Signal transducer and activator of transcription 2 deficiency is a novel disorder of mitochondrial fission

The segmented flavivirus Alongshan virus reduces mitochondrial mass by degrading STAT2 to suppress the innate immune response

Alongshan virus (ALSV) is a newly discovered pathogen in the Flaviviridae family, characterized by a unique multi-segmented genome that is distantly related to the canonical flaviviruses. Understanding the pathogenic mechanism of this emerging segmented flavivirus is crucial for the development of effective intervention strategies. In this study, we demonstrate that ALSV can infect various mammalian cells and induce the expression of antiviral genes. Furthermore, ALSV is sensitive to IFN-β, but it has developed strategies to counteract the host's type I IFN response. Mechanistically, ALSV's nonstructural protein NSP1 interacts with and degrades human STAT2 through an autophagy pathway, with species-dependent effects. This degradation directly inhibits the expression of interferon-stimulated genes (ISGs). Additionally, NSP1-mediated degradation of STAT2 disrupts mitochondrial dynamics, leading to mitophagy and inhibition of mitochondrial biogenesis. This, in turn, suppresses the host's innate immune response. Interestingly, we found that inhibiting mitophagy using 3-methyladenine and enhancing mitochondrial biogenesis with the PPARγ agonist pioglitazone can reverse NSP1-mediated inhibition of ISGs, suggesting that promoting mitochondrial mass could serve as an effective antiviral strategy. Specifically, the NSP1 methyltransferase domain binds to the key sites of F175/R176 located in the coiled-coil domain of STAT2. Our findings provide valuable insights into the intricate regulatory cross talk between ALSV and the host's innate immune response, shedding light on the pathogenesis of this emerging segmented flavivirus and offering potential intervention strategies.IMPORTANCEAlongshan virus (ALSV), a segmented flavivirus belonging to the Flaviviridae family, was first identified in individuals who had been bitten by ticks in Northeastern China. ALSV infection is responsible for causing Alongshan fever, a condition characterized by various clinical symptoms, including fever, headache, skin rash, myalgia, arthralgia, depression, and coma. There is an urgent need for effective antiviral therapies. Here, we demonstrate that ALSV is susceptible to IFN-β but has developed mechanisms to counteract the host's innate immune response. Specifically, the ALSV nonstructural protein NSP1 interacts with STAT2, leading to its degradation via an autophagy pathway that exhibits species-dependent effects. Additionally, NSP1 disrupts mitochondrial dynamics and suppresses mitochondrial biogenesis, resulting in a reduction in mitochondrial mass, which ultimately contributes to the inhibition of the host's innate immune response. Interestingly, we found that inhibiting mitophagy and promoting mitochondrial biogenesis can reverse NSP1-mediated suppression of innate immune response by increasing mitochondrial mass. These findings provide valuable insights into the molecular mechanisms of ALSV pathogenesis and suggest potential therapeutic targets against ALSV infection.

Mitochondrial membrane synthesis, remodelling and cellular trafficking

Mitochondria are dynamic cellular organelles with complex roles in metabolism and signalling. Primary mitochondrial disorders are a group of approximately 400 monogenic disorders arising from pathogenic genetic variants impacting mitochondrial structure, ultrastructure and/or function. Amongst these disorders, defects of complex lipid biosynthesis, especially of the unique mitochondrial membrane lipid cardiolipin, and membrane biology are an emerging group characterised by clinical heterogeneity, but with recurrent features including cardiomyopathy, encephalopathy, neurodegeneration, neuropathy and 3-methylglutaconic aciduria. This review discusses lipid synthesis in the mitochondrial membrane, the mitochondrial contact site and cristae organising system (MICOS), mitochondrial dynamics and trafficking, and the disorders associated with defects of each of these processes. We highlight overlapping functions of proteins involved in lipid biosynthesis and protein import into the mitochondria, pointing to an overarching coordination and synchronisation of mitochondrial functions. This review also focuses on membrane interactions between mitochondria and other organelles, namely the endoplasmic reticulum, peroxisomes, lysosomes and lipid droplets. We signpost disorders of these membrane interactions that may explain the observation of secondary mitochondrial dysfunction in heterogeneous pathological processes. Disruption of these organellar interactions ultimately impairs cellular homeostasis and organismal health, highlighting the central role of mitochondria in human health and disease.

Alizarin attenuates oxidative stress-induced mitochondrial damage in vascular dementia rats by promoting TRPM2 ubiquitination and proteasomal degradation via Smurf2

BACKGROUND

Alizarin (AZ) is a natural anthraquinone with anti-inflammatory and moderate antioxidant properties.

PURPOSE

In this study, we characterized the role of AZ in a rat model of vascular dementia (VaD) and explored its underlying mechanisms.

METHODS

VaD was induced by bilateral common carotid artery occlusion.

RESULTS

We found that AZ attenuated oxidative stress and improved mitochondrial structure and function in VaD rats, which led to the improvement of their learning and memory function. Mechanistically, AZ reduced transient receptor potential melastatin 2 (TRPM2) expression and activation of the Janus-kinase and signal transducer activator of transcription (JAK-STAT) pathway in VaD rats. In particular, the reduction in the expression of TRPM2 channels was the key to the attenuation of the oxidative stress-induced mitochondrial damage, which may be achieved by increasing the expression of the E3 ubiquitin ligase, Smad-ubiquitination regulatory factor 2 (Smurf2); thereby increasing the ubiquitination and degradation levels of TRPM2.

CONCLUSION

Our results suggest that AZ is an effective candidate drug for ameliorating VaD and provide new insights into the current clinical treatment of VaD.

Interferon Stimulated Gene Expression Is a Biomarker for Primary Mitochondrial Disease

OBJECTIVE

Mitochondria are implicated in regulation of the innate immune response. We hypothesized that abnormalities in interferon signaling may contribute to pathophysiology in patients with primary mitochondrial disease (PMD).

METHODS

Expression of interferon stimulated genes (ISGs) was measured by real-time polymerase chain reaction (PCR) in whole blood samples from a cohort of patients with PMD.

RESULTS

Upregulated ISG expression was observed in a high proportion (41/55, 75%) of patients with PMD on at least 1 occasion, most frequently IFI27 upregulation, seen in 50% of the samples. Some patients had extremely high IFI27 levels, similar to those seen in patients with primary interferonopathies. A statistically significant correlation was observed between elevated IFI27 gene expression and PMD, but not between IFI27 and secondary mitochondrial dysfunction, suggesting that ISG upregulation is a biomarker of PMD. In some patients with PMD, ISG abnormalities persisted on repeat measurement over several years, indicative of ongoing chronic inflammation. Subgroup analyses suggested common ISG signatures in patients with similar mitochondrial disease mechanisms and positive correlations with disease severity among patients with identical genetic diagnoses.

INTERPRETATION

Dysregulated interferon signaling is frequently seen in patients with PMD suggesting that interferon dysregulation is a contributor to pathophysiology. This may indicate a role for repurposing of immunomodulatory therapies for the treatment of PMDs by targeting interferon signaling. ANN NEUROL 2024;96:1185-1200.

Genotype and Phenotype Characteristics of 58 Cases of Mitochondrial Epilepsy with Nuclear DNA Mutations in Children

OBJECTIVE

Identify the genotype and clinical characteristics of mitochondrial epilepsy caused by nDNA mutations in Chinese children and explore the treatment and prognosis of the condition.

