Heterogeneity of proteome dynamics between connective tissue phases of adult tendon

Abstract

Maintenance of connective tissue integrity is fundamental to sustain function, requiring protein turnover to repair damaged tissue. However, connective tissue proteome dynamics remain largely undefined, as do differences in turnover rates of individual proteins in the collagen and glycoprotein phases of connective tissue extracellular matrix (ECM). Here, we investigate proteome dynamics in the collagen and glycoprotein phases of connective tissues by exploiting the spatially distinct fascicular (collagen-rich) and interfascicular (glycoprotein-rich) ECM phases of tendon. Using isotope labelling, mass spectrometry and bioinformatics, we calculate turnover rates of individual proteins within rat Achilles tendon and its ECM phases. Our results demonstrate complex proteome dynamics in tendon, with ~1000 fold differences in protein turnover rates, and overall faster protein turnover within the glycoprotein-rich interfascicular matrix compared to the collagen-rich fascicular matrix. These data provide insights into the complexity of proteome dynamics in tendon, likely required to maintain tissue homeostasis.

CD146 Delineates an Interfascicular Cell Sub-Population in Tendon That Is Recruited during Injury through Its Ligand Laminin-α4

“…The production and replacement of these components by IFM resident cells is likely critical to maintain tendon function. Our recent work demonstrates that protein turnover occurs more rapidly in the IFM compared to fascicles, indicative of greater metabolic activity [ 8 , 9 ]. IFM cell populations are, therefore, likely key contributors to maintaining tendon homeostasis and responding to injury.…”

Postnatal mechanical loading drives adaptation of tissues primarily through modulation of the non-collagenous matrix

“…Neopeptide analysis demonstrated ECM protein turnover in the fascicles slows down towards the end of maturation, whilst ECM protein turnover rates in the IFM are maintained. Once a tendon is mature, little collagen turnover occurs ( Birch, 2007 ; Heinemeier et al, 2013 ) and we have previously shown that the minimal turnover in mature tendon is focused to the IFM ( Choi et al, 2020 ; Thorpe et al, 2010 ; Thorpe et al, 2015a ; Thorpe et al, 2016b ). The maintenance of turnover rates observed in the IFM here suggests structural and/or compositional plasticity of the IFM.…”

Microdamage in the equine superficial digital flexor tendon

“…51 Studies have also shown that protein turnover rate is greater in the IFM than within the fascicles, which is likely a mechanism to repair damage to this region. 52,53 While the fascicles in the SDFT do not appear to be specialised to enhance tendon extensibility, they are optimised for improved energy-storing capacity, with a helical structure providing greater compliance and enabling more efficient extension and recoil, as well as enhanced fatigue resistance of the fascicles, properties that are likely conveyed to the whole tendon. 48,54,55 By contrast, fascicles from the CDET, which do not have a helical structure, rely on sliding between collagen fibres to allow fascicle extension, and show a much poorer ability to recover from loading, resulting in decreased fatigue resistance.…”

“…Indeed, the elastin content in the IFM is greater in the SDFT than in the CDET, 43 and enzymatic depletion of elastin in the subunits of the SDFT reduces IFM fatigue resistance and the ability to recover from loading, but does not affect fascicle mechanical properties 51 . Studies have also shown that protein turnover rate is greater in the IFM than within the fascicles, which is likely a mechanism to repair damage to this region 52,53 …”