In This Issue
Can I quote you on that?
Just as a simple phrase can become convoluted in the childhood game of Telephone, research findings can be distorted in the lay press. Journalists and scientists themselves must share the responsibilities of better explaining and interpreting science in an accessible and meaningful context for nonspecialist readers.
Response to Windahl et al.
The great stink of Paris and the nineteenth-century struggle against filth and germs
Science And Society
Drug discovery in jeopardy
Despite striking advances in the biomedical sciences, the flow of new drugs has slowed to a trickle, impairing therapeutic advances as well as the commercial success of drug companies. Reduced productivity in the drug industry is caused mainly by corporate policies that discourage innovation. This is compounded by various consequences of mega-mergers, the obsession for blockbuster drugs, the shift of control of research from scientists to marketers, the need for fast sales growth, and the discontinuation of development compounds for nontechnical reasons. Lessons from the past indicate that these problems can be overcome, and herein, new and improved directions for drug discovery are suggested.
Science In Medicine
Myasthenia gravis: past, present, and future
Myasthenia gravis (MG) is an autoimmune syndrome caused by the failure of neuromuscular transmission, which results from the binding of autoantibodies to proteins involved in signaling at the neuromuscular junction (NMJ). These proteins include the nicotinic AChR or, less frequently, a muscle-specific tyrosine kinase (MuSK) involved in AChR clustering. Much is known about the mechanisms that maintain self tolerance and modulate anti-AChR Ab synthesis, AChR clustering, and AChR function as well as those that cause neuromuscular transmission failure upon Ab binding. This insight has led to the development of improved diagnostic methods and to the design of specific immunosuppressive or immunomodulatory treatments.
Dysfunction of TGF-β signaling in Alzheimer’s disease
Accumulation of β-amyloid peptide (Aβ) in the brain is believed to trigger a complex and poorly understood pathologic reaction that results in the development of Alzheimer’s disease (AD). Despite intensive study, there is no consensus as to how Aβ accumulation causes neurodegeneration in AD. In this issue of the JCI, Tesseur et al. report that the expression of TGF-β type II receptor (TβRII) by neurons is reduced very early in the course of AD and that reduced TGF-β signaling increased Aβ deposition and neurodegeneration in a mouse model of AD (see the related article beginning on page 3060). Intriguingly, reduced TGF-β signaling in neuroblastoma cells resulted in neuritic dystrophy and increased levels of secreted Aβ. Collectively, these data suggest that dysfunction of the TGF-β/TβRII signaling axis in the AD brain may accelerate Aβ deposition and neurodegeneration.
Microglia: a cellular vehicle for CNS gene therapy
Metachromatic leukodystrophy (MLD) is a lysosomal storage disease caused by deficiency of the enzyme arylsulfatase A (ARSA). MLD is characterized by progressive demyelination and neurological deficits. Treatment of MLD is still a challenge due to the fact that the blood-brain barrier is a major obstacle for most therapeutic substances. In this issue of the JCI, Biffi et al. report that genetically modified hematopoietic precursor cells transduced to overexpress ARSA and transplanted into mice with a targeted disruption of the murine Arsa gene (Arsa–/– mice) migrated into the CNS and cross-corrected brain ARSA deficiency (see the related article beginning on page 3070). Microglia served as a cellular vehicle to effectively deliver the enzyme to other brain cells while hepatocytes overexpressing ARSA increased plasma ARSA levels but failed to deliver ARSA into the CNS.
Shaping the sperm head: an ER enzyme leaves its mark
Lipid storage diseases are debilitating inherited metabolic disorders that stem from the absence of specific lysosomal enzymes that degrade selected lipids. Most characteristically, these disorders affect the nervous and the reticulo-endothelial systems, with massive organomegaly resulting from the presence of engorged, lipid-laden macrophages. In this issue of the JCI, Yildiz et al. describe the role of the ER-resident enzyme β-glucosidase 2 (GBA2) in mice (see the related article beginning on page 2985). Surprisingly, GBA2 deficiency leaves bile acid and cholesterol metabolism intact, instead causing lipid accumulation in the ER of testicular Sertoli cells, round-headed sperm (globozoospermia), and impaired male fertility.
The paradoxical patent ductus arteriosus
The ductus arteriosus (DA) is a vessel whose patency is required for fetal survival but is incompatible with postnatal life. Because of developmental insufficiency, the DA in preterm infants often fails to close in a condition known as patent DA (PDA). Although COX inhibitors can be used to close the PDA by lowering circulating prostaglandin levels, their effectiveness is correlated with birth weight, and severely premature infants often require surgical repair. Paradoxically, targeted deletion of COX pathway components in mice results in PDA. In this issue of the JCI, Yokoyama et al. describe dual roles for prostaglandins in DA development and closure, offering new insights into the mechanism of negative effects of COX inhibitors that may influence the treatment of severely premature infants with PDA and lead to improvement of their outcomes (see the related article beginning on page 3026).
