Mitochondria at the interface between danger signaling and metabolism: role of unfolded protein responses in chronic inflammation

The emerging role of oxidative stress in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic immune-mediated condition that affects the digestive system and includes Crohn's disease (CD) and ulcerative colitis (UC). Although the exact etiology of IBD remains uncertain, dysfunctional immunoregulation of the gut is believed to be the main culprit. Amongst the immunoregulatory factors, reactive oxygen species (ROS) and reactive nitrogen species (RNS), components of the oxidative stress event, are produced at abnormally high levels in IBD. Their destructive effects may contribute to the disease's initiation and propagation, as they damage the gut lining and activate inflammatory signaling pathways, further exacerbating the inflammation. Oxidative stress markers, such as malondialdehyde (MDA), 8-hydroxy-2'-deoxyguanosine (8-OHdG), and serum-free thiols (R-SH), can be measured in the blood and stool of patients with IBD. These markers are elevated in patients with IBD, and their levels correlate with the severity of the disease. Thus, oxidative stress markers can be used not only in IBD diagnosis but also in monitoring the response to treatment. It can also be targeted in IBD treatment through the use of antioxidants, including vitamin C, vitamin E, glutathione, and N-acetylcysteine. In this review, we summarize the role of oxidative stress in the pathophysiology of IBD, its diagnostic targets, and the potential application of antioxidant therapies to manage and treat IBD.

Role of mitochondria in pathogenesis and therapy of renal fibrosis

Renal fibrosis, specifically tubulointerstitial fibrosis, represents the predominant pathological consequence observed in the context of progressive chronic kidney conditions. The pathogenesis of renal fibrosis encompasses a multifaceted interplay of mechanisms, including but not limited to interstitial fibroblast proliferation, activation, augmented production of extracellular matrix (ECM) components, and impaired ECM degradation. Notably, mitochondria, the intracellular organelles responsible for orchestrating biological oxidation processes in mammalian cells, assume a pivotal role within this intricate milieu. Mitochondrial dysfunction, when manifest, can incite a cascade of events, including inflammatory responses, perturbed mitochondrial autophagy, and associated processes, ultimately culminating in the genesis of renal fibrosis. This comprehensive review endeavors to furnish an exegesis of mitochondrial pathophysiology and biogenesis, elucidating the precise mechanisms through which mitochondrial aberrations contribute to the onset and progression of renal fibrosis. We explored how mitochondrial dysfunction, mitochondrial cytopathy and mitochondrial autophagy mediate ECM deposition and renal fibrosis from a multicellular perspective of mesangial cells, endothelial cells, podocytes, macrophages and fibroblasts. Furthermore, it succinctly encapsulates the most recent advancements in the realm of mitochondrial-targeted therapeutic strategies aimed at mitigating renal fibrosis.

The intestinal epithelial-macrophage-crypt stem cell axis plays a crucial role in regulating and maintaining intestinal homeostasis

The intestinal tract plays a vital role in both digestion and immunity, making its equilibrium crucial for overall health. This equilibrium relies on the dynamic interplay among intestinal epithelial cells, macrophages, and crypt stem cells. Intestinal epithelial cells play a pivotal role in protecting and regulating the gut. They form vital barriers, modulate immune responses, and engage in pathogen defense and cytokine secretion. Moreover, they supervise the regulation of intestinal stem cells. Macrophages, serving as immune cells, actively influence the immune response through the phagocytosis of pathogens and the release of cytokines. They also contribute to regulating intestinal stem cells. Stem cells, known for their self-renewal and differentiation abilities, play a vital role in repairing damaged intestinal epithelium and maintaining homeostasis. Although research has primarily concentrated on the connections between epithelial and stem cells, interactions with macrophages have been less explored. This review aims to fill this gap by exploring the roles of the intestinal epithelial-macrophage-crypt stem cell axis in maintaining intestinal balance. It seeks to unravel the intricate dynamics and regulatory mechanisms among these essential players. A comprehensive understanding of these cell types' functions and interactions promises insights into intestinal homeostasis regulation. Moreover, it holds potential for innovative approaches to manage conditions like radiation-induced intestinal injury, inflammatory bowel disease, and related diseases.

Investigation of Cerebral Mitochondrial Injury in a Porcine Survivor Model of Carbon Monoxide Poisoning

INTRODUCTION

Carbon monoxide (CO) is a colorless and odorless gas that is a leading cause of environmental poisoning in the USA with substantial mortality and morbidity. The mechanism of CO poisoning is complex and includes hypoxia, inflammation, and leukocyte sequestration in brain microvessel segments leading to increased reactive oxygen species. Another important pathway is the effects of CO on the mitochondria, specifically at cytochrome c oxidase, also known as Complex IV (CIV). One of the glaring gaps is the lack of rigorous experimental models that may recapitulate survivors of acute CO poisoning in the early phase. The primary objective of this preliminary study is to use our advanced swine platform of acute CO poisoning to develop a clinically relevant survivor model to perform behavioral assessment and MRI imaging that will allow future development of biomarkers and therapeutics.

METHODS

Four swine (10 kg) were divided into two groups: control (n = 2) and CO (n = 2). The CO group received CO at 2000 ppm for over 120 min followed by 30 min of re-oxygenation at room air for one swine and 150 min followed by 30 min of re-oxygenation for another swine. The two swine in the sham group received room air for 150 min. Cerebral microdialysis was performed to obtain semi real-time measurements of cerebral metabolic status. Following exposures, all surviving animals were observed for a 24-h period with neurobehavioral assessment and imaging. At the end of the 24-h period, fresh brain tissue (cortical and hippocampal) was immediately harvested to measure mitochondrial respiration.

RESULTS

While a preliminary ongoing study, animals in the CO group showed alterations in cerebral metabolism and cellular function in the acute exposure phase with possible sustained mitochondrial changes 24 h after the CO exposure ended.

CONCLUSIONS

This preliminary research further establishes a large animal swine model investigating survivors of CO poisoning to measure translational metrics relevant to clinical medicine that includes a basic neurobehavioral assessment and post exposure cellular measures.

Mitochondrial dysfunction in the pathogenesis of acute pancreatitis

The mechanism of cell damage during acute pancreatitis (AP) has not been fully elucidated, and there is still a lack of specific or effective treatments. Increasing evidence has implicated mitochondrial dysfunction as a key event in the pathophysiology of AP. Mitochondrial dysfunction is closely related to calcium (Ca2+) overload, intracellular adenosine triphosphate depletion, mitochondrial permeability transition pore openings, loss of mitochondrial membrane potential, mitophagy damage and inflammatory responses. Mitochondrial dysfunction is an early triggering event in the initiation and development of AP, and this organelle damage may precede the release of inflammatory cytokines, intracellular trypsin activation and vacuole formation of pancreatic acinar cells. This review provides further insight into the role of mitochondria in both physiological and pathophysiological aspects of AP, aiming to improve our understanding of the underlying mechanism which may lead to the development of therapeutic and preventive strategies for AP.

