TY - JOUR

T1 - Distinct underlying mechanisms of limb and respiratory muscle fiber weaknesses in nemaline myopathy

AU - Lindqvist, Johan

AU - Cheng, Arthur J.

AU - Renaud, Guillaume

AU - Hardeman, Edna C.

AU - Ochala, Julien

PY - 2013/6

Y1 - 2013/6

N2 - 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.

AB - 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.

KW - Actin

KW - Contractile dysfunction

KW - Limb muscle

KW - Nemaline myopathy

KW - Respiratory muscle

KW - Weakness

UR - http://www.scopus.com/inward/record.url?scp=84878668397&partnerID=8YFLogxK

U2 - 10.1097/NEN.0b013e318293b1cc

DO - 10.1097/NEN.0b013e318293b1cc

M3 - Journal article

C2 - 23656990

AN - SCOPUS:84878668397

VL - 72

SP - 472

EP - 481

JO - Journal of Neuropathology and Experimental Neurology

JF - Journal of Neuropathology and Experimental Neurology

SN - 0022-3069

IS - 6

ER -