{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nSERCA proteins are essential Ca²⁺ pumps that actively transport cytosolic Ca²⁺ into the sarcoplasmic/endoplasmic reticulum, thereby regulating intracellular Ca²⁺ homeostasis that is fundamental for muscle contraction and relaxation. Deficiencies or mutations in SERCA isoforms, such as the absence of SERCA1 in fast‐twitch fibers, lead to disorders such as Brody disease and contribute to the pathogenesis of muscular dystrophies. In various experimental models, overexpression or pharmacological activation of SERCA has been shown to correct Ca²⁺ overload, improving muscle integrity and contractile function."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nFine‐tuning of SERCA function is achieved via regulatory proteins that modulate both its enzymatic activity and its impact on contractility. Inhibition by small regulatory peptides such as sarcolipin, and modulation by phospholamban in adrenergically stressed hearts, highlight an intricate control system that adjusts Ca²⁺ reuptake in response to physiological and pathological cues. Such regulation is critical not only for efficient muscle relaxation and contraction dynamics but also for coordinating metabolic processes like glucose uptake."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "4", "end_ref": "7"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its core role in excitation–contraction coupling, SERCA function is also intertwined with muscle differentiation and cellular Ca²⁺ signaling in diverse tissues. Transcription factors such as Six1 and Ebf3 enhance the expression of SERCA isoforms during myogenic differentiation, thereby supporting the proper development and function of fast‐twitch fibers. Moreover, observations in sensory and other central neurons indicate that interference with SERCA activity, as seen with formaldehyde‐evoked Ca²⁺ release, further underscores its broader contribution to Ca²⁺ signaling. Emerging modulators like neuronostatin have also been implicated in myocardial responses, although their precise mechanisms remain to be elucidated."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "8", "end_ref": "13"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nSERCA activity is highly sensitive to the cellular redox state, lipid composition, and other microenvironmental factors. Oxidative stress or modifications in membrane phospholipid ratios can impair Ca²⁺ uptake, while conditions such as spaceflight‐induced muscle unloading also adversely affect SERCA function. In vitro and in vivo studies demonstrate that such modulatory influences—ranging from redox‐mediated inhibition to alterations in SR membrane composition and regulatory phosphorylation events—profoundly impact muscle force generation and relaxation rates."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "14", "end_ref": "18"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nRecent studies have also highlighted the significance of isoform‐specific roles—such as that of SERCA1b in developing myotubes and SERAC1 in mitochondrial physiology—in maintaining both muscular and metabolic health. In addition to the contribution of CAPN3 deficiency to SERCA protein degradation in limb‐girdle muscular dystrophy, SERAC1 has been shown to participate in mitochondrial serine transport and one‐carbon metabolism; its loss leads to nucleotide insufficiency and mtDNA depletion. These findings extend the importance of SERCA function beyond mere Ca²⁺ handling to encompass the regulation of energy homeostasis and cellular integrity."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "19", "end_ref": "21"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Yan Pan, Elena Zvaritch, A Russ Tupling, et al. 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