The vascular system is comprised of the vast network of arteries and veins, while lymph fluid circulates through the lymphatic system, a parallel network. In this issue, Chen et al. show that lymphatic vessels assume a vascular fate when sheer force in vessels is increased (page 2006). In addition, Felcht et al. demonstrate that Angiopoietin-2 (ANG-2) can promote angiogenesis via TIE2 signaling, or inhibit angiogenesis by binding integrin receptors, and that TIE2-integrin signaling balance determines ANG-2 function (page 1991). Image credit: Shutterstock, Inc. Copyright: hunta.
Squamous cell carcinoma of the head and neck (HNSCC) is a relatively common human cancer characterized by high morbidity, high mortality, and few therapeutic options outside of surgery, standard cytotoxic chemotherapy, and radiation. Although the most important risk factors are tobacco use and alcohol consumption, the disease is also linked to infection with high-risk types of human papilloma viruses (HPVs). Recent genetic analyses have yielded new insights into the molecular pathogenesis of this disease. Overall, while somatic activating mutations within classical oncogenes including PIK3CA and RAS occur in HNSCC, they are relatively uncommon. Instead genetic data point to a contribution of multiple tumor suppressor pathways, including p53, Rb/INK4/ARF, and Notch, in tumor initiation, progression, and maintenance. The increasingly refined knowledge of HNSCC genetics, combined with ever-more-sophisticated animal models and newer drug targeting strategies, should promote novel therapeutic approaches and improved disease outcomes.
In the catabolic state with no food intake, the liver generates ketones by breaking down fatty acids. During the nocturnal fast or longer starvation periods, this protects the brain, which cannot oxidize fatty acids. In 1977, we published a study in the JCI noting the surprising realization that malonyl-CoA, the substrate of fatty acid synthesis, was also an inhibitor of fatty acid oxidation. Subsequent experiments have borne out this finding and furthered our understanding of molecular metabolism.
It is paradoxical that immunodeficiency disorders are associated with autoimmunity. Adenosine deaminase (ADA) deficiency, a cause of X-linked severe combined immunodeficiency (SCID), is a case in point. In this issue of the JCI, Sauer and colleagues investigate the B cell defects in ADA-deficient patients. They demonstrate that ADA patients receiving enzyme replacement therapy had B cell tolerance checkpoint defects. Remarkably, gene therapy with a retrovirus that expresses ADA resulted in the apparent correction of these defects, with normalization of peripheral B cell autoantibody frequencies. In vitro, agents that either block ADA or overexpress adenosine resulted in altered B cell receptor and TLR signaling. Collectively, these data implicate a B cell–intrinsic mechanism for alterations in B cell tolerance in the setting of partial ADA deficiency that is corrected by gene therapy.
Previous studies in mice have demonstrated antagonistic effects of telomerase loss on carcinogenesis. Telomere attrition can promote genome instability, thereby stimulating initiation of early-stage cancers, but can also inhibit tumorigenesis by promoting permanent cell growth arrest or death. Human cancers likely develop in cell lineages with low levels of telomerase, leading to telomere losses in early lesions, followed by subsequent activation of telomerase. Mouse models constitutively lacking telomerase have thus not addressed how telomere losses within telomerase-proficient cells have an impact on carcinogenesis. Using a novel transgenic mouse model, Begus-Nahrmann et al. demonstrate in this issue of the JCI that transient telomere dysfunction in telomerase-proficient animals is a potent stimulus of tumor formation.
A promising approach to cancer therapy is to elicit apoptosis with “BH3 mimetic” drugs, which target proteins of the BCL-2 family. As of yet, however, such drugs can target only certain BCL-2 family proteins. Hence, in this issue of the JCI, LaBelle et al. assess instead the therapeutic potential of a “stapled” BH3 peptide from the BIM protein, which inactivates all its prosurvival relatives. The peptide killed cultured hematologic tumor cells and abated growth of a leukemia xenograft, without perturbing the hematopoietic compartment. Hence, such peptides might eventually provide a new way to treat refractory leukemias.
Inflammation plays an essential role in vascular pathologies, including those associated with sepsis and atherosclerosis. Identifying negative regulators of inflammatory signaling pathways may provide novel therapeutic targets for these diseases. In this issue of the JCI, Sun et al. show that in endothelial cells, microRNA-181b (miR-181b) plays a vital role in controlling inflammation by targeting importin-α3, a regulator of NF-κB nuclear import. These findings provide compelling evidence that modulation of microRNAs may be a useful therapeutic approach for inflammatory vascular diseases.
The mammalian target of rapamycin (mTOR) pathway is activated in the majority of human malignancies and thus seems a likely therapeutic target. However, this pathway is genetically complex, complicating studies using pharmacologic mTOR inhibitors. In this issue of the JCI, Hoshii et al. examined mice deficient in one of the mTOR effector complex proteins, Raptor, to elucidate the role of mTORC1 in leukemia. They convincingly demonstrate that Raptor deficiency, with consequent mTORC1 inhibition, blocks differentiation of leukemia cells and prolongs survival, but also allows a population of leukemia-initiating cells to persist in what appears to be a state of dormancy. Translating this new understanding into effective therapeutic strategies will require further study of the molecular mechanisms that underlie these processes.
