title: Distinct underlying mechanisms of limb and respiratory muscle fiber weaknesses in nemaline myopathy.
abstract: Nemaline myopathy is the most common congenital myopathy and is caused by mutations in various genes such as ACTA1 (encoding skeletal α-actin). It is associated with limb and respiratory muscle weakness. Despite increasing clinical and scientific interest, the molecular and cellular events leading to such weakness remain unknown, which prevents the development of specific therapeutic interventions. To unravel the potential mechanisms involved, we dissected lower limb and diaphragm muscles from a knock-in mouse model of severe nemaline myopathy expressing the ACTA1 His40Tyr actin mutation found in human patients. We then studied a broad range of structural and functional characteristics assessing single-myofiber contraction, protein expression, and electron microscopy. One of the major findings in the diaphragm was the presence of numerous noncontractile areas (including disrupted sarcomeric structures and nemaline bodies). This greatly reduced the number of functional sarcomeres, decreased the force generation capacity at the muscle fiber level, and likely would contribute to respiratory weakness. In limb muscle, by contrast, there were fewer noncontractile areas and they did not seem to have a major role in the pathogenesis of weakness. These divergent muscle-specific results provide new important insights into the pathophysiology of severe nemaline myopathy and crucial information for future development of therapeutic strategies.
authors: Department of Neuroscience, Clinical Neurophysiology, Uppsala University, Uppsala, Sweden. julien.ochala@neuro.uu.se
authors: Johan
authors: J
authors: Lindqvist
authors: Arthur J
authors: AJ
authors: Cheng
authors: Guillaume
authors: G
authors: Renaud
authors: Edna C
authors: EC
authors: Hardeman
authors: Julien
authors: J
authors: Ochala
mesh_terms: D000199:Actins / Q000235:genetics*; D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D003964:Diaphragm / Q000503:physiopathology; D005121:Extremities / Q000503:physiopathology; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018908:Muscle Weakness / Q000235:genetics* / Q000503:physiopathology*; D009154:Mutation / Q000235:genetics; D017696:Myopathies, Nemaline / Q000235:genetics* / Q000503:physiopathology*; D009924:Organ Culture Techniques; D012132:Respiratory Muscles / Q000503:physiopathology
chemical_list: D000199:Actins