This study suggests that human beta defensin-1 and -2 genes in the gingival epithelium show differential expression in patients with specific periodontal diseases, and aggressive and chronic periodontitis types demonstrate different gingival beta defensin-1 and -2 expression patterns.
Most overuse tendinopathies are thought to be associated with repeated microstrain below the failure threshold, analogous to the fatigue failure that affects materials placed under repetitive loading. Investigating the progression of fatigue damage within tendons is therefore of critical importance. There are obvious challenges associated with the sourcing of human tendon samples for in vitro analysis so animal models are regularly adopted. However, data indicates that fatigue life varies significantly between tendons of different species and with different stresses in life. Positional tendons such as rat tail tendon or the bovine digital extensor are commonly applied in in vitro studies of tendon overuse, but there is no evidence to suggest their behaviour is indicative of the types of human tendon particularly prone to overuse injuries. In this study, the fatigue response of the largely positional digital extensor and the more energy storing deep digital flexor tendon of the bovine hoof were compared to the semitendinosus tendon of the human hamstring. Fascicles from each tendon type were subjected to either stress or strain controlled fatigue loading (cyclic creep or cyclic stress relaxation respectively). Gross fascicle mechanics were monitored after cyclic stress relaxation and the mean number of cycles to failure investigated with creep loading. Bovine extensor fascicles demonstrated the poorest fatigue response, while the energy storing human semitendinosus was the most fatigue resistant. Despite the superior fatigue response of the energy storing tendons, confocal imaging suggested a similar degree of damage in all three tendon types; it appears the more energy storing tendons are better able to withstand damage without detriment to mechanics.
Fibroblast-populated collagen matrices provide a simplified tissue model for wound healing and development processes. A technology (CELLDRUM Technology) evaluating lateral mechanical tension in fibroblast-populated collagen matrices (tissue constructs) with a thickness of 1 mm was introduced. Defined mechanical boundary conditions together with the known number and orientation of the cells revealed precise data on the average tension exerted by a single cell. Circular cell-populated collagen gels were manufactured inside the CELLDRUM on top of a flexible membrane. The collagen matrix was then excited by a sound pulse. The resulting resonance oscillation was monitored by a laser-based deflection sensor and frequency and damping were analyzed giving information on mechanical properties of the tissue construct. Several evaluation experiments were performed. Calf serum enhanced contractile forces of fibroblasts dose dependently. After the gels were treated with cytochalasin D for 24 h, the cell forces were reduced by 42% of control. The remaining tension was attributed to the extracellular matrix remodeling occurring during cell growth and to other cytoskeletal structures like microtubules and intermediate filaments. We also found that only after a few hours of culture fibroblast-seeded collagen gels began developing significant mechanical tension. A mechanical tension profile of proliferating fibroblasts in collagen gels over culture time was obtained.
Cyclic mechanical stretching induces biological and biomechanical response in cells. These responses are firstly determined by gene expression regulation in the cells of tissue. A method based on the CellDrum Ò Technology provided the environment for cyclic mechanical stimulation of NIH 3T3 cells in vitro. Cells were cultured on a silicone membrane. mRNA expression levels of the genes Egr1, Fgfr2, Tp53, Itgb3, and Itgb5 was evaluated by real-time PCR at stimulation times ranging from 5 min to 12 h with a cyclic strain of 0.25% at 0.25 Hz in order to decide which time period was most suitable for a subsequent detailed profiling. The genome-wide expression profile of NIH 3T3 cells was carried out by whole mouse genome microarrays. The mRNA expression levels of most genes tested were significantly changed after 1 h of mechanical stimulation. Subsequently, the mRNA samples of the 1-h stretched cells were hybridized to obtain a gene expression profile using microarrays. Real-time PCR results are shown to agree with the microarray results. The early response genes, such as Egr1, Egr2, Fos, Myc, Rela, Fas, Egfr1, and Fgfr2 playing a role in stretch activation of the signal transduction pathways were significantly up-regulated, whereas the only significantly down-regulated gene is Tfrc. Low level of mechanical stimulation was found to effect the expression of early responsive genes initiates alteration of NIH 3T3 behaviors to control the homeostasis of the fibroblasts.
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