LRP4 is an entry receptor for multiple encephalitic alphaviruses

Encephalitic alphaviruses, including Eastern equine encephalitis virus (EEEV), cause severe neurological disease with high mortality rates, and thus are a public health threat. Although members of the low-density lipoprotein receptor (LDLR) family, including VLDLR, LRP8 (ApoER2), and LDLR recently were identified as receptors for EEEV, residual infection in receptor-deficient cells suggests that additional entry factors exist. Using a CRISPR-based activation screen, we identified LDLR-related protein 4 (LRP4) as a candidate entry factor for EEEV and several related alphaviruses (Western equine encephalitis, Semliki Forest, and Sindbis viruses). LRP4 mediates viral attachment and internalization, and its ligand-binding domain binds directly to virions. Soluble LRP4 decoy proteins potently inhibit EEEV infection in primary mouse neuronal cells, male mice, and human brain organoids, suggesting possible therapeutic applications. Mammalian and avian LRP4 orthologs demonstrate conserved functions in promoting EEEV infection, supporting a possible role in its host range of infection and transmission. Our findings establish LRP4 as a shared entry receptor for multiple alphaviruses and expand our understanding of alphavirus tropism, pathogenesis, and countermeasure development. In this study, the authors identify LRP4 as an entry receptor for Eastern equine encephalitis virus, and show that decoy proteins block infection in neuronal cells, mice, and brain organoids, and that it is conserved across birds and mammals indicating a potential role in host range and transmission.