Implication of Melanopsin and Trigeminal Neural Pathways in Blue Light Photosensitivity in vivo

Photophobia may arise from various causes and frequently accompanies numerous ocular diseases. In modern highly illuminated world, complaints about greater photosensitivity to blue light increasingly appear. However, the pathophysiology of photophobia is still debated. In the present work, we investigated in vivo the role of various neural pathways potentially implicated in blue-light aversion. Moreover, we studied the light-induced neuroinflammatory processes on the ocular surface and in the trigeminal pathways. Adult male C57BL/6J mice were exposed either to blue (400–500 nm) or to yellow (530–710 nm) LED light (3 h, 6 mW/cm2). Photosensitivity was measured as the time spent in dark or illuminated parts of the cage. Pharmacological treatments were applied: topical instillation of atropine, pilocarpine or oxybuprocaine, intravitreal injection of lidocaine, norepinephrine or “blocker” of the visual photoreceptor transmission, and intraperitoneal injection of a melanopsin antagonist. Clinical evaluations (ocular surface state, corneal mechanical sensitivity and tear quantity) were performed directly after exposure to light and after 3 days of recovery in standard light conditions. Trigeminal ganglia (TGs), brainstems and retinas were dissected out and conditioned for analyses. Mice demonstrated strong aversion to blue but not to yellow light. The only drug that significantly decreased the blue-light aversion was the intraperitoneally injected melanopsin antagonist. After blue-light exposure, dry-eye-related inflammatory signs were observed, notably after 3 days of recovery. In the retina, we observed the increased immunoreactivity for GFAP, ATF3, and Iba1; these data were corroborated by RT-qPCR. Moreover, retinal visual and non-visual photopigments distribution was altered. In the trigeminal pathway, we detected the increased mRNA expression of cFOS and ATF3 as well as alterations in cytokines’ levels. Thus, the wavelength-dependent light aversion was mainly mediated by melanopsin-containing cells, most likely in the retina. Other potential pathways of light reception were also discussed. The phototoxic message was transmitted to the trigeminal system, inducing both inflammation at the ocular surface and stress in the retina. Further investigations of retina-TG connections are needed

Implication de la chimiokine CCL2 dans la transmission de l’information nociceptive

Les chimiokines sont de petites protéines appartenant à la famille des cytokines inflammatoires dont le rôle princeps est l’attractivité et l’activation des cellules immunes. Ces chimiokines exercent leurs activités biologiques en interagissant avec des récepteurs appartenant à la famille des récepteurs couplés aux protéines G. Il est maintenant clair que les chimiokines et leurs récepteurs, en dehors de tout contexte pathologique, sont exprimés dans le système nerveux. L’exploration de l’implication des chimiokines et de leurs récepteurs dans la nociception est un domaine en pleine expansion. En effet, de nombreuses études s’accordent à dire que les chimiokines s’inscrivent désormais, tant au niveau périphérique que central, comme des modulateurs de l’information nociceptive. Après un bref rappel sur le système « chimiokinergique » nous présentons les derniers travaux portant sur la chimiokine CCL2, qui est une cytokine chimio-attractante exerçant son action par sa liaison au récepteur nommé CCR2. De nombreuses données laissent à penser que la chimiokine CCL2, exprimée et libérée au niveau spinal, pourrait influencer directement la transmission des informations nociceptives, participer ainsi à l’adaptation neuronale et probablement à la plasticité des cellules gliales ainsi qu’à l’attractivité des cellules immunes observée en conditions de douleur chronique de nature neuropathique

Les chimiokines, de nouveaux acteurs dans le système dopaminergique

Les travaux pionniers réalisés par notre équipe ont permis de démontrer l’expression neuronale et gliale de plusieurs chimiokines et de leurs récepteurs dans les voies dopaminergiques (DA) centrales. Ces travaux posent la question du rôle des chimiokines dans la physiologie du neurone DA et de leur implication dans un processus pathologique susceptible d’affecter les voies DA de type dégénératif, comme dans la maladie de Parkinson pour la voie DA nigro-striée. Nous focaliserons notre attention sur deux chimiokines particulières, le SDF-1 (CXCL12) et le MCP-1 (CCL2) et leurs récepteurs respectifs CXCR4 et CCR2, qui sont exprimés par pratiquement tous les neurones DA des noyaux mésencéphaliques. Nous avons démontré, par plusieurs approches in vivo et in vitro, que le SDF-1 et le MCP-1 peuvent moduler la neurotransmission DA dans la voie nigro-striée, modifiant l’état électrique du neurone et la libération de ce neurotransmetteur via leurs récepteurs spécifiques. Parmi les mécanismes impliqués dans ces effets, nous avons révélé la mise en jeu de canaux calciques de type N à haut seuil pour le SDF-1 et de canaux potassiques pour le MCP-1. Nous discutons ensuite l’implication possible du SDF-1 et de son dérivé clivé, le SDF-1 (5-67) dans la survie des neurones DA

