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The vitamin D receptor (VDR) is the single known regulatory mediator of hormonal 1,25-dihydroxyvitamin [D.sub.3] [1,25[(OH).sub.2][D.sub.3]] in higher vertebrates. It acts in the nucleus of vitamin D target cells to regulate the expression of genes whose products control diverse, cell type-specific biological functions that include mineral homeostasis. In this Review we describe progress that has been made in defining new cellular sites of action of this receptor, the mechanisms through which this mediator controls the expression of genes, the biology that ensues, and the translational impact of this receptor on human health and disease. We conclude with a brief discussion of what comes next in understanding vitamin D biology and the mechanisms that underlie its actions., Introduction In the early 1970s, 1,25-dihydroxyvitamin [D.sub.3] [1,25[(OH).sub.2][D.sub.3]] was identified as both the exclusive, metabolically active form of vitamin D and a key component of what proved to be an [...]

Mast cells (MCs) are present in various tissues and are responsible for initiating many of the early inflammatory responses to extrinsic challenges. Recent studies have demonstrated that MCs can tailor their responses, depending on the stimulus encountered and the tissue in which they are stimulated. In this issue of the JCI, Gaudenzio and colleagues examine the mechanistic differences between MC responses observed after engagement of Fcζ receptor I and those seen after MC stimulation via the recently identified G protein-coupled receptor MRGPRX2. By showing that discrete cellular activation patterns affect the phenotype of the MC response in vivo and in vitro, the authors provide important information about how MCs differentially process various stimuli into distinct degranulation programs., Mast cells: sentinel cells and first responders Increasing lines of evidence indicate that mast cells (MCs) are key coordinators of both homeostasis and inflammation in a variety of tissues. Conventionally, [...]

Angiopoietin-1/Tie2 (ANG1/Tie2) signaling is well documented as regulating angiogenesis and vessel maturation. This pathway is complicated by involvement of the orphan receptor Tie1, which has been implicated as both a positive and negative regulator of ANG1/Tie2 signaling, and ANG2, which can serve as both a Tie2 agonist and antagonist, depending on the context. Two papers in this issue of the JCI provide new insight into this complicated pathway. Korhonen et al. reveal that Tie1 acts to modulate the effects of ANG1 and ANG2 on Tie2 in vitro and in vivo. Kim et al. demonstrate that ANG2 acts as a Tie2 agonist in non-pathological conditions, whereas in the setting of inflammation, ANG2 functions as a Tie2 antagonist and promotes vascular dysfunction. Both studies indicate that inflammation promotes cleavage of the ectodomain of Tie1 and that this cleavage event corresponds with the switch of ANG2 from a Tie2 agonist to an antagonist. The results of these studies lay the groundwork for future strategies to therapeutically exploit this pathway in diseases characterized by adverse vascular remodeling and increased permeability., Angiopoietin/Tie receptor signaling: a complex relationship Tie receptors (tyrosine kinases with immunoglobulin and epidermal growth factor homology domains) are a family of receptor tyrosine kinases (RTKs) that are expressed primarily [...]

Adoptive immunotherapy with regulatory T cells (Tregs) is a promising treatment for allograft rejection and graft- versushost disease (GVHD). Emerging data indicate that, compared with polyclonal Tregs, disease-relevant antigen-specific Tregs may have numerous advantages, such as a need for fewer cells and reduced risk of nonspecific immune suppression. Current methods to generate alloantigen-specific Tregs rely on expansion with allogeneic antigen-presenting cells, which requires access to donor and recipient cells and multiple MHC mismatches. The successful use of chimeric antigen receptors (CARs) for the generation of antigen-specific effector T cells suggests that a similar approach could be used to generate alloantigen-specific Tregs. Here, we have described the creation of an [HLA-A2.sup.-]specific CAR (A2-CAR) and its application in the generation of alloantigen-specific human Tregs. In vitro, A2-CAR-expressing Tregs maintained their expected phenotype and suppressive function before, during, and after A2-CAR-mediated stimulation. In mouse models, human A2-CAR-expressing Tregs were superior to Tregs expressing an irrelevant CAR at preventing xenogeneic GVHD caused by [HLA-A2.sup.+] T cells. Together, our results demonstrate that use of CAR technology to generate potent, functional, and stable alloantigen-specific human Tregs markedly enhances their therapeutic potential in transplantation and sets the stage for using this approach for making antigen-specific Tregs for therapy of multiple diseases., Introduction The essential role of regulatory T cells (Tregs) in preventing autoimmunity and controlling responses to alloantigens is well established. Multiple Treg-based cell therapy approaches are now being tested in [...]

