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Switch from ER-mitochondrial to SR-mitochondrial calcium coupling during muscle differentiation.

ABSTRACT: Emerging evidence indicates that mitochondria are locally coupled to endoplasmic reticulum (ER) Ca2+ release in myoblasts and to sarcoplasmic reticulum (SR) Ca2+ release in differentiated muscle fibers in order to regulate cytoplasmic calcium dynamics and match metabolism with cell activity. However, the mechanism of the developmental transition from ER to SR coupling remains unclear. We have studied mitochondrial sensing of IP3 receptor (IP3R)- and ryanodine receptor (RyR)-mediated Ca2+ signals in H9c2 myoblasts and differentiating myotubes, as well as the attendant changes in mitochondrial morphology. Mitochondria in myoblasts were largely elongated, luminally connected and relatively few in number, whereas the myotubes were densely packed with globular mitochondria that displayed limited luminal continuity. Vasopressin, an IP3-linked agonist, evoked a large cytoplasmic Ca2+ ([Ca2+]c) increase in myoblasts, whereas it elicited a smaller response in myotubes. Conversely, RyR-mediated Ca2+ release induced by caffeine, was not observed in myoblasts, but triggered a large [Ca2+]c signal in myotubes. Both the IP3R and the RyR-mediated [Ca2+]c rise was closely associated with a mitochondrial matrix Ca2+ ([Ca2+]m) signal. Every myotube that showed a [Ca2+]c spike also displayed a [Ca2+]m response. Addition of IP3 to permeabilized myoblasts and caffeine to permeabilized myotubes also resulted in a rapid [Ca2+]m rise, indicating that Ca2+ was delivered via local coupling of the ER/SR and mitochondria. Thus, as RyRs are expressed during muscle differentiation, the local connection between RyR and mitochondrial Ca2+ uptake sites also appears. When RyR1 was exogenously introduced to myoblasts by overexpression, the [Ca2+]m signal appeared together with the [Ca2+]c signal, however the mitochondrial morphology remained unchanged. Thus, RyR expression alone is sufficient to induce the steps essential for their alignment with mitochondrial Ca2+ uptake sites, whereas the mitochondrial proliferation and reshaping utilize either downstream or alternative pathways.

SUBMITTER: Yi M

PROVIDER: S-EPMC3607359 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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Switch from ER-mitochondrial to SR-mitochondrial calcium coupling during muscle differentiation.

Yi Muqing M Weaver David D Eisner Verónica V Várnai Péter P Hunyady László L Ma Jianjie J Csordás György G Hajnóczky György G

Cell calcium 20120710 5

Emerging evidence indicates that mitochondria are locally coupled to endoplasmic reticulum (ER) Ca2+ release in myoblasts and to sarcoplasmic reticulum (SR) Ca2+ release in differentiated muscle fibers in order to regulate cytoplasmic calcium dynamics and match metabolism with cell activity. However, the mechanism of the developmental transition from ER to SR coupling remains unclear. We have studied mitochondrial sensing of IP3 receptor (IP3R)- and ryanodine receptor (RyR)-mediated Ca2+ signals ...[more]

PMID: 22784666

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Project description:BackgroundAberrations to endoplasmic/sarcoplasmic reticulum (ER/SR) calcium concentration can result in the departure of endogenous proteins in a phenomenon termed exodosis. Redistribution of the ER/SR proteome can have deleterious effects to cell function and cell viability, often contributing to disease pathogenesis. Many proteins prone to exodosis reside in the ER/SR via an ER retention/retrieval sequence (ERS) and are involved in protein folding, protein modification, and protein trafficking. While the consequences of their extracellular presence have yet to be fully delineated, the proteins that have undergone exodosis may be useful for biomarker development. Skeletal muscle cells rely upon tightly coordinated ER/SR calcium release for muscle contractions, and perturbations to calcium homeostasis can result in myopathies. Ryanodine receptor type-1 (RYR1) is a calcium release channel located in the SR. Mutations to the RYR1 gene can compromise calcium homeostasis leading to a vast range of clinical phenotypes encompassing hypotonia, myalgia, respiratory insufficiency, ophthalmoplegia, fatigue and malignant hyperthermia (MH). There are currently no FDA approved treatments for RYR1-related myopathies (RYR1-RM).ResultsHere we examine the exodosis profile of skeletal muscle cells following ER/SR calcium depletion. Proteomic analysis identified 4,465 extracellular proteins following ER/SR calcium depletion with 1,280 proteins significantly different than vehicle. A total of 54 ERS proteins were identified and 33 ERS proteins significantly increased following ER/SR calcium depletion. Specifically, ERS protein, mesencephalic astrocyte-derived neurotrophic factor (MANF), was elevated following calcium depletion, making it a potential biomarker candidate for human samples. Despite no significant elevation of MANF in plasma levels among healthy volunteers and RYR1-RM individuals, MANF plasma levels positively correlated with age in RYR1-RM individuals, presenting a potential biomarker of disease progression. Selenoprotein N (SEPN1) was also detected only in extracellular samples following ER/SR calcium depletion. This protein is integral to calcium handling and SEPN1 variants have a causal role in SEPN1-related myopathies (SEPN1-RM). Extracellular presence of ER/SR membrane proteins may provide new insight into proteomic alterations extending beyond ERS proteins. Pre-treatment of skeletal muscle cells with bromocriptine, an FDA approved drug recently found to have anti-exodosis effects, curbed exodosis of ER/SR resident proteins.ConclusionChanges to the extracellular content caused by intracellular calcium dysregulation presents an opportunity for biomarker development and drug discovery.

Dataset Information

Switch from ER-mitochondrial to SR-mitochondrial calcium coupling during muscle differentiation.

Publications

Switch from ER-mitochondrial to SR-mitochondrial calcium coupling during muscle differentiation.

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