Developmental Regulation of Corneal Innervation

描述（申请人提供）：角膜是人体神经支配最密集的组织之一。角膜神经主要起源于三叉神经节（TGG）的眼支，主要是感觉神经，通过传递疼痛感觉（痛觉感受器）对有害的机械、热和化学刺激作出反应。它们还参与通过调节眨眼反应和增加泪液的产生来保护角膜免受损害，并且它们是维持角膜处于健康状态所必需的。因此，干扰正常神经支配和神经功能的病理状况可能产生有害的后果，从慢性疼痛到溃疡和丧失透明度。然而，关于角膜神经支配的机制知之甚少。胚胎鸡为研究角膜神经支配提供了一个有利的发育模型，因为在这个物种中，神经支配发生在一系列离散的阶段，这些阶段在时间和空间上彼此可分离。这些阶段是：(1)神经从TGG向角膜的生长和吸引，(2)神经侵入角膜基质，(3)神经进入并支配角膜上皮（CE）并在其终止处形成分支。在即将提出的研究中，目标之一将是阐明参与调节这些事件的机制。另一个研究领域将是检查这些神经进入CE后的命运，因为这里是感觉发生的地方。传统观点认为这些神经以自由神经末梢的形式终止。然而，我们将研究另一种选择，即它们以角膜结构和功能独特的方式与CE细胞相互作用。角膜是人体内神经支配最密集的组织之一。这些神经主要是感觉神经，对有害的机械、热和化学刺激作出反应，将这些刺激转导为疼痛的感觉。角膜神经也参与保护角膜免受损伤，通过调节眨眼反应和增加眼泪的产生，它们也参与维持角膜处于健康状态。因此，干扰正常神经支配和神经功能的病理状况会产生有害的后果——从慢性疼痛到溃疡，再到透明度降低。例如，角膜神经支配的破坏——可能由疱疹感染造成的损伤——会导致退行性神经营养性角膜炎，从而导致角膜溃疡和透明度的丧失。此外，在视力矫正手术（如PRK和LASIK）后，神经支配的减少可能会导致术后并发症。然而，令人惊讶的是，关于角膜神经支配的机制知之甚少，包括那些参与胚胎发育的机制。对于角膜神经支配的发育研究，鸡胚角膜提供了一个有利的模型。在大多数方面，鸡的角膜与人的角膜是无法区分的。在结构上，这个角膜有人类角膜的所有层，这些层的分子组成基本上与人类的相同。此外，在鸡胚角膜中，神经支配发生在一系列离散的阶段，每个阶段都可以单独研究。阐明参与这些不同阶段神经支配的细胞和分子机制是提出的研究的主要目标之一。另一个主要的研究领域将涉及在角膜内，感觉是如何传递到神经的。传统观点认为，这涉及到终止于角膜上皮内的游离神经末梢。然而，根据我们实验室最近的观察，我们将研究另一种选择，即角膜神经的末梢与专门的角膜上皮细胞相互作用，产生角膜结构和功能独特的感觉单元。

DESCRIPTION (provided by applicant): The cornea is one of the most densely innervated tissues in the body. Corneal nerves originate chiefly from the ophthalmic branch of the trigeminal ganglion (TGG) and are largely sensory, responding to noxious mechanical, thermal and chemical stimuli by transducing sensations of pain (nociceptors). They are also involved in protecting the cornea from damage by modulating the blinking reaction and increasing the production of tears, and they are required for maintaining the cornea in a healthy state. Thus, pathological conditions that interfere with normal innervation and nerve function can have deleterious consequences, ranging from chronic pain to ulceration and loss of transparency. However, little is known concerning the mechanisms responsible for corneal innervation. The embryonic chicken provides an advantageous developmental model for investigating corneal innervation, as in this species innervation occurs in a series of discrete stages that are temporally and spatially separable from one another. These stages are: (1) the growth and attraction of nerves from the TGG to the cornea, (2) invasion of nerves into the corneal stroma and (3) the formation of branches from the nerves that enter and innervate the corneal epithelium (CE) where they terminate. In the studies to be proposed one of the goals will be to elucidate the mechanism(s) involved in regulating these events. The other area of investigation will be to examine the fate of these nerves once they enter the CE - as this is where sensation occurs. The conventional belief is that these nerves terminate as free nerve endings. However we will examine an alternative, which is that they interact with CE cells in a manner that is structurally and functionally unique to the cornea. PUBLIC HEALTH RELEVANCE The cornea is one of the most densely innervated tissues in the body. These nerves are largely sensory, responding to noxious mechanical, thermal and chemical stimuli by transducing these as sensations of pain. The corneal nerves are also involved in protecting the cornea from damage, by modulating the blinking reaction and increasing the production of tears, and they are also involved in maintaining the cornea in a healthy state. Thus, pathological conditions that interfere with normal innervation and nerve function can have deleterious consequences - ranging from chronic pain , to ulceration, to decreased transparency. For example, a disruption in corneal innervation - as can occur by damage from herpes infection - can result in degenerative neurotrophic keratitis that can produce corneal ulceration and a loss of transparency. Also, following vision corrective surgical procedures (e.g., PRK and LASIK), a decrease in innervation can occur that can lead to post-surgical complications. However, surprisingly little is known concerning the mechanisms responsible for corneal innervation, including those that are involved in embryonic development. For developmental studies of corneal innervation, the embryonic chicken cornea provides an advantageous model which will be used for the proposed studies. In most aspects the chicken cornea is indistinguishable from that of the human. Structurally this cornea has all the layers of the human cornea, and the molecular compositions of these layers are essentially identical to those of the human. In addition, in the embryonic chicken cornea, innervation occurs as a series of discrete stages, each which can be studied separately. Elucidating the cellular and molecular mechanisms that are involved in these different stages of innervation is one of the major goals of the proposed studies. The other major area of investigation will involve how, within the cornea, sensation is transferred to the nerves. The conventional belief is that this involves nerves that terminate within the corneal epithelium as free nerve endings. However, based on recent observation in our laboratory, we will examine an alternative, which is that the endings of the corneal nerves interact with specialized corneal epithelial cells to produce a sensory unit that is structurally and functionally unique to the cornea.