Enhanced collagen type I synthesis by human tenocytes subjected to periodic in vitro mechanical stimulation

Abstract

BackgroundMechanical stimulation (e.g. slow heavy loading) has proven beneficial in the rehabilitation of chronic tendinopathy, however the optimal parameters of stimulation have not been experimentally determined. In this study of mechanically stimulated human tenocytes, the influence of rest insertion and cycle number on (1) the protein and mRNA levels of type I and III collagen; (2) the mRNA levels of transforming growth factor beta (TGFB1) and scleraxis (SCXA); and (3) tenocyte morphology, were assessed.MethodsHuman hamstring tenocytes were mechanically stimulated using a Flexcell® system. The stimulation regimens were 1) continuous and 2) rest-inserted cyclic equiaxial strain at a frequency of 0.1 Hz for 100 or 1000 cycles. Data were normalized to unstimulated (non-stretched) control groups for every experimental condition. qPCR was performed to determine relative mRNA levels and quantitative immunocytochemistry image analysis was used to assess protein levels and cell morphology.ResultsCollagen type I mRNA level and pro-collagen protein levels were higher in tenocytes that were subjected to rest-inserted mechanical stimulation, compared to continuous stretching (p < 0.05). Rest insertion and increased cycle number also had significant positive effects on the levels of mRNA for TGFB1 and SCXA (p < 0.05). There was no direct relation between cell morphology and gene expression, however mechanical stimulation, overall, induced a metabolically active tenocyte phenotype as evidenced by cells that on average demonstrated a decreased major-minor axis ratio (p < 0.05) with greater branching (p < 0.01).ConclusionsThe incorporation of rest periods in a mechanical stretching regimen results in greater collagen type I synthesis. This knowledge may be beneficial in refining rehabilitation protocols for tendon injury.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2474-15-386) contains supplementary material, which is available to authorized users.

Multifactorial bottom‐up bioengineering approaches for the development of living tissue substitutes

“…Gene expression analysis of TCs indicate that the use of 10% strain and MMC can be conducive to tenogenic phenotype maintenance because SCXA was up‐regulated at d 7 and is typically considered a tenogenic marker. Contrary to our results, mechanical stimulation is commonly associated with increased COL1A1 synthesis in TCs (82, 99). Furthermore, expression of collagen type III, TNC, TNMD, and SCXA is also typically increased (32, 99, 100).…”

“…The confined environment created by the high natural polydispersity of Cr in the culture medium accelerates cleavage of the N‐ and C ‐ propeptides of the procollagen molecules by the N‐ and C ‐ proteinases, thereby creating the insoluble collagen molecule (40, 41). COL1A1 was not increased at 10% strain, which contradicts previous studies in which mechanical stimulation led to increased COL1A1 synthesis in TCs (82, 87–89) and BMSCs (30, 90, 91), a process mediated by TGF‐β1 (92). Increased deposition of collagen types III, IV, V, and VI has been observed in fibroblasts (41), and increased deposition of collagen III has been described in BMSCs (47) and corneal fibroblasts (42) when using Cr as a crowder.…”

“…Furthermore, it has been shown that these cells respond to mechanical stimulation and can adapt their phenotype to strain amplitude (80) and type of stimulation (81). Overall, it is important to consider that the strain applied to the substrate is felt differently by the cells, and it has been suggested that a substrate strain of 10% corresponds to 3–5% of cell strain (82, 83). Moreover, literature indicates that there is a cell‐specific threshold strain below which cells do not reorient when stimulated, given that strain amplitude and necessary loading time are extremely variable (60, 64, 68, 84) and indicating that tailored loading regimes are needed to obtain specific responses from a cell source.…”

Insulin‐like growth factor 1 signaling in tenocytes is required for adult tendon growth

“…The ability of tendon to grow and respond to mechanical and biochemical cues requires the coordination of multiple biologic processes. Studies of 3‐dimensional tissue engineered tendon constructs in culture and exercise training in human subjects have shown that tendons grow best in response to intermittent mechanical loading with adequate rest periods built in between loading regimes (3–5, 61,62). Failure of tendons to respond to these cues can lead to the development of tendinopathies or tendon ruptures (8).…”

The intricate anatomy of the periodontal ligament and its development: Lessons for periodontal regeneration

“…At the same time, fibroblasts need mechanical stimulation for alignment of the collagen fibrils and presumably also for the cells themselves, in a similar manner as osteocytes seem to align . Fibroblasts, in general, are indeed very sensitive to mechanical stimulation and under such conditions produce a wide variety of bioactive compounds, related to both matrix production (COL1, decorin, transforming growth factor‐beta1, scleraxis) and inflammation and remodeling (interleukin‐6, interleukin‐8, matrix metalloproteinase‐13) . Mechanical stimulation is thus an essential feature for the remodeling and production of the extracellular matrix of the PDL.…”