Issue published March 1, 2006

E strogen receptors, PPARs, and liver X receptors are members of the nuclear receptor superfamily of ligand-dependent transcription factors that regulate diverse aspects of development and homeostasis. Recent studies of the biologic roles of these receptors and their mechanisms of action have significantly advanced our understanding of transcriptional programs that control lipid and carbohydrate metabolism, immunity and inflammation, and wound repair. These findings provide insights into the therapeutic actions of existing drugs that target nuclear receptors and raise new possibilities for development of safer, more effective drugs for the prevention and treatment of metabolic and cardiovascular diseases. In this introduction to this Review series, underlying mechanisms that enable nuclear receptors to positively and negatively regulate gene expression are presented as background to the focused reviews on estrogen receptors, PPARs, liver X receptors, and the PPARγ coactivator-1 (PGC-1) family of coactivators.

E strogens influence many physiological processes in mammals, including but not limited to reproduction, cardiovascular health, bone integrity, cognition, and behavior. Given this widespread role for estrogen in human physiology, it is not surprising that estrogen is also implicated in the development or progression of numerous diseases, which include but are not limited to various types of cancer (breast, ovarian, colorectal, prostate, endometrial), osteoporosis, neurodegenerative diseases, cardiovascular disease, insulin resistance, lupus erythematosus, endometriosis, and obesity. In many of these diseases, estrogen mediates its effects through the estrogen receptor (ER), which serves as the basis for many therapeutic interventions. This Review will describe diseases in which estrogen, through the ER, plays a role in the development or severity of disease.

P PARα is a nuclear receptor that regulates liver and skeletal muscle lipid metabolism as well as glucose homeostasis. Acting as a molecular sensor of endogenous fatty acids (FAs) and their derivatives, this ligand-activated transcription factor regulates the expression of genes encoding enzymes and transport proteins controlling lipid homeostasis, thereby stimulating FA oxidation and improving lipoprotein metabolism. PPARα also exerts pleiotropic antiinflammatory and antiproliferative effects and prevents the proatherogenic effects of cholesterol accumulation in macrophages by stimulating cholesterol efflux. Cellular and animal models of PPARα help explain the clinical actions of fibrates, synthetic PPARα agonists used to treat dyslipidemia and reduce cardiovascular disease and its complications in patients with the metabolic syndrome. Although these preclinical studies cannot predict all of the effects of PPARα in humans, recent findings have revealed potential adverse effects of PPARα action, underlining the need for further study. This Review will focus on the mechanisms of action of PPARα in metabolic diseases and their associated vascular pathologies.

T he nuclear receptor family of PPARs was named for the ability of the original member to induce hepatic peroxisome proliferation in mice in response to xenobiotic stimuli. However, studies on the action and structure of the 3 human PPAR isotypes (PPARα, PPARδ, and PPARγ) suggest that these moieties are intimately involved in nutrient sensing and the regulation of carbohydrate and lipid metabolism. PPARα and PPARδ appear primarily to stimulate oxidative lipid metabolism, while PPARγ is principally involved in the cellular assimilation of lipids via anabolic pathways. Our understanding of the functions of PPARγ in humans has been increased by the clinical use of potent agonists and by the discovery of both rare and severely deleterious dominant-negative mutations leading to a stereotyped syndrome of partial lipodystrophy and severe insulin resistance, as well as more common sequence variants with a much smaller impact on receptor function. These may nevertheless have much greater significance for the public health burden of metabolic disease. This Review will focus on the role of PPARγ in human physiology, with specific reference to clinical pharmacological studies, and analysis of PPARG gene variants in the abnormal lipid and carbohydrate metabolism of the metabolic syndrome.

O besity is a growing threat to global health by virtue of its association with insulin resistance, glucose intolerance, hypertension, and dyslipidemia, collectively known as the metabolic syndrome or syndrome X. The nuclear receptors PPARα and PPARγ are therapeutic targets for hypertriglyceridemia and insulin resistance, respectively, and drugs that modulate these receptors are currently in clinical use. More recent work on the less-described PPAR isotype PPARδ has uncovered a dual benefit for both hypertriglyceridemia and insulin resistance, highlighting the broad potential of PPARδ in the treatment of metabolic disease. PPARδ enhances fatty acid catabolism and energy uncoupling in adipose tissue and muscle, and it suppresses macrophage-derived inflammation. Its combined activities in these and other tissues make it a multifaceted therapeutic target for the metabolic syndrome with the potential to control weight gain, enhance physical endurance, improve insulin sensitivity, and ameliorate atherosclerosis.

