ABSTRACT
Tendons transmit contractile muscular force to bone to produce movement, and it is believed cells can generate endogenous forces on the extracellular matrix to maintain tissue homeostasis. However, little is known about the direct mechanical measurement of cell-matrix interaction in cell-generated human tendon constructs. In this study we examined if cell-generated force could be detected and quantified in engineered human tendon constructs, and if glycosaminoglycans (GAGs) contribute to tendon force transmission. Following de-tensioning of the tendon constructs it was possible to quantify an endogenous re-tensioning. Further, it was demonstrated that the endogenous re-tensioning response was markedly blunted after interference with the cytoskeleton (inhibiting non-muscle myosin-dependent cell contraction by blebbistatin), which confirmed that re-tensioning was cell generated. When the constructs were elongated and held at a constant length a stress relaxation response was quantified, and removing 27% of the GAG content of tendon did not alter the relaxation behavior, which indicates that GAGs do not play a meaningful role in force transmission within this system.
Subject(s)
Engineering , Homeostasis , Stress, Mechanical , Tendons/cytology , Tendons/metabolism , Animals , Biomechanical Phenomena , Extracellular Matrix/metabolism , Glycosaminoglycans/metabolism , Humans , Muscle Contraction , Myosins/metabolism , Tendons/physiologyABSTRACT
The main structural component of connective tissues is fibrillar, cross-linked collagen whose fibrillogenesis can be modulated by Small Leucine-Rich Proteins/Proteoglycans (SLRPs). Not all SLRPs' effects on collagen and extracellular matrix in vivo have been elucidated; one of the less investigated SLRPs is asporin. Here we describe the successful generation of an Aspn-/- mouse model and the investigation of the Aspn-/- skin phenotype. Functionally, Aspn-/- mice had an increased skin mechanical toughness, although there were no structural changes present on histology or immunohistochemistry. Electron microscopy analyses showed 7% thinner collagen fibrils in Aspn-/- mice (not statistically significant). Several matrix genes were upregulated, including collagens (Col1a1, Col1a2, Col3a1), matrix metalloproteinases (Mmp2, Mmp3) and lysyl oxidases (Lox, Loxl2), while lysyl hydroxylase (Plod2) was downregulated. Intriguingly no differences were observed in collagen protein content or in collagen cross-linking-related lysine oxidation or hydroxylation. The glycosaminoglycan content and structure in Aspn-/- skin was profoundly altered: chondroitin/dermatan sulfate was more than doubled and had an altered composition, while heparan sulfate was halved and had a decreased sulfation. Also, decorin and biglycan were doubled in Aspn-/- skin. Overall, asporin deficiency changes skin glycosaminoglycan composition, and decorin and biglycan content, which may explain the changes in skin mechanical properties.
Subject(s)
Biglycan/genetics , Decorin/genetics , Extracellular Matrix Proteins/deficiency , Founder Effect , Gene Expression Regulation , Skin/metabolism , Amino Acid Oxidoreductases/genetics , Amino Acid Oxidoreductases/metabolism , Animals , Biglycan/metabolism , Chondroitin Sulfates/genetics , Chondroitin Sulfates/metabolism , Collagen Type I/genetics , Collagen Type I/metabolism , Collagen Type I, alpha 1 Chain , Collagen Type III/genetics , Collagen Type III/metabolism , Decorin/metabolism , Dermatan Sulfate/analogs & derivatives , Dermatan Sulfate/genetics , Dermatan Sulfate/metabolism , Extracellular Matrix/genetics , Extracellular Matrix/metabolism , Extracellular Matrix Proteins/genetics , Female , Heparitin Sulfate/genetics , Heparitin Sulfate/metabolism , Keratan Sulfate/genetics , Keratan Sulfate/metabolism , Male , Matrix Metalloproteinase 2/genetics , Matrix Metalloproteinase 2/metabolism , Matrix Metalloproteinase 3/genetics , Matrix Metalloproteinase 3/metabolism , Mice , Mice, Knockout , Phenotype , Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase/genetics , Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase/metabolism , Skin/ultrastructureABSTRACT
Treatment with lipid-lowering drugs, statins, is common all over the world. Lately, the occurrence of spontaneous tendon ruptures or tendinosis have suggested a negative influence of statins upon tendon tissue. But how statins might influence tendons is not clear. In the present study, we investigated the effect of statin treatment on mechanical strength, cell proliferation, collagen content and gene expression pattern in a tendon-like tissue made from human tenocytes in vitro. Human tendon fibroblasts were grown in a 3D tissue culture model (tendon constructs), and treated with either simvastatin or atorvastatin, low or high dose, respectively, for up to seven days. After seven days of treatment, mechanical testing of the constructs was performed. Collagen content and cell proliferation were also determined. mRNA levels of several target genes were measured after one or seven days. The maximum force and stiffness were reduced by both statins after 7 days (p<0.05), while the cross sectional area was unaffected. Further, the collagen content was reduced by atorvastatin (p = 0.01) and the cell proliferation rate was decreased by both types of statins (p<0.05). Statin treatment also introduced increased mRNA levels of MMP-1, MMP-3, MMP-13, TIMP-1 and decreased levels of collagen type 1 and 3. In conclusion, statin treatment appears to have a negative effect on tendon matrix quality as seen by a reduced strength of the tendon constructs. Further, activated catabolic changes in the gene expression pattern and a reduced collagen content indicated a disturbed balance in matrix production of tendon due to statin administration.
