The role of cathepsin K in lung development and newborn chronic lung injury.

Chronic lung diseases, specifically bronchopulmonary dysplasia (BPD), are still causing mortality and morbidity amongst newborn infants. High protease activity has been suggested to have a deleterious role in oxygen-induced lung injuries. Cathepsin K (CatK) is a potent protease found in fetal lungs, degrading collagen and elastin. We hypothesized that CatK may be an important modulator of chronic lung injury in newborn infants and neonatal mice. First we measured CatK protein levels in repeated tracheal aspirate fluid samples from 13 intubated preterm infants during the first two weeks of life. The amount of CatK at 9-13 days was low in infants developing chronic lung disease. Consequently, we studied CatK mRNA expression in oxygen-exposed wild-type (WT) rats at postnatal day (PN) 14 and found decreased pulmonary mRNA expression of CatK in whole lung samples. Thereafter we demonstrated that CatK deficiency modifies lung development by accelerating the thinning of alveolar walls in newborn mice. In hyperoxia-exposed newborn mice CatK deficiency resulted in increased number of pulmonary foam cells, macrophages and amount of reduced glutathione in lung homogenates indicating intensified pulmonary oxidative stress and worse pulmonary outcome due to CatK deficiency. Conversely, transgenic overexpression of CatK caused slight enlargement of distal airspaces with increased alveolar chord length in room air in neonatal mice. While hyperoxic exposure inhibited alveolarization and resulted in enlarged airspaces in wild-type mice, these changes were significantly milder in CatK overexpressing mice at PN7. Finally, we showed that the expression of macrophage scavenger receptor 2 (MSR2) mRNA was down-regulated in oxygen-exposed CatK-deficient mice analyzed by microarray analysis. Our results demonstrate that CatK seems to participate in normal lung development and its expression is altered during pulmonary injury. In the presence of pulmonary risk factors, like high oxygen exposure, low amount of CatK may contribute to aggravated lung injury while sustained or slightly elevated amount of CatK may even protect the newborn lungs from excessive injury. Besides collagen degrading and antifibrotic function of CatK in the lungs, it is obvious that CatK may affect macrophage activity and modify oxidative stress response. In conclusion, pulmonary proteases, specifically CatK, have distinct roles in lung homeostasis and injury development, and although suggested, broad range inhibition of proteases may not be beneficial in newborn lung injury.

Viral and cellular modulation of virus-induced apoptosis in experimental infection models

The aim of this study was to investigate herpes simplex virus type 1 (HSV-1)- and measles virus (MV)-induced cell death. HSV-1 with deletion in genes encoding infected cell protein (ICP)4 and protein kinase Us3 (d120) induced apoptosis and cathepsin activation in epithelial (HEp-2) and monocytic (U937) cells. Inhibition of cathepsin activity decreased the amount of d120-induced apoptosis indicating that d120-induced apoptosis could be cathepsin-mediated. Also, HSV-1 infection increased caspase activation suggesting that d120-induced apoptosis is probably caspase-mediated. Cystatin treatment decreased the activity of cathepsins and the replication of HSV-1 indicating that cathepsins contribute to HSV-1 infection. Interestingly, d120 induced also necroptosis in monocytic cells. This is the first report on necroptosis in HSV-1- infected cells. MV induced apoptosis in uninfected bystander T lymphocytes, probably via interaction of MV-infected monocytes with uninfected lymphocytes. The expression of death receptor Fas was clearly increased on the surface of lymphocytes. The number of apoptotic cells and the activation of cathepsins and caspases were increased in MVinfected U937 cells suggesting that MV-induced apoptosis could be cathepsin- and caspase-mediated. Cystatin treatment inhibited cathepsin activities but not MV-induced apoptosis. Besides HSV-1-induced apoptosis, innate immune responses were studied in HSV-1-infection. HSV-1 viruses with either ICP4 and Us3, or Us3 deletion only, increased the expression of Toll-like receptor (TLR)3 and stimulated its downstream pathways leading to increased expression of type I interferon gene and to functional interferons. These findings suggest that besides controlling apoptosis, HSV-1 ICP4 and Us3 genes are involved in the control of TLR3 response in infected cell.