T issue damage resulting from chemical, mechanical, and biological injury, or from interrupted blood flow and reperfusion, is often life threatening. The subsequent tissue response involves an intricate series of events including inflammation, oxidative stress, immune cell recruitment, and cell survival, proliferation, migration, and differentiation. In addition, fibrotic repair characterized by myofibroblast transdifferentiation and the deposition of ECM proteins is activated. Failure to initiate, maintain, or stop this repair program has dramatic consequences, such as cell death and associated tissue necrosis or carcinogenesis. In this sense, inflammation and oxidative stress, which are beneficial defense processes, can become harmful if they do not resolve in time. This repair program is largely based on rapid and specific changes in gene expression controlled by transcription factors that sense injury. PPARs are such factors and are activated by lipid mediators produced after wounding. Here we highlight advances in our understanding of PPAR action during tissue repair and discuss the potential for these nuclear receptors as therapeutic targets for tissue injury.

T he liver X receptors (LXRs) are nuclear receptors that play central roles in the transcriptional control of lipid metabolism. LXRs function as nuclear cholesterol sensors that are activated in response to elevated intracellular cholesterol levels in multiple cell types. Once activated, LXRs induce the expression of an array of genes involved in cholesterol absorption, efflux, transport, and excretion. In addition to their function in lipid metabolism, LXRs have also been found to modulate immune and inflammatory responses in macrophages. Synthetic LXR agonists promote cholesterol efflux and inhibit inflammation in vivo and inhibit the development of atherosclerosis in animal models. The ability of LXRs to integrate metabolic and inflammatory signaling makes them particularly attractive targets for intervention in human metabolic disease.

M embers of the PPARγ coactivator-1 (PGC-1) family of transcriptional coactivators serve as inducible coregulators of nuclear receptors in the control of cellular energy metabolic pathways. This Review focuses on the biologic and physiologic functions of the PGC-1 coactivators, with particular emphasis on striated muscle, liver, and other organ systems relevant to common diseases such as diabetes and heart failure.

C a²⁺ plays a pivotal role in both excitation-contraction coupling (ECC) and activation of Ca²⁺-dependent signaling pathways. One of the remaining questions in cardiac biology is how Ca²⁺-dependent signaling pathways are regulated under conditions of continual Ca²⁺ transients that mediate cardiac contraction during each heartbeat. Ca²⁺-calmodulin–dependent protein kinase II (CaMKII) activation and its ability to regulate histone deacetylase 5 (HDAC5) nuclear shuttling represent a critical Ca²⁺-dependent signaling circuit for controlling cardiac hypertrophy and heart failure, yet the mechanism of activation by Ca²⁺ is not known. In this issue of the JCI, Wu et al. convincingly demonstrate that the inositol 1,4,5-trisphosphate receptor (InsP₃R) is involved in local control of Ca²⁺ for activating CaMKII in the nuclear envelope of adult ventricular cardiac myocytes (see the related article beginning on page 675). The overall paradigm that is demonstrated is the best example of a molecular mechanism whereby signaling is directly regulated by a local Ca²⁺ pool that is disparate or geometrically insensitive to cytosolic Ca²⁺ underlying each contractile cycle.

T he precise role of erythropoietin receptor–activated (EpoR-activated) Stat5 in the regulation of erythropoiesis remains unclear. In this issue of the JCI, Menon and colleagues present new experimental data that indicate a distinct role for Stat5 in the regulation of stress-induced erythropoiesis, such as during acute anemic states (see the related article beginning on page 683). A critical function for Stat5 is to promote cell survival, possibly through transcriptional induction of the antiapoptotic protein Bcl-x. In the present experimental system, erythropoietin-Stat5 signals did not induce Bcl-x expression but did induce oncostatin-M. Moreover, oncostatin-M was found to enhance survival of erythroid progenitors. This work differentiates between steady-state (or homeostatic) erythropoiesis and stress-induced erythropoiesis at the level of EpoR signaling.

T he anaphylatoxins complement component 3a and 5a (C3a and C5a, respectively) are classically seen as proinflammatory mediators of allergic asthma that recruit inflammatory cells, induce edema, and cause bronchoconstriction. A few years ago, controversy arose when it was shown that C5-deficient mice were more susceptible to experimental asthma compared with C5-sufficient mice. In a study by Köhl et al. in this issue of the JCI, it is shown in a series of truly “complementary” experiments that C5a receptor (C5aR) blockade promotes Th2 sensitization upon first exposure to inhaled allergen, whereas C5aR blockade during established inflammation suppresses the cardinal features of asthma (see the related article beginning on page 783). Blockade of C5aR alters the function of airway DCs, crucial for inducing and maintaining Th2 responses in the lung. Targeting C5aR as a treatment for established asthma could be beneficial, but might be accompanied by sensitization to novel antigens.

G enetic diseases often reveal the physiological roles of the affected proteins. The identification of mutations in the nuclear envelope proteins lamin A and lamin C as the cause of a diverse group of human diseases has expanded our understanding of the lamin proteins from being merely structural elements of the cell nucleus and has implicated them in novel cellular functions including signal transduction and gene expression. However, it now appears that the physiological relevance of one of the lamin proteins in organismal function has been overestimated. In this issue of the JCI, Fong et al. demonstrate that lamin A–deficient mice are phenotypically normal (see the related article beginning on page 743). The good news is these findings open the door to a new strategy for the therapeutic treatment of diseases caused by mutations in lamin A, such as muscular dystrophies and some types of premature aging syndromes.

