The Compartmentalization of Amyloid-β in Idiopathic Normal Pressure Hydrocephalus Brain Biopsies

Background: Amyloid-beta (A beta) is one of the hallmark lesions of Alzheimer's disease (AD). During the disease process, A beta undergoes biochemical changes, producing toxic beta variants, proposed to be detected within the neurons. Idiopathic normal pressure hydrocephalus (iNPH) causes cognitive impairment, gait, and urinary symptoms in elderly, that can be reversed by a ventriculo-peritoneal shunt. Majority of iNPH subjects display different A beta variants in their brain biopsies, obtained during shunting. Objective: To study the cellular compartmentalization of different A beta variants in brain biopsies from iNPH subjects. Methods: We studied the cellular localization of different proteoforms of A beta using antibodies towards different amino acid sequences or post-translational modifications of A beta, including clones 4G8, 6F/3D, unmodified- (7H3D6), pyroglutamylated-(N3pE), phosphorylated-(1E4E11) A beta and A beta protein precursor (A beta PP), in brain biopsies from 3 iNPH subjects, using immunohistochemistry and light microscopy (LM), light microscopy on semi-thin sections (LMst), and electron microscopy (EM). Results: In LM all A beta variants were detected. In LMst and EM, the A beta 4G8, 6F/3D, and the pyroglutamylated A beta were detected. The A beta PP was visualized by all methods. The A beta labelling was located extracellularly with no specific signal within the intracellular compartment, whereas the A beta PP was seen both intra- and extracellularly. Conclusions: TheA beta markers displayed extracellular localization when visualized by three assessment techniques, reflecting the pathological extracellular accumulation of A beta in the human brain. No intracellular A beta pathology was seen. A beta PP was visualized in intra- and extracellularly, which corresponds to the localization of the protein in the membranes of cells and organelles.