Volume 119, Issue 4, Pages 675-1052
45 total articles
Colored scanning EM of a glomerulus, the basic filtration unit of the kidney. Four
articles in this month’s issue focus on components of nephrology: Liu et al. focus on anti-glomerular
antibody–induced nephritis and lupus nephritis, while Crowley and colleagues study autoimmune glomerulonephritis. Uetani and colleagues detail the signaling that
regulates how the ureter and bladder connect, and finally, Glaudemans et al. describe how the Kv1.1 channel
in the kidney controls magnesium transport.
Image credit: Photo Researchers Inc.
One hundred years ago, in 1909, the American Society for Clinical Investigation (ASCI) held its first annual meeting. The founding members based this new society on a revolutionary approach to research that emphasized newer physiological methods. In 1924 the ASCI started a new journal, the Journal of Clinical Investigation. The ASCI has also held an annual meeting almost every year. The society has long debated who could be a member, with discussions about whether members must be physicians, what sorts of research they could do, and the role of women within the society. The ASCI has also grappled with what else the society should do, especially whether it ought to take a stand on policy issues. ASCI history has reflected changing social, political, and economic contexts, including several wars, concerns about the ethics of biomedical research, massive increases in federal research funding, and an increasingly large and specialized medical environment.
Mental disorders such as schizophrenia, bipolar illness, and depression have become the predominant chronic diseases of young people, accounting for approximately 40% of the medical burden for people aged 15–44 in the United States and Canada. Research is transforming our understanding of these disorders, as exemplified in the articles in this Review Series. Important, “disruptive” insights into pathophysiology are emerging from studies addressing these illnesses as brain disorders, developmental disorders, and complex genetic disorders — rather than only as psychological conflicts or chemical imbalances, as they were considered in the past. Current medications are not sufficient for most patients. A new and deep understanding of the pathophysiology of these disabling disorders is our best hope for a new generation of treatments that will help patients to recover.
Schizophrenia is a severe disorder that disrupts the function of multiple brain systems, resulting in impaired social and occupational functioning. The etiology and pathogenesis of schizophrenia appear to involve the interplay of a potentially large number of genetic liabilities and adverse environmental events that disrupt brain developmental pathways. In this Review, we discuss a strategy for determining how particular common and core clinical features of the illness are associated with pathophysiology in certain circuits of the cerebral cortex. The identification of molecular alterations in these circuits is providing critical insights for the rational development of new therapeutic interventions.
During the last 20 years of neuroscience research, we have witnessed a fundamental shift in the conceptualization of psychiatric disorders, with the dominant psychological and neurochemical theories of the past now complemented by a growing emphasis on developmental, genetic, molecular, and brain circuit models. Facilitating this evolving paradigm shift has been the growing contribution of functional neuroimaging, which provides a versatile platform to characterize brain circuit dysfunction underlying specific syndromes as well as changes associated with their successful treatment. Discussed here are converging imaging findings that established a rationale for testing a targeted neuromodulation strategy, deep brain stimulation, for treatment-resistant major depression.
Bipolar disorder (BPD) is a devastating illness that is characterized by recurrent episodes of mania and depression. In addition to these cyclic episodes, individuals with BPD exhibit changes in psychovegetative function, cognitive performance, and general health and well being. In this article we draw from neuroimaging findings in humans, postmortem data, and human genetic and pharmacological studies as well as data from animal models of behavior to discuss the neurobiology of BPD. We conclude with a synthesis of where the field stands and with suggestions and strategies for future areas of study to further increase our conceptual understanding of this complex illness.
Childhood-onset obsessive-compulsive disorder (OCD) affects 1%–2% of children and adolescents. It is characterized by recurrent obsessions and compulsions that create distress and interfere with daily life. The symptoms reported by children are similar to those seen among individuals who develop OCD in adulthood, and the two groups of patients are treated with similar symptom-relieving behavior therapies and medications. However, there are differences in sex ratios, patterns of comorbidity, and the results of neuroimaging studies that might be important. Here we review the diagnosis and treatment of childhood-onset OCD in light of pediatric and adult studies. We also discuss current knowledge of the pathophysiology of the disorder. Despite advances in this area, further research is needed to understand better the etiopathogenesis of the disorder and to develop new, more effective therapeutic options.
Autism spectrum disorder (ASD) is a common neurodevelopmental disorder with high heritability. Here, we discuss data supporting the view that there are at least two distinct genetic etiologies for ASD: rare, private (de novo) single gene mutations that may have a large effect in causing ASD; and inherited, common functional variants of a combination of genes, each having a small to moderate effect in increasing ASD risk. It also is possible that a combination of the two mechanisms may occur in some individuals with ASD. We further discuss evidence from individuals with a number of different neurodevelopmental syndromes, in which there is a high prevalence of ASD, that some private mutations and common variants converge on dysfunctional ERK and PI3K signaling, which negatively impacts neurodevelopmental events regulated by some receptor tyrosine kinases.
