Mice lacking nerve growth factor display perinatal loss of sensory and sympathetic neurons yet develop basal forebrain cholinergic neurons

P75 neurotrophin receptor is a regulatory factor in sudden cardiac death with myocardial infarction

Sudden cardiac death (SCD) is a major cause of morbidity and mortality in patients with coronary artery diseases and myocardial infarction (MI). Sympathetic stimulation and sympathetic neural remodeling are important in the generation of SCD in diseased heart. The balance of nerve growth factor (NGF) and semaphoring 3A determines the sympathetic innervation patterning. Recently studies showed that P75 neurotrophin receptor (P75 NTR) is the main receptor for NGF mediates sympathetic hyperinnervation in the heart, and also interacts with semaphoring 3A. Sympathetic axons lacking P75 NTR are more sensitive to semaphoring 3A in vitro than control neurons, resulting in decreased sympathetic innervation in the left ventricular subendocardium. P75 NTR(-/-) mice had increased sympathetic heterogeneity and more spontaneous ventricular arrhythmias. Based on current studies, we present a hypothesis that P75 NTR plays an important regulatory role in sudden cardiac after myocardial infarction and hope to find new therapeutic target for SCD.

Specification of neural crest into sensory neuron and melanocyte lineages

Elucidating the mechanisms by which multipotent cells differentiate into distinct lineages is a common theme underlying developmental biology investigations. Progress has been made in understanding some of the essential factors and pathways involved in the specification of different lineages from the neural crest. These include gene regulatory networks involving transcription factor hierarchies and input from signaling pathways mediated from environmental cues. In this review, we examine the mechanisms for two lineages that are derived from the neural crest, peripheral sensory neurons and melanocytes. Insights into the specification of these cell types may reveal common themes in the specification processes that occur throughout development.

IRS2 signalling is required for the development of a subset of sensory spinal neurons

Insulin and insulin-like growth factor-I play important roles in the development and maintenance of neurons and glial cells of the nervous system. Both factors activate tyrosine kinase receptors, which signal through adapter proteins of the insulin receptor substrate (IRS) family. Although insulin and insulin-like growth factor-I receptors are expressed in dorsal root ganglia (DRG), the function of IRS-mediated signalling in these structures has not been studied. Here we address the role of IRS2-mediated signalling in murine DRG. Studies in cultured DRG neurons from different embryonic stages indicated that a subset of nerve growth factor-responsive neurons is also dependent on insulin for survival at very early time points. Consistent with this, increased apoptosis during gangliogenesis resulted in a partial loss of trkA-positive neurons in DRG of Irs2 mutant embryos. Analyses in adult Irs2(-/-) mice revealed that unmyelinated fibre afferents, which express calcitonin gene-related peptide/substance P and isolectin B4, as well as some myelinated afferents to the skin were affected by the mutation. The diminished innervation of glabrous skin in adult Irs2(-/-) mice correlated with longer paw withdrawal latencies in the hot-plate assay. Collectively, these findings indicate that IRS2 signalling is required for the proper development of spinal sensory neurons involved in the perception of pain.

TrkA gene ablation in basal forebrain results in dysfunction of the cholinergic circuitry

Dysfunction of basal forebrain cholinergic neurons (BFCNs) is an early pathological hallmark of Alzheimer's disease (AD). Numerous studies have indicated that nerve growth factor (NGF) supports survival and phenotypic differentiation of BFCNs. Consistent with a potential link to AD pathogenesis, TrkA, a NGF receptor, is expressed in cholinergic forebrain neuronal populations including those in BF and striatum, and is markedly reduced in individuals with mild cognitive impairment (MCI) without dementia and early-stage AD. To investigate the role of TrkA in the development, connectivity, and function of the BF cholinergic system and its contribution to AD pathology, we have generated a forebrain-specific conditional TrkA knock-out mouse line. Our findings show a key role for TrkA signaling in establishing the BF cholinergic circuitry through the ERK pathway, and demonstrate that the normal developmental increase of choline acetyltransferase expression becomes critically dependent on TrkA signaling before neuronal connections are established. Moreover, the anatomical and physiological deficits caused by lack of TrkA signaling in BFCNs have selective impact on cognitive activity. These data demonstrate that TrkA loss results in cholinergic BF dysfunction and cognitive decline that is reminiscent of MCI and early AD.

Midkine in the pathology of cancer, neural disease, and inflammation

Midkine (MK) is a heparin-binding growth factor involved in various cellular processes such as cellular proliferation, survival, and migration. In addition to these typical growth factor activities, MK exhibits several other activities related to fibrinolysis, blood pressure, host defense and other processes. Many cell-surface receptors have been identified to account for the multiple biological activities of MK. The expression of MK is frequently upregulated in many types of human carcinoma. Moreover, blood MK levels are closely correlated with patient outcome. Knockdown and blockade of MK suppress tumorigenesis and tumor development. Thus, MK serves as a tumor marker and a molecular target for cancer therapy. Furthermore, there is growing evidence that MK plays pivotal roles in neural and inflammatory diseases. Understanding of the mechanisms of action of MK is expected to create new therapeutic options for several human diseases.

Development, maturation, and transdifferentiation of cardiac sympathetic nerves

The heart is electrically and mechanically controlled as a syncytium by the autonomic nervous system. The cardiac nervous system comprises the sympathetic, parasympathetic, and sensory nervous systems that together regulate heart function on demand. Sympathetic electric activation was initially considered the main regulator of cardiac function; however, modern molecular biotechnological approaches have provided a new dimension to our understanding of the mechanisms controlling the cardiac nervous system. The heart is extensively innervated, although the innervation density is not uniform within the heart, being high in the subepicardium and the special conduction system. We and others showed previously that the balance between neural chemoattractants and chemorepellents determine cardiac nervous development, with both factors expressed in heart. Nerve growth factor is a potent chemoattractant synthesized by cardiomyocytes, whereas Sema3a is a neural chemorepellent expressed specifically in the subendocardium. Disruption of this well-organized molecular balance and innervation density can induce sudden cardiac death due to lethal arrhythmias. In diseased hearts, various causes and mechanisms underlie cardiac sympathetic abnormalities, although their detailed pathology and significance remain contentious. We reported that cardiac sympathetic rejuvenation occurs in cardiac hypertrophy and, moreover, interleukin-6 cytokines secreted from the failing myocardium induce cholinergic transdifferentiation of the cardiac sympathetic system via a gp130 signaling pathway, affecting cardiac performance and prognosis. In this review, we summarize the molecular mechanisms involved in sympathetic development, maturation, and transdifferentiation, and propose their investigation as new therapeutic targets for heart disease.

NGF, brain and behavioral plasticity

Nerve Growth Factor (NGF) was initially studied for its role as a key player in the regulation of peripheral innervations. However, the successive finding of its release in the bloodstream of male mice following aggressive encounters and its presence in the central nervous system led to the hypothesis that variations in brain NGF levels, caused by psychosocial stressor, and the related alterations in emotionality, could be functional to the development of proper strategies to cope with the stressor itself and thus to survive. Years later this vision is still relevant, and the body of evidence on the role of NGF has been strengthened and expanded from trophic factor playing a role in brain growth and differentiation to a much more complex messenger, involved in psychoneuroendocrine plasticity.

