Defects in mitochondrial clearance predispose human monocytes to interleukin-1β hypersecretion

Mitochondrial DNA Release in Innate Immune Signaling

According to the endosymbiotic theory, most of the DNA of the original bacterial endosymbiont has been lost or transferred to the nucleus, leaving a much smaller (∼16 kb in mammals), circular molecule that is the present-day mitochondrial DNA (mtDNA). The ability of mtDNA to escape mitochondria and integrate into the nuclear genome was discovered in budding yeast, along with genes that regulate this process. Mitochondria have emerged as key regulators of innate immunity, and it is now recognized that mtDNA released into the cytoplasm, outside of the cell, or into circulation activates multiple innate immune signaling pathways. Here, we first review the mechanisms through which mtDNA is released into the cytoplasm, including several inducible mitochondrial pores and defective mitophagy or autophagy. Next, we cover how the different forms of released mtDNA activate specific innate immune nucleic acid sensors and inflammasomes. Finally, we discuss how intracellular and extracellular mtDNA release, including circulating cell-free mtDNA that promotes systemic inflammation, are implicated in human diseases, bacterial and viral infections, senescence and aging.

Proteomic Signatures of Monocytes in Hereditary Recurrent Fevers

Hereditary periodic recurrent fevers (HRF) are monogenic autoinflammatory associated to mutations of some genes, such as diseases caused by mutations of including MEFV, TNFRSF1A and MVK genes. Despite the identification of the causative genes, the intracellular implications related to each gene variant are still largely unknown. A large –scale proteomic analysis on monocytes of these patients is aimed to identify with an unbiased approach the mean proteins and molecular interaction networks involved in the pathogenesis of these conditions. Monocytes from HRF 15 patients (5 with MFV, 5 TNFRSF1A and 5with MVK gene mutation) and 15 healthy donors (HDs) were analyzed by liquid chromatography and tandem mass spectrometry before and after lipopolysaccharide (LPS) stimulation. Significant proteins were analyzed through a Cytoscape analysis using the ClueGo app to identify molecular interaction networks. Protein networks for each HRF were performed through a STRING database analysis integrated with a DISEAE database query. About 5000 proteins for each HRF were identified. LPS treatment maximizes differences between up-regulated proteins in monocytes of HRF patients and HDs, independently from the disease’s activity and ongoing treatments. Proteins significantly modulated in monocytes of the different HRF allowed creating a disease-specific proteomic signatures and interactive protein network. Proteomic analysis is able to dissect the different intracellular pathways involved in the inflammatory response of circulating monocytes in HRF patients. The present data may help to identify a “monocyte proteomic signature” for each condition and unravel new possible unexplored intracellular pathways possibly involved in their pathogenesis. These data will be also useful to identify possible differences and similarities between the different HRFs and some multifactorial recurrent fevers.

Expression of PINK1 and Parkin in human apical periodontitis

AIM

PTEN-induced putative kinase 1 (PINK1) and Parkin E3 ubiquitin-protein ligase (Parkin) are critical for immune and inflammatory regulation in health and disease. PINK1 and Parkin have been confirmed to be involved in the progression of apical periodontitis by affecting mitophagy-related osteoblast apoptosis; however, the expression of PINK1 and Parkin in macrophages, one of the most important cells in apical periodontitis, remains unknown. This study aimed to investigate the expression of PINK1 and Parkin in human apical periodontitis lesions, as well as their possible localization in macrophages.

METHODOLOGY

Thirty-seven human periapical tissues, including periapical granulomas (PGs, n=12), radicular cysts (RCs, n=11), and healthy gingival tissues (n=14) were examined. The inflammatory infiltrates of lesions were evaluated by haemotoxylin staining, and the expression of PINK1 and Parkin was detected by immunohistochemistry. Double immunofluorescence was used to explore the colocalization of microtubule-associated protein 1 light chain 3 (LC3) and TOMM20, as well as the localization of PINK1 and Parkin, in macrophages of human apical periodontitis lesions. The ultrastructural morphology of mitochondria in human apical periodontitis lesions was visualized by transmission electron microscopy (TEM). Data were analyzed by one-way ANOVA with Student-Newman-Keul's test and Mann-Whitney test. P < 0.05 was considered statistically significant.

RESULTS

Immunohistochemistry demonstrated a significantly higher expression of PINK1 and Parkin proteins in human apical periodontitis lesions than in healthy gingival tissues (P < 0.0001), but no significant difference was demonstrated between PGs and RCs (P > 0.05). The higher expression of LC3 and the presence of more LC3-TOMM20 double-positive cells were also observed in human apical periodontitis. Double-labeling analysis of PINK1, Parkin, and LC3 with CD68 indicated that macrophage mitophagy might be present in the progression of human apical periodontitis. Finally, the results of TEM morphological analysis revealed the appearance of double-membraned mitophagosomes and vacuolated mitochondria in macrophage-like cells of apical periodontitis lesions.

CONCLUSIONS

Our findings indicated that PINK1 and Parkin proteins were highly expressed in clinical apical periodontitis lesions.

TFEB signaling attenuates NLRP3-driven inflammatory responses in severe asthma

BACKGROUND

NLRP3-driven inflammatory responses by circulating and lung-resident monocytes are critical drivers of asthma pathogenesis. Autophagy restrains NLRP3-induced monocyte activation in asthma models. Yet, the effects of autophagy and its master regulator, transcription factor EB (TFEB), on monocyte responses in human asthma remain unexplored. Here, we investigated whether activation of autophagy and TFEB signaling suppress inflammatory monocyte responses in asthmatic individuals.

METHODS

Peripheral blood CD14⁺ monocytes from asthmatic patients (n = 83) and healthy controls (n = 46) were stimulated with LPS/ATP to induce NLRP3 activation with or without the autophagy inducer, rapamycin. ASC specks, caspase-1 activation, IL-1β and IL-18 levels, mitochondrial function, ROS release, and mTORC1 signaling were examined. Autophagy was evaluated by LC3 puncta formation, p62/SQSTM1 degradation and TFEB activation. In a severe asthma (SA) model, we investigated the role of NLRP3 signaling using Nlrp3^-/- mice and/or MCC950 administration, and the effects of TFEB activation using myeloid-specific TFEB-overexpressing mice or administration of the TFEB activator, trehalose.

RESULTS

We observed increased NLRP3 inflammasome activation, concomitant with impaired autophagy in circulating monocytes that correlated with asthma severity. SA patients also exhibited mitochondrial dysfunction and ROS accumulation. Autophagy failed to inhibit NLRP3-driven monocyte responses, due to defective TFEB activation and excessive mTORC1 signaling. NLRP3 blockade restrained inflammatory cytokine release and linked airway disease. TFEB activation restored impaired autophagy, attenuated NLRP3-driven pulmonary inflammation, and ameliorated SA phenotype.

CONCLUSIONS

Our studies uncover a crucial role for TFEB-mediated reprogramming of monocyte inflammatory responses, raising the prospect that this pathway can be therapeutically harnessed for the management of SA.

