bims-minimp Biomed News
on Mitochondria, innate immunity, proteostasis
Issue of 2021‒05‒23
thirteen papers selected by
Hanna Salmonowicz
Newcastle University

  1. Front Chem. 2021 ;9 642273
      Extracellular signals drive the nucleation of the NLRP3 inflammasome which leads to the release of cytokines and causes inflammatory events. Hence, the inflammasome has gained enormous momentum in biomedical basic research. The detailed mechanisms of inflammasome generation and regulation remain to be elucidated. Our study was directed toward the design, convergent synthesis, and initial biochemical evaluation of activity-based probes addressing NLRP3. For this purpose, probes were assembled from a CRID3/MCC950-related NLRP3-binding unit, a linker portion and a coumarin 343 fluorophore or biotin. The affinity of our probes to NLRP3 was demonstrated through SPR measurements and their cellular activity was confirmed by reduction of the interleukin 1β release from stimulated bone marrow-derived macrophages. The initial characterizations of NLRP3-targeting probes highlighted the coumarin probe 2 as a suitable tool compound for the cellular and biochemical analysis of the NLRP3 inflammasome.
    Keywords:  CRID3; MCC950; NLRP3; inflammasome; probes; surface plasmon resonance
  2. Inflammation. 2021 May 19.
      The NLRP3 inflammasome is a multi-molecular complex that acts as a molecular platform to mediate caspase-1 activation, leading to IL-1β/IL-18 maturation and release in cells stimulated by various pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). This inflammasome plays an important role in the innate immunity as its activation can further promote the occurrence of inflammation, enhance the ability of host to remove pathogens, and thus facilitate the repair of injured tissues. But if the inflammasome activation is dysregulated, it will cause the development of various inflammatory diseases and metabolic disorders. Therefore, under normal conditions, the activation of inflammasome is tightly regulated by various positive and negative signaling pathways to respond to the stimuli without damaging the host itself while maintaining homeostasis. In this review, we summarize recent advances in the major signaling pathways (including TLRs, MAPK, mTOR, autophagy, PKA, AMPK, and IFNR) that regulate NLRP3 inflammasome activation, providing a brief view of the molecular network that regulates this inflammasome as a theoretical basis for therapeutic intervention of NLRP3 dysregulation-related diseases.
    Keywords:  AMPK; Autophagy; MAPK; NLRP3 inflammasome; PKA; mTOR
  3. Cell Death Dis. 2021 May 21. 12(6): 523
      Tubulointerstitial inflammation plays a key role in the pathogenesis of diabetic nephropathy (DN). Interleukin-1β (IL-1β) is the key proinflammatory cytokine associated with tubulointerstitial inflammation. The NLRP3 inflammasome regulates IL-1β activation and secretion. Reactive oxygen species (ROS) represents the main mediator of NLRP3 inflammasome activation. We previously reported that CD36, a class B scavenger receptor, mediates ROS production in DN. Here, we determined whether CD36 is involved in NLRP3 inflammasome activation and explored the underlying mechanisms. We observed that high glucose induced-NLRP3 inflammasome activation mediate IL-1β secretion, caspase-1 activation, and apoptosis in HK-2 cells. In addition, the levels of CD36, NLRP3, and IL-1β expression (protein and mRNA) were all significantly increased under high glucose conditions. CD36 knockdown resulted in decreased NLRP3 activation and IL-1β secretion. CD36 knockdown or the addition of MitoTempo significantly inhibited ROS production in HK-2 cells. CD36 overexpression enhanced NLRP3 activation, which was reduced by MitoTempo. High glucose levels induced a change in the metabolism of HK-2 cells from fatty acid oxidation (FAO) to glycolysis, which promoted mitochondrial ROS (mtROS) production after 72 h. CD36 knockdown increased the level of AMP-activated protein kinase (AMPK) activity and mitochondrial FAO, which was accompanied by the inhibition of NLRP3 and IL-1β. The in vivo experimental results indicate that an inhibition of CD36 could protect diabetic db/db mice from tubulointerstitial inflammation and tubular epithelial cell apoptosis. CD36 mediates mtROS production and NLRP3 inflammasome activation in db/db mice. CD36 inhibition upregulated the level of FAO-related enzymes and AMPK activity in db/db mice. These results suggest that NLRP3 inflammasome activation is mediated by CD36 in renal tubular epithelial cells in DN, which suppresses mitochondrial FAO and stimulates mtROS production.
