Thesis Seminars

Mark Osabutey - PhD Candidate, Neuroscience PhD Program

Thesis Proposal

Radiation-induced neuroinflammation has emerged as a pivotal clinical challenge, particularly for cancer patients undergoing radiotherapy. These adverse neurological effects are attributed to the activation of various immune cell lines, leading to cognitive impairments. Microglia, the primary immune cells of the central nervous system (CNS), have been identified as key players in these processes. Their essential functions, such as synaptic spine clearance and inflammatory response, undergo significant dysregulation post-radiation. Following genotoxic stress from ionizing radiation exposure, self-DNA is released from nuclear, mitochondrial, and extracellular sources into the cytosol. The cGAS-STING-Interferon pathway, a vital signaling cascade activated by binding to double-stranded DNA, is posited to play a central role in the dysregulated activation of microglia following cranial radiation. This pathway, integral to cellular innate immunity, offers a promising avenue for exploration, especially given the current limited understanding of its role in microglial activation following radiation. Therefore, deciphering the complex interplay between ionizing radiation exposure, microglial activation, and the cGAS-STING-Interferon pathway may contribute to targeted therapeutic strategies that prevent adverse effects. The primary hypothesis is that the cGAS-STING pathway is a key determinant of microglial behavior post-radiation and that its modulation can counteract radiation-induced cognitive impairments.

Aim 1 will employ in vitro techniques to investigate alterations in microglial states post-radiation exposure, emphasizing the role of the cGAS-STING pathway in mediating these changes. Furthermore, Aim 1 will explore the molecular mechanisms by which this pathway influences microglial activation and response.

Aim 2 is centered on elucidating the broader implications of microglial dysregulation on cognitive function post-radiation, utilizing a combination of behavioral tests and histological analyses. Based on preliminary findings, the hypothesis is that modulation of the cGAS-STING pathway can mitigate radiation-induced microglial dysregulation and its associated cognitive deficits.

Aim 3 will focus on potential therapeutic strategies targeting this pathway by using cGAS-STING knockout mice to test efficacy in ameliorating radiation-induced neurological consequences. Collectively, the outcomes from these aims will offer insights into radiation-induced neuroinflammation and pave the way for novel therapeutic interventions.

 Dec 08, 2023 @ 1:30 p.m.
 Medical Center | Lower Adolph (1-7619)

Linh Le - PhD Candidate, Neuroscience Graduate Program

Thesis Defense

Alzheimer’s disease (AD) is the most common cause of age-related dementia, characterized by well-known pathological hallmarks including extracellular amyloid β (Aβ) plaque deposition and neurofibrillary tangle accumulation. In the past decade, neuroinflammation has emerged as a crucial contributor to disease pathogenesis thanks to GWAS studies revealing various genetic variants of immune receptors as AD risk factors. These receptors are largely expressed by microglia, the resident innate immune cells of the central nervous system (CNS), making them a promising translational target for disease-modifying therapies. Here, we sought to elucidate the effects of two different approaches to modulating microglia functions in AD-like mouse models.

First, building on a multitude of evidence on the anti-inflammatory effects of the neurotransmitter norepinephrine (NE) and our previous work revealing that NE inhibits microglia surveillance activity via the β2 adrenergic receptor (AR), we explored the contribution of microglial β2 adrenergic signaling to AD pathology in 5xFAD mice, a commonly used model of amyloidosis. We observed an early degeneration of NE projections followed by locus coeruleus (LC) neuronal loss in more advanced disease stages, accompanied by a mild decrease in the levels of NE and its metabolite normetanephrine. Interestingly, we found that microglia in 5xFAD mice lost their sensitivity to β2AR signaling early and this was particularly evident in microglia that were in close proximity to Aβ plaques. We also described the important role of microglial β2AR signaling on AD, revealing opposing effects on amyloid pathology, whereby activation of microglial β2AR attenuated plaque deposition whereas inhibition worsened plaque pathology.

