bims-nenemi 2023-05-21 papers

bims-nenemi

Biomed News

on Neuroinflammation, neurodegeneration and mitochondria

Issue of 2023–05–21
thirteen papers selected by
Marco Tigano, Thomas Jefferson University

Insights into the mechanism of oligodendrocyte protection and remyelination enhancement by the integrated stress response.
Anaphylatoxin C5a receptor signaling induces mitochondrial fusion and sensitizes retina pigment epithelial cells to oxidative stress.
Analysis of Radiation Toxicity in Mammalian Cells Stably Transduced with Mitochondrial Stat3.
Inflammatory and interferon gene expression signatures in patients with mitochondrial disease.
Polγ coordinates DNA synthesis and proofreading to ensure mitochondrial genome integrity.
The Prohibitin-Binding Compound Fluorizoline Activates the Integrated Stress Response through the eIF2α Kinase HRI.
The mitochondrial intermembrane space protein mitofissin drives mitochondrial fission required for mitophagy.
The cyclic lipopeptide micafungin induces rupture of isolated mitochondria by reprograming the mitochondrial inner membrane anion channel.
IFN-γ and androgens disrupt mitochondrial function in murine myocytes.
MitoQuicLy: a high-throughput method for quantifying cell-free DNA from human plasma, serum, and saliva.
Systematic identification of anticancer drug targets reveals a nucleus-to-mitochondria ROS-sensing pathway.
TXNIP contributes to induction of pro-inflammatory phenotype and caspase-3 activation in astrocytes during Alzheimer's diseases.
SAMHD1 Attenuates Acute Inflammation by Maintaining Mitochondrial Function in Macrophages via Interaction with VDAC1.

Glia. 2023 May 19.

Insights into the mechanism of oligodendrocyte protection and remyelination enhancement by the integrated stress response.

Yanan Chen, Songhua Quan, Vaibhav Patil, Rejani B Kunjamma, Haley M Tokars, Eric D Leisten, Godwin Joy, Samantha Wills, Jonah R Chan, Yvette C Wong, Brian Popko.

  central nervous system (CNS) inflammation triggers activation of the integrated stress response (ISR). We previously reported that prolonging the ISR protects remyelinating oligodendrocytes and promotes remyelination in the presence of inflammation. However, the exact mechanisms through which this occurs remain unknown. Here, we investigated whether the ISR modulator Sephin1 in combination with the oligodendrocyte differentiation enhancing reagent bazedoxifene (BZA) is able to accelerate remyelination under inflammation, and the underlying mechanisms mediating this pathway. We find that the combined treatment of Sephin1 and BZA is sufficient to accelerate early-stage remyelination in mice with ectopic IFN-γ expression in the CNS. IFN-γ, which is a critical inflammatory cytokine in multiple sclerosis (MS), inhibits oligodendrocyte precursor cell (OPC) differentiation in culture and triggers a mild ISR. Mechanistically, we further show that BZA promotes OPC differentiation in the presence of IFN-γ, while Sephin1 enhances the IFN-γ-induced ISR by reducing protein synthesis and increasing RNA stress granule formation in differentiating oligodendrocytes. Finally, pharmacological suppression of the ISR blocks stress granule formation in vitro and partially lessens the beneficial effect of Sephin1 on disease progression in a mouse model of MS, experimental autoimmune encephalitis (EAE). Overall, our findings uncover distinct mechanisms of action of BZA and Sephin1 on oligodendrocyte lineage cells under inflammatory stress, suggesting that a combination therapy may effectively promote restoring neuronal function in MS patients.

Keywords:  integrated stress response; multiple sclerosis; remyelination

DOI:  https://doi.org/10.1002/glia.24386
Biochim Biophys Acta Gen Subj. 2023 May 13. pii: S0304-4165(23)00072-7. [Epub ahead of print] 130374

Anaphylatoxin C5a receptor signaling induces mitochondrial fusion and sensitizes retina pigment epithelial cells to oxidative stress.

Masaaki Ishii, Bärbel Rohrer.

