Reduced sulfation of chondroitin sulfate but not heparan sulfate in kidneys of diabetic db/db mice

Characterizing the human intestinal chondroitin sulfate glycosaminoglycan sulfation signature in inflammatory bowel disease

The intestinal extracellular matrix (ECM) helps maintain appropriate tissue barrier function and regulate host-microbial interactions. Chondroitin sulfate- and dermatan sulfate-glycosaminoglycans (CS/DS-GAGs) are integral components of the intestinal ECM, and alterations in CS/DS-GAGs have been shown to significantly influence biological functions. Although pathologic ECM remodeling is implicated in inflammatory bowel disease (IBD), it is unknown whether changes in the intestinal CS/DS-GAG composition are also linked to IBD in humans. Our aim was to characterize changes in the intestinal ECM CS/DS-GAG composition in intestinal biopsy samples from patients with IBD using mass spectrometry. We characterized intestinal CS/DS-GAGs in 69 pediatric and young adult patients (n = 13 control, n = 32 active IBD, n = 24 IBD in remission) and 6 adult patients. Here, we report that patients with active IBD exhibit a significant decrease in the relative abundance of CS/DS isomers associated with matrix stability (CS-A and DS) compared to controls, while isomers implicated in matrix instability and inflammation (CS-C and CS-E) were significantly increased. This imbalance of intestinal CS/DS isomers was restored among patients in clinical remission. Moreover, the abundance of pro-stabilizing CS/DS isomers negatively correlated with clinical disease activity scores, whereas both pro-inflammatory CS-C and CS-E content positively correlated with disease activity scores. Thus, pediatric patients with active IBD exhibited increased pro-inflammatory and decreased pro-stabilizing CS/DS isomer composition, and future studies are needed to determine whether changes in the CS/DS-GAG composition play a pathogenic role in IBD.

CHST11-modified chondroitin 4-sulfate as a potential therapeutic target for glioblastoma

Aberrant chondroitin sulfate (CS) accumulation in glioblastoma (GBM) tissue has been documented, but the role of excessive CS in GBM progression and whether it can be a druggable target are largely unknown. The aim of this study is to clarify the biological functions of CHST11 in GBM cells, and evaluate therapeutic effects of blocking CHST11-derived chondroitin 4-sulfate (C4S). We investigated the expression of CHST11 in glioma tissue by immunohistochemistry, and analyzed CHST11 associated genes using public RNA sequencing datasets. The effects of CHST11 on aggressive cell behaviors have been studied in vitro and in vivo. We demonstrated that CHST11 is frequently overexpressed in GBM tissue, promoting GBM cell mobility and modulating C4S on GBM cells. We further discovered that CSPG4 is positively correlated with CHST11, and CSPG4 involved in CHST11-mediated cell invasiveness. In addition, GBM patients with high expression of CHST11 and CSPG4 have a significantly shorter survival time. We examined the effects of treating C4S-specific binding peptide (C4Sp) as a therapeutic agent in vitro and in vivo. C4Sp treatment attenuated GBM cell invasiveness and, notably, improved survival rate of orthotopic glioma cell transplant mice. Our results propose a possible mechanism of CHST11 in regulating GBM malignancy and highlight a novel strategy for targeting aberrant chondroitin sulfate in GBM cells.

Endothelial glycocalyx in retina, hyperglycemia, and diabetic retinopathy

The endothelial glycocalyx (EG) is a meshlike network present on the apical surface of the endothelium. Membrane-bound proteoglycans, the major backbone molecules of the EG, consist of glycosaminoglycans attached to core proteins. In addition to maintaining the integrity of the endothelial barrier, the EG regulates inflammation and perfusion and acts as a mechanosensor. The loss of the EG can cause endothelial dysfunction and drive the progression of vascular diseases including diabetic retinopathy. Therefore, the EG presents a novel therapeutic target for treatment of vascular complications. In this review article, we provide an overview of the structure and function of the EG in the retina. Our particular focus is on hyperglycemia-induced perturbations in the glycocalyx structure in the retina, potential underlying mechanisms, and clinical trials studying protective treatments against degradation of the EG.

