Role of CD98 in liver disease

An anti-CD98 antibody displaying pH-dependent Fc-mediated tumour-specific activity against multiple cancers in CD98-humanized mice

The cell-surface glycoprotein CD98-a subunit of the LAT1/CD98 amino acid transporter-is an attractive target for cancer immunotherapies, but its widespread expression has hampered the development of CD98-targeting antibody therapeutics. Here we report that an anti-CD98 antibody, identified via the screening of phage-display libraries of CD98 single-chain variable fragments with mutated complementarity-determining regions, preserves the physiological function of CD98 and elicits broad-spectrum crystallizable-fragment (Fc)-mediated anti-tumour activity (requiring Fcγ receptors for immunoglobulins, macrophages, dendritic cells and CD8⁺ T cells, as well as other components of the innate and adaptive immune systems) in multiple xenograft and syngeneic tumour models established in CD98-humanized mice. We also show that a variant of the anti-CD98 antibody with pH-dependent binding, generated by solving the structure of the antibody-CD98 complex, displayed enhanced tumour-specific activity and pharmacokinetics. pH-dependent antibody variants targeting widely expressed antigens may lead to superior therapeutic outcomes.

Possible Role of Extracellular Vesicles in Hepatotoxicity of Acetaminophen

We examined proteomic profiles of rat liver extracellular vesicles (EVs) shed following treatment with a sub-toxic dose (500 mg/kg) of the pain reliever drug, acetaminophen (APAP). EVs representing the entire complement of hepatic cells were isolated after perfusion of the intact liver and analyzed with LC-MS/MS. The investigation was focused on revealing the function and cellular origin of identified EVs proteins shed by different parenchymal and non-parenchymal liver cells and their possible role in an early response of this organ to a toxic environment. Comparison of EV proteomic profiles from control and APAP-treated animals revealed significant differences. Alpha-1-macroglobulin and members of the cytochrome P450 superfamily were highly abundant proteins in EVs shed by the normal liver. In contrast, proteins like aminopeptidase N, metalloreductase STEAP4, different surface antigens like CD14 and CD45, and most members of the annexin family were detected only in EVs that were shed by livers of APAP-treated animals. In EVs from treated livers, there was almost a complete disappearance of members of the cytochrome P450 superfamily and a major decrease in other enzymes involved in the detoxification of xenobiotics. Additionally, there were proteins that predominated in non-parenchymal liver cells and in the extracellular matrix, like fibronectin, receptor-type tyrosine-protein phosphatase C, and endothelial type gp91. These differences indicate that even treatment with a sub-toxic concentration of APAP initiates dramatic perturbation in the function of this vital organ.

Galectin-3 enhances atrial remodelling and arrhythmogenesis through CD98 signalling

AIM

Galectin-3 (Gal-3) is a biomarker of atrial fibrillation (AF) that mediates atrial inflammation. CD98 is the membrane surface receptor for Gal-3. Nevertheless, the role of the Gal-3/CD98 axis in atrial arrhythmogenesis is unclear. In this study, we investigated the effects of Gal-3/CD98 signalling on atrial pathogenesis.

METHODS

Whole cell patch clamp and western blotting were used to analyse calcium/potassium homeostasis and calcium-related signalling in Gal-3-administrated HL-1 atrial cardiomyocytes with/without CD98 neutralized antibodies. Telemetry electrocardiographic recording, Masson's trichrome staining and immunohistochemistry staining of atrium were obtained from mice having received tail-vein injections with Gal-3.

RESULTS

Gal-3-treated HL-1 myocytes had a shorter action potential duration, smaller L-type calcium current, increased sarcoplasmic reticulum (SR) calcium content, Na⁺ /Ca²⁺ exchanger (NCX) current, transient outward potassium current, and ultrarapid delayed rectifier potassium current than control cells had. Gal-3-treated HL-1 myocytes had greater levels of SR Ca²⁺ ATPase, NCX, Nav1.5, and NLR family pyrin domain containing 3 (NLRP3) expression and increased calcium/calmodulin-dependent protein kinase II (CaMKII), ryanodine receptor 2 (RyR2), and nuclear factor kappa B (NF-κB) phosphorylation than control cells had. Gal-3-mediated activation of CaMKII/RyR2 pathway was diminished in the cotreatment of anti-CD98 antibodies. Mice that were injected with Gal-3 had more atrial ectopic beats, increased atrial fibrosis, and activated NF-κB/NLRP3 signalling than did control mice (nonspecific immunoglobulin) or mice treated with Gal-3 and anti-CD98 antibodies.

CONCLUSION

Gal-3 recombinant protein administration increases atrial fibrosis and arrhythmogenesis through CD98 signalling. Targeting Gal-3/CD98 axis might be a novel therapeutic strategy for patients with AF and high Gal-3 levels.

