Fig. 8.

Model showing some of the hypothesized actions resulting from a depletion of cartilage oligomeric matrix protein (COMP) from bovine pulmonary smooth muscle resulting from organoid culture under hypoxia for 48 h that are potentially contributing to the observed increases in mitochondrial and extra-mitochondrial matrix in superoxide that seem to participate in a depletion of contractile phenotype proteins based on the actions of siRNA depletion of COMP and attenuation of the actions of hypoxia by treatment with COMP. COMP depletion promotes decreases in SOD2 and increases in NADPH oxidase NOX2, associated with increases in mitochondrial superoxide (detected by MitoSOX) and extra-mitochondrial superoxide [detected by dihydroethidium (DHE)]. The actions of superoxide scavengers TEMPO and mitoTEMPO on inhibiting the effects of hypoxia suggest roles for increases in the different sources of superoxide contribute to depleting contractile phenotype protein levels. Depletion of bone morphogenetic protein receptor-2 (BMPR2) by siRNA promoting decreased levels of calponin and adenovirus-BMPR2 reversal of reduced calponin and SM22α caused by COMP siRNA indicate COMP regulation of BMPR2 expression is potentially a key process maintaining the contractile phenotype. Moreover, BMPR2 siRNA increases superoxide (as supported by detection of MitoSOX and DHE) and promotes contractile protein depletion in bovine pulmonary artery, which cannot be prevented by exogenous COMP. Thus, protective effects of COMP on the contractile phenotype of pulmonary artery smooth muscle cells (PASMCs) appear to be via maintenance of BMPR2 signaling. SOD3 and NOX4 are shown in parentheses because changes in the expression of these proteins in pulmonary arteries observed with siRNA depletion of COMP or by more prolonged in vivo exposure of animals to hypoxia reported in the literature were not observed in the 48-h organoid culture hypoxia model used in the present study.