Altering PTPRD via genetics or pharmacology modulates 3xTg-AD mouse neurofibrillary pathology

Densities of neurofibrillary tangles (NFTs), a major Alzheimer's disease (AD) pathology, display genetic associations with variants in the receptor type protein tyrosine phosphatase D (PTPRD) gene. NFTs are rich in tau protein that is hyperphosphorylated, prominently by the glycogen synthase kinases (GSK) 3α/β. PTPRD dephosphorylates GSK3s, reducing their activities and providing an attractive candidate molecular mechanism for PTPRD/NFT associations. We have used AT-8 and Aβ immunohistochemistry to assess hyperphosphorylated tau/NFT and Aβ/senile plaque pathologies, developed and characterized 3xTg-AD mice with wildtype or reduced PTPRD expression and assessed results of treatments with our (a) PTPRD phosphatase inhibitor pentilludin, (b) lead PTPRD positive allosteric modulator (PAM) quercetin and (c) drug candidate PTPRD PAM active metabolite 6BrQ. Four-month 3xTg-AD/PTPRD +/- mice display AT-8 immunoreactivity in hippocampal neurons, much earlier than 3xTg-AD/PTPRD +/+ mice. There are modest effects of reducing PTPRD expression on densities of Aβ/senile plaque structures assessed at 21 months. 3xTg-AD (but not wildtype C57) mice treated (weeks 6-16) with pentilludin display abundant hyperphosphorylated tau at 4 months. 3xTg-AD/PTPRD+/- mice treated (weeks 6-16) with quercetin or 6BrQ display >50% and >95% reductions in AT-8 immunoreactive hippocampal neuron counts, respectively. These results support roles for PTPRD in AD neurofibrillary pathophysiology and for orally-bioavailable drugs that can be metabolized to 6BrQ to slow development of this pathology.