Steady and fluctuant methods of inhibition of acetylcholinesterase differentially regulate neurotrophic factors in the hippocampus of juvenile mice

The present study was designed to evaluate the effects of steady and fluctuant inhibition of acetylcholinesterase (AChE) activity on neurotrophic factors in the hippocampus of juvenile mice. Steady inhibition of AChE activity was induced by an intramuscular injection of huperizine A (HupA) sustained-release microspheres. Fluctuant inhibition of AChE activity was induced by an intragastric administration of HupA tablets. Six days after cessation of steady AChE inhibition, there was a significant increase in the levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF). In contrast, fluctuant AChE inhibition had no effect on BDNF and NGF levels. Additionally, neither steady nor fluctuant inhibition of AChE activity altered the choline acetyltransferase activity or spatial learning in juvenile mice. These findings indicate that steady and fluctuant methods of inhibition of AChE have different effects on the levels of BDNF and NGF in the hippocampus. In addition, the effects of AChE inhibitors may not improve learning in normal juvenile animals.

Mechanisms of disease in hereditary sensory and autonomic neuropathies

Hereditary sensory and autonomic neuropathies (HSANs) are a clinically and genetically heterogeneous group of disorders of the PNS. Progressive degeneration, predominantly of sensory and autonomic neurons, is the main pathological feature in patients with HSAN, and causes prominent sensory loss and ulcerative mutilations in combination with variable autonomic and motor disturbances. Advances in molecular genetics have enabled identification of disease-causing mutations in 12 genes, and studies on the functional effects of these mutations are underway. Although some of the affected proteins--such as nerve growth factor and its receptor--have obvious nerve-specific roles, others are ubiquitously expressed proteins that are involved in sphingolipid metabolism, vesicular transport, transcription regulation and structural integrity. An important challenge in the future will be to understand the common molecular pathways that result in HSANs. Unraveling the mechanisms that underlie sensory and autonomic neurodegeneration could assist in identifying targets for future therapeutic strategies in patients with HSAN. This Review highlights key advances in the understanding of HSANs, including insights into the molecular mechanisms of disease, derived from genetic studies of patients with these disorders.

DLK induces developmental neuronal degeneration via selective regulation of proapoptotic JNK activity

DLK is part of a specialized JNK signaling complex in axons that promotes apoptosis via c-Jun but axon degeneration via distinct JNK substrates.

The c-Jun N-terminal kinase (JNK) signaling pathway is essential for neuronal degeneration in multiple contexts but also regulates neuronal homeostasis. It remains unclear how neurons are able to dissociate proapoptotic JNK signaling from physiological JNK activity. In this paper, we show that the mixed lineage kinase dual leucine zipper kinase (DLK) selectively regulates the JNK-based stress response pathway to mediate axon degeneration and neuronal apoptosis without influencing other aspects of JNK signaling. This specificity is dependent on interaction of DLK with the scaffolding protein JIP3 to form a specialized JNK signaling complex. Local activation of DLK-based signaling in the axon results in phosphorylation of c-Jun and apoptosis after redistribution of JNK to the cell body. In contrast, regulation of axon degeneration by DLK is c-Jun independent and mediated by distinct JNK substrates. DLK-null mice displayed reduced apoptosis in multiple neuronal populations during development, demonstrating that prodegenerative DLK signaling is required in vivo.

Megakaryocyte development is normal in mice with targeted disruption of Tescalcin

BACKGROUND

Tescalcin is an EF-hand calcium-binding protein that interacts with the Na+/H+ exchanger 1 (NHE1). Levay and Slepak recently proposed a role for tescalcin in megakaryopoiesis that was independent of NHE1 activity. Their studies using K562 and HEL cell lines, and human CD34+ hematopoietic stem cells suggested an essential role for tescalcin in megakaryocyte differentiation.

OBJECTIVE

To study the role of tescalcin in megakaryocyte development using a murine model of megakaryopoiesis.

METHODS

We generated a mouse with targeted disruption of tescalcin and investigated megakaryocyte development.

RESULTS

Tescalcin-deficient mice had a normal number of megakaryocytes and platelets. The morphology, polyploidization profile, and expression of Fli-1 in bone marrow-derived megakaryocytes were also normal.

CONCLUSION

Tescalcin does not appear to be necessary for normal megakaryocyte development.

Axonal neuropathy-associated TRPV4 regulates neurotrophic factor-derived axonal growth

Spinal muscular atrophy and hereditary motor and sensory neuropathies are characterized by muscle weakness and atrophy caused by the degenerations of peripheral motor and sensory nerves. Recent advances in genetics have resulted in the identification of missense mutations in TRPV4 in patients with these hereditary neuropathies. Neurodegeneration caused by Ca(2+) overload due to the gain-of-function mutation of TRPV4 was suggested as the molecular mechanism for the neuropathies. Despite the importance of TRPV4 mutations in causing neuropathies, the precise role of TRPV4 in the sensory/motor neurons is unknown. Here, we report that TRPV4 mediates neurotrophic factor-derived neuritogenesis in developing peripheral neurons. TRPV4 was found to be highly expressed in sensory and spinal motor neurons in early development as well as in the adult, and the overexpression or chemical activation of TRPV4 was found to promote neuritogenesis in sensory neurons as well as PC12 cells, whereas its knockdown and pharmacologic inhibition had the opposite effect. More importantly, nerve growth factor or cAMP treatment up-regulated the expression of phospholipase A(2) and TRPV4. Neurotrophic factor-derived neuritogenesis appears to be regulated by the phospholipase A(2)-mediated TRPV4 pathway. These findings show that TRPV4 mediates neurotrophic factor-induced neuritogenesis in developing peripheral nerves. Because neurotrophic factors are essential for the maintenance of peripheral nerves, these findings suggest that aberrant TRPV4 activity may lead to some types of pathology of sensory and motor nerves.

Kidins220/ARMS mediates the integration of the neurotrophin and VEGF pathways in the vascular and nervous systems

Signaling downstream of receptor tyrosine kinases controls cell differentiation and survival. How signals from different receptors are integrated is, however, still poorly understood. In this work, we have identified Kidins220 (Kinase D interacting substrate of 220 kDa)/ARMS (Ankyrin repeat-rich membrane spanning) as a main player in the modulation of neurotrophin and vascular endothelial growth factor (VEGF) signaling in vivo, and a primary determinant for neuronal and cardiovascular development. Kidins220(-/-) embryos die at late stages of gestation, and show extensive cell death in the central and peripheral nervous systems. Primary neurons from Kidins220(-/-) mice exhibit reduced responsiveness to brain-derived neurotrophic factor, in terms of activation of mitogen-activated protein kinase signaling, neurite outgrowth and potentiation of excitatory postsynaptic currents. In addition, mice lacking Kidins220 display striking cardiovascular abnormalities, possibly due to impaired VEGF signaling. In support of this hypothesis, we demonstrate that Kidins220 constitutively interacts with VEGFR2. These findings, together with the data presented in the accompanying paper, indicate that Kidins220 mediates the integration of several growth factor receptor pathways during development, and mediates the activation of distinct downstream cascades according to the location and timing of stimulation.

