Enzymatic digestion does not compromise sliding-mediated cartilage lubrication

Articular cartilage's remarkable low-friction properties are essential to joint function. In osteoarthritis (OA), cartilage degeneration (e.g., proteoglycan loss and collagen damage) decreases tissue modulus and increases permeability. Although these changes impair lubrication in fully depressurized and slowly slid cartilage, new evidence suggests such relationships may not hold under biofidelic sliding conditions more representative of those encountered in vivo. Our recent studies using the convergent stationary contact area (cSCA) configuration demonstrate that articulation (i.e., sliding) generates interfacial hydrodynamic pressures capable of replenishing cartilage interstitial fluid/pressure lost to compressive loading through a mechanism termed tribological rehydration. This fluid recovery sustains in vivo-like kinetic friction coefficients (µk<0.02 in PBS and <0.005 in synovial fluid) with little sensitivity to mechanical properties in healthy tissue. However, the tribomechanical function of compromised cartilage under biofidelic sliding conditions remains unknown. Here, we investigated the effects of OA-like changes in cartilage mechanical properties, modeled via enzymatic digestion of mature bovine cartilage, on its tribomechanical function during cSCA sliding. We found no differences in sliding-driven tribological rehydration behaviors or µk between naïve and digested cSCA cartilage (in PBS or synovial fluid). This suggests that OA-like cartilage retains sufficient functional properties to support naïve-like fluid recovery and lubrication under biofidelic sliding conditions. However, OA-like cartilage accumulated greater total tissue strains due to elevated strain accrual during initial load application. Together, these results suggest that elevated total tissue strains-as opposed to activity-mediated strains or friction-driven wear-might be the key biomechanical mediator of OA pathology in cartilage. STATEMENT OF SIGNIFICANCE: Osteoarthritis (OA) decreases cartilage's modulus and increases its permeability. While these changes compromise frictional performance in benchtop testing under low fluid load support (FLS) conditions, whether such observations hold under sliding conditions that better represent the joints' dynamic FLS conditions in vivo is unclear. Here, we leveraged biofidelic benchtop sliding experiments-that is, those mimicking joints' native sliding environment-to examine how OA-like changes in mechanical properties effect cartilage's natural lubrication. We found no differences in sliding-mediated fluid recovery or kinetic friction behaviors between naïve and OA-like cartilage. However, OA-like cartilage experienced greater strain accumulation during load application, suggesting that elevated tissue strains (not friction-driven wear) may be the primary biomechanical mediator of OA pathology.

Analysis of Extracellular ATP Distribution in the Intervertebral Disc

Progressive loss of proteoglycans (PGs) is the major biochemical change during intervertebral disc (IVD) degeneration. Adenosine triphosphate (ATP) as the primary energy source is not only critical for cell survival but also serves as a building block in PG synthesis. Extracellular ATP can mediate a variety of physiological functions and was shown to promote extracellular matrix (ECM) production in the IVD. Therefore, the objective of this study was to develop a 3D finite element model to predict extracellular ATP distribution in the IVD and evaluate the impact of degeneration on extracellular ATP distribution. A novel 3D finite element model of the IVD was developed by incorporating experimental measurements of ATP metabolism and ATP-PG binding kinetics into the mechano-electrochemical mixture theory. The new model was validated by experimental data of porcine IVD, and then used to analyze the extracellular distribution of ATP in human IVDs. Extracellular ATP was shown to bind specifically with PGs in IVD ECM. It was found that annulus fibrosus cells hydrolyze ATP faster than that of nucleus pulposus (NP) cells whereas NP cells exhibited a higher ATP release. The distribution of extracellular ATP in a porcine model was consistent with experimental data in our previous study. The predictions from a human IVD model showed a high accumulation of extracellular ATP in the NP region, whereas the extracellular ATP level was reduced with tissue degeneration. This study provides an understanding of extracellular ATP metabolism and its potential biological influences on the IVD via purinergic signaling.

Proteoglycan Dysfunction: A Common Link Between Intervertebral Disc Degeneration and Skeletal Dysplasia

Proteoglycans through their sulfated glycosaminoglycans regulate cell-matrix signaling during tissue development, regeneration, and degeneration processes. Large extracellular proteoglycans such as aggrecan, versican, and perlecan are especially important for the structural integrity of the intervertebral disc and cartilage during development. In these tissues, proteoglycans are responsible for hydration, joint flexibility, and the absorption of mechanical loads. Loss or reduction of these molecules can lead to disc degeneration and skeletal dysplasia, evident from loss of disc height or defects in skeletal development respectively. In this review, we discuss the common proteoglycans found in the disc and cartilage and elaborate on various murine models and skeletal dysplasias in humans to highlight how their absence and/or aberrant expression causes accelerated disc degeneration and developmental defects.

Alkali-treated titanium dioxide promotes formation of proteoglycan layer and altered calcification and immunotolerance capacity in bone marrow stem cell

Introduction

In this study, we report that a proteoglycans (PGs)-layer between the bone and titanium dioxide (TiO2) surface after osseointegration improved the calcification capacity and immunotolerance of human bone marrow mesenchymal stem cells (hBMSCs) on TiO2. Alkaline treatment of TiO2 is a method for promoting osteogenesis in hBMSCs. We hypothesized that promotion of osteogenesis due to alkaline treatment was caused by changing PGs-layer on TiO2.

Objective

This study aimed to analyze whether alkaline treatment of TiO2 affects PGs-layer formation and immunotolerance in hBMSCs.

Methods

The topology and wettability of the alkaline-treated titanium (Ti-Al) and unprocessed titanium (Ti-MS) surfaces were characterized. Initial cell attachment, cell proliferation, calcification capacity, alkaline phosphatase activity, PGs-layer formation, PGs function, and the expression of osteogenic and immunotolerance-related genes were analyzed. The conditioned medium (CM) from hBMSCs grown on Ti-Al and Ti-MS was added to macrophages (hMps) and Jurkat cells, and immunotolerance gene expression in these cells was analyzed.

Results

hBMSCs cultured on Ti-Al showed increased initial cell attachment, cell proliferation, PG-layer formation, and osteogenic capacity compared with hBMSCs on Ti-MS. Gene expression of indoleamine 2,3-dioxygenase (IDO) in the hBMSCs cultured on Ti-Al was higher than that in the hBMSCs on Ti-MS. CM from hBMSCs did not affect markers of M1 and M2 macrophages in hMps. CM from hBMSCs cultured on Ti-Al altered the gene expression of Foxp3 in Jurkat cells compared to that of CM from hBMSCs on Ti-MS.

Significance

These results suggest that alkaline treatment of TiO2 altered PGs-layer formation, and changed the osteogenesis and immunotolerance of hBMSCs.

Mechanism of multivalent glycoconjugate-lectin interaction: An update

Lectins are predominantly oligomeric proteins with several binding sites per molecule. Glycoconjugates are their natural ligands, which often possess multiple binding epitopes. Thus, lectin-glycoconjugate interactions are mostly multivalent in nature. The mechanism of multivalent binding is fundamentally different from those described for monovalent interactions in textbooks and research papers. Over the years, binding studies that make use of different lectins and a variety of multivalent glycoconjugate ligands were conducted in order to understand the underlying principles of multivalency. Starting with seemingly simple synthetic multivalent analogs, systematic studies were carried out using natural glycoconjugate ligands with increasing valency and complexity. Those ligands included multivalent glycoproteins, polyvalent polysaccharides, including glycosaminoglycans, as well as supra-valent mucins and proteoglycans. Models and mechanisms of multivalent binding derived from quantitative data are summarized in the present updated review.

Glycosaminoglycans: Roles in wound healing, formation of corneal constructs and synthetic corneas

Maintaining the clarity of the cornea is essential for vision, and is achieved through an exquisite array of collagen fibrils and proteoglycans in the corneal stroma. Alterations in the identity and modifications of the glycosaminoglycans (GAGs) are seen both throughout the normal wound healing process and in pathological conditions resulting in corneal opacity. Understanding these changes has been essential for the development of corneal prostheses and corneal reconstruction. The goal of this review article is to summarize and consolidate research in the alterations seen in glycosaminoglycans in injured and hypoxic states, address the role of proteins that can regulate glycosaminoglycans in the corneal wound healing process, and apply these findings to the context of corneal restoration through reconstruction or the insertion of synthetic devices.

John squire and endothelial glycocalyx structure: an unfinished story

John Squire did not only produce leading works in the muscle field, he also significantly contributed to the vascular permeability field by ultrastructural analysis of the endothelial glycocalyx. Presented here is a review of his involvement in the field by his main collaborator C.C. Michel and his last postdoctoral researcher KP Arkill. We end on a reinterpretation of his work that arguably links to our current understanding of endothelial glycocalyx structure and composition predicting 6 glycosaminoglycans fibres per syndecan core protein, only achieved in the endothelium by dimerization.

