Endocytosis of hyaluronic acid by rat liver endothelial cells. Evidence for receptor recycling

Venous thromboembolic disease genetics: from variants to function

Venous thromboembolic disease (VTE) is a prevalent and potentially life-threatening vascular disease, including both deep vein thrombosis and pulmonary embolism. This review will focus on recent insights into the heritable factors that influence an individual's risk for VTE. Here, we will explore not only the discovery of new genetic risk variants but also the importance of functional characterization of these variants. These genome-wide studies should lead to a better understanding of the biological role of genes inside and outside of the canonical coagulation system in thrombus formation and lead to an improved ability to predict an individual's risk of VTE. Further understanding of the molecular mechanisms altered by genetic variation in VTE risk will be accelerated by further human genome sequencing efforts and the use of functional genetic screens.

The Role and Significance of Non-invasive Methods, with a Particular Focus on Shear Wave Elastography in Hepatic Fibrosis Staging

Shear Wave Elastography (SWE) represents a new, non-invasive method, used in the diagnosis of diffuse liver diseases. The method has been widely used instead of liver biopsy - an invasive procedure with potential major risk complications. Compared to liver biopsy, SWE provides an examination of larger areas of the liver, thus providing better staging of hepatic fibrosis.  30 patients were included in the study on basis of previous clinical, biochemical, and ultrasound findings indicating a presence of a chronic liver lesion.  Patients were divided into three groups: 6 patients with steatosis, 13 patients with viral hepatitis, and 11 patients with liver cirrhosis. Liver damage biochemical markers, serum markers of liver fibrosis, and SWE were determined in all patients. Statistical analysis revealed a positive correlation between SWE results, and the values of biochemical markers of the hepatic lesion, as well as serum markers of liver fibrosis.

Endothelial dysfunction in pathological processes of chronic liver disease during aging

Aging is associated with gradual changes in liver structure and physiological/pathological functions in hepatic cells including hepatocytes, cholangiocytes, Kupffer cells, hepatic stellate cells (HSCs), and liver sinusoidal endothelial cells (LSECs). LSECs are specialized hepatic endothelial cells that regulate liver homeostasis. These cells actively impact the hepatic microenvironment as they have fenestrations and a thin morphology to allow substance exchange between circulating blood and the liver tissue. As aging occurs, LSECs have a reduction in both the number and size of fenestrations, which is referred to as pseudocapillarization. This along with the aging of the liver leads to increased oxidative stress, decreased availability of nitric oxide, decreased hepatic blood flow, and increased inflammatory cytokines in LSECs. Vascular aging can also lead to hepatic hypoxia, HSC activation, and liver fibrosis. In this review, we described the basic structure of LSECs, and the effect of LSECs on hepatic inflammation and fibrosis during aging process. We briefly summarized the changes of hepatic microcirculation during liver inflammation, the effect of aging on the clearance function of LSECs, the interactions between LSECs and immunity, hepatocytes or other hepatic nonparenchymal cells, and the therapeutic intervention of liver diseases by targeting LSECs and vascular system. Since LSECs play an important role in the development of liver fibrosis and the changes of LSEC phenotype occur in the early stage of liver fibrosis, the study of LSECs in the fibrotic liver is valuable for the detection of early liver fibrosis and the early intervention of fibrotic response.

The Scavenger Function of Liver Sinusoidal Endothelial Cells in Health and Disease

The aim of this review is to give an outline of the blood clearance function of the liver sinusoidal endothelial cells (LSECs) in health and disease. Lining the hundreds of millions of hepatic sinusoids in the human liver the LSECs are perfectly located to survey the constituents of the blood. These cells are equipped with high-affinity receptors and an intracellular vesicle transport apparatus, enabling a remarkably efficient machinery for removal of large molecules and nanoparticles from the blood, thus contributing importantly to maintain blood and tissue homeostasis. We describe here central aspects of LSEC signature receptors that enable the cells to recognize and internalize blood-borne waste macromolecules at great speed and high capacity. Notably, this blood clearance system is a silent process, in the sense that it usually neither requires or elicits cell activation or immune responses. Most of our knowledge about LSECs arises from studies in animals, of which mouse and rat make up the great majority, and some species differences relevant for extrapolating from animal models to human are discussed. In the last part of the review, we discuss comparative aspects of the LSEC scavenger functions and specialized scavenger endothelial cells (SECs) in other vascular beds and in different vertebrate classes. In conclusion, the activity of LSECs and other SECs prevent exposure of a great number of waste products to the immune system, and molecules with noxious biological activities are effectively “silenced” by the rapid clearance in LSECs. An undesired consequence of this avid scavenging system is unwanted uptake of nanomedicines and biologics in the cells. As the development of this new generation of therapeutics evolves, there will be a sharp increase in the need to understand the clearance function of LSECs in health and disease. There is still a significant knowledge gap in how the LSEC clearance function is affected in liver disease.

Hyaluronan: Metabolism and Function

As a major polysaccharide component of the extracellular matrix, hyaluronan plays essential roles in the organization of tissue architecture and the regulation of cellular functions, such as cell proliferation and migration, through interactions with cell-surface receptors and binding molecules. Metabolic pathways for biosynthesis and degradation tightly control the turnover rate, concentration, and molecular size of hyaluronan in tissues. Despite the relatively simple chemical composition of this polysaccharide, its wide range of molecular weights mediate diverse functions that depend on molecular size and tissue concentration. Genetic engineering and pharmacological approaches have demonstrated close associations between hyaluronan metabolism and functions in many physiological and pathological events, including morphogenesis, wound healing, and inflammation. Moreover, emerging evidence has suggested that the accumulation of hyaluronan extracellular matrix and fragments due to the altered expression of hyaluronan synthases and hyaluronidases potentiates cancer development and progression by remodeling the tumor microenvironment. In addition to the well-known functions exerted by extracellular hyaluronan, recent metabolomic approaches have also revealed that its synthesis can regulate cellular functions via the reprogramming of cellular metabolism. This review highlights the current advances in knowledge on the biosynthesis and catabolism of hyaluronan and describes the diverse functions associated with hyaluronan metabolism.

Systemic Glycosaminoglycan Clearance by HARE/Stabilin-2 Activates Intracellular Signaling

Scavenger receptors perform essential functions, critical to maintaining mammalian physiologic homeostasis by continuously clearing vast numbers of biomolecules from blood, interstitial fluid and lymph. Stabilin-2 (Stab2) and the Hyaluronic Acid Receptor for Endocytosis (HARE), a proteolytic isoform of Stab2, are important scavenger receptors responsible for the specific binding and internalization (leading to degradation) of 22 discrete molecules, macromolecular complexes and cell types. One-third of these ligands are glycosaminoglycans (GAGs). Full-length Stab2, but not HARE, mediates efficient phagocytosis of apoptotic cells and bacteria via binding to target surface ligands. HARE, the C-terminal half of Stab2, mediates endocytosis of all the known soluble ligands. HA was the first ligand identified, in 1981, prior to receptor purification or cloning. Seven other GAG ligands were subsequently identified: heparin, dermatan sulfate, chondroitin and chondroitin sulfates A, C, D and E. Synthetic dextran sulfate is also a GAG mimic and ligand. HARE signaling during HA endocytosis was first discovered in 2008, and we now know that activation of HARE/Stab2 signaling is stimulated by receptor-mediated endocytosis or phagocytosis of many, but not all, of its ligands. This review focuses on the HARE-mediated GAG activation of intracellular signaling, particularly the Extracellular Signal-Regulated Kinase 1/2 pathway.

Discovery of the Liver Hyaluronan Receptor for Endocytosis (HARE) and Its Progressive Emergence as the Multi-Ligand Scavenger Receptor Stabilin-2

Since the discovery of a novel liver hyaluronan (HA) clearance receptor in 1981 by Laurent, Fraser and coworkers, 22 different ligands cleared by the renamed receptor (the Hyaluronan Receptor for Endocytosis (HARE); Stabilin-2 (Stab2)) were discovered over 37 years. Ligands fall into three groups: (1) 11 anionic polymers, (2) seven cleaved or modified proteins and (3) four types of cells. Seven synthetic ligands, not found normally in serum or tissues, likely mimic natural molecules cleared by the receptor. In 2002 we purified and cloned HARE, based on HA-binding activity, and two other groups cloned full-length receptor; FEEL-2 and Stab2. Macrophages likely require full-length Stab2 for efficient binding and phagocytosis of bacteria or apoptotic cells, since cell-binding domains are throughout the receptor. In contrast, all 16 known single-molecule binding sites are only within the C-terminal half (190HARE). The HARE isoform is generated by proteolysis, not mRNA splicing. The majority of circulating ligands is cleared by HARE, since sinusoidal endothelial cells of liver, spleen and lymph node express twice as many HARE half-receptors as full-length receptors. Based on their significant binding and functional differences, a modified receptor nomenclature is proposed that designates HARE as the C-terminal half-receptor isoform and Stab2 as the full-length receptor isoform.