The Alterations and Roles of Glycosaminoglycans in Human Diseases

Glycosaminoglycans (GAGs) are a heterogeneous family of linear polysaccharides which are composed of a repeating disaccharide unit. They are also linked to core proteins to form proteoglycans (PGs). GAGs/PGs are major components of the cell surface and the extracellular matrix (ECM), and they display critical roles in development, normal function, and damage response in the body. Some properties (such as expression quantity, molecular weight, and sulfation pattern) of GAGs may be altered under pathological conditions. Due to the close connection between these properties and the function of GAGs/PGs, the alterations are often associated with enormous changes in the physiological/pathological status of cells and organs. Therefore, these GAGs/PGs may serve as marker molecules of disease. This review aimed to investigate the structural alterations and roles of GAGs/PGs in a range of diseases, such as atherosclerosis, cancer, diabetes, neurodegenerative disease, and virus infection. It is hoped to provide a reference for disease diagnosis, monitoring, prognosis, and drug development.

Effect of high glucose on glycosaminoglycans in cultured retinal endothelial cells and rat retina

INTRODUCTION

The endothelial glycocalyx regulates vascular permeability, inflammation, and coagulation, and acts as a mechanosensor. The loss of glycocalyx can cause endothelial injury and contribute to several microvascular complications and, therefore, may promote diabetic retinopathy. Studies have shown a partial loss of retinal glycocalyx in diabetes, but with few molecular details of the changes in glycosaminoglycan (GAG) composition. Therefore, the purpose of our study was to investigate the effect of hyperglycemia on GAGs of the retinal endothelial glycocalyx.

METHODS

GAGs were isolated from rat retinal microvascular endothelial cells (RRMECs), media, and retinas, followed by liquid chromatography-mass spectrometry assays. Quantitative real-time polymerase chain reaction was used to study mRNA transcripts of the enzymes involved in GAG biosynthesis.

RESULTS AND CONCLUSIONS

Hyperglycemia significantly increased the shedding of heparan sulfate (HS), chondroitin sulfate (CS), and hyaluronic acid (HA). There were no changes to the levels of HS in RRMEC monolayers grown in high-glucose media, but the levels of CS and HA decreased dramatically. Similarly, while HA decreased in the retinas of diabetic rats, the total GAG and CS levels increased. Hyperglycemia in RRMECs caused a significant increase in the mRNA levels of the enzymes involved in GAG biosynthesis (including EXTL-1,2,3, EXT-1,2, ChSY-1,3, and HAS-2,3), with these increases potentially being compensatory responses to overall glycocalyx loss. Both RRMECs and retinas of diabetic rats exhibited glucose-induced alterations in the disaccharide compositions and sulfation of HS and CS, with the changes in sulfation including N,6-O-sulfation on HS and 4-O-sulfation on CS.

Pathogenesis of COVID-19 described through the lens of an undersulfated and degraded epithelial and endothelial glycocalyx

The glycocalyx surrounds every eukaryotic cell and is a complex mesh of proteins and carbohydrates. It consists of proteoglycans with glycosaminoglycan side chains, which are highly sulfated under normal physiological conditions. The degree of sulfation and the position of the sulfate groups mainly determine biological function. The intact highly sulfated glycocalyx of the epithelium may repel severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) through electrostatic forces. However, if the glycocalyx is undersulfated and 3-O-sulfotransferase 3B (3OST-3B) is overexpressed, as is the case during chronic inflammatory conditions, SARS-CoV-2 entry may be facilitated by the glycocalyx. The degree of sulfation and position of the sulfate groups will also affect functions such as immune modulation, the inflammatory response, vascular permeability and tone, coagulation, mediation of sheer stress, and protection against oxidative stress. The rate-limiting factor to sulfation is the availability of inorganic sulfate. Various genetic and epigenetic factors will affect sulfur metabolism and inorganic sulfate availability, such as various dietary factors, and exposure to drugs, environmental toxins, and biotoxins, which will deplete inorganic sulfate. The role that undersulfation plays in the various comorbid conditions that predispose to coronavirus disease 2019 (COVID-19), is also considered. The undersulfated glycocalyx may not only increase susceptibility to SARS-CoV-2 infection, but would also result in a hyperinflammatory response, vascular permeability, and shedding of the glycocalyx components, giving rise to a procoagulant and antifibrinolytic state and eventual multiple organ failure. These symptoms relate to a diagnosis of systemic septic shock seen in almost all COVID-19 deaths. The focus of prevention and treatment protocols proposed is the preservation of epithelial and endothelial glycocalyx integrity.

