Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biological Sciences
First Advisor
Gasser, Paul J.
Second Advisor
Mantsch, John R.
Third Advisor
Ghasemzadeh, M. B.
Abstract
The noradrenergic system exerts powerful modulatory influences over fundamental brain processes including attention, arousal, learning, and memory by activating adrenergic receptors on neuronal and glial cells. In addition to triggering rapid, transient changes in cellular physiology that drive short-term behavioral actions, these G-protein-coupled receptors also initiate delayed, long-lasting changes in cellular function by regulating gene expression. For example, in astrocytes, norepinephrine-induced activation of β-adrenergic receptors (β-ARs) rapidly induces glucose mobilization from glycogen stores, while simultaneously initiating delayed changes in the expression of glycogen storage genes. Regulation of gene expression requires adrenergic receptor-initiated intracellular signals to reach the nuclear compartment. To date, all effects of norepinephrine, including nuclear actions, have been attributed to adrenergic receptors localized exclusively to plasma membranes. However, recent studies indicate that β-ARs also localize to cardiomyocyte inner nuclear membranes, and that norepinephrine, a membrane-impermeant ligand, accesses intracellular receptors via organic cation transporter 3 (OCT3)-mediated transport. We previously showed that OCT3 localizes to astrocyte plasma- and outer nuclear membranes, suggesting that β-ARs may localize to inner nuclear membranes in these cells. Here, I test the hypothesis that the inner nuclear membrane is a transporter-gated β-AR signaling platform in astrocytes.In the current studies, I employ differential membrane permeabilization and immunofluorescence, as well as subcellular fractionation and western blot, to reveal that β1-adrenergic receptors (β1-AR) localize to inner nuclear membranes and that Gs-coupled signaling partners are present in astrocyte nuclei. I demonstrate that OCT3 and other catecholamine transporters for norepinephrine are expressed in astrocyte plasma and nuclear membranes, providing diverse mechanisms for norepinephrine to access β1-AR at inner nuclear membranes. Additional studies in our laboratory demonstrated that norepinephrine-induced nuclear β1-AR activation triggers rapid increases in nuclear PKA activity. The current studies begin to explore signaling events downstream of PKA and provide evidence that activation of nuclear β-ARs regulates the activity of the PKA substrate salt-inducible kinase 3 (SIK3). These studies demonstrate that the inner nuclear membrane is a functional β1-AR signaling platform in astrocytes. Nuclear β1-ARs represent a powerful mechanism by which norepinephrine may exert long-lasting influence over astrocyte structure and function.