Critical role for Piccolo in synaptic vesicle retrieval

Loss of function of the active zone protein Piccolo has recently been linked to a disease, Pontocerebellar Hypoplasia type 3, which causes brain atrophy. Here, we address how Piccolo inactivation in rat neurons adversely affects synaptic function and thus may contribute to neuronal loss. Our analysis shows that Piccolo is critical for the recycling and maintenance of synaptic vesicles. We find that boutons lacking Piccolo have deficits in the Rab5/EEA1 dependent formation of early endosomes and thus the recycling of SVs. Mechanistically, impaired Rab5 function was caused by reduced synaptic recruitment of Pra1, known to interact selectively with the zinc finger domains of Piccolo. Importantly, over-expression of GTPase deficient Rab5 or the Znf1 domain of Piccolo restores the size and recycling of SV pools. These data provide a molecular link between the active zone and endosome sorting at synapses providing hints to how Piccolo contributes to developmental and psychiatric disorders.

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Critical role for Piccolo in Synaptic Vesicle Retrieval

10.1101/330050 ◽

2018 ◽

Author(s):

Frauke Ackermann ◽

Kay O. Schink ◽

Christine Bruns ◽

Zsuzsanna Izsvák ◽

F. Kent Hamra ◽

...

Keyword(s):

Synaptic Vesicle ◽

Active Zone ◽

Synaptic Vesicles ◽

Depressive Disorders ◽

Critical Role ◽

Neuronal Loss ◽

Synaptic Function ◽

Loss Of Function ◽

Early Endosomes ◽

Presynaptic Active Zone

AbstractLoss of function of the presynaptic active zone protein Piccolo has recently been linked to a devastating disease causing brain atrophy. Here, we address how Piccolo inactivation adversely affects synaptic function and thus may contributes to neuronal loss. Our analysis shows that Piccolo is critical for the activity dependent recycling and maintenance of synaptic vesicles (SVs). Specifically, we find that boutons lacking Piccolo have deficits in the Rab5/EEA1 dependent formation of early endosomes and thus the recycling of SVs. Mechanistically, impaired Rab5 function was caused by the reduced synaptic recruitment of Pra1, known to interact selectively with the zinc fingers of Piccolo. Importantly, over-expression of GTPase deficient Rab5 or the Znf1 domain of Piccolo restores the size and recycling of SV pools. These data provide a molecular link between the active zone and endosome sorting at synapses providing hints to how Piccolo contributes to both developmental and psychiatric disorders.Impact StatementThe efficient recycling of synaptic vesicle proteins is critical for the integrity and reliability of synaptic transmission. Increasingly genetic and environmental insults have been shown to affect this recycling pathway, resulting in both cognitive impairment in humans and neurodegenerative diseases, yet the underlying mechanisms are poorly understood. Here we could show that the presynaptic active zone protein Piccolo regulates efficient recycling of synaptic vesicles via Pra1 and Rab5, perhaps explaining why Piccolo loss of function contributes to Pontocerebellar Hypoplasia and major depressive disorders.

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Trimeric Tau Is Toxic to Human Neuronal Cells at Low Nanomolar Concentrations

International Journal of Cell Biology ◽

10.1155/2013/260787 ◽

2013 ◽

Vol 2013 ◽

pp. 1-9 ◽

Cited By ~ 41

Author(s):

Huilai Tian ◽

Eliot Davidowitz ◽

Patricia Lopez ◽

Sharareh Emadi ◽

James Moe ◽

...

Keyword(s):

Splice Variants ◽

Critical Role ◽

Neuroblastoma Cells ◽

Neuronal Loss ◽

Synaptic Function ◽

Human Neuroblastoma ◽

Force Microscopy ◽

Atomic Force ◽

Therapeutic Development ◽

Human Neuronal Cells

In Alzheimer’s disease (AD), tau aggregates into fibrils and higher order neurofibrillary tangles, a key histopathological feature of AD. However, soluble oligomeric tau species may play a more critical role in AD progression since these tau species correlate better with neuronal loss and cognitive dysfunction. Recent studies show that extracellular oligomeric tau can inhibit memory formation and synaptic function and also transmit pathology to neighboring neurons. However, the specific forms of oligomeric tau involved in toxicity are still unknown. Here, we used two splice variants of recombinant human tau and generated monomeric, dimeric, and trimeric fractions of each isoform. The composition of each fraction was verified chromatographically and also by atomic force microscopy. The toxicity of each fraction toward both human neuroblastoma cells and cholinergic-like neurons was assessed. Trimeric, but not monomeric or dimeric, tau oligomers of both splice variants were neurotoxic at low nanomolar concentrations. Further characterization of tau oligomer species with disease-specific modifications and morphologies is necessary to identify the best targets for the development of biomarker and therapeutic development for AD and related tauopathies.

