Synthesis and fragmentation of hyaluronan in renal ischaemia

Differential expression analysis identifies a prognostically significant extracellular matrix-enriched gene signature in hyaluronan-positive clear cell renal cell carcinoma

Hyaluronan (HA) accumulation in clear cell renal cell carcinoma (ccRCC) is associated with poor prognosis; however, its biology and role in tumorigenesis are unknown. RNA sequencing of 48 HA-positive and 48 HA-negative formalin-fixed paraffin-embedded (FFPE) samples was performed to identify differentially expressed genes (DEG). The DEGs were subjected to pathway and gene enrichment analyses. The Cancer Genome Atlas Kidney Renal Clear Cell Carcinoma (TCGA-KIRC) data and DEGs were used for the cluster analysis. In total, 129 DEGs were identified. HA-positive tumors exhibited enhanced expression of genes related to extracellular matrix (ECM) organization and ECM receptor interaction pathways. Gene set enrichment analysis showed that epithelial-mesenchymal transition-associated genes were highly enriched in the HA-positive phenotype. A protein-protein interaction network was constructed, and 17 hub genes were discovered. Heatmap analysis of TCGA-KIRC data identified two prognostic clusters corresponding to HA-positive and HA-negative phenotypes. These clusters were used to verify the expression levels and conduct survival analysis of the hub genes, 11 of which were linked to poor prognosis. These findings enhance our understanding of hyaluronan in ccRCC.

Low-Molecular-Weight Hyaluronic Acid Contributes to Noise-Induced Cochlear Inflammation

INTRODUCTION

Our previous work indicated that the activation of the Toll-like receptor (TLR) 4 signaling pathway contributed to noise-induced cochlear inflammation. Previous studies have reported that low-molecular-weight hyaluronic acid (LMW-HA) accumulates during aseptic trauma and promotes inflammation by activating the TLR4 signaling pathway. We hypothesized that LMW-HA or enzymes synthesizing or degrading HA might be involved in noise-induced cochlear inflammation.

METHODS

The present study included two arms. The first arm was the noise exposure study, in which TLR4, proinflammatory cytokines, HA, hyaluronic acid synthases (HASs), and hyaluronidases (HYALs) in the cochlea as well as auditory brainstem response (ABR) thresholds were measured before and after noise exposure. The second arm was analysis of HA delivery-induced reactions, in which control solution, high-molecular-weight HA (HMW-HA), or LMW-HA was delivered into the cochlea by cochleostomy or intratympanic injection. Then, the ABR threshold and cochlear inflammation were measured.

RESULTS

After noise exposure, the expression of TLR4, proinflammatory cytokines, HAS1, and HAS3 in the cochlea significantly increased over the 3rd to 7th day post-noise exposure (PE3, PE7). The expression of HYAL2 and HYAL3 dramatically decreased immediately after noise exposure, gradually increased thereafter to levels significantly greater than the preexposure level on PE3, and then rapidly returned to the preexposure level on PE7. The expression of HA, HAS2, and HYAL1 in the cochlea remained unchanged after exposure. After cochleostomy or intratympanic injection, both the hearing threshold shifts and the expression of TLR4, TNF-α, and IL-1β in the cochleae of the LMW-HA group were obviously greater than those of the control group and HMW-HA group. The expression of proinflammatory cytokines in the LMW-HA and control groups on the 7th day (D7) after cochleostomy tended to increase compared to that on the 3rd day (D3), whereas levels in the HMW-HA group tended to decrease on D7 compared to D3.

CONCLUSION

HAS1, HAS3, HYAL2, and HYAL3 in the cochlea are involved in acoustic trauma-induced cochlear inflammation through the potential proinflammatory function of LMW-HA.

The role of hyaluronan in renal cell carcinoma

Renal cell carcinoma (RCC) is associated with high mortality rates worldwide and survival among RCC patients has not improved significantly in the past few years. A better understanding of the pathogenesis of RCC can enable the development of more effective therapeutic strategies against RCC. Hyaluronan (HA) is a glycosaminoglycan located in the extracellular matrix (ECM) that has several roles in biology, medicine, and physiological processes, such as tissue homeostasis and angiogenesis. Dysregulated HA and its receptors play important roles in fundamental cellular and molecular biology processes such as cell signaling, immune modulation, tumor progression and angiogenesis. There is emerging evidence that alterations in the production of HA regulate RCC development, thereby acting as important biomarkers as well as specific therapeutic targets. Therefore, targeting HA or combining it with other therapies are promising therapeutic strategies. In this Review, we summarize the available data on the role of abnormal regulation of HA and speculate on its potential as a therapeutic target against RCC.

