Immunohistochemical Evaluation of Chaperone-Induced Autophagy in Various Parts of the Human Brain During Aging

Abstract

Supporting of the functional pool of neurons during age-related brain involution is closely related to chaperone-mediated autophagy, the main function of which is to provide cellular proteostasis and utilize neurotoxic proteins. Impairment of this type of autophagy underlies the pathogenesis of many age-associated neurodegenerative diseases. In this aspect, it seems relevant to study the relationship between key markers of chaperone-mediated autophagy and their relative contribution to aging and neurodegeneration in order to determine pharmaceutical targets. The aim of the study was to determine the levels of expression of markers of chaperone-mediated autophagy - heat shock protein 70 (HSP70) and lysosome-associated membrane protein type 2A (LAMP2) in neurons of various areas of the human brain during aging. The study was performed on autopsy material of patients whose causes of death were not associated with neurological diseases. Preparations of the cortex of the precentral gyrus, striatum and hippocampus were studied in the group of cases of young age (35-45 years, n=5) and senile age (>75 years, n=10). Immunohistochemical staining was performed using primary antibodies to HSP70 and LAMP2. Optical density was assessed in the perikaryon of 150 large neurons in layer V of the cortex of the precentral gyrus, striatum, and pyramidal layer of the hippocampus. The results of the study demonstrated an increase in the expression of both HSP70 and LAMP2A in brain preparations from cases of senile age. The higher values of the optical density of HSP70 compared to LAMP2A in brain preparations from senile cases were probably due to dissociation between the stage of substrate binding and the stage of its translocation. It can be assumed that the binding of nonfunctioning proteins to HSP70 and cochaperones occurs faster than their movement into the lumen of lysosomes via LAMP2A. The results obtained suggest that the increasing of levels of markers of chaperone-mediated autophagy may be of a compensatory-adaptive nature and ensure the survival of neurons under conditions of chronic stress during physiological aging.