Gene therapy requires efficient gene delivery to cure or prevent disease by modifying the genome of somatic cells. However, gene vectors, which insert themselves into the host genome in order to achieve persistent protein expression, can trigger oncogenesis by upregulating cellular protooncogenes. This adverse event, known as insertional mutagenesis, has become a major hurdle in the field. Vectors developed on the basis of lentiviruses are considered to be less genotoxic than the hitherto used γ-retroviral vectors. For their report in this issue of the JCI, Montini et al. utilized a tumor-prone mouse model to identify the genetic determinants of insertional mutagenesis (see the related article beginning on page 964). They report that the lentiviral integration pattern and additional improvements in vector design reduce the genotoxic risk. These findings will inform future vector design with the goal of limiting genotoxicity for gene therapy or increasing genotoxicity for protooncogene discovery.
The Wnt pathway has been found to play a role in the development of many tissues and to spur growth and differentiation of adult osteoblasts, sparking interest in its potential clinical application for bone growth. However, when deregulated, this pathway can be oncogenic in some tissues. In this issue of the JCI, Kansara and colleagues reveal that Wnt inhibitory factor 1 is epigenetically silenced in human osteosarcomas and that its absence augments osteosarcoma formation in mice (see the related article beginning on page 837). These observations suggest the need for caution in stimulating the Wnt pathway for therapeutic bone growth.
COX-2 promotes colon cancer. While both nonselective NSAIDs and selective COX-2 inhibitors reduce disease burden, their adverse gastrointestinal and cardiovascular side effects limit their therapeutic use. In this issue of the JCI, Zhang et al. used gene silencing and a derivative of licorice root to show that inhibition of the enzyme 11β–hydroxysteroid dehydrogenase type II (11βHSD2) reduces tumor COX-2 activity, tumor growth, and metastasis by increasing the tonic glucocorticoid-mediated suppression of the COX-2 signaling pathway without the adverse effects associated with NSAIDs and selective COX-2 inhibitors (see the related article beginning on page 876). Their findings suggest that 11βHSD2 inhibition may be a potential therapeutic option in colon cancer, warranting further investigation.
Analysis of Mendelian Mg2+ wasting disorders helps us to unravel the mechanisms of Mg2+ homeostasis. In this issue of the JCI, Glaudemans and colleagues show that mutations in voltage-gated K+ channel subtype 1.1 (Kv1.1) cause autosomal dominant hypomagnesemia in humans (see the related article beginning on page 936). Interestingly, other mutations in the same protein cause the neurological disease episodic ataxia type 1. The authors show, using cells with heterologous expression of the wild-type and mutant channels, that the mutant channel is dysfunctional and speculate that Mg2+ wasting results from changes in apical membrane voltage along the nephron. Mechanisms by which the apical voltage is generated and how Kv1.1 fits within this context are discussed herein.
Tumor growth is accompanied by tissue hypoxia, but does this reduced oxygen availability promote further tumor expansion, resulting in a vicious cycle? In this issue of the JCI, Galluzzo et al. report that increasing oxygen tension in tumor cells by ectopically expressing the oxygen-binding hemoprotein myoglobin indeed affects tumorigenesis (see the related article beginning on page 865). Tumors derived from cells transfected with myoglobin grew more slowly, were less hypoxic, and were less metastatic. These results will spur further mechanistic inquiry into the role of hypoxia in tumor expansion.
The kidney kallikrein-kinin system plays important roles in inflammation, coagulation, angiogenesis, and regulation of vessel tone and permeability. In this issue of the JCI, Liu et al. provide data that suggest a protective role for kallikrein in animal models of anti–glomerular basement membrane (GBM) antibody–induced nephritis, an experimental model of Goodpasture disease (see the related article beginning on page 911). Furthermore, human systemic lupus erythematosus and lupus nephritis were shown to be associated with kallikrein 1 (KLK1) and the KLK3 promoter. The authors suggest that kallikrein genes are involved in the development of SLE and lupus nephritis and may exert a renoprotective role. It is possible, however, that the kallikrein-kinin system may play dual roles: protecting the kidney against ischemia and interstitial fibrosis while also mediating vasodilation, inflammation, and activation of the innate immune response.
Idiopathic pulmonary fibrosis (IPF) is characterized by distorted lung architecture and loss of respiratory function. Enhanced (myo)fibroblast activation, ECM deposition, and alveolar epithelial type II (ATII) cell dysfunction contribute to IPF pathogenesis. However, the molecular pathways linking ATII cell dysfunction with the development of fibrosis are poorly understood. Here, we demonstrate, in a mouse model of pulmonary fibrosis, increased proliferation and altered expression of components of the WNT/β-catenin signaling pathway in ATII cells. Further analysis revealed that expression of WNT1-inducible signaling protein–1 (WISP1), which is encoded by a WNT target gene, was increased in ATII cells in both a mouse model of pulmonary fibrosis and patients with IPF. Treatment of mouse primary ATII cells with recombinant WISP1 led to increased proliferation and epithelial-mesenchymal transition (EMT), while treatment of mouse and human lung fibroblasts with recombinant WISP1 enhanced deposition of ECM components. In the mouse model of pulmonary fibrosis, neutralizing mAbs specific for WISP1 reduced the expression of genes characteristic of fibrosis and reversed the expression of genes associated with EMT. More importantly, these changes in gene expression were associated with marked attenuation of lung fibrosis, including decreased collagen deposition and improved lung function and survival. Our study thus identifies WISP1 as a key regulator of ATII cell hyperplasia and plasticity as well as a potential therapeutic target for attenuation of pulmonary fibrosis.
