Recombinant annexin A6 promotes membrane repair and protects against muscle injury
Alexis R. Demonbreun, … , David Y. Barefield, Elizabeth M. McNally
Alexis R. Demonbreun, … , David Y. Barefield, Elizabeth M. McNally
Published September 23, 2019
Citation Information: J Clin Invest. 2019;129(11):4657-4670. https://doi.org/10.1172/JCI128840.
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Research Article Muscle biology Therapeutics

Recombinant annexin A6 promotes membrane repair and protects against muscle injury

Abstract

Membrane repair is essential to cell survival. In skeletal muscle, injury often associates with plasma membrane disruption. Additionally, muscular dystrophy is linked to mutations in genes that produce fragile membranes or reduce membrane repair. Methods to enhance repair and reduce susceptibility to injury could benefit muscle in both acute and chronic injury settings. Annexins are a family of membrane-associated Ca2+-binding proteins implicated in repair, and annexin A6 was previously identified as a genetic modifier of muscle injury and disease. Annexin A6 forms the repair cap over the site of membrane disruption. To elucidate how annexins facilitate repair, we visualized annexin cap formation during injury. We found that annexin cap size positively correlated with increasing Ca2+ concentrations. We also found that annexin overexpression promoted external blebs enriched in Ca2+ and correlated with a reduction of intracellular Ca2+ at the injury site. Annexin A6 overexpression reduced membrane injury, consistent with enhanced repair. Treatment with recombinant annexin A6 protected against acute muscle injury in vitro and in vivo. Moreover, administration of recombinant annexin A6 in a model of muscular dystrophy reduced serum creatinine kinase, a biomarker of disease. These data identify annexins as mediators of membrane-associated Ca2+ release during membrane repair and annexin A6 as a therapeutic target to enhance membrane repair capacity.

Authors

Alexis R. Demonbreun, Katherine S. Fallon, Claire C. Oosterbaan, Elena Bogdanovic, James L. Warner, Jordan J. Sell, Patrick G. Page, Mattia Quattrocelli, David Y. Barefield, Elizabeth M. McNally

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Figure 2

Annexin expression promoted release of blebs from the site if myofiber repair.

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Annexin expression promoted release of blebs from the site if myofiber r...
Myofibers were electroporated with the Ca2+ indicator GCaMP5G (green) with or without tdTomato-labeled annexin A1, annexin A2, or annexin A6. Ca2+ area and fluorescence were assessed after membrane damage. (A) High-magnification Z-projection images illustrate external blebs filled with the Ca2+ indicator emanating from the lesion when annexin A1, A2, or A6 was coexpressed and a corresponding reduction in Ca2+ indicator within the myofiber when compared with GCaMP5G alone (see panel B). (B) Membrane marked by FM 4-64 shows GCaMP5G-negative vesicles form in the absence of annexin overexpression. Scale bars: 5 μm. (C) Expression of annexin A6 or A2 resulted in an increased number of GCaMP5G-positive blebs. (D) Expression of annexin A6 resulted in the formation of the largest GCaMP5G-positive blebs. Data are expressed as mean ± SEM. Differences were tested by 1-way ANOVA with Tukey’s multiple-comparisons test. *P < 0.05 (n = 16 myofibers from n = 3 mice per condition).