Ligand Binding and Signaling of HARE/Stabilin-2

The Stabilin receptors are a two-member family in the type H class of scavenger receptors. These dynamic receptors bind and internalize multiple ligands from the cell surface for the purpose of clearing extracellular material including some synthetic drugs and for sensing the external environment of the cell. Stabilin-1 was the first receptor to be cloned, though the biological activity of Hyaluronic Acid Receptor for Endocytosis (HARE)/Stabilin-2 was observed about 10 years prior to the cloning of Stabilin-1. Stabilin-1 has a more diverse expression profile among the tissues than HARE/Stabilin-2. This review will focus on HARE/Stabilin-2 and its interactions with hyaluronan, heparin, and phosphorothioate antisense oligonucleotides and what is known about how this receptor participates in signaling upon ligand binding.

Hyaluronic acid and TGF-β1 in dogs with hepatobiliary diseases

The aim of the study was to assess serum hyaluronic acid (HA) and transforming growth factor beta 1 (TGF-β1) concentrations: 1) to differentiate hepatic fibrosis from other forms of liver disease, and 2) for the non-invasive staging of canine liver fibrosis. We also evaluated the association between serum HA concentration and the size of the shunt vessel as an indirect marker of decreased liver clearance in patients with single congenital vascular anomaly. Forty-one healthy client-owned dogs and forty dogs diagnosed with hepatobiliary disease were enrolled in the prospective study. Patients were divided into 4 subgroups: 1) congenital portosystemic shunts (CPSS); 2) parenchymal diseases (a. mild and moderate fibrosis, b. advanced fibrosis and cirrhosis); 3) hepatic neoplasia; 4) biliary tract disorders based on thorough clinical, ultrasound and histopathological examination. Serum HA and TGF-β1 concentrations were measured using ELISA. The HA concentration was significantly increased in patients with advanced liver fibrosis/cirrhosis (P < 0.001) and CPSS (P < 0.001) compared to healthy dogs. Using a cut-off HA concentration of 135.94 ng/ml, the sensitivity and specificity for diagnosis for advanced liver fibrosis/cirrhosis was 100% (95% CI, 50.6–100) and 90.8% (95% CI, 81.6–95.7), respectively. The TGF-β1 levels did not significantly differ among groups (P = 0.180). Negligible correlation was found between serum HA concentration and the size of portosystemic shunt vessel (rs = 0.07; P = 0.831). These findings suggest that serum HA concentration is a potential non-invasive biomarker for advanced liver fibrosis and/or cirrhosis in dogs. The utility of measuring serum concentration of TGF-β1 for diagnosing canine liver fibrosis was not supported.

Pursuing Intracellular Pathogens with Hyaluronan. From a 'Pro-Infection' Polymer to a Biomaterial for 'Trojan Horse' Systems

Hyaluronan (HA) is among the most important bioactive polymers in mammals, playing a key role in a number of biological functions. In the last decades, it has been increasingly studied as a biomaterial for drug delivery systems, thanks to its physico-chemical features and ability to target and enter certain cells. The most important receptor of HA is ‘Cluster of Differentiation 44’ (CD44), a cell surface glycoprotein over-expressed by a number of cancers and heavily involved in HA endocytosis. Moreover, CD44 is highly expressed by keratinocytes, activated macrophages and fibroblasts, all of which can act as ‘reservoirs’ for intracellular pathogens. Interestingly, both CD44 and HA appear to play a key role for the invasion and persistence of such microorganisms within the cells. As such, HA is increasingly recognised as a potential target for nano-carriers development, to pursuit and target intracellular pathogens, acting as a ‘Trojan Horse’. This review describes the biological relationship between HA, CD44 and the entry and survival of a number of pathogens within the cells and the subsequent development of HA-based nano-carriers for enhancing the intracellular activity of antimicrobials.

SECs (Sinusoidal Endothelial Cells), Liver Microenvironment, and Fibrosis

Liver fibrosis is a wound-healing response to chronic liver injury such as alcoholic/nonalcoholic fatty liver disease and viral hepatitis with no FDA-approved treatments. Liver fibrosis results in a continual accumulation of extracellular matrix (ECM) proteins and paves the way for replacement of parenchyma with nonfunctional scar tissue. The fibrotic condition results in drastic changes in the local mechanical, chemical, and biological microenvironment of the tissue. Liver parenchyma is supported by an efficient network of vasculature lined by liver sinusoidal endothelial cells (LSECs). These nonparenchymal cells are highly specialized resident endothelial cell type with characteristic morphological and functional features. Alterations in LSECs phenotype including lack of LSEC fenestration, capillarization, and formation of an organized basement membrane have been shown to precede fibrosis and promote hepatic stellate cell activation. Here, we review the interplay of LSECs with the dynamic changes in the fibrotic liver microenvironment such as matrix rigidity, altered ECM protein profile, and cell-cell interactions to provide insight into the pivotal changes in LSEC physiology and the extent to which it mediates the progression of liver fibrosis. Establishing the molecular aspects of LSECs in the light of fibrotic microenvironment is valuable towards development of novel therapeutic and diagnostic targets of liver fibrosis.

Antisense Oligonucleotides: Treatment Strategies and Cellular Internalization

The clinical applicaton of antisense oligonucleotides (ASOs) is becoming more of a reality as several drugs have been approved for the treatment of human disorders and many others are in various phases in development and clinical trials. ASOs are short DNA/RNA oligos which are heavily modified to increase their stability in biological fluids and retain the properties of creating RNA-RNA and DNA-RNA duplexes that knock-down or correct genetic expression. This review outlines several strategies that ASOs utilize for the treatment of various congenital diseases and syndromes that develop with aging. In addition, we discuss some of the mechanisms for specific non-targeted ASO internalization within cells.

Iron overload correlates with serum liver fibrotic markers and liver dysfunction: Potential new methods to predict iron overload-related liver fibrosis in thalassemia patients

BACKGROUND

Early detection of liver fibrosis in thalassemia patients and rapid initiation of treatment to interfere with its progression are extremely important.

OBJECTIVE

This study aimed to find a sensitive, easy-to-detect and noninvasive method other than liver biopsy for early detection of liver fibrosis in thalassemia patients.

METHODS

A total of 244 Chinese Thalassemia patients with non-transfusion-dependent thalassemia (NTDT, n = 105) or thalassemia major (TM, n = 139) and 120 healthy individuals were recruited into the present study, and blood collagen type IV (C IV), precollagen type III (PIIINPC) and hyaluronic acid (HA), aspartate aminotransferase (AST), alanine aminotransferase (ALT) and ferritin were measured. Liver iron concentration was determined by MRI. The correlation of serum markers with liver iron load and liver function was evaluated.

RESULTS

Serum C IV, PIIINPC and HA were significantly elevated in Chinese patients with NTDT and further elevated in TM patients. Moreover, C IV, PIIINPC and HA were also positively correlated to serum ferritin and liver iron concentration and further elevated during the progression to multi-organ damage in NTDT patients. Finally, serum ferritin and liver iron concentration were significantly correlated with liver dysfunction determined by AST and ALT.

CONCLUSION

Taken together, our results indicate that monitoring serum C IV, PIIINPC and HA is a potentially sensitive method to predict the risks for iron overload-related liver fibrosis in Chinese thalassemia patients.

Evaluation of liver fibrosis: "Something old, something new…"

Hepatic fibrogenesis may gradually result to cirrhosis due to the accumulation of extracellular matrix components as a response to liver injury. Thus, therapeutic decisions in chronic liver disease, regardless of the cause, should first and foremost be guided by an accurate quantification of hepatic fibrosis. Detection and assessment of the extent of hepatic fibrosis represent a challenge in modern Hepatology. Although traditional histological staging systems remain the “best standard”, they are not able to quantify liver fibrosis as a dynamic process and may not accurately substage cirrhosis. This review aims to compare the currently used non-invasive methods of measuring liver fibrosis and provide an update in current tissue-based digital techniques developed for this purpose, that may prove of value in daily clinical practice.

