Abstract 323: PPARγ Protects Against Pulmonary Arterial Hypertension (PAH) And Is Central In A Novel Antiproliferative BMP-2–PPARγ–ApoE–Axis in Smooth Muscle Cells (SMC)
Bone morphogenetic protein 2 (BMP-2) is a negative regulator of SMC growth but the mechanism by which it counteracts proliferation induced by growth factors (EGF, PDGF) associated with PAH is unknown. We reported that BMP-2 leads to nuclear shuttling and DNA-binding of PPARγ in human pulmonary artery SMC (HPASMC). We hypothesized that apoE is a transcriptional target of PPARγ since mRNA expression of both factors is decreased in lungs from PAH patients, and since apoE blocks SMC proliferation by inactivating the PDGF-β receptor.
Methods: Using a small hairpin BMP-RII pLenti 6 virus, we established a 85% stable knock down of BMP-receptor II mRNA (shBMP-RIIi) vs. LacZi control in HPASMC by Q-PCR. Quiescent HPASMC, and murine wt and apoE deficient (apoE −/−) PASMC were stimulated with PDGF-BB (20ng/ml) ± BMP-2 (10ng/ml), the PPARγ agonist rosiglitazone (Rosi 1μM), the PPARγ antagonist GW9662 (1μM), or apoE (10μg/ml). SMC proliferation was assessed by cell counts and MTT assay. In addition to DNA-binding, we measured nuclear PPARγ as well as cell-associated and secreted apoE by immunoblot. To determine whether PPARγ in SMC protects against PAH, we created a mouse with SMC deletion of PPARγ using the Cre Lox P system (SM22α Cre PPARγ −/−), and measured right ventricular systolic pressure (RVSP), blood pressure (BP), right and left ventricular (RV, LV) mass and function.
Results: BMP-2 inhibited PDGF-BB-induced proliferation in human wt and LacZi control as well as murine wt PASMC, but not in shBMP-RIIi HPASMC, in wt HPASMC incubated with the PPARγ antagonist GW9662, or in murine apoE −/− PASMC. BMP-2 induced rapid nuclear shuttling and DNA-binding of PPARγ, whereas PDGF-BB had the opposite effect. BMP-2 stimulated production and secretion of apoE. Rosi also induced apoE and inhibited proliferation. SM22α Cre PPARγ −/− mice spontaneously developed PAH (RVSP 29.0 vs. 21.5mmHg) and RV hypertrophy (RV/LV+septum 0.46 vs. 0.26; p<0.01 vs. littermates). BP and cardiac function were similar.
Conclusions: Our data reveal a novel PPARγ-apoE axis downstream of BMP-2 signaling that could explain the antiprolifera-tive effect of BMP-RII activation in HPASMC. We suggest that PPARγ agonists might reverse SMC proliferation in PAH patients with or without BMP-RII dysfunction.