Dysregulated copper transport in multiple sclerosis may cause demyelination via astrocytes.

Demyelination is a key pathogenic feature of multiple sclerosis (MS). Here, we evaluated the astrocyte contribution to myelin loss and focused on the neurotrophin receptor TrkB, whose up-regulation on the astrocyte finely demarcated chronic demyelinated areas in MS and was paralleled by neurotrophin loss. Mice lacking astrocyte TrkB were resistant to demyelination induced by autoimmune or toxic insults, demonstrating that TrkB signaling in astrocytes fostered oligodendrocyte damage. In vitro and ex vivo approaches highlighted that astrocyte TrkB supported scar formation and glia proliferation even in the absence of neurotrophin binding, indicating TrkB transactivation in response to inflammatory or toxic mediators. Notably, our neuropathological studies demonstrated copper dysregulation in MS and model lesions and TrkB-dependent expression of copper transporter (CTR1) on glia cells during neuroinflammation. In vitro experiments evidenced that TrkB was critical for the generation of glial intracellular calcium flux and CTR1 up-regulation induced by stimuli distinct from neurotrophins. These events led to copper uptake and release by the astrocyte, and in turn resulted in oligodendrocyte loss. Collectively, these data demonstrate a pathogenic demyelination mechanism via the astrocyte release of copper and open up the possibility of restoring copper homeostasis in the white matter as a therapeutic target in MS.

iAstrocytes do not restrain T cell proliferation in vitro.

The cross-talk between T cells and astrocytes occurring under physiological and, even more, neuroinflammatory conditions may profoundly impact the generation of adaptive immune responses in the nervous tissue. In this study, we used a standardized in vitro co-culture assay to investigate the immunomodulatory properties of astrocytes differing for age, sex, and species. Mouse neonatal astrocytes enhanced T cell vitality but suppressed T lymphocyte proliferation in response to mitogenic stimuli or myelin antigens, regardless of the Th1, Th2 or Th17 T cell phenotype. Studies comparing glia cells from adult and neonatal animals showed that adult astrocytes were more efficient in inhibiting T lymphocyte activation than neonatal astrocytes, regardless of their sex. Differently from primary cultures, mouse and human astrocytes derived from reprogrammed fibroblasts did not interfere with T cell proliferation. Overall, we describe a standardized astrocyte-T cell interaction in vitro assay and demonstrate that primary astrocytes and iAstrocytes may differ in modulating T cell function.

HNF4α, SP1 and c-myc are master regulators of CNS autoimmunity.

Hepatocyte nuclear factor 4 α (HNF4α), a transcription factor (TF) essential for embryonic development, has been recently shown to regulate the expression of inflammatory genes. To characterize HNF4a function in immunity, we measured the effect of HNF4α antagonists on immune cell responses in vitro and in vivo. HNF4α blockade reduced immune activation in vitro and disease severity in the experimental model of multiple sclerosis (MS). Network biology studies of human immune transcriptomes unraveled HNF4α together with SP1 and c-myc as master TF regulating differential expression at all MS stages. TF expression was boosted by immune cell activation, regulated by environmental MS risk factors and higher in MS immune cells compared to controls. Administration of compounds targeting TF expression or function demonstrated non-synergic, interdependent transcriptional control of CNS autoimmunity in vitro and in vivo. Collectively, we identified a coregulatory transcriptional network sustaining neuroinflammation and representing an attractive therapeutic target for MS and other inflammatory disorders.

Laquinimod Modulates Human Astrocyte Function and Dampens Astrocyte-Induced Neurotoxicity during Inflammation.