Compromised Protein Prenylation as Pathogenic Mechanism in Mevalonate Kinase Deficiency

Mevalonate kinase deficiency (MKD) is an autoinflammatory metabolic disorder characterized by life-long recurring episodes of fever and inflammation, often without clear cause. MKD is caused by bi-allelic pathogenic variants in the MVK gene, resulting in a decreased activity of the encoded enzyme mevalonate kinase (MK). MK is an essential enzyme in the isoprenoid biosynthesis pathway, which generates both non-sterol and sterol isoprenoids. The inflammatory symptoms of patients with MKD point to a major role for isoprenoids in the regulation of the innate immune system. In particular a temporary shortage of the non-sterol isoprenoid geranylgeranyl pyrophosphate (GGPP) is increasingly linked with inflammation in MKD. The shortage of GGPP compromises protein prenylation, which is thought to be one of the main causes leading to the inflammatory episodes in MKD. In this review, we discuss current views and the state of knowledge of the pathogenetic mechanisms in MKD, with particular focus on the role of compromised protein prenylation.

Mitochondrial Nucleic Acid as a Driver of Pathogenic Type I Interferon Induction in Mendelian Disease

The immune response to viral infection involves the recognition of pathogen-derived nucleic acids by intracellular sensors, leading to type I interferon (IFN), and downstream IFN-stimulated gene, induction. Ineffective discrimination of self from non-self nucleic acid can lead to autoinflammation, a phenomenon implicated in an increasing number of disease states, and well highlighted by the group of rare genetic disorders referred to as the type I interferonopathies. To understand the pathogenesis of these monogenic disorders, and polyfactorial diseases associated with pathogenic IFN upregulation, such as systemic lupus erythematosus and dermatomyositis, it is important to define the self-derived nucleic acid species responsible for such abnormal IFN induction. Recently, attention has focused on mitochondria as a novel source of immunogenic self nucleic acid. Best appreciated for their function in oxidative phosphorylation, metabolism and apoptosis, mitochondria are double membrane-bound organelles that represent vestigial bacteria in the cytosol of eukaryotic cells, containing their own DNA and RNA enclosed within the inner mitochondrial membrane. There is increasing recognition that a loss of mitochondrial integrity and compartmentalization can allow the release of mitochondrial nucleic acid into the cytosol, leading to IFN induction. Here, we provide recent insights into the potential of mitochondrial-derived DNA and RNA to drive IFN production in Mendelian disease. Specifically, we summarize current understanding of how nucleic acids are detected as foreign when released into the cytosol, and then consider the findings implicating mitochondrial nucleic acid in type I interferonopathy disease states. Finally, we discuss the potential for IFN-driven pathology in primary mitochondrial disorders.

Characterization of a natural variant of human NDP52 and its functional consequences on mitophagy

The role of mitophagy, a process that allows the removal of damaged mitochondria from cells, remains unknown in multiple sclerosis (MS), a disease that is found associated with dysfunctional mitochondria. Here we have qualitatively and quantitatively studied the main players in PINK1-mediated mitophagy in peripheral blood mononuclear cells (PBMCs) of patients with relapsing-remitting MS. We found the variant c.491G>A (rs550510, p.G140E) of NDP52, one of the major mitophagy receptor genes, associated with a MS cohort. Through the characterization of this variant, we discovered that the residue 140 of human NDP52 is a crucial modulator of NDP52/LC3C binding, promoting the formation of autophagosomes in order to drive efficient mitophagy. In addition, we found that in the PBMC population, NDP52 is mainly expressed in B cells and by ensuring efficient mitophagy, it is able to limit the production of the proinflammatory cytokine TNF-α following cell stimulation. In sum, our results contribute to a better understanding of the role of NDP52 in mitophagy and underline, for the first time, a possible role of NDP52 in MS.

Immune Intervention in Sepsis

Sepsis is a host immune disorder induced by infection. It can lead to multiple organ dysfunction syndrome (MODS), which has high morbidity and mortality. There has been great progress in the clinical diagnosis and treatment of sepsis, such as improvements in pathogen detection technology, innovations regarding anti-infection drugs, and the development of organ function support. Abnormal immune responses triggered by pathogens, ranging from excessive inflammation to immunosuppression, are recognized to be an important cause of the high mortality rate. However, no drugs have been approved specifically for treating sepsis. Here, we review the recent research progress on immune responses in sepsis to provide a theoretical basis for the treatment of sepsis. Constructing and optimizing a dynamic immune system treatment regimen based on anti-infection treatment, fluid replacement, organ function support, and timely use of immunomodulatory interventions may improve the prognosis of sepsis patients.

The NLRP3-Inflammasome-Caspase-1 Pathway Is Upregulated in Idiopathic Pulmonary Fibrosis and Acute Exacerbations and Is Inducible by Apoptotic A549 Cells

Idiopathic pulmonary fibrosis (IPF) is a relentlessly progressive disease harboring significant morbidity and mortality despite recent advances in therapy. Regardless of disease severity acute exacerbations (IPF-AEs) may occur leading to considerable loss of function and are the leading cause of death in IPF. Histologic features of IPF-AE are very similar to acute respiratory distress syndrome (ARDS), but the underlying mechanisms are incompletely understood. We investigated the role of the NLRP3 inflammasome in IPF and IPF-AE. Bronchoalveolar lavage (BAL) cells were sampled from patients with IPF (n = 32), IPF-AE (n = 10), ARDS (n = 7) and healthy volunteers (HV, n = 37) and the NLRP3-inflammasome was stimulated in-vitro. We found the NLRP3 inflammasome to be hyper-inducible in IPF compared to HV with increased IL-1ß and pro-IL-1ß levels on ELISA upon stimulation as well as increased caspase-1 activity measured by caspase-1p20 immunoblotting. In IPF-AE, IL-1ß was massively elevated to an extent similar to ARDS. To evaluate potential mechanisms, we co-cultured BAL cells with radiated A549 cells (a model to simulate apoptotic alveolar epithelial cells), which led to increased NLRP3 mRNA expression and increased caspase-1 dependent IL-1ß production. In the presence of a reactive oxygen species (ROS) inhibitor (diphenyleneiodonium) and a cathepsin B inhibitor (E64D), NLRP3 expression was suppressed indicating that induction of NLRP3 activation following efferocytosis of apoptotic A549 cells is mediated via ROS and cathepsin-B. In summary, we present evidence of involvement of the NLRP3 inflammasome-caspase pathway in the pathogenesis of IPF-AE, similarly to ARDS, which may be mediated by efferocytosis of apoptotic alveolar epithelial cells in IPF.

Mitochondria-cytokine crosstalk following skeletal muscle injury and disuse: a mini-review

Skeletal muscle mitochondria are highly adaptable, highly dynamic organelles that maintain the functional integrity of the muscle fiber by providing ATP for contraction and cellular homeostasis (e.g., Na⁺/K⁺ ATPase). Emerging as early modulators of inflammation, mitochondria sense and respond to cellular stress. Mitochondria communicate with the environment, in part, by release of physical signals called mitochondrial-derived damage-associated molecular patterns (mito-DAMPs) and deviation from routine function (e.g., reduced ATP production, Ca²⁺ overload). When skeletal muscle is compromised, mitochondria contribute to an acute inflammatory response necessary for myofibril regeneration; however, exhaustive signaling associated with altered or reduced mitochondrial function can be detrimental to muscle outcomes. Here, we describe changes in mitochondrial content, structure, and function following skeletal muscle injury and disuse and highlight the influence of mitochondria-cytokine crosstalk on muscle regeneration and recovery. Although the appropriate therapeutic modulation following muscle stressors remains unknown, retrospective gene expression analysis reveals that interleukin-6 (IL-6), interleukin-1β (IL-1β), chemokine C-X-C motif ligand 1 (CXCL1), and monocyte chemoattractant protein 1 (MCP-1) are significantly upregulated following three unique muscle injuries. These cytokines modulate mitochondrial function and execute bona fide pleiotropic roles that can aid functional recovery of muscle, however, when aberrant, chronically disrupt healing partly by exacerbating mitochondrial dysfunction. Multidisciplinary efforts to delineate the opposing regulatory roles of inflammatory cytokines in the muscle mitochondrial environment are required to modulate regenerative behavior following skeletal muscle injury or disuse. Future therapeutic directions to consider include quenching or limited release of mito-DAMPs and cytokines present in cytosol or circulation.