Decay-accelerating factor (DAF, also known as CD55), a glycosylphosphatidylinositol-linked (GPI-linked) plasma membrane protein, protects autologous cells from complement-mediated damage by inhibiting complement component 3 (C3) activation. An important physical property of GPI-anchored complement regulatory proteins such as DAF is their ability to translate laterally in the plasma membrane. Here, we used single-particle tracking and tether-pulling experiments to measure DAF lateral diffusion, lateral confinement, and membrane skeletal associations in human erythrocyte membranes. In native membranes, most DAF molecules exhibited Brownian lateral diffusion. Fluid-phase complement activation caused deposition of C3b, one of the products of C3 cleavage, onto erythrocyte glycophorin A (GPA). We then determined that DAF, C3b, GPA, and band 3 molecules were laterally immobilized in the membranes of complement-treated cells, and GPA was physically associated with the membrane skeleton. Mass spectrometry analysis further showed that band 3, α-spectrin, β-spectrin, and ankyrin were present in a complex with C3b and GPA in complement-treated cells. C3b deposition was also associated with a substantial increase in erythrocyte membrane stiffness and/or viscosity. We therefore suggest that complement activation stimulates the formation of a membrane skeleton–linked DAF-C3b-GPA–band 3 complex on the erythrocyte surface. This complex may promote the removal of senescent erythrocytes from the circulation.
Protein interacting with C kinase 1 (PICK1) is a peripheral membrane protein involved in protein trafficking, a function that has been well characterized in neurons. Here, we report that male mice deficient in PICK1 are infertile and have a phenotype resembling the human disease globozoospermia. The primary defect in the testes of Pick1-knockout mice was fragmentation of acrosomes in the early stages of spermiogenesis. This fragmentation was followed by defects in nuclear elongation and mitochondrial sheath formation, leading to round-headed sperm, reduced sperm count, and severely impaired sperm motility. We found that PICK1 interacted with Golgi-associated PDZ- and coiled-coil motif–containing protein (GOPC) and the primary catalytic subunit of protein kinase 2 (CK2α′), proteins whose deficiencies lead to globozoospermia in mice. PICK1 was highly expressed in round spermatids and localized to Golgi-derived proacrosomal granules. GOPC colocalized with PICK1 in the Golgi region and facilitated formation of PICK1-positive clusters. Furthermore, there was an increase in apoptosis in the seminiferous tubules of Pick1–/– mice, a phenotype also seen in CK2α′-deficient mice. Our results suggest that PICK1 is involved in vesicle trafficking from the Golgi apparatus to the acrosome and cooperates with other proteins such as GOPC and CK2α′ in acrosome biogenesis.
Regulation of the formation and function of bone-resorbing osteoclasts (OCs) is a key to understanding the pathogenesis of skeletal disorders. Gene-targeting studies have shown that the RANK signaling pathway plays a critical role in OC differentiation and function. Although pharmaceutical blockade of RANK may be a viable strategy for preventing bone destruction, RANK is implicated in multiple biological processes. Recently, a cytoplasmic motif of RANK was identified that may be specifically involved in OC differentiation. Here, we developed a cell-permeable inhibitor termed the RANK receptor inhibitor (RRI), which targets this motif. The RRI peptide blocked RANKL-induced OC formation from murine bone marrow–derived macrophages. Furthermore, RRI inhibited the resorptive function of OCs and induced OC apoptosis. Treatment with the peptide impaired downstream signaling of RANK linked to Vav3, Rac1, and Cdc42 and resulted in disruptions of the actin cytoskeleton in differentiated OCs. In addition, RRI blocked inflammation-induced bone destruction and protected against ovariectomy-induced bone loss in mice. These data may be useful in the development of selective therapeutic agents for the treatment of osteoporosis and other bone diseases.
Chromosome translocation to generate the TEL-AML1 (also known as ETV6-RUNX1) chimeric fusion gene is a frequent and early or initiating event in childhood acute lymphoblastic leukemia (ALL). Our starting hypothesis was that the TEL-AML1 protein generates and maintains preleukemic clones and that conversion to overt disease requires secondary genetic changes, possibly in the context of abnormal immune responses. Here, we show that a murine B cell progenitor cell line expressing inducible TEL-AML1 proliferates at a slower rate than parent cells but is more resistant to further inhibition of proliferation by TGF-β. This facilitates the competitive expansion of TEL-AML1–expressing cells in the presence of TGF-β. Further analysis indicated that TEL-AML1 binds to a principal TGF-β signaling target, Smad3, and compromises its ability to activate target promoters. In mice expressing a TEL-AML1 transgene, early, pre-pro-B cells were increased in number and also showed reduced sensitivity to TGF-β–mediated inhibition of proliferation. Moreover, expression of TEL-AML1 in human cord blood progenitor cells led to the expansion of a candidate preleukemic stem cell population that had an early B lineage phenotype (CD34+CD38–CD19+) and a marked growth advantage in the presence of TGF-β. Collectively, these data suggest a plausible mechanism by which dysregulated immune responses to infection might promote the malignant evolution of TEL-AML1–expressing preleukemic clones.
