Click to download
| 098P London, UK Pharmacology 2017 |
Prostanoid-mediated inhibition of IL-6 trans-signalling in pulmonary arterial hypertension: a role for “suppressor of cytokine signalling 3” (SOCS3)?
Introduction: Inflammation has been highlighted as a key factor in pulmonary arterial hypertension (PAH) development (1), in particular interleukin-6 (IL-6) (2). IL-6 trans-signalling activates JAK/STAT signalling to induce transcription of pro-inflammatory and pro-angiogenic genes, enabling PAH progression, as well as the transcription of suppressor of cytokine signalling 3 (SOCS3) which limits IL-6 signalling (3). Current PAH therapies include prostanoid drugs which induce vasodilation via stimulating intracellular cyclic adenosine monophosphate (cAMP) levels. cAMP is also an inhibitor of endothelial dysfunction via induction of SOCS3 (4). Thus, an important mechanism by which cAMP-mobilising prostanoid drugs limit PAH may be via Epac1-mediated SOCS3 inhibition of IL-6 induced JAK/STAT signalling.
Methods: Human pulmonary arterial endothelial cells (HPAECs) were treated with beraprost sodium (BPS) (10μM) and treprostinil (10μM) in the presence of MG-132 (6μM). In addition, HPAECs were treated with BPS and treprostinil in the presence and absence of IL-6 (5ng/ml)/sIL-6Rα (25ng/ml). Treatment with IL-6/sIL-6Rα alone was also carried out. For both experiments, forskolin (50μM) was used as a positive control. RNA and protein induction was measured via qPCR and immunoblotting respectively. Statistical significance was determined using one-way analysis of variance and the Bonferroni post-hoc test. Quantification was performed using Graphpad software.
Results: BPS and treprostinil induce SOCS3 mRNA and protein in PAECs in a time-dependent manner with maximum induction after one hour and two hours respectively. This is equal to SOCS3 induction caused by the positive control, forskolin. IL-6 mediated Tyr705 phosphorylation of STAT3 in HPAECs was inhibited after two hours of BPS and treprostinil treatment by 30 ±8% (P<0.01) and 25 ±9% (P<0.05) for n=4 experiments respectively. Preliminary data in angio-sarcoma derived (AS-M.5) cells suggested this was not SOCS3 dependent.
Conclusion: Our results indicate that prostanoids induce SOCS3 via upregulation of SOCS3 gene transcription and limit IL-6 trans-signalling, whether this is consequential or not needs to be further investigated. However, the functional significance of this mechanism in prostanoid action needs to be determined. From these and future studies, it is anticipated that more effective strategies will emerge with which to target the IL-6/JAK/STAT signalling pathway in PAH.
References:
1.Groth A et al. (2014) Respir Res 15: 47
2.Jasiewicz M et al. (2014) Cytokine 76: 187-192
3.Babon JJ et al. (2014) Semin Immunol 26: 13-19
4.Sands WA et al. (2006) Mol Cel Biol 26: 6333-6346
5.Lee YR et al. (2006) J Gen Virol 87: 3623-3630