EC activation and dysfunction have been linked to a variety of vascular inflammatory disease states. The function of microRNAs (miRNAs) in vascular EC activation and inflammation remains poorly understood. Herein, we report that microRNA-181b (miR-181b) serves as a potent regulator of downstream NF-κB signaling in the vascular endothelium by targeting importin-α3, a protein that is required for nuclear translocation of NF-κB. Overexpression of miR-181b inhibited importin-α3 expression and an enriched set of NF-κB–responsive genes such as adhesion molecules VCAM-1 and E-selectin in ECs in vitro and in vivo. In addition, treatment of mice with proinflammatory stimuli reduced miR-181b expression. Rescue of miR-181b levels by systemic administration of miR-181b “mimics” reduced downstream NF-κB signaling and leukocyte influx in the vascular endothelium and decreased lung injury and mortality in endotoxemic mice. In contrast, miR-181b inhibition exacerbated endotoxin-induced NF-κB activity, leukocyte influx, and lung injury. Finally, we observed that critically ill patients with sepsis had reduced levels of miR-181b compared with control intensive care unit (ICU) subjects. Collectively, these findings demonstrate that miR-181b regulates NF-κB–mediated EC activation and vascular inflammation in response to proinflammatory stimuli and that rescue of miR-181b expression could provide a new target for antiinflammatory therapy and critical illness.
Angiopoietin-2 (ANG-2) is a key regulator of angiogenesis that exerts context-dependent effects on ECs. ANG-2 binds the endothelial-specific receptor tyrosine kinase 2 (TIE2) and acts as a negative regulator of ANG-1/TIE2 signaling during angiogenesis, thereby controlling the responsiveness of ECs to exogenous cytokines. Recent data from tumors indicate that under certain conditions ANG-2 can also promote angiogenesis. However, the molecular mechanisms of dual ANG-2 functions are poorly understood. Here, we identify a model for the opposing roles of ANG-2 in angiogenesis. We found that angiogenesis-activated endothelium harbored a subpopulation of TIE2-negative ECs (TIE2lo). TIE2 expression was downregulated in angiogenic ECs, which abundantly expressed several integrins. ANG-2 bound to these integrins in TIE2lo ECs, subsequently inducing, in a TIE2-independent manner, phosphorylation of the integrin adaptor protein FAK, resulting in RAC1 activation, migration, and sprouting angiogenesis. Correspondingly, in vivo ANG-2 blockade interfered with integrin signaling and inhibited FAK phosphorylation and sprouting angiogenesis of TIE2lo ECs. These data establish a contextual model whereby differential TIE2 and integrin expression, binding, and activation control the role of ANG-2 in angiogenesis. The results of this study have immediate translational implications for the therapeutic exploitation of angiopoietin signaling.
Human vascular malformations cause disease as a result of changes in blood flow and vascular hemodynamic forces. Although the genetic mutations that underlie the formation of many human vascular malformations are known, the extent to which abnormal blood flow can subsequently influence the vascular genetic program and natural history is not. Loss of the SH2 domain–containing leukocyte protein of 76 kDa (SLP76) resulted in a vascular malformation that directed blood flow through mesenteric lymphatic vessels after birth in mice. Mesenteric vessels in the position of the congenital lymphatic in mature Slp76-null mice lacked lymphatic identity and expressed a marker of blood vessel identity. Genetic lineage tracing demonstrated that this change in vessel identity was the result of lymphatic endothelial cell reprogramming rather than replacement by blood endothelial cells. Exposure of lymphatic vessels to blood in the absence of significant flow did not alter vessel identity in vivo, but lymphatic endothelial cells exposed to similar levels of shear stress ex vivo rapidly lost expression of PROX1, a lymphatic fate–specifying transcription factor. These findings reveal that blood flow can convert lymphatic vessels to blood vessels, demonstrating that hemodynamic forces may reprogram endothelial and vessel identity in cardiovascular diseases associated with abnormal flow.
Cancer cells subvert the natural balance between cellular life and death, achieving immortality through pathologic enforcement of survival pathways and blockade of cell death mechanisms. Pro-apoptotic BCL-2 family proteins are frequently disarmed in relapsed and refractory cancer through genetic deletion or interaction-based neutralization by overexpressed antiapoptotic proteins, resulting in resistance to chemotherapy and radiation treatments. New pharmacologic strategies are urgently needed to overcome these formidable apoptotic blockades. We harnessed the natural killing activity of BCL-2–interacting mediator of cell death (BIM), which contains one of the most potent BH3 death domains of the BCL-2 protein family, to restore BH3-dependent cell death in resistant hematologic cancers. A hydrocarbon-stapled peptide modeled after the BIM BH3 helix broadly targeted BCL-2 family proteins with high affinity, blocked inhibitory antiapoptotic interactions, directly triggered proapoptotic activity, and induced dose-responsive and BH3 sequence–specific cell death of hematologic cancer cells. The therapeutic potential of stapled BIM BH3 was highlighted by the selective activation of cell death in the aberrant lymphoid infiltrates of mice reconstituted with BIM-deficient bone marrow and in a human AML xenograft model. Thus, we found that broad and multimodal targeting of the BCL-2 family pathway can overcome pathologic barriers to cell death.
