CD44-specific antibody treatment and CD44 deficiency exert distinct effects on leukocyte recruitment in experimental arthritis

Mutual antagonism between CD44 and integrins in glioblastoma cell traction and migration

Cell migration is the major driver of invasion and metastasis during cancer progression. For cells to migrate, they utilize the actin-myosin cytoskeleton and adhesion molecules, such as integrins and CD44, to generate traction forces in their environment. CD44 primarily binds to hyaluronic acid (HA) and integrins primarily bind to extracellular matrix (ECM) proteins such as collagen. However, the role of CD44 under integrin-mediated conditions and vice versa is not well known. Here, we performed traction force microscopy (TFM) on U251 cells seeded on collagen I-coated polyacrylamide gels to assess the functional mechanical relationship between integrins and CD44. Performing TFM on integrin-mediated adhesion conditions, i.e., collagen, we found that CD44KO U251 cells exerted more traction force than wild-type (WT) U251 cells. Furthermore, untreated WT and CD44-blocked WT exhibited comparable results. Conversely, in CD44-mediated adhesive conditions, integrin-blocked WT cells exerted a higher traction force than untreated WT cells. Our data suggest that CD44 and integrins have a mutually antagonistic relationship where one receptor represses the other's ability to generate traction force on its cognate substrate.

E-selectin in vascular pathophysiology

Selectins are a group of Ca2+-dependent, transmembrane type I glycoproteins which attract cell adhesion and migration. E-selectin is exclusively expressed in endothelial cells, and its expression is strongly enhanced upon activation by pro-inflammatory cytokines. The interaction of E-selectin with its ligands on circulating leukocytes captures and slows them down, further facilitating integrin activation, firm adhesion to endothelial cells and transmigration to tissues. Oxidative stress induces endothelial cell injury, leading to aberrant expression of E-selectin. In addition, the elevated level of E-selectin is positively related to high risk of inflammation. Dysregulation of E-selectin has been found in several pathological conditions including acute kidney injury (AKI), pulmonary diseases, hepatic pathology, Venous thromboembolism (VTE). Deletion of the E-selectin gene in mice somewhat ameliorates these complications. In this review, we describe the mechanisms regulating E-selectin expression, the interaction of E-selectin with its ligands, the E-selectin physiological and pathophysiological roles, and the therapeutical potential of targeting E-selectin.

Inhibition of hyaluronan synthesis prevents β-cell loss in obesity-associated type 2 diabetes

Pancreatic β-cell dysfunction and death are central to the pathogenesis of type 2 diabetes (T2D). We identified a novel role for the inflammatory extracellular matrix polymer hyaluronan (HA) in this pathophysiology. Low concentrations of HA were present in healthy pancreatic islets. However, HA substantially accumulated in cadaveric islets of T2D patients and islets of the db/db mouse model of T2D in response to hyperglycemia. Treatment with 4-methylumbelliferone (4-MU), an inhibitor of HA synthesis, or the deletion of the main HA receptor CD44, preserved glycemic control and insulin concentrations in db/db mice despite ongoing weight gain, indicating a critical role for this pathway in T2D pathogenesis. 4-MU treatment and the deletion of CD44 likewise preserved glycemic control in other settings of β-cell injury including streptozotocin treatment and islet transplantation. Mechanistically, we found that 4-MU increased the expression of the apoptosis inhibitor survivin, a downstream transcriptional target of CD44 dependent on HA/CD44 signaling, on β-cells such that caspase 3 activation did not result in β-cell apoptosis. These data indicated a role for HA accumulation in diabetes pathogenesis and suggested that it may be a viable target to ameliorate β-cell loss in T2D. These data are particularly exciting, because 4-MU is already an approved drug (also known as hymecromone), which could accelerate translation of these findings to clinical studies.

TGF-β1 mediates tumor immunosuppression aggravating at the late stage post-high-light-dose photodynamic therapy

Photodynamic therapy (PDT) is an emerging clinical treatment that is expected to become an important adjuvant strategy for the immunotherapeutic cancer treatment. Recently, numerous works have reported combination strategies. However, clinical data showed that the anti-tumor immune response of PDT was not lasting though existing. The immune activation effect will eventually turn to immunosuppressive effect and get aggravated at the late stage post-PDT. So far, the mechanism is still unclear, which limits the design of specific correction strategies and further development of PDT. Several lines of evidence suggest a role for TGF-β1 in the immunosuppression associated with PDT. Herein, this study systematically illustrated the dynamic changes of immune states post-PDT within the tumor microenvironment. The results clearly demonstrated that high-light-dose PDT, as a therapeutic dose, induced early immune activation followed by late immunosuppression, which was mediated by the activated TGF-β1 upregulation. Then, the mechanism of PDT-induced TGF-β1 accumulation and immunosuppression was elucidated, including the ROS/TGF-β1/MMP-9 positive feedback loop and CD44-mediated local amplification, which was further confirmed by spatial transcriptomics, as well as by the extensive immune inhibitory effect of local high concentration of TGF-β1. Finally, a TGF-β blockade treatment strategy was presented as a promising combinational strategy to reverse high-light-dose PDT-associated immunosuppression. The results of this study provide new insights for the biology mechanism and smart improvement approaches to enhance tumor photodynamic immunotherapy.

Inhibition of hyaluronan synthesis prevents β-cell loss in obesity-associated type 2 diabetes

Pancreatic β-cell dysfunction and death are central to the pathogenesis of type 2 diabetes (T2D). We have identified a novel role for the inflammatory extracellular matrix polymer hyaluronan (HA) in this pathophysiology. Low levels of HA are present in healthy pancreatic islets. However, HA substantially accumulates in cadaveric islets of human T2D and islets of the db/db mouse model of T2D in response to hyperglycemia. Treatment with 4-methylumbelliferone (4-MU), an inhibitor of HA synthesis, or the deletion of the major HA receptor CD44, preserve glycemic control and insulin levels in db/db mice despite ongoing weight gain, indicating a critical role for this pathway in T2D pathogenesis. 4-MU treatment and the deletion of CD44 likewise preserve glycemic control in other settings of β-cell injury including streptozotocin treatment and islet transplantation. Mechanistically, we find that 4-MU increases the expression of the apoptosis inhibitor survivin, a downstream transcriptional target of CD44 dependent on HA/CD44 signaling, on β-cells such that caspase 3 activation does not result in β-cell apoptosis. These data indicate a role for HA accumulation in diabetes pathogenesis and suggest that it may be a viable target to ameliorate β-cell loss in T2D. These data are particularly exciting, because 4-MU is already an approved drug (also known as hymecromone), which could accelerate translation of these findings to clinical studies.

Hyaluronan in the pathogenesis of acute and post-acute COVID-19 infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) recently emerged as the cause of a global pandemic. Infection with SARS-CoV-2 can result in COVID-19 with both acute and chronic disease manifestations that continue to impact many patients long after the resolution of viral replication. There is therefore great interest in understanding the host factors that contribute to COVID-19 pathogenesis. In this review, we address the role of hyaluronan (HA), an extracellular matrix polymer with roles in inflammation and cellular metabolism, in COVID-19 and critically evaluate the hypothesis that HA promotes COVID-19 pathogenesis. We first provide a brief overview of COVID-19 infection. Then we briefly summarize the known roles of HA in airway inflammation and immunity. We then address what is known about HA and the pathogenesis of COVID-19 acute respiratory distress syndrome (COVID-19 ARDS). Next, we examine potential roles for HA in post-acute SARS-CoV-2 infection (PASC), also known as "long COVID" as well as in COVID-associated fibrosis. Finally, we discuss the potential therapeutics that target HA as a means to treat COVID-19, including the repurposed drug hymecromone (4-methylumbelliferone). We conclude that HA is a promising potential therapeutic target for the treatment of COVID-19.

Design of Diselenide-Bridged Hyaluronic Acid Nano-antioxidant for Efficient ROS Scavenging to Relieve Colitis

Overproduction of reactive oxygen species (ROS), a key characteristic of inflammatory bowel disease (IBD), is responsible for dysregulation of signal transduction, inflammatory response, and DNA damage, which ultimately leads to disease progression and deterioration. Thus, ROS scavenging has become a promising strategy to navigate IBD. Inspired by the targeting capability of hyaluronic acid (HA) to CD44-overexpressed inflammatory cells together with the redox regulation capacity of diselenide compounds, we developed an oral nanoformulation, i.e., diselenide-bridged hyaluronic acid nanogel (SeNG), with a view to treat colitis through a ROS scavenging mechanism. Our data demonstrated that SeNG specifically accumulated in colitis tissue that was mediated by highly efficient CD44-HA interaction. This has allowed us to demonstrate a significant anti-inflammatory effect in an acute colitis mouse model induced by dextran sulfate sodium and trinitrobenzenesulfonic acid. Mechanistically, we continued to show SeNG reduced the ROS level via both direct elimination and up-regulation of the Nrf2/HO-1 signal pathway. Collectively, our work provides proof-of-principle evidence for a SeNG-mediated nano-antioxidant strategy, by which colitis could be effectively managed.