Digoxin mitigates diethylnitrosamine-induced acute liver injury in mice via limiting production of inflammatory mediators

The cardiotonic digoxin has been recently shown to possess an anti-inflammatory potential in numerous metabolic and inflammatory disorders. However, data about digoxin’s impact in the setting of acute liver injury and sterile inflammation are still limited. Here, we investigated the potential effect of digoxin pretreatments (0.25 and 0.5 mg/kg, oral) on the severity of acute hepatotoxicity in mice challenged with a single dose of diethylnitrosamine (DN; 150 mg/kg, intraperitoneal) for 24 h. Our results indicated that digoxin pretreatments dose-dependently mitigated DN-induced rise of hepatocellular injury parameters and necroinflammation scores. Digoxin, particularly at dose of 0.5 mg/kg, boosted the number of PCNA positive hepatocytes, leading to improvement of the reparative potential in hepatocytes of DN-intoxicated livers. Digoxin’s ameliorative effect on DN-hepatotoxicity coincided with (i) lowering the increased hepatic production and release of the proinflammatory mediators IL-17A, IL-1β and TNF-α, and (ii) impeding the attraction and infiltration of monocytes to the liver, as denoted by decreasing serum MCP-1 and F4/80 immunohistochemical expression. These effects were attributed to reducing DN-induced activation of NF-κB and overexpression of CD98 in the liver. Meanwhile, DN elicited a decline in the hepatic production and release of the anti-inflammatory cytokines IL-22 and IL-6, which was intensified by digoxin, especially at a dose 0.5 mg/kg. In conclusion, digoxin conferred liver protection against DN-insult by impairing the overproduction of proinflammatory cytokines and infiltration of inflammatory cells to the liver.

CD98-induced CD147 signaling stabilizes the Foxp3 protein to maintain tissue homeostasis

Regulatory T cell (Treg) stability is necessary for the proper control of immune activity and tissue homeostasis. However, it remains unclear whether Treg stability must be continually reinforced or is established during development under physiological conditions. Foxp3 has been characterized as a central mediator of the genetic program that governs Treg stability. Here, we demonstrate that to maintain Foxp3 protein expression, Tregs require cell-to-cell contact, which is mediated by the CD147-CD98 interaction. As Tregs are produced, CD147, which is expressed on their surface, is stimulated by CD98, which is widely expressed in the physiological environment. As a result, CD147's intracellular domain binds to CDK2 and retains it near the membrane, leading to Foxp3 dephosphorylation and the prevention of Foxp3 degradation. In addition, the optimal distribution of Foxp3+ Tregs under both pathological and physiological conditions depends on CD98 expression. Thus, our study provides direct evidence that Foxp3-dependent Treg stability is reinforced in the periphery by the interaction between CD147 and CD98 in the surrounding environment. More importantly, Tregs with high CD147 expression effectively inhibit inflammatory responses and maintain Foxp3 stability, which has guiding significance for the application of Tregs in immunotherapy.

Changes in the proteome of extracellular vesicles shed by rat liver after subtoxic exposure to acetaminophen

To identify changes in extracellular vesicles (EVs) secreted by the liver following drug-induced liver injury (DILI), rats were treated with a subtoxic dose (500 mg/kg) of the analgesic drug, acetaminophen (APAP). EVs were collected by liver perfusion of sham and APAP-treated rats. Changes in EVs morphology were examined by transmission electron microscopic analysis of negatively stained vesicles. Results from morphometric analysis of EVs revealed striking differences in their size and distribution. Proteome composition of EVs collected by liver perfusion was determined by mass spectrometry using methods of sample preparation that enabled better detection of both highly hydrophobic proteins and proteins with complex post-translational modifications. The collection of EVs after liver perfusion is an approach that enables the isolation of EVs shed not only by isolated hepatocytes, but also by the entire complement of hepatic cells. EVs derived after DILI had a lower content of alpha-1-macroglobulin, ferritin, and members of cytochrome 450 family. Fibronectin, aminopeptidase N, metalloreductase STEAP4, integrin beta, and members of the annexin family were detected only in APAP-treated samples of EVs. These results show that the present approach can provide valuable insights into the response of the liver following drug-induced liver injury.

Internalization of Garlic-Derived Nanovesicles on Liver Cells is Triggered by Interaction With CD98

The mechanism of how plant-derived nanovesicles are uptaken by cells remains unknown. In this study, the garlic-derived nanovesicles (GDVs) were isolated and digested with trypsin to remove all surface proteins. Digested GDVs showed less uptake compared to undigested GDVs, confirming that the surface proteins played a role in the endocytosis. On the cell side (HepG2), interestingly, blocking the CD98 receptors significantly reduced the uptake of GDVs. During the cellular internalization of GDVs, we observed that some surface proteins of GDVs were co-localized with CD98. A total lysate of the GDV surface showed a high presence of a mannose-specific binding protein, II lectin. Blocking GDV II lectin (using mannose preincubation) highly reduced the GDV internalization, which supports that direct interaction between II lectin and CD98 plays an important role in internalization. The GDVs also exhibited in vitro anti-inflammatory effect by downregulating proinflammatory factors on the HepG2 cells. This work contributes to understanding a part of the GDV internalization process and the cellular anti-inflammatory effects of garlic.