GPR-68 in human lacrimal gland. Detection and possible role in the pathogenesis of dry eye disease

Abstract

In parallel to ocular surface disease in dry eye there is often a dysfunctionality of the lacrimal gland apparatus. The functionality of the lacrimal gland is of major importance for maintenance of ocular surface integrity and health, even in conditions of enhanced stimulation and secretion requirements. Such enhanced secretion demands can push the lacrimal gland to its limits, with maximized tear fluid secretion and increased flow through the lacrimal ducts. The goal of this study was to investigate whether G protein-coupled receptor GPR-68 is present in the lacrimal gland, as this protein has recently been shown to be sensitive to flow rate and osmolarity. For this purpose, de-identified sections of human lacrimal gland tissue were stained for the presence of G protein-coupled receptor 68 with specific antibodies using immunohistochemistry. Specific staining was detected in the acini and ducts of human lacrimal gland. In the ducts, the specific staining was found around the lumen of the ducts. In the acini, the specific staining was observed more towards the lumen but also intercellularly between the acinar cells. The detection of G protein-coupled receptor GPR-68 in the lacrimal gland, especially around the lumen of the ducts, raises the question about its function and purpose. Activation of GPR68 leads to modification of various cell functions and is associated with regulation of inflammation. Accordingly, enhanced, secretion-induced, augmentation of flow might exert fluid flow stress on the ducts and acini. This might lead to transient, localized activation of GPR-68 and secondary inflammation within the gland. Depending on the intensity, continuity or repetitive nature of the stimuli, exhaustion of the lacrimal gland secretion capacity might follow, and chronicity of the inflammation in the parenchyma as well as around the ducts might be a consequence. G protein-coupled receptor GPR-68, sensitive to flow, is present in the human lacrimal gland. Increased flow, triggered by sensations such as are typical for dry eye, might lead to local inflammation. It is possible that these sensations might serve as a better indicator for the need and success of therapy than the clinical signs of dry eye disease, at least in the early stages of the disease.