CAT-2 amplifies the agonist-evoked force of airway smooth muscle by enhancing spermine-mediated phosphatidylinositol-(4)-phosphate-5-kinase-γ activity

Abstract

We investigated the effect the loss of the CAT-2 gene (CAT-2−/−) has on lung resistance (RL) and tracheal isometric tension. The RL of CAT-2−/− mice at a maximal dose of acetylcholine (ACh) was decreased by 33.66% ( P = 0.05, n = 8) compared with that of C57BL/6 (B6) mice. The isometric tension of tracheal rings from CAT-2−/− mice showed a significant decrease in carbachol (CCh)-induced force generation (33.01%, P < 0.05, n = 8) compared with controls. The isoproterenol- or the sodium nitroprusside-induced relaxation was not affected in tracheal rings from CAT-2−/− mice. The activity of iNOS and arginase in lung tissue lysates of CAT-2−/− mice was indistinguishable from that of B6 mice. Furthermore, the expression of phospholipase-Cβ (PLC-β) and phosphatidylinositol-( 4 )-phosphate-5-kinase-γ (PIP-5K-γ) was examined in the lung tissue of CAT-2−/− and B6 mice. The expression of PIP-5K-γ but not PLC-β was significantly reduced in CAT-2−/− compared with B6 mice. The reduced airway smooth muscle (ASM) contractility to CCh seen in the CAT-2−/− tracheal rings was completely reversed by pretreating the rings with 100 μM spermine. This increase in the CAT-2−/− tracheal ring contraction upon spermine pretreatment correlated with a recovery of the expression of PIP-5K-γ. Our data indicates that CAT-2 exerts control over ASM force development through a spermine-dependent pathway that directly correlates with the expression level of PIP-5K-γ in the lung.