G2A is a G protein-coupled receptor that is predominantly expressed in lymphoid tissues and macrophages. G2A can be induced by diverse stimuli to cause cell cycle arrest in the G 2 /M phase in pro-B and T cells. G2A is also expressed in macrophages within atherosclerotic lesions, suggesting G2A involvement in atherosclerosis. Recently, G2A was discovered to possess proton-sensing ability. In this paper, we report another function of G2A, that is, as a receptor for 9-hydroxyoctadecadienoic acid (9-HODE) and other oxidized free fatty acids. G2A, expressed in CHO-K1 or HEK293 cells, showed 9-HODE-induced intracellular calcium mobilization, inositol phosphate accumulation, inhibition of cAMP accumulation, [35 S]guanosine 5-3-O-(thio)triphosphate binding, and MAP kinase activation. Furthermore, G2A was activated by various oxidized derivatives of linoleic and arachidonic acids, but it was weakly activated by cholesteryl-9-HODE. Oxidized phosphatidylcholine (1-palmitoyl-2-linoleoyl) when hydrolyzed with phospholipase A 2 also evoked intracellular calcium mobilization in G2A-expressing cells. These results indicate that G2A is activated by oxidized free fatty acids produced by oxidation and subsequent hydrolysis of phosphatidylcholine or cholesteryl linoleate. Thus, G2A might have a biological role in diverse pathological conditions including atherosclerosis.

G2A is a stress-inducible G protein-coupled receptor for oxidized free fatty acids, such as 9-hydroxyoctadecadienoic acid (HODE). As skin is routinely and pathologically exposed to many oxidative stresses such as UV radiation, chemical agents, and inflammation that might induce both G2A expression and production of G2A ligands, we examined G2A function in human keratinocytes. G2A was expressed in human epidermis, normal human epidermal keratinocytes (NHEK), and an immortalized human keratinocyte cell line (HaCaT). 9(S)-HODE evoked intracellular calcium mobilization and secretion of cytokines, including IL-6, IL-8, and GM-CSF in NHEK cells. These responses became prominent in HaCaT cells by overexpression of G2A. 9(S)-HODE inhibited proliferation of NHEK cells by suppressing DNA synthesis and arresting the cell cycle in the G0/1-phase. On the other hand, 13(S)-HODE, another major oxidative product from linoleate, showed little or no effect on either cytokine secretion or on proliferation in NHEK cells. A small interfering RNA designed to downregulate G2A caused suppression of 9(S)-HODE-induced inhibitory effects on proliferation of NHEK cells. UVB and H(2)O(2) induced G2A expression and caused oxidation of linoleate to produce 9-HODE in HaCaT cells. These results suggest that 9-HODE-G2A signaling plays proinflammatory roles in skin under oxidative conditions.

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Patients with systemic sclerosis (SSc) usually develop Raynaud's phenomenon, persistent digital ischemia and sometimes develop digital ulcers (DU). Several studies have reported an association of carotid artery atherosclerosis with SSc by evaluating carotid intima-media thickness (IMT) in SSc patients. However, none of those studies analyzed the association between DU and carotid artery atherosclerosis in SSc patients. We examined the association of carotid artery atherosclerosis with digital ulcers by comparing SSc patients with (n = 48, 29.5%) and without (n = 206, 70.5%) DU. The demographic and clinical features of the SSc patients showed that young age, male sex, anti-topoisomerase I antibody positivity, severe skin sclerosis, interstitial lung disease complication and cardiac involvements were significantly prevalent in patients with DU. In addition, diffuse cutaneous type, anti-RNA polymerase III antibody positivity and severe skin sclerosis are more frequent in SSc patients with DU at the extensor surface of joints than SSc patients with DU at the digital tip. There were no differences in serum lipid level, carotid IMT or plaque score between SSc patients with and without DU, suggesting that atherosclerotic changes are not primarily involved in the development of DU.