Tumor cells frequently escape from [CD8.sup.+] T cell recognition by abrogating MHC-I antigen presentation. Deficiency in processing components, like the transporter associated with antigen processing (TAP), results in strongly decreased surface display of peptide/MHC-I complexes. We previously identified a class of hidden self-antigens known as T cell epitopes associated with impaired peptide processing (TEIPP), which emerge on tumor cells with such processing defects. In the present study, we analyzed thymus selection and peripheral behavior of T cells with specificity for the prototypic TEIPP antigen, the 'self' TRH4 peptide/[D.sup.b] complex. TEIPP T cells were efficiently selected in the thymus, egressed with a naive phenotype, and could be exploited for immunotherapy against immune-escaped, TAP-deficient tumor cells expressing low levels of MHC-I (MHC-[I.sup.lo]). In contrast, overt thymus deletion and functionally impaired TEIPP T cells were observed in mice deficient for TAP1 due to TEIPP antigen presentation on all body cells in these mice. Our results strongly support the concept that TEIPPs derive from ubiquitous, nonmutated self-antigens and constitute a class of immunogenic neoantigens that are unmasked during tumor immune evasion. These data suggest that TEIPP-specific [CD8.sup.+] T cells are promising candidates in the treatment of tumors that have escaped from conventional immunotherapies., Introduction Cytotoxic [CD8.sup.+] T cells are key players of the immune system that kill virus-infected and cancerous cells by sensing the state of the cellular proteome. A major focus of [...]

Thrombosis is a common, life-threatening consequence of systemic infection; however, the underlying mechanisms that drive the formation of infection-associated thrombi are poorly understood. Here, using a mouse model of systemic Salmonella Typhimurium infection, we determined that inflammation in tissues triggers thrombosis within vessels via ligation of C-type lectin-like receptor-2 (CLEC-2) on platelets by podoplanin exposed to the vasculature following breaching of the vessel wall. During infection, mice developed thrombi that persisted for weeks within the liver. Bacteria triggered but did not maintain this process, as thrombosis peaked at times when bacteremia was absent and bacteria in tissues were reduced by more than 90% from their peak levels. Thrombus development was triggered by an innate, TLR4-dependent inflammatory cascade that was independent of classical glycoprotein VI-mediated (GPVI-mediated) platelet activation. After infection, IFN-γ release enhanced the number of podoplanin-expressing monocytes and Kupffer cells in the hepatic parenchyma and perivascular sites and absence of TLR4, IFN-γ, or depletion of monocytic-lineage cells or CLEC-2 on platelets markedly inhibited the process. Together, our data indicate that infection-driven thrombosis follows local inflammation and upregulation of podoplanin and platelet activation. The identification of this pathway offers potential therapeutic opportunities to control the devastating consequences of infection-driven thrombosis without increasing the risk of bleeding., Introduction Thrombosis-associated events are among the leading causes of death worldwide. Systemic infections caused by a plethora of bacterial genera can initiate thrombus development. While the mechanisms that underlie this [...]

The small GTPase RAP1 is critical for platelet activation and thrombus formation. RAP1 activity in platelets is controlled by the GEF CalDAG-GEFI and an unknown regulator that operates downstream of the adenosine diphosphate (ADP) receptor, P2Y12, a target of antithrombotic therapy. Here, we provide evidence that the GAP, RASA3, inhibits platelet activation and provides a link between P2Y12 and activation of the RAP1 signaling pathway. In mice, reduced expression of RASA3 led to premature platelet activation and markedly reduced the life span of circulating platelets. The increased platelet turnover and the resulting thrombocytopenia were reversed by concomitant deletion of the gene encoding CalDAG-GEFI. Rasa3 mutant platelets were hyperresponsive to agonist stimulation, both in vitro and in vivo. Moreover, activation of Rasa3 mutant platelets occurred independently of ADP feedback signaling and was insensitive to inhibitors of P2Y12 or PI3 kinase. Together, our results indicate that RASA3 ensures that circulating platelets remain quiescent by restraining CalDAG- GEFI/RAP1 signaling and suggest that P2Y12 signaling is required to inhibit RASA3 and enable sustained RAP1-dependent platelet activation and thrombus formation at sites of vascular injury. These findings provide insight into the antithrombotic effect of P2Y12 inhibitors and may lead to improved diagnosis and treatment of platelet-related disorders., Introduction Mammalian platelets are small anucleated blood cells specialized to continuously monitor and preserve the integrity of the cardiovascular system (hemostasis) (1-3). Once released from megakaryocytes, they circulate for 10 [...]

