Genetic ablation of PLA2G6 in mice leads to cerebellar atrophy characterized by Purkinje cell loss and glial cell activation.
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ABSTRACT:
SUBMITTER: Zhao Z
PROVIDER: S-EPMC3203935 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The cerebellar cortex receives neural information from other brain regions to allow fine motor coordination and motor learning. The primary output neurons from the cerebellum are the Purkinje neurons that transmit inhibitory responses to deep cerebellar nuclei through their myelinated axons. Altered morphological organization and electrical properties of the Purkinje axons lead to detrimental changes in locomotor activity often leading to cerebellar ataxias. Two cytoskeletal scaffolding proteins Band 4.1B (4.1B) and Whirlin (Whrn) have been previously shown to play independent roles in axonal domain organization and maintenance in myelinated axons in the spinal cord and sciatic nerves. Immunoblot analysis had indicated cerebellar expression for both 4.1B and Whrn; however, their subcellular localization and cerebellum-specific functions have not been characterized. Using 4.1B and Whrn single and double mutant animals, we show that both proteins are expressed in common cellular compartments of the cerebellum and play cooperative roles in preservation of the integrity of Purkinje neuron myelinated axons. We demonstrate that both 4.1B and Whrn are required for the maintenance of axonal ultrastructure and health. Loss of 4.1B and Whrn leads to axonal transport defects manifested by formation of swellings containing cytoskeletal components, membranous organelles, and vesicles. Moreover, ablation of both proteins progressively affects cerebellar function with impairment in locomotor performance detected by altered gait parameters. Together, our data indicate that 4.1B and Whrn are required for maintaining proper axonal cytoskeletal organization and axonal domains, which is necessary for cerebellum-controlled fine motor coordination.
| S-EPMC6342677 | biostudies-literature
Project description:Purkinje cells (PC) control deep cerebellar nuclei (DCN), which in turn inhibit inferior olive nucleus, closing a positive feedback loop via climbing fibers. PC highly express potassium BK channels but their contribution to the olivo-cerebellar loop is not clear. Using multiple-unit recordings in alert mice we found in that selective deletion of BK channels in PC induces a decrease in their simple spike firing with a beta-range bursting pattern and fast intraburst frequency (~200?Hz). To determine the impact of this abnormal rhythm on the olivo-cerebellar loop we analyzed simultaneous rhythmicity in different cerebellar structures. We found that this abnormal PC rhythmicity is transmitted to DCN neurons with no effect on their mean firing frequency. Long term depression at the parallel-PC synapses was altered and the intra-burst complex spike spikelets frequency was increased without modification of the mean complex spike frequency in BK-PC-/- mice. We argue that the ataxia present in these conditional knockout mice could be explained by rhythmic disruptions transmitted from mutant PC to DCN but not by rate code modification only. This suggests a neuronal mechanism for ataxia with possible implications for human disease.
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Project description:The Cacna1a gene encodes the ?(1A) subunit of voltage-gated Ca(V)2.1 Ca(2+) channels that are involved in neurotransmission at central synapses. Ca(V)2.1-?(1)-knockout (?1KO) mice, which lack Ca(V)2.1 channels in all neurons, have a very severe phenotype of cerebellar ataxia and dystonia, and usually die around postnatal day 20. This early lethality, combined with the wide expression of Ca(V)2.1 channels throughout the cerebellar cortex and nuclei, prohibited determination of the contribution of particular cerebellar cell types to the development of the severe neurobiological phenotype in Cacna1a mutant mice. Here, we crossed conditional Cacna1a mice with transgenic mice expressing Cre recombinase, driven by the Purkinje cell-specific Pcp2 promoter, to specifically ablate the Ca(V)2.1-?(1A) subunit and thereby Ca(V)2.1 channels in Purkinje cells. Purkinje cell Ca(V)2.1-?(1A)-knockout (PC?1KO) mice aged without difficulties, rescuing the lethal phenotype seen in ?1KO mice. PC?1KO mice exhibited cerebellar ataxia starting around P12, much earlier than the first signs of progressive Purkinje cell loss, which appears in these mice between P30 and P45. Secondary cell loss was observed in the granular and molecular layers of the cerebellum and the volume of all individual cerebellar nuclei was reduced. In this mouse model with a cell type-specific ablation of Ca(V)2.1 channels, we show that ablation of Ca(V)2.1 channels restricted to Purkinje cells is sufficient to cause cerebellar ataxia. We demonstrate that spatial ablation of Ca(V)2.1 channels may help in unraveling mechanisms of human disease.