Exploring the potential function of trace elements in human health: a therapeutic perspective

A trace element, known as a minor element, is a chemical element whose concentration is very low. They are divided into essential and non-essential classes. Numerous physiological and metabolic processes in both plants and animals require essential trace elements. These essential trace elements are so directly related to the metabolic and physiologic processes of the organism that either their excess or deficiency can result in severe bodily malfunction or, in the worst situations, death. Elements can be found in nature in various forms and are essential for the body to carry out its varied functions. Trace elements are crucial for biological, chemical, and molecular cell activity. Nutritional deficits can lead to weakened immunity, increased susceptibility to oral and systemic infections, delayed physical and mental development, and lower productivity. Trace element enzymes are involved in many biological and chemical processes. These compounds act as co-factors for a number of enzymes and serve as centers for stabilizing the structures of proteins and enzymes, allowing them to mediate crucial biological processes. Some trace elements control vital biological processes by attaching to molecules on the cell membrane's receptor site or altering the structure of the membrane to prevent specific molecules from entering the cell. Some trace elements are engaged in redox reactions. Trace elements have two purposes. They are required for the regular stability of cellular structures, but when lacking, they might activate alternate routes and induce disorders. Therefore, thoroughly understanding these trace elements is essential for maintaining optimal health and preventing disease.

Saponins From Platycodon grandiflorum Reduces Cisplatin-Induced Intestinal Toxicity in Mice through Endoplasmic Reticulum Stress-Activated Apoptosis

Saponins from the roots of Platycodon grandiflorum, an edible medicinal plant, have shown a wide range of beneficial effects on various biological processes. In this study, an animal model was established by a single intraperitoneal injection of cisplatin (20[Formula: see text]mg/kg) for evaluating the protective effects of saponins from the roots of P. grandiflorum (PGS, 15[Formula: see text]mg/kg and 30[Formula: see text]mg/kg) in mice. The results indicated that PGS treatment for 10 days restored the destroyed intestinal mucosal oxidative system, and the loosened junctions of small intestinal villi was significantly improved. In addition, a significant mitigation of apoptotic effects deteriorated by cisplatin exposure in small intestinal villi was observed by immunohischemical staining. Also, western blot showed that PGS could effectively prevent endoplasmic reticulum (ER) stress-induced apoptosis caused by cisplatin in mice by restoring the activity of PERK (an ER kinase)-eIF2[Formula: see text]-ATF4 signal transduction pathway. Furthermore, molecular docking results of main saponins in PGS suggested a better binding ability with target proteins. In summary, the present work revealed the underlying protective mechanisms of PGS on intestinal injury induced by cisplatin in mice.

Mitochondria and Inflammatory Bowel Diseases: Toward a Stratified Therapeutic Intervention

Mitochondria serve numerous critical cellular functions, rapidly responding to extracellular stimuli and cellular demands while dynamically communicating with other organelles. Mitochondrial function in the gastrointestinal epithelium plays a critical role in maintaining intestinal health. Emerging studies implicate the involvement of mitochondrial dysfunction in inflammatory bowel disease (IBD). This review presents mitochondrial metabolism, function, and quality control that converge in intestinal epithelial stemness, differentiation programs, barrier integrity, and innate immunity to influence intestinal inflammation. Intestinal and disease characteristics that set the stage for mitochondrial dysfunction being a key factor in IBD, and in turn, pathogenic mitochondrial mechanisms influencing and potentiating the development of IBD, are discussed. These findings establish the basis for potential mitochondrial-targeted interventions for IBD therapy. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Mitochondrial dysfunction in inflammatory bowel disease alters intestinal epithelial metabolism of hepatic acylcarnitines

As the interface between the gut microbiota and the mucosal immune system, there has been great interest in the maintenance of colonic epithelial integrity through mitochondrial oxidation of butyrate, a short-chain fatty acid produced by the gut microbiota. Herein, we showed that the intestinal epithelium could also oxidize long-chain fatty acids, and that luminally delivered acylcarnitines in bile could be consumed via apical absorption by the intestinal epithelium, resulting in mitochondrial oxidation. Finally, intestinal inflammation led to mitochondrial dysfunction in the apical domain of the surface epithelium that may reduce the consumption of fatty acids, contributing to higher concentrations of fecal acylcarnitines in murine Citrobacter rodentium-induced colitis and human inflammatory bowel disease. These results emphasized the importance of both the gut microbiota and the liver in the delivery of energy substrates for mitochondrial metabolism by the intestinal epithelium.

Targeting Mitochondrial Damage as a Therapeutic for Ileal Crohn's Disease

Paneth cell defects in Crohn's disease (CD) patients (called the Type I phenotype) are associated with worse clinical outcomes. Recent studies have implicated mitochondrial dysfunction in Paneth cells as a mediator of ileitis in mice. We hypothesized that CD Paneth cells exhibit impaired mitochondrial health and that mitochondrial-targeted therapeutics may provide a novel strategy for ileal CD. Terminal ileal mucosal biopsies from adult CD and non-IBD patients were characterized for Paneth cell phenotyping and mitochondrial damage. To demonstrate the response of mitochondrial-targeted therapeutics in CD, biopsies were treated with vehicle or Mito-Tempo, a mitochondrial-targeted antioxidant, and RNA transcriptome was analyzed. During active CD inflammation, the epithelium exhibited mitochondrial damage evident in Paneth cells, goblet cells, and enterocytes. Independent of inflammation, Paneth cells in Type I CD patients exhibited mitochondrial damage. Mito-Tempo normalized the expression of interleukin (IL)-17/IL-23, lipid metabolism, and apoptotic gene signatures in CD patients to non-IBD levels. When stratified by Paneth cell phenotype, the global tissue response to Mito-Tempo in Type I patients was associated with innate immune, lipid metabolism, and G protein-coupled receptor (GPCR) gene signatures. Targeting impaired mitochondria as an underlying contributor to inflammation provides a novel treatment approach for CD.

Mechanism of deoxynivalenol mediated gastrointestinal toxicity: Insights from mitochondrial dysfunction

Deoxynivalenol (DON) is a mycotoxin predominantly produced by Fusarium genus, and widely contaminates cereals and associated products all over the world. The intestinal toxicity of DON is well established. However, intestinal homeostasis involves mitochondria, which has rarely been considered in the context of DON exposure. We summarize the recent knowledge on mitochondria as a key player in maintaining intestinal homeostasis based on their functions in cellular energy metabolism, redox homeostasis, apoptosis, intestinal immune responses, and orchestrated bidirectional cross-talk with gut microbe. In addition, we discuss the pivotal roles of mitochondrial dysfunction in the intestinal toxicity of DON and highlight promising mitochondrial-targeted therapeutics for DON-induced intestinal injury. Recent studies support that the intestinal toxicity of DON is attributed to mitochondrial dysfunction as a critical factor. Mitochondrial dysfunction characterized by failure in respiratory capacities and ROS overproduction has been demonstrated in intestinal cells exposed to DON. Perturbation of mitochondrial respiration leading to ROS accumulation is implicated in the early initiation of apoptosis. DON-induced intestinal inflammatory response is tightly linked to the mitochondrial ROS, whereas immunosuppression is intimately associated with mitophagy inhibition. DON perturbs the orchestrated bidirectional cross-talk between gut microbe and host mitochondria, which may be involved in DON-induced intestinal toxicity.

