Common Downstream Mechanism Research Articles

Deep Proteomic Analysis Reveals Shared Terminal Mechanisms for Familial Hemophagocytic Lymphohistiocytosis and Lymphoma-Associated Hyperinflammation

Background: Hemophagocytic lymphohistiocytosis (HLH) is a hyperinflammatory syndrome increasingly observed in patients with hematologic malignancies (HM-HLH). Familial HLH (FHL) is seen in young children and is typically caused by mutations affecting the perforin pathway of lymphocyte cytotoxic function, leading to excessive CD8+ T cell activation and interferon-gamma production. Though HM-HLH has clinical similarities to FHL, little is known regarding the pathophysiology of HM-HLH. We previously developed the ‘Optimized HLH Inflammatory (OHI) index,‘ combining soluble CD25 and ferritin elevations, to improve recognition of hyperinflammation and prognostication in HM patients (Zoref-Lorenz et al., Blood; 2022). Based on these findings, we hypothesize that OHI+ HM's share similar immune pathophysiology with FHL and aim to validate this hypothesis using an unbiased proteomic approach. Methods: We conducted an unbiased proteomic analysis of samples from Schneider Children's, Meir, Sheba, and Beilinson Medical Centers. Our cohort included FHL patients, healthy pediatric controls, and patients with HMs, classified as HM-OHI+(sCD25>3,900 U/mL and ferritin>1,000 ng/mL) or HM-OHI-. SomaLogic proteomics platform, an aptamer-based method, assessed 7,596 serum proteins representing 6,412 genes. Unsupervised clustering techniques (primary component analysis and unbiased hierarchical clustering) were used to group patient results. Gene set enrichment analysis (GSEA) of the hallmark set was used to identify enriched biologic pathways in HM-OHI+ and FHL. Differential expression analysis (Student t-test) identified differentially expressed proteins (DEPs, q<0.1, p<0.05) between FHL vs. healthy controls and HM-OHI+ vs. HM-OHI-. Venn analysis revealed overlapping DEPs between FHL and OHI+ HM-HLH patients. GSEA with hallmark pathways evaluated the overlapping genes in each pairwise comparison within the entire sets and the intersecting genes. Spearman's correlation analysis examined the relationship between fold changes of proteins and normalized enrichment scores of hallmark GSEA comparisons within intersecting proteins and genes of FHL and HM-OHI+. Logistic regression created an equation for the linear curve of these correlations. Results: We analyzed 42 patients, including 14 HM-OHI+ and 14 HM-OHI- patients, matched by malignancy type, 7 FHL patients, and age-matched controls. Unsupervised hierarchical clustering (Figure 1A) showed that HM-OHI+ patients clustered with FHL patients, while healthy controls and HM-OHI- patients clustered together. GSEA analysis identified common enriched biological pathways between HM-OHI+ and FHL: interferon-γ response, IL6 JAK STAT3 signaling, IL2 STAT5 signaling, and oxidative phosphorylation (Normalized enrichment scores of 1.82:1.92; 1.76:2.23; 1.76:1.76 and 1.68:1.78 respectively for HM-OHI+ and FHL). In pairwise statistical comparisons, 841 differential proteins were shared between FHL and HM-OHI+. HM-OHI+ and FHL exhibited highly correlated fold changes (R=0.97, p<0.0001, Y= 1.362 X-0.2597, Figure 1B), with highly significant elevated proteins in HM-OHI+ vs. HM-OHI- that are key in the mechanism of FHL: T cell activation (GRZB, FC-1.6 q=0.01; GRZH: FC-1.5, q= 0.002), IFN-γ response (CXCL10, FC-2.1,q=0.001), and macrophage activation (CD14: FC- 1.6, q=0.001; CSF1:FC- 2.1, 1<0.0001; IL1RL: FC- 1.8,q=0.0009). The intersecting genes in the GSEA analysis revealed a high correlation of the biological pathways (R=0.94, p<0.0001, Y=1.282X+0), with the IFN-γ response, the known driver of FHL being the most significantly over-enriched pathway in both pairwise comparisons (q<0.25). These findings indicate shared pathophysiology mechanisms between HM-OHI+ and FHL. We validated key proteins using ELISA as an orthogonal method. Conclusions: This study establishes a common downstream mechanism of hyperinflammation in hematologic malignancies and FHL, closely linked to the IFN-γ response, and validates the OHI index as a diagnostic tool for HM-HLH. Understanding the shared pathophysiology between HM-OHI+ and FHL sheds light on the poor prognosis of HM-associated hyperinflammation and emphasizes the need to study the upstream mechanisms of HM-HLH to define targets for improved therapeutic approaches.

