Influence of Innervation on Diaphragm Muscle Growth

描述(申请人提供)：在出生后发育过程中，DIAM纤维显示出不成比例的生长，这种生长在表达不同肌球蛋白重链(MHC)亚型的纤维中是不成比例的。DIAM纤维的比力在出生后的增加也因表达不同MHC亚型的纤维而异。单侧去神经(DNV)显著延缓出生后DIAM纤维的生长，并降低比力。这些数据表明，神经源性因子(如神经营养因子家族)在出生后肌肉纤维生长中发挥关键作用。我们假设神经营养因子调节出生后DIAM纤维的生长和MHC蛋白的表达，从而影响比力。本研究的主要目的是：1)探讨DIAM纤维生长过程中MHC蛋白表达的调控机制；2)研究TrkB受体激活对DIAM纤维MHC蛋白表达的影响；3)探讨DNV对MHC蛋白表达的影响；4)探讨DIAM纤维中MHC蛋白含量的变化与DIAM纤维产生的比力变化之间的关系。在拟议的研究中有四个特定目标：特定目标1：检测DNV对出生后DAM纤维肌核区域大小变化的影响假说-DNV之后，肌核域大小减小，并且这种影响因出生后年龄和不同MHC亚型而不同。假设Lb-在培养的肌管/肌纤维中，TrkB受体的激活增加了肌核结构域的大小。具体目的#2：评估DNV对DIAM纤维MHC异构体转录的影响。假设2a-在DNV之后，MHC转录减少，这种影响因出生后年龄和不同的MHC亚型而不同。假设2b-在培养的肌管/肌纤维中，TrkB受体的激活增加了MHC的转录。具体目的#3：评估DNV对出生后每HAT肌节MHC蛋白含量和DIAM纤维MHC蛋白周转的影响。假设3a-在DNV之后，每半个肌节的MHC蛋白含量减少，这种影响因出生后年龄和不同的MHC亚型而不同。假设3b-在DNV之后，MHC的分数合成速率降低而降解率增加，并且这些对MHC周转的影响因出生后年龄和不同的MHC亚型而不同。假设3c-在培养的肌管/肌纤维中，TrkB受体的激活增加了MHC蛋白的表达。具体目的#4：评估DNV对出生后DiAM纤维比力变化的影响。假设4a-DNV后，DIAM纤维的比力降低，这种影响因出生后年龄和表达不同MHC亚型的纤维而异。假设4b-在DNV之后，直径纤维比力的下降既反映了每半肌节MHC含量的减少，也反映了每跨桥的力的减少。

DESCRIPTION (provided by applicant): During postnatal development, DIAm fibers display dramatic growth that is disproportionate across fibers expressing different myosin heavy chain (MHC) isoforms. Postnatal increase in specific force of DIAm fibers also varies across fibers expressing different MHC isoforms. Unilateral denervation (DNV) dramatically retards postnatal growth of DIAm fibers and reduces specific force. These data suggest that nerve-derived factors (such as the family of neurotrophins) play a key role in postnatal muscle fiber growth. We hypothesize that neurotrophins modulate the postnatal growth of DIAm fibers and MHC protein expression and thereby affect specific force. The major goals of the proposed studies are: 1) to explore the mechanisms regulating MHC protein expression during postnatal growth of DIAm fibers, 2) to explore the effects of TrkB receptor activation on MHC protein expression, 3) to explore the effects of DNV (i.e., removal of neurotrophin influence) on MHC protein expression, and 4) to examine the relationship between postnatal changes in MHC protein content and changes in specific force generated by DIAm fibers. There are four specific aims in the proposed studies: Specific Aim #1: To examine the impact of DNV on postnatal changes in myonuclear domain size in DIAm fibers Hypothesis la - Following DNV, myonuclear domain size decreases and this effect varies with postnatal age and across different MHC isoforms. Hypothesis lb - In cultured myotubes/myofibers, TrkB receptor activation increases myonuclear domain size. Specific Aim #2: To evaluate the impact of DNV on postnatal changes in MHC isoform transcription in DIAm fibers. Hypothesis 2a - Following DNV, MHC transcription decreases and this effect varies with postnatal age and across different MHC isoforms. Hypothesis 2b - In cultured myotubes/myofibers, TrkB receptor activation increases MHC transcription. Specific Aim #3: To evaluate the impact of DNV on postnatal changes in MHC protein content per haft sarcomere and MHC protein turnover in DIAm fibers. Hypothesis 3a - Following DNV, MHC protein content per half sarcomere decreases and this effect varies with postnatal age and across different MHC isoforms. Hypothesis 3b - Following DNV, the fractional synthesis rate of MHC decreases while degradation rate increases, and these effects on MHC turnover vary with postnatal age and across different MHC isoforms. Hypothesis 3c - In cultured myotubes/myofibers, TrkB receptor activation increases MHC protein expression. Specific Aim #4: To evaluate the impact of DNV on postnatal changes in specific force of DIAm fibers. Hypothesis 4a - Following DNV, specific force of DIAm fibers decreases and this effect varies with postnatal age and across fibers expressing different MHC isoforms. Hypothesis 4b - Following DNV, the decrease in DIAm fiber specific force reflects both a decrease in MHC content per half sarcomere and a decrease in the force per cross bridge.