Astrocytes greatly participate to inflammatory and neurotoxic reactions occurring in neurodegenerative diseases and are valuable pharmacological targets to support neuroprotection. Here we used human astrocytes generated from reprogrammed fibroblasts as a cellular model to study the effect of the compound Laquinimod and its active metabolite de-Laquinimod on astrocyte functions and the astrocyte-neuron interaction. We show that human iAstrocytes expressed the receptor for the inflammatory mediator IL1 and responded to it via nuclear translocation of NFκB, an event that did not occur if cells were treated with Laquinimod, indicating a direct anti-inflammatory activity of the drug on the human astrocyte. Similarly, while exposure to IL1 downregulated glial glutamate transporters GLAST and GLT1, treatment with Laquinimod supported maintenance of physiological levels of these proteins despite the inflammatory milieu. Laquinimod also induced nuclear translocation of the aryl hydrocarbon receptor (AHR), suggesting that drug action was mediated by activation of the AHR pathway. However, the drug was effective despite AHR inhibition via CH223191, indicating that AHR signaling in the astrocyte is dispensable for drug responses. Finally, in vitro experiments with rat spinal neurons showed that laquinimod did not exert neuroprotection directly on the neuron but dampened astrocyte-induced neurodegeneration. Our findings indicate that fibroblast-derived human astrocytes represent a suitable model to study astrocyte-neuron crosstalk and demonstrate indirect, partial neuroprotective efficacy for laquinimod.

Astrocytes: Key Regulators of Neuroinflammation.

Astrocytes are crucial regulators of innate and adaptive immune responses in the injured central nervous system. Depending on timing and context, astrocyte activity may exacerbate inflammatory reactions and tissue damage, or promote immunosuppression and tissue repair. Recent literature has unveiled key factors and intracellular signaling pathways that govern astrocyte behavior during neuroinflammation. Here we have re-visited in vivo studies on astrocyte signaling in neuroinflammatory models focusing on evidences obtained from the analysis of transgenic mice where distinct genes involved in ligand binding, transcriptional regulation and cell communication have been manipulated in astrocytes. The integration of in vivo observations with in vitro data clarifies precise signaling steps, highlights the crosstalk among pathways and identifies shared effector mechanisms in neuroinflammation.

Neural Stem Cell Transplantation Induces Stroke Recovery by Upregulating Glutamate Transporter GLT-1 in Astrocytes.

Ischemic stroke is the leading cause of disability, but effective therapies are currently widely lacking. Recovery from stroke is very much dependent on the possibility to develop treatments able to both halt the neurodegenerative process as well as to foster adaptive tissue plasticity. Here we show that ischemic mice treated with neural precursor cell (NPC) transplantation had on neurophysiological analysis, early after treatment, reduced presynaptic release of glutamate within the ipsilesional corticospinal tract (CST), and an enhanced NMDA-mediated excitatory transmission in the contralesional CST. Concurrently, NPC-treated mice displayed a reduced CST degeneration, increased axonal rewiring, and augmented dendritic arborization, resulting in long-term functional amelioration persisting up to 60 d after ischemia. The enhanced functional and structural plasticity relied on the capacity of transplanted NPCs to localize in the peri-ischemic and ischemic area, to promote the upregulation of the glial glutamate transporter 1 (GLT-1) on astrocytes and to reduce peri-ischemic extracellular glutamate. The upregulation of GLT-1 induced by transplanted NPCs was found to rely on the secretion of VEGF by NPCs. Blocking VEGF during the first week after stroke reduced GLT-1 upregulation as well as long-term behavioral recovery in NPC-treated mice. Our results show that NPC transplantation, by modulating the excitatory-inhibitory balance and stroke microenvironment, is a promising therapy to ameliorate disability, to promote tissue recovery and plasticity processes after stroke. SIGNIFICANCE STATEMENT: Tissue damage and loss of function occurring after stroke can be constrained by fostering plasticity processes of the brain. Over the past years, stem cell transplantation for repair of the CNS has received increasing interest, although underlying mechanism remain elusive. We here show that neural stem/precursor cell transplantation after ischemic stroke is able to foster axonal rewiring and dendritic plasticity and to induce long-term functional recovery. The observed therapeutic effect of neural precursor cells seems to underlie their capacity to upregulate the glial glutamate transporter on astrocytes through the vascular endothelial growth factor inducing favorable changes in the electrical and molecular stroke microenvironment. Cell-based approaches able to influence plasticity seem particularly suited to favor poststroke recovery.

Fingolimod may support neuroprotection via blockade of astrocyte nitric oxide.

