Pigment epithelium-derived factor induced CRX alterations in the mouse retina

The gene Serpinf1 encodes for Pigment Epithelium-Derived Factor (PEDF), which protects photoreceptors from cell death. The Serpinf1 null mouse exhibits normal retinal function; however, PEDF deficiency increases retinal degeneration susceptibility in rd10 mouse. CRX is a transcription factor that regulates expression of several photoreceptor specific genes, including opsins and phosphodiesterase. This study aims to explore whether regulation of CRX activation is one mechanism by which PEDF exerts photoreceptor survival. Serpinf1-/- , Serpinf1+/- and Serpinf1+/+ mice at 3 months of age were used. We prepared cultures of mouse retinal explants. They were treated with recombinant human PEDF. Zaprinast (a PDE inhibitor) was added to induce photoreceptor death. We determined cell death using PSVue-550, a visible fluorescent probe for detection of phosphatidylserine on the surface of cells. Subcellular distribution of CRX, PDE6A and pan-acetylation was detected by immunofluorescence. The transcriptional levels of Crx, Pde6a, Opn1mw and Opn1sw were assessed using qPCR. PEDF treatment induced the expression of Crx and its regulated genes Pde6a, Opn1mw and Opn1sw. PEDF also enhanced the CRX immunoreactivity in the nuclei of photoreceptors. In contrast, the nuclear CRX immunoreactivity was suppressed in photoreceptors from retinas of Serpinf1-/- mice deficient of PEDF. PDE6A immunoreactivity also decreased in Serpinf1-/- photoreceptors compared to those from Serpinf1+/+ mice. Histone acetylation was detected in discrete photoreceptors in Serpinf1+/+ but was undetectable in the Serpinf1-/- retinas. Zaprinast-induced photoreceptor death was more pronounced in Serpinf1-/- retinal explants than in wild type controls. PEDF pre-treatment prior to the zaprinast treatment improved photoreceptor survival and enhanced CRX immunoreactivity in both Serpinf1-/- and Serpinf1+/+ retinal explants. Deletion in PEDF in the Serpinf1 null mice accelerated retinal degeneration induced by zaprinast, which was prevented by exogenous addition of PEDF in retinal explants. The findings imply that PEDF activated the CRX-associated transcription factor network. They provide a novel insight linking extracellular PEDF to nuclear CRX during photoreceptor survival. © FASEB.