Sustained microglial depletion with CSF1R inhibitor impairs parenchymal plaque development in an Alzheimer's disease model.

Many risk genes for the development of Alzheimer's disease (AD) are exclusively or highly expressed in myeloid cells. Microglia are dependent on colony-stimulating factor 1 receptor (CSF1R) signaling for their survival. We designed and synthesized a highly selective brain-penetrant CSF1R inhibitor (PLX5622) allowing for extended and specific microglial elimination, preceding and during pathology development. We find that in the 5xFAD mouse model of AD, plaques fail to form in the parenchymal space following microglial depletion, except in areas containing surviving microglia. Instead, Aβ deposits in cortical blood vessels reminiscent of cerebral amyloid angiopathy. Altered gene expression in the 5xFAD hippocampus is also reversed by the absence of microglia. Transcriptional analyses of the residual plaque-forming microglia show they exhibit a disease-associated microglia profile. Collectively, we describe the structure, formulation, and efficacy of PLX5622, which allows for sustained microglial depletion and identify roles of microglia in initiating plaque pathogenesis

Childbearing vs. clinical trial participation: is it one or the other?

Abstract Recent advances have shed light on the importance of early therapeutic intervention for neurodegenerative diseases. Primary prevention trials present a potential disease-modifying strategy for pre-symptomatic patients of autosomal dominant neurodegenerative diseases (ADND), such as early onset familial Alzheimer’s disease (AD) and Huntington’s disease (HD). As trials target earlier disease stages, however, prospective participants face new ethical and logistical challenges, namely childbearing and reproductive health decisions. Since pregnancy is an exclusion criteria for such trials, participants of reproductive age must choose between participating in research and having a family. Such decisions carry significant burdens for ADND patients that if left unaddressed could impact patient well-being and the field as whole. We use our perspective as scientists, advocates, and ADND family members to highlight current shortcomings in the field regarding trial participation and family planning issues for ADND patients and call for the establishment of a normative standard to address these concerns

Intravenous infusion of monocytes isolated from 2-week-old mice enhances clearance of Beta-amyloid plaques in an Alzheimer mouse model.

Alzheimer's disease (AD) is characterized by the deposition of β-amyloid (Aβ) senile plaques and tau-associated neurofibrillary tangles. Other disease features include neuroinflammation and cholinergic neurodegeneration, indicating their possible importance in disease propagation. Recent studies have shown that monocytic cells can migrate into the AD brain toward Aβ plaques and reduce plaque burden. The purpose of this study was to evaluate whether the administration of intravenous infusions of 'young' CD11b-positive (+) monocytes into an AD mouse model can enhance Aβ plaque clearance and attenuate cognitive deficits. Peripheral monocytes were isolated from two-week-old wildtype mice using the Pluriselect CD11b+ isolation method and characterized by FACS analysis for surface marker expression and effective phagocytosis of 1 μm fluorescent microspheres, FITC-Dextran or FITC-Aβ1-42. The isolated monocytes were infused via the tail vein into a transgenic AD mouse model, which expresses the Swedish, Dutch/Iowa APP mutations (APPSwDI). The infusions began when animals reached 5 months of age, when little plaque deposition is apparent and were repeated again at 6 and 7 months of age. At 8 months of age, brains were analyzed for Aβ+ plaques, inflammatory processes and microglial (Iba1) activation. Our data show that infusions of two-week-old CD11b+ monocytes into adult APPSwDI mice results in a transient improvement of memory function, a reduction (30%) in Aβ plaque load and significantly in small (<20 μm) and large (>40 μm) plaques. In addition, we observe a reduction in Iba1+ cells, as well as no marked elevations in cytokine levels or other indicators of inflammation. Taken together, our findings indicate that young CD11b+ monocytes may serve as therapeutic candidates for improved Aβ clearance in AD

FACS analysis of CD11b-positive peripheral blood mouse monocytes.

<p>FACS analysis was performed on peripheral blood mouse monocytes isolated from young (14 days; <b>A</b>; n = 13) or adult (6 month, <b>B</b>; n = 9) C57BL/6N mice following CD11b pluriBead (Pluriselect) cell separation. CD11b-positive cells were evaluated immediately following isolation (<b>A&B</b>; n = 9) or following 24 h incubation (<b>C-I</b>; n = 9). Cells were evaluated for surface marker expression of CD11b and CD45 (<b>E&F</b>, green) as well as their ability to phagocyte 1 μm fluorescent microspheres (<b>G</b>; n = 10), or FITC-Dextran (<b>H</b>; n = 11) or FITC-Aβ_1–42 (<b>I</b>; n = 13). IgG controls (IgG2a and IgG1) were used as a negative control (<b>D</b>).</p

Experimental set-up for monocyte infusions, cognitive evaluations and neurobiological analysis.

<p>At 5 months of age (mice do not display any extracellular plaques), APPSwDI mice were evaluated by the black/white (B/W) box and 8-arm radial maze, which included both training, learning and retention sessions. Following these evaluations, mice were infused intravenously with (I) approx. 5 x 10⁶ young CD11b+ monocytes (isolated from 14 day-old wildtype mice; n = 8) or with (II) saline (n = 7). Every two weeks, animals were tested in the B/W box and 8-arm maze for changes in anxiety and memory, respectively. Intravenous infusions were repeated at months 6 and 7, following cognitive evaluations. At 8 months of age, mice were sacrificed (TAKE) following retention and analyzed.</p

To Kill a Microglia: A Case for CSF1R Inhibitors

Microglia, the brain's immune sentinels, have garnered much attention in recent years. Researchers have begun to identify the manifold roles that these cells play in the central nervous system (CNS), and this work has been greatly facilitated by microglial depletion paradigms. The varying degrees of spatiotemporal manipulation afforded by such techniques allow microglial ablation before, during, and/or following insult, injury, or disease. We review the major methods of microglial depletion, including toxin-based, genetic, and pharmacological approaches, which differ in key factors including depletion onset, duration, and off-target effects. We conclude that pharmacological CSF1R inhibitors afford the most extensive versatility in manipulating microglia, making them ideal candidates for future studies investigating microglial function in health and disease

Protein levels of APP, catalase, and cytokines in monocyte-infused APPSwDI mice.

<p>Following monocyte infusions, brains were collected and cortical extracts were evaluated for amyloid precursor protein (APP), catalase, or matrix metalloproteinase-2 (MMP-2) by Western blot (<b>A&B</b>; n = 4–6 per animal group). In addition, cortex (n = 6 per animal group) and plasma (n = 4 per animal group) were evaluated for tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-2 (MIP-2), interleukin-1β (IL-1β), and monocyte chemotactic protein-1 (MCP-1) levels by ELISA (<b>C</b>). APPSwDI mice receiving young peripheral blood monocyte (pM) i.v. infusions are indicated with a shaded gray bar. APPSwDI mice receiving saline (sal) served as negative controls and are indicated with a white bar. Bar graphs display the mean ± SEM (error bars) of protein levels. Statistical analysis was performed using a Student’s t-test (all not significant).</p