Muramyl peptides as paradigms in neuroimmunomodulation

Stimulation of platelet apoptosis by peptidoglycan from Staphylococcus aureus 113

Peptidoglycan (PGN), a component of bacterial cell wall and belonging to "Microbe-Associated Molecular Patterns" (MAMP) triggers host reactions contributing to the pathophysiology of infectious disease. Host cell responses to PGN exposure include apoptosis. Bacterial infections may result in activation of blood platelets and thrombocytopenia. The present study explored, whether HPLC-purified fractions of PGNs from Staphylococcus aureus 113 triggers apoptosis of platelets. To this end platelets were exposed to PGN fractions and annexin-V binding determined to depict cell membrane scrambling, DiOC6 fluorescence to estimate depolarization of mitochondrial potential, Fluo-3AM staining for intracellular Ca(2+) activity ([Ca(2+)](i)) and immunofluorescence to quantify protein abundance of active caspase-3. As a result, a 30 min exposure to monomeric fraction (mPGN) (≥50 ng/ml) was followed by annexin-V binding, paralleled by increase of [Ca(2+)](i), mitochondrial depolarization, caspase-3 activation and integrin α(IIb)β(3) upregulation. The annexin-V binding was significantly blunted by anti-TLR-2 antibodies, in absence of extracellular Ca(2+), and by pancaspase inhibitor zVAD-FMK (1 μM). In conclusion, PGN triggers apoptosis of platelets in activation-dependent manner, characterized by mitochondrial depolarization, caspase-3 activation and cell membrane scrambling.

The transcriptional response of human macrophages to murabutide reflects a spectrum of biological effects for the synthetic immunomodulator

The synthetic immunomodulator murabutide (MB) presents multiple biological activities with minimal toxicity in animals and in man. Although MB is known to target cells of the reticuloendothelial system and to regulate cytokine synthesis, the molecular mechanisms underlying several of its biological effects are still largely unknown. In an effort to define cellular factors implicated in the immunomodulatory and HIV-suppressive activities of MB, we have undertaken profiling the regulated expression of genes in human monocyte-derived macrophages (MDM) following a 6-h stimulation with this synthetic glycopeptide. Oligonucleotide microarray analysis was performed on RNA samples of differentiated MDM from four separate donors, using probe sets corresponding to 1081 genes. We have identified, in a reproducible fashion, the enhanced expression of 40 genes and the inhibition of 16 others in MB-treated MDM. These regulated genes belonged to different families of immune mediators or their receptors, transcription factors and kinases, matrix proteins and their inhibitors, ion channels and transporters, and proteins involved in cell metabolic pathways. Additional verification of the regulated expression of selected genes was carried out using Northern blots or the quantification of released proteins in MDM cultures. The profile of MB-regulated genes in MDM provides a molecular basis for some of its previously reported biological activities, and reveals new set of genes targeted by the immunomodulator suggesting potential application in novel therapeutic indications.