Investigating caveolin-dependent glucocorticoid action in inflammation

Abstract

Glucocorticoids (GC) are steroid hormones that play important physiological roles in a variety of contexts, most notably effects on metabolism and the immune system. By virtue of their potent anti-inflammatory properties, synthetic GC are in wide clinical use and remain the gold standard for treatment of inflammatory diseases including rheumatoid arthritis and asthma. However, their long term use is hindered by the development of severe side effects, including osteoporosis. Understanding how GC mediate this spectrum of effects in vivo, and identifying new points for regulation is important for rational drug design. GC mediate their cellular effects through binding and activating the glucocorticoid receptor (GR). Once activated GR mediates non-genomic (over minutes) and genomic (over hours) effects. The gene regulatory effects of GC have been widely documented in different tissues and inflammatory states, but the mechanism by which GR brings about non genomic effects are less well understood. The interaction of GR with a plasma membrane protein and regulator of kinase signalling, caveolin-1 has been identified. Caveolin is an integral membrane protein that localises to specialised lipid rafts, caveolae, acting as a protein scaffold for signalling complexes. Caveolin may be important to tether GR at the plasma membrane and facilitate non-genomic GC actions. Here, GR-caveolin interaction was investigated in vitro using an immortalised caveolin deficient cell line and then the effect was examined in vivo using a model of pulmonary inflammation using caveolin-1 knockout mice. Although subcellular GR trafficking appeared not to be altered, there were differences in GC induced kinases and transcriptional targets in the absence of caveolin. For example, phosphorylation of p65-NF-kappaB was 8.4-fold lower than the change seen in WT LPS-exposed mice. MT1 showed a 10-fold increase in expression with dexamethasone in CavKO, compared to 5-fold in WT in vitro, and in vivo WT showed a greater increase in expression 16-fold over control, whereas CavKO showed a 5.8-increase over control in lung tissue. The caveolin-dependent differences in glucocorticoid targets MT1, GILZ and Glul and kinase signalling pathways may have an effect on the modulation of glucocorticoid signalling.

Date of Award	1 Aug 2014
Original language	English
Awarding Institution	The University of Manchester
Supervisor	David Ray (Supervisor), Laura Matthews (Supervisor) & Stuart Farrow (Supervisor)