Abstract
Purpose :
Cx43, a gap junction protein expressed in astrocytes, is known to play an important role in modulating the response to CNS injury. Blocking Cx43 hemichannel opening in ischemia/reperfusion models has been shown to rescue RGCs by preventing secondary damage spread. Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common acute optic neuropathy in those older than 50 years old and it presents as sudden, painless visual field loss. Here, we introduced and validated a novel photochemical thrombosis NAION animal model and investigated changes in Cx43 expression in retinal astrocytes.
Methods :
We induced photochemical thrombosis NAION model in adult C57BL/6 mice using a 577nm laser (200μm spot size, 50mW power, 500ms, 15 spots). We assessed retinal and optic nerve in vivo imaging using spectral-domain optical coherence tomography (OCT) at baseline, day 1, 3 and 21 after NAION induction and used immunohistochemistry examine changes in Cx43, VEGF and Brn3a expression.
Results :
One day after NAION induction, there was significant thickening of the peripapillary ganglion cell complex (GCC) (RNFL+GCL+IPL) compared with baseline (baseline: 80 ± 1mm, n=10; day-1: 88 ± 3mm, n=10, p<0.05). Immunohistochemistry showed that NAION also led to the increase in the levels of VEGF (Ctrl: 2319 ± 195, n= 5; day-1: 4549 ± 683 gray mean value, n=5, p<0.05) which correlates with retinal edema (r=0.89, p=0.045). NAION induced a significant increase in Cx43 expression (Ctrl: 1351 ± 80, n=4; NAION day-1: 1791 ± 55, n=5, p<0.05; NAION day-3: 2844 ± 148 puncta/mm2, n=4, p<0.0001), which normalized within 3 weeks (NAION day-21: 1639 ± 100 puncta/mm2, n=4). Twenty one days after NAION, OCT imaging showed a significant thinning of the GCC (69 ± 1, n=9, p<0.01) indicating loss in RGCs, confirmed by a 30% decrease in Brn3a+ cells (Ctrl: 3131 ± 44 cells/mm2, n=4; NAION: 2180 ± 217, n=8, p<0.01).
Conclusions :
A novel protocol of photochemical thrombosis using a 577nm laser induced elevation of VEGF positively correlated to GCC swelling and also led to significant RGCs loss at 21 days, reproducing the expected phenotype of a NAION model. The focal ischemia also led to an increase in Cx43 one day after NAION which was 1.5x more elevated by day 3. Early astrocytic changes in Cx43 expression could be relevant mechanism involved in NAION pathology and therefore a potential therapeutic target.
This is a 2021 ARVO Annual Meeting abstract.