Publications by authors named "Katariina Nurmi"

14 Publications

  • Page 1 of 1

Native and oxidised lipoproteins negatively regulate the serum amyloid A-induced NLRP3 inflammasome activation in human macrophages.

Clin Transl Immunology 2021 3;10(8):e1323. Epub 2021 Aug 3.

Helsinki Rheumatic Diseases and Inflammation Research Group Translational Immunology Research Program University of Helsinki Helsinki University Clinicum Helsinki Finland.

Objectives: The NLRP3 inflammasome plays a key role in arterial wall inflammation. In this study, we elucidated the role of serum lipoproteins in the regulation of NLRP3 inflammasome activation by serum amyloid A (SAA) and other inflammasome activators.

Methods: The effect of lipoproteins on the NLRP3 inflammasome activation was studied in primary human macrophages and THP-1 macrophages. The effect of oxidised low-density lipoprotein (LDL) was examined in an mouse model of SAA-induced peritoneal inflammation.

Results: Native and oxidised high-density lipoproteins (HDL) and LDLs inhibited the interaction of SAA with TLR4. HDL and LDL inhibited the secretion of interleukin (IL)-1β and tumor necrosis factor by reducing their transcription. Oxidised forms of these lipoproteins reduced the secretion of mature IL-1β also by inhibiting the activation of NLRP3 inflammasome induced by SAA, ATP, nigericin and monosodium urate crystals. Specifically, oxidised LDL was found to inhibit the inflammasome complex formation. No cellular uptake of lipoproteins was required, nor intact lipoprotein particles for the inhibitory effect, as the lipid fraction of oxidised LDL was sufficient. The inhibition of NLRP3 inflammasome activation by oxidised LDL was partially dependent on autophagy. Finally, oxidised LDL inhibited the SAA-induced peritoneal inflammation and IL-1β secretion .

Conclusions: These findings reveal that both HDL and LDL inhibit the proinflammatory activity of SAA and this inhibition is further enhanced by lipoprotein oxidation. Thus, lipoproteins possess major anti-inflammatory functions that hinder the NLRP3 inflammasome-activating signals, particularly those exerted by SAA, which has important implications in the pathogenesis of cardiovascular diseases.
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http://dx.doi.org/10.1002/cti2.1323DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8329955PMC
August 2021

Histamine H Receptor Signaling Regulates the NLRP3 Inflammasome Activation in C2C12 Myocyte During Myogenic Differentiation.

Front Pharmacol 2021 31;12:599393. Epub 2021 May 31.

Urodynamic Center and Department of Urology, Institute of Clinical Medicine, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China.

NLRP3 inflammasome has been implicated in impaired post-injury muscle healing and in muscle atrophy. Histamine receptors play an important role in inflammation, but the role of histamine H receptor (HR) in myocyte regeneration and in the regulation of NLRP3 inflammasome is not known. We studied the effects of HR signaling on C2C12 myocyte viability, apoptosis, and tumor necrosis factor alpha (TNFα)-induced NLRP3 inflammasome activation during striated myogenic differentiation at three time points (days 0, 3, and 6). Expression of , interleukin-1β (IL-1β), and myogenesis markers were determined. TNFα reduced overall viability of C2C12 cells, and exposure to TNFα induced apoptosis of cells at D6. Activation of HR had no effect on viability or apoptosis, whereas inhibition of HR increased TNFα-induced apoptosis. Stimulation of C2C12 cells with TNFα increased mRNA expression at D3 and D6. Moreover, TNFα reduced the expression of myogenesis markers MyoD1, Myogenin, and Myosin-2 at D3 and D6. HR attenuated TNFα-induced expression of and further inhibited the myogenesis marker expression; while HR -blockage enhanced the proinflammatory effects of TNFα and increased the myogenesis marker expression. TNFα-induced secretion of mature IL-1β was dependent on the activation of the NLRP3 inflammasome, as shown by the reduced secretion of mature IL-1β upon treatment of the cells with the small molecule inhibitor of the NLRP3 inflammasome (MCC950). The activation of HR reduced TNFα-induced IL-1β secretion, while the HR blockage had an opposite effect. In conclusion, the modulation of HR activity regulates the effects of TNFα on C2C12 myocyte differentiation and TNFα-induced activation of NLRP3 inflammasome. Thus, HR signaling may represent a novel target for limiting postinjury muscle inflammation and muscle atrophy.
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http://dx.doi.org/10.3389/fphar.2021.599393DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8202077PMC
May 2021

Hydroxychloroquine reduces interleukin-6 levels after myocardial infarction: The randomized, double-blind, placebo-controlled OXI pilot trial.

