Single-cell transcriptomic profiling reveals distinct mechanical responses between normal and diseased tendon progenitor cells

Abstract

Regenerative medicine approaches utilizing stem cells offer a promising strategy to address tendinopathy, a class of common tendon disorders associated with pain and impaired function. Tendon progenitor cells (TPCs) are important in healing and maintaining tendon tissues. Here we provide a comprehensive single cell transcriptomic profiling of TPCs from three normal and three clinically classified tendinopathy samples in response to mechanical stimuli. Analysis reveals seven distinct TPC subpopulations including subsets that are responsive to the mechanical stress, highly clonogenic, and specialized in cytokine or growth factor expression. The single cell transcriptomic profiling of TPCs and their subsets serves as a foundation for further investigation into the pathology and molecular hallmarks of tendinopathy in mechanical stimulation conditions.

Single cell multi-omics characterise discrete human tendon cells populations that persist in vitro and on fibrous scaffolds

“…In vitro POSTN_KRT7, PTX3_PAPPA, ITGA7_ NES and DCN_LUM clusters showed increased expression of the top differentially expressed genes initially found in the ex vivo POSTN+, PTX3+, ITGA7+ and APOD+ clusters, respectively. This supported the possibility that human tendon cell clusters represented populations that can be isolated ex vivo and remain discrete subtypes in vitro (Still et al, 2021). There was little in the gene expression profile of cultured DKK1_FGF5 and PRELP_FMOD to relate them to cell clusters found in the ex vivo atlas.…”

“…These results suggested that aligned electrospun PDO fibres provided a useful scaffold and environment for their ongoing investigation in vitro. A similar population of cells expressing IL8, CXCL1/6/8 and PTX3 was described in single-cell transcriptomics of healthy and diseased patellar tendon progenitor cells cultured under mechanical stress (Still et al, 2021). Most of these named "pro-inflammatory tendon progenitor cells" were from diseased human tendon and expressed gene sets enriched for pro-inflammatory signalling pathways, including the "IL-1 regulation of extracellular matrix" category.…”

“…These complementary ex vivo and now in vitro findings add to the increasing evidence supporting pro-inflammatory tendon fibroblasts driving chronic tendon disease, possibly in response to a loss of normal tendon homeostasis (Akbar et al, 2021;Dakin et al, 2018). Focusing on a particular tendon cell subsets will advance the understanding of how tenocytes interact with immune cells (Garcia-Melchor et al, 2021;Stolk et al, 2017). It is now possible to isolate (based on CD10+, CD26+ and CD54+ surface markers) and to culture (PDO aligned fibres) PTX3+ cells implicated in chronic human tendinopathy.…”

“…Therefore, cell yield can be low and necessitates mechanical and enzymatic processing that could influence cell characteristics. Secondly, the previously described tendon cell subpopulations in mouse and human tendon, including most recently healthy versus diseased human tendon cells in vitro (Still et al, 2021), are based on single-cell differential gene expression analysis. While there is some conservation between the species and overlap across different human tendon sites and different studies (Akbar et al, 2021;De Micheli et al, 2020;Giordani et al, 2019;Kendal et al, 2020), it remains possible that the described clusters are a product of confounding transcriptomic variation.…”

“…Therefore, it is unclear how differentiated or pluripotent cells are within a given cluster or if cells across several clusters share a common progenitor. Finally, tendon cells have been shown to be mechano-sensitive, changing their shape, migration, proliferation rate and gene expression profile in response to differing culture surfaces (Bashur et al, 2009;Kendal et al, 2017;Lee et al, 2005;Still et al, 2021). Recreating the normal tendon architecture is likely a requisite condition for examining normal and diseased tendon cell behaviour in vitro.…”