Experimental Aristolochic Acid Nephropathy: A Relevant Model to Study AKI-to-CKD Transition

Aristolochic acid nephropathy (AAN) is a progressive tubulointerstitial nephritis caused by the intake of aristolochic acids (AA) contained in Chinese herbal remedies or contaminated food. AAN is characterized by tubular atrophy and interstitial fibrosis, characterizing advanced kidney disease. It is established that sustained or recurrent acute kidney injury (AKI) episodes contribute to the progression of CKD. Therefore, the study of underlying mechanisms of AA-induced nephrotoxicity could be useful in understanding the complex AKI-to-CKD transition. We developed a translational approach of AKI-to-CKD transition by reproducing human AAN in rodent models. Indeed, in such models, an early phase of acute tubular necrosis was rapidly followed by a massive interstitial recruitment of activated monocytes/macrophages followed by cytotoxic T lymphocytes, resulting in a transient AKI episode. A later chronic phase was then observed with progressive tubular atrophy related to dedifferentiation and necrosis of tubular epithelial cells. The accumulation of vimentin and αSMA-positive cells expressing TGFβ in interstitial areas suggested an increase in resident fibroblasts and their activation into myofibroblasts resulting in collagen deposition and CKD. In addition, we identified 4 major actors in the AKI-to-CKD transition: (1) the tubular epithelial cells, (2) the endothelial cells of the interstitial capillary network, (3) the inflammatory infiltrate, and (4) the myofibroblasts. This review provides the most comprehensive and informative data we were able to collect and examines the pending questions.

Hyaluronan, a double-edged sword in kidney diseases

Over the years, hyaluronic acid (HA) has emerged as an important molecule in nephrological and urological studies involving extracellular matrix (ECM) organization, inflammation, tissue regeneration, and viral sensing. During this time, many have noted the perplexing double-edged nature of the molecule, at times promoting pro-fibrotic events and at other times promoting anti-fibrotic events. Different molecular weights of HA can be attributed to these disparities, though most studies have yet to focus on this subtlety. With regard to the kidney, HA is induced in the initial response phase of injury and is subsequently decreased during disease progression of AKI, CKD, and diabetic nephropathy. These and other kidney diseases force patients, particularly pediatric patients, to face dialysis, surgical procedures, and ultimately, transplant. To summarize the current literature for researchers and pediatric nephrologists, this review aims to expound HA and elucidate its paradoxical effects in multiple kidney diseases using studies that emphasize HA molecular weight when available.

Endogenously-Produced Hyaluronan and Its Potential to Regulate the Development of Peritoneal Adhesions

Formation of peritoneal adhesions (PA) is one of the major complications following intra-abdominal surgery. It is primarily caused by activation of the mesothelial layer and underlying tissues in the peritoneal membrane resulting in the transition of mesothelial cells (MCs) and fibroblasts to a pro-fibrotic phenotype. Pro-fibrotic transition of MCs—mesothelial-to-mesenchymal transition (MMT), and fibroblasts activation to myofibroblasts are interconnected to changes in cellular metabolism and culminate in the deposition of extracellular matrix (ECM) in the form of fibrotic tissue between injured sides in the abdominal cavity. However, ECM is not only a mechanical scaffold of the newly synthetized tissue but reciprocally affects fibrosis development. Hyaluronan (HA), an important component of ECM, is a non-sulfated glycosaminoglycan consisting of N-acetyl-D-glucosamine (GlcNAc) and D-glucuronic acid (GlcUA) that can affect the majority of processes involved in PA formation. This review considers the role of endogenously produced HA in the context of different fibrosis-related pathologies and its overlap in the development of PA.

High molecular weight sodium hyaluronate improves survival of syndecan-1-deficient septic mice by inhibiting neutrophil migration

METHODS

Sepsis was induced by cotton smoke inhalation followed by intranasal administration of Pseudomonas aeruginosa in female (> 6 months) Balb/c and syndecan-1 knockout mice. Survival of mice, lung capillary endothelial glycocalyx integrity, lung water content, and vascular hyper-permeability were determined with or without HMW-SH treatment in these mice. Effects of HMW-SH on endothelial permeability and neutrophil migration were tested in in vitro setting.

RESULTS

In septic wildtype mice, we found a severely damaged pulmonary microvascular endothelial glycocalyx and elevated levels of shed syndecan-1 in the circulation. These changes were associated with significantly increased pulmonary vascular permeability. In septic syndecan-1 knockout mice, extravascular lung water content was higher, and early death was observed. The administration of HMW-SH significantly reduced mortality and lung water content in septic syndecan-1 knockout mice, but not in septic wildtype mice. In in vitro setting, HMW-SH inhibited neutrophil migration and reduced cultured endothelial cell permeability increases. However, these effects were reversed by the addition of recombinant syndecan-1 ectodomain.

CONCLUSIONS

HMW-SH reduced lung tissue damage and mortality in the absence of syndecan-1 protein, possibly by reducing vascular hyper-permeability and neutrophil migration. Our results further suggest that increased shed syndecan-1 protein levels are linked with the inefficiency of HMW-SH in septic wildtype mice.

A hyaluronan synthesis inhibitor delays the progression of diabetic kidney disease in a mouse experimental model

BACKGROUND

The role of hyaluronan (HA) in the development and progression of diabetic kidney disease (DKD), as well as the precise mechanisms and consequences of HA involvement in this pathology are still to be clarified.

METHODS

In this study, we assayed the effects of the HA synthesis inhibitor 4-methylumbelliferone (4-MU) on the development of DKD. Diabetic type 2 model mice (eNOS^-/- C57BLKS/J^db) were fed artificial diets containing 5% 4-MU or not for 9 weeks. Plasma glucose, glomerular filtration rate (GFR), albumin to creatinine ratio (ACR), and biomarkers of kidney function and systemic inflammation were measured at baseline and after treatment. Diabetic nephropathy was further characterized in treated and control mice by histopathology.