The antioxidant activity of polysaccharides: A structure-function relationship overview

Over the last years, polysaccharides have been linked to antioxidant effects using both in vitro chemical and biological models. The reported structures, claimed to act as antioxidants, comprise chitosan, pectic polysaccharides, glucans, mannoproteins, alginates, fucoidans, and many others of all type of biological sources. The structural features linked to the antioxidant action include the polysaccharide charge, molecular weight, and the occurrence of non-carbohydrate substituents. The establishment of structure/function relationships can be, however, biased by secondary phenomena that tailor polysaccharides behavior in antioxidant systems. In this sense, this review confronts some basic concepts of polysaccharides chemistry with the current claim of carbohydrates as antioxidants. It critically discusses how the fine structure and properties of polysaccharides can define polysaccharides as antioxidants. Polysaccharides antioxidant action is highly dependent on their solubility, sugar ring structure, molecular weight, occurrence of positive or negatively charged groups, protein moieties and covalently linked phenolic compounds. However, the occurrence of phenolic compounds and protein as contaminants leads to misleading results in methodologies often used for screening and characterization purposes, as well as in vivo models. Despite falling in the concept of antioxidants, the role of polysaccharides must be well defined according with the matrices where they are involved.

Modeling of glycosaminoglycan biosynthesis in intervertebral disc cells

Loss of proteoglycan (PG) is a potential factor responsible for degeneration of the intervertebral disc (IVD). PG consists of a core protein with covalently attached glycosaminoglycan (GAG) chains. The objective of this study was to develop a mathematical model of GAG biosynthesis to investigate the effects of glycolytic enzymes on GAG biosynthesis of IVD cells. A new mathematical model of GAG biosynthesis was developed for IVD cells by incorporating biosynthesis of uridine diphosphate-sugars into the glycolytic pathway. This new model showed good agreement between the model predictions of intracellular ATP content and GAG biosynthesis and experimental data measured at different external glucose levels. The quantitative analyses demonstrated that GAG biosynthesis may be sensitive to the activities of hexokinase (HK) and phosphofructokinase (PFK), especially at low glucose supply, with GAG biosynthesis being significantly enhanced by a slight increase in activities of HK and PFK. This suggests that metabolic reprogramming could be a potential strategy for promoting PG biosynthesis in IVD cells. Furthermore, it was shown that GAG biosynthesis may be promoted by increasing intracellular glutamine concentration or activity of glutamine:fructose-6-phosphate amidotransferase in the hexamine pathway. This study provides a better understanding of the relationship between glycolysis and PG biosynthesis in IVD cells. The theoretical framework developed in this study is useful for studying the role of glycolysis in disc degeneration and developing new preventive and treatment strategies for degeneration of the IVD.

A proteoglycan isolated from Ganoderma lucidum attenuates diabetic kidney disease by inhibiting oxidative stress-induced renal fibrosis both in vitro and in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Ganoderma lucidum (G. lucidum) was regarded as "miraculous herb" by the Chinese and recorded detailly in the "Shen Nong Ben Cao Jing" as a tonic to improve health and prolong life. A proteoglycan (namely, FYGL) was extracted from Ganoderma lucidum, which was a water-soluble hyperbranched proteoglycan, and was found to be able to protect pancreatic tissue against oxidative stress damage.

AIM OF THE STUDY

Diabetic kidney disease (DKD) is a complication of diabetes, but the effective treatment is still lack. Chronic hyperglycemia in diabetic patients induce the accumulation of ROS, which injure the renal tissue and lead to the renal dysfunction. In this work, the efficacy and target mechanics of FYGL on diabetic renal function were investigated.

MATERIALS AND METHODS

In the present study, the mechanism of the reno-protection of FYGL was analyzed on diabetic db/db mice and rat glomerular mesangial cells (HBZY-1) induced by high glucose (HG) with palmitate (PA) (HG/PA). In vitro, the levels of reactive oxygen species (ROS), malondialdehyde (MDA) and superoxide dismutase (SOD) were evaluated by commercial kits. the expressions of NOX1 and NOX4, phosphorylation of MAPK and NF-κB, and pro-fibrotic proteins were measured by Western blot. In vivo, diabetic db/db mice were gavaged with FYGL for 8 weeks, body weight and fasting blood glucose (FBG) were tested weekly. On 8th week, the serum, urine and renal tissue were collected for glucose tolerance test (OGTT), redox indicator (SOD, CAT, GSH and MDA), lipid metabolism (TC, TG, LDL and HDL), blood urea nitrogen (BUN), serum creatinine (Scr), uric acid (UA), 8-oxo-deoxyguanosine (8-OHdG), and the changes of histopathology and expression of collagen IV and AGEs.

RESULTS

The results in vitro showed that FYGL significantly inhibited the HG/PA-induced HBZY-1 cells proliferation, ROS generation, MDA production, promoted SOD activity, and suppressed NOX1, NOX4, MAPK, NF-κB, and pro-fibrotic proteins expression. In addition, FYGL markedly alleviated blood glucose, antioxidant activity and lipid metabolism, improved renal functions, and relieved renal histopathological abnormalities, especially renal fibrosis.

CONCLUSIONS

The antioxidant activity of FYGL can reduce ROS caused by diabetes and protect renal from oxidative stress-induced dysfunction, thereby improving renal function. This study shows that FYGL has the potential to treat diabetic kidney disease.

AAV Vector Mediated Delivery of NG2 Function Neutralizing Antibody and Neurotrophin NT-3 Improves Synaptic Transmission, Locomotion, and Urinary Tract Function after Spinal Cord Contusion Injury in Adult Rats

NG2 is a structurally unique transmembrane chondroitin sulfate proteoglycan (CSPG). Its role in damaged spinal cord is dual. NG2 is considered one of key inhibitory factors restricting axonal growth following spinal injury. Additionally, we have recently detected its novel function as a blocker of axonal conduction. Some studies, however, indicate the importance of NG2 presence in the formation of synaptic contacts. We hypothesized that the optimal treatment would be neutralization of inhibitory functions of NG2 without its physical removal. Acute intraspinal injections of anti-NG2 monoclonal antibodies reportedly prevented an acute block of axonal conduction by exogenous NG2. For prolonged delivery of NG2 function neutralizing antibody, we have developed a novel gene therapy: adeno-associated vector (AAV) construct expressing recombinant single-chain variable fragment anti-NG2 antibody (AAV-NG2Ab). We examined effects of AAV-NG2Ab alone or in combination with neurotrophin NT-3 in adult female rats with thoracic T10 contusion injuries. A battery of behavioral tests was used to evaluate locomotor function. In vivo single-cell electrophysiology was used to evaluate synaptic transmission. Lower urinary tract function was assessed during the survival period using metabolic chambers. Terminal cystometry, with acquisition of external urethral sphincter activity and bladder pressure, was used to evaluate bladder function. Both the AAV-NG2Ab and AAV-NG2Ab combined with AAV-NT3 treatment groups demonstrated significant improvements in transmission, locomotion, and bladder function compared with the control (AAV-GFP) group. These functional improvements associated with improved remyelination and plasticity of 5-HT fibers. The best results were observed in the group that received combinational AAV-NG2Ab+AAV-NT3 treatment.SIGNIFICANCE STATEMENT We recently demonstrated beneficial, but transient, effects of neutralization of the NG2 proteoglycan using monoclonal antibodies delivered intrathecally via osmotic mini-pumps after spinal cord injury. Currently, we have developed a novel gene therapy tool for prolonged and clinically relevant delivery of a recombinant single-chain variable fragment anti-NG2 antibody: AAV-rh10 serotype expressing scFv-NG2 (AAV-NG2Ab). Here, we examined effects of AAV-NG2Ab combined with transgene delivery of Neurotrophin-3 (AAV-NT3) in adult rats with thoracic contusion injuries. The AAV-NG2Ab and AAV-NG2Ab+AAV-NT3 treatment groups demonstrated significant improvements of locomotor function and lower urinary tract function. Beneficial effects of this novel gene therapy on locomotion and bladder function associated with improved transmission to motoneurons and plasticity of axons in damaged spinal cord.

