Role of Keratin 18 for Stress-induced Adaptive Strength Gains

项目总结 骨质疏松症，随着年龄的增长，肌肉力量和质量的丧失，是虚弱的主要组成部分。肌肉无力 这似乎是至关重要的，因为低强度与更多的脆弱标志有关，而不是年龄。老年病 而虚弱的个体由于骨骼肌无法适应而面临更大的功能障碍风险 身体上的压力。对身体压力或抵抗力训练的力量适应已被联系起来 肌肉质量的丧失，特别是兴奋性收缩(EC)偶联失败。确定可用于 因此，对抗收缩诱导的EC偶联失败和促进骨骼肌适应 是对抗骨质疏松症和虚弱的关键。最近的数据表明，角蛋白18(Krt18)是一种中间体 与肌营养不良蛋白-糖蛋白复合体相关的细丝蛋白可能是一种重要的介体。 压力诱导的适应性力量增加，随着年龄的增长而减少。具体来说，我们观察到Krt18基因 是经过偏心运动获得力量的幼鼠肌肉中最高的(7倍)。 我们还观察到，Krt18蛋白表达的增加和力量的增加与 膜相关蛋白表达增加。在老龄小鼠肌肉中，Krt18的表达减弱 与年轻的老鼠相比，力量的增长要低得多。因此，我们的首要假设是 Krt18通过增加血浆稳定性来维持EC，从而促进骨骼肌对运动的适应 被反复的偏心收缩所扰乱的耦合过程。最终，我们假设Krt18 可能在增加骨骼肌弹性和延缓骨质疏松症的发生和发展中发挥作用 骨质疏松症和脆弱。在目标1中，我们将确定在反复的偏心动作后适应性力量是否会增加 Krt18通过检查幼龄(3-5个月大)雄性和雌性野生型小鼠的收缩反应 (WT)和Krt18基因敲除小鼠。在目标2中，我们将确定Krt18在肌肉中的表达是否与年龄相关 反复的偏心收缩与钝化的力量增长有关。整合与年龄相关的信息 肌肉适应性(或缺乏Krt18表达)，我们将使用年轻(3-5个月)，成年(20-22个月) 和老年(27-29个月)雄性和雌性WT小鼠。所有的小鼠都会反复进行一次又一次的偏心收缩 在体内，等长扭矩和血浆兴奋性的变化将被跟踪。在最后一次之后 收缩试验、体外生理学将被用来间接评估EC偶联失败。肌肉标记物 还将评估损害，并将Krt18和Krt18相互作用蛋白(例如，dystrophin)的含量 量过了。我们预测，骨骼肌重新塑造和适应反复的身体压力的能力 将与Krt18的表达水平直接相关，这与Krt18的缺失随年龄增长的观点是一致的 是骨质疏松症的重要调节因子。

PROJECT SUMMARY Sarcopenia, loss of muscle strength and mass with age, is a major component of frailty. Muscle weakness appears to be critical as low strength is associated with more markers of frailty than chronological age. Geriatric and frail individuals are at greater risk of functional impairments due to an inability of skeletal muscle to adapt to physical stressors. Strength adaptations in response to physical stress or resistance training have been linked to loss of muscle quality, particularly excitation contraction (EC) coupling failure. Identifying mechanisms that counteract contraction-induced EC coupling failure and promote skeletal muscle adaptations are therefore essential to combating sarcopenia and frailty. Recent data suggest that keratin 18 (Krt18), an intermediate filament protein that associates with the dystrophin-glycoprotein complex, may be an important mediator of stress-induced adaptive strength gains that decreases with age. Specifically, we observed that the Krt18 gene was the most highly upregulated (7-fold) in muscle from young mice that gained strength after eccentric exercise. We also observed that increased expression of the Krt18 protein and strength gains were associated with increased expression of membrane-associated proteins. In muscle of old mice, expression of Krt18 was blunted and strength gains were dramatically lower when compared to young mice. Thus, our overarching hypothesis is that Krt18 facilitates skeletal muscle adaptation to exercise by increasing plasmalemmal stability to maintain EC coupling processes that become disrupted by repeated bouts of eccentric contractions. Ultimately, we posit Krt18 may play a role in increasing skeletal muscle resiliency and attenuating development and progression of sarcopenia and frailty. In Aim 1 we will determine if adaptive strength gains following repeated bouts of eccentric contractions are mediated by Krt18 in young mice by examining young (3-5-month-old) male and female wildtype (WT) and Krt18 knockout mice. In Aim 2 we will determine if age-related loss of Krt18 expression in muscle after repeated bouts of eccentric contractions is associated with blunted strength gains. To integrate age-related muscle adaptation (or lack thereof) with Krt18 expression, we will use young (3-5 months), adult (20-22 months) and old (27-29 months) male and female WT mice. All mice will perform repeated bouts of eccentric contractions in vivo and changes in isometric torque and plasmalemmal excitability will be tracked. Following the last contractile test, ex vivo physiology will be utilized to indirectly assess EC coupling failure. Markers of muscle damage will also be assessed and content of Krt18 and Krt18-intereacting proteins (e.g., dystrophin) will be measured. We predict that the ability of skeletal muscle remodel and adapt to repeated bouts of physical stress will correlate directly with the level of expression of Krt18, consistent with the idea, that the loss of Krt18 with age is an important mediator sarcopenia and frailty.