bims-inflin 2025-02-16 papers

Proc Natl Acad Sci U S A. 2025 Feb 18. 122(7): e2420802122

Raver1 links Ripk1 RNA splicing to caspase-8-mediated pyroptotic cell death, inflammation, and pathogen resistance.

Boyao Zhang, Pontus Orning, Jesse W Lehman, Alexandre Dinis, Leslie Torres-Ulloa, Roland Elling, Michelle A Kelliher, John Bertin, Megan K Proulx, Jon D Goguen, Liv Ryan, Richard K Kandasamy, Terje Espevik, Athma A Pai, Katherine A Fitzgerald, Egil Lien.

Multiple cell death and inflammatory signaling pathways converge on two critical factors: receptor-interacting serine/threonine kinase 1 (RIPK1) and caspase-8. Careful regulation of these molecules is critical to control apoptosis, pyroptosis, and inflammation. Here, we found a pivotal role of Raver1 as an essential regulator of Ripk1 pre-mRNA splicing, expression, and functionality and the subsequent caspase-8-dependent inflammatory cell death. We show that Raver1 influences mRNA diversity primarily by repressing alternative exon inclusion. Macrophages from Raver1-deficient mice exhibit altered splicing of Ripk1. As a result, Raver1-deficient primary macrophages display diminished cell death and decreased interleukin-18 and interleukin-1ß production, when infected with Yersinia bacteria, or by restraining TGF-ß-activated kinase 1 or IKKβ in the presence of lipopolysaccharide, tumor necrosis factor family members, or interferon-γ. These responses are accompanied by reduced activation of caspase-8, Gasdermin D and E, and caspase-1 in the absence of Raver1. Consequently, Raver1-deficient mice showed heightened susceptibility to Yersinia infection. Raver1 and RIPK1 also controlled the expression and function of the C-type lectin receptor Mincle. Our study underscores the critical regulatory role of Raver1 in modulating innate immune responses and highlights its significance in directing in vivo and in vitro inflammatory processes.

Keywords: IL-1ß; RIPK1; caspase-8; gasdermin; pyroptosis

DOI: https://doi.org/10.1073/pnas.2420802122

Elife. 2025 Feb 14. pii: RP100820. [Epub ahead of print]13

T3SS translocon induces pyroptosis by direct interaction with NLRC4/NAIP inflammasome.

Yan Zhao, Hanshuo Zhu, Jinqian Li, Hang Xu, Li Sun.

Type III secretion system (T3SS) is a virulence apparatus existing in many bacterial pathogens. Structurally, T3SS consists of the base, needle, tip, and translocon. The NLRC4 inflammasome is the major receptor for T3SS needle and basal rod proteins. Whether other T3SS components are recognized by NLRC4 is unclear. In this study, using Edwardsiella tarda as a model intracellular pathogen, we examined T3SS-inflammasome interaction and its effect on cell death. E. tarda induced pyroptosis in a manner that required the bacterial translocon and the host inflammasome proteins of NLRC4, NLRP3, ASC, and caspase 1/4. The translocon protein EseB triggered NLRC4/NAIP-mediated pyroptosis by binding NAIP via its C-terminal region, particularly the terminal 6 residues (T6R). EseB homologs exist widely in T3SS-positive bacteria and share high identities in T6R. Like E. tarda EseB, all of the representatives of the EseB homologs exhibited T6R-dependent NLRC4 activation ability. Together these results revealed the function and molecular mechanism of EseB to induce host cell pyroptosis and suggested a highly conserved inflammasome-activation mechanism of T3SS translocon in bacterial pathogens.

Keywords: NLRC4; T3SS; human; immunology; infectious disease; inflammation; microbiology; pathogen-host interaction; translocon

DOI: https://doi.org/10.7554/eLife.100820

Nat Commun. 2025 Feb 12. 16(1): 1562

Fungal Als proteins hijack host death effector domains to promote inflammasome signaling.

Tingting Zhou, Norma V Solis, Michaela Marshall, Qing Yao, Eric Pearlman, Scott G Filler, Haoping Liu.

High-damaging Candida albicans strains tend to form hyphae and exacerbate intestinal inflammation in ulcerative colitis patients through IL-1β-dependent mechanisms. Fungal agglutinin-like sequence (Als) proteins worsen DSS-induced colitis in mouse models. FADD and caspase-8 are important regulators of gut homeostasis and inflammation. However, whether they link directly to fungal proteins is not fully understood. Here, we report that Als proteins induce IL-1β release in immune cells. We show that hyphal Als3 is internalized in macrophages and interacts with caspase-8 and the inflammasome adaptor apoptosis-associated speck-like protein containing a CARD (ASC). Caspase-8 is essential for Als3-mediated ASC oligomerization and IL-1β processing. In non-immune cells, Als3 is associated with cell death core components FADD and caspase-8. N-terminal Als3 (N-Als3) expressed in Jurkat cells partially inhibits apoptosis. Mechanistically, N-Als3 promotes oligomerization of FADD and caspase-8 through their death effector domains (DEDs). N-Als3 variants with a mutation in the peptide-binding cavity or amyloid-forming region are impaired in DED oligomerization. Together, these results demonstrate that DEDs are intracellular sensors of Als3. This study identifies additional potential targets to control hypha-induced inflammation.

DOI: https://doi.org/10.1038/s41467-025-56657-5

Int J Mol Sci. 2025 Jan 29. pii: 1178. [Epub ahead of print]26(3):

Impaired LPS Signaling in Macrophages Overexpressing the P2X7 C-Terminal Domain or Anti-P2X7 C-Terminal Domain Intrabody.

Chisato Sakuma, Takato Takenouchi, Mitsuru Sato.

