Targeting Interleukin-6 Signaling in Clinic.

Interleukin-6 (IL-6) is a pleiotropic cytokine with roles in immunity, tissue regeneration, and metabolism. Rapid production of IL-6 contributes to host defense during infection and tissue injury, but excessive synthesis of IL-6 and dysregulation of IL-6 receptor signaling is involved in disease pathology. Therapeutic agents targeting the IL-6 axis are effective in rheumatoid arthritis, and applications are being extended to other settings of acute and chronic inflammation. Recent studies reveal that selective blockade of different modes of IL-6 receptor signaling has different outcomes on disease pathology, suggesting novel strategies for therapeutic intervention. However, some inflammatory diseases do not seem to respond to IL-6 blockade. Here, we review the current state of IL-6-targeting approaches in the clinic and discuss how to apply the growing understanding of the immunobiology of IL-6 to clinical decisions.

Targeting REGNASE-1 programs long-lived effector T cells for cancer therapy.

Adoptive cell therapy represents a new paradigm in cancer immunotherapy, but it can be limited by the poor persistence and function of transferred T cells1. Here we use an in vivo pooled CRISPR-Cas9 mutagenesis screening approach to demonstrate that, by targeting REGNASE-1, CD8+ T cells are reprogrammed to long-lived effector cells with extensive accumulation, better persistence and robust effector function in tumours. REGNASE-1-deficient CD8+ T cells show markedly improved therapeutic efficacy against mouse models of melanoma and leukaemia. By using a secondary genome-scale CRISPR-Cas9 screening, we identify BATF as the key target of REGNASE-1 and as a rheostat that shapes antitumour responses. Loss of BATF suppresses the increased accumulation and mitochondrial fitness of REGNASE-1-deficient CD8+ T cells. By contrast, the targeting of additional signalling factors-including PTPN2 and SOCS1-improves the therapeutic efficacy of REGNASE-1-deficient CD8+ T cells. Our findings suggest that T cell persistence and effector function can be coordinated in tumour immunity and point to avenues for improving the efficacy of adoptive cell therapy for cancer.

Cytokine mRNA Degradation in Cardiomyocytes Restrains Sterile Inflammation in Pressure-Overloaded Hearts.

BACKGROUND: Proinflammatory cytokines play an important role in the pathogenesis of heart failure. The mechanisms responsible for maintaining sterile inflammation within failing hearts remain poorly defined. Although transcriptional control is important for proinflammatory cytokine gene expression, the stability of mRNA also contributes to the kinetics of immune responses. Regnase-1 is an RNase involved in the degradation of a set of proinflammatory cytokine mRNAs in immune cells. The role of Regnase-1 in nonimmune cells such as cardiomyocytes remains to be elucidated. METHODS: To examine the role of proinflammatory cytokine degradation by Regnase-1 in cardiomyocytes, cardiomyocyte-specific Regnase-1-deficient mice were generated. The mice were subjected to pressure overload by means of transverse aortic constriction to induce heart failure. Cardiac remodeling was assessed by echocardiography as well as histological and molecular analyses 4 weeks after operation. Inflammatory cell infiltration was examined by immunostaining. Interleukin-6 signaling was inhibited by administration with its receptor antibody. Overexpression of Regnase-1 in the heart was performed by adeno-associated viral vector-mediated gene transfer. RESULTS: Cardiomyocyte-specific Regnase-1-deficient mice showed no cardiac phenotypes under baseline conditions, but exhibited severe inflammation and dilated cardiomyopathy after 4 weeks of pressure overload compared with control littermates. Four weeks after transverse aortic constriction, the Il6 mRNA level was upregulated, but not other cytokine mRNAs, including tumor necrosis factor-α, in Regnase-1-deficient hearts. Although the Il6 mRNA level increased 1 week after operation in both Regnase-1-deficient and control hearts, it showed no increase in control hearts 4 weeks after operation. Administration of anti-interleukin-6 receptor antibody attenuated the development of inflammation and cardiomyopathy in cardiomyocyte-specific Regnase-1-deficient mice. In severe pressure overloaded wild-type mouse hearts, sustained induction of Il6 mRNA was observed, even though the protein level of Regnase-1 increased. Adeno-associated virus 9-mediated cardiomyocyte-targeted gene delivery of Regnase-1 or administration of anti-interleukin-6 receptor antibody attenuated the development of cardiomyopathy induced by severe pressure overload in wild-type mice. CONCLUSIONS: The degradation of cytokine mRNA by Regnase-1 in cardiomyocytes plays an important role in restraining sterile inflammation in failing hearts and the Regnase-1-mediated pathway might be a therapeutic target to treat patients with heart failure.

