Initiation of phospholipomannan ß-1,2 mannosylation involves Bmts with redundant activity, influences its cell wall location and regulates ß-glucans homeostasis but is dispensable for Candida albicans systemic infection.

Pathogenic and non-pathogenic fungi synthesize glycosphingolipids, which have a crucial role in growth and viability. Glycosphingolipids also contribute to fungal-associated pathogenesis. The opportunistic yeast pathogen Candida albicans synthesizes phospholipomannan (PLM), which is a glycosphingolipid of the mannosylinositol phosphorylceramide family. Through its lipid and glycan moieties, PLM contributes to the initial recognition of the yeast, causing immune system disorder and persistent fungal disease through activation of host signaling pathways. The lipid moiety of PLM activates the deregulation signaling pathway involved in yeast phagocytosis whereas its glycan moiety, composed of ß-1,2 mannosides (ß-Mans), participates to inflammatory processes through a mechanism involving Galectin-3. Biosynthesis of PLM ß-Mans involves two ß-1,2 mannosyltransferases (Bmts) that initiate (Bmt5) and elongate (Bmt6) the glycan chains. After generation of double bmtsΔ mutants, we show that Bmt5 has redundant activity with Bmt2, which can replace Bmt5 in bmt5Δ mutant. We also report that PLM is located in the inner layer of the yeast cell wall. PLM seems to be not essential for systemic infection of the yeast. However, defect of PLM ß-mannosylation increases resistance of C. albicans to inhibitors of ß-glucans and chitin synthesis, highlighting a role of PLM in cell wall homeostasis.

In vitro blood-brain barrier model adapted to repeated-dose toxicological screening.

Toxicity to the central nervous system (CNS) is a key feature in the toxicological profile of compounds and there is a growing interest to use in vitro cell assays. The blood-brain barrier (BBB) is a highly restrictive barrier that preserves homeostasis within the brain microenvironment. By modelling the BBB it is possible to investigate whether a compound is likely to compromise its functionality, which would cause unwanted effects on brain cells. These investigations are usually performed using a single exposure to drugs, whereas CNS side effects usually result from repeated exposures. The main objective of this study was to adapt our established BBB model to the evaluation of repeated-dose toxicity at the BBB. Studies were undertaken within the European Predict-IV consortium to study the effect on BBB permeability of 12 selected drugs after 14 days of repeated treatment to a single pre-selected concentration. Compared to single exposure, a 100-fold lower colchicine concentration in 14 days repeated-dose treatment was toxic. This demonstrates the importance to evaluate the BBB toxicity in repeated-dose testing. Finally, the potentiating effects of cyclosporin A on the BBB toxicity of colchicine illustrate the possibility to use in vitro BBB models to make risk assessment of drug-drug interactions.