SAMHD1 Deficiency Enhances Macrophage-Mediated Clearance of Salmonella Typhimurium via NF-κB Activation in Zebrafish

Alicia Martínez-López ^1,2,3* Sylwia Dominika Tyrkalska ^1,2,3 Francisco Javier Martínez-Morcillo ^2,3 Constantino Abenza-Olmos ³ Juan Manuel Lozano-Gil ^1,2,3 Sergio Candel ^1,2,3 Victoriano Mulero ^1,2,3* Diana García-Moreno ^1,2,3*

• ¹ Biomedical Research Institute of Murcia (IMIB), Palmar, Spain
• ² Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), Madrid, Madrid Community, Spain
• ³ Departamento de Biología Celular e Histología, Facultad de Biología, Universidad de Murcia, MURCIA, Spain

Mutations in the gene encoding the protein containing the sterile alpha motif and the HD domain (SAMHD1) have been implicated in the occurrence of type I interferonopathies. SAMHD1 is also involved in blocking the replication of retroviruses and certain DNA viruses by reducing the intracellular amount of deoxynucleotide triphosphates (dNTPs). It has also been suggested that SAMHD1 negatively regulates interferon (IFN) and inflammatory responses to viral infections, although the functions and mechanisms of SAMHD1 in modulating innate immunity are still under study. In our laboratory, we have generated Samhd1-deficient zebrafish larvae using CRISPR-Cas9 and studied its role in the activation of nuclear factor kB (NF-κB) and the induction of type I IFN (IFN-I). Our results show that Samhd1 deficiency results in overactivation of the IFN-I response, assayed as the increased transcript levels of interferon-stimulated genes (ISGs), but only if the larvae were stimulated with suboptimal doses of IFN-I. However, Samhd1-deficient larvae showed robust spontaneous activation of NF-κB, which led to increased larval resistance to Salmonella enterica serovar Typhimurium (STM) infection. Genetic experiments further showed that activation of NF-κB in macrophages mediated the resistance against STM of Samhd1-deficient larvae. Our findings highlight the evolutionary conserved functions of SAMHD1 in the negative regulation of the inflammatory response of vertebrates and reveal for the first time a critical role for SAMHD1 in the regulation of NF-κB in macrophages to clear intracellular bacterial infection.