Amyloid-β Protein Precursor Deficiency Changes Neuronal Electrical Activity and Levels of Mitochondrial Proteins in the Medial Prefrontal Cortex

Abstract

Background: Neuropathological features of Alzheimer’s disease are characterized by the deposition of amyloid-β (Aβ) plaques and impairments in synaptic activity and memory. However, we know little about the physiological role of amyloid-β protein precursor (AβPP) from which Aβ derives. Objective: Evaluate APP deficiency induced alterations in neuronal electrical activity and mitochondrial protein expression. Methods: Utilizing electrophysiological, biochemical, pharmacological, and behavioral tests, we revealed aberrant local field potential (LFP), extracellular neuronal firing and levels of mitochondrial proteins. Result: We show that APP knockout (APP-/-) leads to increased gamma oscillations in the medial prefrontal cortex (mPFC) at 1-2 months old, which can be restored by baclofen (Bac), a γ-aminobutyric acid type B receptor (GABABR) agonist. A higher dose and longer exposure time is required for Bac to suppress neuronal firing in APP-/- mice than in wild type animals, indicating enhanced GABABR mediated activity in the mPFC of APP-/- mice. In line with increased GABABR function, the glutamine synthetase inhibitor, L-methionine sulfonate, significantly increases GABABR levels in the mPFC of APP-/- mice and this is associated with a significantly lower incidence of death. The results suggest that APP-/- mice developed stronger GABABR mediated inhibition. Using HEK 293 as an expression system, we uncover that AβPP functions to suppress GABABR expression. Furthermore, APP-/- mice show abnormal expression of several mitochondrial proteins. Conclusion: APP deficiency leads to both abnormal network activity involving defected GABABR and mitochondrial dysfunction, suggesting critical role of AβPP in synaptic and network function.