Chronic obstructive pulmonary disease/emphysema (COPD/emphysema) is characterized by chronic inflammation and premature lung aging. Anti-aging sirtuin 1 (SIRT1), a NAD+-dependent protein/histone deacetylase, is reduced in lungs of patients with COPD. However, the molecular signals underlying the premature aging in lungs, and whether SIRT1 protects against cellular senescence and various pathophysiological alterations in emphysema, remain unknown. Here, we showed increased cellular senescence in lungs of COPD patients. SIRT1 activation by both genetic overexpression and a selective pharmacological activator, SRT1720, attenuated stress-induced premature cellular senescence and protected against emphysema induced by cigarette smoke and elastase in mice. Ablation of Sirt1 in airway epithelium, but not in myeloid cells, aggravated airspace enlargement, impaired lung function, and reduced exercise tolerance. These effects were due to the ability of SIRT1 to deacetylate the FOXO3 transcription factor, since Foxo3 deficiency diminished the protective effect of SRT1720 on cellular senescence and emphysematous changes. Inhibition of lung inflammation by an NF-κB/IKK2 inhibitor did not have any beneficial effect on emphysema. Thus, SIRT1 protects against emphysema through FOXO3-mediated reduction of cellular senescence, independently of inflammation. Activation of SIRT1 may be an attractive therapeutic strategy in COPD/emphysema.
Aldosterone, which plays a central role in the regulation of blood pressure, is produced by zona glomerulosa (ZG) cells of the adrenal gland. When dysregulated, aldosterone is pathogenic and contributes to the development and progression of cardiovascular and renal disease. Although sustained production of aldosterone requires persistent Ca2+ entry through low-voltage activated Ca2+ channels, isolated ZG cells are considered nonexcitable, with recorded membrane voltages that are too hyperpolarized to permit Ca2+ entry. Here, we show that mouse ZG cells within adrenal slices spontaneously generate membrane potential oscillations of low periodicity. This innate electrical excitability of ZG cells provides a platform for the production of a recurrent Ca2+ signal that can be controlled by Ang II and extracellular potassium, the 2 major regulators of aldosterone production. We conclude that native ZG cells are electrical oscillators, and that this behavior provides what we believe to be a new molecular explanation for the control of Ca2+ entry in these steroidogenic cells.
Skeletal muscle injury activates adult myogenic stem cells, known as satellite cells, to initiate proliferation and differentiation to regenerate new muscle fibers. The skeletal muscle–specific microRNA miR-206 is upregulated in satellite cells following muscle injury, but its role in muscle regeneration has not been defined. Here, we show that miR-206 promotes skeletal muscle regeneration in response to injury. Genetic deletion of miR-206 in mice substantially delayed regeneration induced by cardiotoxin injury. Furthermore, loss of miR-206 accelerated and exacerbated the dystrophic phenotype in a mouse model of Duchenne muscular dystrophy. We found that miR-206 acts to promote satellite cell differentiation and fusion into muscle fibers through suppressing a collection of negative regulators of myogenesis. Our findings reveal an essential role for miR-206 in satellite cell differentiation during skeletal muscle regeneration and indicate that miR-206 slows progression of Duchenne muscular dystrophy.
Cancer stem cells (CSCs) are a small subpopulation of cancer cells that have increased resistance to conventional therapies and are capable of establishing metastasis. However, only a few biomarkers of CSCs have been identified. Here, we report that ganglioside GD2 (a glycosphingolipid) identifies a small fraction of cells in human breast cancer cell lines and patient samples that are capable of forming mammospheres and initiating tumors with as few as 10 GD2+ cells. In addition, the majority of GD2+ cells are also CD44hiCD24lo, the previously established CSC-associated cell surface phenotype. Gene expression analysis revealed that GD3 synthase (GD3S) is highly expressed in GD2+ as well as in CD44hiCD24lo cells and that interference with GD3S expression, either by shRNA or using a pharmacological inhibitor, reduced the CSC population and CSC-associated properties. GD3S knockdown completely abrogated tumor formation in vivo. Also, induction of epithelial-mesenchymal transition (EMT) in transformed human mammary epithelial cells (HMLER cells) dramatically increased GD2 as well as GD3S expression in these cells, suggesting a role of EMT in the origin of GD2+ breast CSCs. In summary, we identified GD2 as a new CSC-specific cell surface marker and GD3S as a potential therapeutic target for CSCs, with the possibility of improving survival and cure rates in patients with breast cancer.
Hematopoietic stem and progenitor cell (HSPC) functions are governed by intricate signaling networks. The tyrosine kinase JAK2 plays an essential role in cytokine signaling during hematopoiesis. The adaptor protein LNK is a critical determinant of this process through its inhibitory interaction with JAK2, thereby limiting HSPC self-renewal. LNK deficiency promotes myeloproliferative neoplasm (MPN) development in mice, and LNK loss-of-function mutations are found in human MPNs, emphasizing its pivotal role in normal and malignant HSPCs. Here, we report the identification of 14-3-3 proteins as LNK binding partners. 14-3-3 interfered with the LNK-JAK2 interaction, thereby alleviating LNK inhibition of JAK2 signaling and cell proliferation. Binding of 14-3-3 required 2 previously unappreciated serine phosphorylation sites in LNK, and we found that their phosphorylation is mediated by glycogen synthase kinase 3 and PKA kinases. Mutations of these residues abrogated the interaction and augmented the growth inhibitory function of LNK. Conversely, forced 14-3-3 binding constrained LNK function. Furthermore, interaction with 14-3-3 sequestered LNK in the cytoplasm away from the plasma membrane-proximal JAK2. Importantly, bone marrow transplantation studies revealed an essential role for 14-3-3 in HSPC reconstitution that can be partially mitigated by LNK deficiency. We believe that, together, this work implicates 14-3-3 proteins as novel and positive HSPC regulators by impinging on the LNK/JAK2 pathway.