Int J Cardiol 2021 Aug 4;337:21-27. Epub 2021 May 4.

Heart and Lung Center, Helsinki University Hospital, Helsinki University, Helsinki, Finland. Electronic address:

Objectives: To determine the anti-inflammatory effect and safety of hydroxychloroquine after acute myocardial infarction.

Method: In this multicenter, double-blind, placebo-controlled OXI trial, 125 myocardial infarction patients were randomized at a median of 43 h after hospitalization to receive hydroxychloroquine 300 mg (n = 64) or placebo (n = 61) once daily for 6 months and, followed for an average of 32 months. Laboratory values were measured at baseline, 1, 6, and 12 months.

Results: The levels of interleukin-6 (IL-6) were comparable at baseline between study groups (p = 0.18). At six months, the IL-6 levels were lower in the hydroxychloroquine group (p = 0.042, between groups), and in the on-treatment analysis, the difference at this time point was even more pronounced (p = 0.019, respectively). The high-sensitivity C-reactive protein levels did not differ significantly between study groups at any time points. Eleven patients in the hydroxychloroquine group and four in the placebo group had adverse events leading to interruption or withdrawal of study medication, none of which was serious (p = 0.10, between groups).

Conclusions: In patients with myocardial infarction, hydroxychloroquine reduced IL-6 levels significantly more than did placebo without causing any clinically significant adverse events. A larger randomized clinical trial is warranted to prove the potential ability of hydroxychloroquine to reduce cardiovascular endpoints after myocardial infarction.
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http://dx.doi.org/10.1016/j.ijcard.2021.04.062DOI Listing
August 2021

Tumor necrosis factor primes and metal particles activate the NLRP3 inflammasome in human primary macrophages.

Acta Biomater 2020 05 17;108:347-357. Epub 2020 Mar 17.

Department of Medicine, Clinicum, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, 00290 Helsinki, Finland; Translational Immunology Research Program, University of Helsinki, Haartmaninkatu 8, 00290 Helsinki, Finland; ORTON Orthopaedic Hospital of the Orton Foundation, Tenholantie 10, 00280 Helsinki, Finland.

Aseptic loosening of total joint replacements is driven by a macrophage-mediated inflammatory reaction to implant-derived wear particles. Phagocytosis of implant debris has been suggested to activate the NLRP3 inflammasome leading to secretion of interleukin (IL)-1β. However, factors and molecular mechanisms driving the particle-induced inflammasome activation are yet to be fully elucidated. In this study, we investigated the inflammasome response of human primary macrophages to titanium, chromium, and molybdenum particles in vitro. We observed that particles alone were not sufficient to induce IL-1β secretion, but an additional priming signal-such as bacterial lipopolysaccharide (LPS)-was required to license the inflammasome activation. By using specific inhibitors against the inflammasome signaling pathway, we demonstrate that the particle-induced IL-1β secretion depended upon activation of the NLRP3 inflammasome. We further hypothesized that tumor necrosis factor (TNF) could substitute for LPS as a priming signal, and found that particle stimulation together with preceding TNF treatment resulted in inflammasome-dependent IL-1β production as well. Our results show that the NLRP3 inflammasome mediates wear particle responses in human primary macrophages, and its activation does not necessarily require the presence of bacterial components, but can be induced under aseptic conditions by TNF priming. STATEMENT OF SIGNIFICANCE: This study was conducted to elucidate the molecular mechanisms of metal particle-induced IL-1β secretion in human primary macrophages. Production of this pro-inflammatory mediator from wear particle-activated macrophages has been associated with increased bone loss around total joint replacements-a condition eventually requiring revision surgery. Our results confirm that together with a co-stimulatory priming signal, particles of common implant metals elicit macrophage-mediated IL-1β secretion through activation of the NLRP3 inflammasome pathway. We also present a concept of TNF priming in this context, demonstrating that the particle-related IL-1β secretion can take place in a truly sterile environment. Thus, inhibition of inflammasome signaling appears a means to prevent wear particle-induced inflammation and development of peri‑prosthetic osteolysis.
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http://dx.doi.org/10.1016/j.actbio.2020.03.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7729209PMC
May 2020

Gain-of-function CEBPE mutation causes noncanonical autoinflammatory inflammasomopathy.