Chondroitin sulfate is not digested at all in the mouse small intestine but may suppress interleukin 6 expression induced by tumor necrosis factor-α

Salmon nasal cartilage proteoglycan (PG) was orally administered to mice. The PG digest was recovered from the small intestine, and its sugar chain size and unsaturated disaccharide content were examined. The elution position of the PG digest following Sepharose CL-4B chromatography was consistent with that of actinase-digested PG prior to administration. The PG digest was incubated with chondroitinase ABC, which resulted in the elution pattern of the unsaturated disaccharides being identical to that of the degraded product of actinase-digested PG. The core protein of PG was digested in the mouse small intestine, but chondroitin sulfate, which is the sugar chain of PG, was not degraded at all. Then, the effects of chondroitin 4- and 6-sulfates on human colon cancer cells were examined. These chondroitin sulfates were found to suppress the expression of interleukin-6 induced by TNF-α. Overall, the chondroitin sulfate chain may act on the intestinal epithelium and suppress inflammation of the intestinal tract.

Purification and Isolation of Proteins from Hyaline Cartilage

Proteins from hyaline or articular cartilage can be isolated and purified using a series of chemical extraction steps and various identification techniques including mass spectrometry and immunoblotting. The isolation and purification of proteins from cartilage will facilitate the study of specific proteins and multimeric complexes of cartilage proteins to better understand their functions in normal healthy cartilage as well as pathological conditions of cartilage. Cartilage tissue engineering efforts rely on the comprehensive understanding of the composition of cartilage and the function of each of the protein constituents.

Blood vessel remodeling in the cerebral cortex induced by binge alcohol intake in mice

Ethanol is toxic to the brain and causes various neurological disorders. Although ethanol can directly exert toxicity on neurons, it also acts on other cell types in the central nervous system. Blood vessel endothelial cells interact with, and are affected by blood ethanol. However, the effects of ethanol on the vascular structures of the brain have not been well documented. In this study, we examined the effects of binge levels of ethanol on brain vasculature. Immunostaining analysis indicated structural alterations of blood vessels in the cerebral cortex, which became more tortuous than those in the control mice after ethanol administration. The interaction between the blood vessels and astrocytes decreased, especially in the upper layers of the cerebral cortex. Messenger RNA expression analysis revealed a unique downregulation of Vegfa mRNA encoding vascular endothelial growth factor (VEGF)-A among VEGF, angiopoietin, endothelin family angiogenic and blood vessel remodeling factors. The expression of three proteoglycan core proteins, glypican-5, neurocan, and serglycin, was also altered after ethanol administration. Thus, binge levels of ethanol affect the expression of VEGF-A and blood vessel-supporting proteoglycans, resulting in changes in the vascular structure of the cerebral cortex.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-022-00164-y.

Analysis of Aggrecan Glycanation by Western Blot in Cell Culture

Several experimental protocols are available to study the synthesis and secretion of proteoglycans in health and diseases, but there are few methods to analyse the intracellular processing of these macromolecules. We report a western blot analysis on medium and cell layer of primary chondrocyte culture to determine the glycanation status of aggrecan. Using a specific antibody against the aggrecan core protein and digesting an aliquot of sample with chondroitinase ABC, it is possible to analyse the whole aggrecan macromolecule and the core protein in order to evaluate defects in aggrecan glycanation.

Proteoglycan Expression Studied by MicroRNAs

MicroRNAs are small noncoding RNAs that regulate gene expression at the posttranscriptional level. Proteoglycans are glycoproteins characterized by covalent attachment of a glycosaminoglycan chain, which have been identified as regulatory targets of microRNAs in a physiological and pathophysiological context. We present a strategy and detailed methods for the functional analysis of microRNA regulation of proteoglycans using human cancer cells as an application example. The experimental setup includes in silico microRNA target prediction, transfection of cancer cells with microRNA precursors, validation of target regulation by qPCR, flow cytometry and luciferase reporter assays, and an example for functional analysis and phenotype confirmation by complementation analysis.

Nanomechanics of Aggrecan: A New Perspective on Cartilage Biomechanics, Disease and Regeneration

Articular cartilage is a hydrated macromolecular composite mainly composed of type II collagen fibrils and the large proteoglycan, aggrecan. Aggrecan is a key determinant of the load bearing and energy dissipation functions of cartilage. Previously, studies of cartilage biomechanics have been primarily focusing on the macroscopic, tissue-level properties, which failed to elucidate the molecular-level activities that govern cartilage development, function, and disease. This chapter provides a brief summary of Dr. Alan J. Grodzinsky's seminal contribution to the understanding of aggrecan molecular mechanics at the nanoscopic level. By developing and applying a series of atomic force microscopy (AFM)-based nanomechanical tools, Grodzinsky and colleagues revealed the unique structural and mechanical characteristics of aggrecan at unprecedented resolutions. In this body of work, the "bottle-brush"-like ultrastructure of aggrecan was directly visualized for the first time. Meanwhile, molecular mechanics of aggrecan was studied using a physiological-like 2D biomimetic assembly of aggrecan on multiple fronts, including compression, dynamic loading, shear, and adhesion. These studies not only generated new insights into the development, aging, and disease of cartilage, but established a foundation for designing and evaluating novel cartilage regeneration strategies. For example, building on the scientific foundation and methodology infrastructure established by Dr. Grodzinsky, recent studies have elucidated the roles of other proteoglycans in mediating cartilage integrity, such as decorin and perlecan, and evaluated the therapeutic potential of biomimetic proteoglycans in improving cartilage regeneration.

Cadmium induces chondroitin sulfate synthase 1 via protein kinase Cα and elongates chondroitin/dermatan sulfate chains in cultured vascular endothelial cells

Cadmium is an environmental pollutant and a risk factor for atherosclerosis. In the atherosclerotic intima, dermatan sulfate chains accelerate accumulation and oxidation of LDL cholesterol. The major type of dermatan sulfate proteoglycan that is synthesized by vascular endothelial cells is biglycan. In the present study, we analyzed the effect of cadmium on the biglycan synthesis using cultured bovine aortic endothelial cells. Cadmium did not induce biglycan mRNA and core protein expression; however, it elongated the chondroitin/dermatan sulfate chains of biglycan. Among elongation enzymes of the chondroitin/dermatan sulfate chain, chondroitin sulfate synthase 1 (CHSY1) mRNA and protein expression were dose- and time-dependently upregulated by cadmium depending on protein kinase Cα. This finding suggests that CHSY1-dependent elongation of chondroitin/dermatan sulfate chains of biglycan may exacerbate cadmium-induced atherosclerosis.

Immunochemical Detection and Glycosaminoglycan Disaccharide-Based Characterization of Chondroitin Sulfate Proteoglycans

Chondroitin sulfate proteoglycans (CSPGs) are polyanionic extra/pericellular matrix macromolecules that surround almost all cell types and create microenvironmental niches to support miscellaneous cellular events. In general, the multifunctional properties of CSPGs are attributable to the structural divergence of the CS glycosaminoglycan (GAG) moieties. Because the expression profiles of the GAG chains of CSPGs change with developmental stage, aging, and disease progression, characterization of the GAG chains is essential to understand the functional roles of CSPGs. This chapter describes the basic protocols for GAG moiety-based immunochemical detection of CSPGs in biological samples in conjunction with CS disaccharide composition analysis.

Structural elucidation and anti-inflammatory activity of a proteoglycan from spent substrate of Lentinula edodes

A proteoglycan LEPS1 was firstly isolated and purified from the spent substrate of Lentinula edodes, an agricultural waste that may cause environmental pollution. The average molecular weight of LEPS1 was 1.18 × 10⁴ g/mol, and carbohydrate moiety (88.9 %) was composed of glucose, arabinose, galactose, xylose and mannose at a molar ratio of 1.2:1.2:1.0:2.3:1.1. The protein moiety (8.5 %) of LEPS1 was bonded to the polysaccharide chain via O-glycosidic linkage. LEPS1 could significantly improve the inflammatory injury of LPS stimulated RAW264.7 macrophages by inhibiting the secretion of NO and decreasing the levels of pro-inflammatory factors (TNF-α, IL-1β and IL-6). LEPS1 inhibited JAK-STAT1 and p38 MAPK signaling pathway via modulating JAK expression, phosphorylation of STAT1 and phosphorylation of p38, respectively. Moreover, LEPS1 could promote the expression of CD 206 and IL-10 which were the markers for repairing macrophages. Overall, LEPS1 had anti-inflammatory activity and can potentially treat as a novel anti-inflammation agent. This work could provide scientific basis and valuable information for the highly efficient utilization of spent L. edodes substrates as the by-product in mushroom industries.

Working towards arabinogalactan proteins (AGPs) from fruit: carbohydrate composition and impact on fungal growth

BACKGROUND

Arabinogalactan proteins (AGPs) are extracellular matrix constituents involved in plant response to fungal infection. The aim of the current study was to investigate the antifungal effect of AGPs ex situ and to determine the structural features of AGPs that may have an influence on this activity. The features of AGPs isolated from fruit were investigated with molecular tools based on specific monoclonal antibodies recognizing carbohydrate AGP epitopes. The Antifungal (well-diffusion) Susceptibility Test and the Agar Invasion Test were used to assess the impact of AGPs on Penicillium notatum culture.

