Hypoxia, mitochondrial dysfunction and synovial invasiveness in rheumatoid arthritis.
TL;DR: The reprogramming of hypoxia-mediated pathways in synovial cells, such as fibroblasts, dendritic cells, macrophages and T cells, is implicated in the pathogenesis of rheumatoid arthritis and other inflammatory conditions, and might therefore provide an opportunity for therapeutic intervention.
Abstract: Synovial proliferation, neovascularization and leukocyte extravasation transform the normally acellular synovium into an invasive tumour-like 'pannus'. The highly dysregulated architecture of the microvasculature creates a poor oxygen supply to the synovium, which, along with the increased metabolic turnover of the expanding synovial pannus, creates a hypoxic microenvironment. Abnormal cellular metabolism and mitochondrial dysfunction thus ensue and, in turn, through the increased production of reactive oxygen species, actively induce inflammation. When exposed to hypoxia in the inflamed joint, immune-inflammatory cells show adaptive survival reactions by activating key proinflammatory signalling pathways, including those mediated by hypoxia-inducible factor-1α (HIF-1α), nuclear factor κB (NF-κB), Janus kinase-signal transducer and activator of transcription (JAK-STAT) and Notch, which contribute to synovial invasiveness. The reprogramming of hypoxia-mediated pathways in synovial cells, such as fibroblasts, dendritic cells, macrophages and T cells, is implicated in the pathogenesis of rheumatoid arthritis and other inflammatory conditions, and might therefore provide an opportunity for therapeutic intervention.
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TL;DR: The therapeutic potential of MFC-MSNs that simultaneously generate O2 and scavenge ROS, subsequently driving inflammatory macrophages to the anti-inflammatory subtype for RA treatment are highlighted.
Abstract: Poor O2 supply to the infiltrated immune cells in the joint synovium of rheumatoid arthritis (RA) up-regulates hypoxia-inducible factor (HIF-1α) expression and induces reactive oxygen species (ROS) generation, both of which exacerbate synovial inflammation. Synovial inflammation in RA can be resolved by eliminating pro-inflammatory M1 macrophages and inducing anti-inflammatory M2 macrophages. Because hypoxia and ROS in the RA synovium play a crucial role in the induction of M1 macrophages and reduction of M2 macrophages, herein, we develop manganese ferrite and ceria nanoparticle-anchored mesoporous silica nanoparticles (MFC-MSNs) that can synergistically scavenge ROS and produce O2 for reducing M1 macrophage levels and inducing M2 macrophages for RA treatment. MFC-MSNs exhibit a synergistic effect on O2 generation and ROS scavenging that is attributed to the complementary reaction of ceria nanoparticles (NPs) that can scavenge intermediate hydroxyl radicals generated by manganese ferrite NPs in the proce...
276 citations
TL;DR: It is shown that fibroblast-like synoviocytes in rheumatoid arthritis differ from healthy synovial fibroblasts, not only in their marker expression, proto-oncogene expression, or their epigenetic changes, but also in their intracellular metabolism.
Abstract: An increasing number of studies show how changes in intracellular metabolic pathways alter tumor and immune cell function. However, little information about metabolic changes in other cell types, including synovial fibroblasts, is available. In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) are the most common cell type at the pannus–cartilage junction and contribute to joint destruction through their production of cytokines, chemokines, and matrix-degrading molecules and by migrating and invading joint cartilage. In this review, we show that these cells differ from healthy synovial fibroblasts, not only in their marker expression, proto-oncogene expression, or their epigenetic changes, but also in their intracellular metabolism. These metabolic changes must occur due to the stressful microenvironment of inflamed tissues, where concentrations of crucial nutrients such as glucose, glutamine, and oxygen are spatially and temporally heterogeneous. In addition, these metabolic changes will increase metabolite exchange between fibroblast and other synovial cells, which can potentially be activated. Glucose and phospholipid metabolism as well as bioactive lipids, including sphingosine-1-phosphate and lysophosphatidic acid, among others, are involved in FLS activation. These metabolic changes likely contribute to FLS involvement in aspects of immune response initiation or abnormal immune responses and strongly contribute to joint destruction.
266 citations
TL;DR: It is not yet known whether metabolic change is a consequence of disease or whether primary changes to cellular metabolism might underlie or contribute to the pathogenesis of early‐stage disease.
