Molecular Markers of Early Diagnosis of Alzheimer Disease: Prospects for Research in Peripheral Tissues

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder of elderly and old-aged people. Cerebrospinal fluid (CSF) and peripheral tissues—lymphocytes and platelets, buccal and olfactory epithelium, and skin fibroblasts—are used for intravital diagnostics of the expression of signaling molecules (AD markers). There are several changes in the production of hyperphosphorylated τ-protein form, BACE1, and peptide Aβ42 in CSF in the case of AD, but CSF sampling can have a number of side effects. Biopsies of the epithelium and portions of blood are a less traumatic method of obtaining tissue samples for AD diagnosis. An increase in the expression of the hyperphosphorylated form of τ-protein is shown in the blood lymphocytes of AD patients. An increase in the content of high molecular forms of phosphorylated τ protein and amyloid precursor protein (APP) was also detected in the platelets of AD patients. Changes in the amount of two miRNA families, miR-132 and miR-134, were detected in blood cells 1–5 years before the manifestation of clinical signs of AD. An increase in the bound-calcium concentration, Aβ40 and Aβ42 peptide synthesis, and τ protein was observed in AD skin fibroblasts. In olfactory and buccal epithelia, an increase in the expression of hyperphosphorylated τ-protein form and Aβ peptide was detected in AD patients. The detection of AD markers in peripheral tissues available for biopsy is highly important for intravital diagnostics, prevention, and targeted treatment of AD.