OBJECTIVE: Although astrocytes participate in glial scar formation and tissue repair, dysregulation of the NFκB pathway and of nitric oxide (NO) production in these glia cells contributes to neuroinflammation and neurodegeneration. Here we investigated the role of the crosstalk between sphingosine-1-phosphate (S1P) and cytokine signaling cascades in astrocyte activation and inflammation-mediated neurodegeneration, and addressed the effects of fingolimod on astrocyte-neuron interaction and NO synthesis in vivo. METHODS: Immunohistochemistry, immunofluorescence, and confocal microscopy were used to detect S1P receptors, interleukin (IL) 1R, IL17RA, and nitrosative stress in multiple sclerosis (MS) plaques, experimental autoimmune encephalomyelitis (EAE) spinal cord, and the spinal cord of fingolimod-treated EAE mice. An in vitro model was established to study the effects of S1P, IL1, and IL17 stimulation on NFkB translocation and NO production in astrocytes, on spinal neuron survival, and on astrocyte-neuron interaction. Furthermore, fingolimod efficacy in blocking astrocyte-mediated neurodegeneration was evaluated. RESULTS: We found coordinated upregulation of IL1R, IL17RA, S1P1, and S1P3 together with nitrosative markers in astrocytes within MS and EAE lesions. In vitro studies revealed that S1P, IL17, and IL1 induced NFκB translocation and NO production in astrocytes, and astrocyte conditioned media triggered neuronal death. Importantly, fingolimod blocked the 2 activation events evoked in astrocytes by either S1P or inflammatory cytokines, resulting in inhibition of astrocyte-mediated neurodegeneration. Finally, therapeutic administration of fingolimod to EAE mice hampered astrocyte activation and NO production. INTERPRETATION: A neuroprotective effect of fingolimod in vivo may result from its inhibitory action on key astrocyte activation steps.

A ribosomal protein L23-nucleophosmin circuit coordinates Mizl function with cell growth.

The Myc-associated zinc-finger protein, Miz1, is a negative regulator of cell proliferation and induces expression of the cell-cycle inhibitors p15(Ink4b) and p21(Cip1). Here we identify the ribosomal protein L23 as a negative regulator of Miz1-dependent transactivation. L23 exerts this function by retaining nucleophosmin, an essential co-activator of Miz1 required for Miz1-induced cell-cycle arrest, in the nucleolus. Mutant forms of nucleophosmin found in acute myeloid leukaemia fail to co-activate Miz1 and re-localize it to the cytosol. As L23 is encoded by a direct target gene of Myc, this regulatory circuit may provide a feedback mechanism that links translation of Myc target genes and cell growth to Miz1-dependent cell-cycle arrest.

Autocrine and immune cell-derived BDNF in human skeletal muscle: implications for myogenesis and tissue regeneration.

The neurotrophin system has a role in skeletal muscle biology. Conditional depletion of BDNF in mouse muscle precursor cells alters myogenesis and regeneration in vivo. However, the expression, localization and function of BDNF in human skeletal muscle tissue is not known, so the relevance of the rodent findings for human muscle are unknown. Here we address this by combining ex vivo histological investigations on human biopsies with in vitro analyses of human primary myocytes. We found that BDNF was expressed by precursor and differentiated cells both in vitro and in vivo. Differential analysis of BDNF receptors showed expression of p75NTR and not of TrkB in myocytes, suggesting that the BDNF-p75NTR axis is predominant in human skeletal muscle cells. Several in vitro functional experiments demonstrated that BDNF gene silencing or protein blockade in myoblast cultures hampered myogenesis. Finally, histological investigations of inflammatory myopathy biopsies revealed that infiltrating immune cells localized preferentially near p75NTR-positive regenerating fibres and that they produced BDNF. In conclusion, BDNF is an autocrine factor for skeletal muscle cells and may regulate human myogenesis. Furthermore, the preferential localization of BDNF-producing immune cells near p75NTR-positive regenerating myofibres suggests that immune cell-derived BDNF may sustain tissue repair in inflamed muscle.

Recent Advances in Immune-Based Therapies for Acute Myeloid Leukemia.