J Allergy Clin Immunol 2019 11 13;144(5):1364-1376. Epub 2019 Jun 13.

Institute of Biotechnology, HiLIFE, University of Helsinki, Helsinki, Finland.

Background: CCAAT enhancer-binding protein epsilon (C/EBPε) is a transcription factor involved in late myeloid lineage differentiation and cellular function. The only previously known disorder linked to C/EBPε is autosomal recessive neutrophil-specific granule deficiency leading to severely impaired neutrophil function and early mortality.

Objective: The aim of this study was to molecularly characterize the effects of C/EBPε transcription factor Arg219His mutation identified in a Finnish family with previously genetically uncharacterized autoinflammatory and immunodeficiency syndrome.

Methods: Genetic analysis, proteomics, genome-wide transcriptional profiling by means of RNA-sequencing, chromatin immunoprecipitation (ChIP) sequencing, and assessment of the inflammasome function of primary macrophages were performed.

Results: Studies revealed a novel mechanism of genome-wide gain-of-function that dysregulated transcription of 464 genes. Mechanisms involved dysregulated noncanonical inflammasome activation caused by decreased association with transcriptional repressors, leading to increased chromatin occupancy and considerable changes in transcriptional activity, including increased expression of NLR family, pyrin domain-containing 3 protein (NLRP3) and constitutively expressed caspase-5 in macrophages.

Conclusion: We describe a novel autoinflammatory disease with defective neutrophil function caused by a homozygous Arg219His mutation in the transcription factor C/EBPε. Mutated C/EBPε acts as a regulator of both the inflammasome and interferome, and the Arg219His mutation causes the first human monogenic neomorphic and noncanonical inflammasomopathy/immunodeficiency. The mechanism, including widely dysregulated transcription, is likely not unique for C/EBPε. Similar multiomics approaches should also be used in studying other transcription factor-associated diseases.
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http://dx.doi.org/10.1016/j.jaci.2019.06.003DOI Listing
November 2019

Forskolin attenuates the NLRP3 inflammasome activation and IL-1β secretion in human macrophages.

Pediatr Res 2019 12 13;86(6):692-698. Epub 2019 May 13.

Pediatric Urodynamic Center and Department of Urology, Institute of Clinical Medicine, The First Affiliated Hospital of Zhengzhou University, 450052, Zhengzhou, China.

Background: The treatment of nucleotide-binding domain and leucine-rich repeat containing family, pyrin domain containing 3 (NLRP3) inflammasome-mediated pediatric inflammatory diseases is challenging. Here we studied whether cyclic adenosine monophosphate (cAMP) elevator forskolin could attenuate the nigericin-induced NLRP3-inflammasome activation and interleukin-1β (IL-1β) secretion in human macrophages.

Methods: The proteins and messenger RNA (mRNA) levels of inflammasome structural proteins and proinflammatory cytokines were measured in forskolin-stimulated nigericin-activated human THP-1 macrophages and primary macrophages.

Results: Activation of THP-1 macrophages with nigericin increased the mRNA expression of NLRP3, IL-1β, and caspase-1 (P < 0.01). Forskolin stimulation had no effect on the mRNA expression of NLRP3, caspase-1, or IL-1β in nigericin-activated cells (P > 0.05), while their protein levels were significantly decreased (P < 0.05). Forskolin-mediated increase in cytoplasmic cAMP in non-activated cells was attenuated in nigericin-activated macrophages (P < 0.05). Basal IL-1β secretion increased from 584 to 2696 pg/mL (P < 0.01) in nigericin-activated macrophages; forskolin dose-dependently reduced the nigericin-induced secretion of mature IL-1β (P < 0.01). Forskolin also inhibited the IL-1β secretion from activated human primary macrophages.

Conclusions: Forskolin inhibits the NLRP3 inflammasome activation and the secretion of mature IL-1β, in human macrophages. Forskolin and other cAMP elevator drugs could represent a novel approach for treatment of diseases associated with excessive inflammasome activation, like pediatric inflammatory diseases.
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http://dx.doi.org/10.1038/s41390-019-0418-4DOI Listing
December 2019

Damaging heterozygous mutations in NFKB1 lead to diverse immunologic phenotypes.

J Allergy Clin Immunol 2017 Sep 21;140(3):782-796. Epub 2017 Jan 21.

