Sirtuin 6 ameliorates arthritis through modulating cyclic AMP-responsive element binding protein/CCN1/cyclooxygenase 2 pathway in osteoblasts.

INTRODUCTION: CCN1 is an immediate-early gene product pivotal for arthritis progression. We have previously shown that sirtuin 6 (SIRT6) inhibited hypoxia-induced CCN1 expression in osteoblasts. Herein we examined the contribution of cyclic AMP-responsive element binding protein (CREB)/CRE to this suppressive action and the influence of CCN1 on cyclooxygenase (COX) 2 synthesis. MATERIALS AND METHODS: MC3T3-E1 murine osteoblasts were cultured under normoxia (21% oxygen) or hypoxia (2% oxygen). Expressions of CCN1, phospho-CREB (Ser133), COX2 and relevant kinases were assessed by Western blot. SIRT6 was overexpressed in cultured osteoblasts and arthritic joints by a lentiviral-based technique. Activities of CCN1 gene promoter constructs were examined by luciferase reporter assay. Interaction between CREB and CCN1 promoter was assessed by chromatin immunoprecipitation (ChIP). Collagen-induced arthritis (CIA) was established in 20 rats to evaluate the effects of SIRT6 therapy on osteoblastic expressions of phospho-CREB, CCN1 and COX2. RESULTS: SIRT6 suppressed hypoxia-enhanced CCN1 expression and CREB phosphorylation. Attenuation of calcium/calmodulin-dependent protein kinase II (CaMKII) may be responsible for SIRT6-induced CREB inhibition. CRE at - 286 bp upstream of the ATG start codon was essential for CCN1 expression under hypoxia and SIRT6 reduced hypoxia-stimulated CREB/CRE interaction. Forced expression of CREB rescued SIRT6-suppressed CCN1 synthesis. CCN1 induced COX2 expression in osteoblasts. In rat CIA, the therapeutic effect of SIRT6 was accompanied by decreases in osteoblastic expressions of phospho-CREB, CCN1 and COX2. CONCLUSION: Our study indicated that the benefits of SIRT6 to inflammatory arthritis and bone resorption are at least partially derived from its modulation of CREB/CCN1/COX2 pathway in osteoblasts.

An extract of green tea, epigallocatechin-3-gallate, reduces periapical lesions by inhibiting cysteine-rich 61 expression in osteoblasts.

Recent investigations indicate that epigallocatechin-3-gallate (EGCG), the major polyphenol of green tea, has anti-inflammatory properties. This study assessed the effect of EGCG on oncostatin M (OSM)-induced synthesis of cysteine-rich 61 (Cyr61), a potential osteolytic mediator, in MG-63 human osteoblastic cells. The therapeutic effect of EGCG in apical periodontitis in rats was also examined. Western blot analysis showed that OSM stimulated Cyr61 synthesis in MG-63 in a time-dependent manner, whereas EGCG readily attenuated this effect. On the other hand, Cyr61 treatment of MG-63 cells induced the release of CCL2, a chemokine responsible for macrophage chemotaxis. In a rat model of induced apical periodontitis, radiography and histopathology revealed that administration of EGCG markedly diminished the severity of periapical lesions. The numbers of Cyr61-synthesizing osteoblasts and infiltrating macrophages were also decreased. Thus, EGCG suppresses the progression of apical periodontitis, possibly by diminishing Cyr61 expression in osteoblasts and, subsequently, macrophage chemotaxis into the lesions.