Activation of ERK and NF-κB during HARE-Mediated Heparin Uptake Require Only One of the Four Endocytic Motifs

Fifteen different ligands, including heparin (Hep), are cleared from lymph and blood by the Hyaluronan (HA) Receptor for Endocytosis (HARE; derived from Stabilin-2 by proteolysis), which contains four endocytic motifs (M1-M4). Endocytosis of HARE•Hep complexes is targeted to coated pits by M1, M2, and M3 (Pandey et al, Int. J. Cell Biol. 2015, article ID 524707), which activates ERK1/2 and NF-κB (Pandey et al J. Biol. Chem. 288, 14068-79, 2013). Here, we used a NF-κB promoter-driven luciferase gene assay and cell lines expressing different HARE cytoplasmic domain mutants to identify motifs needed for Hep-mediated signaling. Deletion of M1, M2 or M4 singly had no effect on Hep-mediated ERK1/2 activation, whereas signaling (but not uptake) was eliminated in HARE(ΔM3) cells lacking NPLY2519. ERK1/2 signaling in cells expressing WT HARE(Y2519A) or HARE(Y2519A) lacking M1, M2 and M4 (containing M3-only) was decreased by 75% or eliminated, respectively. Deletion of M3 (but not M1, M2 or M4) also inhibited the formation of HARE•Hep•ERK1/2 complexes by 67%. NF-κB activation by HARE-mediated uptake of Hep, HA, dermatan sulfate or acetylated LDL was unaffected in single-motif deletion mutants lacking M1, M2 or M4. In contrast, cells expressing HARE(ΔM3) showed loss of HARE-mediated NF-κB activation during uptake of each of these four ligands. NF-κB activation by the four signaling ligands was also eliminated in HARE(Y2519A) or HARE(M3-only;Y2519A) cells. We conclude that the HARE NPLY2519 motif is necessary for both ERK1/2 and NF-κB signaling and that Tyr2519 is critical for these functions.

Stabilin-1 and Stabilin-2 are specific receptors for the cellular internalization of phosphorothioate-modified antisense oligonucleotides (ASOs) in the liver

Phosphorothioate (PS)-modified antisense oligonucleotides (ASOs) have been extensively investigated over the past three decades as pharmacological and therapeutic agents. One second generation ASO, Kynamro™, was recently approved by the FDA for the treatment of homozygous familial hypercholesterolemia and over 35 second generation PS ASOs are at various stages of clinical development. In this report, we show that the Stabilin class of scavenger receptors, which were not previously thought to bind DNA, do bind and internalize PS ASOs. With the use of primary cells from mouse and rat livers and recombinant cell lines each expressing Stabilin-1 and each isoform of Stabilin-2 (315-HARE and 190-HARE), we have determined that PS ASOs bind with high affinity and these receptors are responsible for bulk, clathrin-mediated endocytosis within the cell. Binding is primarily dependent on salt-bridge formation and correct folding of the intact protein receptor. Increased internalization rates also enhanced ASO potency for reducing expression of the non-coding RNA Malat-1, in Stabilin-expressing cell lines. A more thorough understanding of mechanisms by which ASOs are internalized in cells and their intracellular trafficking pathways will aid in the design of next generation antisense agents with improved therapeutic properties.

Respective roles of hyaluronidases 1 and 2 in endogenous hyaluronan turnover

We studied the physiologic roles of the hyaluronidase (HYAL) 1 and HYAL2 in hyaluronan (HA) turnover. HA was localized and quantified using HA binding proteins in various tissues of Hyal1(-/-) and Hyal2(-/-) mice (knockout mice) as well as control mice. HA MW was determined using gel filtration chromatography. HA endocytosis in liver nonparenchymal cells (NPCs) was quantified in vivo Both Hyal1 and Hyal2 knockout mice showed HA accumulation in peripheral tissues without changes in HA MW distribution. HYAL2 deficiency induced buildup of very high MW (>3.10(6) Da) HA in lymph and serum with severe lymph node distortion. The lack of HYAL2 also impaired high MW HA endocytosis by liver NPCs. HYAL1 deficiency led to a moderate increase in serum HA concentration without changes in HA MW distribution and to HA overload of liver NPCs. Wild-type C57BL/6 mice served as controls. In HA injection experiments, saline-injected mice served as additional controls. We conclude that: 1) HYAL1 and HYAL2 are both needed for tissue HA catabolism; 2) HYAL2 is required for high MW HA clearance in lymph nodes and plasma and for HA endocytosis by liver NPCs; and 3) the main role of HYAL1 is HA degradation within liver NPCs.-Bourguignon, V., Flamion, B. Respective roles of hyaluronidases 1 and 2 in endogenous hyaluronan turnover.

Impact of serum glycosylated Wisteria floribunda agglutinin positive Mac-2 binding protein levels on liver functional reserves and mortality in patients with liver cirrhosis

AIM

Serum glycosylated Wisteria floribunda agglutinin positive Mac-2 binding protein (WFA(+) -M2BP) levels are a non-invasive and reliable marker to assess the degree of liver fibrosis. We investigated the use of WFA(+) -M2BP levels to predict mortality in patients with liver cirrhosis (LC).

METHODS

This retrospective study consisted of 59 consecutive patients. Liver fibrosis was estimated by hyaluronic acid (HA), 7S fragment of type IV collagen (7S collagen), aspartate aminotransferase-to-platelet ratio index (APRI) and FIB-4 index. The severity of liver disease was evaluated by Child-Pugh classification and the Model for End-Stage Liver Disease (MELD) score. Cox proportional hazards regression analysis was performed to evaluate risk factors for mortality, and the diagnostic accuracy of WFA(+) -M2BP levels to predict mortality was examined using receiver-operator curves.

RESULTS

Serum WFA(+) -M2BP levels of Child-Pugh class A, B and C had cut-off indexes (COI) of 2.90, 6.15 and 9.45, respectively. WFA(+) -M2BP levels were positively correlated with HA, 7S collagen, APRI, FIB-4 index, Child-Pugh class and MELD score. Multivariate analysis identified WFA(+) -M2BP levels as an independent risk factor of mortality (hazard ratio = 1.19, 95% confidence interval = 1.02-1.41, P = 0.03), and the optimal cutoff point to predict mortality was 5.0 COI. The survival rate was significantly lower in patients with WFA(+) -M2BP levels 5.0 or more COI than in patients with WFA(+) -M2BP of less than 5.0 COI (P = 0.002).

CONCLUSION

Serum WFA(+) -M2BP levels were significantly correlated with both liver function reserves and liver fibrosis, and were independently associated with mortality in patients with LC.

HARE-Mediated Endocytosis of Hyaluronan and Heparin Is Targeted by Different Subsets of Three Endocytic Motifs

The hyaluronan (HA) receptor for endocytosis (HARE) is a multifunctional recycling clearance receptor for 14 different ligands, including HA and heparin (Hep), which bind to discrete nonoverlapping sites. Four different functional endocytic motifs (M) in the cytoplasmic domain (CD) target coated pit mediated uptake: (YSYFRI²⁴⁸⁵ (M1), FQHF²⁴⁹⁵ (M2), NPLY²⁵¹⁹ (M3), and DPF²⁵³⁴ (M4)). We previously found (Pandey et al. J. Biol. Chem. 283, 21453, 2008) that M1, M2, and M3 mediate endocytosis of HA. Here we assessed the ability of HARE variants with a single-motif deletion or containing only a single motif to endocytose HA or Hep. Single-motif deletion variants lacking M1, M3, or M4 (a different subset than involved in HA uptake) showed decreased Hep endocytosis, although M3 was the most active; the remaining redundant motifs did not compensate for loss of other motifs. Surprisingly, a HARE CD variant with only M3 internalized both HA and Hep, whereas variants with either M2 or M4 alone did not endocytose either ligand. Internalization of HA and Hep by HARE CD mutants was dynamin-dependent and was inhibited by hyperosmolarity, confirming clathrin-mediated endocytosis. The results indicate a complicated relationship among multiple CD motifs that target coated pit uptake and a more fundamental role for motif M3.

