Integrated platform for multiscale molecular imaging and phenotyping of the human brain.

Understanding cellular architectures and their connectivity is essential for interrogating system function and dysfunction. However, we lack technologies for mapping the multiscale details of individual cells and their connectivity in the human organ-scale system. We developed a platform that simultaneously extracts spatial, molecular, morphological, and connectivity information of individual cells from the same human brain. The platform includes three core elements: a vibrating microtome for ultraprecision slicing of large-scale tissues without losing cellular connectivity (MEGAtome), a polymer hydrogel-based tissue processing technology for multiplexed multiscale imaging of human organ-scale tissues (mELAST), and a computational pipeline for reconstructing three-dimensional connectivity across multiple brain slabs (UNSLICE). We applied this platform for analyzing human Alzheimer's disease pathology at multiple scales and demonstrating scalable neural connectivity mapping in the human brain.

Uninterrupted CAG repeat drives striatum-selective transcriptionopathy and nuclear pathogenesis in human Huntingtin BAC mice.

In Huntington's disease (HD), the uninterrupted CAG repeat length, but not the polyglutamine length, predicts disease onset. However, the underlying pathobiology remains unclear. Here, we developed bacterial artificial chromosome (BAC) transgenic mice expressing human mutant huntingtin (mHTT) with uninterrupted, and somatically unstable, CAG repeats that exhibit progressive disease-related phenotypes. Unlike prior mHTT transgenic models with stable, CAA-interrupted, polyglutamine-encoding repeats, BAC-CAG mice show robust striatum-selective nuclear inclusions and transcriptional dysregulation resembling those in murine huntingtin knockin models and HD patients. Importantly, the striatal transcriptionopathy in HD models is significantly correlated with their uninterrupted CAG repeat length but not polyglutamine length. Finally, among the pathogenic entities originating from mHTT genomic transgenes and only present or enriched in the uninterrupted CAG repeat model, somatic CAG repeat instability and nuclear mHTT aggregation are best correlated with early-onset striatum-selective molecular pathogenesis and locomotor and sleep deficits, while repeat RNA-associated pathologies and repeat-associated non-AUG (RAN) translation may play less selective or late pathogenic roles, respectively.

Brainwide Genetic Sparse Cell Labeling to Illuminate the Morphology of Neurons and Glia with Cre-Dependent MORF Mice.

Cajal recognized that the elaborate shape of neurons is fundamental to their function in the brain. However, there are no simple and generalizable genetic methods to study neuronal or glial cell morphology in the mammalian brain. Here, we describe four mouse lines conferring Cre-dependent sparse cell labeling based on mononucleotide repeat frameshift (MORF) as a stochastic translational switch. Notably, the optimized MORF3 mice, with a membrane-bound multivalent immunoreporter, confer Cre-dependent sparse and bright labeling of thousands of neurons, astrocytes, or microglia in each brain, revealing their intricate morphologies. MORF3 mice are compatible with imaging in tissue-cleared thick brain sections and with immuno-EM. An analysis of 151 MORF3-labeled developing retinal horizontal cells reveals novel morphological cell clusters and axonal maturation patterns. Our study demonstrates a conceptually novel, simple, generalizable, and scalable mouse genetic solution to sparsely label and illuminate the morphology of genetically defined neurons and glia in the mammalian brain.

Elevated TREM2 Gene Dosage Reprograms Microglia Responsivity and Ameliorates Pathological Phenotypes in Alzheimer's Disease Models.

Variants of TREM2 are associated with Alzheimer's disease (AD). To study whether increasing TREM2 gene dosage could modify the disease pathogenesis, we developed BAC transgenic mice expressing human TREM2 (BAC-TREM2) in microglia. We found that elevated TREM2 expression reduced amyloid burden in the 5xFAD mouse model. Transcriptomic profiling demonstrated that increasing TREM2 levels conferred a rescuing effect, which includes dampening the expression of multiple disease-associated microglial genes and augmenting downregulated neuronal genes. Interestingly, 5xFAD/BAC-TREM2 mice showed further upregulation of several reactive microglial genes linked to phagocytosis and negative regulation of immune cell activation. Moreover, these mice showed enhanced process ramification and phagocytic marker expression in plaque-associated microglia and reduced neuritic dystrophy. Finally, elevated TREM2 gene dosage led to improved memory performance in AD models. In summary, our study shows that a genomic transgene-driven increase in TREM2 expression reprograms microglia responsivity and ameliorates neuropathological and behavioral deficits in AD mouse models.

Probing the stress and depression circuits with a disease gene.

Selectively deleting a gene that has been linked to depression from specific neurons in mice sheds new light on a neural circuit that controls stress-induced depressive behaviors.

N17 Modifies mutant Huntingtin nuclear pathogenesis and severity of disease in HD BAC transgenic mice.

