Dengue virus non-structural protein 3 inhibits mitochondrial respiration by impairing complex I function

Dengue virus (DENV) infection is known to affect host cell metabolism, but the molecular players involved are still poorly known. Using a proteomics approach, we identified six DENV proteins associated with mitochondria isolated from infected hepatocytes, and most of the peptides identified were from NS3. We also found an at least twofold decrease of several electron transport system (ETS) host proteins. Thus, we investigated whether NS3 could modulate the ETS function by incubating recombinant DENV NS3 constructs in mitochondria isolated from mouse liver. We found that NS3pro (NS3 protease domain), but not the correspondent catalytically inactive mutant (NS3proS135A), impairs complex I (CI)-dependent NADH:ubiquinone oxidoreductase activity, but not the activities of complexes II, III, IV, or V. Accordingly, using high-resolution respirometry, we found that both NS3pro and full-length NS3 decrease the respiratory rates associated with malate/pyruvate oxidation in mitochondria. The NS3-induced impairment in mitochondrial respiration occurs without altering either leak respiration or mitochondria's capacity to maintain membrane potential, suggesting that NS3 does not deeply affect mitochondrial integrity. Remarkably, CI activity is also inhibited in DENV-infected cells, supporting that the NS3 effects observed in isolated mitochondria may be relevant in the context of the infection. Finally, in silico analyses revealed the presence of potential NS3 cleavage sites in 17 subunits of mouse CI and 16 subunits of human CI, most of them located on the CI surface, suggesting that CI is prone to undergo proteolysis by NS3. Our findings suggest that DENV NS3 can modulate mitochondrial bioenergetics by directly affecting CI function.

Dengue virus (DENV) infection is a major public health problem worldwide, affecting about 400 million people yearly. Despite its importance, many molecular aspects of dengue pathogenesis remain poorly known. For several years, our group has been investigating DENV-induced metabolic alterations in the host cells, focusing on the bioenergetics of mitochondrial respiration. The results of the present study reveal that the DENV non-structural protein 3 (NS3) is found in the mitochondria of infected cells, impairing mitochondrial respiration by directly targeting one of the components of the electron transport system, the respiratory complex I (CI). NS3 acts as the viral protease during the DENV replication cycle, and its proteolytic activity seems necessary for inhibiting CI function. Our findings uncover new nuances of DENV-induced metabolic alterations, highlighting NS3 as an important player in the modulation of mitochondria function during infection.