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SAMHD1 Attenuates Acute Inflammation by Maintaining Mitochondrial Function in Macrophages via Interaction with VDAC1
Bowen Xu1, Qianyi Sui1, Han Hu1,2
1National Key Laboratory of Immunity & Inflammation, Institute of Immunology, Naval Medical University, Shanghai 200433, China.
Abstract:
Over-activation of Toll-like receptor 4 (TLR4) is the key mechanism in Gram-negative bacterial infection-induced sepsis. SAM and HD domain-containing deoxynucleoside triphosphate triphosphohydrolase 1 (SAMHD1) inhibits multiple viruses, but whether it plays a role during bacterial invasion remains unelucidated. Monocyte-macrophage specific Samhd1 knockout (Samhd1) mice and Samhd1 macrophage cell line RAW264.7 were constructed and used as research models to evaluate the role of SAMHD1 in TLR4-activated inflammation. In vivo, LPS-challenged Samhd1 mice showed higher serum inflammatory factors, accompanied with more severe inflammation infiltration and lower survival rate. In vitro, Samhd1 peritoneal macrophages had more activated TLR4 pathway upon LPS-stimulation, accompanied with mitochondrial depolarization and dysfunction and a higher tendency to be M1-polarized. These results could be rescued by overexpressing full-length wild-type SAMHD1 or its phospho-mimetic T634D mutant into Samhd1 RAW264.7 cells, whereas the mutants, dNTP hydrolase-function-deprived H238A and phospho-ablative T634A, did not exert the same effect. Lastly, co-IP and immunofluorescence assays confirmed that SAMHD1 interacted with an outer mitochondrial membrane-localized protein, voltage-dependent anion channel-1 (VDAC1). SAMHD1 inhibits TLR4-induced acute inflammation and M1 polarization of macrophages by interacting with VDAC1 and maintaining mitochondria function, which outlines a novel regulatory mechanism of TLR signaling upon LPS stimulation.
Insights
SAMHD1 protein plays a crucial role in regulating inflammation during bacterial infections. It inhibits Toll-like receptor 4 (TLR4)-induced inflammation and macrophage M1 polarization by interacting with VDAC1 and maintaining mitochondrial function.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Over-activation of Toll-like receptor 4 (TLR4) is central to Gram-negative bacterial infection-induced sepsis.
- The role of SAM and HD domain-containing deoxynucleoside triphosphate triphosphohydrolase 1 (SAMHD1) in bacterial infections is not well understood.
Purpose of the Study:
- To investigate the role of SAMHD1 in TLR4-mediated inflammation during bacterial invasion.
- To elucidate the molecular mechanisms by which SAMHD1 regulates inflammation.
Main Methods:
- Generation of monocyte-macrophage specific Samhd1 knockout mice and a Samhd1 macrophage cell line (RAW264.7).
- In vivo LPS challenge experiments and in vitro LPS stimulation of macrophages.
- Co-immunoprecipitation (Co-IP) and immunofluorescence assays to identify protein interactions.
- Rescue experiments using wild-type and mutant SAMHD1 overexpression.
Main Results:
- Samhd1 knockout mice exhibited increased serum inflammatory factors, severe inflammation, and reduced survival rates after LPS challenge.
- Samhd1 macrophages showed enhanced TLR4 pathway activation, mitochondrial dysfunction, and M1 polarization upon LPS stimulation.
- SAMHD1 interacted with voltage-dependent anion channel-1 (VDAC1) on the outer mitochondrial membrane.
- Overexpression of wild-type or phospho-mimetic SAMHD1 rescued these effects, while non-functional mutants did not.
Conclusions:
- SAMHD1 acts as a negative regulator of TLR4-induced acute inflammation and M1 polarization in macrophages.
- SAMHD1 maintains mitochondrial function, thereby inhibiting excessive inflammatory responses.
- The interaction between SAMHD1 and VDAC1 represents a novel regulatory mechanism in TLR signaling pathways.