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MINPP1 prevents intracellular accumulation of the cation chelator inositol hexakisphosphate and is mutated in Pontocerebellar Hypoplasia

10.1101/2020.05.17.100248 ◽

2020 ◽

Author(s):

Ekin Ucuncu ◽

Karthyayani Rajamani ◽

Miranda S.C. Wilson ◽

Daniel Medina-Cano ◽

Nami Altin ◽

...

Keyword(s):

Critical Role ◽

Distinct Type ◽

Cell Physiology ◽

Inositol Polyphosphate ◽

Loss Of Function ◽

Pontocerebellar Hypoplasia ◽

Inositol Polyphosphates ◽

Induced Pluripotent ◽

Basal Ganglia Involvement ◽

Polyphosphate Metabolism

ABSTRACTInositol polyphosphates are vital metabolic and secondary messengers, involved in diverse cellular functions. Therefore, tight regulation of inositol polyphosphate metabolism is essential for proper cell physiology. Here, we describe an early-onset neurodegenerative syndrome caused by loss-of-function mutations in the multiple inositol polyphosphate phosphatase 1 gene (MINPP1). Patients were found to have a distinct type of Pontocerebellar Hypoplasia with typical basal ganglia involvement on neuroimaging. We found that patient-derived and genome edited MINPP1-/- induced pluripotent stem cells (iPSCs) are not able to differentiate efficiently into neurons. MINPP1 deficiency results in an intracellular imbalance of the inositol polyphosphate metabolism. This metabolic defect is characterized by an accumulation of highly phosphorylated inositols, mostly inositol hexakiphosphate (IP6), detected in HEK293, fibroblasts, iPSCs and differentiating neurons lacking MINPP1. In mutant cells, higher IP6 level is expected to be associated with an increased chelation of intracellular cations, such as iron or calcium, resulting in decreased levels of available ions. These data suggest the involvement of IP6-mediated chelation on Pontocerebellar Hypoplasia disease pathology and thereby highlight the critical role of MINPP1 in the regulation of human brain development and homeostasis.

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Oligodendrocyte-encoded Kir4.1 function is required for axonal integrity

eLife ◽

10.7554/elife.36428 ◽

2018 ◽

Vol 7 ◽

Cited By ~ 28

Author(s):

Lucas Schirmer ◽

Wiebke Möbius ◽

Chao Zhao ◽

Andrés Cruz-Herranz ◽

Lucile Ben Haim ◽

...

Keyword(s):

Late Onset ◽

Critical Role ◽

Neuronal Loss ◽

Conditional Knockout ◽

Motor Deficits ◽

Loss Of Function ◽

Axonal Dysfunction ◽

Retinal Thinning

Glial support is critical for normal axon function and can become dysregulated in white matter (WM) disease. In humans, loss-of-function mutations of KCNJ10, which encodes the inward-rectifying potassium channel KIR4.1, causes seizures and progressive neurological decline. We investigated Kir4.1 functions in oligodendrocytes (OLs) during development, adulthood and after WM injury. We observed that Kir4.1 channels localized to perinodal areas and the inner myelin tongue, suggesting roles in juxta-axonal K+ removal. Conditional knockout (cKO) of OL-Kcnj10 resulted in late onset mitochondrial damage and axonal degeneration. This was accompanied by neuronal loss and neuro-axonal dysfunction in adult OL-Kcnj10 cKO mice as shown by delayed visual evoked potentials, inner retinal thinning and progressive motor deficits. Axon pathologies in OL-Kcnj10 cKO were exacerbated after WM injury in the spinal cord. Our findings point towards a critical role of OL-Kir4.1 for long-term maintenance of axonal function and integrity during adulthood and after WM injury.

