Modulation of Replicative Lifespan in : Implications for Virulence.

The fungal pathogen, , has been shown to undergo replicative aging. Old cells are characterized by advanced generational age and phenotypic changes that appear to mediate enhanced resistance to host and antifungal-based killing. As a consequence of this age-associated resilience, old cells accumulate during chronic infection. Based on these findings, we hypothesized that shifting the generational age of a pathogenic yeast population would alter its vulnerability to the host and affect its virulence. is a well-conserved histone deacetylase, and a pivotal target for the development of anti-aging drugs. We tested its effect on ' replicative lifespan (RLS). First, a mutant strain () was generated, and confirmed a predicted shortened RLS in cells consistent with its known role in aging. Next, RLS analysis showed that treatment of with Sir2p-agonists resulted in a significantly prolonged RLS, whereas treatment with a Sir2p-antagonist shortened RLS. RLS modulating effects were dependent on and not observed in cells. Because loss resulted in a slightly impaired fitness, effects of genetic RLS modulation on virulence could not be compared with wild type cells. Instead we chose to chemically modulate RLS, and investigated the effect of Sir2p modulating drugs on cells in a infection model. Consistent with our hypothesis that shifts in the generational age of the infecting yeast population alters its vulnerability to host cells, we observed decreased virulence of in the host when RLS was prolonged by treatment with Sir2p agonists. In contrast, treatment with a Sir2p antagonist, which shortens RLS enhanced virulence in . In addition, combination of Sir2p agonists with antifungal therapy enhanced the antifungal's effect. Importantly, no difference in virulence was observed with drug treatment when cells were used for infection, which confirmed target specificity and ruled out non-specific effects of the drugs on the host. Thus, this study suggests that RLS modulating drugs, such as Sir2p agonists, shift lifespan and vulnerability of the fungal population, and should be further investigated as a potential class of novel antifungal drug targets that can enhance antifungal efficacy.