Chimiokines et attractivité des cellules myéloïdes dans les douleurs neuropathiques périphériques

La douleur chronique est devenue un vrai sujet de société en raison de la difficulté de son traitement et par le handicap qu’elle engendre au quotidien. La compréhension des bases neurobiologiques et des mécanismes physiopathologiques à l’origine des différents syndromes douloureux ne cesse d’évoluer et rend compte de la complexité de ses mécanismes. Cette complexité rend malheureusement difficile la découverte de traitements efficaces contre certains types de douleurs chroniques, notamment en ce qui concerne les douleurs neuropathiques périphériques. Des études récentes font apparaître que lors de ces douleurs, les médiateurs de l’inflammation (notamment les chimiokines), outre leurs implications dans la modulation du message nociceptif et dans les mécanismes neuro-inflammatoires centraux, jouent un rôle essentiel dans l’orchestration de la réponse immunitaire consécutive à une lésion d’un nerf périphérique. Dans cette revue, après de brefs rappels concernant les chimiokines et la neuromodulation du message nociceptif, nous nous attacherons à définir leurs rôles et leurs fonctions dans la réponse immunitaire associée aux douleurs neuropathiques périphériques. Ainsi, la parfaite compréhension de ces communications moléculaires et cellulaires entre le système nerveux et le système immunitaire permettra à terme le développement de stratégies thérapeutiques nouvelles et innovantes contre ce type de pathologies très invalidantes

TRPM8: A therapeutic target for neuroinflammatory symptoms induced by severe dry eye disease

International audienceDry eye disease (DED) is commonly associated with ocular surface inflammation and pain. In this study, we evaluated the effectiveness of repeated instillations of transient receptor potential melastatin 8 (TRPM8) ion channel antagonist M8-B on a mouse model of severe DED induced by the excision of extra-orbital lacrimal and Harderian glands. M8-B was topically administered twice a day from day 7 until day 21 after surgery. Cold and mechanical corneal sensitivities and spontaneous ocular pain were monitored at day 21. Ongoing and cold-evoked ciliary nerve activities were next evaluated by electrophysiological multi-unit extracellular recording. Corneal inflammation and expression of genes related to neuropathic pain and inflammation were assessed in the trigeminal ganglion. We found that DED mice developed a cold allodynia consistent with higher TRPM8 mRNA expression in the trigeminal ganglion (TG). Chronic M8-B instillations markedly reversed both the corneal mechanical allodynia and spontaneous ocular pain commonly associated with persistent DED. M8-B instillations also diminished the sustained spontaneous and cold-evoked ciliary nerve activities observed in DED mice as well as inflammation in the cornea and TG. Overall, our study provides new insight into the effectiveness of TRPM8 blockade for alleviating corneal pain syndrome associated with severe DED, opening a new avenue for ocular pain management

Shhedding New Light on the Role of Hedgehog Signaling in Corneal Wound Healing

The cornea, an anterior ocular tissue that notably serves to protect the eye from external insults and refract light, requires constant epithelium renewal and efficient healing following injury to maintain ocular homeostasis. Although several key cell populations and molecular pathways implicated in corneal wound healing have already been thoroughly investigated, insufficient/impaired or excessive corneal wound healing remains a major clinical issue in ophthalmology, and new avenues of research are still needed to further improve corneal wound healing. Because of its implication in numerous cellular/tissular homeostatic processes and oxidative stress, there is growing evidence of the role of Hedgehog signaling pathway in physiological and pathological corneal wound healing. Reviewing current scientific evidence, Hedgehog signaling and its effectors participate in corneal wound healing mainly at the level of the corneal and limbal epithelium, where Sonic Hedgehog-mediated signaling promotes limbal stem cell proliferation and corneal epithelial cell proliferation and migration following corneal injury. Hedgehog signaling could also participate in corneal epithelial barrier homeostasis and in pathological corneal healing such as corneal injury-related neovascularization. By gaining a better understanding of the role of this double-edged sword in physiological and pathological corneal wound healing, fascinating new research avenues and therapeutic strategies will undoubtedly emerge

<i>Shh</i>edding New Light on the Role of Hedgehog Signaling in Corneal Wound Healing