Doxorubicin-induced p53 interferes with mitophagy in cardiac fibroblasts

Anthracyclines are the critical component in a majority of pediatric chemotherapy regimens due to their broad anticancer efficacy. Unfortunately, the vast majority of long-term childhood cancer survivors will develop a chronic health condition caused by their successful treatments and severe cardiac disease is a common life-threatening outcome that is unequivocally linked to previous anthracycline exposure. The intricacies of how anthracyclines such as doxorubicin, damage the heart and initiate a disease process that progresses over multiple decades is not fully understood. One area left largely unstudied is the role of the cardiac fibroblast, a key cell type in cardiac maturation and injury response. In this study, we demonstrate the effect of doxorubicin on cardiac fibroblast function in the presence and absence of the critical DNA damage response protein p53. In wildtype cardiac fibroblasts, doxorubicin-induced damage correlated with decreased proliferation and migration, cell cycle arrest, and a dilated cardiomyopathy gene expression profile. Interestingly, these doxorubicin-induced changes were completely or partially restored in p53-/- cardiac fibroblasts. Moreover, in wildtype cardiac fibroblasts, doxorubicin produced DNA damage and mitochondrial dysfunction, both of which are well-characterized cell stress responses induced by cytotoxic chemotherapy and varied forms of heart injury. A 3-fold increase in p53 (p = 0.004) prevented the completion of mitophagy (p = 0.032) through sequestration of Parkin. Interactions between p53 and Parkin increased in doxorubicin-treated cardiac fibroblasts (p = 0.0003). Finally, Parkin was unable to localize to the mitochondria in wildtype cardiac fibroblasts, but mitochondrial localization was restored in p53-/- cardiac fibroblasts. These findings strongly suggest that cardiac fibroblasts are an important myocardial cell type that merits further study in the context of doxorubicin treatment. A more robust knowledge of the role cardiac fibroblasts play in the development of doxorubicin-induced cardiotoxicity will lead to novel clinical strategies that will improve the quality of life of cancer survivors.

Lactobacillus johnsonii L531 Ameliorates Escherichia coli-Induced Cell Damage via Inhibiting NLRP3 Inflammasome Activity and Promoting ATG5/ATG16L1-Mediated Autophagy in Porcine Mammary Epithelial Cells

Escherichia coli (E. coli), a main mastitis-causing pathogen in sows, leads to mammary tissue damage. Here, we explored the effects of Lactobacillus johnsonii L531 on attenuating E. coli-induced inflammatory damage in porcine mammary epithelial cells (PMECs). L. johnsonii L531 pretreatment reduced E. coli adhesion to PMECs by competitive exclusion and the production of inhibitory factors and decreased E. coli-induced destruction of cellular morphology and ultrastructure. E. coli induced activation of NLRP3 inflammasome associated with increased expression of NLRP3, ASC, and cleaved caspase-1, however, L. johnsonii L531 inhibited E. coli-induced activation of NLRP3 inflammasome. Up-regulation of interleukin (Il)-1β, Il-6, Il-8, Il-18, tumor necrosis factor alpha, and chemokine Cxcl2 expression after E. coli infection was attenuated by L. johnsonii L531. E. coli infection inhibited autophagy, whereas L. johnsonii L531 reversed the inhibitory effect of E. coli on autophagy by decreasing the expression of autophagic receptor SQSTM1/p62 and increasing the expression of autophagy-related proteins ATG5, ATG16L1, and light chain 3 protein by Western blotting analysis. Our findings suggest that L. johnsonii L531 pretreatment restricts NLRP3 inflammasome activity and induces autophagy through promoting ATG5/ATG16L1-mediated autophagy, thereby protecting against E. coli-induced inflammation and cell damage in PMECs.

Dysregulated NADPH Oxidase Promotes Bone Damage in Murine Model of Autoinflammatory Osteomyelitis

Autoinflammatory diseases are characterized by dysregulation of the innate immune system, leading to spontaneous inflammation. Pstpip2cmo mouse strain is a well-characterized model of this class of disorders. Because of the mutation leading to the lack of adaptor protein PSTPIP2, these animals suffer from autoinflammatory chronic multifocal osteomyelitis similar to several human syndromes. Current evidence suggests that it is driven by hyperproduction of IL-1β by neutrophil granulocytes. In this study, we show that in addition to IL-1β, PSTPIP2 also negatively regulates pathways governing reactive oxygen species generation by neutrophil NOX2 NADPH oxidase. Pstpip2cmo neutrophils display highly elevated superoxide production in response to a range of stimuli. Inactivation of NOX2 NADPH oxidase in Pstpip2cmo mice did not affect IL-1β levels, and the autoinflammatory process was initiated with similar kinetics. However, the bone destruction was almost completely alleviated, suggesting that dysregulated NADPH oxidase activity is a key factor promoting autoinflammatory bone damage in Pstpip2cmo mice.

Hints for Genetic and Clinical Differentiation of Adult-Onset Monogenic Autoinflammatory Diseases

Monogenic autoinflammatory diseases (mAIDs) are inherited errors of innate immunity characterized by systemic inflammation recurring with variable frequency and involving the skin, serosal membranes, synovial membranes, joints, the gastrointestinal tube, and/or the central nervous system, with reactive amyloidosis as a potential severe long-term consequence. Although individually uncommon, all mAIDs set up an emerging chapter of internal medicine: recent findings have modified our knowledge regarding mAID pathophysiology and clarified that protean inflammatory symptoms can be variably associated with periodic fevers, depicting multiple specific conditions which usually start in childhood, such as familial Mediterranean fever, tumor necrosis factor receptor-associated periodic syndrome, cryopyrin-associated periodic syndrome, and mevalonate kinase deficiency. There are no evidence-based studies to establish which potential genotype analysis is the most appropriate in adult patients with clinical phenotypes suggestive of mAIDs. This review discusses genetic and clinical hints for an ideal diagnostic approach to mAIDs in adult patients, as their early identification is essential to prompt effective treatment and improve quality of life, and also highlights the most recent developments in the diagnostic work-up for the most frequent hereditary periodic febrile syndromes worldwide.