RESULTS

Treated animals consumed a daily dose of approximately 6.2 g of 4-MU per kg of body weight. At the end of the experimental period, the 4-MU supplemented diet resulted in a significant decrease in non-fasting plasma glucose (516 [interquartile range 378-1170] vs. 1149 [875.8-1287] mg/dL, P=0.050) and a trend toward lower HA kidney content (5.6 ± 1.5 vs. 8.8 ± 3.1 ng/mg of kidney weight, P=0.070) compared to the control diet, respectively. Diabetic animals treated with 4-MU showed significantly higher GFR and lower urine ACR and plasma cystatin C levels than diabetic controls. Independent histological assessment of DKD also demonstrated a significant decrease in mesangial expansion score and glomerular injury index in 4-MU-treated mice compared to controls. Plasma glucose showed a strong correlation with kidney HA levels (r=0.66, P=0.0098). Both total hyaluronan (r=0.76, P=0.0071) and low-molecular-weight hyaluronan content (r=0.64, P=0.036) in the kidneys correlated with urine ACR in mice.

CONCLUSION

These results show that the hyaluronan synthesis inhibitor 4-MU effectively slowed the progression of DKD and constitutes a potential new therapeutic approach to treat DKD.

The Endothelial Glycocalyx as a Target of Ischemia and Reperfusion Injury in Kidney Transplantation-Where Have We Gone So Far?

The damage of the endothelial glycocalyx as a consequence of ischemia and/or reperfusion injury (IRI) following kidney transplantation has come at the spotlight of research due to potential associations with delayed graft function, acute rejection as well as long-term allograft dysfunction. The disintegration of the endothelial glycocalyx induced by IRI is the crucial event which exposes the denuded endothelial cells to further inflammatory and oxidative damage. The aim of our review is to present the currently available data regarding complex links between shedding of the glycocalyx components, like syndecan-1, hyaluronan, heparan sulphate, and CD44 with the activation of intricate immune system responses, including toll-like receptors, cytokines and pro-inflammatory transcription factors. Evidence on modes of protection of the endothelial glycocalyx and subsequently maintenance of endothelial permeability as well as novel nephroprotective molecules such as sphingosine-1 phosphate (S1P), are also depicted. Although advances in technology are making the visualization and the analysis of the endothelial glycocalyx possible, currently available evidence is mostly experimental. Ongoing progress in understanding the complex impact of IRI on the endothelial glycocalyx, opens up a new era of research in the field of organ transplantation and clinical studies are of utmost importance for the future.

Urine and serum glycosaminoglycan levels in the diagnosis of urological diseases and conditions: A narrative review of the literature

Glycosaminoglycans (GAGs) are sulfated, negatively charged polysaccharides produced in almost every cell of the human body. As GAGs are extracellularly localized, the changes in body fluids such as blood and urine may reflect pathological changes in the urinary system as observed in other pathologies. In this review, we determined the potential of urinary and/or serum GAG levels as a marker for kidney and urothelial system diseases. We performed a search in the PubMed, MEDLINE, and ScienceDirect databases until September 30, 2019. A number of studies reported changes in the urinary and/or plasma GAG levels or composition in urological diseases and conditions, such as renal cell carcinoma, kidney stone, bladder carcinoma, and overactive bladder. GAGs were found to have a predictive biomarker potential that could be limited by generalizability concerns.

High-molecular weight hyaluronan attenuates tubulointerstitial scarring in kidney injury

Renal fibrosis features exaggerated inflammation, extracellular matrix (ECM) deposition, and peritubular capillary loss. We previously showed that IL-10 stimulates high-molecular weight hyaluronan (HMW-HA) expression by fibroblasts, and we hypothesize that HMW-HA attenuates renal fibrosis by reducing inflammation and ECM remodeling. We studied the effects of IL-10 overexpression on HA production and scarring in mouse models of unilateral ureteral obstruction (UUO) and ischemia/reperfusion (I/R) to investigate whether IL-10 antifibrotic effects are HA dependent. C57BL/6J mice were fed with the HA synthesis inhibitor, 4-methylumbelliferone (4-MU), before UUO. We observed that in vivo injury increased intratubular spaces, ECM deposition, and HA expression at day 7 and onward. IL-10 overexpression reduced renal fibrosis in both models, promoted HMW-HA synthesis and stability in UUO, and regulated cell proliferation in I/R. 4-MU inhibited IL-10-driven antifibrotic effects, indicating that HMW-HA is necessary for cytokine-mediated reduction of fibrosis. We also found that IL-10 induces in vitro HMW-HA production by renal fibroblasts via STAT3-dependent upregulation of HA synthase 2. We propose that IL-10-induced HMW-HA synthesis plays cytoprotective and antifibrotic roles in kidney injury, thereby revealing an effective strategy to attenuate renal fibrosis in obstructive and ischemic pathologies.

Glycocalyx in Endotoxemia and Sepsis

Along with the recognition of a crucial role played by endothelial dysfunction secondarily igniting cardiovascular, pulmonary, and renal complications, investigational focus has extended toward endothelial glycocalyx. This delicate coating of cells, including the vascular endothelium, regulates permeability, leukocyte traffic, nitric oxide production, and coagulation, and harbors diverse growth and survival factors. In this brief overview, we discuss the metabolic signatures of sepsis as they relate to the loss of glycocalyx integrity and highlight the contribution of several proteases, heparanase, and hyaluronidase to the shedding of glycocalyx. Clinical manifestations of glycocalyx degradation in unraveling acute respiratory distress syndrome and the cardiovascular, microcirculatory, and renal complications of sepsis are concisely presented. Finally, we list therapeutic strategies for preventing the degradation of, and for restoration of, the glycocalyx.