STUDY DESIGN

This is a retrospective cohort study conducted at a single center, including patients diagnosed with an established nDNA mutation-associated primary mitochondrial disease between October 2012 and March 2023 who also met the practical clinical definition of epilepsy published by the ILAE in 2014.

RESULTS

Of the 58 patients identified, 74.1% had an onset before the age of 1 year and 63.8% had seizures as their initial symptom. Developmental and epileptic encephalopathy (DEE) (31%) are the most common phenotypes. The most frequently observed MRI abnormalities include abnormal signal asymmetry in the bilateral basal ganglia and/or brainstem (34.7%), as well as brain atrophy, myelin sheath dysplasia, and corpus callosum dysplasia (32.7%). Of the 40 patients followed, seizure treatment was effective in 18 of the cases, while it was ineffective in 22. The mitochondrial DNA depletion syndrome (MDS) was found to be more difficult to control seizures than other phenotypes (P < 0.05). Additionally, the MDS was associated with a significantly higher mortality rate compared to alternative phenotypes (P < 0.05).

CONCLUSIONS

The onset of mitochondrial epilepsy due to nDNA mutations is early and seizures are the most common initial symptom. DEE is the most common phenotype. Characteristic MRI abnormalities in the brain may be helpful in the diagnosis of primary mitochondrial disease. People with MDS typically face challenges in seizure control and have a poor prognosis.

Infections in Inborn Errors of STATs

The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway is highly conserved and essential for numerous biological functions triggered by extracellular signals, including cell proliferation, metabolism, immune response, and inflammation. Defects in STATs, either loss-of-function or gain-of-function defects, lead to a broad spectrum of clinical phenotypes in humans, including a wide range of infectious complications. The susceptibility to pathogens can stem from defects in immune cells within the hematopoietic compartment, impaired barrier functions of non-hematopoietic compartment, or a combination of both, depending on the specific STAT defect as well as the pathogen exposure history. Effective management involves antimicrobial prophylaxis tailored to the patient's infection risk and improving disease control with targeted therapies and/or hematopoietic cell transplantation.

The lack of either IRF9, or STAT2, has surprisingly little effect on human natural killer cell development and function

Analysis of genetically defined immunodeficient patients allows study of the effect of the absence of specific proteins on human immune function in real-world conditions. Here we have addressed the importance of type I interferon signalling for human NK cell development by studying the phenotype and function of circulating NK cells isolated from patients suffering primary immunodeficiency disease due to mutation of either the human interferon regulatory factor 9 (IRF9) or the signal transducer and activator of transcription 2 (STAT2) genes. IRF9, together with phosphorylated STAT1 and STAT2, form a heterotrimer called interferon stimulated gene factor 3 (ISGF3) which promotes the expression of hundreds of IFN-stimulated genes that mediate antiviral function triggered by exposure to type I interferons. IRF9- and STAT2-deficient patients are unable to respond efficiently to stimulation by type I interferons and so our experiments provide insights into the importance of type I interferon signalling and the consequences of its impairment on human NK cell biology. Surprisingly, the NK cells of these patients display essentially normal phenotype and function.

In search of a function for human type III interferons: insights from inherited and acquired deficits

The essential and redundant functions of human type I and II interferons (IFNs) have been delineated over the last three decades by studies of patients with inborn errors of immunity or their autoimmune phenocopies, but much less is known about type III IFNs. Patients with cells that do not respond to type III IFNs due to inherited IL10RB deficiency display no overt viral disease, and their inflammatory disease phenotypes can be explained by defective signaling via other interleukine10RB-dependent pathways. Moreover, patients with inherited deficiencies of interferon-stimulated gene factor 3 (ISGF-3) (STAT1, STAT2, IRF9) present viral diseases also seen in patients with inherited deficiencies of the type I IFN receptor (IFNAR1/2). Finally, patients with autoantibodies neutralizing type III IFNs have no obvious predisposition to viral disease. Current findings thus suggest that type III IFNs are largely redundant in humans. The essential functions of human type III IFNs, particularly in antiviral defenses, remain to be discovered.

JAK/STAT defects and immune dysregulation, and guiding therapeutic choices

Inborn errors of immunity (IEIs) encompass a diverse spectrum of genetic disorders that disrupt the intricate mechanisms of the immune system, leading to a variety of clinical manifestations. Traditionally associated with an increased susceptibility to recurrent infections, IEIs have unveiled a broader clinical landscape, encompassing immune dysregulation disorders characterized by autoimmunity, severe allergy, lymphoproliferation, and even malignancy. This review delves into the intricate interplay between IEIs and the JAK-STAT signaling pathway, a critical regulator of immune homeostasis. Mutations within this pathway can lead to a wide array of clinical presentations, even within the same gene. This heterogeneity poses a significant challenge, necessitating individually tailored therapeutic approaches to effectively manage the diverse manifestations of these disorders. Additionally, JAK-STAT pathway defects can lead to simultaneous susceptibility to both infection and immune dysregulation. JAK inhibitors, with their ability to suppress JAK-STAT signaling, have emerged as powerful tools in controlling immune dysregulation. However, questions remain regarding the optimal selection and dosing regimens for each specific condition. Hematopoietic stem cell transplantation (HSCT) holds promise as a curative therapy for many JAK-STAT pathway disorders, but this procedure carries significant risks. The use of JAK inhibitors as a bridge to HSCT has been proposed as a potential strategy to mitigate these risks.

From Mendel to mycoses: Immuno-genomic warfare at the human-fungus interface

Fungi are opportunists: They particularly require a defect of immunity to cause severe or disseminated disease. While often secondary to an apparent iatrogenic cause, fungal diseases do occur in the absence of one, albeit infrequently. These rare cases may be due to an underlying genetic immunodeficiency that can present variably in age of onset, severity, or other infections, and in the absence of a family history of disease. They may also be due to anti-cytokine autoantibodies. This review provides a background on how human genetics or autoantibodies underlie cases of susceptibility to severe or disseminated fungal disease. Subsequently, the lessons learned from these inborn errors of immunity marked by fungal disease (IEI-FD) provide a framework to begin to mechanistically decipher fungal syndromes, potentially paving the way for precision therapy of the mycoses.

Differential inflammation responses determine the variable phenotypes of epilepsy induced by GABRG2 mutations

OBJECTIVE

To explore the mechanism involved in variable phenotypes of epilepsy models induced by γ-aminobutyric acid type A γ2 subunit (GABRG2) mutations.

METHODS

The zebrafish carrying wild-type (WT) GABRG2, mutant GABRG2(P282S), GABRG2(F343L) and GABRG2(I107T) were established by Tol2kit transgenesis system and Gateway method. Behavioral analysis of different transgenic zebrafish was performed with the DanioVision Video-Track framework and the brain activity was analyzed by field potential recording with MD3000 Bio-signal Acquisition and Processing System. The transcriptome analysis was applied to detect the underlying mechanisms of variable phenotypes caused by different GABRG2 mutations.

