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Synaptopodin regulates denervation-induced plasticity at hippocampal mossy fiber synapses

ABSTRACT: Neurological diseases can lead to the denervation of brain regions caused by demyelination, traumatic injury or cell death. Nevertheless, the molecular and structural mechanisms underlying lesion-induced reorganization of denervated brain regions are a matter of ongoing investigation. In order to address this issue, we performed an entorhinal cortex lesion (ECL) in mouse organotypic entorhino-hippocampal tissue cultures of both sexes and studied denervation-induced plasticity of mossy fiber synapses, which connect dentate granule cells (dGCs) with CA3 pyramidal cells (CA3-PCs) and play important roles in spatial learning. Partial denervation caused a strengthening of excitatory neurotransmission in dGCs, in CA3-PCs, and their direct synaptic connections as revealed by paired recordings (GC-to-CA3). These functional changes were accompanied by ultrastructural reorganization of mossy fiber synapses, which regularly contain the plasticity-related protein synaptopodin and the spine apparatus organelle. We demonstrate that the spine apparatus organelle and its integral protein synaptopodin are associated with ribosomes in close proximity to synaptic sites and unravel a synaptopodin-related transcriptome. Notably, synaptopodin-deficient tissue preparations that lack the spine apparatus organelle, failed to express lesion-induced synaptic adjustments. Hence, synaptopodin and the spine apparatus organelle play a crucial role in regulating lesion-induced synaptic plasticity at hippocampal mossy fiber synapses.

ORGANISM(S): Mus musculus

PROVIDER: GSE216509 | GEO | 2022/10/28

REPOSITORIES: GEO

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Project description:Many forms of synaptic plasticity are critically dependent upon production of cGMP to trigger activity-dependent increases in synaptic size and strength. Phosphodiesterase 9A (PDE9A) is a high affinity, cGMP-specific phosphodiesterase with widespread distribution in the central nervous system. Inhibition of PDE9A results in significant accumulation of cGMP in brain tissue and cerebrospinal fluid (CSF) of rodents, and increases CSF cGMP in human volunteers. We hypothesized that chronic exposure to a PDE9A inhibitor, and the associated elevations in brain cGMP could provide a therapeutic benefit to vulnerable synapses chronically exposed to Aβ in transgenic mice over-expressing human mutant amyloid precursor protein (Tg2576 mice). A total of N=20 animals per group of 4 month old Tg2576 mice and non-transgenic littermates (WT) were implanted with Alzet osmotic minipumps to deliver vehicle or the PDE9A inhibitor PF-04447943. Neurobehavioral outcomes were measured as conditioned fear response after 28 days of treatment and subsequently brains were harvested for measurement of Aβ, gene expression profiling or synaptic density as assessed by Golgi staining of dendrites. Dendritic spine density on apical dendrites of CA1 neurons exhibited a small but significant deficit in the density of dendritic spines in vehicle treated Tg2576 mice as compared to WT mice. This deficit was ameliorated by 30 days of exposure to PF-04447943. No significant drug effect was observed in WT mice. No significant effects of drug treatment were observed on Aβ levels in Tg2576 mice. Behavioral analysis of Tg2576 mice showed deficits in fear conditioning as early as 2 months old, and therefore were considered unlikely to be due to the accumulation of oligomeric Aβ. These deficits were not affected by drug treatment. Transcriptional profiles of Tg2576 mice treated with drug compared to vehicle showed evidence of regulation of pathways related to synaptic plasticity and remodeling of the dendritic cytoskeleton, consistent with stabilization of vulnerable spine structure. These data supports the hypothesis that PDE9A inhibition can stabilize vulnerable synapses early in the Alzheimer’s disease process. 4-month old Tg2576 mice and non-transgenic (WT) littermates were implanted with minipumps to deliver vehicle or the PDE9A-inhibitor, PF-04447943, for 28 days. At the end of the study, hippocampus and frontal cortex were dissected from n=8 mice per group, RNA was isolated, and hybridized to Affymetrix 430 2.0 mouse whole genome microarray.

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Synaptopodin regulates denervation-induced plasticity at hippocampal mossy fiber synapses

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