Translation-dependent unwinding of stem-loops by UPF1 licenses Regnase-1 to degrade inflammatory mRNAs.

Regnase-1-mediated mRNA decay (RMD), in which inflammatory mRNAs harboring specific stem-loop structures are degraded, is a critical part of proper immune homeostasis. Prior to initial translation, Regnase-1 associates with target stem-loops but does not carry out endoribonucleolytic cleavage. Single molecule imaging revealed that UPF1 is required to first unwind the stem-loops, thus licensing Regnase-1 to proceed with RNA degradation. Following translation, Regnase-1 physically associates with UPF1 using two distinct points of interaction: The Regnase-1 RNase domain binds to SMG1-phosphorylated residue T28 in UPF1; in addition, an intrinsically disordered segment in Regnase-1 binds to the UPF1 RecA domain, enhancing the helicase activity of UPF1. The SMG1-UPF1-Regnase-1 axis targets pioneer rounds of translation and is critical for rapid resolution of inflammation through restriction of the number of proteins translated by a given mRNA. Furthermore, small-molecule inhibition of SMG1 prevents RNA unwinding in dendritic cells, allowing post-transcriptional control of innate immune responses.

Conserved mRNA-granule component Scd6 targets Dhh1 to repress translation initiation and activates Dcp2-mediated mRNA decay in vivo.

Scd6 protein family members are evolutionarily conserved components of translationally silent mRNA granules. Yeast Scd6 interacts with Dcp2 and Dhh1, respectively a subunit and a regulator of the mRNA decapping enzyme, and also associates with translation initiation factor eIF4G to inhibit translation in cell extracts. However, the role of Scd6 in mRNA turnover and translational repression in vivo is unclear. We demonstrate that tethering Scd6 to a GFP reporter mRNA reduces mRNA abundance via Dcp2 and suppresses reporter mRNA translation via Dhh1. Thus, in a dcp2Δ mutant, tethered Scd6 reduces GFP protein expression with little effect on mRNA abundance, whereas tethered Scd6 has no impact on GFP protein or mRNA expression in a dcp2Δ dhh1Δ double mutant. The conserved LSm domain of Scd6 is required for translational repression and mRNA turnover by tethered Scd6. Both functions are enhanced in a ccr4Δ mutant, suggesting that the deadenylase function of Ccr4-Not complex interferes with a more efficient repression pathway enlisted by Scd6. Ribosome profiling and RNA-Seq analysis of scd6Δ and dhh1Δ mutants suggests that Scd6 cooperates with Dhh1 in translational repression and turnover of particular native mRNAs, with both processes dependent on Dcp2. Our results suggest that Scd6 can (i) recruit Dhh1 to confer translational repression and (ii) activate mRNA decapping by Dcp2 with attendant degradation of specific mRNAs in vivo, in a manner dependent on the Scd6 LSm domain and modulated by Ccr4.

Loss of Cnot6l Impairs Inosine RNA Modifications in Mouse Oocytes.

Mammalian oocytes must degrade maternal transcripts through a process called translational mRNA decay, in which maternal mRNA undergoes translational activation, followed by deadenylation and mRNA decay. Once a transcript is translationally activated, it becomes deadenylated by the CCR4-NOT complex. Knockout of CCR4-NOT Transcription Complex Subunit 6 Like (Cnot6l), a deadenylase within the CCR4-NOT complex, results in mRNA decay defects during metaphase I (MI) entry. Knockout of B-cell translocation gene-4 (Btg4), an adaptor protein of the CCR4-NOT complex, results in mRNA decay defects following fertilization. Therefore, mechanisms controlling mRNA turnover have significant impacts on oocyte competence and early embryonic development. Post-transcriptional inosine RNA modifications can impact mRNA stability, possibly through a translation mechanism. Here, we assessed inosine RNA modifications in oocytes, eggs, and embryos from Cnot6l-/- and Btg4-/- mice, which display stabilization of mRNA and over-translation of the stabilized transcripts. If inosine modifications have a role in modulating RNA stability, we hypothesize that in these mutant backgrounds, we would observe changes or a disruption in inosine mRNA modifications. To test this, we used a computational approach to identify inosine RNA modifications in total and polysomal RNA-seq data during meiotic maturation (GV, MI, and MII stages). We observed pronounced depletion of inosine mRNA modifications in samples from Cnot6l-/-, but not in Btg4-/- mice. Additionally, analysis of ribosome-associated RNA revealed clearance of inosine modified mRNA. These observations suggest a novel mechanism of mRNA clearance during oocyte maturation, in which inosine-containing transcripts decay in an independent, but parallel mechanism to CCR4-NOT deadenylation.

