ABSTRACT
Dendritic spines are the post-synaptic targets of excitatory synaptic inputs that undergo extensive proliferation and maturation during the first postnatal month in mice. However, our understanding of the molecular mechanisms that regulate spines during this critical period is limited. Previous work has shown that Pannexin 1 (Panx1) regulates neurite growth and synaptic plasticity. We therefore investigated the impact of global Panx1 KO on spontaneous cortical neuron activity using Ca2+ imaging and in silico network analysis. Panx1 KO increased both the number and size of spontaneous co-active cortical neuron network ensembles. To understand the basis for these findings, we investigated Panx1 expression in postnatal synaptosome preparations from early postnatal mouse cortex. Between 2 and 4 postnatal weeks, we observed a precipitous drop in cortical synaptosome protein levels of Panx1, suggesting it regulates synapse proliferation and/or maturation. At the same time points, we observed significant enrichment of the excitatory postsynaptic density proteins PSD-95, GluA1 and GluN2a in cortical synaptosomes from global Panx1 knockout mice. Ex vivo analysis of pyramidal neuron structure in somatosensory cortex revealed a consistent increase in dendritic spine densities in both male and female Panx1 KO mice. Similar findings were observed in an excitatory neuron-specific Panx1 KO line (Emx1-Cre driven; Panx1 cKOE) and in primary Panx1 KO cortical neurons cultured in vitro. Altogether, our study suggests that Panx1 negatively regulates cortical dendritic spine development.
Significance Statement Our findings reveal an important regulatory role for Pannexin 1 (Panx1) in the formation of connections between nerve cells. We found that removal of the Panx1 altered the ability of nerve cells from the cerebral cortex to fire together. We studied the impact of removing Panx1 on the formation of 'dendritic spines', which are microscopic protrusions that receive information from other nerve cells. We found that removing Panx1 increased the expression of proteins involved in dendritic spine function and also increased the density of dendritic spines on nerve cells of the cerebral cortex. Together these findings suggest Panx1 is a 'brake' on the development of dendritic spines with important implications for the development of nerve cell connections.
Footnotes
The authors declare no competing financial interests. A disclosure has been made with the University of Victoria Research Partnerships and Knowledge Mobilization, and a provisional patent application has been filed for a peptide targeting a Panx1-Crmp2 interaction (US Application No. 62/767,806).
This work was supported by operating grants from the Canadian Institutes of Health Research (CIHR Grant MOP142215), The Scottish Rite Charitable Foundation of Canada (15118) and the University of Victoria-Division of Medical Sciences to L.A.S. L.A.S. is also supported by a Michael Smith Foundation for Health Research and British Columbia Schizophrenia Society Foundation Scholar Award (5900). J.C.S.A. was supported by a University of Victoria Fellowship Graduate Award. ML received partial salary support from the Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, China. L.A.S. is also grateful for infrastructure support from the Canada Foundation for Innovation (29462) and the BC Knowledge Development Fund (804754) for the Leica SP8 confocal microscope system.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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