PDE4B deficiency aids macrophage Trojan horses to transfer Cryptococcus neoformans into the brain

Cryptococcal meningitis (CM) is a fatal compliation. Macrophages work as Trojan horses transferring Cryptococcus neoformans (C. neoformans) into the brain. Mechanisms for C. neoformans Trojan horses are largely elusive. In this study, we performed scRNA-Seq on immune cells infiltrated into the brain in a murine model of CM. Bioinformatics analysis reveals that phosphodiesterase 4B (PDE4B) ranks top in regulating macrophage Trojan horses. Melanin, a virulence factor for Cn, decreased PDE4B in macrophages. PDE4B inhibitor promoted the Cn Trojan horse across the blood-brain-barrier (BBB) in vitro and in vivo. As similar, PDE4B knockout increased fungi burden in the brain, which is, at least partially, rescued by macrophages depletion. In contrast, PDE4B activation diminished C. neoformans brain infection. Mechanistically, PDE4B inhibition increased CXCR4 and CCR7 on C. neoformans macrophage Trojan horses, a process regulated by the cAMP/PKA signaling pathway. Dexamethasone, commonly used to treat Pneumocystis infections in AIDS patients, significantly decreased PDE4B expression in macrophages. Overall, this study reveals that PDE4B plays a crucial role in C. neoformans macrophage Trojan horses and serves as a potential therapeutic target for CM. Overall design: To elucidate the characteristics of Trojan cells during Cryptococcus neoformans brain infection, we isolated CD45+ cells from the brain tissue of mice infected with the H99Tdtomato strain and conducted single-cell RNA sequencing (scRNA-Seq) analysis. Clustering analysis of the transcriptomic data, based on known marker genes and literature, followed by UMAP dimensionality reduction, revealed the composition of infiltrating cells in the brain tissue post-infection. To further identify the cell types associated with Cryptococcus infection, we analyzed the distribution of fungal RNA across different cell types.