Interleukin-1β and tumor necrosis factor-α have opposite effects on fibroblasts and epithelial cells during basement membrane formation

Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) are typical proinflammatory cytokines that influence various cellular functions, including metabolism of the extracellular matrix. We examined the roles of IL-1β and TNF-α in basement membrane formation in an in vitro model of alveolar epithelial tissue composed of alveolar epithelial cells and pulmonary fibroblasts. Formation of the basement membrane by immortalized rat alveolar type II epithelial (SV40-T2) cells, which ordinarily do not form a continuous basement membrane, was dose-dependently upregulated in the presence of 2 ng/ml IL-1β or 5 ng/ml TNF-α. IL-1β or TNF-α alone induced increased secretion of type IV collagen, laminin-1, and nidogen-1/entactin, all of which contributed to this upregulation. In contrast, while SV40-T2 cells cultured with a fibroblasts-embedded type I collagen gel were able to form a continuous basement membrane, they failed to form a continuous basement membrane in the presence of IL-1β or TNF-α. Fibroblasts treated with IL-1β or TNF-α secreted matrix metalloproteinase (MMP)-9 and MMP-2, and these MMPs inhibited basement membrane formation and degraded the basement membrane architecture. Neither IL-1β- nor TNF-α-treated SV40-T2 cells increased the secretion of MMP-9 and MMP-2. These results suggest that IL-1β participates in basement membrane formation in two ways. One is the induction of MMP-2 and MMP-9 secretion by fibroblasts, which inhibits basement membrane formation, and the other is induction of basement membrane component secretion from alveolar epithelial cells to enhance basement membrane formation.