Targeting NLRP3 Inflammasome Activation in Severe Asthma

Severe asthma (SA) is a chronic lung disease characterized by recurring symptoms of reversible airflow obstruction, airway hyper-responsiveness (AHR), and inflammation that is resistant to currently employed treatments. The nucleotide-binding oligomerization domain-like Receptor Family Pyrin Domain Containing 3 (NLRP3) inflammasome is an intracellular sensor that detects microbial motifs and endogenous danger signals and represents a key component of innate immune responses in the airways. Assembly of the NLRP3 inflammasome leads to caspase 1-dependent release of the pro-inflammatory cytokines IL-1β and IL-18 as well as pyroptosis. Accumulating evidence proposes that NLRP3 activation is critically involved in asthma pathogenesis. In fact, although NLRP3 facilitates the clearance of pathogens in the airways, persistent NLRP3 activation by inhaled irritants and/or innocuous environmental allergens can lead to overt pulmonary inflammation and exacerbation of asthma manifestations. Notably, administration of NLRP3 inhibitors in asthma models restrains AHR and pulmonary inflammation. Here, we provide an overview of the pathophysiology of SA, present molecular mechanisms underlying aberrant inflammatory responses in the airways, summarize recent studies pertinent to the biology and functions of NLRP3, and discuss the role of NLRP3 in the pathogenesis of asthma. Finally, we contemplate the potential of targeting NLRP3 as a novel therapeutic approach for the management of SA.

Interaction among inflammasome, autophagy and non-coding RNAs: new horizons for drug

Autophagy and inflammasomes are shown to interact in various situations including infectious disease, cancer, diabetes and neurodegeneration. Since multiple layers of molecular regulators contribute to the interplay between autophagy and inflammasome activation, the detail of such interplay remains largely unknown. Non-coding RNAs (ncRNAs), which have been implicated in regulating an expanding list of cellular processes including immune defense against pathogens and inflammatory response in cancer and metabolic diseases, may join in the crosstalk between inflammasomes and autophagy in physiological or disease conditions. In this review, we summarize the latest research on the interlink among ncRNAs, inflammasomes and autophagy and discuss the emerging role of these three in multiple signaling transduction pathways involved in clinical conditions. By analyzing these intriguing interconnections, we hope to unveil the mechanism inter-regulating these multiple processes and ultimately discover potential drug targets for some refractory diseases.

Preliminary Study on Clusterin Protein (sCLU) Expression in PC-12 Cells Overexpressing Wild-Type and Mutated (Swedish) AβPP genes Affected by Non-Steroid Isoprenoids and Water-Soluble Cholesterol

In this study we attempted to verify the hypothesis that the mevalonate pathway affects amyloid beta precursor protein (AβPP) processing and regulates clusterin protein levels. AβPP expression was monitored by green fluorescence (FL) and Western blot (WB). WB showed soluble amyloid protein precursor alpha (sAβPPα) presence in AβPP-wt cells and Aβ expression in AβPP-sw cells. Nerve growth factor (NGF)-differentiated rat neuronal pheochromocytoma PC-12 cells were untreated/treated with statins alone or together with non-sterol isoprenoids. Co-treatment with mevalonate, dolichol, ubiquinol, farnesol, geranylgeraniol, or water-soluble cholesterol demonstrated statin-dependent neurotoxicity resulted from the attenuated activity of mevalonate pathway rather than lower cholesterol level. Atorvastatin (50 μM) or simvastatin (50 μM) as well as cholesterol chelator methyl-β-cyclodextrin (0.2 mM) diminished cell viability (p < 0.05) and clusterin levels. Interestingly, co-treatment with mevalonate, dolichol, ubiquinol, farnesol, geranylgeraniol, or water-soluble cholesterol stimulated (p < 0.05) clusterin expression. Effects of non-sterol isoprenoids, but not water soluble cholesterol (Chol-PEG), were the most significant in mock-transfected cells. Geranylgeraniol (GGOH) overcame atorvastatin (ATR)-dependent cytotoxicity. This effect does not seem to be dependent on clusterin, as its level became lower after GGOH. The novelty of these findings is that they show that the mevalonate (MEV) pathway rather than cholesterol itself plays an important role in clusterin expression levels. In mock-transfected, rather than in AβPP-overexpressing cells, GGOH/farnesol (FOH) exerted a protective effect. Thus, protein prenylation with GGOH/FOH might play substantial role in neuronal cell survival.

The Mevalonate Pathway Is Indispensable for Adipocyte Survival

The mevalonate pathway is essential for the synthesis of isoprenoids and cholesterol. Adipose tissue is known as a major site for cholesterol storage; however, the role of the local mevalonate pathway and its synthesized isoprenoids remains unclear. In this study, adipose-specific mevalonate pathway-disrupted (aKO) mice were generated through knockout of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase (HMGCR). aKO mice showed serious lipodystrophy accompanied with glucose and lipid metabolic disorders and hepatomegaly. These metabolic variations in aKO mice were dramatically reversed after fat transplantation. In addition, HMGCR-disrupted adipocytes exhibited loss of lipid accumulation and an increase of cell death, which were ameliorated by the supplementation of mevalonate and geranylgeranyl pyrophosphate but not farnesyl pyrophosphate and squalene. Finally, we found that apoptosis may be involved in adipocyte death induced by HMGCR down-regulation. Our findings indicate that the mevalonate pathway is essential for adipocytes and further suggest that this pathway is an important regulator of adipocyte turnover.

Loss of sterol metabolic homeostasis triggers inflammasomes - how and why

Proper regulation of sterol biosynthesis is critical for eukaryotic cellular homeostasis. Cholesterol and isoprenoids serve key roles in eukaryotic cells by regulating membrane fluidity and correct localization of proteins. It is becoming increasingly appreciated that dysregulated sterol metabolism engages pathways that lead to inflammation. Of particular importance are inflammasomes, which are multiplatform protein complexes that activate caspase-1 in order to process the pro-inflammatory and pyrogenic cytokines IL-1β and IL-18. In this review, we highlight recent research that links altered sterol biosynthetic pathway activity to inflammasome activation. We discuss how clues from human genetics have led to new insights into how alterations in isoprenoid biosynthesis connect to inflammation. We also discuss new mechanisms that show how macrophage cholesterol buildup can lead to inflammasome activation.

Targeting the NLRP3 inflammasome in inflammatory diseases

Danger signals are a hallmark of many common inflammatory diseases, and these stimuli can function to activate the cytosolic innate immune signalling receptor NLRP3 (NOD-, LRR- and pyrin domain-containing 3). Once activated, NLRP3 nucleates the assembly of an inflammasome, leading to caspase 1-mediated proteolytic activation of the interleukin-1β (IL-1β) family of cytokines, and induces an inflammatory, pyroptotic cell death. Pharmacological inhibition of NLRP3 activation results in potent therapeutic effects in a wide variety of rodent models of inflammatory diseases, effects that are mirrored by genetic ablation of NLRP3. Although these findings highlight the potential of NLRP3 as a drug target, an understanding of NLRP3 structure and activation mechanisms is incomplete, which has hampered the discovery and development of novel therapeutics against this target. Here, we review recent advances in our understanding of NLRP3 activation and regulation, highlight the evolving landscape of NLRP3 modulators and discuss opportunities for pharmacologically targeting NLRP3 with novel small molecules.

