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Hyperactivity mediated by synaptotoxic β-amyloid (Aβ) oligomers is one of the earliest forms of neuronal dysfunction in Alzheimer’s disease. In the search for a preventive treatment strategy, we tested the effect of scavenging Aβ peptides prior to Aβ plaque formation. We demonstrate that an Aβ binding anticalin protein (Aβ-anticalin) can suppress early neuronal hyperactivity. Unexpectedly, the sole targeting of Aβ monomers was sufficient for the hyperactivity-suppressing effect of the Aβ-anticalin. Biochemical and neurophysiological analysis suggest that Aβ-anticalin-dependent depletion of naturally secreted Aβ monomers interrupts aggregation to neurotoxic oligomers and, thereby, prevents synaptic dysfunction. Our results demonstrate that Aβ monomer scavenging can reverse early neuronal dysfunction and, thus, offers a promising strategy for the preventive treatment of AD.

Studies of the structural and molecular features of the lymphatic vasculature, which clears fluid, macromolecules and leukocytes from the tissue microenvironment, have largely relied on animal models, with limited information in human organs beyond traditional immunohistochemical assessment. Here, we use three-dimensional imaging and single-cell RNA-sequencing to study lymphatics in the human kidney. We found a hierarchical arrangement of lymphatic vessels within human kidneys, initiating along specialised nephron epithelium in the renal cortex and displaying a distinct, kidney-specific transcriptional profile. In chronic transplant rejection we found kidney allograft lymphatic expansion alongside a loss of structural hierarchy, with human leukocyte antigen-expressing lymphatic vessels infiltrating the medulla, presenting a putative target for alloreactive antibodies. This occurred concurrently with lymphatic vessels invading and interconnecting tertiary lymphoid structures at early stages of lymphocyte colonisation. Analysis of intercellular signalling revealed upregulation of co-inhibitory molecule-mediated CD4+T cell-lymphatic crosstalk in rejecting kidneys, potentially acting to limit local alloimmune responses. Overall, we delineate novel structural and molecular features of human kidney lymphatics and reveal perturbations to their phenotype and transcriptome in the context of alloimmunity.SUMMARYLymphatics regulate fluid balance and immune cell accumulation but are under-studied in human organs such as the kidney. Jafree and colleagues profiled human kidney lymphatics using three-dimensional imaging and single-cell RNA-sequencing, revealing structural and transcriptional perturbations in rejecting kidney transplants.

Patients with Alzheimer's disease (AD) present with both extracellular amyloid-β (Aβ) plaques and intracellular tau-containing neurofibrillary tangles in the brain. For many years, the prevailing view of AD pathogenesis has been that changes in Aβ precipitate the disease process and initiate a deleterious cascade involving tau pathology and neurodegeneration. Beyond this 'triggering' function, it has been typically presumed that Aβ and tau act independently and in the absence of specific interaction. However, accumulating evidence now suggests otherwise and contends that both pathologies have synergistic effects. This could not only help explain negative results from anti-Aβ clinical trials but also suggest that trials directed solely at tau may need to be reconsidered. Here, drawing from extensive human and disease model data, we highlight the latest evidence base pertaining to the complex Aβ-tau interaction and underscore its crucial importance to elucidating disease pathogenesis and the design of next-generation AD therapeutic trials.

It is becoming increasingly recognized that patients with a variety of neurodegenerative diseases exhibit disordered sleep/wake patterns. While sleep impairments have typically been thought of as sequelae of underlying neurodegenerative processes in sleep-wake cycle regulating brain regions, including the brainstem, hypothalamus, and basal forebrain, emerging evidence now indicates that sleep deficits may also act as pathophysiological drivers of brain-wide disease progression. Specifically, recent work has indicated that impaired sleep can impact on neuronal activity, brain clearance mechanisms, pathological build-up of proteins, and inflammation. Altered sleep patterns may therefore be novel (potentially reversible) dynamic functional markers of proteinopathies and modifiable targets for early therapeutic intervention using non-invasive stimulation and behavioral techniques. Here we highlight research describing a potentially reciprocal interaction between impaired sleep and circadian patterns and the accumulation of pathological signs and features in Alzheimer's disease, the most prevalent neurodegenerative disease in the elderly.

