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Troponin activator augments muscle force in nemaline myopathy patients with nebulin mutations
  1. Josine Marieke de Winter1,2,
  2. Danielle Buck2,
  3. Carlos Hidalgo2,
  4. Jeffrey R Jasper3,
  5. Fady I Malik3,
  6. Nigel F Clarke4,
  7. Ger J M Stienen1,5,
  8. Michael W Lawlor6,7,
  9. Alan H Beggs7,
  10. Coen A C Ottenheijm1,2,
  11. Henk Granzier2
  1. 1Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands
  2. 2Department of Physiology, University of Arizona, Tucson, Arizona, USA
  3. 3Research & Early Development, Cytokinetics, Inc, South San Francisco, California, USA
  4. 4INMR, The Children's Hospital at Westmead and Discipline of Paediatrics & Child Health, University of Sydney, Sydney, Australia
  5. 5Faculty of Science, Department of Physics and Astronomy, VU University, Amsterdam, The Netherlands
  6. 6Division of Pediatric Pathology, Department of Pathology and Laboratory Medicine, Medical College of Wisconsin, WI, Milwaukee, USA
  7. 7Division of Genetics and Program in Genomics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
  1. Correspondence to Professor Henk Granzier, Department of Physiology, University of Arizona, Tucson, AZ 85724, USA; granzier{at}email.arizona.edu; Dr Coen Ottenheijm, Department of Physiology, VU University Medical Center, Amsterdam 1081 BT, The Netherlands; c.ottenheijm{at}vumc.nl

Abstract

Background Nemaline myopathy—the most common non-dystrophic congenital myopathy—is caused by mutations in thin filament genes, of which the nebulin gene is the most frequently affected one. The nebulin gene codes for the giant sarcomeric protein nebulin, which plays a crucial role in skeletal muscle contractile performance. Muscle weakness is a hallmark feature of nemaline myopathy patients with nebulin mutations, and is caused by changes in contractile protein function, including a lower calcium-sensitivity of force generation. To date no therapy exists to treat muscle weakness in nemaline myopathy. Here, we studied the ability of the novel fast skeletal muscle troponin activator, CK-2066260, to augment force generation at submaximal calcium levels in muscle cells from nemaline myopathy patients with nebulin mutations.

Methods Contractile protein function was determined in permeabilised muscle cells isolated from frozen patient biopsies. The effect of 5 μM CK-2066260 on force production was assessed.

Results Nebulin protein concentrations were severely reduced in muscle cells from these patients compared to controls, while myofibrillar ultrastructure was largely preserved. Both maximal active tension and the calcium-sensitivity of force generation were lower in patients compared to controls. Importantly, CK-2066260 greatly increased the calcium-sensitivity of force generation—without affecting the cooperativity of activation—in patients to levels that exceed those observed in untreated control muscle.

Conclusions Fast skeletal troponin activation is a therapeutic mechanism to augment contractile protein function in nemaline myopathy patients with nebulin mutations and with other neuromuscular diseases.

  • Muscle disease

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