Role for IKK2 in muscle: waste not, want not
Activation of transcription factor NF-κB, the major regulator of the inflammatory response, depends on the inhibitor of NF-κB kinase (IKK) complex, which is composed of 2 catalytic subunits, IKK1 and IKK2 (also known as IKKα and IKKβ), and a regulatory subunit, IKKγ (also known as NEMO). In this issue of the JCI, Mourkioti et al. show that muscle-specific disruption in mice of the gene encoding IKK2 prevents NF-κB activation in response to denervation or toxin-induced injury (see the related article beginning on page 2945). Importantly, this genetic manipulation prevents muscle wasting, thereby providing strong evidence in support of a major pathogenic role for inflammation in a variety of muscular dystrophies characterized by progressive muscle fiber degeneration.
PLCγ2 regulates osteoclastogenesis via its interaction with ITAM proteins and GAB2
Dailing Mao, Holly Epple, Brian Uthgenannt, Deborah V. Novack, Roberta FaccioAbstract | Full text | PDF (Page 2869)
Excessive bone loss in arthritic diseases is mostly due to abnormal activation of the immune system leading to stimulation of osteoclasts. While phospholipase Cγ (PLCγ) isoforms are known modulators of T and B lymphocyte–mediated immune responses, we found that blockade of PLCγ enzymatic activity also blocks early osteoclast development and function. Importantly, targeted deletion of Plcg2 in mice led to an osteopetrotic phenotype. PLCγ2, independent of PLCγ1, was required for receptor activator of NF-κB ligand–induced (RANKL-induced) osteoclastogenesis by differentially regulating nuclear factor of activated T cells c1 (NFATc1), activator protein–1 (AP1), and NF-κB. Specifically, we show that NFATc1 upregulation is dependent on RANKL-mediated phosphorylation of PLCγ2 downstream of Dap12/Fc receptor γ (Dap12/FcRγ) receptors and is blocked by the PLCγ inhibitor U73122. In contrast, activation of JNK and NF-κB was not affected by U73122 or Dap12/FcRγ deletion. Interestingly, we found that in osteoclasts, PLCγ2 formed a complex with the regulatory adapter molecule GAB2, was required for GAB2 phosphorylation, and modulated GAB2 recruitment to RANK. Thus, PLCγ2 mediates RANKL-induced osteoclastogenesis and is a potential candidate for antiresorptive therapy.
Hyperactivation of p21ras and PI3K cooperate to alter murine and human neurofibromatosis type 1–haploinsufficient osteoclast functions
Feng-Chun Yang, Shi Chen, Alexander G. Robling, Xijie Yu, Todd D. Nebesio, Jincheng Yan, Trent Morgan, Xiaohong Li, Jin Yuan, Janet Hock, David A. Ingram, D. Wade ClappAbstract | Full text | PDF (Page 2880)
Individuals with neurofibromatosis type 1 (NF1) have a high incidence of osteoporosis and osteopenia. However, understanding of the cellular and molecular basis of these sequelae is incomplete. Osteoclasts are specialized myeloid cells that are the principal bone-resorbing cells of the skeleton. We found that Nf1+/– mice contain elevated numbers of multinucleated osteoclasts. Both osteoclasts and osteoclast progenitors from Nf1+/– mice were hyperresponsive to limiting concentrations of M-CSF and receptor activator of NF-κB ligand (RANKL) levels. M-CSF–stimulated p21ras-GTP and Akt phosphorylation was elevated in Nf1+/– osteoclasts associated with gains of function in survival, proliferation, migration, adhesion, and lytic activity. These gains of function are associated with more severe bone loss following ovariectomy as compared with that in syngeneic WT mice. Intercrossing Nf1+/– mice and mice deficient in class 1A PI3K (p85α) restored elevated PI3K activity and Nf1+/– osteoclast functions to WT levels. Furthermore, in vitro–differentiated osteoclasts from NF1 patients also displayed elevated Ras/PI3K activity and increased lytic activity analogous to those in murine Nf1+/– osteoclasts. Collectively, our results identify a what we believe to be a novel cellular and biochemical NF1-haploinsufficient phenotype in osteoclasts that has potential implications for the pathogenesis of NF1 bone disease.
