Mechanical stretching induces calcification and cartilage matrix metabolism, causing degeneration of the acetabular labrum

Purpose: The acetabular labrum plays an important role in joint lubrication, and damage to this structure leads to osteoarthritis. This study aimed to histologically classify the degree of degeneration of the acetabular labrum and to investigate the changes in gene expression induced by mechanical stretching. Methods: We obtained acetabular labrum cells from patients with hip osteoarthritis during total hip arthroplasty ( n = 25). The labrum was stained with safranin O, and images were histologically evaluated using a new parameter, the red/blue (R/B) value. The samples were divided into the degenerated group (D group: n = 18) and the healthy group (H group: n = 7) in accordance with the Kellgren-Lawrence (KL) grade. The cultured acetabular labral cells were subjected to loaded uniaxial cyclic tensile strain (CTS). After CTS, changes in gene expression were examined in both groups. Results: Spearman’s correlation analysis revealed that the R/B value was significantly correlated with the KL grade and the Krenn score. The expression levels of genes related to cartilage metabolism, osteogenesis and angiogenesis significantly increased after CTS in the H group, while gene expression in the D group showed weaker changes after CTS than that in the H group compared to the nonstretched control group. Conclusions: The degree of labral degeneration could be classified histologically using the R/B value and the KL grade. Mechanical stretching caused changes in gene expression that support the pathological features of labral degeneration.

Role of the Hyaluronan Receptor, Stabilin-2/HARE, in Health and Disease

Stabilin-2/HARE is the primary clearance receptor for circulating hyaluronan (HA), a polysaccharide found in the extracellular matrix (ECM) of metazoans. HA has many biological functions including joint lubrication, ocular turgor pressure, skin elasticity and hydration, cell motility, and intercellular signaling, among many others. The regulatory system for HA content in the tissues, lymphatics, and circulatory systems is due, in part, to Stabilin-2/HARE. The activity of this receptor was discovered about 40 years ago (early 1980s), cloned in the mid-1990s, and has been characterized since then. Here, we discuss the overall domain organization of this receptor and how it correlates to ligand binding, cellular signaling, and its role in known physiological disorders such as cancer.

Assessment of Vitamin D Supplementation on Articular Cartilage Morphology in a Young Healthy Sedentary Rat Model

Deficiency in vitamin D (Vit D) has been widely associated with several musculoskeletal diseases. However, the effects of the exogenous Vit D supplementation are still unclear in the prevention of the latter, especially in the cartilage developmental period. The aim of this study was to compare the effects of Vit D supplementation and restriction on the articular cartilage development in healthy young sedentary rats. To this aim, twelve nine-week-old healthy Sprague–Dawley male rats were subjected to Vit D-based experimental diets: R, with a content in Vit D of 1400 IU/kg; R-DS, with a Vit D supplementation (4000 IU/kg); R-DR, with a Vit D restriction (0 IU/kg) for 10 weeks. The morphology, thickness and expression of cartilage-associated molecules such as collagen type II/X, lubricin and Vit D receptor (VDR), were assessed. Histological, histomorphometric and immunohistochemical evaluations were made on rat tibial cartilage samples. In the present experimental model, restriction of Vit D intake induced: The lower thickness of cartilage compared both to R (p = < 0.0001) and R-DS (p = < 0.0001); reduction of proteoglycans in the extracellular matrix (ECM) compared both to R (p = 0.0359) and R-DS (p = < 0.0001); decreased collagen II (Col II) with respect both to R (p = 0.0076) and R-DS (p = 0.0016); increased collagen X (Col X) immunoexpression when compared both to R (p = < 0.0001) and R-DS (p = < 0.0001), confirming data from the literature. Instead, supplementation of Vit D intake induced: Higher cartilage thickness with respect both to R (p = 0.0071) and R-DR (p = < 0.0001); increase of ECM proteoglycan deposition compared both to R (p = 0.0175) and R-DR (p = < 0.0001); higher immunoexpression of lubricin with respect both to R (p = 0.001) and R-DR (p = 0.0008). These results suggest that Vit D supplementation with diet, already after 10 weeks, has a favorable impact on the articular cartilage thickness development, joint lubrication and ECM fibers deposition in a young healthy rat model.

The Effect of Dexamethasone, Adrenergic and Cholinergic Receptor Agonists on Phospholipid Metabolism in Human Osteoarthritic Synoviocytes

Phospholipids (PLs) possess the unique ability to contribute to synovial joint lubrication. The aim of our study was to determine for the first time the effect of dexamethasone and some adrenergic and cholinergic agonists on the biosynthesis and release of PLs from human fibroblast-like synoviocytes (FLS). Osteoarthritic human knee FLS were treated with dexamethasone, terbutaline, epinephrine, carbachol, and pilocarpine, or the glucocorticoid receptor antagonist RU 486. Simultaneously PL biosynthesis was determined through the incorporation of stable isotope-labeled precursors into PLs. Radioactive isotope-labeled precursors were used to radiolabel PLs for the subsequent quantification of their release into nutrient media. Lipids were extracted and quantified using electrospray ionization tandem mass spectrometry or liquid scintillation counting. Dexamethasone significantly decreased the biosynthesis of phosphatidylcholine, phosphatidylethanolamine (PE), PE-based plasmalogen, and sphingomyelin. The addition of RU 486 abolished these effects. A release of PLs from FLS into nutrient media was not recognized by any of the tested agents. None of the adrenergic or cholinergic receptor agonists modulated the PL biosynthesis. We demonstrate for the first time an inhibitory effect of dexamethasone on the PL biosynthesis of FLS from human knees. Moreover, our study indicates that the PL metabolism of synovial joints and lungs are differently regulated.

Opinion Article: Articular Cartilage: Lamellar-Repulsive Lubrication of Natural Joints by Zenon Pawlak

This monograph attempts to explain a new joint lubrication mechanism with surface active phospholipids as a lubricant. It provides studies of the principles of cartilage (smart material) of biological micro- and Nano tribology.

Squeeze flows in liquid films bound by porous disks

Squeeze flows in liquid films between a porous disk and an impermeable disk generated by the relative motion of the disks are analysed. Two configurations that differ by the arrangement of (im)permeable external surfaces that bound the porous disk (i.e. not in contact with the liquid film) are considered. Such configurations allow for bearings with tuneable load-bearing characteristics and are also encountered in joint lubrication, adhesion, printing and composite manufacturing. In the present study, flow in the porous disk is governed by Darcy’s law and flow in the liquid film is described using lubrication theory. The present analysis also allows for slip between the liquid film and porous disk. Analytical solutions of the coupled system of equations governing flow in the liquid film and the porous disk are found. Under certain conditions, somewhat unexpected flow patterns are observed in the porous disk. The load-bearing capacity for both configurations is also examined as a function of the permeability and geometry of the permeable disk.

Articular cartilage: Chemical, Physical, and Tribological Properties

The cartilage surface was characterized using wettability test fresh and depleted AC samples. In this work, we demonstrated experimentally that the cartilage smart biomaterial at varies pH is sensitive to friction and introduces a novel concept in joint lubrication on charged surfaces.The surface charge density of the articular cartilage surface is related to the amphoteric character of phospholipids, PLs functional groups (-NH3+) and (-PO4-). The maximum surface energy of AC was found to occur at pH for isoelectric point ~4.5 (H3N+(CH2)n PO4- -R1R2) and with a wide range minimum of pH 6.5 to 9.5 of the phospholipidic membrane covering biological pH ~7.4 lubrication condition. The hydrophilic and hydrophobic character of cartilage was determined.