An unappreciated cell survival-independent role for BAFF initiating chronic lymphocytic leukemia

Background

Chronic Lymphocytic Leukemia (CLL) is characterized by the expansion of CD19+ CD5+ B cells but its origin remains debated. Mutated CLL may originate from post-germinal center B cells and unmutated CLL from CD5+ mature B cell precursors. Irrespective of precursor types, events initiating CLL remain unknown. The cytokines BAFF and APRIL each play a significant role in CLL cell survival and accumulation, but their involvement in disease initiation remains unclear.

Methods

We generated novel CLL models lacking BAFF or APRIL. In vivo experiments were conducted to explore the impact of BAFF or APRIL loss on leukemia initiation, progression, and dissemination. Additionally, RNA-seq and quantitative real-time PCR were performed to unveil the transcriptomic signature influenced by BAFF in CLL. The direct role of BAFF in controlling the expression of tumor-promoting genes was further assessed in patient-derived primary CLL cells ex-vivo.

Results

Our findings demonstrate a crucial role for BAFF, but not APRIL, in the initiation and dissemination of CLL cells. In the absence of BAFF or its receptor BAFF-R, the TCL1 transgene only increases CLL cell numbers in the peritoneal cavity, without dissemination into the periphery. While BAFF binding to BAFF-R is dispensable for peritoneal CLL cell survival, it is necessary to activate a tumor-promoting gene program, potentially linked to CLL initiation and progression. This direct role of BAFF in controlling the expression of tumor-promoting genes was confirmed in patient-derived primary CLL cells ex-vivo.

Conclusions

Our study, involving both mouse and human CLL cells, suggests that BAFF might initiate CLL through mechanisms independent of cell survival. Combining current CLL therapies with BAFF inhibition could offer a dual benefit by reducing peripheral tumor burden and suppressing transformed CLL cell output.

MUC13 Cell Surface Mucin Limits Salmonella Typhimurium Infection by Protecting the Mucosal Epithelial Barrier

BACKGROUND & AIMS

MUC13 cell surface mucin is highly expressed on the mucosal surface throughout the intestine, yet its role against bacterial infection is unknown. We investigated how MUC13 impacts Salmonella typhimurium (S Tm) infection and elucidated its mechanisms of action.

METHODS

Muc13-/- and wild-type littermate mice were gavaged with 2 isogenic strains of S Tm after pre-conditioning with streptomycin. We assessed clinical parameters, cecal histology, local and systemic bacterial load, and proinflammatory cytokines after infection. Cecal enteroids and epithelial cell lines were used to evaluate the mechanism of MUC13 activity after infection. The interaction between bacterial SiiE and MUC13 was assessed by using siiE-deficient Salmonella.

RESULTS

S Tm-infected Muc13-/- mice had increased disease activity, histologic damage, and higher local and systemic bacterial loads. Mechanistically, we found that S Tm binds to MUC13 through its giant SiiE adhesin and that MUC13 acts as a pathogen-binding decoy shed from the epithelial cell surface after pathogen engagement, limiting bacterial invasion. In addition, MUC13 reduces epithelial cell death and intestinal barrier breakdown by enhancing nuclear factor kappa B signaling during infection, independent of its decoy function.

CONCLUSIONS

We show for the first time that MUC13 plays a critical role in antimicrobial defense against pathogenic S Tm at the intestinal mucosal surface by both acting as a releasable decoy limiting bacterial invasion and reducing pathogen-induced cell death. This further implicates the cell surface mucin family in mucosal defense from bacterial infection.

Influence of the MUC1 Cell Surface Mucin on Gastric Mucosal Gene Expression Profiles in Response to Helicobacter pylori Infection in Mice

