Evaluation of the effect of hypoxia on the expression and activity of neprilysin (EC 3.4.24.11), a protease involved on Alzheimer’s disease

Abstract

Hypoxia is characterized by reduced oxygen content in blood and is related to several pathologies, including Obstructive Sleep Apnea Syndrome (OSAS). Its consequences are not completely understood, but some evidences from the literature show that hypoxia has biochemical effects that lead to changes on behavior and significant outcomes in systems like the central nervous, respiratory and cardiovascular. Hypoxia and ageing seem to have a very close involvement in the development of Alzheimer’s disease. Neprilysin or neutralendopeptidase (NEP, EC 3.4.24.11) is a metalloprotease present in various body tissues such as kidneys, intestines, lungs, brain, among others. It was recently shown that one of its main activities in the central nervous system is the degradation of beta amyloid (A β ) , a peptide involved in the onset and progression of Alzheimer’s disease. Our goal is to study the gene and protein relative expression of NEP using chronic intermittent hypoxia (CIH), a model of OSAS. 24 Wistar male rats, 3 months old, were separated in 3 groups: Control ( n = 8), CIH group ( n = 8, 3-min cycles of 21–5% O2 from 9 to 17 h for 6 weeks), and CIH + 2 group ( n = 8, 3-min cycles of 21–5% O2 from 9 to 17 h for 6 weeks), followed by two weeks of normoxia. Gene and protein relative expression from the hippocampus, frontal and temporal cortices were analyzed by the RT-PCR and Western blot (WB). A 3-times fold increase for the relative NEP gene expression was shown in the hippocampus, although protein expression remained unaltered. On the other hand, in the temporal cortex, relative protein expression for NEP increased, while the relative gene expression maintained unaltered. As observed, CIH can increase the gene and/or protein expression of NEP in specific brain tissues, which returned to control levels after 2 weeks of normoxia. On hippocampus, although the levels of mRNA increased almost 3 times on CIH group, the protein levels remained unaltered compared to control group, which indicates a possible regulation mechanism of gene expression. On the other hand, the increase NEP levels on temporal cortex, a region known to be involved in the onset of Alzeheimer’s disease, possibly results from a positive feedback control, induced by A β peptide. This study was developed on the Department of Psychobiology.