The Protective Effects of Thymosin-β-4 in a Rat Model of Ischemic Acute Kidney Injury

BACKGROUND

Despite the progress in the treatment of acute kidney injury (AKI), current curative approaches fail to provide adequate treatment. In this study, we aimed to investigate the possible protective effects of thymosin-β-4(Tβ4) on an ischemic AKI model in rats.

METHODS

Rats were randomly assigned into four groups (n = 8/group): The control group (sham-operated), the ischemia-reperfusion (I/R) group; renal ischemia (90 min) by infrarenal abdominal aortic occlusion followed by reperfusion (3 h), the Tβ4 + I/R group; treated with Tβ4 before I/R, and the I/Tβ4/R group; treated with Tβ4 just before reperfusion. Besides renal function determination (creatinine (Cr) and blood urea nitrogen (BUN)); histological evaluation was also conducted. Renal tissue caspase-9, matrix metalloproteinase (MMP-9) activities, and hyaluronan levels were measured. Additionally, renal tissue oxidative stress (lipid hydroperoxide, malondialdehyde, superoxide dismutase, glutathione, pro-oxidant-antioxidant balance, ferric reducing antioxidant power, nitric oxide), inflammation (tumor necrosis factor-α, interleukin-1β, interleukin-6, nuclear factor-κβ) were evaluated.

RESULTS

I/R increased the level of caspase-9, MMP-9 activity, and hyaluronan (p < 0.001) and these were significantly decreased in both Tβ4 groups. Moreover, I/R led to increases in oxidative stress and inflammation parameters (p < 0.001) while the levels of antioxidants were decreased. Nevertheless, Tβ4 in both groups were able to restore oxidative stress and inflammation parameters. Furthermore, Tβ4 attenuated histologic injury caused by I/R (p < 0.01) and diminished serum urea-creatinine levels (p < 0.001).

CONCLUSION

These results suggest that Tβ4 has significant improving effects in ischemic acute kidney injury. This beneficial effect might be a result of the inhibition of extracellular matrix remodeling and apoptosis cascade via modulation in renal redox status and inflammation.

Targeting renal fibrosis: Mechanisms and drug delivery systems

Renal fibrosis is the common outcome of many chronic kidney diseases (CKD) independent of the underlying etiology. Despite a host of promising experimental data, currently available strategies only ameliorate or delay the progression of CKD but do not reverse fibrosis. One of the major impediments of translating novel antifibrotic strategies from bench to bedside is due to the intricacies of the drug delivery process. In this review, we briefly describe mechanisms of renal fibrosis and methods of drug transfer into the kidney. Various tools used in gene therapy to administer nucleic acids in vivo are discussed. Furthermore, we review the modes of action of protein- or peptide-based drugs with target-specific antibodies and cytokines incorporated in hydrogels. Additionally, we assess an intriguing new method to deliver drugs specifically to tubular epithelial cells via conjugation with ligands binding to the megalin receptor. Finally, plant-derived compounds with antifibrotic properties are also summarized.

Urinary Glycosaminoglycans Predict Outcomes in Septic Shock and Acute Respiratory Distress Syndrome

RATIONALE

Degradation of the endothelial glycocalyx, a glycosaminoglycan (GAG)-rich layer lining the vascular lumen, is associated with the onset of kidney injury in animal models of critical illness. It is unclear if similar pathogenic degradation occurs in critically ill patients.

OBJECTIVES

To determine if urinary indices of GAG fragmentation are associated with outcomes in patients with critical illnesses such as septic shock or acute respiratory distress syndrome (ARDS).

METHODS

We prospectively collected urine from 30 patients within 24 hours of admission to the Denver Health Medical Intensive Care Unit (ICU) for septic shock. As a nonseptic ICU control, we collected urine from 25 surgical ICU patients admitted for trauma. As a medical ICU validation cohort, we obtained serially collected urine samples from 70 patients with ARDS. We performed mass spectrometry on urine samples to determine GAG (heparan sulfate, chondroitin sulfate, and hyaluronic acid) concentrations as well as patterns of heparan sulfate/chondroitin sulfate disaccharide sulfation. We compared these indices to measurements obtained using dimethylmethylene blue, an inexpensive, colorimetric urinary assay of sulfated GAGs.

MEASUREMENTS AND MAIN RESULTS

In septic shock, indices of GAG fragmentation correlated with both the development of renal dysfunction over the 72 hours after urine collection and with hospital mortality. This association remained after controlling for severity of illness and was similarly observed using the inexpensive dimethylmethylene blue assay. These predictive findings were corroborated using urine samples previously collected at three consecutive time points from patients with ARDS.

CONCLUSIONS

Early indices of urinary GAG fragmentation predict acute kidney injury and in-hospital mortality in patients with septic shock or ARDS. Clinical trial registered with www.clinicaltrials.gov (NCT01900275).