The cell surface mucin MUC1 is an important host factor limiting Helicobacter pylori (H. pylori) pathogenesis in both humans and mice by providing a protective barrier and modulating mucosal epithelial and leukocyte responses. The aim of this study was to establish the time-course of molecular events in MUC1-modulated gene expression profiles in response to H. pylori infection in wild type (WT) and MUC1-deficient mice using microarray-determined mRNA expression, gene network analysis and Ingenuity Pathway Analysis (IPA). A time-course over the first 72 h of infection showed significantly higher mucosal loads of bacteria at 8 h of infection in Muc1^−/− mice compared with WT, confirming its importance in the early stages of infection (P = 0.0003). Microarray analysis revealed 266 differentially expressed genes at one or more time-points over 72 h in the gastric mucosa of Muc1^−/− mice compared with WT control using a threshold of 2-fold change. The SPINK1 pancreatic cancer canonical pathway was strongly inhibited in Muc1^−/− mice compared with WT at sham and 8 h infection (P = 6.08E-14 and P = 2.25 E-19, respectively) but potently activated at 24 and 72 h post-infection (P = 1.38E-22 and P = 5.87E-13, respectively). The changes in this pathway are reflective of higher expression of genes mediating digestion and absorption of lipids, carbohydrates, and proteins at sham and 8 h infection in the absence of MUC1, but that this transcriptional signature is highly down regulated as infection progresses in the absence of MUC1. Uninfected Muc1^−/− gastric tissue was highly enriched for expression of factors involved in lipid metabolism and 8 h infection further activated this network compared with WT. As infection progressed, a network of antimicrobial and anti-inflammatory response genes was more highly activated in Muc1^−/− than WT mice. Key target genes identified by time-course microarrays were independently validated using RT-qPCR. These results highlight the dynamic interplay between the host and H. pylori, and the role of MUC1 in host defense, and provide a general picture of changes in cellular gene expression modulated by MUC1 in a time-dependent manner in response to H. pylori infection.

Airway Mucus Hyperconcentration in Non-Cystic Fibrosis Bronchiectasis

Rationale: Non-cystic fibrosis bronchiectasis is characterized by airway mucus accumulation and sputum production, but the role of mucus concentration in the pathogenesis of these abnormalities has not been characterized.Objectives: This study was designed to: 1) measure mucus concentration and biophysical properties of bronchiectasis mucus; 2) identify the secreted mucins contained in bronchiectasis mucus; 3) relate mucus properties to airway epithelial mucin RNA/protein expression; and 4) explore relationships between mucus hyperconcentration and disease severity.Methods: Sputum samples were collected from subjects with bronchiectasis, with and without chronic erythromycin administration, and healthy control subjects. Sputum percent solid concentrations, total and individual mucin concentrations, osmotic pressures, rheological properties, and inflammatory mediators were measured. Intracellular mucins were measured in endobronchial biopsies by immunohistochemistry and gene expression. MUC5B (mucin 5B) polymorphisms were identified by quantitative PCR. In a replication bronchiectasis cohort, spontaneously expectorated and hypertonic saline-induced sputa were collected, and mucus/mucin concentrations were measured.Measurements and Main Results: Bronchiectasis sputum exhibited increased percent solids, total and individual (MUC5B and MUC5AC) mucin concentrations, osmotic pressure, and elastic and viscous moduli compared with healthy sputum. Within subjects with bronchiectasis, sputum percent solids correlated inversely with FEV₁ and positively with bronchiectasis extent, as measured by high-resolution computed tomography, and inflammatory mediators. No difference was detected in MUC5B rs35705950 SNP allele frequency between bronchiectasis and healthy individuals. Hypertonic saline inhalation acutely reduced non-cystic fibrosis bronchiectasis mucus concentration by 5%.Conclusions: Hyperconcentrated airway mucus is characteristic of subjects with bronchiectasis, likely contributes to disease pathophysiology, and may be a target for pharmacotherapy.

[Dose-response relationship between maternal hemoglobin concentration and preterm birth, in pregnant women]

Objective: To investigate the dose-response relationship between hemoglobin concentration and preterm birth, during pregnancy. Methods: With Zhuang ethnicity, a total of 12 780 pregnant women and their infants that admitted to Wuming、Pingguo、Jingxi、Debao、Longan and Tiandong hospitals, were recruited, in Guangxi Zhuang Autonomous Region, from January 2015 to December 2017. Non-conditional logistic regression method was used to analyze the effect of anemia on preterm birth during pregnancy. Dose-response relationship between hemoglobin concentration and preterm birth was explored, using the restrictive cubic spline model. Results: After excluding 2 053 pregnant women with hypertension or aged 35 years and over, results from the non-conditional logistic regression analysis showed that the risk of preterm birth in the anemia group was 1.29 times (OR=1.29, 95%CI: 1.04-1.59, P=0.019) of the non-anemia group in the first trimester. Data from the restricted cubic sample showed that there appeared nonlinear "L" dose-response relationship between hemoglobin concentration and preterm birth in the first trimester and "U" shape in the third trimester (non-linearity test P<0.001). Conclusion: There appeared nonlinear dose-response relationship between the hemoglobin concentration and preterm birth, both in the first and third trimesters.

