The role of exocytotic proteins in the (dys)regulation of human reflex tearing and aqueous‐deficient dry eye syndrome

Abstract

Aims/Purpose: Reflex tears triggered by various external and internal stimuli play vital functions in the protection of the ocular surface and visual acuity. The impairment of the molecular processes involved in reflex tearing is conjectured to be associated with the progression of dry eye syndrome (DES). Therefore, this study was undertaken to unravel the intricate proteome changes in the reflex and DES tears.Methods: Thirty six subjects underwent basic secretory test (BST) via Schirmer I (without anaesthetics) to determine the secretory rate of the lacrimal gland due to the irritating nature of the strip and were divided into reflex (RF, n = 12, BST = 35.0 ± 0.0), normal (NR, n = 12, BST = 15.3 ± 3.0) and severe aqueous‐deficient DES (DRY, n = 12, BST = 3.4 ± 1.4). The individual tear samples were analysed employing the state‐of‐the‐art mass spectrometry‐based proteomics strategy, followed by bioinformatics analyses to elucidate the underlying molecular processes.Results: A total of 293 and 237 proteins were found to be significantly (p < 0.05) differentially regulated in the RFL vs. NR (up‐regulated, UR = 12; down‐regulated, DR = 281) and DRY vs. NR (UR = 197; DR = 40), respectively. The hallmark of this study was the identification of 10 lacrimal gland‐specific proteins (e.g., LYZ, LCN1, LTF, PRR4, ZG16B) secreted mainly via the exocytotic pathway, which were significantly up‐regulated in the RFL vs. NR but down‐regulated in the DRY vs. NR. Antibacterial response was also significantly activated in RFL (p = 1.9 × 10−2) compared to DRY (p > 0.05). The activated inflammatory response (e.g. S100A8/A9, ANXA1) associated with DRY (p = 2.7 × 10−8, z = 4.0) was found to be inhibited in the RFL (p = 2.7 × 10−9, z = −3.5). Likewise, proteins involved in glycolysis (z = −2.8), acute phase response (z = −2.7) and actin cytoskeleton signalling (z = −2.1) were also inhibited in the RFL compared to DRY.Conclusions: In summary, this study has demonstrated that protein markers involved in the exocytotic pathway play major roles in the production of reflex tears and their regulation is impaired in the DES. Importantly, the abrogation of the vicious cycle of pathways involved in the progression of DES, especially inflammation, was observed in the reflex tears, which may be the key for the protection and maintenance of dynamic balance of the ocular surface.