Molecular Mechanism Responsible for Fibronectin-controlled Alterations in Matrix Stiffness in Advanced Chronic Liver Fibrogenesis.

Fibrosis is characterized by extracellular matrix (ECM) remodeling and stiffening. However, the functional contribution of tissue stiffening to noncancer pathogenesis remains largely unknown. Fibronectin (Fn) is an ECM glycoprotein substantially expressed during tissue repair. Here we show in advanced chronic liver fibrogenesis using a mouse model lacking Fn that, unexpectedly, Fn-null livers lead to more extensive liver cirrhosis, which is accompanied by increased liver matrix stiffness and deteriorated hepatic functions. Furthermore, Fn-null livers exhibit more myofibroblast phenotypes and accumulate highly disorganized/diffuse collagenous ECM networks composed of thinner and significantly increased number of collagen fibrils during advanced chronic liver damage. Mechanistically, mutant livers show elevated local TGF-ß activity and lysyl oxidase expressions. A significant amount of active lysyl oxidase is released in Fn-null hepatic stellate cells in response to TGF-ß1 through canonical and noncanonical Smad such as PI3 kinase-mediated pathways. TGF-ß1-induced collagen fibril stiffness in Fn-null hepatic stellate cells is significantly higher compared with wild-type cells. Inhibition of lysyl oxidase significantly reduces collagen fibril stiffness, and treatment of Fn recovers collagen fibril stiffness to wild-type levels. Thus, our findings indicate an indispensable role for Fn in chronic liver fibrosis/cirrhosis in negatively regulating TGF-ß bioavailability, which in turn modulates ECM remodeling and stiffening and consequently preserves adult organ functions. Furthermore, this regulatory mechanism by Fn could be translated for a potential therapeutic target in a broader variety of chronic fibrotic diseases.

In vitro stability of open wedge high tibial osteotomy with synthetic bone graft.

It has been predicted that significant stress will be applied to the plate and lateral cortical hinge of an osteotomy site when early full weight bearing is commenced after an open wedge high tibial osteotomy. We hypothesized that the stress concentration on the plate or at the lateral cortical hinge would be reduced by inserting bone substitutes into the osteotomy gap. Two different types of tibia model were investigated: Group A, fixation with TomoFix with the osteotomy site left as an open space; and Group B, two beta-TCP wedges are inserted into osteotomy site and fixed with TomoFix. Stress at five points was measured using strain gauges. Specimens were mounted onto a testing machine with an FTA (femoro-tibial angle) of 170 degrees . Cyclic load tests and an ultimate load test were then performed. The mean stress on the plate was measured at 15.5+/-1.8Mpa in Group A. On the other hand, this value in Group B was only 9.52+/-2.1Mpa and this was a significant difference (P<0.01). The mean stress on the lateral hinge in Groups A and B was 3.31+/-0.5 and 2.49+/-0.2, respectively which was also a significant difference (P<0.05). The mean maximum breaking load in Group A was 2500+/-280N and in Group B 4270+/-420N which was a significant difference (P<0.01). Hence, for OWHTO procedures, the use of beta-TCP wedges and TomoFix is thus likely to improve the initial axial and possibly rotational stability at the osteotomy site in comparison with methods that leave the osteotomy gap open.

Low-intensity pulsed ultrasound activates the phosphatidylinositol 3 kinase/Akt pathway and stimulates the growth of chondrocytes in three-dimensional cultures: a basic science study.

INTRODUCTION: The effect of low-intensity pulsed ultrasound (LIPUS) on cell growth was examined in three-dimensional-cultured chondrocytes with a collagen sponge. To elucidate the mechanisms underlying the mechanical activation of chondrocytes, intracellular signaling pathways through the Ras/mitogen-activated protein kinase (MAPK) and the integrin/phosphatidylinositol 3 kinase (PI3K)/Akt pathways as well as proteins involved in proliferation of chondrocytes were examined in LIPUS-treated chondrocytes. METHODS: Articular cartilage tissue was obtained from the metatarso-phalangeal joints of freshly sacrificed pigs. Isolated chondrocytes mixed with collagen gel and culture medium composites were added to type-I collagen honeycomb sponges. Experimental cells were cultured with daily 20-minute exposures to LIPUS. The chondrocytes proliferated and a collagenous matrix was formed on the surface of the sponge. Cell counting, histological examinations, immunohistochemical analyses and western blotting analysis were performed. RESULTS: The rate of chondrocyte proliferation was slightly but significantly higher in the LIPUS group in comparison with the control group during the 2-week culture period. Western blot analysis showed intense staining of type-IX collagen, cyclin B1 and cyclin D1, phosphorylated focal adhesion kinase, and phosphorylated Akt in the LIPUS group in comparison with the control group. No differences were detected, however, in the MAPK, phosphorylated MAPK and type-II collagen levels. CONCLUSION: LIPUS promoted the proliferation of cultured chondrocytes and the production of type-IX collagen in a three-dimensional culture using a collagen sponge. In addition, the anabolic LIPUS signal transduction to the nucleus via the integrin/phosphatidylinositol 3-OH kinase/Akt pathway rather than the integrin/MAPK pathway was generally associated with cell proliferation.

Effects of vibration and hyaluronic acid on activation of three-dimensional cultured chondrocytes.

OBJECTIVE: To investigate the effects of vibration (Vib) and hyaluronic acid (HA) on 3-dimensional cultured cartilage. METHODS: Chondrocytes were obtained from metatarsophalangeal joints of freshly killed 6-month-old pigs. Twenty-four-well plates containing type I collagen sponge disks were used to culture samples. The frequency and the amplitude of the vibration of the well plate were 100 Hz and 0.5 nm, respectively. We produced 3-dimensional cartilage tissue using HA and vibration with collagen sponge as a carrier. Four different culture conditions were examined: a control HA-Vib- group, an HA-Vib+ group, an HA+Vib- group, and an HA+Vib+ group. Each group was cultured for 2 weeks. After culture days 3, 7, 10, and 14 (every 3.5 days), the levels of chondroitin 4-sulfate (C4S) and chondroitin 6-sulfate (C6S) isomers synthesized in each culture medium were measured. Histologic analysis, immunohistochemical analysis, and electron microscopic examination were performed. RESULTS: Mean C4S and C6S synthesis had increased rapidly after 7 days of culture and continued to increase thereafter. There were significant differences among the 4 groups (P < 0.01). Synthesis of both C4S and C6S was most abundant in the HA+Vib+ group and the lowest in the HA-Vib- group. After 1 and 2 weeks of culture, the chondrocytes had formed stratified structures on the collagen sponges in all groups, although the thickest structure was observed in the HA+Vib+ group and the thinnest in the HA-Vib- group. Under immunofluorescence, the HA+Vib+ group exhibited the strongest chromatic features. Under electron microscopy, the chondrocytes in the HA+Vib+ group exhibited many long and slender prominences on their surface, and extracellular substance could be observed associated with the cells. CONCLUSION: Our results indicate that the combination of vibration and HA activates the production of proteoglycan in 3-dimensional cultured chondrocytes and stimulates MAPK and beta-catenin. This suggests that some mechanoreceptors for vibration exist on the plasma membrane of chondrocytes and activate the intracellular signal transduction system.