A hyaluronan receptor for endocytosis (HARE) link domain N-glycan is required for extracellular signal-regulated kinase (ERK) and nuclear factor-κB (NF-κB) signaling in response to the uptake of hyaluronan but not heparin, dermatan sulfate, or acetylated low density lipoprotein (LDL)

The human hyaluronan (HA) receptor for endocytosis (HARE; the 190-kDa C terminus of Stab2) is a major clearance receptor for multiple circulating ligands including HA, heparin (Hep), acetylated LDL (AcLDL), dermatan sulfate (DS), apoptotic debris, and chondroitin sulfate types A, C, D, and E. We previously found that HARE contains an N-glycan in the HA binding Link domain (at Asn(2280)), and cells expressing membrane-bound HARE(N2280A) bind and endocytose HA normally (Harris, E. N., Parry, S., Sutton-Smith, M., Pandey, M. S., Panico, M., Morris, H. R., Haslam, S. M., Dell, A., and Weigel, P. H. (2010) Glycobiology 20, 991-1001). Also, NF-κB-mediated signaling is activated by HARE-mediated endocytosis of HA, Hep, AcLDL, or DS but not by chondroitin sulfates (Pandey, M. S., and Weigel, P. H. (2014) J. Biol. Chem. 289, 1756-1767). Here we investigated the role of Link N-glycans in ligand uptake and NF-κB and ERK1/2 signaling. HA·HARE-mediated ERK1/2 activation was HA size- dependent, as found for NF-κB activation. HARE(N2280A) cells internalized HA, Hep, AcLDL, and DS normally. No ERK1/2 activation occurred during HA endocytosis by HARE(N2280A) cells, but activation did occur with Hep. Dual-luciferase recorder assays showed that NF-κB-mediated gene expression occurred normally in HARE(N2280A) cells endocytosing Hep, AcLDL, or DS but did not occur with HA. Activation of NF-κB by endogenous degradation of IκB-α was observed for HARE(N2280A) cells endocytosing Hep, AcLDL, or DS but not HA. We conclude that a Link domain complex N-glycan is required specifically for HARE·HA-mediated activation of ERK1/2 and NF-κB-mediated gene expression and that this initial activation mechanism is different from and independent of the initial mechanisms for HARE-mediated signaling in response to Hep, AcLDL, or DS uptake.

Hyaluronic acid receptor for endocytosis (HARE)-mediated endocytosis of hyaluronan, heparin, dermatan sulfate, and acetylated low density lipoprotein (AcLDL), but not chondroitin sulfate types A, C, D, or E, activates NF-κB-regulated gene expression

The hyaluronan (HA) receptor for endocytosis (HARE; Stab2) clears 14 systemic ligands, including HA and heparin. Here, we used NF-κB promoter-driven luciferase reporter assays to test HARE-mediated intracellular signaling during the uptake of eight ligands, whose binding sites in the HARE ectodomain were mapped by competition studies (Harris, E. N., and Weigel, P. H. (2008) Glycobiology 18, 638-648). Unique intermediate size Select-HA(TM), heparin, dermatan sulfate, and acetylated LDL stimulated dose-dependent HARE-mediated NF-κB activation of luciferase expression, with half-maximal values of 10-25 nM. In contrast, chondroitin sulfate types A, C, D, and E did not stimulate NF-κB activation. Moreover, degradation of endogenous IkB-α (an NF-κB inhibitor) was stimulated only by the signaling ligands. The stimulatory activities of pairwise combinations of the four signaling ligands were additive. The four nonstimulatory chondroitin sulfate types, which compete for HA binding, also effectively blocked HA-stimulated signaling. Clathrin siRNA decreased clathrin expression by ∼50% and completely eliminated NF-κB-mediated signaling by all four ligands, indicating that activation of signaling complexes occurs after endocytosis. These results indicate that HARE not only binds and clears extracellular matrix degradation products (e.g. released normally or during infection, injury, tumorigenesis, or other stress situations) but that a subset of ligands also serves as signaling indicator ligands. HARE may be part of a systemic tissue-stress sensor feedback system that responds to abnormal tissue turnover or damage as a danger signal; the signaling indicator ligands would reflect the homeostatic status, whether normal or pathological, of tissue cells and biomatrix components.

The hyaluronan receptor for endocytosis (HARE) activates NF-κB-mediated gene expression in response to 40-400-kDa, but not smaller or larger, hyaluronans

The hyaluronan (HA) receptor for endocytosis (HARE; Stabilin-2) binds and clears 14 different ligands, including HA and heparin, via clathrin-mediated endocytosis. HA binding to HARE stimulates ERK1/2 activation (Kyosseva, S. V., Harris, E. N., and Weigel, P. H. (2008) J. Biol. Chem. 283, 15047-15055). To assess a possible HA size dependence for signaling, we tested purified HA fractions of different weight-average molar mass and with narrow size distributions and Select-HA(TM) for stimulation of HARE-mediated gene expression using an NF-κB promoter-driven luciferase reporter system. Human HARE-mediated gene expression was stimulated in a dose-dependent manner with small HA (sHA) >40 kDa and intermediate HA (iHA) <400 kDa. The hyperbolic dose response saturated at 20-50 nM with an apparent K(m) ~10 nM, identical to the Kd for HA-HARE binding. Activation was not detected with oligomeric HA (oHA), sHA <40 kDa, iHA >400 kDa, or large HA (lHA). Similar responses occurred with rat HARE. Activation by sHA-iHA was blocked by excess nonsignaling sHA, iHA, or lHA, deletion of the HA-binding LINK domain, or HA-blocking antibody. Endogenous NF-κB activation also occurred in the absence of luciferase plasmids, as assessed by degradation of IκB-α. ERK1/2 activation was also HA size-dependent. The results show that HA-HARE interactions stimulate NF-κB-activated gene expression and that HARE senses a narrow size range of HA degradation products. We propose a model in which optimal length HA binds multiple HARE proteins to allow cytoplasmic domain interactions that stimulate intracellular signaling. This HARE signaling system during continuous HA clearance could monitor the homeostasis of tissue biomatrix turnover throughout the body.

Preoperative liver function assessments to estimate the prognosis and safety of liver resections

Liver function assessment is important to ensure safe surgical procedures in patients with hepatocellular disease. Because the liver influences a wide variety of functions, including protein synthesis and metabolic, immune and storage functions, no single parameter is sufficient to adequately address all of these functions. We reviewed the relevant literature concerning the scoring systems, functional tests, plasma parameters and imaging modalities currently used to evaluate the liver function in an attempt to determine which parameters provide the most comprehensive and useful results. While the Child-Pugh scoring system is the gold standard for liver disease assessment, the liver damage grading system recommended by the Liver Cancer Study Group of Japan is also useful. Various models for end-stage liver disease scoring are used for organ allocation. While the indocyanine green clearance test is widely accepted throughout the world, other assessments have not been used routinely for clinical evaluations. The levels of plasma proteins, including albumin, prealbumin, retinol binding protein, apolipoprotein, coagulation factors and antithrombin III, represent the liver productivity. Liver fibrotic markers also correlate with liver function. Imaging modalities such as (99m)Tc-galactosyl serum albumin scintigraphy, (99m)Tc-mebrofenin hepatobiliary scintigraphy and transient elastography are also available, but future studies are needed to validate their clinical efficacy.

Serum markers for predicting significant necroinflammatory activity in patients with chronic hepatitis B

OBJECTIVES

The aim of this study was to determine the serum markers that predict significant inflammation in patients with chronic hepatitis B (CHB).

DESIGN AND METHODS

Between October 2005 and June 2009, 384 subjects with CHB were enrolled.

RESULTS

Multiple logistic regression analysis identified the ALT, hyaluronic acid (HA) and procollagen III N-terminal peptide (PIIINP) as independent predictors of significant inflammation (grade≥3). We constructed a formula for predicting significant inflammation. A significant inflammation (SI) score=1.773×ALT score+1.599×PIIINP score+0.677×HA score-1.962. The area under receiver operating characteristic curve of the SI score was 0.831. The sensitivity, specificity, positive predictive value and negative predictive value of the SI score were 79.5%, 70.8%, 76.8% and 74.3%, respectively.

CONCLUSIONS

A simple scoring system including ALT, PIIINP and HA is an accurate non-invasive predictor of significant inflammatory activities in patients with CHB.

Molecular serum markers of liver fibrosis

Fibrosis is a hallmark histologic event of chronic liver diseases and is characterized by the excessive accumulation and reorganization of the extracellular matrix (ECM). The gold standard for assessment of fibrosis is liver biopsy. As this procedure has various limitations, including risk of patient injury and sampling error, a non-invasive serum marker for liver fibrosis is desirable. The increasing understanding of the pathogenesis of hepatic fibrosis has suggested several markers which could be useful indicators of hepatic fibrogenesis and fibrosis. These markers include serum markers of liver function, ECM synthesis, fibrolytic processes, ECM degradation and fibrogenesis related cytokines. Recently, neo-epitopes, which are post-translational modifications of proteins, have been successfully used in bone and cartilage diseases which are characterized by extensive ECM remodeling. Increasing numbers of studies are being undertaken to identify neo-epitopes generated during liver fibrosis, and which ultimately might be useful for diagnosing and monitoring fibrogenesis. To date, the metalloproteinases generated fragment of collagen I, III, IV and VI have been proven to be elevated in two rat models of fibrosis. This review summarizes the recent efforts that have been made to identify potentially reliable non-invasive serum markers. We used the recently proposed BIPED (Burden of disease, Investigative, Prognostic, Efficacy and Diagnostic) system to characterize potential serum markers and neo-epitope markers that have been identified to date.

