Molecular signatures underlying neurofibrillary tangle susceptibility in Alzheimer's disease

Tau aggregation in neurofibrillary tangles (NFTs) is closely associated with neurodegeneration and cognitive decline in Alzheimer's disease (AD). However, the molecular signatures that distinguish between aggregation-prone and aggregation-resistant cell states are unknown. We developed methods for the high-throughput isolation and transcriptome profiling of single somas with NFTs from the human AD brain, quantified the susceptibility of 20 neocortical subtypes for NFT formation and death, and identified both shared and cell-type-specific signatures. NFT-bearing neurons shared a marked upregulation of synaptic transmission-related genes, including a core set of 63 genes enriched for synaptic vesicle cycling. Oxidative phosphorylation and mitochondrial dysfunction were highly cell-type dependent. Apoptosis was only modestly enriched, and the susceptibilities of NFT-bearing and NFT-free neurons for death were highly similar. Our analysis suggests that NFTs represent cell-type-specific responses to stress and synaptic dysfunction. We provide a resource for biomarker discovery and the investigation of tau-dependent and tau-independent mechanisms of neurodegeneration.

Genome-wide association study and functional validation implicates JADE1 in tauopathy

Primary age-related tauopathy (PART) is a neurodegenerative pathology with features distinct from but also overlapping with Alzheimer disease (AD). While both exhibit Alzheimer-type temporal lobe neurofibrillary degeneration alongside amnestic cognitive impairment, PART develops independently of amyloid-β (Aβ) plaques. The pathogenesis of PART is not known, but evidence suggests an association with genes that promote tau pathology and others that protect from Aβ toxicity. Here, we performed a genetic association study in an autopsy cohort of individuals with PART (n = 647) using Braak neurofibrillary tangle stage as a quantitative trait. We found some significant associations with candidate loci associated with AD (SLC24A4, MS4A6A, HS3ST1) and progressive supranuclear palsy (MAPT and EIF2AK3). Genome-wide association analysis revealed a novel significant association with a single nucleotide polymorphism on chromosome 4 (rs56405341) in a locus containing three genes, including JADE1 which was significantly upregulated in tangle-bearing neurons by single-soma RNA-seq. Immunohistochemical studies using antisera targeting JADE1 protein revealed localization within tau aggregates in autopsy brains with four microtubule-binding domain repeats (4R) isoforms and mixed 3R/4R, but not with 3R exclusively. Co-immunoprecipitation in post-mortem human PART brain tissue revealed a specific binding of JADE1 protein to four repeat tau lacking N-terminal inserts (0N4R). Finally, knockdown of the Drosophila JADE1 homolog rhinoceros (rno) enhanced tau-induced toxicity and apoptosis in vivo in a humanized 0N4R mutant tau knock-in model, as quantified by rough eye phenotype and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) in the fly brain. Together, these findings indicate that PART has a genetic architecture that partially overlaps with AD and other tauopathies and suggests a novel role for JADE1 as a modifier of neurofibrillary degeneration.

An atlas of cortical arealization identifies dynamic molecular signatures

The human brain is subdivided into distinct anatomical structures, including the neocortex, which in turn encompasses dozens of distinct specialized cortical areas. Early morphogenetic gradients are known to establish early brain regions and cortical areas, but how early patterns result in finer and more discrete spatial differences remains poorly understood¹. Here we use single-cell RNA sequencing to profile ten major brain structures and six neocortical areas during peak neurogenesis and early gliogenesis. Within the neocortex, we find that early in the second trimester, a large number of genes are differentially expressed across distinct cortical areas in all cell types, including radial glia, the neural progenitors of the cortex. However, the abundance of areal transcriptomic signatures increases as radial glia differentiate into intermediate progenitor cells and ultimately give rise to excitatory neurons. Using an automated, multiplexed single-molecule fluorescent in situ hybridization approach, we find that laminar gene-expression patterns are highly dynamic across cortical regions. Together, our data suggest that early cortical areal patterning is defined by strong, mutually exclusive frontal and occipital gene-expression signatures, with resulting gradients giving rise to the specification of areas between these two poles throughout successive developmental timepoints.