Long-Lived Species of Bivalves Exhibit Low MT-DNA Substitution Rates

Bivalves represent valuable taxonomic group for aging studies given their wide variation in longevity (from 1–2 to >500 years). It is well known that aging is associated to the maintenance of Reactive Oxygen Species homeostasis and that mitochondria phenotype and genotype dysfunctions accumulation is a hallmark of these processes. Previous studies have shown that mitochondrial DNA mutation rates are linked to lifespan in vertebrate species, but no study has explored this in invertebrates. To this end, we performed a Bayesian Phylogenetic Covariance model of evolution analysis using 12 mitochondrial protein-coding genes of 76 bivalve species. Three life history traits (maximum longevity, generation time and mean temperature tolerance) were tested against 1) synonymous substitution rates (dS), 2) conservative amino acid replacement rates (Kc) and 3) ratios of radical over conservative amino acid replacement rates (Kr/Kc). Our results confirm the already known correlation between longevity and generation time and show, for the first time in an invertebrate class, a significant negative correlation between dS and longevity. This correlation was not as strong when generation time and mean temperature tolerance variations were also considered in our model (marginal correlation), suggesting a confounding effect of these traits on the relationship between longevity and mtDNA substitution rate. By confirming the negative correlation between dS and longevity previously documented in birds and mammals, our results provide support for a general pattern in substitution rates.

Mitochondrial Metabolism in the Intestinal Stem Cell Niche-Sensing and Signaling in Health and Disease

Mitochondrial metabolism, dynamics, and stress responses in the intestinal stem cell niche play a pivotal role in regulating intestinal epithelial cell homeostasis, including self-renewal and differentiation. In addition, mitochondria are increasingly recognized for their involvement in sensing the metabolic environment and their capability of integrating host and microbial-derived signals. Gastrointestinal diseases such as inflammatory bowel diseases and colorectal cancer are characterized by alterations of intestinal stemness, the microbial milieu, and mitochondrial metabolism. Thus, mitochondrial function emerges at the interface of determining health and disease, and failure to adapt mitochondrial function to environmental cues potentially results in aberrant tissue responses. A mechanistic understanding of the underlying role of mitochondrial fitness in intestinal pathologies is still in its infancy, and therapies targeting mitochondrial (dys)function are currently lacking. This review discusses mitochondrial signaling and metabolism in intestinal stem cells and Paneth cells as critical junction translating host- and microbe-derived signals into epithelial responses. Consequently, we propose mitochondrial fitness as a hallmark for intestinal epithelial cell plasticity, determining the regenerative capacity of the epithelium.

Mitochondrial impairment drives intestinal stem cell transition into dysfunctional Paneth cells predicting Crohn's disease recurrence

OBJECTIVE

Reduced Paneth cell (PC) numbers are observed in inflammatory bowel diseases and impaired PC function contributes to the ileal pathogenesis of Crohn's disease (CD). PCs reside in proximity to Lgr5⁺ intestinal stem cells (ISC) and mitochondria are critical for ISC-renewal and differentiation. Here, we characterise ISC and PC appearance under inflammatory conditions and describe the role of mitochondrial function for ISC niche-maintenance.

DESIGN

Ileal tissue samples from patients with CD, mouse models for mitochondrial dysfunction (Hsp60^Δ/ΔISC) and CD-like ileitis (TNF^ΔARE), and intestinal organoids were used to characterise PCs and ISCs in relation to mitochondrial function.

RESULTS

In patients with CD and TNF^ΔARE mice, inflammation correlated with reduced numbers of Lysozyme-positive granules in PCs and decreased Lgr5 expression in crypt regions. Disease-associated changes in PC and ISC appearance persisted in non-inflamed tissue regions of patients with CD and predicted the risk of disease recurrence after surgical resection. ISC-specific deletion of Hsp60 and inhibition of mitochondrial respiration linked mitochondrial function to the aberrant PC phenotype. Consistent with reduced stemness in vivo, crypts from inflamed TNF^ΔARE mice fail to grow into organoids ex vivo. Dichloroacetate-mediated inhibition of glycolysis, forcing cells to shift to mitochondrial respiration, improved ISC niche function and rescued the ability of TNF^ΔARE mice-derived crypts to form organoids.

CONCLUSION

We provide evidence that inflammation-associated mitochondrial dysfunction in the intestinal epithelium triggers a metabolic imbalance, causing reduced stemness and acquisition of a dysfunctional PC phenotype. Blocking glycolysis might be a novel drug target to antagonise PC dysfunction in the pathogenesis of CD.

Mitochondrial dysfunction during loss of prohibitin 1 triggers Paneth cell defects and ileitis

OBJECTIVE

Although perturbations in mitochondrial function and structure have been described in the intestinal epithelium of Crohn's disease and ulcerative colitis patients, the role of epithelial mitochondrial stress in the pathophysiology of inflammatory bowel diseases (IBD) is not well elucidated. Prohibitin 1 (PHB1), a major component protein of the inner mitochondrial membrane crucial for optimal respiratory chain assembly and function, is decreased during IBD.

DESIGN

Male and female mice with inducible intestinal epithelial cell deletion of Phb1 (Phb1^iΔIEC ) or Paneth cell-specific deletion of Phb1 (Phb1^ΔPC ) and Phb1^fl/fl control mice were housed up to 20 weeks to characterise the impact of PHB1 deletion on intestinal homeostasis. To suppress mitochondrial reactive oxygen species, a mitochondrial-targeted antioxidant, Mito-Tempo, was administered. To examine epithelial cell-intrinsic responses, intestinal enteroids were generated from crypts of Phb1^iΔIEC or Phb1^ΔPC mice.

RESULTS

Phb1^iΔIEC mice exhibited spontaneous ileal inflammation that was preceded by mitochondrial dysfunction in all IECs and early abnormalities in Paneth cells. Mito-Tempo ameliorated mitochondrial dysfunction, Paneth cell abnormalities and ileitis in Phb1^iΔIEC ileum. Deletion of Phb1 specifically in Paneth cells (Phb1^ΔPC ) was sufficient to cause ileitis. Intestinal enteroids generated from crypts of Phb1^iΔIEC or Phb1^ΔPC mice exhibited decreased viability and Paneth cell defects that were improved by Mito-Tempo.

CONCLUSION

Our results identify Paneth cells as highly susceptible to mitochondrial dysfunction and central to the pathogenesis of ileitis, with translational implications for the subset of Crohn's disease patients exhibiting Paneth cell defects.

Intestinal Immune Homeostasis and Inflammatory Bowel Disease: A Perspective on Intracellular Response Mechanisms

The pathogenesis of inflammatory bowel disease (IBD) involves perturbation of intestinal immune homeostasis in genetically susceptible individuals. A mutual interplay between intestinal epithelial cells (IECs) and gut resident microbes maintains a homeostatic environment across the gut. An idiopathic gastrointestinal (GI) complication triggers aberrant physiological stress in the epithelium and peripheral myeloid cells, leading to a chronic inflammatory condition. Indeed, events in the endoplasmic reticulum (ER) and mitochondria contribute to orchestrating intracellular mechanisms such as the unfolded protein response (UPR) and oxidative stress, respectively, to resolve aberrant cellular stress. This review highlights the signaling cascades encrypted within ER and mitochondria in IECs and/or myeloid cells to dissipate chronic stress in maintaining intestinal homeostasis.