  Mitochondrial dynamics is a morphological balance between fragmented and elongated shapes, reflecting mitochondrial metabolic status, cellular damage, and mitochondrial dysfunction. The anaphylatoxin C5a derived from complement component 5 cleavage, enhances cellular responses involved in pathological stimulation, innate immune responses, and host defense. However, the specific response of C5a and its receptor, C5a receptor (C5aR), in mitochondria is unclear. Here, we tested whether the C5a/C5aR signaling axis affects mitochondrial morphology in human-derived retinal pigment epithelial cell monolayers (ARPE-19). C5aR activation with the C5a polypeptide-induced mitochondrial elongation. In contrast, oxidatively stressed cells (H2O2) responded to C5a with an enhancement of mitochondrial fragmentation and an increase in the number of pyknotic nuclei. C5a/C5aR signaling increased the expression of mitochondrial fusion-related protein, mitofusin-1 (MFN1) and - 2 (MFN2), as well as enhanced optic atrophy-1 (Opa1) cleavage, which are required for mitochondrial fusion events, whereas the mitochondrial fission protein, dynamin-related protein-1 (Drp1), and mitogen-activated protein kinase (MAPK)-dependent extracellular signal-regulated protein kinase (Erk1/2) phosphorylation were not affected. Moreover, C5aR activation increased the frequency of endoplasmic reticulum (ER)-mitochondria contacts. Finally, oxidative stress induced in a single cell within an RPE monolayer (488 nm blue laser spot stimulation) induced a bystander effect of mitochondrial fragmentation in adjacent surrounding cells only in C5a-treated monolayers. These results suggest that C5a/C5aR signaling produced an intermediate state, characterized by increased mitochondrial fusion and ER-mitochondrial contacts, that sensitizes cells to oxidative stress, leading to mitochondrial fragmentation and cell death.

Keywords:  Anaphylatoxin; ER-mitochondria contact; G-protein coupled receptor; Mitochondrial dynamics

DOI:  https://doi.org/10.1016/j.bbagen.2023.130374
Int J Mol Sci. 2023 May 04. pii: 8232. [Epub ahead of print]24(9):

Analysis of Radiation Toxicity in Mammalian Cells Stably Transduced with Mitochondrial Stat3.

Alisa Zanin, Giacomo Meneghetti, Luca Menilli, Annachiara Tesoriere, Francesco Argenton, Maddalena Mognato.

  A coordinated action between nuclear and mitochondrial activities is essential for a proper cellular response to genotoxic stress. Several nuclear transcription factors, including STAT3, translocate to mitochondria to exert mitochondrial function regulation; however, the role of mitochondrial STAT3 (mitoSTAT3) under stressed conditions is still poorly understood. In this study, we examined whether the stable expression of mitoSTAT3 wild-type or mutated at the conserved serine residue (Ser727), which is involved in the mitochondrial function of STAT3, can affect the DNA damage response to UVC radiation. To address this issue, we generated mammalian cells (NIH-3T3 and HCT-116 cells) stably transduced to express the mitochondrial-targeted Stat3 gene in its wild-type or Ser727 mutated forms. Our results show that cell proliferation is enhanced in mitoStat3-transduced cells under both non-stressed and stressed conditions. Once irradiated with UVC, cells expressing wild-type mitoSTAT3 showed the highest cell survival, which was associated with a significant decrease in cell death. Low levels of oxidative stress were detected in UVC-irradiated NIH-3T3 cells expressing mitoSTAT3 wild-type or serine-related dominant active form (Ser727D), confirming a role of mitochondrial STAT3 in minimizing oxidant cellular stress that provides an advantage for cell survival.

Keywords:  UVC radiation; cell death; cell survival; genotoxic stress; mitochondrial STAT3

DOI:  https://doi.org/10.3390/ijms24098232
J Transl Med. 2023 May 19. 21(1): 331

Inflammatory and interferon gene expression signatures in patients with mitochondrial disease.

Emily B Warren, Eliza M Gordon-Lipkin, Foo Cheung, Jinguo Chen, Amrita Mukherjee, Richard Apps, John S Tsang, Jillian Jetmore, Melissa L Schlein, Shannon Kruk, Yuanjiu Lei, A Phillip West, Peter J McGuire.

