Ablation of TrkA function in the immune system causes B cell abnormalities

ELP1, the Gene Mutated in Familial Dysautonomia, Is Required for Normal Enteric Nervous System Development and Maintenance and for Gut Epithelium Homeostasis

Familial dysautonomia (FD) is a rare sensory and autonomic neuropathy that results from a mutation in the ELP1 gene. Virtually all patients report gastrointestinal (GI) dysfunction and we have recently shown that FD patients have a dysbiotic gut microbiome and altered metabolome. These findings were recapitulated in an FD mouse model and moreover, the FD mice had reduced intestinal motility, as did patients. To understand the cellular basis for impaired GI function in FD, the enteric nervous system (ENS; both female and male mice) from FD mouse models was analyzed during embryonic development and adulthood. We show here that not only is Elp1 required for the normal formation of the ENS, but it is also required in adulthood for the regulation of both neuronal and non-neuronal cells and for target innervation in both the mucosa and in intestinal smooth muscle. In particular, CGRP innervation was significantly reduced as was the number of dopaminergic neurons. Examination of an FD patient's gastric biopsy also revealed reduced and disoriented axons in the mucosa. Finally, using an FD mouse model in which Elp1 was deleted exclusively from neurons, we found significant changes to the colon epithelium including reduced E-cadherin expression, perturbed mucus layer organization, and infiltration of bacteria into the mucosa. The fact that deletion of Elp1 exclusively in neurons is sufficient to alter the intestinal epithelium and perturb the intestinal epithelial barrier highlights a critical role for neurons in regulating GI epithelium homeostasis.

Selenoprotein I is indispensable for ether lipid homeostasis and proper myelination

Selenoprotein I (SELENOI) catalyzes the final reaction of the CDP-ethanolamine branch of the Kennedy pathway, generating the phospholipids phosphatidylethanolamine (PE) and plasmenyl-PE. Plasmenyl-PE is a key component of myelin and is characterized by a vinyl ether bond that preferentially reacts with oxidants, thus serves as a sacrificial antioxidant. In humans, multiple loss-of-function mutations in genes affecting plasmenyl-PE metabolism have been implicated in hereditary spastic paraplegia, including SELENOI. Herein, we developed a mouse model of nervous system-restricted SELENOI deficiency that circumvents embryonic lethality caused by constitutive deletion and recapitulates phenotypic features of hereditary spastic paraplegia. Resulting mice exhibited pronounced alterations in brain lipid composition, which coincided with motor deficits and neuropathology including hypomyelination, elevated reactive gliosis, and microcephaly. Further studies revealed increased lipid peroxidation in oligodendrocyte lineage cells and disrupted oligodendrocyte maturation both in vivo and in vitro. Altogether, these findings detail a critical role for SELENOI-derived plasmenyl-PE in myelination that is of paramount importance for neurodevelopment.

Functional Classification of Fusion Proteins in Sarcoma

Sarcomas comprise a heterogeneous group of malignant tumors of mesenchymal origin. More than 80 entities are associated with different mesenchymal lineages. Sarcomas with fibroblastic, muscle, bone, vascular, adipocytic, and other characteristics are distinguished. Nearly half of all entities contain specific chromosomal translocations that give rise to fusion proteins. These are mostly pathognomonic, and their detection by various molecular techniques supports histopathologic classification. Moreover, the fusion proteins act as oncogenic drivers, and their blockade represents a promising therapeutic approach. This review summarizes the current knowledge on fusion proteins in sarcoma. We categorize the different fusion proteins into functional classes, including kinases, epigenetic regulators, and transcription factors, and describe their mechanisms of action. Interestingly, while fusion proteins acting as transcription factors are found in all mesenchymal lineages, the others have a more restricted pattern. Most kinase-driven sarcomas belong to the fibroblastic/myofibroblastic lineage. Fusion proteins with an epigenetic function are mainly associated with sarcomas of unclear differentiation, suggesting that epigenetic dysregulation leads to a major change in cell identity. Comparison of mechanisms of action reveals recurrent functional modes, including antagonism of Polycomb activity by fusion proteins with epigenetic activity and recruitment of histone acetyltransferases by fusion transcription factors of the myogenic lineage. Finally, based on their biology, we describe potential approaches to block the activity of fusion proteins for therapeutic intervention. Overall, our work highlights differences as well as similarities in the biology of fusion proteins from different sarcomas and provides the basis for a functional classification.

Detection of NTRK gene fusions in solid tumors: recommendations from a Latin American group of oncologists and pathologists

NTRK gene fusions have been detected in more than 25 types of tumors and their prevalence is approximately 0.3% in solid tumors. This low prevalence makes identifying patients who could benefit from TRK inhibitors a considerable challenge. Furthermore, while numerous papers on the evaluation of NTRK fusion genes are available, not all countries have guidelines that are suitable for their setting, as is the case with Latin America. Therefore, a group of oncologists and pathologists from several countries in Latin America (Argentina, Chile, Ecuador, Mexico, Peru and Uruguay) met to discuss and reach consensus on how to identify patients with NTRK gene fusions in solid tumors. To do so, they developed a practical algorithm, considering their specific situation and limitations.

Development and Biodistribution of a Nerve Growth Factor Radioactive Conjugate for PET Imaging

PURPOSE

The purpose of these studies was to develop a nerve growth factor (NGF) radiometal-chelator conjugate to determine the biodistribution and brain uptake of NGF by positron emission tomography/computerized tomography (PET-CT).

PROCEDURES

Purified NGF from llama seminal plasma was conjugated with FITC, and the chelator NOTA or DFO. NGF conjugates were evaluated for bioactivity. NOTA- and DFO-conjugated NGF were radiolabeled with gallium-68 or zirconium-89 ([68 Ga]GaCl3, half-life = 68 min; [89Zr]Zr(oxalate)4, half-life = 3.3 days). [89Zr]Zr-NGF was evaluated for biodistribution (0.5, 1, or 24 h), PET imaging (60 min), and brain autoradiography in mice.