It is becoming increasingly recognized that patients with a variety of neurodegenerative diseases exhibit disordered sleep/wake patterns. While sleep impairments have typically been thought of as sequelae of underlying neurodegenerative processes in sleep-wake cycle regulating brain regions, including the brainstem, hypothalamus, and basal forebrain, emerging evidence now indicates that sleep deficits may also act as pathophysiological drivers of brain-wide disease progression. Specifically, recent work has indicated that impaired sleep can impact on neuronal activity, brain clearance mechanisms, pathological build-up of proteins, and inflammation. Altered sleep patterns may therefore be novel (potentially reversible) dynamic functional markers of proteinopathies and modifiable targets for early therapeutic intervention using non-invasive stimulation and behavioral techniques. Here we highlight research describing a potentially reciprocal interaction between impaired sleep and circadian patterns and the accumulation of pathological signs and features in Alzheimer's disease, the most prevalent neurodegenerative disease in the elderly.

Our incomplete understanding of the link between Alzheimer's Disease pathology and symptomatology is a crucial obstacle for therapeutic success. Recently, translational studies have begun to connect the dots between protein alterations and deposition, brain network dysfunction and cognitive deficits. Disturbance of neuronal activity, and in particular an imbalance in underlying excitation/inhibition (E/I), appears early in AD, and can be regarded as forming a central link between structural brain pathology and cognitive dysfunction. While there are emerging (non-)pharmacological options to influence this imbalance, the complexity of human brain dynamics has hindered identification of an optimal approach. We suggest that focusing on the integration of neurophysiological aspects of AD at the micro-, meso- and macroscale, with the support of computational network modeling, can unite fundamental and clinical knowledge, provide a general framework, and suggest rational therapeutic targets., M.A.B. is supported by the UK Dementia Research Institute which receives its funding from DRI Ltd, funded by the Medical Research Council, Alzheimer’s Society and Alzheimer Research UK (UKDRI1010). M.A.B. is also funded by a UK RI Future Leaders Fellowship (MR/S017003/1) and a grant from the right Focus Foundation (A2019112S). F.M is supported by the Spanish Minister of Science (RTI2018-098762-B-C31), University of Texas Houston Research Staff grant, NIH− HCP (Connectomics of Aging Brain and Dementia). J.dF was supported by Centro de Investigacion ´ en Red sobre Enfermedades Neurodegenerativas (CIBERNED, CB06/05/0066, Spain); theSpanish “Ministerio de Ciencia e Innovacion´ ”(grant PGC2018-094307-B-I00 and the Cajal Blue Brain Project [the Spanish partner of the Blue Brain Project initiative from EPFL, Switzerland]).

The membrane protein seizure 6–like (SEZ6L) is a neuronal substrate of the Alzheimer’s disease protease BACE1, and little is known about its physiological function in the nervous system. Here, we show that SEZ6L constitutive knockout mice display motor phenotypes in adulthood, including changes in gait and decreased motor coordination. Additionally, SEZ6L knockout mice displayed increased anxiety-like behaviour, although spatial learning and memory in the Morris water maze were normal. Analysis of the gross anatomy and proteome of the adult SEZ6L knockout cerebellum did not reveal any major differences compared to wild type, indicating that lack of SEZ6L in other regions of the nervous system may contribute to the phenotypes observed. In summary, our study establishes physiological functions for SEZ6L in regulating motor coordination and curbing anxiety-related behaviour, indicating that aberrant SEZ6L function in the human nervous system may contribute to movement disorders and neuropsychiatric diseases.

Identifying effective treatments for Alzheimer's disease (AD) has proven challenging and has instigated a shift in AD research focus toward the earliest disease-initiating cellular mechanisms. A key insight has been an increase in soluble Aβ oligomers in early AD that is causally linked to neuronal and circuit hyperexcitability. However, other accumulating AD-related peptides and proteins, including those derived from the same amyloid precursor protein, such as Aη or sAPPα, and autonomously, such as tau, exhibit surprising opposing effects on circuit dynamics. We propose that the effects of these on neuronal circuits have profound implications for our understanding of disease complexity and heterogeneity and for the development of personalized diagnostic and therapeutic strategies in AD. Here, we highlight important peptide-specific mechanisms of dynamic pathological disequilibrium of cellular and circuit activity in AD and discuss approaches in which these may be further understood, and theoretically and experimentally leveraged, to elucidate AD pathophysiology.