   BACKGROUND: People with mitochondrial disease (MtD) are susceptible to metabolic decompensation and neurological symptom progression in response to an infection. Increasing evidence suggests that mitochondrial dysfunction may cause chronic inflammation, which may promote hyper-responsiveness to pathogens and neurodegeneration. We sought to examine transcriptional changes between MtD patients and healthy controls to identify common gene signatures of immune dysregulation in MtD.
METHODS: We collected whole blood from a cohort of MtD patients and healthy controls and performed RNAseq to examine transcriptomic differences. We performed GSEA analyses to compare our findings against existing studies to identify commonly dysregulated pathways.
RESULTS: Gene sets involved in inflammatory signaling, including type I interferons, interleukin-1β and antiviral responses, are enriched in MtD patients compared to controls. Monocyte and dendritic cell gene clusters are also enriched in MtD patients, while T cell and B cell gene sets are negatively enriched. The enrichment of antiviral response corresponds with an independent set of MELAS patients, and two mouse models of mtDNA dysfunction.
CONCLUSIONS: Through the convergence of our results, we demonstrate translational evidence of systemic peripheral inflammation arising from MtD, predominantly through antiviral response gene sets. This provides key evidence linking mitochondrial dysfunction to inflammation, which may contribute to the pathogenesis of primary MtD and other chronic inflammatory disorders associated with mitochondrial dysfunction.

Keywords:  Anti-viral signaling; Inflammation; Interferon; Mitochondrial disease; PBMCs

DOI:  https://doi.org/10.1186/s12967-023-04180-w
Nat Struct Mol Biol. 2023 May 18.

Polγ coordinates DNA synthesis and proofreading to ensure mitochondrial genome integrity.

Joon Park, Geoffrey K Herrmann, Patrick G Mitchell, Michael B Sherman, Y Whitney Yin.

Accurate replication of mitochondrial DNA (mtDNA) by DNA polymerase γ (Polγ) is essential for maintaining cellular energy supplies, metabolism, and cell cycle control. To illustrate the structural mechanism for Polγ coordinating polymerase (pol) and exonuclease (exo) activities to ensure rapid and accurate DNA synthesis, we determined four cryo-EM structures of Polγ captured after accurate or erroneous incorporation to a resolution of 2.4-3.0 Å. The structures show that Polγ employs a dual-checkpoint mechanism to sense nucleotide misincorporation and initiate proofreading. The transition from replication to error editing is accompanied by increased dynamics in both DNA and enzyme, in which the polymerase relaxes its processivity and the primer-template DNA unwinds, rotates, and backtracks to shuttle the mismatch-containing primer terminus 32 Å to the exo site for editing. Our structural and functional studies also provide a foundation for analyses of Polγ mutation-induced human diseases and aging.

DOI: https://doi.org/10.1038/s41594-023-00980-2
Int J Mol Sci. 2023 Apr 29. pii: 8064. [Epub ahead of print]24(9):

The Prohibitin-Binding Compound Fluorizoline Activates the Integrated Stress Response through the eIF2α Kinase HRI.

Ismael Sánchez-Vera, Sonia Núñez-Vázquez, José Saura-Esteller, Ana M Cosialls, Judith Heib, Pau Nadal Rodríguez, Ouldouz Ghashghaei, Rodolfo Lavilla, Gabriel Pons, Joan Gil, Daniel Iglesias-Serret.

  Fluorizoline is a synthetic molecule that induces apoptosis, by selectively targeting prohibitins (PHBs), through induction of the BH3-only protein NOXA. This induction is transcriptionally regulated by the integrated stress response (ISR)-related transcription factors ATF3 and ATF4. Here, we evaluate the role of the four eIF2α kinases, to decipher which is responsible for the mechanism of ISR activation triggered by fluorizoline in HeLa and HAP1 cells. First, we demonstrated the involvement of the eIF2α kinases using ISR inhibitor (ISRIB) and by simultaneous downregulation of all four eIF2α kinases, as both approaches were able to increase cell resistance to fluorizoline-induced apoptosis. Furthermore, we confirmed that fluorizoline treatment results in endoplasmic reticulum (ER) stress, as evidenced by PERK activation. Despite PERK activation, this kinase was not directly involved in the ISR activation by fluorizoline. In this regard, we found that the eIF2α kinases are capable of compensating for each other's loss of function. Importantly, we demonstrated that the mitochondrial-stress-related eIF2α kinase HRI mediates ISR activation after fluorizoline treatment.

