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Biology and function of ADAM10 isoforms for differential diagnosis of Alzheimer's Disease by electrochemical sensors

Abstract

Alzheimer's Disease (AD) is a gradual and progressive neurodegenerative disease characterized by extensive neuronal losses and deposits of neurofibrillary tangles and senile plaques. Mild neurocognitive impairment (MCI) is characterized by cognitive decline, but with preservation of functionality, being an intermediate stage between normal AD cognition, but that can be reversed. ADAM10 is the main neuronal ±-secretase and is also present in platelets, leukocytes and cerebrospinal fluid (CSF). This protein is able to act in the non-amyloidogenic pathway of cleavage of the amyloid precursor protein (APP) and, therefore, prevent the formation of the ²-amyloid peptide (A²), one of the pathological hallmarks of AD. Biomarkers that can diagnose AD in its early stages as MCI, preferably in samples that do not require highly invasive collection procedures, are the target of many recent studies and present a major clinical challenge in the area. Our group has been studying peripheral biomarkers for AD since 2010 with results that indicate that ADAM10 levels are decreased in platelets and increased in plasma of elderly people with this dementia, compared with older adults with MCI or cognitively healthy. We also identified that the ADAM10 platelet and plasma isoforms have distinct molecular weights, 60 and 50kDa, respectively, and that the plasma isoform, also present in the CSF, is inactive to cleave a specific fluorogenic substrate for ADAM10. More importantly, a recent longitudinal study showed that increased levels of plasma ADAM10 are able to predict the participants' cognitive worsening at the follow-up. The cognitive decline was more pronounced in individuals who had normal scores on the mini-mental state examination (MMSE) in the initial evaluation, when compared with those with altered scores at the beginning of the study. Thus, the assessment of ADAM10 levels in the plasma of patients with suspected cognitive decline, but who have not yet reached such a decline, may allow early interventions that could delay or even prevent AD onset. In this sense, the objectives of this study are: to evaluate the activity of ADAM10 in different cell fractions; to correlate the plasma and platelet levels of ADAM10 with the CSF levels, in the different groups of the study; to determine, by mass spectrometry, the complete sequences of the two isoforms of ADAM10 to better understand its biological functions and; finally, improve the detection of this protein in a electrochemical sensor already developed by the group, assessing ADAM10 levels in other types of dementia as well. The clinical impact of this study is related to a new approach that could be used in the diagnosis of this type of dementia, forming a panel of blood biomarkers with greater discriminative potential. In addition, this study will contribute to a better understanding of the biology of ADAM10 and the disease itself. (AU)

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