Norman Barbara, Esbjörnsson Mona, Rundqvist Håkan, Osterlund Ted, von Walden Ferdinand, Tesch Per A
Department of Laboratory Medicine, Division of Clinical Physiology, Karolinska University Hospital, Huddinge, Stockholm, Sweden.
J Appl Physiol (1985). 2009 Mar;106(3):959-65. doi: 10.1152/japplphysiol.91435.2008. Epub 2009 Jan 15.
Alpha-actinins are structural proteins of the Z-line. Human skeletal muscle expresses two alpha-actinin isoforms, alpha-actinin-2 and alpha-actinin-3, encoded by their respective genes ACTN2 and ACTN3. ACTN2 is expressed in all muscle fiber types, while only type II fibers, and particularly the type IIb fibers, express ACTN3. ACTN3 (R577X) polymorphism results in loss of alpha-actinin-3 and has been suggested to influence skeletal muscle function. The X allele is less common in elite sprint and power athletes than in the general population and has been suggested to be detrimental for performance requiring high power. The present study investigated the association of ACTN3 genotype with muscle power during 30-s Wingate cycling in 120 moderately to well-trained men and women and with knee extensor strength and fatigability in a subset of 21 men performing isokinetic exercise. Muscle biopsies were obtained from the vastus lateralis muscle to determine fiber-type composition and ACTN2 and ACTN3 mRNA levels. Peak and mean power and the torque-velocity relationship and fatigability output showed no difference across ACTN3 genotypes. Thus this study suggests that R577X polymorphism in ACTN3 is not associated with differences in power output, fatigability, or force-velocity characteristics in moderately trained individuals. However, repeated exercise bouts prompted an increase in peak torque in RR but not in XX genotypes, suggesting that ACTN3 genotype may modulate responsiveness to training. Our data further suggest that alpha-actinins do not play a significant role in determining muscle fiber-type composition. Finally, we show that ACTN2 expression is affected by the content of alpha-actinin-3, which implies that alpha-actinin-2 may compensate for the lack of alpha-actinin-3 and hence counteract the phenotypic consequences of the deficiency.
α-辅肌动蛋白是Z线的结构蛋白。人类骨骼肌表达两种α-辅肌动蛋白异构体，即α-辅肌动蛋白-2和α-辅肌动蛋白-3，分别由各自的基因ACTN2和ACTN3编码。ACTN2在所有肌纤维类型中均有表达，而只有II型纤维，特别是IIb型纤维表达ACTN3。ACTN3（R577X）多态性导致α-辅肌动蛋白-3缺失，并被认为会影响骨骼肌功能。X等位基因在精英短跑和力量型运动员中比在普通人群中更少见，并且被认为对需要高功率的运动表现不利。本研究调查了120名中度至训练有素的男性和女性在30秒温盖特自行车测试中的肌肉功率与ACTN3基因型的关联，以及21名进行等速运动的男性亚组中膝关节伸肌力量和疲劳性与ACTN3基因型的关联。从股外侧肌获取肌肉活检样本，以确定纤维类型组成以及ACTN2和ACTN3 mRNA水平。峰值功率和平均功率以及扭矩-速度关系和疲劳性输出在ACTN3基因型之间没有差异。因此，本研究表明ACTN3中的R577X多态性与中度训练个体的功率输出、疲劳性或力-速度特征差异无关。然而，重复运动回合促使RR基因型的峰值扭矩增加，而XX基因型则没有，这表明ACTN3基因型可能调节对训练的反应性。我们的数据进一步表明，α-辅肌动蛋白在决定肌肉纤维类型组成方面不发挥重要作用。最后，我们表明ACTN2的表达受α-辅肌动蛋白-3含量的影响，这意味着α-辅肌动蛋白-2可能补偿α-辅肌动蛋白-3的缺乏，从而抵消缺乏症的表型后果。
