SARS-CoV-2 ORF3c impairs mitochondrial respiratory metabolism, oxidative stress and autophagic flow

Coronaviruses encode a variable number of accessory proteins that play a role in host-virus interactions, in the suppression of immune responses, or in immune evasion. Accessory proteins in SARS-CoV-2 consist of at least twelve viral proteins whose roles during infection have been extensively studied. Nevertheless, the role of the ORF3c accessory protein, an alternative open reading frame of ORF3a, has remained elusive. Herein, we characterized ORF3c in terms of cellular localization, host’s antiviral response modulation, and effects on mitochondrial metabolism. We show that ORF3c has a mitochondrial localization and alters mitochondrial metabolism, resulting in increased ROS production, block of the autophagic flux, and accumulation of autophagosomes/autolysosomes. Notably, we also found that ORF3c induces a shift from glucose to fatty acids oxidation and enhanced oxidative phosphorylation. This is similar to the condition observed in the chronic degenerative phase of COVID-19. Altogether these data suggest that ORF3c could be a key protein for SARS-CoV-2 pathogenesis and that it may play a role in disease progression.