Abstract
The objective was to seek evidence of hypoxia in early human tendinopathy and thereafter, to explore mechanisms whereby tissue hypoxia may regulate apoptosis, inflammatory mediators and matrix regulation in human tenocytes.
Fifteen torn supraspinatus tendon (established pathology) and matched intact subscapularis tendon (representing ‘early pathology’) biopsies were collected from patients undergoing arthroscopic shoulder surgery. Control samples of subscapularis tendon were collected from 10 patients undergoing arthroscopic stabilisation surgery. Markers of hypoxia were quantified by immunohistochemical methods. Human tendon-derived primary cells were derived from hamstring tendon tissue obtained during hamstring tendon ACL reconstruction. The impact of hypoxia upon tenocyte biology ex vivo was measured using quantitative RT-PCR, multiplex cytokine assays, apoptotic proteomic profiling, immunohistochemistry and annexin V FACS staining.
Increased expression of HIF 1a, Bcl-2 and clusterin (hypoxic and apoptotic markers) was detected in subscapularis tendon samples compared to both matched torn samples and non matched control samples (p<0.01). Hypoxic tenocytes exhibited increased production of proinflammatory cytokines (p<0.001), altered matrix regulation (p<0.01) with increased production of Collagen type III operating through a MAPK dependent pathway. Finally, hypoxia increased expression of several mediators of apoptosis and thereby promoted tenocyte apoptosis.
Hypoxia promotes expression of proinflammatory cytokines, key apoptotic mediators and drives matrix component synthesis towards a collagen type III profile by human tenocytes. We propose hypoxic cell injury as a critical pathophysiological mechanism in early tendinopathy offering novel therapeutic opportunities in the management of tendon disorders.
