Chin Eva R, Grange Robert W, Viau Francois, Simard Alain R, Humphries Caroline, Shelton John, Bassel-Duby Rhonda, Williams R Sanders, Michel Robin N
Department of Internal Medicine, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, NB11.200, Dallas, TX 75235-8573, USA.
J Physiol. 2003 Mar 1;547(Pt 2):649-63. doi: 10.1113/jphysiol.2002.024760. Epub 2003 Jan 17.
The purpose of this study was to determine whether induced expression of the Ca2+ buffering protein parvalbumin (PV) in slow-twitch fibres would lead to alterations in physiological, biochemical and molecular properties reflective of a fast fibre phenotype. Transgenic (TG) mice were generated that overexpressed PV in slow (type I) muscle fibres. In soleus muscle (SOL; 58 % type I fibres) total PV expression was 2- to 6-fold higher in TG compared to wild-type (WT) mice. Maximum twitch and tetanic tensions were similar in WT and TG but force at subtetanic frequencies (30 and 50 Hz) was reduced in TG SOL. Twitch time-to-peak tension and half-relaxation time were significantly decreased in TG SOL (time-to-peak tension: 39.3 +/- 2.6 vs. 55.1 +/- 4.7 ms; half-relaxation time: 42.1 +/- 3.5 vs. 68.1 +/- 9.6 ms, P < 0.05 for TG vs. WT, respectively; n = 8-10). There was a significant increase in expression of type IIa myosin heavy chain (MHC) and ryanodine receptor at the mRNA level in TG SOL but there were no differences in MHC expression at the protein level and thus no difference in fibre type. Whole muscle succinate dehydrogenase activity was reduced by 12 +/- 0.4 % in TG SOL and single fibre glycerol-3-phosphate dehydrogenase activity was decreased in a subset of type IIa fibres. These differences were associated with a 64 % reduction in calcineurin activity in TG SOL. These data show that overexpression of PV, resulting in decreased calcineurin activity, can alter the functional and metabolic profile of muscle and influence the expression of key marker genes in a predominantly slow-twitch muscle with minimal effects on the expression of muscle contractile proteins.
本研究的目的是确定在慢肌纤维中诱导表达钙离子缓冲蛋白小白蛋白（PV）是否会导致反映快肌纤维表型的生理、生化和分子特性发生改变。构建了在慢（I型）肌纤维中过表达PV的转基因（TG）小鼠。在比目鱼肌（SOL；58%为I型纤维）中，TG小鼠的总PV表达量比野生型（WT）小鼠高2至6倍。WT和TG小鼠的最大抽搐和强直张力相似，但TG SOL在亚强直频率（30和50 Hz）下的肌力降低。TG SOL的抽搐达到峰值张力时间和半松弛时间显著缩短（达到峰值张力时间：39.3±2.6对55.1±4.7毫秒；半松弛时间：42.1±3.5对68.1±9.6毫秒，TG与WT相比，P均<0.05；n = 8 - 10）。TG SOL中IIa型肌球蛋白重链（MHC）和兰尼碱受体的mRNA水平表达显著增加，但蛋白质水平的MHC表达无差异，因此纤维类型无差异。TG SOL的全肌肉琥珀酸脱氢酶活性降低了12±0.4%，IIa型纤维亚群中的单纤维甘油-3-磷酸脱氢酶活性降低。这些差异与TG SOL中钙调神经磷酸酶活性降低64%有关。这些数据表明，PV过表达导致钙调神经磷酸酶活性降低，可改变肌肉的功能和代谢特征，并影响主要为慢肌纤维的关键标记基因的表达，而对肌肉收缩蛋白的表达影响最小。