Altered norepinephrine content and ventricular function in p75NTR-/- mice after myocardial infarction

Cardiac sympathetic neurons stimulate heart rate and the force of contraction through release of norepinephrine. Nerve growth factor modulates sympathetic transmission through activation of TrkA and p75NTR. Nerve growth factor plays an important role in post-infarct sympathetic remodeling. We used mice lacking p75NTR to examine the effect of altered nerve growth factor signaling on sympathetic neuropeptide expression, cardiac norepinephrine, and ventricular function after myocardial infarction. Infarct size was similar in wildtype and p75NTR-/- mice after ischemia-reperfusion surgery. Likewise, mRNAs encoding vasoactive intestinal peptide, galanin, and pituitary adenylate cyclase activating peptides were identical in wildtype and p75NTR-/- cardiac sympathetic neurons, as was expression of the TrkA neurotrophin receptor. Norepinephrine content was elevated in the base of the p75NTR-/- ventricle compared to wildtype, but levels were identical below the site of occlusion. Left ventricular pressure, dP/dt(MAX), and dP/dt(MIN) were measured under isoflurane anesthesia 3 and 7 days after surgery. Ventricular pressure decreased significantly 3 days after infarction, and deficits in dP/dt(MAX) were revealed by stimulating beta receptors with dobutamine and release of endogenous norepinephrine with tyramine. dP/dt(MIN) was not altered by genotype or surgical group. Few differences were observed between genotypes 3 days after surgery, in contrast to low pressure and dP/dt(MAX) previously reported in control p75NTR-/- animals. Seven days after surgery ventricular pressure and dP/dt(MAX) were significantly lower in p75NTR-/- hearts compared to WT hearts. Thus, the lack of p75NTR did not enhance cardiac function after myocardial infarction.

Semaphorin3A regulates neuronal polarization by suppressing axon formation and promoting dendrite growth

Semaphorin 3A (Sema3A) is a secreted factor known to guide axon/dendrite growth and neuronal migration. We found that it also acts as a polarizing factor for axon/dendrite development in cultured hippocampal neurons. Exposure of the undifferentiated neurite to localized Sema3A suppressed its differentiation into axon and promoted dendrite formation, resulting in axon formation away from the Sema3A source, and bath application of Sema3A to polarized neurons promoted dendrite growth but suppressed axon growth. Fluorescence resonance energy transfer (FRET) imaging showed that Sema3A elevated the cGMP but reduced cAMP and protein kinase A (PKA) activity, and its axon suppression is attributed to the downregulation of PKA-dependent phosphorylation of axon determinants LKB1 and GSK-3β. Downregulating Sema3A signaling in rat embryonic cortical progenitors via in utero electroporation of siRNAs against the Sema3A receptor neuropilin-1 also resulted in polarization defects in vivo. Thus, Sema3A regulates the earliest step of neuronal morphogenesis by polarizing axon/dendrite formation.

Predictive validity of pharmacologic interventions in animal models of neuropathic pain

Introduction

The pathophysiologic and neurochemical characteristics of neuropathic pain must be considered in the search for new treatment targets. Breakthroughs in the understanding of the structural and biochemical changes in neuropathy have opened up possibilities to explore new treatment paradigms. However, long term sequels from the damage are still difficult to treat.

Aim of the study

To examine the validity of pharmacological treatments in humans and animals for neuropathic pain.

Method

An overview from the literature and own experiences of pharmacological treatments employed to interfere in pain behavior in different animal models was performed.

Results

The treatment principles tested in animal models of neuropathic pain may have predictive validity for treatment of human neuropathies. Opioids, neurotransmitter blockers, drugs interfering with the prostaglandin syntheses as well as voltage gated sodium channel blockers and calcium channel blockers are treatment principles having efficacy and similar potency in humans and in animals. Alternative targets have been identified and have shown promising results in the validated animal models. Modulators of the glutamate system with an increased expression of glutamate re-uptake transporters, inhibition of pain promoters as nitric oxide and prostaglandins need further exploration. Modulation of cytokines and neurotrophins in neuropathic pain implies new targets for study. Further, a combination of different analgesic treatments may as well improve management of neuropathic pain, changing the benefit/risk ratio.

Implications

Not surprisingly most pharmacologic principles that are tested in animal models of neuropathic pain are also found to be active in humans. Whereas many candidate drugs that were promising in animal models of neuropathic pain turned out not to be effective or too toxic in humans, animal models for neuropathic pain are still the best tools available to learn more about mechanisms of neuropathic pain. Better understanding of pathogenesis is the most hopeful approach to improve treatment of neuropathic pain.

Egr3 dependent sympathetic target tissue innervation in the absence of neuron death

Nerve Growth Factor (NGF) is a target tissue derived neurotrophin required for normal sympathetic neuron survival and target tissue innervation. NGF signaling regulates gene expression in sympathetic neurons, which in turn mediates critical aspects of neuron survival, axon extension and terminal axon branching during sympathetic nervous system (SNS) development. Egr3 is a transcription factor regulated by NGF signaling in sympathetic neurons that is essential for normal SNS development. Germline Egr3-deficient mice have physiologic dysautonomia characterized by apoptotic sympathetic neuron death and abnormal innervation to many target tissues. The extent to which sympathetic innervation abnormalities in the absence of Egr3 is caused by altered innervation or by neuron death during development is unknown. Using Bax-deficient mice to abrogate apoptotic sympathetic neuron death in vivo, we show that Egr3 has an essential role in target tissue innervation in the absence of neuron death. Sympathetic target tissue innervation is abnormal in many target tissues in the absence of neuron death, and like NGF, Egr3 also appears to effect target tissue innervation heterogeneously. In some tissues, such as heart, spleen, bowel, kidney, pineal gland and the eye, Egr3 is essential for normal innervation, whereas in other tissues such as lung, stomach, pancreas and liver, Egr3 appears to have little role in innervation. Moreover, in salivary glands and heart, two tissues where Egr3 has an essential role in sympathetic innervation, NGF and NT-3 are expressed normally in the absence of Egr3 indicating that abnormal target tissue innervation is not due to deregulation of these neurotrophins in target tissues. Taken together, these results clearly demonstrate a role for Egr3 in mediating sympathetic target tissue innervation that is independent of neuron survival or neurotrophin deregulation.

