MODULATION OF LAMININ INTEGRIN RECEPTORS IN THE POSTNATAL AND ADULT-RAT LUNG

Recent studies have shown that type II pneumocytes, at birth and day 3 postnatally, have a diffuse distribution and localize at alveolar 'co rners' between 3 and 7 days. Since alpha(1)beta(1) and alpha(6)beta(1) are laminin-binding re ceptors that are well expressed by rat type II alveolar epithelial cells, we postulated that they may play a role in the localization of the cells in the alveolus. To begin the evaluatio n of this hypothesis, we studied the temporal and spatial expression o f the alpha(3), alpha(6), and beta(1) integrin subunit protein and mRN A in whole rat lungs during postnatal development by immunofluorescenc e, confocal microscopy, and Northern blot analysis. The temporal expre ssion of proteins analyzed by immunochemistry, with integrin subunit s pecific antibodies, increased during the 3- to 7-day postnatal period and in adult lungs. Densitometric values of the alpha(3), alpha(6), an d beta(1) mRNA expression, normalized to 28S rRNA, quadrupled from day I to day 3 postnatally. The mRNA expression of different integrin cha ins was elevated 1.5- to threefold from days 5 to 7 postnatally compar ed to day 1 levels. The alpha(3) and alpha(6) integrin subunit mRNA de creased to newborn levels in adult lungs, whereas the beta(1) integrin mRNA in adult lungs was expressed at approximately 50% of its level i n newborn lungs. We postulate that the increases in alpha(3), alpha(6) , and beta(1) integrin mRNA expression during the early neonatal perio d may be important for the spatial distribution of type II pneumocytes .