Tumor necrosis factor-alpha stimulated gene-6: A biomarker reflecting disease activity in rheumatoid arthritis

BACKGROUND

To explore the serum tumor necrosis factor-alpha stimulated gene-6 (TSG-6) level and its association with disease activity in rheumatoid arthritis (RA) patients.

METHODS

We recruited 176 RA patients, 178 non-RA patients (lupus erythematosus, osteoarthritis, ulcerative colitis, ankylosing spondylitis and psoriasis) and 71 healthy subjects. Serum TSG-6 levels were detected by enzyme-linked immunosorbent assay (ELISA). RA patients were divided into inactive RA and active RA groups by disease activity score of 28 joints based on C-reactive protein (DAS28-CRP). The receiver operating characteristic (ROC) curve and Spearman's rank correlation test analyzed the correlation between TSG-6 concentration and RA disease activity.

RESULTS

Tumor necrosis factor-alpha stimulated gene-6 levels in the RA group were increased (p < 0.01). TSG-6 concentrations indicated an upward tendency with increased disease activity; The area under the curve (AUC) of TSG-6 for diagnosing RA and assessing the severity of RA were 0.78 and 0.80, respectively; The combination of TSG-6 and anti-mutated citrullinated vimentin antibodies (anti-MCV) (sensitivity:98.4%)improved the diagnostic accuracy of RA. Binary logistic regression analysis showed that TSG-6 was an independent risk factor related to the severity of RA, and OR (95% CI) was 1.2 (1.003-1.453).

CONCLUSION

The TSG-6 levels in RA patients were elevated and related to disease activity. Therefore, TSG-6 may serve as a new potential biomarker for evaluating RA disease activity.

Can Heart Valve Decellularization Be Standardized? A Review of the Parameters Used for the Quality Control of Decellularization Processes

When a tissue or an organ is considered, the attention inevitably falls on the complex and delicate mechanisms regulating the correct interaction of billions of cells that populate it. However, the most critical component for the functionality of specific tissue or organ is not the cell, but the cell-secreted three-dimensional structure known as the extracellular matrix (ECM). Without the presence of an adequate ECM, there would be no optimal support and stimuli for the cellular component to replicate, communicate and interact properly, thus compromising cell dynamics and behaviour and contributing to the loss of tissue-specific cellular phenotype and functions. The limitations of the current bioprosthetic implantable medical devices have led researchers to explore tissue engineering constructs, predominantly using animal tissues as a potentially unlimited source of materials. The high homology of the protein sequences that compose the mammalian ECM, can be exploited to convert a soft animal tissue into a human autologous functional and long-lasting prosthesis ensuring the viability of the cells and maintaining the proper biomechanical function. Decellularization has been shown to be a highly promising technique to generate tissue-specific ECM-derived products for multiple applications, although it might comprise very complex processes that involve the simultaneous use of chemical, biochemical, physical and enzymatic protocols. Several different approaches have been reported in the literature for the treatment of bone, cartilage, adipose, dermal, neural and cardiovascular tissues, as well as skeletal muscle, tendons and gastrointestinal tract matrices. However, most of these reports refer to experimental data. This paper reviews the most common and latest decellularization approaches that have been adopted in cardiovascular tissue engineering. The efficacy of cells removal was specifically reviewed and discussed, together with the parameters that could be used as quality control markers for the evaluation of the effectiveness of decellularization and tissue biocompatibility. The purpose was to provide a panel of parameters that can be shared and taken into consideration by the scientific community to achieve more efficient, comparable, and reliable experimental research results and a faster technology transfer to the market.

Stabilization of Endothelial Receptor Arrays by a Polarized Spectrin Cytoskeleton Facilitates Rolling and Adhesion of Leukocytes

Multivalent complexes of endothelial adhesion receptors (e.g., selectins) engage leukocytes to orchestrate their migration to inflamed tissues. Proper anchorage and sufficient density (clustering) of endothelial receptors are required for efficient leukocyte capture and rolling. We demonstrate that a polarized spectrin network dictates the stability of the endothelial cytoskeleton, which is attached to the apical membrane, at least in part, by the abundant transmembrane protein CD44. Single-particle tracking revealed that CD44 undergoes prolonged periods of immobilization as it tethers to the cytoskeleton. The CD44-spectrin "picket fence" alters the behavior of bystander molecules-notably, selectins-curtailing their mobility, inducing their apical accumulation, and favoring their clustering within caveolae. Accordingly, depletion of either spectrin or CD44 virtually eliminated leukocyte rolling and adhesion to the endothelium. Our results indicate that a unique spectrin-based apical cytoskeleton tethered to transmembrane pickets-notably, CD44-is essential for proper extravasation of leukocytes in response to inflammation.

Anti-inflammatory activity of CD44 antibodies in murine immune thrombocytopenia is mediated by Fcγ receptor inhibition

Monoclonal immunoglobulin G (IgG) antibodies to CD44 (anti-CD44) are anti-inflammatory in numerous murine autoimmune models, but the mechanisms are poorly understood. Anti-CD44 anti-inflammatory activity shows complete therapeutic concordance with IV immunoglobulin (IVIg) in treating autoimmune disease models, making anti-CD44 a potential IVIg alternative. In murine immune thrombocytopenia (ITP), there is no mechanistic explanation for anti-CD44 activity, although anti-CD44 ameliorates disease similarly to IVIg. Here, we demonstrate a novel anti-inflammatory mechanism of anti-CD44 that explains disease amelioration by anti-CD44 in murine ITP. Macrophages treated with anti-CD44 in vitro had dramatically suppressed phagocytosis through FcγRs in 2 separate systems of IgG-opsonized platelets and erythrocytes. Phagocytosis inhibition by anti-CD44 was mediated by blockade of the FcγR IgG binding site without changing surface FcγR expression. Anti-CD44 of different subclasses revealed that FcγR blockade was specific to receptors that could be engaged by the respective anti-CD44 subclass, and Fc-deactivated anti-CD44 variants lost all FcγR-inhibiting activity. In vivo, anti-CD44 functioned analogously in the murine passive ITP model and protected mice from ITP when thrombocytopenia was induced through an FcγR that could be engaged by the CD44 antibody's subclass. Consistent with FcγR blockade, Fc-deactivated variants of anti-CD44 were completely unable to ameliorate ITP. Together, anti-CD44 inhibits macrophage FcγR function and ameliorates ITP consistent with an FcγR blockade mechanism. Anti-CD44 is a potential IVIg alternative and may be of particular benefit in ITP because of the significant role that FcγRs play in human ITP pathophysiology.

Antihuman CD44 antibody BJ18 inhibits platelet phagocytosis by correcting aberrant FcɣR expression and M1 polarization in immune thrombocytopenia

BACKGROUND

Immune thrombocytopenia (ITP) is an autoimmune hemorrhagic disease with a low platelet count. CD44 is a pivotal component involved in phagocytosis and inflammation, and monoclonal antibodies (mAbs) against CD44 have been shown to be beneficial in several autoimmune diseases. In the present study, we investigated the correlation between CD44 levels and disease severity in patients with ITP and explored the immunomodulatory mechanisms of the antihuman CD44 mAb BJ18 on platelet phagocytosis mediated by monocytes/macrophages.

METHODS

Plasma was collected from 45 participants to measure the circulating concentration of CD44 using ELISA. Peripheral blood mononuclear cells from patients and controls were isolated and induced to differentiate into monocytes/macrophages utilizing cytokines and drugs. CD44 expression on circulating cells and the effects of BJ18 on platelet phagocytosis, Fcɣ receptor (FcɣR) expression and M1/M2 polarization of macrophages were evaluated using flow cytometry and qPCR.

RESULTS

CD44 levels of both the soluble form found in plasma and the form expressed on the surface of circulating monocytes/macrophages were significantly elevated in ITP patients. Linear correlations were verified between the CD44 levels and major clinical characteristics. In an in vitro study, BJ18 successfully inhibited platelet phagocytosis by monocytes/macrophages obtained from ITP patients. Further studies indicated that BJ18 corrected abnormal FcγR expression on monocytes/macrophages. Moreover, the polarization of proinflammatory M1 macrophages could also be regulated by BJ18.

