Muscle ankyrin repeat protein 1 (MARP1) locks titin to the sarcomeric thin filament and is a passive force regulator |
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| Authors: | Robbert J. van der Pijl Marloes van den Berg Martijn van de Locht Shengyi Shen Sylvia J.P. Bogaards Stefan Conijn Paul Langlais Pleuni E. Hooijman Siegfried Labeit Leo M.A. Heunks Henk Granzier Coen A.C. Ottenheijm |
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| Affiliation: | 1.Department of Physiology, Amsterdam University Medical Centers, Amsterdam, Netherlands;2.Intensive Care Medicine, Amsterdam University Medical Centers, Amsterdam, Netherlands;3.Department of Cellular and Molecular Medicine, University of Arizona, Tuscon, AZ;4.Division of Endocrinology, University of Arizona, Tucson, AZ;5.Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany. |
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| Abstract: | Muscle ankyrin repeat protein 1 (MARP1) is frequently up-regulated in stressed muscle, but its effect on skeletal muscle function is poorly understood. Here, we focused on its interaction with the titin–N2A element, found in titin’s molecular spring region. We show that MARP1 binds to F-actin, and that this interaction is stronger when MARP1 forms a complex with titin–N2A. Mechanics and super-resolution microscopy revealed that MARP1 “locks” titin–N2A to the sarcomeric thin filament, causing increased extension of titin’s elastic PEVK element and, importantly, increased passive force. In support of this mechanism, removal of thin filaments abolished the effect of MARP1 on passive force. The clinical relevance of this mechanism was established in diaphragm myofibers of mechanically ventilated rats and of critically ill patients. Thus, MARP1 regulates passive force by locking titin to the thin filament. We propose that in stressed muscle, this mechanism protects the sarcomere from mechanical damage. |
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