Keywords:  ER-stress; HRI; ISR; apoptosis; fluorizoline; mitochondrial-stress; prohibitin

DOI:  https://doi.org/10.3390/ijms24098064
Mol Cell. 2023 May 06. pii: S1097-2765(23)00316-7. [Epub ahead of print]

The mitochondrial intermembrane space protein mitofissin drives mitochondrial fission required for mitophagy.

Tomoyuki Fukuda, Kentaro Furukawa, Tatsuro Maruyama, Shun-Ichi Yamashita, Daisuke Noshiro, Chihong Song, Yuta Ogasawara, Kentaro Okuyama, Jahangir Md Alam, Manabu Hayatsu, Tetsu Saigusa, Keiichi Inoue, Kazuho Ikeda, Akira Takai, Lin Chen, Vikramjit Lahiri, Yasushi Okada, Shinsuke Shibata, Kazuyoshi Murata, Daniel J Klionsky, Nobuo N Noda, Tomotake Kanki.

  Mitophagy plays an important role in mitochondrial homeostasis by selective degradation of mitochondria. During mitophagy, mitochondria should be fragmented to allow engulfment within autophagosomes, whose capacity is exceeded by the typical mitochondria mass. However, the known mitochondrial fission factors, dynamin-related proteins Dnm1 in yeasts and DNM1L/Drp1 in mammals, are dispensable for mitophagy. Here, we identify Atg44 as a mitochondrial fission factor that is essential for mitophagy in yeasts, and we therefore term Atg44 and its orthologous proteins mitofissin. In mitofissin-deficient cells, a part of the mitochondria is recognized by the mitophagy machinery as cargo but cannot be enwrapped by the autophagosome precursor, the phagophore, due to a lack of mitochondrial fission. Furthermore, we show that mitofissin directly binds to lipid membranes and brings about lipid membrane fragility to facilitate membrane fission. Taken together, we propose that mitofissin acts directly on lipid membranes to drive mitochondrial fission required for mitophagy.

Keywords:  Atg44; autophagy; crystal structure analysis; dynamin-related protein; high-speed atomic force microscopy; mitochondria; mitochondrial fission; mitofissin; mitophagy; yeast

DOI:  https://doi.org/10.1016/j.molcel.2023.04.022
Mitochondrion. 2023 May 16. pii: S1567-7249(23)00037-5. [Epub ahead of print]

The cyclic lipopeptide micafungin induces rupture of isolated mitochondria by reprograming the mitochondrial inner membrane anion channel.

Jonathan Hosler, Ngoc Hoang, Kristin Shirey Edwards.

  The antifungal activity of the drug micafungin, a cyclic lipopeptide that interacts with membrane proteins, may involve inhibition of fungal mitochondria. In humans, mitochondria are spared by the inability of micafungin to cross the cytoplasmic membrane. Using isolated mitochondria, we find that micafungin initiates the uptake of salts, causing rapid swelling and rupture of mitochondria with release of cytochrome c. The inner membrane anion channel (IMAC) is altered by micafungin to transfer both cations and anions. We propose that binding of anionic micafungin to IMAC attracts cations into the ion pore for the rapid transfer of ion pairs.

Keywords:  Anion transport; Cyclic lipopeptides; Inner mitochondrial anion channel; Ion channel; Micafungin; Mitochondrial respiratory chain complex; Mitochondrial transport

DOI:  https://doi.org/10.1016/j.mito.2023.05.004
J Pathol. 2023 Apr 27.

IFN-γ and androgens disrupt mitochondrial function in murine myocytes.

John M Fenimore, Danielle A Springer, Maria E Romero, Elijah F Edmondson, Dan W McVicar, Sudhirkumar Yanpallewar, Michael Sanford, Thea Spindel, Elizabeth Engle, Thomas J Meyer, Julio C Valencia, Howard A Young.