A clinical update on inflammasomopathies

Inflammasomes are important elements of the innate immune defense. The most common autoinflammatory syndromes, as well a number of rare ones, are due to hereditary defects in the inflammasomes, hence are called inflammasomopathies. The recent clinical advances in these diseases will be reviewed, with special emphasis on reflecting the international collaborative work in the field. Recent recommendations for familial Mediterranean fever, cryopyrin-associated periodic syndromes and hyper-IgD syndrome/mevalonate kinase deficiency will be presented and diagnostics tests, treatment alternatives and follow-up recommendations will be summarized. The other rare inflammasomopathies will be briefly discussed based on clinical features; these diseases are pyogenic arthritis, pyoderma gangrenosum and acne, NLRC4-related macrophage-activation syndrome of enterocolitis, mutations in NLRP12 that cause hereditary periodic fever syndromes (familial cold inflammatory syndrome 2) and NLRP1-associated autoinflammation with arthritis and dyskeratosis.

Neuronal Dysfunction Associated with Cholesterol Deregulation

Cholesterol metabolism is crucial for cells and, in particular, its biosynthesis in the central nervous system occurs in situ, and its deregulation involves morphological changes that cause functional variations and trigger programmed cell death. The pathogenesis of rare diseases, such as Mevalonate Kinase Deficiency or Smith–Lemli–Opitz Syndrome, arises due to enzymatic defects in the cholesterol metabolic pathways, resulting in a shortage of downstream products. The most severe clinical manifestations of these diseases appear as neurological defects. Expanding the knowledge of this biological mechanism will be useful for identifying potential targets and preventing neuronal damage. Several studies have demonstrated that deregulation of the cholesterol pathway induces mitochondrial dysfunction as the result of respiratory chain damage. We set out to determine whether mitochondrial damage may be prevented by using protective mitochondria-targeted compounds, such as MitoQ, in a neuronal cell line treated with a statin to induce a biochemical block of the cholesterol pathway. Evidence from the literature suggests that mitochondria play a crucial role in the apoptotic mechanism secondary to blocking the cholesterol pathway. Our study shows that MitoQ, administered as a preventive agent, could counteract the cell damage induced by statins in the early stages, but its protective role fades over time.

Prolonged treatment with mevalonolactone induces oxidative stress response with reactive oxygen species production, mitochondrial depolarization and inflammation in human glioblastoma U-87 MG cells

Mevalonate pathway impairment has been observed in diverse diseases, including Mevalonate Kinase Deficiency (MKD). MKD is a hereditary auto-inflammatory disorder, due to mutations at mevalonate kinase gene (MVK), encoding mevalonate kinase (MK) enzyme. To date, the most accredited MKD pathogenic hypothesis suggests that the typical MKD phenotypes might be due to a decreased isoprenoid production rather than to the excess and accumulation of mevalonic acid, as initially supported. Nevertheless, recent studies provide clear evidences that accumulating metabolites might be involved in MKD pathophysiology by exerting a toxic effect. Our work aims at describing the effects of accumulating mevalonolactone, mostly produced by a dehydration reaction due to mevalonic acid accumulation, using an in vitro cellular model mimicking the glial component of the central nervous system (human glioblastoma U-87 MG cells). In order to mimic its progressive increase, occurring during the disease, U-87 MG cells have been treated repeatedly with growing doses of mevalonolactone, followed by the assessment of oxidative stress response (evaluated by measuring SOD2 and HemeOX expression levels), ROS production, mitochondrial damage and inflammatory response (evaluated by measuring IL1B expression levels). Our results suggest that protracted treatments with mevalonolactone induce oxidative stress with augmented ROS production and mitochondrial damage accompanied by membrane depolarization. Furthermore, an increment in IL1B expression has been observed, thus correlating the accumulation of the metabolite with the development of a neuroinflammatory response. Our experimental work suggests to reconsider the presence of a possible synergy between the two major MKD pathogenic hypotheses in attempt of unravelling the different pathogenic pathways responsible for the disease.

Inflammation, a significant player of Ataxia-Telangiectasia pathogenesis?

INTRODUCTION

Ataxia-Telangiectasia (A-T) syndrome is an autosomal recessive neurodegenerative disorder characterized by cerebellar ataxia, oculocutaneous telangiectasia, immunodeficiency, chromosome instability, radiosensitivity, and predisposition to malignancy. There is growing evidence that A-T patients suffer from pathologic inflammation that is responsible for many symptoms of this syndrome, including neurodegeneration, autoimmunity, cardiovascular disease, accelerated aging, and insulin resistance. In addition, epidemiological studies have shown A-T heterozygotes, somewhat like deficient patients, are susceptible to ionizing irradiation and have a higher risk of cancers and metabolic disorders.

AREA COVERED

This review summarizes clinical and molecular findings of inflammation in A-T syndrome.

CONCLUSION

Ataxia-Telangiectasia Mutated (ATM), a master regulator of the DNA damage response is the protein known to be associated with A-T and has a complex nuclear and cytoplasmic role. Loss of ATM function may induce immune deregulation and systemic inflammation.

The Inflammasome: Regulation of Nitric Oxide and Antimicrobial Host Defence

Nitric oxide (NO) is a gaseous signalling molecule that plays diverse physiological functions including antimicrobial host defence. During microbial infection, NO is synthesized by inducible NO synthase (iNOS), which is expressed by host immune cells through the recognition of microbial pattern molecules. Therefore, sensing pathogens or their pattern molecules by pattern recognition receptors (PRRs), which are located at the cell surface, endosomal and phagosomal compartment, or in the cytosol, is key in inducing iNOS and eliciting antimicrobial host defence. A group of cytosolic PRRs is involved in inducing NO and other antimicrobial molecules by forming a molecular complex called the inflammasome. Assembled inflammasomes activate inflammatory caspases, such as caspase-1 and caspase-11, which in turn process proinflammatory cytokines IL-1β and IL-18 into their mature forms and induce pyroptotic cell death. IL-1β and IL-18 play a central role in immunity against microbial infection through activation and recruitment of immune cells, induction of inflammatory molecules, and regulation of antimicrobial mediators including NO. Interestingly, NO can also regulate inflammasome activity in an autocrine and paracrine manner. Here, we discuss molecular mechanisms of inflammasome formation and the inflammasome-mediated regulation of host defence responses during microbial infections.

Mechanisms and function of autophagy in intestinal disease

The discovery of numerous genetic variants in the human genome that are associated with inflammatory bowel disease (IBD) has revealed critical pathways that play important roles in intestinal homeostasis. These genetic studies have identified a critical role for macroautophagy/autophagy and more recently, lysosomal function, in maintaining the intestinal barrier and mucosal homeostasis. This review highlights recent work on the functional characterization of IBD-associated human genetic variants in cell type-specific functions for autophagy.

Efficacy of Continuous Interleukin 1 Blockade in Mevalonate Kinase Deficiency: A Multicenter Retrospective Study in 13 Adult Patients and Literature Review

OBJECTIVE

To report efficacy and tolerance of interleukin 1 blockade in adult patients with mevalonate kinase deficiency (MKD).

METHODS

We retrospectively collected data on 13 patients with MKD who had received anakinra (n = 10) and canakinumab (n = 7).

RESULTS

Anakinra resulted in complete or partial remission in 3/10 and 5/10 patients, respectively, and no efficacy in 2/10, but a switch to canakinumab led to partial remission. Canakinumab resulted in complete or partial remission in 3/7 and 4/7 patients, respectively.

CONCLUSION

These data support frequent partial responses, showing a better response with canakinumab. The genotype and therapeutic outcomes correlation should help in the personalization of treatment.

