S327 phosphorylation of the presynaptic protein SEPTIN5 increases in the early stages of neurofibrillary pathology and alters the functionality of SEPTIN5

Mikko Hiltunen,Rita F Belo,Luı́sa V Lopes ,Petra Mäkinen,Kaisa M A Paldanius ,João Fonseca‐Gomes ,Luukas Leppänen,Sara R Tanqueiro,Maria José Diógenes,Ian Pike,Ville Leinonen,Hilkka Soininen,Catarinab Ferreira ,Mari Takalo,Annakaisa Haapasalo,Alexandre De Mendonça,Sandra H Vaz,Catarina Miranda-Lourenço,Mikael Marttinen,Ana M Sebastião ,Joana Coelho

doi:10.1016/j.nbd.2021.105603

Abstract

Alzheimer's disease (AD) is the most common form of dementia, which is neuropathologically characterized by extracellular senile plaques containing amyloid-β and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. Previous studies have suggested a role for septin (SEPTIN) protein family members in AD-associated cellular processes. Here, we elucidated the potential role of presynaptic SEPTIN5 protein and its post-translational modifications in the molecular pathogenesis of AD. RNA and protein levels of SEPTIN5 showed a significant decrease in human temporal cortex in relation to the increasing degree of AD-related neurofibrillary pathology. Conversely, an increase in the phosphorylation of the functionally relevant SEPTIN5 phosphorylation site S327 was observed already in the early phases of AD-related neurofibrillary pathology, but not in the cerebrospinal fluid of individuals fulfilling the criteria for mild cognitive impairment due to AD. According to the mechanistic assessments, a link between SEPTIN5 S327 phosphorylation status and the effects of SEPTIN5 on amyloid precursor protein processing and markers of autophagy was discovered in mouse primary cortical neurons transduced with lentiviral constructs encoding wild type SEPTIN5 or SEPTIN5 phosphomutants (S327A and S327D). C57BL/6 J mice intrahippocampally injected with lentiviral wild type SEPTIN5 or phosphomutant constructs did not show changes in cognitive performance after five to six weeks from the start of injections. However, SEPTIN5 S327 phosphorylation status was linked to changes in short-term synaptic plasticity ex vivo at the CA3-CA1 synapse. Collectively, these data suggest that SEPTIN5 and its S327 phosphorylation status play a pivotal role in several cellular processes relevant for AD.

Highlights

Alzheimer’s disease (AD), the most common form of dementia, is neuropathologically characterized by extracellular senile plaques con taining amyloid-β (Aβ), intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein (p-tau), and neuronal cell loss (Jack Jr et al, 2018)
We have recently shown that the downregulation of SEPTIN5 resulted in the increased autophagosomal degradation of amyloid precursor protein (APP) C-termi nal fragments as well as Aβ clearance in neuronal cells both in in vitro and in vivo (Marttinen et al, 2020)
We found a significant decrease in the RNA and protein levels of SEPTIN5 in the late stages of neurofibrillary pathology (Braak stages V and VI) as compared to the early-stage samples (Braak stages I and II, but not Braak stage 0)

Summary

Introduction

Alzheimer’s disease (AD), the most common form of dementia, is neuropathologically characterized by extracellular senile plaques con taining amyloid-β (Aβ), intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein (p-tau), and neuronal cell loss (Jack Jr et al, 2018). According to the prevailing amyloid cascade hypothesis, the pathogenesis of AD is initiated by abnormal accumulation of Aβ in the brain (Müller and Deller, 2017), followed by the aggregation of ptau, leading to loss of synapses and neuronal cell death (Merluzzi et al, 2018). In AD, different isoforms of Aβ generated from the amyloid precursor protein (APP) owing to cleavage by β- and γ-secretases, are prone to aggregate in neurotoxic forms, triggering a cascade of events related to calcium dyshomeostasis, inflammation, oxidative stress, and synaptic dysfunction (Hardy and Selkoe, 2002). Recent studies have identified SEPTIN5 and SEPTIN8 as potential modulators of APP processing and Aβ accumulation (Kurkinen et al, 2016; Marttinen et al, 2020). Mechanistic characteriza tions in neuronal cells have revealed that SEPTIN8 regulates the gen eration of Aβ via mechanisms altering the intracellular sorting and accumulation of β-site APP cleaving enzyme 1 (BACE1) (Kurkinen et al, 2016). The downregulation of SEPTIN5 resulted in increased autophagosomal degradation of APP C-terminal fragments (APP CTFs) as well as Aβ clearance in neuronal cells (Marttinen et al, 2020)

Objectives

Methods

Results

Conclusion