RESULTS

The established Tg(hGABRG2P282S ) zebrafish showed hyperactivity and spontaneous seizures, which were more sensitive to chemical and physical epileptic stimulations. Traditional antiepileptic drugs, such as Clonazepam (CBZ) and valproic acid (VPA), could ameliorate the hyperactivity in Tg(hGABRG2P282S ) zebrafish. The metabolic pathway was significantly changed in the brain transcriptome of Tg(hGABRG2P282S ) zebrafish. In addition, the behavioral activity, production of pro-inflammatory factors, and activation of the IL-2 receptor signal pathway varied among the three mutant zebrafish lines.

CONCLUSION

We successfully established transgenic zebrafish epileptic models expressing human mutant GABRG2(P282S), in which CBZ and VPA showed antiepileptic effects. Differential inflammatory responses, especially the SOCS/JAK/STAT signaling pathway, might be related to the phenotypes of genetic epilepsy induced by GABRG2 mutations. Further study will expand the pathological mechanisms of genetic epilepsies and provide a theoretical basis for searching for effective drug treatment.

The role of JAK/STAT signaling pathway in cerebral ischemia-reperfusion injury and the therapeutic effect of traditional Chinese medicine: A narrative review

Cerebral ischemia is a cerebrovascular disease with symptoms caused by insufficient blood or oxygen supply to the brain. When blood supplied is restored after cerebral ischemia, secondary brain injury may occur, which is called cerebral ischemia-reperfusion injury (CIRI). In this process, the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway plays an important role. It mediates neuroinflammation and participates in the regulation of physiological activities, such as cell proliferation, differentiation, and apoptosis. After CIRI, M1 microglia is activated and recruited by the damaged tissue. The inflammatory factors are produced by M1 microglia through the JAK/STAT pathway, eventually leading to cell apoptosis. Meanwhile, the JAK2/STAT3 signaling pathway and the expression of lipocalin-2 and caspase-3 could increase. In the pathway, phosphorylated JAK2 and phosphorylated STAT3 function of 2 ways. They not only promote the proliferation of neurons, but also affect the differentiation direction of neural stem cells by further acting on the Notch signaling pathway. Recently, traditional Chinese medicine (TCM) is a key player in CIRI, through JAK2, STAT3, STAT1 and their phosphorylation. Therefore, the review focuses on the JAK/STAT signaling pathway and its relationship with CIRI as well as the influence of the TCM on this pathway. It is aimed at providing the basis for future clinical research on the molecular mechanism of TCM in the treatment of CIRI.

Mitochondrial DNA damage triggers spread of Parkinson's disease-like pathology

In the field of neurodegenerative diseases, especially sporadic Parkinson's disease (sPD) with dementia (sPDD), the question of how the disease starts and spreads in the brain remains central. While prion-like proteins have been designated as a culprit, recent studies suggest the involvement of additional factors. We found that oxidative stress, damaged DNA binding, cytosolic DNA sensing, and Toll-Like Receptor (TLR)4/9 activation pathways are strongly associated with the sPDD transcriptome, which has dysregulated type I Interferon (IFN) signaling. In sPD patients, we confirmed deletions of mitochondrial (mt)DNA in the medial frontal gyrus, suggesting a potential role of damaged mtDNA in the disease pathophysiology. To explore its contribution to pathology, we used spontaneous models of sPDD caused by deletion of type I IFN signaling (Ifnb-/-/Ifnar-/- mice). We found that the lack of neuronal IFNβ/IFNAR leads to oxidization, mutation, and deletion in mtDNA, which is subsequently released outside the neurons. Injecting damaged mtDNA into mouse brain induced PDD-like behavioral symptoms, including neuropsychiatric, motor, and cognitive impairments. Furthermore, it caused neurodegeneration in brain regions distant from the injection site, suggesting that damaged mtDNA triggers spread of PDD characteristics in an "infectious-like" manner. We also discovered that the mechanism through which damaged mtDNA causes pathology in healthy neurons is independent of Cyclic GMP-AMP synthase and IFNβ/IFNAR, but rather involves the dual activation of TLR9/4 pathways, resulting in increased oxidative stress and neuronal cell death, respectively. Our proteomic analysis of extracellular vesicles containing damaged mtDNA identified the TLR4 activator, Ribosomal Protein S3 as a key protein involved in recognizing and extruding damaged mtDNA. These findings might shed light on new molecular pathways through which damaged mtDNA initiates and spreads PD-like disease, potentially opening new avenues for therapeutic interventions or disease monitoring.

Aberrant mitochondrial dynamics contributes to diaphragmatic weakness induced by mechanical ventilation

In critical care patients, the ""temporary inactivity of the diaphragm caused by mechanical ventilation (MV) triggers a series of events leading to diaphragmatic dysfunction and atrophy, commonly known as ventilator-induced diaphragm dysfunction (VIDD). While mitochondrial dysfunction related to oxidative stress is recognized as a crucial factor in VIDD, the exact molecular mechanism remains poorly understood. In this study, we observe that 6 h of MV triggers aberrant mitochondrial dynamics, resulting in a reduction in mitochondrial size and interaction, associated with increased expression of dynamin-related protein 1 (DRP1). This effect can be prevented by P110, a molecule that inhibits the recruitment of DRP1 to the mitochondrial membrane. Furthermore, isolated mitochondria from the diaphragms of ventilated patients exhibited increased production of reactive oxygen species (ROS). These mitochondrial changes were associated with the rapid oxidation of type 1 ryanodine receptor (RyR1) and a decrease in the stabilizing subunit calstabin 1. Subsequently, we observed that the sarcoplasmic reticulum (SR) in the ventilated diaphragms showed increased calcium leakage and reduced contractile function. Importantly, the mitochondrial fission inhibitor P110 effectively prevented all of these alterations. Taken together, the results of our study illustrate that MV leads, in the diaphragm, to both mitochondrial fragmentation and dysfunction, linked to the up-/down-regulation of 320 proteins, as assessed through global comprehensive quantitative proteomics analysis, primarily associated with mitochondrial function. These outcomes underscore the significance of developing compounds aimed at modulating the balance between mitochondrial fission and fusion as potential interventions to mitigate VIDD in human patients.

Human inherited complete STAT2 deficiency underlies inflammatory viral diseases

STAT2 is a transcription factor activated by type I and III IFNs. We report 23 patients with loss-of-function variants causing autosomal recessive (AR) complete STAT2 deficiency. Both cells transfected with mutant STAT2 alleles and the patients' cells displayed impaired expression of IFN-stimulated genes and impaired control of in vitro viral infections. Clinical manifestations from early childhood onward included severe adverse reaction to live attenuated viral vaccines (LAV) and severe viral infections, particularly critical influenza pneumonia, critical COVID-19 pneumonia, and herpes simplex virus type 1 (HSV-1) encephalitis. The patients displayed various types of hyperinflammation, often triggered by viral infection or after LAV administration, which probably attested to unresolved viral infection in the absence of STAT2-dependent types I and III IFN immunity. Transcriptomic analysis revealed that circulating monocytes, neutrophils, and CD8+ memory T cells contributed to this inflammation. Several patients died from viral infection or heart failure during a febrile illness with no identified etiology. Notably, the highest mortality occurred during early childhood. These findings show that AR complete STAT2 deficiency underlay severe viral diseases and substantially impacts survival.

