The effect of exercise on the protein profile of rat knee joint intra- and extra-articular ligaments

Abstract

Injuries to the intra-articular knee joint ligament (anterior cruciate ligament (ACL)) together with the extra-articular medial collateral ligament (MCL) result in significant joint instability, pain and immobility for the affected individual. Moderate endurance type exercise has been shown to increase ligament strength, however little is known on the effect of short-term high intensity exercise regimes such as treadmill training on the ACL and MCL and whether they may be beneficial to the extracellular matrix (ECM) structure of these ligaments. This study aimed to identify the effect of short-term high intensity exercise on the proteome of the rat ACL and MCL using mass spectrometry. Sprague Dawley male rats (n=12) were split into equal groups of control and exercise animals, which were subjected to high intensity training and followed by proteomic analysis of the ACL and MCL. Knee joint and ligament health was assessed using OARSI scoring or using a validated histological scoring system. Histopathological analyses demonstrated no significant changes in the ACL, MCL or cartilage of the knee joint, indicating that the exercise regime used in this study did not have substantial impact on tissue structure and health of several tissues within the rat knee joint. Some proteins were found to be significantly more abundant in the ACL in the exercised group than the control group. However, no proteins with a significantly different expression were identified between MCL control and MCL exercised groups. The majority of proteins expressed at higher levels in the ACL exercise group were cytoskeletal proteins, ribosomal proteins and enzymes. Several matrisomal proteins were also more abundant such as collagen proteins and proteoglycans in ACL exercise group. In conclusion, our results indicate that short-term high intensity exercise has an impact on ACL ECM protein expression, with the majority of differential expressed proteins being cellular proteins such as actins, ribosomal and heat shock proteins, indicative of metabolic and molecular responses. Further study is necessary to determine the impact of these short-term changes on ligament structure and function.