Abstract 3564: MUC13 protects colorectal cancer cells from death by activating the NF-κb pathway and is a potential therapeutic target

MUC13 is a transmembrane mucin glycoprotein that is overexpressed by many cancers, although its functions are not fully understood. NF-κB is a key transcription factor promoting cancer cell survival, but therapeutically targeting this pathway has proved difficult because NF-κB has pleiotropic functions. Here, we report that MUC13 prevents colorectal cancer cell death by promoting two distinct pathways of NF-kB activation, consequently up-regulating BCL-XL. MUC13 promoted TNF-induced NF-κB activation by interacting with TNFR1 and the E3 ligase, cIAP1, to increase ubiquitination of RIPK1. MUC13 also promoted genotoxin-induced NF-κB activation by increasing phosphorylation of ATM and SUMOylation of NEMO. Moreover, elevated expression of cytoplasmic MUC13 and NF-κB correlated with colorectal cancer progression and metastases. Our demonstration that MUC13 enhances NF-κB signalling in response to both TNF and DNA damaging agents provides a new molecular target for specific inhibition of NF-κB activation. As proof of principle, silencing MUC13 sensitized colorectal cancer cells to death in response to cytotoxic drugs and inflammatory signals and abolished chemotherapy-induced enrichment of CD133+ CD44+ cancer stem cells, slowed xenograft growth in mice, and synergized with 5-fluourouracil to induce tumor regression. Therefore, these data indicate that combining chemotherapy and MUC13 antagonism could improve the treatment of metastatic cancers.

Citation Format: Yong H. Sheng, Yaowu He, sumaira Z. hasnain, Ran Wang, Hui Tong, Daniel T. Clarke, Rohan Lourie, Iulia Oancea, kuanyau wong, John W. Lumley, Timothy H. Florin, Philip Sutton, John. D. Hooper, Nigel A. Mcmillan, Michael A. Mcguckin. MUC13 protects colorectal cancer cells from death by activating the NF-κb pathway and is a potential therapeutic target. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3564.

MUC13 protects colorectal cancer cells from death by activating the NF-κB pathway and is a potential therapeutic target

MUC13 is a transmembrane mucin glycoprotein that is over produced by many cancers, although its functions are not fully understood. Nuclear factor-κB (NF-κB) is a key transcription factor promoting cancer cell survival, but therapeutically targeting this pathway has proved difficult because NF-κB has pleiotropic functions. Here, we report that MUC13 prevents colorectal cancer cell death by promoting two distinct pathways of NF-kB activation, consequently upregulating BCL-X_L. MUC13 promoted tumor necrosis factor (TNF)-induced NF-κB activation by interacting with TNFR1 and the E3 ligase, cIAP1, to increase ubiquitination of RIPK1. MUC13 also promoted genotoxin-induced NF-κB activation by increasing phosphorylation of ATM and SUMOylation of NF-κB essential modulator. Moreover, elevated expression of cytoplasmic MUC13 and NF-κB correlated with colorectal cancer progression and metastases. Our demonstration that MUC13 enhances NF-κB signaling in response to both TNF and DNA-damaging agents provides a new molecular target for specific inhibition of NF-κB activation. As proof of principle, silencing MUC13 sensitized colorectal cancer cells to killing by cytotoxic drugs and inflammatory signals and abolished chemotherapy-induced enrichment of CD133⁺ CD44⁺ cancer stem cells, slowed xenograft growth in mice, and synergized with 5-fluourouracil to induce tumor regression. Therefore, these data indicate that combining chemotherapy and MUC13 antagonism could improve the treatment of metastatic cancers.

