Regulation of Kininogen Gene Expression and Localization in the Lung after Monocrotaline-Induced Pulmonary Hypertension in Rats

Abstract

Pyrrolizidine monocrotaline (MCT) from plant seed produces pulmonary endothelial cell injury, pulmonary hypertension, and inflammation in rats, providing a useful animal model for studying progressive pulmonary vascular disease. Kininogen is the precursor of proinflammatory kinins and may also exert anti-inflammatory actions by inhibiting cysteine proteinases. Given the potential roles of kininogen in vascular injury and inflammation, we have investigated the regulation of kininogen gene expression in the MCT-induced pulmonary hypertensive rat model. Sprague-Dawley rats, in groups of six, were given a single subcutaneous injection of monocrotatine (60 mg/kg body wt) and sacrificed 10 and 20 days later. Northern blot hybridization using a kininogen cDNA probe showed kininogen gene expression in the liver, lung, and kidney. MCT treatment induced a time-dependent increase in kininogen mRNA levels, whereas it reduced rat α₁-antitrypsin and kallikrein-binding protein mRNA levels in the liver. Similarly, kininogen mRNA levels were low in the normal lung and were increased 7.5- and 13.7-fold, respectively, after MCT injection for 10 and 20 days. Immunoreactive kininogen levels in perfused liver and lung extracts of rats receiving MCT injection increased up to 20-fold, as measured by a T-kininogen radioimmunoassay. Western blot analyses showed that a 68-kilodalton immunoreactive kininogen increased in the serum and lung extracts of MCT-treated rats compared to those in the control rats. In control rats, immunostaining for kininogen in the lung was most marked in venous endothelial cells and alveolar macrophages. After MCT treatment, staining for kininogen increased dramatically throughout the lung tissues, often covering the epithelial surfaces of alveoli and bronchi. The present studies have shown that the toxin MCT altered the synthesis and distribution of pulmonary kininogen and suggest that the kininogen/kinin system may be associated with the pulmonary vascular injury, remodeling, and inflammation seen in this animal model.