Combined novel homozygous variants in both SGPL1 and STAT1 presenting with severe combined immune deficiency: case report and literature review

Background

Sphingosine phosphate lyase insufficiency syndrome (SPLIS) is associated with biallelic variants in SGPL1, comprising a multisystemic disease characterized by steroid resistant nephrotic syndrome, primary adrenal insufficiency, neurological problems, skin abnormalities and immunodeficiency in described cases. Signal transducer and activator of transcription 1 (STAT1) plays an important role in orchestrating an appropriate immune response through JAK-STAT pathway. Biallelic STAT1 loss of function (LOF) variants lead to STAT1 deficiency with a severe phenotype of immunodeficiency with increased frequency of infections and poor outcome if untreated.

Case presentation

We report novel homozygous SGPL1 and STAT1 variants in a newborn of Gambian ethnicity with clinical features of SPLIS and severe combined immunodeficiency. The patient presented early in life with nephrotic syndrome, severe respiratory infection requiring ventilation, ichthyosis, and hearing loss, with T-cell lymphopenia. The combination of these two conditions led to severe combined immunodeficiency with inability to clear respiratory tract infections of viral, fungal, and bacterial nature, as well as severe nephrotic syndrome. The child sadly died at 6 weeks of age despite targeted treatments.

Conclusion

We report the finding of two novel, homozygous variants in SGPL1 and STAT1 in a patient with a severe clinical phenotype and fatal outcome early in life. This case highlights the importance of completing the primary immunodeficiency genetic panel in full to avoid missing a second diagnosis in other patients presenting with similar severe clinical phenotype early in life. For SPLIS no curative treatment is available and more research is needed to investigate different treatment modalities. Hematopoietic stem cell transplantation (HSCT) shows promising results in patients with autosomal recessive STAT1 deficiency. For this patient's family, identification of the dual diagnosis has important implications for future family planning. In addition, future siblings with the familial STAT1 variant can be offered curative treatment with HSCT.

JAK/STAT Signaling and Cervical Cancer: From the Cell Surface to the Nucleus

The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway constitutes a rapid signaling module from the cell surface to the nucleus, and activates different cellular responses, such as proliferation, survival, migration, invasion, and inflammation. When the JAK/STAT pathway is altered, it contributes to cancer progression and metastasis. STAT proteins play a central role in developing cervical cancer, and inhibiting the JAK/STAT signaling may be necessary to induce tumor cell death. Several cancers show continuous activation of different STATs, including cervical cancer. The constitutive activation of STAT proteins is associated with a poor prognosis and overall survival. The human papillomavirus (HPV) oncoproteins E6 and E7 play an essential role in cervical cancer progression, and they activate the JAK/STAT pathway and other signals that induce proliferation, survival, and migration of cancer cells. Moreover, there is a crosstalk between the JAK/STAT signaling cascade with other signaling pathways, where a plethora of different proteins activate to induce gene transcription and cell responses that contribute to tumor growth. Therefore, inhibition of the JAK/STAT pathway shows promise as a new target in cancer treatment. In this review, we discuss the role of the JAK/STAT pathway components and the role of the HPV oncoproteins associated with cellular malignancy through the JAK/STAT proteins and other signaling pathways to induce tumor growth.

Deficiencies and Dysregulation of STAT Pathways That Drive Inborn Errors of Immunity: Lessons from Patients and Mouse Models of Disease

The STAT family proteins provide critical signals for immune cell development, differentiation, and proinflammatory and anti-inflammatory responses. Inborn errors of immunity (IEIs) are caused by single gene defects leading to immune deficiency and/or dysregulation, and they have provided opportunities to identify genes important for regulating the human immune response. Studies of patients with IEIs due to altered STAT signaling, and mouse models of these diseases, have helped to shape current understanding of the mechanisms whereby STAT signaling and protein interactions regulate immunity. Although many STAT signaling pathways are shared, clinical and immune phenotypes in patients with monogenic defects of STAT signaling highlight both redundant and nonredundant pathways. In this review, we provide an overview of the shared and unique signaling pathways used by STATs, phenotypes of IEIs with altered STAT signaling, and recent discoveries that have provided insight into the human immune response and treatment of disease.

EGCG Attenuates CA1 Neuronal Death by Regulating GPx1, NF-κB S536 Phosphorylation and Mitochondrial Dynamics in the Rat Hippocampus following Status Epilepticus

Epigallocatechin-3-gallate (EGCG) is an antioxidant that directly scavenges reactive oxygen species (ROS) and inhibits pro-oxidant enzymes. Although EGCG protects hippocampal neurons from status epilepticus (SE, a prolonged seizure activity), the underlying mechanisms are not fully understood. As the preservation of mitochondrial dynamics is essential for cell viability, it is noteworthy to elucidate the effects of EGCG on impaired mitochondrial dynamics and the related signaling pathways in SE-induced CA1 neuronal degeneration, which are yet unclear. In the present study, we found that EGCG attenuated SE-induced CA1 neuronal death, accompanied by glutathione peroxidase-1 (GPx1) induction. EGCG also abrogated mitochondrial hyperfusion in these neurons by the preservation of extracellular signal-regulated kinase 1/2 (ERK1/2)-dynamin-related protein 1 (DRP1)-mediated mitochondrial fission, independent of c-Jun N-terminal kinase (JNK) activity. Furthermore, EGCG abolished SE-induced nuclear factor-κB (NF-κB) serine (S) 536 phosphorylation in CA1 neurons. ERK1/2 inhibition by U0126 diminished the effect of EGCG on neuroprotection and mitochondrial hyperfusion in response to SE without affecting GPx1 induction and NF-κB S536 phosphorylation, indicating that the restoration of ERK1/2-DRP1-mediated fission may be required for the neuroprotective effects of EGCG against SE. Therefore, our findings suggest that EGCG may protect CA1 neurons from SE insults through GPx1-ERK1/2-DRP1 and GPx1-NF-κB signaling pathways, respectively.

Inborn Error of STAT2-Dependent IFN-I Immunity in a Patient Presented with Hemophagocytic Lymphohistiocytosis and Multisystem Inflammatory Syndrome in Children

Human inborn errors of immunity (IEI) affecting the type I interferon (IFN-I) induction pathway have been associated with predisposition to severe viral infections. Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening systemic hyperinflammatory syndrome that has been increasingly associated with inborn errors of IFN-I-mediated innate immunity. Here is reported a novel case of complete deficiency of STAT2 in a 3-year-old child that presented with typical features of HLH after mumps, measles, and rubella vaccination at the age of 12 months. Due to the life-threatening risk of viral infection, she received SARS-CoV-2 mRNA vaccination. Unfortunately, she developed multisystem inflammatory syndrome in children (MIS-C) after SARS-CoV-2 infection, 4 months after the last dose. Functional studies showed an impaired IFN-I-induced response and a defective IFNα expression at later stages of STAT2 pathway induction. These results suggest a possible more complex mechanism for hyperinflammatory reactions in this type of patients involving a possible defect in the IFN-I production. Understanding the cellular and molecular links between IFN-I-induced signaling and hyperinflammatory syndromes can be critical for the diagnosis and tailored management of these patients with predisposition to severe viral infection.