The influence of mitochondrial-directed regulation of Wnt signaling on tumorigenesis

Mitochondria are dynamic organelles that play a key role in integrating cellular signaling. Mitochondrial alterations are evident in all stages of tumorigenesis and targeting mitochondrial pathways has emerged as an anticancer therapeutic strategy. The Wnt-signaling pathway regulates many fundamental cellular functions such as proliferation, survival, migration, stem-cell maintenance, and mitochondrial metabolism and dynamics. Emerging evidence demonstrates that mitochondrial-induced regulation of Wnt signaling provides an additional mechanism to influence cell-fate decisions. Crosstalk between mitochondria and Wnt signaling presents a feedforward loop in which Wnt activation regulates mitochondrial function that, in turn, drives Wnt signaling. In this mini-review, we will discuss the recent evidence revealing the mitochondrial control of Wnt signaling and its implications for tumorigenesis and anticancer therapeutic targeting.

New Insights into the Role of Trace Elements in IBD

Micronutrient deficiencies are common in inflammatory bowel disease and have clinical impact, being both a sign of complicated disease and a cause of morbidity. The involved systemic inflammatory response is responsible for altering the concentration of a wide range of trace elements in the serum, including zinc and selenium. This review summarizes recent advances and evidence-based knowledge regarding the impact of selenium and zinc on oxidative stress and microbiota changes in IBD patients. Getting new insight into the impact of malnutrition, particularly on the micronutrients' impact on the development, composition, and metabolism of microbiota, as well as the influence of oxidative stress and the mucosal immune response, could help in implementing new management strategies for IBD patients, with focus on a more integrated approach.

Mitochondrial function - gatekeeper of intestinal epithelial cell homeostasis

The intestinal epithelium is a multicellular interface in close proximity to a dense microbial milieu that is completely renewed every 3-5 days. Pluripotent stem cells reside at the crypt, giving rise to transient amplifying cells that go through continuous steps of proliferation, differentiation and finally anoikis (a form of programmed cell death) while migrating upwards to the villus tip. During these cellular transitions, intestinal epithelial cells (IECs) possess distinct metabolic identities reflected by changes in mitochondrial activity. Mitochondrial function emerges as a key player in cell fate decisions and in coordinating cellular metabolism, immunity, stress responses and apoptosis. Mediators of mitochondrial signalling include molecules such as ATP and reactive oxygen species and interrelate with pathways such as the mitochondrial unfolded protein response (MT-UPR) and AMP kinase signalling, in turn affecting cell cycle progression and stemness. Alterations in mitochondrial function and MT-UPR activation are integral aspects of pathologies, including IBD and cancer. Mitochondrial signalling and concomitant changes in metabolism contribute to intestinal homeostasis and regulate IEC dedifferentiation-differentiation programmes in the context of diseases, suggesting that mitochondrial function as a cellular checkpoint critically contributes to disease outcome. This Review highlights mitochondrial function and MT-UPR signalling in epithelial cell stemness, differentiation and lineage commitment and illustrates mitochondrial function in intestinal diseases.

Reduced intestinal epithelial mitochondrial function enhances in vitro interleukin-8 production in response to commensal Escherichia coli

Uncoupling of oxidative phosphorylation in epithelial mitochondria results in decreased epithelial barrier function as characterized by increased internalization of non-invasive Escherichia coli and their translocation across the epithelium. We hypothesized that the increased burden of intracellular commensal bacteria would activate the enterocyte, with the potential to promote inflammation. Treatment of human colon-derived epithelial cell lines in vitro with dinitrophenol (DNP) and commensal E. coli (strains F18, HB101) provoked increased production of interleukin (IL-8), which was not observed with conditioned medium from the bacteria, lipopolysaccharide or inert beads. The IL-8 response was inhibited by co-treatment with cytochalasin-D (blocks F-actin rearrangement), chloroquine (blocks phagosome acidification) and a MyD88 inhibitor (blocks TLR signaling), consistent with TLR-signaling mediating IL-8 synthesis subsequent to bacterial internalization. Use of the mitochondria-targeted antioxidant, mitoTEMPO, or U0126 to block ERK1/2 MAPK signalling inhibited DNP+E. coli-evoked IL-8 production. Mutations in the NOD2 (the intracellular sensor of bacteria) or ATG16L1 (autophagy protein) genes are susceptibility traits for Crohn's, and epithelia lacking either protein displayed enhanced IL-8 production in comparison to wild-type cells when exposed to DNP + E coli. Thus, metabolic stress perturbs the normal epithelial-bacterial interaction resulting in increased IL-8 production due to uptake of bacteria into the enterocyte: this potentially pro-inflammatory event is enhanced in cells lacking NOD2 or ATG16L1 that favor increased survival of bacteria within the enterocyte. We speculate that by increasing epithelial permeability and IL-8 production, reduced mitochondria function in the enteric epithelium would contribute to the initiation, pathophysiology, and reactivation of inflammatory disease in the gut.

A novel role of endocan in alleviating LPS-induced acute lung injury

AIMS

Endotoxin induced acute lung injury (ALI) is a critical complication of some clinical illnesses. Endothelial cell dysfunction and excessive pro-inflammation cytokine release are pivotal to the injury of alveolar-capillary membrane which is the typical characteristic of endotoxic lung injury. As a potential marker of endothelial cells, endocan plays an important role in many endothelial-dependent pathophysiological diseases. We speculated that endocan have anti-inflammatory property in ALI. Here, we investigated the role of endocan in LPS-induced ALI.

MATERIALS AND METHODS

Mice were randomly divided into 4 groups. LPS were used to construct ALI mice model by aerosolization for 20 min. Endocan was intraperitoneal injected at 30 min before LPS exposure. Levels of TNF-α, IFN-γ, IL-1β, IL-6 and MPO activities were detected by indicated ELISA. Cell apoptotic rate was determined by Annexin V/PI kit, ROS level and MPTP were detected by DCFH-DA and JC-1 kit, respectively. Seahorse XF96 was applied to evaluate the alteration of OCR and ECAR. Western blot and qRT-PCR were used to detect indicated molecules.

KEY FINDINGS

Endocan effectively decreased TNF-α, IFN-γ, IL-1β, and IL-6 levels as well as relieved pulmonary epithelium cell apoptosis caused by LPS exposure. Endocan significantly reversed LPS induced UPR^mt and promoted cell metabolism reprogramming which were crucial for the protective characteristic of endocan in ALI mice model.

SIGNIFICANCE

The above findings suggested endocan could significantly suppress inflammatory response in ALI model through attenuating UPR^mt associated apoptosis and switch cellular bioenergetics, indicating endocan could be considered as a promising compound against LPS induced ALI.