Despite advancements, acute myeloid leukemia (AML) remains unconquered by current therapies. Evidence of immune evasion during AML progression, such as HLA loss and T-cell exhaustion, suggests that antileukemic immune responses contribute to disease control and could be harnessed by immunotherapy. In this review, we discuss a spectrum of AML immunotherapy targets, encompassing cancer cell-intrinsic and surface antigens as well as targeting in the leukemic milieu, and how they can be tailored for personalized approaches. These targets are overviewed across major immunotherapy modalities applied to AML: immune checkpoint inhibitors, antibody-drug conjugates, therapeutic vaccines, bispecific/trispecific antibodies, and chimeric antigen receptor (CAR)-T and CAR-NK cells. Significance: Immune therapies in AML treatment show evolving promise. Ongoing research aims to customize approaches for varied patient profiles and clinical scenarios. This review covers immune surveillance mechanisms, therapy options like checkpoint inhibitors, antibodies, CAR-T/NK cells, and vaccines, as well as resistance mechanisms and microenvironment considerations.

High-sensitivity analysis of clonal hematopoiesis reveals increased clonal complexity of potential-driver mutations in severe COVID-19 patients.

Whether Clonal Hematopoiesis (CH) represents a risk factor for severity of the COVID-19 disease remains a controversial issue. We report the first high- sensitivity analysis of CH in COVID-19 patients (threshold of detection at 0.5% vs 1 or 2% in previous studies). We analyzed 24 patients admitted to ICU for COVID-19 (COV-ICU) and 19 controls, including healthy subjects and asymptomatic SARS-CoV2-positive individuals. Despite the significantly higher numbers of CH mutations identified (80% mutations with <2% variant allele frequency, VAF), we did not find significant differences between COV-ICU patients and controls in the prevalence of CH or in the numbers, VAF or functional categories of the mutated genes, suggesting that CH is not overrepresented in patients with COVID-19. However, when considering potential drivers CH mutations (CH-PD), COV-ICU patients showed higher clonal complexity, in terms of both mutation numbers and VAF, and enrichment of variants reported in myeloid neoplasms. However, we did not score an impact of increased CH-PD on patient survival or clinical parameters associated with inflammation. These data suggest that COVID-19 influence the clonal composition of the peripheral blood and call for further investigations addressing the potential long-term clinical impact of CH on people experiencing severe COVID-19. We acknowledge that it will indispensable to perform further studies on larger patient cohorts in order to validate and generalize our conclusions. Moreover, we performed CH analysis at a single time point. It will be necessary to consider longitudinal approaches with long periods of follow-up in order to assess if the COVID-19 disease could have an impact on the evolution of CH and long-term consequences in patients that experienced severe COVID-19.

Caloric restriction leads to druggable LSD1-dependent cancer stem cells expansion.

Caloric Restriction (CR) has established anti-cancer effects, but its clinical relevance and molecular mechanism remain largely undefined. Here, we investigate CR's impact on several mouse models of Acute Myeloid Leukemias, including Acute Promyelocytic Leukemia, a subtype strongly affected by obesity. After an initial marked anti-tumor effect, lethal disease invariably re-emerges. Initially, CR leads to cell-cycle restriction, apoptosis, and inhibition of TOR and insulin/IGF1 signaling. The relapse, instead, is associated with the non-genetic selection of Leukemia Initiating Cells and the downregulation of double-stranded RNA (dsRNA) sensing and Interferon (IFN) signaling genes. The CR-induced adaptive phenotype is highly sensitive to pharmacological or genetic ablation of LSD1, a lysine demethylase regulating both stem cells and dsRNA/ IFN signaling. CR + LSD1 inhibition leads to the re-activation of dsRNA/IFN signaling, massive RNASEL-dependent apoptosis, and complete leukemia eradication in ~90% of mice. Importantly, CR-LSD1 interaction can be modeled in vivo and in vitro by combining LSD1 ablation with pharmacological inhibitors of insulin/IGF1 or dual PI3K/MEK blockade. Mechanistically, insulin/IGF1 inhibition sensitizes blasts to LSD1-induced death by inhibiting the anti-apoptotic factor CFLAR. CR and LSD1 inhibition also synergize in patient-derived AML and triple-negative breast cancer xenografts. Our data provide a rationale for epi-metabolic pharmacologic combinations across multiple tumors.