Osteoclasts are bone-resorbing cells that are Important for maintenance of bone remodeling and mineral homeostasis. Regulation of osteoclast differentiation and activity is important for the pathogenesis and treatment of diseases associated with bone loss. Here, we demonstrate that retinoid X receptors (RXRs) are key elements of the transcriptional program of differentiating osteoclasts. Loss of RXR function in hematopoietic cells resulted in formation of giant, nonresorbing osteoclasts and increased bone mass in male mice and protected female mice from bone loss following ovariectomy, which induces osteoporosis in WT females. The increase in bone mass associated with RXR deficiency was due to lack of expression of the RXR-dependent transcription factor v-maf musculoaponeurotic fibrosarcoma oncogene family, protein B (MAFB) in osteoclast progenitors. Evaluation of osteoclast progenitor cells revealed that RXR homodimers directly target and bind to the Mafb promoter, and this interaction is required for proper osteoclast proliferation, differentiation, and activity. Pharmacological activation of RXRs inhibited osteoclast differentiation due to the formation of RXR/liver X receptor (LXR) heterodimers, which induced expression of sterol regulatory element binding protein-1c (SREBP-1c), resulting in indirect MAFB upregulation. Our study reveals that RXR signaling mediates bone homeostasis and suggests that RXRs have potential as targets for the treatment of bone pathologies such as osteoporosis., Introduction Bone undergoes constant remodeling by balancing the antagonistic activities of bone-forming osteoblasts and bone lytic osteoclasts (1-3). Bone loss resulting from increased osteoclast differentiation and activity (1, 4) can [...]

Learning and memory deficits are early clinical manifestations of Huntington's disease (HD). These cognitive impairments have been mainly associated with frontostriatal HD pathology; however, compelling evidence provided by several HD murine models suggests that the hippocampus may contribute to synaptic deficits and memory dysfunction in HD. The neurotrophin receptor [p75.sup.NTR] negatively regulates spine density, which is associated with learning and memory; therefore, we explored whether disturbed [p75.sup.NTR] function in the hippocampus could contribute to synaptic dysfunction and memory deficits in HD. Here, we determined that levels of [p75.sup.NTR] are markedly increased in the hippocampus of 2 distinct mouse models of HD and in HD patients. Normalization of [p75.sup.NTR] levels in HD mutant mice heterozygous for [p75.sup.NTR] prevented memory and synaptic plasticity deficits and ameliorated dendritic spine abnormalities, likely through normalization of the activity of the GTPase RhoA. Moreover, viral-mediated overexpression of [p75.sup.NTR] in the hippocampus of WT mice reproduced HD learning and memory deficits, while knockdown of [p75.sup.NTR] in the hippocampus of HD mice prevented cognitive decline. Together, these findings provide evidence of hippocampus-associated memory deficits in HD and demonstrate that [p75.sup.NTR] mediates synaptic, learning, and memory dysfunction in HD., Introduction Evidence of cognitive deficits including altered acquisition of new motor skills, paired attention, planning, and memory has been demonstrated in Huntington's disease (HD) patients before the onset of motor [...]