We next asked whether global pharmacologically-induced renewal of microglia, which is suggested to have “rejuvenating” and beneficial effects, could be a potential pathology-modifying therapy for AD. We induced microglial repopulation by depleting microglia with PLX5622 (a colony stimulating factor 1 receptor (CSF1R) inhibitor) and allowing them to replenish upon PLX5622withdrawal in two common models of AD: APP/PS1 and 3xTg mice. However, we observed no changes in amyloid pathology after forced repopulation of microglia, accompanied by a lack of cognitive improvement in a battery of behavioral tests.

We then set out to address sexual dimorphism in microglia, which potentially underlies the well-known differences in amyloid pathology in male versus female mice, with pathogenesis in females progressing much faster. To first understand how male and female microglia might differ in their survival and proliferation mechanisms, we examined the sex-specific effects of CSF1R inhibition using PLX3397. We confirmed that CSF1R inhibition resulted in significantly less depletion in female mice compared to male mice. Transcriptomic analysis of microglia revealed differential upregulation of autophagy, mitochondrial dynamics, and surveillance in PLX3397-treated female microglia compared to male microglia. Further studies are warranted to establish mechanistic links between these observations.

Taken together, our results suggested that specific, rather than global, manipulation of microglia might be effective in treating AD. Specifically, we highlighted the potential of leveraging microglial β2AR signaling for disease-modifying therapy.

 Dec 11, 2023 @ 12:00 p.m.
 Medical Center | Ryan Case Method Rm (1-9576)

Lia Calcines Rodriguez - PhD Candidate, Neuroscience Degree Program

In Alzheimer’s disease (AD), the most common form of dementia, women seem to be more susceptible as they show greater rates of cognitive decline, brain atrophy, and increased global pathology compared to men. AD is characterized by amyloid-β (Aβ) plaques, neurofibrillary tangles and neuroinflammation. In multiple rodent models of AD, sex differences have been identified in which pathology and neuroinflammation are more severe in females. Microglia, the resident innate immune cells of the central nervous system and key drivers of neuroinflammation, have been implicated in AD pathogenesis. Interestingly, recent studies have demonstrated that female AD mice exhibit an accelerated progression into the disease-associated microglia (DAM) state relative to male mice. Moreover, females exhibit impaired phagocytosis and higher Aβ plaque burden compared to male mice. In human post-mortem AD brains, sex differences in microglia morphology and transcriptome have also been reported where females exhibit a more inflammatory profile. Despite these observations, the contributions of microglia to the establishment of sex differences in AD is largely unexplored. We hypothesize that microglia possess cell-intrinsic sex-specific properties that drive differences in their functional responses to Aβ pathology and that these contribute to the sex differences in Aβ pathology. To address this question, we will isolate microglia of each sex from adult C57BL/6 (WT) mice and transplant them into adult microglia-deficient 5xFAD (5xFAD-FIRE) host brains of the same or opposite sex prior to the development of Aβ pathology.

Specific Aim 1: Characterize sex differences in the 5xFAD mouse model of amyloidosis. We will first characterize changes in Aβ burden, microglial reactivity, and microglia-plaque interaction in male and female 5.5-month-old 5xFAD mice using immunohistochemistry (IHC). We will also isolate microglia using fluorescent-activated cell sorting (FACS) and assess expression changes in DAM genes using real-time quantitative polymerase chain reaction (RT-qPCR).

Specific Aim 2: Determine whether microglia possess sex-specific cell-intrinsic differential responses to Aβ pathology and whether this drives the sex differences in Aβ pathology. First, we will isolate WT microglia via magnetic-activated cell sorting and confirm their purity and homeostatic state. We will then intracranially transplant female or male WT microglia into the male or female hippocampi of 2-month-old 5xFAD-FIRE mice, a model that exhibits aggressive amyloidosis and congenitally lacks microglia. Following transplantation, we will analyze the brains at 5.5 months of age as described in Aim 1. Moreover, using RT-qPCR, we will confirm that microglia retain their sex identity with a panel of sexually dimorphic genes that have previously been shown to remain unchanged upon transplantation. To our knowledge, no other study has sought to disentangle the intrinsic or extrinsic factors that give rise to the sex differences in AD. We believe that unraveling sex-specific cell-intrinsic properties of microglia in AD is the gateway to precision medicine.

 Dec 15, 2023 @ 12:00 p.m.
 Medical Center | Lower Adolph Aud (1-7619)