Wnt signaling increases bone mass by stimulating osteoblast lineage commitment and expansion and forms the basis for novel anabolic therapeutic strategies being developed for osteoporosis. These strategies include derepression of Wnt signaling by targeting secreted Wnt pathway antagonists, such as sclerostin. However, such therapies are associated with safety concerns regarding an increased risk of osteosarcoma, the most common primary malignancy of bone. Here, we analyzed 5 human osteosarcoma cell lines in a high-throughput screen for epigenetically silenced tumor suppressor genes and identified Wnt inhibitory factor 1 (WIF1), which encodes an endogenous secreted Wnt pathway antagonist, as a candidate tumor suppressor gene. In vitro, WIF1 suppressed β-catenin levels in human osteosarcoma cell lines, induced differentiation of human and mouse primary osteoblasts, and suppressed the growth of mouse and human osteosarcoma cell lines. Wif1 was highly expressed in the developing and mature mouse skeleton, and, although it was dispensable for normal development, targeted deletion of mouse Wif1 accelerated development of radiation-induced osteosarcomas in vivo. In primary human osteosarcomas, silencing of WIF1 by promoter hypermethylation was associated with loss of differentiation, increased β-catenin levels, and increased proliferation. These data lead us to suggest that derepression of Wnt signaling by targeting secreted Wnt antagonists in osteoblasts may increase susceptibility to osteosarcoma.
Acute megakaryoblastic leukemia (AMKL) is a form of acute myeloid leukemia (AML) associated with a poor prognosis. The genetics and pathophysiology of AMKL are not well understood. We generated a knockin mouse model of the one twenty-two–megakaryocytic acute leukemia (OTT-MAL) fusion oncogene that results from the t(1;22)(p13;q13) translocation specifically associated with a subtype of pediatric AMKL. We report here that OTT-MAL expression deregulated transcriptional activity of the canonical Notch signaling pathway transcription factor recombination signal binding protein for immunoglobulin κ J region (RBPJ) and caused abnormal fetal megakaryopoiesis. Furthermore, cooperation between OTT-MAL and an activating mutation of the thrombopoietin receptor myeloproliferative leukemia virus oncogene (MPL) efficiently induced a short-latency AMKL that recapitulated all the features of human AMKL, including megakaryoblast hyperproliferation and maturation block, thrombocytopenia, organomegaly, and extensive fibrosis. Our results establish that concomitant activation of RBPJ (Notch signaling) and MPL (cytokine signaling) transforms cells of the megakaryocytic lineage and suggest that specific targeting of these pathways could be of therapeutic value for human AMKL.
As a tumor grows, it requires increased amounts of oxygen. However, the tumor blood vessels that form to meet this demand are functionally impaired, leading to regions of hypoxia within the tumor. Such hypoxia is one of the hallmarks of malignancy and is thought to promote a number of tumorigenic properties. Here, we sought to determine how tumors without hypoxia would progress by engineering A549 human lung carcinoma cells to ectopically express myoglobin (Mb), a multifunctional heme protein that specializes in oxygen transport, storage, and buffering. Mb expression prevented the hypoxic response in vitro and delayed tumor engraftment and reduced tumor growth following xenotransplantation into mice. Experimental tumors expressing Mb displayed reduced or no hypoxia, minimal HIF-1α levels, and a homogeneously low vessel density. Mb-mediated tumor oxygenation promoted differentiation of cancer cells and suppressed both local and distal metastatic spreading. These effects were primarily due to reduced tumor hypoxia, because they were not observed using point-mutated forms of myoglobin unable to bind oxygen and they were abrogated by expression of a constitutively active form of HIF-1α. Although limited to xenograft models, these data provide experimental proof of the concept that hypoxia is not just a side effect of deregulated growth but a key factor on which the tumor relies in order to promote its own expansion.
Colorectal cancer (CRC) is a leading cause of cancer death, yet primary prevention remains the best approach to reducing overall morbidity and mortality. Studies have shown that COX-2–derived PGE2 promotes CRC progression, and both nonselective COX inhibitors (NSAIDs) and selective COX-2 inhibitors (such as glucocorticoids) reduce the number and size of colonic adenomas. However, increased gastrointestinal side effects of NSAIDs and increased cardiovascular risks of selective COX-2 inhibitors limit their use in chemoprevention of CRC. We found that expression of 11β–hydroxysteroid dehydrogenase type II (11βHSD2), which converts active glucocorticoids to inactive keto-forms, increased in human colonic and Apc+/min mouse intestinal adenomas and correlated with increased COX-2 expression and activity. Furthermore, pharmacologic inhibition or gene silencing of 11βHSD2 inhibited COX-2–mediated PGE2 production in tumors and prevented adenoma formation, tumor growth, and metastasis in mice. Inhibition of 11βHSD2 did not reduce systemic prostacyclin production or accelerate atherosclerosis in mice, thereby avoiding the major cardiovascular side effects seen with systemic COX-2 inhibitors. Therefore, 11βHSD2 inhibition represents what we believe to be a novel approach for CRC chemoprevention and therapy by increasing tumor glucocorticoid activity, which in turn selectively blocks local COX-2 activity.