Purinergic receptors of the P2Y family are G protein-coupled surface receptors that respond to extracellular nucleotides and can mediate responses to local cell damage. P2Y-dependent signaling contributes to thrombotic and/or inflammatory consequences of tissue injury by altering platelet and endothelial activation and immune cell phagocytosis. Here, we have demonstrated that [P2Y.sub.14] modifies cell senescence and cell death in response to tissue stress, thereby enabling preservation of hematopoietic stem/progenitor cell function. In mice, [P2Y.sub.14] deficiency had no demonstrable effect under homeostatic conditions; however, radiation stress, aging, sequential exposure to chemotherapy, and serial bone marrow transplantation increased senescence in animals lacking [P2Y.sub.14]. Enhanced senescence coincided with increased ROS, elevated [p16.sup.INK4a] expression, and hypophosphorylated Rb and was inhibited by treatment with a ROS scavenger or inhibition of p38/MAPK and JNK. Treatment of WT cells with pertussis toxin recapitulated the [P2Y.sub.14] phenotype, suggesting that [P2Y.sub.14] mediates antisenescence effects through Gi/o protein-dependent pathways. Primitive hematopoietic cells lacking [P2Y.sub.14] were compromised in their ability to restore hematopoiesis in irradiated mice. Together, these data indicate that [P2Y.sub.14] on stem/progenitor cells of the hematopoietic system inhibits cell senescence by monitoring and responding to the extracellular manifestations of tissue stress and suggest that [P2Y.sub.14]-mediated responses prevent the premature decline of regenerative capacity after injury., Introduction Organisms inevitably encounter a variety of stresses during their lifetimes, including radiation, oxidation, and infection. The nature and efficiency of the response to stress is a fundamental determinant of [...]

Activation of the GPCR sphingosine-1-phosphate receptor 1 (S1P1) by sphingosine-1-phosphate (S1P) regulates key physiological processes. S1P1 activation also has been implicated in pathologic processes, including autoimmunity and inflammation; however, the in vivo sites of S1P1 activation under normal and disease conditions are unclear. Here, we describe the development of a mouse model that allows in vivo evaluation of S1P1 activation. These mice, known as S1P1 GFP signaling mice, produce a S1P1 fusion protein containing a transcription factor linked by a protease cleavage site at the C terminus as well as a β-arrestin/protease fusion protein. Activated S1P1 recruits the β-arrestin/protease, resulting in the release of the transcription factor, which stimulates the expression of a GFP reporter gene. Under normal conditions, S1P1 was activated in endothelial cells of lymphoid tissues and in cells in the marginal zone of the spleen, while administration of an S1P1 agonist promoted S1P1 activation in endothelial cells and hepatocytes. In S1P1 GFP signaling mice, LPS-mediated systemic inflammation activated S1P1 in endothelial cells and hepatocytes via hematopoietically derived S1P. These data demonstrate that S1P1 GFP signaling mice can be used to evaluate S1P1 activation and S1P1-active compounds in vivo. Furthermore, this strategy could be potentially applied to any GPCR to identify sites of receptor activation during normal physiology and disease., Introduction Sphingosine-1-phosphate receptor 1 (S1P1), originally named EDG-1, is the founding member of a family of 5 GPCRs with high affinity for the lipid ligand sphingosine-1-phosphate (S1P) (1-3). Activation ofS1P1 [...]

Dysfunctional bone morphogenetic protein receptor-2 (BMPR2) signaling is implicated in the pathogenesis of pulmonary arterial hypertension (PAH). We used a transcriptional high-throughput luciferase reporter assay to screen 3,756 FDA-approved drugs [...]

Cholecystokinin (CCK) is a satiety hormone produced by discrete enteroendocrine cells scattered among absorptive cells of the small intestine. CCK is released into blood following a meal; however, the mechanisms [...]

Cells of the immune system have evolved various molecular mechanisms to sense their environment and react to alterations of self. NK cells are lymphocytes with effector and regulatory functions, which are remarkably adaptable to changes in self. In a study published in this issue of the JCI, Tarek and colleagues report the clinical benefits of manipulating NK cell adaptation to self in an innovative mAb-based therapy against neuroblastoma (NB). This novel therapeutic strategy should stimulate further research on NK cell therapies., NK cells are involved in the elimination of tumor cells and infected cells (1); they can kill their cellular targets via cytotoxic granule exocytosis and also secrete cytokines such as [...]