AMPK differentially alters sulphated glycosaminoglycans under normal and high glucose milieu in proximal tubular cells

Glycosaminoglycans (GAGs) and AMP-activated protein kinase (AMPK) are two critical molecular players involved in cellular homeostasis. Both of them are altered due to hyperglycaemia in the kidney, leading to the pathogenesis of diabetic nephropathy. Here, we have looked into the effect of AMPK modulation on sulphated GAG (sGAG) levels of tubular cells of proximal and distal origin to understand the mechanism of hyperglycaemia-mediated pathogenesis of the diabetic nephropathy. In MDCK cells (distal tubular cell) and NRK-52E (proximal tubular cell), AMPK inhibition resulted in increased sGAG levels under normal glucose conditions characteristically of heparan sulphate class, whereas AMPK activation did not have any effect. High glucose (HG) condition did not alter sGAG levels in MDCK cell despite a decrease in AMPK phosphorylation. Subjecting NRK-52E cells to HG milieu significantly decreased sGAG levels more so of chondroitin/dermatan sulphate, which is significantly prevented when HG is co-treated with AMPK activator. Interestingly, knockdown of AMPK by AMPKα1/α2 siRNA showed increased sGAG levels in NRK-52E. Our results suggest that changes in sGAG level, in particular, as a result of AMPK modulation is differentially regulated and is dependent on cell type as well as its physiological status. Furthermore, activation of AMPK is beneficial in preventing the HG-mediated decrease in sGAGs in proximal tubular cells.

High-Throughput Liquid Chromatography-Tandem Mass Spectrometry Quantification of Glycosaminoglycans as Biomarkers of Mucopolysaccharidosis II

We recently developed a blood–brain barrier (BBB)-penetrating enzyme transport vehicle (ETV) fused to the lysosomal enzyme iduronate 2-sulfatase (ETV:IDS) and demonstrated its ability to reduce glycosaminoglycan (GAG) accumulation in the brains of a mouse model of mucopolysaccharidosis (MPS) II. To accurately quantify GAGs, we developed a plate-based high-throughput enzymatic digestion assay coupled with liquid chromatography–tandem mass spectrometry (LC-MS/MS) to simultaneously measure heparan sulfate and dermatan sulfate derived disaccharides in tissue, cerebrospinal fluid (CSF) and individual cell populations isolated from mouse brain. The method offers ultra-high sensitivity enabling quantitation of specific GAG species in as low as 100,000 isolated neurons and a low volume of CSF. With an LOD at 3 ng/mL and LLOQs at 5–10 ng/mL, this method is at least five times more sensitive than previously reported approaches. Our analysis demonstrated that the accumulation of CSF and brain GAGs are in good correlation, supporting the potential use of CSF GAGs as a surrogate biomarker for brain GAGs. The bioanalytical method was qualified through the generation of standard curves in matrix for preclinical studies of CSF, demonstrating the feasibility of this assay for evaluating therapeutic effects of ETV:IDS in future studies and applications in a wide variety of MPS disorders.

Retinal Physiology and Circulation: Effect of Diabetes

In this article, we present a discussion of diabetes and its complications, including the macrovascular and microvascular effects, with the latter of consequence to the retina. We will discuss the anatomy and physiology of the retina, including aspects of metabolism and mechanisms of oxygenation, with the latter accomplished via a combination of the retinal and choroidal blood circulations. Both of these vasculatures are altered in diabetes, with the retinal circulation intimately involved in the pathology of diabetic retinopathy. The later stages of diabetic retinopathy involve poorly controlled angiogenesis that is of great concern, but in our discussion, we will focus more on several alterations in the retinal circulation occurring earlier in the progression of disease, including reductions in blood flow and a possible redistribution of perfusion that may leave some areas of the retina ischemic and hypoxic. Finally, we include in this article a more recent area of investigation regarding the diabetic retinal vasculature, that is, the alterations to the endothelial surface layer that normally plays a vital role in maintaining physiological functions. © 2020 American Physiological Society. Compr Physiol 10:933-974, 2020.

Polyunsaturated fatty acid deficiency affects sulfatides and other sulfated glycans in lysosomes through autophagy-mediated degradation

Metabolic changes in sulfatides and other sulfated glycans have been related to various diseases, including Alzheimer's disease (AD). However, the importance of polyunsaturated fatty acids (PUFA) in sulfated lysosomal substrate metabolism and its related disorders is currently unknown. We investigated the effects of deficiency or supplementation of PUFA on the metabolism of sulfatides and sulfated glycosaminoglycans (sGAGs) in sulfatide-rich organs (brain and kidney) of mice. A PUFA-deficient diet for over 5 weeks significantly reduced the sulfatide expression by increasing the sulfatide degradative enzymes arylsulfatase A and galactosylceramidase in brain and kidney. This sulfatide degradation was clearly associated with the activation of autophagy and lysosomal hyperfunction, the former of which was induced by suppression of the Erk/mTOR pathway. A PUFA-deficient diet also activated the degradation of sGAGs in the brain and kidney and that of amyloid precursor proteins in the brain, indicating an involvement in general lysosomal function and the early developmental process of AD. PUFA supplementation prevented all of the above abnormalities. Taken together, a PUFA deficiency might lead to sulfatide and sGAG degradation associated with autophagy activation and general lysosomal hyperfunction and play a role in many types of disease development, suggesting a possible benefit of prophylactic PUFA supplementation.

