Not All Lacrimal Epithelial Cells are Created Equal—Heterogeneity of the Rabbit Lacrimal Gland and Differential Secretion

Abstract

Aims: To test the hypotheses that some epithelial cells in the rabbit lacrimal gland (LG) are mucin-secreting cells that are also particularly rich in aquaporin 5 (AQP5) and sodium potassium ATPase β₁ subunit (NKAβ₁), LG-secreted mucins contribute to the total mucin pool in tear film, and that the rabbit LG is a heterogenic gland where proteins secreted in response to different agonists are varied. Materials and methods: LGs were obtained from adult female rabbits and processed for paraffin sections for hematoxylin and eosin (HE) staining, periodic acid-Schiff (PAS), mucicarmine, and Alcian blue (pH 0.4, 1.0, and 2.5) for the detection of mucins. Serial sections were used for immunohistochemistry (IHC) and PAS. LG lysates and fluids were assayed by dot blot for detection of mucins, and by SDS-PAGE to detect differences in protein profiles of LG fluids stimulated by different agonists. Results: HE staining demonstrated that the LG is a heterogeneous gland where most epithelial cells are serous, while all duct cells are mucous cells. Some acini and individual acinar cells within serous acini are also mucous or seromucous cells and these cells are particularly rich in AQP5 and NKAβ₁. Dot blot assay showed the presence of mucins in the LG fluids. The protein profiles of LG fluids from pilocarpine, phenylephrine, and isoproterenol varied significantly, particularly in the mid range. Conclusions: Our data indicated that the rabbit LG is a heterogeneous gland that is composed of both serous and mucin-secreting cells, and mucins produced by the LG contribute to the mucin pool in the tear film. The heterogeneity of the rabbit LG supports the notion of differential secretion, i.e. the volume and composition of the LG fluids vary depending on various circumstances in the ocular surface and the body’s needs.

Keywords::

• Lacrimal gland
• Heterogeneity
• Mucin
• Dry eye
• Differential secretion

ACKNOWLEDGEMENTS

This work was supported by NIH grants EY017731 (CD), DK048522 (Core Facilities of the USC Research Center for Liver Diseases), and EY03040 (Doheny Eye Institute Core). The authors thank Maria Edman, Ernesto Barron, and Qinggao Deng for helpful comments and discussions.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.