Lyssavirus matrix protein stabilizes RGS4 to suppress ferroptosis via incomplete autophagy and iron metabolic reprogramming.

Rabies virus (RABV), the prototypical lyssavirus, suppresses neuronal ferroptosis through lipid droplet (LD) biogenesis, which is a critical immune evasion strategy we previously identified. However, the mechanistic link between LD formation and ferroptosis regulation during RABV infection remains poorly defined. Here, we report that RABV upregulate Regulator of G Protein Signaling 4 (RGS4), a ferroptosis-associated regulator, and this induction is strictly dependent on triglyceride synthesis and subsequent LD formation. Functionally, genetic or pharmacological inhibition of RGS4 elevates ferroptosis susceptibility, thereby restricting viral replication. Mechanistically, RGS4 depletion reduces HERC2, impairing the assembly of branched K48/K63 ubiquitin chains on NCOA4, which is essential for its proteasomal degradation, thereby enhancing NCOA4 stability. Stabilized NCOA4 promotes ferritinophagy, leading to degradation of ferritin heavy chain (FTH) and ultimately inducing ferroptosis. Critically, we identified that the lyssavirus matrix (M) protein directly counteracts this pathway: M protein inhibits RGS4 degradation via the Cys/N-degron system through incomplete autophagy, stabilizing RGS4 to maintain HERC2 expression, promote NCOA4 ubiquitination, and attenuate ferritinophagy. This mechanism reduces ferroptosis susceptibility and enables viral replication. Our findings unveil a novel lyssavirus-specific regulatory axis, RGS4-HERC2-NCOA4-FTH, that modulates ferroptosis, highlighting the critical role of ferroptosis in lyssavirus infection and pathogenesis.