Regnase-1 and Roquin Nonredundantly Regulate Th1 Differentiation Causing Cardiac Inflammation and Fibrosis.

Regnase-1 and Roquin are RNA binding proteins that are essential for degradation of inflammatory mRNAs and maintenance of immune homeostasis. Although deficiency of either of the proteins leads to enhanced T cell activation, their functional relationship in T cells has yet to be clarified because of lethality upon mutation of both Regnase-1 and Roquin. By using a Regnase-1 conditional allele, we show that mutations of both Regnase-1 and Roquin in T cells leads to massive lymphocyte activation. In contrast, mutation of either Regnase-1 or Roquin affected T cell activation to a lesser extent than the double mutation, indicating that Regnase-1 and Roquin function nonredundantly in T cells. Interestingly, Regnase-1 and Roquin double-mutant mice suffered from severe inflammation and early formation of fibrosis, especially in the heart, along with the increased expression of Ifng, but not Il4 or Il17a Consistently, mutation of both Regnase-1 and Roquin leads to a huge increase in the Th1, but not the Th2 or Th17, population in spleens compared with T cells with a single Regnase-1 or Roquin deficiency. Regnase-1 and Roquin are capable of repressing the expression of a group of mRNAs encoding factors involved in Th1 differentiation, such as Furin and Il12rb1, via their 3' untranslated regions. Moreover, Regnase-1 is capable of repressing Roquin mRNA. This cross-regulation may contribute to the synergistic control of T cell activation/polarization. Collectively, our results demonstrate that Regnase-1 and Roquin maintain T cell immune homeostasis and regulate Th1 polarization synergistically.

Essential Role of Endothelial MCPIP in Vascular Integrity and Post-Ischemic Remodeling.

MCP-1-induced protein (MCPIP, also known as Zc3h12a or Regnase-1), a newly identified suppressor of cytokine signaling, is expressed in endothelial cells (ECs). To investigate the role of endothelial MCPIP in vascular homeostasis and function, we deleted the MCPIP gene specifically in ECs using the Cre-LoxP system. EC-specific MCPIP deletion resulted in systemic inflammation, increased vessel permeability, edema, thrombus formation, and premature death in mice. Serum levels of cytokines, chemokines, and biomarkers of EC dysfunction were significantly elevated in these mice. Upon lipopolysaccharide (LPS) challenge, mice with EC-specific MCPIP depletion were highly susceptible to LPS-induced death. When subjected to ischemia, these mice showed defective post-ischemic angiogenesis and impaired blood flow recovery in hind limb ischemia. In aortic ring cultures, the MCPIP-deficient ECs displayed significantly impaired vessel sprouting and tube elongation. Mechanistically, silencing of MCPIP by small interfering RNAs in cultured ECs enhanced NF-κΒ activity and dysregulated synthesis of microRNAs linked with elevated cytokines and biomarkers of EC dysfunction. Collectively, these results establish that constitutive expression of MCPIP in ECs is essential to maintaining endothelial homeostasis and function by serving as a key negative feedback regulator that keeps the inflammatory signaling suppressed.

PAT-seq: a method to study the integration of 3'-UTR dynamics with gene expression in the eukaryotic transcriptome.

A major objective of systems biology is to quantitatively integrate multiple parameters from genome-wide measurements. To integrate gene expression with dynamics in poly(A) tail length and adenylation site, we developed a targeted next-generation sequencing approach, Poly(A)-Test RNA-sequencing. PAT-seq returns (i) digital gene expression, (ii) polyadenylation site/s, and (iii) the polyadenylation-state within and between eukaryotic transcriptomes. PAT-seq differs from previous 3' focused RNA-seq methods in that it depends strictly on 3' adenylation within total RNA samples and that the full-native poly(A) tail is included in the sequencing libraries. Here, total RNA samples from budding yeast cells were analyzed to identify the intersect between adenylation state and gene expression in response to loss of the major cytoplasmic deadenylase Ccr4. Furthermore, concordant changes to gene expression and adenylation-state were demonstrated in the classic Crabtree-Warburg metabolic shift. Because all polyadenylated RNA is interrogated by the approach, alternative adenylation sites, noncoding RNA and RNA-decay intermediates were also identified. Most important, the PAT-seq approach uses standard sequencing procedures, supports significant multiplexing, and thus replication and rigorous statistical analyses can for the first time be brought to the measure of 3'-UTR dynamics genome wide.