Pancreatic ductal adenocarcinoma (PDAC) has the lowest survival rate of all cancers and shows remarkable resistance to cell stress. Nuclear protein 1 (Nupr1), which mediates stress response in the pancreas, is frequently upregulated in pancreatic cancer. Here, we report that Nupr1 plays an essential role in pancreatic tumorigenesis. In a mouse model of pancreatic cancer with constitutively expressed oncogenic KrasG12D, we found that loss of Nupr1 protected from the development of pancreatic intraepithelial neoplasias (PanINs). Further, in cultured pancreatic cells, nutrient deprivation activated Nupr1 expression, which we found to be required for cell survival. We found that Nupr1 protected cells from stress-induced death by inhibiting apoptosis through a pathway dependent on transcription factor RelB and immediate early response 3 (IER3). NUPR1, RELB, and IER3 proteins were coexpressed in mouse PanINs from KrasG12D-expressing pancreas. Moreover, pancreas-specific deletion of Relb in a KrasG12D background resulted in delayed in PanIN development associated with a lack of IER3 expression. Thus, efficient PanIN formation was dependent on the expression of Nupr1 and Relb, with likely involvement of IER3. Finally, in patients with PDAC, expression of NUPR1, RELB, and IER3 was significantly correlated with a poor prognosis. Cumulatively, these results reveal a NUPR1/RELB/IER3 stress-related pathway that is required for oncogenic KrasG12D-dependent transformation of the pancreas.
Thrombosis, or blood clot formation, and its sequelae remain a leading cause of morbidity and mortality, and recurrent thrombosis is common despite current optimal therapy. Protein disulfide isomerase (PDI) is an oxidoreductase that has recently been shown to participate in thrombus formation. While currently available antithrombotic agents inhibit either platelet aggregation or fibrin generation, inhibition of secreted PDI blocks the earliest stages of thrombus formation, suppressing both pathways. Here, we explored extracellular PDI as an alternative target of antithrombotic therapy. A high-throughput screen identified quercetin-3-rutinoside as an inhibitor of PDI reductase activity in vitro. Inhibition of PDI was selective, as quercetin-3-rutinoside failed to inhibit the reductase activity of several other thiol isomerases found in the vasculature. Cellular assays showed that quercetin-3-rutinoside inhibited aggregation of human and mouse platelets and endothelial cell–mediated fibrin generation in human endothelial cells. Using intravital microscopy in mice, we demonstrated that quercetin-3-rutinoside blocks thrombus formation in vivo by inhibiting PDI. Infusion of recombinant PDI reversed the antithrombotic effect of quercetin-3-rutinoside. Thus, PDI is a viable target for small molecule inhibition of thrombus formation, and its inhibition may prove to be a useful adjunct in refractory thrombotic diseases that are not controlled with conventional antithrombotic agents.
Although dysregulation of mTOR complex 1 (mTORC1) promotes leukemogenesis, how mTORC1 affects established leukemia is unclear. We investigated the role of mTORC1 in mouse hematopoiesis using a mouse model of conditional deletion of Raptor, an essential component of mTORC1. Raptor deficiency impaired granulocyte and B cell development but did not alter survival or proliferation of hematopoietic progenitor cells. In a mouse model of acute myeloid leukemia (AML), Raptor deficiency significantly suppressed leukemia progression by causing apoptosis of differentiated, but not undifferentiated, leukemia cells. mTORC1 did not control cell cycle or cell growth in undifferentiated AML cells in vivo. Transplantation of Raptor-deficient undifferentiated AML cells in a limiting dilution revealed that mTORC1 is essential for leukemia initiation. Strikingly, a subset of AML cells with undifferentiated phenotypes survived long-term in the absence of mTORC1 activity. We further demonstrated that the reactivation of mTORC1 in those cells restored their leukemia-initiating capacity. Thus, AML cells lacking mTORC1 activity can self-renew as AML stem cells. Our findings provide mechanistic insight into how residual tumor cells circumvent anticancer therapies and drive tumor recurrence.
Glucocorticoids acting through the glucocorticoid receptor (GR) inhibit TNF-induced lethal inflammation. Here, we demonstrate that GR dimerization plays a role in reducing TNF sensitivity. In mutant mice unable to dimerize GR, we found that TNF failed to induce MAPK phosphatase 1 (MKP1). We assessed TNF sensitivity in Mkp1–/– mice and found increased inflammatory gene induction in livers, increased circulating cytokines, cell death in intestinal epithelium, severe intestinal inflammation, hypothermia, and death. Mkp1–/– mice had increased levels of phosphorylated JNK, which promotes apoptosis, in liver tissue. We further examined JNK-deficient mice for their response to TNF. Although Jnk1–/– mice showed no change in sensitivity to TNF, Jnk2–/– mice were significantly protected against TNF, identifying JNK2 as an essential player in inflammation induced by TNF. Furthermore, we found that loss of Jnk2 partially rescued the increased sensitivity of Mkp1–/– and mutant GR mice to TNF. Our data show that GR dimerization inhibits JNK2 through MKP1 and protects from TNF-induced apoptosis and lethal inflammation.