Unlocking life-threatening COVID-19 through two types of inborn errors of type I IFNs

Since 2003, rare inborn errors of human type I IFN immunity have been discovered, each underlying a few severe viral illnesses. Autoantibodies neutralizing type I IFNs due to rare inborn errors of autoimmune regulator (AIRE)-driven T cell tolerance were discovered in 2006, but not initially linked to any viral disease. These two lines of clinical investigation converged in 2020, with the discovery that inherited and/or autoimmune deficiencies of type I IFN immunity accounted for approximately 15%-20% of cases of critical COVID-19 pneumonia in unvaccinated individuals. Thus, insufficient type I IFN immunity at the onset of SARS-CoV-2 infection may be a general determinant of life-threatening COVID-19. These findings illustrate the unpredictable, but considerable, contribution of the study of rare human genetic diseases to basic biology and public health.

Life-threatening viral disease in a novel form of autosomal recessive IFNAR2 deficiency in the Arctic

Type I interferons (IFN-I) play a critical role in human antiviral immunity, as demonstrated by the exceptionally rare deleterious variants of IFNAR1 or IFNAR2. We investigated five children from Greenland, Canada, and Alaska presenting with viral diseases, including life-threatening COVID-19 or influenza, in addition to meningoencephalitis and/or hemophagocytic lymphohistiocytosis following live-attenuated viral vaccination. The affected individuals bore the same homozygous IFNAR2 c.157T>C, p.Ser53Pro missense variant. Although absent from reference databases, p.Ser53Pro occurred with a minor allele frequency of 0.034 in their Inuit ancestry. The serine to proline substitution prevented cell surface expression of IFNAR2 protein, small amounts of which persisted intracellularly in an aberrantly glycosylated state. Cells exclusively expressing the p.Ser53Pro variant lacked responses to recombinant IFN-I and displayed heightened vulnerability to multiple viruses in vitro-a phenotype rescued by wild-type IFNAR2 complementation. This novel form of autosomal recessive IFNAR2 deficiency reinforces the essential role of IFN-I in viral immunity. Further studies are warranted to assess the need for population screening.

Sphingosine-1-phosphate in mitochondrial function and metabolic diseases

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid metabolite. The past decade has witnessed exponential growth in the field of S1P research, partly attributed to drugs targeting its receptors or kinases. Accumulating evidence indicates that changes in the S1P axis (i.e., S1P production, transport, and receptors) may modify metabolism and eventually mediate metabolic diseases. Dysfunction of the mitochondria on a master monitor of cellular metabolism is considered the leading cause of metabolic diseases, with aberrations typically induced by abnormal biogenesis, respiratory chain complex disorders, reactive oxygen species overproduction, calcium deposition, and mitophagy impairment. Accordingly, we discuss decades of investigation into changes in the S1P axis and how it controls mitochondrial function. Furthermore, we summarize recent scientific advances in disorders associated with the S1P axis and their involvement in the pathogenesis of metabolic diseases in humans, including type 2 diabetes mellitus and cardiovascular disease, from the perspective of mitochondrial function. Finally, we review potential challenges and prospects for S1P axis application to the regulation of mitochondrial function and metabolic diseases; these data may provide theoretical guidance for the treatment of metabolic diseases.

A Novel Case of Homozygous Interferon Alpha/Beta Receptor Alpha Chain (IFNAR1) Deficiency With Hemophagocytic Lymphohistiocytosis

We present a case of complete deficiency of the interferon alpha/beta receptor alpha chain (IFNAR1) in a child with fatal systemic hyperinflammation, apparently provoked by live-attenuated viral vaccination. Such pathologic hyperinflammation, fulfilling criteria for hemophagocytic lymphohistiocytosis, is an emerging phenotype accompanying inborn errors of type I interferon immunity.

JAK-STAT signaling in human disease: From genetic syndromes to clinical inhibition

Since its discovery, the Janus kinase-signal transduction and activation of transcription (JAK-STAT) pathway has become recognized as a central mediator of widespread and varied human physiological processes. The field of JAK-STAT biology, particularly its clinical relevance, continues to be shaped by 2 important advances. First, the increased use of genomic sequencing has led to the discovery of novel clinical syndromes caused by mutations in JAK and STAT genes. This has provided insights regarding the consequences of aberrant JAK-STAT signaling for immunity, lymphoproliferation, and malignancy. In addition, since the approval of ruxolitinib and tofacitinib, the therapeutic use of JAK inhibitors (jakinibs) has expanded to include a large spectrum of diseases. Efficacy and safety data from over a decade of clinical studies have provided additional mechanistic insights while improving the care of patients with inflammatory and neoplastic conditions. This review discusses major advances in the field, focusing on updates in genetic diseases and in studies of clinical jakinibs in human disease.

Herpes simplex encephalitis in a patient with a distinctive form of inherited IFNAR1 deficiency

Inborn errors of TLR3-dependent IFN-α/β- and IFN-λ-mediated immunity in the CNS can underlie herpes simplex virus 1 (HSV-1) encephalitis (HSE). The respective contributions of IFN-α/β and IFN-λ are unknown. We report a child homozygous for a genomic deletion of the entire coding sequence and part of the 3'-UTR of the last exon of IFNAR1, who died of HSE at the age of 2 years. An older cousin died following vaccination against measles, mumps, and rubella at 12 months of age, and another 17-year-old cousin homozygous for the same variant has had other, less severe, viral illnesses. The encoded IFNAR1 protein is expressed on the cell surface but is truncated and cannot interact with the tyrosine kinase TYK2. The patient's fibroblasts and EBV-B cells did not respond to IFN-α2b or IFN-β, in terms of STAT1, STAT2, and STAT3 phosphorylation or the genome-wide induction of IFN-stimulated genes. The patient's fibroblasts were susceptible to viruses, including HSV-1, even in the presence of exogenous IFN-α2b or IFN-β. HSE is therefore a consequence of inherited complete IFNAR1 deficiency. This viral disease occurred in natural conditions, unlike those previously reported in other patients with IFNAR1 or IFNAR2 deficiency. This experiment of nature indicates that IFN-α/β are essential for anti-HSV-1 immunity in the CNS.

Human Disease Phenotypes Associated with Loss and Gain of Function Mutations in STAT2: Viral Susceptibility and Type I Interferonopathy

STAT2 is distinguished from other STAT family members by its exclusive involvement in type I and III interferon (IFN-I/III) signaling pathways, and its unique behavior as both positive and negative regulator of IFN-I signaling. The clinical relevance of these opposing STAT2 functions is exemplified by monogenic diseases of STAT2. Autosomal recessive STAT2 deficiency results in heightened susceptibility to severe and/or recurrent viral disease, whereas homozygous missense substitution of the STAT2-R148 residue is associated with severe type I interferonopathy due to loss of STAT2 negative regulation. Here we review the clinical presentation, pathogenesis, and management of these disorders of STAT2.

