Parvalbumin affects skeletal muscle trophism through modulation of mitochondrial calcium uptake.
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ABSTRACT:
SUBMITTER: Butera G
PROVIDER: S-EPMC8113653 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Muscle atrophy contributes to the poor prognosis of many pathophysiological conditions, but pharmacological therapies are still limited. Muscle activity leads to major swings in mitochondrial [Ca(2+)], which control aerobic metabolism, cell death, and survival pathways. We investigated in vivo the effects of mitochondrial Ca(2+) homeostasis in skeletal muscle function and trophism by overexpressing or silencing the mitochondrial calcium uniporter (MCU). The results demonstrate that in both developing and adult muscles, MCU-dependent mitochondrial Ca(2+) uptake has a marked trophic effect that does not depend on aerobic control but impinges on two major hypertrophic pathways of skeletal muscle, PGC-1?4 and IGF1-Akt/PKB. In addition, MCU overexpression protects from denervation-induced atrophy. These data reveal a novel Ca(2+)-dependent organelle-to-nucleus signaling route that links mitochondrial function to the control of muscle mass and may represent a possible pharmacological target in conditions of muscle loss.
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Project description:As muscle contraction requires ATP and Ca(2+), skeletal muscle function is highly dependent on communication between two major intracellular organelles: mitochondria and sarcoplasmic reticulum (SR). In adult skeletal muscle, mitochondria located within the I-band of the sarcomere are connected to the SR by small ?10 nm electron dense tethers that bridge the outer mitochondrial membrane to the region of SR that is ?130 nm from the site of Ca(2+) release. However, the molecular composition of tethers and their precise impact on mitochondrial Ca(2+) uptake in skeletal muscle is unclear. Mitofusin-2 (Mfn2) is a transmembrane GTPase present in both mitochondria and ER/SR membranes that forms trans-dimers and participates in mitochondrial fusion. Here we evaluated the role Mfn2 plays in mitochondrial morphology, localization, and functional SR-mitochondrial Ca(2+) crosstalk in adult skeletal muscle. Compared to a non-targeting (CTRL) siRNA, in vivo electroporation of 400 nM Mfn2 siRNA (Mfn2 KD) into mouse footpads resulted in a marked acute reduction (67±3%) in Mfn2 protein levels in flexor digitorum brevis (FDB) muscles that occurred without a change in other key Ca(2+) regulatory proteins. Electron microscopy analyses revealed that Mfn2 knockdown resulted in a change in mitochondria morphology and mis-localization of some mitochondria from the I-band to the A-band region of the sarcomere. To assess the role of Mfn2 in SR-mitochondrial crosstalk, we measured mitochondrial Ca(2+) uptake and myoplasmic Ca(2+) transients with rhod-2 and mag-fluo-4, respectively, during repetitive high frequency tetanic stimulation (5×100 Hz tetani, 500 ms/tetani, 0.2 duty cycle) in CTRL and Mfn2 KD fibers. Mitochondrial Ca(2+) uptake during repetitive tetanic stimulation was significantly reduced (40%) in Mfn2 KD FDB fibers, which was accompanied by a parallel elevation in the global electrically evoked myoplasmic Ca(2+) transient. Mfn2 KD also resulted in a reduction of the mitochondrial membrane potential, which contributed to the observed decrease in activity-dependent mitochondrial Ca(2+) uptake. Consistent with this idea, a similar decrease in mitochondrial Ca(2+) uptake was also observed in wild type fibers following a comparable reduction in mitochondrial membrane potential induced by acute exposure to a low concentration (50 nM) of carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP). In addition, both global and mitochondrial Ca(2+) transients during repetitive tetanic stimulation were similarly reduced by both slow (EGTA) and fast (BAPTA) Ca(2+) chelating agents. Together, these results indicate that Mfn2 promotes proper mitochondrial morphology, localization, and membrane potential required for optimal activity-dependent mitochondrial Ca(2+) uptake and buffering of the global myoplasmic Ca(2+) transient in adult skeletal muscle.
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Project description:Age-related sarcopenia is characterized by a progressive loss of muscle mass with decline in specific force, having dramatic consequences on mobility and quality of life in seniors. The etiology of sarcopenia is multifactorial and underlying mechanisms are currently not fully elucidated. Physical exercise is known to have beneficial effects on muscle trophism and force production. Alterations of mitochondrial Ca2+ homeostasis regulated by mitochondrial calcium uniporter (MCU) have been recently shown to affect muscle trophism in vivo in mice. To understand the relevance of MCU-dependent mitochondrial Ca2+ uptake in aging and to investigate the effect of physical exercise on MCU expression and mitochondria dynamics, we analyzed skeletal muscle biopsies from 70-year-old subjects 9 weeks trained with either neuromuscular electrical stimulation (ES) or leg press. Here, we demonstrate that improved muscle function and structure induced by both trainings are linked to increased protein levels of MCU Ultrastructural analyses by electron microscopy showed remodeling of mitochondrial apparatus in ES-trained muscles that is consistent with an adaptation to physical exercise, a response likely mediated by an increased expression of mitochondrial fusion protein OPA1. Altogether these results indicate that the ES-dependent physiological effects on skeletal muscle size and force are associated with changes in mitochondrial-related proteins involved in Ca2+ homeostasis and mitochondrial shape. These original findings in aging human skeletal muscle confirm the data obtained in mice and propose MCU and mitochondria-related proteins as potential pharmacological targets to counteract age-related muscle loss.
