Purpose: To clarify the optic nerve head (ONH) gene expression responses associated with a single, axon-damaging exposure to elevated IOP in relation to the composite cellular events previously identified in models of chronically elevated IOP.
Methods: Anesthetized rats were exposed unilaterally to an 8-hour pulse-train controlled elevation of IOP (PT-CEI) at 60 mm Hg, while others received normotensive CEI at 20 mm Hg. ONH RNA was harvested at 0 hours and 1, 2, 3, 7, and 10 days after either CEI and from naïve animals. RNA sequencing was performed to analyze ONH gene expression. DAVID Bioinformatics tools were used to identify significant functional annotation clusters. Gene function was compared between PT-CEI and two models of chronic ocular hypertension from the literature.
Results: The number of significantly changed genes peaked immediately (n = 1354) after PT-CEI (0 hours). This was followed by a lull (<4 genes per time point) at 1 and 2 days after PT-CEI. Gene activity increased again at 3 days (136 genes) and persisted at 7 (78 genes) and 10 (339 genes) days. Significant gene functional categories included an immediate upregulation of Defense Response at 0 hours, followed by upregulation in Cell Cycle, a reduction in Axonal-related genes at 3 to 10 days, and upregulation of Immune Response-related genes at 10 days following PT-CEI. The most commonly upregulated gene expression across our PT-CEI study and two chronic models of ocular hypertension were cell cycle related.
Conclusions: The PT-CEI model places in sequence ONH gene expression responses previously reported in models with chronically elevated IOP and may provide insights into their role in optic nerve damage.