Dipeptidyl peptidase IV contributes to the pathogenesis of Cryptococcus neoformans.

We previously identified isoleucine-proline-isoleucine (IPI) as a small molecule associated with extracellular vesicles (EVs) in Cryptococcus. The administration of IPI in vivo resulted in the control of experimental cryptococcal infection through mechanisms that remain unknown. IPI is an inhibitor of dipeptidyl peptidase 4 (Dpp4), an enzyme that regulates insulin and glucose homeostasis in mammals and may also influence pathogenic processes in fungi. Based on these observations, we investigated the biological and pathogenic roles of cryptococcal Dpp4. We demonstrate that Cryptococcus neoformans synthesizes an active, surface-associated Dpp4 that is inhibited by IPI. Deletion of the Dpp4-encoding gene (CNAG_06416) abolished Dpp4 enzymatic activity and resulted in marked physiological alterations, including changes in the proteomic composition of whole cells and EVs, as well as increased accumulation of undivided cells at 37°C both in vitro and in vivo. The dpp4Δ mutant was less lethal than wild-type (WT) cells in a Galleria mellonella infection model. In contrast, increased Dpp4 activity did not enhance lethality, as demonstrated by the ability of WT and 19 high-Dpp4-expressing mutant strains to kill G. mellonella. In a murine model, loss of Dpp4 partially affected fungal virulence, delaying host mortality, and reducing fungal burden, particularly in the brain. This finding is consistent with the observation that dpp4Δ cells were markedly less efficient at crossing endothelial and extracellular matrix layers than WT cells. Collectively, these findings establish DPP4 as an important regulator of cryptococcal physiology and pathogenesis, and support the concept that targeting Dpp4 may offer translational opportunities distinct from conventional antifungal strategies.IMPORTANCECryptococcosis is a life-threatening fungal disease that mainly affects people with weakened immune systems, and current treatments remain limited. In this study, we show that the enzyme dipeptidyl peptidase 4 (Dpp4) plays a central role in the ability of the fungus to cause damage to the host. When Dpp4 is absent, the fungus becomes less virulent, disseminates less efficiently to the brain, and is less likely to kill the host. These findings reveal a previously unrecognized role for Dpp4 in fungal infection and identify this enzyme as a promising target for new therapeutic strategies. By focusing on a fungal pathway distinct from those targeted by existing drugs, this work opens new avenues for developing treatments against a major human fungal pathogen.