  4. Food Funct. 2021 May 21.
      Green tea has been considered as a health-promoting beverage and is widely consumed worldwide. Epigallocatechin-3-gallate (EGCG), the most abundant polyphenol derived from green tea leaves with potent antioxidative and chemopreventive activities, has been reported to offer protection against inflammation-driven tissue damage. Here, we evaluated the protective effects of EGCG against lung injury during acute pancreatitis (AP) and further revealed the detailed mechanism. The results showed that EGCG significantly attenuated l-arginine-induced AP and the consequent pulmonary damage in mice. Moreover, EGCG substantially attenuated oxidative stress and concurrently suppressed NOD-like receptor protein 3 (NLRP3) inflammasome activation in the lung. In vitro, EGCG considerably reduced the production of mitochondrial reactive oxygen species (mtROS) and oxidized mitochondrial DNA (ox-mtDNA) in alveolar macrophages (AMs) challenged with AP-conditioned plasma. Meanwhile, the amount of ox-mtDNA bound to NLRP3 decreased significantly by the treatment with EGCG, resulting in impaired NLRP3 inflammasome activation. In addition, the antagonism of NLRP3 signaling by EGCG was affected in the presence of the mtROS stimulant rotenone or scavenger Mito-TEMPO. Altogether, EGCG possesses potent activity to attenuate lung injury during AP progression by inhibiting NLRP3 inflammasome activation. As for the mechanism, the EGCG-conferred restriction of NLRP3 inflammasome activation probably arises from the elimination of mtROS as well as its oxidative product ox-mtDNA, which consequently enables the protection against AP-associated lung injury.
  5. Brain Res. 2021 May 16. pii: S0006-8993(21)00382-6. [Epub ahead of print] 147525
      The NLR family pyrin domain-containing 3 (NLRP3) multiprotein complex is associated with neuroinflammation and poor prognosis after subarachnoid hemorrhage (SAH). Accumulating evidence shows that Mer tyrosine kinase (MerTK) alleviates inflammatory responses via a negative feedback mechanism. However, the contribution and function of MerTK in SAH remain to be determined. In this study, we explored the role of MerTK during microglial NLRP3 inflammasome activation and evaluated its contribution to the outcome of SAH in mice. Activating MerTK with growth arrest-specific 6 (Gas6) alleviated brain edema, neuronal degeneration and neurological deficits after SAH by regulating neuroinflammation. Gas6 did not change the mRNA levels of Nlrp3 or Casp1 but decreased the protein expression of NLRP3, cleaved caspase1 (p20), interleukin-1β and interleukin-18. Furthermore, Gas6 increased the expression of Beclin1, the ratio of LC3-II/LC3-I and the level of autophagic flux. Inhibiting autophagy with 3-MA reversed the inhibition of NLRP3 inflammasome activation and diminished the neuroprotective effects of Gas6. Thus, MerTK activation may exert protective effects by limiting neuroinflammation and promoting neurological recovery after SAH via autophagy induction.
    Keywords:  MerTK; NLRP3 inflammasome; autophagy; subarachnoid hemorrhage
  6. Cell Rep. 2021 May 18. pii: S2211-1247(21)00473-3. [Epub ahead of print]35(7): 109134
      Axonal generation of Alzheimer's disease (AD)-associated amyloid-β (Aβ) plays a key role in AD neuropathology, but the cellular mechanisms involved in its release have remained elusive. We previously reported that palmitoylated APP (palAPP) partitions to lipid rafts where it serves as a preferred substrate for β-secretase. Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) are cholesterol-rich lipid rafts that are upregulated in AD. Here, we show that downregulating MAM assembly by either RNA silencing or pharmacological modulation of the MAM-resident sigma1 receptor (S1R) leads to attenuated β-secretase cleavage of palAPP. Upregulation of MAMs promotes trafficking of palAPP to the cell surface, β-secretase cleavage, and Aβ generation. We develop a microfluidic device and use it to show that MAM levels alter Aβ generation specifically in neuronal processes and axons, but not in cell bodies. These data suggest therapeutic strategies for reducing axonal release of Aβ and attenuating β-amyloid pathology in AD.