RESULTS

The results definitely ruled out the influence of AGPs on fungal growth. The immunochemical analyses revealed that AGPs consist mainly of carbohydrate chains composed of β-linked glucuronosyl residues recognized by LM2 and GlcA-β(1 → 3)-GalA-α(1 → 2) Rha recognized by JIM13, which do not have the same functional properties outside the plant cell in in vitro experimental conditions.

CONCLUSIONS

The action of a single cell wall component does not elicit any influence ex situ. The extensive accumulation of glycan chains of AGPs in infected tissue as a result of a complex mechanism occurring in the cell wall emphasizes the importance of dependencies between particular components of the extracellular matrix in response to fungal attack.

Associations of human femoral condyle cartilage structure and composition with viscoelastic and constituent-specific material properties at different stages of osteoarthritis

The relationships between structure and function in human knee femoral cartilage are not well-known at different stages of osteoarthritis. Thus, our aim was to characterize the depth-dependent composition and structure (proteoglycan content, collagen network organization and collagen content) of normal and osteoarthritic human femoral condyle cartilage (n = 47) and relate them to their viscoelastic and constituent-specific mechanical properties that are obtained through dynamic sinusoidal testing and fibril-reinforced poroelastic material modeling of stress-relaxation testing, respectively. We characterized the proteoglycan content using digital densitometry, collagen network organization (orientation angle and anisotropy) using polarized light microscopy and collagen content using Fourier transform infrared spectroscopy. In the superficial cartilage (0-10 % of thickness), the collagen network disorganization and proteoglycan loss were associated with the smaller initial fibril network modulus - a parameter representing the pretension of the collagen network. Furthermore, the proteoglycan loss was associated with the greater strain-dependent fibril network modulus - a measure of nonlinear mechanical behavior. The proteoglycan loss was also associated with greater cartilage viscosity at a low loading frequency (0.005 Hz), while the collagen network disorganization was associated with greater cartilage viscosity at a high loading frequency (1 Hz). Our results suggest that proteoglycan loss and collagen network disorganization reduce the pretension of the collagen network while proteoglycan degradation also increases the nonlinear mechanical behavior of the collagen network. Further, the results also highlight that proteoglycan loss and collagen disorganization increase the viscosity of femoral cartilage, but their contribution to increased viscosity occurs in completely different loading frequencies.

Cardiomyocyte-specific overexpression of syndecan-4 in mice results in activation of calcineurin-NFAT signalling and exacerbated cardiac hypertrophy

BACKGROUND

Cardiomyocyte hypertrophy is a hallmark of cardiac dysfunction in patients with aortic stenosis (AS), and can be triggered by left ventricular (LV) pressure overload in mice by aortic banding (AB). Syndecan-4 is a transmembrane heparan sulphate proteoglycan which is found increased in the myocardium of AS patients and AB mice. The role of syndecan-4 in cardiomyocyte hypertrophy is not well understood.

PURPOSE OF THE STUDY

We developed mice with cardiomyocyte-specific overexpression of syndecan-4 (Sdc4-Tg) and subjected these to AB to examine the role of syndecan-4 in hypertrophy and activation of the pro-hypertrophic calcineurin-NFAT signalling pathway.

METHODS AND RESULTS

Sdc4-Tg mice showed exacerbated cardiac remodelling upon AB compared to wild type (WT). At 2-6 weeks post-AB, Sdc4-Tg and WT mice showed similar hypertrophic growth, while at 20 weeks post-AB, exacerbated hypertrophy and dysfunction were evident in Sdc4-Tg mice. After cross-breeding of Sdc4-Tg mice with NFAT-luciferase reporter mice, we found increased NFAT activation in Sdc4-Tg hearts after AB. Immunoprecipitation showed that calcineurin bound to syndecan-4 in Sdc4-Tg hearts. Isolated cardiomyocytes from Sdc4-Tg mice showed alterations in Ca2+ fluxes, suggesting that syndecan-4 regulated Ca2+ levels, and thereby, activating the syndecan-4-calcineurin complex resulting in NFAT activation and hypertrophic growth. Similarly, primary cardiomyocyte cultures from neonatal rats showed increased calcineurin-NFAT-dependent hypertrophic growth upon viral Sdc4 overexpression.

CONCLUSION

Our study of mice with cardiomyocyte-specific overexpression of Sdc4 have revealed that syndecan-4 is important for activation of the Ca2+-dependent calcineurin-NFAT signalling pathway, hypertrophic remodelling and dysfunction in cardiomyocytes in response to pressure overload.

Jellyfish mucin (qniumucin) extracted with a modified protocol indicated its existence as a constituent of the extracellular matrix

Jellyfish (JF) mucin (precisely, a mucin-type glycoprotein named qniumucin: Q-mucin) first discovered in JF is mainly composed of highly O-glycosylated domains, and its unique structure suggests its wide applications as a smart material. In this study, the standard protocol used to date was thoroughly reinvestigated because the processing of raw JF was rather difficult and continuous production from frozen sources was also indispensable. Finally, we concluded that Q-mucin is involved not in mucus but in the mesoglea, i.e., the extracellular matrix (ECM), as a part of a very large polymer complex. We added a treatment procedure with a chelate reagent (e.g. EDTA) to inactivate endogenous proteases that induce the spontaneous decomposition of the collagens in ECM. The amino acid composition (AAC) of each precipitate formed upon EtOH addition indicated that Q-mucin dissociates from the biopolymer complex as a constituent highly soluble in deionized water. Since the remaining portion of ECM still seemed to contain a large amount of the precursor of Q-mucin even after the extraction with water is completed, the yield of Q-mucin is expected to increase markedly if an innovative method to decompose EtOH precipitates is developed. The existence of Q-mucin in ECM seems to be described in parallel with that of proteoglycans (PG) in mammalian cartilage because they resemble each other.

Reducing Proteoglycan Synthesis and NOX Activity by ROCK Inhibitors: Therapeutic Targets in Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the arteries characterized by accumulation of inflammatory cells in the arterial wall. Hypertension, dyslipidemia, and hyperglycemia are major risk factors of atherosclerosis. Rho-associated protein kinase (ROCK), a serine/threonine kinase, is a downstream effector of the small GTPase RhoA. ROCK is involved in different stages of atherosclerosis. Accumulating evidence has demonstrated that ROCK signaling plays vital roles in various cellular functions, such as contraction, migration, and proliferation of smooth muscle cells. Dysregulation of the ROCK pathway is associated with atherosclerosis and hypertension. Experimental studies have shown that ROCK inhibitors may have favorable effects in ameliorating atherosclerosis. ROCK signaling has a role in proteoglycan synthesis through transactivation of the TGF-β receptor Type I (TβRI) mediated by G-protein-coupled receptor (GPCR) agonists (endothelin-1, angiotensin II and …), and ROCK inhibitors could decrease proteoglycan synthesis and atherosclerotic plaque formation. Based on the hypothesis that targeting ROCK pathway may be effective in ameliorating atherosclerosis, we suggest that ROCK inhibitors may have a potential therapeutic role in inhibition or slowing atherogenesis. However, for this hypothesis more research is needed.

The relation between the biochemical composition of knee articular cartilage and quantitative MRI: a systematic review and meta-analysis

OBJECTIVE

Early and non-invasive detection of osteoarthritis (OA) is required to enable early treatment and monitoring of interventions. Some of the earliest signs of OA are the change in proteoglycan and collagen composition. The aim of this study is to establish the relations between quantitative magnetic resonance imaging (MRI) and biochemical concentration and organization in knee articular cartilage.

METHODS

A preregistered systematic literature review was performed using the databases PubMed and Embase. Papers were included if quantitative MRI and a biochemical assay or polarized light microscopy (PLM) was performed on knee articular cartilage, and a quantified correlation was described. The extracted correlations were pooled using a random effects model.

RESULTS

21 papers were identified. The strongest pooled correlation was found for delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) vs proteoglycan concentration (r = 0.59). T1ρ relaxation times are inversely correlated to proteoglycan concentration (r = -0.54). A weak correlation between T2 relaxation times and proteoglycans was found (r = -0.38). No correlation between T2 relaxation time and collagen concentration was found (r = -0.02). A heterogeneous set of correlations between T2 relaxation times and PLM were identified, including strong correlations to anisotropy.

