MAVS maintains mitochondrial import competence and also limits RNA virus replication independently of interferon signaling

Intrinsic, cell-autonomous antiviral defenses can restrict infection without involving paracrine interferon (IFN) programs. Previous studies have demonstrated the importance of intact mitochondrial homeostasis in antiviral immunity. Mitochondrial antiviral signaling (MAVS) protein is a critical adaptor molecule in the RLR pathway that regulates IFN production in response to RNA viral infections. Here, we identify a potent intrinsic antiviral immunity that is orchestrated through stable mitochondria. We further identify MAVS as a regulator of mitochondrial import machinery whose activity is required for an IFN-independent antiviral state. Loss of MAVS leads to severe mitochondrial fragmentation, depolarization, and mitophagy, accompanied by diminished mitochondrial bioenergetics and protein import. Mechanistically, MAVS maintains mitochondrial integrity by maintaining the expression and assembly of the translocase of the outer membrane complex and sustaining the abundance of its core components. Restoration of MAVS expression reverses these defects and reinstates a robust antiviral state. Remarkably, this mitochondrial-driven immunity efficiently restricts SARS-CoV-2 replication even under IFN-deficient conditions and operates alongside the IFN pathways during infection by RNA viruses, such as the Japanese encephalitis virus. Our findings reveal a mitochondrial maintenance function of MAVS that operates in parallel to, and independently of, canonical interferon signaling during RNA virus infection. These findings highlight mitochondrial integrity as a common determinant behind a broad, collective antiviral immunity that involves both intrinsic and IFN-dependent mechanisms.IMPORTANCEHow do mitochondria contribute to the intrinsic cellular antiviral defense even when the primary immune arsenal is silenced? This work reveals that MAVS, long known for triggering interferon, acts as a vital bridge that stabilizes mitochondria to impart a potent intrinsic antiviral state against RNA viruses. We show that MAVS serves as a structural guardian of the organelle, a function it orchestrates by stabilizing the translocase of the outer membrane complex, the essential gateway for mitochondrial protein import. When MAVS is lost or targeted by viruses like SARS-CoV-2 and Japanese encephalitis virus (JEV), this gateway collapses, leading to organelle failure that viruses exploit. Crucially, we demonstrate that MAVS can restrict viral replication entirely independently of traditional interferon signaling. This discovery shifts our understanding of MAVS from a simple signal transducer to a multidimensional protector. By safeguarding the cell's "powerhouse," MAVS provides a fundamental layer of intrinsic immunity that remains active even when other immune responses are evaded.