Preparation and the kinetic stability of hyaluronan radiolabeled with 111In, 125I and 14C

Three different procedures for the labeling of hyaluronan (HA) with (111)In, (125)I and (14)C radionuclides were compared, and the kinetic stability of radiolabeled HA under different conditions (saline, artificial gastric juice and plasma) was established. Modification of HA structure with bifunctional chelating agents (DTPA) or with the prosthetic group (tyramine or tyrosine) was essential prior (111)In and (125)I labeling. These chemical labeling techniques were fast, simple and inexpensive, and labeled agents with a high specific activity were obtained. The only disadvantage of these methods was the occurrence of unknown functional groups in the HA molecule requiring further characterization of the compound. Conversely, HA labeling with (14)C by biotechnological synthesis was found to be rather expensive and time-consuming process. Although, the final product (14)C-HA was identical to natural HA its low specific activity presents certain limitation for its application in biological experiments. Stability studies showed that (14)C-HA and (125)I-Tm-HA were stable in all studied mediums. In the case of (125)I-Trs-HA, stability slightly decreased in rat plasma and in artificial gastric juice with increasing time. The least stable was (111)In-DTPA-HA, which degraded completely after 48h in artificial gastric juice. Kinetic stability studies may provide primary information concerning the properties of radiolabeled HA in vitro, which is essential for the use and explanation of its behavior in biological experiments.

Staging of liver fibrosis in chronic hepatitis B patients with a composite predictive model: A comparative study

AIM: To evaluate the efficacy of 6 noninvasive liver fibrosis models and to identify the most valuable model for the prediction of liver fibrosis stage in chronic hepatitis B (CHB) patients.

METHODS: Seventy-eight CHB patients were consecutively enrolled in this study. Liver biopsy was performed and blood serum was obtained at admission. Histological diagnosis was made according to the METAVIR system. Significant fibrosis was defined as stage score ≥ 2, severe fibrosis as stage score ≥ 3. The diagnostic accuracy of 6 noninvasive liver fibrosis models, including serum aspartate aminotransferase (AST) to platelet ratio index (APRI), FIB-4, Forn’s index, Fibrometer, Hepascore, and Shanghai Liver Fibrosis Group’s index (SLFG), was investigated.

RESULTS: The APRI, FIB-4 and Forn’s index under receiver operating characteristic curve (AUROC) for significant fibrosis were 0.71, 0.75 and 0.79, respectively, with a diagnosis accuracy of 67%, 77% and 80%, respectively, and 0.80, 0.87 and 0.86, respectively, under the AUROC for severe fibrosis. The Hepascore, SLFG, and Fibrometer were 0.80, 0.83 and 0.85, respectively under the AUROC for significant fibrosis (P < 0.01). The diagnosis accuracy of Hepascore and SLFG was 86% and 88%, respectively. The Hepascore, SLFG, and Fibrometer were 0.95, 0.93, and 0.94, respectively, under the AUROC for severe fibrosis (P < 0.01).

CONCLUSION: The models containing direct serum markers have a better diagnostic value than those not containing direct serum markers.

The cytoplasmic domain of the hyaluronan receptor for endocytosis (HARE) contains multiple endocytic motifs targeting coated pit-mediated internalization

The hyaluronic acid (HA) receptor for endocytosis (HARE) is the primary scavenger receptor for HA and chondroitin sulfates in mammals. The two human isoforms of HARE (full-length 315-kDa and a 190-kDa proteolytic cleavage product), which are type I single-pass membrane proteins, are highly expressed in sinusoidal endothelial cells of lymph nodes, liver, and spleen. Their identical HARE cytoplasmic domains contain four candidate AP-2/clathrin-mediated endocytic signaling motifs as follows: YSYFRI(2485), FQHF(2495), NPLY(2519), and DPF(2534) (315-HARE numbering). Stably transfected cells expressing 190-HARE(DeltaYSYFRI), 190-HARE(DeltaFQHF), or 190-HARE(DeltaNPLY) (lacking Motifs 1, 2, or 3) had decreased (125)I-HA endocytosis rates of approximately 49, approximately 39, and approximately 56%, respectively (relative to wild type). In contrast, 190-HARE(DeltaDPF) cells (lacking Motif 4) showed no change in HA endocytic rate. Deletions of motifs 1 and 2 or of 1, 2, and 4 decreased the rate of HA endocytosis by only approximately 41%. Endocytosis was approximately 95% decreased in mutants lacking all four motifs. Cells expressing a 190-HARE(Y2519A) mutant of the NPLY motif retained 85-90% of wild type endocytosis, whereas this mutation in the triple motif deletant decreased endocytosis to approximately 7% of wild type. Tyr in NPLY(2519) is thus important for endocytosis. All HARE mutants showed similar HA binding and degradation of the internalized HA, indicating that altering endocytic motifs did not affect ectodomain binding of HA or targeting of internalized HA to lysosomes. We conclude that, although NPLY may be the most important motif, it functions together with two other endocytic motifs; thus three signal sequences (YSYFRI, FQHF, and NPLY) provide redundancy to mediate coated pit targeting and endocytosis of HARE.

Diagnosis and quantitation of fibrosis

Hepatic fibrosis is the final common pathway for many different liver insults. Originally considered to be irreversible, hepatic fibrosis is now known to be a dynamic process with a significant potential for resolution. The diagnosis and quantitation of fibrosis have traditionally relied on liver biopsy. However, there are a number of drawbacks including the invasive nature of the procedure, sampling error, and interobserver variability. This article reviews the current role of liver biopsy in the assessment of hepatic fibrosis and discusses the role of the newer noninvasive methods including serum markers and radiologic tests.

The human hyaluronan receptor for endocytosis (HARE/Stabilin-2) is a systemic clearance receptor for heparin

The hyaluronic acid receptor for endocytosis (HARE; also designated Stabilin-2) mediates systemic clearance of hyaluronan and chondroitin sulfates from the vascular and lymphatic circulations. The internalized glycosaminoglycans are degraded in lysosomes, thus completing their normal turnover process. Sinusoidal endothelial cells of human liver, lymph node, and spleen express two HARE isoforms of 315 and 190 kDa. Here we report that the 190- and 315-kDa HARE isoforms, expressed stably either in Flp-In 293 cell lines or as soluble ectodomains, specifically bind heparin (Hep). The K(d) for Hep binding to purified 190- and 315-kDa HARE ectodomains was 17.2 +/- 4.9 and 23.4 +/- 5.3 nm, respectively. Cells expressing HARE readily and specifically internalized (125)I-streptavidin-biotin-Hep complexes, which was inhibited >70% by hyperosmolar conditions, confirming that uptake is mediated by the clathrin-coated pit pathway. Internalization of Hep occurred for many hours with an estimated HARE recycling time of approximately 12 min. Internalized fluorescent streptavidin-biotin-Hep was present in a typical endocytic vesicular pattern and was delivered to lysosomes. We conclude that HARE in the sinusoidal endothelial cells of lymph nodes and liver likely mediates the efficient systemic clearance of Hep and many different Hep-binding protein complexes from the lymphatic and vascular circulations.

The hyaluronan receptor for endocytosis mediates hyaluronan-dependent signal transduction via extracellular signal-regulated kinases

The hyaluronan (HA) receptor for endocytosis (HARE) mediates the endocytotic clearance of HA and other glycosaminoglycans from lymph and blood. Two isoforms of human HARE, 315- and 190-kDa, are highly expressed in sinusoidal endothelial cells of liver, lymph node, and spleen; HARE is also in specialized cells in the eye, heart, brain, and kidney. Here we determined whether HA binding to HARE initiates intracellular signaling in Flp-In 293 cells stably expressing either the 315- and 190-kDa HARE or the 190-kDa HARE alone. HARE was co-immunoprecipitated with extracellular signal-regulated kinase 1 and 2 (ERK1/2), c-Jun N-terminal protein kinase (JNK), and p38 members of the mitogen-activated protein kinase signaling cascade. ERK phosphorylation increased in a dose- and time-dependent manner when HA was added to cells expressing full-length or 190-kDa HARE, but not cells with vector-only or a HARE(DeltaLink) construct with greatly decreased ( approximately 90%) HA uptake. HA did not induce phosphorylation of JNK or p38. A maximum increase in phospho-ERK1/2 occurred within 30 min at 5 mug/ml HA, and the response was dampened at >20 mug/ml HA. HA binding did not increase the level of HARE-ERK complexes, but did increase HARE phosphorylation. These findings demonstrate a novel functional response, when HARE binds HA, that leads to activation of ERK1/2, important mediators of intracellular signal transduction.

