In a first for Alzheimer’s disease (AD) research, investigators from Cleveland Clinic are attempting to identify sex-based differences in the blood-based proteome of patients with the disease. Through analysis of thousands of plasma proteins in cerebrospinal fluid (CSF) biospecimens, they hope to identify candidate biomarkers that can one day be used to improve clinical care for women with AD.
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“The evidence from this project will provide critical missing information about the female plasma proteome signature in AD, which is needed for accurate biomarkers and effective therapeutic strategies for women,” says Lynn Bekris, PhD, principal investigator of the pilot study and a researcher in Cleveland Clinic’s Genomic Medicine Institute. “Our ultimate goal is to enhance precision medicine targeting sex-specific AD pathological processes.”
Supported by funding from a Women’s Alzheimer’s Movement Research Award, the study has a novel design in that findings in CSF, rather than a clinical diagnosis, will be used to classify participants as having AD-related pathology. Relative levels of plasma proteins will be measured in an unbiased, multiplex fashion with aptamer-based SomaScan® technology.
This research is an outgrowth of a previous exploratory study of plasma from patients with early-stage AD conducted by the same Cleveland Clinic investigators. It provided support for the hypothesis that alterations in sTREM2-related inflammatory activity in plasma is stage-specific, but the mechanisms underlying the association are not fully understood.
While amyloid and tau pathology in AD has been well studied, genetic research suggests that other mechanisms, such as dysfunctional immune activity and lipid metabolism, also play a role in the disease. In addition, although more than 60% of AD cases are in women, little is known about sex differences in peripheral biological systems specifically altered in women with the disease. Autopsy studies have shown that women appear to have a more rapid cognitive decline after AD diagnosis while living longer and having more amyloid and tau than men.
“Age is the strongest risk factor for AD, so some of the heightened risk is related to women generally living longer than men,” Dr. Bekris notes. “But not all of the risk to women can be attributed to that. Analyzing blood from living patients is a great way to understand sex differences because plasma harbors many of the signaling proteins involved in the immune response and we can also track disease progression over time.”
The cohort for the new exploratory study consists of consists of people with known AD-related pathology defined by their CSF amyloid-tau-neurodegeneration (ATN) status. This includes cognitively normal controls, cognitively impaired patients with early AD who have mild cognitive impairment (MCI) and patients with AD. CSF measures of ATN will be provided by the Cleveland Clinic Lou Ruvo Center for Brain Health Biobank and the Cleveland Alzheimer’s Disease Research Center.
The research has two aims. One is to define sex differences in plasma inflammatory factors, including the soluble TREM2 protein, by ATN group and validate those findings with the SomaScan assay to test the hypothesis that the inflammatory response profile is different in women than in men with AD. Another aim is to discover sex differences in the plasma proteome and identify and establish the feasibility of an aptamer-based biomarker.
In the first part of the study, the investigators will analyze 39 inflammatory factors in the CSF specimens with a Luminex® multiplex bead- and antibody-based assay. They will perform differential analyses within each sex between ATN groups and between sexes within ATN groups, with adjustment for age, APOE4 genotype and cognitive status (MCI vs. AD). ATN network analyses also will be done to identify overlapping biomarker candidates specific to women rather than men.
In the second part of the study, biological systems will be delineated through a SomaLogic aptamer-based assay of 7,000 different proteins and ATN differential and network analyses. Results of those analyses will be used to select significant candidate biomarkers. Receiver operating characteristic analyses will then be performed to determine which single candidate biomarker or panel of candidate biomarkers have the highest sensitivity and specificity in women or in men.
Once the project aims are achieved, the researchers plan to apply for a grant to support replication and longitudinal studies to gain an understanding of how other biological systems contribute to AD progression in women. The Cleveland Alzheimer’s Disease Research Center also will be collecting biospecimens from participants annually. This will enable the investigators to track disease progression in patients with AD and in those who are cognitively normal but at risk for AD to determine sex-specific trajectories of candidate biomarkers.
“Neurodegenerative diseases in adults are complex and each has a specific alteration or pathology that defines it,” says Dr. Bekris. “In many patients, the proteins from different diseases overlap. One of our future goals, once we have identified female-specific, blood-based biomarkers associated with AD-related pathology, is to validate them in a population with Lewy body dementia.”
She notes that Lewy body dementia can sometimes have a mix of both AD-related pathology (ATN) and Lewy body hallmarks specific to Lewy body dementia. “For this reason, it will be important to understand whether patients, especially women, with both Lewy body pathology and AD-related pathology also have a similar ATN-specific plasma signature as AD patients,” Dr. Bekris explains. “This will further enhance sex-specific precision medicine therapeutic strategies for adult-onset neurodegenerative diseases with mixed pathologies that include AD-related pathology.”