The lymphoma-associated NPM-ALK oncogene elicits a p16INK4a/pRb-dependent tumor-suppressive pathway.

Oncogene-induced senescence (OIS) is a barrier for tumor development. Oncogene-dependent DNA damage and activation of the ARF/p53 pathway play a central role in OIS and, accordingly, ARF and p53 are frequently mutated in human cancer. A number of leukemia/lymphoma-initiating oncogenes, however, inhibit ARF/p53 and only infrequently select for ARF or p53 mutations, suggesting the involvement of other tumor-suppressive pathways. We report that NPM-ALK, the initiating oncogene of anaplastic large cell lymphomas (ALCLs), induces DNA damage and irreversibly arrests the cell cycle of primary fibroblasts and hematopoietic progenitors. This effect is associated with inhibition of p53 and is caused by activation of the p16INK4a/pRb tumor-suppressive pathway. Analysis of NPM-ALK lymphomagenesis in transgenic mice showed p16INK4a-dependent accumulation of senescent cells in premalignant lesions and decreased tumor latency in the absence of p16INK4a. Accordingly, human ALCLs showed no expression of either p16INK4a or pRb. Up-regulation of the histone-demethylase Jmjd3 and de-methylation at the p16INK4a promoter contributed to the effect of NPM-ALK on p16INK4a, which was transcriptionally regulated. These data demonstrate that p16INK4a/pRb may function as an alternative pathway of oncogene-induced senescence, and suggest that the reactivation of p16INK4a expression might be a novel strategy to restore the senescence program in some tumors.

High-resolution Nanopore methylome-maps reveal random hyper-methylation at CpG-poor regions as driver of chemoresistance in leukemias.

Aberrant DNA methylation at CpG dinucleotides is a cancer hallmark that is associated with the emergence of resistance to anti cancer treatment, though molecular mechanisms and biological significance remain elusive. Genome scale methylation maps by currently used methods are based on chemical modification of DNA and are best suited for analyses of methylation at CpG rich regions (CpG islands). We report the first high coverage whole-genome map in cancer using the long read nanopore technology, which allows simultaneous DNA-sequence and -methylation analyses on native DNA. We analyzed clonal epigenomic/genomic evolution in Acute Myeloid Leukemias (AMLs) at diagnosis and relapse, after chemotherapy. Long read sequencing coupled to a novel computational method allowed definition of differential methylation at unprecedented resolution, and showed that the relapse methylome is characterized by hypermethylation at both CpG islands and sparse CpGs regions. Most differentially methylated genes, however, were not differentially expressed nor enriched for chemoresistance genes. A small fraction of under-expressed and hyper-methylated genes at sparse CpGs, in the gene body, was significantly enriched in transcription factors (TFs). Remarkably, these few TFs supported large gene-regulatory networks including 50% of all differentially expressed genes in the relapsed AMLs and highly-enriched in chemoresistance genes. Notably, hypermethylated regions at sparse CpGs were poorly conserved in the relapsed AMLs, under-represented at their genomic positions and showed higher methylation entropy, as compared to CpG islands. Analyses of available datasets confirmed TF binding to their target genes and conservation of the same gene-regulatory networks in large patient cohorts. Relapsed AMLs carried few patient specific structural variants and DNA mutations, apparently not involved in drug resistance. Thus, drug resistance in AMLs can be mainly ascribed to the selection of random epigenetic alterations at sparse CpGs of a few transcription factors, which then induce reprogramming of the relapsing phenotype, independently of clonal genomic evolution.

GASOLINE: detecting germline and somatic structural variants from long-reads data.