Integrative multiplatform-based molecular profiling of human colorectal cancer reveals proteogenomic alterations underlying mitochondrial inactivation

Mitochondria play leading roles in initiation and progression of colorectal cancer (CRC). Proteogenomic analyses of mitochondria of CRC tumor cells would likely enhance our understanding of CRC pathogenesis and reveal new independent prognostic factors and treatment targets. However, comprehensive investigations focused on mitochondria of CRC patients are lacking. Here, we investigated global profiles of structural variants, DNA methylation, chromatin accessibility, transcriptome, proteome, and phosphoproteome on human CRC. Proteomic investigations uncovered greatly diminished mitochondrial proteome size in CRC relative to that found in adjacent healthy tissues. Integrated with analysis of RNA-Seq datasets obtained from the public database containing mRNA data of 538 CRC patients, the proteomic analysis indicated that proteins encoded by 45.5% of identified prognostic CRC genes were located within mitochondria, highlighting the association between altered mitochondrial function and CRC. Subsequently, we compared structural variants, DNA methylation, and chromatin accessibility of differentially expressed genes and found that chromatin accessibility was an important factor underlying mitochondrial gene expression. Furthermore, phosphoproteomic profiling demonstrated decreased phosphorylation of most mitochondria-related kinases within CRC versus adjacent healthy tissues, while also highlighting MKK3/p38 as an essential mitochondrial regulatory pathway. Meanwhile, systems-based analyses revealed identities of key kinases, transcriptional factors, and their interconnections. This research uncovered a close relationship between mitochondrial dysfunction and poor CRC prognosis, improve our understanding of molecular mechanism underlying mitochondrial linked to human CRC, and facilitate identifies of clinically relevant CRC prognostic factors and drug targets.

Monogenic susceptibility to live viral vaccines

Live attenuated viral vaccines (LAV) have saved millions of lives globally through their capacity to elicit strong, cross-reactive and enduring adaptive immune responses. However, LAV can also act as a Trojan horse to reveal inborn errors of immunity, thereby highlighting important protective elements of the healthy antiviral immune response. In the following article, we draw out these lessons by reviewing the spectrum of LAV-associated disease reported in a variety of inborn errors of immunity. We note the contrast between adaptive disorders, which predispose to both LAV and their wild type counterparts, and defects of innate immunity in which parenterally delivered LAV behave in a particularly threatening manner. Recognition of the underlying pathomechanisms can inform our approach to disease management and vaccination in a wider group of individuals, including those receiving immunomodulators that impact the relevant pathways.

Melatonin and Melatonergic Influence on Neuronal Transcription Factors: Implications for the Development of Novel Therapies for Neurodegenerative Disorders

Melatonin is a multifunctional signalling molecule that is secreted by the mammalian pineal gland, and also found in a number of organisms including plants and bacteria. Research has continued to uncover an ever-increasing number of processes in which melatonin is known to play crucial roles in mammals. Amongst these functions is its contribution to cell multiplication, differentiation and survival in the brain. Experimental studies show that melatonin can achieve these functions by influencing transcription factors which control neuronal and glial gene expression. Since neuronal survival and differentiation are processes that are important determinants of the pathogenesis, course and outcome of neurodegenerative disorders; the known and potential influences of melatonin on neuronal and glial transcription factors are worthy of constant examination. In this review, relevant scientific literature on the role of melatonin in preventing or altering the course and outcome of neurodegenerative disorders, by focusing on melatonin's influence on transcription factors is examined. A number of transcription factors whose functions can be influenced by melatonin in neurodegenerative disease models have also been highlighted. Finally, the therapeutic implications of melatonin's influences have also been discussed and the potential limitations to its applications have been highlighted.

Viral infections in humans and mice with genetic deficiencies of the type I IFN response pathway

Type I IFNs are so-named because they interfere with viral infection in vertebrate cells. The study of cellular responses to type I IFNs led to the discovery of the JAK-STAT signaling pathway, which also governs the response to other cytokine families. We review here the outcome of viral infections in mice and humans with engineered and inborn deficiencies, respectively, of (i) IFNAR1 or IFNAR2, selectively disrupting responses to type I IFNs, (ii) STAT1, STAT2, and IRF9, also impairing cellular responses to type II (for STAT1) and/or III (for STAT1, STAT2, IRF9) IFNs, and (iii) JAK1 and TYK2, also impairing cellular responses to cytokines other than IFNs. A picture is emerging of greater redundancy of human type I IFNs for protective immunity to viruses in natural conditions than was initially anticipated. Mouse type I IFNs are essential for protection against a broad range of viruses in experimental conditions. These findings suggest that various type I IFN-independent mechanisms of human cell-intrinsic immunity to viruses have yet to be discovered.

IFN-β rescues neurodegeneration by regulating mitochondrial fission via STAT5, PGAM5, and Drp1

Mitochondrial homeostasis is essential for providing cellular energy, particularly in resource-demanding neurons, defects in which cause neurodegeneration, but the function of interferons (IFNs) in regulating neuronal mitochondrial homeostasis is unknown. We found that neuronal IFN-β is indispensable for mitochondrial homeostasis and metabolism, sustaining ATP levels and preventing excessive ROS by controlling mitochondrial fission. IFN-β induces events that are required for mitochondrial fission, phosphorylating STAT5 and upregulating PGAM5, which phosphorylates serine 622 of Drp1. IFN-β signaling then recruits Drp1 to mitochondria, oligomerizes it, and engages INF2 to stabilize mitochondria-endoplasmic reticulum (ER) platforms. This process tethers damaged mitochondria to the ER to separate them via fission. Lack of neuronal IFN-β in the Ifnb^-/- model of Parkinson disease (PD) disrupts STAT5-PGAM5-Drp1 signaling, impairing fission and causing large multibranched, damaged mitochondria with insufficient ATP production and excessive oxidative stress to accumulate. In other PD models, IFN-β rescues dopaminergic neuronal cell death and pathology, associated with preserved mitochondrial homeostasis. Thus, IFN-β activates mitochondrial fission in neurons through the pSTAT5/PGAM5/^S622 Drp1 pathway to stabilize mitochondria/ER platforms, constituting an essential neuroprotective mechanism.

A virus-induced conformational switch of STAT1-STAT2 dimers boosts antiviral defenses

Type I interferons (IFN-I) protect us from viral infections. Signal transducer and activator of transcription 2 (STAT2) is a key component of interferon-stimulated gene factor 3 (ISGF3), which drives gene expression in response to IFN-I. Using electron microscopy, we found that, in naive cells, U-STAT2, lacking the activating tyrosine phosphorylation, forms a heterodimer with U-STAT1 in an inactive, anti-parallel conformation. A novel phosphorylation of STAT2 on T404 promotes IFN-I signaling by disrupting the U-STAT1-U-STAT2 dimer, facilitating the tyrosine phosphorylation of STATs 1 and 2 and enhancing the DNA-binding ability of ISGF3. IKK-ε, activated by virus infection, phosphorylates T404 directly. Mice with a T-A mutation at the corresponding residue (T403) are highly susceptible to virus infections. We conclude that T404 phosphorylation drives a critical conformational switch that, by boosting the response to IFN-I in infected cells, enables a swift and efficient antiviral defense.

Genetic Lesions of Type I Interferon Signalling in Human Antiviral Immunity

The concept that type I interferons (IFN-I) are essential to antiviral immunity derives from studies on animal models and cell lines. Virtually all pathogenic viruses have evolved countermeasures to IFN-I restriction, and genetic loss of viral IFN-I antagonists leads to virus attenuation. But just how important is IFN-I to antiviral defence in humans? The recent discovery of genetic defects of IFN-I signalling illuminates this and other questions of IFN biology, including the role of the mucosa-restricted type III IFNs (IFN-III), informing our understanding of the place of the IFN system within the concerted antiviral response. Here we review monogenic lesions of IFN-I signalling pathways and summarise the organising principles which emerge.

