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Pivotal role of mitochondria in development and treatment of severe phenotypes of desmin-mutated cardiomyocytes from a patient with myofibrillar myopathy

ABSTRACT: Desmin-related myofibrillar myopathy, a severe muscle disease, is caused by mutations in the desmin-encoding gene, leading to skeletal myopathies and/or cardiomyopathy. Although previous studies suggested that desmin mutations alter the cellular structure and mitochondria function in myocyte, the pathophysiological mechanism by which mutated desmin impairs cardiac function has been poorly explored in physiologically relevant human disease models. In this attempt, we generated cardiomyocytes from induced pluripotent stem cells (hiPSC) of a patient carrying the heterozygous DESE439K mutation together with an isogenic pair of mutant hiPSC harboring the same mutation. Using 2D and 3D models as well as cardiac biopsies, we demonstrated that in mutant cardiomyocytes this heterozygous desmin mutation leads to disorganization in their cytoarchitecture and to a perturbation of their mitochondrial architecture and function. Finally, we then demonstrated that transfer of exogenous healthy mitochondria rescues the phenotypic impairment of mitochondrial function in desmin-mutated cardiomyocytes leading to the reversion of the diseased phenotype. This work advances our understanding on the critical role of mitochondria in the development of cardiomyopathy related to desmin mutation and opens up new potential therapeutic perspectives for this debilitating and still incurable disease.

ORGANISM(S): Homo sapiens

PROVIDER: GSE245583 | GEO | 2023/12/05

REPOSITORIES: GEO

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Project description:Desmin, the major intermediate filament (IF) protein in muscle cells, interlinks neighboring myofibrils and connects the whole myofibrillar apparatus to myonuclei, mitochondria, and the sarcolemma. However, desmin is also known to be enriched at postsynaptic membranes of neuromuscular junctions (NMJs). The pivotal role of the desmin IF cytoskeletal network is underscored by the fact that over 100 mutations of the human DES gene cause hereditary and sporadic myopathies and cardiomyopathies. A subgroup of human desminopathies comprises autosomal recessive cases resulting in complete abolition of desmin protein. In these patients, who display a more severe phenotype than the autosomal dominant cases, it has been reported that some individuals also suffer from a myasthenic syndrome in addition to the classical occurrence of myopathy and cardiomyopathy. Since further studies on the NMJ pathology is hampered by the lack of available human striated muscle biopsy specimens, we exploited homozygous desmin knock-out mice which closely mirror the striated muscle pathology of human patients lacking desmin protein. Here, we report on the impact of the lack of desmin on the structure and function of NMJs and on the transcription of genes coding for postsynaptic proteins. Desmin knock-out mice display a fragmentation of NMJs in soleus, but not in extensor digitorum longus muscle. Moreover, soleus muscle fibers show larger NMJs. Further, transcription levels of acetylcholine receptor (AChR) genes are increased in muscles from desmin knock-out mice, especially of the AChR subunit, which is known as a marker of muscle fiber regeneration. Electrophysiological recordings depicted a pathological decrement of nerve-dependent endplate potentials and a faster rise time of the nerve-independent miniature endplate potentials. The latter is indicating an enhanced opening time of the AChR channels. Our study highlights the essential role of desmin for the structural and functional integrity of mammalian neuromuscular junctions.

