Lactoferrin Rescues Tear Secretion in a Restraint and Desiccating Stress Model of Dry Eye Disease Possibly by Upregulating Brain Derived Neurotrophic Factor

摘要

Purpose: Dry eye disease (DED) is a common multifactorial disease that is detrimental to the quality of life of sufferers. DED is characterised by tear hyposecretion and tear film instability, resulting in painful gritty eyes. Lactoferrin (Lf) is a glycoprotein found in tears with links to lacrimal gland (LG) function. Lf possesses a plethora of properties including anti-inflammation, anti-oxidation, and the ability to upregulate brain derived neurotrophic factor (BDNF). We previously demonstrated that Lf retains tear secretion in a restraint and desiccating stress (RDS) model of DED. We hypothesize that this increase in BDNF aids neural stimulation and Ca2+ release in the LG leading to tear secretion. Methods: 8-week-old female C57Bl/6J mice were randomly divided into 3 groups of 5: negative control (NC), vehicle (V) and high (H)-Lf. V and H-Lf mice were given a daily 500??l oral administration of either PBS or 100mg/kg of bovine Lf, respectively. 100mg/kg Lf was deemed appropriate due to the positive effects observed in our previous study. Experiments lasted 7 days (-1-5). From day 0 onwards V and H-Lf mice were exposed to RDS for 4 hours per day, and sacrificed on day 5. NC were not given oral administration, nor exposed to RDS. Tissues were fixated using a paraformaldehyde perfusion method. Immunohistochemistry (IHC) and qPCR was performed on the LG and brain tissue, specifically the hippocampus (HC). Results: We observed a decrease in the area of positive BDNF IHC staining in the HC of V (83470??m2) but an increase in H-Lf (154825??m2), when compared to that of NC (129063??m2). The alteration in staining was primarily observed in the CA3 and hilus regions. When again compared to NC mice, qPCR indicated an increase in BDNF mRNA in both the HC (p=0.0001) and LG (p=0.06) of H-Lf mice, and a small decrease in V mice. Conclusions: In addition to Lfa??s ability to sequester inflammation and oxidative stress, factors critical to the pathogenesis of DED, the upregulation of BNDF may also play a role in the maintenance of tear secretion. BNDF acts in a positive feedback loop increasing the expression of muscarinic acetylcholine receptors, subsequently leading to further expression of IP3 and Ca2+ release. It therefore may be possible that Lf-treated mice are more receptive to stimulation of innervated acinar cells, leading to further tear secretion.