Reduced serpinB9-mediated caspase-1 inhibition can contribute to autoinflammatory disease

Patients who suffer from autoinflammatory disease (AID) exhibit seemingly uncontrolled release of interleukin (IL)-1β. The presence of this inflammatory cytokine triggers immune activation in absence of pathogens and foreign material. The mechanisms that contribute to ‘sterile inflammation’ episodes in AID patients are not fully understood, although for some AIDs underlying genetic causes have been identified. We show that the serine protease inhibitor B9 (serpinB9) regulates IL-1β release in human monocytes. SerpinB9 function is more commonly known for its role in control of granzyme B. SerpinB9 however also serves to restrain IL-1β maturation through caspase-1 inhibition. We here describe an autoinflammatory disease-associated serpinB9 (c.985G>T, A329S) variant, which we discovered in a patient with unknown AID. Using patient cells and serpinB9 overexpressing monocytic cells, we show the A329S variant of serpinB9 exhibits unobstructed granzyme B inhibition, but compromised caspase-1 inhibition. SerpinB9 gene variants might contribute to AID development.

Autophagy dysfunction in autoinflammatory diseases

Autoinflammatory diseases (AUIDs) are a genetically heterogeneous group of rheumatic diseases characterized by episodic inflammation linked with dysregulated innate immune responses. In this review, we summarize the molecular mechanisms altered by disease-associated variants in several AUIDs, including NOD2-associated diseases, TNF receptor-associated periodic syndrome (TRAPS), familial Mediterranean fever (FMF) and hyperimmunoglobulinemia D and periodic fever syndrome (HIDS), and highlight the roles dysregulated autophagy plays in disease pathogenesis. Autophagy is a conserved eukaryotic pathway for the elimination of cellular stressors, such as misfolded proteins, damaged organelles, or intracellular microorganisms. It is now recognized that autophagy also functions to control inflammation through regulatory interactions with innate immune signaling pathways. AUID-associated genetic variants are known to directly activate inflammatory signaling pathways. Recent evidence also indicates that these variants may also cause impairment of autophagy, thus augmenting inflammatory responses indirectly. Intriguingly, these variants can impair autophagy by different mechanisms, further implicating the autophagic response pathway in AUIDs. These discoveries provide evidence that autophagy could be investigated as a new therapeutic target for AUIDs.

25-Hydroxycholesterol and inflammation in Lovastatin-deregulated mevalonate pathway

Mevalonate pathway deregulation has been observed in several diseases, including Mevalonate kinase deficiency (MKD). MKD is a hereditary auto-inflammatory disorder, due to mutations at mevalonate kinase gene (MVK), encoding mevalonate kinase (MK) enzyme. MVK mutations have been reported as associated with impairment of mevalonate pathway with consequent decrease of protein prenylation levels, defective autophagy and increase of IL-1β secretion, followed by cell death. Since 25-hydroxycholesterol (25-HC), a metabolite of cholesterol, can suppress IL-1β production, thus reducing inflammation, we evaluated the effect of 25-HC in an in vitro model of mevalonate pathway alteration, obtained using Lovastatin. Human glioblastoma cell line (U87-MG) was chosen to mimic, at least in part, the central nervous system impairment observed in MKD; 25-HC effects were evaluated aimed at disclosing if this compound could be considered as novel potential drug for MKD. Our results showed that 25-HC is able to reduce inflammation but it is ineffective to restore autophagy flux and to decrease apoptosis levels, both caused by lower protein prenylation; so, in spite of its anti-inflammatory action it is not useful to rescue defective prenylation/autophagy impairment-driven apoptosis in Lovastatin impaired mevalonate pathway. We hypothesize the presence in the mevalonate pathway of alternative mechanisms acting between inflammation and apoptotic autophagy impairment.

The Role of Monocyte Percentage in Osteoporosis in Male Rheumatic Diseases

Osteoporosis is easily overlooked in male patients, especially in the field of rheumatic diseases mostly prevalent with female patients, and its link to pathogenesis is still lacking. Attenuated monocyte apoptosis from a transcriptome-wide expression study illustrates the role of monocytes in osteoporosis. This study tested the hypothesis that the monocyte percentage among leukocytes could be a biomarker of osteoporosis in rheumatic diseases. Eighty-seven males with rheumatic diseases were evaluated in rheumatology outpatient clinics for bone mineral density (BMD) and surrogate markers, such as routine peripheral blood parameters and autoantibodies. From the total number of 87 patients included in this study, only 15 met the criteria for diagnosis of osteoporosis. Both age and monocyte percentage remained independently associated with the presence of osteoporosis. Steroid dose (equivalent prednisolone dose) was negatively associated with BMD of the hip area and platelet counts were negatively associated with BMD and T score of the spine area. Besides age, monocyte percentage meets the major requirements for osteoporosis in male rheumatic diseases. A higher monocyte percentage in male rheumatic disease patients, aged over 50 years in this study, and BMD study should be considered in order to reduce the risk of osteoporosis-related fractures.

Inflammasomes on the Crossroads of Innate Immune Recognition and Metabolic Control

Inflammasomes are protein complexes formed upon encounter of microbial or damage-associated stimuli. The main output of inflammasome assembly is activation of caspase-1, a protease involved in both pro-inflammatory and host-protective responses. Defined bacterial or viral ligands have been identified for the inflammasome-forming receptors AIM2, NLRP1, and NLRC4. The signals activating other inflammasomes, NLRP3, NLRP6, and pyrin, are less well understood. Recent studies implicated several low-molecular-weight compounds traditionally linked to metabolism, not immunity, in modulation of inflammasome signaling. Furthermore, genetic, pharmacological, or pathogen-mediated interference with energy metabolism also affects inflammasome activation. Here we review the findings on how microbial- and host-derived metabolites regulate activation of the NLRP3 and NLRP6 inflammasomes. We discuss the different models of how glycolysis and mitochondrial metabolism control the NLRP3 inflammasome. Finally, we summarize the findings on metabolic control of pyrin and point to open questions to be addressed to broaden our understanding of metabolism-inflammasome interactions.

Prolonged fasting suppresses mitochondrial NLRP3 inflammasome assembly and activation via SIRT3-mediated activation of superoxide dismutase 2

Twenty-four hours of fasting is known to blunt activation of the human NLRP3 inflammasome. This effect might be mediated by SIRT3 activation, controlling mitochondrial reactive oxygen species. To characterize the molecular underpinnings of this fasting effect, we comparatively analyzed the NLRP3 inflammasome response to nutrient deprivation in wild-type and SIRT3 knock-out mice. Consistent with previous findings for human NLRP3, prolonged fasting blunted the inflammasome in wild-type mice but not in SIRT3 knock-out mice. In SIRT3 knock-out bone marrow-derived macrophages, NLRP3 activation promoted excess cytosolic extrusion of mitochondrial DNA along with increased reactive oxygen species and reduced superoxide dismutase 2 (SOD2) activity. Interestingly, the negative regulatory effect of SIRT3 on NLRP3 was not due to transcriptional control or priming of canonical inflammasome components but, rather, occurred via SIRT3-mediated deacetylation of mitochondrial SOD2, leading to SOD2 activation. We also found that siRNA knockdown of SIRT3 or SOD2 increased NLRP3 supercomplex formation and activation. Moreover, overexpression of wild-type and constitutively active SOD2 similarly blunted inflammasome assembly and activation, effects that were abrogated by acetylation mimic-modified SOD2. Finally, in vivo administration of lipopolysaccharide increased liver injury and the levels of peritoneal macrophage cytokines, including IL-1β, in SIRT3 KO mice. These results support the emerging concept that enhancing mitochondrial resilience against damage-associated molecular patterns may play a pivotal role in preventing inflammation and that the anti-inflammatory effect of fasting-mimetic diets may be mediated, in part, through SIRT3-directed blunting of NLRP3 inflammasome assembly and activation.

