Since April 4, 2023 I can now say my name is Dr. Diana Zajac; I’m still getting used to saying it. I joined Dr. Steve Estus’ lab in March of 2019 and have focused my research on Alzheimer’s Disease (AD) genetics and the gut microbiome. Alzheimer’s Disease is an aging-related disease that has greatly increased in prevalence correlating with increased lifespans. AD patients show a progressive loss of memory and language skills that eventually leads to long-term memory impairment, a loss of self-sustaining daily life skills, and delusions. I’ve been a witness to the deleterious effects of AD on patients and caregivers when my grandmother Maria—Babcia Marysia—and later my grandfather Emil—Dziadek Emil—were diagnosed with the disease. I’ve dedicated my Dissertation to them. In my Defense presentation, I referenced the Forget-me-not flower, a small periwinkle-blue wildflower with yellow eyes that stands as a symbol of remembrance and love, and has been used to represent the cause to finding a cure for AD and Dementia. I discovered my connection to this flower when visiting my grandparents in Poland, so it has an additional depth of meaning for me as I’ve pursued a career in AD research.
During my four years in the Estus Lab, I focused on two major projects evaluating possible mechanisms of action of AD-associated genetic variants. My Dissertation work was focused on gut microbiome modulation in the context of AD. I first investigated APOE allelic effects on the gut microbiome profiles in murine transgenic models. I analyzed alpha- and beta-diversity of the gut microbiome and used a Classical Univariate Analysis and a Linear Discriminant Analysis of Effect Size to determine individual taxa associated with APOE status. I found APOE status affects the microbial community composition (beta-diversity) and that APOE4 mice had increased richness and evenness (alpha-diversity) of the microbiome, indicating better gut health. Additionally, changes in relative abundance of specific microbiota suggested short-chain fatty acid (SCFA)-producing bacteria were increased with APOE2 status compared with APOE3/3 and APOE4 status.
Association of the AD-protective APOE2 allele with increased SCFA-producing bacteria prompted our follow up study wherein we investigated the effect of SCFA treatment on gut microbiome profiles, amyloid accumulation, and cognitive decline in an APP/PS1 murine model of AD. In this study, we found that SCFA supplementation increased alpha-diversity in the gut of male mice, as well as the relative abundance of SCFA-producing microbiota, suggesting a feedforward mechanism. However, SCFA treatment did not affect AD pathology or memory. Whether or not SCFA supplementation can modify the gut microbiome in a way that improves cognitive decline or AD pathology remains inconclusive, as other studies with germ free or specific pathogen free mice have shown a positive effect.
To enhance my molecular genetics skills, I chose to do a second major project focused on the AD-risk gene INPP5D, quantifying splice isoforms as a function of AD-associated single nucleotide polymorphisms and neuropathology. I found that INPP5D isoforms increase in expression in patients with increased AD neuropathology, indicating that full-length and truncated isoforms of this gene may contribute to AD risk. This project then led me to investigate allelic expression imbalance of INPP5D in relation to the AD-associated SNP rs35349669. Through next generation sequencing I was able to confirm a SNP effect on INPP5D expression. Future directions for this work include haplotyping the samples to determine the direction of effect of the unequal allele expression.
The completion of both of these projects has led to three first-author publications and three middle-author publications. I’ve developed skills in genetics, genomics, microbiome analysis analysis, and bioinformatics. This diverse skillset is an example of the innovative research being done in the pursuit of a treatment for AD. This research lends itself to a deeper understanding of AD mechanisms, biomarkers and genetics that is another step towards a cure. Although most AD risk comes from genetics, this work supports the beneficial effects of healthy lifestyle choices—in this case, modulation of the gut microbiome. Now, I’m moving onto the next steps in my research career, and as I do so, I honor the memory of my grandparents by planting Forget-me-nots in my garden.