Vaccinomics and Adversomics in the Era of Precision Medicine: A Review Based on HBV, MMR, HPV, and COVID-19 Vaccines

Precision medicine approaches based on pharmacogenomics are now being successfully implemented to enable physicians to predict more efficient treatments and prevention strategies for a given disease based on the genetic background of the patient. This approach has already been proposed for vaccines, but research is lagging behind the needs of society, and precision medicine is far from being implemented here. While vaccinomics concerns the effectiveness of vaccines, adversomics concerns their side effects. This area has great potential to address public concerns about vaccine safety and to promote increased public confidence, higher vaccination rates, and fewer serious adverse events in genetically predisposed individuals. The aim here is to explore the contemporary scientific literature related to the vaccinomic and adversomic aspects of the three most-controversial vaccines: those against hepatitis B, against measles, mumps, and rubella, and against human Papilloma virus. We provide detailed information on the genes that encode human leukocyte antigen, cytokines and their receptors, and transcription factors and regulators associated with the efficacy and safety of the Hepatitis B and Measles, Mumps and Rubella virus vaccines. We also investigate the future prospects of vaccinomics and adversomics of a COVID-19 vaccine, which might represent the fastest development of a vaccine ever.

The Dynamic Interface of Viruses with STATs

Viruses commonly antagonize the antiviral type I interferon response by targeting signal transducer and activator of transcription 1 (STAT1) and STAT2, key mediators of interferon signaling. Other STAT family members mediate signaling by diverse cytokines important to infection, but their relationship with viruses is more complex. Importantly, virus-STAT interaction can be antagonistic or stimulatory depending on diverse viral and cellular factors. While STAT antagonism can suppress immune pathways, many viruses promote activation of specific STATs to support viral gene expression and/or produce cellular conditions conducive to infection. It is also becoming increasingly clear that viruses can hijack noncanonical STAT functions to benefit infection. For a number of viruses, STAT function is dynamically modulated through infection as requirements for replication change. Given the critical role of STATs in infection by diverse viruses, the virus-STAT interface is an attractive target for the development of antivirals and live-attenuated viral vaccines. Here, we review current understanding of the complex and dynamic virus-STAT interface and discuss how this relationship might be harnessed for medical applications.

Stat2-Drp1 mediated mitochondrial mass increase is necessary for pro-inflammatory differentiation of macrophages

Macrophage recruitment and pro-inflammatory differentiation are hallmarks of various diseases, including infection and sepsis. Although studies suggest that mitochondria may regulate macrophage immune responses, it remains unclear whether mitochondrial mass affects macrophage pro-inflammatory differentiation. Here, we found that lipopolysaccharide (LPS)-activated macrophages possess higher mitochondrial mass than resting cells. Therefore, this study aimed to explore the functional role and molecular mechanisms of increased mitochondrial mass in pro-inflammatory differentiated macrophages. Results show that an increase in the mitochondrial mass of macrophages positively correlates with inflammatory cytokine generation in response to LPS. RNA-seq analysis revealed that LPS promotes signal transducers and activators of transcription 2 (Stat2) and dynamin-related protein 1 (Drp1) expression, which are enriched in positive mitochondrial fission regulation. Meanwhile, knockdown or pharmacological inhibition of Drp1 blunts LPS-induced mitochondrial mass increase and pro-inflammatory differentiation. Moreover, Stat2 boosts Drp1 phosphorylation at serine 616, required for Drp1-mediated mitochondrial fission. LPS also causes Stat2-and Drp1-dependent biogenesis, which contributes to the generation of additional mitochondria. However, these mitochondria are profoundly remodeled, displaying fragmented morphology, loose cristae, reduced Δψm, and metabolic programming. Furthermore, these remodeled mitochondria shift their function from ATP synthesis to reactive oxygen species (ROS) production, which drives NFκB-dependent inflammatory cytokine transcription. Interestingly, an increase in mitochondrial mass with constitutively active phosphomimetic mutant of Drp1 (Drp1^S616E) boosted pro-inflammatory response in macrophages without LPS stimulation. In vivo, we also demonstrated that Mdivi-1 administration inhibits LPS-induced macrophage pro-inflammatory differentiation. Importantly, we observed Stat2 phosphorylation and Drp1-dependent mitochondrial mass increase in macrophages isolated from LPS-challenged mice. In conclusion, we comprehensively demonstrate that a Stat2-Drp1 dependent mitochondrial mass increase is necessary for pro-inflammatory differentiation of macrophages. Therefore, targeting the Stat2-Drp1 axis may provide novel therapeutic approaches for treating infection and inflammatory diseases.

Mitochondrial diseases: expanding the diagnosis in the era of genetic testing

Mitochondrial diseases are clinically and genetically heterogeneous. These diseases were initially described a little over three decades ago. Limited diagnostic tools created disease descriptions based on clinical, biochemical analytes, neuroimaging, and muscle biopsy findings. This diagnostic mechanism continued to evolve detection of inherited oxidative phosphorylation disorders and expanded discovery of mitochondrial physiology over the next two decades. Limited genetic testing hampered the definitive diagnostic identification and breadth of diseases. Over the last decade, the development and incorporation of massive parallel sequencing has identified approximately 300 genes involved in mitochondrial disease. Gene testing has enlarged our understanding of how genetic defects lead to cellular dysfunction and disease. These findings have expanded the understanding of how mechanisms of mitochondrial physiology can induce dysfunction and disease, but the complete collection of disease-causing gene variants remains incomplete. This article reviews the developments in disease gene discovery and the incorporation of gene findings with mitochondrial physiology. This understanding is critical to the development of targeted therapies.

Early type I IFN blockade improves the efficacy of viral vaccines

Type I interferons (IFN-I) are a major antiviral defense and are critical for the activation of the adaptive immune system. However, early viral clearance by IFN-I could limit antigen availability, which could in turn impinge upon the priming of the adaptive immune system. In this study, we hypothesized that transient IFN-I blockade could increase antigen presentation after acute viral infection. To test this hypothesis, we infected mice with viruses coadministered with a single dose of IFN-I receptor–blocking antibody to induce a short-term blockade of the IFN-I pathway. This resulted in a transient “spike” in antigen levels, followed by rapid antigen clearance. Interestingly, short-term IFN-I blockade after coronavirus, flavivirus, rhabdovirus, or arenavirus infection induced a long-lasting enhancement of immunological memory that conferred improved protection upon subsequent reinfections. Short-term IFN-I blockade also improved the efficacy of viral vaccines. These findings demonstrate a novel mechanism by which IFN-I regulate immunological memory and provide insights for rational vaccine design.

Monogenetic causes of chilblains, panniculitis and vasculopathy: the Type I interferonopathies

Type I interferonopathies are a clinically heterogeneous group of inherited disorders of the innate immune system characterized by constitutive activation of the type I interferon signaling pathway. Cutaneous vasculopathy, lipodystrophy, interstitial lung disease and brain calcifications are the typical manifestations characterizing affected patients. The pathogenic mechanism commonly underlying these disorders is the abnormal activation of immune pathways involved in recognition of non-self-oligonucleotides. These natural defenses against virus consent humans to survive the infections. Target therapies capable of inhibiting type I interferon signaling pathway seem effective in these patients, albeit with possible incomplete responses and severe side effects.

