Dynamic and static mechanical compression affects Akt phosphorylation in porcine patellofemoral joint cartilage

Protein kinase B (Akt)-dependent signaling pathways induced by mechanical loading have been identified in a variety of tissue. However, there is no evidence for a potential regulation of Akt in cartilage mechanotransduction. This study was conducted in order to determine whether or not the Akt in chondrocytes is regulated by mechanical loading. Porcine patellofemoral joints were loaded in compression at 500 N for 150 s either dynamically at 12 Hz or 1 Hz or statically using a custom-designed loading frame. Left-sided knees served as intervention, right-sided as unloaded control. Cartilage samples were harvested at different time points after mechanical loading and the phosphorylation of Akt was analyzed immunohistochemically. A downregulation of Akt phosphorylation was seen in cartilage 300 s after mechanical loading whereas Akt phosphorylation remained unchanged in unloaded specimens. In addition, regulation of Akt appeared to change with the frequency of loading, presenting different patterns in Akt phosphorylation with static and dynamic loading. Variations in Akt phosphorylation were detected through different zones of cartilage. Overall, our findings indicate that Akt signaling in porcine patellofemoral joint cartilage is dependent upon frequency of loading, cartilage zone, and the time interval between loading and cartilage harvest. It may be concluded that Akt plays a role in cartilage mechanotransduction.