To elucidate the pathogenesis of ocular surface abnormalities in patients with Sjögren's syndrome (SS) by comparing global gene expression patterns in conjunctival epithelial cells from normal individuals and SS patients.
The study population consisted of 56 subjects (26 SS patients and 30 normal volunteers). RNA extracted from their conjunctival epithelial cells was subjected to introduced amplified fragment length polymorphism (iAFLP), a competitive PCR-based gene expression assay, to measure gene expression in the 56 samples against 931 genes. Data were analyzed by two-dimensional clustering analysis and discriminant analysis. Disease-related genes were identified and the feasibility of gene expression-based diagnosis of SS was examined.
Two-dimensional clustering- and discriminant analysis clearly distinguished between SS patients and normal subjects. Of 931 genes tested, 34 were significantly up-regulated and 12 were significantly down-regulated in SS (p<0.05). Up-regulated genes included kallikrein 7 (x 15.8) and small proline-rich protein 2A (x 9.6), markers for the terminal differentiation of epidermis, and the inflammation-related genes HLA-DR and IL-6. Monokine-induced-by-gamma-interferon, i.e. c-fos, fibronectin, amphiregulin, defensin beta 2, and keratin 16, -6b and -6c were also up-regulated. Among the 12 down-regulated genes, interferon-gamma receptor 1 was most notable (x1/27.3).
The up-regulated expression of keratin 6 and -16, small proline-rich protein 2A, and kallikrein 7 in the conjunctival epithelium of SS patients suggests an anomalous keratinization pattern. Epithelial thickening may be due to amphiregulin and/or c-fos-stimulated cell cycle progression. The up-regulation of monokine-induced-by-gamma-interferon, HLA-DR, keratin 6b, -6c, and -16 suggests that in SS, interferon-gamma may play an important role in the altered gene expression in the conjunctival epithelium.