The solitary skin lesions of IgG(4)-related disease were similar histologically and immunohistochemically to the skin lesions of Kimura's disease. The concept of IgG(4)-related disease may help clarify the pathomechanism of diseases of unknown aetiology that possess features of IgG(4)-related disease.

The precise mechanisms of tissue fibrosis have not yet been elucidated in systemic sclerosis (SSc). However, studies of the regulation of DNA methylation, the most widely studied epigenetic mechanism, have confirmed the involvement of the TET family proteins, recently identified DNA demethylases, in the pathogenesis of SSc. The mRNA levels of TET family members were compared in normal and SSc fibroblasts. The effects of hypoxia and siRNA specific to HIF-1α on TET expression were also examined. Global methylation status was analysed by LUMA. The presence of 5-hydroxymethylcytosine (5hmC) in SSc was examined by immunohistochemistry. The level of TET1 mRNA in SSc fibroblasts was elevated by 1.68 fold compared with that of normal fibroblasts, but the expression levels of TET2 and TET3 were comparable between both cell types. The expression levels of DNMT1 and DNMT3B mRNA have a tendency to elevate in SSc fibroblasts. Among TET family members, the expression of TET1 was exclusively induced by hypoxia via HIF-1α-independent pathways in SSc fibroblasts, but not in normal fibroblasts. The methylation level was decreased in SSc fibroblasts relative to normal fibroblasts, and 5hmC was present in dermal fibroblasts of skin sections from patients with SSc. TET1 expression in SSc fibroblasts was abnormally regulated in the hypoxic environment and accompanied by global DNA hypomethylation, suggesting the involvement of aberrant DNA methylation in the pathogenesis of SSc.

Pseudoxanthoma elasticum (PXE) is a hereditary disease, causing calcification and degeneration of elastic fibers, which affects the skin, eye, cardiovascular systems and gastrointestinal tract. PXE is caused by mutations in the ABCC6 gene. Neither detailed nor large-scale analyses have been accomplished in Japanese patients with PXE. We, therefore, investigated clinical symptoms and ABCC6 gene mutations in 76 Japanese patients. Japanese PXE patients (n = 76) had a significantly lower incidence of vascular lesions than 505 PXE patients in the Leiden Open Variation Database (LOVD) (38.7% vs 65.1%, respectively; P = 1.34E-06); however, the incidences of the skin, eye, cardiac and gastrointestinal lesion symptoms were not significantly different. Symptom severity scores for skin, eye and vascular lesions, calculated using the Phenodex™ system, were significantly lower in Japanese PXE patients than in LOVD PXE patients. Genetic analysis revealed three nonsense, four frame-shift, one exon deletion and 13 missense mutations in ABCC6 in 73 patients; however, we were unable to detect pathogenic mutations in three patients. Frequent mutations differed between Japanese and LOVD PXE patients. In Japanese PXE patients, the top five mutations accounted for more than 60% of all pathogenic changes, suggesting the presence of founder effects. Consistent with previous reports, no obvious correlations between genotypes and phenotypes were identified in this study. In conclusion, we consider that the milder clinical phenotypes, observed even in older Japanese PXE patients, could be attributed to environmental factors such as dietary habits and lifestyle, as well as genetic background.

Eighteen patients with adult-onset Still's disease have been followed up for 3-22 years in our department. Initial manifestations were fever with skin rash in 14 patients, fever, skin rash and sore throat in two, skin rash in one and arthralgia in one. During the follow-up period, typical skin rash was seen in all patients, of them five patients (29%) revealed atypical skin rash simultaneously. Atypical rash included persistent erythema with pigmentation in two, persistent plaques and papules with linear erythema in two and edema of the eyelids mimicking dermatomyositis in one. Persistent papules and plaques revealed histologically characteristic features, such as dyskeratotic keratinocyte and liquefaction degeneration as well as a sparse superficial dermal infiltrate containing scattered neutrophils. In patients of chronic articular type and polycyclic systemic type, atypical skin rash, lymphadenopathy and hyperferritinemia were noted to be significantly higher than those of monocyclic type. These factors might be prognostic factors of adult-onset Still's disease in our study.