Adult Immunodeficiency Unit, Infectious Diseases, Inflammation Center, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; Rare Diseases Center, Children's Hospital, University of Helsinki and Helsinki University Hospital, Helsinki, Finland.

Background: The nuclear factor κ light-chain enhancer of activated B cells (NF-κB) signaling pathway is a key regulator of immune responses. Accordingly, mutations in several NF-κB pathway genes cause immunodeficiency.

Objective: We sought to identify the cause of disease in 3 unrelated Finnish kindreds with variable symptoms of immunodeficiency and autoinflammation.

Methods: We applied genetic linkage analysis and next-generation sequencing and functional analyses of NFKB1 and its mutated alleles.

Results: In all affected subjects we detected novel heterozygous variants in NFKB1, encoding for p50/p105. Symptoms in variant carriers differed depending on the mutation. Patients harboring a p.I553M variant presented with antibody deficiency, infection susceptibility, and multiorgan autoimmunity. Patients with a p.H67R substitution had antibody deficiency and experienced autoinflammatory episodes, including aphthae, gastrointestinal disease, febrile attacks, and small-vessel vasculitis characteristic of Behçet disease. Patients with a p.R157X stop-gain experienced hyperinflammatory responses to surgery and showed enhanced inflammasome activation. In functional analyses the p.R157X variant caused proteasome-dependent degradation of both the truncated and wild-type proteins, leading to a dramatic loss of p50/p105. The p.H67R variant reduced nuclear entry of p50 and showed decreased transcriptional activity in luciferase reporter assays. The p.I553M mutation in turn showed no change in p50 function but exhibited reduced p105 phosphorylation and stability. Affinity purification mass spectrometry also demonstrated that both missense variants led to altered protein-protein interactions.

Conclusion: Our findings broaden the scope of phenotypes caused by mutations in NFKB1 and suggest that a subset of autoinflammatory diseases, such as Behçet disease, can be caused by rare monogenic variants in genes of the NF-κB pathway.
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http://dx.doi.org/10.1016/j.jaci.2016.10.054DOI Listing
September 2017

Hemin and Cobalt Protoporphyrin Inhibit NLRP3 Inflammasome Activation by Enhancing Autophagy: A Novel Mechanism of Inflammasome Regulation.

J Innate Immun 2017 22;9(1):65-82. Epub 2016 Sep 22.

Wihuri Research Institute, Helsinki, Finland.

Inflammasomes are intracellular protein platforms, which, upon activation, produce the highly proinflammatory cytokines interleukin (IL)-1β and IL-18. Heme, hemin and their degradation products possess significant immunomodulatory functions. Here, we studied whether hemin regulates inflammasome function in macrophages. Both hemin and its derivative, cobalt protoporphyrin (CoPP), significantly reduced IL-1β secretion by cultured human primary macrophages, the human monocytic leukemia cell line and also mouse bone marrow-derived and peritoneal macrophages. Intraperitoneal administration of CoPP to mice prior to urate crystal-induced peritonitis alleviated IL-1β secretion to the peritoneal cavity. In cultured macrophages, hemin and CoPP inhibited NLRP3 inflammasome assembly by reducing the amount of intracellular apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC). The reduction of ASC was associated with enhanced autophagosome formation and autophagic flux. Inhibition of autophagy prevented the CoPP-induced depletion of ASC, implying that the depletion was caused by increased autophagy. Our data indicate that hemin functions as an endogenous negative regulator of the NLRP3 inflammasome. The inhibition is mediated via enhanced autophagy that results in increased degradation of ASC. This regulatory mechanism may provide a novel approach for the treatment of inflammasome-related diseases.
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http://dx.doi.org/10.1159/000448894DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6738905PMC
October 2017

Calpain Activity Is Essential for ATP-Driven Unconventional Vesicle-Mediated Protein Secretion and Inflammasome Activation in Human Macrophages.

J Immunol 2016 10 16;197(8):3315-3325. Epub 2016 Sep 16.

