New Insights into Phosphodiesterase 1C as a Novel Target for Pulmonary Arterial Hypertension

Introduction/Background & aims: Pulmonary arterial hypertension (PAH) is a disease characterized by increased pulmonary vascular resistance and remodelling of the pulmonary artery. PAH is associated with increased phosphodiesterase 1C expression and activity (PDE1C, catalyse the hydrolysis of cAMP and cGMP), which in part accounts for lower cyclic nucleotide levels and increased proliferation of pulmonary artery smooth muscle cells (PASMC)¹. Recently, a phosphodiesterase 1 inhibitor (16 K) has been developed for central nervous system disorders and tested in preclinical studies². We aimed to investigate the utility of such PDE1 inhibitors for PAH alone and in combi-nation with prostacyclin receptor (IP) agonists.
Method/Summary of work: Human PASMCs were cultured under normoxia and hypoxia (1% O2, 72 hr) to investigate PDE1C expression (Real-time PCR) and the effect of 16 K (0.01–10 μM) and IP agonists (0.001–1 μM, Selexipag, MRE-293 or Iloprost) on PASMC sproliferation (MTS) and cAMP accumulation (ELISA). PDE1C cDNA (SinoBiological) and IP cDNA (cDNA.org) were used to generate stableHEK293-IP-PDE1C (Lipofectamine 2000, ThermoFisher). Lysosomal inhibitor (chloroquine, 100 μM) and proteasomal inhibition (MG132,10 μM) were used to assess IP receptor degradation, via fluorescence microscopy. Experiments were performed at least three times and data presented as means ± S.E.M and compared by ANOVA or student t-test
Results/Discussion: PDE1C mRNA was increased in hypoxic-PASMC(62.9 ± 6.7, n= 3), which correlated with lower cAMP and increased proliferation. 16 K restored cAMP (65. 3 ± 3.5 vs. 106. 2 ±8.8 pmol/million cells, n= 3), induced PASMC relaxation and inhibited hypoxia-induced proliferation (21 ± 2.4%, n= 3). Hypoxia reduced the efficacy of IP agonists (selexipag, Iloprost and MRE-269) to generate cAMP and induce PASMC relaxation, which was restored with 16 K. In HEK-293-IP-PDE1C cells we found increased PDE1C was associated with the proteasomal degradation of the IP receptor and blunted signalling. 16 K restored both the expression of the IP receptor andMRE-269 mediated cAMP accumulation (168.4 ± 13. 3 vs.381 ± 25.84 pmol/million cell).
Conclusion(s): PDE1C contributes to increased PASMC proliferation and interacts with the IP receptor to limit agonist induced cAMP and relaxation. PDE1 specific inhibitors could be novel drugs for PAH and also enhance the response of IP agonists