Zc3h12a is an RNase essential for controlling immune responses by regulating mRNA decay.

Toll-like receptors (TLRs) recognize microbial components, and evoke inflammation and immune responses. TLR stimulation activates complex gene expression networks that regulate the magnitude and duration of the immune reaction. Here we identify the TLR-inducible gene Zc3h12a as an immune response modifier that has an essential role in preventing immune disorders. Zc3h12a-deficient mice suffered from severe anaemia, and most died within 12 weeks. Zc3h12a(-/-) mice also showed augmented serum immunoglobulin levels and autoantibody production, together with a greatly increased number of plasma cells, as well as infiltration of plasma cells to the lung. Most Zc3h12a(-/-) splenic T cells showed effector/memory characteristics and produced interferon-gamma in response to T-cell receptor stimulation. Macrophages from Zc3h12a(-/-) mice showed highly increased production of interleukin (IL)-6 and IL-12p40 (also known as IL12b), but not TNF, in response to TLR ligands. Although the activation of TLR signalling pathways was normal, Il6 messenger RNA decay was severely impaired in Zc3h12a(-/-) macrophages. Overexpression of Zc3h12a accelerated Il6 mRNA degradation via its 3'-untranslated region (UTR), and destabilized RNAs with 3'-UTRs for genes including Il6, Il12p40 and the calcitonin receptor gene Calcr. Zc3h12a contains a putative amino-terminal nuclease domain, and the expressed protein had RNase activity, consistent with a role in the decay of Il6 mRNA. Together, these results indicate that Zc3h12a is an essential RNase that prevents immune disorders by directly controlling the stability of a set of inflammatory genes.

Pbp1 is involved in Ccr4- and Khd1-mediated regulation of cell growth through association with ribosomal proteins Rpl12a and Rpl12b.

The Saccharomyces cerevisiae Pbp1 [poly(A)-binding protein (Pab1)-binding protein] is believed to be involved in RNA metabolism and regulation of translation, since Pbp1 regulates a length of poly(A) tail and is involved in stress granule (SG) formation. However, a physiological function of Pbp1 remains unclear, since the pbp1Δ mutation has no obvious effect on cell growth. In this study, we showed that PBP1 genetically interacts with CCR4 and KHD1, which encode a cytoplasmic deadenylase and an RNA-binding protein, respectively. Ccr4 and Khd1 modulate a signal from Rho1 in the cell wall integrity pathway by regulating the expression of RhoGEF and RhoGAP, and the double deletion of CCR4 and KHD1 confers a severe growth defect displaying cell lysis. We found that the pbp1Δ mutation suppressed the growth defect caused by the ccr4Δ khd1Δ mutation. The pbp1Δ mutation also suppressed the growth defect caused by double deletion of POP2, encoding another cytoplasmic deadenylase, and KHD1. Deletion of the gene encoding previously known Pbp1-interacting factor Lsm12, Pbp4, or Mkt1 did not suppress the growth defect of the ccr4Δ khd1Δ mutant, suggesting that Pbp1 acts independently of these factors in this process. We then screened novel Pbp1-interacting factors and found that Pbp1 interacts with ribosomal proteins Rpl12a and Rpl12b. Similarly to the pbp1Δ mutation, the rpl12aΔ and rpl12bΔ mutations also suppressed the growth defect caused by the ccr4Δ khd1Δ mutation. Our results suggest that Pbp1 is involved in the Ccr4- and Khd1-mediated regulation of cell growth through the association with Rpl12a and Rpl12b.

The Aicardi-Goutières syndrome. Molecular and clinical features of RNAse deficiency and microRNA overload.