  The effect of cytokines on non-traditional immunological targets under conditions of chronic inflammation is an ongoing subject of study. Fatigue is a symptom often associated with autoimmune diseases. Chronic inflammatory response and activated cell-mediated immunity are associated with cardiovascular myopathies which can be driven by muscle weakness and fatigue. Thus, we hypothesize that immune dysfunction-driven changes in myocyte mitochondria may play a critical role in fatigue-related pathogenesis. We show that persistent low-level expression of IFN-γ in designated IFN-γ AU-Rich Element deletion mice (ARE mice) under androgen exposure resulted in mitochondrial and metabolic deficiencies in myocytes from male or castrated ARE mice. Most notably, echocardiography unveiled that low ejection fraction in the left ventricle post-stress correlated with mitochondrial deficiencies, explaining how heart function decreases under stress. We report that inefficiencies and structural changes in mitochondria, with changes to expression of mitochondrial genes, are linked to male-biased fatigue and acute cardiomyopathy under stress. Our work highlights how male androgen hormone backgrounds and active autoimmunity reduce mitochondrial function and the ability to cope with stress and how pharmacological blockade of stress signal protects heart function. These studies provide new insight into the diverse actions of IFN-γ in fatigue, energy metabolism, and autoimmunity. © 2023 The Pathological Society of Great Britain and Ireland. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Keywords:  IFN-γ; autoimmune disease; cardiomyopathy; inflammation; mitochondria; systemic lupus erythematosus (SLE)

DOI:  https://doi.org/10.1002/path.6081
Mitochondrion. 2023 May 10. pii: S1567-7249(23)00038-7. [Epub ahead of print]

MitoQuicLy: a high-throughput method for quantifying cell-free DNA from human plasma, serum, and saliva.

Jeremy Michelson, Shannon Rausser, Amanda Peng, Temmie Yu, Gabriel Sturm, Caroline Trumpff, Brett A Kaufman, Alex J Rai, Martin Picard.

  Circulating cell-free mitochondrial DNA (cf-mtDNA) is an emerging biomarker of psychobiological stress and disease which predicts mortality and is associated with various disease states. To evaluate the contribution of cf-mtDNA to health and disease states, standardized high-throughput procedures are needed to quantify cf-mtDNA in relevant biofluids. Here, we describe MitoQuicLy: Mitochondrial DNA Quantification in cell-free samples by Lysis. We demonstrate high agreement between MitoQuicLy and the commonly used column-based method, although MitoQuicLy is faster, cheaper, and requires a smaller input sample volume. Using 10 µL of input volume with MitoQuicLy, we quantify cf-mtDNA levels from three commonly used plasma tube types, two serum tube types, and saliva. We detect, as expected, significant inter-individual differences in cf-mtDNA across different biofluids. However, cf-mtDNA levels between concurrently collected plasma, serum, and saliva from the same individual differ on average by up to two orders of magnitude and are poorly correlated with one another, pointing to different cf-mtDNA biology or regulation between commonly used biofluids in clinical and research settings. Moreover, in a small sample of healthy women and men (n=34), we show that blood and saliva cf-mtDNAs correlate with clinical biomarkers differently depending on the sample used. The biological divergences revealed between biofluids, together with the lysis-based, cost-effective, and scalable MitoQuicLy protocol for biofluid cf-mtDNA quantification, provide a foundation to examine the biological origin and significance of cf-mtDNA to human health.

Keywords:  Cell-free DNA; Circulating nucleic acids; DNA isolation; Mitochondria; Mitochondrial DNA; Protocol

DOI:  https://doi.org/10.1016/j.mito.2023.05.001
Cell. 2023 May 11. pii: S0092-8674(23)00422-1. [Epub ahead of print]

Systematic identification of anticancer drug targets reveals a nucleus-to-mitochondria ROS-sensing pathway.

Junbing Zhang, Claire M Simpson, Jacqueline Berner, Harrison B Chong, Jiafeng Fang, Zehra Ordulu, Tommy Weiss-Sadan, Anthony P Possemato, Stefan Harry, Mariko Takahashi, Tzu-Yi Yang, Marianne Richter, Himani Patel, Abby E Smith, Alexander D Carlin, Adriaan F Hubertus de Groot, Konstantin Wolf, Lei Shi, Ting-Yu Wei, Benedikt R Dürr, Nicholas J Chen, Tristan Vornbäumen, Nina O Wichmann, Mohammed S Mahamdeh, Venkatesh Pooladanda, Yusuke Matoba, Shaan Kumar, Eugene Kim, Sara Bouberhan, Esther Oliva, Bo R Rueda, Roy J Soberman, Nabeel Bardeesy, Brian B Liau, Michael Lawrence, Matt P Stokes, Sean A Beausoleil, Liron Bar-Peled.

