Hyperglycemia induces osteogenic differentiation of tendon derived mesenchymal stem cells

Introduction: The physiopathology of calcific tendinopathy is largely unknown, but it could be the result of an active cell-mediated process. Many endocrine and metabolic diseases may impair the homeostasis of the tendon, and recent studies focus on the influence of extracellular matrix on the differentiation pathway of mesenchymal stem cells (MSCs). The present study investigates whether hyperglycemia may influence the differentiation of tendon derived-MSCs (TD-MSCs) into an osteoblast lineage. Methods: MSCs were harvested from discarded human tendon excised during arthroscopic rotator cuff repair. The resulting TD-MSCs were counted, plated and grown to confluence in supplemented medium ( α MEM). TD-MSCs were treated with α MEM containing low (5.0 mM), physiological (10 mM) or high (25 mM) glucose, (+) and (-) 10 -10 mM insulin for 0, and 24 hours, 7, 14 and 30 days. Control cells were treated with α MEM. Only quantitative polymerase chain reaction (qPCR) was used to measure changes in gene expression levels specific for fibrocartilage of TD-MSCs (collagen type I-II-III, aggrecan, osteopontin, fibronectin and alkaline phosphatase). Calcium levels were measured after 30 days in culture. Immunohistochemistry staining was used to determine the amount of the specific proteins present in each group tested. Results: There was an increased gene expression of collagen type I, alkaline phosphatase, aggrecan and osteopontin in TD-MSCs supplemented with high glucose compared to other groups (p<0.05). When insulin was added to the α MEM, a higher increase of collagen type I and III was found in TD-MSCs cultured with high dose glucose. The synthesis of alkaline phosphatase and the expression of aggrecan and osteopontin genes were higher in TD-MSCs cultured with high dose glucose and high dose glucose with insulin. After 30 days, calcium content was increased in the high glucose group and in the high glucose medium and insulin. Conclusions: When cultured in a high glucose medium, TD-MSCs express bone markers, and are able to differentiate toward an osteoblast lineage. These results reinforce the concept that calcific tendinopathy may be caused by erroneous differentiation of MSCs in the presence of high levels of serum glucose.