Biomarkers for epithelial cells and basement membranes in the human meibomian gland

Abstract

Purpose : The meibomian gland (MG) is a sebaceous gland (SG) that secretes through a holocrine process. Because such secretion requires the destruction of MG acinar epithelial cells, they need constant renewal and differentiation. The processes that promote these regenerative events in the human MG are unknown. Indeed, it is not even known how to distinguish MG progenitor and differentiated cells. Such identifying ability would have tremendous value in clinical efforts to restore MG function, and to regenerate MGs after disease-induced dropout. We hypothesize that Lrig1 and Lgr6 serve as biomarkers for human MG progenitor cells, and that DNase2 is a marker for differentiated cells. Our rationale is that both Lrig1 and Lgr6 are biomarkers for progenitor cells that give rise to differentiated SG epithelial cells (sebocytes). Further, DNase2 is known to initiate sebocyte holocrine secretion, the terminal step of differentiation. We also hypothesize that the human MG basement membrane, which is critical for epithelial cell function, will have a distinct immunophenotype. Our study began to test our hypotheses.

Methods : We utilized human lid tissues and immortalized human meibomian gland epithelial cells (IHMGECs). The use of human tissues was approved by the Massachusetts Eye and Ear IRB. Samples were processed for immunofluorescent and Western blotting procedures.

Results : Lrig1 and Lgr6 are expressed in MG basal epithelial cells in the acinar periphery, a location in which progenitor epithelial cells originate in SGs. Lrig1 and Lgr6 are not expressed in the differentiating cells in the central section of the MG acinus. In contrast, DNase 2 is expressed in the differentiated epithelial cells of the MG central acinus, but not in basal cells. Proliferation stimulates, and differentiation suppresses, Lrig1 expression in IHMGECs. The opposite is true for DNase 2 expression. We also discovered that basement membranes show immunoreactivity for collagen type IV a1, a2, a5 and a6 chains, laminin a2 and b1, nidogen-2 and perlecan, and that staining for most of these markers is predominantly in the acinar, as compared to ductal, areas.

Conclusions : These results support our hypotheses and demonstrate that [a] Lrig1, Lgr6 and DNase2 serve as biomarkers for either progenitor or differentiated cells in the human MG; and [b] the MG basement membrane features a distinct phenotype.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.