Psychedelics reopen the social reward learning critical period

Psychedelics are a broad class of drugs defined by their ability to induce an altered state of consciousness1,2. These drugs have been used for millennia in both spiritual and medicinal contexts, and a number of recent clinical successes have spurred a renewed interest in developing psychedelic therapies3–9. Nevertheless, a unifying mechanism that can account for these shared phenomenological and therapeutic properties remains unknown. Here we demonstrate in mice that the ability to reopen the social reward learning critical period is a shared property across psychedelic drugs. Notably, the time course of critical period reopening is proportional to the duration of acute subjective effects reported in humans. Furthermore, the ability to reinstate social reward learning in adulthood is paralleled by metaplastic restoration of oxytocin-mediated long-term depression in the nucleus accumbens. Finally, identification of differentially expressed genes in the ‘open state’ versus the ‘closed state’ provides evidence that reorganization of the extracellular matrix is a common downstream mechanism underlying psychedelic drug-mediated critical period reopening. Together these results have important implications for the implementation of psychedelics in clinical practice, as well as the design of novel compounds for the treatment of neuropsychiatric disease.

NMDA Receptor Activation-Dependent Antidepressant-Relevant Behavioral and Synaptic Actions of Ketamine.

Ketamine is a well-characterized NMDA receptor (NMDAR) antagonist, although the relevance of this pharmacology to its rapid (within hours of administration) antidepressant actions, which depend on mechanisms convergent with strengthening of excitatory synapses, is unclear. Activation of synaptic NMDARs is necessary for the induction of canonical long-term potentiation (LTP) leading to a sustained expression of increased synaptic strength. We tested the hypothesis that induction of rapid antidepressant effects requires NMDAR activation, by using behavioral pharmacology, western blot quantification of hippocampal synaptoneurosomal protein levels, and ex vivo hippocampal slice electrophysiology in male mice. We found that ketamine exerts an inverted U-shaped dose-response in antidepressant-sensitive behavioral tests, suggesting that an excessive NMDAR inhibition can prevent ketamine's antidepressant effects. Ketamine's actions to induce antidepressant-like behavioral effects, up-regulation of hippocampal AMPAR subunits GluA1 and GluA2, as well as metaplasticity measured ex vivo using electrically-stimulated LTP, were abolished by pretreatment with other non-antidepressant NMDAR antagonists, including MK-801 and CPP. Similarly, the antidepressant-like actions of other putative rapid-acting antidepressant drugs (2R,6R)-hydroxynorketamine (ketamine metabolite), MRK-016 (GABAAα5 negative allosteric modulator), and LY341495 (mGlu2/3 receptor antagonist) were blocked by NMDAR inhibition. Ketamine acted synergistically with an NMDAR positive allosteric modulator to exert antidepressant-like behavioral effects and activation of the NMDAR subunit GluN2A was necessary and sufficient for such relevant effects. We conclude rapid-acting antidepressant compounds share a common downstream NMDAR-activation dependent effector mechanism, despite variation in initial pharmacological targets. Promoting NMDAR signaling or other approaches that enhance NMDAR-dependent LTP-like synaptic potentiation may be an effective antidepressant strategy.SIGNIFICANCE STATEMENT The anesthetic and antidepressant drug ketamine is well-characterized as an NMDA receptor (NMDAR) antagonist; though, the relevance and full impact of this pharmacology to its antidepressant actions is unclear. We found that NMDAR activation, which occurs downstream of their initial actions, is necessary for the beneficial effects of ketamine and several other putative antidepressant compounds. As such, promoting NMDAR signaling, or other approaches that enhance NMDAR-dependent long-term potentiation (LTP)-like synaptic potentiation in vivo may be an effective antidepressant strategy directly, or acting synergistically with other drug or interventional treatments.

Targeting Circuit Abnormalities in Neurodegenerative Disease.