High Fat Diets Induce Colonic Epithelial Cell Stress and Inflammation that is Reversed by IL-22

Prolonged high fat diets (HFD) induce low-grade chronic intestinal inflammation in mice, and diets high in saturated fat are a risk factor for the development of human inflammatory bowel diseases. We hypothesized that HFD-induced endoplasmic reticulum (ER)/oxidative stress occur in intestinal secretory goblet cells, triggering inflammatory signaling and reducing synthesis/secretion of proteins that form the protective mucus barrier. In cultured intestinal cells non-esterified long-chain saturated fatty acids directly increased oxidative/ER stress leading to protein misfolding. A prolonged HFD elevated the intestinal inflammatory cytokine signature, alongside compromised mucosal barrier integrity with a decrease in goblet cell differentiation and Muc2, a loss in the tight junction protein, claudin-1 and increased serum endotoxin levels. In Winnie mice, that develop spontaneous colitis, HFD-feeding increased ER stress, further compromised the mucosal barrier and increased the severity of colitis. In obese mice IL-22 reduced ER/oxidative stress and improved the integrity of the mucosal barrier, and reversed microbial changes associated with obesity with an increase in Akkermansia muciniphila. Consistent with epidemiological studies, our experiments suggest that HFDs are likely to impair intestinal barrier function, particularly in early life, which partially involves direct effects of free-fatty acids on intestinal cells, and this can be reversed by IL-22 therapy.

Expressions of survivin, P16(INK4a), COX-2, and Ki-67 in cervical cancer progression reveal the potential clinical application

PURPOSE OF INVESTIGATION

To explore the significance of survivin, P16(INK4a), COX-2, and Ki-67 expressions for prediction of cervical cancer progression.

MATERIALS AND METHODS

A retrospective study was performed in 129 cases including 24 squamous carcinoma of the cervix (SCC), 70 cervical intraepithelial neoplasias (CIN), 15 cervical condyloma acuminatum (CCA), ten chronic cervicitis (CC), and ten normal cervix (NC). Protein expressions were evaluated using immunohistochemistry.

RESULTS

Survivin, P16(INK4a); COX-2, and Ki-67 were highly expressed in SCC and CIN compared with others. Their expression rates were gradually increased in CIN I, CIN II, CIN III, and SCC groups, showing 72.00%, 88.00%, 90.00%, and 95.83% for P16(INK4a), 68.00%, 84.00%, 95.00% and 100.00% for COX-2, 76.00%, 96.00%, 100.00%, and 100.00 for Ki-67, respectively. There were significant correlations between survivin and P16(INK4a), COX-2, Ki-67, as well as P16(INK4a) and Ki-67.

CONCLUSION

Survivin, P16(INK4a), COX-2 and Ki-67 play critical roles for development and progression of cervical cancer.

Mucins in inflammatory bowel diseases and colorectal cancer

The gastrointestinal tract is protected by a mucus barrier with both secreted and cell-surface mucins contributing to the exclusion of luminal microbes and toxins. Alterations in the structure and/or quantity of mucins alter the barrier function of mucus and could play roles in initiating and maintaining mucosal inflammation in inflammatory bowel diseases (IBD), and in driving cancer development in the intestine. The aim of this review is to focus on the roles of the mucins in IBD. The polymorphisms of mucin genes that have been associated with susceptibility to IBD, and alterations in mucin expression as well as factors that regulate production of the mucins in IBD, are summarized. Data from animal models of intestinal inflammation, which support the importance of mucins in IBD and cancer development, are also discussed.

Techniques for assessment of interactions of mucins with microbes and parasites in vitro and in vivo

Most mammalian pathogens and parasites infect their hosts via the mucosal surfaces. The first barrier they encounter in all mucosal tissues is a layer of viscous mucus which can be modulated by immune responses to the pathogen or parasite. The major macromolecular constituents of mucus are secreted mucin glycoproteins which give mucus its viscous properties. Underneath the mucus layer, the mucosal epithelial cells have a cell surface glycocalyx that is rich in transmembrane mucin glycoproteins. Both the cell surface and secreted mucins present a vast array of potential binding sites for pathogens and parasites and both forms of mucins are involved in protecting the host from infection. However, many pathogens and parasites have evolved mechanisms to subvert the mucin barrier. Thus, studying mucin interactions with pathogens and parasites is critical to understanding host-pathogen interactions at the mucosal surfaces. In this chapter, we describe methods for studying the interactions between mucins and pathogens and parasites, methods for studying the degradation of mucins by pathogens and parasites, and in vitro and in vivo methods for exploring the functional significance of the mucins in host defence from infection.

