Role of Keratin 18 for Stress-induced Adaptive Strength Gains

项目摘要 肌肉减少症，随着年龄的增长肌肉力量和质量的损失，是虚弱的主要组成部分。肌肉无力 似乎是至关重要的，因为低强度与比实际年龄更多的虚弱标志物相关。老年 和虚弱的个体由于骨骼肌不能适应 生理压力源应对身体压力或阻力训练的力量适应已被联系起来 肌肉质量的损失，特别是兴奋收缩（EC）耦合失败。确定机制， 因此，抵消收缩诱导的EC偶联失败并促进骨骼肌适应， 对抗肌肉减少症和虚弱的关键。最近的数据表明，角蛋白18（Krt 18），一种中间体， 与肌营养不良蛋白-糖蛋白复合物相关的丝蛋白，可能是一种重要的介导剂， 应力诱导的适应性强度增加，随年龄的增长而下降。具体来说，我们观察到Krt 18基因 在离心运动后获得力量的年轻小鼠的肌肉中上调最高（7倍）。 我们还观察到Krt 18蛋白表达的增加和力量的增加与 增加膜相关蛋白的表达。在老年小鼠肌肉中，Krt 18的表达减弱， 与年轻的老鼠相比，力量的增长明显降低。因此，我们的总体假设是 Krt 18通过增加质膜稳定性以维持EC，促进骨骼肌对运动的适应， 耦合过程被反复的偏心收缩打断。最后，我们将讨论Krt 18 可能在增加骨骼肌弹性和减弱发育和进展中发挥作用， 肌肉减少症和虚弱在目标1中，我们将确定在反复的偏心运动后， 通过检查年轻（3-5个月大）雄性和雌性野生型， (WT)和Krt 18敲除小鼠。在目标2中，我们将确定在注射后肌肉中Krt 18表达的年龄相关性损失是否与肌肉中的年龄相关性损失有关。 反复发作的离心收缩与变钝的力量增益有关。将与年龄相关的 肌肉适应（或缺乏）与Krt 18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。所有的老鼠都将进行反复的离心收缩 并将跟踪等长扭矩和质膜兴奋性的变化。继上一 收缩试验，离体生理学将用于间接评估EC偶联失败。肌肉标志物 还将评估损伤并测定Krt 18和Krt 18相互作用蛋白的含量（例如，肌营养不良蛋白）将是 测定了我们预测，骨骼肌重塑和适应反复发作的物理应激的能力， 将与Krt 18的表达水平直接相关，这与Krt 18随年龄增长而丢失的观点一致。 是肌肉减少症和虚弱的重要媒介。

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.