Name: Murine Corneal Nerve Axotomy for the Induction of Neurotrophic Keratitis
Uploaded: 2023-12-08T14:20:00
Description: Watch this Scientific Journal Video about Murine Corneal Nerve Axotomy for the Induction of Neurotrophic Keratitis at JoVE.com

murine corneal nerve axotomy for the induction of neurotrophic keratitis

Protocolos de daño de las fibras sensoriales corneales para estudios de regeneración de axones

The cornea, which is the transparent surface of the eye, is composed of three distinct layers: the epithelium, the stroma, and the endothelium. This organ has the highest density of innervation in the body and is composed mainly of sensory fibers (types A&#948; and C) originating from the ophthalmic branch of the trigeminal ganglion. Sensory fibers penetrate the periphery of the cornea in the mid-stroma in the form of big bundles that branch out to cover the surface. They then bifurcate to pierce the Bowmann&#39;s membrane and form the subbasal plexus, which is easily recognizable by the formation of a vortex in the center of the cornea. Those fibers terminate as free nerve endings at the external surface of the epithelium. They are able to transduce thermal, mechanical, and chemical stimuli and to release trophic factors that are essential for epithelium homeostasis1,2. Neurotrophic keratitis (NK) is a degenerative disease affecting the corneal sensory innervation. This rare disease stems from a decrease or a loss of corneal sensitivity that results in lower tear production and poor healing properties of the cornea3. NK progresses through three well-described stages, from stage 1 where patients suffer epithelial defects, to stage 3 where stromal melting and/or corneal perforation occur4.
Clinically, the origins of this disease can be diverse. Patients can lose corneal innervation after physical injury to the eye, surgery, or through chronic diseases, such as diabetes5,6. To date, the NK pathogenesis process remains poorly understood, and therapeutical options for this sight-threatening condition are very limited. Therefore, a better understanding of the characteristics of epithelial defects is needed to better understand the mechanisms behind the regeneration of those fibers and potentially promote them. Here, we propose several models of corneal injury that induce NK in mice.
The first model is the abrasion of the epithelial layer of the cornea with an ocular burr. This model has mainly been studied in the context of the regeneration of the epithelium in different animals, such as rodents and fish7,8,9, and to test molecules promoting corneal healing10,11. Physiologically, it takes 2-3 days for the epithelial cells to close the wound. The physiological pattern of the innervation, however, takes more than four weeks to recover from the abrasion12,13. During the surgery, the ocular burr removes the epithelial layer of the cornea that contains the subbasal plexus and the fibers&#39; free nerve endings. This procedure can be clinically compared to patients with photorefractive keratectomy (PRK) to correct eye refractive defects. The procedure consists of removing the epithelium of the cornea and then reshaping the stroma with a laser14. Patients can experience several side effects following such surgery, such as a decrease of corneal nerve density for 2 years and a reduction in sensitivity for a duration of 3 months to one year post-surgery15. Given that the surgery induces a fragility of the corneal microenvironment, this model could help investigate these side effects and develop therapeutical approaches that would promote faster reinnervation, thus reducing the side effects in question.
The second model consists of sectioning the axons at the periphery of the cornea with a biopsy punch, inducing a Wallerian degeneration of the central innervation 16. Clinically, this method could be compared to anterior lamellar keratoplasty, in which the surgeon realizes a partial trephination of the cornea to remove a part of the anterior thickness of the cornea and replace it with a donor transplant 17. Following lamellar keratoplasty, patients may suffer from a number of symptoms including dry eye, loss of corneal innervation and graft rejection18. This axotomy model performed on corneal nerves could provide insight into the mechanisms of fiber degeneration, which occurs after a graft, followed by the axons&#39; regeneration.
The third method damages the corneal nerves with a laser. By using a multiphoton microscope on the cornea of anesthetized animals, degeneration of the nerves localized in the optical field is induced as a result of reactive oxygen species (ROS) formation, which leads to DNA damage and cellular cavitation19. This method recapitulates the corneal photodamage induced by overexposure to natural UV (sunburn), which also triggers ROS formation, leading to DNA damage20. Patients who suffer from corneal sunburn experience great pain, as the deterioration of epithelial cells deprives the corneal fibers&#39; extremities of all.
The three methods described here are designed to enable the investigation of the NK pathogenesis process and axon regeneration. They are easily reproducible and precise. Moreover, they allow quick recovery and easy monitoring of the animals.