Despite significant improvement in our ability to diagnose both common and rare neurodegenerative diseases and understand their underlying biologic mechanisms, there remains a disproportionate lack of effective treatments, reflecting the complexity of these disorders. Successfully advancing novel treatments for neurodegenerative disorders will require reconsideration of traditional approaches, which to date have focused largely on specific disease proteins or cells of origin. This article proposes reframing these diseases as conditions of dysfunctional circuitry as a complement to ongoing efforts. Specifically reviewed is how aberrant spiking is a common downstream mechanism in numerous neurodegenerative diseases, often driven by dysfunction in specific ion channels. Surgical modification of this electrical activity via deep brain stimulation is already an approved modality for many of these disorders. Therefore, restoring proper electrical activity by targeting these channels pharmacologically represents a viable strategy for intervention, not only for symptomatic management but also as a potential disease-modifying therapy. Such an approach is likely to be a promising route to treating these devastating disorders, either as monotherapy or in conjunction with current drugs. SIGNIFICANCE STATEMENT: Despite extensive research and improved understanding of the biology driving neurodegenerative disease, there has not been a concomitant increase in approved therapies. Accordingly, it is time to shift our perspective and recognize these diseases also as disorders of circuitry to further yield novel drug targets and new interventions. An approach focused on treating dysfunctional circuitry has the potential to reduce or reverse patient symptoms and potentially modify disease course.

Hepatocyte nuclear factors play an important role in the pathogenesis of nephropathy

Hepatocyte nuclear factors play an important role in the pathogenesis of nephropathy

Hebbian and Homeostatic Synaptic Plasticity-Do Alterations of One Reflect Enhancement of the Other?

During the past 50 years, the cellular and molecular mechanisms of synaptic plasticity have been studied in great detail. A plethora of signaling pathways have been identified that account for synaptic changes based on positive and negative feedback mechanisms. Yet, the biological significance of Hebbian synaptic plasticity (= positive feedback) and homeostatic synaptic plasticity (= negative feedback) remains a matter of debate. Specifically, it is unclear how these opposing forms of plasticity, which share common downstream mechanisms, operate in the same networks, neurons, and synapses. Based on the observation that rapid and input-specific homeostatic mechanisms exist, we here discuss a model that is based on signaling pathways that may adjust a balance between Hebbian and homeostatic synaptic plasticity. Hence, “alterations” in Hebbian plasticity may, in fact, resemble “enhanced” homeostasis, which rapidly returns synaptic strength to baseline. In turn, long-lasting experience-dependent synaptic changes may require attenuation of homeostatic mechanisms or the adjustment of homeostatic setpoints at the single-synapse level. In this context, we propose a role for the proteolytic processing of the amyloid precursor protein (APP) in setting a balance between the ability of neurons to express Hebbian and homeostatic synaptic plasticity.

Pathogenic alpha-synuclein aggregates preferentially bind to mitochondria and affect cellular respiration

Misfolded alpha-synuclein (αSyn) is a major constituent of Lewy bodies and Lewy neurites, which are pathological hallmarks of Parkinson’s disease (PD). The contribution of αSyn to PD is well established, but the detailed mechanism remains obscure. Using a model in which αSyn aggregation in primary neurons was seeded by exogenously added, preformed αSyn amyloid fibrils (PFF), we found that a majority of pathogenic αSyn (indicated by serine 129 phosphorylated αSyn, ps-αSyn) was membrane-bound and associated with mitochondria. In contrast, only a minuscule amount of physiological αSyn was mitochondrial bound. In vitro, αSyn PFF displayed a stronger binding to purified mitochondria than did αSyn monomer, revealing a preferential mitochondria binding by aggregated αSyn. This selective mitochondrial ps-αSyn accumulation was confirmed in other neuronal and animal αSyn aggregation models that do not require exogenously added PFF and, more importantly, in postmortem brain tissues of patients suffering from PD and other neurodegenerative diseases with αSyn aggregation (α-synucleinopathies). We also showed that the mitochondrial ps-αSyn accumulation was accompanied by defects in cellular respiration in primary neurons, suggesting a link to mitochondrial dysfunction. Together, our results show that, contrary to physiological αSyn, pathogenic αSyn aggregates preferentially bind to mitochondria, indicating mitochondrial dysfunction as the common downstream mechanism for α-synucleinopathies. Our findings suggest a plausible model explaining the formation and the peculiar morphology of Lewy body and reveal that disrupting the interaction between ps-αSyn and the mitochondria is a therapeutic target for α-synucleinopathies.