ER stress occurs in macrophage-rich areas of advanced atherosclerotic lesions and contributes to macrophage apoptosis and subsequent plaque necrosis. Therefore, signaling pathways that alter ER stress–induced apoptosis may affect advanced atherosclerosis. Here we placed Apoe–/– mice deficient in macrophage p38α MAPK on a Western diet and found that they had a marked increase in macrophage apoptosis and plaque necrosis. The macrophage p38α–deficient lesions also exhibited a significant reduction in collagen content and a marked thinning of the fibrous cap, which suggests that plaque progression was advanced in these mice. Consistent with our in vivo data, we found that ER stress–induced apoptosis in cultured primary mouse macrophages was markedly accelerated under conditions of p38 inhibition. Pharmacological inhibition or genetic ablation of p38 suppressed activation of Akt in cultured macrophages and in atherosclerotic lesions. In addition, inhibition of Akt enhanced ER stress–induced macrophage apoptosis, and expression of a constitutively active myristoylated Akt blocked the enhancement of ER stress–induced apoptosis that occurred with p38 inhibition in cultured cells. Our results demonstrate that p38α MAPK may play a critical role in suppressing ER stress–induced macrophage apoptosis in vitro and advanced lesional macrophage apoptosis in vivo.
The transcription factor serum response factor (SRF) plays a crucial role in the development of several organs. However, its role in the skin has not been explored. Here, we show that keratinocytes in normal human and mouse skin expressed high levels of SRF but that SRF expression was strongly downregulated in the hyperproliferative epidermis of wounded and psoriatic skin. Keratinocyte-specific deletion within the mouse SRF locus during embryonic development caused edema and skin blistering, and all animals died in utero. Postnatal loss of mouse SRF in keratinocytes resulted in the development of psoriasis-like skin lesions. These lesions were characterized by inflammation, hyperproliferation, and abnormal differentiation of keratinocytes as well as by disruption of the actin cytoskeleton. Ultrastructural analysis revealed markedly reduced cell-cell and cell-matrix contacts and loss of cell compaction in all epidermal layers. siRNA-mediated knockdown of SRF in primary human keratinocytes revealed that the cytoskeletal abnormalities and adhesion defects were a direct consequence of the loss of SRF. In contrast, the hyperproliferation observed in vivo was an indirect effect that was most likely a consequence of the inflammation. These results reveal that loss of SRF disrupts epidermal homeostasis and strongly suggest its involvement in the pathogenesis of hyperproliferative skin diseases, including psoriasis.
Immune-mediated nephritis contributes to disease in systemic lupus erythematosus, Goodpasture syndrome (caused by antibodies specific for glomerular basement membrane [anti-GBM antibodies]), and spontaneous lupus nephritis. Inbred mouse strains differ in susceptibility to anti-GBM antibody–induced and spontaneous lupus nephritis. This study sought to clarify the genetic and molecular factors that may be responsible for enhanced immune-mediated renal disease in these models. When the kidneys of 3 mouse strains sensitive to anti-GBM antibody–induced nephritis were compared with those of 2 control strains using microarray analysis, one-fifth of the underexpressed genes belonged to the kallikrein gene family, which encodes serine esterases. Mouse strains that upregulated renal and urinary kallikreins exhibited less evidence of disease. Antagonizing the kallikrein pathway augmented disease, while agonists dampened the severity of anti-GBM antibody–induced nephritis. In addition, nephritis-sensitive mouse strains had kallikrein haplotypes that were distinct from those of control strains, including several regulatory polymorphisms, some of which were associated with functional consequences. Indeed, increased susceptibility to anti-GBM antibody–induced nephritis and spontaneous lupus nephritis was achieved by breeding mice with a genetic interval harboring the kallikrein genes onto a disease-resistant background. Finally, both human SLE and spontaneous lupus nephritis were found to be associated with kallikrein genes, particularly KLK1 and the KLK3 promoter, when DNA SNPs from independent cohorts of SLE patients and controls were compared. Collectively, these studies suggest that kallikreins are protective disease-associated genes in anti-GBM antibody–induced nephritis and lupus.
