Glial progenitor cells of the adult human white and grey matter are contextually distinct.

Genomic analyses have revealed heterogeneity among glial progenitor cells (GPCs), but the compartment selectivity of human GPCs (hGPCs) is unclear. Here, we asked if GPCs of human grey and white brain matter are distinct in their architecture and associated gene expression. RNA profiling of NG2-defined hGPCs derived from adult human neocortex and white matter differed in their expression of genes involved in Wnt, NOTCH, BMP and TGFß signaling, suggesting compartment-selective biases in fate and self-renewal. White matter hGPCs over-expressed the BMP antagonists BAMBI and CHRDL1, suggesting their tonic suppression of astrocytic fate relative to cortical hGPCs, whose relative enrichment of cytoskeletal genes presaged their greater morphological complexity. In human glial chimeric mice, cortical hGPCs assumed larger and more complex morphologies than white matter hGPCs, and both were more complex than their mouse counterparts. These findings suggest that human grey and white matter GPCs comprise context-specific pools with distinct functional biases.

Astrogliosis, neuritic microstructure, and sex effects: GFAP is an indicator of neuritic orientation in women.

BACKGROUND: Data from human studies suggest that immune dysregulation is associated with Alzheimer's disease (AD) pathology and cognitive decline and that neurites may be affected early in the disease trajectory. Data from animal studies further indicate that dysfunction in astrocytes and inflammation may have a pivotal role in facilitating dendritic damage, which has been linked with negative cognitive outcomes. To elucidate these relationships further, we have examined the relationship between astrocyte and immune dysregulation, AD-related pathology, and neuritic microstructure in AD-vulnerable regions in late life. METHODS: We evaluated panels of immune, vascular, and AD-related protein markers in blood and conducted in vivo multi-shell neuroimaging using Neurite Orientation Dispersion and Density Imaging (NODDI) to assess indices of neuritic density (NDI) and dispersion (ODI) in brain regions vulnerable to AD in a cohort of older adults (n = 109). RESULTS: When examining all markers in tandem, higher plasma GFAP levels were strongly related to lower neurite dispersion (ODI) in grey matter. No biomarker associations were found with higher neuritic density. Associations between GFAP and neuritic microstructure were not significantly impacted by symptom status, APOE status, or plasma Aß42/40 ratio; however, there was a large sex effect observed for neurite dispersion, wherein negative associations between GFAP and ODI were only observed in females. DISCUSSION: This study provides a comprehensive, concurrent appraisal of immune, vascular, and AD-related biomarkers in the context of advanced grey matter neurite orientation and dispersion methodology. Sex may be an important modifier of the complex associations between astrogliosis, immune dysregulation, and brain microstructure in older adults.

Incorporating ethical principles into clinical research protocols: a tool for protocol writers and ethics committees.

A novel Protocol Ethics Tool Kit ('Ethics Tool Kit') has been developed by a multi-stakeholder group of the Multi-Regional Clinical Trials Center of Brigham and Women's Hospital and Harvard. The purpose of the Ethics Tool Kit is to facilitate effective recognition, consideration and deliberation of critical ethical issues in clinical trial protocols. The Ethics Tool Kit may be used by investigators and sponsors to develop a dedicated Ethics Section within a protocol to improve the consistency and transparency between clinical trial protocols and research ethics committee reviews. It may also streamline ethics review and may facilitate and expedite the review process by anticipating the concerns of ethics committee reviewers. Specific attention was given to issues arising in multinational settings. With the use of this Tool Kit, researchers have the opportunity to address critical research ethics issues proactively, potentially speeding the time and easing the process to final protocol approval.

Scaled Complexity of Mammalian Astrocytes: Insights From Mouse and Macaque.

Astrocytes intricately weave within the neuropil, giving rise to characteristic bushy morphologies. Pioneering studies suggested that primate astrocytes are more complex due to increased branch numbers and territory size compared to rodent counterparts. However, there has been no comprehensive comparison of astrocyte morphology across species. We employed several techniques to investigate astrocyte morphology and directly compared them between mice and rhesus macaques in cortical and subcortical regions. We assessed astrocyte density, territory size, branching structure, fine morphological complexity, and interactions with neuronal synapses using a combination of techniques, including immunohistochemistry, adeno-associated virus-mediated transduction of astrocytes, diOlistics, confocal imaging, and electron microscopy. We found significant morphological similarities between primate and rodent astrocytes, suggesting that astrocyte structure has scaled with evolution. Our findings show that primate astrocytes are larger and more numerous than those in rodents but contest the view that primate astrocytes are morphologically far more complex.

Synergistic effects of GFAP and Aß42: Implications for white matter integrity and verbal memory across the cognitive spectrum.

