Differential Expression of miR-146a, IL-31, and IL-33 in Osteoporosis and their Associations with Disease Severity

Osteoporosis is a metabolic disorder characterized by reduced bone mass and microarchitectural deterioration, and it is closely associated with inflammatory processes. This study investigated the expression of microRNA-146a (miR-146a), interleukin-31 (IL-31), and interleukin-33 (IL-33) in osteoporosis and their correlations with disease severity.

Peripheral blood mononuclear cells (PBMCs) were isolated from 31 patients with moderate and severe osteoporosis and 28 healthy controls. Expression levels of miR-146a, IL-31, and IL-33 were assessed using real-time PCR. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DXA). Demographic and clinical data, including age, gender, fracture history, and femoral and spinal T-scores, were recorded.

MiR-146a expression was significantly lower in patients with moderate and severe osteoporosis than in healthy controls (P < 0.05). MiR-146a levels were inversely correlated with patient age (r = -0.316, P < 0.05). No significant differences in IL-31 or IL-33 expression were observed between patient and control groups. Furthermore, no significant differences in miR-146a, IL-31, or IL-33 levels were found between patients with moderate and severe osteoporosis. However, IL-31 levels were strongly correlated with IL-33 levels in patients (r = 0.76, P < 0.0001), and IL-33 levels were positively associated with C-reactive protein (CRP) values (r = 0.366, P < 0.05). ROC analysis indicated modest discriminative ability of miR-146a between patients with osteoporosis and healthy controls. Because miR-146a expression was lower in patients, the ROC direction was oriented toward the control classification, yielding an AUC of 0.655 (P < 0.05). This represents the same underlying discrimination as the complementary AUC obtained when osteoporosis is defined as the positive class and should not be interpreted as a separate metric for "non-occurrence" prediction. A cut-off value of 0.02 yielded a sensitivity of 82.1% and a specificity of 51.6% for the control classification direction.

The significant downregulation of miR-146a in osteoporotic patients and its positive correlation with femoral T-scores suggest a potential role for this microRNA in the pathophysiology of osteoporosis, possibly through its regulatory function in inflammatory pathways. However, the weak correlation and modest discriminative performance indicate that miR-146a alone is unlikely to serve as a reliable diagnostic biomarker. The strong correlation between IL-31 and IL-33 levels, along with the positive association between IL-33 and CRP, points to a potential interplay between these interleukins and systemic inflammation in osteoporosis. Nonetheless, the absence of significant differences in IL- 31 and IL-33 between patients and controls raises questions about their direct involvement in disease pathogenesis. These findings should be interpreted within the context of the study's limitations, particularly its small sample size and the possibility that it was underpowered to detect modest effect sizes.

Reduced miR-146a is weakly associated with osteoporosis but lacks predictive value. Critically, the study may be underpowered due to the small sample size and an overestimated effect size of 0.9. Consequently, the non-significant findings for IL-31 and IL-33 should be interpreted with caution. Future studies with larger sample sizes are needed to validate our findings and provide more definitive conclusions.