Bone morphogenetic protein-2 and transforming growth factor-β1 regulate cell proliferation and ectopic claudin-4 expression in parotid acinar cells

Objectives: Salivary gland secretory function is impaired by tissue injury, but subsequently recovers if the damage is not severe. We previously reported that tissue injury can cause secretory granule loss and ectopic expression of claudins and stem cell markers including nestin in parotid acinar cells. Such alterations may indicate acinar cell dedifferentiation contributing to cell survival. We investigated transforming growth factor (TGF)-β superfamily member expression profiles and functions to identify tissue injury responsive signals.

Methods: Acinar cells were isolated from the rat parotid glands via extracellular matrix digestion with collagenase and hyaluronidase and cultured in the absence or presence of the Src kinase inhibitor PP1. TGF-β superfamily expression was determined by reverse transcription quantitative PCR (RT-qPCR). Acinar cells were then cultured with inhibitors of bone morphogenetic protein (BMP) or TGF-β. A Cell Counting Kit-8 was used to assess cell proliferation, and immunoblotting was used to examine the expression of cell adhesion molecules and the stem cell marker nestin.

Results: Increased BMP-2, BMP-6, and TGF-β1 expression was observed in primary culture of parotid acinar cells. Their expression decreased under Src Inhibitor treatment. BMP-2/4 and TGF-β signaling inhibitors suppressed cell proliferation. These inhibitors also decreased claudin-4 and nestin expression, which was absent in intact acinar tissue, but present after Cell Isolation.

Conclusions: BMP-2 and TGF-β1 may contribute to tissue regeneration and protection by enhancing paracellular barrier function.

Salivary gland; Stem cell; TGF-β superfamily; Tight junction.