Molecular regulation of stretch activation.
Molecular regulation of stretch activation.
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拉伸激活的分子调节。
DOI：
10.1152/ajpcell.00101.2022
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
McDonald,KerryS
中科院分区：
文献类型：
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作者：
Robinett,JoelC;Hanft,LaurinM;Biesiadecki,Brandon;McDonald,KerryS
拉伸激活被定义为快速拉伸后延迟的力量增加。尽管有大量证据表明在分离的心肌纤维制剂中拉伸激活，但很少有研究测量哺乳动物骨骼肌纤维中拉伸激活的机制。在蛋白激酶A （PKA）磷酸化慢肌凝蛋白结合蛋白c之前和之后，我们测量了大鼠渗透性慢抽搐骨骼肌纤维在快速步拉伸[~ 1%-4%肌节长度（SL）]的亚极大Ca2+激活期间的拉伸激活。PKA在低（~ 25%）Ca2+激活期间显著增加拉伸激活，并在低和半最大Ca2+激活期间加速延迟力发展（kef）的速率。在台阶拉伸和随后的力发展之后，纤维迅速缩短到原来的肌节长度，这通常会引起缩短引起的短暂力超调。PKA后，在低Ca2+激活水平下，台阶缩短引起的瞬态力超调增加了~ 10倍。在低和半最大Ca2+激活时，PKA后的kdfollow步缩短也增加了。接下来，我们研究了细丝对拉伸激活的调节。我们测试了典型PKA位点的心肌肌钙蛋白I （cTnI）磷酸化和新型酪氨酸激酶位点在拉伸激活中的相互作用。将天然慢骨架Tn复合物与具有不同人类cTnI n端伪磷酸化分子的重组人cTn复合物交换：1)非磷酸化野生型（WT），2)典型的S22/23D PKA位点，3)酪氨酸激酶Y26E位点，4)组合的S22/23D + Y26E cTnI。所有三种伪磷酸化的cTnI都比WT引发了更大的拉伸激活。拉伸激活后，伪磷酸化的cTnI达到了一个新的、升高的拉伸诱导的稳态力。组合S22/23D + Y26E伪磷酸化cTnI增加kdf。这些结果表明，慢骨肌球蛋白结合蛋白c （sMyBP-C）磷酸化通过交叉桥募集和更快的循环动力学结合调节拉伸激活，而cTnI磷酸化通过冗余和协同机制调节拉伸激活；总之，这些肌小体磷蛋白为增强收缩性提供了精确的靶标。
Stretch activation is defined as a delayed increase in force after rapid stretches. Although there is considerable evidence for stretch activation in isolated cardiac myofibrillar preparations, few studies have measured mechanisms of stretch activation in mammalian skeletal muscle fibers. We measured stretch activation following rapid step stretches [∼1%–4% sarcomere length (SL)] during submaximal Ca2+activations of rat permeabilized slow-twitch skeletal muscle fibers before and after protein kinase A (PKA), which phosphorylates slow myosin binding protein-C. PKA significantly increased stretch activation during low (∼25%) Ca2+activation and accelerated rates of delayed force development (kef) during both low and half-maximal Ca2+activation. Following the step stretches and subsequent force development, fibers were rapidly shortened to original sarcomere length, which often elicited a shortening-induced transient force overshoot. After PKA, step shortening-induced transient force overshoot increased ∼10-fold following an ∼4% SL shortening during low Ca2+activation levels.kdffollowing step shortening also increased after PKA during low and half-maximal Ca2+activations. We next investigated thin filament regulation of stretch activation. We tested the interplay between cardiac troponin I (cTnI) phosphorylation at the canonical PKA and novel tyrosine kinase sites on stretch activation. Native slow-skeletal Tn complexes were exchanged with recombinant human cTn complex with different human cTnI N-terminal pseudo-phosphorylation molecules:1) nonphosphorylated wild type (WT),2) the canonical S22/23D PKA sites,3) the tyrosine kinase Y26E site, and4) the combinatorial S22/23D + Y26E cTnI. All three pseudo-phosphorylated cTnIs elicited greater stretch activation than WT. Following stretch activation, a new, elevated stretch-induced steady-state force was reached with pseudo-phosphorylated cTnI. Combinatorial S22/23D + Y26E pseudo-phosphorylated cTnI increasedkdf. These results suggest that slow-skeletalmyosinbindingprotein-C(sMyBP-C) phosphorylation modulates stretch activation by a combination of cross-bridge recruitment and faster cycling kinetics, whereas cTnI phosphorylation regulates stretch activation by both redundant and synergistic mechanisms; and, taken together, these sarcomere phosphoproteins offer precision targets for enhanced contractility.