Gardnerella Vaginolysin Potentiates Glycan Molecular Mimicry by Neisseria gonorrhoeae.

Bacterial vaginosis (BV) is a dysbiotic condition of the vaginal microbiome associated with higher risk of infection by Neisseria gonorrhoeae-the cause of gonorrhea. Here we test if one known facet of BV-the presence of bacterial cytolysins-leads to mobilization of intracellular contents that enhance gonococcal virulence. We cloned and expressed recombinant vaginolysin (VLY), a cytolysin produced by the BV-associated bacterium Gardnerella, verifying that it liberates contents of cervical epithelial (HeLa) cells, while vector control preparations did not. We tested if VLY mediates a well-known gonococcal virulence mechanism-the molecular mimicry of host glycans. To evade host immunity, N. gonorrhoeae caps its lipooligosaccharide (LOS) with α2-3-linked sialic acid. For this, gonococci must scavenge a metabolite made inside host cells. Flow cytometry-based lectin-binding assays showed that gonococci exposed to vaginolysin-liberated contents of HeLa cells displayed greater sialic acid capping of their LOS. This higher level of bacterial sialylation was accompanied by increased binding of the complement regulatory protein factor H, and greater resistance to complement attack. Together these results suggest that cytolytic activities present during BV may enhance the ability of N. gonorrhoeae to capture intracellular metabolites and evade host immunity via glycan molecular mimicry.

Decreased erythrocyte binding of Siglec-9 increases neutrophil activation in sickle cell disease.

Oxidative stress and inflammation promote vaso-occlusion in sickle cell disease (SCD). CD33-related Sialic acid-binding immunoglobulin-type lectins (CD33rSiglecs) are cell surface proteins that recognize sialic acids inhibit innate immune cell functions. We have shown that Siglec-9 on human neutrophils interact with erythrocyte sialic acids (prominently glycophorin-A (GYPA) to suppress neutrophil reactive oxygen species (ROS). We hypothesized that altered sickle erythrocyte membrane sialic acid leads to decreased Siglec-9 binding capability, and thus a decreased neutrophil oxidative burst. SS erythrocytes express significantly more sialic acid than AA erythrocytes (p = 0.02). SS erythrocytes displayed significantly less Siglec-9-Fc binding 39% ± 11 (mean ± SEM) compared to AA erythrocytes 78% ± 5 (p = 0.009). Treatment of AA erythrocytes with sialidase to remove sialic acid decreased binding to 3% ± 7.9 (p ≤ 0.001). When freshly isolated neutrophils were incubated with AA erythrocytes, neutrophils achieved 16% ± 6 of the oxidative burst exhibited by a stimulated neutrophil without erythrocytes. In contrast, neutrophils incubated with SS erythrocytes achieved 47% ± 6 of the oxidative burst (AA versus SS, p = 0.03). Stimulated neutrophils incubated with AA erythrocytes showed minimal NET formation while with SS erythrocytes NETs increased. SS erythrocytes are deficient in binding to neutrophil Siglec-9 which may contribute to the increased oxidative stress in SCD.

The glycans of stem cells.

Glycans cover all cellular surfaces and, not surprisingly, are involved in many facets of stem cell biology and technology. For instance, coaxing stem cells to either proliferate or differentiate into the specific cell types needed for transplantation requires intricate glycan-dependent modulation of signalling molecules such as FGF-2, Wnt, and Notch. Moreover, owing to their prominent cell-surface localization and lineage-specific signatures, glycan epitopes such as the stage-specific embryonic antigens (Lewis X/SSEA-1, SSEA3-4) and tumor-rejection antigens (TRA1-60, 1-81) are ideally suited for identifying and isolating specific cell types from heterogeneous populations. Finally, the non-human sialic acid Neu5Gc has been detected on the surface of human embryonic stem cells because of metabolic incorporation from animal products used for their culture. Transplantation of Neu5Gc-contaminated cells poses immunological risks due to the presence, in humans, of circulating antibodies recognizing this glycan epitope.

Blasts from the past.

With this issue of the JCI, we celebrate the 80th anniversary of the Journal. While 80 years is not a century, we still feel it is important to honor what the JCI has meant to the biomedical research community for 8 decades. To illustrate why the JCI is the leading general-interest translational research journal edited by and for biomedical researchers, we have asked former JCI editors-in-chief to reflect on some of the major scientific advances reported in the pages of the Journal during their tenures.