Role of Detrusor Interstitial Cells in Overactive Bladder

摘要 膀胱始终具有维持低肌肉兴奋性和低膀胱内压的能力。 大部分的灌装期。这种调节肌肉兴奋性的能力的丧失与 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 拉伸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 这似乎是必要的，以抑制SMC在充填期间兴奋性的发展。最近，我们发现和 描述了一种新的控制机制，这种机制是逼尿肌固有的，由PDGFRαInterstial提供 并调节逼尿肌兴奋性。PDGFRα细胞已被鉴定，并在人、豚鼠体内大量存在 猪和老鼠的逼尿肌。该调节机制由以下分子和 功能元件：1)PDGFRα细胞表达Kcnn3通道(Kcnn3)和高电流密度(由于SK 频道。2)PDGFRα细胞中SK通道对电偶联的膜电位具有稳定作用 SMC。3)TRPV4通道，也由PDGFRα细胞表达，提供一种牵张依赖的钙来源， 在填充过程中激活SK通道。DO的发展与PDGFRα细胞的丧失同步，如图所示 在膀胱充盈过程中，SMC束内出现过多的钙瞬变和一过性收缩。 从初步的实验中，我们发现在脊髓损伤后，pdgfrα细胞发生了显著的损伤。 脊髓损伤(SCI)的动物模型，已知也发展为DO。我们还发现了一个机制 对PDGFR型α细胞的损伤及脊髓损伤后修复细胞的方法。PDGFRα细胞表达 神经营养因子受体(主要是TrkB)和脊髓损伤与TrkB表达降低有关。减少 TrkB信号与神经细胞和非神经细胞的凋亡有关，初步实验 显示脊髓损伤后PDGFRα细胞中与凋亡信号相关的基因表达增强。我们还发现， 脊髓损伤后不久用trkB激动剂局部治疗逼尿肌挽救了PDGFRα细胞表型 阻碍了DO的发展。因此，在目前的提案中，我们将追求以下几点 最重要的假设：PDGFRα细胞或关键分子成分的丢失或缺陷 PDGFRα细胞提供的抑制调节导致逼尿肌功能障碍和逼尿肌的发展 过度活跃的表型。这项研究的具体目标的完成将为我们提供令人兴奋的新见解 膀胱在充盈过程中被调节，以及脊髓损伤后如何处理功能障碍：i)PDGFRα 细胞是充盈过程中逼尿肌兴奋性的关键调节器；ii)这些细胞的丢失或损伤会导致DO 表型；iii)修复PDGFRα细胞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.