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Autoantibodies to synapsin I sequestrate synapsin I and alter synaptic function

Cell Death and Disease ◽

10.1038/s41419-019-2106-z ◽

2019 ◽

Vol 10 (11) ◽

Cited By ~ 1

Author(s):

Anna Rocchi ◽

Silvio Sacchetti ◽

Antonio De Fusco ◽

Silvia Giovedi ◽

Barbara Parisi ◽

...

Keyword(s):

Synaptic Vesicles ◽

Hippocampal Neurons ◽

Neurological Diseases ◽

Synaptic Function ◽

Inhibitory Synapses ◽

Synapsin I ◽

Loss Of Function ◽

Reduced Density ◽

Cytoplasmic Side

AbstractSynapsin I is a phosphoprotein that coats the cytoplasmic side of synaptic vesicles and regulates their trafficking within nerve terminals. Autoantibodies against Syn I have been described in sera and cerebrospinal fluids of patients with numerous neurological diseases, including limbic encephalitis and clinically isolated syndrome; however, the effects and fate of autoantibodies in neurons are still unexplored. We found that in vitro exposure of primary hippocampal neurons to patient’s autoantibodies to SynI decreased the density of excitatory and inhibitory synapses and impaired both glutamatergic and GABAergic synaptic transmission. These effects were reproduced with a purified SynI antibody and completely absent in SynI knockout neurons. Autoantibodies to SynI are internalized by FcγII/III-mediated endocytosis, interact with endogenous SynI, and promote its sequestration and intracellular aggregation. Neurons exposed to human autoantibodies to SynI display a reduced density of SVs, mimicking the SynI loss-of-function phenotype. Our data indicate that autoantibodies to intracellular antigens such as SynI can reach and inactivate their targets and suggest that an antibody-mediated synaptic dysfunction may contribute to the evolution and progression of autoimmune-mediated neurological diseases positive for SynI autoantibodies.

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Bi-allelic variants in TSPOAP1, encoding the active zone protein RIMBP1, cause autosomal recessive dystonia

10.1101/2020.05.24.086215 ◽

2020 ◽

Cited By ~ 1

Author(s):

Niccolò E. Mencacci ◽

Marisa M. Brockmann ◽

Jinye Dai ◽

Sander Pajusalu ◽

Burcu Atasu ◽

...

Keyword(s):

Active Zone ◽

Autosomal Recessive ◽

Critical Role ◽

Cerebellar Atrophy ◽

Missense Variant ◽

Loss Of Function ◽

Generalized Dystonia ◽

Motor Abnormalities ◽

Vitro Analysis

ABSTRACTDystonia is a debilitating hyperkinetic movement disorder, frequently transmitted as a monogenic trait. Here, we describe homozygous frameshift, nonsense and missense variants in TSPOAP1, encoding the active zone RIM-binding protein 1 (RIMBP1), as a novel genetic cause of autosomal recessive dystonia in seven subjects from three unrelated families. Subjects carrying loss-of-function variants presented with juvenile- onset progressive generalized dystonia, associated with intellectual disability and cerebellar atrophy. Conversely, subjects carrying a pathogenic missense variant (p.Gly1808Ser) presented with isolated adult-onset focal dystonia. In mice, complete loss of RIMBP1, known to reduce neurotransmission, led to motor abnormalities reminiscent of dystonia, decreased Purkinje cell dendritic arborization, and reduced numbers of cerebellar synapses. In vitro analysis of the p.Gly1808Ser variant showed larger spike-evoked calcium transients and enhanced neurotransmission, suggesting that RIMBP1-linked dystonia can be caused by either reduced or enhanced rates of spike-evoked release in relevant neural networks. Our findings establish a direct link between presynaptic RIMBP1 dysfunction and dystonia and highlight the critical role played by well-balanced neurotransmission in motor control and disease pathogenesis.

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Loss of Piccolo function in rats induces Pontocerebellar Hypoplasia type 3-like phenotypes

10.1101/774422 ◽

2019 ◽

Author(s):

Joanne Falck ◽

Christine Bruns ◽

Sheila Hoffmann ◽

Isabelle Straub ◽

Erik J. Plautz ◽

...