Regulation of Excitatory Amino Acid Transmission in the Retina: Studies on Neuroprotection.

Excitotoxicity occurs in neurons due to the accumulation of excitatory amino acids such as glutamate in the synaptic and extrasynaptic locations. In the retina, excessive glutamate concentrations trigger a neurotoxic cascade involving several mechanisms, including the elevation of intracellular calcium (Ca2+) and the activation of α-amino-3-hydroxy 5-methyl-4-iso-xazole-propionic acid/kainate (AMPA/KA) and N-methyl-d-aspartate (NMDA) receptors leading to retinal degeneration. Both ionotropic glutamate receptors (iGluRs) and metabotropic glutamate receptors (mGluRs) are present in the mammalian retina. Indeed, due to the abundant expression of GluRs, the mammalian retina is highly susceptible to excitotoxic neurodegeneration. Excitotoxicity has been postulated to present a common downstream mechanism for several stimuli, including hypoglycemia, hypoxia, ischemia, and chronic neurodegenerative diseases. Experimental approaches to the study of neuroprotection in the retina have utilized insults that trigger hypoxia, hypoglycemia, or excitotoxicity. Using these experimental approaches, the neuroprotective potential of GluR agents, including the NMDA receptor modulators (MK801, ifenprodil, memantine); AMPA/KA receptor antagonist (CNQX); Group II and III mGluR agonists (LY354740, quisqualate); and Ca2+-channel blockers (diltiazem, lomerizine, verapamil, ω-conotoxin), and others (pituitary adenylate cyclase activating polypeptide, neuropeptide Y, acetylcholine receptor agonists) have been elucidated. In addition to corroborating the exocytotic role of excitatory amino acids in retinal degeneration, these studies affirm that multiple mechanism/s contribute to the prevention of damage caused by excitotoxicity in the retina. Therefore, it is feasible that several pathways are involved in protecting the retina from toxic insults in ocular neurodegenerative conditions such as glaucoma and retinal ischemia. Furthermore, these experimental models are viable tools for evaluating therapeutic candidates in ocular neuropathies.

Small nucleoli are a cellular hallmark of longevity

Animal lifespan is regulated by conserved metabolic signalling pathways and specific transcription factors, but whether these pathways affect common downstream mechanisms remains largely elusive. Here we show that NCL-1/TRIM2/Brat tumour suppressor extends lifespan and limits nucleolar size in the major C. elegans longevity pathways, as part of a convergent mechanism focused on the nucleolus. Long-lived animals representing distinct longevity pathways exhibit small nucleoli, and decreased expression of rRNA, ribosomal proteins, and the nucleolar protein fibrillarin, dependent on NCL-1. Knockdown of fibrillarin also reduces nucleolar size and extends lifespan. Among wildtype C. elegans, individual nucleolar size varies, but is highly predictive for longevity. Long-lived dietary restricted fruit flies and insulin-like-peptide mutants exhibit small nucleoli and fibrillarin expression, as do long-lived dietary restricted and IRS1 knockout mice. Furthermore, human muscle biopsies from individuals who underwent modest dietary restriction coupled with exercise also display small nucleoli. We suggest that small nucleoli are a cellular hallmark of longevity and metabolic health conserved across taxa.

Inactivation of Hv1 proton channels is not responsible for bicarbonate‐mediated reductions in tubular cast formation in Dahl salt‐sensitive rats

We have shown that oral bicarbonate promotes a marked reduction in tubular cast formation and fibrosis in the Dahl salt‐sensitive (SS) rat model when fed a high salt diet, independent of arterial blood pressure, glomerular sclerosis, and proteinuria. Rats lacking the voltage‐gated proton channel (Hv1), which is highly expressed in mTAL, denoted a similar phenotype. In the current study, we examined whether bicarbonate intake protected from cast formation in the Dahl SS rat model by inactivation of the voltage‐gated Hv1 proton channel. Wild‐type Dahl SS (WT) and Hv1 knock‐out (KO) Dahl SS rats were treated with either vehicle (0.1M NaCl; n=9) or bicarbonate (0.1M NaHCO3; n=11) in drinking water for the length of the study. Following a 4 day baseline period in which both groups were fed a 0.4% NaCl diet (Dyets AIN76A), rats were placed on an 8% NaCl diet for 14 days. Urine was collected at day 4 of baseline, day 7, and day 14 high salt; telemetry was used to measure blood pressure. On day 14, rats were anesthetized, and the right kidney taken for histology. Mean arterial pressure (mmHg) showed no difference between the WT and KO groups regardless of vehicle or bicarbonate treatment. Tubular casts were significantly decreased (pSTRAIN=0.008) in KO rats when compared to WT. Importantly, bicarbonate treatment had an additive effect, further decreasing tubular cast formation and by a similar magnitude in both KO and WT rats (PTREATMENT=0.02; PTREATMENT*STRAIN=N.S). In conclusion, bicarbonate‐induced inactivation of Hv1 proton channels does not mediate the reduction of cast formation in Dahl SS rats. Further investigation will be required to determine whether a common downstream mechanism is responsible for limiting tubular cast formation in the absence of blood pressure changes or glomerular injury in bicarbonate treated and Hv1−/− Dahl SS rats.Support or Funding InformationThe authors would like to acknowledge funding from the National Institute of Health: NIDDK R01099548