Blocking TGF-β Signaling Pathway Preserves Mitochondrial Proteostasis and Reduces Early Activation of PDGFRβ+ Pericytes in Aristolochic Acid Induced Acute Kidney Injury in Wistar Male Rats

BACKGROUND

The platelet-derived growth factor receptor β (PDGFRβ)+ perivascular cell activation becomes increasingly recognized as a main source of scar-associated kidney myofibroblasts and recently emerged as a new cellular therapeutic target.

AIMS

In this regard, we first confirmed the presence of PDGFRβ+ perivascular cells in a human case of end-stage aristolochic acid nephropathy (AAN) and thereafter we focused on the early fibrosis events of transforming growth factor β (TGFβ) inhibition in a rat model of AAN.

MATERIALS AND METHODS

Neutralizing anti-TGFβ antibody (1D11) and its control isotype (13C4) were administered (5 mg/kg, i.p.) at Days -1, 0, 2 and 4; AA (15 mg/kg, sc) was injected daily.

RESULTS

At Day 5, 1D11 significantly suppressed p-Smad2/3 signaling pathway improving renal function impairment, reduced the score of acute tubular necrosis, peritubular capillaritis, interstitial inflammation and neoangiogenesis. 1D11 markedly decreased interstitial edema, disruption of tubular basement membrane loss of brush border, cytoplasmic edema and organelle ultrastructure alterations (mitochondrial disruption and endoplasmic reticulum edema) in proximal tubular epithelial cells. Moreover, 1D11 significantly inhibited p-PERK activation and attenuated dysregulation of unfolded protein response (UPR) pathways, endoplasmic reticulum and mitochondrial proteostasis in vivo and in vitro.

CONCLUSIONS

The early inhibition of p-Smad2/3 signaling pathway improved acute renal function impairment, partially prevented epithelial-endothelial axis activation by maintaining PTEC proteostasis and reduced early PDGFRβ+ pericytes-derived myofibroblasts accumulation.

Angiotensin II AT1 receptor alters ACE2 activity, eNOS expression and CD44-hyaluronan interaction in rats with hypertension and myocardial fibrosis

AIM

This study tested the hypothesis that angiotensin II (Ang II) AT1 receptor is involved in development of hypertension and cardiac fibrosis via modifying ACE2 activity, eNOS expression and CD44-hyaluronan interaction.

MAIN METHODS

Male Sprague-Dawley rats were subjected to Ang II infusion (500ng/kg/min) using osmotic minipumps up to 4weeks and the AT1 receptor blocker, telmisartan was administered by gastric gavage (10mg/kg/day) during Ang II infusion.

KEY FINDINGS

Our results indicated that Ang II enhances AT1 receptor, downregulates AT2 receptor, ACE2 activity and eNOS expression, and increases CD44 expression and hyaluronidase activity, an enzyme for hyaluronan degradation. Further analyses revealed that Ang II increases blood pressure and augments vascular/interstitial fibrosis. Comparison of the Ang II group, treatment with telmisartan significantly increased ACE2 activity and eNOS expression in the intracardiac vessels and intermyocardium. These changes occurred in coincidence with decreased blood pressure. Furthermore, the locally-expressed AT1 receptor was downregulated, as evidenced by an increased ratio of the AT2 over AT1 receptor (1.4±0.4% vs. 0.4±0.1% in Ang II group, P<0.05). Along with these modulations, telmisartan inhibited membrane CD44 expression and hyaluronidase activity, decreased populations of macrophages and myofibroblasts, and reduced expression of TGFβ1 and Smads. Collagen I synthesis and tissue fibrosis were attenuated as demonstrated by the less extensive collagen-rich area.

SIGNIFICANCE

These results suggest that the AT1 receptor is involved in development of hypertension and cardiac fibrosis. Selective activating ACE2/eNOS and inhibiting CD44/HA interaction might be considered as the therapeutic targets for attenuating Ang II induced deleterious cardiovascular effects.

An update on the role of the inflammasomes in the pathogenesis of kidney diseases

Innate immune response pathways play a critical role as the first line of defense. Initiation of an immune response requires sensors that can detect noxious stimuli within the cellular microenvironment. Inflammasomes are signaling platforms that are assembled in response to both microbe-specific and nonmicrobial antigens. Upon activation, proinflammatory cytokines are released to engage immune defenses and to trigger an inflammatory cell death referred to as pyroptosis. The aim of this review is to provide an overview of the current knowledge of the role of the inflammasomes in the pathogenesis of kidney diseases. As crystal deposition in the kidney is a frequent cause of acute kidney injury and chronic kidney disease in children, recent insights into mechanisms of inflammasome activation by renal crystals are highlighted. This may be of particular interest to pediatric patients and nephrologists in need of new therapeutic approaches. Lastly, current data findings that inflammasomes are not only of major importance in host defense but are also a key regulator of the intestinal microbiota and the progression of systemic diseases are reviewed.

Differential effects of hyaluronan synthase 3 deficiency after acute vs chronic liver injury in mice

Background

Hyaluronan (HA) is a ubiquitous extracellular matrix (ECM) glycosaminoglycan synthesized by three different enzymes, hyaluronan synthase (HAS)1, 2, and 3. HA synthesis mediated by HAS3 promotes inflammation and is pathogenic in animal models of human lung and intestinal disease. Liver fibrosis is a common endpoint to chronic liver injury and inflammation for which there is no cure. Although plasma HA is a commonly used biomarker for liver disease, if and how HA contributes to disease pathogenesis remains unclear. Here, we tested the hypothesis that HA synthesized by HAS3 enhances inflammation and fibrosis. To test this hypothesis, we exposed wild-type or Has3−/− mice to carbon tetrachloride (CCl₄) once (acute) or ten (chronic) times.