PAX5, a B cell-specific transcription factor, is overexpressed through chromosomal translocations in a sub-set of B cell lymphomas. Previously, we had shown that activation of immunoreceptor tyrosine-based activa-tion motif (ITAM) proteins and B cell receptor (BCR) signaling by PAX5 contributes to B-lymphomagenesis. However, the effect of PAX5 on other oncogenic transcription factor-controlled pathways is unknown. Using a MYC-induced murine lymphoma model as well as MYC-transformed human B cell lines, we found that PAX5 controls c-MYC protein stability and steady-state levels. This promoter-independent, posttranslational mechanism of c-MYC regulation was independent of ITAM/BCR activity. Instead it was controlled by another PAX5 target, CD19, through the PI3K-AKT-GSK3 β axis. Consequently, MYC levels in B cells from CD19-defi-cient mice were sharply reduced. Conversely, reexpression of CD19 in murine lymphomas with spontaneous silencing of PAX5 boosted MYC levels, expression of its key target genes, cell proliferation in vitro, and over-all tumor growth in vivo. In human B-lymphomas, CD19 mRNA levels were found to correlate with those of MYC-activated genes. They also negatively correlated with the overall survival of patients with lymphoma in the same way that MYC levels do. Thus, CD19 is a major BCR-independent regulator of MYC-driven neoplastic growth in B cell neoplasms., Introduction The concept of oncogene addiction (1) is particularly well validated in hematological malignancies. 'Liquid' tumors are thought to depend on fewer genetic alterations and thus be more sensitive to [...]

In order to prime T cells, DCs integrate signals emanating directly from pathogens and from their noxious action on the host. DNGR-1 (CLEC9A) is a DC-restricted receptor that detects dead cells. Therefore, we investigated the possibility that DNGR-1 affects immunity to cytopathic viruses. DNGR-1 was essential for cross-presentation of dying vaccinia virus-infected (VACV-infected) cells to CD8+ T cells in vitro. Following injection of VACV or VACV-infected cells into mice, DNGR-1 detected the ligand in dying infected cells and mediated cross-priming of anti-VACV CD8+ T cells. Loss of DNGR-1 impaired the CD8+ cytotoxic response to VACV, especially against those virus strains that are most dependent on cross-presentation. The decrease in total anti-VACV CTL activity was associated with a profound increase in viral load and delayed resolution of the primary lesion. In addition, lack of DNGR-1 markedly diminished protection from infection induced by vaccination with the modified vaccinia Ankara (MVA) strain. DNGR-1 thus contributes to anti-VACV immunity, following both primary infection and vaccination. The non-redundant ability of DNGR-1 to regulate cross-presentation of viral antigens suggests that this form of regulation of antiviral immunity could be exploited for vaccination., Introduction Pressure to detect infection has shaped the evolution of the immune system. Several families of pathogen recognition receptors (PRRs) detect pathogen-associated molecular patterns (PAMPs) and activate myeloid cells to [...]

DNGR-1 (CLEC9A) is a receptor for necrotic cells required by DCs to cross-prime CTLs against dead cell antigens in mice. It is currently unknown how DNGR-1 couples dead cell recognition to cross-priming. Here we found that DNGR-1 did not mediate DC activation by dead cells but rather diverted necrotic cell cargo into a recycling endosomal compartment, favoring cross-presentation to CD [8.sup.+] T cells. DNGR-1 regulated cross-priming in non-infectious settings such as immunization with antigen-bearing dead cells, as well as in highly immunogenic situations such as infection with herpes simplex virus type 1. Together, these results suggest that DNGR-1 is a dedicated receptor for cross-presentation of cell-associated antigens. Our work thus underscores the importance of cross-priming in immunity and indicates that antigenicity and adjuvanticity can be decoded by distinct innate immune receptors. The identification of specialized receptors that regulate antigenicity of virus-infected cells reveals determinants of antiviral immunity that might underlie the human response to infection and vaccination., Introduction DCs are central players in the establishment and maintenance of self-tolerance, as well as in the induction of immunity against invading microorganisms (1, 2). In mice and humans, distinct [...]

Immunological and neural synapses share properties such as the synaptic cleft, adhesion molecules, stability, and polarity. However, the mismatch in scale has limited the utility of these comparisons. The discovery of phosphatase micro-exclusion from signaling elements in immunological synapses and innate phagocytic synapses define a common functional unit at a common sub-micron scale across synapse types. Bundling of information from multiple antigen receptor microclusters by an immunological synapse has parallels to bundling of multiple synaptic inputs into a single axonal output by neurons, allowing integration and coincidence detection. Bonafide neuroimmune synapses control the inflammatory reflex. A better understanding of the shared mechanisms between immunological and neural synapses could aid in the development of new therapeutic modalities for immunological, neurological, and neuroimmunological disorders alike., Introduction Cell-cell communication systems in the immune and nervous systems share several features, which has led to the adoption of the common term 'synapse' to describe the close cell-cell contacts [...]