CONCLUSIONS

Our data indicated that the CD44 level has potential predictive value for disease severity and that the antihuman CD44 mAb BJ18 may be a promising therapy for ITP patients.

89Zr anti-CD44 immuno-PET monitors CD44 expression on splenic myeloid cells and HT29 colon cancer cells

CD44 is a cell-surface glycoprotein involved in cell–cell interaction, adhesion, and migration. CD44 is found on colon cancer cells and on immune cells. Previous studies of ⁸⁹Zr PET imaging of CD44 have relied on an anti-human antibody (Ab), which can influence biodistribution in murine models. In this study, we used an Ab that cross-reacts with both human and mouse origin CD44 of all isoforms to unveil the type of leukocyte responsible for high splenic anti-CD44 uptake and investigate how its regulation can influence tumor immuno-PET. The Ab was site-specifically labeled with ⁸⁹Zr-deferoxamine on cysteine residues. ⁸⁹Zr-anti-CD44 demonstrated high-specific binding to HT29 human colon cancer cells and monocytic cells that showed CD44 expression. When ⁸⁹Zr-anti-CD44 was administered to Balb/C nude mice, there was remarkably high splenic uptake but low SNU-C5 tumor uptake (1.2 ± 0.7%ID/g). Among cells isolated from Balb/C mouse spleen, there was greater CD44 expression on CD11b positive myeloid cells than lymphocytes. In cultured monocytic and macrophage cells, LPS stimulation upregulated CD44 expression and increased ⁸⁹Zr-anti-CD44 binding. Similarly, normal Balb/C mice that underwent lipopolysaccharide (LPS) stimulation showed a significant upregulation of CD44 expression on splenic myeloid cells. Furthermore, LPS treatment stimulated a 2.44-fold increase of ⁸⁹Zr-anti-CD44 accumulation in the spleen, which was attributable to splenic myeloid cells. Finally, in Balb/C nude mice bearing HT29 tumors, we injected ⁸⁹Zr-anti-CD44 with greater Ab doses to reduce binding to splenic cells. The results showed lower spleen uptake and improved tumor uptake (2.9 ± 1.3%ID/g) with a total of 300 μg of Ab dose, and further reduction of spleen uptake and greater tumor uptake (5.7 ± 0.0%ID/g) with 700 μg Ab dose. Thus, using an ⁸⁹Zr labeled Ab that cross-reacts with both human and mouse CD44, we demonstrate that CD44 immuno-PET has the capacity to monitor CD44 regulation on splenic myeloid cells and may also be useful for imaging colon tumors.

Hyaluronan oligosaccharides modulate inflammatory response, NIS and thyreoglobulin expression in human thyrocytes

Autoimmune thyroid diseases, such as Hashimoto's thyroiditis, are characterized by lymphocytic infiltration and altered function of the thyroid. During inflammation, it has been reported a decreased expression in Tg and NIS, accompanied by an increase in HA production that accumulates in the gland. HA fragments produced in different pathological states can modulate gene expression in a variety of cell types and may prime inflammatory response by interacting with the TLR-2, TLR-4 and CD44 that, in turn, induce NF-kB activation finally responsible of inflammatory mediator transcription, such as IL-1β, TNF-α and IL-6. The aim of this study was to investigate the potential inflammatory effect and the biochemical pathways activated by 6-mer HA oligosaccharides in cultured human thyrocytes. 6-mer HA treatment induced up-regulation of TLR-2, TLR-4, CD44 mRNA and related protein levels, increased HA production and NF-kB activation, that in turn increased IL-1β and IL-6 concentrations. Instead, we found evidence of an opposite effect on thyroid specific-gene Tg and NIS, that were decreased after 6-mer HA addition. Thyrocytes exposition to specific blocking antibodies for TLR-2, TLR-4 and CD44 abolished up-regulation of NF-κB activation and the consequent pro-inflammatory cytokine production, while restored Tg and NIS levels. A further goal of this study was demonstrate that also other LMW HA have pro inflammatory proprieties. These data suggest that HA fragments, through the involvement of TLR-2, TLR-4 and CD44 signaling cascade, contribute to prime the inflammatory response in thyrocytes and, by reducing the expression of thyroid-specific genes, could promote the loss of function of gland such as in Hashimoto's thyroiditis.

Essential role and therapeutic targeting of the glomerular endothelial glycocalyx in lupus nephritis

Lupus nephritis (LN) is a major organ complication and cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). There is an unmet medical need for developing more efficient and specific, mechanism-based therapies, which depends on improved understanding of the underlying LN pathogenesis. Here we present direct visual evidence from high-power intravital imaging of the local kidney tissue microenvironment in mouse models showing that activated memory T cells originated in immune organs and the LN-specific robust accumulation of the glomerular endothelial glycocalyx played central roles in LN development. The glomerular homing of T cells was mediated via the direct binding of their CD44 to the hyaluronic acid (HA) component of the endothelial glycocalyx, and glycocalyx-degrading enzymes efficiently disrupted homing. Short-course treatment with either hyaluronidase or heparinase III provided long-term organ protection as evidenced by vastly improved albuminuria and survival rate. This glycocalyx/HA/memory T cell interaction is present in multiple SLE-affected organs and may be therapeutically targeted for SLE complications, including LN.

A combined immunology and renal pathophysiology study of the local kidney tissue microenvironment in lupus identifies a key role of glomerular endothelial glycocalyx in disease development.

Lack of the hyaluronan receptor CD44 affects the course of bacterial otitis media and reduces leukocyte recruitment to the middle ear

BACKGROUND

CD44 is a multifunctional molecule that plays major roles in both leukocyte recruitment and tissue proliferation. Since mucosal hyperplasia and leukocyte infiltration of the middle ear cavity are major features of otitis media, we evaluated the role of CD44 in the pathophysiology and course of this disease in a mouse model of middle ear infection. Expression of genes related to CD44 function were evaluated using gene arrays in wild-type mice. The middle ears of mice deficient in CD44 were inoculated with non-typeable Haemophilus influenzae. Histopathology and bacterial clearance were compared to that seen in wild-type controls.

RESULTS

We observed strong up-regulation of CD44 and of genes related to its role in leukocyte extravasation into the middle ear, during the course of acute otitis media. Mice deficient in CD44 exhibited reduced early mucosal hyperplasia and leukocyte recruitment, followed by delayed resolution of infection and persistent inflammation.

CONCLUSIONS

CD44 plays an important role in OM pathogenesis by altering the mucosal growth and neutrophil enlistment. Targeted therapies based on CD44 could be useful adjuncts to the treatment of middle ear infections.

Hyaluronan fragments produced during tissue injury: A signal amplifying the inflammatory response

Inflammation is a complex mechanism that plays a key role during diseases. Dynamic features of the extracellular matrix (ECM), in particular, during phases of tissue inflammation, have long been appreciated, and a great deal of several investigations has focused on the effects of ECM derivatives on cell function. It has been well defined that during inflammatory and tissue injury, ECM components were degraded. ECM degradation direct consequence is the loss of cell homeostasis, while a further consequence is the generation of fragments from larger precursor molecules. These bio-functional ECM shred defined matrikines as capable of playing different actions, especially when they function as powerful initiators, able to prime the inflammatory mechanism. Non-sulphated glycosaminoglycan hyaluronan (HA) is the major component of the ECM that undergoes specific modulation during tissue damage and inflammation. HA fragments at very low molecular weight are produced as a result of HA depolymerization. Several evidence has considered the plausibility that HA breakdown products play a modulatory action in the sequential stages of inflammation, although the effective mechanism of these HA derivative compounds act is not completely defined. This review will focus on the pro-inflammatory effects of HA fragments in recent years obtained by in vitro investigations.

Extracellular matrix and the maintenance and loss of peripheral immune tolerance in autoimmune insulitis

There is a growing appreciation that the extracellular matrix (ECM) contributes to both the maintenance of immune tolerance in healthy tissues and to its loss at sites of autoimmunity. Here, we review recent literature on the role of ECM and particularly the glycosaminoglycans hyaluronan and heparan sulfate in the development of autoimmune, type 1 diabetes (T1D). Data from transplant models suggest that healthy islets are embedded within an intact ECM that supports beta-cell homeostasis and provides physical and immunoregulatory barriers against immune infiltration. However, studies of human insulitis as well as the non-obese diabetic (NOD) and DORmO mouse models of T1D indicate that autoimmune insulitis is associated with the degradation of basement membrane structures, the catabolism of the islet interstitium, and the accumulation of a hyaluronan-rich, pro-inflammatory ECM. Moreover, in these models of autoimmune diabetes, either the pharmacologic inhibition of heparan sulfate catabolism, the reduction of hyaluronan synthesis, or the targeting of the pathways that sense these ECM changes can all prevent beta-cell destruction. Together these data support an emerging paradigm that in healthy islets the local ECM contributes to both immune tolerance and beta-cell homeostasis while in chronic inflammation the islet ECM is permissive to immune infiltration and beta-cell destruction. Therapies that support ECM-mediated 'barrier tolerance' may have potential as adjunctive agents in combination regimens designed to prevent or treat autoimmunity.