Finnish Institute of Occupational Health, 00250 Helsinki, Finland;

Extracellular ATP is an endogenous danger signal that is known to activate inflammatory responses in innate immune cells, including macrophages. Activated macrophages start to secrete proteins to induce an immune response, as well as to recruit other immune cells to the site of infection and tissue damage. In this study, we characterized the secretome (i.e., the global pattern of secreted proteins) of ATP-stimulated human macrophages. We show that ATP stimulation activates robust vesicle-mediated unconventional protein secretion, including exosome release and membrane shedding, from human macrophages. Pathway analysis of the identified secreted proteins showed that calpain-related pathways were overrepresented in the secretome of ATP-stimulated cells. In accordance with this, calpains, which are calcium-dependent nonlysosomal cysteine proteases, were activated upon ATP stimulation through a P2X purinoceptor 7 receptor-dependent pathway. Functional studies demonstrated that calpain activity is essential for the P2X purinoceptor 7 receptor-mediated activation of unconventional protein secretion. Unconventional protein secretion was followed by cell necrosis and NLRP3 inflammasome-mediated secretion of the mature form of the proinflammatory cytokine IL-1β. Furthermore, ATP-driven NLRP3 inflammasome activation was also dependent on calpain activity. Interestingly, pro-IL-1β and inflammasome components ASC and caspase-1 were released by ATP-activated macrophages through a vesicle-mediated secretion pathway. In conclusion, to our knowledge, we provide the first global characterization of proteins secreted by ATP-activated human macrophages and show a pivotal role for calpains in the activation of the inflammatory response during ATP exposure.
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http://dx.doi.org/10.4049/jimmunol.1501840DOI Listing
October 2016

p38δ MAPK: A Novel Regulator of NLRP3 Inflammasome Activation With Increased Expression in Coronary Atherogenesis.

Arterioscler Thromb Vasc Biol 2016 09 14;36(9):1937-46. Epub 2016 Jul 14.

From the Wihuri Research Institute, Helsinki, Finland (K.R., K.N., K.Ö., P.T.K.); University of Helsinki, Clinicum, Helsinki, Finland (K.R., K.K.E.); Department of Pathology, University of Helsinki, Helsinki, Finland (M.I.M.); Division of Pathology, HUSLAB, Meilahti Laboratories of Pathology, Helsinki University Central Hospital, Helsinki, Finland (M.I.M.); Department of Immunology and Oncology, Centro Nacional de Biotecnología/Consejo Superior de Investigaciones Cientificas (CNB/CSIC), Madrid, Spain (A.R., A.C.); RS-koulutus, Helsinki, Finland (J.T.); and Helsinki University Central Hospital, Department of Rheumatology, Helsinki, Finland (K.K.E.).

Objective: Activation of the inflammasome pathway in macrophages results in the secretion of 2 potent proinflammatory and proatherogenic cytokines, interleukin (IL)-1β, and IL-18. Atherosclerotic lesions are characterized by the presence of various endogenous activators of the NLR family pyrin domain containing 3 (NLRP3) inflammasome, including cholesterol crystals and extracellular ATP. The aim of this study was to comprehensively characterize the expression of inflammasome pathway components and regulators in human atherosclerotic lesions.

Approach And Results: Twenty human coronary artery RNA samples from 10 explanted hearts were analyzed using an inflammasome pathway-focused quantitative polymerase chain reaction array. Advanced atherosclerotic plaques, when compared with early-to-intermediate lesions from the same coronary trees, displayed significant upregulation of 12 target genes, including the key inflammasome components apoptosis-associated speck-like protein containing a CARD domain, caspase-1, and IL-18. Immunohistochemical stainings of the advanced plaques revealed macrophage foam cells positive for NLRP3 inflammasome components around the necrotic lipid cores. The polymerase chain reaction array target p38δ mitogen-activated protein kinase was upregulated in advanced plaques and strongly expressed by lesional macrophage foam cells. In cultured human monocyte-derived macrophages, the p38δ mitogen-activated protein kinase was activated by intracellular stress signals triggered during ATP- and cholesterol crystal-induced NLRP3 inflammasome activation and was required for NLRP3-mediated IL-1β secretion.

Conclusions: Increased expression of the key inflammasome components in advanced coronary lesions implies enhanced activity of the inflammasome pathway in progression of coronary atherosclerosis. The p38δ mitogen-activated protein kinase was identified as a novel regulator of NLRP3 inflammasome activation in primary human macrophages, and thus, represents a potential target for modulation of atherosclerotic inflammation.
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http://dx.doi.org/10.1161/ATVBAHA.115.307312DOI Listing
September 2016

Carboxyl-Terminal Cleavage of Apolipoprotein A-I by Human Mast Cell Chymase Impairs Its Anti-Inflammatory Properties.

Arterioscler Thromb Vasc Biol 2016 Feb 17;36(2):274-84. Epub 2015 Dec 17.