Background: Plasma glial fibrillary acidic protein (GFAP), an astrocytic biomarker, has previously been linked with Alzheimer's disease (AD) status, amyloid levels, and memory performance in older adults. The neuroanatomical pathways by which astrogliosis/astrocyte reactivity might impact cognitive outcomes remains unclear. We evaluated whether plasma GFAP and amyloid levels had a synergistic effect on fornix structure, which is critically involved in AD-associated cholinergic pathways. We also examined whether fornix structure mediates associations between GFAP and verbal memory. Methods: In a cohort of both asymptomatic and symptomatic older adults (total n = 99), we assessed plasma GFAP, amyloid-ß42 (Aß42), other AD-related proteins, and vascular markers, and we conducted comprehensive memory testing. Tractography-based methods were used to assess fornix structure with whole brain diffusion metrics to control for diffuse alterations in brain white matter. Results: In individuals in the low plasma amyloid-ß42 (Aß42) group, higher plasma GFAP was associated with lower fractional anisotropy (FA; p = 0.007), higher mean diffusivity (MD; p < 0.001), higher radial diffusivity (RD; p < 0.001), and higher axial diffusivity (DA; p = 0.001) in the left fornix. These associations were independent of APOE gene status, plasma levels of total tau and neurofilament light, plasma vascular biomarkers, and whole brain diffusion metrics. In a sub-analysis of participants in the low plasma Aß42 group (n = 33), fornix structure mediated the association between higher plasma GFAP levels and lower verbal memory performance. Discussion: Higher plasma GFAP was associated with altered fornix microstructure in the setting of greater amyloid deposition. We also expanded on our prior GFAP-verbal memory findings by demonstrating that in the low plasma Aß42 group, left fornix integrity may be a primary white matter conduit for the negative associations between GFAP and verbal memory performance. Overall, these findings suggest that astrogliosis/astrocyte reactivity may play an early, pivotal role in AD pathogenesis, and further demonstrate that high GFAP and low Aß42 in plasma may reflect a particularly detrimental synergistic role in forniceal-memory pathways.

Building and Characterization of an Affordable diOlistic Device for Single-Cell Labeling in Rodent and Non-Human Primate Brain Slices.

In the brain, cell morphology often reflects function and thus provides a first glance into cell-specific changes in health and disease. Studying the morphology of individual cells, including neurons and glia, is essential to fully understand brain connectivity and changes in disease states. Many recent morphological studies of brain cells have relied on transgenic animals and viral vectors to label individual cells. However, transgenic animals are not always available, and in non-human primate (NHP) models, viral transduction poses several practical and financial challenges, limiting the number of researchers that can thoroughly investigate cell morphology in NHP or other non-transgenic animals. The diOlistic system for delivering fluorescent lipophilic dye-coated gold or tungsten particles into brain tissue has been used to label single cells, but the currently available systems are expensive, have limited applications, and are rare in laboratories. Investigations of cell morphology without transgenic or viral approaches rely on immunohistochemical markers that may not reveal structural detail, such as in astrocytes. To overcome these practical limitations to expand our understanding of cell morphology across species with an emphasis on astrocytes, we constructed a low-cost ballistic method to deliver dye-coated gold or tungsten particles into NHP and rodent brain slices. We have optimized the tissue processing parameters to achieve penetration of DiI-coated particles, allowing for the complete reconstruction of individual cells within a brain slice. While we report on astrocytes in rodent and NHP brain slices, this protocol can be adapted and implemented across species and tissue types to evaluate cell morphology. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Building the diOlistic device Basic Protocol 2: Preparation of dye "bullet" carriers Basic Protocol 3: Perfusion, brain sectioning, and diOlistic labeling Alternate Protocol: Immunohistochemical labeling of sections prior to diOlistic bombardment.

Characterization of the GfaABC1D promoter to selectively target astrocytes in the rhesus macaque brain.

BACKGROUND: The study of astrocytic functions in non-human primates (NHPs) has been hampered by the lack of genetic tools to selectively target astrocytes. Viral vectors with selective and efficient transduction of astrocytes could be a potent tool to express marker proteins, modulators, or sensors in NHP astrocytes, but the availability of thoroughly characterized astrocytic selective promoter sequences to use in these species remains extremely limited. NEW METHOD: We describe the specificity and efficiency of an astrocyte-specific promoter, GfaABC1D in the brain of the rhesus macaque, with emphasis in basal ganglia regions. AAV5-pZac2.1-GfaABC1D-tdTomato was locally injected into the globus pallidus external segment (GPe) and putamen. The extent, efficiency, and specificity of transduction was analyzed with immunohistochemistry at the light and electron microscope levels. RESULTS: The GfaABC1D promoter directed the expression of tdTomato in an astrocyte-specific manner in directly or indirectly targeted regions (including both segments of the globus pallidus, putamen, subthalamic nucleus and cortex). COMPARISON WITH EXISTING METHODS: Due to its small size, the GfaABC1D promoter is advantageous over other previously used glial fibrillary acidic protein-based promoter sequences, facilitating its use to drive expression of various transgenes in adeno-associated viruses (AAV) or other viral vectors. CONCLUSION: GfaABC1D is an efficient promoter that selectively targets astrocytes in the monkey basal ganglia and expands the viral vector toolbox to study astrocytic functions in non-human primates.

