Laboratory Investigation (2019) 99:210–230 https://doi.org/10.1038/s41374-018-0118-4 ARTICLE Sensory nerve supports epithelial stem cell function in healing of corneal epithelium in mice: the role of trigeminal nerve transient receptor potential vanilloid 4 1 1 1 2 2 3 Yuka Okada ● Takayoshi Sumioka ● Kana Ichikawa ● Hiromi Sano ● Atsushi Nambu ● Kenta Kobayashi ● 4,5 4,5 4,5 6 7 8 Kunitoshi Uchida ● Yoshiro Suzuki ● Makoto Tominaga ● Peter Sol Reinach ● Syu-ichi Hirai ● James V. Jester ● 1 1 1 9 10 1 Masayasu Miyajima ● Kumi Shirai ● Hiroki Iwanishi ● Winston Whei-Yang Kao ● Chia-Yang Liu ● Shizuya Saika Received: 13 June 2018 / Revised: 6 July 2018 / Accepted: 9 July 2018 / Published online: 9 November 2018 © United States & Canadian Academy of Pathology 2018 Abstract In order to understand the pathobiology of neurotrophic keratopathy, we established a mouse model by coagulating the first branch of the trigeminal nerve (V1 nerve). In our model, the sensory nerve in the central cornea disappeared and remaining fibers were sparse in the peripheral limbal region. Impaired corneal epithelial healing in the mouse model was associated with suppression of both cell proliferation and expression of stem cell markers in peripheral/limbal epithelium as well as a 1234567890();,: 1234567890();,: reduction of transient receptor potential vanilloid 4 (TRPV4) expression in tissue. TRPV4 gene knockout also suppressed epithelial repair in mouse cornea, although it did not seem to directly modulate migration of epithelium. In a co-culture experiment, TRPV4-introduced KO trigeminal ganglion upregulated nerve growth factor (NGF) in cultured corneal epithelial cells, but ganglion with a control vector did not. TRPV4 gene introduction into a damaged V1 nerve rescues the impairment of epithelial healing in association with partial recovery of the stem/progenitor cell markers and upregulation of cell proliferation and of NGF expression in the peripheral/limbal epithelium. Gene transfer of TRPV4 did not accelerate the regeneration of nerve fibers. Sensory nerve TRPV4 is critical to maintain stemness of peripheral/limbal basal cells, and is one of the major mechanisms of homeostasis maintenance of corneal epithelium. Introduction such as mechanical or chemical injury or infection by microorganisms. Rapid healing of an epithelial defect in the Integrity of corneal epithelium is essential to maintain cornea is critical for the avoidance of infection and further proper vision by serving as a barrier against external stimuli damage to the underlying tissue. Cell migration and pro- liferation are both the main components of the process of corneal epithelial wound healing [1–3]. Healthy stem cells that locate to the basal layer of the limbal zone (around the Electronic supplementary material The online version of this article (https://doi.org/10.1038/s41374-018-0118-4) contains supplementary periphery of the cornea) play an important role in providing material, which is available to authorized users. daughter cells to the corneal epithelium for its repair [4, 5]. * Shizuya Saika Graduate University for Advanced Studies), Okazaki, Japan [email protected] 6 Wenzhou Medical University School of Ophthalmology and Optometry, Wenzhou, China 1 Department of Ophthalmology, Wakayama Medical University School of Medicine, Wakayama, Japan 7 Educational Phyilosophy/Cell Biology, Wakayama Medical University School of Medicine, Wakayama, Japan 2 Division of System Neurophysiology, National Institute for Physiological Sciences, Okazaki, Japan 8 Department of Ophthalmology, School of Medicine, University of California, Irvine, Irvine, CA, USA 3 Section of Viral Vector Development, National Institute for Physiological Sciences, Okazaki, Japan 9 Department of Ophthalmology, University of Cincinnati School of Medicine, Cincinnati, OH, USA 4 Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan 10 School of Optometry, Indiana University Bloomington, Bloomington, IN, USA 5 Department of Physiological Sciences, SOKENDAI (The Sensory nerve supports epithelial stem cell function in healing of corneal epithelium in mice: the role. 211 Various growth factors are believed to orchestrate the epi- One of the presumed reasons why there is currently no thelial cell behaviors during tissue repair [1–3]. Among effective therapy for neurotrophic keratopathy might be the them, nerve growth factor (NGF) and its receptors, p75 and fact that a suitable experimental mouse model is not avail- TrkA, are reportedly involved in maintenance of stemness able. Ferrari et al. [37] developed a trigeminal stereotactic of limbal basal cells with high proliferating potential [6–9]. electrolysis model of clinical neurotrophic keratitis and The cornea is one of the most densely innervated