RESULTS

Cell-based in vitro assays confirmed that the NGF conjugates maintained NGF receptor-binding and biological activity. Zirconium-89 and gallium-68 radiolabeling showed a high efficiency; however, only[89Zr]Zr-NGF was stable in vitro. Biodistribution studies showed that, as with most small proteins < 70 kDa, [89Zr]Zr-NGF uptake was predominantly in the kidney and was cleared rapidly with almost complete elimination of NGF at 24 h. Dynamic PET imaging from 0-60 min showed a similar pattern to ex vivo biodistribution with some transient liver uptake. Interestingly, although absolute brain uptake was very low, at 24 h after treatment, cerebral cortex uptake was higher than any other brain area examined and blood.

CONCLUSIONS

We conclude that conjugation of DFO to NGF through a thiourea linkage allows effective radiolabeling with zirconium-89 while maintaining NGF bioactivity. Following intravenous administration, the radiolabeled NGF targets non-neuronal tissues (e.g., kidney, liver), and although absolute brain uptake was very low, the brain uptake that was observed was restricted to the cortex.

Safety of current treatment options for NTRK fusion-positive cancers

INTRODUCTION

Oncogenic NTRK fusions have been found in multiple cancer types affecting adults and/or children, including rare tumors with pathognomonic fusions and common cancers in which fusions are rare. The tropomyosin receptor kinase inhibitors (TRKi) larotrectinib and entrectinib are among the first agents with tissue agnostic FDA approvals for cancer treatment, and additional TRKi are undergoing development. As experience with TRKi grow, novel mechanisms of resistance and on/off target side effects have become increasingly important considerations.

AREAS COVERED

Authors reviewed literature published through July 2023 on platforms such as PubMed, clinicaltrials.gov, and manufacturer/FDA drug labels, focusing on the development of TRKi, native functions of TRK, phenotype of congenital TRK aberrancies, efficacy, and safety profile of TRKi in clinical trials and investigator reports, and on/off target adverse effects associated with TRKi (Appendix A).

EXPERT OPINION

TRKi have histology-agnostic activity against tumors with NTRK gene fusions. TRKi are generally well tolerated with a side effect profile that compares favorably to cytotoxic chemotherapy. There are numerous ongoing studies investigating TRKi as frontline, adjuvant, and salvage therapy. It will be critical to continue to gather long-term safety data on the use of these agents, particularly in children.

At the heart of the matter: how mental stress and negative emotions affect atrial fibrillation

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia, affecting 2%-3% of the world's population. Mental and emotional stress, as well as some mental health conditions (e.g., depression) have been shown to significantly impact the heart and have been suggested to act both as independent risk factors and triggers in the onset of AF. In this paper, we review the current literature to examine the role that mental and emotional stress have in the onset of AF and summarise the current knowledge on the interaction between the brain and heart, and the cortical and subcortical pathways involved in the response to stress. Review of the evidence suggests that mental and emotional stress negatively affect the cardiac system, potentially increasing the risk for developing and/or triggering AF. Further studies are required to further understand the cortical and sub-cortical structures involved in the mental stress response and how these interact with the cardiac system, which may help in defining new strategies and interventions to prevent the development of, and improve the management of AF.

Spitz Tumor With SQSTM1::NTRK2 Fusion: A Clinicopathological Study of 5 Cases

ABSTRACT

Spitz tumors are melanocytic neoplasms characterized by specific, mutually exclusive driver molecular events, namely genomic rearrangements involving the threonine kinase BRAF and the tyrosine kinase receptors ALK , NTRK1 , NTRK2 , NTRK3 , MET , RET , ROS1 , and MAP3K8 or less commonly, mutations in HRAS or MAP2K1 . We hereby report 5 Spitz tumors with a SQSTM1::NTRK2 fusion. All patients were woman with the ages at diagnosis ranging from 30 to 50 years. Locations included the lower extremity (n = 3), forearm, and back (one each). All the neoplasms were superficial melanocytic proliferation with a flat to dome-shaped silhouette, in which junctional spindled and polygonal dendritic melanocytes were mainly arranged as horizontal nests associated with conspicuous lentiginous involvement of the follicular epithelium. Only one case showed heavily pigmented, vertically oriented melanocytic nests resembling Reed nevus. A superficial intradermal component observed in 2 cases appeared as small nests with a back-to-back configuration. In all lesions, next-generation sequencing analysis identified a SQSTM1::NTRK2 fusion. A single case studied with fluorescence in situ hybridization for copy number changes in melanoma-related genes proved negative. No further molecular alterations were detected, including TERT-p hotspot mutations.

A Microglial Function for the Nerve Growth Factor: Predictions of the Unpredictable

Microglia are the only immune cell population present in the brain parenchyma. Their vantage position in the central nervous system (CNS) enables these myeloid cells to perform the most disparate of tasks: from the classical immune functions of fighting infections and surveilling the extracellular space for pathogens and damage, to sculpting the neuronal circuitry by pruning unnecessary synapses and assisting neurons in spine formation, aiding in the maintenance of brain homeostasis. The neurotrophin field has always been dominated by the neurocentric view that the primary target of these molecules must be neurons: this holds true even for the Nerve Growth Factor (NGF), which owes its popularity in the neuroscience community to its trophic and tropic activity towards sensory and sympathetic neurons in the peripheral nervous system, and cholinergic neurons in the CNS. The increasing evidence that microglia are an integral part of neuronal computation calls for a closer look as to whether these glial cells are capable of responding directly to NGF. In this review, we will first outline evidence in support of a role for NGF as a molecule mediating neuroimmune communication. Then, we will illustrate some of those non-immune features that have made microglial cells one of the hottest topics of this last decade. In conclusion, we will discuss evidence in support of a microglial function for NGF.