Review of Alterations in Perlecan-Associated Vascular Risk Factors in Dementia

Perlecan is a heparan sulfate proteoglycan protein in the extracellular matrix that structurally and biochemically supports the cerebrovasculature by dynamically responding to changes in cerebral blood flow. These changes in perlecan expression seem to be contradictory, ranging from neuroprotective and angiogenic to thrombotic and linked to lipid retention. This review investigates perlecan's influence on risk factors such as diabetes, hypertension, and amyloid that effect Vascular contributions to Cognitive Impairment and Dementia (VCID). VCID, a comorbidity with diverse etiology in sporadic Alzheimer's disease (AD), is thought to be a major factor that drives the overall clinical burden of dementia. Accordingly, changes in perlecan expression and distribution in response to VCID appears to be injury, risk factor, location, sex, age, and perlecan domain dependent. While great effort has been made to understand the role of perlecan in VCID, additional studies are needed to increase our understanding of perlecan's role in health and in cerebrovascular disease.

Differential Expression of Specific Dermatan Sulfate Domains in Renal Pathology

Dermatan sulfate (DS), also known as chondroitin sulfate (CS)-B, is a member of the linear polysaccharides called glycosaminoglycans (GAGs). The expression of CS/DS and DS proteoglycans is increased in several fibrotic renal diseases, including interstitial fibrosis, diabetic nephropathy, mesangial sclerosis and nephrosclerosis. Little, however, is known about structural alterations in DS in renal diseases. The aim of this study was to evaluate the renal expression of two different DS domains in renal transplant rejection and glomerular pathologies. DS expression was evaluated in normal renal tissue and in kidney biopsies obtained from patients with acute interstitial or vascular renal allograft rejection, patients with interstitial fibrosis and tubular atrophy (IF/TA), and from patients with focal segmental glomerulosclerosis (FSGS), membranous glomerulopathy (MGP) or systemic lupus erythematosus (SLE), using our unique specific anti-DS antibodies LKN1 and GD3A12. Expression of the 4/2,4-di-O-sulfated DS domain recognized by antibody LKN1 was decreased in the interstitium of transplant kidneys with IF/TA, which was accompanied by an increased expression of type I collagen, decorin and transforming growth factor beta (TGF-β), while its expression was increased in the interstitium in FSGS, MGP and SLE. Importantly, all patients showed glomerular LKN1 staining in contrast to the controls. Expression of the IdoA-Gal-NAc4SDS domain recognized by GD3A12 was similar in controls and patients. Our data suggest a role for the DS domain recognized by antibody LKN1 in renal diseases with early fibrosis. Further research is required to delineate the exact role of different DS domains in renal fibrosis.

Effects of restoring normoglycemia in type 1 diabetes on inflammatory profile and renal extracellular matrix structure after simultaneous pancreas and kidney transplantation

AIMS

Patients with type 1 diabetes and end-stage renal disease with simultaneous pancreas and kidney (SPK) or kidney transplants alone (KA) were recruited 9-12 years post transplantation. We investigated differences between these groups with regard to inflammatory parameters and long-term structural changes in kidneys.

METHODS

Blood samples were analyzed by ELISA and multiplex for chemokines, cytokines, growth factors, cell adhesion molecules and matrix metalloproteinases. Kidney graft biopsies were analyzed by electron microscopy for glomerular basement membrane thickness. Heparan- and chondroitin sulfate disaccharide structures were determined by size exclusion chromatography mass-spectrometry.

RESULTS

The SPK and the KA group had average glycated hemoglobin A1c (HbA1c) of 5.8% (40 mmol/mol) and 8.6% (70 mmol/mol) respectively. SPK recipients also had 16.2% lower body mass index (BMI) and 46.4% lower triglyceride levels compared with KA recipients, compatible with an improved metabolic profile in the SPK group. Plasminogen activator inhibitor (PAI-1), C-reactive protein (CRP) and vascular endothelial growth factor (VEGF) were lower in the SPK group. In kidney graft biopsies of the KA-patients an 81.2% increase in average glomerular basement membrane thickness was observed, accompanied by alterations in heparan sulfate proteoglycan structure. In addition to a decrease in 6-O-sulfated disaccharides, an increase in non-N-sulfated disaccharides with a corresponding slight decrease in N-sulfation was found in kidney biopsies from hyperglycemic patients.