Adenosine deaminase (ADA) gene defects are among the most common causes of SCID. Restoration of purine metabolism and immune functions can be achieved by enzyme replacement therapy, or more effectively by bone marrow transplant or HSC gene therapy (HSC-GT). However, autoimmune complications and autoantibody production, including anti-nuclear antibodies (ANAs), frequently occur in ADA-SCID patients after treatment. To assess whether ADA deficiency affects the establishment of B cell tolerance, we tested the reactivity of recombinant antibodies isolated from single B cells of ADA-SCID patients before and after HSC-GT. We found that before HSC-GT, new emigrant/transitional and mature naive B cells from ADA-SCID patients contained more autoreactive and ANA-expressing clones, indicative of defective central and peripheral B cell tolerance checkpoints. We further observed impaired B cell receptor (BCR) and TLR functions in B cells after ADA inhibition, which may underlie the defects in B cell tolerance. Strikingly, after HSC-GT, ADA-SCID patients displayed quasi-normal early B cell tolerance checkpoints, as evidenced by restored removal of developing autoreactive and ANA-expressing B cells. Hence, ADA plays an essential role in controlling autoreactive B cell counterselection by regulating BCR and TLR functions.
Beare-Stevenson cutis gyrata syndrome (BSS) is a human genetic disorder characterized by skin and skull abnormalities. BSS is caused by mutations in the FGF receptor 2 (FGFR2), but the molecular mechanisms that induce skin and skull abnormalities are unclear. We developed a mouse model of BSS harboring a FGFR2 Y394C mutation and identified p38 MAPK as an important signaling pathway mediating these abnormalities. Fgfr2+/Y394C mice exhibited epidermal hyperplasia and premature closure of cranial sutures (craniosynostosis) due to abnormal cell proliferation and differentiation. We found ligand-independent phosphorylation of FGFR2 and activation of p38 signaling in mutant skin and calvarial tissues. Treating Fgfr2+/Y394C mice with a p38 kinase inhibitor attenuated skin abnormalities by reversing cell proliferation and differentiation to near normal levels. This study reveals the pleiotropic effects of the FGFR2 Y394C mutation evidenced by cutis gyrata, acanthosis nigricans, and craniosynostosis and provides a useful model for investigating the molecular mechanisms of skin and skull development. The demonstration of a pathogenic role for p38 activation may lead to the development of therapeutic strategies for BSS and related conditions, such as acanthosis nigricans or craniosynostosis.
Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies resistant to current chemotherapies or radiotherapies, which makes it urgent to identify new therapeutic targets for HCC. In this study, we found that checkpoint kinase 1 (CHK1) was frequently overexpressed and correlated with poor clinical outcome in patients with HCC. We further showed that the CHK1 inhibitor GÖ6976 was capable of sensitizing HCC cells to cisplatin, indicating that CHK1 may have oncogenic function in HCC. We found that CHK1 phosphorylated the tumor suppressor spleen tyrosine kinase (L) (SYK[L]) and identified the phosphorylation site at Ser295. Furthermore, CHK1 phosphorylation of SYK(L) promoted its subsequent proteasomal degradation. Expression of a nonphosphorylated mutant of SYK(L) was more efficient at suppressing proliferation, colony formation, mobility, and tumor growth in HCC lines. Importantly, a strong inverse correlation between the expression levels of CHK1 and SYK(L) was observed in patients with HCC. Collectively, our data demonstrate that SYK(L) is a substrate of CHK1 in tumor cells and suggest that targeting the CHK1/SYK(L) pathway may be a promising strategy for treating HCC.
Nonalcoholic fatty liver disease (NAFLD) is associated with all features of the metabolic syndrome. Although deposition of excess triglycerides within liver cells, a hallmark of NAFLD, is associated with a loss of insulin sensitivity, it is not clear which cellular abnormality arises first. We have explored this in mice overexpressing carbohydrate responsive element–binding protein (ChREBP). On a standard diet, mice overexpressing ChREBP remained insulin sensitive, despite increased expression of genes involved in lipogenesis/fatty acid esterification and resultant hepatic steatosis (simple fatty liver). Lipidomic analysis revealed that the steatosis was associated with increased accumulation of monounsaturated fatty acids (MUFAs). In primary cultures of mouse hepatocytes, ChREBP overexpression induced expression of stearoyl-CoA desaturase 1 (Scd1), the enzyme responsible for the conversion of saturated fatty acids (SFAs) into MUFAs. SFA impairment of insulin-responsive Akt phosphorylation was therefore rescued by the elevation of Scd1 levels upon ChREBP overexpression, whereas pharmacological or shRNA-mediated reduction of Scd1 activity decreased the beneficial effect of ChREBP on Akt phosphorylation. Importantly, ChREBP-overexpressing mice fed a high-fat diet showed normal insulin levels and improved insulin signaling and glucose tolerance compared with controls, despite having greater hepatic steatosis. Finally, ChREBP expression in liver biopsies from patients with nonalcoholic steatohepatitis was increased when steatosis was greater than 50% and decreased in the presence of severe insulin resistance. Together, these results demonstrate that increased ChREBP can dissociate hepatic steatosis from insulin resistance, with beneficial effects on both glucose and lipid metabolism.