Hyaluronan in immune dysregulation and autoimmune diseases

The tissue microenvironment contributes to local immunity and to the pathogenesis of autoimmune diseases - a diverse set of conditions characterized by sterile inflammation, immunity against self-antigens, and destruction of tissues. However, the specific factors within the tissue microenvironment that contribute to local immune dysregulation in autoimmunity are poorly understood. One particular tissue component implicated in multiple autoimmune diseases is hyaluronan (HA), an extracellular matrix (ECM) polymer. HA is abundant in settings of chronic inflammation and contributes to lymphocyte activation, polarization, and migration. Here, we first describe what is known about the size, amount, and distribution of HA at sites of autoimmunity and in associated lymphoid structures in type 1 diabetes, multiple sclerosis, and rheumatoid arthritis. Next, we examine the recent literature on HA and its impact on adaptive immunity, particularly in regards to the biology of lymphocytes and Foxp3+ regulatory T-cells (Treg), a T-cell subset that maintains immune tolerance in healthy individuals. We propose that HA accumulation at sites of chronic inflammation creates a permissive environment for autoimmunity, characterized by CD44-mediated inhibition of Treg expansion. Finally, we address potential tools and strategies for targeting HA and its receptor CD44 in chronic inflammation and autoimmunity.

Modified High-Molecular-Weight Hyaluronan Promotes Allergen-Specific Immune Tolerance

The extracellular matrix in asthmatic lungs contains abundant low-molecular-weight hyaluronan, and this is known to promote antigen presentation and allergic responses. Conversely, high-molecular-weight hyaluronan (HMW-HA), typical of uninflamed tissues, is known to suppress inflammation. We investigated whether HMW-HA can be adapted to promote tolerance to airway allergens. HMW-HA was thiolated to prevent its catabolism and was tethered to allergens via thiol linkages. This platform, which we call "XHA," delivers antigenic payloads in the context of antiinflammatory costimulation. Allergen/XHA was administered intranasally to mice that had been sensitized previously to these allergens. XHA prevents allergic airway inflammation in mice sensitized previously to either ovalbumin or cockroach proteins. Allergen/XHA treatment reduced inflammatory cell counts, airway hyperresponsiveness, allergen-specific IgE, and T helper type 2 cell cytokine production in comparison with allergen alone. These effects were allergen specific and IL-10 dependent. They were durable for weeks after the last challenge, providing a substantial advantage over the current desensitization protocols. Mechanistically, XHA promoted CD44-dependent inhibition of nuclear factor-κB signaling, diminished dendritic cell maturation, and reduced the induction of allergen-specific CD4 T-helper responses. XHA and other potential strategies that target CD44 are promising alternatives for the treatment of asthma and allergic sinusitis.

An Analysis of Trafficking Receptors Shows that CD44 and P-Selectin Glycoprotein Ligand-1 Collectively Control the Migration of Activated Human T-Cells

Selectins guide the traffic of activated T-cells through the blood stream by mediating their tethering and rolling onto inflamed endothelium, in this way acting as beacons to help navigate them to sites of inflammation. Here, we present a comprehensive analysis of E-selectin ligands expressed on activated human T-cells. We identified several novel glycoproteins that function as E-selectin ligands. Specifically, we compared the role of P-selectin glycoprotein ligand-1 (PSGL-1) and CD43, known E-selectin ligands, to CD44, a ligand that has not previously been characterized as an E-selectin ligand on activated human T-cells. We showed that CD44 acts as a functional E-selectin ligand when expressed on both CD4⁺ and CD8⁺ T-cells. Moreover, the CD44 protein carries a binding epitope identifying it as hematopoietic cell E- and/or L-selectin ligand (HCELL). Furthermore, by knocking down these ligands individually or together in primary activated human T-cells, we demonstrated that CD44/HCELL, and not CD43, cooperates with PSGL-1 as a major E-selectin ligand. Additionally, we demonstrated the relevance of our findings to chronic autoimmune disease, by showing that CD44/HCELL and PSGL-1, but not CD43, from T-cells isolated from psoriasis patients, bind E-selectin.

Fluorescent Ly6G antibodies determine macrophage phagocytosis of neutrophils and alter the retrieval of neutrophils in mice

Fluorescently labeled Ly6G antibodies enable the tracking of neutrophils in mice, whereas purified anti-Ly6G rapidly depletes neutrophils from the circulation. The mechanisms underlying neutrophil depletion are still under debate. Here, we examined how identical Ly6G antibodies coupled to different fluorochromes affect neutrophil fate in vivo. BM cells stained with Ly6G antibodies were injected into mice. The number of retrieved anti-Ly6G-FITC(+) cells was reduced significantly in comparison with anti-Ly6G-APC(+) or anti-Ly6G-PE(+) cells. Flow cytometry and multispectral imaging flow cytometry analyses revealed that anti-Ly6G-FITC(+) neutrophils were preferentially phagocytosed by BMMs in vitro and by splenic, hepatic, and BM macrophages in vivo. Direct antibody injection of anti-Ly6G-FITC but not anti-Ly6G-PE depleted neutrophils to the same degree as purified anti-Ly6G, indicating that the FITC-coupled antibody eliminates neutrophils by a similar mechanism as the uncoupled antibody. With the use of a protein G-binding assay, we demonstrated that APC and PE but not FITC coupling inhibited access to interaction sites on the anti-Ly6G antibody. We conclude the following: 1) that neutrophil phagocytosis by macrophages is a central mechanism in anti-Ly6G-induced neutrophil depletion and 2) that fluorochrome-coupling can affect functional properties of anti-Ly6G antibodies, thereby modifying macrophage uptake of Ly6G-labeled neutrophils and neutrophil retrieval following adoptive cell transfer or injection of fluorescent anti-Ly6G.

Interactions between Hyaluronan and Its Receptors (CD44, RHAMM) Regulate the Activities of Inflammation and Cancer

The glycosaminoglycan hyaluronan (HA), a major component of extracellular matrices, and cell surface receptors of HA have been proposed to have pivotal roles in cell proliferation, migration, and invasion, which are necessary for inflammation and cancer progression. CD44 and receptor for HA-mediated motility (RHAMM) are the two main HA-receptors whose biological functions in human and murine inflammations and tumor cells have been investigated comprehensively. HA was initially considered to be only an inert component of connective tissues, but is now known as a “dynamic” molecule with a constant turnover in many tissues through rapid metabolism that involves HA molecules of various sizes: high molecular weight HA (HMW HA), low molecular weight HA, and oligosaccharides. The intracellular signaling pathways initiated by HA interactions with CD44 and RHAMM that lead to inflammatory and tumorigenic responses are complex. Interestingly, these molecules have dual functions in inflammations and tumorigenesis. For example, the presence of CD44 is involved in initiation of arthritis, while the absence of CD44 by genetic deletion in an arthritis mouse model increases rather than decreases disease severity. Similar dual functions of CD44 exist in initiation and progression of cancer. RHAMM overexpression is most commonly linked to cancer progression, whereas loss of RHAMM is associated with malignant peripheral nerve sheath tumor growth. HA may similarly perform dual functions. An abundance of HMW HA can promote malignant cell proliferation and development of cancer, whereas antagonists to HA-CD44 signaling inhibit tumor cell growth in vitro and in vivo by interfering with HMW HA-CD44 interaction. This review describes the roles of HA interactions with CD44 and RHAMM in inflammatory responses and tumor development/progression, and how therapeutic strategies that block these key inflammatory/tumorigenic processes may be developed in rodent and human diseases.

Deciphering the cellular source of tumor relapse identifies CD44 as a major therapeutic target in pancreatic adenocarcinoma

It has been commonly found that in patients presenting Pancreatic Ductal Adenocarcinoma (PDAC), after a period of satisfactory response to standard treatments, the tumor becomes non-responsive and patient death quickly follows. This phenomenon is mainly due to the rapid and uncontrolled development of the residual tumor. The origin and biological characteristics of residual tumor cells in PDAC still remain unclear. In this work, using PDACs from patients, preserved as xenografts in nude mice, we demonstrated that a residual PDAC tumor originated from a small number of CD44+ cells present in the tumor. During PDAC relapse, proliferating CD44+ cells decrease expression of ZEB1, while overexpressing the MUC1 protein, and gain morphological and biological characteristics of differentiation. Also, we report that CD44+ cells, in primary and residual PDAC tumors, are part of a heterogeneous population, which includes variable numbers of CD133+ and EpCAM+ cells. We confirmed the propagation of CD44+ cells in samples from cases of human relapse, following standard PDAC treatment. Finally, using systemic administration of anti-CD44 antibodies in vivo, we demonstrated that CD44 is an efficient therapeutic target for treating tumor relapse, but not primary PDAC tumors. We conclude that CD44+ cells generate the relapsing tumor and, as such, are themselves promising therapeutic targets for treating patients with recurrent PDAC.