    Keywords:  AD; APP; Alzheimer's disease; MAMs; axonal Abeta; lipid rafts; mitochondria-associated ER membranes; palmitoylation
  7. Toxicol Appl Pharmacol. 2021 May 18. pii: S0041-008X(21)00189-7. [Epub ahead of print] 115582
      NLRP3 inflammasome is involved in several chronic inflammatory diseases. The inflammatory effect of the NLRP3 inflammasome is executed through IL-1β and IL-18. Therefore, IL-1β is one of the primary targets in chronic inflammatory conditions. However, current treatment regimens are dependent on anti- IL-1β biologicals. The therapies targeting IL-1β through inhibition of NLRP3 inflammasome are thus being actively explored. We identified safranal, a small molecule responsible for the essence of saffron as a potential inhibitor of the NLRP3 inflammasome. Safranal significantly suppressed the release of IL-1β from ATP stimulated J774A.1 and bone marrow-derived macrophages (BMDMs) by regulating CASP1 and CASP8 dependent cleavage of pro-IL-1β. Safranal markedly suppressed the expression of NLRP3 and its ATPase activity. Safranal treatment enhanced the expression of NRF2, whereas, si-RNA mediated silencing of Nrf2 abrogated the anti-NLRP3 effect of safranal. Furthermore, safranal inhibited ASC oligomerization and formation of ASC specks. Safranal also displayed anti-NLRP3 activity in multiple mice models. Treatment of animals with safranal reduced the production of IL-1β in ATP elicited peritoneal inflammation, MSU induced air pouch inflammation, and MSU injected foot paw edema in mice. Thus, our data projects safranal as a potential preclinical drug candidate against NLRP3 inflammasome triggered chronic inflammation.
    Keywords:  ASC; Caspase-1; IL-1β; Macrophages; NLRP3 inflammasome; Saffron; Safranal
  8. Front Physiol. 2021 ;12 659751
      NLRP3-mediated inflammation is closely related to the pathological progression of diabetic nephropathy (DN). DsbA-L, an antioxidant enzyme, plays a protective role in a variety of diseases by inhibiting ER stress and regulating metabolism. However, the relationship of DsbA-L with inflammation, especially the NLRP3 inflammasome, has not been examined. In this study, we note that activation of the NLRP3 inflammasome and exacerbated fibrosis were observed in the kidneys of diabetic DsbA-L-knockout mice and were accompanied by decreased phosphorylation of AMP-activated protein kinase (AMPK). Moreover, correlation analysis shows that the phosphorylation of AMPK was negatively correlated with NLRP3 expression and tubular damage. In addition, the decreased AMPK phosphorylation and NLRP3 activation induced by high glucose (HG) in HK-2 cells could be alleviated by the overexpression of DsbA-L. Interestingly, the protective effect of DsbA-L was eliminated after treatment with compound C, a well-known AMPK inhibitor. Our findings suggest that DsbA-L inhibits NLRP3 inflammasome activation by promoting the phosphorylation of AMPK.
    Keywords:  AMPK; DsbA-L; NLRP3 inflammasome; diabetic nephropathy; inflammation
  9. EMBO Mol Med. 2021 May 20. e13579
      Mutations in OPA1 cause autosomal dominant optic atrophy (DOA) as well as DOA+, a phenotype characterized by more severe neurological deficits. OPA1 deficiency causes mitochondrial fragmentation and also disrupts cristae, respiration, mitochondrial DNA (mtDNA) maintenance, and cell viability. It has not yet been established whether phenotypic severity can be modulated by genetic modifiers of OPA1. We screened the entire known mitochondrial proteome (1,531 genes) to identify genes that control mitochondrial morphology using a first-in-kind imaging pipeline. We identified 145 known and novel candidate genes whose depletion promoted elongation or fragmentation of the mitochondrial network in control fibroblasts and 91 in DOA+ patient fibroblasts that prevented mitochondrial fragmentation, including phosphatidyl glycerophosphate synthase (PGS1). PGS1 depletion reduces CL content in mitochondria and rebalances mitochondrial dynamics in OPA1-deficient fibroblasts by inhibiting mitochondrial fission, which improves defective respiration, but does not rescue mtDNA depletion, cristae dysmorphology, or apoptotic sensitivity. Our data reveal that the multifaceted roles of OPA1 in mitochondria can be functionally uncoupled by modulating mitochondrial lipid metabolism, providing novel insights into the cellular relevance of mitochondrial fragmentation.
