Mechanisms of murine lacrimal gland repair after experimentally induced inflammation.

Purpose: The authors recently reported that a severe inflammatory response resulting in substantial loss of acinar cells was induced by a single injection of interleukin-1alpha into the lacrimal gland and that this effect was reversible. The purpose of the present study was to determine the mechanisms involved in lacrimal gland injury and repair.
Methods: Inflammation was induced by direct injection of recombinant human interleukin-1alpha (IL-1alpha, 1 microg in 2 microL) into the exorbital lacrimal glands of anesthetized female BALB/c mice. Animals were killed 1, 2, 3, 4, 5, 6, or 7 days after injection. Exorbital lacrimal glands were then removed and processed for measurement of protein secretion, histology, immunohistochemistry, and Western blotting.
Results: The results show that lacrimal gland acinar cells are lost through programmed cell death (apoptosis) and autophagy. They also show that the number of nestin (a stem cell marker)-positive cells increased 2 to 3 days after injury and that some of these cells were also positive for Ki67 (a cell proliferation marker) and alpha-smooth muscle actin (a marker of myoepithelial cells). Finally, they show that the amount of phosphorylated Smad1/5/8 (effector molecules of bone morphogenetic protein 7 [BMP7]) increased 2 to 3 days after injury and could also be detected in nestin-positive cells.
Conclusions: The lacrimal gland contains stem/progenitor cells capable of tissue repair after injury. Programmed cell death after injury triggers proliferation and differentiation of these cells, presumably through activation of the BMP7 pathway.