ER-stress mobilization of death-associated protein kinase-1-dependent xenophagy counteracts mitochondria stress-induced epithelial barrier dysfunction

The gut microbiome contributes to inflammatory bowel disease (IBD), in which bacteria can be present within the epithelium. Epithelial barrier function is decreased in IBD, and dysfunctional epithelial mitochondria and endoplasmic reticulum (ER) stress have been individually associated with IBD. We therefore hypothesized that the combination of ER and mitochondrial stresses significantly disrupt epithelial barrier function. Here, we treated human colonic biopsies, epithelial colonoids, and epithelial cells with an uncoupler of oxidative phosphorylation, dinitrophenol (DNP), with or without the ER stressor tunicamycin and assessed epithelial barrier function by monitoring internalization and translocation of commensal bacteria. We also examined barrier function and colitis in mice exposed to dextran sodium sulfate (DSS) or DNP and co-treated with DAPK6, an inhibitor of death-associated protein kinase 1 (DAPK1). Contrary to our hypothesis, induction of ER stress (i.e. the unfolded protein response) protected against decreased barrier function caused by the disruption of mitochondrial function. ER stress did not prevent DNP-driven uptake of bacteria; rather, specific mobilization of the ATF6 arm of ER stress and recruitment of DAPK1 resulted in enhanced autophagic killing (xenophagy) of bacteria. Of note, epithelia with a Crohn's disease-susceptibility mutation in the autophagy gene ATG16L1 exhibited less xenophagy. Systemic delivery of the DAPK1 inhibitor DAPK6 increased bacterial translocation in DSS- or DNP-treated mice. We conclude that promoting ER stress-ATF6-DAPK1 signaling in transporting enterocytes counters the transcellular passage of bacteria evoked by dysfunctional mitochondria, thereby reducing the potential for metabolic stress to reactivate or perpetuate inflammation.

MDR1 deficiency impairs mitochondrial homeostasis and promotes intestinal inflammation

The multidrug resistance-1 (MDR1) gene encodes an ATP-dependent efflux transporter that is highly expressed in the colon. In mice, loss of MDR1 function results in colitis with similarities to human inflammatory bowel diseases (IBD). Here, we show that MDR1 has an unexpected protective role for the mitochondria where MDR1 deficiency results in mitochondrial dysfunction with increased mitochondrial reactive oxygen species (mROS) driving the development of colitis. Exogenous induction of mROS accelerates, while inhibition attenuates colitis in vivo; these effects are amplified in MDR1 deficiency. In human IBD, MDR1 is negatively correlated to SOD2 gene expression required for mROS detoxification. To provide direct evidential support, we deleted intestinal SOD2 gene in mice and showed an increased susceptibility to colitis. We exploited the genome-wide association data sets and found many (∼5%) of IBD susceptibility genes with direct roles in regulating mitochondria homeostasis. As MDR1 primarily protects against xenotoxins via its efflux function, our findings implicate a distinct mitochondrial toxin+genetic susceptibility interaction leading to mitochondrial dysfunction, a novel pathogenic mechanism that could offer many new therapeutic opportunities for IBD.

Mitochondrial function controls intestinal epithelial stemness and proliferation

Control of intestinal epithelial stemness is crucial for tissue homeostasis. Disturbances in epithelial function are implicated in inflammatory and neoplastic diseases of the gastrointestinal tract. Here we report that mitochondrial function plays a critical role in maintaining intestinal stemness and homeostasis. Using intestinal epithelial cell (IEC)-specific mouse models, we show that loss of HSP60, a mitochondrial chaperone, activates the mitochondrial unfolded protein response (MT-UPR) and results in mitochondrial dysfunction. HSP60-deficient crypts display loss of stemness and cell proliferation, accompanied by epithelial release of WNT10A and RSPO1. Sporadic failure of Cre-mediated Hsp60 deletion gives rise to hyperproliferative crypt foci originating from OLFM4⁺ stem cells. These effects are independent of the MT-UPR-associated transcription factor CHOP. In conclusion, compensatory hyperproliferation of HSP60⁺ escaper stem cells suggests paracrine release of WNT-related factors from HSP60-deficient, functionally impaired IEC to be pivotal in the control of the proliferative capacity of the stem cell niche.

It is unclear what role mitochondrial function plays in maintaining intestinal epithelial cell (IEC) homeostasis. Here, the authors deplete a mitochondrial chaperone, heat shock protein 60 (HSP60) in IEC and observe a loss of stemness and cell proliferation, and suggest this is accompanied by a compensatory release of WNT-related factors.

Edible ginger-derived nanoparticles: A novel therapeutic approach for the prevention and treatment of inflammatory bowel disease and colitis-associated cancer

There is a clinical need for new, more effective treatments for chronic and debilitating inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis. In this study, we characterized a specific population of nanoparticles derived from edible ginger (GDNPs 2) and demonstrated their efficient colon targeting following oral administration. GDNPs 2 had an average size of ∼230 nm and exhibited a negative zeta potential. These nanoparticles contained high levels of lipids, a few proteins, ∼125 microRNAs (miRNAs), and large amounts of ginger bioactive constituents (6-gingerol and 6-shogaol). We also demonstrated that GDNPs 2 were mainly taken up by intestinal epithelial cells (IECs) and macrophages, and were nontoxic. Using different mouse colitis models, we showed that GDNPs 2 reduced acute colitis, enhanced intestinal repair, and prevented chronic colitis and colitis-associated cancer (CAC). 2D-DIGE/MS analyses further identified molecular target candidates of GDNPs 2 involved in these mouse models. Oral administration of GDNPs 2 increased the survival and proliferation of IECs and reduced the pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β), and increased the anti-inflammatory cytokines (IL-10 and IL-22) in colitis models, suggesting that GDNPs 2 has the potential to attenuate damaging factors while promoting the healing effect. In conclusion, GDNPs 2, nanoparticles derived from edible ginger, represent a novel, natural delivery mechanism for improving IBD prevention and treatment with an added benefit of overcoming limitations such as potential toxicity and limited production scale that are common with synthetic nanoparticles.

Comorbidity between depression and inflammatory bowel disease explained by immune-inflammatory, oxidative, and nitrosative stress; tryptophan catabolite; and gut-brain pathways

The nature of depression has recently been reconceptualized, being conceived as the clinical expression of activated immune-inflammatory, oxidative, and nitrosative stress (IO&NS) pathways, including tryptophan catabolite (TRYCAT), autoimmune, and gut-brain pathways. IO&NS pathways are similarly integral to the pathogenesis of inflammatory bowel disease (IBD). The increased depression prevalence in IBD associates with a lower quality of life and increased morbidity in IBD, highlighting the role of depression in modulating the pathophysiology of IBD.This review covers data within such a wider conceptualization that better explains the heightened co-occurrence of IBD and depression. Common IO&NS underpinning between both disorders is evidenced by increased pro-inflammatory cytokine levels, eg, interleukin-1 (IL-1) and tumor necrosis factor-α, IL-6 trans-signalling; Th-1- and Th-17-like responses; neopterin and soluble IL-2 receptor levels; positive acute phase reactants (haptoglobin and C-reactive protein); lowered levels of negative acute phase reactants (albumin, transferrin, zinc) and anti-inflammatory cytokines (IL-10 and transforming growth factor-β); increased O&NS with damage to lipids, proteinsm and DNA; increased production of nitric oxide (NO) and inducible NO synthase; lowered plasma tryptophan but increased TRYCAT levels; autoimmune responses; and increased bacterial translocation. As such, heightened IO&NS processes in depression overlap with the biological underpinnings of IBD, potentially explaining their increased co-occurrence. This supports the perspective that there is a spectrum of IO&NS disorders that includes depression, both as an emergent comorbidity and as a contributor to IO&NS processes. Such a frame of reference has treatment implications for IBD when "comorbid" with depression.

