Early Functional Impairment in Experimental Glaucoma Is Accompanied by Disruption of the GABAergic System and Inceptive Neuroinflammation

Abstract

Glaucoma is a leading cause of irreversible blindness worldwide, and increased intraocular pressure (IOP) is a major risk factor. We aimed to determine if early functional and molecular differences in the glaucomatous retina manifest before significant retinal ganglion cell (RGC) loss is apparent. Adenoviral vectors expressing a pathogenic form of myocilin (Ad5.MYOC) were used to induce IOP elevation in C57BL/6 mice. IOP and pattern electroretinograms (pERG) were recorded, and retinas were prepared for RNA sequencing, immunohistochemistry, or to determine RGC loss. Ocular injection of Ad5.MYOC leads to reliable IOP elevation, resulting in significant loss of RGC after nine weeks. A significant decrease in the pERG amplitude was evident in eyes three weeks after IOP elevation. Retinal gene expression analysis revealed increased expression for 291 genes related to complement cascade, inflammation, and antigen presentation in hypertensive eyes. Decreased expression was found for 378 genes associated with the γ-aminobutyric acid (GABA)ergic and glutamatergic systems and axon guidance. These data suggest that early functional changes in RGC might be due to reduced GABAA receptor signaling and neuroinflammation that precedes RGC loss in this glaucoma model. These initial changes may offer new targets for early detection of glaucoma and the development of new interventions.

Systemic Treatment with Pioglitazone Reverses Vision Loss in Preclinical Glaucoma Models

“…Finally, the determination of IOP is difficult in this strain, possibly due to the development of corneal calcification with age, which affects the accuracy of rebound tonometry. In order to confirm the protective effect and functionally evaluate this finding, we employed a distinct mouse model of glaucoma that is reliant upon adenoviral-mediated expression of a pathogenic variant of human myocilin in the trabecular meshwork of mice [ 29 , 30 , 44 ].…”

“…Elevated IOP causes a number of morphologic and molecular adaptations to RGCs that may aid their survival, but reduce their functional state. One example is the disruption of GABAergic signaling that occurs rapidly after IOP elevation and causes a decrease in the pERG signal [ 30 , 57 ]. It is conceivable that resolution of either metabolic or neuroinflammatory stress through PPARγ activity reverses the dysregulation and leads to the observed increase in retinal function.…”

“…Elevated IOP was induced in C57BL/6J mice by injections of the adenoviral vector Ad5RSVmyocillinY437H (Ad5myoc, University of Iowa Viral Vector Core, Iowa City, IA, USA) as previously described [ 29 , 30 , 31 ]. Briefly, newborn (P2–P4) B6 mice received a subcutaneous injection of Ad5myoc (3 × 103 PfU) to induce tolerance to the vector and prevent ocular inflammation.…”

Immune Responses in the Glaucomatous Retina: Regulation and Dynamics

“…Whether or not autoantibodies contribute to glaucomatous damage in humans remains a matter of debate, but it has also been demonstrated that POAG patients exhibit a more robust T-cell response upon stimulation with HSP 60 or HSP 27 than controls [23,172]. Thus, it is conceivable that elevated expression of HSP results in increased loading of their proteolytic fragments on major histocompatibility complex I and II, which is also expressed at elevated levels in the glaucomatous retina, that can then serve to initiate T-cell recall responses [22,173].…”

“…Progressive and irreversible structural changes of the optic nerve head (ONH) and the lamina cribrosa are characteristic of glaucoma [17], and it is likely that these changes increasingly compromise axonal survival in the ONH. However, there is also substantial experimental evidence demonstrating that immediate early innate immune responses, facilitated by multifactorial mechanical, hypoxic, or metabolic stresses [18][19][20][21][22], are succeeded by a sustained adaptive immune response and leucocyte translocation into glaucomatous retinas and optic nerves [23][24][25].…”