The specific interaction between fibrin(ogen) and hyaluronan: possible consequences in haemostasis, inflammation and wound healing

We have proposed that fibrin and hyaluronan (HA) are macromolecular regulators during inflammation and wound healing. Here we extend our studies to characterize the specific interaction between fibrin(ogen) and HA. 125I-labelled HA (Mr approximately 32,000) was bound by plastic surfaces coated with human fibrinogen but not bovine serum albumin, ovalbumin, beta-lactoglobin or rabbit immunoglobulin G. 125I-labelled fibrinogen bound to a unique hexylamine derivative of HA coupled to Sepharose and was eluted specifically by HA oligosaccharides in a size-dependent manner. A dot blot assay, in which proteins are adsorbed to nitrocellulose and probed with 125I-HA, also showed specific binding to human fibrinogen. This assay was used to examine fibrinogens from other mammalian species. No specific 125I-HA binding was observed with the protein from horse, rat or cow. Significant binding was detected with human, sheep, rabbit, dog, baboon, goat and pig fibrinogens. Thrombin-induced formation of fibrin clots is also affected by HA, which decreases the lag time before clotting and increases the rate of clot formation. The rate of fibrin polymerization increased over 500% in the presence of 60 microM HA. Furthermore, the structure of the fibrin gel, as assessed by light scattering, was altered by HA or chondroitin sulphate in a concentration-dependent manner. The results support the proposed wound-healing model and indicate that an increase in circulating HA levels could adversely affect haemostasis and increase the risk of thrombosis or bleeding. The interaction between HA and fibrinogen emphasizes the importance of the liver endothelial cell HA receptor in the removal of glycosaminoglycans from the blood. Cultured cells continuously endocytosing 125I-HA for 4 h reutilized their total cellular HA receptors at least once every 50 min even in the presence of cycloheximide. This endocytotic receptor was therefore shown to be part of a recycling system.

Changes in hyaluronan concentration in tissues and body fluids in disease states

Proteins which specifically bind hyaluronan have been used to develop sensitive immunoassay-like analytical techniques. These assays have made it possible to analyse hyaluronan concentrations in nanogram amounts in tissues and body fluids. The normal adult human circulating level of hyaluronan varies between 10 and 100 micrograms/l. Increased levels of serum hyaluronan (greater than 1 mg/l) have been found in inflammatory rheumatic diseases such as rheumatoid arthritis, scleroderma and psoriatic arthritis. Even higher levels occur in serum from patients with cirrhotic liver diseases and in patients with malignant mesothelioma. Elevated serum hyaluronan levels are a sign either of increased production and/or outflow from the tissues or of decreased elimination of the polysaccharide in the liver endothelial cells or in other parts of the reticuloendothelial system or through the kidneys. The serum concentration is also influenced by increased age and by the degree of physical activity. Important information on pathological processes has been gained by analysing the hyaluronan concentration in other body fluids such as urine, perfusion fluid from the intestine and bronchoalveolar lavage fluid. In the future these analyses should also be useful in clinical work.

Liver dysfunction after lung recruitment manoeuvres during pressure-controlled ventilation in experimental acute respiratory distress

Introduction

Consequences of lung recruitment with prolonged high positive end-expiratory pressure (PEEP) ventilation for liver function are unclear. We therefore investigated liver dysfunction during two different ventilation treatment regimens of experimental acute respiratory distress syndrome.

Methods

Sixteen anaesthetised juvenile pietrain pigs were ventilated in the pressure-controlled mode (PCV) with an inspiratory fraction of oxygen (FiO₂) of 1.0, a respiratory frequency of 30 per minute, a tidal volume of 6 ml/kg, and a PEEP of 5 cm H₂O. After lung injury was induced by repeated pulmonary lavage with normal saline, animals were randomly assigned into two groups (n = 8 each) for a 24-hour trial: PCV (unchanged ventilation) and PCV with recruitment (PCV+R) (starting with a sustained inflation of 50 cm H₂O for 1 minute, the ventilation was continued while increasing PEEP in increments of 3 cm H₂O every 15 minutes as long as arterial oxygen tension [PaO₂] improved). After recruitment, FiO₂ was reduced to 0.4 and the PEEP was lowered every 15 minutes until PaO₂ decreased to 12.0 to 14.7 kPa (90 to 110 torr). Serum levels of hyaluronic acid (HA), routine liver serum markers, and plasma disappearance rate of indocyanine green (ICG) were tested before and after lung injury, and 6 and 18 hours after randomisation. Liver serum markers were also tested at 24 hours. Paraffin sections of liver tissue stained by haematoxylin and eosin were made after euthanisation.

Results

The PCV+R group exhibited more polymorphonuclear neutrophils and lymphocytes in the liver sinusoids: median score (interquartile range) of 1.5 (1.4 to 1.5) compared to 0.9 (0.7 to 1.1) (p = 0.01). Elevation of bilirubin, aspartate aminotransferase, and lactate dehydrogenase was more prominent in the PCV+R group. Plasma disappearance rate of ICG indicated no liver dysfunction. HA levels in the PCV+R group gradually increased and were significantly higher (p < 0.001) at 6 and 18 hours with 59 (57 to 64) and 75 (66 to 84) ng/ml, respectively, than in the PCV group with 34 (32 to 48) and 41 (38 to 42) ng/ml, respectively.

Conclusion

The PCV+R group showed a more prominent inflammatory reaction in their liver sinusoids accompanied by increased serum levels of liver enzymes and HA. Therefore, recruitment with higher PEEP levels for treatment of respiratory failure might lead to liver dysfunction.

Expression, processing, and glycosaminoglycan binding activity of the recombinant human 315-kDa hyaluronic acid receptor for endocytosis (HARE)

The hyaluronic acid (HA) receptor for endocytosis (HARE; also designated stabilin-2 and FEEL-2) mediates systemic clearance of glycosaminoglycans from the circulatory and lymphatic systems via coated pit-mediated uptake. HARE is primarily found as two isoforms (315- and 190-kDa) in sinusoidal endothelial cells of the liver, lymph node, and spleen. Here we characterize the ligand specificity and function of the large stably expressed 315-HARE isoform in Flp-In 293 cell lines. Like human spleen sinusoidal endothelial cells, Flp-In 293 cell lines transfected with a single cDNA encoding the full-length 315-HARE express both the 315-kDa and the proteolytically truncated 190-kDa isoforms in a ratio of approximately 3-4:1. The 190-kDa HARE isoform generated from the 315-kDa HARE and the 315-kDa HARE specifically bound 125I-HA. Like the 190-kDa HARE expressed alone (Harris, E. N., Weigel, J. A., and Weigel, P. H. (2004) J. Biol. Chem. 279, 36201-36209), the 190- and 315-kDa HARE isoforms expressed in 315-HARE cell lines were recognized by anti-HARE monoclonal antibodies 30, 154, and 159. All 315-HARE cell lines could endocytose and degrade 125I-HA. Competition studies with live cells indicate that 190-HARE and 315-HARE bind HA with higher apparent affinity (Kd approximately 10-20 nM) than chondroitin sulfate (CS) types A, C, D, or E. Only slight competition of HA endocytosis was observed with CS-B (dermatan sulfate) and chondroitin. Direct binding assays with the 315-HARE ectodomain revealed high affinity HA binding, and lower binding affinities for CS-C, CS-D, and CS-E. A majority of each HARE isoform was intracellular, within the endocytic system, suggesting transient surface residency typical of an active endocytic recycling receptor.

