Immune Netw.  2002 Dec;2(4):208-216. 10.4110/in.2002.2.4.208.

Suppressed DNA Repair Mechanisms in Rheumatoid Arthritis

• Lee SH
• Firestein

• KMID: 1974519
• DOI: http://doi.org/10.4110/in.2002.2.4.208

Abstract

BACKGROUND: Reactive oxygen and nitrogen are produced by rheumatoid arthritis (RA) synovial tissue and can induce mutations in key genes. Normally, this process is prevented by a DNA mismatch repair (MMR) system that maintains sequence fidelity. Key members of the MMR system include MutS alpha (comprised of hMSH2 and hMSH6), which can sense and repair single base mismatches and 8-oxoguanine, and MutS beta (comprised of hMSH2 and hMSH3), which repairs longer insertion/deletion loops.
METHODS
To provide further evidence of DNA damage, we analyzed synovial tissues for microsatellite instability (MSI). MSI was examined by PCR on genomic DNA of paired synovial tissue and peripheral blood cells (PBC) of RA patients using specific primer sequences for 5 key microsatellites.
RESULTS
Surprisingly, abundant MSI was observed in RA synovium compared with osteoarthritis (OA) tissue. Western blot analysis of the same tissues for the expression of MMR proteins demonstrated decreased hMSH6 and increased hMSH3 in RA synovium. To evaluate potential mechanisms of MMR regulation in arthritis, fibroblast-like synoviocytes (FLS) were isolated from synovial tissues and incubated with the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP). Western blot analysis demonstrated constitutive expression of hMSH2, 3 and 6 in RA and OA FLS. When FLS were cultured with SNAP, the RA synovial pattern of MMR expression was reproduced (high hMSH3, low hMSH6).
CONCLUSION
Therefore, oxidative stress can relax the DNA MMR system in RA by suppressing hMSH6. Decreased hMSH6 can subsequently interfere with repair of single base mutations, which is the type observed in RA. We propose that oxidative stress not only creates DNA adducts that are potentially mutagenic, but also suppresses the mechanisms that limit the DNA damage.

Keyword

Mismatch repair enzyme; rheumatoid arthritis; microsatellite instability

MeSH Terms

Arthritis
Arthritis, Rheumatoid*
Blood Cells
Blotting, Western
DNA Adducts
DNA Damage
DNA Mismatch Repair
DNA Repair*
DNA*
Humans
Microsatellite Instability
Microsatellite Repeats
Nitric Oxide
Nitrogen
Osteoarthritis
Oxidative Stress
Oxygen
Polymerase Chain Reaction
S-Nitroso-N-Acetylpenicillamine
Synovial Membrane
Tissue Donors
DNA
DNA Adducts
Nitric Oxide
Nitrogen
Oxygen
S-Nitroso-N-Acetylpenicillamine