Pediatric myelodysplastic/myeloproliferative neoplasms and related diseases

Myelodysplastic/myeloproliferative neoplasms (MDS/MPN) are clonal hematopoietic disorders with myeloproliferative features, varying degrees of dysplasia and cytopenias, and increased propensity for progression to acute myeloid leukemia (AML). MDS/MPN are uncommon in the pediatric age group, and best exemplified by Juvenile myelomonocytic leukemia (JMML), a rare but aggressive leukemia of early childhood. Remarkable progress has been made in understanding the genetic basis of JMML leading to improved diagnostic criteria and better management. It is now understood that JMML is associated with somatic or germ line mutations in NF1, NRAS, KRAS, PTPN11, and CBL in greater than 90 % of cases with the common downstream mechanism being uncontrolled activation of the RAS/MAPK pathway. More recently, KRAS and NRAS mutations have also been identified in RAS-associated autoimmune leukoproliferative disorder (RALD), which shares some clinical, hematopathological, and genetic features with JMML, but has an indolent clinical course. Hematopoietic stem cell transplant (HSCT) is currently the only curative therapy for JMML, although newer therapeutic agents are currently in clinical trials. This review will focus primarily on the current clinical features, diagnostic criteria, pathologic features, and therapy of JMML and provide a brief description of RALD.

Bone Morphogenetic Proteins: Inhibitors of Myelination in Development and Disease.

Myelin, the lipid membrane that surrounds axons, is critical for the propagation of nervous impulses and axonal maintenance. The destruction of myelin or lack of myelin formation due to disease or injury causes severe motor and cognitive disability. Regeneration of myelin is theoretically possible but rarely happens. Myelin is synthesized as the plasma membrane of the oligodendrocyte in the central nervous system. During development, myelin and oligodendrocytes are generated from oligodendrocyte progenitors through a process modulated by extrinsic growth factors signaling to cell-intrinsic proteins. Among the key extrinsic factors are the bone morphogenetic proteins (BMPs), potent inhibitors of oligodendrocyte differentiation and myelin protein expression, likely serving to regulate myelination temporally and spatially. BMPs also promote astrocyte generation. Given the inhibitory role of BMP in oligodendrogliogenesis during development, the expression of BMP during demyelinating disease or injury was investigated, as was whether BMP upregulation could serve to prevent regeneration by both direct inhibition of myelination and increases in astrogliosis. BMPs, predominantly BMP4, were increased in animal models of spinal cord injury, stroke, multiple sclerosis, and perinatal white matter injury. A number of studies inhibited BMP signaling by infusing the injury site with the BMP-specific inhibitor noggin or transplanting stem cells engineered to secrete noggin. In most cases, noggin increased the numbers of mature oligodendrocytes and decreased numbers of astrocytes. Some studies also showed functional improvement. BMP is one of several inhibitory growth factors that now appear to inhibit myelin regeneration. Common downstream mechanisms among these factors are likely to be identified.

