Influence of Innervation on Diaphragm Muscle Growth

描述（由申请人提供）：在出生后发育过程中，DIAm纤维在表达不同肌球蛋白重链（MHC）异构体的纤维中表现出显著的不成比例的生长。产后DIAm纤维比力的增加也因表达不同MHC亚型的纤维而异。单侧去神经支配（DNV）显著延缓了出生后DIAm纤维的生长并降低了比力。这些数据表明，神经源性因子（如神经营养因子家族）在产后肌纤维生长中起关键作用。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。拟开展的研究主要目的为：1)探索出生后DIAm纤维生长过程中MHC蛋白表达的调控机制，2)探索TrkB受体活化对MHC蛋白表达的影响，3)探索DNV（即去除神经营养因子的影响）对MHC蛋白表达的影响，4)研究出生后MHC蛋白含量变化与DIAm纤维比力变化的关系。在拟议的研究中有四个具体目的：具体目的#1：检查DNV对出生后DIAm纤维肌核结构域大小变化的影响假设la - DNV后，肌核结构域大小减小，这种影响随出生后年龄和不同MHC亚型而变化。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。具体目标2：评估DNV对出生后DIAm纤维中MHC异构体转录变化的影响。假设2a - DNV后，MHC转录减少，这种影响随出生后年龄和不同MHC亚型而异。假设2b -在培养的肌管/肌纤维中，TrkB受体激活会增加MHC转录。具体目标#3：评估DNV对出生后每半节肌节MHC蛋白含量变化和DIAm纤维MHC蛋白周转的影响。假设3a - DNV后，每半个肌节的MHC蛋白含量降低，这种影响随出生后年龄和不同MHC亚型而异。假设3b - DNV后，MHC的部分合成率降低，降解率增加，这些对MHC周转的影响随出生后年龄和不同MHC亚型而异。假设3c -在培养的肌管/肌纤维中，TrkB受体激活会增加MHC蛋白的表达。具体目的#4：评估DNV对产后DIAm纤维比力变化的影响。假设4a - DNV后，DIAm纤维的比力下降，这种影响随出生后年龄和表达不同MHC亚型的纤维而变化。假设4b - DNV后，DIAm纤维比力的下降反映了每半个肌节中MHC含量的下降和每个交叉桥的力的下降。

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.