R adial patterning in the urinary tract and gut depends on reciprocal signaling between epithelial cells, which form mucosa, and mesenchyme, which forms smooth muscle and connective tissue. These interactions depend on sonic hedgehog (Shh), which is secreted by epithelial cells and induces expression of bone morphogenetic protein 4 (Bmp4), a signaling molecule required for differentiation of smooth muscle progenitors. Patterning of the specialized mucosa lining the anterior-posterior (A-P) axis may be controlled independently by regionally expressed mesenchymal transcription factors. A study by Airik et al. in this issue of the JCI reveals that T-box 18 (Tbx18), a transcription factor selectively expressed in ureteral mesenchyme, regulates smooth muscle differentiation by maintaining Shh1 responsiveness in mesenchymal progenitors (see the related article beginning on page 663). Deletion of Tbx18 resulted in defective urothelial differentiation at the level of the ureter, suggesting that Tbx18 acts via mesenchyme as an important regulator of A-P patterning in the urinary tract.

R adial patterning in the urinary tract and gut depends on reciprocal signaling between epithelial cells, which form mucosa, and mesenchyme, which forms smooth muscle and connective tissue. These interactions depend on sonic hedgehog (Shh), which is secreted by epithelial cells and induces expression of bone morphogenetic protein 4 (Bmp4), a signaling molecule required for differentiation of smooth muscle progenitors. Patterning of the specialized mucosa lining the anterior-posterior (A-P) axis may be controlled independently by regionally expressed mesenchymal transcription factors. A study by Airik et al. in this issue of the JCI reveals that T-box 18 (Tbx18), a transcription factor selectively expressed in ureteral mesenchyme, regulates smooth muscle differentiation by maintaining Shh1 responsiveness in mesenchymal progenitors. Deletion of Tbx18 resulted in defective urothelial differentiation at the level of the ureter, suggesting that Tbx18 acts via mesenchyme as an important regulator of A-P patterning in the urinary tract.

T he ghrelin receptor is known from in vitro studies to signal in the absence of the hormone ghrelin at almost 50% of its maximal capacity. But, as for many other 7-transmembrane receptors, the in vivo importance of this ligand-independent signaling has remained unclear. In this issue of the JCI, Pantel et al. find that a natural mutation in the ghrelin receptor, Ala204Glu, which is associated with a selective loss of constitutive activity without affecting ghrelin affinity, potency, or efficacy, segregates in 2 families with the development of short stature (see the related article beginning on page 760). By combination of the observations from this study with those related to the phenotype of subjects carrying another natural ghrelin receptor mutation, Phe279Leu, having identical molecular-pharmacological properties, it is proposed that selective lack of ghrelin receptor constitutive signaling leads to a syndrome characterized not only by short stature, but also by obesity that apparently develops during puberty.

P reviously we observed that neural cell adhesion molecule (NCAM) deficiency in β tumor cells facilitates metastasis into distant organs and local lymph nodes. Here, we show that NCAM-deficient β cell tumors grew leaky blood vessels with perturbed pericyte-endothelial cell-cell interactions and deficient perivascular deposition of ECM components. Conversely, tumor cell expression of NCAM in a fibrosarcoma model (T241) improved pericyte recruitment and increased perivascular deposition of ECM molecules. Together, these findings suggest that NCAM may limit tumor cell metastasis by stabilizing the microvessel wall. To directly address whether pericyte dysfunction increases the metastatic potential of solid tumors, we studied β cell tumorigenesis in primary pericyte-deficient Pdgfb^ret/ret mice. This resulted in β tumor cell metastases in distant organs and local lymph nodes, demonstrating a role for pericytes in limiting tumor cell metastasis. These data support a new model for how tumor cells trigger metastasis by perturbing pericyte-endothelial cell-cell interactions.

C D34⁺ bone marrow–derived progenitor cells contribute to tissue repair by differentiating into endothelial cells, vascular smooth muscle cells, hematopoietic cells, and possibly other cell types. However, the mechanisms by which circulating progenitor cells home to remodeling tissues remain unclear. Here we show that integrin α₄β₁ (VLA-4) promotes the homing of circulating progenitor cells to the α₄β₁ ligands VCAM and cellular fibronectin, which are expressed on actively remodeling neovasculature. Progenitor cells, which express integrin α₄β₁, homed to sites of active tumor neovascularization but not to normal nonimmune tissues. Antagonists of integrin α₄β₁, but not other integrins, blocked the adhesion of these cells to endothelia in vitro and in vivo as well as their homing to neovasculature and outgrowth into differentiated cell types. These studies describe an adhesion event that facilitates the homing of progenitor cells to the neovasculature.