Serum hyaluronate level for predicting subclinical liver dysfunction after hepatectomy

The serum hyaluronate (HA) level reflects sinusoidal endothelial cell function correlated with liver function. We have reviewed multiple liver function indicators from 37 patients who underwent hepatectomy for various liver diseases. The serum HA level was well correlated with the indocyanine green retention rate at 15 minutes (ICGR15), lectin-cholesterol (LCAT), hepatocyte growth factor (HGF), liver uptake ratio of technetium-99m galactosyl human serum albumin (99mTc-GSA) at 15 minutes (HH15), prealbumin, and hepatic uptake ratio of 99mTc-GSA at 15 minutes (LHL15). In addition, the model for end-stage liver disease (MELD) score at 7 days after operation was well correlated with serum HA, ICGR15, HH15, and LHL15. In patients who showed serum an HA level of = 100 ng/ml before hepatectomy, the MELD score had significantly deteriorated by 7 days after hepatectomy. Of the 20 patients who showed a serum HA level < 100 ng/ml before hepatectomy, 11 had high serum HA after hepatectomy. The bilirubin level 7 days after operation in this group was much higher than that for patients who maintained a serum HA level < 100 ng/ml after hepatectomy. In addition, the serum HGF level before hepatectomy in this group was significantly lower. We concluded that the serum HA level is a reliable indicator when evaluating liver function and predicting liver dysfunction after hepatectomy. Furthermore, patients with a significantly low HGF level who have a normal HA level are susceptible to liver dysfunction after hepatectomy.

Rapid plasma membrane-endosomal trafficking of the lymph node sinus and high endothelial venule scavenger receptor/homing receptor stabilin-1 (FEEL-1/CLEVER-1)

The sinusoidal endothelia of liver, spleen, and lymph node are major sites for uptake and recycling of waste macromolecules through promiscuous binding to a disparate family of scavenger receptors. Among the most complex is stabilin-1, a large multidomain protein containing tandem fasciclin domains, epidermal growth factor-like repeats, and a C-type lectin-like hyaluronan-binding Link module, which functions as an endocytic receptor for acetylated low density lipoprotein and advanced glycation end products. Intriguingly, stabilin-1 has also been reported to mediate both homing of leukocytes across lymph node high endothelial venules and adhesion of metastatic tumor cells to peritumoral lymphatic vessels. Currently, however, it is not clear how stabilin-1 mediates these distinct functions. To address the issue, we have investigated the tissue and subcellular localization of stabilin-1 in detail and assessed the functional status of its Link module. We show that stabilin-1 is almost entirely intracellular in lymph node high endothelial venules, lymphatic sinus endothelium, and cultured endothelial cells but that a finite population, detectable only by fluorescent antibody or fluorescein-labeled (Fl)-acetylated low density lipoprotein uptake, cycles rapidly between the plasma membrane and EEA-1+ve (early endosome antigen 1) early endosomes. In addition, we show using full-length stabilin-1 cDNA and a stabilin-1/CD44 chimera in HeLa cells that intracellular targeting is influenced by the transmembrane domain/cytoplasmic tail, which contains a putative dileucine (DXXLL) Golgi to endosomal sorting signal. Finally, we provide evidence that the stabilin-1 Link domain binds neither hyaluronan nor other glycosaminoglycans. These properties support a role for stabilin-1 as a rapidly recycling scavenger receptor and argue against a role in cell adhesion or lymphocyte homing.

Hyaluronan blocks human neutrophil elastase (HNE)-induced airway responses in sheep

Hyaluronan (HA) blocks inhaled porcine pancreatic elastase-induced bronchoconstriction in sheep with airway hypersensitivity to Ascaris suum antigen. Since elastases from other species may display different catalytic properties compared to the human enzyme, we tested the efficacy of HA on human neutrophil elastase (HNE)-induced airway responses. We measured pulmonary resistance in allergic sheep before and after inhalation of HNE alone and after pretreatment with a 150 kD-HA (LKDHA; 3 and 15 mg), or a 300 kD-HA (HKDHA; 6, 7.5, and 15 mg). HKDHA (3 mg) was given either 0.5, 4, or 8 h before HNE challenge; LKDHA (15 mg) and HKDHA (6, 7.5, and 15 mg) were given 8 h before challenge. HNE caused an acute bronchoconstriction which was blocked by 3 mg LKDHA given 0.5 or 4 h before challenge. LKDHA (3 mg) given 8 h before challenge was ineffective, but protection was achieved by increasing the dose to 15 mg. When HKDHA at 6, 7.5, and 15 mg was given 8 h before challenge a dose-dependent inhibition of the HNE-induced airway response was observed. We conclude that HA inhibits HNE-induced airway responses and that within the range of 150-300 kD, dose rather than molecular weight may be the most important determinant of pretreatment time resulting in a protective effect.

Endocytic function, glycosaminoglycan specificity, and antibody sensitivity of the recombinant human 190-kDa hyaluronan receptor for endocytosis (HARE)

The human hyaluronan receptor for endocytosis (hHARE) mediates the endocytic clearance of hyaluronan (HA) and chondroitin sulfate from lymph fluid and blood. Two hHARE isoforms (190 and 315 kDa) are present in sinusoidal endothelial cells of liver, spleen, and lymph nodes (Zhou, B., McGary, C. T., Weigel, J. A., Saxena, A., and Weigel, P. H. (2003) Glycobiology 13, 339-349). Here we report the specificity and function of the 190-kDa HARE, expressed without the larger isoform, in Flp-In 293 cell lines (190hHARE cells). Like the native protein, recombinant hHARE contains approximately 25 kDa of N-linked oligosaccharides, binds HA in a ligand blot assay, cross-reacts with three anti-rat HARE monoclonal antibodies, and is inactivated by reduction. The 190hHARE cell lines mediated rapid, continuous (125)I-HA endocytosis and degradation for >1 day. About 30-50% of the total cellular receptors were on the cell surface, and their recycling time for reutilization was approximately 8.5 min. The average K(d) for the binding of HA to the 190-kDa hHARE at 4 degrees C was 7 nm with 118,000 total HA binding sites per cell. Competition studies at 37 degrees C indicated that the 190-kDa hHARE binds HA and chondroitin better than dermatan sulfate and chondroitin sulfates A, C, D, and E, but it does not bind to heparin, heparan sulfate, or keratan sulfate. Although competition was observed at 37 degrees C, none of the glycosaminoglycans tested, except HA, competed for (125)I-HA binding by 190hHARE cells at 4 degrees C. Anti-HARE monoclonal antibodies #30 and #154, which do not inhibit (125)I-HA uptake mediated by the 175-kDa rat HARE, partially blocked HA endocytosis by the 190-kDa hHARE. We conclude that the 190-kDa hHARE can function independently of other hHARE isoforms to mediate the endocytosis of multiple glycosaminoglycans. Furthermore, the rat and human small HARE isoforms have different glycosaminoglycan specificities and sensitivities to inhibition by cross-reacting antibodies.

Characterization of the recombinant rat 175-kDa hyaluronan receptor for endocytosis (HARE)

Hyaluronan (HA) and chondroitin sulfate (CS) clearance from lymph and blood in mammals is mediated by the HA receptor for endocytosis (HARE), which is present as two isoforms in rat and human (175/300 kDa and 190/315 kDa, respectively) in the sinusoidal endothelial cells of liver, spleen, and lymph nodes (Zhou, B., McGary, C. T., Weigel, J. A., Saxena, A., and Weigel, P. H. (2003) Glycobiology 13, 339-349). The small rat and human HARE proteins are not encoded directly by mRNA but are derived from larger precursors. Here we characterize the specificity and function of the 175-kDa HARE, expressed in the absence of the 300-kDa species, in stably transfected SK-Hep-1 cells. The HARE cDNA was fused with a leader sequence to allow correct orientation of the membrane protein. The recombinant rHARE contained approximately 25 kDa of N-linked oligosaccharides and, like the native protein, was able to bind HA in a ligand blot assay, even after de-N-glycosylation. SK-HARE cell lines demonstrated specific 125I-HA endocytosis, receptor recycling, and delivery of HA to lysosomes for degradation. The Kd for the binding of HA (number-average molecular mass approximately 133 kDa) to the 175-kDa HARE at 4 degrees C was 4.1 nm with 160,000 to 220,000 HA-binding sites per cell. The 175-kDa rHARE binds HA, dermatan sulfate, and chondroitin sulfates A, C, D, and E, but not chondroitin, heparin, heparan sulfate, or keratan sulfate. Surprisingly, recognition of glycosaminoglycans (GAGs) other than HA by native or recombinant HARE was temperature-dependent. Although competition was observed at 37 degrees C, none of the other GAGs competed for 125I-HA binding to SK-HARE cells at 4 degrees C. Anti-HARE monoclonal antibody-174 showed a similar temperature-dependence in its ability to block HA endocytosis. These data suggest that temperature-induced conformational changes may alter the GAG specificity of HARE. The results confirm that the 175-kDa rHARE does not require the larger HARE isoform to mediate endocytosis of multiple GAGs.