Spatiotemporal Expression Dynamics of Selectins Govern the Sequential Extravasation of Neutrophils and Monocytes in the Acute Inflammatory Response

Objective—

Leukocyte recruitment to the site of inflammation is a key event in a variety of cardiovascular pathologies. Infiltrating neutrophils constitute the first line of defense that precedes a second wave of emigrating monocytes reinforcing the inflammatory reaction. The mechanisms initiating this sequential process remained largely obscure.

Approach and Results—

Using advanced in vivo microscopy and in vitro/ex vivo techniques, we identified individual spatiotemporal expression patterns of selectins and their principal interaction partners on neutrophils, resident/inflammatory monocytes, and endothelial cells. Coordinating the intraluminal trafficking of neutrophils and inflammatory monocytes to common sites of extravasation, selectins assign different sites to these immune cells for their initial interactions with the microvascular endothelium. Whereas constitutively expressed leukocyte L-selectin/CD62L and endothelial P-selectin/CD62P together with CD44 and P-selectin glycoprotein ligand-1/CD162 initiate the emigration of neutrophils, de novo synthesis of endothelial E-selectin/CD62E launches the delayed secondary recruitment of inflammatory monocytes. In this context, P-selectin/CD62P and L-selectin/CD62L together with P-selectin glycoprotein ligand-1/CD162 and CD44 were found to regulate the flux of rolling neutrophils and inflammatory monocytes, whereas E-selectin/CD62E selectively adjusts the rolling velocity of inflammatory monocytes. Moreover, selectins and their interaction partners P-selectin glycoprotein ligand-1/CD162 and CD44 differentially control the intraluminal crawling behavior of neutrophils and inflammatory monocytes collectively enabling the sequential extravasation of these immune cells to inflamed tissue.

Conclusions—

Our findings provide novel insights into the mechanisms initiating the sequential infiltration of the perivascular tissue by neutrophils and monocytes in the acute inflammatory response and might thereby contribute to the development of targeted therapeutic strategies for prevention and treatment of cardiovascular diseases.

Methods for detecting circulating cancer stem cells (CCSCs) as a novel approach for diagnosis of colon cancer relapse/metastasis

Cancer stem cells (CSCs) are believed to be resistant to currently available therapies and may be responsible for relapse of cancer in patients. Measuring circulating tumor cells (CTCs) in the blood of patients has emerged as a non-invasive diagnostic procedure for screening patients who may be at high risk for developing metastatic cancers or relapse of the cancer disease. However, accurate detection of CTCs has remained a problem, as epithelial-cell markers used to date are not always reliable for detecting CTCs, especially during epithelial-mesenchymal transition. As CSCs are required to initiate metastatic tumors, our goal was to optimize and standardize a method for identifying circulating CSCs (CCSCs) in patients, using established CSC markers. Here, we report for the first time the detection of CCSCs in the blood of athymic nude mice, bearing metastatic tumors, and in the blood of patients positive for colonic adenocarcinomas. Using a simple and non-expensive method, we isolated a relatively pure population of CSCs (CD45-/CK19+), free of red blood cells and largely free of contaminating CD45+ white blood cells. Enriched CCSCs from patients with colon adenocarcinomas had a malignant phenotype and co-expressed CSC markers (DCLK1/LGR5) with CD44/Annexin A2. CSCs were not found in the blood of non-cancer patients, free of colonic growths. Enriched CCSCs from colon cancer patients grew primary spheroids, suggesting the presence of tumor-initiating cells in the blood of these patients. In conclusion, we have developed a novel diagnostic assay for detecting CSCs in circulation, which may more accurately predict the risk of relapse or metastatic disease in patients. As CSCs can potentially initiate metastatic growths, patients positive for CCSCs can be treated with inhibitory agents that selectively target CSCs, besides conventional treatments, to reduce the risk of relapse/metastatic disease for improving clinical outcomes.

Suppression of proteoglycan-induced autoimmune arthritis by myeloid-derived suppressor cells generated in vitro from murine bone marrow

Background

Myeloid-derived suppressor cells (MDSCs) are innate immune cells capable of suppressing T-cell responses. We previously reported the presence of MDSCs with a granulocytic phenotype in the synovial fluid (SF) of mice with proteoglycan (PG)-induced arthritis (PGIA), a T cell-dependent autoimmune model of rheumatoid arthritis (RA). However, the limited amount of SF-MDSCs precluded investigations into their therapeutic potential. The goals of this study were to develop an in vitro method for generating MDSCs similar to those found in SF and to reveal the therapeutic effect of such cells in PGIA.

Methods

Murine bone marrow (BM) cells were cultured for 3 days in the presence of granulocyte macrophage colony-stimulating factor (GM-CSF), interleukin-6 (IL-6), and granulocyte colony-stimulating factor (G-CSF). The phenotype of cultured cells was analyzed using flow cytometry, microscopy, and biochemical methods. The suppressor activity of BM-MDSCs was tested upon co-culture with activated T cells. To investigate the therapeutic potential of BM-MDSCs, the cells were injected into SCID mice at the early stage of adoptively transferred PGIA, and their effects on the clinical course of arthritis and PG-specific immune responses were determined.

Results

BM cells cultured in the presence of GM-CSF, IL-6, and G-CSF became enriched in MDSC-like cells that showed greater phenotypic heterogeneity than MDSCs present in SF. BM-MDSCs profoundly inhibited both antigen-specific and polyclonal T-cell proliferation primarily via production of nitric oxide. Injection of BM-MDSCs into mice with PGIA ameliorated arthritis and reduced PG-specific T-cell responses and serum antibody levels.

Conclusions

Our in vitro enrichment strategy provides a SF-like, but controlled microenvironment for converting BM myeloid precursors into MDSCs that potently suppress both T-cell responses and the progression of arthritis in a mouse model of RA. Our results also suggest that enrichment of BM in MDSCs could improve the therapeutic efficacy of BM transplantation in RA.

Tissue integrity signals communicated by high-molecular weight hyaluronan and the resolution of inflammation

The extracellular matrix polysaccharide hyaluronan (HA) exerts size-dependent effects on leukocyte behavior. Low-molecular weight HA is abundant at sites of active tissue catabolism and promotes inflammation via effects on Toll-like receptor signaling. Conversely, high-molecular weight HA is prevalent in uninjured tissues and is anti-inflammatory. We propose that the ability of high-molecular weight but not low-molecular weight HA to cross-link CD44 functions as a novel form of pattern recognition that recognizes intact tissues and communicates "tissue integrity signals" that promote resolution of local immune responses.

Hyaluronan, a crucial regulator of inflammation

Hyaluronan (HA), a major component of the extracellular matrix (ECM), plays a key role in regulating inflammation. Inflammation is associated with accumulation and turnover of HA polymers by multiple cell types. Increasingly through the years, HA has become recognized as an active participant in inflammatory, angiogenic, fibrotic, and cancer promoting processes. HA and its binding proteins regulate the expression of inflammatory genes, the recruitment of inflammatory cells, the release of inflammatory cytokines, and can attenuate the course of inflammation, providing protection against tissue damage. A growing body of evidence suggests the cell responses are HA molecular weight dependent. HA fragments generated by multiple mechanisms throughout the course of inflammatory pathologies, elicit cellular responses distinct from intact HA. This review focuses on the role of HA in the promotion and resolution of inflammation.