Itch, also known as pruritus, is a common, intractable symptom of several skin diseases, such as atopic dermatitis and xerosis. TLRs mediate innate immunity and regulate neuropathic pain, but their roles in pruritus are elusive. Here, we report that scratching behaviors induced by histamine-dependent and -independent pruritogens are markedly reduced in mice lacking the Tlr3 gene. TLR3 is expressed mainly by small-sized primary sensory neurons in dorsal root ganglions (DRGs) that coexpress the itch signaling pathway components transient receptor potential subtype V1 and gastrin-releasing peptide. Notably, we found that treatment with a TLR3 agonist induces inward currents and action potentials in DRG neurons and elicited scratching in WT mice but not Tlr3–/– mice. Furthermore, excitatory synaptic transmission in spinal cord slices and long-term potentiation in the intact spinal cord were impaired in Tlr3–/– mice but not Tlr7–/– mice. Consequently, central sensitization–driven pain hypersensitivity, but not acute pain, was impaired in Tlr3–/– mice. In addition, TLR3 knockdown in DRGs also attenuated pruritus in WT mice. Finally, chronic itch in a dry skin condition was substantially reduced in Tlr3–/– mice. Our findings demonstrate a critical role of TLR3 in regulating sensory neuronal excitability, spinal cord synaptic transmission, and central sensitization. TLR3 may serve as a new target for developing anti-itch treatment.
Streptococcus pneumoniae is the most common cause of severe bacterial meningitis in children, the elderly, and immunocompromised individuals. To identify virulence factors preferentially expressed during meningitis, we conducted niche-specific genome-wide in vivo transcriptomic analysis after intranasal infection of mice with serotype 4 or 6A pneumococci. The expression of 34 bacterial genes was substantially altered in brain tissue of mice infected with either of the 2 strains. Ten upregulated genes were common to both strains, 7 of which were evaluated for their role in the development of meningitis. One previously uncharacterized protein, α-glycerophosphate oxidase (GlpO), was cytotoxic for human brain microvascular endothelial cells (HBMECs) via generation of H2O2. A glpO deletion mutant was defective in adherence to HBMECs in vitro as well as in progression from the blood to the brain in vivo. Mutant bacteria also induced markedly reduced meningeal inflammation and brain pathology compared with wild type, despite similar levels of bacteremia. Immunization of mice with GlpO protected against invasive pneumococcal disease and provided additive protection when formulated with pneumolysin toxoid. Our results provide the basis of a strategy that can be adapted to identify genes that contribute to the development of meningitis caused by other pathogens.
Vα24-invariant NKT cells inhibit tumor growth by targeting tumor-associated macrophages (TAMs). Tumor progression therefore requires that TAMs evade NKT cell activity through yet-unknown mechanisms. Here we report that a subset of cells in neuroblastoma (NB) cell lines and primary tumors expresses membrane-bound TNF-α (mbTNF-α). These proinflammatory tumor cells induced production of the chemokine CCL20 from TAMs via activation of the NF-κB signaling pathway, an effect that was amplified in hypoxia. Flow cytometry analyses of human primary NB tumors revealed selective accumulation of CCL20 in TAMs. Neutralization of the chemokine inhibited in vitro migration of NKT cells toward tumor-conditioned hypoxic monocytes and localization of NKT cells to NB grafts in mice. We also found that hypoxia impaired NKT cell viability and function. Thus, CCL20-producing TAMs served as a hypoxic trap for tumor-infiltrating NKT cells. IL-15 protected antigen-activated NKT cells from hypoxia, and transgenic expression of IL-15 in adoptively transferred NKT cells dramatically enhanced their antimetastatic activity in mice. Thus, tumor-induced chemokine production in hypoxic TAMs and consequent chemoattraction and inhibition of NKT cells represents a mechanism of immune escape that can be reversed by adoptive immunotherapy with IL-15–transduced NKT cells.
Acute graft-versus-host disease (GvHD) is a serious complication of allogeneic hematopoietic cell transplantation (allo-HCT) that results from donor allogeneic T cell attack on host tissues. Based on previous work implicating immune cell–derived C3a and C5a as regulators of T cell immunity, we examined the effects of locally produced C3a and C5a on murine T cell–mediated GvHD. We found that total body irradiation, a conditioning regimen required to permit engraftment of allo-HCT, caused upregulation and activation of alternative pathway complement components by recipient APCs. Allo-HCT with decay accelerating factor–null (Daf1–/–) host BM and Daf1–/– donor lymphocytes led to exacerbated GvHD outcome and resulted in splenic and organ-infiltrating T cell expansion. T cells deficient in C3a receptor (C3aR) and/or C5a receptor (C5aR) responded weakly in allogeneic hosts and exhibited limited ability to induce GvHD. Using a clinically relevant treatment strategy, we showed that pharmacological C5aR blockade reduced GvHD morbidity. Our data mechanistically link APC-derived complement to T cell–mediated GvHD and support complement inhibition as a therapeutic strategy for GvHD in humans.
