DNA Methylation-Mediated Modulation of Endocytosis as Potential Mechanism for Synaptic Function Regulation in Murine Inhibitory Cortical Interneurons

Abstract

The balance of excitation and inhibition is essential for cortical information processing, relying on the tight orchestration of the underlying subcellular processes. Dynamic transcriptional control by DNA methylation, catalyzed by DNA methyltransferases (DNMTs), and DNA demethylation, achieved by ten–eleven translocation (TET)-dependent mechanisms, is proposed to regulate synaptic function in the adult brain with implications for learning and memory. However, focus so far is laid on excitatory neurons. Given the crucial role of inhibitory cortical interneurons in cortical information processing and in disease, deciphering the cellular and molecular mechanisms of GABAergic transmission is fundamental. The emerging relevance of DNMT and TET-mediated functions for synaptic regulation irrevocably raises the question for the targeted subcellular processes and mechanisms. In this study, we analyzed the role dynamic DNA methylation has in regulating cortical interneuron function. We found that DNMT1 and TET1/TET3 contrarily modulate clathrin-mediated endocytosis. Moreover, we provide evidence that DNMT1 influences synaptic vesicle replenishment and GABAergic transmission, presumably through the DNA methylation-dependent transcriptional control over endocytosis-related genes. The relevance of our findings is supported by human brain sample analysis, pointing to a potential implication of DNA methylation-dependent endocytosis regulation in the pathophysiology of temporal lobe epilepsy, a disease characterized by disturbed synaptic transmission.

DNA Methyltransferase 1 (DNMT1) Function Is Implicated in the Age-Related Loss of Cortical Interneurons

“…In general, far more genes were differentially expressed (3,868 genes) and/or methylated (3,135 genes) between young genotypes (Pensold et al, 2020). However, among neither the differentially expressed genes, nor among those genes both differentially expressed and methylated, we found a significant enrichment of apoptosis or cell death-related genes (data not shown).…”

“…In stark contrast to the comparison of the 18 months old genotypes, we determined a highly significant overlap (P = 2.2E-16, Fisher's Exact test for gene set enrichment analysis; odds ratio = 0.434) of 645 genes between young control and Dnmt1 knockout interneurons, which display significant differences in both DNA methylation and gene expression (Pensold et al, 2020).…”

“…Among the genes which we identified as repressed by DNMT1-dependent DNA methylation in young controls, we found an overrepresentation of endocytosis and endosome-related genes (Pensold et al, 2020). Furthermore, during analysis of all genes differentially expressed upon Dnmt1 deletion, irrespective of altered DNA methylation, lysosome and ubiquitination-related genes were also found repressed by DNMT1 (Pensold et al, 2020; Figure 4G). Together these results demonstrate that endocytosis and degradative pathways are controlled by DNMT1.…”

“…DNA methylation executed by DNA methyltransferases (DNMTs) affects gene expression through diverse mechanisms (Maunakea et al, 2010;Gelfman et al, 2013;Lyko, 2018) and is implicated in the pathogenesis of brain aging (Cui and Xu, 2018). We have recently found that DNMT1-dependent DNA methylation modulates synaptic function of cortical PV interneurons by acting on endocytosis-mediated vesicle recycling (Pensold et al, 2020). Since regulation of both synaptic function and DNA methylation are involved in brain aging, we here investigate whether DNMT1-dependent transcriptional control in PV interneurons contributes to their age-related defects.…”

DNA Methylation-Dependent Dysregulation of GABAergic Interneuron Functionality in Neuropsychiatric Diseases

“…Instead, repressive DNMT1-dependent DNA methylation was identified to act on endocytosis-related gene expression in parvalbuminergic cortical interneurons. Functional validation experiments proposed that DNA methylation catalyzed by DNMT1 restricts clathrin-mediated endocytosis at pre-synapses, and through this synaptic vesicle recycling and GABAergic transmission (Pensold et al, 2020). Data obtained from human hippocampal biopsies of patients with temporal lobe epilepsy revealed a correlation between DNA methylation-dependent transcriptional regulation of endocytosis-related genes with the patients' seizure rates (Pensold et al, 2020).…”