Congenital anomalies affecting the ureter-bladder junction are frequent in newborns and are often associated with other developmental defects. However, the molecular and morphological processes underlying these malformations are still poorly defined. In this study, we identified the leukocyte antigen–related (LAR) family protein tyrosine phosphatase, receptor type, S and F (Ptprs and Ptprf [also known as Lar], respectively), as crucially important for distal ureter maturation and craniofacial morphogenesis in the mouse. Embryos lacking both Ptprs and Ptprf displayed severe urogenital malformations, characterized by hydroureter and ureterocele, and craniofacial defects such as cleft palate, micrognathia, and exencephaly. The detailed analysis of distal ureter maturation, the process by which the ureter is displaced toward its final position in the bladder wall, leads us to propose a revised model of ureter maturation in normal embryos. This process was deficient in embryos lacking Ptprs and Ptprf as a result of a marked reduction in intrinsic programmed cell death, thereby causing urogenital system malformations. In cell culture, Ptprs bound and negatively regulated the phosphorylation and signaling of the Ret receptor tyrosine kinase, whereas Ptprs-induced apoptosis was inhibited by Ret expression. Together, these results suggest that ureter positioning is controlled by the opposing actions of Ret and LAR family phosphatases regulating apoptosis-mediated tissue morphogenesis.
Primary hypomagnesemia is a heterogeneous group of disorders characterized by renal or intestinal magnesium (Mg2+) wasting, resulting in tetany, cardiac arrhythmias, and seizures. The kidney plays an essential role in maintaining blood Mg2+ levels, with a prominent function for the Mg2+-transporting channel transient receptor potential cation channel, subfamily M, member 6 (TRPM6) in the distal convoluted tubule (DCT). In the DCT, Mg2+ reabsorption is an active transport process primarily driven by the negative potential across the luminal membrane. Here, we studied a family with isolated autosomal dominant hypomagnesemia and used a positional cloning approach to identify an N255D mutation in KCNA1, a gene encoding the voltage-gated potassium (K+) channel Kv1.1. Kv1.1 was found to be expressed in the kidney, where it colocalized with TRPM6 along the luminal membrane of the DCT. Upon overexpression in a human kidney cell line, patch clamp analysis revealed that the KCNA1 N255D mutation resulted in a nonfunctional channel, with a dominant negative effect on wild-type Kv1.1 channel function. These data suggest that Kv1.1 is a renal K+ channel that establishes a favorable luminal membrane potential in DCT cells to control TRPM6-mediated Mg2+ reabsorption.
Studies in humans and animal models indicate a key contribution of angiotensin II to the pathogenesis of glomerular diseases. To examine the role of type 1 angiotensin (AT1) receptors in glomerular inflammation associated with autoimmune disease, we generated MRL-Faslpr/lpr (lpr) mice lacking the major murine type 1 angiotensin receptor (AT1A); lpr mice develop a generalized autoimmune disease with glomerulonephritis that resembles SLE. Surprisingly, AT1A deficiency was not protective against disease but instead substantially accelerated mortality, proteinuria, and kidney pathology. Increased disease severity was not a direct effect of immune cells, since transplantation of AT1A-deficient bone marrow did not affect survival. Moreover, autoimmune injury in extrarenal tissues, including skin, heart, and joints, was unaffected by AT1A deficiency. In murine systems, there is a second type 1 angiotensin receptor isoform, AT1B, and its expression is especially prominent in the renal glomerulus within podocytes. Further, expression of renin was enhanced in kidneys of AT1A-deficient lpr mice, and they showed evidence of exaggerated AT1B receptor activation, including substantially increased podocyte injury and expression of inflammatory mediators. Administration of losartan, which blocks all type 1 angiotensin receptors, reduced markers of kidney disease, including proteinuria, glomerular pathology, and cytokine mRNA expression. Since AT1A-deficient lpr mice had low blood pressure, these findings suggest that activation of type 1 angiotensin receptors in the glomerulus is sufficient to accelerate renal injury and inflammation in the absence of hypertension.
Treatments for primary and metastatic melanomas are rarely effective. Even therapeutics such as retinoic acid (RA) that are successfully used to treat several other forms of cancer are ineffective. Recent evidence indicates that the antiproliferative effects of RA are mediated by the transcription factor SOX9 in human cancer cell lines. As we have previously shown that SOX9 is expressed in normal melanocytes, here we investigated SOX9 expression and function in human melanomas. Although SOX9 was expressed in normal human skin, it was increasingly downregulated as melanocytes progressed to the premalignant and then the malignant and metastatic states. Overexpression of SOX9 in both human and mouse melanoma cell lines induced cell cycle arrest by increasing p21 transcription and restored sensitivity to RA by downregulating expression of PRAME, a melanoma antigen. Furthermore, SOX9 overexpression in melanoma cell lines inhibited tumorigenicity both in mice and in a human ex vivo model of melanoma. Treatment of melanoma cell lines with PGD2 increased SOX9 expression and restored sensitivity to RA. Thus, combined treatment with PGD2 and RA substantially decreased tumor growth in human ex vivo and mouse in vivo models of melanoma. The results of our experiments targeting SOX9 provide insight into the pathophysiology of melanoma. Further, the effects of SOX9 on melanoma cell proliferation and RA sensitivity suggest the encouraging possibility of a noncytotoxic approach to the treatment of melanoma.