Abstract: Metabolomic studies of body fluids show that immune-mediated inflammatory diseases such as rheumatoid arthritis (RA) are associated with metabolic disruption. This is likely to reflect the increased bioenergetic and biosynthetic demands of sustained inflammation and changes in nutrient and oxygen availability in damaged tissue. The synovial membrane lining layer is the principal site of inflammation in RA. Here, the resident cells are fibroblast-like synoviocytes (FLS) and synovial tissue macrophages, which are transformed toward overproduction of enzymes that degrade cartilage and bone and cytokines that promote immune cell infiltration. Recent studies have shown metabolic changes in both FLS and macrophages from RA patients, and these may be therapeutically targetable. However, because the origins and subset-specific functions of synoviocytes are poorly understood, and the signaling modules that control metabolic deviation in RA synovial cells are yet to be explored, significant additional research is needed to translate these findings to clinical application. Furthermore, in many inflamed tissues, different cell types can forge metabolic collaborations through solute carriers in their membranes to meet a high demand for energy or biomolecules. Such relationships are likely to exist in the synovium and have not been studied. Finally, it is not yet known whether metabolic change is a consequence of disease or whether primary changes to cellular metabolism might underlie or contribute to the pathogenesis of early-stage disease. In this review article, we collate what is known about metabolism in synovial tissue cells and highlight future directions of research in this area.
189 citations
Cites background from "Hypoxia, mitochondrial dysfunction ..."
...(PDGF), which are associated with RA and related inflammatory conditions (58,61)....
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...Additional in vitro studies indicated an increased number of mtDNA mutations and ROS levels in RA FLS compared with OA FLS (63), correlating with elevated matrix metalloproteinase expression and an invasive phenotype in RA (61,64)....
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TL;DR: The metabolic challenges faced byimmune cells in states of homeostasis and inflammation are outlined, as well as the variety of metabolic configurations utilized by immune cells during differentiation and activation.
Abstract: Immune cells constantly patrol the body via the bloodstream and migrate into multiple tissues where they face variable and sometimes demanding environmental conditions. Nutrient and oxygen availability can vary during homeostasis, and especially during the course of an immune response, creating a demand for immune cells that are highly metabolically dynamic. As an evolutionary response, immune cells have developed different metabolic programmes to supply them with cellular energy and biomolecules, enabling them to cope with changing and challenging metabolic conditions. In the past 5 years, it has become clear that cellular metabolism affects immune cell function and differentiation, and that disease-specific metabolic configurations might provide an explanation for the dysfunctional immune responses seen in rheumatic diseases. This Review outlines the metabolic challenges faced by immune cells in states of homeostasis and inflammation, as well as the variety of metabolic configurations utilized by immune cells during differentiation and activation. Changes in cellular metabolism that contribute towards the dysfunctional immune responses seen in rheumatic diseases are also briefly discussed.
183 citations
TL;DR: This work declares the first example of using bio-active nanoparticles for RA treatment without loading any drugs, and highlights the potential of FA-AgNPs for targeted RA therapy via simultaneous M1 macrophage apoptosis and M1-to-M2 macrophages re-polarization.
174 citations
References
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TL;DR: It is indicated that the interaction between HIF-1 and pVHL is iron dependent, and that it is necessary for the oxygen-dependent degradation of HIF α-subunits, which may underlie the angiogenic phenotype of VHL-associated tumours.
Abstract: Hypoxia-inducible factor-1 (HIF-1) has a key role in cellular responses to hypoxia, including the regulation of genes involved in energy metabolism, angiogenesis and apoptosis. The alpha subunits of HIF are rapidly degraded by the proteasome under normal conditions, but are stabilized by hypoxia. Cobaltous ions or iron chelators mimic hypoxia, indicating that the stimuli may interact through effects on a ferroprotein oxygen sensor. Here we demonstrate a critical role for the von Hippel-Lindau (VHL) tumour suppressor gene product pVHL in HIF-1 regulation. In VHL-defective cells, HIF alpha-subunits are constitutively stabilized and HIF-1 is activated. Re-expression of pVHL restored oxygen-dependent instability. pVHL and HIF alpha-subunits co-immunoprecipitate, and pVHL is present in the hypoxic HIF-1 DNA-binding complex. In cells exposed to iron chelation or cobaltous ions, HIF-1 is dissociated from pVHL. These findings indicate that the interaction between HIF-1 and pVHL is iron dependent, and that it is necessary for the oxygen-dependent degradation of HIF alpha-subunits. Thus, constitutive HIF-1 activation may underlie the angiogenic phenotype of VHL-associated tumours. The pVHL/HIF-1 interaction provides a new focus for understanding cellular oxygen sensing.
