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Annual Review of Neuroscience Jul 2022The cerebellar cortex is an important system for relating neural circuits and learning. Its promise reflects the longstanding idea that it contains simple, repeated... (Review)
Review
The cerebellar cortex is an important system for relating neural circuits and learning. Its promise reflects the longstanding idea that it contains simple, repeated circuit modules with only a few cell types and a single plasticity mechanism that mediates learning according to classical Marr-Albus models. However, emerging data have revealed surprising diversity in neuron types, synaptic connections, and plasticity mechanisms, both locally and regionally within the cerebellar cortex. In light of these findings, it is not surprising that attempts to generate a holistic model of cerebellar learning across different behaviors have not been successful. While the cerebellum remains an ideal system for linking neuronal function with behavior, it is necessary to update the cerebellar circuit framework to achieve its great promise. In this review, we highlight recent advances in our understanding of cerebellar-cortical cell types, synaptic connections, signaling mechanisms, and forms of plasticity that enrich cerebellar processing.
Topics: Cerebellar Cortex; Cerebellum; Learning; Neuronal Plasticity; Purkinje Cells
PubMed: 35803588
DOI: 10.1146/annurev-neuro-091421-125115 -
Neuron Oct 2022Dysregulation of long interspersed nuclear element 1 (LINE-1, L1), a dominant class of transposable elements in the human genome, has been linked to neurodegenerative...
Dysregulation of long interspersed nuclear element 1 (LINE-1, L1), a dominant class of transposable elements in the human genome, has been linked to neurodegenerative diseases, but whether elevated L1 expression is sufficient to cause neurodegeneration has not been directly tested. Here, we show that the cerebellar expression of L1 is significantly elevated in ataxia telangiectasia patients and strongly anti-correlated with the expression of epigenetic silencers. To examine the role of L1 in the disease etiology, we developed an approach for direct targeting of the L1 promoter for overexpression in mice. We demonstrated that L1 activation in the cerebellum led to Purkinje cell dysfunctions and degeneration and was sufficient to cause ataxia. Treatment with a nucleoside reverse transcriptase inhibitor blunted ataxia progression by reducing DNA damage, attenuating gliosis, and reversing deficits of molecular regulators for calcium homeostasis in Purkinje cells. Our study provides the first direct evidence that L1 activation can drive neurodegeneration.
Topics: Animals; Humans; Mice; Ataxia; Calcium; Cerebellum; DNA Transposable Elements; Nucleosides; Purkinje Cells; Reverse Transcriptase Inhibitors; Long Interspersed Nucleotide Elements
PubMed: 36070749
DOI: 10.1016/j.neuron.2022.08.011 -
Nature May 2022Cellular diversification is critical for specialized functions of the brain including learning and memory. Single-cell RNA sequencing facilitates transcriptomic...
Cellular diversification is critical for specialized functions of the brain including learning and memory. Single-cell RNA sequencing facilitates transcriptomic profiling of distinct major types of neuron, but the divergence of transcriptomic profiles within a neuronal population and their link to function remain poorly understood. Here we isolate nuclei tagged in specific cell types followed by single-nucleus RNA sequencing to profile Purkinje neurons and map their responses to motor activity and learning. We find that two major subpopulations of Purkinje neurons, identified by expression of the genes Aldoc and Plcb4, bear distinct transcriptomic features. Plcb4, but not Aldoc, Purkinje neurons exhibit robust plasticity of gene expression in mice subjected to sensorimotor and learning experience. In vivo calcium imaging and optogenetic perturbation reveal that Plcb4 Purkinje neurons have a crucial role in associative learning. Integrating single-nucleus RNA sequencing datasets with weighted gene co-expression network analysis uncovers a learning gene module that includes components of FGFR2 signalling in Plcb4 Purkinje neurons. Knockout of Fgfr2 in Plcb4 Purkinje neurons in mice using CRISPR disrupts motor learning. Our findings define how diversification of Purkinje neurons is linked to their responses in motor learning and provide a foundation for understanding their differential vulnerability to neurological disorders.
Topics: Animals; Cerebellum; Learning; Mice; Mice, Knockout; Neuronal Plasticity; Neurons; Purkinje Cells; Transcriptome
PubMed: 35545673
DOI: 10.1038/s41586-022-04711-3 -
Neuron Feb 2024Neurodegeneration is a protracted process involving progressive changes in myriad cell types that ultimately results in the death of vulnerable neuronal populations. To...
Neurodegeneration is a protracted process involving progressive changes in myriad cell types that ultimately results in the death of vulnerable neuronal populations. To dissect how individual cell types within a heterogeneous tissue contribute to the pathogenesis and progression of a neurodegenerative disorder, we performed longitudinal single-nucleus RNA sequencing of mouse and human spinocerebellar ataxia type 1 (SCA1) cerebellar tissue, establishing continuous dynamic trajectories of each cell population. Importantly, we defined the precise transcriptional changes that precede loss of Purkinje cells and, for the first time, identified robust early transcriptional dysregulation in unipolar brush cells and oligodendroglia. Finally, we applied a deep learning method to predict disease state accurately and identified specific features that enable accurate distinction of wild-type and SCA1 cells. Together, this work reveals new roles for diverse cerebellar cell types in SCA1 and provides a generalizable analysis framework for studying neurodegeneration.