Stroke is the third leading cause of death in the United States. Fewer than 5% of patients benefit from the only intervention approved to treat stroke. Thus, there is an [...]

The successful treatment of certain autoimmune conditions with the humanized anti-IL-6 receptor (IL-6R) antibody tocilizumab has emphasized the clinical importance of cytokines that signal through the β -receptor subunit glycoprotein 130 (gp130). In this Review, we explore how gp130 signaling controls disease progression and examine why IL-6 has a special role among these cytokines as an inflammatory regulator. Attention will be given to the role of the soluble IL-6R, and we will provide a perspective into the clinical blockade of IL-6 activity in autoimmunity, inflammation, and cancer., Introduction Inflammation is not a disease but a consequence of disease and is the body's defense against infection or injury. When effective, the inflammatory response ensures successful resolution of the [...]

We have previously shown that mouse atherosclerosis regression involves monocyte-derived ([CD68.sup.+]) cell emigration from plaques and is dependent on the chemokine receptor CCR7. Concurrent with regression, mRNA levels of the gene encoding LXRα are increased in plaque [CD68.sup.+] cells, suggestive of a functional relationship between LXR and CCR7. To extend these results, atherosclerotic [Apoe.sup.-/-] mice sufficient or deficient in CCR7 were treated with an LXR agonist, resulting in a CCR7-dependent decrease in plaque [CD68.sup.+] cells. To test the requirement for LXR for CCR7-dependent regression, we transplanted aortic arches from atherosclerotic [Apoe.sup.-/-] mice, or from [Apoe.sup.-/-] mice with BM deficiency of LXRα or LXRβ, into WT recipients. Plaques from both LXRα-and LXRβ-deficient [Apoe.sup.-/-] mice exhibited impaired regression. In addition, the [CD68.sup.+] cells displayed reduced emigration and CCR7 expression. Using an immature DC line, we found that LXR agonist treatment increased Ccr7 mRNA levels. This increase was blunted when LXRα and LXRβ levels were reduced by siRNAs. Moreover, LXR agonist treatment of primary human immature DCs resulted in functionally significant upregulation of CCR7. We conclude that LXR is required for maximal effects on plaque [CD68.sup.+] cell expression of CCR7 and monocyte-derived cell egress during atherosclerosis regression in mice., Introduction Atherosclerosis is the leading underlying cause of death worldwide (1). Absolute risk for cardiovascular disease rises with age because of the progression of coronary atherosclerosis (2-6). To date, the [...]

During the classic 'fight-or-flight' stress response, sympathetic nervous system activation leads to catechol-amine release, which increases heart rate and contractility, resulting in enhanced cardiac output. Catecholamines bind to β-adrenergic receptors, causing cAMP generation and activation of PKA, which phosphorylates multiple targets in cardiac muscle, including the cardiac ryanodine receptor/calcium release channel (RyR2) required for muscle contraction. PKA phosphorylation of RyR2 enhances channel activity by sensitizing the channel to cytosolic calcium ([Ca.sup.2+]). Here, we found that mice harboring RyR2 channels that cannot be PKA phosphorylated (referred to herein as RyR2-[S2808A.sup.+/+] mice) exhibited blunted heart rate and cardiac contractile responses to catecholamines (isoproterenol). The isoproterenol-induced enhancement of ventricular myocyte [Ca.sup.2+] transients and fractional shortening (contraction) and the spontaneous beating rate of sinoatrial nodal cells were all blunted in RyR2-[S2808A.sup.+/+] mice. The blunted cardiac response to catecholamines in RyR2-[S2808A.sup.+/+] mice resulted in impaired exercise capacity. RyR2-[S2808A.sup.+/+] mice were protected against chronic catecholaminergic-induced cardiac dysfunction. These studies identify what we believe to be new roles for PKA phosphorylation of RyR2 in both the heart rate and contractile responses to acute catecholaminergic stimulation., Introduction During exercise, heart rate (chronotropy) and cardiac contractility (inotropy) increase to meet the metabolic demands of the organs. Stress-induced activation of the sympathetic nervous system (SNS) results in catecholamine [...]