    Keywords:  OPA1; genetic modifiers; high-throughput screening; mitochondrial dynamics; phospholipid metabolism
  10. Curr Biol. 2021 May 14. pii: S0960-9822(21)00609-6. [Epub ahead of print]
      Mutations in Vps13D cause defects in autophagy, clearance of mitochondria, and human movement disorders. Here, we discover that Vps13D functions in a pathway downstream of Vmp1 and upstream of Marf/Mfn2. Like vps13d, vmp1 mutant cells exhibit defects in autophagy, mitochondrial size, and clearance. Through the relationship between vmp1 and vps13d, we reveal a novel role for Vps13D in the regulation of mitochondria and endoplasmic reticulum (ER) contact. Significantly, the function of Vps13D in mitochondria and ER contact is conserved between fly and human cells, including fibroblasts derived from patients suffering from VPS13D mutation-associated neurological symptoms. vps13d mutants have increased levels of Marf/MFN2, a regulator of mitochondrial fusion. Importantly, loss of marf/MFN2 suppresses vps13d mutant phenotypes, including mitochondria and ER contact. These findings indicate that Vps13d functions at a regulatory point between mitochondria and ER contact, mitochondrial fusion and autophagy, and help to explain how Vps13D contributes to disease.
    Keywords:  Drosophila; Vmp1; Vps13D; autophagy; membrane contact; mitochondria
  11. Mol Ther Nucleic Acids. 2021 Jun 04. 24 743-754
      Preeclampsia (PE) is one of the leading causes of maternal death worldwide. Elevated fatty acid binding protein 4 (FABP4) levels have been observed in patients with PE, however, the mechanism by which FABP4 contributes to the pathogenesis of PE remains unclear. In this study, we compared the levels of FABP4 and cytokines between 20 PE patients and 10 healthy pregnant women by using ELISA, immunohistochemistry (IHC) analysis, and flow cytometry (fluorescence-activated cell sorting, FACS). Elevated FABP4 was accompanied by regulatory T (Treg)/T helper type 17 (Th17) imbalance in PE. Knockdown of FABP4 attenuated lipopolysaccharide (LPS)-induced NLR family pyrin domain containing 3 (NLRP3) inflammasome activation and interleukin-17A (IL-17A) production in primary macrophages. In addition, silencing of FABP4 also suppressed Th17 differentiation via paracrine signaling. Overexpression of FABP4 promoted Th17 differentiation via increasing IL-17A/IL-23 release. Reciprocally, IL-17A upregulated FABP4 and activated the NLRP3 inflammasome in vitro and in vivo. The in vivo studies revealed that FABP4 inhibitor BMS309403 ameliorated PE clinical phenotypes, the Treg/Th17 imbalance, and NLRP3 inflammasome activation in PE mice model. In conclusion, FABP4 facilitates inflammasome activation to induce the imbalance of Treg/Th17 in PE via forming a positive feedback with IL-17A.
    Keywords:  FABP4; IL-17A; NLRP3; Th17; Treg; preeclampsia
  12. Nat Metab. 2021 May 17.
      Non-alcoholic fatty liver disease (NAFLD), the most prevalent liver pathology worldwide, is intimately linked with obesity and type 2 diabetes. Liver inflammation is a hallmark of NAFLD and is thought to contribute to tissue fibrosis and disease pathogenesis. Uncoupling protein 1 (UCP1) is exclusively expressed in brown and beige adipocytes, and has been extensively studied for its capacity to elevate thermogenesis and reverse obesity. Here we identify an endocrine pathway regulated by UCP1 that antagonizes liver inflammation and pathology, independent of effects on obesity. We show that, without UCP1, brown and beige fat exhibit a diminished capacity to clear succinate from the circulation. Moreover, UCP1KO mice exhibit elevated extracellular succinate in liver tissue that drives inflammation through ligation of its cognate receptor succinate receptor 1 (SUCNR1) in liver-resident stellate cell and macrophage populations. Conversely, increasing brown and beige adipocyte content in mice antagonizes SUCNR1-dependent inflammatory signalling in the liver. We show that this UCP1-succinate-SUCNR1 axis is necessary to regulate liver immune cell infiltration and pathology, and systemic glucose intolerance in an obesogenic environment. As such, the therapeutic use of brown and beige adipocytes and UCP1 extends beyond thermogenesis and may be leveraged to antagonize NAFLD and SUCNR1-dependent liver inflammation.