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Project description:Autophagy is responsible for the maintenance of skeletal muscle homeostasis, thanks to the removal of aberrant and dysfunctional macromolecules and organelles. During fasting, increased autophagy ensures the maintenance of the amino acid pool required for energy production. The activity of the mitochondrial Ca2+ uniporter (MCU), the highly selective channel responsible for mitochondrial Ca2+ uptake, controls skeletal muscle size, force, and nutrient utilization. Thus, both autophagy and mitochondrial Ca2+ accumulation play a pivotal role to maintain muscle homeostasis and to sustain muscle function. Here, we address whether, in skeletal muscle, mitochondrial Ca2+ uptake and autophagy are mutually related. Muscle-restricted MCU silencing partially inhibits the autophagy flux. Moreover, skeletal muscle-specific deletion of the essential autophagy gene Atg7, known to cause the accumulation of dysfunctional mitochondria, drastically reduces mitochondrial Ca2+ accumulation. Thus, a vicious cycle takes place, in which reduced MCU activity hampers the autophagic flux, and loss of autophagy further impairs mitochondrial Ca2+ signaling.
| S-EPMC6754932 | biostudies-literature
Project description:The mitochondrial calcium uniporter (MCU) gene codifies for the inner mitochondrial membrane (IMM) channel responsible for mitochondrial Ca(2 +) uptake. Cytosolic Ca(2 +) transients are involved in sarcomere contraction through cycles of release and storage in the sarcoplasmic reticulum. In addition cytosolic Ca(2 +) regulates various signaling cascades that eventually lead to gene expression reprogramming. Mitochondria are strategically placed in close contact with the ER/SR, thus cytosolic Ca(2 +) transients elicit large increases in the [Ca(2 +)] of the mitochondrial matrix ([Ca(2 +)]mt). Mitochondrial Ca(2 +) uptake regulates energy production and cell survival. In addition, we recently showed that MCU-dependent mitochondrial Ca(2 +) uptake controls skeletal muscle trophism. In the same report, we dissected the effects of MCU-dependent mitochondrial Ca(2 +) uptake on gene expression through microarray gene expression analysis upon modulation of MCU expression by in vivo AAV infection. Analyses were performed on single skeletal muscle fibers at two time points (7 and 14 days post-AAV injection). Raw and normalized data are available on the GEO database (http://www.ncbi.nlm.nih.gov/geo/) (GSE60931).
| S-EPMC4583640 | biostudies-literature
Project description:The sarcoplasmic reticulum (SR) plays an important role in calcium homeostasis. SR calcium mishandling is described in pathological conditions, such as myopathies. Here, we investigated whether the nuclear receptor subfamily 1 group D member (NR1D1, also called REV-ERBα) regulates skeletal muscle SR calcium homeostasis. Our data demonstrate that NR1D1 deficiency in mice impaired sarco/endoplasmic reticulum calcium ATPase-dependent (SERCA-dependent) SR calcium uptake. NR1D1 acts on calcium homeostasis by repressing the SERCA inhibitor myoregulin through direct binding to its promoter. Restoration of myoregulin counteracted the effects of NR1D1 overexpression on SR calcium content. Interestingly, myoblasts from patients with Duchenne muscular dystrophy displayed lower NR1D1 expression, whereas pharmacological NR1D1 activation ameliorated SR calcium homeostasis and improved muscle structure and function in dystrophic mdx/Utr+/- mice. Our findings demonstrate that NR1D1 regulates muscle SR calcium homeostasis, pointing to its therapeutic potential for mitigating myopathy.
