Objective. The boundary lubrication function of articular cartilage is mediated in part by proteoglycan 4 (PRG4) molecules at the articular surface and in synovial fluid. The objective of this study was to determine the effects of dynamic shear stimulation on PRG4 biosynthesis by bovine cartilage explants.Methods. Cartilage disks with intact articular surfaces were harvested from immature bovines. Some disks were subjected to 24 hours (day 1) of loading, consisting of a step load of 20% static compression either alone or with superimposed dynamic shear (3% amplitude and 0.1 Hz), while other disks were cultured free-swelling as controls. After the 24-hour loading period, disks were terminated or were further incubated for up to 72 hours (days 2-4) in free-swelling culture to assess chondrocyte responses to, and following, unloading. PRG4 products secreted into culture medium were quantified by enzyme-linked immunosorbent assay and characterized by Western blotting. Chondrocytes expressing PRG4 were localized by immunohistochemistry, and depth-associated variations in chondrocyte PRG4 expression were quantified by image analysis.Results. Dynamic shear stimulation increased PRG4 secretion to 3-4 times that of unloaded controls and statically compressed samples. Sheared cartilage secreted more PRG4 of 345 kd relative to smaller molecular weight species, as compared with unloaded controls. Immunohistochemistry revealed that shear stimulation also increased the total number of cells expressing PRG4 by inducing expression by cells at a depth of 200-400 m.Conclusion. The paradigm that certain mechanical stimuli up-regulate biosynthesis in cartilage appears operative not only for load-bearing matrix constituents, but also for PRG4 molecules that mediate lubrication.

Gentle exercise-imposed mechanical stimulation did not markedly affect articular cartilage function or structure. However, the marked site-associated variation suggests that biomechanical environment can initiate degenerative changes in immature cartilage during joint growth and maturation.

Because of the limited availability of donor cartilage for resurfacing defects in articular surfaces, there is tremendous interest in the in vitro bioengineering of cartilage replacements for clinical applications. However, attaining mechanical properties in engineered cartilaginous constructs that approach those of native cartilage has not been previously achieved when constructs are cultured under free-swelling conditions. One approach toward stimulating the development of constructs that are mechanically more robust is to expose them to physical environments that are similar, in certain ways, to those encountered by native cartilage. This is a strategy motivated by observations in numerous short-term experiments that certain mechanical signals are potent stimulators of cartilage metabolism. On the other hand, excess mechanical loading can have a deleterious effect on cartilage. Culture conditions that include a physical stimulation component are made possible by the use of specialized bioreactors. This chapter addresses some of the issues involved in using bioreactors as integral components of cartilage tissue engineering and in studying the physical regulation of cartilage. We first consider the generation of cartilaginous constructs in vitro. Next we describe the rationale and design of bioreactors that can impart either mechanical deformation or fluid-induced mechanical signals.

In areas of high joint loading, the subchondral bone had high vBMD and the articular cartilage surface layer had high tensile stiffness but signs of structural wear (fibrillation and low failure strain). The site-dependent variations and relationships in this study support the concept that articular cartilage and subchondral bone normally adapt to physiologic loading in a coordinated way.

Background:The aim of the study was to demonstrate the efficacy of human muscle stem cells (MuSCs) isolated using innovative technology in restoring internal urinary sphincter function in a preclinical animal model. Methods:Colonies of pure human MuSCs were obtained from muscle biopsy specimens. Athymic rats were subjected to internal urethral sphincter damage by electrocauterization. Five days after injury, 2 × 10 5 muscle stem cells or medium as control were injected into the area of sphincter damage (n = 5 in each group). Peak bladder pressure and rise in pressure were chosen as outcome measures. To repeatedly obtain the necessary pressure values, telemetry sensors had been implanted into the rat bladders 10 days prior to injury.Results: There was a highly significant improvement in the ability to build up peak pressure as well as a pressure rise in animals that had received muscle stem cells as compared to control (p = 0.007) 3 weeks after the cells had been injected. Only minimal histologic evidence of scarring was observed in treated rats. Conclusion:Primary human muscle stem cells obtained using innovative technology functionally restore internal urethral sphincter function after injury. Translation into use in clinical settings is foreseeable.

Swine are important translational research models for developing and gaining regulatory approval for novel therapies for heart failure. Three swine species in particular are utilized in these studies, the Domestic Yorkshire (DY), Yucatan Minipigs (Yuc), and Göttingen minipigs (Gott). Selecting the right swine breed is important to the translational success of novel therapies and is the source of debate in the field. The current study compared interventionally induced Ischemia-reperfusion injury (IRI), a method that mimics clinical myocardial infarction and subsequent heart failure, in these breeds. Interventional IRI was induced by occluding the Left Anterior Descending Coronary Artery for 90 minutes using a PTCA balloon placed distal to the first diagonal branch. Yuc have the highest rate of survival of the three breeds following a 90 min occlusion (81%; 56 out of 69), Gott survival was 70% (28 out of 40), and DY survival was 57% (75 out of 131). Assessment of serum levels of Cardiac Troponin I (CTnI) revealed significant increases in this parameter that peak at 3 hrs following occlusion. Gott have the highest levels at 122ng/mL, followed by Yuc (99ng/mL), and DY (85ng/mL) at this time point. Functionally, all three breeds displayed an Ejection Fraction assessed by echocardiography of less than 40%, with Gott having the lowest mean, followed by Yuc, and DY. These levels remain low or decrease slightly over 1 to 4 months. Magnetic Resonance imaging demonstrates infarct sizes are approximately 25% of the left ventricle following 1 month and decreasing over time to 22% at 2 months post and 13% 4 months post. Additionally, all three species lose their hemodynamic responsiveness to dobutamine challenge following IRI. All three breeds respond similarly to IRI functionally and structurally, and they develop the clinical features of congestive heart failure, the main distinguishing factor in the current study was survival of the IRI procedure. Based on this data, factors such as rate of body weight gain in relation to the ability to obtain functional endpoints, availability, and other practical considerations should drive the selection of breed for translational studies.