Lacritin, But Not Carbachol, Induces Secretion Of Tear Proteins From Cytokine-treated Monkey Acinar Cells

Abstract

Purpose: : Secretion of tear proteins from the lacrimal gland responds to signals from sympathetic and parasympathetic nerves. For example, cholinergic agonists increase intracellular Ca²⁺ and promote secretion of tear proteins such as lacritin. However, during inflammation of the ocular surface, increased pro-inflammatory cytokines depress tear protein secretion and cause corneal epithelial cell death. This leads to dry eye, and suggests functional decline in acinar cells. Lacritin, a primate-specific, autocrine factor, may actually stimulate tear protein secretion. If true, lacritin may be useful in treatment of dry eye. Therefore, the purpose of the present experiment was to document the influence of lacritin on protein secretion in cytokine-stimulated monkey acinar cells.

Methods: : Acinar cells were isolated from monkey lacrimal glands and cultured with or without TNF-α plus IFN-γ. After 1 day of culture, protein secretion was induced by lacritin or by carbachol (Cch, positive control). Proteins were detected by immunoblotting, and intracellular calcium was measured by Fluo-4. Cell death was determined by release of LDH into the culture medium.

Results: : The initial dosing levels of TNF-α plus IFN-γ caused release of LDH from sensitive human corneal epithelial cells. Even higher doses of TNF-α plus IFN-γ did not cause release of LDH from monkey acinar cells, although phosphorylation of STAT1 and breakdown of IΚB were similar between corneal epithelial cells and acinar cells. This suggested higher tolerability of acinar cells to these cytokines. Treatment of Cch-stimulated monkey acinar cells with TNF-α plus IFN-γ did suppress intracellular Ca²⁺and inhibited release of tear proteins. In contrast, lacritin induced protein secretion from acinar cells treated with or without cytokines. This occurred without increasing in intracellular Ca²⁺, suggesting an alternative mechanism for lacritin control that is different from Cch.

Conclusions: : These data confirmed that lacritin might be a useful biotechnology-based medicine for treatment of ocular surface diseases where endogenous lacritin is inadequate.

Keywords: lacrimal gland • cornea: tears/tear film/dry eye • inflammation