Fryer, John D.

Abstract INTRODUCTION Anti‐amyloid beta (Aβ) monoclonal antibodies are effective at lowering amyloid in Alzheimer's disease (AD). However, whether Fc‐mediated effector function is absolutely required for efficacy is not completely understood. This is important for optimizing therapeutic efficacy and mitigating side effects such as amyloid‐related imaging abnormalities (ARIA). Antibodies lacking Fc effector function, like single‐domain antibodies (nanobodies), offer a unique tool to dissect these mechanisms, as their small size facilitates blood–brain barrier (BBB) penetration and allows Fc‐mediated functions to be studied independently. METHODS We immunized a llama with Aβ aggregates and constructed a phage display library to screen for aggregate‐specific nanobodies. Lead candidates were characterized by epitope mapping and binding affinity to amyloid plaques in both murine and human AD brain tissues. We further assessed their BBB permeability and evaluated their efficacy in clearing pre‐existing plaques in amyloid precursor protein (APP)/presenilin 1 (PS1) mice. RESULTS We identified two lead nanobodies, 3A11 and 2D10, that bind distinct epitopes and specifically bind Aβ plaques in murine and human AD brain tissues. Following systemic administration, the monovalent, unmodified (Fc‐less) 2D10 nanobody, but not 3A11, successfully crossed the BBB and engaged amyloid plaques in APP/PS1 mice. However, despite robust target engagement, the Fc‐less 2D10 failed to recruit microglia or reduce plaque burden. In contrast, an engineered 2D10‐Fc fusion antibody potently cleared amyloid plaques, achieving a reduction in pathology comparable to aducanumab treatment. This efficacy was directly correlated with Fc‐mediated microglial recruitment and activation, demonstrating that the Fc domain is essential for phagocytic plaque removal. DISCUSSION Our findings demonstrate that Fc effector function is indispensable for microglial‐mediated amyloid clearance in vivo. By clarifying this fundamental mechanism, this study provides a framework for the rational design of next‐generation immunotherapies. Furthermore, 2D10‐Fc represents a promising therapeutic candidate, combining the high‐affinity targeting of nanobodies with the effector power necessary for robust plaque clearance.

Abstract INTRODUCTION Neurodegenerative diseases often involve overlapping alpha‐synuclein (asyn), amyloid beta, and tau proteinopathies, yet the mechanisms, impact, and directionality of their interactions remain unclear. METHODS We induced brain‐wide neuronal asyn/tau pathologies via viral expression of wild‐type asyn, mutant asyn E46K , mutant tau A152T , or both asyn E46K /tau A152T in adult amyloidosis knock‐in mice and controls, either post‐plaque deposition (6 months old) or pre‐plaque (3 months old). Open‐field behavior was assessed baseline and 3 and 6 months post‐transduction, followed by neuropathology and neuroinflammation analyses. RESULTS Post‐plaque induction in amyloid mice increased asyn/tau total and phosphorylated levels and exacerbated amyloid‐related hyperlocomotion/anxiety. Pre‐plaque induction produced robust phosphorylated pathologies irrespective of amyloid, while causing similar amyloid‐dependent behavioral synergy. Tau pathology drove LGALS3 + inflammatory glial responses in white‐matter fibers. DISCUSSION Amyloid context gates vulnerability, with certain synergies manifesting across stages. White‐matter gliosis is a novel mechanism of tau A152T risk. Together, our data argue for the development of stage‐aware, multitarget interventions and biomarkers.

Significance Deposition of amyloid-β (Aβ) peptide in the form of parenchymal plaques and Aβ accumulation in the walls of cerebral vessels as cerebral amyloid angiopathy (CAA) are pathological hallmarks of Alzheimer’s disease (AD). The clusterin ( CLU ) gene, which confers AD risk, is associated with amyloid deposition. Here we show that loss of CLU promotes cerebrovascular CAA, yet significantly reduces the amount of parenchymal plaques by altering perivascular drainage of Aβ in the APP/PS1 mouse model of AD. The absence of CLU in these mice is associated with a lower number of hemorrhages and a decrease in inflammation. These results suggest that CLU functions as a major Aβ chaperone to maintain Aβ solubility along interstitial fluid drainage pathways and prevent CAA formation.

Poly(GP) proteins are a promising pharmacodynamic marker for developing and testing therapeutics for treating C9ORF72 -associated amyotrophic lateral sclerosis.