Topics: Animals; Mice; Humans; Ataxin-1; Mice, Transgenic; Spinocerebellar Ataxias; Cerebellum; Purkinje Cells; Disease Models, Animal
PubMed: 38016472
DOI: 10.1016/j.neuron.2023.10.039 -
Neuron Aug 2023Toxic proteinaceous deposits and alterations in excitability and activity levels characterize vulnerable neuronal populations in neurodegenerative diseases. Using...
Toxic proteinaceous deposits and alterations in excitability and activity levels characterize vulnerable neuronal populations in neurodegenerative diseases. Using in vivo two-photon imaging in behaving spinocerebellar ataxia type 1 (Sca1) mice, wherein Purkinje neurons (PNs) degenerate, we identify an inhibitory circuit element (molecular layer interneurons [MLINs]) that becomes prematurely hyperexcitable, compromising sensorimotor signals in the cerebellum at early stages. Mutant MLINs express abnormally elevated parvalbumin, harbor high excitatory-to-inhibitory synaptic density, and display more numerous synaptic connections on PNs, indicating an excitation/inhibition imbalance. Chemogenetic inhibition of hyperexcitable MLINs normalizes parvalbumin expression and restores calcium signaling in Sca1 PNs. Chronic inhibition of mutant MLINs delayed PN degeneration, reduced pathology, and ameliorated motor deficits in Sca1 mice. Conserved proteomic signature of Sca1 MLINs, shared with human SCA1 interneurons, involved the higher expression of FRRS1L, implicated in AMPA receptor trafficking. We thus propose that circuit-level deficits upstream of PNs are one of the main disease triggers in SCA1.
Topics: Mice; Humans; Animals; Purkinje Cells; Parvalbumins; Proteomics; Mice, Transgenic; Spinocerebellar Ataxias; Cerebellum; Interneurons; Nerve Degeneration; Disease Models, Animal; Ataxin-1; Membrane Proteins; Nerve Tissue Proteins
PubMed: 37321222
DOI: 10.1016/j.neuron.2023.05.016 -
Experimental Neurology Dec 2021The dystonias are a group of disorders characterized by excessive muscle contractions leading to abnormal repetitive movements or postures. In blepharospasm, the face is...
BACKGROUND
The dystonias are a group of disorders characterized by excessive muscle contractions leading to abnormal repetitive movements or postures. In blepharospasm, the face is affected, leading to excessive eye blinking and spasms of muscles around the eyes. The pathogenesis of blepharospasm is not well understood, but several imaging studies have implied subtle structural defects in several brain regions, including the cerebellum.
OBJECTIVE
To delineate cerebellar pathology in brains collected at autopsy from 7 human subjects with blepharospasm and 9 matched controls.
METHODS
Sections from 3 cerebellar regions were sampled and processed using Nissl and silver impregnation stains. Purkinje neurons were the focus of the evaluation, along with as several other subtle pathological features of cerebellar dysfunction such as Purkinje neuron axonal swellings (torpedo bodies), proliferation of basket cell processes around Purkinje neurons (hairy baskets), empty baskets (missing Purkinje neurons), and displacement of cell soma from their usual location (ectopic Purkinje neurons).
RESULTS
The results revealed a significant reduction in Purkinje neuron and torpedo body density, but no changes in any of the other measures.
CONCLUSIONS
These findings demonstrate subtle neuropathological changes similar to those reported for subjects with cervical dystonia. These findings may underly some of the subtle imaging changes reported for blepharospasm.
Topics: Aged; Aged, 80 and over; Blepharospasm; Cerebellum; Female; Humans; Male; Middle Aged; Purkinje Cells
PubMed: 34464652
DOI: 10.1016/j.expneurol.2021.113855 -
Nature Jan 2024The expansion of the neocortex, a hallmark of mammalian evolution, was accompanied by an increase in cerebellar neuron numbers. However, little is known about the... (Comparative Study)
Comparative Study
The expansion of the neocortex, a hallmark of mammalian evolution, was accompanied by an increase in cerebellar neuron numbers. However, little is known about the evolution of the cellular programmes underlying the development of the cerebellum in mammals. In this study we generated single-nucleus RNA-sequencing data for around 400,000 cells to trace the development of the cerebellum from early neurogenesis to adulthood in human, mouse and the marsupial opossum. We established a consensus classification of the cellular diversity in the developing mammalian cerebellum and validated it by spatial mapping in the fetal human cerebellum. Our cross-species analyses revealed largely conserved developmental dynamics of cell-type generation, except for Purkinje cells, for which we observed an expansion of early-born subtypes in the human lineage. Global transcriptome profiles, conserved cell-state markers and gene-expression trajectories across neuronal differentiation show that cerebellar cell-type-defining programmes have been overall preserved for at least 160 million years. However, we also identified many orthologous genes that gained or lost expression in cerebellar neural cell types in one of the species or evolved new expression trajectories during neuronal differentiation, indicating widespread gene repurposing at the cell-type level. In sum, our study unveils shared and lineage-specific gene-expression programmes governing the development of cerebellar cells and expands our understanding of mammalian brain evolution.
