SAMHD1 prevents autoimmunity by maintaining genome stability.

Area of Science:

• Molecular Biology
• Immunology
• Genetics

Background:

• SAMHD1 (SAM domain and HD domain-containing protein 1) is a HIV restriction factor that degrades deoxyribonucleoside triphosphates (dNTPs).
• Mutations in SAMHD1 cause Aicardi-Goutières syndrome (AGS), an inflammatory disorder with similarities to systemic lupus erythematosus, including type 1 interferon (IFN) activation.
• Understanding SAMHD1's physiological role is crucial for defining the pathomechanisms of SAMHD1-associated autoimmunity.

Purpose of the Study:

• To investigate the physiological properties of SAMHD1.
• To elucidate the link between SAMHD1 mutations, genome instability, and autoimmune responses.

Main Methods:

• Analysis of primary patient fibroblasts for dNTP levels, proliferation, senescence, cell cycle progression, and DNA damage.
• Genome-wide transcriptional profiling via RNA sequencing.
• Assessment of SAMHD1-cyclin A interaction, cell cycle-dependent phosphorylation, and effects of SAMHD1 knockdown.

Main Results:

• SAMHD1 deficiency leads to increased dNTP pools, causing genome instability and constitutive DNA damage signaling in AGS patient fibroblasts.
• DNA damage is associated with cell cycle delay, senescence, and upregulation of IFN-stimulated genes.
• SAMHD1 phosphorylation is cell cycle-dependent, and its knockdown recapitulates DNA damage and type 1 IFN activation.

Conclusions:

• SAMHD1 is essential for maintaining genome integrity through balanced dNTP pools.
• Imbalanced dNTP levels due to SAMHD1 deficiency trigger DNA damage, leading to intrinsic activation of IFN signaling.
• This study establishes a novel connection between DNA damage signaling and innate immune activation in autoimmune pathogenesis.