Role of Detrusor Interstitial Cells in Overactive Bladder

总结 膀胱有能力自始至终保持低肌肉兴奋性和低膀胱内压 大部分的填充期。这种调节肌肉兴奋性的能力的丧失与以下疾病的发展有关： 逼尿肌过度活动（DO）。逼尿肌平滑肌细胞（SMC）倾向于被拉伸激活，这是由于 伸展激活的非选择性阳离子通道的表达。所以其他细胞，如神经元或间质细胞 似乎是必要的，以抑制发展的SMC兴奋性在填充。最近，我们发现， 表征了一种新的控制机制，该机制是逼尿肌固有的，由PDGFRα+间质性 细胞和调节逼尿肌兴奋性。PDGFRα+细胞在人、豚鼠和哺乳动物中大量存在， 猪和小鼠逼尿肌。调节机制由以下分子和 功能元件：1）PDGFRα+细胞表达SK 3通道（Kcnn 3）和SK引起的高电流密度 渠道2)PDGFRα+细胞中的SK通道对电偶联的细胞膜电位具有稳定作用 SMC。3)TRPV 4通道也由PDGFRα+细胞表达，提供了一种牵张依赖性的Ca 2+来源， 在灌装过程中激活SK通道。与PDGFRα+细胞丢失同步的是DO的发展，如图所示。 平滑肌细胞束中钙离子浓度过高和膀胱充盈时短暂收缩。 从初步的实验中，我们发现脊髓损伤后PDGFRα+细胞发生了显著的损伤， 脊髓损伤（SCI）的动物模型，其也已知发展为DO。我们还发现了一种机制 对PDGFRα+细胞的损伤和SCI后细胞的拯救手段。PDGFRα+细胞表达 神经营养因子受体（主要是TrkB）和SCI与TrkB的表达减少有关。减少 TrkB信号传导与神经和非神经细胞中的细胞凋亡相关，并且初步实验 显示SCI后PDGFRα+细胞中与凋亡信号相关的基因增强。我们还发现 SCI后不久，用TrkB激动剂局部治疗逼尿肌，挽救了PDGFRα+细胞表型 并阻止了DO的发展。因此，在目前的提案中，我们将追求以下目标 总体假设：PDGFRα+细胞或负责PDGFRα表达的关键分子组分的缺失或缺陷。 PDGFRα+细胞提供的抑制性调节导致逼尿肌功能障碍和逼尿肌发育 过度活跃表型完成这项研究的具体目标将提供令人兴奋的新的见解，如何 膀胱在充盈过程中受到调节，SCI后如何管理功能障碍，显示：i）PDGFRα+ 细胞是充盈期间逼尿肌兴奋性的关键调节器; ii）这些细胞的损失或损伤导致DO 表型; iii）PDGFRα+细胞的恢复可以挽救对膀胱充盈的正常反应。

SUMMARY The bladder has the capability of maintaining low muscle excitability and low intravesical pressure throughout most of the filling period. Loss of this ability to moderate muscle excitability is associated with development of detrusor overactivity (DO). Detrusor smooth muscle cells (SMC) tend to be activated by stretch due to expression of stretch-activated non-selective cation channels. So other cells, such as neurons or interstitial cells appear to be necessary to restrain development of SMC excitability during filling. Recently, we discovered and characterized a novel control mechanism that is intrinsic to detrusor muscles, provided by PDGFRα+ interstitial cells and regulates detrusor excitability. PDGFRα+ cells have been identified and are abundant in human, guinea pig and mouse detrusor muscles. The regulatory mechanism is composed of the following molecular and functional elements: 1) PDGFRα+ cells express SK3 channels (Kcnn3) and high current density due to SK channels. 2) SK channels in PDGFRα+ cells exert membrane potential-stabilizing effects on electrically coupled SMC. 3) TRPV4 channels, also expressed by PDGFRα+ cells, provide a stretch-dependent source of Ca2+ that activates SK channels during filling. In phase with loss of PDGFRα+ cells is the development of DO, as shown by the development of excessive Ca2+ transients in SMC bundles and transient contractions during bladder filling. From preliminary experiments, we have discovered that significant damage to PDGFRα+ cells occurs after spinal cord injury (SCI) in an animal model that is known also to develop DO. We have also discovered a mechanism for the damage to PDGFRα+ cells and a means of rescuing the cells after SCI. PDGFRα+ cells express neurotrophin receptors (predominantly TrkB) and SCI are associated with reduced expression of TrkB. Reduced TrkB signaling has been associated with apoptosis in neural and non-neural cells, and preliminary experiments show that genes related to apoptotic signaling are enhanced in PDGFRα+ cells after SCI. We also found that localized treatment of the detrusor with a TrkB agonist, shortly after SCI, rescued the PDGFRα+ cell phenotype and prevented the development of DO. Therefore, in the current proposal we will pursue the following overarching hypothesis: loss or defects in PDGFRα+ cells or in key molecular components responsible for the inhibitory regulation provided by PDGFRα+ cells leads to detrusor dysfunction and development of detrusor overactive phenotype. Completion of the specific aims of this study will provide exciting novel insights into how the bladder is regulated during filling and how dysfunction might be managed after SCI by showing: i) PDGFRα+ cells are critical regulators of detrusor excitability during filling; ii) loss or damage to these cells leads to an DO phenotype; iii) restoration of PDGFRα+ cells can rescue normal responses to bladder filling.