The controlled generation of functional basal forebrain cholinergic neurons from human embryonic stem cells

An early substantial loss of basal forebrain cholinergic neurons (BFCN) is a constant feature of Alzheimer's disease and is associated with deficits in spatial learning and memory. The ability to selectively control the differentiation of human embryonic stem cells (hESCs) into BFCN would be a significant step toward a cell replacement therapy. We demonstrate here a method for the derivation of a predominantly pure population of BFCN from hESC cells using diffusible ligands present in the forebrain at developmentally relevant time periods. Overexpression of two relevant human transcription factors in hESC-derived neural progenitors also generates BFCN. These neurons express only those markers characteristic of BFCN, generate action potentials, and form functional cholinergic synapses in murine hippocampal slice cultures. siRNA-mediated knockdown of the transcription factors blocks BFCN generation by the diffusible ligands, clearly demonstrating the factors both necessary and sufficient for the controlled derivation of this neuronal population. The ability to selectively control the differentiation of hESCs into BFCN is a significant step both for understanding mechanisms regulating BFCN lineage commitment and for the development of both cell transplant-mediated therapeutic interventions for Alzheimer's disease and high-throughput screening for agents that promote BFCN survival.

Role of LKB1-SAD/MARK pathway in neuronal polarization

The formation of axon/dendrite polarity is critical for the neuron to perform its signaling function in the brain. Recent advance in our understanding of cellular and molecular mechanisms underlying the development and maintenance of neuronal polarity has been greatly facilitated by the use of the culture system of dissociated hippocampal neurons. Among many polarization-related proteins, we here focus on the mammalian LKB1, the counterpart of the C. elegans Par-4, which is an upstream regulator among six Par (partitioning-defective) genes that act as master regulators of cell polarity in different cell types across evolutionary distant species. Recent studies have identified LKB1 and its downstream targets SAD/MARK kinases (mammalian homologs of Par-1) as key regulators of neuronal polarization and axon development in cultured neurons and in developing cortical neurons in vivo. We will review the properties of and interactions among proteins in this LKB1-SAD/MARK pathway, drawing upon information obtained from both neuronal and non-neuronal systems. Due to central role of the protein kinase A-dependent phosphorylation of LKB1 in the activation of this pathway, we will review recent findings on how cAMP and cGMP signaling may serve as antagonistic second messengers for axon/dendrite development, and how these cyclic nucleotides may mediate the action of extracellular polarizing factors by modulating the activity of the LKB1-SAD/MARK pathway.

Emerging drugs for osteoarthritis

INTRODUCTION

Osteoarthritis (OA), the most prevalent form of joint disease, affects as much as 13% of the world's population. In the USA, it is the leading cause of disability in people over age 65 and is characterized by progressive cartilage loss, bone remodeling, osteophyte formation and synovial inflammation with resultant joint pain and disability. There are no treatments marketed for structural disease modification; current treatments mainly target symptoms, with > 75% of patients reporting need for additional symptomatic treatment.

AREAS COVERED

Drugs in later development (Phase II - III) for OA pain and joint structural degeneration are reviewed. Topics that are not covered in this article are procedural-based (e.g., arthrocentesis, physical therapy), behavioral-based (e.g., weight loss, pain coping techniques) or device-based (e.g., knee braces, surgical implants) treatments.

EXPERT OPINION

More in-depth understanding of the pathophysiology of the disease, as well as elucidation of the link between clinical symptomatology and structural changes in the joint will likely lead to the development of novel target classes with promising efficacy in the future. Efficacy notwithstanding, there remain significant hurdles to overcome in clinical development of these therapeutics, inherent in the progression pattern of the disease as well as challenges with readouts for both pain and structure modification trials.

New molecules for the treatment of pain

PURPOSE OF REVIEW

To inform on preclinical and early clinical advances in the effort to identify novel classes of analgesic drugs.

RECENT FINDINGS

Human genetic and animal preclinical studies have identified several mechanisms that appear to make important contributions to abnormal pain states. From human genetics, a small number of patients with mutations in the genes encoding nerve growth factor/TrkA signaling and in a particular sodium channel subunit (SCN9a, encoding Nav1.7) show congenital analgesia with limited other effects. There are, therefore, considerable hopes that pharmacological manipulation of these systems in chronic pain patients might be an effective analgesic strategy. A substantial body of preclinical work has focussed on interactions between the immune and the nervous system and this has led to the identification of a number of novel putative inflammatory mediators and receptors, which are being explored as potential analgesic targets. A recent preclinical effort has studied intracellular signaling cascades recruited in the transition from acute to chronic pain states - the analgesic opportunities on offer here are being pursued in early clinical trials.

SUMMARY

Existing analgesic drugs are small in number, limited in efficacy and associated with significant side-effects. There is, therefore, a need for new pain medications. In the last decade or so, clinical and preclinical research have progressed rapidly and this work has identified multiple plausible drug targets, which are currently being evaluated. We review here the rationale of some of the most promising mechanisms and report on progress in drug development.

Paracrine control of vascular innervation in health and disease

Proper vascular regulation is of paramount importance for the control of blood flow to tissues. In particular, the regulation of peripheral resistance arteries is essential for several physiological processes, including control of blood pressure, thermoregulation and increase of blood flow to central nervous system and heart under stress conditions such as hypoxia. Arterial tone is regulated by the periarterial autonomic nervous plexus, as well as by endothelium-dependent, myogenic and humoral mechanisms. Underscoring the importance of proper vascular regulation, defects in these processes can lead to diseases such as hypertension, orthostatic hypotension, Raynaud's phenomenon, defective thermoregulation, hand-foot syndrome, migraine and congestive heart failure. Here, we review the molecular mechanisms controlling the development of the periarterial nerve plexus, retrograde and localized signalling at neuro-effector junctions, the molecular and cellular mechanisms of vascular regulation and adult plasticity and maintenance of periarterial innervation. We particularly highlight a newly discovered role for vascular endothelial growth factor in the structural and functional maintenance of arterial neuro-effector junctions. Finally, we discuss how defects in neuronal vascular regulation can lead to disease.

Isoform-specific dephosphorylation of dynamin1 by calcineurin couples neurotrophin receptor endocytosis to axonal growth

Endocytic events are critical for neuronal survival in response to target-derived neurotrophic cues, but whether local axon growth is mediated by endocytosis-dependent signaling mechanisms remains unclear. Here, we report that Nerve Growth Factor (NGF) promotes endocytosis of its TrkA receptors and axon growth by calcineurin-mediated dephosphorylation of the endocytic GTPase dynamin1. Conditional deletion of calcineurin in sympathetic neurons disrupts NGF-dependent innervation of peripheral target tissues. Calcineurin signaling is required locally in sympathetic axons to support NGF-mediated growth in a manner independent of transcription. We show that calcineurin associates with dynamin1 via a PxIxIT interaction motif found only in specific dynamin1 splice variants. PxIxIT-containing dynamin1 isoforms colocalize with surface TrkA receptors, and their phosphoregulation is selectively required for NGF-dependent TrkA internalization and axon growth in sympathetic neurons. Thus, NGF-dependent phosphoregulation of dynamin1 is a critical event coordinating neurotrophin receptor endocytosis and axonal growth.

