Abstract
Purpose :
Lamina cribrosa (LC) astrocytes respond early in glaucoma, changing in structure and function before observable neurodegeneration. Elevated intraocular pressure (IOP) induces astrocyte changes, resulting in downstream retinal ganglion cell axon damage and vision loss. Much of what is known about IOP-induced astrocyte changes comes from mouse models, which lack the LC collagen that heavily influences the biomechanics of the region in larger eyes, like those of humans and sheep. We characterized the IOP-induced distortions suffered by individual LC astrocytes, ex vivo. We hypothesized that acute IOP increase causes greater deformation of astrocyte regions within pores than along beams.
Methods :
6 sheep eyes were obtained within 4 hours of death. Optic nerve was cut coronally to expose the LC. Individual LC astrocytes were stochastically labeled across their cell membranes, in situ, with DiOlistic labeling. LC collagen and labeled astrocytes were imaged with SHG and multiphoton microscopy at low (5mmHg) and high (40mmHg) IOPs. Images of 9 astrocytes and surrounding collagen at low and high IOP were analyzed using tracking techniques to determine IOP-induced stretch, compression, and changes in branch tortuosity.
Results :
Stretch (15.3±22.2%) and compression (19.4±20.6%) of astrocyte regions along LC beams were significantly higher than stretch (10.7±14.6%) and compression (14.0±15.2%) of respective astrocyte regions within pores (p<0.001, p<0.001). Astrocyte branches were significantly more tortuous at low IOP (7.8±6.1%) than at high IOP, (5.6±6.0%, p=0.002, n=40 branches) with astrocyte branch tortuosity decreasing up to 13.9%.
Conclusions :
We were able to visualize individual LC astrocytes, ex vivo, within the context of their complex 3D environments, at different IOPs. LC astrocytes are exposed to two different mechanical environments: they contact the robust LC collagenous beams and the soft neural tissue pores. Astrocyte distortions with IOP were diverse, with regions of astrocytes along collagen beams deforming more than regions of astrocytes in neural tissue pores. Further studies are needed to determine how these specific deformations may cause differences in cell signaling which lead to glaucomatous vision loss. Also unclear are the implications for culture systems that often subject astrocytes to homogeneous deformations.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.