Selective endocytosis of Ca2+-permeable AMPARs by the Alzheimer's disease risk factor CALM bidirectionally controls synaptic plasticity

AMPA-type glutamate receptors (AMPARs) mediate fast excitatory neurotransmission, and the plastic modulation of their surface levels determines synaptic strength. AMPARs of different subunit compositions fulfill distinct roles in synaptic long-term potentiation (LTP) and depression (LTD) to enable learning. Largely unknown endocytic mechanisms mediate the subunit-selective regulation of the surface levels of GluA1-homomeric Ca2+-permeable (CP) versus heteromeric Ca2+-impermeable (CI) AMPARs. Here, we report that the Alzheimer's disease risk factor CALM controls the surface levels of CP-AMPARs and thereby reciprocally regulates LTP and LTD in vivo to modulate learning. We show that CALM selectively facilitates the endocytosis of ubiquitinated CP-AMPARs via a mechanism that depends on ubiquitin recognition by its ANTH domain but is independent of clathrin. Our data identify CALM and related ANTH domain-containing proteins as the core endocytic machinery that determines the surface levels of CP-AMPARs to bidirectionally control synaptic plasticity and modulate learning in the mammalian brain.

Elp1 is required for development of visceral sensory peripheral and central circuitry

Cardiovascular instability and a blunted respiratory drive in hypoxic conditions are hallmark features of the genetic sensory and autonomic neuropathy, familial dysautonomia (FD). FD results from a mutation in the gene ELP1, the encoded protein of which is a scaffolding subunit of the six-subunit Elongator complex. In mice, we and others have shown that Elp1 is essential for the normal development of neural crest-derived dorsal root ganglia sensory neurons. Whether Elp1 is also required for development of ectodermal placode-derived visceral sensory receptors, which are required for normal baroreception and chemosensory responses, has not been investigated. Using mouse models for FD, we here show that the entire circuitry underlying baroreception and chemoreception is impaired due to a requirement for Elp1 in the visceral sensory neuron ganglia, as well as for normal peripheral target innervation, and in their central nervous system synaptic partners in the medulla. Thus, Elp1 is required in both placode- and neural crest-derived sensory neurons, and its reduction aborts the normal development of neuronal circuitry essential for autonomic homeostasis and interoception.

This article has an associated First Person interview with the first author of the paper.

Summary: Our data indicate that Elp1 is required in both placode- and neural crest-derived sensory neurons, and that it exerts comparable effects, including survival, axonal morphology and target innervation in both lineages.

NGF-TrkA signaling dictates neural ingrowth and aberrant osteochondral differentiation after soft tissue trauma

Pain is a central feature of soft tissue trauma, which under certain contexts, results in aberrant osteochondral differentiation of tissue-specific stem cells. Here, the role of sensory nerve fibers in this abnormal cell fate decision is investigated using a severe extremity injury model in mice. Soft tissue trauma results in NGF (Nerve growth factor) expression, particularly within perivascular cell types. Consequently, NGF-responsive axonal invasion occurs which precedes osteocartilaginous differentiation. Surgical denervation impedes axonal ingrowth, with significant delays in cartilage and bone formation. Likewise, either deletion of Ngf or two complementary methods to inhibit its receptor TrkA (Tropomyosin receptor kinase A) lead to similar delays in axonal invasion and osteochondral differentiation. Mechanistically, single-cell sequencing suggests a shift from TGFβ to FGF signaling activation among pre-chondrogenic cells after denervation. Finally, analysis of human pathologic specimens and databases confirms the relevance of NGF-TrkA signaling in human disease. In sum, NGF-mediated TrkA-expressing axonal ingrowth drives abnormal osteochondral differentiation after soft tissue trauma. NGF-TrkA signaling inhibition may have dual therapeutic use in soft tissue trauma, both as an analgesic and negative regulator of aberrant stem cell differentiation.

Potential Relation between Plasma BDNF Levels and Human Coronary Plaque Morphology

Coronary artery disease (CAD) patients are at high ischemic risk, and new biomarkers reflecting atherosclerotic disease severity and coronary plaque vulnerability are required. The Brain-Derived Neurotrophic Factor (BDNF) affects endothelial and macrophage activation suggesting its involvement in atherosclerotic plaque behavior. To investigate whether plasma BDNF is associated with in vivo coronary plaque features, assessed by optical coherence tomography (OCT), in both acute myocardial infarction (AMI) and stable angina (SA) patients, we enrolled 55 CAD patients (31 SA and 24 AMI), and 21 healthy subjects (HS). BDNF was lower in CAD patients than in HS (p < 0.0001), and it decreased with the presence, clinical acuity and severity of CAD. The greater BDNF levels were associated with OCT features of plaque vulnerability in overall CAD as well as in SA and AMI patients (p < 0.03). Specifically, in SA patients, BDNF correlated positively with macrophages’ infiltration within atherosclerotic plaque (p = 0.01) and inversely with minimal lumen area (p = 0.02). In AMI patients a negative correlation between BDNF and cap thickness was found (p = 0.02). Despite a small study population, our data suggest a relationship between BDNF and coronary plaque vulnerability, showing that vulnerable plaque is positively associated with plasma BDNF levels, regardless of the clinical CAD manifestation.

Tropomyosin receptor kinase (TRK) biology and the role of NTRK gene fusions in cancer

The tropomyosin receptor kinase (TRK) family of receptor tyrosine kinases are encoded by NTRK genes and have a role in the development and normal functioning of the nervous system. Since the discovery of an oncogenic NTRK gene fusion in colorectal cancer in 1986, over 80 different fusion partner genes have been identified in a wide array of adult and paediatric tumours, providing actionable targets for targeted therapy. This review describes the normal function and physiology of TRK receptors and the biology behind NTRK gene fusions and how they act as oncogenic drivers in cancer. Finally, an overview of the incidence and prevalence of NTRK gene fusions in various types of cancers is discussed.

