A novel non-canonical pathway with potential for safer modulation of TGF-beta1 in steroid-resistant airway diseases
AffiliationPharmacology and Therapeutics
Document TypePhD thesis
Access StatusThis item is embargoed and will be available on 2020-03-09.
© 2017 Dr. Meina Li
Glucocorticoids remain central to treatment regimens for chronic airway inflammatory diseases, but the therapeutic responses are often limited by impaired responses in severe diseases. Glucocorticoid activity can be negatively regulated by the inflammatory microenvironment. Of the mechanisms investigated to date, the glucocorticoid insensitivity caused by transforming growth factor (TGF-beta1) in airway epithelium demands most attention, because of its extraordinary capacity at the pathophysiologically relevant picomolar concentrations to ablate glucocorticoid activity, as well as acting as a key mediator of viral infection-induced glucocorticoid insensitivity. Global inhibition of TGF-beta1 carries known risks, including autoimmune diseases, increased cancer risks and mitral valve defects. Therefore, the identification of signals downstream of TGF-beta1 receptors, through which TGF-beta1 suppresses glucocorticoid activity may provide novel and safe therapeutic targets to improve glucocorticoid effectiveness in inflammatory airway diseases. Data presented within this thesis has provided evidence that TGF-beta1 has a broad suppressive effect in impact on the glucocorticoid transcriptome. Hypothesis-free proteomic analysis of airway epithelial cells identified 24 candidate mediators from which an increase in the levels of phosphorylated cofilin1 was prioritized for analysis, because: cofilin1 phosphorylation was not inhibited by a cocktail of small molecule inhibitors of non-canonical kinases; and, cofilin1 phosphorylation was induced by TGF-beta1 and TGF-beta3 which impair glucocorticoid activity, but not by TGF-beta2 which has no effect on glucocorticoid activity. Pharmacological and genetic approaches established that TGF-beta1-induced glucocorticoid insensitivity is mediated by a novel signaling cascade involving LIM domain kinase 2 (LIMK2)-mediated phosphorylation of cofilin1. Phospho-cofilin1 activates phospholipase D (PLD) to generate the effectors (lyso)phosphatidic acid (PA). These PLD products mediate the TGF-beta1-induced glucocorticoid insensitivity, causing the impairment of both glucocorticoid inducible GRE activity and endogenous gene expression. Data obtained during these thesis studies identified that inhibition the CLOCK regulator casein kinase 1delta/epsilon (CK1delta/epsilon) represents a promising strategy for targeted treatment in inflammatory pulmonary diseases with TGF-beta1 involvement. We have shown that pharmacological inhibition of CK1delta/epsilon reduced TGF-beta1-induced fibrogenic signals, and also attenuated TGF-beta1 signals subserving glucocorticoid insensitivity. In addition, inhibition of CK1delta/epsilon suppressed inflammogen-induced inflammatory cytokine production by airway epithelial cells. This study has provided extensive evidence that TGF-beta1 has broad impact on the glucocorticoid transcriptome. Furthermore, through the systematic investigation into the underlying mechanisms through which this insensitivity is induced, this study has provided novel insights into new targets with potential for safer and more selective modulation of TGF-beta1 activity in glucocorticoid-resistant airway inflammatory diseases, than are afforded by global inhibition of TGF-beta1 activity.
KeywordsTGF-beta1; glucocorticoid insensitivity; phospho-cofilin1; LIM kinase; phospholipase D; (lyso)phosphatidic acid
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