| Summary: | Prostacyclin and its stable analogues are used to treat pulmonary arterial hypertension (PAH), a disease associated with abnormal smooth muscle cell (SMC) proliferation. These analogues are thought to mediate their anti proliferative effects through prostacyclin (IP) receptors linked to cyclic AMP (cAMP) generation, though other targets may be involved including peroxisome proliferator activated receptors (PPARs), transcription factors known to regulate cell growth. Thus the aim was to assess the role of the IP receptor and PPARy in mediating the anti-proliferative effects of prostacyclin analogues in HEK-293 cells stably expressing the IP receptor (HEK-293-IP) and in SMCs derived from normal and hypertensive lungs. In proliferation assays, the growth rate of HEK-293-IP cells was significantly decreased compared to cells expressing the empty vector. Furthermore, treprostinil and carbacyclin, and non receptor-dependent cAMP-elevating agents only inhibited proliferation in HEK-293-IP cells, suggesting the physical presence of the IP receptor is crucial in mediating the effects of both analogues and agents working downstream of the receptor. Protein kinase A and to a lesser extent, PPARy appear to be involved since antagonists of these two pathways partially reversed the anti-proliferative effects of treprostinil. Using a dual luciferase reporter gene assay, I demonstrated that analogues could activate PPARy via a novel IP receptor- dependent, cAMP-independent mechanism, likely to involve phosphorylation. In separate studies, pulmonary SMC derived from young idiopathic PAH patients replicated at a faster rate compared to control cells. RT-PCR and immnuostaining showed that PAH cells expressed fewer IP receptors, although treprostinil still inhibited SMC proliferation, albeit through a mechanism largely involving PPARy but not the IP receptor or cAMP. This contrasted to normal pulmonary SMC, where treprostinil inhibited proliferation via the IP receptor, cAMP and PPARy. In conclusion, the IP receptor appears to play an important role in regulating cell growth and mediating the effects of prostacyclin analogues in normal but not in pulmonary hypertensive SMC.
|
|---|