Role of different pathways of the complement cascade in experimental bullous pemphigoid
Kelly C. Nelson, Minglang Zhao, Pamela R. Schroeder, Ning Li, Rick A. Wetsel, Luis A. Diaz, Zhi LiuAbstract | Full text | PDF (Page 2892)
Bullous pemphigoid (BP) is an autoimmune subepidermal blistering disease associated with autoantibodies directed against the hemidesmosomal proteins BP180 and BP230 and inflammation. Passive transfer of antibodies to the murine BP180 (mBP180) induces a skin disease that closely resembles human BP. In the present study, we defined the roles of the different complement activation pathways in this model system. Mice deficient in the alternative pathway component factor B (Fb) and injected with pathogenic anti-mBP180 IgG developed delayed and less intense subepidermal blisters. Mice deficient in the classical pathway component complement component 4 (C4) and WT mice pretreated with neutralizing antibody against the first component of the classical pathway, C1q, were resistant to experimental BP. These mice exhibited a significantly reduced level of mast cell degranulation and polymorphonuclear neutrophil (PMN) infiltration in the skin. Intradermal administration of compound 48/80, a mast cell degranulating agent, restored BP disease in C4–/– mice. Furthermore, C4–/– mice became susceptible to experimental BP after local injection of PMN chemoattractant IL-8 or local reconstitution with PMNs. These findings provide the first direct evidence to our knowledge that complement activation via the classical and alternative pathways is crucial in subepidermal blister formation in experimental BP.
Inhibition of TNF receptor 1 internalization by adenovirus 14.7K as a novel immune escape mechanism
Wulf Schneider-Brachert, Vladimir Tchikov, Oliver Merkel, Marten Jakob, Cora Hallas, Marie-Luise Kruse, Peter Groitl, Alexander Lehn, Eberhard Hildt, Janka Held-Feindt, Thomas Dobner, Dieter Kabelitz, Martin Krönke, Stefan SchützeAbstract | Full text | PDF | Supplemental material (Page 2901)
The adenoviral protein E3-14.7K (14.7K) is an inhibitor of TNF-induced apoptosis, but the molecular mechanism underlying this protective effect has not yet been explained exhaustively. TNF-mediated apoptosis is initiated by ligand-induced recruitment of TNF receptor–associated death domain (TRADD), Fas-associated death domain (FADD), and caspase-8 to the death domain of TNF receptor 1 (TNFR1), thereby establishing the death-inducing signaling complex (DISC). Here we report that adenovirus 14.7K protein inhibits ligand-induced TNFR1 internalization. Analysis of purified magnetically labeled TNFR1 complexes from murine and human cells stably transduced with 14.7K revealed that prevention of TNFR1 internalization resulted in inhibition of DISC formation. In contrast, 14.7K did not affect TNF-induced NF-κB activation via recruitment of receptor-interacting protein 1 (RIP-1) and TNF receptor–associated factor 2 (TRAF-2). Inhibition of endocytosis by 14.7K was effected by failure of coordinated temporal and spatial assembly of essential components of the endocytic machinery such as Rab5 and dynamin 2 at the site of the activated TNFR1. Furthermore, we found that the same TNF defense mechanisms were instrumental in protecting wild-type adenovirus–infected human cells expressing 14.7K. This study describes a new molecular mechanism implemented by a virus to escape immunosurveillance by selectively targeting TNFR1 endocytosis to prevent TNF-induced DISC formation.
Absence of bacterially induced RELMβ reduces injury in the dextran sodium sulfate model of colitis
Laila D. McVay, Sue A. Keilbaugh, Tracie M.H. Wong, Sonja Kierstein, Marcus E. Shin, Michael Lehrke, Martina I. Lefterova, D. Edward Shifflett, Sean L. Barnes, Fabio Cominelli, Steven M. Cohn, Gail Hecht, Mitchell A. Lazar, Angela Haczku, Gary D. WuAbstract | Full text | PDF (Page 2914)
Although inflammatory bowel disease (IBD) is the result of a dysregulated immune response to commensal gut bacteria in genetically predisposed individuals, the mechanism(s) by which bacteria lead to the development of IBD are unknown. Interestingly, deletion of intestinal goblet cells protects against intestinal injury, suggesting that this epithelial cell lineage may produce molecules that exacerbate IBD. We previously reported that resistin-like molecule β (RELMβ; also known as FIZZ2) is an intestinal goblet cell–specific protein that is induced upon bacterial colonization whereupon it is expressed in the ileum and colon, regions of the gut most often involved in IBD. Herein, we show that disruption of this gene reduces the severity of colitis in the dextran sodium sulfate (DSS) model of murine colonic injury. Although RELMβ does not alter colonic epithelial proliferation or barrier function, we show that recombinant protein activates macrophages to produce TNF-α both in vitro and in vivo. RELMβ expression is also strongly induced in the terminal ileum of the SAMP1/Fc model of IBD. These results suggest a model whereby the loss of epithelial barrier function by DSS results in the activation of the innate mucosal response by RELMβ located in the lumen, supporting the hypothesis that this protein is a link among goblet cells, commensal bacteria, and the pathogenesis of IBD.