Triggering receptor expressed on myeloid cells 2 (TREM2) is an innate immune receptor expressed in microglia in the brain. A soluble form of TREM2 (sTREM2) derived from proteolytic cleavage of the cell surface receptor is increased in the preclinical stages of AD and positively correlates with the amounts of total and phosphorylated tau in the cerebrospinal fluid. However, the physiological and pathological functions of sTREM2 remain unknown. Here, we show that sTREM2 promotes microglial survival in a PI3K/Akt-dependent manner and stimulates the production of inflammatory cytokines depending on NF-κB. Variants of sTREM2 carrying AD risk-associated mutations were less potent in both suppressing apoptosis and triggering inflammatory responses. Importantly, sTREM2 delivered to the hippocampi of both wild-type and Trem2-knockout mice elevated the expression of inflammatory cytokines and induced morphological changes of microglia. Collectively, these data indicate that sTREM2 triggers microglial activation inducing inflammatory responses and promoting survival. This study has implications for the pathogenesis of AD and provides insights into targeting sTREM2 pathway for AD therapy.

ObjectiveApolipoprotein E (apoE), a major cholesterol carrier in the brain, is associated with a strong risk for Alzheimer disease. Compared to the risky APOE4 gene allele, the effects of the protective APOE2 gene allele are vastly understudied, and thus need to be further clarified.MethodsWe reviewed National Alzheimer's Coordinating Center clinical records and performed preclinical experiments using human apoE‐targeted replacement (apoE‐TR) mice, which do not show amyloid pathology.ResultsClinically, the APOE2 allele was associated with less cognitive decline during aging. This effect was also seen in subjects with little amyloid pathology, or after adjusting for Alzheimer disease‐related pathologies. In animal studies, aged apoE2‐TR mice also exhibited preserved memory function in water maze tests. Regardless, apoE2‐TR mice showed similar or greater age‐related changes in synaptic loss, neuroinflammation, and oxidative stress compared to apoE3‐TR or apoE4‐TR mice. Interestingly, apoE concentrations in the cortex, hippocampus, plasma, and cerebrospinal fluid (CSF) were positively correlated with memory performance across apoE isoforms, where apoE2‐TR mice had higher apoE levels. Moreover, apoE2‐TR mice exhibited the lowest levels of cholesterol in the cortex, despite higher levels in CSF and plasma. These cholesterol levels were associated with apoE levels and memory performance across apoE isoforms.InterpretationAPOE2 is associated with less cognitive decline during aging. This can occur independently of age‐related synaptic/neuroinflammatory changes and amyloid accumulation. Higher levels of apoE and associated cholesterol metabolism in APOE2 carriers might contribute to this protective effect. Ann Neurol 2016;79:758–774

A mouse model for ALS A G4C2 repeat expansion in C9ORF72 is known to be the major genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis (c9FTD/ALS). However, a lack of animal models recapitulating key disease features has hindered efforts to understand and prevent c9FTD/ALS-related neurodegeneration. Until now. Chew et al. describe a mouse model that mimics both neuropathological and clinical phenotypes of c9FTD/ALS. Science , this issue p. 1151

We have previously shown that voluntary wheel running (VWR) attenuates, whereas forced treadmill running (FTR) exacerbates, intestinal inflammation and clinical outcomes in a mouse model of colitis. As the gut microbiome is implicated in colitis, we hypothesized that VWR and FTR would differentially affect the gut microbiome. Mice (9-10/treatment) were randomly assigned to VWR, FTR, or sedentary home cage control (SED) for 6 wk. VWR were given running wheel access, whereas FTR ran on a treadmill for 40 min/day at 8–12 m/min, 5% grade. Forty-eight hours after the last exercise session, DNA was isolated from the fecal pellets and cecal contents, and the conserved bacterial 16S rRNA gene was amplified and sequenced using the Illumina Miseq platform. Permutational multivariate analysis of variance based on weighted UniFrac distance matrix revealed different bacterial clusters between feces and cecal contents in all groups ( P < 0.01). Interestingly, the community structures of the three treatment groups clustered separately from each other in both gut regions ( P < 0.05). Contrary to our hypothesis, the α-diversity metric, Chao1, indicated that VWR led to reduced bacterial richness compared with FTR or SED ( P < 0.05). Taxonomic evaluation revealed that both VWR and FTR altered many individual bacterial taxa. Of particular interest, Turicibacter spp., which has been strongly associated with immune function and bowel disease, was significantly lower in VWR vs. SED/FTR. These data indicate that VWR and FTR differentially alter the intestinal microbiome of mice. These effects were observed in both the feces and cecum despite vastly different community structures between each intestinal region.

Significance Noninvasive brain imaging holds great promise for expanding our capabilities of treating human neurologic and psychiatric disorders. However, key limitations exist in human-only studies, and the ability to use animal models would greatly advance our understanding of human brain function. Mice offer sophisticated genetic and molecular methodology, but correlating these data to functional brain imaging in the mouse brain has remained a major hurdle. This study is the first, to our knowledge, to use whole-brain functional imaging to show large-scale functional architecture with structural correlates in the mouse. Perhaps more important is the finding of conservation in brain topology and default network among rodents and primates, thereby clearing the way for a bridge measurement between human and mouse models.