Keyword(s):

Active Zone ◽

Motor Coordination ◽

Mossy Fiber ◽

Brain Size ◽

Pontocerebellar Hypoplasia ◽

Functional Link ◽

Genetic Studies ◽

Presynaptic Active Zone ◽

And Function ◽

Type 3

AbstractPiccolo, a presynaptic active zone protein, is best known for its role in the regulated assembly and function of vertebrate synapses. Genetic studies suggest a further link to several psychiatric disorders as well as Pontocerebellar Hypoplasia type 3 (PCH3), although a causal relationship is lacking. We have characterized recently generated knockout (Pclogt/gt) rats. Analysis revealed a dramatic reduction in brain size compared to wildtype (Pclowt/wt) animals, attributed to a decrease in the size of the cerebral cortical, cerebellar and pontine regions. Analysis of the cerebellum and brainstem revealed a reduced granule cell (GC) layer and a reduction in size of pontine nuclei. Moreover, the maturation of mossy fiber (MF) afferents from pontine neurons and the expression of the α6 GABAA receptor subunit at the MF-GC synapse are perturbed, as well as the innervation of Purkinje cells by cerebellar climbing fibers (CFs). Ultrastructural and functional studies revealed a reduced size of MF boutons, with fewer synaptic vesicles and altered synaptic transmission. These data imply that Piccolo is required for the normal development, maturation and function of neuronal networks formed between the brainstem and cerebellum. Consistently, behavioral studies demonstrated that adult Pclogt/gt rats display impaired motor coordination, despite adequate performance in tasks that reflect muscle strength and locomotion. Together these data suggest that loss of Piccolo function in patients with PCH3 could be causal for many of the observed anatomical and behavioral symptoms, and that the further analysis of these animals could provide fundamental mechanistic insights into this devastating disorder.Significance StatementPontocerebellar Hypoplasia type 3 is a devastating developmental disorder associated with severe developmental delay, progressive microcephaly with brachycephaly, optic atrophy, seizures and hypertonia with hyperreflexia. Recent genetic studies have identified non-sense mutations in the coding region of the Piccolo gene, suggesting a functional link between this disorder and the presynaptic active zone. Our analysis of Piccolo knockout rats supports this hypothesis, formally demonstrating that anatomical and behavioral phenotypes seen in patients with PCH3 are also exhibited by these Piccolo deficient animals.

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MINPP1 prevents intracellular accumulation of the chelator inositol hexakisphosphate and is mutated in Pontocerebellar Hypoplasia

Nature Communications ◽

10.1038/s41467-020-19919-y ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

Ekin Ucuncu ◽

Karthyayani Rajamani ◽

Miranda S. C. Wilson ◽

Daniel Medina-Cano ◽

Nami Altin ◽

...

Keyword(s):

Critical Role ◽

Distinct Type ◽

Hek293 Cells ◽

Cell Physiology ◽

Inositol Polyphosphate ◽

Loss Of Function ◽

Pontocerebellar Hypoplasia ◽

Inositol Hexakisphosphate ◽

Inositol Polyphosphates ◽

Polyphosphate Metabolism

AbstractInositol polyphosphates are vital metabolic and secondary messengers, involved in diverse cellular functions. Therefore, tight regulation of inositol polyphosphate metabolism is essential for proper cell physiology. Here, we describe an early-onset neurodegenerative syndrome caused by loss-of-function mutations in the multiple inositol-polyphosphate phosphatase 1 gene (MINPP1). Patients are found to have a distinct type of Pontocerebellar Hypoplasia with typical basal ganglia involvement on neuroimaging. We find that patient-derived and genome edited MINPP1−/− induced stem cells exhibit an inefficient neuronal differentiation combined with an increased cell death. MINPP1 deficiency results in an intracellular imbalance of the inositol polyphosphate metabolism. This metabolic defect is characterized by an accumulation of highly phosphorylated inositols, mostly inositol hexakisphosphate (IP6), detected in HEK293 cells, fibroblasts, iPSCs and differentiating neurons lacking MINPP1. In mutant cells, higher IP6 level is expected to be associated with an increased chelation of intracellular cations, such as iron or calcium, resulting in decreased levels of available ions. These data suggest the involvement of IP6-mediated chelation on Pontocerebellar Hypoplasia disease pathology and thereby highlight the critical role of MINPP1 in the regulation of human brain development and homeostasis.

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