Defining the nature of human pluripotent stem cell-derived interneurons via single-cell analysis

The specification of inhibitory neurons has been described for the mouse and human brain, and many studies have shown that pluripotent stem cells (PSCs) can be used to create interneurons in vitro. It is unclear whether in vitro methods to produce human interneurons generate all the subtypes found in brain, and how similar in vitro and in vivo interneurons are. We applied single-nuclei and single-cell transcriptomics to model interneuron development from human cortex and interneurons derived from PSCs. We provide a direct comparison of various in vitro interneuron derivation methods to determine the homogeneity achieved. We find that PSC-derived interneurons capture stages of development prior to mid-gestation, and represent a minority of potential subtypes found in brain. Comparison with those found in fetal or adult brain highlighted decreased expression of synapse-related genes. These analyses highlight the potential to tailor the method of generation to drive formation of particular subtypes.

Hepatic arginase deficiency fosters dysmyelination during postnatal CNS development

Deficiency of arginase is associated with hyperargininemia, and prominent features include spastic diplegia/tetraplegia, clonus, and hyperreflexia; loss of ambulation, intellectual disability and progressive neurological decline are other signs. To gain greater insight into the unique neuromotor features, we performed gene expression profiling of the motor cortex of a murine model of the disorder. Coexpression network analysis suggested an abnormality with myelination, which was supported by limited existing human data. Utilizing electron microscopy, marked dysmyelination was detected in 2-week-old homozygous Arg1-KO mice. The corticospinal tract was found to be adversely affected, supporting dysmyelination as the cause of the unique neuromotor features and implicating oligodendrocyte impairment in a deficiency of hepatic Arg1. Following neonatal hepatic gene therapy to express Arg1, the subcortical white matter, pyramidal tract, and corticospinal tract all showed a remarkable recovery in terms of myelinated axon density and ultrastructural integrity with active wrapping of axons by nearby oligodendrocyte processes. These findings support the following conclusions: arginase deficiency is a leukodystrophy affecting the brain and spinal cord while sparing the peripheral nervous system, and neonatal AAV hepatic gene therapy can rescue the defects associated with myelinated axons, strongly implicating the functional recovery of oligodendrocytes after restoration of hepatic arginase activity.

Extending the socio-sexual brain: arginine-vasopressin immunoreactive circuits in the telencephalon of mice

Quantitative analysis of the immunoreactivity for arginine-vasopressin (AVP-ir) in the telencephalon of male (intact and castrated) and female CD1 mice allows us to precisely locate two sexually dimorphic (more abundant in intact than castrated males and females) AVP-ir cell groups in the posterior bed nucleus of the stria terminalis (BST) and the amygdala. Chemoarchitecture (NADPH diaphorase) reveals that the intraamygdaloid AVP-ir cells are located in the intra-amygdaloid BST (BSTIA) rather than the medial amygdala (Me), as previously thought. Then, we have used for the first time tract tracing (combined with AVP immunofluorescence) and fiber-sparing lesions of the BST to analyze the projections of the telencephalic AVP-ir cell groups. The results demonstrate that the posterior BST originates the sexually dimorphic innervation of the lateral septum, the posterodorsal Me and a substance P-negative area in the medioventral striato-pallidum (mvStP).The BSTIA may also contribute to some of these terminal fields. Our material also reveals non-dimorphic AVP-ir processes in two locations of the amygdala. First, the ventral Me shows dendrite-like AVP-ir processes apparently belonging supraoptic neurons, whose possible functions are discussed. Second, the Ce shows sparse, thick AVP-ir axons with high individual variability in density and distribution, whose possible influence on stress coping in relation to the affiliative or agonistic behaviors mediated by the Me are discussed. Finally, we propose that the region of the mvStP showing sexually dimorphic AVP-ir innervation is part of the brain network for socio-sexual behavior, in which it would mediate motivational aspects of chemosensory-guided social interactions.