Muscular atrophy of caveolin-3–deficient mice is rescued by myostatin inhibition
Yutaka Ohsawa, Hiroki Hagiwara, Masashi Nakatani, Akihiro Yasue, Keiji Moriyama, Tatsufumi Murakami, Kunihiro Tsuchida, Sumihare Noji, Yoshihide SunadaAbstract | Full text | PDF | Supplemental material (Page 2924)
Caveolin-3, the muscle-specific isoform of caveolins, plays important roles in signal transduction. Dominant-negative mutations of the caveolin-3 gene cause autosomal dominant limb-girdle muscular dystrophy 1C (LGMD1C) with loss of caveolin-3. However, identification of the precise molecular mechanism leading to muscular atrophy in caveolin-3–deficient muscle has remained elusive. Myostatin, a member of the muscle-specific TGF-β superfamily, negatively regulates skeletal muscle volume. Here we report that caveolin-3 inhibited myostatin signaling by suppressing activation of its type I receptor; this was followed by hypophosphorylation of an intracellular effector, Mad homolog 2 (Smad2), and decreased downstream transcriptional activity. Loss of caveolin-3 in P104L mutant caveolin-3 transgenic mice caused muscular atrophy with increase in phosphorylated Smad2 (p-Smad2) as well as p21 (also known as Cdkn1a), a myostatin target gene. Introduction of the myostatin prodomain, an inhibitor of myostatin, by genetic crossing or intraperitoneal administration of the soluble type II myostatin receptor, another inhibitor, ameliorated muscular atrophy of the mutant caveolin-3 transgenic mice with suppression of p-Smad2 and p21 levels. These findings suggest that caveolin-3 normally suppresses the myostatin-mediated signal, thereby preventing muscular atrophy, and that hyperactivation of myostatin signaling participates in the pathogenesis of muscular atrophy in a mouse model of LGMD1C. Myostatin inhibition may be a promising therapy for LGMD1C patients.
Local application of FTY720 to the lung abrogates experimental asthma by altering dendritic cell function
Marco Idzko, Hamida Hammad, Menno van Nimwegen, Mirjam Kool, Tobias Müller, Thomas Soullié, Monique A.M. Willart, Daniëlle Hijdra, Henk C. Hoogsteden, Bart N. LambrechtAbstract | Full text | PDF | Supplemental material (Page 2935)
Airway DCs play a crucial role in the pathogenesis of allergic asthma, and interfering with their function could constitute a novel form of therapy. The sphingosine 1–phosphate receptor agonist FTY720 is an oral immunosuppressant that retains lymphocytes in lymph nodes and spleen, thus preventing lymphocyte migration to inflammatory sites. The accompanying lymphopenia could be a serious side effect that would preclude the use of FTY720 as an antiasthmatic drug. Here we show in a murine asthma model that local application of FTY720 via inhalation prior to or during ongoing allergen challenge suppresses Th2-dependent eosinophilic airway inflammation and bronchial hyperresponsiveness without causing lymphopenia and T cell retention in the lymph nodes. Effectiveness of local treatment was achieved by inhibition of the migration of lung DCs to the mediastinal lymph nodes, which in turn inhibited the formation of allergen-specific Th2 cells in lymph nodes. Also, FTY720-treated DCs were intrinsically less potent in activating naive and effector Th2 cells due to a reduced capacity to form stable interactions with T cells and thus to form an immunological synapse. These data support the concept that targeting the function of airway DCs with locally acting drugs is a powerful new strategy in the treatment of asthma.
Targeted ablation of IKK2 improves skeletal muscle strength, maintains mass, and promotes regeneration
Foteini Mourkioti, Paschalis Kratsios, Tom Luedde, Yao-Hua Song, Patrick Delafontaine, Raffaella Adami, Valeria Parente, Roberto Bottinelli, Manolis Pasparakis, Nadia RosenthalAbstract | Full text | PDF | Supplemental material | Correction (Page 2945)
NF-κB is a major pleiotropic transcription factor modulating immune, inflammatory, cell survival, and proliferative responses, yet the relevance of NF-κB signaling in muscle physiology and disease is less well documented. Here we show that muscle-restricted NF-κB inhibition in mice, through targeted deletion of the activating kinase inhibitor of NF-κB kinase 2 (IKK2), shifted muscle fiber distribution and improved muscle force. In response to denervation, IKK2 depletion protected against atrophy, maintaining fiber type, size, and strength, increasing protein synthesis, and decreasing protein degradation. IKK2-depleted mice with a muscle-specific transgene expressing a local Igf-1 isoform (mIgf-1) showed enhanced protection against muscle atrophy. In response to muscle damage, IKK2 depletion facilitated skeletal muscle regeneration through enhanced satellite cell activation and reduced fibrosis. Our results establish IKK2/NF-κB signaling as an important modulator of muscle homeostasis and suggest a combined role for IKK inhibitors and growth factors in the therapy of muscle diseases.