γ-Retroviral vectors (γRVs), which are commonly used in gene therapy, can trigger oncogenesis by insertional mutagenesis. Here, we have dissected the contribution of vector design and viral integration site selection (ISS) to oncogenesis using an in vivo genotoxicity assay based on transplantation of vector-transduced tumor-prone mouse hematopoietic stem/progenitor cells. By swapping genetic elements between γRV and lentiviral vectors (LVs), we have demonstrated that transcriptionally active long terminal repeats (LTRs) are major determinants of genotoxicity even when reconstituted in LVs and that self-inactivating (SIN) LTRs enhance the safety of γRVs. By comparing the genotoxicity of vectors with matched active LTRs, we were able to determine that substantially greater LV integration loads are required to approach the same oncogenic risk as γRVs. This difference in facilitating oncogenesis is likely to be explained by the observed preferential targeting of cancer genes by γRVs. This integration-site bias was intrinsic to γRVs, as it was also observed for SIN γRVs that lacked genotoxicity in our model. Our findings strongly support the use of SIN viral vector platforms and show that ISS can substantially modulate genotoxicity.
How Ca2+-dependent signaling effectors are regulated in cardiomyocytes, given the extreme cytoplasmic Ca2+ concentration changes that underlie contraction, remains unknown. Cardiomyocyte plasma membrane Ca2+-ATPase (PMCA) extrudes Ca2+ but has little effect on excitation-contraction coupling, suggesting its potential role in controlling Ca2+-dependent signaling effectors such as calcineurin. We generated cardiac-specific inducible PMCA4b transgenic mice that displayed normal global Ca2+ transient and cellular contraction levels and reduced cardiac hypertrophy following transverse aortic constriction (TAC) or phenylephrine/Ang II infusion, but showed no reduction in exercise-induced hypertrophy. Transgenic mice were protected from decompensation and fibrosis following long-term TAC. The PMCA4b transgene reduced the hypertrophic augmentation associated with transient receptor potential canonical 3 channel overexpression, but not that associated with activated calcineurin. Furthermore, Pmca4 gene–targeted mice showed increased cardiac hypertrophy and heart failure events after TAC. Physical associations between PMCA4b and calcineurin were enhanced by TAC and by agonist stimulation of cultured neonatal cardiomyocytes. PMCA4b reduced calcineurin nuclear factor of activated T cell–luciferase activity after TAC and in cultured neonatal cardiomyocytes after agonist stimulation. PMCA4b overexpression inhibited cultured cardiomyocyte hypertrophy following agonist stimulation, but much less so in a Ca2+ pumping–deficient PMCA4b mutant. Thus, Pmca4b likely reduces the local Ca2+ signals involved in reactive cardiomyocyte hypertrophy via calcineurin regulation.
Myocardial Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibition improves cardiac function following myocardial infarction (MI), but the CaMKII-dependent pathways that participate in myocardial stress responses are incompletely understood. To address this issue, we sought to determine the transcriptional consequences of myocardial CaMKII inhibition after MI. We performed gene expression profiling in mouse hearts with cardiomyocyte-delimited transgenic expression of either a CaMKII inhibitory peptide (AC3-I) or a scrambled control peptide (AC3-C) following MI. Of the 8,600 mRNAs examined, 156 were substantially modulated by MI, and nearly half of these showed markedly altered responses to MI with CaMKII inhibition. CaMKII inhibition substantially reduced the MI-triggered upregulation of a constellation of proinflammatory genes. We studied 1 of these proinflammatory genes, complement factor B (Cfb), in detail, because complement proteins secreted by cells other than cardiomyocytes can induce sarcolemmal injury during MI. CFB protein expression in cardiomyocytes was triggered by CaMKII activation of the NF-κB pathway during both MI and exposure to bacterial endotoxin. CaMKII inhibition suppressed NF-κB activity in vitro and in vivo and reduced Cfb expression and sarcolemmal injury. The Cfb–/– mice were partially protected from the adverse consequences of MI. Our findings demonstrate what we believe is a novel target for CaMKII in myocardial injury and suggest that CaMKII is broadly important for the genetic effects of MI in cardiomyocytes.
HIV infection results in CD4+ T cell deficiency, but efficient combination antiretroviral therapy (c-ART) restores T cells and decreases morbidity and mortality. However, immune restoration by c-ART remains variable, and prolonged T cell deficiency remains in a substantial proportion of patients. In a prospective open-label phase I/IIa trial, we evaluated the safety and efficacy of administration of the T cell regulator IL-7. The trial included 13 c-ART–treated HIV-infected patients whose CD4+ cell counts were between 100 and 400 cells/μl and plasma HIV RNA levels were less than 50 copies/ml. Patients received a total of 8 subcutaneous injections of 2 different doses of recombinant human IL-7 (rhIL-7; 3 or 10 μg/kg) 3 times per week over a 16-day period. rhIL-7 was well tolerated and induced a sustained increase of naive and central memory CD4+ and CD8+ T cells. In the highest dose group, 4 patients experienced transient increases in viral replication. However, functional assays showed that the expanded T cells responded to HIV antigen by producing IFN-γ and/or IL-2. In conclusion, in lymphopenic HIV-infected patients, rhIL-7 therapy induced substantial functional and quantitative changes in T cells for 48 weeks. Therefore, patients may benefit from intermittent therapy with IL-7 in combination with c-ART.
