Estrogen up-regulation of metalloproteinase-2 and -9 expression in rabbit lacrimal glands

Increased levels of the matrix metalloproteinases (MMPs)-2 and -9 have been found in tear fluids of patients with dry eye disease, suggesting that these MMPs may be implicated in the pathogenesis of this disease. One of the main causes of dry eye disease is lacrimal gland insufficiency. However, the contribution of the lacrimal gland (LG) to the expression and production of MMP-2 and MMP-9 in tears is not known. Since dry eye disease occurs more frequently in women, sex hormones, especially estrogens, have also been implicated in the pathogenesis of this disease. Estrogens have been shown to regulate the synthesis levels of MMP-2 and MMP-9 in several tissues, Thus, the purpose of these studies was to determine if: (1) rabbit lacrimal glands secrete MMP-2 and MMP-9; (2) MMP-2 and MMP-9 are produced by lacrimal epithelial cells and/or lacrimal lymphocytes; and (3) the expression, activity and level of these enzymes are regulated by sex hormones. Lacrimal epithelial cells (LEC) and lacrimal lymphocytes (LL) from sexually mature New Zealand White female rabbits were isolated, purified and cultured with and without 10−6 M dihydrotestosterone (DHT) or 10−6, 10−8, 10−9 and 10−10 M 17β-estradiol (E2). The culture supernatants were analyzed by zymography and western blotting (WB) using polyclonal anti-human MMP-2 and MMP-9 antibodies. LGs were also collected from rabbits 7 days after being sham-operated, ovariectomized (OVX), OVX treated with 4 mg/kg DHT, and OVX treated with 0.5 mg/kg of E2. LGs were collected and processed for RNA extraction as well as protein determination using WB and immunocytochemistry. The pro-forms of MMP-2 and MMP-9 were detected in primary LEC and LL culture medium by zymography and WB. Pro-MMP-2 and pro-MMP-9 were also detected at the gene and protein levels in the lacrimal glands of all four treatment groups, with the highest levels and gene expression found in the estrogen-treated group. These results suggest that both pro-MMP-2 and pro-MMP-9 are secreted by the lacrimal gland and appear to be up-regulated by estrogen. The role of the lacrimal MMPs in the pathogenesis of dry eye disease needs to be further investigated.