NF-κB regulation of endothelial cell function during LPS-induced toxemia and cancer
Tatiana Kisseleva, Li Song, Marina Vorontchikhina, Nikki Feirt, Jan Kitajewski, Christian SchindlerAbstract | Full text | PDF | Supplemental material (Page 2955)
The transcription factor NF-κB is an important regulator of homeostatic growth and inflammation. Although gene-targeting studies have revealed important roles for NF-κB, they have been complicated by component redundancy and lethal phenotypes. To examine the role of NF-κB in endothelial tissues, Tie2 promoter/enhancer–IκBαS32A/S36A transgenic mice were generated. These mice grew normally but exhibited enhanced sensitivity to LPS-induced toxemia, notable for an increase in vascular permeability and apoptosis. Moreover, B16-BL6 tumors grew significantly more aggressively in transgenic mice, underscoring a new role for NF-κB in the homeostatic response to cancer. Tumor vasculature in transgenic mice was extensive and disorganized. This correlated with a marked loss in tight junction formation and suggests that NF-κB plays an important role in the maintenance of vascular integrity and response to stress.
NF-κB2 is required for the establishment of central tolerance through an Aire-dependent pathway
Mingzhao Zhu, Robert K. Chin, Peter A. Christiansen, James C. Lo, Xiaojuan Liu, Carl Ware, Ulrich Siebenlist, Yang-Xin FuAbstract | Full text | PDF | Supplemental material (Page 2964)
NF-κB2–deficient mice have impaired T and B cell responses. We found, however, that in these mice there was severe infiltration of lymphocytes into multiple organs and increased activity of autoantibodies to peripheral tissue antigens in a manner similar to that of autoimmune regulator–deficient (Aire-deficient) mice. We further demonstrated that NF-κB2 was required for thymic Aire gene transcriptional regulation. The Nfkb2–/– thymus had distinct cortical and medullar structures, but reduced Aire and target gene expression of peripheral tissue antigens. Engraftment of Nfkb2–/– thymic stroma to nude mice recapitulated the autoimmune phenotype of the native Nfkb2–/– mice, confirming a key defect in central tolerance. Lymphotoxin β receptor (LTβR) ligation–induced Aire gene expression was also largely abolished in the absence of NF-κB2. Thus NF-κB2 downstream of LTβR plays an important role in the regulation of central tolerance in an Aire-dependent manner.
Aberrant accumulation of PTTG1 induced by a mutated thyroid hormone β receptor inhibits mitotic progression
Hao Ying, Fumihiko Furuya, Li Zhao, Osamu Araki, Brian L. West, John A. Hanover, Mark C. Willingham, Sheue-yann ChengAbstract | Full text | PDF (Page 2972)
Overexpression of pituitary tumor–transforming 1 (PTTG1) is associated with thyroid cancer. We found elevated PTTG1 levels in the thyroid tumors of a mouse model of follicular thyroid carcinoma (TRβPV/PV mice). Here we examined the molecular mechanisms underlying elevated PTTG1 levels and the contribution of increased PTTG1 to thyroid carcinogenesis. We showed that PTTG1 was physically associated with thyroid hormone β receptor (TRβ) as well as its mutant, designated PV. Concomitant with thyroid hormone–induced (T3-induced) degradation of TRβ, PTTG1 proteins were degraded by the proteasomal machinery, but no such degradation occurred when PTTG1 was associated with PV. The degradation of PTTG1/TRβ was activated by the direct interaction of the liganded TRβ with steroid receptor coactivator 3 (SRC-3), which recruits proteasome activator PA28γ. PV, which does not bind T3, could not interact directly with SRC-3/PA28γ to activate proteasome degradation, resulting in elevated PTTG1 levels. The accumulated PTTG1 impeded mitotic progression in cells expressing PV. Our results unveil what we believe to be a novel mechanism by which PTTG1, an oncogene, is regulated by the liganded TRβ. The loss of this regulatory function in PV led to an aberrant accumulation of PTTG1 disrupting mitotic progression that could contribute to thyroid carcinogenesis.