The mechanisms of BM hematopoietic stem/progenitor cell (HSPC) adhesion, engraftment, and mobilization remain incompletely identified. Here, using WT and transgenic mice, we have shown that membrane-anchored plasminogen activator, urokinase receptor (MuPAR) marks a subset of HSPCs and promotes the preservation of the size of this pool of cells in the BM. Loss or inhibition of MuPAR increased HSPC proliferation and impaired their homing, engraftment, and adhesion to the BM microenvironment. During mobilization, MuPAR was inactivated by plasmin via proteolytic cleavage. Cell-autonomous loss of the gene encoding MuPAR also impaired long-term engraftment and multilineage repopulation in primary and secondary recipient mice. These findings identify MuPAR and plasmin as regulators of the proliferation, marrow pool size, homing, engraftment, and mobilization of HSPCs and possibly also of HSCs.
Chronic infections are associated with progressively declining T cell function. Infections with helminth parasites, such as Schistosoma mansoni, are often chronic and characterized by the development of strong Th2 responses that peak during the acute stage of infection and then decline despite ongoing infection; this minimizes Th2-dependent immunopathology during the chronic stage of infection. We sought to understand the basis for the decline in Th2 responses in chronic schistosomiasis. Using IL-4 reporter mice (mice that express EGFP as a reporter for Il4 gene expression) to identify Th2 cells, we found that Th2 cell numbers plateaued during acute infection and remained constant thereafter. However, the percentages of Th2 cells proliferating during late infection were strikingly lower than those during acute infection. Th2 cell hyporesponsiveness was evident within 10 d of initiation of the Th2 response and became progressively ingrained thereafter, in response to repeated Ag stimulation. Gene expression analyses implicated the E3-ubiquitin ligase gene related to anergy in lymphocytes (GRAIL) in the hyporesponsive state. Consistent with this, suppression of GRAIL expression using retrovirally delivered siRNA prevented the development of hyporesponsiveness induced by repeated Ag stimulation in vitro or in vivo. Together, these data indicate that the decline in Th2 cell responsiveness during chronic schistosomiasis is the net result of the upregulation of GRAIL expression in response to repeated Ag stimulation.
Type 2 diabetes is associated with accelerated atherogenesis, which may result from a combination of factors, including dyslipidemia characterized by increased VLDL secretion, and insulin resistance. To assess the hypothesis that both hepatic and peripheral insulin resistance contribute to atherogenesis, we crossed mice deficient for the LDL receptor (Ldlr–/– mice) with mice that express low levels of IR in the liver and lack IR in peripheral tissues (the L1B6 mouse strain). Unexpectedly, compared with Ldlr–/– controls, L1B6Ldlr–/– mice fed a Western diet showed reduced VLDL and LDL levels, reduced atherosclerosis, decreased hepatic AKT signaling, decreased expression of genes associated with lipogenesis, and diminished VLDL apoB and lipid secretion. Adenovirus-mediated hepatic expression of either constitutively active AKT or dominant negative glycogen synthase kinase (GSK) markedly increased VLDL and LDL levels such that they were similar in both Ldlr–/– and L1B6Ldlr–/– mice. Knocking down expression of hepatic IR by adenovirus-mediated shRNA decreased VLDL triglyceride and apoB secretion in Ldlr–/– mice. Furthermore, knocking down hepatic IR expression in either WT or ob/ob mice reduced VLDL secretion but also resulted in decreased hepatic Ldlr protein. These findings suggest a dual action of hepatic IR on lipoprotein levels, in which the ability to increase VLDL apoB and lipid secretion via AKT/GSK is offset by upregulation of Ldlr.
Elevated plasma concentrations of HDL cholesterol (HDL-C) are associated with protection from atherosclerotic cardiovascular disease. Animal models indicate that decreased expression of endothelial lipase (LIPG) is inversely associated with HDL-C levels, and genome-wide association studies have identified LIPG variants as being associated with HDL-C levels in humans. We hypothesized that loss-of-function mutations in LIPG may result in elevated HDL-C and therefore performed deep resequencing of LIPG exons in cases with elevated HDL-C levels and controls with decreased HDL-C levels. We identified a significant excess of nonsynonymous LIPG variants unique to cases with elevated HDL-C. In vitro lipase activity assays demonstrated that these variants significantly decreased endothelial lipase activity. In addition, a meta-analysis across 5 cohorts demonstrated that the low-frequency Asn396Ser variant is significantly associated with increased HDL-C, while the common Thr111Ile variant is not. Functional analysis confirmed that the Asn396Ser variant has significantly decreased lipase activity both in vitro and in vivo, while the Thr111Ile variant has normal lipase activity. Our results establish that loss-of-function mutations in LIPG lead to increased HDL-C levels and support the idea that inhibition of endothelial lipase may be an effective mechanism to raise HDL-C.
Copyright © 2014 American Society for Clinical Investigation