Antagonism of nerve growth factor-TrkA signaling and the relief of pain

Nerve growth factor (NGF) was originally discovered as a neurotrophic factor essential for the survival of sensory and sympathetic neurons during development. However, in the adult NGF has been found to play an important role in nociceptor sensitization after tissue injury. The authors outline mechanisms by which NGF activation of its cognate receptor, tropomyosin-related kinase A receptor, regulates a host of ion channels, receptors, and signaling molecules to enhance acute and chronic pain. The authors also document that peripherally restricted antagonism of NGF-tropomyosin-related kinase A receptor signaling is effective for controlling human pain while appearing to maintain normal nociceptor function. Understanding whether there are any unexpected adverse events and how humans may change their behavior and use of the injured/degenerating tissue after significant pain relief without sedation will be required to fully appreciate the patient populations that may benefit from these therapies targeting NGF.

Motor neuron trophic factors: therapeutic use in ALS?

The modest effects of neurotrophic factor (NTF) treatment on lifespan in both animal models and clinical studies of Amyotropic Lateral Sclerosis (ALS) may result from any one or combination of the four following explanations: 1.) NTFs block cell death in some physiological contexts but not in ALS; 2.) NTFs do not rescue motoneurons (MNs) from death in any physiological context; 3.) NTFs block cell death in ALS but to no avail; and 4.) NTFs are physiologically effective but limited by pharmacokinetic constraints. The object of this review is to critically evaluate the role of both NTFs and the intracellular cell death pathway itself in regulating the survival of spinal and cranial (lower) MNs during development, after injury and in response to disease. Because the role of molecules mediating MN survival has been most clearly resolved by the in vivo analysis of genetically engineered mice, this review will focus on studies of such mice expressing reporter, null or other mutant alleles of NTFs, NTF receptors, cell death or ALS-associated genes.

Classification of cell signalling in tissue development

The traditional classification of signalling in biological systems is insufficient and outdated and novel efforts must take into account advances in systems theory, information theory and linguistics. We present some of the classification systems currently used both within and outside of the biological field and discuss some specific aspects of the nature of signalling in tissue development. The analytical methods used in understanding non-biological networks provide a valuable vocabulary, which requires integration and a system of classification to further facilitate development.

Nrf2 regulates NGF mRNA induction by carnosic acid in T98G glioblastoma cells and normal human astrocytes

Nerve growth factor (NGF) is a neurotrophic factor that plays an important role in neuronal cell development and survival. Carnosic acid (CA), a hydrophobic constituent of the herb rosemary, induces NGF production in human T98G glioblastoma cells, but the mechanism through which it works remains unknown. In the present study, we found a redox-sensitive transcription factor, Nrf2, which coordinates the expression of cytoprotective phase 2 genes, also participates in CA-inducible NGF expression. In T98G cells, CA caused NGF gene induction in a dose- and time-dependent manner without altering NGF mRNA stability. Simultaneously, CA increased Nrf2 nuclear accumulation and activated expression of prototypical Nrf2 target genes such as haem oxygenase 1 (HO-1) and thioredoxin reductase 1 (TXNRD1). Knockdown of endogenous Nrf2 by Nrf2-specific siRNA significantly reduced constitutive and CA-inducible NGF gene expression. In addition, NGF gene expression was enhanced by knockdown of Keap1, an Nrf2 inhibitor, in the absence of CA. Furthermore, CA induced NGF expression in normal human astrocytes in an Nrf2-dependent manner. These results highlight a role of Nrf2 in NGF gene expression in astroglial cells.

Sox11 regulates survival and axonal growth of embryonic sensory neurons

Sensory neurons transduce various stimuli including temperature, pain, and touch from the periphery to the central nervous system. Sensory neuron development is governed by a combination of extracellular cues and specific gene expression. We demonstrated that the transcription factor Sox11 was highly expressed in the developing sensory neurons. To test the function of Sox11, we used a knockin mouse model where the entire coding region of Sox11 was replaced by a LacZ reporter. The ablation of Sox11 caused severe reduction in sensory neuron survival in the trigeminal and dorsal root ganglia, although it did not affect migration of neural crest cells or acquisition of major sensory neuron subtypes. We further demonstrated that ablating Sox11 caused an arrest of axonal outgrowth in vivo and in vitro. This defect could not be fully rescued by blocking cell death. Our data suggest that Sox11 is a key regulator of sensory neuron development.

Neurosteroid dehydroepiandrosterone interacts with nerve growth factor (NGF) receptors, preventing neuronal apoptosis

The neurosteroid dehydroepiandrosterone (DHEA), produced by neurons and glia, affects multiple processes in the brain, including neuronal survival and neurogenesis during development and in aging. We provide evidence that DHEA interacts with pro-survival TrkA and pro-death p75^NTR membrane receptors of neurotrophin nerve growth factor (NGF), acting as a neurotrophic factor: (1) the anti-apoptotic effects of DHEA were reversed by siRNA against TrkA or by a specific TrkA inhibitor; (2) [³H]-DHEA binding assays showed that it bound to membranes isolated from HEK293 cells transfected with the cDNAs of TrkA and p75^NTR receptors (K_D: 7.4±1.75 nM and 5.6±0.55 nM, respectively); (3) immobilized DHEA pulled down recombinant and naturally expressed TrkA and p75^NTR receptors; (4) DHEA induced TrkA phosphorylation and NGF receptor-mediated signaling; Shc, Akt, and ERK1/2 kinases down-stream to TrkA receptors and TRAF6, RIP2, and RhoGDI interactors of p75^NTR receptors; and (5) DHEA rescued from apoptosis TrkA receptor positive sensory neurons of dorsal root ganglia in NGF null embryos and compensated NGF in rescuing from apoptosis NGF receptor positive sympathetic neurons of embryonic superior cervical ganglia. Phylogenetic findings on the evolution of neurotrophins, their receptors, and CYP17, the enzyme responsible for DHEA biosynthesis, combined with our data support the hypothesis that DHEA served as a phylogenetically ancient neurotrophic factor.

Dehydroepiandrosterone (DHEA) and its sulphate ester are the most abundant steroid hormones in humans, and DHEA was described as the first neurosteroid produced in the brain. DHEA is known to participate in multiple events in the brain, including neuronal survival and neurogenesis. However, to date no specific cellular receptor has been described for this important neurosteroid. In this study, we provide evidence that DHEA exerts its neurotrophic effects by directly interacting with the TrkA and p75^NTR membrane receptors of nerve growth factor (NGF), and efficiently activates their downstream signaling pathways. This activation prevents the apoptotic loss of NGF receptor positive sensory and sympathetic neurons. The interaction of DHEA with NGF receptors may also offer a mechanistic explanation for the multiple actions of DHEA in other peripheral biological systems expressing NGF receptors, such as the immune, reproductive, and cardiovascular systems.

