Project description:Mitochondrial biogenesis requires precise regulation of both mitochondrial-encoded and nuclear-encoded genes. Nuclear receptor Nur77 is known to regulate mitochondrial metabolism in macrophages and skeletal muscle cells. Here, we compared genome-wide Nur77 binding site and target gene expression in these two cell types, which revealed conserved roles for this nuclear receptor in the regulation of nuclear-encoded mitochondrial ribosomal proteins (MRP) and enrichment of motifs for the transcription factor Yin-Yang 1 (YY1). We show that Nur77 and YY1 interact, that YY1 increases Nur77 activity, and that their binding sites are co-enriched at MRP gene loci. Nur77 and YY1 co-expression synergistically increases mitochondrial abundance and activity in macrophages but not skeletal muscle. As such, we identify a macrophage-specific Nur77-YY1 interaction that enhances mitochondrial metabolism.
Project description:Mitochondrial biogenesis requires precise regulation of both mitochondrial-encoded and nuclear-encoded genes. Nuclear receptor Nur77 is known to regulate mitochondrial metabolism in macrophages and skeletal muscle cells. Here, we compared genome-wide Nur77 binding site and target gene expression in these two cell types, which revealed conserved roles for this nuclear receptor in the regulation of nuclear-encoded mitochondrial ribosomal proteins (MRP) and enrichment of motifs for the transcription factor Yin-Yang 1 (YY1). We show that Nur77 and YY1 interact, that YY1 increases Nur77 activity, and that their binding sites are co-enriched at MRP gene loci. Nur77 and YY1 co-expression synergistically increases mitochondrial abundance and activity in macrophages but not skeletal muscle. As such, we identify a macrophage-specific Nur77-YY1 interaction that enhances mitochondrial metabolism.
Project description:Mitochondria import over 1000 proteins encoded by the nuclear genome, but the RNA contained within the organelle is generally thought to be only that which is transcribed from the mitochondrial genome. Recent evidence however suggests the presence of specific nuclear-encoded small- and long-non-coding RNAs (ncRNAs) in the mitochondrial matrix, hinting at a previously underappreciated level of subcellular, ncRNA-mediated regulation on mitochondrial function. The aim of this study was to characterise the population of RNAs contained within mitochondria isolated from rat skeletal muscle, and to investigate whether it was altered in response to endurance training, a potent metabolic stimulus that induces mitochondrial adaptations. Rats underwent four weeks of moderate intensity treadmill exercise training that induced typical adaptive responses at the transcriptome and functional levels in heart and skeletal muscle. Mitochondria from gastrocnemius skeletal muscle were isolated by immunoprecipitation, further purified, then sequenced to assess the mitochondrial transcriptome. Approximately 24 nuclear-encoded, coding or non-coding ‘long’ RNAs were detected in purified mitochondria, in addition to ~50 miRNAs with >100 normalised read counts. None were differentially expressed in the exercise vs control group at FDR < 0.05, but exploratory analyses (p<0.05) pointed towards 3 differentially regulated miRNAs in the mitochondria isolated from trained compared with sedentary muscle. In conclusion, we report the presence of a small population of nuclear-encoded long- and small RNAs in the mitochondria isolated from rat muscle tissue. Further research is required to investigate how these are imported into the mitochondria, and their role(s) in regulating exercise adaptations and mitochondrial biology
Project description:Mitochondria are central to cellular function, particularly in metabolically active tissues such as skeletal muscle. Nuclear-encoded RNAs typically localise within the nucleus and cytosol but a small population may also translocate to subcellular compartments such as mitochondria. We aimed to investigate the nuclear-encoded RNAs that localise within the mitochondria of skeletal muscle cells and tissue. Intact mitochondria were isolated via immunoprecipitation (IP) followed by enzymatic treatments (RNase-A and proteinase-K) to remove transcripts located exterior to mitochondria, making it amenable for high-throughput transcriptomic sequencing. Whole-transcriptome RNA sequencing of enzymatically-purified mitochondria isolated by IP from skeletal muscle tissue showed a striking similarity in the degree of purity compared to mitoplast preparations which lack an outer mitochondrial membrane. In summary, we describe a novel, powerful sequencing approach applicable to animal and human tissues and cells that can facilitate the discovery of nuclear-encoded RNA transcripts localised within skeletal muscle mitochondria.
Project description:Sarcopenia, the age-related loss of skeletal muscle mass and function, can dramatically impinge on quality of life and mortality. While mitochondrial dysfunction and imbalanced proteostasis are recognized as hallmarks of sarcopenia, the regulatory and functional link between these processes is underappreciated and unresolved. We therefore investigated how mitochondrial proteostasis, a crucial process that coordinates the expression of nuclear- and mitochondrial-encoded mitochondrial proteins with supercomplex formation and respiratory activity, is affected in skeletal muscle aging. Intriguingly, a robust mitochondrial translation impairment was observed in sarcopenic muscle, which is regulated by the peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1alpha) with the estrogen-related receptor alpha (ERRalpha). Exercise, a potent inducer of PGC-1alpha activity, rectifies age-related reduction in mitochondrial translation, in conjunction with quality control pathways. These results highlight the importance of mitochondrial proteostasis in muscle aging, and elucidate regulatory interactions that underlie the powerful benefits of physical activity in this context.
