Phosphatidylinositol 5-Kinase (PIKfyve) Negatively Regulates Photoreceptor Neuroprotection

Abstract

Purpose : Phosphatidylinositol-3-phosphate 5-kinase (PIKfyve) is a phosphoinositide 5-kinase that phosphorylates PI(3)P to generate PI(3,5)P₂. PI(3)P is generated from PI by the action of class III PI3K, Vps34. Vps34 loss in rods resulted in rod degeneration. The 5’-phosphatase (called FIG4) dephosphorylates PI(3,5)P₂ to PI(3)P. FIG4 loss also resulted in retinal degeneration. The role of PIKfyve in photoreceptor functions is unknown. This study examined the role of PIKfyve in the retina.

Methods : PIKfyve KO mice were generated under the control of retina-specific Chx10 (abbreviated as ^retPikfyve^-/-) promoter. PI(3,5)P₂ levels were measured and immunoblot analysis with anti-PIKfyve, anti-rhodopsin, cone-arrestin, and sodium-potassium ATPase-alpha (NKAα) antibodies was performed in PIKfyve floxed and ^retPikfyve^-/- mouse retinas. Structure and function were assessed at 8 months of age. PIKfyve floxed and ^retPikfyve^-/- mice were subjected to light stress (LS) at 10,000 lux for 7 days. PI(3,5)P₂ is needed for late endosome and lysosome maturation. We examined the expression of NKAα, removed through the lysosomal degradation pathway. One week after LS, mice were subjected to ERG, followed by histological examination.

Results : ^retPikfyve^-/- retina had 70% less PIKfyve protein and more than 80% less PI(3,5)P₂ when compared to PIKfyve floxed retina. However, there was no significant difference in retinal function and structure between PIKfyve floxed and ^retPikfyve^-/- mice at 8 months of age. Light-stressed PIKfyve floxed mice exhibited photoreceptor degeneration; the structure was well preserved in light-stressed ^retPikfyve^-/- mice. Immunoblots showed no significant difference in the levels of rhodopsin, NKAα, and cone arrestin between PIKfyve floxed and ^retPikfyve^-/- mice without LS. Light-stressed PIKfyve floxed mice had significantly reduced levels of rhodopsin, cone arrestin, and NKAα compared with light-stressed ^retPikfyve^-/- mice. Light-stressed ^retPikfyve^-/- mice had a normal retinal function and well-preserved retinal structure, whereas light-stressed PIKfyve floxed mice had significantly reduced function and exhibited retinal degeneration.

Conclusions : The data suggest that PIKfyve-generated PI(3,5)P₂ regulates late endosome and lysosome maturation, and loss of PIKfyve promotes photoreceptor neuroprotection. Modulating the PIKfyve activity under retinal degenerative conditions may have therapeutic benefits.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.