C ongenital malformations of the urinary tract are a major cause of renal failure in children and young adults. They are often caused by physical obstruction or by functional impairment of the peristaltic machinery of the ureter. The underlying molecular and cellular defects are, however, poorly understood. Here we present the phenotypic characterization of a new mouse model for congenital ureter malformation that revealed the molecular pathway important for the formation of the functional mesenchymal coating of the ureter. The gene encoding the T-box transcription factor Tbx18 was expressed in undifferentiated mesenchymal cells surrounding the distal ureter stalk. In Tbx18^–/– mice, prospective ureteral mesenchymal cells largely dislocalized to the surface of the kidneys. The remaining ureteral mesenchymal cells showed reduced proliferation and failed to differentiate into smooth muscles, but instead became fibrous and ligamentous tissue. Absence of ureteral smooth muscles resulted in a short hydroureter and hydronephrosis at birth. Our analysis also showed that the ureteral mesenchyme derives from a distinct cell population that is separated early in kidney development from that of other mesenchymal cells of the renal system.

P revious work showed that calmodulin (CaM) and Ca²⁺-CaM–dependent protein kinase II (CaMKII) are somehow involved in cardiac hypertrophic signaling, that inositol 1,4,5-trisphosphate receptors (InsP₃Rs) in ventricular myocytes are mainly in the nuclear envelope, where they associate with CaMKII, and that class II histone deacetylases (e.g., HDAC5) suppress hypertrophic gene transcription. Furthermore, HDAC phosphorylation in response to neurohumoral stimuli that induce hypertrophy, such as endothelin-1 (ET-1), activates HDAC nuclear export, thereby regulating cardiac myocyte transcription. Here we demonstrate a detailed mechanistic convergence of these 3 issues in adult ventricular myocytes. We show that ET-1, which activates plasmalemmal G protein–coupled receptors and InsP₃ production, elicits local nuclear envelope Ca²⁺ release via InsP₃R. This local Ca²⁺ release activates nuclear CaMKII, which triggers HDAC5 phosphorylation and nuclear export (derepressing transcription). Remarkably, this Ca²⁺-dependent pathway cannot be activated by the global Ca²⁺ transients that cause contraction at each heartbeat. This novel local Ca²⁺ signaling in excitation-transcription coupling is analogous to but separate (and insulated) from that involved in excitation-contraction coupling. Thus, myocytes can distinguish simultaneous local and global Ca²⁺ signals involved in contractile activation from those targeting gene expression.

A nemia due to chronic disease or chemotherapy often is ameliorated by erythropoietin (Epo). Present studies reveal that, unlike steady-state erythropoiesis, erythropoiesis during anemia depends sharply on an Epo receptor–phosphotyrosine-343–Stat5 signaling axis. In mice expressing a phosphotyrosine-null (PY-null) Epo receptor allele (EpoR-HM), severe and persistent anemia was induced by hemolysis or 5-fluorouracil. In short-term transplantation experiments, donor EpoR-HM bone marrow cells also failed to efficiently repopulate the erythroid compartment. In each context, stress erythropoiesis was rescued to WT levels upon the selective restoration of an EpoR PY343 Stat5-binding site (EpoR-H allele). As studied using a unique primary culture system, EpoR-HM erythroblasts exhibited marked stage-specific losses in Epo-dependent growth and survival. EpoR-H PY343 signals restored efficient erythroblast expansion, and the selective Epo induction of the Stat5 target genes proviral integration site-1 (Pim-1) and oncostatin-M. Bcl2-like 1 (Bcl-x), in contrast, was not significantly induced via WT-EpoR, EpoR-HM, or EpoR-H alleles. In Kit⁺CD71⁺ erythroblasts, EpoR-PY343 signals furthermore enhanced SCF growth effects, and SCF modulation of Pim-1 kinase and oncostatin-M expression. In maturing Kit^–CD71⁺ erythroblasts, oncostatin-M exerted antiapoptotic effects that likewise depended on EpoR PY343–mediated events. Stress erythropoiesis, therefore, requires stage-specific EpoR-PY343-Stat5 signals, some of which selectively bolster SCF and oncostatin-M action.

I n models of acute lung injury, CXC chemokine receptor 2 (CXCR2) mediates migration of polymorphonuclear leukocytes (PMNs) into the lung. Since CXCR2 ligands, including CXCL1 and CXCL2/3, are chemotactic for PMNs, CXCR2 is thought to recruit PMNs by inducing chemotactic migration. In a model of PMN recruitment to the lung, aerosolized bacterial LPS inhalation induced PMN recruitment to the lung in wild-type mice, but not in littermate CXCR2^–/– mice. Surprisingly, lethally irradiated wild-type mice reconstituted with CXCR2^–/– BM still showed about 50% PMN recruitment into bronchoalveolar lavage fluid and into lung interstitium, but CXCR2^–/– mice reconstituted with CXCR2^–/– BM showed no PMN recruitment. Conversely, CXCR2^–/– mice reconstituted with wild-type BM showed a surprisingly large defect in PMN recruitment, inconsistent with a role of CXCR2 on PMNs alone. Cell culture, immunohistochemistry, flow cytometry, and real-time RT-PCR were used to show expression of CXCR2 on pulmonary endothelial and bronchial epithelial cells. The LPS-induced increase in lung microvascular permeability as measured by Evans blue extravasation required CXCR2 on nonhematopoietic cells. Our data revealed what we believe to be a previously unrecognized role of endothelial and epithelial CXCR2 in LPS-induced PMN recruitment and lung injury.

