Скачать или смотреть Candida albicans and drug tolerance

Mike Hallett gave this talk at the first Canadian Fungal Networks meeting in July of 2020.

Candida albicans exhibits a cytoprotective response to anti-fungal drugs that facilitates the evolution of drug resistance


Abstract

Background. Candida albicans is both a human commensal and opportunistic pathogen. Nosocomial infections due to pathogenic C. albicans are the fourth most important in North America and are associated with significant socioeconomic burden. Systemic Candida infections of immune-compromised individuals are frequently lethal even when treated optimally. Drug resistance is sometimes due to the pre-existence of genetic polymorphisms that bypass the mode of action of the drug, thus conferring a long-term survival benefit. In other cases, resistance is acquired via the evolution of de novo genetic polymorphisms. There is evidence that C. albicans possess a drug tolerance response which “buys time” for individuals to evolve beneficial mutations. In fact, there is some evidence that this is facilitated by the (inherent or possibly induced) instability of the C. albicans genome. Our goal here is to characterize this poorly understood epigenetic cytoprotective program at the single cell molecular level.
Methods. We tweaked a nano-litre droplet based single cell sequencing platform for the fungal setting. The system is capable of transcriptionally profiling several thousand individual cells in an efficient, cost effective manner. We exploit this platform to profile both untreated and anti-fungal drug exposed (incl. fluconazole, caspofungin and nystatin) populations at early time points post-treatment (tolerance) and late time points (resistance) in order to understand survival trajectories.
Results. We show that prototrophic Candida populations exhibit “bet hedging”, stochastically expressing cytoprotective epigenetic programs, and use live cell imaging to establish that these cells are more likely to survive drug exposure. Moreover, the drug tolerant individuals partition into distinct subpopulations, each with a unique survival strategy involving different transcriptional programs. Deep learning microscopy based approaches establish that “classic” morphologies of C. albicans are insufficient to capture the observed heterogeneity. Whole genome DNA-sequencing of these populations establishes a trend of increased instability during the tolerance phase until resistance, when the genome re-stabilizes.
Discussion. Our single cell approach highlights that survivor subpopulations pass through a tolerance phase that involves a multivariate epigenetic response including upregulation of efflux pumps, chaperones and transport mechanisms, and cell wall maintenance. Together this suggests that targeting the tolerance response concomitantly with standard therapies could represent an efficient approach to ablating clinical persistence.