Autosomal Dominant Alzheimer’s Disease (ADAD) can result from a pathogenic variant in the PSEN2 gene, which encodes an integral membrane protein called Presenilin 2. This variant has been shown to result in a harmful change in the balance of amyloid-β types in neurons, which has been hypothesized to increase risk of dementia. The diverse capabilities of Presenilin give reason to hypothesize that there may be other effects of the variant protein that are connected to ADAD pathogenesis. Reduced spine density, a feature of ADAD pathology, may be caused by overactivity of synaptic pruning. This activity is mediated by resident innate immune cells in the brain called microglia. We sought to explore the effects of PSEN2 variants on microglia-neuronal interactions via the assessment of synaptic pruning in a human induced pluripotent stem cell (hiPSC) derived in vitro model. We differentiated CVIA2 isogenic and PSEN2 N141I variant hiPSCs into both microglia and neurons. Utilizing a coculture of both wild-type neurons and microglia with the PSEN2 N141I variant, we performed immunocytochemistry for synaptic proteins Synapsin 1 and PSD95a. We then imaged the microglia and neurons using confocal microscopy. We assessed differences in synaptic pruning by quantifying immunofluorescent signal of Synapsin in microglia. Specifically, we looked at the colocalization of synaptic protein expression with signal from microglia-specific protein Iba1. We hypothesized that the variant microglia would contain a significantly different amount of signal for Synapsin compared to that of a control sample of wild-type microglia and neurons, implying a change to synaptic pruning function. If altered microglial synaptic pruning activity is shown to play a role in ADAD pathogenesis, targeting microglia could become a possible therapeutic treatment for patients.

Alzheimer’s disease (AD) is a neurodegenerative disease that impacts millions of people and costs billions of dollars annually, with both estimates increasing as our aging population grows. Women are diagnosed with AD at a 2:1 higher rate than men, although the biological drivers of this difference remain elusive. Previous studies have demonstrated that changes to the function of microglia – the brain’s immune cells – observed during AD may be driving disease progression. Furthermore, microglia morphology is related to its function. Thus, we seek to characterize differences in microglia morphology between men and women with and without AD. We hypothesize that microglia from women have, on average, a more disease-associated morphology than those of men, and that differences are exacerbated in individuals with AD. We obtained tissue from the dorsolateral prefrontal cortex of 48 individuals who donated their brains to AD research at UW. We conducted immunohistochemistry (IHC) to stain for microglia markers (IBA1) and two markers of AD pathology (AT8 to stain for phosphorylated Tau and a pan-amyloid β stain). I imaged the samples on a Leica SP8 confocal microscope at multiple depths, which allowed us to compose a 3D rendering of the tissue through an image analysis software called IMARIS. Using IMARIS, I quantitatively measured key aspects of each microglia, such as volume and branching details. Using the data from 12-20 microglia per person, we used multiple regression to test for differences between men and women in both healthy and AD cohorts. We anticipate there are differences in the various measurements of microglial morphology between men and women with AD, which may partially explain the discrepancy in AD rates between sexes. This research is important to better understand the role of sex in AD pathology and help contextualize molecular differences observed in the larger project to which it belongs.

Some older individuals exhibit the pathological hallmarks (i.e., amyloid-beta plaques and tau-containing neurofibrillary tangles) of Alzheimer’s disease (AD) yet remain cognitively intact, a phenomenon known as resilience. Microglia, the primary immune cells of the central nervous system are important for clearance of debris and responding to injury in the brain. When exposed to aggregated proteins, they can release inflammatory molecules toxic to neurons.  Because neuroinflammation has been implicated in neurodegeneration, understanding how microglia interact with Aβ could provide insight into immune mechanisms that support cognitive preservation despite AD pathology. In patients with AD who have dementia, it is known that their microglia cluster around amyloid-beta (Aβ) plaques which possibly contribute to damaging inflammation.  Whether microglia in resilient individuals share the same relationship to plaque is unknown. This study investigated whether microglia in resilient individuals differ in their spatial relationship to amyloid plaques compared to non-resilient individuals in the dorsolateral prefrontal cortex. Using confocal montage images from postmortem human brain tissue where immunofluorescence stained for Iba1+ microglia and PanAβ+ Aβ plaques, I quantified the proportion of microglia clustering around Aβ in three groups: 1) individuals with symptomatic AD, 2) cognitively intact individuals with AD pathology (resilient), and 3) cognitively intact individuals with no/low AD pathology (resistant). By generating 2D surface reconstructions, I measured microglia-Aβ overlap and proximity to assess colocalization patterns. I identified differences in microglia-Aβ colocalization between these three groups. This approach can help understand how microglial interactions with Aβ may contribute to resilience mechanisms and could inform novel therapeutic strategies for AD.