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Functions of PDLIM2 protein in maintaining intestinal homeostasis
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Date
2024
Authors
Ward, Stephanie
Journal Title
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Volume Title
Publisher
University College Cork
Published Version
Abstract
Disruption to epithelial integrity is a common feature across disease pathogenesis and in tumour biology. Regulation of important cellular signalling pathways often becomes dysregulated resulting in aberrant activity, which contributes to the disease progression. In the context of cellular adhesion, loss of cell-cell and cell-extracellular matrix adhesions weakens the integrity of the epithelium which sensitises tissues to injury, exposure to microbial content, or permits cancer cells to undergo epithelial-mesenchymal transition (EMT) and metastasise.
PDLIM2 is a cytoskeletal and nuclear associated protein which regulates the stability of many transcription factors associated with adhesion, inflammation, and EMT. Its repression during disease and cancer alters the stability of adhesion molecules, disrupts epithelial polarisation, and sustains activation of pro-inflammatory pathways which further aggravates symptoms. Nevertheless, high PDLIM2 expression in the tumour epithelia also contributes to an aggressive cancer phenotype. Thus, the balance in PDLIM2 expression is essential for maintaining epithelial homeostasis. This thesis, therefore, aims to investigate how expression of PDLIM2 may contribute to disease pathophysiology and the development of cancer.
PDLIM2’s function was evaluated in the colorectal cancer cell line, Caco-2, as well as in murine models. In Caco-2 cells, PDLIM2 expression was either suppressed or knocked out to characterise the phenotypic changes which occur in the absence of PDLIM2, and to identify potential mechanistic factors. PDLIM2 wildtypes (PDLIM2+/+) and knockout (PDLIM2-/-) mice were assessed in relation to ulcerative colitis and colitis-associated colorectal cancer development to analyse PDLIM2’s function in disease and this data was compared to existing datasets of human colitis.
Suppression and knockout of PDLIM2 in the Caco-2 cell line altered key adhesion pathways within the cell. These pathways were strongly associated with integrin signalling, which changed the cell’s capacity to adhere and migrate. Aberrant activation of adhesion pathways upon PDLIM2 suppression was sufficient to alter the metabolic dependencies of Caco-2 cells and increase their oxidative stress, which further contributed to the disruption of their adhesion signalling. In murine models, the absence of PDLIM2 increased epithelial injury during chronic colitis. PDLIM2-/- mice also retained higher numbers of pro-inflammatory immune populations in their colon tissue, with corresponding elevation in the expression of pro-inflammatory genes. The expression of PDLIM2 was also decreased in PDLIM2+/+ mice during acute colitis and, despite the recovery of their epithelium following chronic colitis, PDLIM2 levels were not restored. The absence of PDLIM2 also altered the biodiversity of the microbial populations in the colon, including the loss of commensal colonies. In human patients, the expression of PDLIM2 is reduced in patients with ulcerative colitis even in the absence of inflammation. This loss correlated with increased expression of adhesion-associated genes and decreased those associated with mitochondrial function.
Overall, the data from this thesis highlight PDLIM2 as a key regulator of adhesion signals. The absence of its expression in colorectal epithelial cells dysregulates their adhesion signalling, with downstream impairment of antioxidant activity and cellular metabolism as a consequence. In the context of colitis, this loss of PDLIM2 likely contributed to the severity of the phenotype observed in our murine model, which showed reduced epithelial integrity and an altered microbiome. Furthermore, data from human ulcerative colitis patients support the cell line and murine data reported in this thesis, solidifying PDLIM2’s importance in protecting against disease development.
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Keywords
PDLIM2 , Intestinal homeostasis , Epithelial barrier , Gut microbiota , Antioxidant response , Adhesion signalling , Metabolism
Citation
Ward, S. 2024. Functions of PDLIM2 protein in maintaining intestinal homeostasis. PhD Thesis, University College Cork.