tissues found that corneal denervation by this procedure resulted in with ophthalmic sensory terminal branches of the trigeminal breakdown of the integrity of corneal epithelium and was nerve [10–13]. Nerve fibers enter the limbus and the per- associated with increased apoptosis and reduced prolifera- ipheral cornea and distribute over the cornea in a radial tion of epithelial cells. We obtained a similar result by pattern. Then, the fibers penetrate the Bowman’s membrane employing a procedure with stereotactic intracranial coa- upward and distribute beneath epithelial basal cells, forming gulation of the first branch of the trigeminal nerve by using the sub-basal nerve plexus that supplies the overlying cor- an 18-guage needle (supplemental data 1). We herein show neal epithelium [10, 14]. Interaction between sensory nerve that use of a 20-guage needle in the same stereotactic pro- and local tissues, i.e., skin or epithelia of internal organs, is cedure reduced the damage of the first branch of the tri- required for the homeostasis of the tissue [15–20]. Healthy geminal nerve and produced a mouse model of neurotrophic innervation is essential to the maintenance of corneal keratopathy more similar to clinical cases. This mouse structure and function, i.e., barrier function, proliferation, model of neurotrophic keratopathy exhibits a normal- differentiation or wound healing. In turn, impaired sensory looking cornea without obvious tissue inflammation under innervation or function may impair homeostasis of the physiological conditions, but impairment of epithelial corneal epithelium, leading to persistent disorders or wound healing is apparent upon epithelial debridement. Our abnormal repair in the tissue (neurotrophic keratopathy) detailed analysis showed delayed epithelial healing was [21–23]. It was reported that sensory innervation plays an attributable to the loss of stemness and cell proliferation important role in maintenance of stemness of limbal basal caused by sensory denervation in peripheral/limbal epithe- epithelial cells by expressing ATP-binding cassette sub- lium. In the current investigation, we employed this mouse family G member 2 (ABCG2), p63 and hairy enhancer of model of neurotrophic keratopathy. split 1 (Hes1), a Notch signal-related component [24]. The Transient receptor potential (TRP) channels constitute a causes of impaired trigeminal sensation include direct injury superfamily of 28 genes that are subdivided into 7 sub- to the intracranial trigeminal nerve by brain trauma or families, including TRP vanilloid (TRPV) and TRP ankyrin tumor, diabetes mellitus, herpes virus infection or injury in type (TRPA), among others. Each TRP superfamily mem- the sensory nerve fibers in the corneal tissue by trauma or bers is a nonselective cation channel that possesses variable surgery such as corneal refractive surgery [25–29]. Ca2+ permeability and acts as a sensor to a wide array of Although the causes of neurotrophic keratopathy are evi- inputs, including temperature, pressure, pH alteration, che- dent in many cases, neurotrophic keratopathy is refractory micals and lipids. In skin, many of the TRP family members to classical treatments, which include wearing a bandage are expressed in both keratinocytes and in sensory nerve contact lens, tarsorrhaphy or supplementation with an arti- fibers and are involved in sensing and maintaining tissue ficial tear solution [30–32]. Refractory persistent corneal homeostasis [38]. In the cornea, TRP channel subtypes from epithelial neurotrophic keratopathy could lead to corneal different subfamilies are involved in mediating responses to stromal perforation, with or without intraocular infection, injuries that affect the process of wound healing. We pre- that could potentially cause widespread destruction of eye viously reported that the loss of either TRPV1, TRPV4 or tissue and permanent severe vision loss. Sosne et al. [33] TRPA1 attenuates excessive inflammatory fibrogenic reac- reported the potential efficacy of thymosin β4 in the treat- tion in a mouse cornea injured by an alkali exposure, and is ment of this condition. The notion that neuropeptides could minimally dependent on the genotype of inflammatory cells have a promoting effect on epithelial healing in the cornea [39–41]. On the other hand, we also previously showed that was first proposed by Nishida and Yanai [34]. They blockage of TRPV1 activation or TRPV1 gene ablation reported that topical application of a combination of pep- suppressed healing of defective epithelial animal corneas in tides derived from insulin-like growth factor and substance association with suppression of expression of substance P P exerts a significant therapeutic effect on refractory corneal and interleukin-6