Results

HAS3-deficient mice exhibited increased hepatic injury and inflammatory chemokine production 48 h after acute CCl₄; this was associated with a threefold reduction in plasma HA levels and alterations in the proportions of specific molecular weight HA polymer pools. Hepatic accumulation of fibrosis-associated transcripts was also greater in livers from HAS3-deficient mice compared to controls after acute CCl₄ exposure. Surprisingly, fibrosis was not different between genotypes. Hepatic matrix metalloproteinase (MMP)13 mRNA and MMP13 activity was greater in livers from Has3-null mice after chronic CCl₄; this was prevented by a MMP13-specific inhibitor. Collectively, these data suggest that Has3, or more likely HA produced by HAS3, limits hepatic inflammation after acute injury and attenuates MMP13-mediated matrix metabolism after chronic injury.

Conclusions

These data suggest that HA should be investigated further as a novel therapeutic target for acute and chronic liver disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13069-016-0041-5) contains supplementary material, which is available to authorized users.

Hyaluronan Synthase 3 Null Mice Exhibit Decreased Intestinal Inflammation and Tissue Damage in the DSS-Induced Colitis Model

Hyaluronan (HA) overproduction is a hallmark of multiple inflammatory diseases, including inflammatory bowel disease (IBD). Hyaluronan can act as a leukocyte recruitment molecule and in the most common mouse model of intestinal inflammation, the chemically induced dextran sodium sulfate (DSS) experimental colitis model, we previously determined that changes in colon distribution of HA occur before inflammation. Therefore, we hypothesized that, during a pathologic challenge, HA promotes inflammation. In this study, we tested the progression of inflammation in mice null for the hyaluronan synthase genes (HAS1, HAS3, or both HAS1 and HAS3) in the DSS-colitis model. Our data demonstrate that both the HAS1/HAS3 double and the HAS3 null mice are protected from colitis, compared to wild-type and HAS1 null mice, as determined by measurement of weight loss, disease activity, serum IL-6 levels, histologic scoring, and immunohistochemistry. Most notable is the dramatic increase in submucosal microvasculature, hyaluronan deposition, and leukocyte infiltration in the inflamed colon tissue of wild-type and HAS1 null mice. Our data suggest, HAS3 plays a crucial role in driving gut inflammation. Developing a temporary targeted therapeutic intervention of HAS3 expression or function in the microcirculation may emerge as a desirable strategy toward tempering colitis in patients undergoing flares of IBD.

Epigenetic profiles of pre-diabetes transitioning to type 2 diabetes and nephropathy

AIM: To examine DNA methylation profiles in a longitudinal comparison of pre-diabetes mellitus (Pre-DM) subjects who transitioned to type 2 diabetes mellitus (T2DM).

METHODS: We performed DNA methylation study in bisulphite converted DNA from Pre-DM (n = 11) at baseline and at their transition to T2DM using Illumina Infinium HumanMethylation27 BeadChip, that enables the query of 27578 individual cytosines at CpG loci throughout the genome, which are focused on the promoter regions of 14495 genes.

RESULTS: There were 694 CpG sites hypomethylated and 174 CpG sites hypermethylated in progression from Pre-DM to T2DM, representing putative genes involved in glucose and fructose metabolism, inflammation, oxidative and mitochondrial stress, and fatty acid metabolism. These results suggest that this high throughput platform is able to identify hundreds of prospective CpG sites associated with diverse genes that may reflect differences in Pre-DM compared with T2DM. In addition, there were CpG hypomethylation changes associated with a number of genes that may be associated with development of complications of diabetes, such as nephropathy. These hypomethylation changes were observed in all of the subjects.

CONCLUSION: These data suggest that some epigenomic changes that may be involved in the progression of diabetes and/or the development of complications may be apparent at the Pre-DM state or during the transition to diabetes. Hypomethylation of a number of genes related to kidney function may be an early marker for developing diabetic nephropathy.

Sugars in the microenvironment: the sticky problem of HA turnover in tumors

The properties and behavior of tumor cells are closely regulated by their microenvironment. Accordingly, stromal cells and extracellular matrix components can have a pronounced effect on cancer initiation, growth, and progression. The linear glycosaminoglycan hyaluronan (HA) is a major component of the extracellular matrix. Altered synthesis and degradation of HA in the tumor context has been implicated in many aspects of tumor biology. In particular, the accumulation of small HA oligosaccharides (sHA) in the tumor interstitial space may play a decisive role, due to the ability of sHA to activate a number of biological processes that are not modulated by high molecular weight (HMW)-HA. In this article, we review the normal physiological role and metabolism of HA and then survey the evidence implicating HA in tumor growth and progression, focusing in particular on the potential contribution of sHA to these processes.