| S-EPMC3311848 | biostudies-literature
Project description:TMEM106B has been recently implicated in multiple neurodegenerative diseases. Here, Rademakers et al. report a late-onset cerebellar Purkinje cell loss and progressive decline in motor function and gait deficits in a conventional Tmem106b-/- mouse model. By using high-power microscopy and bulk RNA sequencing, the authors further identify lysosomal and immune dysfunction as potential underlying mechanisms of the Purkinje cell loss.
| S-EPMC8412084 | biostudies-literature
Project description:Alterations in the expression and activity of the transcriptional coactivator peroxisome proliferator-activated receptor ? coactivator-1? (ppargc1a or PGC-1?) have been reported in multiple movement disorders, yet it is unclear how a lack of PGC-1? impacts transcription and function of the cerebellum, a region with high PGC-1? expression. We show here that mice lacking PGC-1? exhibit ataxia in addition to the previously described deficits in motor coordination. Using q-RT-PCR in cerebellar homogenates from PGC-1?(-/-) mice, we measured expression of 37 microarray-identified transcripts upregulated by PGC-1? in SH-SY5Y neuroblastoma cells with neuroanatomical overlap with PGC-1? or parvalbumin (PV), a calcium buffer highly expressed by Purkinje cells. We found significant reductions in transcripts with synaptic (complexin1, Cplx1; Pacsin2), structural (neurofilament heavy chain, Nefh), and metabolic (isocitrate dehydrogenase 3a, Idh3a; neutral cholesterol ester hydrolase 1, Nceh1; pyruvate dehydrogenase alpha 1, Pdha1; phytanoyl-CoA hydroxylase, Phyh; ubiquinol-cytochrome c reductase, Rieske iron-sulfur polypeptide 1, Uqcrfs1) functions. Using conditional deletion of PGC-1? in PV-positive neurons, we determined that 50% of PGC-1? expression and a reduction in a subset of these transcripts could be explained by its concentration in PV-positive neuronal populations in the cerbellum. To determine whether there were functional consequences associated with these changes, we conducted stereological counts and spike rate analysis in Purkinje cells, a cell type rich in PV, from PGC-1?(-/-) mice. We observed a significant loss of Purkinje cells by 6 weeks of age, and the remaining Purkinje cells exhibited a 50% reduction in spike rate. Together, these data highlight the complexity of PGC-1?'s actions in the central nervous system and suggest that dysfunction in multiple cell types contribute to motor deficits in the context of PGC-1? deficiency.
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Project description:The climbing fiber input to the cerebellar cortex is thought to provide instructive signals that drive the induction of motor skill learning. We found that optogenetic activation of Purkinje cells, the sole output neurons of the cerebellar cortex, can also drive motor learning in mice. This dual control over the induction of learning by climbing fibers and Purkinje cells can expand the learning capacity of motor circuits.
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Project description:Although the cerebellum is traditionally associated with balance and motor function, it also plays wider roles in affective and cognitive behaviors. Evidence suggests that the cerebellar vermis may regulate aggressive behavior, though the cerebellar circuits and patterns of activity that influence aggression remain unclear. We used optogenetic methods to bidirectionally modulate the activity of spatially-delineated cerebellar Purkinje cells to evaluate the impact on aggression in mice. Increasing Purkinje cell activity in the vermis significantly reduced the frequency of attacks in a resident-intruder assay. Reduced aggression was not a consequence of impaired motor function, because optogenetic stimulation did not alter motor performance. In complementary experiments, optogenetic inhibition of Purkinje cells in the vermis increased the frequency of attacks. These results suggest Purkinje cell activity in the cerebellar vermis regulates aggression, and further support the importance of the cerebellum in driving affective behaviors that could contribute to neurological disorders.