In search of antiaging modalities: Evaluation of mTOR‐ and ROS/DNA damage‐signaling by cytometry

This review presents the evidence in support of the IGF-1/mTOR/S6K1 signaling as the primary factor contributing to aging and cellular senescence. Reviewed are also specific interactions between mTOR/S6K1 and ROS-DNA damage signaling pathways. Outlined are critical sites along these pathways, including autophagy, as targets for potential antiaging (gero-suppressive) and/or chemopreventive agents. Presented are applications of flow- and laser scanning- cytometry utilizing phospho-specific Abs, to monitor activation along these pathways in response to the reported antiaging drugs rapamycin, metformin, berberine, resveratrol, vitamin D3, 2-deoxyglucose, and acetylsalicylic acid. Specifically, effectiveness of these agents to attenuate the level of constitutive mTOR signaling was tested by cytometry and confirmed by Western blotting through measuring phosphorylation of the mTOR-downstream targets including ribosomal protein S6. The ratiometric analysis of phosphorylated to total protein along the mTOR pathway offers a useful parameter reporting the effects of gero-suppressive agents. In parallel, their ability to suppress the level of constitutive DNA damage signaling induced by endogenous ROS was measured. While the primary target of each of these agents may be different the data obtained on several human cancer cell lines, WI-38 fibroblasts and normal lymphocytes suggest common downstream mechanism in which the decline in mTOR/S6K1 signaling and translation rate is coupled with a reduction of oxidative phosphorylation and ROS that leads to decreased oxidative DNA damage. The combined assessment of constitutive γH2AX expression, mitochondrial activity (ROS, ΔΨm), and mTOR signaling provides an adequate gamut of cell responses to test effectiveness of gero-suppressive agents. Described is also an in vitro model of induction of cellular senescence by persistent replication stress, its quantitative analysis by laser scanning cytometry, and application to detect the property of the studied agents to attenuate the induction of senescence. Discussed is cytometric analysis of cell size and heterogeneity of size as a potential biomarker used to asses gero-suppressive agents and longevity.

Caspase-mediated cleavage of actin and tubulin is a common feature and sensitive marker of axonal degeneration in neural development and injury

BackgroundAxon degeneration is a characteristic feature of multiple neuropathologic states and is also a mechanism of physiological neurodevelopmental pruning. The vast majority of in vivo studies looking at axon degeneration have relied on the use of classical silver degeneration stains, which have many limitations including lack of molecular specificity and incompatibility with immunolabeling methods. Because Wallerian degeneration is well known to involve cytoskeletal disassembly and because caspases are recently implicated in aspects of this process, we asked whether antibodies directed at caspase-generated neoepitopes of beta-actin and alpha-tubulin would be useful immunohistochemical markers of pathological and developmental axon degeneration.ResultsHere we demonstrate that several forms of axon degeneration involve caspase-mediated cleavage of these cytoskeletal elements and are well-visualized using this approach. We demonstrate the generation of caspase-induced neoepitopes in a) an in vitro neuronal culture model using nerve growth factor-deprivation-induced degeneration and b) an in vivo model using ethanol-induced neuronal apoptosis, and c) during normal developmental pruning and physiological turnover of neurons.ConclusionsOur findings support recent experimental data that suggests caspase-3 and caspase-6 have specific non-redundant roles in developmental pruning. Finally, these findings may have clinical utility, as these markers highlight degenerating neurites in human hypoxic-ischemic injury. Our work not only confirms a common downstream mechanism involved in axon degeneration, but also illuminates the potential utility of caspase-cleavage-neoepitope antibodies as markers of neurodegeneration.

An emerging double burden of disease: the prevalence of individuals with cardiovascular disease and cancer

Cardiovascular disease (CVD) and cancer are the two leading causes of death in the United States; at the same time, the number of survivors is increasing as therapies continue to improve. The primary objective of this study is to determine the prevalence and characteristics of individuals affected by both CVD and cancer. We conducted a prevalence study using the 2009 and 2010 national Behavioural Risk Factor Surveillance System population survey. Data from a random sample of individuals (aged 25-99 years) from all states were collected. All participants provided information regarding their CVD and cancer status. Multivariable regression identified associations between participants' characteristics and the prevalence of double disease burden. Amongst 442,964 study participants, the overall prevalence rates were 11% for CVD and 15% for cancer; 3% of participants reported being survivors of both CVD and cancer. The prevalence of CVD+cancer increased twofold by 65 years of age (odds ratio [OR] 2.4, 95% confidence interval [CI] 2.3-2.5) and doubled again at ≥75 years (OR 4.9, 95% CI 4.6-5.1) and was higher amongst men (OR 1.6, 95% CI 1.6-1.7), multiracial individuals (OR 1.8, 95% CI 1.5-2.0) and those without a high school diploma (OR 1.3, 95% CI 1.2-1.4). Amongst individuals with CVD, 25% also reported having cancer, whilst 19% of all cancer survivors reported having CVD. The prevalence of the double burden of disease increased with age; this is particularly important as the 'baby boomers' reach this high-risk age group. Future studies should explore potential common upstream or downstream mechanisms of CVD and cancer as well as public health strategies to cope with the double burden of disease.