Inhibition of Tropomyosin Receptor Kinase A Signaling Negatively Regulates Megakaryopoiesis and induces Thrombopoiesis

Neurotrophin signaling modulates the differentiation and function of mature blood cells. The expression of neurotrophin receptors and ligands by hematopoietic and stromal cells of the bone marrow indicates that neurotrophins have the potential to regulate hematopoietic cell fate decisions. This study investigates the role of neurotrophins and Tropomyosin receptor kinases (Trk) in the development of megakaryocytes (MKs) and their progeny cells, platelets. Results indicate that primary human MKs and MK cells lines, DAMI, Meg-01 and MO7e express TrkA, the primary receptor for Nerve Growth Factor (NGF) signaling. Activation of TrkA by NGF enhances the expansion of human MK progenitors (MKPs) and, to some extent, MKs. Whereas, inhibition of TrkA receptor by K252a leads to a 50% reduction in the number of both MKPs and MKs and is associated with a 3-fold increase in the production of platelets. In order to further confirm the role of TrkA signaling in platelet production, TrkA deficient DAMI cells were generated using CRISPR-Cas9 technology. Comparative analysis of wild-type and TrkA-deficient Dami cells revealed that loss of TrkA signaling induced apoptosis of MKs and increased platelet production. Overall, these findings support a novel role for TrkA signaling in platelet production and highlight its potential as therapeutic target for Thrombocytopenia.

Inhibiting TRK Proteins in Clinical Cancer Therapy

Gene rearrangements resulting in the aberrant activity of tyrosine kinases have been identified as drivers of oncogenesis in a variety of cancers. The tropomyosin receptor kinase (TRK) family of tyrosine receptor kinases is emerging as an important target for cancer therapeutics. The TRK family contains three members, TRKA, TRKB, and TRKC, and these proteins are encoded by the genes NTRK1, NTRK2, and NTRK3, respectively. To activate TRK receptors, neurotrophins bind to the extracellular region stimulating dimerization, phosphorylation, and activation of downstream signaling pathways. Major known downstream pathways include RAS/MAPK/ERK, PLCγ, and PI3K/Akt. While being rare in most cancers, TRK fusions with other proteins have been well-established as oncogenic events in specific malignancies, including glioblastoma, papillary thyroid carcinoma, and secretory breast carcinomas. TRK protein amplification as well as alternative splicing events have also been described as contributors to cancer pathogenesis. For patients harboring alterations in TRK expression or activity, TRK inhibition emerges as an important therapeutic target. To date, multiple trials testing TRK-inhibiting compounds in various cancers are underway. In this review, we will summarize the current therapeutic trials for neoplasms involving NTKR gene alterations, as well as the promises and setbacks that are associated with targeting gene fusions.

Role of TrkA signalling and mast cells in the initiation of osteoarthritis pain in the monoiodoacetate model

OBJECTIVE

Aiming to delineate novel neuro-immune mechanisms for NGF/TrkA signalling in osteoarthritis (OA) pain, we evaluated inflammatory changes in the knee joints following injection of monoiodoacetate (MIA) in mice carrying a TrkA receptor mutation (P782S; TrkA KI mice).

METHOD

In behavioural studies we monitored mechanical hypersensitivity following intra-articular MIA and oral prostaglandin D₂ (PGD₂) synthase inhibitor treatments. In immunohistochemical studies we quantified joint mast cell numbers, calcitonin gene-related peptide expression in synovia and dorsal root ganglia, spinal cord neuron activation and microgliosis. We quantified joint leukocyte infiltration by flow cytometry analysis, and PGD₂ generation and cyclooxygenase-2 (COX-2) expression in mast cell lines by ELISA and Western blot.

RESULTS

In TrkA KI mice we observed rapid development of mechanical hypersensitivity and amplification of dorsal horn neurons and microglia activation 7 days after MIA. In TrkA KI knee joints we detected significant leukocyte infiltration and mast cells located in the vicinity of synovial nociceptive fibres. We demonstrated that mast cells exposure to NGF results in up-regulation of COX-2 and increase of PGD₂ production. Finally, we observed that a PGD₂ synthase inhibitor prevented MIA-mechanical hypersensitivity in TrkA KI, at doses which were ineffective in wild type (WT) mice.

CONCLUSION

Using the TrkA KI mouse model, we delineated a novel neuro-immune pathway and suggest that NGF-induced production of PGD₂ in joint mast cells is critical for referred mechanical hypersensitivity in OA, probably through the activation of PGD₂ receptor 1 in nociceptors: TrkA blockade in mast cells constitutes a potential target for OA pain.

Larotrectinib (LOXO-101)

One of the most challenging issues in oncology research and treatment is identifying oncogenic drivers within an individual patient's tumor which can be directly targeted by a clinically available therapeutic drug. In this context, gene fusions as one important example of genetic aberrations leading to carcinogenesis follow the widely accepted concept that cell growth and proliferation are driven by the accomplished fusion (usually involving former proto-oncogenes) and may therefore be successfully inhibited by substances directed against the fusion. This concept has already been established with oncogenic gene fusions like BCR-ABL in chronic myelogenous leukemia (CML) or anaplastic lymphoma kinase (ALK) in lung cancer, including special tyrosine kinase inhibitors (TKIs) which are able to block the activation of the depending downstream proliferation pathways and, consequently, tumor growth. During the last decade, the NTRK1, 2, and 3 genes, encoding the TRKA, B, and C proteins, have attracted increasing attention as another significant and targetable gene fusion in a variety of cancers. Several TRK inhibitors have been developed, and one of them, Larotrectinib (formerly known as LOXO-101), represents an orally available, selective inhibitor of the TRK receptor family that has already shown substantial clinical benefit in both pediatric and adult patients harboring an NTRK gene fusion over the last few years.

