Our Research

Apolipoprotein E (APOE) is the most significant genetic risk factor for sporadic Alzheimer’s disease (AD). It is a protein that binds and transports lipids; this is critical in the brain and the body for normal cell functions such as building new membranes as well as many other functions. There are three common genotypes, with each genotype causing a change at a single amino acid. APOE2 (Cys112, Cys158) reduces the risk of AD, APOE3 (Cys112, Arg158) is considered neutral risk, and APOE4 (Arg112, Arg158) increases risk. These amino acids changes alter the structure of the protein, and hence their lipid binding properties, which can strongly impact the brain as lipids are crucial to its function, accounting for over 50% of its dry weight.

APOE is an O-glycoprotein, meaning it has carbohydrates bound to it. This is quite common with more than half of all proteins holding glycans. We have undertaken a detailed investigation of the glycosylation held by APOE in the cerebrospinal fluid (CSF) and plasma using mass spectrometry. We found that the glycosylation was quantitatively different with the CSF APOE holding more glycosylation and larger glycosylation particularly in the C-terminal lipid-binding domain. Plasma APOE on the other hand held more glycosylation on the N-terminal. This suggests that APOE glycosylation may aid in optimizing the binding properties of the APOE molecule for the specific region it is produced in, given that APOE in the brain and periphery bind different lipid molecules of vastly different sizes and compositions.

There is so much we need to understand about this molecule to really know why APOE4 behaves (or rather misbehaves) the way it does, and glycosylation is an important part of this missing information. Glycosylation is critical because it responds to the surrounding environment, changing with inflammation and disease. Dr. Flowers has worked on these types of modifications for over 10 years and has extensive expertise on how to analyze these modifications as well as how they change and why. She has broad experience developing the techniques to quantify these modifications and glycopeptides as well as determine their structures and deciphering the biological implications.

By understanding these changes in aging and AD we may be able to utilize this knowledge to diagnose AD at the very early stages. This has the potential to open up new early-treatment opportunities as we will be able to identify individuals who are at risk of developing AD well before any symptoms or amyloid accumulation occurs, which is when potential treatments may be more successful.

An early indicator of AD are brain metabolism changes, with reduced glucose uptake being seen in patients with mild cognitive impairment (MCI) and AD, indicating hypometabolism, and may even predict cognitive decline and AD conversion. AD risk factors also impact uptake: middle aged women, especially post-menopause, have significantly decreased glucose uptake and it is also reduced in APOE4 carriers.

Mitochondrial dysfunction is very likely involved in the metabolic deficiencies of AD. Mitochondrial enzyme activity is decreased in AD patient brain tissue, and the metabolic deficiencies are more pronounced in APOE4 carriers, with this genotype having reduced mitochondrial activity and proficiency. We are examining the metabolic differences in iPSC derived cells of different APOE genotypes, to further dissect the mechanisms behind such an important AD pathogenic indicator.