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Embryonic Essential Myosin Light Chain Regulates Fetal Lung Development in Rats

Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Braga, Portugal; Proteomics Core Facility, Biocenter Oulu, Department of Biochemistry, University of Oulu, Finland; and Division of Pediatric Surgery, Hospital S João, Porto, Portugal

Correspondence and requests for reprints should be addressed to Prof. Jorge Correia-Pinto, M.D., Ph.D., Escola de Ciências da Saúde, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal. E-mail: jcp{at}ecsaude.uminho.pt

Congenital diaphragmatic hernia (CDH) is currently the most life-threatening congenital anomaly the major finding of which is lung hypoplasia. Lung hypoplasia pathophysiology involves early developmental molecular insult in branching morphogenesis and a late mechanical insult by abdominal herniation in maturation and differentiation processes. Since early determinants of lung hypoplasia might appear as promising targets for prenatal therapy, proteomics analysis of normal and nitrofen-induced hypoplastic lungs was performed at 17.5 days after conception. The major differentially expressed protein was identified by mass spectrometry as myosin light chain 1a (MLC1a). Embryonic essential MLC1a and regulatory myosin light chain 2 (MLC2) were characterized throughout normal and abnormal lung development by immunohistochemistry and Western blot. Disruption of MLC1a expression was assessed in normal lung explant cultures by antisense oligodeoxynucleotides. Since early stages of normal lung development, MLC1a was expressed in vascular smooth muscle (VSM) cells of pulmonary artery, and MLC2 was present in parabronchial smooth muscle and VSM cells of pulmonary vessels. In addition, early smooth muscle differentiation delay was observed by immunohistochemistry of -smooth muscle actin and transforming growth factor-1. Disruption of MLC1a expression during normal pulmonary development led to significant growth and branching impairment, suggesting a role in branching morphogenesis. Both MLC1a and MLC2 were absent from hypoplastic fetal lungs during pseudoglandular stage of lung development, whereas their expression partially recovered by prenatal treatment with vitamin A. Thus, a deficiency in contractile proteins MLC1a and MLC2 might have a role among the early molecular determinants of lung hypoplasia in the rat model of nitrofen-induced CDH.

Key Words: congenital diaphragmatic hernia • lung hypoplasia • proteomics • myosin light chains • smooth muscle

CLINICAL RELEVANCE We report the first proteomic analysis of hypoplastic lungs associated with congenital diaphragmatic hernia, where we found a major protein change, the embryonic essential myosin light chain. This study emphasizes its role in lung branching morphogenesis.