BDNF - A key player in cardiovascular system

Neurotrophins (NTs) were first identified as target-derived survival factors for neurons of the central and peripheral nervous system (PNS). They are known to control neural cell fate, development and function. Independently of their neuronal properties, NTs exert unique cardiovascular activity. The heart is innervated by sensory, sympathetic and parasympathetic neurons, which require NTs during early development and in the establishment of mature properties, contributing to the maintenance of cardiovascular homeostasis. The identification of molecular mechanisms regulated by NTs and involved in the crosstalk between cardiac sympathetic nerves, cardiomyocytes, cardiac fibroblasts, and vascular cells, has a fundamental importance in both normal heart function and disease. The article aims to review the recent data on the effects of Brain-Derived Neurotrophic Factor (BDNF) on various cardiovascular neuronal and non-neuronal functions such as the modulation of synaptic properties of autonomic neurons, axonal outgrowth and sprouting, formation of the vascular and neural networks, smooth muscle migration, and control of endothelial cell survival and cardiomyocytes. Understanding these mechanisms may be crucial for developing novel therapeutic strategies, including stem cell-based therapies.

Repurposed JAK1/JAK2 Inhibitor Reverses Established Autoimmune Insulitis in NOD Mice

Recent advances in immunotherapeutics have not yet changed the routine management of autoimmune type 1 diabetes. There is an opportunity to repurpose therapeutics used to treat other diseases to treat type 1 diabetes, especially when there is evidence for overlapping mechanisms. Janus kinase (JAK) 1/JAK2 inhibitors are in development or clinical use for indications including rheumatoid arthritis. There is good evidence for activation of the JAK1/JAK2 and signal transducer and activator of transcription (STAT) 1 pathway in human type 1 diabetes and in mouse models, especially in β-cells. We tested the hypothesis that using these drugs to block the JAK-STAT pathway would prevent autoimmune diabetes. The JAK1/JAK2 inhibitor AZD1480 blocked the effect of cytokines on mouse and human β-cells by inhibiting MHC class I upregulation. This prevented the direct interaction between CD8⁺ T cells and β-cells, and reduced immune cell infiltration into islets. NOD mice treated with AZD1480 were protected from autoimmune diabetes, and diabetes was reversed in newly diagnosed NOD mice. This provides mechanistic groundwork for repurposing clinically approved JAK1/JAK2 inhibitors for type 1 diabetes.

Retrograde transport of TrkB-containing autophagosomes via the adaptor AP-2 mediates neuronal complexity and prevents neurodegeneration

Autophagosomes primarily mediate turnover of cytoplasmic proteins or organelles to provide nutrients and eliminate damaged proteins. In neurons, autophagosomes form in distal axons and are trafficked retrogradely to fuse with lysosomes in the soma. Although defective neuronal autophagy is associated with neurodegeneration, the function of neuronal autophagosomes remains incompletely understood. We show that in neurons, autophagosomes promote neuronal complexity and prevent neurodegeneration in vivo via retrograde transport of brain-derived neurotrophic factor (BDNF)-activated TrkB receptors. p150^Glued/dynactin-dependent transport of TrkB-containing autophagosomes requires their association with the endocytic adaptor AP-2, an essential protein complex previously thought to function exclusively in clathrin-mediated endocytosis. These data highlight a novel non-canonical function of AP-2 in retrograde transport of BDNF/TrkB-containing autophagosomes in neurons and reveal a causative link between autophagy and BDNF/TrkB signalling.

The endocytic adaptor protein complex AP-2 is mostly known for its role in endocytosis and in synaptic vesicle reformation. Here the authors show that AP-2 also mediates retrograde transport of TrkB-containing autophagosomes in neurons; this process promotes neuronal complexity and prevents the degeneration of cortical and thalamic neurons.

The familial dysautonomia disease gene IKBKAP is required in the developing and adult mouse central nervous system

Hereditary sensory and autonomic neuropathies (HSANs) are a genetically and clinically diverse group of disorders defined by peripheral nervous system (PNS) dysfunction. HSAN type III, known as familial dysautonomia (FD), results from a single base mutation in the gene IKBKAP that encodes a scaffolding unit (ELP1) for a multi-subunit complex known as Elongator. Since mutations in other Elongator subunits (ELP2 to ELP4) are associated with central nervous system (CNS) disorders, the goal of this study was to investigate a potential requirement for Ikbkap in the CNS of mice. The sensory and autonomic pathophysiology of FD is fatal, with the majority of patients dying by age 40. While signs and pathology of FD have been noted in the CNS, the clinical and research focus has been on the sensory and autonomic dysfunction, and no genetic model studies have investigated the requirement for Ikbkap in the CNS. Here, we report, using a novel mouse line in which Ikbkap is deleted solely in the nervous system, that not only is Ikbkap widely expressed in the embryonic and adult CNS, but its deletion perturbs both the development of cortical neurons and their survival in adulthood. Primary cilia in embryonic cortical apical progenitors and motile cilia in adult ependymal cells are reduced in number and disorganized. Furthermore, we report that, in the adult CNS, both autonomic and non-autonomic neuronal populations require Ikbkap for survival, including spinal motor and cortical neurons. In addition, the mice developed kyphoscoliosis, an FD hallmark, indicating its neuropathic etiology. Ultimately, these perturbations manifest in a developmental and progressive neurodegenerative condition that includes impairments in learning and memory. Collectively, these data reveal an essential function for Ikbkap that extends beyond the peripheral nervous system to CNS development and function. With the identification of discrete CNS cell types and structures that depend on Ikbkap, novel strategies to thwart the progressive demise of CNS neurons in FD can be developed.

Summary:Ikbkap is essential for normal CNS development, neuronal survival and behavior, adding to our understanding of the role of the Elongator complex in the mammalian CNS.