Development of the Colorado posterior cortical questionnaire within an Alzheimer's disease study cohort.

INTRODUCTION: Non-amnestic presentations of neurodegenerative dementias, including posterior- and visual-predominant cognitive forms, are under-recognized. Specific screening measures for posterior cortical symptoms could allow for earlier, more accurate diagnosis and directed treatment. METHODS: Based on clinical experience with posterior cortical atrophy evaluations, high-yield screening questions were collected and organized into a 15-item self-report questionnaire, titled the Colorado Posterior Cortical Questionnaire (CPC-Q). The CPC-Q was then piloted within a longitudinal cohort of cognitive aging, including 63 older adults, including healthy older adults (n = 33) and adults with either amnestic Alzheimer's disease (n = 21) or posterior cortical atrophy (PCA, n = 9). RESULTS: The CPC-Q demonstrated acceptable psychometric properties (internal consistency, α = 0.89; mean item-total correlation = 0.62), correlated strongly with visuospatial measures on cognitive testing (p < 0.001), and could distinguish PCA from non-PCA groups (p < 0.001; AUC 0.95 (95% CI 0.88, 1.0)). CONCLUSIONS: The CPC-Q captured posterior cortical symptoms in older adults, using a gold standard of expert consensus PCA diagnosis. Future studies will validate the CPC-Q in a larger cohort, with recruitment of additional PCA participants, to evaluate its convergent and discriminant validity more thoroughly. As a short, self-report tool, the CPC-Q demonstrates potential to improve detection of non-amnestic neurodegenerative dementias in the clinical setting.

Neural correlates of daily function: A pilot study of the white matter retrogenesis hypothesis and three separate performance-based functional assessments.

OBJECTIVE: Increasing evidence points to mild alterations in everyday functioning early in the course of Alzheimer's disease and related dementias (ADRD), despite prior research suggesting functional declines occur primarily in later stages. However, daily function assessment is typically accomplished with subjective self- or informant-report, which can be prone to error due to various factors. Performance-based functional assessments (PBFAs) allow for objective evaluation of daily function abilities, but little is known on their sensitivity to the earliest ADRD-related brain alterations. We aimed to determine the neural correlates of three different PBFAs in a pilot study. METHOD: A total of 40 older participants (age = 70.9 ± 6.5 years; education = 17.0 ± 2.6 years; 51.5% female; 10.0% non-White; 67.5% cognitively normal) completed standardized PBFAs related to medication management (MM), finances (FIN), and communication abilities (COM). Participants underwent diffusion tensor imaging (DTI) scans, from which mean fractional anisotropy (FA) composite scores of late- (LMF) and early myelinated (EMF) fibers were calculated. Linear regression analyses controlling for age and global cognition were used to assess the relationship of PBFAs with FA. RESULTS: Better performance on MM was associated with higher mean FA on LMF composite (t38 = 2.231, p = .032), while FIN and COM were not (ps > .05). PBFAs were not associated with EMF (p > .05). CONCLUSIONS: Our preliminary findings demonstrate better performance on a PBFA of medication management is associated with higher FA in late-myelinated white matter tracts. Despite a small sample size, these results are consistent with growing evidence that performance-based functional assessments may be a useful tool in identifying early changes related to ADRD. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Lifetime surgical exposure, episodic memory, and forniceal microstructure in older adults.

Introduction: Aging is associated with heterogeneous cognitive trajectories. There is considerable interest in identifying risk factors for pathological aging, with recent studies demonstrating a link between surgical procedures and proximal cognitive decline; however, the role of lifetime exposure to surgical procedures and cognitive function has been relatively unexplored. This pilot study aimed to evaluate the association between total lifetime surgical procedures and memory function in older adults. Methods: A cohort of 62 older adults underwent a neuropsychological evaluation and health history assessment. Self-reported lifetime surgical history was categorized as "cardiac" or "non-cardiac." General linear models were fit with demographics as nuisance covariates, and the total number of non-cardiac surgeries as our predictor of interest. Total scores on measures of episodic memory, language, working memory, fluency, and visuospatial function were separate outcome variables. In a secondary analysis, vascular risk factors were included as covariates. Diffusion tensor imaging was obtained for exploratory analyses of selected regions of interest. Results: The mean age of participants was 70, and 0-13 lifetime non-cardiac surgical procedures were reported. Higher numbers of lifetime non-cardiac surgical procedures were associated with worse verbal learning and memory (p = .04). The negative association between lifetime non-cardiac procedures and cognition was specific to memory. Exploratory analyses showed that higher number of lifetime non-cardiac procedures was related to lower FA in the fornix body (p = .02). Conclusions: These results of this pilot study suggest that greater lifetime exposure to surgery may be associated with worse verbal learning and memory in healthy older adults. These findings add to a growing body of literature suggesting that cumulative medical events may be risk factors for negative cognitive outcomes.

