Early and late postnatal lung distribution of collagen type VI in preterm and term infants

Collagen type VI (COL6) is an important component of the extracellular matrix (EM) and may have a major role in lung development and disease. Studies on COL6 expression during lung development are mainly based on animal models. The aim of the study was to define COL6 expression pattern in lung parenchyma in infants with different lung maturational stages. COL6 expression in 115 lung samples from deceased newborn infants (21-41 weeks' gestational age; 0-228 days' postnatal age) was studied by immunohistochemistry combined with digital image analysis. The distribution of COL6 expression was generally heterogeneous in the lung parenchyma of preterm and term infants. The size of the high-density and low-density areas appeared with logarithmic correlation and COL6 defined the basement membrane (BM) with a prominent expression around the air spaces in the canalicular stage during the first postnatal week. Infants at the alveolar stage showed linear correlation and a fine filamentous appearance during the first week of postnatal life, similarly to adults. COL6 is condensed to areas corresponding to the BM during the first postnatal week of the canalicular stage of lung development. After the first postnatal week COL6 expression changes to a microfibrillar appearance in the ECM, similar to the pattern that characterizes the later alveolar stage and adults. The localization of COL6 during the canalicular and saccular stages might have a higher impact on lung development than the amount of COL6.