Pressure-Induced Changes in Astrocyte GFAP, Actin, and Nuclear Morphology in Mouse Optic Nerve

Abstract

Purpose To conduct quantitative analysis of astrocytic glial fibrillary acidic protein (GFAP), actin and nuclei distribution in mouse optic nerve (ON) and investigate changes in the measured features after 3 days of ocular hypertension (OHT). Method Serial cross-sections of 3-day microbead-induced OHT and control ONs were fluorescently labelled and imaged using confocal microscope. Eighteen structural features were measured from the acquired images, including GFAP coverage, actin area fraction, process thickness, and aspect ratio of cell nucleus. The measured features were analyzed for variations with axial locations along ON and radial zones transverse to ON, as well as for the correlations with degree of intraocular pressure (IOP) change. Results The most significant changes in structural features after 3-day OHT occurred in the unmyelinated ON region (R1), and the changes were greater with greater IOP elevation. Although the GFAP, actin, axonal, and ON areas all increased in 3-day OHT ONs in R1 ( P ≤ 0.004 for all), the area fraction of GFAP actually decreased ( P = 0.02), the actin area fraction was stable and individual axon compartments were unchanged in size. Within R1, the number of nuclear clusters increased ( P < 0.001), but the mean size of nuclear clusters was smaller ( P = 0.02) and the clusters became rounder ( P < 0.001). In all cross-sections of control ONs, astrocytic processes were thickest in the rim zone compared with the central and peripheral zones ( P ≤ 0.002 for both), whereas the overall process width in R1 decreased after 3 days of OHT ( P < 0.001). Conclusions The changes in structure elucidated IOP-generated alterations that underlie astrocyte mechanotranslational responses relevant to glaucoma.

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

“…By analogy, it suggests that the astrocyte process area of a zone without AQP4 channels would have lower astrocyte area. Indeed, in quantitative analysis of astrocyte area as a proportion of ON tissue in fixed, cryosectioned mouse tissue, we found that the astrocyte area in the UON, which is devoid of AQP4, is less than half that of the MON [ 51 ].…”

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

“…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 ]. Up to now, there has been no data on the amounts of DCN in the ONH of glaucoma patients, which would be of great interest since increased amounts of TGF-β are known to be present in the ONH [ 26 , 28 , 47 ]…”

Biomechanics of the optic nerve head and peripapillary sclera in a mouse model of glaucoma

“…The assumption of a stiffer PPS than the AL is supported by strain measurements herein and by the tissues' load-bearing components, predominantly collagen fibres in the PPS and astrocytic processes in the AL [44,45]. The astrocytic processes align predominantly in-plane across the AL and can span the entirety of the AL [46–49]. The AL periphery has denser astrocytic processes, thicker filamentous cytoarchitecture and transcellular contacts through their basement membranes with the PPS [49,50].…”

“…The astrocytic processes align predominantly in-plane across the AL and can span the entirety of the AL [46–49]. The AL periphery has denser astrocytic processes, thicker filamentous cytoarchitecture and transcellular contacts through their basement membranes with the PPS [49,50]. This morphology could make the AL stiffer peripherally, resulting in locally smaller tensile strain.…”