Seizure protein 6 (SEZ6) is required for the development and maintenance of the nervous system, is a major substrate of the protease BACE1 and is linked to Alzheimer's disease (AD) and psychiatric disorders, but its molecular functions are not well understood. Here, we demonstrate that SEZ6 controls glycosylation and cell surface localization of kainate receptors composed of GluK2/3 subunits. Loss of SEZ6 reduced surface levels of GluK2/3 in primary neurons and reduced kainate‐evoked currents in CA1 pyramidal neurons in acute hippocampal slices. Mechanistically, loss of SEZ6 in vitro and in vivo prevented modification of GluK2/3 with the human natural killer‐1 (HNK‐1) glycan, a modulator of GluK2/3 function. SEZ6 interacted with GluK2 through its ectodomain and promoted post‐endoplasmic reticulum transport of GluK2 in the secretory pathway in heterologous cells and primary neurons. Taken together, SEZ6 acts as a new trafficking factor for GluK2/3. This novel function may help to better understand the role of SEZ6 in neurologic and psychiatric diseases., The beta‐secretase/BACE1 substrate SEZ6 regulates the trafficking of GluK2/3 to modulate their subcellular localization and glycosylation.

A major mystery of many types of neurological and psychiatric disorders, such as Alzheimer's disease (AD), remains the underlying, disease-specific neuronal damage. Because of the strong interconnectivity of neurons in the brain, neuronal dysfunction necessarily disrupts neuronal circuits. In this article, we review evidence for the disruption of large-scale networks from imaging studies of humans and relate it to studies of cellular dysfunction in mouse models of AD. The emerging picture is that some forms of early network dysfunctions can be explained by excessively increased levels of neuronal activity. The notion of such neuronal hyperactivity receives strong support from in vivo and in vitro cellular imaging and electrophysiological recordings in the mouse, which provide mechanistic insights underlying the change in neuronal excitability. Overall, some key aspects of AD-related neuronal dysfunctions in humans and mice are strikingly similar and support the continuation of such a translational strategy.

Ocular motor apraxia (OA) is an inability to initiate voluntary saccades in a head-fixed position, while saccades can be initiated by the vestibulo-ocular reflex (indicating dysfunction in the frontal eye fields).

Amyloid-β (Aβ) is thought to play an essential pathogenic role in Alzheimer´s disease (AD). A key enzyme involved in the generation of Aβ is the β-secretase BACE, for which powerful inhibitors have been developed and are currently in use in human clinical trials. However, although BACE inhibition can reduce cerebral Aβ levels, whether it also can ameliorate neural circuit and memory impairments remains unclear. Using histochemistry, in vivo Ca2+ imaging, and behavioral analyses in a mouse model of AD, we demonstrate that along with reducing prefibrillary Aβ surrounding plaques, the inhibition of BACE activity can rescue neuronal hyperactivity, impaired long-range circuit function, and memory defects. The functional neuronal impairments reappeared after infusion of soluble Aβ, mechanistically linking Aβ pathology to neuronal and cognitive dysfunction. These data highlight the potential benefits of BACE inhibition for the effective treatment of a wide range of AD-like pathophysiological and cognitive impairments.

Patients with Alzheimer's disease (AD) present with both extracellular amyloid-β (Aβ) plaques and intracellular tau-containing neurofibrillary tangles in the brain. For many years, the prevailing view of AD pathogenesis has been that changes in Aβ precipitate the disease process and initiate a deleterious cascade involving tau pathology and neurodegeneration. Beyond this 'triggering' function, it has been typically presumed that Aβ and tau act independently and in the absence of specific interaction. However, accumulating evidence now suggests otherwise and contends that both pathologies have synergistic effects. This could not only help explain negative results from anti-Aβ clinical trials but also suggest that trials directed solely at tau may need to be reconsidered. Here, drawing from extensive human and disease model data, we highlight the latest evidence base pertaining to the complex Aβ-tau interaction and underscore its crucial importance to elucidating disease pathogenesis and the design of next-generation AD therapeutic trials.

