NEURAL FACTORS AND UPPER AIRWAY MUSCLE DEVELOPMENT

呼吸是一个高度调节的过程，需要引起通气的肌肉和负责维持上呼吸道通畅的肌肉之间的精确协调。吸气动力增加时，不能正确激活上呼吸道扩张肌，可导致上呼吸道阻塞。通过神经肌肉连接处的高保真突触信号是精确调节与吸气驱动水平相对应的上呼吸道通畅所必需的。神经肌肉连接的主要突触成分是烟碱乙酰胆碱受体（nAChR），这是一种配体（ACh）门控通道，由四个同源跨膜亚基（α 2, β, ε, γ）组成，排列成五聚体。在出生后早期发育过程中，nAChR经历了结构修饰，影响了其对运动神经元释放的乙酰胆碱的反应能力。在新生儿中，nAChR含有一个-亚基而不是-亚基。nachr - γ表现出比成人nAChR-epsilon更低的单通道电导。因此，表达更多的nachr - γ和更少的nAChR-epsilon的肌肉可能倾向于低张力和对突触输入的反应较差。我们假设nachr - γ和nAChR-epsilon亚型的不一致调控可能导致上气道通畅减少和气道阻塞。越来越多的证据表明，在出生后早期发育过程中，肌肉中相反的激酶和磷酸酶途径调节着nachr - γ向nAChR-epsilon的转变。此外，最近的研究结果表明，激酶和磷酸酶的活性都受运动神经元释放的“营养”因子的调节。本研究将探讨四肽生长抑素（SST）在肌肉中酪氨酸磷酸酶（PTPase）活性调控中的作用。初步结果表明，SST在发育过程中在支配上呼吸道的运动神经元中表达，可阻止激酶途径诱导-亚基基因表达。具体目的是：1)鉴定和表征被SST激活并抑制epsilon亚基基因表达的蛋白酪氨酸磷酸酶；2)确定sst诱导的PTPases对抗激酶途径阻止epsilon亚基基因表达激活的机制；3)确定SST-SSTR-PTPase途径持续表达对基因工程小鼠epsilon-亚基基因表达的影响。

Breathing is a highly regulated process that requires precise coordination among the muscles that cause ventilation and those responsible for maintenance of upper airway patency. Failure to properly activate the upper airway dilator muscles in response to an increase in inspiratory drive can result in obstruction of the upper airways. High fidelity synaptic signaling across the neuromuscular junction is required for precise regulation of upper airway patency that corresponds to the level of inspiratory drive. The major synaptic component of the neuromuscular junction is the nicotinic acetylcholine receptor (nAChR), a ligand (ACh)- gated channel that is composed of four homologous trans-membrane subunits (alpha2, beta, epsilon, gamma) arranged in a pentamer. During early postnatal development the nAChR undergoes a structural modification which impacts on its ability to respond to ACh released from motoneurons. In the neonate, the nAChR contains a gamma- instead of the epsilon-subunit. The nAChR-gamma exhibits a lower single channel conductance than the adult nAChR-epsilon. Thus, muscles that express more nACh-gamma and less nAChR-epsilon might be prone to hypotonicity and less responsive to synaptic input. We hypothesize that discordant regulation of the nAChR-gamma and nAChR-epsilon isoforms could lead to reduced upper airway patency and airway obstruction There is growing evidence that opposing kinase and phosphatase pathways in muscle regulate the nAChR-gamma to nAChR-epsilon transition during early postnatal development. Moreover, recent findings indicate that both the kinase and phosphatase activities are regulated by "trophic" factors released from the motoneurons. The proposed research will investigate the role of the tetradecapeptide somatostatin (SST) in the regulation of tyrosyl phosphatase (PTPase) activities in muscle. Preliminary results show that SST, which is expressed developmentally in the motoneurons that innervate the upper airways, prevents induction of -subunit gene expression by the kinase pathway. The specific aims are: 1) Identify and characterize the protein tyrosyl phosphatases that are activated by SST and cause inhibition of epsilon-subunit gene expression; 2) Determine the mechanism by which SST-induced PTPases oppose kinase pathways to prevent activation of epsilon-subunit gene expression; and 3) Determine the effect of continuous expression of the SST-SSTR-PTPase pathway on epsilon-subunit gene expression in genetically engineered mice.