CONCLUSION

DGEMRIC measures are significantly correlated to proteoglycan concentration. The needed contrast agent is however a disadvantage; the T1ρ sequence was found as a non-invasive alternative. Remarkably, no correlation was found between T2 relaxation times and collagen concentration. T2 relaxation times is related to organization, rather than concentration of collagen fibers.

PROSPERO ID

CRD42020168337.

Proteoglycans and proteoglycan mimetics for tissue engineering

Proteoglycans play a crucial role in proper tissue morphology and function throughout the body that is defined by a combination of their core protein and the attached glycosaminoglycan chains. Although they serve a myriad of roles, the functions of extracellular proteoglycans can be generally sorted into four categories: modulation of tissue mechanical properties, regulation and protection of the extracellular matrix, sequestering of proteins, and regulation of cell signaling. The loss of proteoglycans can result in significant tissue disfunction, ranging from poor mechanical properties to uncontrolled inflammation. Because of the key roles they play in proper tissue function and due to their complex synthesis, the past two decades have seen significant research into the development of proteoglycan mimetic molecules to recapitulate the function of proteoglycans for therapeutic and tissue engineering applications. These strategies have ranged from semisynthetic graft copolymers to recombinant proteoglycan domains synthesized by genetically engineered cells. In this review, we highlight some of the important functions of extracellular proteoglycans, as well as the strategies developed to recapitulate these functions.

Antioxidation of a proteoglycan from Ganoderma lucidum protects pancreatic β-cells against oxidative stress-induced apoptosis in vitro and in vivo

Oxidative stress is one of the major factors in induction of pancreatic β-cell apoptosis and diabetes. Here, we investigated systematically the roles of a proteoglycan (namely, FYGL) from Ganoderma lucidum in protection and repair of pancreatic β-cells against oxidative stress-induced injury and apoptosis on molecular, cellular and animal basis. FYGL in vitro had antioxidant activity in terms of scavenging of free radicals and reduction power. FYGL improved cells viability, insulin secretion, redox indicator expressions, and mitochondrial membrane potential in H₂O₂-induced INS-1 cell via regulating the activations of apoptosis-related mitogen-activated protein kinases (MAPK) and nuclear factor kappa B (NF-κB) pathways as well as the insulin secretion-related pathway. Thrillingly in vivo, FYGL repaired the injured pancreas, reduced the pancreatic β-cells apoptosis, and improved insulin secretion because of regulating the balance of oxidation-reduction, therefore well managed blood glucose in db/db diabetic mice. These results demonstrated that FYGL is promising to be used as a novel natural remedy for protection of pancreatic β-cells against oxidative stress in diabetes treatment.

Informatics Ecosystems to Advance the Biology of Glycans

Glycomics researchers have identified the need for integrated database systems for collecting glycomics information in a consistent format. The goal is to create a resource for knowledge discovery and dissemination to wider research communities. This has the potential and has exhibited initial success, to extend the research community to include biologists, clinicians, chemists, and computer scientists. This chapter discusses the technology and approach needed to create integrated data resources and informatics ecosystems to empower the broader community to leverage extant glycomics data. The focus is on glycosaminoglycan (GAGs) and proteoglycan research, but the approach can be generalized. The methods described span the development of glycomics standards from CarbBank to Glyco Connection Tables. Integrated data sets provide a foundation for novel methods of analysis such as machine learning and deep learning for knowledge discovery. The implications of predictive analysis are examined in relation to disease biomarker to expand the target audience of GAG and proteoglycan research.

Sulfated Glycoprotein Synthesis

Chemical protein synthesis has achieved tremendous progress in the past decades. With the development of chemical ligation as powerful tools, the scope of synthetic protein is greatly expanded. Proteoglycans are a class of sulfated glycoproteins widely distributed on the cell surface and in the extracellular matrix, which are extensively engaged in cellular communication events. Consisting of protein backbone and glycosaminoglycan(s) side chain, proteoglycans are highly complex and heterogeneous in nature. Chemical synthesis provides facile and reliable approach to these molecules, with defined glycan structure and sulfation pattern. One remaining problem is that the acid-labile sulfates could hardly survive during the typical solid phase peptide synthesis (SPPS) process. In this chapter, strategic design of a "glycopeptide cassette" for the preparation of sulfated glycoprotein is described. In particular, we provide protocols for the chemical synthesis of ectodomain fragment (23-120) of sulfated glycoprotein syndecan-1.

Mapping Proteoglycan Function Using Novel Genetic Strategies

Multiple intrinsic and extrinsic factors contribute to stem and neuronal precursor cell maintenance and/or differentiation. Proteoglycans, major residents of the stem cell microenvironment, modulate key signaling cues and are of particular importance. The complexity and diversity of the glycan structure of proteoglycans make their functional characterization a challenging task. In order to test the functional role of glycosaminoglycans (GAGs) in cell self-renewal, maintenance, and differentiation, we have taken a loss-of-function approach by developing a library of both biosynthetic and degradative enzymes to specifically remodel the ECM.

Site- and Zone-Dependent Changes in Proteoglycan Content and Biomechanical Properties of Bluntly and Sharply Grooved Equine Articular Cartilage

In this study, we mapped and quantified changes of proteoglycan (PG) content and biomechanical properties in articular cartilage in which either blunt or sharp grooves had been made, both close to the groove and more remote of it, and at the opposing joint surface (kissing site) in equine carpal joints. In nine adult Shetland ponies, standardized blunt and sharp grooves were surgically made in the radiocarpal and middle carpal joints of a randomly chosen front limb. The contralateral control limb was sham-operated. At 39 weeks after surgery, ponies were euthanized. In 10 regions of interest (ROIs) (six remote from the grooves and four directly around the grooves), PG content as a function of tissue-depth and distance-to-groove was estimated using digital densitometry. Biomechanical properties of the cartilage were evaluated in the six ROIs remote from the grooves. Compared to control joints, whole tissue depth PG loss was found in sites adjacent to sharp and, to a larger extent, blunt grooves. Also, superficial PG loss of the surgically untouched kissing cartilage layers was observed. Significant PG loss was observed up to 300 µm (sharp) and at 500 µm (blunt) from the groove into the surrounding tissue. Equilibrium modulus was lower in grooved cartilage than in controls. Grooves, in particular blunt grooves, gave rise to severe PG loss close to the grooved sites and to mild degeneration more remote from the grooves in both sharply and bluntly grooved cartilage and at the kissing sites, resulting in loss of mechanical strength over the 9-month period.

Novel regulatory roles of small leucine-rich proteoglycans in remodeling of the uterine cervix in pregnancy

The cervix undergoes rapid and dramatic shifts in collagen and elastic fiber structure to achieve its disparate physiological roles of competence during pregnancy and compliance during birth. An understanding of the structure-function relationships of collagen and elastic fibers to maintain extracellular matrix (ECM) homeostasis requires an understanding of the mechanisms executed by non-structural ECM molecules. Small-leucine rich proteoglycans (SLRPs) play key functions in biology by affecting collagen fibrillogenesis and regulating enzyme and growth factor bioactivities. In the current study, we evaluated collagen and elastic fiber structure-function relationships in mouse cervices using mice with genetic ablation of decorin and/or biglycan genes as representative of Class I SLRPs, and lumican gene representative of Class II SLRP. We identified structural defects in collagen fibril and elastic fiber organization in nonpregnant mice lacking decorin, or biglycan or lumican with variable resolution of defects noted during pregnancy. The severity of collagen and elastic fiber defects was greater in nonpregnant mice lacking both decorin and biglycan and defects were maintained throughout pregnancy. Loss of biglycan alone reduced tissue extensibility in nonpregnant mice while loss of both decorin and biglycan manifested in decreased rupture stretch in late pregnancy. Collagen cross-link density was similar in the Class I SLRP null mice as compared to wild-type nonpregnant and pregnant controls. A broader range in collagen fibril diameter along with an increase in mean fibril spacing was observed in the mutant mice compared to wild-type controls. Collectively, these findings uncover functional redundancy and hierarchical roles of Class I and Class II SLRPs as key regulators of cervical ECM remodeling in pregnancy. These results expand our understating of the critical role SLRPs play to maintain ECM homeostasis in the cervix.

Recent advances on glycosyltransferases involved in the biosynthesis of the proteoglycan linkage region

Proteoglycans (PGs) are an essential family of glycoproteins, which can play roles in many important biological events including cell proliferation, cancer development, and pathogen infections. Proteoglycans consist of a core protein with one or multiple glycosaminoglycan (GAG) chains, which are covalently attached to serine residues of serine-glycine dipeptide within the core protein through a common tetrasaccharide linkage. In the past three decades, four key glycosyl transferases involved in the biosynthesis of PG linkage have been discovered and investigated. This review aims to provide an overview on progress made on these four enzymes, with foci on enzyme expression/purification, substrate specificity, activity determination, product characterization, and structure-activity relationship analysis.