Glial cell line-derived neurotrophic factor (GDNF) enhances sympathetic neurite growth in rat hearts at early developmental stages

Molecular signaling of sympathetic innervation of myocardium is an unresolved issue. The purpose of this study was to investigate the effect of neurotrophic factors on sympathetic neurite growth towards cardiomyocytes. Cardiomyocytes (CMs) and sympathetic neurons (SNs) were isolated from neonatal rat hearts and superior cervical ganglia, and were co-cultured, either in a random or localized way. Neurite growth from SNs toward CMs was assessed by immunohistochemistry for neurofilament M and α-actinin in response to neurotrophic factors-nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), ciliary neurotrophic factor (CNTF) and a chemical repellent, semaphorin 3A. As a result, GDNF as well as NGF and BDNF stimulated neurite growth. GDNF enhanced neurite outgrowth even under the NGF-depleted culture condition, excluding an indirect effect of GDNF via NGF. Quantification of mRNA and protein by real-time PCR and immunohistochemistry at different developmental stages revealed that GDNF is abundantly expressed in the hearts of embryos and neonates, but not in adult hearts. GDNF plays an important role in inducing cardiac sympathetic innervation at the early developmental stages. A possible role in (re)innervation of injured or transplanted or cultured and transplanted myocardium may deserve investigation.

Neuroprotection signaling pathway of nerve growth factor and brain-derived neurotrophic factor against staurosporine induced apoptosis in hippocampal H19-7/IGF-IR [corrected]

Neurotrophins protect neurons against excitotoxicity; however the signaling mechanisms for this protection remain to be fully elucidated. Here we report that activation of the phosphatidyl inositol 3 kinase (PI3K)/Akt pathway is critical for protection of hippocampal cells from staurosporine (STS) induced apoptosis, characterized by nuclear condensation and activation of the caspase cascade. Both nerve growth factor (NGF) and brain-derived growth factor (BDNF) prevent STS-induced apoptotic morphology and caspase-3 activity by upregulating phosphorylation of the tropomyosin receptor kinase (Trk) receptor. Inhibition of Trk receptor by K252a altered the neuroprotective effect of both NGF and BDNF whereas inhibition of the p75 neurotrophin receptor (p75NTR) had no effect. Impairment of the PI3K/Akt pathway or overexpression of dominant negative (DN)-Akt abolished the protective effect of both neurotrophins, while active Akt prevented cell death. Moreover, knockdown of Akt by si-RNA was able to block the survival effect of both NGF and BDNF. Thus, the survival action of NGF and BDNF against STS-induced neurotoxicity was mediated by the activation of PI3K/Akt signaling through the Trk receptor.

Accumulation of nerve growth factor and its receptors in the uterus and dorsal root ganglia in a mouse model of adenomyosis

BACKGROUND

Adenomyosis is a common gynecological disease, which is accompanied by a series of immunological and neuroendocrinological changes. Nerve growth factor (NGF) plays a critical role in producing pain, neural plasticity, immunocyte aggregation and release of inflammatory factors. This study aimed to investigate the expression of NGF and its two receptors in uteri and dorsal root ganglia (DRG) in an adenomyosis mouse model, as well as their relationship with the severity of adenomyosis.

METHODS

Forty newborn ICR mice were randomly divided into the adenomyosis model group and control group (n = 20 in each group). Mice in the adenomyosis model group were orally dosed with 2.7 μmol/kg tamoxifen on days 2-5 after birth. Experiments were conducted to identify the expression of NGF- beta and its receptors, tyrosine kinase receptor (trkA) and p75 neurotrophin receptor (p75NTR), in the uterus and DRG in four age groups (90+/-5 d, 140+/-5 d, 190+/-5 d and 240+/-5 d; n = 5 mice in each group) by western bolt, immunochemistry and real time reverse transcription-polymerase chain reaction.

RESULTS

Adenomyosis, which became more serious as age increased, was successfully induced in dosed ICR mice. NGF-beta, trkA and p75NTR protein levels in the uterus and trkA mRNA levels in DRG were higher in the older aged adenomyosis model group than those in controls (190+/-5 d and 240+/-5 d groups, P < 0.05). The expression of NGF-beta and its receptors in the uterus increased gradually as age increased for adenomyosis mice (190+/-5 d and 240+/-5 d, P < 0.05, compared with 90+/-5 d) but it showed little change in control mice. The mRNA level of trkA in DRG also increased as age increased in the adenomyosis model group (190+/-5 d and 240+/-5 d, P < 0.05, compared with 90+/-5 d) but was unchanged in controls. The mRNA level of p75NTR in DRG was not different between the adenomyosis and control groups and was stable from young to old mice.

CONCLUSIONS

NGF- beta can be used as an indicator for the severity of adenomyosis. The gradually increasing level of NGF- beta and its receptors while the disease becomes more severe suggests an effect of NGF- beta on pathogenic mechanisms of adenomyosis.

Peripheral somatosensation: a touch of genetics

The somatosensory system processes information that organisms 'feel': joint position, muscle stretch, pain, pressure, temperature, and touch. The system is composed of a diverse array of peripheral nerve endings specialized to detect these sensory modalities. Several recent discoveries have shed light on the genetic pathways that control specification and differentiation of these neurons, how they accurately innervate their central and peripheral targets, and the molecules that enable them to detect mechanical stimuli. Here, we review the cadre of genes that control these processes, focusing on mechanosensitive neurons and support cells of the skin that mediate different aspects of the sense of touch.

TrkB receptor controls striatal formation by regulating the number of newborn striatal neurons

In the peripheral nervous system, target tissues control the final size of innervating neuronal populations by producing limited amounts of survival-promoting neurotrophic factors during development. However, it remains largely unknown if the same principle works to regulate the size of neuronal populations in the developing brain. Here we show that neurotrophin signaling mediated by the TrkB receptor controls striatal size by promoting the survival of developing medium-sized spiny neurons (MSNs). Selective deletion of the gene for the TrkB receptor in striatal progenitors, using the Dlx5/6-Cre transgene, led to a hindpaw-clasping phenotype and a 50% loss of MSNs without affecting striatal interneurons. This loss resulted mainly from increased apoptosis of newborn MSNs within their birthplace, the lateral ganglionic eminence. Among MSNs, those expressing the dopamine receptor D2 (DRD2) were most affected, as indicated by a drastic loss of these neurons and specific down-regulation of the DRD2 and enkephalin. This specific phenotype of mutant animals is likely due to preferential TrkB expression in DRD2 MSNs. These findings suggest that neurotrophins can control the size of neuronal populations in the brain by promoting the survival of newborn neurons before they migrate to their final destinations.

The genetics of pain: implications for evaluation and treatment of spinal disease

BACKGROUND CONTEXT

Variability in human pain experience appears to be at least partially determined by genetic inheritance. To the extent that awareness of individual pain sensitivity and the tendency to develop chronic pain after injury or surgery would be informative for clinical decision making, development and use of genetic testing for specific pain markers could contribute to improved outcomes in management of spinal disease.

PURPOSE

To review important and illustrative results from both classical and modern pain genetics studies and to introduce readers to critical definitions and concepts necessary to interpret the growing body of genetics literature relevant to spinal disease.

STUDY DESIGN/SETTING

Literature review and commentary.

METHODS

A review was performed of published English language studies in which genetic techniques were used to analyze the molecular basis of nociceptive signaling or processing with a particular emphasis on studies addressing genetic determinants of interindividual variability in pain sensitivity or predisposition to chronic pain.

