Astrocyte responses to experimental glaucoma in mouse optic nerve head

Abstract

Purpose To delineate responses of optic nerve head astrocytes to sustained intraocular pressure (IOP) elevation in mice. Methods We elevated IOP for 1 day to 6 weeks by intracameral microbead injection in 4 strains of mice. Astrocyte alterations were studied by transmission electron microscopy (TEM) including immunogold molecular localization, and by laser scanning microscopy (LSM) with immunofluorescence for integrin β1, α-dystroglycan, and glial fibrillary acidic protein (GFAP). Astrocyte proliferation and apoptosis were quantified by Ki67 and TUNEL labeling, respectively. Results Astrocytes in normal optic nerve head expressed integrin β1 and α-dystroglycan by LSM and TEM immunogold labeling at electron dense junctional complexes that were found only on cell membrane zones bordering their basement membranes (BM) at the peripapillary sclera (PPS) and optic nerve head capillaries. At 1–3 days after IOP elevation, abnormal extracellular spaces appeared between astrocytes near PPS, and axonal vesical and mitochondrial accumulation indicated axonal transport blockade. By 1 week, abnormal spaces increased, new collagen formation occurred, and astrocytes separated from their BM, leaving cell membrane fragments. Electron dense junctional complexes separated or were absent at the BM. Astrocyte proliferation was modest during the first week, while only occasional apoptotic astrocytes were observed by TEM and TUNEL. Conclusions Astrocytes normally exhibit junctions with their BM which are disrupted by extended IOP elevation. Responses include reorientation of cell processes, new collagen formation, and cell proliferation.

The role of aquaporin-4 in optic nerve head astrocytes in experimental glaucoma

“…The astrocyte processes at the junctional area with the peripapillary sclera were not different in appearance between the two strains of mice. Features identified in a recent publication (Quillen et al 2020 [ 39 ]) were similar, including multiple infoldings of astrocyte processes as they join their basement membrane in the zone adjoining the choroid and sclera ( Fig 9 ). Dense junctional complexes were seen along the astrocyte border facing their basement membrane, but not elsewhere in the membrane of astrocyte processes.…”

“…Bilaterally untreated (naïve) and contralateral controls had no mitotic cells (labeling frequency similar to background level). We have previously reported significant proliferation in UON after 3 day and 1 week IOP elevations, followed by return to control Ki67 labeling after 6W-GL [ 39 ]. B6 ON had significantly more Ki67 labeled cells than AQP4 null in PL, MTZ and MON, but Ki67 labeling in UON was not significantly different between the two strains (p ≤ 0.03, p ≤ 0.04, p ≤ 0.01, and p = 0.22, respectively, unpaired t-tests, Table 4 ).…”

Decorin—An Antagonist of TGF-β in Astrocytes of the Optic Nerve

“…Along with the increase of TGF-β2, a substantial alteration of the ECM occurs in the ONH and in the peripapillary sclera of glaucomatous patients. Astrocytes play a pivotal role in the restructuring process by de novo collagen synthesis [ 55 ], which occurs in an IOP dependent manner [ 56 ]. A lack of DCN in the ON and ONH could contribute to the observed disorganization of ECM in ONH and the peripapillary sclera in glaucomatous eyes [ 57 , 58 , 59 ], since DCN is essential for binding and arranging collagen fibers [ 60 , 61 ].…”

“…Alterations in the ECM arrangement of the lamina cribrosa and the peripapillary sclera cause changes in the mechanical support of this region and thereby affect the mechanosensation mechanisms of astrocytes by their junctional complexes upon IOP elevation [ 55 ]. In DCN-deficient mice we reported previously that the increase in IOP and the loss of ON axons is accompanied by an enhanced expression and synthesis of GFAP by astrocytes [ 32 ], which, from a biomechanical perspective, would cause together with ECM changes an increase in tissue stiffness [ 62 , 63 ].…”

Multifactorial Pathogenic Processes of Retinal Ganglion Cell Degeneration in Glaucoma towards Multi-Target Strategies for Broader Treatment Effects

“…Both astrocytes [129,[153][154][155][156][157] and microglia [154,[158][159][160][161][162] robustly respond to glaucoma-related stress by finely regulated morphological, molecular, and functional alterations. In addition to astrocytes and microglia, Müller glia in the retina [163], lamina cribrosa cells in the optic nerve head [164], and myelinating oligodendrocytes in the optic nerve [165,166] also prominently respond.…”