All ETDs from UAB

Advisory Committee Chair

Michelle Olsen

Advisory Committee Members

John Hablitz

Harald Sontheimer

Michelle Theus

Pamela Vandevord

Document Type

Dissertation

Date of Award

2020

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Astrocytes are the most numerous cells in the brain and play a critical role in maintaining homeostatic extracellular potassium ([K+]e). Maintaining low [K+]e is essential for many cellular functions including maintenance of intensely negative resting membrane potentials in the central nervous system. This process is mediated, in part, by a glial-specific, inwardly rectifying potassium channel, Kir4.1. Underscoring the role of Kir4.1 in CNS functioning, genetic mutations in Kcnj10, the gene which encodes Kir4.1, causes seizures, ataxia and developmental disability in humans. Notably, loss of Kir4.1 protein and mRNA are consistently observed after CNS injury, and in a number of neurological diseases linked to hyperexcitability and neuronal dysfunction, suggesting that Kir4.1 could represent a potential therapeutic target.  Despite this, little is known about how Kir4.1 expression is regulated under pathological conditions.  Our lab has previously identified DNA hypomethylation of the Kcnj10 gene as a driver for the increases in Kir4.1 mRNA and protein levels during astrocyte maturation. Treatment of cultured astrocytes with DNMT inhibitors was sufficient to increase Kcnj10 mRNA expression as well as Kir4.1 currents in these astrocytes. Alternatively, hypermethylation of the Kcnj10 CpG islands in the promoter of an in-vivo luciferase assay lead to decreased promoter activity, suggesting increases in DNA methylation may drive reductions in Kir4.1 expression.  This dissertation utilizes two immensely different injury models to evaluate changes in methylation of Kcnj10 as a potential epigenetic mechanism for the early and sustained loss of Kir4.1 mRNA and protein commonly identified in both pathologies. Using whole hippocampal tissue and isolated astrocytes, from a lithium-pilocarpine model of epilepsy, we identified consistent hypermethylation of the intronic CpG island 2.  This data was further supported by second injury paradigm, a fifth cervical (C5) vertebral hemi-contusion model of spinal cord injury model that showed strikingly similar changes in DNA methylation.  Interestingly, previous work indicates the same gene region is significantly hypomethylated when transcription increases during astrocyte maturation. Together this suggest that DNA methylation can act as a bidirectional modulator of Kcnj10 expression and may represent a valid target for the restoring astroglial Kir4.1 expression following CNS insult.

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