Mechanical stimulus is a regulator of tenocyte metabolism. The present study investigated temporal regulation of the expression of selected genes by tenocytes in isolated fascicles subjected to tensile strain in vitro. Cyclic tensile strain with a 3% amplitude superimposed on a 2% static strain was provided for 10 min, followed by either an unstrained period or continuous cyclic strain until the end of a 24-h incubation period. mRNA expression of selected anabolic and catabolic genes were evaluated with quantitative PCR at 10 min, 1 h, 6 h, and 24 h. The application of 6-h cyclic strain significantly upregulated type III collagen mRNA expression in strained fascicles compared with unstrained controls, but no alterations were observed in mRNA expression of type I collagen and biglycan. Significant downregulation in the expression of the decorin core protein was observed in fascicles subjected to 24-h cyclic strain. MMP3 and MMP13 expression levels were upregulated by the application of 10 min of cyclic strain, followed by a progressive downregulation until the end of the incubation period in both the absence and the presence of the continuing cyclic strain. Accordingly, alterations in the expression of anabolic genes were limited to the upregulation of type III collagen by prolonged exposure to cyclic strain, whereas catabolic genes were upregulated by a small number of strain cycles and downregulated by a prolonged cyclic strain. These findings demonstrate distinctive patterns of mechanoregulation for anabolic and catabolic genes and help our understanding of tenocyte response to mechanical stimulation.
"And yet it is the very change in cell length, leading to a reorganization of the cytoskeleton, which is most likely to trigger the adaptation process in response to strain. That tenocytes indeed react to cyclic strain by changing the expression of certain genes has been described extensively   . "
"It might be assumed that changes in collagen synthesis would be preceded by changes in collagen gene expression . However, COL1A1 mRNA expression remained unchanged (Maeda et al., 2009) while collagen synthesis , as determined by [ 3 H]-proline incorporation, increased (Maeda et al., 2007), following cyclic tensile strain of a 3% amplitude superimposed on a 2% static strain applied to rat tail tendon fascicles over a 24-h period. Exercise has even been shown to lead to a decrease in collagen mRNA expression; when 12 recreationally active men and women performed a regime of resistance exercises consisting of unilateral knee extensions (three sets of 10 repetitions at 70% of the one repetition maximum), COL1A1 mRNA expression in the patellar tendon decreased significantly 4 h post-exercise and returned to resting levels after 24 h (Sullivan et al., 2009). "
[Show abstract][Hide abstract] ABSTRACT: Repetitive strain or 'overuse' is thought to be a major factor contributing to the development of tendinopathy. The aims of our study were to develop a novel cyclic loading system, and use it to investigate the effect of defined loading conditions on the mechanical properties and gene expression of isolated tendon fascicles. Tendon fascicles were dissected from bovine-foot extensors and subjected to cyclic tensile strain (1 Hz) at 30% or 60% of the strain at failure, for 0 h (control), 15 min, 30 min, 1 h, or 5 h. Post loading, a quasi-static test to failure assessed damage. Gene expression at a selected loading regime (1 h at 30% failure strain) was analyzed 6 h post loading by quantitative real-time polymerase chain reaction. Compared with unloaded controls, loading at 30% failure strain took 5 h to lead to a significant decrease in failure stress, whereas loading to 60% led to a significant reduction after 15 min. Loading for 1 h at 30% failure strain did not create significant structural damage, but increased Collagen-1-alpha-chain-1 and interleukin-6 (IL6) expression, suggesting a role of IL6 in tendon adaptation to exercise. Correlating failure properties with fatigue damage provides a method by which changes in gene expression can be associated with different degrees of fatigue damage.
Scandinavian Journal of Medicine and Science in Sports 11/2011; 23(1). DOI:10.1111/j.1600-0838.2011.01410.x · 2.90 Impact Factor
"The concomitant upregulation of Cx43 expression may suggest that tenocytes may respond to the reduced communication and disruption of gap junction organization via upregulation of gap junction turnover, associated with enhance connexin synthesis that may result in the subsequent re-establishment of functional gap junctions at later time points. This may, potentially , be associated with the activation of a recovery response similar to that reported previously following extended periods of mechanical loading (Maeda et al. 2009). In summary, we have developed and validated a method to quantify the intercellular gap junction permeability in tendon fascicles using a combined experimental and mathematical approach based upon FLIP. "
[Show abstract][Hide abstract] ABSTRACT: Gap junction communication is an essential component in the mechanosensitive response of tenocytes. However, little is known about direct mechanoregulation of gap junction turnover and permeability. The present study tests the hypothesis that mechanical loading alters gap junction communication between tenocyte within tendon fascicles. Viable tenocytes within rat tail tendon fasicles were labelled with calcein-AM and subjected to a fluorescent loss induced by photobleaching (FLIP) protocol. A designated target cell within a row of tenocytes was continuously photobleached at 100% laser power whilst recording the fluorescent intensity of neighbouring cells. A mathematical compartment model was developed to estimate the intercellular communication between tenocytes based upon the experimental FLIP data. This produced a permeability parameter, k, which quantifies the degree of functioning gap functions between cells as confirmed by the complete inhibition of FLIP by the inhibitor 18α-glycyrrhentic acid. The application of 1N static tensile load for 10 min had no effect on gap junction communication. However, when loading was increased to 1 h, there was a statistically significant reduction in gap junction permeability. This coincided with suppression of connexin 43 protein expression in loaded samples as determined by confocal immunofluorescence. However, there was an upregulation of connexin 43 mRNA. These findings demonstrate that tenocytes remodel their gap junctions in response to alterations in mechanical loading with a complex mechanosensitive mechanism of breakdown and remodelling. This is therefore the first study to show that tenocyte gap junctions are not only important in transmitting mechanically activated signals but that mechanical loading directly regulates gap junction permeability.
Biomechanics and Modeling in Mechanobiology 06/2011; 11(3-4):439-47. DOI:10.1007/s10237-011-0323-1 · 3.15 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.