Gene Expression of Pneumocystis murina after Treatment with Anidulafungin Results in Strong Signals for Sexual Reproduction, Cell Wall Integrity, and Cell Cycle Arrest, Indicating a Requirement for Asci Formation for Proliferation. [PublishAheadOfPrint]

The echinocandins are a class of anti-fungal agents that target β-1,3-D-glucan (BG) biosynthesis. In the ascigerous Pneumocystis species, treatment with these drugs deplete the asci life cycle stage which contain BG, but large numbers of forms which do not express BG remain in the infected lungs. In the present study, the gene expression profiles of Pneumocystis murina were compared between infected untreated mice and those treated with anidulafungin for 2 weeks to understand the metabolism of the persisting forms. Almost 80 genes were significantly up- or down-regulated. Like other fungi exposed to echinocandins, genes associated with sexual replication, cell wall integrity, cell cycle arrest and stress comprised the strongest up-regulated signals in P. murina from the treated mice. The up-regulation of the P. murina β-1,3-D-glucan endohydrolase and endo-1,3-glucanase was notable and may explain the disappearance of the existing asci in the lungs of treated mice since both enzymes can degrade BG. The biochemical measurement of BG in the lungs of treated mice and fluorescent microscopy with an anti-BG antibody supported the loss of BG. Down-regulated signals included genes involved in cell replication, genome stability, ribosomal biogenesis and function, and the Pneumocystis-specific genes encoding the major surface glycoproteins (Msg). These studies suggest that P. murina attempted to undergo sexual replication in response to a stressed environment and were halted in any type of proliferative cycle, likely due to a lack of BG. Asci appear to be a required part of the life cycle stage of Pneumocystis and BG may be needed to facilitate progression through the life cycle via sexual replication.

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