The MUC13 cell-surface mucin protects against intestinal inflammation by inhibiting epithelial cell apoptosis

BACKGROUND AND AIMS

The MUC13 transmembrane mucin is highly and constitutively expressed in the small and large intestine. Although MUC13 polymorphisms have been associated with human inflammatory bowel diseases and susceptibility to Escherichia coli infection in pigs, the biological functions of MUC13 are unknown. This study aimed to explore whether MUC13 modulates intestinal inflammation.

METHODS

Muc13(-/-) mice were generated, phenotyped and challenged with the colitis-inducing agent, dextran sodium sulphate (DSS). Colitis was assessed by clinical symptoms and intestinal histopathology. Intestinal epithelial cell apoptosis and proliferation, macrophage infiltration and cytokine production were also quantified. Apoptosis of human LS513 intestinal epithelial cells in response to apoptotic agents, including DSS, was also measured, following knockdown of MUC13 with siRNA.

RESULTS

Muc13(-/-) mice were viable, fertile and developed normally, with no spontaneous intestinal pathology except mild focal neutrophilic inflammation in the small and large intestines of old mice. In response to DSS challenge, Muc13(-/-) mice developed more severe acute colitis, as reflected by increased weight loss, rectal bleeding, diarrhoea and histological colitis scores compared with wild-type mice. Increased numbers of F4/80(+) macrophages in inflamed mucosa of Muc13(-/-) mice were accompanied by increased expression of intestinal IL-1β and TNFα mRNA. Muc13(-/-) mice had significantly increased intestinal epithelial cell apoptosis within 3 days of DSS exposure. LS513 cells were more susceptible to DSS, actinomycin-D, ultraviolet irradiation and TRAIL-induced apoptosis when MUC13 was knocked down by siRNA.

CONCLUSIONS

These novel findings indicate a protective role for Muc13 in the colonic epithelium by inhibiting toxin-induced apoptosis and have important implications for intestinal infections, inflammatory diseases and the development of intestinal cancer.

MUC1 limits Helicobacter pylori infection both by steric hindrance and by acting as a releasable decoy

The bacterium Helicobacter pylori can cause peptic ulcer disease, gastric adenocarcinoma and MALT lymphoma. The cell-surface mucin MUC1 is a large glycoprotein which is highly expressed on the mucosal surface and limits the density of H. pylori in a murine infection model. We now demonstrate that by using the BabA and SabA adhesins, H. pylori bind MUC1 isolated from human gastric cells and MUC1 shed into gastric juice. Both H. pylori carrying these adhesins, and beads coated with MUC1 antibodies, induced shedding of MUC1 from MKN7 human gastric epithelial cells, and shed MUC1 was found bound to H. pylori. Shedding of MUC1 from non-infected cells was not mediated by the known MUC1 sheddases ADAM17 and MMP-14. However, knockdown of MMP-14 partially affected MUC1 release early in infection, whereas ADAM17 had no effect. Thus, it is likely that shedding is mediated both by proteases and by disassociation of the non-covalent interaction between the alpha- and beta-subunits. H. pylori bound more readily to MUC1 depleted cells even when the bacteria lacked the BabA and SabA adhesins, showing that MUC1 inhibits attachment even when bacteria cannot bind to the mucin. Bacteria lacking both the BabA and SabA adhesins caused less apoptosis in MKN7 cells than wild-type bacteria, having a greater effect than deletion of the CagA pathogenicity gene. Deficiency of MUC1/Muc1 resulted in increased epithelial cell apoptosis, both in MKN7 cells in vitro, and in H. pylori infected mice. Thus, MUC1 protects the epithelium from non-MUC1 binding bacteria by inhibiting adhesion to the cell surface by steric hindrance, and from MUC1-binding bacteria by acting as a releasable decoy.