Serum hyaluronate correlates with histological progression in alcoholic liver disease

OBJECTIVES

Chronic alcohol consumption may lead to the development of liver cirrhosis. Serum concentrations of hyaluronate were suggested as a predictor in chronic liver disease, but its power to distinguish between severity of fibrosis and inflammation had not been assessed. In order to evaluate hyaluronate as a marker to detect early stages of alcoholic liver disease and to establish a possible correlation with hepatic histology, serum concentrations were measured by radioimmunoassay in 87 patients with biopsy-proven fatty liver, fatty liver and mild fibrosis, fatty liver and inflammation, severe fibrosis and inflammation, and cirrhosis, and in 12 non-alcoholic control subjects. In addition, serum hyaluronate was determined in 40 non-cirrhotic alcoholic patients with either a normal serum aspartate aminotransferase (AST) or an AST elevated at least two-fold.

RESULTS

Serum hyaluronate increased significantly with advanced stages of alcoholic liver disease, while levels in patients with fatty liver were elevated only slightly without reaching significance. Hyaluronate correlated well with histological stage and was highly sensitive for detecting fibrosis in general and perivenular fibrosis as an indicator of progression to cirrhosis. Hyaluronate levels were not influenced by AST levels.

CONCLUSION

Serum hyaluronate is a good predictor of the presence of even moderate hepatic fibrosis in alcoholic liver disease, justifying its clinical use to assess morphological alterations of the liver in alcoholics.

A blocking antibody to the hyaluronan receptor for endocytosis (HARE) inhibits hyaluronan clearance by perfused liver

Hyaluronan (HA) and chondroitin sulfate clearance from lymph and blood is mediated by the hyaluronan receptor for endocytosis (HARE). The purification and molecular cloning (Zhou, B., Weigel, J. A., Saxena, A., and Weigel, P. H. (2002) Mol. Biol. Cell 13, 2853-2868) of this cell surface receptor were finally achieved after we developed monoclonal antibodies (mAbs) against HARE. There are actually two independent isoreceptors for HA, which in rat are designated the 175-kDa HARE and 300-kDa HARE. Only one mAb (number 174) effectively and completely blocked the specific uptake of 125I-HA at 37 degrees C by rat liver sinusoidal endothelial cells. 125I-HA binding to both the 175-kDa and 300-kDa HARE proteins in a ligand blot assay was almost completely inhibited by <1 microg/ml mAb-174, whereas mouse IgG had little or no effect. MAb-174 also performed very well in Western analysis, indirect fluorescence microscopy, and a variety of immuno-procedures. Immunohistochemistry using mAb-174 localized HARE to the sinusoidal cells of rat liver, spleen, and lymph node. Western analysis using mAb-174 revealed that the sizes of both HARE glycoproteins were the same in these three tissues. 125I-HA was taken up and degraded by excised rat livers that were continuously perfused ex vivo with a recirculating medium. This HA clearance and metabolism by liver, which is a physiological function of HARE, was very effectively blocked by mAb-174 but not by mouse IgG. The results indicate that mAb-174 will be a useful tool to study the functions of HARE and the physiological significance of HA clearance.

Use of Iodinated Hyaluronan Derivatives to Study Hyaluronan Binding, Endocytosis, and Metabolism by Cultured Cells

We have described several simple procedures to determine whether cells have specific receptors or binding proteins for HA. The advantage of using the uniquely modified 125I-labeled HA as a probe is that low levels of binding can be detected. It has been straightforward and productive to use 125I-labeled HA to quantitate cell surface and intracellular binding sites to determine affinity constants for HA binding and to determine whether the cell type being studied can efficiently endocytose and degrade the HA. The 125I-labeled HA preparations and assays described here and in Chapter 26 provide a very useful array of methods for studying the biochemistry and cell biology of HA.

Molecular cloning and functional expression of the rat 175-kDa hyaluronan receptor for endocytosis

We recently purified the rat liver hyaluronan receptor for endocytosis (HARE) and found abundant expression of 175- and approximately 300-kDa HARE species in sinusoidal endothelial cells of the liver, spleen, and lymph nodes. We report herein the first cloning and functional expression of the rat 175-kDa HARE. Peptide sequences were obtained from the purified 175-kDa HARE, and degenerate oligonucleotide primers were designed for reverse transcription-polymerase chain reaction and cDNA cloning. Results of 5'-rapid amplification of cDNA ends, Northern analysis, N-terminal sequence, and antibody reactivity analyses indicated the absence of mRNA directly encoding the 175-kDa HARE. This protein is most likely derived from a larger precursor. Accordingly, we constructed an artificial 4.7-kb cDNA encoding the 1431 amino acid 175-kDa HARE. The predicted type I membrane protein has a mass of 156,393 Da and a pI of 7.86. The 175-kDa HARE cDNA, fused to the N-terminal leader sequence of the Ig kappa-chain, was transfected transiently into COS-7 cells and stably into SK-Hep-1 cells, respectively, to assess hyaluronan or hyaluronic acid (HA)-binding activity and endocytosis. In both cases, HARE expression and HA-binding activity were detected. Furthermore, stable SK-175HARE cells demonstrated specific endocytosis of (125)I-HA and receptor recycling. Fluorescence-activated cell sorting analysis confirmed that recombinant HARE was expressed on the cell surface and that fluorescent HA uptake was inhibited by a specific blocking monoclonal antibody against HARE. Additionally, HARE was substantially colocalized with clathrin, but not with internalized HA that was delivered to lysosomes. The results confirm that recombinant 175-kDa HARE is an authentic endocytic receptor for HA and that this receptor can function independently of the approximately 300-kDa HARE. HARE is the first functionally identified member of a protein family that shares a similar organization of Fasciclin, epidermal growth factor-like, Xlink, and transmembrane domains.

The hyaluronan receptor for endocytosis (HARE) is not CD44 or CD54 (ICAM-1)

Mammalian liver contains an endocytic, recycling receptor that mediates the clearance of hyaluronan (HA) and chondroitin sulfate from the circulation. McCourt et al. [J. Biol. Chem. 269 (1994) 30081] previously reported that this endocytic liver HA receptor was ICAM-1. In contrast, we purified this HA receptor for endocytosis (HARE) from rat liver sinusoidal endothelial cells (LECs) and obtained two novel large proteins [Zhou et al., J. Biol. Chem. 274 (1999) 33831]. The goal of the present study was to clarify this inconsistency and determine whether CD44, which is also an HA receptor, or ICAM-1 (CD54) is identical to, or is part of, HARE. Although isolated liver LECs contain HARE, CD44, and ICAM-1, confocal fluorescence microscopy showed that the two latter proteins have cellular distributions that are distinct from and essentially nonoverlapping with HARE. HA accumulation by cultured LECs was inhibited >98% by an antibody against HARE and unaffected by antibodies to ICAM-1 or CD44, indicating that virtually all specific HA uptake is mediated by HARE and not by ICAM-1 or CD44. Finally, no reactivity was observed against purified HARE in an ELISA-based assay using CD44 or ICAM-1 antibodies. The results confirm that the mammalian endocytic HA receptor is HARE and is not ICAM-1 or CD44.

Changes in serum hyaluronic acid levels and expression of CD44 and CD44 mRNA in hepatic sinusoidal endothelial cells after major hepatectomy in cirrhotic rats

Serum hyaluronic acid (HA) is widely distributed in connective tissues, and the majority of circulating HA is degraded by hepatic sinusoidal endothelial cells (SECs) via a receptor recycling pathway. Our previous clinical study revealed that monitoring serum HA levels after hepatectomy is useful in predicting the development of liver failure. In the present study, to determine the mechanism of the high HA levels after hepatectomy, especially in patients with liver cirrhosis, expression of the major HA receptor, CD44, and its mRNA was investigated in SECs isolated from rats with thioacetamide-induced liver cirrhosis subjected to 70% hepatectomy (group I) and from rats with a normal liver that were subjected to 70% hepatectomy (group II). The 48-hour postoperative survival rate in group I (13.3%) was significantly lower than in group II (100%). In group II, the expression of CD44 mRNA had increased significantly at 6 hours after hepatectomy, and this was followed by progressive increases in expression of CD44, indicating activation of SEC function. The increased serum HA levels after hepatectomy in group II became normal as CD44 expression increased. By contrast, the expression of CD44 and CD44 mRNA in group I was markedly attenuated after hepatectomy. The very low CD44 expression was followed by a significant and sustained increase in serum HA levels, indicating functional failure of the SECs. These results suggest that the significantly impaired functional reserve of SECs in liver cirrhosis is associated with increased mortality after 70% hepatectomy.