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

Area of Science:

• Molecular Biology
• Cell Biology
• Immunology

Background:

• CCN1 is crucial for arthritis development and is upregulated by hypoxia in osteoblasts.
• Sirtuin 6 (SIRT6) has been previously shown to inhibit hypoxia-induced CCN1 expression in osteoblasts.

Purpose of the Study:

• To investigate the role of cyclic AMP-responsive element binding protein (CREB)/CRE in SIRT6's suppression of CCN1.
• To examine the effect of CCN1 on cyclooxygenase (COX) 2 synthesis.
• To evaluate the therapeutic potential of SIRT6 in a rat model of collagen-induced arthritis (CIA).

Main Methods:

• Osteoblast cultures under normoxia and hypoxia.
• Western blot analysis for CCN1, phospho-CREB, COX2, and kinases.
• Lentiviral overexpression of SIRT6 in vitro and in vivo.
• Luciferase reporter assays for CCN1 promoter activity.
• Chromatin immunoprecipitation (ChIP) for CREB-CCN1 promoter interaction.
• Induction of CIA in rats to assess SIRT6 therapy.

Main Results:

• SIRT6 suppressed hypoxia-induced CCN1 expression and CREB phosphorylation, potentially via CaMKII inhibition.
• The CRE element (-286 bp) is critical for CCN1 expression under hypoxia, and SIRT6 reduced CREB binding to this element.
• Forced CREB expression reversed SIRT6-mediated CCN1 suppression.
• CCN1 induced COX2 expression in osteoblasts.
• In CIA rats, SIRT6 therapy reduced phospho-CREB, CCN1, and COX2 levels in osteoblasts.

Conclusions:

• SIRT6 modulates the CREB/CCN1/COX2 pathway in osteoblasts.
• SIRT6's beneficial effects in inflammatory arthritis and bone resorption are partly mediated by this pathway.