Mutation of β-glucosidase 2 causes glycolipid storage disease and impaired male fertility
Yildiz Yildiz, Heidrun Matern, Bonne Thompson, Jeremy C. Allegood, Rebekkah L. Warren, Denise M.O. Ramirez, Robert E. Hammer, F. Kent Hamra, Siegfried Matern, David W. RussellAbstract | Full text | PDF (Page 2985)
β-Glucosidase 2 (GBA2) is a resident enzyme of the endoplasmic reticulum thought to play a role in the metabolism of bile acid–glucose conjugates. To gain insight into the biological function of this enzyme and its substrates, we generated mice deficient in GBA2 and found that these animals had normal bile acid metabolism. Knockout males exhibited impaired fertility. Microscopic examination of sperm revealed large round heads (globozoospermia), abnormal acrosomes, and defective mobility. Glycolipids, identified as glucosylceramides by mass spectrometry, accumulated in the testes, brains, and livers of the knockout mice but did not cause obvious neurological symptoms, organomegaly, or a reduction in lifespan. Recombinant GBA2 hydrolyzed glucosylceramide to glucose and ceramide; the same reaction catalyzed by the β-glucosidase acid 1 (GBA1) defective in subjects with the Gaucher’s form of lysosomal storage disease. We conclude that GBA2 is a glucosylceramidase whose loss causes accumulation of glycolipids and an endoplasmic reticulum storage disease.
Secreted PCSK9 decreases the number of LDL receptors in hepatocytes and inlivers of parabiotic mice
Thomas A. Lagace, David E. Curtis, Rita Garuti, Markey C. McNutt, Sahng Wook Park, Heidi B. Prather, Norma N. Anderson, Y.K. Ho, Robert E. Hammer, Jay D. HortonAbstract | Full text | PDF | Supplemental material (Page 2995)
Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a member of the proteinase K subfamily of subtilases that reduces the number of LDL receptors (LDLRs) in liver through an undefined posttranscriptional mechanism. We show that purified PCSK9 added to the medium of HepG2 cells reduces the number of cell-surface LDLRs in a dose- and time-dependent manner. This activity was approximately 10-fold greater for a gain-of-function mutant, PCSK9(D374Y), that causes hypercholesterolemia. Binding and uptake of PCSK9 were largely dependent on the presence of LDLRs. Coimmunoprecipitation and ligand blotting studies indicated that PCSK9 and LDLR directly associate; both proteins colocalized to late endocytic compartments. Purified PCSK9 had no effect on cell-surface LDLRs in hepatocytes lacking autosomal recessive hypercholesterolemia (ARH), an adaptor protein required for endocytosis of the receptor. Transgenic mice overexpressing human PCSK9 in liver secreted large amounts of the protein into plasma, which increased plasma LDL cholesterol concentrations to levels similar to those of LDLR-knockout mice. To determine whether PCSK9 was active in plasma, transgenic PCSK9 mice were parabiosed with wild-type littermates. After parabiosis, secreted PCSK9 was transferred to the circulation of wild-type mice and reduced the number of hepatic LDLRs to nearly undetectable levels. We conclude that secreted PCSK9 associates with the LDLR and reduces hepatic LDLR protein levels.
Virus-induced type I IFN stimulates generation of immunoproteasomes at the site of infection
Eui-Cheol Shin, Ulrike Seifert, Takanobu Kato, Charles M. Rice, Stephen M. Feinstone, Peter-M. Kloetzel, Barbara RehermannAbstract | Full text | PDF | Supplemental material (Page 3006)
IFN-γ is known as the initial and primary inducer of immunoproteasomes during viral infections. We now report that type I IFN induced the transcription and translation of immunoproteasome subunits, their incorporation into the proteasome complex, and the generation of an immunoproteasome-dependent CD8 T cell epitope in vitro and provide in vivo evidence that this mechanism occurs prior to IFN-γ responses at the site of viral infection. Type I IFN–mediated generation of immunoproteasomes was initiated by either poly(I:C) or HCV RNA in human hepatoma cells and was inhibited by neutralization of type I IFN. In serial liver biopsies of chimpanzees with acute HCV infection, increases in immunoproteasome subunit mRNA preceded intrahepatic IFN-γ responses by several weeks, instead coinciding with intrahepatic type I IFN responses. Thus, viral RNA–induced innate immune responses regulate the antigen-processing machinery, which occurs prior to the detection of IFN-γ at the site of infection. This mechanism may contribute to the high effectiveness (95%) of type I IFN–based therapies if administered early during HCV infection.
TLR4 links innate immunity and fatty acid–induced insulin resistance
Hang Shi, Maia V. Kokoeva, Karen Inouye, Iphigenia Tzameli, Huali Yin, Jeffrey S. FlierAbstract | Full text | PDF (Page 3015)
TLR4 is the receptor for LPS and plays a critical role in innate immunity. Stimulation of TLR4 activates proinflammatory pathways and induces cytokine expression in a variety of cell types. Inflammatory pathways are activated in tissues of obese animals and humans and play an important role in obesity-associated insulin resistance. Here we show that nutritional fatty acids, whose circulating levels are often increased in obesity, activate TLR4 signaling in adipocytes and macrophages and that the capacity of fatty acids to induce inflammatory signaling in adipose cells or tissue and macrophages is blunted in the absence of TLR4. Moreover, mice lacking TLR4 are substantially protected from the ability of systemic lipid infusion to (a) suppress insulin signaling in muscle and (b) reduce insulin-mediated changes in systemic glucose metabolism. Finally, female C57BL/6 mice lacking TLR4 have increased obesity but are partially protected against high fat diet–induced insulin resistance, possibly due to reduced inflammatory gene expression in liver and fat. Taken together, these data suggest that TLR4 is a molecular link among nutrition, lipids, and inflammation and that the innate immune system participates in the regulation of energy balance and insulin resistance in response to changes in the nutritional environment.
