The location and functional role for the K+-dependent Na+/Ca2+-exchanger, subtype 4 (NCKX4), in mouse brain
Date
2024-04-18
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Abstract
The K+-dependent Na+/Ca2+ exchanger (NCKX) family has emerged as a major regulator of Ca2+ homeostasis. The family comprises five members (NCKX1-5) that are involved in various neuronal functions. In this thesis, I focus on the fourth member (NCKX4) in the brain. While gene expression analysis and immunoblotting of brain lysates demonstrated high expression of NCKX4 in the brain, the regional distribution of the protein product across the brain is unknown. In Chapter 2, I map the expression of NCKX4 throughout the mouse brain. My data reveal that NCKX4 demonstrates distinct and intense expression in multiple areas involved in crucial functions such as learning and memory, reward processing, movement, and cerebrospinal fluid production. Of interest, NCKX4 expression in the choroid plexus epithelial cells (CPECs) exhibited unexpected intracellular distribution. In Chapter 3, I investigate how NCKX4 contributes to the normal function of CPECs by examining the intracellular structure at which NCKX4 is located and changes induced in Nckx4–/– mice, such as CPEC morphology, CSF composition and secretion, and CPEC subcellular Ca2+ dynamics. My data suggest that NCKX4 is partially localized with markers associated with acidic compartments like endo/lysosomal and secretory vesicles, and loss of NCKX4 may lead to alterations in CSF protein composition. However, no changes in CPEC morphology, CSF ionic concentrations, lateral ventricles volume, or Ca2+ activity were found in Nckx4–/– mice. Finally, based on previous reports that link NCKX4 to Alzheimer’s disease and my data (Chapter 2) that show high expression of NCKX4 in hippocampal mossy fibers, in Chapter 4 I investigate the involvement of NCKX4 in learning and memory through a battery of behavioural experiments. Nckx4–/– mice demonstrate deficits in contextual memory formation and recall as well as less anxiety when placed in an open field. No difference was found in the performance of Nckx4–/– mice in novel object recognition task or Barnes maze compared to wildtype controls. The data presented in this thesis provide an expression map in the brain, with an unexpected subcellular location within CPECs, and reveal undiscovered roles for NCKX4 in neuronal function. Many of these results warrant further investigation.
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Keywords
K+-dependent Na+/Ca2+-exchanger, Calcium transport, Choroid plexus epithelial cells, Neurons, Hippocampus
Citation
Hassan, M. T. A. (2024). The location and functional role for the K+ -dependent Na+ /Ca2+-exchanger, subtype 4 (NCKX4), in mouse brain (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.