Editorial: Chronic Inflammation and Neurodegeneration in Retinal Disease, Volume II

Chronic Inflammation and Neurodegeneration in Retinal DiseaseInflammation and neurodegeneration have a widely recognized role in the pathogenesis of the main retinal conditions.However, the exact mechanism through which inflammation causes alteration of the retinal structure-with consequent dysfunction of the retinal pigment epithelium, of neurons, and ultimately of photoreceptors-is not entirely known.This Research Topic "Chronic Inflammation and Neurodegeneration in Retinal Disease, Volume II" presents eight original research articles and one mini review from seven different countries with important contributions in the field of retinal inflammation.Most of the contributions are related to diabetic retinopathy (DR), the others cover age-related macular degeneration (AMD), retinitis pigmentosa, and the spontaneous polygenic model of inherited retinal dystrophy.The review by Stravalaci et al. focused on long pentraxin 3 (PTX3), an emerging new player in ocular homeostasis and a potential pharmacological target in neurodegenerative disorders of the retina.Physiologically present in the human eye and induced in inflammatory conditions, this protein is strategically positioned at the blood retinal barrier interface, where it acts as a "molecular trap" for complement and modulates inflammation both in homeostatic and pathological conditions such as AMD and DR.Gesualdo et al. presented an interesting study on fingolimod and DR, investigating the interactions between fingolimod, a sphingosine 1-phosphate receptor (S1PR) agonist, and melanocortin receptors 1 and 5 (MCR1, MCR5).This Research Topic is a typical example of repurposing since fingolimod is a drug approved to treat relapsing-remitting multiple sclerosis.The authors demonstrated, in an in vivo model of DR, that fingolimod has anti-angiogenic activity mediated not only through S1P1R, but also by melanocortin receptors.Another interesting pre-clinical study on DR was provided by Canovai et al.The authors showed the efficacy of a novel substance containing cyanidin-3-glucoside (C3G), verbascoside, and zinc to maintain the integrity of the blood retinal barrier and retinal function in streptozotocin-induced diabetic rats.Accumulating data provide evidence for a pivotal role of Müller cells in the pathogenesis of DR.In this regard the in vitro study by Schmalen et al. underlined the importance of Müller cell signaling in the inflamed retina, indicating an active role in chronic retinal inflammation.These authors demonstrated an intense signaling capacity of Müller cells, which reacted in a highly discriminating manner upon treatment with different cytokines, showing several characteristics of atypical antigen-presenting cells.