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Osteoarthritis is more common in women than men in older age, but researchers have struggled to pinpoint precisely why this is. A new study may have shed light on the issue, after identifying differences in the synovial fluid of men and women with the disease.

Synovial fluid is the fluid that surrounds the joints which helps to protect cartilage against damage caused by friction during movement. Study co-author Dr. Monte Hunter, and colleagues recently published their findings in the journal Scientific Reports. The team analyzed samples of synovial fluid taken from the knees of men and women both with and without OA.

The analysis revealed significant differences in miRNA activity between men and women with OA. Synovial fluid of men showed 69 downregulated and 45 upregulated miRNAs, while the the synovial fluid of women had 91 downregulated and 53 upregulated miRNAs.

The team noted that lower estrogen levels – which normally arise as a result of menopause – are associated with a greater production of bone-destroying cells. Additionally, studies have linked hormone replacement therapy, which boosts estrogen levels, with a lower risk of OA. Taking this information into account, the researchers believe that their findings indicate that estrogen influences miRNA levels within the exosomes of synovial fluid. The researchers also found that blocking estrogen availability in exosomes using aromatase inhibitors led to a reduction in miRNAs.

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