Investigating the role of phosphodiesterases in myofibroblast transformation in Peyronie's disease

Introduction: Peyronie’s disease (PD) is characterised by a fibrous plaque that forms in the penile tunica albuginea (TA), leading to pain, penile deformity, and erectile dysfunction. There is currently no effective medical treatment available. The transformation of fibroblasts into myofibroblasts is a key event in the pathophysiology of PD, and previous work has shown that phosphodiesterase type 5 (PDE5) inhibitors can prevent this transformation in vitro and in vivo. This study aims to identify the molecular mechanism of the anti-myofibroblast action of PDE5 inhibitors.

Materials and Methods: Primary fibroblasts were isolated from the TA of patients undergoing corrective surgery for PD. In-cell ELISA (ICE) assays were used to quantify expression of myofibroblast marker α-smooth muscle actin in response to TGF-β1. Concentration response curves of PDE5 inhibitors and activators/inhibitors of cGMP/cAMP pathway components were generated. Intracellular cGMP/cAMP concentrations were measured using cAMP/cGMP assays. RT-qPCR and ICE were used to investigate mRNA/protein expression.

Results: PDE5 inhibitors (vardenafil, sildenafil and tadalafil), a nitric oxide (NO) donor, and soluble guanylyl cyclase (sGC) stimulators prevented TGF-β1-induced myofibroblast transformation, but natriuretic peptides and a protein kinase G (PKG) activator did not. Addition of a sGC inhibitor or a PKG inhibitor did not prevent the antifibrotic action of vardenafil. Forskolin and a cAMP analog abrogated myofibroblast transformation, whilst a combination of forskolin and vardenafil synergised. Addition of a protein kinase A (PKA) inhibitor prevented the antifibrotic action of vardenafil. No PDE5 inhibitors increased intracellular cGMP, but vardenafil and tadalafil significantly increased cAMP levels. RT-qPCR and ICE confirmed the expression of PDE1A, PDE1C, PDE4, PDE5A, PDE7B, and PDE8B. PDE1 inhibitor ITI-214 and PDE4 inhibitor roflumilast N-oxide inhibited myofibroblast transformation and significantly increased intracellular cAMP at a 10-1000-fold greater potency than PDE5 inhibitors.

Discussion: Contrary to my initial hypothesis, these results suggest that PDE5 inhibitors, at pharmacological concentrations, prevent TGF-β1-induced transformation of myofibroblasts through the cAMP/PKA pathway, potentially via off-target inhibition of PDE1/PDE4. This is the first demonstration that PD fibroblasts express PDE1, PDE7 and PDE8, and that PDE1 and PDE4 inhibitors prevent myofibroblast transformation. This study suggests the development of PDE1/4 inhibitors for the treatment of acute PD.