Increased sarcoplasmic reticulum (SR) [Ca.sup.2+] leak via the cardiac ryanodine receptor/calcium release channel (RyR2) is thought to play a role in heart failure (HF) progression. Inhibition of this leak is an emerging therapeutic strategy. To explore the role of chronic PKA phosphorylation of RyR2 in HF pathogenesis and treatment, we generated a knockin mouse with aspartic acid replacing serine 2808 (mice are referred to herein as RyR2-[S2808D.sup.+/+] mice). This mutation mimics constitutive PKA hyperphosphorylation of RyR2, which causes depletion of the stabilizing subunit FKBP12.6 (also known as calstabin2), resulting in leaky RyR2. RyR2-[S2808D.sup.+/+] mice developed age-dependent cardiomyopathy, elevated RyR2 oxidation and nitrosylation, reduced SR [Ca.sup.2+] store content, and increased diastolic SR [Ca.sup.2+] leak. After myocardial infarction, RyR2-[S2808D.sup.+/+] mice exhibited increased mortality compared with WT littermates. Treatment with S107, a 1,4-benzothiazepine derivative that stabilizes RyR2-calstabin2 interactions, inhibited the RyR2-mediated diastolic SR [Ca.sup.2+] leak and reduced HF progression in WT and RyR2-[S2808D.sup.+/+] mice. In contrast, β-adrenergic receptor blockers improved cardiac function in WT but not in RyR2-[S2808D.sup.+/+] mice.Thus, chronic PKA hyperphosphorylation of RyR2 results in a diastolic leak that causes cardiac dysfunction. Reversing PKA hyperphosphorylation of RyR2 is an important mechanism underlying the therapeutic action of β-blocker therapy in HF., Introduction Heart failure (HF), a syndrome characterized by progressive deterioration of cardiac function, represents a major public health burden and is a leading cause of morbidity and mortality in the [...]

In situations of stress the heart beats faster and stronger. According to Marks and colleagues, this response is, to a large extent, the consequence of facilitated [Ca.sup.2+] release from intracellular [Ca.sup.2+] stores via ryanodine receptor 2 (RyR2), thought to be due to catecholamine-induced increases in RyR2 phosphorylation at serine 2808 (S2808). If catecholamine stimulation is sustained (for example, as occurs in heart failure), RyR2 becomes hyperphosphorylated and 'leaky,' leading to arrhythmias and other pathology. This 'leaky RyR2 hypothesis' is highly controversial. In this issue of the JCI, Marks and colleagues report on two new mouse lines with mutations in S2808 that provide strong evidence supporting their theory. Moreover, the experiments revealed an influence of redox modifications of RyR2 that may account for some discrepancies in the field., The heart has a remarkable capacity to react to altered demand by changing the rate at which it beats and the force with which it contracts, thereby changing its output. [...]

Sphingosine kinase 1 (SphK1) and SphK2 are ubiquitous enzymes that generate sphingosine-1-phosphate (S1P), a ligand for a family of G protein-coupled receptors (S1PR1-S1PR5) with important functions in the vascular and immune systems. Here we explore the role of these kinases and receptors in recovery from anaphylaxis in mice. We found that [Sphk2.sup.[-/-]] mice had a rapid recovery from anaphylaxis. In contrast, [Sphk1.sup.[-/-]] mice showed poor recovery from anaphylaxis and delayed histamine clearance. Injection of S1P into [Sphk1.sup.[-/-]] mice increased histamine clearance and promoted recovery from anaphylaxis. Adoptive cell transfer experiments demonstrated that SphK1 activity was required in both the hematopoietic and nonhematopoietic compartments for recovery from anaphylaxis. Mice lacking the S1P receptor S1PR2 also showed a delay in plasma histamine clearance and a poor recovery from anaphylaxis. However, S1P did not promote the recovery of [S1pr2.sup.[-/-]] mice from anaphylaxis, whereas [S1pr2.sup.±] mice showed partial recovery. Unlike [Sphk2.sup.[-/-]] mice, [Sphk1.sup.[-/-]] and [S1pr2.sup.[-/-]] mice had severe hypotension during anaphylaxis. Thus, SphK1-produced S1P regulates blood pressure, histamine clearance, and recovery from anaphylaxis in a manner that involves S1PR2. This suggests that specific S1PR2 agonists may serve to counteract the vasodilation associated with anaphylactic shock., Introduction Anaphylaxis is a serious allergic reaction that typically involves the activation of mast cells and basophils (1-3). Unlike other allergic reactions involving mast cells, anaphylaxis affects the function of [...]