Chronic activation of the prostaglandin receptor EP4 promotes hyaluronan-mediated neointimal formation in the ductus arteriosus
Utako Yokoyama, Susumu Minamisawa, Hong Quan, Shibnath Ghatak, Toru Akaike, Eri Segi-Nishida, Shiho Iwasaki, Mari Iwamoto, Suniti Misra, Kouichi Tamura, Hideaki Hori, Shumpei Yokota, Bryan P. Toole, Yukihiko Sugimoto, Yoshihiro IshikawaAbstract | Full text | PDF | Supplemental material (Page 3026)
PGE, a potent vasodilator, plays a primary role in maintaining the patency of the ductus arteriosus (DA). Genetic disruption of the PGE-specific receptor EP4, however, paradoxically results in fatal patent DA (PDA) in mice. Here we demonstrate that EP4-mediated signals promote DA closure by hyaluronic acid–mediated (HA-mediated) intimal cushion formation (ICF). Chronic EP4 stimulation by ONO-AE1-329, a selective EP4 agonist, significantly enhanced migration and HA production in rat DA smooth muscle cells. When HA production was inhibited, EP4-mediated migration was negated. Activation of EP4, adenylyl cyclase, and PKA all increased HA production and the level of HA synthase 2 (HAS2) transcripts. In immature rat DA explants, ICF was promoted by EP4/PKA stimuli. Furthermore, adenovirus-mediated Has2 gene transfer was sufficient to induce ICF in EP4-disrupted DA explants in which the intimal cushion had not formed. Accordingly, signals through EP4 have 2 essential roles in DA development, namely, vascular dilation and ICF. The latter would lead to luminal narrowing, helping adhesive occlusion and permanent closure of the vascular lumen. Our results imply that HA induction serves as an alternative therapeutic strategy for the treatment of PDA to the current one, i.e., inhibition of PGE signaling by cyclooxygenase inhibitors, which might delay PGE-mediated ICF in immature infants.
Rai1 duplication causes physical and behavioral phenotypes in a mouse model of dup(17)(p11.2p11.2)
Katherina Walz, Richard Paylor, Jiong Yan, Weimin Bi, James R. LupskiAbstract | Full text | PDF | Supplemental material (Page 3035)
Genomic disorders are conditions that result from DNA rearrangements, such as deletions or duplications. The identification of the dosage-sensitive gene(s) within the rearranged genomic interval is important for the elucidation of genes responsible for complex neurobehavioral phenotypes. Smith-Magenis syndrome is associated with a 3.7-Mb deletion in 17p11.2, and its clinical presentation is caused by retinoic acid inducible 1 (RAI1) haploinsufficiency. The reciprocal microduplication syndrome, dup(17)(p11.2p11.2), manifests several neurobehavioral abnormalities, but the responsible dosage-sensitive gene(s) remain undefined. We previously generated a mouse model for dup(17)(p11.2p11.2), Dp(11)17/+, that recapitulated most of the phenotypes observed in human patients. We have now analyzed compound heterozygous mice carrying a duplication [Dp(11)17] in one chromosome 11 along with a null allele of Rai1 in the other chromosome 11 homologue [Dp(11)17/Rai1– mice] in order to study the relationship between Rai1 gene copy number and the Dp(11)17/+ phenotypes. Normal disomic Rai1 gene dosage was sufficient to rescue the complex physical and behavioral phenotypes observed in Dp(11)17/+ mice, despite altered trisomic copy number of the other 18 genes present in the rearranged genomic interval. These data provide a model for variation in copy number of single genes that could influence common traits such as obesity and behavior.
Impaired regulation of NF-κB and increased susceptibility to colitis-associated tumorigenesis in CYLD-deficient mice
Jun Zhang, Brigid Stirling, Stephane T. Temmerman, Chi A. Ma, Ivan J. Fuss, Jonathan M.J. Derry, Ashish JainAbstract | Full text | PDF | Supplemental material (Page 3042)
Cylindromatosis (CYLD) is a deubiquitinating enzyme that is altered in patients with familial cylindromatosis, a condition characterized by numerous benign adnexal tumors. However, the regulatory function of CYLD remains unsettled. Here we show that the development of B cells, T cells, and myeloid cells was unaffected in CYLD-deficient mice, but that the activation of these cells with mediators of innate and adaptive immunity resulted in enhanced NF-κB and JNK activity associated with increased TNF receptor–associated factor 2 (TRAF2) and NF-κB essential modulator (NEMO) ubiquitination. CYLD-deficient mice were more susceptible to induced colonic inflammation and showed a dramatic increase in the incidence of tumors compared with controls in a colitis-associated cancer model. These results suggest that CYLD limits inflammation and tumorigenesis by regulating ubiquitination in vivo.