Alzheimer's disease (AD) is characterized by the pathological accumulation of amyloid-beta (Abeta) and tau peptides in the brain. Recent evidence suggests that the soluble peptide amyloid-eta (Aeta) may have an additional role in the pathogenesis of AD. The detailed investigation of the cellular and neurophysiological mechanisms underlying AD has revealed surprising results that may become highly relevant for the early diagnosis and treatment of the disease. By analyzing the function of single neurons and large-scale networks in intact brains in vivo it has been shown that A-beta, tau and A-eta abnormally modulate brain activity and obviously unfold contrasting effects: while A-beta promotes neuronal hyperactivity as well as epileptiform activity, tau and A-eta reduce the activity of neurons. Promising new evidence from animal studies and humans with AD indicates that the treatment of hyperactivity may improve cognitive dysfunctions and even slow the underlying disease process.

The coexistence of amyloid-β (Aβ) plaques and tau neurofibrillary tangles in the neocortex is linked to neural system failure and cognitive decline in Alzheimer’s disease. However, the underlying neuronal mechanisms are unknown. By employing in vivo two-photon Ca(2+) imaging of layer 2/3 cortical neurons in mice expressing human Aβ and tau, we reveal a dramatic tau-dependent suppression of activity and silencing of many neurons, which dominates over Aβ-dependent neuronal hyperactivity. We show that neurofibrillary tangles are neither sufficient nor required for the silencing, which instead is dependent on soluble tau. Surprisingly, although rapidly effective in tau mice, suppression of tau gene expression was much less effective in rescuing neuronal impairments in mice containing both Aβ and tau. Together, our results reveal how Aβ and tau synergize to impair the functional integrity of neural circuits in vivo and suggest a possible cellular explanation contributing to disappointing results from anti-Aβ therapeutic trials.

The use of in vivo two-photon microscopy in mouse models of Alzheimer's disease (AD) has propelled studies of disease mechanisms and treatments. For instance, this approach allowed for the first time to study in the intact brain the dynamics of individual amyloid plaques, and the effects of anti-amyloid therapies on plaque formation and growth. Moreover, by combining two-photon microscopy with fluorescent calcium indicators, an amyloid-dependent abnormal hyperactivity of cortical and hippocampal neurons was revealed as a primary neuronal impairment, which was not predicted from previous in vitro analyses. Here, a method for in vivo two-photon calcium imaging with single-cell and single-action potential accuracy in the hippocampus of Alzheimer mouse models is presented.

The use of in vivo two-photon microscopy in mouse models of Alzheimer's disease (AD) has propelled studies of disease mechanisms and treatments. For instance, this approach allowed for the first time to study in the intact brain the dynamics of individual amyloid plaques, and the effects of anti-amyloid therapies on plaque formation and growth. Moreover, by combining two-photon microscopy with fluorescent calcium indicators, an amyloid-dependent abnormal hyperactivity of cortical and hippocampal neurons was revealed as a primary neuronal impairment, which was not predicted from previous in vitro analyses. Here, a method for in vivo two-photon calcium imaging with single-cell and single-action potential accuracy in the hippocampus of Alzheimer mouse models is presented.

