Thrombospondin-1-mediated regulation of microglia activation after retinal injury.
ABSTRACT Thrombospondin (TSP)-1 has been demonstrated to play a vital role in immune privilege. The functional phenotype of ocular antigen-presenting cells that contributes to the immune privilege status of the eye is dependent on their expression of TSP-1. Microglia, the local antigen-presenting cells in the retina, undergo rapid activation in response to injury and have the ability to produce both proinflammatory and regenerative neurotrophic factors. In this study, the authors examined TSP-1 as a potential regulator of these phenotype of microglia activated in response to retinal injury.
Expression of markers associated with activated microglia were examined by immunofluorescent staining and semiquantitative real-time PCR analysis of retina derived from WT or TSP-1 null mice at various time intervals after light- or laser-induced retinal injury.
In the absence of TSP-1, microglia in uninjured retina express major histocompatibility complex class II and migrate to the outer layers of the retina. Constitutively increased expression of activated microglia-derived inflammatory molecules such as TNF-alpha and iNOS is detectable in TSP-1 null retina compared with WT controls. After both light-induced and laser-induced retinal injury, enhanced migration of microglia is detected in TSP-1 null retina, and these microglia express markers associated with a proinflammatory phenotype. Compared with WT retina, TSP-1 null retina fails to recover from the laser-induced injury, resulting in irreversible damage.
TSP-1 supports an anti-inflammatory phenotype of microglia in the retina and promotes recovery from injury.
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ABSTRACT: Purpose To determine the association of single nucleotide polymorphisms (SNPs) of the thrombospondin 1 (THBS1) gene with development of chronic ocular surface inflammation (keratoconjunctivitis) after refractive surgery. Design Retrospective cohort study. Participants Active duty U.S. Army soldiers (n = 143) who opted for refractive surgery. Methods Conjunctival impression cytology samples collected from participants before the surgery were used to harvest DNA for genotyping 5 THBS1 SNPs (rs1478604, rs2228262, rs2292305, rs2228262, and rs3743125) using the Sequenom iPLEX Gold platform (Sequenom, San Diego, CA). Samples collected after surgery were used to harvest RNA for gene expression analysis by real-time polymerase chain reaction (PCR). Participants were followed for 1 year after surgery to monitor the status of keratoconjunctivitis. Main Outcome Measures Genetic basis of the development of chronic keratoconjunctivitis after refractive surgery. Results Carriers of minor alleles of 3 SNPs each were found to be more susceptible to developing chronic keratoconjunctivitis (rs1478604: odds ratio [OR], 2.5; 95% confidence interval [CI], 1.41–4.47; P = 2.5×10−3; rs2228262 and rs2292305: OR, 1.9; 95% CI, 1.05–3.51; P = 4.8×10−2). Carriers of the rs1478604 minor allele expressed significantly reduced levels of thrombospondin 1 (TSP1) (P = 0.042) and increased levels of an inflammatory cytokine associated with keratoconjunctivitis, interleukin-1β (P = 0.025), in their ocular surface epithelial cells compared with homozygous major allele controls. Conclusions Genetic variation in the THBS1 gene that results in decreased expression of the encoded glycoprotein TSP1 in ocular surface epithelial cells significantly increases the susceptibility to develop chronic ocular surface inflammation after refractive surgery. Further investigation of THBS1 SNPs in a larger sample size is warranted.Ophthalmology 07/2014; · 5.56 Impact Factor
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ABSTRACT: Gliosis of retinal Müller glial cells may have both beneficial and detrimental effects on neurons. To investigate the role of purinergic signaling in ischemia-induced reactive gliosis, transient retinal ischemia was evoked by elevation of the intraocular pressure in wild-type (Wt) mice and in mice deficient in the glia-specific nucleotide receptor P2Y1 (P2Y1 receptor-deficient (P2Y1R-KO)). While control retinae of P2Y1R-KO mice displayed reduced cell numbers in the ganglion cell and inner nuclear layers, ischemia induced apoptotic death of cells in all retinal layers in both, Wt and P2Y1R-KO mice, but the damage especially on photoreceptors was more pronounced in retinae of P2Y1R-KO mice. In contrast, gene expression profiling and histological data suggest an increased survival of amacrine cells in the postischemic retina of P2Y1R-KO mice. Interestingly, measuring the ischemia-induced downregulation of inwardly rectifying potassium channel (Kir)-mediated K(+) currents as an indicator, reactive Müller cell gliosis was found to be weaker in P2Y1R-KO (current amplitude decreased by 18%) than in Wt mice (decrease by 68%). The inner retina harbors those neurons generating action potentials, which strongly rely on an intact ion homeostasis. This may explain why especially these cells appear to benefit from the preserved Kir4.1 expression in Müller cells, which should allow them to keep up their function in the context of spatial buffering of potassium. Especially under ischemic conditions, maintenance of this Müller cell function may dampen cytotoxic neuronal hyperexcitation and subsequent neuronal cell loss. In sum, we found that purinergic signaling modulates the gliotic activation pattern of Müller glia and lack of P2Y1 has janus-faced effects. In the end, the differential effects of a disrupted P2Y1 signaling onto neuronal survival in the ischemic retina call the putative therapeutical use of P2Y1-antagonists into question.Cell Death & Disease 07/2014; 5:e1353. · 5.18 Impact Factor
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ABSTRACT: Resident microglial cells can be regarded as the immunological watchdogs of the brain and the retina. They are active sensors of their neuronal microenvironment and rapidly respond to various insults with a morphological and functional transformation into reactive phagocytes. There is strong evidence from animal models and in situ analyses of human tissue that microglial reactivity is a common hallmark of various retinal degenerative and inflammatory diseases. These include rare hereditary retinopathies such as retinitis pigmentosa and X-linked juvenile retinoschisis but also comprise more common multifactorial retinal diseases such as age-related macular degeneration, diabetic retinopathy, glaucoma, and uveitis as well as neurological disorders with ocular manifestation. In this review, we describe how microglial function is kept in balance under normal conditions by cross-talk with other retinal cells and summarize how microglia respond to different forms of retinal injury. In addition, we present the concept that microglia play a key role in local regulation of complement in the retina and specify aspects of microglial aging relevant for chronic inflammatory processes in the retina. We conclude that this resident immune cell of the retina cannot be simply regarded as bystander of disease but may instead be a potential therapeutic target to be modulated in the treatment of degenerative and inflammatory diseases of the retina.Progress in Retinal and Eye Research 12/2014; · 9.90 Impact Factor