| S-EPMC9536258 | biostudies-literature
Project description:Muscle atrophy contributes to the poor prognosis of many physiopathological conditions, but pharmacological therapies are still limited. Muscle activity leads to major swings in mitochondrial [Ca2+] which control aerobic metabolism, cell death and survival pathways. We have investigated in vivo the effects of mitochondrial Ca2+ homeostasis in skeletal muscle function and trophism, by overexpressing or silencing the Mitochondrial Calcium Uniporter (MCU). The results coherently demonstrate that both in developing and in adult muscles MCU-dependent mitochondrial Ca2+ uptake has a marked trophic effect that does not depend on autophagy or aerobic control, but impinges on two major hypertrophic pathways of skeletal muscle, PGC-1M-NM-14 and Igf1-Akt/PKB. In adult mice, MCU overexpression protects from denervation-induced atrophy. These data reveal a novel Ca2+-dependent organelle-to-nucleus signaling route, which links mitochondrial function to the control of muscle mass and may represent a possible pharmacological target in sarcopenia. Experiments were performed on biological replicates of single skeletal muscle fibres. Seven fibres were chosen for their Mutochondrial Calcium Uniporter (MCU) overexpression and other seven fibres because MCU was silenced. Overexpression and silencing were performed injecting skeletal muscle with AAV containing MCU gene or short interfering oligos specific for MCU. As control was profiled eigth fibres transfected with AAV and eigth wild type fibres. Analyses were performed 7 days and 14 days after the AAV injection (3 fibers after 7 days and 4 fibers after 14 days for MCU overexpression and silencing, four fibres after 7 days and four after 14 days for control).
2015-03-05 | E-GEOD-60931 | biostudies-arrayexpress
Project description:Calcium (Ca(2+)) uptake into the mitochondrial matrix is critically important to cellular function. As a regulator of matrix Ca(2+) levels, this flux influences energy production and can initiate cell death. If large, this flux could potentially alter intracellular Ca(2+) ([Ca(2+)]i) signals. Despite years of study, fundamental disagreements on the extent and speed of mitochondrial Ca(2+) uptake still exist. Here, we review and quantitatively analyze mitochondrial Ca(2+) uptake fluxes from different tissues and interpret the results with respect to the recently proposed mitochondrial Ca(2+) uniporter (MCU) candidate. This quantitative analysis yields four clear results: (i) under physiological conditions, Ca(2+) influx into the mitochondria via the MCU is small relative to other cytosolic Ca(2+) extrusion pathways; (ii) single MCU conductance is ?6-7 pS (105 mM [Ca(2+)]), and MCU flux appears to be modulated by [Ca(2+)]i, suggesting Ca(2+) regulation of MCU open probability (P(O)); (iii) in the heart, two features are clear: the number of MCU channels per mitochondrion can be calculated, and MCU probability is low under normal conditions; and (iv) in skeletal muscle and liver cells, uptake per mitochondrion varies in magnitude but total uptake per cell still appears to be modest. Based on our analysis of available quantitative data, we conclude that although Ca(2+) critically regulates mitochondrial function, the mitochondria do not act as a significant dynamic buffer of cytosolic Ca(2+) under physiological conditions. Nevertheless, with prolonged (superphysiological) elevations of [Ca(2+)]i, mitochondrial Ca(2+) uptake can increase 10- to 1,000-fold and begin to shape [Ca(2+)]i dynamics.
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Project description:The Ca2+-binding protein parvalbumin (PV) and mitochondria play important roles in Ca2+ signaling, buffering and sequestration. Antagonistic regulation of PV and mitochondrial volume is observed in in vitro and in vivo model systems. Changes in mitochondrial morphology, mitochondrial volume and dynamics (fusion, fission, mitophagy) resulting from modulation of PV were investigated in MDCK epithelial cells with stable overexpression/downregulation of PV. Increased PV levels resulted in smaller, roundish cells and shorter mitochondria, the latter phenomenon related to reduced fusion rates and decreased expression of genes involved in mitochondrial fusion. PV-overexpressing cells displayed increased mitophagy, a likely cause for the decreased mitochondrial volumes and the smaller overall cell size. Cells showed lower mobility in vitro, paralleled by reduced protrusions. Constitutive PV down-regulation in PV-overexpressing cells reverted mitochondrial morphology and fractional volume to the state present in control MDCK cells, resulting from increased mitochondrial movement and augmented fusion rates. PV-modulated, bi-directional and reversible mitochondrial dynamics are key to regulation of mitochondrial volume.
| S-EPMC6208788 | biostudies-literature
Project description:The mitochondrial Ca2+ uniporter (MCU) complex mediates acute mitochondrial Ca2+ influx. In skeletal muscle, MCU links Ca2+ signaling to energy production by directly enhancing the activity of key metabolic enzymes in the mitochondria. Here, we examined the role of MCU in skeletal muscle development and metabolic function by generating mouse models for the targeted deletion of Mcu in embryonic, postnatal, and adult skeletal muscle. Loss of Mcu did not affect muscle growth and maturation or otherwise cause pathology. Skeletal muscle-specific deletion of Mcu in mice also did not affect myofiber intracellular Ca2+ handling, but it did inhibit acute mitochondrial Ca2+ influx and mitochondrial respiration stimulated by Ca2+, resulting in reduced acute exercise performance in mice. However, loss of Mcu also resulted in enhanced muscle performance under conditions of fatigue, with a preferential shift toward fatty acid metabolism, resulting in reduced body fat with aging. Together, these results demonstrate that MCU-mediated mitochondrial Ca2+ regulation underlies skeletal muscle fuel selection at baseline and under enhanced physiological demands, which affects total homeostatic metabolism.
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