Summary
Lung development is a highly orchestrated process characterized by timed expression
and activation of growth factor and protease/antiprotease systems. This interplay
is essential in regulating vasculogenesis, alveolarization, and epithelial to mesenchymal
transition during lung development. Alterations in the proteolytic/antiproteolytic
balance of the lung have been associated with several respiratory diseases characterized
by changes in the lung extracellular matrix (ECM). Here, we characterized the expression
pattern of matrix metalloproteases (MMP) and their inhibitors, the tissue inhibitors
of metalloproteases (TIMP), in human and mouse lung development. Using MMP/TIMP expression
arrays, RT-PCR, Western Blotting, and ELISA analyses, we demonstrate that fetal human
lung is characterized by a dominant proteolytic profile with high MMP-2 and little
TIMP-3 expression. Adult human lung, in contrast, exhibits a more anti-proteolytic
profile with decreased MMP-2 and increasedTIMP-3 expression. MMP-14, MMP-20,TIMP-1,
and TIMP-2 were constitutively expressed, irrespective of the developmental stage.
Similar results were obtained using mouse lungs of different developmental stages,
with the addition that in mouse lung, TIMP-2 and TIMP-3 were upregulated as lung development
progressed. Exposure of neonatal mice to chronic hypoxia (10% O2), a stimulus that leads to an arrest of lung development, resulted in upregulation
of MMP-2 with a concomitant downregulation of TIMP-2.These results provide a comprehensive
analysis of MMP and TIMP expression during human and mouse lung development. MMP-2,
TIMP-2, and TIMP-3 may be key regulatory enzymes during lung development, possibly
through their complex action on ECM components, membrane receptor ectodomain shedding,
and growth factor bioactivity.
Keywords
MMP - TIMP - lung development - ECM - remodeling