Alzheimer's disease (AD) is characterized by the accumulation of amyloid plaques, which are predominantly composed of amyloid β-peptide (Aβ)1. Two principal physiological pathways either prevent or promote Aβ generation from its precursor (amyloid precursor protein; APP) in a competitive manner1. Modulation of the amyloidogenic pathway is currently exploited by anti-Aβ therapeutic strategies2. Although APP processing has been studied in great detail, unknown proteolytic events appear to hinder stoichiometric analyses of APP metabolism in vivo3. We now identified higher molecular weight C-terminal fragments of APP (CTF-η) in addition to the long-known α- and β-secretase (a disintegrin and metalloproteinase; ADAM10 and β-site APP cleaving enzyme 1; BACE1) generated CTF-α and CTF-β. Generation of CTF-η is mediated in part by membrane bound matrix-metalloproteinases such as MT5-MMP, referred to as η-secretase activity. η-Secretase cleavage occurs primarily at amino acids 504/505 of APP(695) releasing a truncated, soluble APP ectodomain (sAPP-η). Upon shedding of sAPP-η CTF-η is further processed by ADAM10 and BACE1 to release long and short Aη peptides (Aη-α and Aη-β). Aη peptides are therefore distinct from N-terminally extended Aβ variants4,5, since they do not extend to the γ-secretase cleavage sites. η-Secretase produced CTFs are enriched in dystrophic neurites in an AD mouse model and human AD brains6. Genetic and pharmacological inhibition of BACE1 activity results in a robust accumulation of CTF-η and Aη-α. In mice treated with a potent BACE1 inhibitor hippocampal long-term potentiation (LTP) was reduced. Strikingly, when recombinant or synthetic Aη-α was applied on hippocampal slices ex vivo, LTP was lowered. Furthermore, in vivo single cell two-photon calcium imaging revealed that hippocampal neuronal activity was attenuated by Aη-α. These findings not only demonstrate a major physiologically relevant APP processing pathway but may also suggest potential translational relevance for therapeutic strategies targeting APP processing.

Traditionally, the impairment of cognitive functions in Alzheimer's disease (AD) is thought to result from a reduction in neuronal and synaptic activities, and ultimately cell death. Here, we review recent in vivo evidence from mouse models and human patients indicating that, particularly in early stages of AD, neuronal circuits are hyperactive instead of hypoactive. Functional analyses at many levels, from single neurons to neuronal populations to large-scale networks, with a variety of electrophysiological and imaging techniques have revealed two forms of AD-related hyperactivity and provided first insights into the synaptic mechanisms. The unexpected finding that hyperactivity is an early neuronal dysfunction represents a major conceptual shift in our understanding of AD that may have important implications for the development of therapeutic approaches.

Among the most promising approaches for treating Alzheimer's disease is immunotherapy with amyloid-β (Aβ)-targeting antibodies. Using in vivo two-photon imaging in mouse models, we found that two different antibodies to Aβ used for treatment were ineffective at repairing neuronal dysfunction and caused an increase in cortical hyperactivity. This unexpected finding provides a possible cellular explanation for the lack of cognitive improvement by immunotherapy in human studies.

Alzheimer's disease (AD) is characterized by the pathological accumulation of amyloid-beta (Abeta) and tau peptides in the brain. Recent evidence suggests that the soluble peptide amyloid-eta (Aeta) may have an additional role in the pathogenesis of AD. The detailed investigation of the cellular and neurophysiological mechanisms underlying AD has revealed surprising results that may become highly relevant for the early diagnosis and treatment of the disease. By analyzing the function of single neurons and large-scale networks in intact brains in vivo it has been shown that A-beta, tau and A-eta abnormally modulate brain activity and obviously unfold contrasting effects: while A-beta promotes neuronal hyperactivity as well as epileptiform activity, tau and A-eta reduce the activity of neurons. Promising new evidence from animal studies and humans with AD indicates that the treatment of hyperactivity may improve cognitive dysfunctions and even slow the underlying disease process.

The neurodegeneration observed in Alzheimer's disease has been associated with synaptic dismantling and progressive decrease in neuronal activity. We tested this hypothesis in vivo by using two-photon Ca 2+ imaging in a mouse model of Alzheimer's disease. Although a decrease in neuronal activity was seen in 29% of layer 2/3 cortical neurons, 21% of neurons displayed an unexpected increase in the frequency of spontaneous Ca 2+ transients. These “hyperactive” neurons were found exclusively near the plaques of amyloid β–depositing mice. The hyperactivity appeared to be due to a relative decrease in synaptic inhibition. Thus, we suggest that a redistribution of synaptic drive between silent and hyperactive neurons, rather than an overall decrease in synaptic activity, provides a mechanism for the disturbed cortical function in Alzheimer's disease.

