PKCα deficiency in mice is associated with pulmonary vascular hyperresponsiveness to thromboxane A ₂ via increased TXA ₂ receptor expression

Introduction: Pulmonary vascular hyperresponsiveness is a main characteristic of pulmonary arterial hypertension (PAH) and elevated levels of thromboxane A 2 (TXA 2 ) and endothelin-1 (ET-1) in PAH patients have been described. Downstream signaling of TXA 2 and ET-1 involves activation of the protein kinase C (PKC) family, and PKC inhibition has been proposed as therapeutic strategy in PAH. However, the effects of PKC isoenzyme alpha deficiency (PKCα -/- ) on pulmonary vascular responsiveness have not been investigated. Methods: Pulmonary vascular responsiveness to TXA 2 receptor analog U46619 and ET-1 was investigated in isolated perfused and ventilated lungs of PKCα -/- and corresponding wildtype mice (wt), with or without prior administration of pan-PKC inhibitor bisindolylmaleimide. TXA 2 receptor and PKC isoenzyme mRNA expression of microdissected pulmonary arteries and whole lung tissue was quantified. Results: Surprisingly, isolated lungs of PKCα -/- mice showed pulmonary vascular hyperresponsiveness to U46619 compared to wt mice, whereas pulmonary vascular responsiveness to ET-1 was reduced in PKCα -/- mice and after pan-PKC inhibition. mRNA analysis showed increased TXA 2 receptor expression in PKCα -/- pulmonary arteries compared to wt, while PKC isoenzyme expression was comparable between PKCα -/- and wt. Conclusion: PKCα deficiency was associated with increased pulmonary vascular responsiveness to TXA 2 due to increased pulmonary arterial TXA 2 receptor expression.