MUC1 limits Helicobacter pylori infection both by steric hindrance and by acting as a releasable decoy

The bacterium Helicobacter pylori can cause peptic ulcer disease, gastric adenocarcinoma and MALT lymphoma. The cell-surface mucin MUC1 is a large glycoprotein which is highly expressed on the mucosal surface and limits the density of H. pylori in a murine infection model. We now demonstrate that by using the BabA and SabA adhesins, H. pylori bind MUC1 isolated from human gastric cells and MUC1 shed into gastric juice. Both H. pylori carrying these adhesins, and beads coated with MUC1 antibodies, induced shedding of MUC1 from MKN7 human gastric epithelial cells, and shed MUC1 was found bound to H. pylori. Shedding of MUC1 from non-infected cells was not mediated by the known MUC1 sheddases ADAM17 and MMP-14. However, knockdown of MMP-14 partially affected MUC1 release early in infection, whereas ADAM17 had no effect. Thus, it is likely that shedding is mediated both by proteases and by disassociation of the non-covalent interaction between the alpha- and beta-subunits. H. pylori bound more readily to MUC1 depleted cells even when the bacteria lacked the BabA and SabA adhesins, showing that MUC1 inhibits attachment even when bacteria cannot bind to the mucin. Bacteria lacking both the BabA and SabA adhesins caused less apoptosis in MKN7 cells than wild-type bacteria, having a greater effect than deletion of the CagA pathogenicity gene. Deficiency of MUC1/Muc1 resulted in increased epithelial cell apoptosis, both in MKN7 cells in vitro, and in H. pylori infected mice. Thus, MUC1 protects the epithelium from non-MUC1 binding bacteria by inhibiting adhesion to the cell surface by steric hindrance, and from MUC1-binding bacteria by acting as a releasable decoy.

Theoretical studies on alkyne addition to molybdenum alkylidenes: the preference of alpha- and beta-additions

The addition of alkynes HC=CR to Mo(NH)(CH(2))(OR')(2) (R = H, Me, Ph; R' = CH(3), CF(3)) has been studied with both ab initio molecular orbital and density functional calculations. Geometry optimizations were carried out with the HF/3-21G, HF/HW3, and B3LYP/HW3 methods. The transition structures for these addition reactions are in distorted trigonal bipyramidal geometries, similar to those of alkene additions. The calculated activation enthalpy for HC=CH addition to Mo(NH)(CH(2))(OR')(2) is about 10.3 kcal/mol for R' = CH(3) and about 2.3 kcal/mol for R' = CF(3), indicating a significant preference for acetylene addition to Mo(NH)(CH(2))(OCF(3))(2) over Mo(NH)(CH(2))(OCH(3))(2). These barriers are higher than those of the corresponding ethylene addition by about 2-4 kcal/mol, even though the reaction of acetylene is much more exothermic. The alpha-addition of HC=CR (R = Me, Ph) is found to be considerably more favorable than the beta-addition to Mo(NH)(CH(2))(OR')(2). Interestingly, the alpha-addition has a lower activation energy, while the beta-addition has a higher activation energy, compared to that of the parent acetylene addition. Thus, alpha-addition is intrinsically favored over beta-addition by over 4 kcal/mol. This preference is reduced by solvent effect. All these can be explained by a destabilizing interaction between the nonreacting pi-orbital of alkyne and one of the lone pairs on the imido nitrogen. The steric effect of the bulky ligands in the real catalysts is also investigated qualitatively by the PM3 method. These studies give results in good accord with the experimentally observed regioselectivity.

Epitope studies with anti-beta 2-glycoprotein I antibodies from autoantibody and immunized sources

This paper examines the methodology of anti-beta(2)-glycoprotein I (beta(2)-GPI) epitope determination and provides further epitope studies using human sera containing anti-beta(2)-GPI autoantibodies. Studies in this field may be misleading as the antigen coating density using mutant forms of beta(2)-GPI may be below the threshold required for monogamous divalent binding by low affinity anti-beta(2)-GPI autoantibodies, while being easily detected by high affinity anti-beta(2)-GPI from immunized animals. The antigen density threshold effect is found in anti-beta(2)-GPI autoantibodies from humans and from monoclonal anti-beta(2)-GPI derived from mice with models of autoimmune disease. Anti-beta(2)-GPI from an autoimmune mouse and from 18/21 human sera did not bind above background levels to a domain-I-deleted mutant. In addition, single point mutations in domain I result in dramatic changes in the binding of many human sera containing anti-beta(2)-GPI. These findings support a conclusion that domain I of beta(2)-GPI contains significant epitopes for the anti-beta(2)-GPI antibodies found in the antiphospholipid syndrome.

