MMP13 and atrial fibrillation: In a rat AF-defect model, intradiscal WPG administration preserved disc height and T<sub>2</sub>-weighted MRI signal, reduced MMP13 while increasing Collagen I and Aggrecan expression, suppressed nuclear P-p65 and LCN2, and improved segment biomechanics-without eliciting adverse hematological or organ responses.