Two Novel PDE11A Genetic Variants Increase Tau Phosphorylations in Early-onset Alzheimer's Disease

Abstract

Background: Alzheimer’s disease (AD) is a leading cause of dementia in the elderly and has become a major health issue. However, a large number of genetic risk factors remain undiscovered. Methods: To identify novel risk genes and better understand the molecular pathway underlying AD, whole-exome sequencing (WES) was performed in 215 early-onset AD (EOAD) patients and 55 unrelated healthy controls of Han Chinese ethnicity. Subsequent direct sequencing was performed in 4962 individuals to validate the selected rare mutations. Computational annotation and in vitro functional studies were performed to evaluate the role of candidate mutations in EOAD and the underlying mechanisms.Results: We identified two rare missense mutations in the phosphodiesterase 11A (PDE11A) gene, resulting in p.Arg202His, and p.Leu756Gln, in individuals with EOAD. Both mutations are located in evolutionarily highly conserved amino acids, are predicted to alter the protein conformation, and classified as pathogenic. Furthermore, we found significantly decreased protein levels of PDE11A in brain samples of AD patients. Expression of PDE11A variants and knockdown experiments with specific short hairpin RNA (shRNA) for PDE11A both resulted in an increase of AD-associated Tau hyperphosphorylation at T181, S404, S202, S416, S214, S396 and AT8 epitopes in vitro. PDE11A variants or PDE11A shRNA also caused increased cAMP levels, protein kinase A (PKA) activation, and cAMP response element-binding protein (CREB) phosphorylation. Additionally, pretreatment with a PKA inhibitor (H89) suppressed PDE11A mutation-induced p-Tau formation.Conclusions: Our results demonstrate that both PDE11A mutations and PDE11A knockdown increase Tau phosphorylation through the cAMP/PKA pathway, suggesting that PDE11A is a novel risk gene for AD. This study provides insight into the involvement of Tau phosphorylation via the cAMP/PKA pathway in EOAD pathogenesis and provides a potential new target for intervention.