Age-related epigenetic drift deregulates SIRT6 expression and affects its downstream genes in human peripheral blood mononuclear cells

Sirtuin 6 (SIRT6) exerts a protective effect on health and extends the lives of model organisms. We, therefore, aimed to clarify whether age-related epigenetic drift is responsible for differences in SIRT6 expression in peripheral blood mononuclear cells (PBMCs) of healthy young (n = 55, mean age 27.5 ± 4.4 years), middle-aged (n = 51, 65.4 ± 3.3 years), and long-lived (n = 51, 93.9 ± 3.6 years) humans. In silico analysis was performed using the STRING network. No age-related differences were observed in the percentage of SIRT6 CpG island methylation. However, the age affected the expression of miR-34a-5p, miR-125a-5p, miR-186-5p, miR-342-5p and miR-766-3p (all p < 0.0001), miR-181-2-3p and Let-7c (both p = 0.0003), and miR-103a-3p (p = 0.0069). A negative association was observed between SIRT6 mRNA and miR-186-5p (r_s = -0.25, p = 0.026), and a positive association was observed with miR-34a-5p (r_s = 0.31, p = 0.0055) and miR-181a-2-3p (r_s = 0.39, p = 0.0002). SIRT6 mRNA also negatively correlated with the expression of TP53 (r_s = -0.41, p = 0.0126) and MYC (r_s = -0.35, p = 0.0448). Notably, the expression of several miRNAs and genes was similar in young and long-lived groups but different from the middle-aged group. We conclude that age-related epigenetic changes can affect the expression of SIRT6 in PBMCs and, in this way, possibly influence immunosenescence. Moreover, molecular events could differentiate 'normal' ageing from that of long-lived individuals.

Mitochondrial disease in children

Mitochondrial disease presenting in childhood is characterized by clinical, biochemical and genetic complexity. Some children are affected by canonical syndromes, but the majority have nonclassical multisystemic disease presentations involving virtually any organ in the body. Each child has a unique constellation of clinical features and disease trajectory, leading to enormous challenges in diagnosis and management of these heterogeneous disorders. This review discusses the classical mitochondrial syndromes presenting most frequently in childhood and then presents an organ-based perspective including systems less frequently linked to mitochondrial disease, such as skin and hair abnormalities and immune dysfunction. An approach to diagnosis is then presented, encompassing clinical evaluation and biochemical, neuroimaging and genetic investigations, and emphasizing the problem of phenocopies. The impact of next-generation sequencing is discussed, together with the importance of functional validation of novel genetic variants never previously linked to mitochondrial disease. The review concludes with a brief discussion of currently available and emerging therapies. The field of mitochondrial medicine has made enormous strides in the last 30 years, with approaching 400 different genes across two genomes now linked to primary mitochondrial disease. However, many important questions remain unanswered, including the reasons for tissue specificity and variability of clinical presentation of individuals sharing identical gene defects, and a lack of disease-modifying therapies and biomarkers to monitor disease progression and/or response to treatment.

Huntingtin Aggregates and Mitochondrial Pathology in Skeletal Muscle but not Heart of Late-Stage R6/2 Mice

BACKGROUND

Cell or tissue specific background may influence the consequences of expressing the Huntington's disease (HD) mutation. Aggregate formation is known to occur in skeletal muscle, but not heart of the R6/2 fragment HD model.

OBJECTIVE

We asked whether aggregate formation and the expression and subcellular localization of huntingtin species was associated with mitochondrial dysfunction.

METHODS

We analyzed levels of soluble HTT and HTT aggregates, as well as important fission and fusion proteins and mitochondrial respiratory chain activities, in quadriceps and heart of the R6/2 N-terminal fragment mouse model (12 weeks, 160±10 CAG repeats).

RESULTS

Soluble mutant HTT was present in both tissues with expression higher in cytoplasmic/mitochondrial than nuclear fractions. HTT aggregates were only detectable in R6/2 quadriceps, in association with increased levels of the pro-fission factor DRP1 and its phosphorylated active form, and decreased levels of the pro-fusion factor MFN2. In addition, respiratory chain complex activities were decreased. In heart that was without detectable HTT aggregates, we found no evidence for mitochondrial dysfunction.

CONCLUSION

Tissue specific factors may exist that protect the R6/2 heart from HTT aggregate formation and mitochondrial pathology.

Human genetics of life-threatening influenza pneumonitis

Influenza viruses infect millions of people around the globe annually, usually causing self-limited upper respiratory tract infections. However, a small but non-negligible proportion of patients suffer from life-threatening pulmonary disease. Those affected include otherwise healthy individuals, and children with primary infections in particular. Much effort has been devoted to virological studies of influenza and vaccine development. By contrast, the enormous interindividual variability in susceptibility to influenza has received very little attention. One interesting hypothesis is that interindividual variability is driven largely by the genetic makeup of the infected patients. Unbiased genomic approaches have been used to search for genetic lesions in children with life-threatening pulmonary influenza. Four monogenic causes of severe influenza pneumonitis—deficiencies of GATA2, IRF7, IRF9, and TLR3—have provided evidence that severe influenza pneumonitis can be genetic and often in patients with no other severe infections. These deficiencies highlight the importance of human type I and III IFN-mediated immunity for host defense against influenza. Clinical penetrance is incomplete, and the underlying mechanisms are not yet understood. However, human genetic studies have clearly revealed that seemingly sporadic and isolated life-threatening influenza pneumonitis in otherwise healthy individuals can be genetic.

JAK/STAT Cytokine Signaling at the Crossroad of NK Cell Development and Maturation

Natural Killer (NK) cells are cytotoxic lymphocytes of the innate immune system and play a critical role in anti-viral and anti-tumor responses. NK cells develop in the bone marrow from hematopoietic stem cells (HSCs) that differentiate through common lymphoid progenitors (CLPs) to NK lineage-restricted progenitors (NKPs). The orchestrated action of multiple cytokines is crucial for NK cell development and maturation. Many of these cytokines such as IL-2, IL-7, IL-12, IL-15, IL-21, IL-27, and interferons (IFNs) signal via the Janus Kinase / Signal Transducer and Activator of Transcription (JAK/STAT) pathway. We here review the current knowledge about these cytokines and the downstream signaling involved in the development and maturation of conventional NK cells and their close relatives, innate lymphoid cells type 1 (ILC1). We further discuss the role of suppressor of cytokine signaling (SOCS) proteins in NK cells and highlight their potential for therapeutic application.

The Goldilocks Zone of Type I IFNs: Lessons from Human Genetics

Type I IFNs (IFN-Is) are powerful cytokines. They provide remarkable protection against viral infections, but their indiscriminate production causes severe self-inflicted damage that can be lethal, particularly in early development. In humans, inappropriately high IFN-I levels caused by defects in the regulatory mechanisms that control IFN-I production and response result in clinical conditions known as type I interferonopathies. In essence, type I interferonopathies define the upper limit of safe, IFN-related inflammation in vivo. Conversely, the loss of IFN-I responsiveness increases susceptibility to viral infections, but, surprisingly, most affected individuals survive despite these inborn errors of immunity. These findings suggest that too much IFN-I early in life is toxic, but that insensitivity to IFN-I is perhaps not the death sentence it was initially thought to be. Human genetic analyses have suggested that seemingly insignificant levels of IFN-regulated gene activity may be sufficient for most of the antiviral defenses used by humans in natura.