The neuropilin 2 axis in smooth muscle contractility

 描述（由申请人提供）：膀胱功能取决于平滑肌（SM）收缩和舒张的周期，以分别实现排尿和储存。膀胱SM收缩的强度或持续时间的损害表征了一种普遍但知之甚少的临床病症，称为逼尿肌活动不足（DU）。DU是一种复杂的疾病，（i）由各种神经肌肉损伤引起，包括慢性膀胱出口梗阻、衰老和持续性糖尿病;（ii）降低排尿效率和（iii）可导致严重的泌尿系统并发症。无论病因如何，DU患者的正常膀胱收缩功能丧失是一个严重的临床问题，其机制尚不清楚。DU的药物治疗是有限的，主要包括拟副交感神经药物，其具有可疑的疗效和不良副作用。更有效和耐受的治疗方案，以恢复膀胱收缩力将代表一个重大的治疗进展，患者患有DU。然而，DU的成功的药理学治疗的目标将只能通过了解调节膀胱SM收缩和调节异常的DU机制来实现。我们最近确定了逼尿肌平滑肌神经纤毛蛋白2（Nrp 2）的表达的一个主要网站。膀胱平滑肌细胞暴露于神经纤毛蛋白2配体脑信号蛋白3F（SEMA 3F）引起了深刻的细胞骨架变化，伴随着抑制RhoA，肌球蛋白轻链磷酸化减少，细胞骨架刚度降低。与此相一致，通过腺病毒转导在体内强制表达SEMA 3F导致膀胱SM收缩性降低。相反，与非缺失对照相比，敲除Nrp 2或Sema 3F在体内增强膀胱SM收缩性。新的数据显示，在部分膀胱出口梗阻（pBOO）后发生失代偿的膀胱中，与未缺失的对照相比，Nrp 2缺失恢复了SM收缩性。最后，对人类膀胱标本的新分析揭示了逼尿肌收缩力和NRP 2表达之间的负相关性。基于这些观察，我们假设SEMA 3F-神经纤毛蛋白2网络抑制体内膀胱SM收缩性，并且靶向该轴恢复收缩性。 该假设将用以下具体目的进行检验：（1）确定Sema 3F-Nrp 2介导的膀胱SM收缩性抑制的潜在机制。(2)确定在pBOO模型中靶向Sema 3F-Nrp 2轴的功能后果。我们将采用Nrp 2-和Sema 3F-缺陷的新型小鼠模型、肌条张力测试、生化和组织学分析、膀胱测压评估和膀胱出口梗阻的生理相关小鼠模型来实现我们的目标。在项目期结束时，我们预计已经确定了Sema 3F-Nrp 2轴抑制平滑肌收缩性的机制，Sema 3F和Nrp 2扰动对膀胱病理生理学的影响，以及如何在治疗上利用Sema 3F-Nrp 2网络来恢复DU的收缩性。

 DESCRIPTION (provided by applicant): Bladder function depends on cycles of smooth muscle (SM) contraction and relaxation to achieve voiding and storage, respectively. Impairment of the strength or duration of bladder SM contraction characterizes a prevalent but poorly understood clinical condition termed detrusor underactivity (DU). DU is a complex disorder that (i) arises from diverse neuromuscular insults, including chronic bladder outlet obstruction, aging and persistent diabetes; (ii) reduces voiding efficiency and (iii) can lead to significant urologic complications. Irrespective of etiology, the loss of normal bladder contractilty in DU is a serious clinical problem that is not understood in mechanistic terms. Pharmacotherapy for DU is limited, comprising primarily parasympathomimetic agents, which have questionable efficacy and adverse side effects. More effective and tolerable treatment options to restore bladder contractility would represent a major therapeutic advance for patients suffering from DU. However, the goal of successful pharmacologic treatment of DU will only be realized by understanding mechanisms regulating bladder SM contraction and their dysregulation in DU. We recently identified the detrusor smooth muscle as a major site of expression of neuropilin 2 (Nrp2). Exposure of bladder smooth muscle cells to the neuropilin 2 ligand semaphorin 3F (SEMA3F) evoked profound cytoskeletal changes, accompanied by inhibition of RhoA, decreased myosin light chain phosphorylation, and reduced cytoskeletal stiffness. Consistent with this, forced expression of SEMA3F via adenoviral transduction in vivo led to reduced bladder SM contractility. Conversely, knockout of either Nrp2 or Sema3F in vivo enhanced bladder SM contractility compared to non-deleted controls. New data show that in bladders undergoing decompensation following partial bladder outlet obstruction (pBOO), Nrp2 deletion restored SM contractility compared to non-deleted controls. Lastly, new analysis of human bladder specimens revealed an inverse correlation between detrusor contractility and NRP2 expression. Based on these observations, we hypothesize that the SEMA3F-neuropilin 2 network inhibits bladder SM contractility in vivo and that targeting this axis restores contractile function under conditions of DU. The hypothesis will be tested with the following Specific Aims: (1) Determine the mechanisms underlying Sema3F- Nrp2-mediated inhibition of bladder SM contractility. (2) Determine the functional consequences of targeting the Sema3F-Nrp2 axis in a model of pBOO. We will employ novel mouse models of Nrp2- and Sema3F- deficiency, tension testing in muscle strips, biochemical and histological analyses, cystometric evaluation and a physiologically relevant mouse model of bladder outlet obstruction to achieve our objectives. At the end of the project period we expect to have determined the mechanism(s) whereby the Sema3F-Nrp2 axis inhibits smooth muscle contractility, the consequences of Sema3F and Nrp2 perturbation for bladder pathophysiology and how the Sema3F-Nrp2 network may be exploited therapeutically to restore contractility in DU.