Modeling the Mechanical Parameters of Glaucoma

The Importance of Coating Surface and Composition for Attachment and Survival of Neuronal Cells Under Mechanical Stimulation

Cell culture of neuronal cells places high demands on the surface for these cells to adhere to and grow on. Native extracellular matrix (ECM) proteins are often applied to the cell culture surface. The substrate is even more important when mechanical strain is applied to the cells in culture. These cells will easily detach and die, precluding the study of how mechanical factors affect these cells. Mechanical factors are, for example, important in the eye disorder glaucoma, which is characterized by the loss of the retinal ganglion cells (RGCs), the retinal neurons that transfer the visual information from the retina via the optic nerve to the brain. High intraocular pressure is the main risk factor of glaucoma. Here, we aimed to find an optimal coating formulation for mechanical testing of the two cell types that are often used for in vitro studies on glaucoma: primary rat retinal ganglion cells (RGCs) and the neuronal PC-12 cell line. Glass and polymer coverslips as well as well plate wells were coated with various substrates: fibronectin, collagen 1, RGD peptide, polyethyleneimine (PEI), poly-D-lysine (PDL), and laminin. We used a thermomixer for 1 min at 500RPM and 37°C to apply mechanical strain and test cell attachment in medium throughput during mechanical stimulation. Cell density, morphology, and cell death were measured to evaluate the coatings. First, a screen of various surfaces and coatings was performed using PC-12 cells, after which a selection of coating strategies was tested with RGCs. For PC-12 cells, the best results were obtained using a coating with a mixture of 10 μg/mL PDL with 2 or 50 μg/mL laminin in PBS (M2). This resulted in the highest cell density, with and without mechanical stimulation. Many other coating strategies failed to provide an effective substrate for adherence and growth of PC-12 cells. Coating composition as well as coating strategy influenced cell attachment and survival. Contrary to PC-12 cells, RGCs performed better in a sequential coating of first 10 μg/mL PDL and then 2 μg/mL laminin (S2). With this protocol, RGCs showed best neurite growth and highest cell density. Based on this difference between PC-12 cells and RGCs, we conclude that the optimal coating depends on the cell type. When reporting cell culture studies, it is important to fully specify culture surface, surface treatment, and coating protocol since all these factors influence cell attachment, growth, and survival.

Beneficial and Detrimental Pressure-Related Effects on Inner Neurons in the Adult Porcine In Vitro Retina

Purpose

To explore pressure-related effects in the adult porcine retina in vitro.

Methods

Retinal explants were subjected to 0, 10, 30, or 60 mmHg of pressure for 24 or 48 hours in culture. Overall tissue damage in sections was assessed by lactate dehydrogenase media levels, hematoxylin and eosin staining, and TUNEL staining. Inner retinal neurons were evaluated by protein kinase C alpha (rod bipolar cells), CHX10 (overall bipolar cell population), parvalbumin (amacrine cells), and RBPMS (ganglion cells) immunohistochemistry.

Results

All retinas kept in culture displayed increased pyknosis and apoptosis compared with directly fixed controls. The 10-mmHg explants displayed attenuation of overall tissue damage compared with the 0-, 30-, and 60-mmHg counterparts. No difference in the number of rod bipolar cells was seen in the 10-mmHg explants compared with directly fixed controls, whereas significantly fewer cells were detected in the remaining pressure groups. No difference in the number of ganglion cells in the 0-, 10-, and 60-mmHg groups was seen compared with directly fixed controls after 24 hours, whereas a lower number was found in the 30-mmHg counterpart. A decline of ganglion cells was found in the 0-, 10-, and 60-mmHg group after 48 hours, but no further decrease was seen in the 30-mmHg group. No differences were detected in overall bipolar and amacrine cells in the pressure groups after 24 hours compared with directly fixed controls.

Conclusions

A moderate amount of pressure attenuates culture-related retinal neurodegeneration. Rod bipolar cells are specifically vulnerable to excessive pressure.

Translational Relevance

These findings are relevant for glaucoma-related research.

Sodium Hyaluronate-Induced Ocular Hypertension in Rats Damages the Direction-Selective Circuit and Inner/Outer Retinal Plexiform Layers

Purpose

To assess the changes in retinal morphology in a rat model of chronic glaucoma induced by ocular hypertension.

Methods

Intraocular pressure (IOP) was surgically increased through weekly injections of sodium hyaluronate (HYA) in the anterior eye chamber of the left eye of male Wistar rats, whereas the right eyes were sham operated (salt solution). During the 10-week experimental period, IOP was measured weekly with a rebound tonometer. Retinal cryosections were prepared for histological/immunohistochemical analysis and morphometry.

Results

IOP was higher in HYA-treated eyes than in sham-operated eyes along the 10-week period, which was significant from the fourth to the nineth week. Ocular hypertension in HYA-treated eyes was associated with morphologic and morphometric changes in bipolar cells, ON-OFF direction-selective ganglion cells, ON/OFF starburst amacrine cells, and inner plexiform layer sublamina.

Conclusions

Serial HYA treatment in the rat anterior eye chamber results in mild-to-moderate elevated and sustained IOP and ganglion cell death, which mimics most human open-angle glaucoma hallmarks. The reduced number of direction-selective ganglion cells and starburst amacrine cells accompanied by a deteriorated ON/OFF plexus in this glaucoma model could lend insight to the abnormalities in motion perception observed in patients with glaucoma.