Intracellular RNAses are involved in various functions, including microRNA maturation and turnover. Mutations occurring in genes encoding RNAses cause Aicardi-Goutiéres syndrome (AGS). AGS mutations silence RNAse activity, thus inducing accumulation of endogenous RNAs, mainly consisting of short RNAs and microRNAs. Overload of intracellular RNA triggers Toll like receptor-dependent interferon-alpha production in the brain, which in turn activates neurotoxic lymphocytes and inhibits angiogenesis thus inducing the typical clinical phenotype of AGS. However, these pathogenic mechanisms are attenuated after three years of age by the endogenous production of DNAJP58IPK and Cystatin F, which arrest AGS progression. Because RNAses are involved in microRNA turnover, we evaluated the expression of 957 microRNAs in lymphocytes from AGS patients and control patients. Our results indicate that microRNA overload occurs in AGS patients. This upregulation inhibits microRNA turnover impeding the synthesis of the novel microRNAs required for the differentiation and myelination of the brain during the initial period of postnatal life. These pathogenic mechanisms result in AGS, a neurological syndrome characterized by irritability, mild hyperpyrexia, pyramidal and extrapyramidal signs, and spastic-dystonic tetraplegia. Typical cerebrospinal fluid alterations include lymphocytosis and elevated interferon-alpha levels. Brain imaging demonstrates cerebral calcifications, white matter abnormalities, and progressive cerebral atrophy.Thus, evidence exists that mutations silencing intracellular RNases affect microRNA turnover resulting in the severe clinical consequences in the brain characterizing the clinical feature of AGS.

Role of Mcpip1 in obesity-induced hepatic steatosis as determined by myeloid and liver-specific conditional knockouts.

Monocyte chemoattractant protein-induced protein 1 (MCPIP1, alias Regnase 1) is a negative regulator of inflammation, acting through cleavage of transcripts coding for proinflammatory cytokines and by inhibition of NFκB activity. Moreover, it was demonstrated that MCPIP1 regulates lipid metabolism both in adipose tissue and in hepatocytes. In this study, we investigated the effects of tissue-specific Mcpip1 deletion on the regulation of hepatic metabolism and development of nonalcoholic fatty liver disease (NAFLD). We used control Mcpip1fl/fl mice and animals with deletion of Mcpip1 in myeloid leukocytes (Mcpip1fl/fl LysMCre ) and in hepatocytes (Mcpip1fl/fl AlbCre ), which were fed chow or a high-fat diet (HFD) for 12 weeks. Mcpip1fl/fl LysMCre mice fed a chow diet were characterized by a significantly reduced hepatic expression of genes regulating lipid and glucose metabolism, which subsequently resulted in low plasma glucose level and dyslipidemia. These animals also displayed systemic inflammation, demonstrated by increased concentrations of cytokines in the plasma and high Tnfa, Il6, IL1b mRNA levels in the liver and brown adipose tissue (BAT). Proinflammatory leukocyte infiltration into BAT, together with low expression of Ucp1 and Ppargc1a, resulted in hypothermia of 22-week-old Mcpip1fl/fl LysMCre mice. On the other hand, there were no significant changes in phenotype in Mcpip1fl/fl AlbCre mice. Although we detected a reduced hepatic expression of genes regulating glucose metabolism and ß-oxidation in these mice, they remained asymptomatic. Upon feeding with a HFD, Mcpip1fl/fl LysMCre mice did not develop obesity, glucose intolerance, nor hepatic steatosis, but were characterized by low plasma glucose level and dyslipidemia, along with proinflammatory phenotype. Mcpip1fl/fl AlbCre animals, following a HFD, became hypercholesterolemic, but accumulated lipids in the liver at the same level as Mcpip1fl/fl mice, and no changes in the level of soluble factors tested in the plasma were detected. We have demonstrated that Mcpip1 protein plays an important role in the liver homeostasis. Depletion of Mcpip1 in myeloid leukocytes, followed by systemic inflammation, has a more pronounced effect on controlling liver metabolism and homeostasis than the depletion of Mcpip1 in hepatocytes.

RTEC-intrinsic IL-17-driven inflammatory circuit amplifies antibody-induced glomerulonephritis and is constrained by Regnase-1.