RESULTS

There is compelling evidence indicating that interindividual differences in pain sensitivity and the risk of developing chronic pain syndromes are genetically determined. Despite a growing list of putative "pain genes," genetic association studies remain plagued with difficulty replicating initial findings in different cohorts.

CONCLUSIONS

Genome-wide association studies are potentially powerful means of identifying clinically relevant genetic markers predicting disease susceptibility, severity, and treatment response. However, accurate results require rigorous study design with use of large homogeneous populations and precise phenotypes.

Long-distance control of synapse assembly by target-derived NGF

We report a role for long-distance retrograde neurotrophin signaling in the establishment of synapses in the sympathetic nervous system. Target-derived NGF is both necessary and sufficient for formation of postsynaptic specializations on dendrites of sympathetic neurons. This, in turn, is a prerequisite for formation of presynaptic specializations, but not preganglionic axonal ingrowth from the spinal cord into sympathetic ganglia. We also find that NGF-TrkA signaling endosomes travel from distal axons to cell bodies and dendrites where they promote PSD clustering. Furthermore, the p75 neurotrophin receptor restricts PSD formation, suggesting an important role for antagonistic NGF-TrkA and p75 signaling pathways during retrograde control of synapse establishment. Thus, in addition to defining the appropriate number of sympathetic neurons that survive the period of developmental cell death, target-derived NGF also exerts control over the degree of connectivity between the spinal cord and sympathetic ganglia through retrograde control of synapse assembly.

Structural neuroplasticity following T5 spinal cord transection: increased cardiac sympathetic innervation density and SPN arborization

When the spinal cord is injured at or below thoracic level 5 (T5), cardiovascular control is markedly unbalanced as the heart and blood vessels innervated by upper thoracic segments remain under brain stem control, whereas the vasculature of the lower body is affected by unregulated spinal reflexes. Importantly, the regulation of heart rate and cardiac function is abnormal after spinal cord injury (SCI) at T5 because sympathetic outflow to the heart is increased. An increase in tonic sympathetic outflow may be attributable to multiple mechanisms, such as increases in cardiac sympathetic innervation density, altered morphology of stellate ganglia neurons, and/or structural neuroplasticity of cardiac sympathetic preganglionic neurons (SPNs). Furthermore, these neuroplastic changes associated with SCI may be mediated by nerve growth factor (NGF). NGF is a neurotrophin that supports the survival and differentiation of sympathetic neurons and enhances target innervation. Therefore, we tested the hypothesis that T5 spinal cord transection (T5X) is associated with an increased left ventricular (LV) NGF content, LV sympathetic innervation density, and cardiac SPN arborization. In intact and paraplegic (9 wk posttransection) rats, LV NGF content (ELISA), LV sympathetic innervation density (tyrosine hydroxylase immunohistochemistry), and cardiac SPN arborization (cholera toxin B immunohistochemistry and Sholl Analysis) were determined. Paraplegia, compared with intact, significantly increased LV NGF content, LV sympathetic innervation density, and cardiac SPN arborization. Thus, altered autonomic behavior following SCI is associated with structural neuroplastic modifications.

Development and neuronal dependence of cutaneous sensory nerve formations: Lessons from neurotrophins

Null mutations of genes from the NGF family of NTs and their receptors (NTRs) lead to loss/reduction of specific neurons in sensory ganglia; conversely, cutaneous overexpression of NTs results in skin hyperinnervation and increase or no changes in the number of sensory neurons innervating the skin. These neuronal changes are paralleled with loss of specific types of sensory nerve formations in the skin. Therefore, mice carrying mutations in NT or NTR genes represent an ideal model to identify the neuronal dependence of each type of cutaneous sensory nerve ending from a concrete subtype of sensory neuron, since the development, maintenance, and structural integrity of sensory nerve formations depend upon sensory neurons. Results obtained from these mouse strains suggest that TrkA positive neurons are connected to intraepithelial nerve fibers and other sensory nerve formations depending from C and Adelta nerve fibers; the neurons expressing TrkB and responding to BDNF and NT-4 innervate Meissner corpuscles, a subpopulation of Merkell cells, some mechanoreceptors of the piloneural complex, and the Ruffini's corpuscles; finally, a subpopulation of neurons, which are responsive to NT-3, support postnatal survival of some intraepithelial nerve fibers and Merkel cells in addition to the muscle mechanoreceptors. On the other hand, changes in NTs and NTRs affect the structure of non-nervous structures of the skin and are at the basis of several cutaneous pathologies. This review is an update about the role of NTs and NTRs in the maintenance of normal cutaneous innervation and maintenance of skin integrity.

Modulation of brain-derived neurotrophic factor (BDNF) actions in the nervous system by adenosine A(2A) receptors and the role of lipid rafts

In this paper we review some novel aspects related to the way adenosine A(2A) receptors (A(2A)R) modulate the action of BDNF or its high-affinity receptors, the TrkB receptors, on synaptic transmission and plasticity, as well as upon cholinergic currents and GABA transporters. Evidence has been accumulating that adenosine A(2A)Rs are required for most of the synaptic actions of BDNF. In some cases, where A(2A)Rs are constitutively activated (e.g. by endogenous extracellular adenosine), the need for A(2A)R activation for the maintenance of the synaptic influences of BDNF can be envisaged from the loss of BDNF effects upon blockade of adenosine A(2A)Rs or upon removal of extracellular adenosine with adenosine deaminase. In some other cases, it is necessary to enhance extracellular adenosine levels (e.g. depolarization) or to further activate A(2A)Rs (e.g. with selective agonists) to trigger a BDNF neuromodulatory role at the synapses. Age- and cell-dependent differences may determine the above two possibilities, but in all cases it is quite clear that there is close interplay between adenosine A(2A)Rs and BDNF TrkB receptors at synapses. The role of lipid rafts in this cross-talk will be discussed. This article is part of a Special Issue entitled: "Adenosine Receptors".

Heterogeneous ventricular sympathetic innervation, altered beta-adrenergic receptor expression, and rhythm instability in mice lacking the p75 neurotrophin receptor

Sympathetic nerves stimulate cardiac function through the release of norepinephrine and the activation of cardiac beta(1)-adrenergic receptors. The sympathetic innervation of the heart is sculpted during development by chemoattractive factors including nerve growth factor (NGF) and the chemorepulsive factor semaphorin 3a. NGF acts through the TrkA receptor and the p75 neurotrophin receptor (p75(NTR)) in sympathetic neurons. NGF stimulates sympathetic axon extension into the heart through TrkA, but p75(NTR) modulates multiple coreceptors that can either stimulate or inhibit axon outgrowth. In mice lacking p75(NTR), the sympathetic innervation density in target tissues ranges from denervation to hyperinnervation. Recent studies have revealed significant changes in the sympathetic innervation density of p75NTR-deficient (p75(NTR-/-)) atria between early postnatal development and adulthood. We examined the innervation of adult p75(NTR-/-) ventricles and discovered that the subendocardium of the p75(NTR-/-) left ventricle was essentially devoid of sympathetic nerve fibers, whereas the innervation density of the subepicardium was normal. This phenotype is similar to that seen in mice overexpressing semaphorin 3a, and we found that sympathetic axons lacking p75(NTR) are more sensitive to semaphorin 3a in vitro than control neurons. The lack of subendocardial innervation was associated with decreased dP/dt, altered cardiac beta(1)-adrenergic receptor expression and sensitivity, and a significant increase in spontaneous ventricular arrhythmias. The lack of p75(NTR) also resulted in increased tyrosine hydroxylase content in cardiac sympathetic neurons and elevated norepinephrine in the right ventricle, where innervation density was normal.