Long-read sequencing allows analyses of single nucleic-acid molecules and produces sequences in the order of tens to hundreds kilobases. Its application to whole-genome analyses allows identification of complex genomic structural-variants (SVs) with unprecedented resolution. SV identification, however, requires complex computational methods, based on either read-depth or intra- and inter-alignment signatures approaches, which are limited by size or type of SVs. Moreover, most currently available tools only detect germline variants, thus requiring separate computation of sample pairs for comparative analyses. To overcome these limits, we developed a novel tool (Germline And SOmatic structuraL varIants detectioN and gEnotyping; GASOLINE) that groups SV signatures using a sophisticated clustering procedure based on a modified reciprocal overlap criterion, and is designed to identify germline SVs, from single samples, and somatic SVs from paired test and control samples. GASOLINE is a collection of Perl, R and Fortran codes, it analyzes aligned data in BAM format and produces VCF files with statistically significant somatic SVs. Germline or somatic analysis of 30[Formula: see text] sequencing coverage experiments requires 4-5 h with 20 threads. GASOLINE outperformed currently available methods in the detection of both germline and somatic SVs in synthetic and real long-reads datasets. Notably, when applied on a pair of metastatic melanoma and matched-normal sample, GASOLINE identified five genuine somatic SVs that were missed using five different sequencing technologies and state-of-the art SV calling approaches. Thus, GASOLINE identifies germline and somatic SVs with unprecedented accuracy and resolution, outperforming currently available state-of-the-art WGS long-reads computational methods.

Lessons from S1P receptor targeting in multiple sclerosis.

Sphingosine 1-phosphate (S1P) is a potent bioactive sphingolipid binding to specific G protein-coupled receptors expressed in several organs. The relevance of S1P-S1P receptor axis in the pathophysiology of immune and nervous systems has encouraged the development of S1P receptor modulators for the treatment of neurological, autoimmune and/or inflammatory disorders. Currently, four S1P receptor modulators are approved drugs for multiple sclerosis (MS), an inflammatory disorder of the central nervous system. As main pharmacologic effect, these treatments induce lymphopenia due to the loss of responsiveness to S1P gradients guiding lymphocyte egress from lymphoid organs into the bloodstream. Recent data point to immunological effects of the S1P modulators beyond the inhibition of lymphocyte trafficking. Further, these drugs may cross the blood-brain barrier and directly target CNS resident cells expressing S1P receptors. Here we review the role of S1P signalling in neuroimmunology at the light of the evidences generated from the study of the mechanism of action of S1P receptor modulators in MS and integrate this information with findings derived from neuroinflammatory animal models and in vitro observations. These insights can direct the application of therapeutic approaches targeting S1P receptors in other disease areas.

Proprotein convertase subtilisin/kexin type 9 inhibitors treatment in dyslipidemic patients: a real world prescription.

AIM: Dyslipidemia is recognized as one of the major risk factors for cardiovascular diseases. This retrospective observational study was aimed to assess the effect of proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors in dyslipidemic patients with a lipid profile not well controlled by maximally tolerated statin therapy or intolerant to these lipid-lowering drugs. We enrolled 151 patients, of whom, 119 were taking evolocumab and 32 alirocumab. RESULTS: Total cholesterol significantly decreased progressively until the fourth year; after 4 years there was a significant reduction (-125.5 mg/dl, -51.5%, P < 0.0001 vs baseline, and P < 0.05 vs 1 year and P < 0.05 vs 2 years) and -2.8 mg/dl (-2.3%) compared with the third year. Low-density lipoprotein-cholesterol (LDL-C) also decreased significantly until the fourth year. After 3 years, there was a significant reduction (-117.8 mg/dl, -71.5%, P < 0.0001 vs baseline, and P < 0.05 vs 1 year) and -13.9 mg/dl (-22.8%) compared with the second year; after 4 years there was a significant reduction (-121.4 mg/dl, -73.7%, P < 0.0001 vs baseline, and P < 0.05 vs 1 year and P < 0.05 vs 2 years) and -3.6 mg/dl (-7.7%) compared with the third year. High-density lipoprotein-cholesterol increased significantly only during the fourth year of detection. After 3 years, there was a nonsignificant increase (4.9 mg/dl, 10.0%, P = 0.061 vs baseline) and 1.6 mg/dl (3.1%) compared with the second year; after 4 years, there was a significant increase (5.2 mg/dl, 10.6%, P < 0.05 vs baseline) and 0.3 mg/dl (0.6%) compared with the third year. The value of Tg was significantly reduced progressively until the second year and then stabilized in the third and fourth years. After 3 years, the value of Tg stabilized (-48.6 mg/dl, -32.4%, P < 0.01 vs baseline, and P < 0.05 vs 1 year) and -4.8 mg/dl (-4.5%) compared with the second year; after 4 years (-46.4 mg/dl, -31.0%, P < 0.01 vs baseline, and P < 0.05 vs 1 year) there was a slight and nonsignificant increase of 2.2 mg/dl (2.2%) compared with the third year. Regarding adverse events, both drugs were well tolerated. CONCLUSIONS: We showed that PCSK9 inhibitors are well tolerated and provide long-term significant LDL-C lowering in individuals with hyperlipidemia.