From the Wihuri Research Institute, Biomedicum Helsinki, Helsinki, Finland (S.D.N., K.M., J.L., K.N., K.Ö., M.L.-R., P.T.K.); National Institute for Health and Welfare, Genomics and Biomarkers Unit, Biomedicum Helsinki, Helsinki, Finland (J.M., M.J.); and Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles (M.N., A.M.F.).

Objective: Apolipoprotein A-I (apoA-I) has been shown to possess several atheroprotective functions, including inhibition of inflammation. Protease-secreting activated mast cells reside in human atherosclerotic lesions. Here we investigated the effects of the neutral proteases released by activated mast cells on the anti-inflammatory properties of apoA-I.

Approach And Results: Activation of human mast cells triggered the release of granule-associated proteases chymase, tryptase, cathepsin G, carboxypeptidase A, and granzyme B. Among them, chymase cleaved apoA-I with the greatest efficiency and generated C-terminally truncated apoA-I, which failed to bind with high affinity to human coronary artery endothelial cells. In tumor necrosis factor-α-activated human coronary artery endothelial cells, the chymase-cleaved apoA-I was unable to suppress nuclear factor-κB-dependent upregulation of vascular cell adhesion molecule-1 (VCAM-1) and to block THP-1 cells from adhering to and transmigrating across the human coronary artery endothelial cells. Chymase-cleaved apoA-I also had an impaired ability to downregulate the expression of tumor necrosis factor-α, interleukin-1β, interleukin-6, and interleukin-8 in lipopolysaccharide-activated GM-CSF (granulocyte-macrophage colony-stimulating factor)- and M-CSF (macrophage colony-stimulating factor)-differentiated human macrophage foam cells and to inhibit reactive oxygen species formation in PMA (phorbol 12-myristate 13-acetate)-activated human neutrophils. Importantly, chymase-cleaved apoA-I showed reduced ability to inhibit lipopolysaccharide-induced inflammation in vivo in mice. Treatment with chymase blocked the ability of the apoA-I mimetic peptide L-4F, but not of the protease-resistant D-4F, to inhibit proinflammatory gene expression in activated human coronary artery endothelial cells and macrophage foam cells and to prevent reactive oxygen species formation in activated neutrophils.

Conclusions: The findings identify C-terminal cleavage of apoA-I by human mast cell chymase as a novel mechanism leading to loss of its anti-inflammatory functions. When targeting inflamed protease-rich atherosclerotic lesions with apoA-I, infusions of protease-resistant apoA-I might be the appropriate approach.
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http://dx.doi.org/10.1161/ATVBAHA.115.306827DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4725095PMC
February 2016

Ethanol inhibits activation of NLRP3 and AIM2 inflammasomes in human macrophages--a novel anti-inflammatory action of alcohol.

PLoS One 2013 11;8(11):e78537. Epub 2013 Nov 11.

Wihuri Research Institute, Helsinki, Finland.

Objective: In the pathogenesis of coronary atherosclerosis, local macrophage-driven inflammation and secretion of proinflammatory cytokines, interleukin-1β (IL-1β) in particular, are recognized as key factors. Moderate alcohol consumption is associated with a reduced risk of coronary artery disease mortality. Here we examined in cultured human macrophages whether ethanol modulates the intracellular processes involved in the secretion of IL-1β.

Results: Ethanol decreased dose-dependently the production of mature IL-1β induced by activators of the NLRP3 inflammasome, i.e. ATP, cholesterol crystals, serum amyloid A and nigericin. Ethanol had no significant effect on the expression of NLRP3 or IL1B mRNA in LPS-primed macrophages. Moreover, secretion of IL-1β was decreased in parallel with reduction of caspase-1 activation, demonstrating that ethanol inhibits inflammasome activation instead of synthesis of pro-IL-1β. Acetaldehyde, a highly reactive metabolite of ethanol, had no effect on the ATP-induced IL-1β secretion. Ethanol also attenuated the secretion of IL-1β triggered by synthetic double-stranded DNA, an activator of the AIM2 inflammasome. Ethanol conferred the inhibitory functions by attenuating the disruption of lysosomal integrity and ensuing leakage of the lysosomal protease cathepsin B and by reducing oligomerization of ASC.

