SB-202190

Several kinase inhibitors including pyridinyl imidazole class p38 MAPK inhibitors and specific PIKFYVE inhibitors have been shown to induce endosomal swelling and micron-scale vacuolation, by inhibiting a PIKFYVE-dependent pathway. We performed a screen to identify small molecule modulators of micron-scale vacuolation and identified septin inhibitor Forchlorfenuron (FCF) as an inhibitor of vacuolation. FCF inhibited vacuolation induced by SB202190, PIKFYVE inhibitors and VE-821. shRNA-mediated depletion of SEPT9 suppressed kinase inhibitor-induced vacuolation, while SEPT7 knockdown did not affect vacuolation. Similar results were obtained when experiments were performed using penfluridol as another modulator of septin cytoskeleton. The kinase-inhibitor induced vesicles, identified as swollen RAB7+ late endosomes colocalized with CD63 and FCF treatment led to the loss of these RAB7-labelled micron-scale vacuoles. FCF not only abrogates vacuole formation but also suppresses resolution of vacuoles upon SB202190 withdrawal. However, septin filaments do not colocalize with the vacuoles. Unlike bafilomycin, which inhibits vacuolation with parallel blockade of autophagic proteolysis, FCF mediated suppression of vacuoles doesn't involve accumulation of autophagy markers. The role of septins in micron scale vacuolation may be linked to their role in endosome maturation and septins may contribute towards the cell-type specificity of micron-scale vacuolation.

Toxoplasma gondii is a widespread parasite that impacts both human and animal health. Increasing use of organoid model systems has made previously challenging aspects of the T. gondii lifecycle more accessible. The media for these organoid systems are highly complex with many growth factors and pathway inhibitors that promote stem cell retention or differentiation of the cells. We noticed changes in T. gondii growth and development in our intestinal organoid system and wanted to determine if this was driven by cell type or media components. We found that low concentrations of SB202190 (a p38 MAPK inhibitor) and A83-01 (an ALK 4/5/7 receptor inhibitor) are each sufficient to alter T. gondii growth even in fibroblast cells. Further investigation with our qPCR panel of T. gondii stage markers revealed that these compounds promote bradyzoite cyst development and prime parasites for pre-sexual and sexual stage gene expression. As these complex organoid systems become more common in microbiology research, this study highlights the role of organoid media components in controlling pathogen growth and development.

The use of complex cell culture model systems is becoming more common across many fields. Maintenance of these systems often includes growth factors and inhibitors not found in standard media. These added components have the potential to impact pathogen growth and development and can influence how experimental results may be interpreted. This study improves our understanding of the Toxoplasma gondii lifecycle in one of those systems. It also serves as a template for other pathogen researchers to consider influences within their own systems.