Loss of Ikbkap Causes Slow, Progressive Retinal Degeneration in a Mouse Model of Familial Dysautonomia

Familial dysautonomia (FD) is an autosomal recessive congenital neuropathy that is caused by a mutation in the gene for inhibitor of kappa B kinase complex-associated protein (IKBKAP). Although FD patients suffer from multiple neuropathies, a major debilitation that affects their quality of life is progressive blindness. To determine the requirement for Ikbkap in the developing and adult retina, we generated Ikbkap conditional knockout (CKO) mice using a TUBA1a promoter-Cre (Tα1-Cre). In the retina, Tα1-Cre expression is detected predominantly in retinal ganglion cells (RGCs). At 6 months, significant loss of RGCs had occurred in the CKO retinas, with the greatest loss in the temporal retina, which is the same spatial phenotype observed in FD, Leber hereditary optic neuropathy, and dominant optic atrophy. Interestingly, the melanopsin-positive RGCs were resistant to degeneration. By 9 months, signs of photoreceptor degeneration were observed, which later progressed to panretinal degeneration, including RGC and photoreceptor loss, optic nerve thinning, Müller glial activation, and disruption of layers. Taking these results together, we conclude that although Ikbkap is not required for normal development of RGCs, its loss causes a slow, progressive RGC degeneration most severely in the temporal retina, which is later followed by indirect photoreceptor loss and complete retinal disorganization. This mouse model of FD is not only useful for identifying the mechanisms mediating retinal degeneration, but also provides a model system in which to attempt to test therapeutics that may mitigate the loss of vision in FD patients.

Potential therapeutic action of natural products from traditional Chinese medicine on Alzheimer's disease animal models targeting neurotrophic factors

Alzheimer's disease (AD) is a neurodegenerative disorder in which the death of brain cells leads to memory loss and cognitive decline. To reduce the death rate and improve the biological activity of neurocytes, neurotrophic factors (NTFs) exhibit therapeutic effect on AD. However, therapeutic application of exogenous NTFs in treatment of AD is largely limited due to short half-life, poor stability, etc. Various extracts of traditional Chinese medicine (TCM) have been shown to exhibit therapeutic effects on AD, and some of these effects are associated with regulation on the expression of nerve growth factor, brain-derived neurotrophic factor (BDNF), and glial cell line-derived neurotrophic factor (GDNF) and their associated receptors. This article reviews the progress on promotion of Panax ginseng, Rehmannia glutinosa Libosch., Epimedium, Polygala tenuifolia Willd, and seven other TCMs on secretion of NTFs during AD, with a view to preparation development and clinical application of these TCMs on AD.

proBDNF and p75NTR Control Excitability and Persistent Firing of Cortical Pyramidal Neurons

Persistent firing of entorhinal cortex (EC) pyramidal neurons is a key component of working and spatial memory. We report here that a pro-brain-derived neurotrophic factor (proBDNF)-dependent p75NTR signaling pathway plays a major role in excitability and persistent activity of pyramidal neurons in layer V of the EC. Using electrophysiological recordings, we show that proBDNF suppresses persistent firing in entorhinal slices from wild-type mice but not from p75NTR-null mice. Conversely, function-blocking proBDNF antibodies enhance excitability of pyramidal neurons and facilitate their persistent firing, and acute exposure to function-blocking p75NTR antibodies results in enhanced firing activity of pyramidal neurons. Genetic deletion of p75NTR specifically in neurons or during adulthood also induces enhanced excitability and persistent activity, indicating that the proBDNF-p75NTR signaling cascade functions within adult neurons to inhibit pyramidal activity. Phosphatidylinositol 4,5-bisphosphate (PIP2)-sensitive transient receptor potential canonical channels play a critical role in mediating persistent firing in the EC and we hypothesized that proBDNF-dependent p75NTR activation regulates PIP2 levels. Accordingly, proBDNF decreases cholinergic calcium responses in cortical neurons and affects carbachol-induced depletion of PIP2. Further, we show that the modulation of persistent firing by proBDNF relies on a p75NTR-Rac1-PI4K pathway. The hypothesis that proBDNF and p75NTR maintain network homeostasis in the adult CNS was tested in vivo and we report that p75NTR-null mice show improvements in working memory but also display an increased propensity for severe seizures. We propose that the proBDNF-p75NTR axis controls pyramidal neuron excitability and persistent activity to balance EC performance with the risk of runaway activity.

SIGNIFICANCE STATEMENT

Persistent firing of entorhinal cortex (EC) pyramidal neurons is required for working memory. We report here that pro-brain-derived neurotrophic factor (proBDNF) activates p75NTR to induce a Rac1-dependent and phosphatidylinositol 4,5-bisphosphate-dependent signaling cascade that suppresses persistent activity. Conversely, using loss-of-function approaches, we find that endogenous proBDNF or p75NTR activation strongly decreases pyramidal neuron excitability and persistent firing, suggesting that a physiological role of this proBDNF-p75NTR cascade may be to regulate working memory in vivo. Consistent with this, mice rendered null for p75NTR during adulthood show improvements in working memory but also display an increased propensity for severe seizures. We propose that by attenuating EC network performance, the proBDNF-p75NTR signaling cascade reduces the probability of epileptogenesis.

TRKing down an old oncogene in a new era of targeted therapy

The use of high-throughput next-generation sequencing techniques in multiple tumor types during the last few years has identified NTRK1, 2, and 3 gene rearrangements encoding novel oncogenic fusions in 19 different tumor types to date. These recent developments have led us to revisit an old oncogene, Trk (originally identified as OncD), which encodes the TPM3-NTRK1 gene fusion and was one of the first transforming chromosomal rearrangements identified 32 years ago. However, no drug has yet been approved by the FDA for cancers harboring this oncogene. This review will discuss the biology of the TRK family of receptors, their role in human cancer, the types of oncogenic alterations, and drugs that are currently in development for this family of oncogene targets.

