Aquaporins in Eye

The major part of the eye consists of water. Continuous movement of water and ions between the ocular compartments and to the systemic circulation is pivotal for many physiological functions in the eye. The movement of water facilitates removal of the many metabolic products of corneal-, ciliary body-, lens-, and retinal metabolism, while maintaining transparency in the optical compartments. Transport across the corneal epithelium and endothelium maintains the corneal transparency. Also, aqueous humor is continuously secreted by the epithelia of the ciliary body and maintains the intraocular pressure. In the retina, water is transported into the vitreous body and across the retinal pigment epithelium to regulate the extracellular environment and the hydration of the retina. Aquaporins are a major contributor in the water transport throughout the eye.

Transcriptomic Characterization of Human Choroidal Neovascular Membranes Identifies Calprotectin as a Novel Biomarker for Patients with Age-Related Macular Degeneration

Recent studies deciphering the transcriptional profile of choroidal neovascularization (CNV) in body donor eyes with neovascular age-related macular degeneration are limited by the time span from death to preservation and the associated 5'-RNA degradation. This study therefore used CNV and control specimens that were formalin-fixed and paraffin-embedded immediately after surgical extraction and analyzed them by a 3'-RNA sequencing approach. Transcriptome profiles were analyzed to estimate content of immune and stromal cells and to define disease-associated gene signatures by using statistical and bioinformatics methods. This study identified 158 differentially expressed genes (DEGs) that were significantly increased in CNV compared with control tissue. Cell type enrichment analysis revealed a diverse cellular landscape with an enrichment of endothelial cells, macrophages, T cells, and natural killer T cells in the CNV. Gene ontology enrichment analysis found that DEGs contributed to blood vessel development, extracellular structure organization, response to wounding, and several immune-related terms. The S100 calcium-binding proteins A8 (S100A8) and A9 (S100A9) emerged among the top DEGs, as confirmed by immunohistochemistry on CNV tissue and protein analysis of vitreous samples. This study provides a high-resolution RNA-sequencing-based transcriptional signature of human CNV, characterizes its compositional pattern of immune and stromal cells, and reveals S100A8/A9 to be a novel biomarker and promising target for therapeutics and diagnostics directed at age-related macular degeneration.

Potential Interplay between Hyperosmolarity and Inflammation on Retinal Pigmented Epithelium in Pathogenesis of Diabetic Retinopathy

Diabetic retinopathy is a frequent eyesight threatening complication of type 1 and type 2 diabetes. Under physiological conditions, the inner and the outer blood-retinal barriers protect the retina by regulating ion, protein, and water flux into and out of the retina. During diabetic retinopathy, many factors, including inflammation, contribute to the rupture of the inner and/or the outer blood-retinal barrier. This rupture leads the development of macular edema, a foremost cause of sight loss among diabetic patients. Under these conditions, it has been speculated that retinal pigmented epithelial cells, that constitute the outer blood-retinal barrier, may be subjected to hyperosmolar stress resulting from different mechanisms. Herein, we review the possible origins and consequences of hyperosmolar stress on retinal pigmented epithelial cells during diabetic retinopathy, with a special focus on the intimate interplay between inflammation and hyperosmolar stress, as well as the current and forthcoming new pharmacotherapies for the treatment of such condition.

Mechanisms of macular edema: Beyond the surface

Macular edema consists of intra- or subretinal fluid accumulation in the macular region. It occurs during the course of numerous retinal disorders and can cause severe impairment of central vision. Major causes of macular edema include diabetes, branch and central retinal vein occlusion, choroidal neovascularization, posterior uveitis, postoperative inflammation and central serous chorioretinopathy. The healthy retina is maintained in a relatively dehydrated, transparent state compatible with optimal light transmission by multiple active and passive systems. Fluid accumulation results from an imbalance between processes governing fluid entry and exit, and is driven by Starling equation when inner or outer blood-retinal barriers are disrupted. The multiple and intricate mechanisms involved in retinal hydro-ionic homeostasis, their molecular and cellular basis, and how their deregulation lead to retinal edema, are addressed in this review. Analyzing the distribution of junction proteins and water channels in the human macula, several hypotheses are raised to explain why edema forms specifically in the macular region. "Pure" clinical phenotypes of macular edema, that result presumably from a single causative mechanism, are detailed. Finally, diabetic macular edema is investigated, as a complex multifactorial pathogenic example. This comprehensive review on the current understanding of macular edema and its mechanisms opens perspectives to identify new preventive and therapeutic strategies for this sight-threatening condition.