The cornea, an anterior ocular tissue that notably serves to protect the eye from external insults and refract light, requires constant epithelium renewal and efficient healing following injury to maintain ocular homeostasis. Although several key cell populations and molecular pathways implicated in corneal wound healing have already been thoroughly investigated, insufficient/impaired or excessive corneal wound healing remains a major clinical issue in ophthalmology, and new avenues of research are still needed to further improve corneal wound healing. Because of its implication in numerous cellular/tissular homeostatic processes and oxidative stress, there is growing evidence of the role of Hedgehog signaling pathway in physiological and pathological corneal wound healing. Reviewing current scientific evidence, Hedgehog signaling and its effectors participate in corneal wound healing mainly at the level of the corneal and limbal epithelium, where Sonic Hedgehog-mediated signaling promotes limbal stem cell proliferation and corneal epithelial cell proliferation and migration following corneal injury. Hedgehog signaling could also participate in corneal epithelial barrier homeostasis and in pathological corneal healing such as corneal injury-related neovascularization. By gaining a better understanding of the role of this double-edged sword in physiological and pathological corneal wound healing, fascinating new research avenues and therapeutic strategies will undoubtedly emerge

Capsazepine decreases corneal pain syndrome in severe dry eye disease

International audienceBackground: Dry eye disease (DED) is a multifactorial disease of the ocular surface accompanied by neurosensory abnormalities. Here, we evaluated the effectiveness of transient receptor potential vanilloid-1 (TRPV1) blockade to alleviate ocular pain, neuroinflammation, and anxiety-like behavior associated with severe DED.Methods: Chronic DED was induced by unilateral excision of the Harderian and extraorbital lacrimal glands of adult male mice. Investigations were conducted at 21 days after surgery. The mRNA levels of TRPV1, transient receptor potential ankyrin-1 (TRPA1), and acid-sensing ion channels 1 and 3 (ASIC1 and ASIC3) in the trigeminal ganglion (TG) were evaluated by RNAscope in situ hybridization. Multi-unit extracellular recording of ciliary nerve fiber activity was used to monitor spontaneous and stimulated (cold, heat, and acid) corneal nerve responsiveness in ex vivo eye preparations. DED mice received topical instillations of the TRPV1 antagonist (capsazepine) twice a day for 2 weeks from d7 to d21 after surgery. The expression of genes involved in neuropathic and inflammatory pain was evaluated in the TG using a global genomic approach. Chemical and mechanical corneal nociception and spontaneous ocular pain were monitored. Finally, anxiety-like behaviors were assessed by elevated plus maze and black and white box tests.Results: First, in situ hybridization showed DED to trigger upregulation of TRPV1, TRPA1, ASIC1, and ASIC3 mRNA in the ophthalmic branch of the TG. DED also induced overexpression of genes involved in neuropathic and inflammatory pain in the TG. Repeated instillations of capsazepine reduced corneal polymodal responsiveness to heat, cold, and acidic stimulation in ex vivo eye preparations. Consistent with these findings, chronic capsazepine instillation inhibited the upregulation of genes involved in neuropathic and inflammatory pain in the TG of DED animals and reduced the sensation of ocular pain, as well as anxiety-like behaviors associated with severe DED.Conclusion: These data provide novel insights on the effectiveness of TRPV1 antagonist instillation in alleviating abnormal corneal neurosensory symptoms induced by severe DED, opening an avenue for the repositioning of this molecule as a potential analgesic treatment for patients suffering from chronic DED

Transient Receptor Potential Channels: Important Players in Ocular Pain and Dry Eye Disease

Dry eye disease (DED) is a multifactorial disorder in which the eyes respond to minor stimuli with abnormal sensations, such as dryness, blurring, foreign body sensation, discomfort, irritation, and pain. Corneal pain, as one of DED&rsquo;s main symptoms, has gained recognition due to its increasing prevalence, morbidity, and the resulting social burden. The cornea is the most innervated tissue in the body, and the maintenance of corneal integrity relies on a rich density of nociceptors, such as polymodal nociceptor neurons, cold thermoreceptor neurons, and mechano-nociceptor neurons. Their sensory responses to different stimulating forces are linked to the specific expression of transient receptor potential (TRP) channels. TRP channels are a group of unique ion channels that play important roles as cellular sensors for various stimuli. These channels are nonselective cation channels with variable Ca2+ selectivity. TRP homologs are a superfamily of 28 different members that are subdivided into 7 different subfamilies based on differences in sequence homology. Many of these subtypes are expressed in the eye on both neuronal and non-neuronal cells, where they affect various stress-induced regulatory responses essential for normal vision maintenance. This article reviews the current knowledge about the expression, function, and regulation of TRPs in ocular surface tissues. We also describe their implication in DED and ocular pain. These findings contribute to evidence suggesting that drug-targeting TRP channels may be of therapeutic benefit in the clinical setting of ocular pain

Approfondissement de l’annotation du lipidome en associant la réaction de métathèse croisée à la spectrométrie de masse : application à un modèle in vitro de toxicité cornéenne

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