Jennifer Marie Coughlin, M.D. - US grants

PROJECT SUMMARY The goal of this project is to understand the contribution of persistent immune signaling to brain injury and repair in former National Football League (NFL) players through imaging and the study of circulating cytokines. We are concerned that such individuals develop cognitive impairment at a higher rate than the general population, which may be generalizable to those participating in other sports or with other forms of repeated traumatic brain injury (TBI). We focus on measuring the activity of microglia, the resident immune cells of the CNS, because of their importance in responding to brain injury. Based on published evidence and our preliminary data, we hypothesize that former NFL players have functionally hyper-activated microglia located in brain regions vulnerable to injury from collision sports. Such injury is marked by increased expression of translocator protein 18 KDa (TSPO) by microglial cells and reactive astrocytes. We further hypothesize that prolonged microglial activation in regions of repeated axonal injury causes neuronal energy and functional deficits that are mechanistically linked to neurodegeneration. We recently showed that [11C]DPA-713 (DPA) positron emission tomography (PET) can be used to measure increased expression of TSPO, a marker of brain injury and repair, in human neurodegenerative disease. In the first study of TSPO in NFL players, we found higher DPA binding in the brains of elderly players compared to elderly controls. Our newer published findings also reveal higher DPA binding in a cohort of young, active or recently retired NFL players compared to a control group of non-collision sport athletes in several of the same cortical and mesial temporal lobe structures tested in the published pilot of older players. Two young players recently returned for two-year follow-up imaging that revealed stable TSPO distribution in all brain regions tested, and one of them also showed PET-based evidence of increased tau burden in several brain regions at this second visit. He was among eight of 15 young NFL players with high peripheral pro-inflammatory marker profile at his baseline DPA imaging, supporting the hypothesized link between pro-inflammatory signaling and vulnerability to aberrant tau deposition after repeated TBI. We now propose to measure the distribution of TSPO using DPA PET in the brains of 35 recently former NFL players compared to a control group of 35 healthy, non-collision sport athletes (Aim 1) in parallel with biofluid (CSF, plasma) assays for markers of inflammation in the same population (Aim 2). The (two-year) persistence of these immune markers will be tested in Aim 3. Our design uses DPA, which has advantages over other 2nd-generation radiotracers for imaging TSPO. Our infrastructure for research of carefully selected young, former NFL players and controls is unique and yet aligns with methodology of other groups studying elderly NFL players. By characterizing the persistent inflammatory response in the brains of young, former NFL players, we will provide a basis for understanding ensuing symptomatology, informing prognosis, and suggesting new therapies that may generalize to other populations with TBI.

PROJECT SUMMARY This project will image the proliferation of activated microglia, resident immune cells in the brain, in virally suppressed people with human immunodeficiency virus (VS+PWH). The proposed work builds on our prior data that support a link between domain-specific cognitive impairment and localized, microglial activation in VS+PWH. In order to specifically image microglia in the living brain, we developed a radiotracer, [11C]CPPC that targets the colony stimulating factor 1 receptor (CSF1R) expressed by microglia. High CSF1R in brain has been reported in human postmortem cases of neurodegeneration including VS+PWH. High CSF1R was also found in frontal cortex of a simian immunodeficiency virus-infected macaque model of HIV, including virally suppressed cases after antiretroviral therapy. Furthermore, its role in potentiating proliferation of neurotoxic microglial response makes CSF1R an attractive target for therapeutic depletion of microglia in neurodegenerative disease. Use of [11C]CPPC with positron emission tomography (PET) in humans is well tolerated and allows us to localize and estimate microglial density in human brain in vivo. Based on published evidence and our preliminary data, we hypothesize higher CSF1R, consistent with proliferation of activated microglia, in the brains of VS+PWH compared to matched, uninfected controls (HIV-CON). Within VS+PWH, we hypothesize that higher regional CSF1R will be associated with lower cognitive performance, with the affected cognitive domains shaped by the regional pattern of high CSF1R. We therefore propose to use [11C]CPPC PET cross-sectionally in VS+PWH and HIV-CON to assess group differences in the CSF1R that marks microglial activation and proliferation. We will also assess relationships between regional CSF1R and cognitive performance. In summary, early detection of pathological microglial activity that is linked to neuropsychological impairment remains an unmet medical need, and CSF1R is a compelling microglial target for both imaging and therapy. Our study will provide preliminary data toward design of a larger scale proposal to study further the role of CSF1R signaling in cognitive impairment within VS+PWH. Furthermore, it may establish CPPC PET as a promising tool for studies aimed at monitoring localized microglial response in VS+PWH over aging and in response to neuroimmune therapy.