SIGNIFICANCE

Precision oncology approaches have accelerated recently due to advancements in our ability to detect oncogenic mutations in tumor samples. Oncogenic alterations, most commonly gene fusions, have now been detected for the genes encoding the TRKA, TRKB, and TRKC receptor tyrosine kinases across multiple tumor types. The scientific rationale for the targeting of the TRK oncogene family will be discussed here.

Cerebellar hypoplasia in mice lacking selenoprotein biosynthesis in neurons

Selenium exerts many, if not most, of its physiological functions as a selenocysteine moiety in proteins. Selenoproteins are involved in many biochemical processes including regulation of cellular redox state, calcium homeostasis, protein biosynthesis, and degradation. A neurodevelopmental syndrome called progressive cerebello-cortical atrophy (PCCA) is caused by mutations in the selenocysteine synthase gene, SEPSECS, demonstrating that selenoproteins are essential for human brain development. While we have shown that selenoproteins are required for correct hippocampal and cortical interneuron development, little is known about the functions of selenoproteins in the cerebellum. Therefore, we have abrogated neuronal selenoprotein biosynthesis by conditional deletion of the gene encoding selenocysteyl tRNA([Ser]Sec) (gene symbol Trsp). Enzymatic activity of cellular glutathione peroxidase and cytosolic thioredoxin reductase is reduced in cerebellar extracts from Trsp-mutant mice. These mice grow slowly and fail to gain postural control or to coordinate their movements. Histological analysis reveals marked cerebellar hypoplasia, associated with Purkinje cell death and decreased granule cell proliferation. Purkinje cell death occurs along parasagittal stripes as observed in other models of Purkinje cell loss. Neuron-specific inactivation of glutathione peroxidase 4 (Gpx4) used the same Cre driver phenocopies tRNA([Ser]Sec) mutants in several aspects: cerebellar hypoplasia, stripe-like Purkinje cell loss, and reduced granule cell proliferation. Parvalbumin-expressing GABAergic interneurons (stellate and/or basket cells) are virtually absent in tRNA([Ser]Sec)-mutant mice, while some remained in Gpx4-mutant mice. Our data show that selenoproteins are specifically required in postmitotic neurons of the developing cerebellum, thus providing a rational explanation for cerebellar hypoplasia as occurring in PCCA patients.

Trkb signaling in pericytes is required for cardiac microvessel stabilization

Pericyte and vascular smooth muscle cell (SMC) recruitment to the developing vasculature is an important step in blood vessel maturation. Brain-derived neurotrophic factor (BDNF), expressed by endothelial cells, activates the receptor tyrosine kinase TrkB to stabilize the cardiac microvasculature in the perinatal period. However, the effects of the BDNF/TrkB signaling on pericytes/SMCs and the mechanisms downstream of TrkB that promote vessel maturation are unknown. To confirm the involvement of TrkB in vessel maturation, we evaluated TrkB deficient (trkb^−/−) embryos and observed severe cardiac vascular abnormalities leading to lethality in late gestation to early prenatal life. Ultrastructural analysis demonstrates that trkb^−/− embryos exhibit defects in endothelial cell integrity and perivascular edema. As TrkB is selectively expressed by pericytes and SMCs in the developing cardiac vasculature, we generated mice deficient in TrkB in these cells. Mice with TrkB deficiency in perivascular cells exhibit reduced pericyte/SMC coverage of the cardiac microvasculature, abnormal endothelial cell ultrastructure, and increased vascular permeability. To dissect biological actions and the signaling pathways downstream of TrkB in pericytes/SMCs, human umbilical SMCs were treated with BDNF. This induced membranous protrusions and cell migration, events dependent on myosin light chain phosphorylation. Moreover, inhibition of Rho GTPase and the Rho-associated protein kinase (ROCK) prevented membrane protrusion and myosin light chain phosphorylation in response to BDNF. These results suggest an important role for BDNF in regulating migration of TrkB-expressing pericytes/SMCs to promote cardiac blood vessel ensheathment and functional integrity during development.

Trk receptors

The tropomyosin-related tyrosine kinase (Trk) receptors were initially described as a family of growth factor receptors required for neuronal survival. They have since been shown to influence many aspects of neuronal development and function, including differentiation, outgrowth, and synaptic plasticity. This chapter will give an overview on the biology of Trk receptors within the nervous system. The structure and downstream signaling pathways of the full-length receptors will be described, as well as the biological functions of their truncated isoforms. Finally, the role of Trk receptors in the nervous system in health and disease will be discussed.

Chemotherapy-induced bone marrow nerve injury impairs hematopoietic regeneration

Anti-cancer chemotherapy drugs challenge hematopoietic tissues to regenerate, but commonly produce long-term sequelae. Deficits in hematopoietic stem or stromal cell function have been described, but the mechanisms mediating chemotherapy-induced hematopoietic dysfunction remain unclear. Administration of multiple cycles of cisplatin chemotherapy causes significant sensory neuropathy. Here, we demonstrate that chemotherapy-induced nerve injury in the bone marrow is a critical lesion impairing hematopoietic regeneration. We show using various pharmacological and genetic models that the selective loss of adrenergic innervation in the BM alters its regeneration following genotoxic insult. Sympathetic nerves in the marrow promote the survival of stem cell niche constituents that initiate recovery. Neuroprotection by deletion of Trp53 in sympathetic neurons or neuro-regeneration using 4-methylcatechol or glial-derived neurotrophic factor (GDNF) administration can restore hematopoietic recovery. Thus, these results shed light on the potential benefit of adrenergic nerve protection to shield hematopoietic niches from injury.

