Caffeine administration is an important part of the therapeutic treatment of
bronchopulmonary dysplasia (BPD) in preterm infants. However,
caffeine mediated effects on
airway remodelling are still undefined. The TGF-β/Smad signalling pathway is one of the key pathways involved in
airway remodelling.
Connective tissue growth factor (CTGF), a downstream mediator of TGF-β, and
transgelin, a binding and stabilising
protein of the cytoskeleton, are both regulated by TGF-β1 and play an important role in
airway remodelling. Both have also been implicated in the pathogenesis of BPD. The aim of the present study was to clarify whether
caffeine, an unspecific
phosphodiesterase (PDE) inhibitor, and
rolipram, a prototypical PDE-4 selective inhibitor, were both able to affect TGF-β1-induced Smad signalling and CTGF/
transgelin expression in lung epithelial cells. Furthermore, the effect of
transgelin knock-down on Smad signalling was studied. The pharmacological effect of
caffeine and
rolipram on Smad signalling was investigated by means of a
luciferase assay via transfection of a TGF-β1-inducible reporter plasmid in A549 cells. The regulation of CTGF and
transgelin expression by
caffeine and
rolipram were studied by promoter analysis, real-time PCR and Western blot. Endogenous
transgelin expression was down-regulated by lentiviral transduction mediating
transgelin-specific
shRNA expression. The addition of
caffeine and
rolipram inhibited TGF-β1 induced reporter gene activity in a concentration-related manner. They also antagonized the TGF-β1 induced up-regulation of CTGF and
transgelin on the promoter-, the
mRNA-, and the
protein-level. Functional analysis showed that
transgelin silencing reduced TGF-β1 induced Smad-signalling and CTGF induction in lung epithelial cells. The present study highlights possible new molecular mechanisms of
caffeine and
rolipram including an inhibition of Smad signalling and of TGF-β1 regulated genes involved in
airway remodelling. An understanding of these mechanisms might help to explain the protective effects of
caffeine in prevention of BPD and suggests
rolipram to be a potent replacement for
caffeine.