I FN regulatory factor 4–binding (IRF-4–binding) protein (IBP) is a novel type of activator of Rho GTPases that is recruited to the immunological synapse upon TCR stimulation. Here we demonstrate that loss of IBP leads to the spontaneous development of a systemic autoimmune disorder characterized by the accumulation of effector/memory T cells and IgG⁺ B cells, profound hypergammaglobulinemia, and autoantibody production. Similar to human SLE, this syndrome primarily affects females. T cells from IBP-deficient mice are resistant to death in vitro as well as in vivo and exhibit selective defects in effector function. In the absence of IBP, T cells respond suboptimally to TCR engagement, as demonstrated by diminished ERK1/2 activation, decreased c-Fos induction, impaired immunological synapse formation, and defective actin polymerization. Transduction of IBP-deficient T cells with a WT IBP protein, but not with an IBP mutant lacking the Dbl-like domain required for Rho GTPase activation, rescues the cytoskeletal defects exhibited by these cells. Collectively, these findings indicate that IBP, a novel regulator of Rho GTPases, is required for optimal T cell effector function, lymphocyte homeostasis, and the prevention of systemic autoimmunity.

A ntagonists to α4 integrin show promise for several autoimmune and inflammatory diseases but may exhibit mechanism-based toxicities. We tested the capacity of blockade of α4 integrin signaling to perturb functions involved in inflammation, while limiting potential adverse effects. We generated and characterized mice bearing a Y991A mutation in α4 integrin [α4(Y991A) mice], which blocks paxillin binding and inhibits α4 integrin signals that support leukocyte migration. In contrast to the embryonic-lethal phenotype of α4 integrin–null mice, mice bearing the α4(Y991A) mutation were viable and fertile; however, they exhibited defective recruitment of mononuclear leukocytes into thioglycollate-induced peritonitis. α4 Integrins are essential for definitive hematopoiesis; however, the α4(Y991A) mice had intact lymphohematopoiesis and, with the exception of reduced Peyer’s patches, normal architecture and cellularity of secondary lymphoid tissues. We conclude that interference with α4 integrin signaling can selectively impair mononuclear leukocyte recruitment to sites of inflammation while sparing vital functions of α4 integrins in development and hematopoiesis.

B cells have multiple roles in immune activation and inflammation separate from their capacity to produce antibodies. B cell depletion is currently under intense investigation as a therapeutic strategy for autoimmune diseases. The TNF family members B cell–activating factor of the TNF family (BAFF) and its homolog A proliferation-inducing ligand (APRIL) are B cell survival and differentiation factors and are therefore rational therapeutic targets. We compared the effects of BAFF receptor–Ig, which blocks only BAFF, with those of transmembrane activator and calcium modulator ligand interactor–Ig, which blocks both BAFF and APRIL, in a murine SLE model. Both reagents prolonged the life of NZB/W F1 mice when given either before or after disease onset. Many immunologic effects of the 2 reagents were similar, including B cell and B cell subset depletion and prevention of the progressive T cell activation and dendritic cell accumulation that occurs with age in NZB/W mice without substantial effects on the emergence of the IgG anti–double-stranded DNA response. Furthermore, both reagents inhibited the T cell–independent marginal zone B cell response to particulate antigen delivered i.v., but not the B1 B cell response to the same antigen delivered i.p. In contrast, blockade of both BAFF and APRIL, but not blockade of BAFF alone, reduced the serum levels of IgM antibodies, decreased the frequency of plasma cells in the spleen, and inhibited the IgM response to a T cell–dependent antigen. The differences between selective and nonselective BAFF blockade are relevant to the choice of a BAFF blocking agent for the treatment of autoimmune and malignant diseases.

K aposi sarcoma–associated herpesvirus (KSHV) is a human lymphotropic herpesvirus. It is implicated in B cell neoplasias such as primary effusion lymphoma and multicentric Castleman disease in AIDS patients. The KSHV latency-associated nuclear antigen (LANA) is consistently expressed in all KSHV-associated tumor cells and was shown to bind the tumor suppressor proteins p53 and pRb. To test LANA’s contribution to lymphomagenesis in vivo we generated transgenic mice expressing LANA under the control of its own promoter, which is B cell specific. All of the transgenic mice developed splenic follicular hyperplasia due to an expansion of IgM⁺IgD⁺ B cells and showed increased germinal center formation. We also observed lymphomas, implying that LANA can activate B cells and provide the first step toward lymphomagenesis.