CD44 antibodies and immune thrombocytopenia in the amelioration of murine inflammatory arthritis

Antibodies to CD44 have been used to successfully ameliorate murine models of autoimmune disease. The most often studied disease model has been murine inflammatory arthritis, where a clear mechanism for the efficacy of CD44 antibodies has not been established. We have recently shown in a murine passive-model of the autoimmune disease immune thrombocytopenia (ITP) that some CD44 antibodies themselves can induce thrombocytopenia in mice, and the CD44 antibody causing the most severe thrombocytopenia (IM7), also is known to be highly effective in ameliorating murine models of arthritis. Recent work in the K/BxN serum-induced model of arthritis demonstrated that antibody-induced thrombocytopenia reduced arthritis, causing us to question whether CD44 antibodies might primarily ameliorate arthritis through their thrombocytopenic effect. We evaluated IM7, IRAWB14.4, 5035-41.1D, KM201, KM114, and KM81, and found that while all could induce thrombocytopenia, the degree of protection against serum-induced arthritis was not closely related to the length or severity of the thrombocytopenia. CD44 antibody treatment was also able to reverse established inflammation, while thrombocytopenia induced by an anti-platelet antibody targeting the GPIIbIIIa platelet antigen, could not mediate this effect. While CD44 antibody-induced thrombocytopenia may contribute to some of its therapeutic effect against the initiation of arthritis, for established disease there are likely other mechanisms contributing to its efficacy. Humans are not known to express CD44 on platelets, and are therefore unlikely to develop thrombocytopenia after CD44 antibody treatment. An understanding of the relationship between arthritis, thrombocytopenia, and CD44 antibody treatment remains critical for continued development of CD44 antibody therapeutics.

Ly6 family proteins in neutrophil biology

The murine Ly6 complex was identified 35 years ago using antisera to lymphocytes. With advances in mAb development, molecular cloning, and genome sequencing, >20 structurally related genes have been identified within this complex on chromosome 15. All members of the Ly6 family and their human homologues share the highly conserved LU domain and most also possess a GPI anchor. Interestingly, many Ly6 proteins are expressed in a lineage-specific fashion, and their expression often correlates with stages of differentiation. As a result, Ly6 proteins are frequently used as surface markers for leukocyte subset identification and targets for antibody-mediated depletion. Murine neutrophils display prominent surface expression of several Ly6 proteins, including Ly6B, Ly6C, and Ly6G. Although the physiology of most Ly6 proteins is not well understood, a role in neutrophil functions, such as migration, is recognized increasingly. In this review, we will provide an overview of the Ly6 complex and discuss, in detail, the specific Ly6 proteins implicated in neutrophil biology.

CD44 deficiency contributes to enhanced experimental autoimmune encephalomyelitis: a role in immune cells and vascular cells of the blood-brain barrier

Adhesion molecule CD44 is expressed by multiple cell types and is implicated in various cellular and immunological processes. In this study, we examined the effect of global CD44 deficiency on myelin oligodendrocyte glycoprotein peptide (MOG)-induced experimental autoimmune encephalomyelitis (EAE), a murine model of multiple sclerosis. Compared to C57BL/6 wild-type mice, CD44-deficient mice presented with greater disease severity, increased immune cell numbers in the central nervous system, and increased anti-MOG antibody and proinflammatory cytokine production, especially those associated with T helper 17 (Th17) cells. Further, decreased numbers of peripheral CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) were observed in CD44-knockout mice throughout the disease course. CD44-knockout CD4 T cells exhibited reduced transforming growth factor-β receptor type I (TGF-β RI) expression that did not impart a defect in Treg polarization in vitro, but did correlate with enhanced Th17 polarization in vitro. Further, EAE in bone marrow-chimeric animals suggested CD44 expression on both circulating and noncirculating cells limited disease severity. Endothelial expression of CD44 limited T-cell adhesion to and transmigration through murine endothelial monolayers in vitro. Importantly, we also identified increased permeability of the blood-brain barrier in vivo in CD44-deficient mice before and following immunization. These data suggest that CD44 has multiple protective roles in EAE, with effects on cytokine production, T-cell differentiation, T-cell-endothelial cell interactions, and blood-brain barrier integrity.

The stimulation of adenosine 2A receptor reduces inflammatory response in mouse articular chondrocytes treated with hyaluronan oligosaccharides

The adenosine 2A receptor (A(2A)R) is greatly involved in inflammation pathologies such as rheumatoid arthritis. By interacting with A(2A)R, the purine nucleoside adenosine acts as a potent endogenous inhibitor of the inflammatory process in a variety of tissues. Hyaluronan (HA) fragments act to prime inflammation via CD44 and the toll-like receptor 4 (TLR-4). The aim of this study was to investigate whether the inhibition/stimulation of A(2A)R modulates the inflammation cascade primed by small HA fragments in mouse articular chondrocytes. 6-mer HA treatment induced up-regulation of CD44, TLR4 and A(2A)R mRNA expression and the related protein levels, and NF-kB activation, that in turn increased TNF-α, IL-1β, and IL-6 and production. Treatment with a selective (2)A adenosine receptor agonist (2-phenylaminoadenosine) enhanced A(2A)R increase, as well as the inhibition of CD44 and TLR4 activity using two specific antibodies abolished up-regulation of CD44 and TLR4, and significantly reduced, especially by antibody inhibition, NF-kB activation and pro-inflammatory cytokine production. Furthermore, the exposure of chondrocytes to A(2A)R specific interference mRNA (A(2A)R siRNA) enhanced HA 6-mer induced NF-kB activation and inflammatory cytokine increase. Finally, the use of an exchange protein activated by cAMP (EPAC) siRNA and a specific PKA inhibitor showed a predominant EPAC involvement in the mediation of the anti-inflammatory activity exerted by A(2A)R stimulation. These data suggest that HA depolymerization occurring during inflammation contributes to priming of the inflammatory cascade, while endogenous adenosine, by exerting anti-inflammatory response via A(2A)R, could be a modulatory mechanism that attempts to attenuate the inflammation process.

Ly6G ligation blocks recruitment of neutrophils via a β2-integrin-dependent mechanism

Ly6G is a glycosylphosphatidylinositol (GPI)-anchored protein of unknown function that is commonly targeted to induce experimental neutrophil depletion in mice. In the present study, we found that doses of anti-Ly6G Abs too low to produce sustained neutropenia remained capable of inhibiting experimental arthritis, leaving joint tissues free of infiltrating neutrophils. Thioglycollate-stimulated peritonitis was also attenuated. No alteration in neutrophil apoptosis was observed, implicating impaired recruitment. Indeed, Ly6G ligation abrogated neutrophil migration toward LTB(4) and other chemoattractants in a transwell system. Exploring the basis for this blockade, we identified colocalization of Ly6G and β2-integrins by confocal microscopy and confirmed close association by both coimmunoprecipitation and fluorescence lifetime imaging microscopy. Anti-Ly6G Ab impaired surface expression of β2-integrins in LTB(4)-stimulated neutrophils and mimicked CD11a blockade in inhibiting both ICAM-1 binding and firm adhesion to activated endothelium under flow conditions. Correspondingly, migration of β2-integrin-deficient neutrophils was no longer inhibited by anti-Ly6G. These results demonstrate that experimental targeting of Ly6G has functional effects on the neutrophil population and identify a previously unappreciated role for Ly6G as a modulator of neutrophil migration to sites of inflammation via a β2-integrin-dependent mechanism.

Adenosine A2A receptor activation and hyaluronan fragment inhibition reduce inflammation in mouse articular chondrocytes stimulated with interleukin-1β

Small hyaluronan (HA) fragments produced from native HA during inflammation contribute greatly to cell injury in many pathologies. HA oligosaccharides increase proinflammatory cytokine levels by activating both CD44 and toll-like receptor (TLR)-4. Stimulation of CD44 and TLR-4 then activates nuclear factor-κB, which induces the production of proinflammatory cytokines. The adenosine 2A receptor (A(2A)R) is also involved in several inflammation pathologies, and the nucleoside adenosine acts as a potent endogenous inhibitor of inflammation in various tissues by interacting with this receptor. The aim of this study was to investigate the effects of an HA-blocking peptide that inhibits the proinflammatory action of HA oligosaccharides produced during inflammation, together with a specific A(2A)R agonist in a model of normal mouse articular chondrocytes stimulated with interleukin (IL)-1β. IL-1β stimulation significantly increased mRNA expression and the related protein production of TLR-4, TLR-2, CD44 and A(2A)R in articular chondrocytes. The induced nuclear factor-κB activation was also associated with increased levels of inflammatory cytokines, including tumor necrosis factor-α and IL-6, and other inflammatory mediators, such as matrix metalloprotease-13 and inducible nitric oxide synthase. Treatment of chondrocytes with the HA-blocking peptide Pep-1 and/or a specific A(2A)R agonist (CGS-21680) significantly reduced all of the inflammatory parameters upregulated by IL-1β. These results suggest that the inflammatory response may be reduced either by blocking oligosaccharides from HA degradation or by A(2A)R stimulation.

