Cryptococcus neoformans induces alterations in the cytoskeleton of human brain microvascular endothelial cells

Abstract

The fungal pathogen Cryptococcus neoformans has a predilection for the central nervous system (CNS), resulting in devastating meningoencephalitis. At present, it is unclear how C. neoformans traverses the blood-brain barrier (BBB) and causes CNS infection. The present study has examined and characterized the interaction of C. neoformans with human brain microvascular endothelial cells (HBMEC), which constitute the BBB. Adhesion of and transcytosis of HBMEC by C. neoformans was inoculum- and time-dependent and occurred with both encapsulated and acapsulated strains. C. neoformans induced marked morphological changes in HBMEC, for example membrane ruffling, irregular nuclear morphology and swelling of the mitochondria and the ER. These findings suggest that C. neoformans induced actin cytoskeletal reorganization of the host cells. In addition, it was observed that the dephosphorylated form of cofilin was increased during cryptococcal adherence to HBMEC, concomitant with the actin rearrangement. Cryptococcal binding to HBMEC was increased in the presence of Y27632, a Rho kinase (ROCK)-specific inhibitor. Since ROCK activates LIM kinase (LIMK), which phosphorylates cofilin (inactive form), this suggests the involvement of the ROCK-->LIMK-->cofilin pathway. In contrast, the phosphatase inhibitor sodium orthovanadate decreased adherence of Cryptococcus to HBMEC, concomitant with the increase of phosphorylation of cofilin. Furthermore, the tight junction marker protein occludin became Triton-extractable, indicating alteration of tight junctions in brain endothelial cells. This is the first demonstration that C. neoformans is able to adhere to and transcytose across the HBMEC monolayer and alter the cytoskeleton morphology in HBMEC. Further characterization of the interactions between C. neoformans and HBMEC should help the development of novel strategies to prevent cryptococcal meningitis and its associated morbidity.