L amin A and lamin C, both products of Lmna, are key components of the nuclear lamina. In the mouse, a deficiency in both lamin A and lamin C leads to slow growth, muscle weakness, and death by 6 weeks of age. Fibroblasts deficient in lamins A and C contain misshapen and structurally weakened nuclei, and emerin is mislocalized away from the nuclear envelope. The physiologic rationale for the existence of the 2 different Lmna products lamin A and lamin C is unclear, although several reports have suggested that lamin A may have particularly important functions, for example in the targeting of emerin and lamin C to the nuclear envelope. Here we report the development of lamin C–only mice (Lmna^+/+), which produce lamin C but no lamin A or prelamin A (the precursor to lamin A). Lmna^+/+ mice were entirely healthy, and Lmna^+/+ cells displayed normal emerin targeting and exhibited only very minimal alterations in nuclear shape and nuclear deformability. Thus, at least in the mouse, prelamin A and lamin A appear to be dispensable. Nevertheless, an accumulation of farnesyl–prelamin A (as occurs with a deficiency in the prelamin A processing enzyme Zmpste24) caused dramatically misshapen nuclei and progeria-like disease phenotypes. The apparent dispensability of prelamin A suggested that lamin A–related progeroid syndromes might be treated with impunity by reducing prelamin A synthesis. Remarkably, the presence of a single Lmna^LCO allele eliminated the nuclear shape abnormalities and progeria-like disease phenotypes in Zmpste24^–/– mice. Moreover, treating Zmpste24^–/– cells with a prelamin A–specific antisense oligonucleotide reduced prelamin A levels and significantly reduced the frequency of misshapen nuclei. These studies suggest a new therapeutic strategy for treating progeria and other lamin A diseases.

M ice lacking macrophage elastase (matrix metalloproteinase-12, or MMP-12) were previously shown to be protected from the development of cigarette smoke–induced emphysema and from the accumulation of lung macrophages normally induced by chronic exposure to cigarette smoke. To determine the basis for macrophage accumulation in experimental emphysema, we now show that bronchoalveolar lavage fluid from WT smoke-exposed animals contained chemotactic activity for monocytes in vitro that was absent in lavage fluid from macrophage elastase–deficient mice. Fractionation of the bronchoalveolar lavage fluid demonstrated the presence of elastin fragments only in the fractions containing chemotactic activity. An mAb against elastin fragments eliminated both the in vitro chemotactic activity and cigarette smoke–induced monocyte recruitment to the lung in vivo. Porcine pancreatic elastase was used to recruit monocytes to the lung and to generate emphysema. Elastin fragment antagonism in this model abrogated both macrophage accumulation and airspace enlargement.

T he growth hormone (GH) secretagogue receptor (GHSR) was cloned as the target of a family of synthetic molecules endowed with GH release properties. As shown recently through in vitro means, this receptor displays a constitutive activity whose clinical relevance is unknown. Although pharmacological studies have demonstrated that its endogenous ligand — ghrelin — stimulates, through the GHSR, GH secretion and appetite, the physiological importance of the GHSR-dependent pathways remains an open question that gives rise to much controversy. We report the identification of a GHSR missense mutation that segregates with short stature within 2 unrelated families. This mutation, which results in decreased cell-surface expression of the receptor, selectively impairs the constitutive activity of the GHSR, while preserving its ability to respond to ghrelin. This first description, to our knowledge, of a functionally significant GHSR mutation, which unveils the critical importance of the GHSR-associated constitutive activity, discloses an unusual pathogenic mechanism of growth failure in humans.

C D154 is a cell surface molecule expressed on activated T cells that binds to CD40, an activating molecule on APCs. Its blockade has been shown to prevent allograft rejection, presumably by interrupting interactions between T cells and APCs. It is known that activated human platelets express and shed CD154 and can induce APC activation and other immune processes in vitro. Here we show that platelet-derived CD154 is sufficient to initiate cardiac allograft rejection independent of any cellular source of this molecule. CD154-KO mice reject cardiac allografts after receiving CD154-expressing human platelets or recombinant CD154 (rCD154) trimers. Treatment with the human CD154-specific mAb 5c8 specifically prevents this induced rejection. Soluble trimers, but not platelets, induce rejection when infused temporally remote from the surgical procedure, suggesting that surgically induced platelet activation is required for CD154 release. Allograft rejection can thus be instigated by activated platelets through CD154. These data implicate platelets as a proximal component of acquired alloimmunity, providing insight into the mechanisms of allograft rejection and the physiological response to trauma in general.