JAB1 deletion in oligodendrocytes causes senescence-induced inflammation and neurodegeneration in mice.

Oligodendrocytes are the primary target of demyelinating disorders, and progressive neurodegenerative changes may evolve in the CNS. DNA damage and oxidative stress are considered key pathogenic events, but the underlying molecular mechanisms remain unclear. Moreover, animal models do not fully recapitulate human diseases, complicating the path to effective treatments. Here we report that mice with cell-autonomous deletion of the nuclear COP9 signalosome component CSN5 (JAB1) in oligodendrocytes develop DNA damage and defective DNA repair in myelinating glial cells. Interestingly, oligodendrocytes lacking JAB1 expression underwent a senescence-like phenotype that fostered chronic inflammation and oxidative stress. These mutants developed progressive CNS demyelination, microglia inflammation, and neurodegeneration, with severe motor deficits and premature death. Notably, blocking microglia inflammation did not prevent neurodegeneration, whereas the deletion of p21CIP1 but not p16INK4a pathway ameliorated the disease. We suggest that senescence is key to sustaining neurodegeneration in demyelinating disorders and may be considered a potential therapeutic target.

The multifunctional protein nucleophosmin (NPM1) is a human linker histone H1 chaperone.

Linker histone H1 plays an essential role in chromatin organization. Proper deposition of linker histone H1 as well as its removal is essential for chromatin dynamics and function. Linker histone chaperones perform this important task during chromatin assembly and other DNA-templated phenomena in the cell. Our in vitro data show that the multifunctional histone chaperone NPM1 interacts with linker histone H1 through its first acidic stretch (residues 120-132). Association of NPM1 with linker histone H1 was also observed in cells in culture. NPM1 exhibited remarkable linker histone H1 chaperone activity, as it was able to efficiently deposit histone H1 onto dinucleosomal templates. Overexpression of NPM1 reduced the histone H1 occupancy on the chromatinized template of HIV-1 LTR in TZM-bl cells, which led to enhanced Tat-mediated transactivation. These data identify NPM1 as an important member of the linker histone chaperone family in humans.

Nucleophosmin regulates the stability and transcriptional activity of p53.

Nucleophosmin (NPM) is a ubiquitously expressed nucleolar phosphoprotein that continuously shuttles between the nucleus and cytoplasm. It has been proposed to function in ribosomal protein assembly and transport, and also as a molecular chaperone that prevents proteins from aggregating in the crowded environment of the nucleolus. The NPM gene is involved in several tumour-associated chromosome translocations, which have resulted in the formation of fusion proteins that retain the amino terminus of NPM, including NPM ALK, NPM RAR and NPM MLF1 (ref. 6). It is generally thought that the NPM component is not involved in the transforming potential of these fusion proteins, but instead provides a dimerization interface for the oligomerization and the oncogenic conversion of the various NPM partners (ALK, RAR, MLF1). Here we show that NPM interacts directly with the tumour suppressor p53, regulates the increase in stability and transcriptional activation of p53 after different types of stress, and induces p53-dependent premature senescence on overexpression in diploid fibroblasts. These findings indicate that NPM is a crucial regulator of p53 and suggest that alterations of the NPM function by NPM fusion proteins might lead to deregulation of p53 in tumours.