Soluble guanylyl cyclase expression is reduced in LPS-induced lung injury

Soluble guanylyl cyclase (sGC) is a cGMP-generating enzyme implicated in the control of smooth muscle tone that also regulates platelet aggregation. Moreover, sGC activation has been shown to reduce leukocyte adherence to the endothelium. Herein, we investigated the expression of sGC in a murine model of LPS-induced lung injury and evaluated the effects of sGC inhibition in the context of acute lung injury (ALI). Lung tissue sGC alpha1 and beta1 subunit protein levels were determined by Western blot and immunohistochemistry, and steady-state mRNA levels for the beta1 subunit were assessed by real-time PCR. LPS inhalation resulted in a decrease in beta1 mRNA levels, as well as a reduction in both sGC subunit protein levels. Decreased alpha1 and beta1 expression was observed in bronchial smooth muscle and epithelial cells. TNF-alpha was required for the LPS-triggered reduction in sGC protein levels, as no change in alpha1 and beta1 levels was observed in TNF-alpha knockout mice. To determine the effects of sGC blockade in LPS-induced lung injury, mice were exposed to 1H-[1,2,4]oxodiazolo[4,3-a]quinoxalin-l-one (ODQ) prior to the LPS challenge. Such pretreatment led to a further increase in total cell number (mainly due to an increase in neutrophils) and protein concentration in the bronchoalveoalar lavage fluid; the effects of ODQ were reversed by a cell-permeable cGMP analog. We conclude that sGC expression is reduced in LPS-induced lung injury, while inhibition of the enzyme with ODQ worsens lung inflammation, suggesting that sGC exerts a protective role in ALI.