The interplay between autophagy and tumorigenesis: exploiting autophagy as a means of anticancer therapy

In wild-type cells, autophagy represents a tumour-suppressor mechanism, and dysfunction of the autophagy machinery increases genomic instability, DNA damage, oxidative stress and stem/progenitor expansion, which are events associated with cancer onset. Autophagy occurs at a basal level in all cells depending on cell type and cellular microenvironment. However, the role of autophagy in cancer is diverse and can promote different outcomes even in a single tumour. For example, in hypoxic tumour regions, autophagy emerges as a protective mechanism and allows cancer cell survival. By contrast, in cancer cells surrounding the tumour mass, the induction of autophagy by radio- or chemotherapy promotes cell death and significantly reduces the tumour mass. Importantly, inhibition of autophagy compromises tumorigenesis by mechanisms that are not entirely understood. The aim of this review is to explain the apparently contradictory role of autophagy as a mechanism that both promotes and inhibits tumorigenesis using different models. The induction/inhibition of autophagy as a mechanism for cancer treatment is also discussed.

Inflammasome activation by nucleic acids and nucleosomes in sterile inflammation… or is it sterile?

Inflammasomes are multiprotein complexes that form in the cytoplasm in response to cellular damage and cytosolic pathogen-associated molecules during infection. These complexes play important roles in initiating innate and adaptive immune responses to infectious disease. In addition, inflammasomes are now recognized as important mediators of sterile inflammation in various autoimmune and autoinflammatory diseases. Interestingly, microbiota and infection play critical roles in the development of 'sterile inflammation'. Herein, we highlight recent advances in our understanding of the role for inflammasomes in nucleic acid-, nucleosome-, and histone-driven sterile inflammation and discuss knowledge gaps and areas of potential future research.

Mitochondrial DNA in innate immune responses and inflammatory pathology

Mitochondrial DNA (mtDNA) - which is well known for its role in oxidative phosphorylation and maternally inherited mitochondrial diseases - is increasingly recognized as an agonist of the innate immune system that influences antimicrobial responses and inflammatory pathology. On entering the cytoplasm, extracellular space or circulation, mtDNA can engage multiple pattern-recognition receptors in cell-type- and context-dependent manners to trigger pro-inflammatory and type I interferon responses. Here, we review the expanding research field of mtDNA in innate immune responses to highlight new mechanistic insights and discuss the physiological and pathological relevance of this exciting area of mitochondrial biology.

Dysregulated IL-1β Secretion in Autoinflammatory Diseases: A Matter of Stress?

Infectious and sterile inflammation is induced by activation of innate immune cells. Triggering of toll-like receptors by pathogen-associated molecular pattern or damage-associated molecular pattern (PAMP or DAMP) molecules generates reactive oxygen species that in turn induce production and activation of pro-inflammatory cytokines such as IL-1β. Recent evidence indicates that cell stress due to common events, like starvation, enhanced metabolic demand, cold or heat, not only potentiates inflammation but may also directly trigger it in the absence of PAMPs or DAMPs. Stress-mediated inflammation is also a common feature of many hereditary disorders, due to the proteotoxic effects of mutant proteins. We propose that harmful mutant proteins can induce dysregulated IL-1β production and inflammation through different pathways depending on the cell type involved. When expressed in professional inflammatory cells, stress induced by the mutant protein activates in a cell-autonomous way the onset of inflammation and mediates its aberrant development, resulting in the explosive responses that hallmark autoinflammatory diseases. When expressed in non-immune cells, the mutant protein may cause the release of transcellular stress signals that trigger and propagate inflammation.

Hepatic Fgf21 Expression Is Repressed after Simvastatin Treatment in Mice

Fibroblast growth factor 21 (Fgf21) is a hormone with emerging beneficial roles in glucose and lipid homeostasis. The interest in Fgf21 as a potential antidiabetic drug and the factors that regulate its production and secretion is growing. Statins are the most widely prescribed drug for the treatment of dyslipidemia. However, the function of statins is not limited to the lowering of cholesterol as they are associated with pleiotropic actions such as antioxidant, anti-inflammatory and cytoprotective effects. The recently described effect of statins on mitochondrial function and the induction of Fgf21 by mitochondrial stress prompted us to investigate the effect of statin treatment on Fgf21 expression in the liver. To this end, C57BL6J male mice and primary mouse hepatocytes were treated with simvastatin, and Fgf21 expression was subsequently assessed by immunoblotting and quantitative real-time PCR. Hepatic Fgf21 protein and mRNA and circulating levels of FGF21significantly decreased in mice that had received simvastatin in their food (0.1% w/w) for 1 week. This effect was also observed with simvastatin doses as low as 0.01% w/w for 1 week or following 2 intraperitoneal injections within a single day. The reduction in Fgf21 mRNA levels was further verified in primary mouse hepatocytes, indicating that the effect of simvastatin is cell autonomous. In conclusion, simvastatin treatment reduced the circulating and hepatic Fgf21 levels and this effect warrants further investigation with reference to its role in metabolism.

Recent Advances of the NLRP3 Inflammasome in Central Nervous System Disorders

Inflammasomes are multiprotein complexes that trigger the activation of caspases-1 and subsequently the maturation of proinflammatory cytokines interleukin-1β and interleukin-18. These cytokines play a critical role in mediating inflammation and innate immunity response. Among various inflammasome complexes, the NLRP3 inflammasome is the best characterized, which has been demonstrated as a crucial role in various diseases. Here, we review recently described mechanisms that are involved in the activation and regulation of NLRP3 inflammasome. In addition, we summarize the recent researches on the role of NLRP3 inflammasome in central nervous system (CNS) diseases, including traumatic brain injury, ischemic stroke and hemorrhagic stroke, brain tumor, neurodegenerative diseases, and other CNS diseases. In conclusion, the NLRP3 inflammasome may be a promising therapeutic target for these CNS diseases.

Activation of autophagy by FOXO3 regulates redox homeostasis during osteogenic differentiation

Bone remodeling is a continuous physiological process that requires constant generation of new osteoblasts from mesenchymal stem cells (MSCs). Differentiation of MSCs to osteoblast requires a metabolic switch from glycolysis to increased mitochondrial respiration to ensure the sufficient energy supply to complete this process. As a consequence of this increased mitochondrial metabolism, the levels of endogenous reactive oxygen species (ROS) rise. In the current study we analyzed the role of forkhead box O3 (FOXO3) in the control of ROS levels in human MSCs (hMSCs) during osteogenic differentiation. Treatment of hMSCs with H₂O₂ induced FOXO3 phosphorylation at Ser294 and nuclear translocation. This ROS-mediated activation of FOXO3 was dependent on mitogen-activated protein kinase 8 (MAPK8/JNK) activity. Upon FOXO3 downregulation, osteoblastic differentiation was impaired and hMSCs lost their ability to control elevated ROS levels. Our results also demonstrate that in response to elevated ROS levels, FOXO3 induces autophagy in hMSCs. In line with this, impairment of autophagy by autophagy-related 7 (ATG7) knockdown resulted in a reduced capacity of hMSCs to regulate elevated ROS levels, together with a reduced osteoblast differentiation. Taken together our findings are consistent with a model where in hMSCs, FOXO3 is required to induce autophagy and thereby reduce elevated ROS levels resulting from the increased mitochondrial respiration during osteoblast differentiation. These new molecular insights provide an important contribution to our better understanding of bone physiology.

