What can we agree upon?

Transcription

1 What is tendinopathy and why does it happen? What can we agree upon? Clinical Pain with activity Tenderness upon palpation Swelling of tendon Impaired performance Structure - Imaging (US or MRI) Thickening of tendon Hypoechoic tendon areas (US) Altered water content Hyperperfusion Morphology - Histology Areas with cell rounding Areas wth disorganized collagen fibril fragment Accumulation of osmotic active molecules (e.g. glucosaminoglycans) and thus water Vascular growth - angiogenesis

2 Tendon overuse is associated with rounded cells, swelling, hypervascularization and disorganized connective tissue Healthy human Achilles tendon Tendinopathy (Pingel et al, J.Anat., 2014)

3 Accumulation of other osmotic active proteins than collagen in tendinopathic human tendon - glucosaminoglycans (Heinemeier et al FASEB J, 2018)

4 Tendinopathy and inflammation - most likely present in the early stage Macrophages Human supraspinatus/subscapularis tendon Inflammation markers (Dakin et al, Science Transl Med, 2015)

5 Tendinopathy pathogenesis Mechanical damage, micro or macro failed healing Exaggerated tendon breakdown metalloproteinase activity Hypoxia, oxidative stress - hypervascularity, nerve ingrowth Tendon immune response vasculature permeability Compressive overload and reactive change in connective tissue Homeostasis perturbation constant overload and lack of recovery time results in tissue accumulation within the tendon Predisposition and thus high vulnerability towards tendinopathy

6 Fibril length in human tendon (FIB-SEM, combined focused ion beam and scanning EM) Tendon of both patellar and Achilles tendon have fibril continuity through the entire tendon Tendinopathy does not reveal breakage of fibrils but rather of infiltration of disorganized tissue between fibrils/fascicles (Svensson et al, ACTA Biomat 2017)

7 Fibroblasts responsive to physiological loading? Daily work horses between fascicles/outer tendon layer 1. Collagen fibril formation and adaptation is very dynamic in childhood/adolesence after that time 90-95% is stable Tendon 2. Mechanical loading stimulates turnover daily in a small pool of collagen (5-10%) Fibroblasts relatively dormant under normal conditions z z z z z z z z z (Drawing by K.Heinemeier)

8 Matrix remodeling and inflammation related primarily to the inter-fascicular area Collagen in fibrils/fascicles no turnover (95% stable) High turnover Collagen (5% - fibril fragments interfascicular?) Tendinopathy is mostly related to inter-fascicular accumulation (Spiesz EM et al J Orthop Res 33: , 2015)

9 Circadian regulation of tendon homeostasis SCN tendon (745) cartilage (615) skeletal muscle (295) 3 h 7 h 11 h 15 h 19 h 23 h >745 rhythmic genes in tendon = potentially 745 biological processes (Yeung et al Sci Rep 2005, Yeung et al PNAS 2018)

10 Relative bioluminescence Relative bioluminescence Human patella tenocytes have circadian rhythms Mouse tendons BMAL1 CLOCK 8000 Cry Luc Per Time (days) Primary human tenocytes Clock genes blocked = dysfunctional tendon 2000 Wild type ClockΔ Tendon stiffness (Yeung, Sci Rep 2005, Taylor, elife 2015) Time (days)

11 Clock control of matrix homeostasis in tendon Night-time Rest phase: removal of damaged matrix Day-time Active phase: secretion of matrix - but also fragments and damaged matrix (Yeung et al Sci Rep 2005, Yeung et al PNAS 2018) (drawing by Karl Kadler)

12 Matrix remodeling and inflammation related primarily to the inter-fascicular area Collagen in fibrils/fascicles no turnover (95% stable) High turnover Collagen (5% - fibril fragments interfascicular?) Tendinopathy is mostly related to inter-fascicular accumulation Circadian rhythm involved in 24-h regulation of tendon (Spiesz EM et al J Orthop Res 33: , 2015)

13 Tendon turnover slows down at age yrs in humans - 14C bomb pulse incorporation Tendon turnover slows down in adults in several types and regions of tendon (Heinemeier et al FASEB J 2018)

14 Tendon collagen turnover is higher in tendinopathic vs healthy tendon Tendinopathic tendon has 47% new collagen The new collagen in sick tendons is yrs old (Heinemeier et al FASEB J, 2018)

15 What is tendinopathy and why does it happen? Most likely a disturbed homeostasis of the tendon tissue a mismatch between daily breakdown and build-up - resulting in an accumulation of disorganized matrix tissue proteins, rounded cells and water, especially in the region between fascicles. This is accompanied by early inflammatory signalling, tendon thickening and angiogenesis. Increased tissue turnover is found in persons with tendinopathy and this has been going on for years, most likely due to earlier injury or to chronic high tendon collagen exchange ( persons at risk )