The inhibition of hyaluronan degradation reduced pro-inflammatory cytokines in mouse synovial fibroblasts subjected to collagen-induced arthritis

Hyaluronan (HA) degradation produces small oligosaccharides that are able to increase pro-inflammatory cytokines in rheumatoid arthritis synovial fibroblasts (RASF) by activating both CD44 and the toll-like receptor 4 (TLR-4). CD44 and TLR-4 stimulation in turn activate the NF-kB that induces the production of pro-inflammatory cytokines. Degradation of HA occurs via two mechanisms: one exerted by reactive oxygen species (ROS) and one controlled by different enzymes in particular hyaluronidases (HYALs). We aimed to investigate the effects of inhibiting HA degradation (which prevents the formation of small HA fragments) on synovial fibroblasts obtained from normal DBA/J1 mice (NSF) and on synovial fibroblasts (RASF) obtained from mice subjected to collagen induced arthritis (CIA), both fibroblast types stimulated with tumor necrosis factor alpha (TNF-α). TNF-α stimulation produced high mRNA expression and the related protein production of CD44 and TLR-4 in both NSF and RASF, and activation of NF-kB was also found in all fibroblasts. TNF-α also up-regulated the inflammatory cytokines, interleukin-1beta (IL-1beta) and interleukin-6 (IL-6), and other pro-inflammatory mediators, such as matrix metalloprotease-13 (MMP-13), inducible nitric oxide synthase (iNOS), as well as HA levels and small HA fragment production. Treatment of RASF with antioxidants and specific HYAL1, HYAL2, and HYAL3 small interference RNA (siRNAs) significantly reduced TLR-4 and CD44 increase in the mRNA expression and the related protein synthesis, as well as the release of inflammatory mediators up-regulated by TNF-α. These data suggest that the inhibition of HA degradation during arthritis may contribute to reducing TLR-4 and CD44 activation and the inflammatory mediators response.

Expression-based genome-wide association study links the receptor CD44 in adipose tissue with type 2 diabetes

Type 2 diabetes (T2D) is a complex, polygenic disease affecting nearly 300 million people worldwide. T2D is primarily characterized by insulin resistance, and growing evidence has indicated the causative link between adipose tissue inflammation and the development of insulin resistance. Genetic association studies have successfully revealed a number of important genes consistently associated with T2D to date. However, these robust T2D-associated genes do not fully elucidate the mechanisms underlying the development and progression of the disease. Here, we report an alternative approach, gene expression-based genome-wide association study (eGWAS): searching for genes repeatedly implicated in functional microarray experiments (often publicly available). We performed an eGWAS across 130 independent experiments (totally 1,175 T2D case-control microarrays) to find additional genes implicated in the molecular pathogenesis of T2D and identified the immune-cell receptor CD44 as our top candidate (P = 8.5 × 10(-20)). We found CD44 deficiency in a diabetic mouse model ameliorates insulin resistance and adipose tissue inflammation and also found that anti-CD44 antibody treatment decreases blood glucose levels and adipose tissue macrophage accumulation in a high-fat, diet-fed mouse model. Further, in humans, we observed CD44 is expressed in inflammatory cells in obese adipose tissue and discovered serum CD44 levels were positively correlated with insulin resistance and glycemic control. CD44 likely plays a causative role in the development of adipose tissue inflammation and insulin resistance in rodents and humans. Genes repeatedly implicated in publicly available experimental data may have unique functionally important roles in T2D and other complex diseases.

Hyaluronan in part mediates IL-1beta-induced inflammation in mouse chondrocytes by up-regulating CD44 receptors

Interleukin-1beta (IL-1beta) elicits the expression of inflammatory mediators through a mechanism involving the CD44 receptor. Hyaluronan (HA) depolymerization also contributes to CD44 activation. This study investigated the potential of HA fragments, obtained by hyaluronidase (HYAL) treatment, as mediators of CD44 activation on IL-1beta-induced inflammation in mouse chondrocytes. mRNA and related protein levels were measured for CD44, tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), matrix metalloproteinase-13 (MMP-13) and inducible nitric oxide synthase (iNOS) in chondrocytes, treated or untreated with IL-1beta, either with or without the addition of HYAL. The level of NF-kB activation was also assayed. CD44 mRNA expression was higher than controls in chondrocytes treated with IL-1beta. IL-1beta also induced NF-kB up-regulation and increased TNF-alpha, IL-6, MMP-13 and iNOS expression. Different effects resulted from HYAL treatment. Treatment of chondrocytes exposed to IL-1beta with HYAL synergistically increased the same parameters up-regulated by IL-1beta, while the same parameters were increased by HYAL in chondrocytes not exposed to IL-1beta but to a lesser extent. Specific CD44 blocking antibody and hyaluronan binding protein (HABP), which inhibit HA activity, were used to confirm CD44 to be the target of IL-1beta action through HA mediation. HA levels and molecular size further confirm the role of degraded HA. These findings suggest that IL-1beta exerts inflammatory activity via CD44 by the mediation of HA fragments derived from HA depolymerization.

Inhibition of hyaluronan synthesis reduced inflammatory response in mouse synovial fibroblasts subjected to collagen-induced arthritis

Hyaluronan (HA) fragments are able to induce inflammation by stimulating both CD44 and toll-like receptor 4 (TLR-4). CD44 and TLR-4 activation stimulates the liberation of NF-kB and pro-inflammatory cytokine responses. The aim of this study was to investigate the effects of hyaluronidase (HYAL) treatment, which depolymerises HA into small fragments, and of the addition of specific hyaluronan synthases-1, 2, and 3 small interference RNA (HASs siRNA), which silence HASs activity, on normal mouse synovial fibroblasts (NSF) and on rheumatoid arthritis synovial fibroblasts (RASF) obtained from mice subjected to collagen induced arthritis (CIA). The addition of HYAL to NSF and/or RASF significantly increased the TLR-4, CD44 and NF-kB activity, as well as the pro-inflammatory cytokines, interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and interleukin-33 (IL-33) in both groups, but to a greater extent in RASF. The addition to NSF and/or RASF of the HASs siRNA, which block HASs activity and therefore the availability of HA substrate for HYAL, was able to reduce HYAL effects in both NSF and RASF. Finally, the HA evaluation confirmed the increment of HA at low molecular weight after HYAL treatment.

Leukocyte ligands for endothelial selectins: specialized glycoconjugates that mediate rolling and signaling under flow

Reversible interactions of glycoconjugates on leukocytes with P- and E-selectin on endothelial cells mediate tethering and rolling of leukocytes in inflamed vascular beds, the first step in their recruitment to sites of injury. Although selectin ligands on hematopoietic precursors have been identified, here we review evidence that PSGL-1, CD44, and ESL-1 on mature leukocytes are physiologic glycoprotein ligands for endothelial selectins. Each ligand has specialized adhesive functions during tethering and rolling. Furthermore, PSGL-1 and CD44 induce signals that activate the β2 integrin LFA-1 and promote slow rolling, whereas ESL-1 induces signals that activate the β2 integrin Mac-1 in adherent neutrophils. We also review evidence for glycolipids, CD43, L-selectin, and other glycoconjugates as potential physiologic ligands for endothelial selectins on neutrophils or lymphocytes. Although the physiologic characterization of these ligands has been obtained in mice, we also note reported similarities and differences with human selectin ligands.

Targeting CD44 expressed on neutrophils inhibits lung damage in abdominal sepsis

Neutrophil infiltration is an insidious feature in septic lung injury, although the specific adhesive mechanisms regulating pulmonary recruitment of neutrophils in polymicrobial sepsis remain elusive. The aim of this present study was to define the role of CD44 in sepsis-induced neutrophil infiltration and lung damage. Mice were treated with a monoclonal antibody against CD44 before cecal ligation and puncture (CLP) induction. Edema formation, bronchoalveolar accumulation of neutrophils, myeloperoxidase activity, and macrophage inflammatory protein 2 (MIP-2) levels in the lung were determined after CLP. Expression of Mac-1 and CD44 on neutrophils was quantified by using flow cytometry. In separate experiments, fluorescent-labeled neutrophils coincubated with an anti-CD44 antibody were adoptively transferred to CLP mice. Cecal ligation and puncture triggered clear-cut lung damage characterized by edema formation, neutrophil infiltration, and increased levels of MIP-2 in the lung. Notably, immunoneutralization of CD44 reduced CLP-induced pulmonary accumulation of neutrophils. In addition, functional inhibition of CD44 decreased CLP-induced lung damage and edema. However, formation of MIP-2 in the lung and neutrophil expression of Mac-1 were intact in septic mice pretreated with the anti-CD44 antibody. Adoptive transfer experiments revealed that neutrophil rather than lung CD44 mediates neutrophil accumulation in septic lung injury. Moreover, administration of hyaluronidase had no effect on CLP-induced neutrophil recruitment and tissue damage in the lung. Our data demonstrate that CD44 contributes to pulmonary infiltration of neutrophils and lung damage associated with abdominal sepsis. Thus, these novel findings suggest that CD44 may serve as a target to protect against lung injury in polymicrobial sepsis.

