P3-199: ptpn11 is involved in regulating tau protein phosphorylation in the retina

Tau is an axonally expressed microtubule-associated protein that plays a critical role in maintenance of neuronal structure and function. Tau phosphorylation is associated with neurofibrillary tangle formation in the brain in Alzheimer's disease (AD). Substantial research has shown that retinal ganglion cell (RGC) function is also negatively affected in AD. AD pathology in the retina demonstrates molecular overlap with pathological features observed in glaucoma. Both amyloid β and tau are affected in the eyes in glaucoma and our research has shown tau hyperphosphorylation in the retinas of APP/PS1 mouse model of AD. We recently showed that PTPN11 phosphatase upregulation promotes RGC injury. Here, we modulated PTPN11 expression in the retina using AAV mediated gene therapy and studied its effects on tau expression and phosphorylation. SD rats were subjected to weekly microbead injections in the anterior chamber of the eye for 2 months to induce chronic intraocular pressure (IOP) elevation (20.84±1.65 mm Hg). Immunoblotting and immunofluorescence were performed to determine the effects of PTPN11 expression changes on the glaucoma retinas. We designed PTPN11 and PTPN11-shRNA constructs along with GFP expression in AAV2 under the control of CAG hybrid promoter. Intravitreal AAV injections were carried out to either upregulate or silence PTPN11 in the ganglion cells for 8 weeks (n=40). The effects of PTPN11 modulation on Tau protein expression and phosphorylation were assessed by immunoblotting and immunohistochemistry. Tau protein hyperphosphorylation (Ser404) was identified in the retinas exposed to increased IOP using immunoblot analysis (p<0.05). Immunofluorescence studies further revealed tau hyperphosphorylation in the inner retinal layers in the glaucomatous retinal sections. AAV2 mediated PTPN11 over-expression promoted tau phosphorylation (Ser404) in the RGCs in retina. PTPN11 over-expressing retinas exhibited increased pTau levels (Ser404) (p<0.024, ANOVA, Tukey's test) as identified in immunoblotting compared to the GFP expressing controls. This study demonstrates regulatory effects of PTPN11 modulation on endogenous phsopho-Tau (Ser404) in the RGCs. Increased Tau (Ser404) phosphorylation was observed in the retina in chronic model of experimentally increased IOP. These findings suggest PTPN11 as a novel target to modulate Tau protein, which could have applications to understand AD and other neurodegenerative disorders involving Tau pathologies.