Rationale: Idiopathic Pulmonary Arterial Hypertension (IPAH) is a progressive disorder with limited therapeutic options and excessive morbidity and mortality. IPAH is characterized by abnormal vasoconstriction and remodeling of the pulmonary arteries driven by apoptotic-resistant endothelial and smooth muscle cells. Alpha-B crystallin (CRYAB) is implicated in angiogenesis, cell survival, and apoptotic resistance in cancer. Here, we hypothesize that CRYAB contributes to abnormal vascular remodeling and apoptotic resistance in IPAH.

Methods: siRNA transfection was utilized to knock out CRYAB protein in pulmonary arterial smooth muscle cells (PASMCs) cultured from IPAH individuals. At 72 hrs post siRNA transfection, cells were treated with staurosporine and caspase 3 activity was measured. Immunohistochemical staining of CRYAB protein was performed on lung sections from age-matched IPAH and control subjects. RNA isolated from partially muscularized pulmonary vessels obtained by laser capture microdissection was sequenced and underwent Ingenuity pathway analysis.

Results: CRYAB siRNA transfection reduced CRYAB protein level in PASMCs by ~70%. Staurosporine-induced caspase 3 activity was enhanced by 1.6-fold in cells transfected with CRYAB siRNA compared to scramble siRNA. CRYAB protein staining was increased in pulmonary vascular smooth muscle in IPAH. CRYAB mRNA was highly differentially expressed in IPAH pulmonary vessels compared to control.

Conclusions: These results suggest that CRYAB prevents apoptosis in PASMCs and its dysregulation may contribute to the development of IPAH. Therefore, further studies targeting CRYAB may provide novel therapeutic strategies for IPAH treatment.