Autor destacado: Avance de la investigación de la inervación corneal a través de modelos innovadores 

Tres estrategias para inducir queratitis neurotrófica y regeneración nerviosa en la córnea murina

The cornea, which is the transparent tissue covering the eye, requires a balanced microenvironment to maintain its integrity. The dense innervation of the cornea participates to this microenvironment. If there is a loss, which could be partial or total, of this innervation, then a specific condition arises, which is called neurotrophic keratitis.To find new cures and efficient cures for this disease, we need to have specific models. The expansion of the use of transgenic animal bearing fluorescent reporters and microscopic advances have opened new possibilities in visualizing axonary generation. In vivo imagine has become more accessible to any research lab willing to follow the neurogeneration process.The various causes inducing neurotrophic keratitis underlying the difficulties of having only one model to test nerve regeneration therapies. These three models are reproducing various situations seen in clinics, and sharing those methods will allow other labs to uncover new aspects of corneal innervation from which innovative treatments will be designed.

Watch this Scientific Journal Video about Murine Corneal Nerve Axotomy for the Induction of Neurotrophic Keratitis at JoVE.com

Murine Corneal Nerve Axotomy for the Induction of Neurotrophic Keratitis  

Axotomía del nervio corneal murino para la inducción de queratitis neurotrófica

Para comenzar la axotomía del nervio corneal, coloque un ratón anestesiado sobre una mesa. Aplicar una gota de lágrima artificial sobre el ojo sometido a la cirugía. Aplicar una gota de gel ocular sobre el ojo contralateral.Coloque el ratón debajo de una lupa binocular para evaluar el ojo que se está operando. Coloca la parte inferior de una placa de Petri debajo de la cabeza del ratón para mantener el ojo horizontal. Con un bastoncillo de algodón, retire con cuidado la lágrima artificial del ojo y retire las pestañas sin tocar el ojo.Coloca un par de pilares suaves y curvos debajo del ojo del animal y sácalo suavemente de la órbita. Coloque suavemente un punzón de biopsia verticalmente contra la superficie de la córnea, aplique presión y gire el punzón varias veces. Luego, retire el punzón de biopsia y una marca circular debe ser visible en la córnea.Se observó un anillo periférico delgado en el punto donde se aplicó la punción de biopsia, que dañó el epitelio basal. Los nervios periféricos parecían estar seccionados, lo que desencadenó la degeneración del axón walleriano. Se observó una fuerte degeneración, lo que llevó a la pérdida total de la inervación en el centro de la córnea.Esto dio lugar a la desintegración de la capa epitelial, creando una úlcera.

Research

JoVE Journal

Neuroscience

Murine Corneal Nerve Axotomy for the Induction of Neurotrophic Keratitis

Three Strategies to Induce Neurotrophic Keratitis and Nerve Regeneration in Murine Cornea

The cornea is a transparent tissue that covers the eye and is crucial for clear vision. It is the most innervated tissue in the body. This innervation ...

Investigación

Neurociencias

Murine Corneal Nerve Abrasion for the Induction of Neurotrophic Keratitis

Abrasión del nervio corneal murino para la inducción de queratitis neurotrófica

Localized Laser Ablation of Murine Corneal Nerves for the Induction of Neurotrophic Keratitis

Ablación localizada con láser de los nervios corneales murinos para la inducción de queratitis neurotrófica