Decorin: a multifunctional proteoglycan involved in oocyte maturation and trophoblast migration

Decorin (DCN) is a proteoglycan belonging to the small leucine-rich proteoglycan family. It is composed of a protein core containing leucine repeats with a glycosaminoglycan chain consisting of either chondroitin sulfate or dermatan sulfate. DCN is a structural component of connective tissues that can bind to type I collagen. It plays a role in the assembly of the extracellular matrix (ECM), and it is related to fibrillogenesis. It can interact with fibronectin, thrombospondin, complement component C1, transforming growth factor (TGF), and epidermal growth factor receptor. Normal DCN expression regulates a wide range of cellular processes, including proliferation, migration, apoptosis, and autophagy, through interactions with various molecules. However, its aberrant expression is associated with oocyte maturation, oocyte quality, and poor extravillous trophoblast invasion of the uterus, which underlies the occurrence of preeclampsia and intrauterine growth restriction. Spatiotemporal hormonal control of successful pregnancy should regulate the concentration and activity of specific proteins such as proteoglycan participating in the ECM remodeling of trophoblastic and uterine cells in fetal membranes and uterus. At the human feto-maternal interface, TGF-β and DCN play crucial roles in the regulation of trophoblast invasion of the uterus. This review summarizes the role of the proteoglycan DCN as an important and multifunctional molecule in the physiological regulation of oocyte maturation and trophoblast migration. This review also shows that recombinant DCN proteins might be useful for substantiating diverse functions in both animal and in vitro models of oogenesis and implantation.

Ehlers Danlos Syndrome with Glycosaminoglycan Abnormalities

Ehlers-Danlos syndrome (EDS) is a genetically and clinically heterogeneous group of connective tissue disorders that typically present with skin hyperextensibility, joint hypermobility, and tissue fragility. The major cause of EDS appears to be impaired biosynthesis and enzymatic modification of collagen. In this chapter, we discuss two types of EDS that are associated with proteoglycan abnormalities: spondylodysplastic EDS and musculocontractural EDS. Spondylodysplastic EDS is caused by pathogenic variants in B4GALT7 or B3GALT6, both of which encode key enzymes that initiate glycosaminoglycan synthesis. Musculocontractural EDS is caused by mutations in CHST14 or DSE, both of which encode enzymes responsible for the post-translational biosynthesis of dermatan sulfate. The clinical and molecular characteristics of both types of EDS are described in this chapter.

The thermodynamic and kinetic mechanisms of a Ganoderma lucidum proteoglycan inhibiting hIAPP amyloidosis

Ganoderma lucidum is a valuable medicinal herbal which has been reported to prevent type 2 diabetes (T2D). A natural hyperbranched proteoglycan extracted from Ganoderma lucidum, namely, FYGL, has been demonstrated to inhibit the amyloidosis of human islet amyloid polypeptide (hIAPP) previously by our lab. However, the effective active components and the mechanisms of FYGL in inhibiting hIAPP amyloidosis are unknown. To identify the effective active components, different components from FYGL were isolated: the polysaccharide FYGL-1, the proteoglycans of FYGL-2 and FYGL-3. We further separated and sequenced the protein moieties of FYGL-2 and FYGL-3, namely, FYGL-2-P and FYGL-3-P, respectively, and compared their abilities to inhibit hIAPP amyloidosis, and systematically explored the inhibitory mechanisms by spectroscopy, microscopy and molecular dynamic simulation methods. Results showed that the protein moieties of FYGL played essential roles in inhibiting hIAPP amyloidosis. The strong, specific, and enthalpy-driven interaction by π-π stacking and electrostatic forces between hIAPP and FYGL-3-P dramatically inhibited hIAPP amyloidosis. These results suggested that FYGL-3-P had enormous potential to prevent hIAPP misfolding-induced diabetes and structurally helped researchers to seek or design inhibitors against polypeptide amyloidosis.

An injectable hydrogel having proteoglycan-like hierarchical structure supports chondrocytes delivery and chondrogenesis

The ECM of cartilage is composed of proteoglycans (PG) that contain glycosaminoglycan (GAG), aggrecan, hyaluronic acid (HA) and other molecular components which play an important role in regulating chondrocyte functions via cell-matrix interactions, integrin-mediated signalling etc. Implantation of chondrocytes encapsulated in scaffolds that mimic the micro-architecture of proteoglycan, is expected to enhance cartilage repair. With an aim to create a hydrogel having macromolecular structure that resembles the cartilage-specific ECM, we constructed a hierarchal structure that mimic the PG. The bottle brush structure of the aggrecan was obtained using chondroitin sulphate and carboxymethyl cellulose which served as GAG and core protein mimic respectively. A proteoglycan-like structure was obtained by cross-linking it with modified chitosan that served as a HA substitute. The physico-chemical characteristics of the above cross-linked injectable hydrogel supported long term human articular chondrocyte subsistence and excellent post-injection viability. The chondrocytes encapsulated in the PMH expressed significant levels of articular cartilage specific markers like collagen II, aggrecan, GAGs etc., indicating the ability of the hydrogel to support chondrocyte differentiation. The biocompatibility and biodegradability of the hydrogels was confirmed using suitable in vivo studies. The results revealed that the PG-mimetic hydrogel could serve as a promising scaffold for chondrocyte implantation.

Identification of novel ADAMTS1, ADAMTS4 and ADAMTS5 cleavage sites in versican using a label-free quantitative proteomics approach

The chondroitin sulfate proteoglycan versican is important for embryonic development and several human disorders. The versican V1 splice isoform is widely expressed and cleaved by ADAMTS proteases at a well-characterized site, Glu441-Ala442. Since ADAMTS proteases cleave the homologous proteoglycan aggrecan at multiple sites, we hypothesized that additional cleavage sites existed within versican. We report a quantitative label-free approach that ranks abundance of liquid chromatography-tandem mass spectrometry (LC-MS/MS)-identified semi-tryptic peptides after versican digestion by ADAMTS1, ADAMTS4 and ADAMTS5 to identify site-specific cleavages. Recombinant purified versican V1 constructs were digested with the recombinant full-length proteases, using catalytically inactive mutant proteases in control digests. Semi-tryptic peptide abundance ratios determined by LC-MS/MS in ADAMTS:control digests were compared to the mean of all identified peptides to obtain a z-score by which outlier peptides were ranked, using semi-tryptic peptides identifying Glu441 -Ala442 cleavage as the benchmark. Tryptic peptides with higher abundance in control digests supported cleavage site identification. We identified several novel cleavage sites supporting the ADAMTS1/4/5 cleavage site preference for a P1-Glu residue in proteoglycan substrates. Digestion of proteins in vitro and application of this z-score approach is potentially widely applicable for mapping protease cleavage sites using label-free proteomics. SIGNIFICANCE: Versican abundance and turnover are relevant to the pathogenesis of several human disorders. Versican is cleaved by A Disintegrin-like And Metalloprotease with Thrombospondin type 1 motifs (ADAMTS) family members at Glu441-Ala442, generating a bioactive proteoform called versikine, but additional cleavage sites and the site-specificity of individual ADAMTS proteases is unexplored. Here, we used a label-free proteomics strategy to identify versican cleavage sites for 3 ADAMTS proteases, applying a novel z-score-based statistical approach to compare the protease digests of versican to controls (digests with inactive protease) using the known protease cleavage site as a benchmark. We identified 21 novel cleavage sites that had a comparable z-score to the benchmark. Given the functional significance of versikine, they represent potentially significant cleavages and helped to refine a substrate site preference for each protease.The z-score approach is potentially widely applicable for discovery of site-specific cleavages within an purified protein or small ensemble of proteins using any protease.

Loss of Hs3st3a1 or Hs3st3b1 enzymes alters heparan sulfate to reduce epithelial morphogenesis and adult salivary gland function

Heparan sulfate 3-O-sulfotransferases generate highly sulfated but rare 3-O-sulfated heparan sulfate (HS) epitopes on cell surfaces and in the extracellular matrix. Previous ex vivo experiments suggested functional redundancy exists among the family of seven enzymes but that Hs3st3a1 and Hs3st3b1 sulfated HS increases epithelial FGFR signaling and morphogenesis. Single-cell RNAseq analysis of control SMGs identifies increased expression of Hs3st3a1 and Hs3st3b1 in endbud and myoepithelial cells, both of which are progenitor cells during development and regeneration. To analyze their in vivo functions, we generated both Hs3st3a1^-/- and Hs3st3b1^-/- single knockout mice, which are viable and fertile. Salivary glands from both mice have impaired fetal epithelial morphogenesis when cultured with FGF10. Hs3st3b1^-/- mice have reduced intact SMG branching morphogenesis and reduced 3-O-sulfated HS in the basement membrane. Analysis of HS biosynthetic enzyme transcription highlighted some compensatory changes in sulfotransferases expression early in development. The overall glycosaminoglycan composition of adult control and KO mice were similar, although HS disaccharide analysis showed increased N- and non-sulfated disaccharides in Hs3st3a1^-/- HS. Analysis of adult KO gland function revealed normal secretory innervation, but without stimulation there was an increase in frequency of drinking behavior in both KO mice, suggesting basal salivary hypofunction, possibly due to myoepithelial dysfunction. Understanding how 3-O-sulfation regulates myoepithelial progenitor function will be important to manipulate HS-binding growth factors to enhance tissue function and regeneration.