RET signaling is required for survival and normal function of nonpeptidergic nociceptors

Small unmyelinated sensory neurons classified as nociceptors are divided into two subpopulations based on phenotypic differences, including expression of neurotrophic factor receptors. Approximately half of unmyelinated nociceptors express the NGF receptor TrkA, and half express the GDNF family ligand (GFL) receptor Ret. The function of NGF/TrkA signaling in the TrkA population of nociceptors has been extensively studied, and NGF/TrkA signaling is a well established mediator of pain. The GFLs are analgesic in models of neuropathic pain emphasizing the importance of understanding the physiological function of GFL/Ret signaling in nociceptors. However, perinatal lethality of Ret-null mice has precluded the study of the physiological role of GFL/Ret signaling in the survival, maintenance, and function of nociceptors in viable mice. We deleted Ret exclusively in nociceptors by crossing nociceptor-specific Na(v)1.8 Cre and Ret conditional mice to produce Ret-Na(v)1.8 conditional knock-out (CKO) mice. Loss of Ret exclusively in nociceptors results in a reduction in nociceptor number and size, indicating that Ret signaling is important for the survival and trophic support of these cells. Ret-Na(v)1.8 CKO mice exhibit reduced epidermal innervation but normal central projections. In addition, Ret-Na(v)1.8 CKO mice have increased sensitivity to cold and increased formalin-induced pain, demonstrating that Ret signaling modulates the function of nociceptors in vivo. Enhanced inflammation-induced pain may be mediated by decreased prostatic acid phosphatase (PAP), as PAP levels are markedly reduced in Ret-Na(v)1.8 CKO mice. The results of this study identify the physiological role of endogenous Ret signaling in the survival and function of nociceptors.

Gene therapy in Alzheimer's disease - potential for disease modification

Alzheimer's disease (AD) is the major cause of dementia in the elderly, leading to memory loss and cognitive decline. The mechanism underlying onset of the disease has not been fully elucidated. However, characteristic pathological manifestations include extracellular accumulation and aggregation of the amyloid beta-peptide (Abeta) into plaques and intracellular accumulation and aggregation of hyperphosphorylated tau, forming neurofibrillary tangles. Despite extensive research worldwide, no disease modifying treatment is yet available. In this review, we focus on gene therapy as a potential treatment for AD, and summarize recent work in the field, ranging from proof-of-concept studies in animal models to clinical trials. The multifactorial causes of AD offer a variety of possible targets for gene therapy, including two neurotrophic growth factors, nerve growth factor and brain-derived neurotrophic factor, Abeta-degrading enzymes, such as neprilysin, endothelin-converting enzyme and cathepsin B, and AD associated apolipoprotein E. This review also discusses advantages and drawbacks of various rapidly developing virus-mediated gene delivery techniques for gene therapy. Finally, approaches aiming at down-regulating amyloid precursor protein (APP) and beta-site APP cleaving enzyme 1 levels by means of siRNA-mediated knockdown are briefly summarized. Overall, the prospects appear hopeful that gene therapy has the potential to be a disease modifying treatment for AD.

Cardiovascular dementia - a different perspective

The number of dementia patients has been growing in recent years and dementia represents a significant threat to aging people all over the world. Recent research has shown that the number of people affected by Alzheimer's disease (AD) and dementia is growing at an epidemic pace. The rapidly increasing financial and personal costs will affect the world's economies, health care systems, and many families. Researchers are now exploring a possible connection among AD, vascular dementia (VD), diabetes mellitus (type 2, T2DM) and cardiovascular diseases (CD). This correlation may be due to a strong association of cardiovascular risk factors with AD and VD, suggesting that these diseases share some biologic pathways. Since heart failure is associated with an increased risk of AD and VD, keeping the heart healthy may prove to keep the brain healthy as well. The risk for dementia is especially high when diabetes mellitus is comorbid with severe systolic hypertension or heart disease. In addition, the degree of coronary artery disease (CAD) is independently associated with cardinal neuropathological lesions of AD. Thus, the contribution of T2DM and CD to AD and VD implies that cardiovascular therapies may prove useful in preventing AD and dementia.

Sequential requirement of Sox4 and Sox11 during development of the sympathetic nervous system

The highly related transcription factors Sox4 and Sox11 are expressed in the developing sympathetic nervous system. In the mouse, Sox11 appears first, whereas Sox4 is prevalent later. Using mouse mutagenesis and overexpression strategies in chicken, we studied the role of both SoxC proteins in this tissue. Neither Sox4 nor Sox11 predominantly functioned by promoting pan-neuronal or noradrenergic differentiation of sympathetic neurons as might have been expected from studies in neuronal precursors of the central nervous system. The transcriptional network that regulates the differentiation of sympathetic neurons remained intact and expression of noradrenergic markers showed only minor alterations. Instead, Sox11 was required in early sympathetic ganglia for proliferation of tyrosine hydroxylase-expressing cells, whereas Sox4 ensured the survival of these cells at later stages. In the absence of both Sox4 and Sox11, sympathetic ganglia remained hypoplastic throughout embryogenesis because of consecutive proliferation and survival defects. As a consequence, sympathetic ganglia were rudimentary in the adult and sympathetic innervation of target tissues was impaired leading to severe dysautonomia.

Multi-system disorders of glycosphingolipid and ganglioside metabolism

Glycosphingolipids (GSLs) and gangliosides are a group of bioactive glycolipids that include cerebrosides, globosides, and gangliosides. These lipids play major roles in signal transduction, cell adhesion, modulating growth factor/hormone receptor, antigen recognition, and protein trafficking. Specific genetic defects in lysosomal hydrolases disrupt normal GSL and ganglioside metabolism leading to their excess accumulation in cellular compartments, particularly in the lysosome, i.e., lysosomal storage diseases (LSDs). The storage diseases of GSLs and gangliosides affect all organ systems, but the central nervous system (CNS) is primarily involved in many. Current treatments can attenuate the visceral disease, but the management of CNS involvement remains an unmet medical need. Early interventions that alter the CNS disease have shown promise in delaying neurologic involvement in several CNS LSDs. Consequently, effective treatment for such devastating inherited diseases requires an understanding of the early developmental and pathological mechanisms of GSL and ganglioside flux (synthesis and degradation) that underlie the CNS diseases. These are the focus of this review.