D iabetes is associated with defective β cell function and altered β cell mass. The mechanisms regulating β cell mass and its adaptation to insulin resistance are unknown. It is unclear whether compensatory β cell hyperplasia is achieved via proliferation of existing β cells or neogenesis from progenitor cells embedded in duct epithelia. We have used transgenic mice expressing a mutant form of the forkhead-O1 transcription factor (FoxO1) in both pancreatic ductal and endocrine β cells to assess the contribution of these 2 compartments to islet expansion. We show that the mutant FoxO1 transgene prevents β cell replication in 2 models of β cell hyperplasia, 1 due to peripheral insulin resistance (Insulin receptor transgenic knockouts) and 1 due to ectopic local expression of IGF2 (Elastase-IGF2 transgenics), without affecting insulin secretion. In contrast, we failed to detect a specific effect of the FoxO1 transgene on the number of periductal β cells. We propose that β cell compensation to insulin resistance is a proliferative response of existing β cells to growth factor signaling and requires FoxO1 nuclear exclusion.

C omplement component 5 (C5) has been described as either promoting or protecting against airway hyperresponsiveness (AHR) in experimental allergic asthma, suggesting pleomorphic effects of C5. Here we report that local pharmacological targeting of the C5a receptor (C5aR) prior to initial allergen sensitization in murine models of inhalation tolerance or allergic asthma resulted in either induction or marked enhancement of Th2-polarized immune responses, airway inflammation, and AHR. Importantly, C5aR-deficient mice exhibited a similar, increased allergic phenotype. Pulmonary allergen exposure in C5aR-targeted mice resulted in increased sensitization and accumulation of CD4⁺CD69⁺ T cells associated with a marked increase in pulmonary myeloid, but not plasmacytoid, DC numbers. Pulmonary DCs from C5aR-targeted mice produced large amounts of CC chemokine ligand 17 (CCL17) and CCL22 ex vivo, suggesting a negative impact of C5aR signaling on pulmonary homing of Th2 cells. In contrast, C5aR targeting in sensitized mice led to suppressed airway inflammation and AHR but was still associated with enhanced production of Th2 effector cytokines. These data suggest a dual role for C5a in allergic asthma, i.e., protection from the development of maladaptive type 2 immune responses during allergen sensitization at the DC/T cell interface but enhancement of airway inflammation and AHR in an established inflammatory environment.

C omplement component 5 (C5) has been described as either promoting or protecting against airway hyperresponsiveness (AHR) in experimental allergic asthma, suggesting pleomorphic effects of C5. Here we report that local pharmacological targeting of the C5a receptor (C5aR) prior to initial allergen sensitization in murine models of inhalation tolerance or allergic asthma resulted in either induction or marked enhancement of Th2-polarized immune responses, airway inflammation, and AHR. Importantly, C5aR-deficient mice exhibited a similar, increased allergic phenotype. Pulmonary allergen exposure in C5aR-targeted mice resulted in increased sensitization and accumulation of CD4⁺CD69⁺ T cells associated with a marked increase in pulmonary myeloid, but not plasmacytoid, DC numbers. Pulmonary DCs from C5aR-targeted mice produced large amounts of CC chemokine ligand 17 (CCL17) and CCL22 ex vivo, suggesting a negative impact of C5aR signaling on pulmonary homing of Th2 cells. In contrast, C5aR targeting in sensitized mice led to suppressed airway inflammation and AHR but was still associated with enhanced production of Th2 effector cytokines. These data suggest a dual role for C5a in allergic asthma, i.e., protection from the development of maladaptive type 2 immune responses during allergen sensitization at the DC/T cell interface but enhancement of airway inflammation and AHR in an established inflammatory environment.

T he cystic fibrosis transmembrane conductance regulator (CFTR) Cl^– channel plays vital roles in fluid transport in many epithelia. While CFTR is expressed along the entire nephron, its function in renal tubule epithelial cells remains unclear, as no specific renal phenotype has been identified in cystic fibrosis. CFTR has been proposed as a regulator of the 30 pS, ATP-sensitive renal K channel (Kir1.1, also known as renal outer medullar K [ROMK]) that is critical for K secretion by cells of the thick ascending limb (TAL) and distal nephron segments responsive to aldosterone. We report here that both ATP and glibenclamide sensitivities of the 30 pS K channel in TAL cells were absent in mice lacking CFTR and in mice homozygous for the ΔF508 mutation. Curcumin treatment in ΔF508-CFTR mice partially reversed the defect in ATP sensitivity. We demonstrate that the effect of CFTR on ATP sensitivity was abrogated by increasing PKA activity. We propose that CFTR regulates the renal K secretory channel by providing a PKA-regulated functional switch that determines the distribution of open and ATP-inhibited K channels in apical membranes. We discuss the potential physiological role of this functional switch in renal K handling during water diuresis and the relevance to renal K homeostasis in cystic fibrosis.