CONCLUSIONS

Patients with end stage renal disease subjected to KA transplantation showed impaired inflammatory profile, increased thickness of basement membranes and distinct changes in heparan sulfate structures compared with SPK recipients.

The protective role of fucosylated chondroitin sulfate, a distinct glycosaminoglycan, in a murine model of streptozotocin-induced diabetic nephropathy

BACKGROUND

Heparanase-1 activation, albuminuria, and a decrease in glomerular heparan sulfate (HS) have been described in diabetic nephropathy (DN). Glycosaminoglycan (GAG)-based drugs have been shown to have renoprotective effects in this setting, although recent trials have questioned their clinical effectiveness. Here, we describe the effects of fucosylated chondroitin sulfate (FCS), a novel GAG extracted from a marine echinoderm, in experimentally induced DN compared to a widely used GAG, enoxaparin (ENX).

METHODS

Diabetes mellitus (DM) was induced by streptozotocin in male Wistar rats divided into three groups: DM (without treatment), FCS (8 mg/kg), and ENX (4 mg/kg), administered subcutaneously. After 12 weeks, we measured blood glucose, blood pressure, albuminuria, and renal function. The kidneys were evaluated for mesangial expansion and collagen content. Immunohistochemical quantifications of macrophages, TGF-β, nestin and immunofluorescence analysis of heparanase-1 and glomerular basement membrane (GBM) HS content was also performed. Gene expression of proteoglycan core proteins and enzymes involved in GAG assembly/degradation were analyzed by TaqMan real-time PCR.

RESULTS

Treatment with GAGs prevented albuminuria and did not affect the glucose level or other functional aspects. The DM group exhibited increased mesangial matrix deposition and tubulointerstitial expansion, and prevention was observed in both GAG groups. TGF-β expression and macrophage infiltration were prevented by the GAG treatments, and podocyte damage was halted. The diabetic milieu resulted in the down-regulation of agrin, perlecan and collagen XVIII mRNAs, along with the expression of enzymes involved in GAG biosynthesis. Treatment with FCS and ENX positively modulated such changes. Heparanase-1 expression was significantly reduced after GAG treatment without affecting the GBM HS content, which was uniformly reduced in all of the diabetic animals.

CONCLUSIONS

Our results demonstrate that the administration of FCS prevented several pathological features of ND in rats. This finding should stimulate further research on GAG treatment for this complication of diabetes.

Assay for Glycosaminoglycans by Tandem Mass Spectrometry and its Applications

Glycosaminoglycans (GAGs) are distributed in the whole body and play a variety of important physiological roles associated with inflammation, growth, coagulation, fibrinolysis, lipolysis, and cell-matrix biology. Accumulation of undegraded GAGs in lysosomes gives rise to a distinct clinical syndrome, mucopolysaccharidoses. Measurement of each specific GAG in a variety of specimens is urgently required to understand GAG interaction with other molecules, physiological status of patients, and prognosis and pathogenesis of the disease. We established a highly sensitive and accurate tandem mass spectrometry (LC-MS/MS) method for measurements of disaccharides derived from four specific GAGs [dermatan sulfate (DS), heparan sulfate (HS), keratan sulfate (KS), and chondroitin sulfate (CS)]. Disaccharides were produced by specific enzyme digestion of each GAG, and quantified by negative ion mode of multiple reaction monitoring. Subclasses of HS and GAGs with identical molecular weights can be separated using a Hypercarbcolumn (2.0 mm×50 mm, 5 μm) with an aectonitrile gradient in ammonium acetate (pH 11.0). We also developed a GAG assay by RapidFire with tandem mass spectrometry (RF-MS/MS). The RF system consists of an integrated solid phase extraction robot that binds and de-salts samples from assay plates and directly injects them into a MS/MS detector, reducing sample processing time to ten seconds. RF-MS/MS consequently yields much faster throughput than conventional LC-MS/MS-based methods. However, the RF system does not have a chromatographic step, and therefore, cannot distinguish GAGs that have identical molecular weights. Both methods can be applied to analysis of dried blood spots, blood, and urine specimens. In this article, we compare the assay methods for GAGs and describe their potential applications.