Role of Detrusor Interstitial Cells in Overactive Bladder

摘要 膀胱具有在整个过程中维持低肌肉兴奋性和低膀胱内压力的能力 大部分填充期。失去这种调节肌肉兴奋性的能力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) 往往会因拉伸而被激活，原因是 拉伸激活的非选择性阳离子通道的表达。所以其他细胞，例如神经元或间质细胞 似乎有必要抑制充盈过程中 SMC 兴奋性的发展。最近，我们发现并 描述了一种逼尿肌固有的新型控制机制，由 PDGFRα 间质提供 细胞并调节逼尿肌兴奋性。 PDGFRα 细胞已被鉴定并且在人类、几内亚中含量丰富 猪和小鼠逼尿肌。调控机制由以下分子组成： 功能元件：1）PDGFRα细胞表达SK3通道（Kcnn3）以及SK带来的高电流密度 渠道。 2）PDGFRα细胞中的SK通道对电耦合发挥膜电位稳定作用 SMC。 3) TRPV4 通道（也由 PDGFRα 细胞表达）提供拉伸依赖性的 Ca2 来源， 在填充过程中激活 SK 通道。与 PDGFRα 细胞损失相一致的是 DO 的发展，如图所示 SMC 束中出现过多的 Ca2 瞬变以及膀胱充盈期间的短暂收缩。 通过初步实验，我们发现脊髓损伤后PDGFRα细胞发生显着损伤。 动物模型中的脊髓损伤 (SCI) 也已知会导致 DO。我们还发现了一个机制 针对 PDGFRα 细胞的损伤以及 SCI 后细胞的拯救方法。 PDGFRα细胞表达 神经营养蛋白受体（主要是 TrkB）和 SCI 与 TrkB 表达减少有关。减少 TrkB信号传导与神经和非神经细胞的凋亡有关，初步实验 研究表明，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 激动剂对逼尿肌进行局部治疗，挽救了 PDGFRα 细胞表型 并阻止了DO的发展。因此，在当前的提案中，我们将追求以下目标： 总体假设：PDGFRα细胞或负责的关键分子成分的损失或缺陷 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 过度活跃的表型。完成本研究的具体目标将为我们提供令人兴奋的新颖见解 膀胱在充盈过程中受到调节，以及 SCI 后如何管理功能障碍，方法是：i) PDGFRα 细胞是充盈过程中逼尿肌兴奋性的关键调节因子； ii) 这些细胞的丢失或损坏导致 DO 表型； iii) PDGFRα 细胞的恢复可以挽救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.