Feng Han-Zhong, Jin J-P
Department of Physiology, Wayne State University School of Medicine Detroit, MI, USA.
Front Physiol. 2016 Dec 15;7:597. doi: 10.3389/fphys.2016.00597. eCollection 2016.
Carbonic anhydrase III (CAIII) is a metabolic enzyme and a regulator for intracellular pH. CAIII has been reported with high level expression in slow twitch skeletal muscles. Here we demonstrate that CAIII is expressed in multiple slow and fast twitch muscles of adult mouse independent of the expression of myosin isoforms. Expressing similar fast type of myofilament proteins, CAIII-positive tibial anterior (TA) muscle exhibits higher tolerance to fatigue than that of CAIII-negative fast twitch extensor digitorum longus (EDL) muscle in contractility studies. We further studied the muscles of CAIII knockout (-KO) mice. The loss of CAIII in soleus and TA muscles in -KO mice did not change muscle mass, sarcomere protein isoform contents, and the baseline twitch and tetanic contractility as compared with age-matched wild type (WT) controls. On the other hand, -KO TA muscle showed faster force reduction at the beginning but higher resistance at the end during a fatigue test, followed by slower post fatigue recovery than that of WT TA muscle. Superfused -KO soleus muscle also had faster total force reduction during fatigue test than that of WT soleus. However, it showed a less elevation of resting tension followed by a better post fatigue recovery under acidotic stress. CAIII was detected in neonatal TA and EDL muscle, downregulated during development, and then re-expressed in adult TA but not EDL muscles. The expression of CAIII in -KO myopathy mouse soleus muscle that has diminished slow fiber contents due to the loss of slow troponin T remained high. -KO EDL, TA, and soleus muscles showed no change in the expression of mitochondria biomarker proteins. The data suggest a fiber type independent expression of CAIII with a role in the regulation of intracellular pH in skeletal muscle and may be explored as a target for improving fatigue resistance and for the treatment of myopathies.
碳酸酐酶III（CAIII）是一种代谢酶，也是细胞内pH值的调节剂。据报道，CAIII在慢肌纤维骨骼肌中高水平表达。在此我们证明，CAIII在成年小鼠的多种慢肌和快肌纤维中均有表达，且与肌球蛋白亚型的表达无关。在收缩性研究中，表达相似快肌型肌丝蛋白的CAIII阳性胫骨前肌（TA）比CAIII阴性的快肌纤维趾长伸肌（EDL）对疲劳具有更高的耐受性。我们进一步研究了CAIII基因敲除（-KO）小鼠的肌肉。与年龄匹配的野生型（WT）对照相比，-KO小鼠比目鱼肌和TA肌中CAIII的缺失并未改变肌肉质量、肌节蛋白亚型含量以及基线抽搐和强直收缩性。另一方面，在疲劳试验中，-KO TA肌在开始时力下降更快，但在试验结束时具有更高的耐力，且疲劳后恢复比WT TA肌更慢。在疲劳试验中，超灌注的-KO比目鱼肌总力下降也比WT比目鱼肌更快。然而，在酸中毒应激下，其静息张力升高较少，随后疲劳后恢复较好。在新生TA肌和EDL肌中可检测到CAIII，其在发育过程中表达下调，然后在成年TA肌中重新表达，但在EDL肌中未重新表达。在-KO肌病小鼠比目鱼肌中，由于慢肌钙蛋白T的缺失导致慢肌纤维含量减少，但CAIII的表达仍然很高。-KO EDL肌、TA肌和比目鱼肌中线粒体生物标志物蛋白的表达没有变化。这些数据表明CAIII的表达与纤维类型无关，在调节骨骼肌细胞内pH值方面发挥作用，有望作为改善抗疲劳能力和治疗肌病的靶点进行探索。
