Concomitant reduction of phosphorylation of LKB1 and AMPKα in aged mouse knee cartilages. Knee sections of mice 6, 12 and 24 months old were analyzed for phosphorylation of liver kinase B1 (LKB1) and AMP-activated protein kinase alpha (AMPKα) by immunohistochemistry, as described in Materials and methods. Cellularity of each section was confirmed with hematoxylin staining. Only the cells present in the noncalcified region of femoral and tibial cartilage were subjected to analysis. Cells staining positively for LKB1 and AMPKα were presented as percentage relative to cells stained for hematoxylin. Data representative of two individual experiments (n = 4 for each time point). *P <0.01, #P <0.05 relative to the 6-month-old mouse knee cartilage.