Modulation of Neutrophil Apoptosis and the Resolution of Inflammation through β2 Integrins

Precise control of the neutrophil death program provides a balance between their defense functions and safe clearance, whereas impaired regulation of neutrophil death is thought to contribute to a wide range of inflammatory pathologies. Apoptosis is essential for neutrophil functional shutdown, removal of emigrated neutrophils, and timely resolution of inflammation. Neutrophils receive survival and pro-apoptosis cues from the inflammatory microenvironment and integrate these signals through surface receptors and common downstream mechanisms. Among these receptors are the leukocyte-specific membrane receptors β2 integrins that are best known for regulating adhesion and phagocytosis. Accumulating evidence indicate that outside-in signaling through the β2 integrin Mac-1 can generate contrasting cues in neutrophils, leading to promotion of their survival or apoptosis. Binding of Mac-1 to its ligands ICAM-1, fibrinogen, or the azurophilic granule enzyme myeloperoxidase suppresses apoptosis, whereas Mac-1-mediated phagocytosis of bacteria evokes apoptotic cell death. Mac-1 signaling is also target for the anti-inflammatory, pro-resolving mediators, including lipoxin A4, aspirin-triggered lipoxin A4, and resolvin E1. This review focuses on molecular mechanisms underlying Mac-1 regulation of neutrophil apoptosis and highlights recent advances how hierarchy of survival and pro-apoptosis signals can be harnessed to facilitate neutrophil apoptosis and the resolution of inflammation.

Pull-Push Neuromodulation of LTP and LTD Enables Bidirectional Experience-Induced Synaptic Scaling in Visual Cortex

Neuromodulatory input, acting on G protein-coupled receptors, is essential for the induction of experience-dependent cortical plasticity. Here we report that G-coupled receptors in layer II/III of visual cortex control the polarity of synaptic plasticity through a pull-push regulation of LTP and LTD. In slices, receptors coupled to Gs promote LTP while suppressing LTD; conversely, receptors coupled to Gq11 promote LTD and suppress LTP. In vivo, the selective stimulation of Gs- or Gq11-coupled receptors brings the cortex into LTP-only or LTD-only states, which allows the potentiation or depression of targeted synapses with visual stimulation. The pull-push regulation of LTP/LTD occurs via direct control of the synaptic plasticity machinery and it is independent of changes in NMDAR activation or neuronal excitability. We propose these simple rules governing the pull-push control of LTP/LTD form a general metaplasticity mechanism that may contribute to neuromodulation of plasticity in other cortical circuits.

The Molecular Pathogenesis of Hereditary Hemochromatosis

Hereditary hemochromatosis is a genetic disorder of iron overload. Over the past 15 years, significant advances have been made in understanding the molecular pathogenesis of this disorder. First, genetic studies linked this disorder to mutations in several genes, including HFE, transferrin receptor 2 ( TFR2), hepcidin ( HAMP), ferroportin ( SLC40A1), and hemojuvelin ( HFE2). Recent progress has generated significant insight into the function of these molecules in systemic iron homeostasis, and has revealed that despite the genetic and phenotypic diversity of hereditary hemochromatosis, there are common pathogenic mechanisms underlying this disease. The common downstream mechanism of iron overload in hereditary hemochromatosis is abnormal regulation of the hepcidin-ferroportin axis, leading to a failure to prevent excess iron from entering the circulation. Recent data are starting to unravel the molecular mechanisms by which iron regulates hepcidin production, and has demonstrated a key role for the bone morphogenetic protein-hemojuvelin-SMAD signaling pathway in this process. Future studies will be needed to more fully understand the molecular mechanisms of iron sensing and the roles of HFE and TFR2 in this process. Here, the authors review the current state of knowledge on the molecular pathogenesis of hereditary hemochromatosis.

