Endosulfatases SULF1 and SULF2 limit Chlamydia muridarum infection

Sulfatase 1 and sulfatase 2 as novel regulators of macrophage antigen presentation and phagocytosis

Background

Sulfation of heparan sulfate proteoglycans (HSPGs) is critical for the binding and signaling of ligands that mediate inflammation. Extracellular 6-O-endosulfatases regulate posttranslational sulfation levels and patterns of HSPGs. In this study, extracellular 6-O-endosulfatases, sulfatase (Sulf)-1 and Sulf-2, were evaluated for their expression and function in inflammatory cells and tissues.

Methods

Harvested human peripheral blood mononuclear cells were treated with phytohemagglutinin and lipopolysaccharide, and murine peritoneal macrophages were stimulated with interleukin (IL)-1β for the evaluation of Sulf-1 and Sulf-2 expression. Sulf expression in inflammatory cells was examined in the human rheumatoid arthritis (RA) synovium by immunofluorescence staining. The antigen presentation and phagocytic activities of macrophages were compared according to the expression state of Sulfs. Sulfs-knockdown macrophages and Sulfs-overexpressing macrophages were generated using small interfering RNAs and pcDNA3.1 plasmids for Sulf-1 and Sulf-2, respectively.

Results

Lymphocytes and monocytes showed weak Sulf expression, which remained unaffected by IL-1β. However, peritoneal macrophages showed increased expression of Sulfs upon stimulation with IL-1β. In human RA synovium, two-colored double immunofluorescent staining of Sulfs and CD68 revealed active upregulation of Sulfs in macrophages of inflamed tissues, but not in lymphocytes of lymphoid follicles. Macrophages are professional antigen-presenting cells. The antigen presentation and phagocytic activities of macrophages were dependent on the level of Sulf expression, suppressed in Sulfs-knockdown macrophages, and enhanced in Sulfs-overexpressing macrophages.

Conclusion

The results demonstrate that upregulation of Sulfs in macrophages occurs in response to inflammation, and Sulfs actively regulate the antigen presentation and phagocytic activities of macrophages as novel immune regulators.

Therapeutic strategies to target microbial protein-glycosaminoglycan interactions

Glycans are involved in a plethora of human pathologies including infectious diseases. Especially, glycosaminoglycans (GAGs), like heparan sulfate and chondroitin sulfate, have been found to be involved in different crucial stages of microbial invasion. Here, we review various therapeutic approaches, which target the interface of host GAGs and microbial proteins and discuss their limitations and challenges for drug development.

Targeting heparin and heparan sulfate protein interactions

Heparin and heparan sulfate glycosaminoglycans are long, linear polysaccharides that are made up of alternating dissacharide sequences of sulfated uronic acid and amino sugars. Unlike heparin, which is only found in mast cells, heparan sulfate is ubiquitously expressed on the cell surface and in the extracellular matrix of all animal cells. These negatively-charged glycans play essential roles in important cellular functions such as cell growth, adhesion, angiogenesis, and blood coagulation. These biomolecules are also involved in pathophysiological conditions such as pathogen infection and human disease. This review discusses past and current methods for targeting these complex biomolecules as a novel therapeutic strategy to treating disorders such as cancer, neurodegenerative diseases, and infection.

Chlamydia cell biology and pathogenesis

Chlamydia spp. are important causes of human disease for which no effective vaccine exists. These obligate intracellular pathogens replicate in a specialized membrane compartment and use a large arsenal of secreted effectors to survive in the hostile intracellular environment of the host. In this Review, we summarize the progress in decoding the interactions between Chlamydia spp. and their hosts that has been made possible by recent technological advances in chlamydial proteomics and genetics. The field is now poised to decipher the molecular mechanisms that underlie the intimate interactions between Chlamydia spp. and their hosts, which will open up many exciting avenues of research for these medically important pathogens.

Characterization of the interaction between the chlamydial adhesin OmcB and the human host cell

In a previous study, we reported that the OmcB protein from Chlamydia pneumoniae mediates adhesion of the infectious elementary body to human HEp-2 cells by interacting with heparin/heparan sulfate-like glycosaminoglycans (GAGs) via basic amino acids located in the first of a pair of XBBXBX heparin-binding motifs (K. Moelleken and J. H. Hegemann, Mol. Microbiol. 67:403-419, 2008). In the present study, we show that the basic amino acid at position 57 (arginine) in the first XBBXBX motif, the basic amino acid at position 61 (arginine) in the second motif, and another amino acid (lysine 69) C terminal to it play key roles in the interaction. In addition, we show that discrimination between heparin-dependent and -independent adhesion by C. trachomatis OmcBs is entirely dependent on three variable amino acids in the so-called variable domain C terminal to the conserved XBBXBX motif. Here, the predicted conformational change in the secondary structure induced by the proline at position 66 seems to be crucial for heparin recognition. Finally, we performed neutralization experiments using different anti-heparan sulfate antibodies to gain insight into the nature of the GAGs recognized by OmcB. The results suggest that C. trachomatis serovar L2 OmcB interacts with 6-O-sulfated domains of heparan sulfate, while C. pneumoniae OmcB apparently interacts with domains of heparan sulfate harboring a diverse subset of O-sulfations.