Role of HSPGs in Systemic Bacterial Infections

Heparan sulfate proteoglycans (HSPGs) are at the forefront of host-microbe interactions. Cell surface HSPGs are thought to promote infection as attachment and internalization receptors for many bacterial pathogens and as soluble inhibitors of host immunity when released from the cell surface by ectodomain shedding. However, the importance of HSPG-pathogen interactions in vivo has yet to be clearly established. Here we describe several representative methods to study the role of HSPGs in systemic bacterial infections, such as bacteremia and sepsis. The overall experimental strategy is to use mouse models to establish the physiological significance of HSPGs, to determine the identity of HSPGs that specifically promote infection, and to define key structural features of HSPGs that enhance bacterial virulence in systemic infections.

Production and HPLC-Based Disaccharide Analysis of Xyloside-Primed Glycosaminoglycans

Although glycosaminoglycans (GAGs) are known to be involved in a variety of physiological and pathological processes, knowledge about their expression by cells or tissues, the GAGome, is limited. Xylosides can be used to induce the formation of GAGs without the presence of a proteoglycan core protein. The administration of xylosides to living cells tends to result in a considerable amplification in GAG production, and the xylosides can, therefore, be used as analytical tools to study the GAG produced by a certain cell type. One of the most common ways to analyze the GAGs structurally is by disaccharide analysis, which involves depolymerization of the GAGs into disaccharides, fluorescent labeling of the disaccharides with 2-aminoacridone, and quantification using high-pressure liquid chromatography (HPLC). Here, we describe the procedure of producing xyloside-primed GAGs and how to study them structurally by disaccharide analysis.

Identification of Cell Autonomous and Non-Cell Autonomous Functions of Heparan Sulfate Glycosaminoglycan Chains by Creating Chimeric Mouse Embryos

Cell surface-tethered heparan sulfate glycosaminoglycan chains primarily function in a cell autonomous manner, while extracellular matrix-associated heparan sulfate glycosaminoglycan chains function in a non-cell autonomous manner. In addition, the cleaved forms of cell surface-tethered heparan sulfate chains enzymatically released by proteases and heparanases, called shedding, can contribute to non-cell autonomous mechanisms. The movement of heparan sulfate chains to surrounding cells mediated by transcytosis or filopodia also involves another non-cell autonomous mechanism. To determine cell autonomous or non-cell autonomous roles of heparan sulfate glycosaminoglycan chains during early embryogenesis, direct conclusions can be drawn by analyzing chimeric embryos which are composed of wild-type and heparan sulfate glycosaminoglycan chain-deficient cells. Here, we describe methods of production of these chimeric embryos and analysis of their cellular phenotypes with immunohistochemistry at a single-cell level.

Functional and structural properties of human patellar articular cartilage in osteoarthritis

Changes in the fibril-reinforced poroelastic (FRPE) mechanical material parameters of human patellar cartilage at different stages of osteoarthritis (OA) are not known. Further, the patellofemoral joint loading is thought to include more sliding and shear compared to other knee joint locations, thus, the relations between structural and functional changes may differ in OA. Thus, our aim was to determine the patellar cartilage FRPE properties followed by associating them with the structure and composition. Osteochondral plugs (n = 14) were harvested from the patellae of six cadavers. Then, the FRPE material properties were determined, and those properties were associated with proteoglycan content, collagen fibril orientation angle, optical retardation (fibril parallelism), and the state of OA of the samples. The initial fibril network modulus and permeability strain-dependency factor were 72% and 63% smaller in advanced OA samples when compared to early OA samples. Further, we observed a negative association between the initial fibril network modulus and optical retardation (r = -0.537, p < 0.05). We also observed positive associations between 1) the initial permeability and optical retardation (r = 0.547, p < 0.05), and 2) the initial fibril network modulus and optical density (r = 0.670, p < 0.01).These results suggest that the reduced pretension of the collagen fibrils, as shown by the reduced initial fibril network modulus, is linked with the loss of proteoglycans and cartilage swelling in human patellofemoral OA. The characterization of these changes is important to improve the representativeness of knee joint models in tissue and cell scale.

Differentiated activities of decorin and biglycan in the progression of post-traumatic osteoarthritis

OBJECTIVE

To delineate the activities of decorin and biglycan in the progression of post-traumatic osteoarthritis (PTOA).

DESIGN

Three-month-old inducible biglycan (BgniKO) and decorin/biglycan compound (Dcn/BgniKO) knockout mice were subjected to the destabilization of the medial meniscus (DMM) surgery to induce PTOA. The OA phenotype was evaluated by assessing joint structure and sulfated glycosaminoglycan (sGAG) staining via histology, surface collagen fibril nanostructure and calcium content via scanning electron microscopy, tissue modulus via atomic force microscopy-nanoindentation, as well as subchondral bone structure and meniscus ossification via micro-computed tomography. Outcomes were compared with previous findings in the inducible decorin (DcniKO) knockout mice.

RESULTS

In the DMM model, BgniKO mice developed similar degree of OA as the control (0.44 [-0.18 1.05] difference in modified Mankin score), different from the more severe OA phenotype observed in DcniKO mice (1.38 [0.91 1.85] difference). Dcn/BgniKO mice exhibited similar histological OA phenotype as DcniKO mice (1.51 [0.97 2.04] difference vs control), including aggravated loss of sGAGs, salient surface fibrillation and formation of osteophyte. Meanwhile, Dcn/BgniKO mice showed further cartilage thinning than DcniKO mice, resulting in the exposure of underlying calcified tissues and aberrantly high surface modulus. BgniKO and Dcn/BgniKO mice developed altered subchondral trabecular bone structure in both Sham and DMM groups, while DcniKO and control mice did not.

CONCLUSION

In PTOA, decorin plays a more crucial role than biglycan in regulating cartilage degeneration, while biglycan is more important in regulating subchondral bone structure. The two have distinct activities and modest synergy in the pathogenesis of PTOA.

Proteoglycans and their functions in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is a highly malignant disease that has a poor prognosis. Its high lethality is mainly due to the lack of symptoms at early stages, which culminates in diagnosis at a late stage when the tumor has already metastasized. Unfortunately, the common cancer biomarkers have low sensitivity and specificity in esophageal cancer. Therefore, a better understanding of the molecular mechanisms underlying ESCC progression is needed to identify novel diagnostic markers and therapeutic targets for intervention. The invasion of cancer cells into the surrounding tissue is a crucial step for metastasis. During metastasis, tumor cells can interact with extracellular components and secrete proteolytic enzymes to remodel the surrounding tumor microenvironment. Proteoglycans are one of the major components of extracellular matrix. They are involved in multiple processes of cancer cell invasion and metastasis by interacting with soluble bioactive molecules, surrounding matrix, cell surface receptors, and enzymes. Apart from having diverse functions in tumor cells and their surrounding microenvironment, proteoglycans also have diagnostic and prognostic significance in cancer patients. However, the functional significance and underlying mechanisms of proteoglycans in ESCC are not well understood. This review summarizes the proteoglycans that have been studied in ESCC in order to provide a comprehensive view of the role of proteoglycans in the progression of this cancer type. A long term goal would be to exploit these molecules to provide new strategies for therapeutic intervention.

Autophagy: Instructions from the extracellular matrix

In recent years, extensive research has uncovered crucial regulatory roles for the extracellular matrix (ECM) in regulating autophagy. Autophagy is a ubiquitous and highly conserved catabolic process that allows the selective removal and recycling of cytosolic components via lysosomal or vacuolar degradation. Due to its pivotal role in cellular homeostasis, the impairment of autophagy is involved in the pathophysiology of numerous diseases, comprising infectious diseases, immune and neurodegenerative disorders, renal and hepatic diseases, intervertebral and cartilage disorders, as well as fibrosis and cancer. Several ECM-derived proteoglycans and proteins, including decorin, biglycan, endorepellin, endostatin, collagen VI, and plasminogen kringle 5, have been identified as strong inducers of autophagy. In contrast, laminin α2, perlecan, and lumican exert opposite function by suppressing autophagy. Importantly, by direct interaction with various receptors, which interplay with their co-receptors and adhesion molecules, the ECM is able to direct autophagy in a molecular and cell context-specific manner. Thus, vast pharmacological potential resides in translating this knowledge into the development of ECM-derived therapeutics selectively regulating autophagy.