An integrative analysis of gene expression and molecular interaction data to identify dys-regulated sub-networks in inflammatory bowel disease

Background

Inflammatory bowel disease (IBD) consists of two main disease-subtypes, Crohn’s disease (CD) and ulcerative colitis (UC); these subtypes share overlapping genetic and clinical features. Genome-wide microarray data enable unbiased documentation of alterations in gene expression that may be disease-specific. As genetic diseases are believed to be caused by genetic alterations affecting the function of signalling pathways, module-centric optimisation algorithms, whose aim is to identify sub-networks that are dys-regulated in disease, are emerging as promising approaches.

Results

In order to account for the topological structure of molecular interaction networks, we developed an optimisation algorithm that integrates databases of known molecular interactions with gene expression data; such integration enables identification of differentially regulated network modules. We verified the performance of our algorithm by testing it on simulated networks; we then applied the same method to study experimental data derived from microarray analysis of CD and UC biopsies and human interactome databases. This analysis allowed the extraction of dys-regulated subnetworks under different experimental conditions (inflamed and uninflamed tissues in CD and UC). Optimisation was performed to highlight differentially expressed network modules that may be common or specific to the disease subtype.

Conclusions

We show that the selected subnetworks include genes and pathways of known relevance for IBD; in particular, the solutions found highlight cross-talk among enriched pathways, mainly the JAK/STAT signalling pathway and the EGF receptor signalling pathway. In addition, integration of gene expression with molecular interaction data highlights nodes that, although not being differentially expressed, interact with differentially expressed nodes and are part of pathways that are relevant to IBD. The method proposed here may help identifying dys-regulated sub-networks that are common in different diseases and sub-networks whose dys-regulation is specific to a particular disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-016-0886-z) contains supplementary material, which is available to authorized users.

Flavaglines Ameliorate Experimental Colitis and Protect Against Intestinal Epithelial Cell Apoptosis and Mitochondrial Dysfunction

BACKGROUND

Flavaglines are a family of natural compounds shown to have anti-inflammatory and cytoprotective effects in neurons and cardiomyocytes. Flavaglines target prohibitins as ligands, which are scaffold proteins that regulate mitochondrial function, cell survival, and transcription. This study tested the therapeutic potential of flavaglines to promote intestinal epithelial cell homeostasis and to protect against a model of experimental colitis in which inflammation is driven by epithelial ulceration.

METHODS

Survival and homeostasis of Caco2-BBE and IEC-6 intestinal epithelial cell lines were measured during treatment with the flavaglines FL3 or FL37 alone and in combination with the proinflammatory cytokines tumor necrosis factor (TNF) α and interferon γ. Wild-type mice were intraperitoneally injected with 0.1 mg/kg FL3 or vehicle once daily for 4 days during dextran sodium sulfate-induced colitis to test the in vivo anti-inflammatory effect of FL3.

RESULTS

FL3 and FL37 increased basal Caco2-BBE and IEC-6 cell viability, decreased apoptosis, and decreased epithelial monolayer permeability. FL3 and FL37 inhibited TNFα- and interferon γ-induced nuclear factor kappa B and Cox2 expression, apoptosis, and increased permeability in Caco2-BBE cells. FL3 and FL37 protected against TNFα-induced mitochondrial superoxide generation by preserving respiratory chain complex I activity and prohibitin expression. p38-MAPK activation was essential for the protective effect of FL3 and FL37 on barrier permeability and mitochondrial-derived reactive oxygen species production during TNFα treatment. Mice administered FL3 during dextran sodium sulfate colitis exhibited increased colonic prohibitin expression and p38-MAPK activation, preserved barrier function, and less inflammation.

CONCLUSIONS

These results suggest that flavaglines exhibit therapeutic potential against colitis and preserve intestinal epithelial cell survival, mitochondrial function, and barrier integrity.

Mechanisms of Microbe-Host Interaction in Crohn's Disease: Dysbiosis vs. Pathobiont Selection

Crohn’s disease (CD) is a systemic chronic inflammatory condition mainly characterized by discontinuous transmural pathology of the gastrointestinal tract and frequent extraintestinal manifestations with intermittent episodes of remission and relapse. Genome-wide association studies identified a number of risk loci that, catalyzed by environmental triggers, result in the loss of tolerance toward commensal bacteria based on dysregulated innate effector functions and antimicrobial defense, leading to exacerbated adaptive immune responses responsible for chronic immune-mediated tissue damage. In this review, we discuss the inter-related role of changes in the intestinal microbiota, epithelial barrier integrity, and immune cell functions on the pathogenesis of CD, describing the current approaches available to investigate the molecular mechanisms underlying the disease. Substantial effort has been dedicated to define disease-associated changes in the intestinal microbiota (dysbiosis) and to link pathobionts to the etiology of inflammatory bowel diseases. A cogent definition of dysbiosis is lacking, as well as an agreement of whether pathobionts or complex shifts in the microbiota trigger inflammation in the host. Among the rarely available animal models, SAMP/Yit and TNF^deltaARE mice are the best known displaying a transmural CD-like phenotype. New hypothesis-driven mouse models, e.g., epithelial-specific Caspase8^−/−, ATG16L1^−/−, and XBP1^−/− mice, validate pathway-focused function of specific CD-associated risk genes highlighting the role of Paneth cells in antimicrobial defense. To study the causal role of bacteria in initiating inflammation in the host, the use of germ-free mouse models is indispensable. Unraveling the interactions of genes, immune cells and microbes constitute a criterion for the development of safe, reliable, and effective treatment options for CD.

Uncoupling lipid metabolism from inflammation through fatty acid binding protein-dependent expression of UCP2

Chronic inflammation in obese adipose tissue is linked to endoplasmic reticulum (ER) stress and systemic insulin resistance. Targeted deletion of the murine fatty acid binding protein (FABP4/aP2) uncouples obesity from inflammation although the mechanism underlying this finding has remained enigmatic. Here, we show that inhibition or deletion of FABP4/aP2 in macrophages results in increased intracellular free fatty acids (FFAs) and elevated expression of uncoupling protein 2 (UCP2) without concomitant increases in UCP1 or UCP3. Silencing of UCP2 mRNA in FABP4/aP2-deficient macrophages negated the protective effect of FABP loss and increased ER stress in response to palmitate or lipopolysaccharide (LPS). Pharmacologic inhibition of FABP4/aP2 with the FABP inhibitor HTS01037 also upregulated UCP2 and reduced expression of BiP, CHOP, and XBP-1s. Expression of native FABP4/aP2 (but not the non-fatty acid binding mutant R126Q) into FABP4/aP2 null cells reduced UCP2 expression, suggesting that the FABP-FFA equilibrium controls UCP2 expression. FABP4/aP2-deficient macrophages are resistant to LPS-induced mitochondrial dysfunction and exhibit decreased mitochondrial protein carbonylation and UCP2-dependent reduction in intracellular reactive oxygen species. These data demonstrate that FABP4/aP2 directly regulates intracellular FFA levels and indirectly controls macrophage inflammation and ER stress by regulating the expression of UCP2.