Intestinal barrier function requires intricate cooperation between intestinal epithelial cells and immune cells. Enteropathogens are able to invade the intestinal lymphoid tissue known as Peyer’s patches (PPs) and disrupt the integrity of the intestinal barrier. However, the underlying molecular mechanisms of this process are poorly understood. In mice infected with Yersinia pseudotuberculosis, we found that PP barrier dysfunction is dependent on the Yersinia virulence plasmid and the expression of TLR-2 by hematopoietic cells, but not by intestinal epithelial cells. Upon TLR-2 stimulation, Y. pseudotuberculosis–infected monocytes activated caspase-1 and produced IL-1β. In turn, IL-1β increased NF-κB and myosin light chain kinase activation in intestinal epithelial cells, thus disrupting the intestinal barrier by opening the tight junctions. Therefore, Y. pseudotuberculosis subverts intestinal barrier function by altering the interplay between immune and epithelial cells during infection.
Psoriasis is a common, relapsing inflammatory skin disease characterized by erythematous scaly plaques. Histological manifestations of psoriasis include keratinocyte dysregulation and hyperproliferation, elongated rete ridges, and inflammatory infiltrates consisting of T cells, macrophages, dendritic cells, and neutrophils. Despite the availability of new effective drugs to treat psoriasis, the underlying mechanisms of pathogenesis are still poorly understood. Recent studies have shown that Aldara cream, used to treat benign skin abnormalities, triggers psoriasis-like disease in humans and mice and have implicated Th17 cells in disease initiation. Using this as a model, we found a predominant role for the Th17 signature cytokines IL-17A, IL-17F, and IL-22 in psoriasiform plaque formation in mice. Using gene-targeted mice, we observed that loss of Il17a, Il17f, or Il22 strongly reduced disease the severity of psoriasis. However, we found that Th17 cells were not the primary source of these pathogenic cytokines. Rather, IL-17A, IL-17F, and IL-22 were produced by a skin-invading population of γδ T cells and RORγt+ innate lymphocytes. Furthermore, our findings establish that RORγt+ innate lymphocytes and γδ T cells are necessary and sufficient for psoriatic plaque formation in an experimental disease model that closely resembles human psoriatic plaque formation.
PAX5, a B cell–specific transcription factor, is overexpressed through chromosomal translocations in a subset of B cell lymphomas. Previously, we had shown that activation of immunoreceptor tyrosine-based activation motif (ITAM) proteins and B cell receptor (BCR) signaling by PAX5 contributes to B-lymphomagenesis. However, the effect of PAX5 on other oncogenic transcription factor-controlled pathways is unknown. Using a MYC-induced murine lymphoma model as well as MYC-transformed human B cell lines, we found that PAX5 controls c-MYC protein stability and steady-state levels. This promoter-independent, posttranslational mechanism of c-MYC regulation was independent of ITAM/BCR activity. Instead it was controlled by another PAX5 target, CD19, through the PI3K-AKT-GSK3β axis. Consequently, MYC levels in B cells from CD19-deficient mice were sharply reduced. Conversely, reexpression of CD19 in murine lymphomas with spontaneous silencing of PAX5 boosted MYC levels, expression of its key target genes, cell proliferation in vitro, and overall tumor growth in vivo. In human B-lymphomas, CD19 mRNA levels were found to correlate with those of MYC-activated genes. They also negatively correlated with the overall survival of patients with lymphoma in the same way that MYC levels do. Thus, CD19 is a major BCR-independent regulator of MYC-driven neoplastic growth in B cell neoplasms.
Understanding the mechanisms underlying oro-gustatory detection of dietary fat is critical for the prevention and treatment of obesity. The lipid-binding glycoprotein CD36, which is expressed by circumvallate papillae (CVP) of the mouse tongue, has been implicated in oro-gustatory perception of dietary lipids. Here, we demonstrate that stromal interaction molecule 1 (STIM1), a sensor of Ca2+ depletion in the endoplasmic reticulum, mediates fatty acid–induced Ca2+ signaling in the mouse tongue and fat preference. We showed that linoleic acid (LA) induced the production of arachidonic acid (AA) and lysophosphatidylcholine (Lyso-PC) by activating multiple phospholipase A2 isoforms via CD36. This activation triggered Ca2+ influx in CD36-positive taste bud cells (TBCs) purified from mouse CVP. LA also induced the production of Ca2+ influx factor (CIF). STIM1 was found to regulate LA-induced CIF production and the opening of multiple store-operated Ca2+ (SOC) channels. Furthermore, CD36-positive TBCs from Stim1–/– mice failed to release serotonin, and Stim1–/– mice lost the spontaneous preference for fat that was observed in wild-type animals. Our results suggest that fatty acid–induced Ca2+ signaling, regulated by STIM1 via CD36, might be implicated in oro-gustatory perception of dietary lipids and the spontaneous preference for fat.