The nucleus is a critical subcellular compartment for the pathogenesis of polyglutamine disorders, including Huntington's disease (HD). Recent studies suggest the first 17-amino-acid domain (N17) of mutant huntingtin (mHTT) mediates its nuclear exclusion in cultured cells. Here, we test whether N17 could be a molecular determinant of nuclear mHTT pathogenesis in vivo. BAC transgenic mice expressing mHTT lacking the N17 domain (BACHD-ΔN17) show dramatically accelerated mHTT pathology exclusively in the nucleus, which is associated with HD-like transcriptionopathy. Interestingly, BACHD-ΔN17 mice manifest more overt disease-like phenotypes than the original BACHD mice, including body weight loss, movement deficits, robust striatal neuron loss, and neuroinflammation. Mechanistically, N17 is necessary for nuclear exclusion of small mHTT fragments that are part of nuclear pathology in HD. Together, our study suggests that N17 modifies nuclear pathogenesis and disease severity in HD mice by regulating subcellular localization of known nuclear pathogenic mHTT species.

Targeted expression of µ-opioid receptors in a subset of striatal direct-pathway neurons restores opiate reward.

µ-opioid receptors (MORs) are necessary for the analgesic and addictive effects of opioids such as morphine, but the MOR-expressing neuronal populations that mediate the distinct opiate effects remain elusive. Here we devised a new conditional bacterial artificial chromosome rescue strategy to show, in mice, that targeted MOR expression in a subpopulation of striatal direct-pathway neurons enriched in the striosome and nucleus accumbens, in an otherwise MOR-null background, restores opiate reward and opiate-induced striatal dopamine release and partially restores motivation to self administer an opiate. However, these mice lack opiate analgesia or withdrawal. We used Cre-mediated deletion of the rescued MOR transgene to establish that expression of the MOR transgene in the striatum, rather than in extrastriatal sites, is needed for the restoration of opiate reward. Our study demonstrates that a subpopulation of striatal direct-pathway neurons is sufficient to support opiate reward-driven behaviors and provides a new intersectional genetic approach to dissecting neurocircuit-specific gene function in vivo.

An antisense CAG repeat transcript at JPH3 locus mediates expanded polyglutamine protein toxicity in Huntington's disease-like 2 mice.

Huntington's disease-like-2 (HDL2) is a phenocopy of Huntington's disease caused by CTG/CAG repeat expansion at the Junctophilin-3 (JPH3) locus. The mechanisms underlying HDL2 pathogenesis remain unclear. Here we developed a BAC transgenic mouse model of HDL2 (BAC-HDL2) that exhibits progressive motor deficits, selective neurodegenerative pathology, and ubiquitin-positive nuclear inclusions (NIs). Molecular analyses reveal a promoter at the transgene locus driving the expression of a CAG repeat transcript (HDL2-CAG) from the strand antisense to JPH3, which encodes an expanded polyglutamine (polyQ) protein. Importantly, BAC-HDL2 mice, but not control BAC mice, accumulate polyQ-containing NIs in a pattern strikingly similar to those in the patients. Furthermore, BAC mice with genetic silencing of the expanded CUG transcript still express HDL2-CAG transcript and manifest polyQ pathogenesis. Finally, studies of HDL2 mice and patients revealed CBP sequestration into NIs and evidence for interference of CBP-mediated transcriptional activation. These results suggest overlapping polyQ-mediated pathogenic mechanisms in HD and HDL2.

A micromachined pressure sensor based on an array of microswitches.

A micromachined pressure sensor based on an array of microswitches is presented. The pressure sensor consists of a silicon substrate that has a thin metal-deposited diaphragm and indium tin oxide (ITO)-based switch arrays patterned on a Pyrex glass. When pressure is applied to the thin diaphragm through a small tube, the diaphragm starts to deform and contact the array of switches at a certain pressure level. The increase in the contact area due to the diaphragm deformation causes the change in electrical resistance between two terminals of the ITO resistor. The change in resistance that corresponds to electrical output in the pressure sensor is measured by the use of a simple circuit. We also describe the results of numerical simulations that are carried out to find a suitable range of the pressure. The simulation results are in good agreement with the experimental results.

Aberrant expression of synaptic plasticity-related genes in the NF1+/- mouse hippocampus.

Neurofibromatosis 1 (NF1) is a common single-gene disorder that causes learning impairments in patients. Neurofibromin encoded by the NF1 causal gene regulates Ras/MAPK and cAMP signaling pathways. These signaling pathways play critical roles in controlling gene transcription during synaptic plasticity and memory formation. We hypothesized that NF1 mutations disturb the expression of genes important for memory formation. To test this hypothesis, we performed DNA microarray analysis on the hippocampus of NF1(+/-) mice, the mouse model for NF1 learning disabilities. Our results indicated that genes involved in a wide spectrum of biological processes are dysregulated in the NF1(+/-) hippocampus. Many of the NF1-affected genes play critical roles in synaptic plasticity, such as Rabs, synaptotagmins, NMDAR1, CaMKII, and CREB1. Because NF1-associated learning disabilities can be reversed by lovastatin, we also determined the effect of lovastatin treatment on genome-wide expression patterns of the NF1(+/-) hippocampus. We found that lovastatin altered the expression of a large number of genes, including those disturbed by NF1 mutations. Our results reveal a genome-wide overview of the molecular abnormalities in the NF1(+/-) hippocampus and should be useful for further identifying the novel molecular pathways that cause NF1 learning deficits.

