A quantitative label-free analysis of the extracellular proteome of human supraspinatus tendon reveals damage to the pericellular and elastic fibre niches in torn and aged tissue

Abstract

Tears of the human supraspinatus tendon are common and often cause painful and debilitating loss of function. Progressive failure of the tendon leading to structural abnormality and tearing is accompanied by numerous cellular and extra-cellular matrix (ECM) changes in the tendon tissue. This proteomics study aimed to compare torn and aged rotator cuff tissue to young and healthy tissue, and provide the first ECM inventory of human supraspinatus tendon generated using label-free quantitative LC-MS/MS. Employing two digestion protocols (trypsin and elastase), we analysed grain-sized tendon supraspinatus biopsies from older patients with torn tendons and from healthy, young controls. Our findings confirm measurable degradation of collagen fibrils and associated proteins in old and torn tendons, suggesting a significant loss of tissue organisation. A particularly marked reduction of cartilage oligomeric matrix protein (COMP) raises the possibility of using changes in levels of this glycoprotein as a marker of abnormal tissue, as previously suggested in horse models. Surprisingly, and despite using an elastase digestion for validation, elastin was not detected, suggesting that it is not highly abundant in human supraspinatus tendon as previously thought. Finally, we identified marked changes to the elastic fibre, fibrillin-rich niche and the pericellular matrix. Further investigation of these regions may yield other potential biomarkers and help to explain detrimental cellular processes associated with tendon ageing and tendinopathy.

The “other” 15–40%: The Role of Non‐Collagenous Extracellular Matrix Proteins and Minor Collagens in Tendon

“…The properties of the PCM can be modulated by the activity of cell‐surface‐associated proteases or by altering the gene expression of PCM components in response to physiological and pathological stimuli . Recently, proteomics studies identified more than 100 proteins at the cell surface and the PCM of tenocytes, illuminating the complexity of this ECM compartment . Some of these PCM components, for which functions have been established, are discussed below.…”

“…105,106 Recently, proteomics studies identified more than 100 proteins at the cell surface and the PCM of tenocytes, illuminating the complexity of this ECM compartment. 103,107 Some of these PCM components, for which functions have been established, are discussed below.…”

Identification of human tendon cell populations in healthy and diseased tissue using combined single cell transcriptomics and proteomics

“…It remains possible that the tendon sub-populations identified above represent confounding transcriptomic variation within a single tendon population and/or that a number of cell types failed to survive the digestion process. Hakimi et al investigated the extracellular proteome of human tendon by comparing healthy and torn shoulder (supraspinatus) tissue (20). As well as identifying a group of proteins up-regulated in diseased tissue, their work serves to provide a catalogue of the most abundant matrix proteins in healthy and diseased human tendon.…”

“…The five cell clusters that expressed tendon matrix COL1A1/2 were provisionally labelled Tenocyte A-E. In order to delineate these groups further, the expression of genes coding for the commonest matrix proteins found in human tendon (20) was compared across the five clusters ( Figure 3A, dot plot). The gene expression of any given COL1A+ cluster was also directly compared to the remaining four clusters to highlight any additional differences between clusters ( Figure 3B and Tenocyte E cells (CD26 + /CD90 low CD54 low CD10 neg ).…”

Spectrum of Tendon Pathologies: Triggers, Trails and End-State

“…Furthermore, the authors found distinct regional protein composition of the fascicular and interfascicular matrix and proposed that the interfascicular matrix has higher turnover [44]. Furthermore, proteomics of human supraspinatus disease identified marked protein changes to the elastic fiber, fibrillin-rich and pericellular matrix niches [45]. Additional information related to protein synthesis and degradation can be yield by metabolomics.…”