The Content and Size of Hyaluronan in Biological Fluids and Tissues

Hyaluronan is a simple repeating disaccharide polymer, synthesized at the cell surface by integral membrane synthases. The repeating sequence is perfectly homogeneous, and is the same in all vertebrate tissues and fluids. The polymer molecular mass is more variable. Most commonly, hyaluronan is synthesized as a high-molecular mass polymer, with an average molecular mass of approximately 1000–8000 kDa. There are a number of studies showing increased hyaluronan content, but reduced average molecular mass with a broader range of sizes present, in tissues or fluids when inflammatory or tissue-remodeling processes occur. In parallel studies, exogenous hyaluronan fragments of low-molecular mass (generally, <200 kDa) have been shown to affect cell behavior through binding to receptor proteins such as CD44 and RHAMM (gene name HMMR), and to signal either directly or indirectly through toll-like receptors. These data suggest that receptor sensitivity to hyaluronan size provides a biosensor of the state of the microenvironment surrounding the cell. Sensitive methods for isolation and characterization of hyaluronan and its fragments have been developed and continue to improve. This review provides an overview of the methods and our current state of knowledge of hyaluronan content and size distribution in biological fluids and tissues.

Hyaluronan - a functional and structural sweet spot in the tissue microenvironment

Transition from homeostatic to reactive matrix remodeling is a fundamental adaptive tissue response to injury, inflammatory disease, fibrosis, and cancer. Alterations in architecture, physical properties, and matrix composition result in changes in biomechanical and biochemical cellular signaling. The dynamics of pericellular and extracellular matrices, including matrix protein, proteoglycan, and glycosaminoglycan modification are continually emerging as essential regulatory mechanisms underlying cellular and tissue function. Nevertheless, the impact of matrix organization on inflammation and immunity in particular and the consequent effects on tissue healing and disease outcome are arguably under-studied aspects of adaptive stress responses. Herein, we review how the predominant glycosaminoglycan hyaluronan (HA) contributes to the structure and function of the tissue microenvironment. Specifically, we examine the evidence of HA degradation and the generation of biologically active smaller HA fragments in pathological settings in vivo. We discuss how HA fragments versus nascent HA via alternate receptor-mediated signaling influence inflammatory cell recruitment and differentiation, resident cell activation, as well as tumor growth, survival, and metastasis. Finally, we discuss how HA fragmentation impacts restoration of normal tissue function and pathological outcomes in disease.

Fluorescence resonance energy transfer (FRET) and proximity ligation assays reveal functionally relevant homo- and heteromeric complexes among hyaluronan synthases HAS1, HAS2, and HAS3

In vertebrates, hyaluronan is produced in the plasma membrane from cytosolic UDP-sugar substrates by hyaluronan synthase 1-3 (HAS1-3) isoenzymes that transfer N-acetylglucosamine (GlcNAc) and glucuronic acid (GlcUA) in alternative positions in the growing polysaccharide chain during its simultaneous extrusion into the extracellular space. It has been shown that HAS2 immunoprecipitates contain functional HAS2 homomers and also heteromers with HAS3 (Karousou, E., Kamiryo, M., Skandalis, S. S., Ruusala, A., Asteriou, T., Passi, A., Yamashita, H., Hellman, U., Heldin, C. H., and Heldin, P. (2010) The activity of hyaluronan synthase 2 is regulated by dimerization and ubiquitination. J. Biol. Chem. 285, 23647-23654). Here we have systematically screened in live cells, potential interactions among the HAS isoenzymes using fluorescence resonance energy transfer (FRET) and flow cytometric quantification. We show that all HAS isoenzymes form homomeric and also heteromeric complexes with each other. The same complexes were detected both in Golgi apparatus and plasma membrane by using FRET microscopy and the acceptor photobleaching method. Proximity ligation assays with HAS antibodies confirmed the presence of HAS1-HAS2, HAS2-HAS2, and HAS2-HAS3 complexes between endogenously expressed HASs. C-terminal deletions revealed that the enzymes interact mainly via uncharacterized N-terminal 86-amino acid domain(s), but additional binding site(s) probably exist in their C-terminal parts. Of all the homomeric complexes HAS1 had the lowest and HAS3 the highest synthetic activity. Interestingly, HAS1 transfection reduced the synthesis of hyaluronan obtained by HAS2 and HAS3, suggesting functional cooperation between the isoenzymes. These data indicate a general tendency of HAS isoenzymes to form both homomeric and heteromeric complexes with potentially important functional consequences on hyaluronan synthesis.

Lack of hyaluronidases exacerbates renal post-ischemic injury, inflammation, and fibrosis

Renal ischemia-reperfusion injury (IRI) is a pathological process that may lead to acute renal failure and chronic dysfunction in renal allografts. During IRI, hyaluronan (HA) accumulates in the kidney, but suppression of HA accumulation during IRI protects the kidney from ischemic insults. Here we tested whether Hyal1-/- and Hyal2-/- mice display exacerbated renal damage following unilateral IRI due to a higher HA accumulation in the post-ischemic kidney compared with that in the kidney of wild-type mice. Two days after IRI in male mice there was accumulation of HA and CD44 in the kidney, marked tubular damage, infiltration, and increase creatininemia in wild-type mice. Knockout mice exhibited higher amounts of HA and higher creatininemia. Seven days after injury, wild-type mice had a significant decrease in renal damage, but knockout mice still displayed exacerbated inflammation. HA and CD44 together with α-smooth muscle actin and collagen types I and III expression were increased in knockout compared with wild-type mice 30 days after IRI. Thus, both HA-degrading enzymes seem to be protective against IRI most likely by reducing HA accumulation in the post-ischemic kidney and decreasing the inflammatory processes. Deficiency in either HYAL1 or HYAL2 leads to enhanced HA accumulation in the post-ischemic kidney and consequently worsened inflammatory response, increased tubular damage, and fibrosis.