Topics: Animals; Humans; Mice; Cell Lineage; Cerebellum; Evolution, Molecular; Fetus; Gene Expression Regulation, Developmental; Neurogenesis; Neurons; Opossums; Purkinje Cells; Single-Cell Gene Expression Analysis; Species Specificity; Transcriptome; Mammals
PubMed: 38029793
DOI: 10.1038/s41586-023-06884-x -
Cells Sep 2022Despite their homogeneous appearance, Purkinje cells are remarkably diverse with respect to their molecular phenotypes, physiological properties, afferent and efferent... (Review)
Review
Despite their homogeneous appearance, Purkinje cells are remarkably diverse with respect to their molecular phenotypes, physiological properties, afferent and efferent connectivity, as well as their vulnerability to insults. Heterogeneity in Purkinje cells arises early in development, with molecularly distinct embryonic cell clusters present soon after Purkinje cell specification. Traditional methods have characterized cerebellar development and cell types, including Purkinje cell subtypes, based on knowledge of selected markers. However, recent single-cell RNA sequencing studies provide vastly increased resolution of the whole cerebellar transcriptome. Here we draw together the results of multiple single-cell transcriptomic studies in developing and adult cerebellum in both mouse and human. We describe how this detailed transcriptomic data has increased our understanding of the intricate development and function of Purkinje cells and provides first clues into features specific to human cerebellar development.
Topics: Animals; Biomarkers; Cerebellum; Humans; Mice; Nerve Tissue Proteins; Phenotype; Purkinje Cells
PubMed: 36139493
DOI: 10.3390/cells11182918 -
Pharmacological Research May 2023Specific medications to combat cerebellar ataxias, a group of debilitating movement disorders characterized by difficulty with walking, balance and coordination, are...
Specific medications to combat cerebellar ataxias, a group of debilitating movement disorders characterized by difficulty with walking, balance and coordination, are still lacking. Notably, cerebellar microglial activation appears to be a common feature in different types of ataxic patients and rodent models. However, direct evidence that cerebellar microglial activation in vivo is sufficient to induce ataxia is still lacking. Here, by employing chemogenetic approaches to manipulate cerebellar microglia selectively and directly, we found that specific chemogenetic activation of microglia in the cerebellar vermis directly leads to ataxia symptoms in wild-type mice and aggravated ataxic motor deficits in 3-acetylpyridine (3-AP) mice, a classic mouse model of cerebellar ataxia. Mechanistically, cerebellar microglial proinflammatory activation induced by either chemogenetic M3D(Gq) stimulation or 3-AP modeling hyperexcites Purkinje cells (PCs), which consequently triggers ataxia. Blockade of microglia-derived TNF-α, one of the most important proinflammatory cytokines, attenuates the hyperactivity of PCs driven by microglia. Moreover, chemogenetic inhibition of cerebellar microglial activation or suppression of cerebellar microglial activation by PLX3397 and minocycline reduces the production of proinflammatory cytokines, including TNF-α, to effectively restore the overactivation of PCs and alleviate motor deficits in 3-AP mice. These results suggest that cerebellar microglial activation may aggravate the neuroinflammatory response and subsequently induce dysfunction of PCs, which in turn triggers ataxic motor deficits. Our findings thus reveal a causal relationship between proinflammatory activation of cerebellar microglia and ataxic motor symptoms, which may offer novel evidence for therapeutic intervention for cerebellar ataxias by targeting microglia and microglia-derived inflammatory mediators.
Topics: Mice; Animals; Cerebellar Ataxia; Purkinje Cells; Microglia; Tumor Necrosis Factor-alpha; Cerebellum; Cytokines
PubMed: 37068531
DOI: 10.1016/j.phrs.2023.106773 -
Biomolecules May 2023Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder that affects one or two individuals per 100,000. The disease is caused by an... (Review)
Review
Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder that affects one or two individuals per 100,000. The disease is caused by an extended CAG repeat in exon 8 of the gene and is characterized mostly by a profound loss of cerebellar Purkinje cells, leading to disturbances in coordination, balance, and gait. At present, no curative treatment is available for SCA1. However, increasing knowledge on the cellular and molecular mechanisms of SCA1 has led the way towards several therapeutic strategies that can potentially slow disease progression. SCA1 therapeutics can be classified as genetic, pharmacological, and cell replacement therapies. These different therapeutic strategies target either the (mutant) RNA or the ataxin-1 protein, pathways that play an important role in downstream SCA1 disease mechanisms or which help restore cells that are lost due to SCA1 pathology. In this review, we will provide a summary of the different therapeutic strategies that are currently being investigated for SCA1.
Topics: Humans; Cerebellum; Spinocerebellar Ataxias; Ataxin-1; Purkinje Cells
PubMed: 37238658
DOI: 10.3390/biom13050788