Mevalonate kinase deficiency: current perspectives

Mevalonate kinase deficiency (MKD) is a recessively inherited autoinflammatory disorder with a spectrum of manifestations, including the well-defined clinical phenotypes of hyperimmunoglobulinemia D and periodic fever syndrome and mevalonic aciduria. Patients with MKD have recurrent attacks of hyperinflammation associated with fever, abdominal pain, arthralgias, and mucocutaneous lesions, and more severely affected patients also have dysmorphisms and central nervous system anomalies. MKD is caused by mutations in the gene encoding mevalonate kinase, with the degree of residual enzyme activity largely determining disease severity. Mevalonate kinase is essential for the biosynthesis of nonsterol isoprenoids, which mediate protein prenylation. Although the precise pathogenesis of MKD remains unclear, increasing evidence suggests that deficiency in protein prenylation leads to innate immune activation and systemic hyperinflammation. Given the emerging understanding of MKD as an autoinflammatory disorder, recent treatment approaches have largely focused on cytokine-directed biologic therapy. Herein, we review the current genetic and pathologic understanding of MKD, its various clinical phenotypes, and the evolving treatment approach for this multifaceted disorder.

Mevalonate kinase deficiency leads to decreased prenylation of Rab GTPases

Mevalonate kinase deficiency (MKD) is caused by mutations in a key enzyme of the mevalonate–cholesterol biosynthesis pathway, leading to recurrent autoinflammatory disease characterised by enhanced release of interleukin-1β (IL-1β). It is currently believed that the inflammatory phenotype of MKD is triggered by temperature-sensitive loss of mevalonate kinase activity and reduced biosynthesis of isoprenoid lipids required for the prenylation of small GTPase proteins. However, previous studies have not clearly shown any change in protein prenylation in patient cells under normal conditions. With lymphoblast cell lines from two compound heterozygous MKD patients, we used a highly sensitive in vitro prenylation assay, together with quantitative mass spectrometry, to reveal a subtle accumulation of unprenylated Rab GTPases in cells cultured for 3 days or more at 40 °C compared with 37 °C. This included a 200% increase in unprenylated Rab7A, Rab14 and Rab1A. Inhibition of sterol regulatory element-binding protein (SREBP) activation by fatostatin led to more pronounced accumulation of unprenylated Rab proteins in MKD cells but not parent cells, suggesting that cultured MKD cells may partially overcome the loss of isoprenoid lipids by SREBP-mediated upregulation of enzymes required for isoprenoid biosynthesis. Furthermore, while inhibition of Rho/Rac/Rap prenylation promoted the release of IL-1β, specific inhibition of Rab prenylation by NE10790 had no effect in human peripheral blood mononuclear cells or human THP-1 monocytic cells. These studies demonstrate for the first time that mutations in mevalonate kinase can lead to a mild, temperature-induced defect in the prenylation of small GTPases, but that loss of prenylated Rab GTPases is not the cause of enhanced IL-1β release in MKD.

Autophagy Proteins ATG5 and ATG7 Are Essential for the Maintenance of Human CD34(+) Hematopoietic Stem-Progenitor Cells

Autophagy is a highly regulated catabolic process that involves sequestration and lysosomal degradation of cytosolic components such as damaged organelles and misfolded proteins. While autophagy can be considered to be a general cellular housekeeping process, it has become clear that it may also play cell type-dependent functional roles. In this study, we analyzed the functional importance of autophagy in human hematopoietic stem/progenitor cells (HSPCs), and how this is regulated during differentiation. Western blot-based analysis of LC3-II and p62 levels, as well as flow cytometry-based autophagic vesicle quantification, demonstrated that umbilical cord blood-derived CD34(+) /CD38(-) immature hematopoietic progenitors show a higher autophagic flux than CD34(+) /CD38(+) progenitors and more differentiated myeloid and erythroid cells. This high autophagic flux was critical for maintaining stem and progenitor function since knockdown of autophagy genes ATG5 or ATG7 resulted in reduced HSPC frequencies in vitro as well as in vivo. The reduction in HSPCs was not due to impaired differentiation, but at least in part due to reduced cell cycle progression and increased apoptosis. This is accompanied by increased expression of p53, proapoptotic genes BAX and PUMA, and the cell cycle inhibitor p21, as well as increased levels of cleaved caspase-3 and reactive oxygen species. Taken together, our data demonstrate that autophagy is an important regulatory mechanism for human HSCs and their progeny, reducing cellular stress and promoting survival. Stem Cells 2016;34:1651-1663.

Autoinflammatory Syndromes in Children

Systemic autoinflammatory diseases are rare disorders of innate immunity which usually present in childhood with recurrent or continuous attacks of fever and systemic inflammation. The discovery of the genetic defect underlying Familial Mediterranean fever in 1997 has proved exceptionally informative about the innate immune system and the regulation of pro inflammatory cytokines particularly IL-1. Although extremely rare, systemic autoinflammatory diseases are important to recognise as many can now be completely controlled by long term drug therapies. Diagnosis relies on clinical suspicion followed by genetic testing. This review will focus on the main systemic autoinflammatory diseases.

Mild mitochondrial metabolic deficits by α-ketoglutarate dehydrogenase inhibition cause prominent changes in intracellular autophagic signaling: Potential role in the pathobiology of Alzheimer's disease

Brain activities of the mitochondrial enzyme α-ketoglutarate dehydrogenase complex (KGDHC) are reduced in Alzheimer's disease and other age-related neurodegenerative disorders. The goal of the present study was to test the consequences of mild impairment of KGDHC on the structure, protein signaling and dynamics (mitophagy, fusion, fission, biogenesis) of the mitochondria. Inhibition of KGDHC reduced its in situ activity by 23-53% in human neuroblastoma SH-SY5Y cells, but neither altered the mitochondrial membrane potential nor the ATP levels at any tested time-points. The attenuated KGDHC activity increased translocation of dynamin-related protein-1 (Drp1) and microtubule-associated protein 1A/1B-light chain 3 (LC3) from the cytosol to the mitochondria, and promoted mitochondrial cytochrome c release. Inhibition of KGDHC also increased the negative surface charges (anionic phospholipids as assessed by Annexin V binding) on the mitochondria. Morphological assessments of the mitochondria revealed increased fission and mitophagy. Taken together, our results suggest the existence of the regulation of the mitochondrial dynamism including fission and fusion by the mitochondrial KGDHC activity via the involvement of the cytosolic and mitochondrial protein signaling molecules. A better understanding of the link among mild impairment of metabolism, induction of mitophagy/autophagy and altered protein signaling will help to identify new mechanisms of neurodegeneration and reveal potential new therapeutic approaches.