Neurobiology of Disease (Jan 2016)

Relationship between ubiquilin-1 and BACE1 in human Alzheimer's disease and APdE9 transgenic mouse brain and cell-based models

  • Teemu Natunen,
  • Mari Takalo,
  • Susanna Kemppainen,
  • Stina Leskelä,
  • Mikael Marttinen,
  • Kaisa M.A. Kurkinen,
  • Juha-Pekka Pursiheimo,
  • Timo Sarajärvi,
  • Jayashree Viswanathan,
  • Sami Gabbouj,
  • Eino Solje,
  • Eveliina Tahvanainen,
  • Tiina Pirttimäki,
  • Mitja Kurki,
  • Jussi Paananen,
  • Tuomas Rauramaa,
  • Pasi Miettinen,
  • Petra Mäkinen,
  • Ville Leinonen,
  • Hilkka Soininen,
  • Kari Airenne,
  • Rudolph E. Tanzi,
  • Heikki Tanila,
  • Annakaisa Haapasalo,
  • Mikko Hiltunen

Journal volume & issue
Vol. 85
pp. 187 – 205

Abstract

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Accumulation of β-amyloid (Aβ) and phosphorylated tau in the brain are central events underlying Alzheimer's disease (AD) pathogenesis. Aβ is generated from amyloid precursor protein (APP) by β-site APP-cleaving enzyme 1 (BACE1) and γ-secretase-mediated cleavages. Ubiquilin-1, a ubiquitin-like protein, genetically associates with AD and affects APP trafficking, processing and degradation. Here, we have investigated ubiquilin-1 expression in human brain in relation to AD-related neurofibrillary pathology and the effects of ubiquilin-1 overexpression on BACE1, tau, neuroinflammation, and neuronal viability in vitro in co-cultures of mouse embryonic primary cortical neurons and microglial cells under acute neuroinflammation as well as neuronal cell lines, and in vivo in the brain of APdE9 transgenic mice at the early phase of the development of Aβ pathology. Ubiquilin-1 expression was decreased in human temporal cortex in relation to the early stages of AD-related neurofibrillary pathology (Braak stages 0–II vs. III–IV). There was a trend towards a positive correlation between ubiquilin-1 and BACE1 protein levels. Consistent with this, ubiquilin-1 overexpression in the neuron-microglia co-cultures with or without the induction of neuroinflammation resulted in a significant increase in endogenously expressed BACE1 levels. Sustained ubiquilin-1 overexpression in the brain of APdE9 mice resulted in a moderate, but insignificant increase in endogenous BACE1 levels and activity, coinciding with increased levels of soluble Aβ40 and Aβ42. BACE1 levels were also significantly increased in neuronal cells co-overexpressing ubiquilin-1 and BACE1. Ubiquilin-1 overexpression led to the stabilization of BACE1 protein levels, potentially through a mechanism involving decreased degradation in the lysosomal compartment. Ubiquilin-1 overexpression did not significantly affect the neuroinflammation response, but decreased neuronal viability in the neuron-microglia co-cultures under neuroinflammation. Taken together, these results suggest that ubiquilin-1 may mechanistically participate in AD molecular pathogenesis by affecting BACE1 and thereby APP processing and Aβ accumulation.

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