  Multiple anticancer drugs have been proposed to cause cell death, in part, by increasing the steady-state levels of cellular reactive oxygen species (ROS). However, for most of these drugs, exactly how the resultant ROS function and are sensed is poorly understood. It remains unclear which proteins the ROS modify and their roles in drug sensitivity/resistance. To answer these questions, we examined 11 anticancer drugs with an integrated proteogenomic approach identifying not only many unique targets but also shared ones-including ribosomal components, suggesting common mechanisms by which drugs regulate translation. We focus on CHK1 that we find is a nuclear H2O2 sensor that launches a cellular program to dampen ROS. CHK1 phosphorylates the mitochondrial DNA-binding protein SSBP1 to prevent its mitochondrial localization, which in turn decreases nuclear H2O2. Our results reveal a druggable nucleus-to-mitochondria ROS-sensing pathway-required to resolve nuclear H2O2 accumulation and mediate resistance to platinum-based agents in ovarian cancers.

Keywords:  CHK1; chemical proteomics; chemoresistance; mitochondrial translation; nuclear ROS; nucleus-to-mitochondria signaling

DOI:  https://doi.org/10.1016/j.cell.2023.04.026
Redox Biol. 2023 May 06. pii: S2213-2317(23)00136-2. [Epub ahead of print]63 102735

TXNIP contributes to induction of pro-inflammatory phenotype and caspase-3 activation in astrocytes during Alzheimer's diseases.

Junhyung Kim, Jaejoon Lim, Ik Dong Yoo, Samel Park, Jong-Seok Moon.

  Neuroinflammation and oxidative stress have been implicated in the pathogenesis of Alzheimer's disease (AD). Neuroinflammation and oxidative stress are associated with neuronal death in AD. Astrocytes are linked to neuroinflammation during AD. Astrocytes are important contributors to AD progression. Although the role of thioredoxin-interacting protein (TXNIP) has been identified in inflammation and oxidative stress, the mechanism by which TXNIP regulates inflammation and oxidative stress in astrocytes during AD remains unclear. In the present study, we found that TXNIP gene levels were elevated in cerebral cortex of patients with AD. The protein levels of TXNIP were elevated in GFAP-positive astrocytes of cerebral cortex from patients with AD and APP/PS1 double-transgenic mouse model of AD. Our results showed that TXNIP increased expression of genes related to pro-inflammatory reactive astrocytes and pro-inflammatory cytokines and chemokines in human astrocytes. Moreover, TXNIP increased production of pro-inflammatory cytokines and chemokines in human astrocytes. TXNIP induced activation of NK-kB signaling and over-production of mitochondrial reactive oxygen species (mtROS) in human astrocytes. TXNIP also induced mitochondrial oxidative stress by reduction of mitochondrial respiration and ATP production in human astrocytes. Furthermore, elevated TXNIP levels are correlated with caspase-3 activation of GFAP-positive astrocytes in patients with AD and mouse AD. TXNIP induced mitochondria-dependent apoptosis via caspase-9 and caspase-3 activation in human astrocytes. These results suggest that TXNIP contributes to induction of pro-inflammatory phenotype and caspase-3 activation in astrocytes during AD.

Keywords:  Alzheimer’s disease; Astrocytes; Caspase-3; Inflammation; Mitochondrial oxidative stress; TXNIP

DOI:  https://doi.org/10.1016/j.redox.2023.102735
Int J Mol Sci. 2023 Apr 26. pii: 7888. [Epub ahead of print]24(9):

SAMHD1 Attenuates Acute Inflammation by Maintaining Mitochondrial Function in Macrophages via Interaction with VDAC1.

Bowen Xu, Qianyi Sui, Han Hu, Xiangjia Hu, Xuchang Zhou, Cheng Qian, Nan Li.

  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.

Keywords:  M1 polarization; SAMHD1; TLR4 signaling; VDAC1; acute inflammation; innate immunity; macrophage; mitochondrion; molecular mechanism; sepsis

DOI:  https://doi.org/10.3390/ijms24097888