Abstract
Purpose :
Dry AMD is a complex disease exhibiting a great degree of heterogeneity, which is both poorly modelled and understood. In AMD, mitochondrial dysfunction is an important genetic factor and smoking is the strongest environmental risk factor, however the joint effect of these two risk factors have not been investigated in the context of AMD. Dysfunction and dysmorphology of the retinal pigment epithelial (RPE) cells is an early feature in AMD and here we investigate the effect of Pink1 loss, the master regulator of mitophagy and smoking on RPE structure and function in Pink1-/- mice. In AMD, RPE cells show both EMT (epithelial to mesenchymal transition) and cell death, decrease in expression of RPE specific markers and overall structural and functional decline.
Methods :
Four-month-old C57 and Pink1-/- mice were smoked on Kentucky Reference Cigarettes or on air in a smoking chamber for 2hrs/day, 5days/week for 6months and evaluated for: i. RPE morphology and shape using RPE flatmounts, ii. Sub-cellular deposits and RPE inclusions using TEM, iii. Gene expression of RPE specific genes – Lrat, Best1, Rpe65 using qPCR and western blots, iv. Gene expression of EMT (e-Cadherin, Vimentin, Snail1) and cell death (Bcl-2, Caspase-3,9) related genes using qPCR and western blots, v. Functional evaluation using scotopic electroretinogram (ERG).
Results :
Pink1-/- mice even without smoking showed dysmorphic RPE with typical EMT morphology and 2-fold increase in EMT markers (P<0.005 for all markers), basal laminar deposits and significantly decreased ERG b and c waves compared to C57 (both air and smoked) mice. However, Pink1-/- mice which were smoked showed evidence of increased cell death both morphologically (non-nucleated, vacuole filled RPE cells in TEM) and biochemically (increased caspase expression) and showed more pronounced basal deposits. ERG a, b and c waves were significantly decreased compared to both C57 smoked and Pink1 air-raised mice. C57 smoked mice compared to C57 air mice showed slight increase in EMT markers and some evidence of basal deposits but not as strong as those seen in Pink1-/- mice.
Conclusions :
Thus, Pink1-/- mimics dysfunctional RPE which are still surviving undergoing EMT whereas an added environmental insult drives the cells towards cell death. Our model helps capture the typical heterogeneity seen in the RPE of AMD patients.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.