4,845 citations
TL;DR: Findings provide a basis for understanding how inhibition of IFN-γ signaling enhances development of pathogenic TH-17 effector cells that can exacerbate autoimmunity.
Abstract: CD4(+) T cells producing interleukin 17 (IL-17) are associated with autoimmunity, although the precise mechanisms that control their development are undefined. Here we present data that challenge the idea of a shared developmental pathway with T helper type 1 (T(H)1) or T(H)2 lineages and instead favor the idea of a distinct effector lineage we call 'T(H)-17'. The development of T(H)-17 cells from naive precursor cells was potently inhibited by interferon-gamma (IFN-gamma) and IL-4, whereas committed T(H)-17 cells were resistant to suppression by T(H)1 or T(H)2 cytokines. In the absence of IFN-gamma and IL-4, IL-23 induced naive precursor cells to differentiate into T(H)-17 cells independently of the transcription factors STAT1, T-bet, STAT4 and STAT6. These findings provide a basis for understanding how inhibition of IFN-gamma signaling enhances development of pathogenic T(H)-17 effector cells that can exacerbate autoimmunity.
4,616 citations
TL;DR: It is shown that mitophagy/autophagy blockade leads to the accumulation of damaged, ROS-generating mitochondria, and this in turn activates the NLRP3 inflammasome, and may explain the frequent association of mitochondrial damage with inflammatory diseases.
Abstract: An inflammatory response initiated by the NLRP3 inflammasome is triggered by a variety of situations of host 'danger', including infection and metabolic dysregulation. Previous studies suggested that NLRP3 inflammasome activity is negatively regulated by autophagy and positively regulated by reactive oxygen species (ROS) derived from an uncharacterized organelle. Here we show that mitophagy/autophagy blockade leads to the accumulation of damaged, ROS-generating mitochondria, and this in turn activates the NLRP3 inflammasome. Resting NLRP3 localizes to endoplasmic reticulum structures, whereas on inflammasome activation both NLRP3 and its adaptor ASC redistribute to the perinuclear space where they co-localize with endoplasmic reticulum and mitochondria organelle clusters. Notably, both ROS generation and inflammasome activation are suppressed when mitochondrial activity is dysregulated by inhibition of the voltage-dependent anion channel. This indicates that NLRP3 inflammasome senses mitochondrial dysfunction and may explain the frequent association of mitochondrial damage with inflammatory diseases.
3,985 citations
TL;DR: HIF plays a central role in the transcriptional response to changes in oxygen availability and is modulated by FIH1-mediated asparagine hydroxylation, and HIF-modulatory drugs are now being developed for diverse diseases.
2,623 citations
TL;DR: This study suggests that autophagic proteins regulate NALP3-dependent inflammation by preserving mitochondria integrity and cytosolic translocation of mitochondrial DNA in response to lipopolysaccharide and ATP in macrophages.
Abstract: Autophagy, a cellular process for organelle and protein turnover, regulates innate immune responses. Here we demonstrate that depletion of the autophagic proteins LC3B and beclin 1 enhanced the activation of caspase-1 and secretion of interleukin 1β (IL-1β) and IL-18. Depletion of autophagic proteins promoted the accumulation of dysfunctional mitochondria and cytosolic translocation of mitochondrial DNA (mtDNA) in response to lipopolysaccharide (LPS) and ATP in macrophages. Release of mtDNA into the cytosol depended on the NALP3 inflammasome and mitochondrial reactive oxygen species (ROS). Cytosolic mtDNA contributed to the secretion of IL-1β and IL-18 in response to LPS and ATP. LC3B-deficient mice produced more caspase-1-dependent cytokines in two sepsis models and were susceptible to LPS-induced mortality. Our study suggests that autophagic proteins regulate NALP3-dependent inflammation by preserving mitochondrial integrity.
2,352 citations