Toll-like receptor 4 deficiency causes pulmonary emphysema
Xuchen Zhang, Peiying Shan, Ge Jiang, Lauren Cohn, Patty J. LeeAbstract | Full text | PDF | Supplemental material (Page 3050)
TLRs have been studied extensively in the context of pathogen challenges, yet their role in the unchallenged lung is unknown. Given their direct interface with the external environment, TLRs in the lungs are prime candidates to respond to air constituents, namely particulates and oxygen. The mechanism whereby the lung maintains structural integrity in the face of constant ambient exposures is essential to our understanding of lung disease. Emphysema is characterized by gradual loss of lung elasticity and irreversible airspace enlargement, usually in the later decades of life and after years of insult, most commonly cigarette smoke. Here we show Tlr4–/– mice exhibited emphysema as they aged. Adoptive transfer experiments revealed that TLR4 expression in lung structural cells was required for maintaining normal lung architecture. TLR4 deficiency led to the upregulation of what we believe to be a novel NADPH oxidase (Nox), Nox3, in lungs and endothelial cells, resulting in increased oxidant generation and elastolytic activity. Treatment of Tlr4–/– mice or endothelial cells with chemical NADPH inhibitors or Nox3 siRNA reversed the observed phenotype. Our data identify a role for TLR4 in maintaining constitutive lung integrity by modulating oxidant generation and provide insights into the development of emphysema.
Deficiency in neuronal TGF-β signaling promotes neurodegeneration and Alzheimer’s pathology
Ina Tesseur, Kun Zou, Luke Esposito, Frederique Bard, Elisabeth Berber, Judith Van Can, Amy H. Lin, Leslie Crews, Patrick Tremblay, Paul Mathews, Lennart Mucke, Eliezer Masliah, Tony Wyss-CorayAbstract | Full text | PDF (Page 3060)
Alzheimer’s disease (AD) is characterized by progressive neurodegeneration and cerebral accumulation of the β-amyloid peptide (Aβ), but it is unknown what makes neurons susceptible to degeneration. We report that the TGF-β type II receptor (TβRII) is mainly expressed by neurons, and that TβRII levels are reduced in human AD brain and correlate with pathological hallmarks of the disease. Reducing neuronal TGF-β signaling in mice resulted in age-dependent neurodegeneration and promoted Aβ accumulation and dendritic loss in a mouse model of AD. In cultured cells, reduced TGF-β signaling caused neuronal degeneration and resulted in increased levels of secreted Aβ and β-secretase–cleaved soluble amyloid precursor protein. These results show that reduced neuronal TGF-β signaling increases age-dependent neurodegeneration and AD-like disease in vivo. Increasing neuronal TGF-β signaling may thus reduce neurodegeneration and be beneficial in AD.
Gene therapy of metachromatic leukodystrophy reverses neurological damage and deficits in mice
Alessandra Biffi, Alessia Capotondo, Stefania Fasano, Ubaldo del Carro, Sergio Marchesini, Hisaya Azuma, Maria Chiara Malaguti, Stefano Amadio, Riccardo Brambilla, Markus Grompe, Claudio Bordignon, Angelo Quattrini, Luigi NaldiniAbstract | Full text | PDF (Page 3070)
Metachromatic leukodystrophy (MLD) is a demyelinating lysosomal storage disorder for which new treatments are urgently needed. We previously showed that transplantation of gene-corrected hematopoietic stem progenitor cells (HSPCs) in presymptomatic myeloablated MLD mice prevented disease manifestations. Here we show that HSC gene therapy can reverse neurological deficits and neuropathological damage in affected mice, thus correcting an overt neurological disease. The efficacy of gene therapy was dependent on and proportional to arylsulfatase A (ARSA) overexpression in the microglia progeny of transplanted HSPCs. We demonstrate a widespread enzyme distribution from these cells through the CNS and a robust cross-correction of neurons and glia in vivo. Conversely, a peripheral source of enzyme, established by transplanting ARSA-overexpressing hepatocytes from transgenic donors, failed to effectively deliver the enzyme to the CNS. These results indicate that the recruitment of gene-modified, enzyme-overexpressing microglia makes the enzyme bioavailable to the brain and makes therapeutic efficacy and disease correction attainable. Overall, our data provide a strong rationale for implementing HSPC gene therapy in MLD patients.