Generational distribution of a Candida glabrata population: Resilient old cells prevail, while younger cells dominate in the vulnerable host

Abstract

Similar to other yeasts, the human pathogen Candida glabrata ages when it undergoes asymmetric, finite cell divisions, which determines its replicative lifespan. We sought to investigate if and how aging changes resilience of C. glabrata populations in the host environment. Our data demonstrate that old C. glabrata are more resistant to hydrogen peroxide and neutrophil killing, whereas young cells adhere better to epithelial cell layers. Consequently, virulence of old compared to younger C. glabrata cells is enhanced in the Galleria mellonella infection model. Electron microscopy images of old C. glabrata cells indicate a marked increase in cell wall thickness. Comparison of transcriptomes of old and young C. glabrata cells reveals differential regulation of ergosterol and Hog pathway associated genes as well as adhesion proteins, and suggests that aging is accompanied by remodeling of the fungal cell wall. Biochemical analysis supports this conclusion as older cells exhibit a qualitatively different lipid composition, leading to the observed increased emergence of fluconazole resistance when grown in the presence of fluconazole selection pressure. Older C. glabrata cells accumulate during murine and human infection, which is statistically unlikely without very strong selection. Therefore, we tested the hypothesis that neutrophils constitute the predominant selection pressure in vivo. When we altered experimentally the selection pressure by antibody-mediated removal of neutrophils, we observed a significantly younger pathogen population in mice. Mathematical modeling confirmed that differential selection of older cells is sufficient to cause the observed demographic shift in the fungal population. Hence our data support the concept that pathogenesis is affected by the generational age distribution of the infecting C. glabrata population in a host. We conclude that replicative aging constitutes an emerging trait, which is selected by the host and may even play an unanticipated role in the transition from a commensal to a pathogen state.

Difficult but Not Impossible: in Search of an Anti-Candida Vaccine

“…The molecule used against them is mannose-binding lectin (MBL), a protein that is synthesized in the liver and involved in complement cascade activation. Investigations of its function have found MBL-induced agglutination in the yeast Recombinant heat shock proteins: r-hsp90-CA [9,11] Laminarin: CRM197 [12] Replicative aging [23][24][25] Respiratory pathways: Mir1 [26] Sphingolipid metabolism: BHBM, D13 [27] Micafungin activated metacaspase complexes [28] Tricyclic antidepressants [16] Genetically engineered organisms: Lactobacillus casei containing the Eno1p antigen [29] phase to treat both C. glabrata and C. albicans. This was achieved through binding to the mannoproteins covering the fungal cell surface, inducing complement activation [15•].…”

“…Fungal aging, a more novel area of research that looks into the microevolution of the pathogen, has also demonstrated potential for an antifungal vaccine. Studies in Cryptococcus neoformans and C. glabrata have demonstrated that the cell wall undergoes changes with the age of the cell [23,24]. Additional observations revealed that phenotypic switching can lower the number of replications that daughter cells undergo compared to the parent cell.…”

Enhanced Efflux Pump Activity in Old Candida glabrata Cells

“…This finding is relevant because, in vivo, the host's neutrophils selectively kill younger cells, which causes old yeast cells to accumulate in the host. Aging C. glabrata mother cells have larger cell bodies and thicker cell walls than those of the younger daughter cells (1).…”

“…C andida glabrata is a formidable pathogen that, analogous to other yeasts, undergoes replicative aging (1). We have reported that growth of older (defined as more generations lived) C. glabrata cells was more inhibited by fluconazole (FLC) (1). This finding is relevant because, in vivo, the host's neutrophils selectively kill younger cells, which causes old yeast cells to accumulate in the host.…”

“…Several ABC transporters have been linked to drug resistance in C. glabrata, of which Cdr1p and Pdh1p have been extensively investigated (12)(13)(14)(15)(16). Previously published transcriptome data comparing young and 14-generation-old C. glabrata cells of the FLC-sensitive BG2 strain demonstrated increased expression of the genes CDR1 (2-fold), PDR16 (8-fold), and YBT1 (10-fold), all of which encode ABC transporters associated with FLC resistance (1).…”