eNOS-Dependent Mechanoregulation of Intraocular Pressure

青光眼中的高眼压是由于眼内房水引流阻力增加引起的。 传统的流出途径，包括小梁网（TM）和施累姆氏管（SC）。 不幸的是，负责产生抗性的细胞机制在很大程度上是未知的。我们以前的 资金周期已经证明，一氧化氮（NO）是流出阻力和眼内阻力的关键调节剂， 压力（IOP）。此外，我们已经表明，剪切应力刺激SC内皮细胞产生NO， 比如血管内皮。此外，作用于SC细胞的剪切应力的大小取决于IOP，这是由于 压力引起的SC管腔狭窄。由于已知NO会降低流出阻力，因此剪切诱导 NO的产生可能作为一个“快速”的稳态信号，以对抗眼压升高的来源，并有助于维持眼压升高。 IOP在窄范围内。这种“快速”体内平衡由SC剪切应力感测，并在时间尺度上起作用， 秒至分钟，与TM牵拉感测到的“缓慢”IOP稳态形成对比，TM牵拉刺激 细胞外基质（ECM）重塑。这些“快”和“慢”机制是 互补，因为它们允许流出途径感知和响应流出中的扰动， 从急性流出道阻塞到ECM的慢性重塑，在一系列时间尺度上发挥作用。我们 最近的数据提供了对NO的稳态作用以及NO如何维持健康和功能的进一步了解。 传统的外流途径。例如，我们的数据表明，SC细胞的NO产生被放大， 脉动剪切应力，这是由于眼睛的脉冲而产生的，并导致立即的脉动诱导 流出阻力减小。我们还表明，NO有助于清除颗粒物，如 作为色素和细胞碎片，它们会自然地积聚在小管TM中。第三，我们的模型 研究表明，TM硬度升高（如原发性开角型青光眼; POAG）消除了 通过抑制SC中的脉动诱导的剪切应力来“快速”IOP稳态。 允许碎片在TM中不受限制地积聚，导致最终的流出功能障碍和IOP升高。 综上所述，我们的中心假设是NO在维持IOP稳态中具有两个关键作用， 短时间尺度：（i）作为机械敏感反馈回路中的关键信号分子， SC腔中的剪切应力，和（ii）作为内壁渗透性和TM收缩性的调节剂，以冲洗细胞 来自下小管TM的碎片/色素。我们用三个特定目标（SA）来检验我们的假设。 SA 1：确定眼脉冲如何通过NO信号调节流出功能。 SA 2：确定NO如何响应TM中的颗粒负荷而促进IOP稳态。 SA 3：确定NO如何调节内壁渗透性，使颗粒从TM中清除。 影响：本研究的结果将剖析NO信号在IOP稳态中的多方面作用， 我们利用这一知识，为POAG患者开发靶向的、基于SC的治疗方法。

Ocular hypertension in glaucoma arises from increased drainage resistance for aqueous humor in the conventional outflow pathway, which includes the trabecular meshwork (TM) and Schlemm’s canal (SC). Unfortunately, the cellular mechanisms responsible for resistance generation are largely unknown. Our previous funding cycles have demonstrated that nitric oxide (NO) is a key regulator of outflow resistance and intraocular pressure (IOP). Moreover, we have shown that shear stress stimulates NO production by SC endothelial cells, like vascular endothelia. Further, the magnitude of shear stress acting on SC cells depends on IOP, due to pressure-induced narrowing of the SC lumen. As NO is known to decrease outflow resistance, shear-induced NO production may act as a “fast” homeostatic signal to oppose the source of IOP elevation and help to maintain IOP in a narrow range. This “fast” homeostasis is sensed by SC shear stress and operates over time scales of seconds to minutes, and contrasts with the “slow” IOP homeostasis that is sensed by TM stretch that stimulates extracellular matrix (ECM) remodeling over several days. These “fast” and “slow” mechanisms are complementary because they allow the outflow pathway to sense and respond to perturbations in outflow function over a range of temporal scales, from acute outflow obstruction to chronic remodeling of ECM. Our recent data provide further insight into the homeostatic role of NO and how NO maintains the health and function of the conventional outflow pathway. For example, our data show that NO production by SC cells is amplified by pulsatile shear stress, which arises due to the ocular pulse and results in an immediate pulsation-induced decrease in outflow resistance. We also show that NO contributes to the clearance of particulate matter, such as pigment and cell debris, that would naturally accumulate in the juxtacanalicular TM. Thirdly, our modelling studies suggest that elevated TM stiffness (as occurs in primary open angle glaucoma; POAG) eliminates the “fast” IOP homeostasis by suppressing pulsation-induced shear stress in SC. Consequently, this desensitization allows debris to accumulate unchecked in the TM, leading to eventual outflow dysfunction and IOP elevation. Taken together, our central hypothesis is that NO has two critical roles in maintaining IOP homeostasis over short time scales: (i) as a key signaling molecule in a mechanosensitive feedback loop potentiated by pulsatile shear stress in the SC lumen, and (ii) as a modulator of inner wall permeability and TM contractility to flush cell debris/pigment from the juxtacanalicular TM. We test our hypothesis with three Specific Aims (SAs). SA1: To determine how the ocular pulse modulates outflow facility through NO signaling. SA2: To determine how NO contributes to IOP homeostasis in response to particulate load in the TM. SA3: To determine how NO regulates inner wall permeability, enabling particulate clearance from the TM. Impact: Outcomes from this study will dissect the multifaceted role of NO signaling in IOP homeostasis, allowing us to exploit this knowledge for the development of targeted, SC-based therapeutics for patients with POAG.