Antibody-mediated glomerulonephritis (AGN) is a clinical manifestation of many autoimmune kidney diseases for which few effective treatments exist. Chronic inflammatory circuits in renal glomerular and tubular cells lead to tissue damage in AGN. These cells are targeted by the cytokine IL-17, which has recently been shown to be a central driver of the pathogenesis of AGN. However, surprisingly little is known about the regulation of pathogenic IL-17 signaling in the kidney. Here, using a well-characterized mouse model of AGN, we show that IL-17 signaling in renal tubular epithelial cells (RTECs) is necessary for AGN development. We also show that Regnase-1, an RNA binding protein with endoribonuclease activity, is a negative regulator of IL-17 signaling in RTECs. Accordingly, mice with a selective Regnase-1 deficiency in RTECs exhibited exacerbated kidney dysfunction in AGN. Mechanistically, Regnase-1 inhibits IL-17-driven expression of the transcription factor IκBξ and, consequently, its downstream gene targets, including Il6 and Lcn2. Moreover, deletion of Regnase-1 in human RTECs reduced inflammatory gene expression in a IκBξ-dependent manner. Overall, these data identify an IL-17-driven inflammatory circuit in RTECs during AGN that is constrained by Regnase-1.

The RNase MCPIP3 promotes skin inflammation by orchestrating myeloid cytokine response.

CCCH zinc finger proteins resolve immune responses by degrading the mRNAs of inflammatory cytokines such as tumor necrosis factor (TNF) and interleukin (IL)-6. Here we report that one such family member, monocyte chemotactic protein-induced protein 3 (MCPIP3, also named ZC3H12C or Regnase-3), promotes skin inflammation by simultaneously enhancing TNF in macrophages and repressing IL-6 in plasmacytoid dendritic cells (pDCs). MCPIP3 is positively associated with psoriasis pathogenesis, and highly expressed by macrophages and pDCs. MCPIP3-deficient macrophages produce less TNF and IL-12p40. However, MCPIP3-deficient pDCs secrete significantly more IL-6. This enhanced intradermal IL-6 may alleviate imiquimod-induced skin inflammation. As a result, MCPIP3-deficient mice are protected from imiquimod-induced psoriasiform lesions. Furthermore, early exposure to pDC-derived IL-6 suppresses macrophage-derived TNF and IL-12p40. Mechanistically, MCPIP3 could directly degrade mRNAs of IL-6, Regnase-1, and IκBζ. In turn, Regnase-1 could degrade MCPIP3 mRNAs. Our study identifies a critical post-transcriptional mechanism that synchronizes myeloid cytokine secretion to initiate autoimmune skin inflammation.

Depletion of mammalian CCR4b deadenylase triggers elevation of the p27Kip1 mRNA level and impairs cell growth.

The stability of mRNA influences the abundance of cellular transcripts and proteins. Deadenylases play critical roles in mRNA turnover and thus are important for the regulation of various biological events. Here, we report the identification and characterization of CCR4b/CNOT6L, which is homologous to yeast CCR4 mRNA deadenylase. CCR4b is localized mainly in the cytoplasm and displays deadenylase activity both in vitro and in vivo. CCR4b forms a multisubunit complex similar to the yeast CCR4-NOT complex. Suppression of CCR4b by RNA interference results in growth retardation of NIH 3T3 cells accompanied by elevation of both p27(Kip1) mRNA and p27(Kip1) protein. Reintroduction of wild-type CCR4b, but not mutant CCR4b lacking deadenylase activity, restores the growth of CCR4b-depleted NIH 3T3 cells. The data suggest that CCR4b regulates cell growth in a manner dependent on its deadenylase activity. We also show that p27(Kip1) mRNA is stabilized and its poly(A) tail is preserved in CCR4b-depleted cells. Our findings provide evidence that CCR4b deadenylase is a constituent of the mammalian CCR4-NOT complex and regulates the turnover rate of specific target mRNAs. Thus, CCR4b may be involved in various cellular events that include cell proliferation.

Zebrafish disease model of human RNASET2-deficient cystic leukoencephalopathy displays abnormalities in early microglia.

Human infantile-onset RNASET2-deficient cystic leukoencephalopathy is a Mendelian mimic of in utero cytomegalovirus brain infection with prenatally developing inflammatory brain lesions. We used an RNASET2-deficient zebrafish model to elucidate the underlying disease mechanisms. Mutant and wild-type zebrafish larvae brain development between 2 and 5 days post fertilization (dpf) was examined by confocal live imaging in fluorescent reporter lines of the major types of brain cells. In contrast to wild-type brains, RNASET2-deficient larvae displayed increased numbers of microglia with altered morphology, often containing inclusions of neurons. Furthermore, lysosomes within distinct populations of the myeloid cell lineage including microglia showed increased lysosomal staining. Neurons and oligodendrocyte precursor cells remained unaffected. This study provides a first look into the prenatal onset pathomechanisms of human RNASET2-deficient leukoencephalopathy, linking this inborn lysosomal disease to the innate immune system and other immune-related childhood encephalopathies like Aicardi-Goutières syndrome (AGS).