Project description:Background: The phospholamban (PLN) p.Arg14del mutation belongs to the established causes of dilated cardiomyopathy, with the molecular disease mechanisms incompletely understood. We used human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes, CRISPR/Cas9 gene editing and patient heart samples to investigate the molecular pathomechanisms of PLN p.Arg14del cardiomyopathy. Methods and results: Patient dermal fibroblasts carrying the PLN p.Arg14del mutation were reprogrammed into hiPSC, isogenic controls were established by CRISPR/Cas9. Cells were differentiated into cardiomyocytes and characterized in 2D and 3D-engineered heart tissue (EHT) format. Mutant cardiomyocytes revealed significantly prolonged Ca2+ transient decay time, Ca2+-load dependent irregular beating pattern and lower peak force compared to isogenic controls. While this data support the reported super-inhibitory effect of PLN p.Arg14del on the sarcoplasmic/endoplasmic reticulum Ca2+ ATPase, an unchanged SR Ca2+ content argued against disturbed SR Ca2+ cycling as the sole cause of contractile dysfunction. Label-free proteomic analysis of p.Arg14del EHTs revealed less endoplasmic reticulum (ER), ribosomal and mitochondrial proteins. Electron microscopy showed dilation of the rough ER, large lipid droplets in close association with mitochondria and reduced mitochondrial number. Follow-up experiments confirmed impairment of the rough ER/mitochondria compartment and enhanced oxidative stress in PLN p.Arg14del. Relevance for human disease was demonstrated by immunohistochemistry of human heart samples. PLN p.Arg14del end-stage heart failure samples revealed perinuclear aggregates positive for ER marker proteins and oxidative stress in comparison to ischemic heart failure - and non-failing donor heart samples. Surprisingly, transduction of PLN p.Arg14del EHTs with the Ca2+ binding protein GCaMP6f reversed the contractile, molecular and morphological disease phenotype. Conclusion: This study identified impairment of the rough ER/mitochondria compartment without SR dysfunction as a novel disease mechanism underlying PLN p.Arg14del cardiomyopathy. The pathology was improved by Ca2+-scavenging, suggesting impaired local Ca2+ cycling as an important disease culprit.

Project description:Background: Mutations of the desmin gene cause familial and sporadic cardiomyopathies and myopathies. Previous studies showed that both the lack of desmin and expression of mutated desmin negatively impact on number, structure and function mitochondria implying a metabolic dysfunction as disease promoting factor. Here, we exploited desmin knock-out mice to analyse the general metabolic performance of cardiac tissue. Methods: We analysed left ventricular cardiac muscle tissue derived from six-month-old homozygous desmin knock-out mice as well as wild-type siblings. Employing a multi-method approach comprising morphological, clinical chemistry, biochemical, genetic, and proteomic techniques, we specifically addressed energy, fatty acid, glucose, and amino acid metabolism. Results: We demonstrated that the lack of desmin in left ventricular cardiac tissue led to a significant decrease in the number of mitochondria in conjunction with ultrastructural defects of mitochondria. Analysis of mitochondria-related metabolic pathways revealed significantly impaired processes of fatty acid transport, activation, and catabolism associated with increased blood levels of short, medium, and long chain acyl-carnitines. In addition to increased amounts of glucose transporter 1 and hexokinase 1, we detected a significantly increased hexokinase enzyme activity. While the amount of mitochondrial creatine kinase was markedly reduced, fetal creatine kinase was increased. The picture of a highly dysbalanced metabolic state was complemented by our quantitative proteomic analysis that revealed significantly reduced levels of multiple proteins centrally involved in electron transport mainly of complexes I and II, oxidative phosphorylation, citrate cycle, beta oxidation including auxiliary pathways, amino acid catabolism, and redox reactions and oxidative stress. Conclusions: Our data denoted a picture of widespread metabolic dysfunction far reaching beyond the level of mitochondria in left ventricular cardiac tissue of desmin knock-out mice. The increase of glucose utilisation along with increased level of fetal creatine kinase likely is a compensatory measure counteracting the severely hampered fatty acid metabolism and oxidative phosphorylation. The degree of metabolic disbalance, already observed in desmin knock-out mice kept under standard ‘sedentary’ housing conditions, renders it likely that acute strenuous physical exercise with its steeply increased energy demand will push the cardiac tissue into severe metabolic crisis.

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Pivotal role of mitochondria in development and treatment of severe phenotypes of desmin-mutated cardiomyocytes from a patient with myofibrillar myopathy

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