent with greatly reduced DMPK expression from the mutant allele and normal expression from the unaffected allele in this autosomal dominant disorder. In normal fetuses, DMPK protein levels increased dramatically between 9 and 16 weeks and remained high throughout the remaining gestation period. DM1 fetuses showed impaired skeletal muscle development, characterized by a persistence of embryonic and fetal myosin heavy chains and almost total absence of slow myosin heavy chains at the end of gestation. DMPK expression, however, was similar in both fast and slow fibers from normal adult muscle. The reduced DMPK and the delayed slow fiber maturation in congenital DM1 may be two separate consequences of nuclear retention of DMPK RNA transcripts with expanded CUG repeats.

Substantial changes in gene expression level due to the storage temperature and storage duration of human whole blood

Blood is a valuable clinical sample for high-throughput analysis of gene expression and is likely to become more popular as a diagnostic tool and as a predictive measure of disease progression and drug responsiveness. Gene expression data from blood that has been stored at ambient temperature for greater than 1 h vs. blood samples that have been lysed immediately post-collection shows dramatic changes in relative gene expression for a number of cytokines, chemokines, and transcription factors. Results indicate significant changes in the relative expression of several genes, many of which were either up-regulated or down-regulated, because of storage at ambient temperature: (1) In only 4 h of storage at ambient temperature, greater than 10-fold increases in relative gene expression were observed for interleukin-8 (IL-8), c-myc, and c-fos; (2) Up-regulation of IL-8, a chemokine that mediates inflammatory cell migration, took place only 1-h after collection and increased nearly 100-fold by 4 h; (3) Down-regulation of several anti-inflammatory genes was observed for blood stored at ambient temperature; and (4) A general trend toward selective enhancement of inflammatory responses was observed, mediated by possible mRNA transcription and turnover. These results validate the need for the rapid lysis of whole blood after removal from the source.