Regulation of microRNA expression by induction of bidirectional synaptic plasticity.

Activity-induced protein synthesis is critical for long-lasting synaptic plasticity and subject to tight controls. MicroRNAs (miRNAs) are negative regulators of mRNA translation, but their role during synaptic plasticity is not clear. In this study, we have investigated how induction of long-term potentiation (LTP) and long-term depression (LTD) regulates the expression of miRNAs. Using miRNA arrays, we determined the temporal expression profiles of 62 hippocampal miRNAs following induction of chemical LTP (C-LTP) and metabotropic glutamate receptor-dependent LTD (mGluR-LTD). Several striking features were observed. First, C-LTP or mGluR-LTD induction changed the expression levels of most hippocampal miRNAs. Second, the majority of miRNAs regulated by C-LTP or mGluR-LTD induction followed a similar temporal expression profile. Third, most miRNAs were regulated by both C-LTP and mGluR-LTD induction, but displayed distinct expression dynamics. Fourth, many miRNAs were upregulated at specific time points C-LTP and mGluR-LTD induction, suggesting that C-LTP and mGluR-LTD induction elicits miRNA-mediated suppression of mRNA translation. We propose that the upregulated miRNA expression provides a mechanism to prevent excess protein synthesis during the expression of synaptic plasticity. The extensive regulation of miRNA expression by C-LTP and mGluR-LTD induction suggests a critical role of miRNAs in synaptic plasticity.

Molecular network and chromosomal clustering of genes involved in synaptic plasticity in the hippocampus.

Gene transcription is required for establishing and maintaining the enduring form of long term potentiation (LTP). However, the transcriptome and its associated molecular programs that support LTP are not well understood. The purpose of this study was to identify activity-regulated genes (ARGs) and their molecular pathways that are modulated by LTP induction and to investigate the genomic mechanism for coordinating the transcription of ARGs. We performed time course DNA microarray analyses on the mouse dentate gyrus to determine the temporal genomic expression profiles of ARGs in response to LTP-inducing tetanic stimulation. Our studies uncovered ARGs that regulate various cellular processes, including the structure and function of the synapse, and offered an overview of the dynamic molecular programs that are probably important for LTP. Surprisingly, we found that ARGs are clustered on chromosomes, and ARG clusters are conserved during evolution. Although ARGs in the same cluster have apparently different molecular properties, they are functionally correlated by regulating LTP. In addition, ARGs in specific clusters are co-regulated by the cAMP-response element-binding protein. We propose that chromosomal clustering provides a genomic mechanism for coordinating the transcription of ARGs involved in LTP.

Roles of glutamate receptors and the mammalian target of rapamycin (mTOR) signaling pathway in activity-dependent dendritic protein synthesis in hippocampal neurons.

Local protein synthesis in neuronal dendrites is critical for synaptic plasticity. However, the signaling cascades that couple synaptic activation to dendritic protein synthesis remain elusive. The purpose of this study is to determine the role of glutamate receptors and the mammalian target of rapamycin (mTOR) signaling in regulating dendritic protein synthesis in live neurons. We first characterized the involvement of various subtypes of glutamate receptors and the mTOR kinase in regulating dendritic synthesis of a green fluorescent protein (GFP) reporter controlled by alphaCaMKII 5' and 3' untranslated regions in cultured hippocampal neurons. Specific antagonists of N-methyl-d-aspartic acid (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and metabotropic glutamate receptors abolished glutamate-induced dendritic GFP synthesis, whereas agonists of NMDA and metabotropic but not AMPA glutamate receptors activated GFP synthesis in dendrites. Inhibitions of the mTOR signaling, as well as its upstream activators, phosphatidylinositol 3-kinase and AKT, blocked NMDA receptor-dependent dendritic GFP synthesis. Conversely, activation of mTOR signaling stimulated dendritic GFP synthesis. In addition, we also found that inhibition of the mTOR kinase blocked dendritic synthesis of the endogenous alphaCaMKII and MAP2 proteins induced by tetanic stimulations in hippocampal slices. These results identify critical roles of NMDA receptors and the mTOR signaling pathway for control of synaptic activity-induced dendritic protein synthesis in hippocampal neurons.

Activity-dependent synaptic Wnt release regulates hippocampal long term potentiation.

Wnts are important for various developmental and oncogenic processes. Here we show that Wnt signaling functions at synapses in hippocampal neurons. Tetanic stimulations induce N-methyl-d-aspartate receptor-dependent synaptic Wnt3a release, nuclear beta-catenin accumulations, and the activation of Wnt target genes. Suppression of Wnt signaling impairs long term potentiation. Conversely, activation of Wnt signaling facilitates long term potentiation. These findings suggest that Wnt signaling plays a critical role in regulating synaptic plasticity.