Project description:Mitochondria are central to cellular function, particularly in metabolically active tissues such as skeletal muscle. Nuclear-encoded RNAs typically localise within the nucleus and cytosol but a small population may also translocate to subcellular compartments such as mitochondria. We aimed to investigate the nuclear-encoded RNAs that localise within the mitochondria of skeletal muscle tissue. Intact mitochondria were isolated via immunoprecipitation (IP) followed by enzymatic treatments (RNase-A and proteinase-K) optimised to remove transcripts located exterior to mitochondria, making it amenable for high-throughput transcriptomic sequencing. Whole-transcriptome RNA sequencing of enzymatically-purified mitochondria isolated by IP from skeletal muscle tissue showed a high degree of purity. In summary, we describe a novel, powerful sequencing approach applicable to animal and human tissues and cells that can facilitate the discovery of nuclear-encoded RNA transcripts localised within skeletal muscle mitochondria.
Project description:Some forms of mitochondrial dysfunction induce sterile inflammation through mitochondrial DNA (mtDNA) recognition by intracellular DNA sensors. However, the involvement of mitochondrial dynamics mitigating such processes and their impact on muscle fitness remain unaddressed. Here we report that opposite mitochondrial morphologies induce distinct inflammatory signatures, caused by differential activation of DNA sensors TLR9 or cGAS. In the context of mitochondrial fragmentation, we demonstrate that mitochondria-endosome contacts mediated by the endosomal protein Rab5C are required in TLR9 activation in cells. Skeletal muscle mitochondrial fragmentation promotes TLR9-dependent inflammation, muscle atrophy, reduced physical performance and enhanced IL6 response to exercise, which improved upon chronic anti-inflammatory treatment. Taken together, our data demonstrate that mitochondrial dynamics is key in preventing sterile inflammatory responses, which precede the development of muscle atrophy and impaired physical performance. Thus, we propose the targeting of mitochondrial dynamics as an approach to treating disorders characterized by chronic inflammation and mitochondrial dysfunction.
Project description:Mutations in genes encoding nuclear envelope proteins lead to diseases known as nuclear envelopathies, characterized by skeletal muscle and heart abnormalities, such as Emery-Dreifuss Muscular Dystrophy (EDMD). The tissue-specific role of the nuclear envelope in the etiology of these diseases has not been extensively explored. We previously showed that global deletion of the muscle-specific nuclear envelope protein NET39 in mice leads to neonatal lethality due to skeletal muscle dysfunction. To study the potential role of the Net39 gene in adulthood, we generated a muscle-specific conditional knockout (cKO) of Net39 in mice. cKO mice recapitulated key skeletal muscle features of EDMD, including muscle wasting, impaired muscle contractility, abnormal myonuclear morphology, and DNA damage. The loss of Net39 rendered myoblasts hypersensitive to mechanical stretch, resulting in stretch-induced DNA damage. Net39 was downregulated in a mouse model of congenital myopathy, and restoration of Net39 expression through AAV gene delivery extended lifespan and ameliorated the muscle abnormalities. These findings establish NET39 as a direct contributor to the pathogenesis of EDMD by protecting against mechanical stress and DNA damage.
Project description:Mutations in genes encoding nuclear envelope proteins lead to diseases known as nuclear envelopathies, characterized by skeletal muscle and heart abnormalities, such as Emery-Dreifuss Muscular Dystrophy (EDMD). The tissue-specific role of the nuclear envelope in the etiology of these diseases has not been extensively explored. We previously showed that global deletion of the muscle-specific nuclear envelope protein NET39 in mice leads to neonatal lethality due to skeletal muscle dysfunction. To study the potential role of the Net39 gene in adulthood, we generated a muscle-specific conditional knockout (cKO) of Net39 in mice. cKO mice recapitulated key skeletal muscle features of EDMD, including muscle wasting, impaired muscle contractility, abnormal myonuclear morphology, and DNA damage. The loss of Net39 rendered myoblasts hypersensitive to mechanical stretch, resulting in stretch-induced DNA damage. Net39 was downregulated in a mouse model of congenital myopathy, and restoration of Net39 expression through AAV gene delivery extended lifespan and ameliorated the muscle abnormalities. These findings establish NET39 as a direct contributor to the pathogenesis of EDMD by protecting against mechanical stress and DNA damage.
Project description:Mutations in genes encoding nuclear envelope proteins lead to diseases known as nuclear envelopathies, characterized by skeletal muscle and heart abnormalities, such as Emery-Dreifuss Muscular Dystrophy (EDMD). The tissue-specific role of the nuclear envelope in the etiology of these diseases has not been extensively explored. We previously showed that global deletion of the muscle-specific nuclear envelope protein NET39 in mice leads to neonatal lethality due to skeletal muscle dysfunction. To study the potential role of the Net39 gene in adulthood, we generated a muscle-specific conditional knockout (cKO) of Net39 in mice. cKO mice recapitulated key skeletal muscle features of EDMD, including muscle wasting, impaired muscle contractility, abnormal myonuclear morphology, and DNA damage. The loss of Net39 rendered myoblasts hypersensitive to mechanical stretch, resulting in stretch-induced DNA damage. Net39 was downregulated in a mouse model of congenital myopathy, and restoration of Net39 expression through AAV gene delivery extended lifespan and ameliorated the muscle abnormalities. These findings establish NET39 as a direct contributor to the pathogenesis of EDMD by protecting against mechanical stress and DNA damage.