Risk factors for keratoconus in Israel: a case-control study.

PURPOSE: Keratoconus (KC) is a progressive corneal thinning disorder with an uncertain aetiology. Environmental and genetic factors, including consanguinity, eye rubbing and possibly sun exposure, play a role in the aetiology of KC. Here we test for risk factors for KC in an Israeli population with particular emphasis on sun exposure. METHODS: This case-control study included KC patients who were diagnosed at Care Laser Medical Group, a refractive surgery clinic with branches throughout Israel. The control group included age, sex and ethnicity matched individuals who were randomly selected from patients presenting at the clinic for refractive surgery, but without KC. Study subjects were asked to fill out a self-administered questionnaire that included demographic and geographic details, questions on ocular and general health and sun exposure. Conditional logistic regression was used to analyse univariable and multivariable data to identify risk factors for KC. RESULTS: Seventy-three KC patients and 146 controls participated in the study. Univariable analyses demonstrated that eye rubbing [odds ratio (OR) = 3.76], positive family history of KC (OR = 6.10) and parents' education (<12 years, OR = 0.27, 0.23 for father's and mother's education respectively) were significant risk factors for KC. Univariable analyses of sun exposure behaviour during teenage years proved equivocal with some behaviours emerging as protective for KC (wearing a hat outdoors, OR = 3.13) or as risk factors (spending time in the shade, OR = 0.45), while others showed no association [limiting time in the sun (p = 0.51), and wearing sunglasses (p = 0.20)]. Most of the factors that were significant in the univariable analyses, also emerged as statistically significant in the multivariable model (OR = 3.37, 9.68, 0.35, 5.51 for eye rubbing, family history, parental education, wearing a hat outdoors, with the exception of spending time in the shade (p = 0.88). CONCLUSIONS: Eye rubbing, parents' education (as a measure of socio-economic status) and having family members with KC emerged as significant risk factors for KC. The role of sun exposure in KC remains equivocal and warrants further research.

IL-8-induced migratory responses through CXCR1 and CXCR2: association with phosphorylation and cellular redistribution of focal adhesion kinase.

CXCR1 and CXCR2 mediate migratory activities in response to IL-8 and other ELR+-CXC chemokines (e.g., GCP-2 and NAP-2). In vitro, activation of migration is induced by low IL-8 concentrations (10-50 ng/mL), whereas migratory shut-off is induced by high IL-8 concentrations (1000 ng/mL). The stimulation of CXCR1 and CXCR2 by IL-8 concentrations that result in migratory activation induced focal adhesion kinase (FAK) phosphorylation in a G(alpha)i-dependent manner. The expression of FRNK, a dominant negative mutant of FAK, perturbed migratory responses to the activating dose of 50 ng/mL IL-8. The migration-activating concentrations of 50 ng/mL GCP-2 and NAP-2 induced less potent migratory responses and FAK phosphorylation in CXCR2-expressing cells as compared with IL-8. These results indicate that FAK is phosphorylated, and required, for the chemotactic response under conditions of migratory activation by ELR+-CXC chemokines. In addition, FAK phosphorylation was determined following exposure to migration-attenuating concentrations of IL-8. In CXCR1-RBL cells this treatment resulted in FAK phosphorylation, in similar levels to those induced by activating concentrations of IL-8. In contrast, in CXCR2-RBL cells the migration-attenuating concentrations of IL-8 induced promoted levels of FAK phosphorylation and different patterns of FAK phosphorylation on its six potential tyrosine phosphorylation sites, as compared to activating concentrations of the chemokine. Exposure to IL-8 resulted not only in FAK phosphorylation but also in its cellular redistribution, indicated by the formation of defined contact regions with the substratum, enriched in phosphorylated FAK and vinculin. Overall, FAK phosphorylation was associated with, and found to be differently regulated upon, ELR+-CXC chemokine-induced migration.

Intracellular trafficking of human CXCR1 and CXCR2: regulation by receptor domains and actin-related kinases.

In this study we investigated the regulation of CXCR1 and CXCR2 intracellular trafficking. First, we produced a chimeric CXCR2 receptor that contained the internalization motifs of both CXCR2 and CXCR1 (CXCR2: LLKIL sequence; CXCR1: C-terminal phosphorylation sites). Elevated levels of internalization were induced by different ELR-expressing CXC chemokines on the chimeric receptor, as compared to wild-type CXCR2. Analysis of inter-relationships between CXCR1 and CXCR2 during internalization indicated that the exposure of cells that expressed both CXCR1 and CXCR2 to CXCL8 or CXCL6 resulted in decreased levels of CXCR1 internalization as compared to those in cells that expressed only CXCR1. To characterize the role of actin-related components in CXCR1 and CXCR2 trafficking, wortmannin, a potent inhibitor of phosphatidylinositol kinases, was used. The presence of wortmannin during receptor recycling inhibited CXCR1 and CXCR2 re-expression following CXCL8-induced internalization, and resulted in a marked disruption of the proper organization of actin filaments. The kinase-dependent recycling process required CXCR2 C-terminal phosphorylation sites. Our results suggest that actin-related kinases are required for the proper functionality of actin filaments, which are the instrumental factors needed for receptor recycling. In all, CXCR1 and CXCR2 internalization and recycling are tightly regulated by receptor domains and by actin-related kinases.