Over the last decade, in vivo calcium imaging became a powerful tool for studying brain function. With the use of two-photon microscopy and modern labelling techniques, it allows functional studies of individual living cells, their processes and their interactions within neuronal networks. In vivo calcium imaging is even more important for studying the aged brain, which is hard to investigate in situ due to the fragility of neuronal tissue. In this article, we give a brief overview of the techniques applicable to image aged rodent brain at cellular resolution. We use multicolor imaging to visualize specific cell types (neurons, astrocytes, microglia) as well as the autofluorescence of the “aging pigment” lipofuscin. Further, we illustrate an approach for simultaneous imaging of cortical cells and senile plaques in mouse models of Alzheimer’s disease.

Alzheimer's disease (AD) is associated with defects of synaptic connectivity. Such defects may not be restricted to local neuronal interactions but may extend to long-range brain activities, such as slow-wave oscillations that are particularly prominent during non-rapid eye movement (non-REM) sleep and are important for integration of information across distant brain regions involved in memory consolidation. There is increasing evidence that sleep is often impaired in AD, but it is unclear whether this impairment is directly related to amyloid-β (Aβ) pathology. Here we demonstrate that slow-wave activity is severely altered in the neocortex, thalamus and hippocampus in mouse models of AD amyloidosis. Most notably, our results reveal an Aβ-dependent impairment of slow-wave propagation, which causes a breakdown of the characteristic long-range coherence of slow-wave activity. The finding that the impairment can be rescued by enhancing GABAAergic inhibition identifies a synaptic mechanism underlying Aβ-dependent large-scale circuit dysfunction.

An essential feature of Alzheimer's disease (AD) is the accumulation of amyloid-β (Aβ) peptides in the brain, many years to decades before the onset of overt cognitive symptoms. We suggest that during this very extended early phase of the disease, soluble Aβ oligomers and amyloid plaques alter the function of local neuronal circuits and large-scale networks by disrupting the balance of synaptic excitation and inhibition ( E / I balance) in the brain. The analysis of mouse models of AD revealed that an Aβ-induced change of the E / I balance caused hyperactivity in cortical and hippocampal neurons, a breakdown of slow-wave oscillations, as well as network hypersynchrony. Remarkably, hyperactivity of hippocampal neurons precedes amyloid plaque formation, suggesting that hyperactivity is one of the earliest dysfunctions in the pathophysiological cascade initiated by abnormal Aβ accumulation. Therapeutics that correct the E / I balance in early AD may prevent neuronal dysfunction, widespread cell loss and cognitive impairments associated with later stages of the disease. This article is part of the themed issue ‘Evolution brings Ca 2+ and ATP together to control life and death’.

Alzheimer’s disease (AD) is characterized by a progressive dysfunction of central neurons. Recent experimental evidence indicates that in the cortex, in addition to the silencing of a fraction of neurons, other neurons are hyperactive in amyloid-β (Aβ) plaque-enriched regions. However, it has remained unknown what comes first, neuronal silencing or hyperactivity, and what mechanisms might underlie the primary neuronal dysfunction. Here we examine the activity patterns of hippocampal CA1 neurons in a mouse model of AD in vivo using two-photon Ca 2+ imaging. We found that neuronal activity in the plaque-bearing CA1 region of older mice is profoundly altered. There was a marked increase in the fractions of both silent and hyperactive neurons, as previously also found in the cortex. Remarkably, in the hippocampus of young mice, we observed a selective increase in hyperactive neurons already before the formation of plaques, suggesting that soluble species of Aβ may underlie this impairment. Indeed, we found that acute treatment with the γ-secretase inhibitor LY-411575 reduces soluble Aβ levels and rescues the neuronal dysfunction. Furthermore, we demonstrate that direct application of soluble Aβ can induce neuronal hyperactivity in wild-type mice. Thus, our study identifies hippocampal hyperactivity as a very early functional impairment in AD transgenic mice and provides direct evidence that soluble Aβ is crucial for hippocampal hyperactivity.

Sleep plays an essential role in memory consolidation. Although sleep problems are common in Alzheimer's disease, they are not usually thought to be key features of the disease; however, new experimental research has shown that sleep disturbances not only occur before the onset of typical cognitive deficits but are also associated with the pathogenesis of Alzheimer's disease and may have a decisive influence on the symptoms and course. Thus, sleep disturbances may be potentially modifiable risk factors for Alzheimer's disease that deserve more attention in research, diagnostics and treatment.