OPA1 deficiency drives muscle inflammation = La deficiència d'OPA1 resulta en inflamació muscular
[eng] Opa1 is a mitochondrial dynamics protein responsible for the fusion of the inner mitochondrial membrane, the maintenance of cristae morphology, and involved in mitochondrial DNA stability. In this study we have explored the origin of the effects of Opa1 deficiency in skeletal muscle, as well a...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2018 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/123201 |
| Acceso en línea: | https://hdl.handle.net/2445/123201 http://hdl.handle.net/10803/586046 |
| Access Level: | acceso abierto |
| Palabra clave: | Proteïnes Inflamació Aparell locomotor Proteins Inflammation Musculoskeletal system |
| Sumario: | [eng] Opa1 is a mitochondrial dynamics protein responsible for the fusion of the inner mitochondrial membrane, the maintenance of cristae morphology, and involved in mitochondrial DNA stability. In this study we have explored the origin of the effects of Opa1 deficiency in skeletal muscle, as well as the cellular mechanisms that give rise to the primary responses derived from its deficiency in the muscle context. Chronic treatment with an anti-inflammatory compound rescued the growth defects that suffer mice defective of Opa1 in skeletal muscle, observed in previous studies. These results indicate that inflammation is the primary cause of this growth impairment. The analysis of the origin of this inflammation allows us to describe that it is a NF- κB activation-mediated, local, primary and autonomous process of the muscle cell. At the intracellular level, the data show that the deficiency of Opa1 generates mitochondrial network fragmentation and disarrangement, and a reduction in the oxidative capacity of the electron transport chain of the mitochondria. These observations were made both in muscle cells and in skeletal muscle, which correlates with a dysfunctionality of the mitochondrial fusion as well as of the morphogenesis of the cristae of the organelle. Likewise, the loss of Opa1 function in muscle cells results in a 50% reduction in the mitochondrial DNA content, accompanied by a comparable reduction on TFAM protein levels. Confocal microscopy analysis show a reduction in the number of mitochondrial DNA nucleoids per cell, as well as an enhancement of the relative area of each nucleoids, which has been described as mitochondrial DNA stress. Given the features of mitochondrial DNA, owing to the past of mitochondria as free living bacteria, it has a powerful immunogenic capacity as a damage associated molecular pattern. From the two main pathways with potential to detect misplaced mitochondrial DNA and induce NF-κB activation, we discarded cGAS activation due to the fact that mitochondrial DNA is not detected in the cytosol and that cGAS deficiency is unable to normalize the expression of NF-κB target genes. Given the absence of the molecule in the cytosolic fraction, we analyzed the functionality of mitophagy. Although in Opa1 loss-of-function cells mitophagy initiates normally, the completion of the mitophagic process is impaired, probably resulting in an accumulation of undegraded mitochondrial components, which has been reported that can produce an intracellular inflammatory response. Studies of the location of mitochondrial DNA indicate that all nucleoids are found in mitochondria-containing compartments. In addition, more than half are located in late endosomes. Approximately the same portion is localized in compartments also positive for TLR9. We assessed the importance of this two key components, mitochondrial DNA and TLR9, in the development of the inflammatory response by ablating one or the other and assessing the normalization of NF-κB target gene expression. Indeed, reduction of mitochondrial DNA copy number to a residual 5% rescued the expression pro-inflammatory genes. Moreover, treatment with TLR9 antagonist also restored NF-κB target genes expression and extracellular concentration of IL-6. In parallel to these data, TLR9 depletion can as well normalize inflammatory genes expression. The data compiled in this study indicate that Opa1 deficiency results in mitochondrial dysfunction together with mitochondrial DNA stress. The mitophagy machinery of the cell is able to identify this damage and restrain the damaged mitochondria into mito-autophagosome that, by a mechanism that still needs further investigation, is re-routed to the endosomal pathway. In late endosomes mtDNA can interact with TLR9 which in turn results in activation of NF-κB pro-inflammatory pathway resulting, eventually, in the secretion of cytokines that may potentially cause the growth defects observed in the skeletal muscle specific Opa1 deficient mouse model. |
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