Project description:The resident astrocytes-retinal ganglion cell lipoxin circuit is impaired during retinal stress that include exocytotoxic- and ocular hypertension-induced neuropathy. Two endogenous lipoxins (Lipoxin A4 and Lipoxin B4) produced by homeostatic astrocytes directly act on RGCs. LXB4 is the most potent lipoxin in the retina and directly increases RGC survival and function in ocular hypertension-induced neuropathy. Homeostatic roles and cellular targets of LXB4 in the retina and optic nerve are a critical gap in knowledge. Single-cell RNA sequencing was used to define cellular targets and signaling of LXB4 in the retina. For modeling neurodegeneration, sustained ocular hypertension was induced by silicone-oil injection in the anterior chamber of mouse eyes. For morphological characterization of microglia populations in the retina and optic nerve, we used MorphOMICs and pseudotime trajectory analysis. Bulk RNA sequencing of optic nerves was performed to characterize pathways and mechanism of action for LXB4. qPCR and immunohistochemistry were used for validation of transcriptomics data. Student’s t-test and one-way ANOVA were used to determine differences between experimental groups. Single Cell transcriptomic identified microglia as a primary target for LXB4 in the healthy retina. LXB4 downregulated genes that drive microglia environmental sensing and reactivity responses. Analysis of microglia function uncovered that ocular hypertension induces distinct, temporally defined and dynamic phenotypes in the retina and, unexpectedly, in the distal myelinated optic nerve. Microglial expression of CD74, a marker of disease-associated microglia (DAM) in the brain, was only induced in a unique population of optic nerve microglia but not the retina. Genetic deletion of lipoxin formation correlated with presence of a CD74 optic nerve microglia population in normotensive eyes optic, while LXB4 treatment during ocular hypertension shifted optic nerve microglia toward a homeostatic morphology and non-reactive state and downregulated expression of CD74. Furthermore, we identified a correlation between CD74 and phospho-PI3K (p-PI3K) expression levels in the optic nerve, that was reduced by LXB4 treatment. Results identify distal optic nerve microglial dynamic and reactive responses as a key feature of ocular hypertension induce neurodegeneration. Our findings establish microglia regulation as a new LXB4 cell target in the retina and optic nerve. LXB4 maintenance of optic nerve microglia homeostatic phenotype and inhibition of a disease-associated phenotype are potential mechanisms for LXB4 neuroprotection.

Project description:Purpose: The optic nerve head (ONH) is the likely site of initial damage in the glaucomatous eye. Despite the recognition of elevated intraocular pressure (IOP) as a leading risk factor for the development of glaucoma, ocular hypertension (OHT) eyes displaying consistently elevated IOP do not experience ONH damage. This study aims to identify global gene expression variations in glaucomatous ONHs and their relationship to those identified in OHT derived ONHs in order to improve our understanding of IOP-induced ONH damage. Methods: (N=6) ONHs were collected from clinically confirmed glaucoma, OHT and age-matched control donor eyes. Total RNA extracted from ONHs was reverse transcribed and assayed using the Affymetrix Human Exon 1.0 ST array. Differentially expressed genes in glaucoma versus control and OHT derived ONHs were identified using an ANOVA analysis with a 1.25 fold change limit and P-value < 0.05. Quantitative RT-PCR was performed to validate selected differentially expressed genes. Results: Microarray analysis revealed 149 under under-expressed genes in POAG versus control ONHs, many of which are involved in ion transport, axonogenesis and macromolecule catabolic processes. 297 genes were over expressed in OHT versus glaucoma derived ONHs. Mediators of oxidation-reduction and chemical homeostasis were among the most prominent gene groups identified. The over expression of prostaglandin-endoperoxide synthase 2, integrin, beta-like 1 and fibulin 5 in glaucomatous ONHs was confirmed by qRT-PCR. Conclusions: Our data demonstrates marked alteration in global gene expression patterns in the glaucomatous ONH, likely due to extensive tissue injury. The observed overlapping of several differentially expressed genes in glaucoma and OHT derived ONHs suggests the induction of common mechanisms in response to elevated IOP. Preferential over-expression of certain gene groups in OHT but not glaucoma derived ONHs may confer possible protection against IOP-induced ONH damage, which remains to be investigated in future studies. (N=6) Glaucoma, ocular hypertension and age-matched control ONHs were assayed to investigate and compare global gene expression patterns in each sample group.

Project description:Glaucoma leads to vision loss due to retinal ganglion cell death. Astrocyte reactivity contributes to neurodegeneration. Our recent study found that lipoxin B4 (LXB4), produced by retinal astrocytes, has direct neuroprotective actions on retinal ganglion cells. In this study, we aimed to investigate how the autacoid LXB4 influences astrocyte reactivity in the retina under inflammatory cytokine-induced activation and ocular hypertension conditions. The protective activity of LXB4 was investigatedin vivousing the mouse silicone-oil model of chronic ocular hypertension (n=40). By employing a range of analytical techniques, including bulk RNA-seq, RNAscope in-situhybridization, qPCR, and lipidomic analyses, we discovered the formation of neuroprotective lipoxins in rodents (including the retina and optic nerve), primates (optic nerve), and human brain astrocytes, indicating their presence across various species. Our findings in the mouse retina demonstrated significant dysregulation of the lipoxin pathway in response to chronic ocular hypertension, leading to an increase in 5-lipoxygenase (5-LOX) activity and a decrease in 15-lipoxygenase activity. This dysregulation was coincident with a marked upregulation of astrocyte reactivity. Reactive human brain astrocytes also showed a significant increase in 5-LOX. Administration of LXB4 regulated the lipoxin pathway, restored and amplified LXA4 generation (another lipoxin with distinct bioactions), and mitigated astrocyte reactivity in mouse retinas and human brain astrocytes. In conclusion, the lipoxin pathway is functionally expressed in rodents, primates, and human astrocytes, and is a resident neuroprotective pathway that is downregulated in reactive astrocytes. Novel cellular targets for LXB4’s neuroprotective action are inhibition of astrocyte reactivity and restoration of lipoxin generation. Amplifying the lipoxin pathway is a potential target to disrupt or prevent astrocyte reactivity in neurodegenerative diseases.

Dataset Information

Proteomics-Based Identification of Retinal Protein Networks Impacted by Elevated Intraocular Pressure in the Hypertonic Saline Injection Model of Experimental Glaucoma

Publications

Proteomics-Based Identification of Retinal Protein Networks Impacted by Elevated Intraocular Pressure in the Hypertonic Saline Injection Model of Experimental Glaucoma.

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