Human beta 2-glycoprotein I binds to endothelial cells through a cluster of lysine residues that are critical for anionic phospholipid binding and offers epitopes for anti-beta 2-glycoprotein I antibodies

Beta 2-Glycoprotein I (beta 2GPI) is a phospholipid-binding protein recognized by serum autoantibodies from the anti-phospholipid syndrome both in cardiolipin- and beta 2GPI-coated plates. We found that: 1) recombinant wild-type beta 2GPI bound to HUVEC and was recognized by both human monoclonal IgM and affinity-purified polyclonal IgG anti-beta 2GPI anti-phospholipid syndrome Abs; and 2) a single amino acid change from Lys286 to Glu significantly reduced endothelial adhesion. Double and triple mutants (from Lys284,287 to Glu284,287, from Lys286,287 to Glu286,287, and from Lys284,286,287 to Glu284,286,287) completely abolished endothelial binding. A synthetic peptide (P1) spanning the sequence Glu274-Cys288 of the beta 2GPI fifth domain still displayed endothelial adhesion. Another peptide (P8), identical with P1 except that Cys281 and Cys288 were substituted with serine residues, did not bind to HUVEC. Anti-beta 2GPI Abs, once bound to P1 adhered to HUVEC, induced E-selectin expression and up-regulated IL-6 secretion. Control experiments conducted with irrelevant Abs as well as with the P8 peptide did not show any endothelial Ab binding nor E-selectin and IL-6 modulation. Our results suggest that: 1) beta 2GPI binds to endothelial cells through its fifth domain; 2) the major phospholipid-binding site that mediates the binding to anionic phospholipids is also involved in endothelial binding; 3) HUVEC provide a suitable surface for beta 2GPI binding comparable to that displayed by anionic phospholipids dried on microtiter wells; and 4) the formation of the complex between beta 2GPI and the specific Abs leads to endothelial activation in vitro.

beta 2-Glycoprotein I: target antigen for autoantibodies in the 'antiphospholipid syndrome'

Antiphospholipid' (aPL) antibodies are of important clinical significance because of their association with thrombosis both arterial and venous, recurrent foetal loss, specific neurological sequelae like seizures and chorea, cardiac valvular abnormalities and thrombocytopenia. Traditionally these autoantibodies have been assayed using phospholipid (PL) dependent tests and are classified as lupus anticoagulants (LA) and anticardiolipin (aCL) antibodies based on the method of detection. The antibodies thus, had been thought to bind PLs but it has now become clear that the true antigens are PL-binding proteins. The major protein consistently found as the target antigen for these autoantibodies is beta 2-glycoprotein I (beta 2-GPI). Other candidate PL-binding proteins have also been investigated including prothrombin, protein C and protein S but thus far appear to play less important roles in the binding of these antibodies.

The role of beta 2-glycoprotein I in the antiphospholipid syndrome

Antiphospholipid antibodies were originally thought to bind negatively-charged (anionic) phospholipids. Current evidence suggest that the target antigen is considerably more complex and includes beta 2-glycoprotein I, a phospholipid-binding plasma protein. Our understanding of the pathophysiology of the antiphospholipid syndrome has increased exponentially with a number of studies into the interactions of antiphospholipid antibodies and beta 2-glycoprotein I.

[Vitreous prolapse during cataract surgery]

Clinical data of 427 cases (458 eyes) of extracapsular cataract extraction and IOL implantation gave the impression that vitreous prolapse due to disruption of the zonula and the posterior capsule was a malpractical complication. Forcible capsulotomy too large or deep and uneven irrigating pressure were the common causes of zonular disruption. Obstructed passage and insufficient separation of the nucleus from the posterior cortical bed leading to difficult nuclear delivery, aspiration of cortex in the posterior chamber, poorly filled anterior chamber, insufficient room for the IOL, improper insertion of the posterior haptics and traumatic dialing were risk factors for posterior capsular rupture and vitreous prolapse.