Conclusion: Ethanol-induced inhibition of the NLRP3 inflammasome activation in macrophages may represent a biological pathway underlying the protective effect of moderate alcohol consumption on coronary heart disease.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0078537PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3823849PMC
July 2014

Extracellular acidosis is a novel danger signal alerting innate immunity via the NLRP3 inflammasome.

J Biol Chem 2013 May 25;288(19):13410-9. Epub 2013 Mar 25.

Wihuri Research Institute, Biomedicum Helsinki, Haartmaninkatu 8, FI-00290 Helsinki, Finland.

Background: Local acidosis has been demonstrated in ischemic tissues and at inflammatory sites.

Results: Acidic extracellular pH triggers NLRP3 inflammasome activation and interleukin-1β secretion in human macrophages.

Conclusion: Acidic pH represents a novel danger signal alerting the innate immunity.

Significance: Local acidosis may promote inflammation at ischemic and inflammatory sites. Local extracellular acidification has been demonstrated at sites of ischemia and inflammation. IL-1β is one of the key proinflammatory cytokines, and thus, its synthesis and secretion are tightly regulated. The NLRP3 (nucleotide-binding domain leucine-rich repeat containing family, pyrin domain containing 3) inflammasome complex, assembled in response to microbial components or endogenous danger signals, triggers caspase-1-mediated maturation and secretion of IL-1β. In this study, we explored whether acidic environment is sensed by immune cells as an inflammasome-activating danger signal. Human macrophages were exposed to custom cell culture media at pH 7.5-6.0. Acidic medium triggered pH-dependent secretion of IL-1β and activation of caspase-1 via a mechanism involving potassium efflux from the cells. Acidic extracellular pH caused rapid intracellular acidification, and the IL-1β-inducing effect of acidic medium could be mimicked by acidifying the cytosol with bafilomycin A1, a proton pump inhibitor. Knocking down the mRNA expression of NLRP3 receptor abolished IL-1β secretion at acidic pH. Remarkably, alkaline extracellular pH strongly inhibited the IL-1β response to several known NLRP3 activators, demonstrating bipartite regulatory potential of pH on the activity of this inflammasome. The data suggest that acidic environment represents a novel endogenous danger signal alerting the innate immunity. Low pH may thus contribute to inflammation in acidosis-associated pathologies such as atherosclerosis and post-ischemic inflammatory responses.
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http://dx.doi.org/10.1074/jbc.M112.426254DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3650379PMC
May 2013

Chemically modified tetracyclines induce apoptosis in cultured mast cells.

Int Immunopharmacol 2005 Oct;5(11):1611-21

Department of Medicine, Division of Rheumatology, Helsinki University Central Hospital, Kasarmikatu 11-13, 00130 Helsinki, Finland.

Chemically modified tetracyclines are a group of non-antimicrobial tetracycline derivatives, which possess antiinflammatory, anticollagenolytic and antiproliferative properties. Here we studied the effects of four different chemically modified tetracyclines (CMT-1, CMT-3, CMT-8 and CMT-308) on proliferation and viability of cultured mouse and human mast cells. All studied CMTs (25 microM) effectively inhibited the viability and proliferation of human mast cell line (HMC-1) cells and mouse bone marrow derived mast cells (mBMMCs), as judged by trypan blue exclusion and by incorporation of [(3)H]thymidine. The antiproliferative effect of CMTs was not dependent on the stimulating growth factor, i.e. CMTs inhibited both IL-3 and c-kit ligand-induced proliferation of mBMMCs. The reduced viability of mast cells was due to induction of apoptosis, as indicated by the increased amount of apoptotic nucleosomes and the appearance of TUNEL positive cells in the presence of CMTs. The induction of apoptosis was further confirmed by showing that CMT-3 induces activation of caspase-3 and caspase-9 in HMC-1 cells. Additionally, CMT-3 induced downregulation of the expression of antiapoptotic Bcl-2 protein in HMC-1 cells. Compared to doxycycline, the antiproliferative and proapoptotic effects of different CMTs were clearly more pronounced. Of the studied CMTs, CMT-3 and CMT-8 appeared to be the most potent inhibitors of mast cell proliferation and survival. The present results show that CMTs have an antiproliferative and proapoptotic effect on both malignant and non-malignant mast cells. In conclusion, CMTs could offer a novel means to treat disorders with inappropriate expansion of mast cells, such as rheumatoid arthritis and systemic mast cell diseases.
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http://dx.doi.org/10.1016/j.intimp.2005.04.013DOI Listing
October 2005
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