Downregulation of STIM2 in PAH-PASMCs reduces the resting [Ca<sup>2+</sup>]<sub>cyt</sub>, whereas overexpression of STIM2 in normal PASMCs increases the resting [Ca<sup>2+</sup>]<sub>cyt</sub> The increased resting [Ca<sup>2+</sup>]<sub>cyt</sub> in PAH-PASMCs is associated with enhanced phosphorylation (p) of CREB (cAMP response element-binding protein), STAT3 (signal transducer and activator of transcription 3), and AKT, increased NFAT (nuclear factor of activated T-cell) nuclear translocation, and elevated level of Ki67 (a marker of cell proliferation).
In vitro, using PASMCs isolated from PAH and healthy patients, we demonstrated that RAGE is overexpressed in PAH-PASMC (6-fold increase), thus inducing STAT3 activation (from 10% to 40% positive cells) and decrease in BMPR2 and PPARγ levels (>50% decrease).
Moreover, through the down-regulation of miR-204, STAT3 enhances a positive feedback loop sustaining its own activation, showing that miRNA regulation is critical in PAH.