| S-EPMC7202893 | biostudies-literature
Project description:The PLA2G6 gene encodes a group VIA calcium-independent phospholipase A2 beta enzyme that selectively hydrolyses glycerophospholipids to release free fatty acids. Mutations in PLA2G6 have been associated with disorders such as infantile neuroaxonal dystrophy, neurodegeneration with brain iron accumulation type II and Karak syndrome. More recently, PLA2G6 was identified as the causative gene in a subgroup of patients with autosomal recessive early-onset dystonia-parkinsonism. Neuropathological examination revealed widespread Lewy body pathology and the accumulation of hyperphosphorylated tau, supporting a link between PLA2G6 mutations and parkinsonian disorders. Here we show that knockout of the Drosophila homologue of the PLA2G6 gene, iPLA2-VIA, results in reduced survival, locomotor deficits and organismal hypersensitivity to oxidative stress. Furthermore, we demonstrate that loss of iPLA2-VIA function leads to a number of mitochondrial abnormalities, including mitochondrial respiratory chain dysfunction, reduced ATP synthesis and abnormal mitochondrial morphology. Moreover, we show that loss of iPLA2-VIA is strongly associated with increased lipid peroxidation levels. We confirmed our findings using cultured fibroblasts taken from two patients with mutations in the PLA2G6 gene. Similar abnormalities were seen including elevated mitochondrial lipid peroxidation and mitochondrial membrane defects, as well as raised levels of cytoplasmic and mitochondrial reactive oxygen species. Finally, we demonstrated that deuterated polyunsaturated fatty acids, which inhibit lipid peroxidation, were able to partially rescue the locomotor abnormalities seen in aged flies lacking iPLA2-VIA gene function, and restore mitochondrial membrane potential in fibroblasts from patients with PLA2G6 mutations. Taken together, our findings demonstrate that loss of normal PLA2G6 gene activity leads to lipid peroxidation, mitochondrial dysfunction and subsequent mitochondrial membrane abnormalities. Furthermore we show that the iPLA2-VIA knockout fly model provides a useful platform for the further study of PLA2G6-associated neurodegeneration.
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Project description:The large-conductance voltage- and calcium-activated potassium (BK) channels are ubiquitously expressed in the brain and play an important role in the regulation of neuronal excitation. Previous work has shown that the total deletion of these channels causes an impaired motor behavior, consistent with a cerebellar dysfunction. Cellular analyses showed that a decrease in spike firing rate occurred in at least two types of cerebellar neurons, namely in Purkinje neurons (PNs) and in Golgi cells. To determine the relative role of PNs, we developed a cell-selective mouse mutant, which lacked functional BK channels exclusively in PNs. The behavioral analysis of these mice revealed clear symptoms of ataxia, indicating that the BK channels of PNs are of major importance for normal motor coordination. By using combined two-photon imaging and patch-clamp recordings in these mutant mice, we observed a unique type of synaptic dysfunction in vivo, namely a severe silencing of the climbing fiber-evoked complex spike activity. By performing targeted pharmacological manipulations combined with simultaneous patch-clamp recordings in PNs, we obtained direct evidence that this silencing of climbing fiber activity is due to a malfunction of the tripartite olivo-cerebellar feedback loop, consisting of the inhibitory synaptic connection of PNs to the deep cerebellar nuclei (DCN), followed by a projection of inhibitory DCN afferents to the inferior olive, the origin of climbing fibers. Taken together, our results establish an essential role of BK channels of PNs for both cerebellar motor coordination and feedback regulation in the olivo-cerebellar loop.
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Project description:Cerebellar circuits are patterned into an array of topographic parasagittal domains called zones. The proper connectivity of zones is critical for motor coordination and motor learning, and in several neurological diseases cerebellar circuits degenerate in zonal patterns. Despite recent advances in understanding zone function, we still have a limited understanding of how zones are formed. Here, we focused our attention on Purkinje cells to gain a better understanding of their specific role in establishing zonal circuits. We used conditional mouse genetics to test the hypothesis that Purkinje cell neurotransmission is essential for refining prefunctional developmental zones into sharp functional zones. Our results show that inhibitory synaptic transmission in Purkinje cells is necessary for the precise patterning of Purkinje cell zones and the topographic targeting of mossy fiber afferents. As expected, blocking Purkinje cell neurotransmission caused ataxia. Using in vivo electrophysiology, we demonstrate that loss of Purkinje cell communication altered the firing rate and pattern of their target cerebellar nuclear neurons. Analysis of Purkinje cell complex spike firing revealed that feedback in the cerebellar nuclei to inferior olive to Purkinje cell loop is obstructed. Loss of Purkinje neurotransmission also caused ectopic zonal expression of tyrosine hydroxylase, which is only expressed in adult Purkinje cells when calcium is dysregulated and if excitability is altered. Our results suggest that Purkinje cell inhibitory neurotransmission establishes the functional circuitry of the cerebellum by patterning the molecular zones, fine-tuning afferent circuitry, and shaping neuronal activity.
| S-EPMC4051975 | biostudies-literature