Emerging regulators of the inflammatory process in osteoarthritis

Chronic, low-grade inflammation in osteoarthritis (OA) contributes to symptoms and disease progression. Effective disease-modifying OA therapies are lacking, but better understanding inflammatory pathophysiology in OA could lead to transformative therapy. Networks of diverse innate inflammatory danger signals, including complement and alarmins, are activated in OA. Through inflammatory mediators, biomechanical injury and oxidative stress compromise the viability of chondrocytes, reprogramming them to hypertrophic differentiation and proinflammatory and pro-catabolic responses. Integral to this reprogramming are 'switching' pathways in transcriptional networks, other than the well-characterized effects of NFκB and mitogen-activated protein kinase signalling; HIF-2α transcriptional signalling and ZIP8-mediated Zn(2+) uptake, with downstream MTF1 transcriptional signalling, have been implicated but further validation is required. Permissive factors, including impaired bioenergetics via altered mitochondrial function and decreased activity of bioenergy sensors, interact with molecular inflammatory responses and proteostasis mechanisms such as the unfolded protein response and autophagy. Bioenergy-sensing by AMPK and SIRT1 provides 'stop signals' for oxidative stress, inflammatory, and matrix catabolic processes in chondrocytes. The complexity of molecular inflammatory processes in OA and the involvement of multiple inflammatory mediators in tissue repair responses, raises daunting questions about how to therapeutically target inflammatory processes and macroscopic inflammation in OA. Bioenergy sensing might provide a pragmatic 'entry point'.

Stat3: friend or foe in colitis and colitis-associated cancer?

Chronic inflammation predisposes tissue to cancer development. Individuals afflicted with inflammatory bowel diseases are at an increased risk of developing colorectal cancer depending on disease severity, duration, and management. The intestinal epithelium exhibits mitochondrial dysfunction during colitis and colitis-associated cancer. Signal Transducer and Activator of Transcription (Stat)-3 is a transcription factor involved in growth-promoting and antiapoptotic signaling pathways. In addition to its activities as a transcription factor, Stat3 resides in the mitochondria of cells where it is required for optimal electron transport chain activity and protects against stress-induced mitochondrial dysfunction. The function of mitochondrial Stat3 is not completely understood; dichotomous roles include protecting against cellular injury but also supporting malignant transformation. This review discusses the roles of Stat3 in the regulation of intestinal epithelial cell fate during colitis and colorectal cancer with an emphasis on mitochondrial dysfunction and the potential involvement of mitochondrial Stat3 during disease progression.

Emerging significance of NLRs in inflammatory bowel disease

Pattern recognition receptors are essential mediators of host defense and inflammation in the gastrointestinal system. Recent data have revealed that toll-like receptors and nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs) function to maintain homeostasis between the host microbiome and mucosal immunity. The NLR proteins are a diverse class of cytoplasmic pattern recognition receptors. In humans, only about half of the identified NLRs have been adequately characterized. The majority of well-characterized NLRs participate in the formation of a multiprotein complex, termed the inflammasome, which is responsible for the maturation of interleukin-1β and interleukin-18. However, recent observations have also uncovered the presence of a novel subgroup of NLRs that function as positive or negative regulators of inflammation through modulating critical signaling pathways, including NF-κB. Dysregulation of specific NLRs from both proinflammatory and inhibitory subgroups have been associated with the development of inflammatory bowel disease (IBD) in genetically susceptible human populations. Our own preliminary retrospective data mining efforts have identified a diverse range of NLRs that are significantly altered at the messenger RNA level in colons from patients with IBD. Likewise, studies using genetically modified mouse strains have revealed that multiple NLR family members have the potential to dramatically modulate the immune response during IBD. Targeting NLR signaling represents a promising and novel therapeutic strategy. However, significant effort is necessary to translate the current understanding of NLR biology into effective therapies.

Prohibitin 1 modulates mitochondrial function of Stat3

Mitochondrial dysfunction in intestinal epithelial cells (IEC) is thought to precede the onset of inflammatory bowel diseases (IBD). Expression of Prohibitin 1 (PHB), a mitochondrial protein required for optimal electron transport chain (ETC) activity, is decreased in mucosal biopsies during active and inactive IBD. In addition to its activities as a transcription factor, Signal Transducer and Activator of Transcription 3 (Stat3) resides in the mitochondria of cells where phosphorylation at S727 is required for optimal ETC activity and protects against stress-induced mitochondrial dysfunction. Here, we show that PHB overexpression protects against mitochondrial stress and apoptosis of cultured IECs induced by TNFα, which is a pro-inflammatory cytokine involved in IBD pathogenesis. Expression of pS727-Stat3 dominant negative eliminates protection by PHB against TNFα-induced mitochondrial stress and apoptosis. PHB interacts with pS727-Stat3 in the mitochondria of cultured IECs and in colonic epithelium from wild-type mice. Our data suggest a protective role of PHB that is dependent on pS727-Stat3 to prevent mitochondrial dysfunction in IECs. Reduced levels of PHB during IBD may be an underlying factor promoting mitochondrial dysfunction of the intestinal epithelium.

The biochemistry and cell biology of aging: metabolic regulation through mitochondrial signaling

Cellular and organ metabolism affects organismal lifespan. Aging is characterized by increased risks for metabolic disorders, with age-associated degenerative diseases exhibiting varying degrees of mitochondrial dysfunction. The traditional view of the role of mitochondria generated reactive oxygen species (ROS) in cellular aging, assumed to be causative and simply detrimental for a long time now, is in need of reassessment. While there is little doubt that high levels of ROS are detrimental, mounting evidence points toward a lifespan extension effect exerted by mild to moderate ROS elevation. Dietary caloric restriction, inhibition of insulin-like growth factor-I signaling, and inhibition of the nutrient-sensing mechanistic target of rapamycin are robust longevity-promoting interventions. All of these appear to elicit mitochondrial retrograde signaling processes (defined as signaling from the mitochondria to the rest of the cell, for example, the mitochondrial unfolded protein response, or UPR(mt)). The effects of mitochondrial retrograde signaling may even spread to other cells/tissues in a noncell autonomous manner by yet unidentified signaling mediators. Multiple recent publications support the notion that an evolutionarily conserved, mitochondria-initiated signaling is central to the genetic and epigenetic regulation of cellular aging and organismal lifespan.