Hyaluronan synthase 1: a mysterious enzyme with unexpected functions

Hyaluronan synthase 1 (HAS1) is one of three isoenzymes responsible for cellular hyaluronan synthesis. Interest in HAS1 has been limited because its role in hyaluronan production seems to be insignificant compared to the two other isoenzymes, HAS2 and HAS3, which have higher enzymatic activity. Furthermore, in most cell types studied so far, the expression of its gene is low and the enzyme requires high concentrations of sugar precursors for hyaluronan synthesis, even when overexpressed in cell cultures. Both expression and activity of HAS1 are induced by pro-inflammatory factors like interleukins and cytokines, suggesting its involvement in inflammatory conditions. Has1 is upregulated in states associated with inflammation, like atherosclerosis, osteoarthritis, and infectious lung disease. In addition, both full length and splice variants of HAS1 are expressed in malignancies like bladder and prostate cancers, multiple myeloma, and malignant mesothelioma. Interestingly, immunostainings of tissue sections have demonstrated the role of HAS1 as a poor predictor in breast cancer, and is correlated with high relapse rate and short overall survival. Utilization of fluorescently tagged proteins has revealed the intracellular distribution pattern of HAS1, distinct from other isoenzymes. In all cell types studied so far, a high proportion of HAS1 is accumulated intracellularly, with a faint signal detected on the plasma membrane and its protrusions. Furthermore, the pericellular hyaluronan coat produced by HAS1 is usually thin without induction by inflammatory agents or glycemic stress and depends on CD44–HA interactions. These specific interactions regulate the organization of hyaluronan into a leukocyte recruiting matrix during inflammatory responses. Despite the apparently minor enzymatic activity of HAS1 under normal conditions, it may be an important factor under conditions associated with glycemic stress like metabolic syndrome, inflammation, and cancer.

Inhibition of mTOR activity in diabetes mellitus reduces proteinuria but not renal accumulation of hyaluronan

OBJECTIVES

Accumulation of extracellular matrix (ECM) components is an early sign of diabetic nephropathy. Also the glycosaminoglycan hyaluronan (HA) is elevated in the renal interstitium during experimental diabetes. The mammalian target of rapamycin (mTOR) pathway participates in the signaling of hyperglycemia-induced ECM accumulation in the kidney, but this has not yet been investigated for HA. We hypothesized that interstitial HA accumulation during diabetes may involve mTOR activation.

METHODS

Diabetic rats (6 weeks post-streptozotocin (STZ)) were treated with rapamycin to inhibit mTOR or vehicle for 2 additional weeks. Kidney function (glomerular filtration rate, renal blood flow, urine output) and regional renal HA content were thereafter analyzed. The ability of the animals to respond to desmopressin was also tested.

RESULTS

Diabetic animals displayed hyperglycemia, proteinuria, hyperfiltration, renal hypertrophy, increased diuresis with reduced urine osmolality, and reduced weight gain. Cortical and outer medullary HA was elevated in diabetic rats. Urine hyaluronidase activity was almost doubled in diabetic rats compared with controls. The ability to respond to desmopressin was absent in diabetic rats. Renal blood flow and arterial blood pressure were unaffected by the diabetic state. In diabetic rats treated with rapamycin the proteinuria was reduced by 32%, while all other parameters were unaffected.

CONCLUSION

Regional renal accumulation of the ECM component HA is not sensitive to mTOR inhibition by rapamycin, while proteinuria is reduced in established STZ-induced diabetes. Whether the diabetes-induced renal accumulation of HA occurs through different pathways than other ECM components, or is irreversible after being established, remains to be shown.

Inhibition of hyaluronan is protective against renal ischaemia-reperfusion injury

BACKGROUND

Ischaemia-reperfusion injury (IRI) to the kidney is a complex pathophysiological process that leads to acute renal failure and chronic dysfunction in renal allografts. It was previously demonstrated that during IRI, hyaluronan (HA) accumulates in the cortical and external medullary interstitium along with an increased expression of its main receptor, CD44, on inflammatory and tubular cells. The HA-CD44 pair may be involved in persistent post-ischaemic inflammation. Thus, we sought to determine the role of HA in the pathophysiology of ischaemia-reperfusion (IR) by preventing its accumulation in post-ischaemic kidney.

METHODS

C57BL/6 mice received a diet containing 4-methylumbelliferone (4-MU), a potent HA synthesis inhibitor. At the end of the treatment, unilateral renal IR was induced and mice were euthanized 48 h or 30 days post-IR.

RESULTS

4-MU treatment for 14 weeks reduced the plasma HA level and intra-renal HA content at 48 h post-IR, as well as CD44 expression, creatininemia and histopathological lesions. Moreover, inflammation was significantly attenuated and proliferation was reduced in animals treated with 4-MU. In addition, 4-MU-treated mice had a significantly reduced expression of α-SMA and collagen types I and III, i.e. less renal fibrosis, 30 days after IR compared with untreated mice.

CONCLUSION

Our results demonstrate that HA plays a significant role in the pathogenesis of IRI, perhaps in part through reduced expression of CD44. The suppression of HA accumulation during IR may protect renal function against ischaemic insults.