PEDF Deletion Induces Senescence and Defects in Phagocytosis in the RPE.

Abstract

The retinal pigment epithelium (RPE) expresses the <i>Serpinf1</i> gene to produce pigment epithelium-derived factor (PEDF), a retinoprotective protein that is downregulated with cell senescence, aging and retinal degenerations. We determined the expression of senescence-associated genes in the RPE of 3-month-old mice that lack the <i>Serpinf1</i> gene and found that <i>Serpinf1</i> deletion induced <i>H2ax</i> for histone H2AX protein, <i>Cdkn1a</i> for p21 protein, and <i>Glb1</i> gene for β-galactosidase. Senescence-associated β-galactosidase activity increased in the <i>Serpinf1</i> null RPE when compared with wild-type RPE. We evaluated the subcellular morphology of the RPE and found that ablation of <i>Serpinf1</i> increased the volume of the nuclei and the nucleoli number of RPE cells, implying chromatin reorganization. Given that the RPE phagocytic function declines with aging, we assessed the expression of the <i>Pnpla2</i> gene, which is required for the degradation of photoreceptor outer segments by the RPE. We found that both the <i>Pnpla2</i> gene and its protein PEDF-R declined with the <i>Serpinf1</i> gene ablation. Moreover, we determined the levels of phagocytosed rhodopsin and lipids in the RPE of the <i>Serpinf1</i> null mice. The RPE of the <i>Serpinf1</i> null mice accumulated rhodopsin and lipids compared to littermate controls, implying an association of PEDF deficiency with RPE phagocytosis dysfunction. Our findings establish PEDF loss as a cause of senescence-like changes in the RPE, highlighting PEDF as both a retinoprotective and a regulatory protein of aging-like changes associated with defective degradation of the photoreceptor outer segment in the RPE.