Angiogenin loss-of-function mutations in amyotrophic lateral sclerosis.

OBJECTIVE: Heterozygous missense mutations in the coding region of angiogenin (ANG), an angiogenic ribonuclease, have been reported in amyotrophic lateral sclerosis (ALS) patients. However, the role of ANG in motor neuron physiology and the functional consequences of these mutations are unknown. We searched for new mutations and sought to define the functional consequences of these mutations. METHODS: We sequenced the coding region of ANG in an independent cohort of North American ALS patients. Identified ANG mutations were then characterized using functional assays of angiogenesis, ribonucleolysis, and nuclear translocation. We also examined expression of ANG in normal human fetal and adult spinal cords. RESULTS: We identified four mutations in the coding region of ANG from 298 ALS patients. Three of these mutations are present in the mature protein. Among the four mutations, P(-4)S, S28N, and P112L are novel, and K17I has been reported previously. Functional assays show that these ANG mutations result in complete loss of function. The mutant ANG proteins are unable to induce angiogenesis because of a deficiency in ribonuclease activity, nuclear translocation, or both. As a correlate, we demonstrate strong ANG expression in both endothelial cells and motor neurons of normal human spinal cords from the developing fetus and adult. INTERPRETATION: We provide the first evidence that ANG mutations, identified in ALS patients, are associated with functional loss of ANG activity. Moreover, strong ANG expression, in normal human fetal and adult spinal cord neurons and endothelial cells, confirms the plausibility of ANG dysfunction being relevant to the pathogenesis of ALS.

IreA Controls Endoplasmic Reticulum Stress-Induced Autophagy and Survival through Homeostasis Recovery.

The unfolded protein response (UPR) is an adaptive pathway that restores cellular homeostasis after endoplasmic reticulum (ER) stress. The ER-resident kinase/RNase Ire1 is the only UPR sensor conserved during evolution. Autophagy, a lysosomal degradative pathway, also contributes to the recovery of cell homeostasis after ER stress, but the interplay between these two pathways is still poorly understood. We describe the Dictyostelium discoideum ER stress response and characterize its single bona fide Ire1 orthologue, IreA. We found that tunicamycin (TN) triggers a gene-expression reprogramming that increases the protein folding capacity of the ER and alleviates ER protein load. Further, IreA is required for cell survival after TN-induced ER stress and is responsible for nearly 40% of the transcriptional changes induced by TN. The response of Dictyostelium cells to ER stress involves the combined activation of an IreA-dependent gene expression program and the autophagy pathway. These two pathways are independently activated in response to ER stress but, interestingly, autophagy requires IreA at a later stage for proper autophagosome formation. We propose that unresolved ER stress in cells lacking IreA causes structural alterations of the ER, leading to a late-stage blockade of autophagy clearance. This unexpected functional link may critically affect eukaryotic cell survival under ER stress.

Regnase-1 Maintains Iron Homeostasis via the Degradation of Transferrin Receptor 1 and Prolyl-Hydroxylase-Domain-Containing Protein 3 mRNAs.

Iron metabolism is regulated by transcriptional and post-transcriptional mechanisms. The mRNA of the iron-controlling gene, transferrin receptor 1 (TfR1), has long been believed to be negatively regulated by a yet-unidentified endonuclease. Here, we show that the endonuclease Regnase-1 is critical for the degradation of mRNAs involved in iron metabolism in vivo. First, we demonstrate that Regnase-1 promotes TfR1 mRNA decay. Next, we show that Regnase-1-/- mice suffer from severe iron deficiency anemia, although hepcidin expression is downregulated. The iron deficiency anemia is induced by a defect in duodenal iron uptake. We reveal that duodenal Regnase-1 controls the expression of PHD3, which impairs duodenal iron uptake via HIF2α suppression. Finally, we show that Regnase-1 is a HIF2α-inducible gene and thus provides a positive feedback loop for HIF2α activation via PHD3. Collectively, these results demonstrate that Regnase-1-mediated regulation of iron-related transcripts is essential for the maintenance of iron homeostasis.