Endogenous opioid peptides contribute to associative LTP in the hippocampal CA3 region

The medial and lateral perforant path projections to the hippocampal CA3 region display distinct mechanisms of long-term potentiation (LTP) induction, N-methyl-d-aspartate (NMDA) and opioid receptor dependent, respectively. However, medial and lateral perforant path projections to the CA3 region display associative LTP with coactivation, suggesting that while they differ in receptors involved in LTP induction they may share common downstream mechanisms of LTP induction. Here we address this interaction of LTP induction mechanisms by evaluating the contribution of opioid receptors to the induction of associative LTP among the medial and lateral perforant path projections to the CA3 region in vivo. Local application of the opioid receptor antagonists naloxone or Cys2-Tyr3-Orn5-Pen7-amide (CTOP) normally block induction of lateral perforant path-CA3 LTP. However, these opioid receptor antagonists failed to block associative LTP in lateral perforant path-CA3 synapses when it was induced by strong coactivation of the medial perforant pathway which displays NMDAR-dependent LTP. Thus strong activation of non-opioidergic afferents can substitute for the opioid receptor activation required for lateral perforant path LTP induction. Conversely, medial perforant path-CA3 associative LTP was blocked by opioid receptor antagonists when induced by strong coactivation of the opioidergic lateral perforant path. These data indicate endogenous opioid peptides contribute to associative LTP at coactive synapses when induced by strong coactivation of an opioidergic afferent system. These data further suggest that associative LTP induction is regulated by the receptor mechanisms of the strongly stimulated pathway. Thus, while medial and lateral perforant path synapses differ in their mechanisms of LTP induction, associative LTP at these synapses share common downstream mechanisms of induction.

Linking Klotho, Nrf2, MAP kinases and aging

Oxidative damage of DNA, proteins, lipids and other molecules is one of the oldest mechanisms proposed to explain the phenomenon of aging [1,2]. Reactive oxygen species (ROS) are generated in the mitchondria as by-products of normal aerobic respiration and in the cytosol by oxidases such as NADPH oxidase. It has been proposed that a decline in mitochondrial function leads to aging because of higher ROS production and increased damage to macromolecules [1]. This is debatable, however, because age-dependent mitochondrial DNA mutations can promote aging without causing increased ROS production [2]. High ROS levels can also regulate signaling via the stress activated-kinases, p38 and JNK. These pathways are often activated in aged tissues and contribute to the inflammation, apoptosis and senescence that is associated with old age. For example, JNK is activated in the liver of old rats and p38 is activated in the liver and brain of old rats as well as in the liver of old mice [3,4]. In the September issue of Aging, C-C Hseih et al. report that the p38 kinase is activated in Klotho -/- mice and suppressed by Klotho overexpression [5]. This is dependent on the oxidation and dissociation of Ask-1 bound thioredoxin to generate the active Ask1-signalosome which, as previously shown, is an activator of p38 [6]. Klotho overexpressing mice live longer and are characterized by their resistance to oxidative stress [7]. Previous studies by C-C Hseih et al. have shown that the ASK1-signalosome-p38 pathway is suppressed in the long-lived and stress-resistant Ames and Snell dwarf mice [6,8]. The current study demonstrates that a similar suppression of p38 signaling occurs in Klotho overexpressing cells and provides further evidence that oxidative stress, p38 activity and lifespan are closely linked. Interestingly, this study also reveals that the stress-protective transcription factor Nrf2 localizes to the nucleus in Klotho overexpressing cells. Nrf2 is activated by oxidative stress and enhances transcription of genes containing an antioxidant response element (ARE). It is also believed to play an important role in some of the protective effects caused by caloric restriction and by GH/IGF-I deficiencies [9,10]. Also, thioredoxin which is an inhibitor of Ask1, is a target of Nrf2 [11]. This implies that Nrf2 can regulate the expression of thioredoxin in Klotho mice thereby inhibiting the Ask1-signalosome-p38 pathway. Thus it is possible that the beneficial effects of Klotho are mediated, at least partially, by inactivation of p38 signaling. The premature aging phenotype of Klotho -/- mice has been attributed to the absence of Klotho mediated suppression of the Insulin/IGF-I pathway [7,12]. Klotho can activate the transcription factor FOXO, causing up-regulation of the mitochondrial MnSOD [7]. Because many of these cellular phenotypes are also promoted by reduced IGF-I signaling, the new study by C-C Hseih et al. not only confirms the major overlap between the pro-aging effects of Klotho -/- and IGF-I but also adds new players that can help identify common downstream anti-aging mechanisms.