PROJECT SUMMARY This project will assess the availability of the cerebral ?7 nicotinic acetylcholine receptor (?7-nAChR) as a contributing factor in the early pathophysiology of Alzheimer's disease (AD). Converging data suggest that the ?7-nAChR promotes accumulation of A?42 in cholinergic neurons, particularly in basal forebrain and neocortical regions where the ?7-nAChR is more highly expressed. High cerebral ?7-nAChR availability (as we have observed in normal aging), promotes intracellular sequestration of A?42 in cholinergic cells, and the A?42-?7-nAChR interaction functionally antagonizes the ?7-nAChR, which may be linked to progressive, localized cell-death, synaptic loss, and aberrant neuronal activity long before spread of extracellular amyloid plaque. The A?42-?7-nAChR complex drives upregulated expression of the ?7-nAChR, fueling its further interactions with soluble A?42 species. Based on published evidence and our preliminary data, we hypothesize that higher, cerebral ?7-nAChR binding will be observed in patients with MCI, the prodrome to AD, compared to cognitively normal elderly controls using [18F]ASEM (ASEM) with positron emission tomography (PET). We further hypothesize that higher availability of ?7-nAChR in targeted brain regions will be associated with 1. lower cognitive performance and 2. higher circulating, AD-relevant, biofluid biomarkers such as ?7-nAChR autoantibodies within these participants. We will thus test for hypothesized high availability of the ?7-nAChR in MCI compared to cognitively normal individuals, and its relationship to cognitive performance (Aim 1), as well as its correlation with targeted biofluid markers that include plasma ?7- nAChR autoantibodies (Aim 2). Finally, in Aim 3, we will evaluate changes in ?7-nAChR availability using ASEM PET and its relationship to cognitive performance and these biofluid markers between baseline and two-year follow-up in a subset of participants from Aims 1 and 2. The goal of this proposal is to test for high brain availability of the ?7-nAChR in MCI and its relationship to cognition and circulating AD-relevant biomarkers - a critical step toward evaluating the ?7-nAChR as an AD imaging biomarker with diagnostic and therapeutic implications.

PROJECT SUMMARY/ABSTRACT Neuropsychiatric complications persist in people with HIV (PWH) despite suppressive antiretroviral therapy. Two common, often disabling conditions in PWH are cognitive impairment (CI) and major depressive disorder (MDD). However, the pathophysiology of central nervous system (CNS) dysfunction in PWH that results in these conditions remain elusive and thus a HIV high priority topic. The trafficking of activated peripheral blood mononuclear cells (PBMCs), specifically CD14+CD16+ monocytes, into brains of virally suppressed (VS)-PWH has emerged a putative contributor to neuroinflammation. We propose to test our hypothesis that VS-PWH will have blood brain barrier (BBB) disruption mechanistically linked to targeted, circulating soluble cytokines/chemokines and upregulation of PBMC surface proteins. The latter interact with tight junction and adherens junction proteins to weaken the BBB, promoting PBMC diapedesis into brain. BBB disruption may promote persistent neuroinflammation and altered neuronal activity contributing to neuropsychiatric sequela. To this end, we propose cross-sectional imaging and lumbar puncture to assess BBB integrity, with baseline and longitudinal neuropsychiatric assessments and blood sampling. 350 VS-PWH and 100 HIV-uninfected (HIV-) individuals will be recruited from the Johns G. Bartlett Clinic within the Johns Hopkins Hospital and in the surrounding Baltimore community. First, we aim to assess the effects of well-controlled HIV on the BBB and its contribution to neuropsychiatric conditions (Aim 1). We will assess BBB integrity using a novel, non-contrast magnetic resonance imaging technique that uses water-extraction-with-phase-contrast-arterial-spin-tagging (WEPCAST), to determine BBB permeability to water, and thereby to small molecules. We have shown this to be sensitive to BBB change in mild cognitive impairment, a precursor to Alzheimer?s disease. Moreover, we have found WEPCAST to be well-tolerated and estimate PS values well in VS-PWH. Second, we aim to assess the relationship between circulating soluble markers, PBMC-associated markers, and BBB permeability to small molecules, which collectively may promote diapedesis into brain (Aim 2). We target factors implicated in a heightened transmigration of activated PBMCs across the BBB into brain, where they may contribute to neuronal damage and neuropsychiatric burden in VS-PWH. Finally, we aim to examine the relationship of activated PBMCs that transmigrate an intact BBB model to BBB permeability to small molecules (Aim 3). We innovate with the real-time assessment of ex vivo cellular function (BBB model) and in vivo BBB measures (WEPCAST). After 5 years of funding, this R01 will advance our understanding of BBB integrity and related PBMC migration into the brains of VS-PWH, which may contribute to neuroinflammation and related neuropsychiatric burden. These findings will inform next steps in the development of therapeutic approaches to minimize PBMC contribution to neuroinflammation in VS-PWH.