T ransgenic sickle mice expressing β^S hemoglobin have activated vascular endothelium that exhibits enhanced expression of NF-κB and adhesion molecules that promote vascular stasis in sickle, but not in normal, mice in response to hypoxia/reoxygenation. Sickle mice hemolyze rbcs in vivo as demonstrated by increased reticulocyte counts, plasma hemoglobin and bilirubin, and reduced plasma haptoglobin. The heme content is elevated in sickle organs, which promotes vascular inflammation and heme oxygenase-1 expression. Treatment of sickle mice with hemin further increases heme oxygenase-1 expression and inhibits hypoxia/reoxygenation–induced stasis, leukocyte-endothelium interactions, and NF-κB, VCAM-1, and ICAM-1 expression. Heme oxygenase inhibition by tin protoporphyrin exacerbates stasis in sickle mice. Furthermore, treatment of sickle mice with the heme oxygenase enzymatic product carbon monoxide or biliverdin inhibits stasis and NF-κB, VCAM-1, and ICAM-1 expression. Local administration of heme oxygenase-1 adenovirus to subcutaneous skin increases heme oxygenase-1 and inhibits hypoxia/reoxygenation–induced stasis in the skin of sickle mice. Heme oxygenase-1 plays a vital role in the inhibition of vaso-occlusion in transgenic sickle mice.

H epatic steatosis is a core feature of the metabolic syndrome and type 2 diabetes and leads to hepatic insulin resistance. Malonyl-CoA, generated by acetyl-CoA carboxylases 1 and 2 (Acc1 and Acc2), is a key regulator of both mitochondrial fatty acid oxidation and fat synthesis. We used a diet-induced rat model of nonalcoholic fatty liver disease (NAFLD) and hepatic insulin resistance to explore the impact of suppressing Acc1, Acc2, or both Acc1 and Acc2 on hepatic lipid levels and insulin sensitivity. While suppression of Acc1 or Acc2 expression with antisense oligonucleotides (ASOs) increased fat oxidation in rat hepatocytes, suppression of both enzymes with a single ASO was significantly more effective in promoting fat oxidation. Suppression of Acc1 also inhibited lipogenesis whereas Acc2 reduction had no effect on lipogenesis. In rats with NAFLD, suppression of both enzymes with a single ASO was required to significantly reduce hepatic malonyl-CoA levels in vivo, lower hepatic lipids (long-chain acyl-CoAs, diacylglycerol, and triglycerides), and improve hepatic insulin sensitivity. Plasma ketones were significantly elevated compared with controls in the fed state but not in the fasting state, indicating that lowering Acc1 and -2 expression increases hepatic fat oxidation specifically in the fed state. These studies suggest that pharmacological inhibition of Acc1 and -2 may be a novel approach in the treatment of NAFLD and hepatic insulin resistance.

D isruption of cholinergic neurotransmission contributes to the memory impairment that characterizes Alzheimer disease (AD). Since the amyloid cascade hypothesis of AD pathogenesis postulates that amyloid β (Aβ) peptide accumulation in critical brain regions also contributes to memory impairment, we assessed cholinergic function in transgenic mice where the human Aβ peptide is overexpressed. We first measured hippocampal acetylcholine (ACh) release in young, freely moving PDAPP mice, a well-characterized transgenic mouse model of AD, and found marked Aβ-dependent alterations in both basal and evoked ACh release compared with WT controls. We also found that Aβ could directly interact with the high-affinity choline transporter which may impair steady-state and on-demand ACh release. Treatment of PDAPP mice with the anti-Aβ antibody m266 rapidly and completely restored hippocampal ACh release and high-affinity choline uptake while greatly reducing impaired habituation learning that is characteristic of these mice. Thus, soluble “cholinotoxic” species of the Aβ peptide can directly impair cholinergic neurotransmission in PDAPP mice leading to memory impairment in the absence of overt neurodegeneration. Treatment with certain anti-Aβ antibodies may therefore rapidly reverse this cholinergic dysfunction and relieve memory deficits associated with early AD.

A lthough it has long been hypothesized that allergen immunotherapy inhibits allergy, in part, by inducing production of IgG Abs that intercept allergens before they can cross-link mast cell FcεRI-associated IgE, this blocking Ab hypothesis has never been tested in vivo. In addition, evidence that IgG-allergen interactions can induce anaphylaxis by activating macrophages through FcγRIII suggested that IgG Ab might not be able to inhibit IgE-mediated anaphylaxis without inducing anaphylaxis through this alternative pathway. We have studied active and passive immunization models in mice to approach these issues and to determine whether any inhibition of anaphylaxis observed was a direct effect of allergen neutralization by IgG Ab or an indirect effect of cross-linking of FcεRI to the inhibitory IgG receptor FcγRIIb. We demonstrate that IgG Ab produced during the course of an immune response or administered passively can completely suppress IgE-mediated anaphylaxis; that these IgG blocking Abs inhibit IgE-mediated anaphylaxis without inducing FcγRIII-mediated anaphylaxis only when IgG Ab concentration is high and challenge allergen dose is low; that allergen epitope density correlates inversely with the allergen dose required to induce both IgE- and FcγRIII-mediated anaphylaxis; and that both allergen interception and FcγRIIb-dependent inhibition contribute to in vivo blocking Ab activity.