Cerebrospinal Fluid and Plasma Levels of Inflammation Differentially Relate to CNS Markers of Alzheimer's Disease Pathology and Neuronal Damage.

Inflammatory markers have been shown to predict neurocognitive outcomes in aging adults; however, the degree to which peripheral markers mirror the central nervous system remains unknown. We investigated the association between plasma and cerebrospinal fluid (CSF) markers of inflammation, and explored whether these markers independently predict CSF indicators of Alzheimer's disease (AD) pathology or neuronal damage. Plasma and CSF samples were analyzed for inflammatory markers in a cohort of asymptomatic older adults (n = 173). CSF samples were analyzed for markers of AD pathology (Aß42, phosphorylated tau [p-tau], sAßPPß) or neuronal damage (total tau; neurofilament light chain) (n = 147). Separate linear models for each analyte were conducted with CSF and plasma levels entered simultaneously as predictors and markers of AD pathology or neuronal damage as outcome measures. Strong associations were noted between CSF and plasma MIP-1ß levels, and modest associations were observed for remaining analytes. With respect to AD pathology, higher levels of plasma and CSF IL-8, CSF MIP-1ß, and CSF IP-10 were associated with higher levels of p-tau. Higher levels of CSF IL-8 were associated with higher levels of CSF Aß42. Higher CSF sAßPPß levels were associated with higher plasma markers only (IL-8; MCP-1). In terms of neuronal injury, higher levels of plasma and CSF IL-8, CSF IP-10, and CSF MIP-1ß were associated with higher levels of CSF total tau. Exploratory analyses indicated that CSF Aß42 modifies the relationship between plasma inflammatory levels and CSF tau levels. Results suggest that both plasma and CSF inflammatory markers independently relay integral information about AD pathology and neuronal damage.

Are Transplant Recipients Human Subjects When Research Is Conducted on Organ Donors?

Interventional research on deceased organ donors and donor organs prior to transplant holds the promise of reducing the number of patients who die waiting for an organ by expanding the pool of transplantable organs and improving transplant outcomes. However, one of the key challenges researchers face is an assumption that someone who receives an organ that was part of an interventional research protocol is always a human subject of that same study. The consequences of this assumption include the need for oversight by an institutional review board and for research-level informed consent from transplant recipients, all within the complex practical realities of the organ donation and transplantation process in the United States. The current national focus on this issue provides an opportunity to think critically about the policy goals of the human subjects regulations and their application to the nascent field of deceased organ donor intervention research. We propose that for donor research where the transplant recipient does not fall under the definition of human subject, the clinical consent model-rather than the consent model used for human research subjects-best facilitates the policy objectives of balancing clinical innovation, transparency, and protection of patients in an ethically responsible and legally compliant manner.

A Framework for Conducting Deceased Donor Research in the United States.

There are a number of regulatory barriers both perceived and real that have hampered widespread clinical research in the field of donation and transplantation. This article sets forth a framework clarifying the existing legal requirements and their application to the conduct of research on deceased donors and donor organs within the United States. Recommendations are focused on resolving some of the ambiguity surrounding deceased donor authorization for research, Health Insurance Portability and Accountability Act requirements and the role of institutional review board oversight. The successful conduct of clinical research in the field of donation and transplantation requires an understanding of these regulatory nuances as well as identification of important ethical principles to consider. Facilitation of these concepts will ultimately provide support for innovative research designed to increase the availability of organs for transplantation. Further work identifying the optimal infrastructure for overview of clinical research in the field should be given priority.

Centralized banks for human embryonic stem cells: a worthwhile challenge.

Centralized banking of human embryonic stem (hES) cells is an endeavor that can benefit individual research efforts and enhance international collaboration but is complicated by the fact that the science is rapidly evolving in an environment of heterogeneous laws, guidelines, and ethical standards. Written from the vantage point of regulatory professionals, this article provides an overview of the benefits of and challenges facing hESC banking enterprises in general with a focus on a global centralized banking effort.