Diabetic and hyperglycemic patients have a higher incidence of tendinopathy than healthy populations. Proposed explanations, including a direct effect of glucose on tenocytes, are speculative. This project aims to determine the molecular changes that occur in tenocytes in a hyperglycemic environment using tendon explants and cells in vitro.

Ovine infraspinatus tendon explants were cultured for 5 or 17 days in normal (5.5mM), moderate (15.3mM) and high (25mM) glucose in isotonic media (+10% FBS). After 8 days in the longer term cultures, fibroblastic cells had grown out from the explants onto the culture plastic so the explants were moved to fresh plates and both continued in varied glucose media. Total RNA was isolated from tendon and cells and realtime RT-PCR performed using ovine-specific primers for matrix proteins and enzymes involved in matrix metabolism.

Stress depriving tendon in culture significantly affected 14 of 16 matrix protein genes and all 16 matrix-modifying enzymes tested compared to ex vivo tendon. COL2A1, COMP, DCN, ELN, FMOD, VCAN and LOXL4 expression decreased; the other 23 changed genes increased. Higher glucose concentrations in the media significantly increased tendon explant expression of 8 of 16 matrix protein genes (COL1A1, COL3A1, COL5A1, COMP, DCN, ELN, FBN1 and LUM) and 5 of 16 enzymes (ADAMTS4, ADAMTS5, MMP13, LOXL3 and LOXL4). Increased glucose had no significant effect on the expression of any gene by isolated tendon outgrowth cells in monolayer culture.

Hyperglycemic conditions significantly affected tenocyte matrix metabolism only in cells within their extracellular matrix (ECM) microenvironment. This suggests that the effects of excess glucose on tenocytes, though substantial, is indirect and via modifications to the ECM, perhaps by the action of advanced glycation endproducts.