ag-490 and Glaucoma

Astrocytes play an important role in the pathogenesis of glaucoma. Abnormal activation and/or proliferation of astrocytes, termed astrogliosis, have been observed during optic nerve degeneration. Our previous study identified signal transducer and activator of transcription 3 (STAT3) signaling as an important regulator of astrogliosis in the optic nerve in a rat transient ischemia/reperfusion model. In this study, we used pharmacological inhibition of STAT3 activation in the same model to assess whether it could attenuate reactive astrogliosis and to observe its influence on optic nerve damage and retinal ganglion cell (RGC) damage. Our findings show that retrobulbar inhibition of STAT3 in optic nerve head astrocytes leads to (a) increased nerve fiber bundle survival in the optic nerve, (b) increased nerve fiber bundle and RGC survival in the retina, (c) decreased astrocyte reactivation in the optic nerve (d) decreased remodeling of astrocytes in the optic nerve, and (e) no influence of astrocyte reactivation inside the retina. Taken together, the Janus kinase/STAT3 pathway contributes to astrocyte reactivation in the optic nerve, which plays a pivotal role in neurodegeneration after transient ischemia/reperfusion in vivo. Inhibition of this pathway provides a potential therapeutic strategy for the treatment of glaucomatous neuropathy, and could extend to other neurodegenerative diseases.

Topics: Animals; Astrocytes; Disease Models, Animal; Drug Evaluation; Glaucoma; Gliosis; Injections, Intraocular; Janus Kinase 2; Nerve Tissue Proteins; Ocular Hypertension; Optic Disk; Optic Neuropathy, Ischemic; Protein Kinase Inhibitors; Random Allocation; Rats; Rats, Wistar; Reperfusion Injury; Retinal Ganglion Cells; Signal Transduction; STAT3 Transcription Factor; Tyrphostins

Intraocular pressure (IOP) elevation is an important cause of glaucoma. Animal models of ocular hypertension have been widely used to mimic glaucoma to investigate the mechanisms underlying retinal ganglion cell (RGC) death and search for possible cure. The aim of the present study was to examine the role of JAK/STAT pathway in RGC viability in normal condition or after acute IOP elevation. Retinal explants obtained from intact or IOP-elevated eyes were firstly used to examine the effect of the JAK/STAT pathway inhibitors, AG490 and Jak Inhibitor I, on RGC viability in vitro. The role of this signal pathway was further investigated and confirmed in vivo. AG490 and Jak Inhibitor I were applied into the left eye on days 3, 9, and 15 post 2-h IOP elevation at 110mmHg. Fluorescence dye Fluorogold was used to retrogradely label surviving RGCs. Because macrophage recruitment was seen in the IOP-elevated eyes after inhibition of this pathway, clodronate liposomes were used to remove phagocytic cells in the eye and examine the role of JAK/STAT pathway in RGC survival independent of macrophages. Activities and location of JAK/STAT pathway in the retina were examined using Western blotting and immunohistochemistry. We found that inhibition of JAK/STAT pathway did not affect RGC survival in the retinal explants derived from intact eye but caused RGC death in the retinal explants that were derived from IOP-elevated eye. Importantly, the detrimental effect of JAK/STAT pathway inhibition on RGC survival was also observed in vivo following acute IOP elevation, but not in intact eye. In addition, both in vitro and in vivo experiments confirmed a detrimental action of phagocytic cells following acute IOP elevation and the pathway inhibition. Compatible with what were observed in vivo, Western blotting and immunohistochemistry showed that JAK/STAT activities were not present in intact retina, but acute IOP elevation activated JAK/STAT pathway in the retina, in the regions of inner nuclear layer and ganglion cell layer, including RGCs. The IOP elevation-induced JAK/STAT activities were effectively abolished by intravitreal application of AG490. This study thus shows that (1) acute IOP elevation activates JAK/STAT pathway in RGCs, and (2) JAK/STAT pathway mediates RGC survival following IOP elevation but not under normal condition.

Topics: Acute Disease; Animals; Cell Survival; Disease Models, Animal; Enzyme Inhibitors; Eye Proteins; Glaucoma; Janus Kinases; Macrophages; Rats; Rats, Sprague-Dawley; Retinal Ganglion Cells; Signal Transduction; STAT Transcription Factors; Tissue Culture Techniques; Tyrphostins