Telomere shortening limits the proliferative capacity of a cell, but perhaps surprisingly, shortening is also known to be associated with increased rates of tumor initiation. A current hypothesis suggests that telomere dysfunction increases tumor initiation by induction of chromosomal instability, but that initiated tumors need to reactivate telomerase for genome stabilization and tumor progression. This concept has not been tested in vivo, since appropriate mouse models were lacking. Here, we analyzed hepatocarcinogenesis in a mouse model of inducible telomere dysfunction on a telomerase-proficient background, in telomerase knockout mice with chronic telomere dysfunction (G3 mTerc–/–), and in WT mice with functional telomeres and telomerase. Transient or chronic telomere dysfunction enhanced the rates of chromosomal aberrations during hepatocarcinogenesis, but only telomerase-proficient mice exhibited significantly increased rates of macroscopic tumor formation in response to telomere dysfunction. In contrast, telomere dysfunction resulted in pronounced accumulation of DNA damage, cell-cycle arrest, and apoptosis in telomerase-deficient liver tumors. Together, these data provide in vivo evidence that transient telomere dysfunction during early or late stages of tumorigenesis promotes chromosomal instability and carcinogenesis in telomerase-proficient mice.
Individuals with type 2 diabetes are at increased risk of acquiring melioidosis, a disease caused by Burkholderia pseudomallei infection. Although up to half of melioidosis patients have underlying diabetes, the mechanisms involved in this increased susceptibility are unknown. We found that B. pseudomallei–infected PBMCs from diabetic patients were impaired in IL-12p70 production, which resulted in decreased IFN-γ induction and poor bacterial killing. The defect was specific to the IL-12–IFN-γ axis. Defective IL-12 production was also observed during Mycobacterium tuberculosis infection, in which diabetes is likewise known to be a strong risk factor. In contrast, IL-12 production in diabetic cells was not affected upon Salmonella enterica infection or in response to TLR2, -3, -4, and -5 ligands. Poor IL-12 production correlated with a deficiency in intracellular reduced glutathione (GSH) concentrations in diabetic patients. Addition of GSH or N-acetylcysteine to PBMCs selectively restored IL-12 and IFN-γ production and improved bacterial killing. Furthermore, the depletion of GSH in mice led to increased susceptibility to melioidosis, reduced production of IL-12p70, and poorer disease outcome. Our data thus establish a link between GSH deficiency in diabetes and increased susceptibility to melioidosis that may open up new therapeutic avenues to protect diabetic patients against some intracellular bacterial pathogens.
Effective control and eradication of malaria will require new tools to prevent transmission. Current antimalarial therapies targeting the asexual stage of Plasmodium do not prevent transmission of circulating gametocytes from infected humans to mosquitoes. Here, we describe a new class of transmission-blocking compounds, bumped kinase inhibitors (BKIs), which inhibit microgametocyte exflagellation. Oocyst formation and sporozoite production, necessary for transmission to mammals, were inhibited in mosquitoes fed on either BKI-1–treated human blood or mice treated with BKI-1. BKIs are hypothesized to act via inhibition of Plasmodium calcium-dependent protein kinase 4 and predicted to have little activity against mammalian kinases. Our data show that BKIs do not inhibit proliferation of mammalian cell lines and are well tolerated in mice. Used in combination with drugs active against asexual stages of Plasmodium, BKIs could prove an important tool for malaria control and eradication.
Glyoxalase 1 (Glo1) expression has previously been associated with anxiety in mice; however, its role in anxiety is controversial, and the underlying mechanism is unknown. Here, we demonstrate that GLO1 increases anxiety by reducing levels of methylglyoxal (MG), a GABAA receptor agonist. Mice overexpressing Glo1 on a Tg bacterial artificial chromosome displayed increased anxiety-like behavior and reduced brain MG concentrations. Treatment with low doses of MG reduced anxiety-like behavior, while higher doses caused locomotor depression, ataxia, and hypothermia, which are characteristic effects of GABAA receptor activation. Consistent with these data, we found that physiological concentrations of MG selectively activated GABAA receptors in primary neurons. These data indicate that GLO1 increases anxiety by reducing levels of MG, thereby decreasing GABAA receptor activation. More broadly, our findings potentially link metabolic state, neuronal inhibitory tone, and behavior. Finally, we demonstrated that pharmacological inhibition of GLO1 reduced anxiety, suggesting that GLO1 is a possible target for the treatment of anxiety disorders.
Nitric oxide (NO) plays an essential role in regulating hypertension and blood flow by inducing relaxation of vascular smooth muscle. Male mice deficient in a NO receptor component, the α1 subunit of soluble guanylate cyclase (sGCα1), are prone to hypertension in some, but not all, mouse strains, suggesting that additional genetic factors contribute to the onset of hypertension. Using linkage analyses, we discovered a quantitative trait locus (QTL) on chromosome 1 that was linked to mean arterial pressure (MAP) in the context of sGCα1 deficiency. This region is syntenic with previously identified blood pressure–related QTLs in the human and rat genome and contains the genes coding for renin. Hypertension was associated with increased activity of the renin-angiotensin-aldosterone system (RAAS). Further, we found that RAAS inhibition normalized MAP and improved endothelium-dependent vasorelaxation in sGCα1-deficient mice. These data identify the RAAS as a blood pressure–modifying mechanism in a setting of impaired NO/cGMP signaling.
Copyright © 2014 American Society for Clinical Investigation