The P2X7 receptor is involved in innate immune responses, with its intracellular C-terminal domain capable of interacting with signaling molecules to regulate immune cell activation; however, the mechanisms underlying the signaling complexes remain unclear. To elucidate the function of the P2X7 C-terminal domain, we established bone marrow-derived macrophage (BMDM) cell lines from transgenic (Tg) mice overexpressing the C-terminal domain of P2X7 or anti-P2X7 C-terminal domain single-chain variable fragment (scFv) intrabody. In contrast to wild-type mouse BMDMs, the Tg BMDMs showed impairment of inflammatory responses induced by lipopolysaccharide (LPS) stimulation, such as NF-κB activation and subsequent TNF-α, IL-1β, and IL-6 expression. Furthermore, P2X7 was specifically associated with myeloid differentiation primary response gene 88 (MyD88) in wild-type BMDMs; its specific interaction was strongly interfered with by overexpression of the P2X7 C-terminal domain or anti-P2X7 C-terminal domain scFv in Tg BMDMs. These observations strongly suggest that P2X7 may have pivotal roles in LPS signaling cascades and could modulate macrophage inflammatory responses through its C-terminal domain.

Keywords: P2X7; Toll-like receptor 4; innate immunity; lipopolysaccharide; macrophage; myeloid differentiation primary response gene 88

DOI: https://doi.org/10.3390/ijms26031178

Autophagy. 2025 Feb 12.

Lysosomal Fe2+ influx through the MCOLN1 channel prevents sustained inflammation by limiting PHDs-regulated NFKB activation in macrophages.

Meng-Meng Wang, Wuyang Wang, Jiansong Qi.

Lysosomes are best known for their involvement in inflammatory responses, where they participate in the macroautophagy/autophagy process to eliminate inflammasomes. Recently, we have identified a previously overlooked function of lysosomes in regulating macrophage inflammatory responses. Specifically, lysosomes finely control the production of IL1B (interleukin 1 beta) by manipulating the release of lysosomal Fe2+ through MCOLN1. Mechanistically, reactive oxygen species (ROS), accumulated during sustained inflammation in macrophages, cause activation of the MCOLN1, a lysosomal cationic channel. The activation of MCOLN1 triggers the release of lysosomal Fe2 toward the cytosol, which in turn activates prolyl hydroxylase domain enzymes (PHDs). PHDs' activation represses the transcriptional regulator NFKB/NF-kB (nuclear factor kappa B) activity by restraining RELA/p65 in the cytosol, leading to decreased IL1B transcription in macrophages. Consequently, the property of controlling production and subsequent release of IL1B from macrophages allows the lysosome to finely restrict sustained inflammatory responses. These findings demonstrate that apart from relying on its degradative capability, the lysosome also limits excessive inflammatory responses to facilitate the restoration of cellular and tissue homeostasis in macrophages by modulating the release of lysosomal Fe2+ through MCOLN1. Even more, by suppressing IL1B production, in vivo stimulation of the MCOLN1 channel alleviates multiple clinical symptoms of dextran sulfate sodium (DSS)-induced colitis in mice, highlighting MCOLN1 as a promising therapeutic target for inflammatory bowel disease (IBD) in clinical settings.

Keywords: Lysosomes; MCOLN1; PHDs

DOI: https://doi.org/10.1080/15548627.2025.2465396

Nat Immunol. 2025 Feb 10.

Mechanisms of NLRP3 activation and inhibition elucidated by functional analysis of disease-associated variants.

Shouya Feng, Matthew C Wierzbowski, Katja Hrovat-Schaale, Andreas Dumortier, Yaoyuan Zhang, Maria Zyulina, Paul J Baker, Thomas Reygaerts, Annemarie Steiner, Dominic De Nardo, Dhanya Lakshmi Narayanan, Florian Milhavet, Alberto Pinzon-Charry, Juan Ignacio Arostegui, Raju P Khubchandani, Matthias Geyer, Guilaine Boursier, Seth L Masters.

The NLRP3 inflammasome is a multiprotein complex that mediates caspase-1 activation and the release of proinflammatory cytokines, including interleukin (IL)-1β and IL-18. Gain-of-function variants in the gene encoding NLRP3 (also called cryopyrin) lead to constitutive inflammasome activation and excessive IL-1β production in cryopyrin-associated periodic syndromes (CAPS). Here we present functional screening and automated analysis of 534 NLRP3 variants from the international INFEVERS registry and the ClinVar database. This resource captures the effect of NLRP3 variants on ASC speck formation spontaneously, at low temperature, after inflammasome stimulation and with the specific NLRP3 inhibitor MCC950. Most notably, our analysis facilitated the updated classification of NLRP3 variants in INFEVERS. Structural analysis suggested multiple mechanisms by which CAPS variants activate NLRP3, including enhanced ATP binding, stabilizing the active NLRP3 conformation, destabilizing the inactive NLRP3 complex and promoting oligomerization of the pyrin domain. Furthermore, we identified pathogenic variants that can hypersensitize the activation of NLRP3 in response to nigericin and cold temperature exposure. We also found that most CAPS-related NLRP3 variants can be inhibited by MCC950; however, NLRP3 variants with changes to proline affecting helices near the inhibitor binding site are resistant to MCC950, as are variants in the pyrin domain, which likely trigger activation directly with the pyrin domain of ASC. Our findings could help stratify the CAPS population for NLRP3 inhibitor clinical trials and our automated methodologies can be implemented for molecules with a different mechanism of activation and in laboratories worldwide that are interested in adding new functionally validated NLRP3 variants to the resource. Overall, our study provides improved diagnosis for patients with CAPS, mechanistic insight into the activation of NLRP3 and stratification of patients for the future application of targeted therapeutics.

DOI: https://doi.org/10.1038/s41590-025-02088-9