MODULATION OF T1-ALPHA EXPRESSION WITH ALVEOLAR EPITHELIAL-CELL PHENOTYPE IN-VITRO

T1 alpha is a recently identified gene expressed in the adult rat lung by alveolar type I (AT1) epithelial cells but not by alveolar type II (AT2) epithelial cells. We evaluated the effects of modulating alveol ar epithelial cell (AEC) phenotype in vitro on T1 alpha expression usi ng either soluble factors or changes in cell shape to influence phenot ype. For studies on the effects of soluble factors on Tla expression, rat AT2 cells were grown on polycarbonate filters in serum-free medium (MDSF) or in MDSF supplemented with either bovine serum (BS, 10%), ra t serum (RS, 5%), or keratinocyte growth factor (KGF, 10 ng/ml) from e ither day 0 or day 4 through day 8 in culture. For studies on the effe cts of cell shape on T1 alpha expression, AT2 cells were plated on thi ck collagen gels in MDSF supplemented with BS. Gels were detached on e ither day 1 (DG1) or day 4 (DG4) or were left attached until day 8. RN A and protein were harvested at intervals between days 1 and 8 in cult ure, and T1 alpha expression was quantified by Northern and Western bl otting, respectively. Expression of Tier progressively increases in AE C grown in MDSF +/- BS between day 1 and day 8 in culture, consistent with transition toward an ATI cell phenotype. Exposure to RS or KGF fr om day 0 prevents the increase in T1 alpha expression on day 8, wherea s addition of either factor from day 4 through day 8 reverses the incr ease. AEC cultured on attached gels express high levels of T1 alpha on days 4 and 8. T1 alpha expression is markedly inhibited in both DG1 a nd DG4 cultures, consistent with both inhibition and reversal of the t ransition toward the AT1 cell phenotype. These results demonstrate tha t both soluble factors and alterations in cell shape modulate T1 alpha expression in parallel with AEC phenotype and provide further, suppor t for the concept that transdifferentiation between AT2 and AT1 cell p henotypes is at least partially reversible.