The dendritic cell response to classic, emerging, and homeostatic danger signals. Implications for autoimmunity

Dendritic cells (DCs) initiate and control immune responses, participate in the maintenance of immunological tolerance and are pivotal players in the pathogenesis of autoimmunity. In patients with autoimmune disease and in experimental animal models of autoimmunity, DCs show abnormalities in both numbers and activation state, expressing immunogenic levels of costimulatory molecules and pro-inflammatory cytokines. Exogenous and endogenous danger signals activate DCs to stimulate the immune response. Classic endogenous danger signals are released, activated, or secreted by host cells and tissues experiencing stress, damage, and non-physiologic cell death; and are therefore referred to as damage-associated molecular patterns (DAMPs). Some DAMPs are released from cells, where they are normally sequestered, during necrosis (e.g., heat shock proteins, uric acid, ATP, HMGB1, mitochondria-derived molecules). Others are actively secreted, like Type I Interferons. Here we discuss important DAMPs in the context of autoimmunity. For some, there is a clear pathogenic link (e.g., nucleic acids and lupus). For others, there is less evidence. Additionally, we explore emerging danger signals. These include inorganic materials and man-made technologies (e.g., nanomaterials) developed as novel therapeutic approaches. Some nanomaterials can activate DCs and may trigger unintended inflammatory responses. Finally, we will review “homeostatic danger signals,” danger signals that do not derive directly from pathogens or dying cells but are associated with perturbations of tissue/cell homeostasis and may signal pathological stress. These signals, like acidosis, hypoxia, and changes in osmolarity, also play a role in inflammation and autoimmunity.

Evaluating and responding to mitochondrial dysfunction: the mitochondrial unfolded-protein response and beyond

During development and cellular differentiation, tissue- and cell-specific programs mediate mitochondrial biogenesis to meet physiological needs. However, environmental and disease-associated factors can perturb mitochondrial activities, requiring cells to adapt to protect mitochondria and maintain cellular homeostasis. Several mitochondrion-to-nucleus signaling pathways, or retrograde responses, have been described, but the mechanisms by which mitochondrial stress or dysfunction is sensed to coordinate precisely the appropriate response has only recently begun to be understood. Recent studies of the mitochondrial unfolded-protein response (UPRmt) indicate that the cell monitors mitochondrial protein import efficiency as an indicator of mitochondrial function. Here, we review how the cell evaluates mitochondrial function and regulates transcriptional induction of the UPRmt, adapts protein-synthesis rates and activates mitochondrial autophagy to promote mitochondrial function and cell survival during stress.

IL-10 promotes production of intestinal mucus by suppressing protein misfolding and endoplasmic reticulum stress in goblet cells

BACKGROUND & AIMS

Protein misfolding and endoplasmic reticulum (ER) stress have been observed in intestinal secretory cells from patients with inflammatory bowel diseases and induce intestinal inflammation in mice. However, it is not clear how immune factors affect ER stress and therefore disease symptoms.

METHODS

We analyzed the effects of interleukin (IL)-10 on ER stress in intestinal tissues in wild-type C57BL/6, Winnie, IL-10(-/-), and Winnie × IL-10(+/-) mice. In Winnie mice, misfolding of the intestinal mucin Muc2 initiates ER stress and inflammation. We also analyzed the effects of different inhibitors of IL-10 signaling and the N-glycosylation inhibitor tunicamycin in cultured human LS174T goblet cells.

RESULTS

Administration of neutralizing antibodies against IL-10 or its receptor (IL-10R1) to Winnie mice rapidly exacerbated ER stress and intestinal inflammation compared with mice given vehicle (controls). Antibodies against IL-10 also increased accumulation of misfolded Muc2 in the ER of goblet cells of Winnie mice and increased T-cell production of inflammatory cytokines. Winnie × IL-10(+/-) mice and IL-10(-/-) mice with a single Winnie allele each developed more severe inflammation than Winnie mice or IL-10(-/-) mice. Administration of tunicamycin to wild-type mice caused intestinal ER stress, which increased when IL-10R1 was blocked. In LS174T cells, induction of ER stress with tunicamycin and misfolding of MUC2 were reduced by administration of IL-10; this reduction required STAT1 and STAT3. In LS174T cells incubated with tunicamycin, IL-10 up-regulated genes involved in MUC2 folding and in ER-associated degradation and maintained correct folding of MUC2, its transport from the ER, and its O-glycosylation and secretion.

CONCLUSIONS

IL-10 prevents protein misfolding and ER stress by maintaining mucin production in goblet cells and helps the intestine preserve the mucus barrier.

Unfolded protein responses in the intestinal epithelium: sensors for the microbial and metabolic environment

In inflammatory bowel disease, the intestinal microbiota is a key driver of inflammation. Hence, efficient sensing of luminal antigens and subsequent initiation of adequate immune responses is crucial for maintaining homeostasis, particularly in intestinal epithelial cells. Pathways such as Toll-like receptor-mediated signaling and autophagy sense microbial products to activate inflammatory processes and, concomitantly, interact with cellular stress responses such as the unfolded protein response (UPR). Proteostasis is particularly sensitive toward environmental challenges and triggers, such as oxidative stress and metabolic alterations, and impact protein folding in different cellular compartments. In contrast, disturbances in energy supply including impaired mitochondrial function and epithelial β-oxidation have been suspected to contribute toward intestinal inflammation. Interestingly, the 2 main organelles linking metabolic pathways, inflammatory signaling and pathogen-sensing, endoplasmic reticulum (ER) and mitochondria (mt), can trigger distinct UPRs, and both ER UPR and mt UPR have been shown to be disease-relevant in inflammatory bowel disease. The ER is essential for the coordination of metabolic responses through controlling the synthetic and catabolic pathways of various nutrients and furthermore, ER UPR signaling directly intersects with inflammation-associated NF-κB and Toll-like receptor pathways. Consistently, next to their function in cellular energy supply, mitochondria are increasingly recognized as integrators of immune responses. For instance, mitochondria participate in innate immunity to viral infection through the pattern recognition receptor retinoic acid inducible gene-I and are involved in inflammasome activation. Thus, we hypothesize that a concerted UPR activation might represent an innate mechanism to sense potentially threatening changes of the mucosal metabolic environment and impacts host cellular functions and immune responses.

αSynuclein and Mitochondrial Dysfunction: A Pathogenic Partnership in Parkinson's Disease?

Parkinson's Disease (PD) is a complex, chronic, progressive, and debilitating neurodegenerative disorder. Neither a cure nor effective long-term therapy exist and the lack of knowledge of the molecular mechanisms responsible for PD development is a major impediment to therapeutic advances. The protein αSynuclein is a central component in PD pathogenesis yet its cellular targets and mechanism of toxicity remains unknown. Mitochondrial dysfunction is also a common theme in PD patients and this review explores the strong possibility that αSynuclein and mitochondrial dysfunction have an inter-relationship responsible for underlying the disease pathology. Amplifying cycles of mitochondrial dysfunction and αSynuclein toxicity can be envisaged, with either being the disease-initiating factor yet acting together during disease progression. Multiple potential mechanisms exist in which mitochondrial dysfunction and αSynuclein could interact to exacerbate their neurodegenerative properties. Candidates discussed within this review include autophagy, mitophagy, mitochondrial dynamics/fusion/fission, oxidative stress and reactive oxygen species, endoplasmic reticulum stress, calcium, nitrosative stress and αSynuclein Oligomerization.