Bone morphogenic protein-2 signaling in human disc degeneration and correlation to the Pfirrmann MRI grading system

BACKGROUND CONTEXT

Back and neck pain secondary to disc degeneration is a major public health burden. There is a need for therapeutic treatments to restore intervertebral disc (IVD) composition and function.

PURPOSE

To quantify ALK3, BMP-2, pSMAD1/5/8 and MMP-13 expression in IVD specimens collected from patients undergoing surgery for disc degeneration, to correlate ALK3, BMP-2, pSMAD1/5/8 and MMP-13 expression in IVD specimens to the 5-level Pfirrmann MRI grading system, and to compare ALK3, BMP-2, pSMAD1/5/8 and MMP-13 expression between cervical and lumbar degenerative disc specimens.

STUDY DESIGN

An immunohistochemical study assessing ALK3, BMP-2, pSMAD1/5/8, and MMP-13 expression levels in human control and degenerative IVD specimens.

METHODS

Human IVD specimens were collected from surgical patients who underwent discectomy and interbody fusion at our institution between 1/2015 and 8/2017. Each patient underwent MRI prior to surgery. The degree of disc degeneration was measured according to the 5-level Pfirrmann MRI grading system. Patients were categorized into either the 1) control group (Pfirrmann grades I-II) or 2) degenerative group (Pfirrmann grades III-V). Histology slides of the collected IVD specimens were prepared and immunohistochemical staining was performed to assess ALK3, BMP-2, pSMAD1/5/8, and MMP-13 expression levels in the control and degenerative specimens. Expression levels were also correlated to the Pfirrmann criteria. Lastly, the degenerative specimens were stratified according to their vertebral level and expression levels between the degenerative lumbar and cervical discs were compared.

RESULTS

Fifty-two patients were enrolled; however, 2 control and 2 degenerative patients were excluded due to incomplete data sets. Of the remaining 48 patients, there were 12 control and 36 degenerative specimens. Degenerative specimens had increased expression levels of BMP-2 (p=.0006) and pSMAD1/5/8 (p<.0001). Pfirrmann grade 3 (p=.0365) and grade 4 (p=.0008) discs had significantly higher BMP-2 expression as compared to grade 2 discs. Pfirrmann grade 4 discs had higher pSMAD1/5/8 expression as compared to grade 2 discs (p<.0001). There were no differences in ALK3 or MMP-13 expression between the control and degenerative discs (p>.05). Stratifying the degenerative specimens according to their vertebral level showed no significant differences in expression levels between the lumbar and cervical discs (p>.05).

CONCLUSIONS

BMP-2 and pSMAD1/5/8 signaling activity was significantly upregulated in the human degenerative specimens, while ALK3 and MMP-13 expression were not significantly changed. The expression levels of BMP-2 and pSMAD1/5/8 correlate positively with the degree of disc degeneration measured according to the Pfirrmann MRI grading system.

CLINICAL SIGNIFICANCE

BMP-SMAD signaling represents a promising therapeutic target to restore IVD composition and function in the setting of disc degeneration.

Solanum xanthocarpum fruit extract promotes chondrocyte proliferation in vitro and protects cartilage damage in collagenase induced osteoarthritic rats (article reference number: JEP 114028)

ETHNOPHARMACOLOGICAL RELEVANCE

Osteoarthritis (OA), a degenerative joint disease, is characterized by cartilage erosion and matrix degradation. Solanum xanthocarpum Schrad. & Wendl. fruits (SXF) and leaves have long been used as folk remedy in the treatment of pain in rheumatism.

AIM OF THE STUDY

This study was aimed to investigate the phytochemical components and protective benefits of SXF on in vitro chondrocytes proliferation, and in vivo suppression of collagenase-induced OA.

MATERIALS AND METHODS

Phytochemical components in ethanolic SXF extract were evaluated using gas chromatography-mass spectrometry (GC-MS). Effect of SXF on in vitro cell proliferation of primary chondrocytes was determined by cell proliferation assay and cell cycle analysis by flow cytometry. OA was induced in the right knees of rats through intra-articular injection of collagenase type-II. To evaluate in vivo preventive function of SXF, body weight, blood ALP, histopathological changes in the knee joint, proteoglycan, and collagen content were determined. The mRNA expression of COL-2, MMP-3 and COX-2 genes through qRT-PCR was studied. Antioxidant activities, total phenolics and flavonoid contents of SXF were also examined.

RESULTS

GC-MS analysis revealed that SXF constitutes 28 phytochemicals including flavonoids (3-methoxy apigenin, quercetin, luteolin), tannin (quinic acid), terpenes (oleanolic acid, lupeol, psi.psi carotene), phytosterols (campesterol, stigmasterol, β-sitosterol), and ascorbic acid. In vitro studies demonstrated that SXF enhanced the cell proliferation in a dose-dependent manner and has no cytotoxic effect on primary chondrocytes. In vivo study suggests that SXF protects the cartilage destruction induced by collagenase. The histological study revealed that SXF restored the synthesis of collagen and proteoglycan, vital factors for cartilage restoration, and reduced the arthritic score. An up-regulation in COL-2 expression and suppression of MMP-3 and COX-2 were detected by qRT-PCR analysis. Thus, in vivo study suggests the protective effects of SXF on cartilage destruction induced by collagenase.

CONCLUSIONS

Our results imply that SXF benefits and ameliorates OA by enhancing the chondrocytes proliferation and preventing the articular cartilage damage through the restoration of their structural molecules, arthritic score reduction, suppression of MMP-3 and COX-2 expression level and up regulation of COL-2 genes expression. These results suggest that SXF could be a promising alternative treatment candidate for osteoarthritis.

A new mouse mutant with cleavage-resistant versican and isoform-specific versican mutants demonstrate that proteolysis at the Glu441-Ala442 peptide bond in the V1 isoform is essential for interdigital web regression

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• A novel Vcan mouse allele, Vcan^AA, has ADAMTS protease-resistant versican.

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• Vcan^AA/AA mice are viable and develop soft tissue-syndactyly (STS)

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• Vcan^AA/AA STS is rendered more severe in combination with Adamts20^Bt/Bt.

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• Mice lacking the versican GAGβ domain, but not the GAGα domain, also have STS.

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• The versican GAGβ proteolytic fragment versikine is necessary for web regression.

Two inherent challenges in the mechanistic interpretation of protease-deficient phenotypes are defining the specific substrate cleavages whose reduction generates the phenotypes and determining whether the phenotypes result from loss of substrate function, substrate accumulation, or loss of a function(s) embodied in the substrate fragments. Hence, recapitulation of a protease-deficient phenotype by a cleavage-resistant substrate would stringently validate the importance of a proteolytic event and clarify the underlying mechanisms. Versican is a large proteoglycan required for development of the circulatory system and proper limb development, and is cleaved by ADAMTS proteases at the Glu⁴⁴¹-Ala⁴⁴² peptide bond located in its alternatively spliced GAGβ domain. Specific ADAMTS protease mutants have impaired interdigit web regression leading to soft tissue syndactyly that is associated with reduced versican proteolysis. Versikine, the N-terminal proteolytic fragment generated by this cleavage, restores interdigit apoptosis in ADAMTS mutant webs. Here, we report a new mouse transgene, Vcan^AA, with validated mutations in the GAGβ domain that specifically abolish this proteolytic event. Vcan^AA/AA mice have partially penetrant hindlimb soft tissue syndactyly. However, Adamts20 inactivation in Vcan^AA/AA mice leads to fully penetrant, more severe syndactyly affecting all limbs, suggesting that ADAMTS20 cleavage of versican at other sites or of other substrates is an additional requirement for web regression. Indeed, immunostaining with a neoepitope antibody against a cleavage site in the versican GAGα domain demonstrated reduced staining in the absence of ADAMTS20. Significantly, mice with deletion of Vcan exon 8, encoding the GAGβ domain, consistently developed soft tissue syndactyly, whereas mice unable to include exon 7, encoding the GAGα domain in Vcan transcripts, consistently had fully separated digits. These findings suggest that versican is cleaved within each GAG-bearing domain during web regression, and affirms that proteolysis in the GAGβ domain, via generation of versikine, has an essential role in interdigital web regression.