Spontaneous insertion of a b2 element in the ptpn6 gene drives a systemic autoinflammatory disease in mice resembling neutrophilic dermatosis in humans

We found a spontaneous autosomal mutation in a mouse leading to neutrophil infiltration with ulceration in the upper dermis of homozygous offspring. These animals had increased neutrophil numbers, associated with normal lymphocyte count, in peripheral blood and bone marrow, suggesting a myeloproliferative disorder; however, granulocyte precursor proliferation in bone marrow was actually reduced (because circulating neutrophils were less susceptible to apoptosis). Neutrophil infiltration of the skin and other organs and high serum levels of immunoglobulins and autoantibodies, cytokines, and acute-phase proteins were additional abnormalities, all of which could be reduced by high-dose corticosteroid treatment or neutrophil depletion by antibodies. Use of genome-wide screening localized the mutation within an 0.4-Mbp region on mouse chromosome 6. We identified insertion of a B2 element in exon 6 of the Ptpn6 gene (protein tyrosine phosphatase, non-receptor type 6; also known as Shp-1). This insertion involves amino acid substitutions that significantly reduced the enzyme activity in mice homozygous for the mutation. Disease onset was delayed, and the clinical phenotype was milder than the phenotypes of other Ptpn6-mutants described in motheaten (me, mev) mice; we designated this new genotype as Ptpn6(meB2/meB2) and the phenotype as meB2. This new phenotype encompasses an autoinflammatory disease showing similarities to many aspects of the so-called neutrophilic dermatoses, a heterogeneous group of skin diseases with unknown etiology in humans.

TSG-6 protein, a negative regulator of inflammatory arthritis, forms a ternary complex with murine mast cell tryptases and heparin

TSG-6 (TNF-α-stimulated gene/protein 6), a hyaluronan (HA)-binding protein, has been implicated in the negative regulation of inflammatory tissue destruction. However, little is known about the tissue/cell-specific expression of TSG-6 in inflammatory processes, due to the lack of appropriate reagents for the detection of this protein in vivo. Here, we report on the development of a highly sensitive detection system and its use in cartilage proteoglycan (aggrecan)-induced arthritis, an autoimmune murine model of rheumatoid arthritis. We found significant correlation between serum concentrations of TSG-6 and arthritis severity throughout the disease process, making TSG-6 a better biomarker of inflammation than any of the other arthritis-related cytokines measured in this study. TSG-6 was present in arthritic joint tissue extracts together with the heavy chains of inter-α-inhibitor (IαI). Whereas TSG-6 was broadly detectable in arthritic synovial tissue, the highest level of TSG-6 was co-localized with tryptases in the heparin-containing secretory granules of mast cells. In vitro, TSG-6 formed complexes with the tryptases murine mast cell protease-6 and -7 via either heparin or HA. In vivo TSG-6-tryptase association could also be detected in arthritic joint extracts by co-immunoprecipitation. TSG-6 has been reported to suppress inflammatory tissue destruction by enhancing the serine protease-inhibitory activity of IαI against plasmin. TSG-6 achieves this by transferring heavy chains from IαI to HA, thus liberating the active bikunin subunit of IαI. Because bikunin is also present in mast cell granules, we propose that TSG-6 can promote inhibition of tryptase activity via a mechanism similar to inhibition of plasmin.

Small hyaluronan oligosaccharides induce inflammation by engaging both toll-like-4 and CD44 receptors in human chondrocytes

Small degradation fragments of hyaluronan (HA) may stimulate an inflammatory response in a variety of tissues at the injury site. HA oligosaccharides are endogenous ligands for the cluster determinant 44 (CD44) receptor as well as for toll-like receptor 4 (TLR-4). Previous data have shown that HA fragments may induce pro-inflammatory cytokine expression by interacting with both the CD44 receptor and TLR-4. CD44 and TLR-4 stimulation activates different inflammatory pathways that culminate with the activation of the transcriptional nuclear factor kappaB (NF-kappaB) which is responsible for the expression of inflammation mediators such as tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-1 beta (IL-1beta). The aim of this study was to investigate the inflammatory effects of very small HA oligosaccharides on both TLR-4 and CD44 involvement in normal human articular chondrocytes. Adding HA fragments to chondrocyte cultures up-regulated CD44 and TLR-4 expression, activated NF-kappaB translocation and increased the pro-inflammatory cytokines TNF-alpha, IL-6 and IL-1beta. The addition of a specific CD44 blocking antibody reduced CD44 and all inflammatory cytokine expression as well as protein production. However, cytokine expression remained significantly higher than in untreated chondrocytes. TLR-4 expression was not affected. The treatment with TLR-4 blocking antibody decreased TLR-4 and inflammatory cytokine expression, although cytokine expression was significantly higher than in control cells. CD44 expression was unaffected. The addition of both CD44 and TLR-4 blocking antibodies significantly reduced CD44, TLR-4 and inflammatory cytokine expression.

Development of proteoglycan-induced arthritis depends on T cell-supported autoantibody production, but does not involve significant influx of T cells into the joints

INTRODUCTION

Inflammatory joint destruction in rheumatoid arthritis (RA) may be triggered by autoantibodies, the production of which is supported by autoreactive T cells. Studies on RA and animal models of the disease suggest that T cells recruited in the joints can locally initiate or propagate arthritis. Herein, we investigated the role of joint-homing versus lymphoid organ-homing T cells in the development of proteoglycan-induced arthritis (PGIA), an autoimmune model of RA.

METHODS

To identify T cells migrating to the joints before and during development of autoimmune arthritis, we transferred fluorescence-labeled T cells, along with antigen-presenting cells, from BALB/c mice with PGIA to naïve syngeneic severe combined immunodeficient (SCID) mice. We then monitored the recruitment of donor T cells in the ankle joints and joint-draining lymph nodes of the recipients using in vivo two-photon microscopy and ex vivo detection methods. To limit T-cell access to the joints, we selectively depleted T cells in the blood circulation by treatment with FTY720, an inhibitor of lymphocyte egress from lymphoid organs. Reduction of T cell presence in both lymphoid organs and blood was achieved by injection of donor cells from which T cells were removed prior to transfer. T and B cells were quantitated by flow cytometry, and antigen (PG)-specific responses were assessed by cell proliferation and serum antibody assays.

RESULTS

Despite development of adoptively transferred arthritis in the recipient SCID mice, we found very few donor T cells in their joints after cell transfer. Treatment of recipient mice with FTY720 left the T-cell pool in the lymphoid organs intact, but reduced T cells in both peripheral blood and joints. However, FTY720 treatment failed to inhibit PGIA development. In contrast, arthritis was not seen in recipient mice after transfer of T cell-depleted cells from arthritic donors, and serum autoantibodies to PG were not detected in this group of mice.

CONCLUSIONS

Our results suggest that antigen-specific T cells, which home to lymphoid organs and provide help to B cells for systemic autoantibody production, play a greater role in the development and progression of autoimmune arthritis than the small population of T cells that migrate to the joints.

Differential effect of molecular size HA in mouse chondrocytes stimulated with PMA

BACKGROUND

Hyaluronan (HA) fragments elicit the expression of inflammatory mediators through a mechanism involving the CD44 receptor. This study investigated the effects of HA at different molecular weights on PMA-induced inflammation in mouse chondrocytes.

METHODS

mRNA and related protein levels were measured for CD44, PKCdelta, PKCepsilon, TNF-alpha, IL-1beta, MMP-13, and iNOS in chondrocytes, untreated or PMA treated, with and without the addition of HA. The level of NF-kB activation was also assayed.

RESULTS

CD44, PKCdelta, and PKCepsilon mRNA expression resulted higher than controls in chondrocytes treated with PMA. PMA also induced NF-kB up-regulation and increased TNF-alpha, IL-1beta, MMP-13, and iNOS expression. HA treatment produced different effects: low MW HA up-regulated CD44 expression, increased PKCdelta and PKCepsilon levels, and enhanced inflammation in untreated chondrocytes; while in PMA-treated cells it increased CD44, PKCdelta, PKCepsilon, NF-kB, TNF-alpha, IL-1beta, MMP-13, and iNOS expression and enhanced the effects of PMA; medium MW HA did not exert action; high MW HA had no effect on untreated chondrocytes; however, it reduced PKCdelta, PKCepsilon, NF-kB activation and inflammation in PMA-stimulated cells. Specific CD44 blocking antibody was utilised to confirm CD44 as the target of HA modulation.

GENERAL SIGNIFICANCE

These data suggest that HA via CD44 may modulate inflammation via its different molecular mass.