Tropomyosin receptor kinases B and C are tumor progressive and metastatic marker in colorectal carcinoma

Members of the tropomyosin receptor kinase (Trk) family have a high affinity for neurotrophins and regulate neuronal survival. The role of Trks in cancer is still controversial. The expression and role of TrkB and TrkC were examined in colorectal cancer (CRC). Immunohistochemical analysis of TrkB and TrkC was performed in 133 patients with CRC. Using human CRC cell lines, expression of vascular endothelial growth factor (VEGF) and transforming growth factor β, cell growth, invasion, and apoptosis were examined by knockdown methods. Immunohistochemistry showed positive results of TrkB and TrkC (23.3% and 12.8%, respectively). TrkB expression was associated with local progression (P = .0284), clinical stage (P = .0026), nodal metastasis (P = .0068), and peritoneal metastasis (P = .0026). TrkC expression was only related to liver metastasis (P = .0001). Coexpression of TrkB or TrkC and their ligands was found in 80.6% and 82.4% of cases, respectively. In vitro analysis using human CRC cells showed that TrkB positively regulated gene expression of VEGF-A (P < .05) and VEGF-C (P < .05), whereas TrkC suppressed transforming growth factor β expression (P < .05). TrkB and TrkC induced cell growth (P < .05) and invasion (P < .05), respectively. Both TrkB and TrkC showed antiapoptotic effect (P < .05). These results suggest that TrkB and TrkC have a tumor progressive function and may be a useful diagnostic and therapeutic target in CRC.

Endogenous neurotrophins and Trk signaling in diffuse large B cell lymphoma cell lines are involved in sensitivity to rituximab-induced apoptosis

Background

Diffuse large B-cell lymphoma (DLBCL) is a common and often fatal malignancy. Immunochemotherapy, a combination of rituximab to standard chemotherapy, has resulted in improved survival. However a substantial proportion of patients still fail to reach sustained remission. We have previously demonstrated that autocrine brain-derived neurotrophic factor (BDNF) production plays a function in human B cell survival, at least partly via sortilin expression. As neurotrophin receptor (Trks) signaling involved activation of survival pathways that are inhibited by rituximab, we speculated that neurotrophins may provide additional support for tumour cell survival and therapeutic resistance in DLBCL.

Methodology/Principal Findings

In the present study, we used two DLBCL cell lines, SUDHL4 and SUDHL6, known to be respectively less and more sensitive to rituximab. We found by RT-PCR, western blotting, cytometry and confocal microscopy that both cell lines expressed, in normal culture conditions, BDNF and to a lesser extent NGF, as well as truncated TrkB and p75^NTR/sortilin death neurotrophin receptors. Furthermore, BDNF secretion was detected in cell supernatants. NGF and BDNF production and Trk receptor expression, including TrkA, are regulated by apoptotic conditions (serum deprivation or rituximab exposure). Indeed, we show for the first time that rituximab exposure of DLBCL cell lines induces NGF secretion and that differences in rituximab sensitivity are associated with differential expression patterns of neurotrophins and their receptors (TrkA). Finally, these cells are sensitive to the Trk-inhibitor, K252a, as shown by the induction of apoptosis. Furthermore, K252a exhibits additive cytotoxic effects with rituximab.

Conclusions/Significance

Collectively, these data strongly suggest that a neurotrophin axis, such NGF/TrkA pathway, may contribute to malignant cell survival and rituximab resistance in DLBCL.

Constitutive reductions in mTOR alter cell size, immune cell development, and antibody production

Mammalian TOR (mTOR) regulates cell growth, proliferation, and migration. Because mTOR knock-outs are embryonic lethal, we generated a viable hypomorphic mouse by neo-insertion that partially disrupts mTOR transcription and creates a potential physiologic model of mTORC1/TORC2 inhibition. Homozygous knock-in mice exhibited reductions in body, organ, and cell size. Although reductions in most organ sizes were proportional to decreased body weight, spleens were disproportionately smaller. Decreases in the total number of T cells, particularly memory cells, and reduced responses to chemokines suggested alterations in T-cell homing/homeostasis. T-cell receptor-stimulated T cells proliferated less, produced lower cytokine levels, and expressed FoxP3. Decreased neutrophil numbers were also observed in the spleen, despite normal development and migration in the bone marrow. However, B-cell effects were most pronounced, with a partial block in B-cell development in the bone marrow, altered splenic populations, and decreases in proliferation, antibody production, and migration to chemokines. Moreover, increased AKT(Ser473) phosphorylation was observed in activated B cells, reminiscent of cancers treated with rapamycin, and was reduced by a DNA-pk inhibitor. Thus, mTOR is required for the maturation and differentiation of multiple immune cell lineages. These mice provide a novel platform for studying the consequences of constitutively reduced mTORC1/TORC2 activity.

Neurotrophic and neuroimmune responses to early-life Pseudomonas aeruginosa infection in rat lungs

Early-life respiratory infection with Pseudomonas aeruginosa is common in children with cystic fibrosis or immune deficits. Although many of its clinical manifestations involve neural reflexes, little information is available on the peripheral nervous system of infected airways. This study sought to determine whether early-life infection triggers a neurogenic-mediated immunoinflammatory response, the mechanisms of this response, and its relationship with other immunoinflammatory pathways. Weanling and adult rats were inoculated with suspensions containing P. aeruginosa (PAO1) coated on alginate microspheres suspended in Tris-CaCl(2) buffer. Five days after infection, rats were injected with capsaicin to stimulate nociceptive nerves in the airway mucosa, and microvascular permeability was measured using Evans blue as a tracer. PAO1 increased neurogenic inflammation in the extra- and intrapulmonary compartments of weanlings but not in adults. The mechanism involves selective overexpression of NGF, which is critical for the local increase in microvascular permeability and for the infiltration of polymorphonuclear leukocytes into infected lung parenchyma. These effects are mediated in part by induction of downstream inflammatory cytokines and chemokines, especially IL-1beta, IL-18, and leptin. Our data suggest that neurogenic-mediated immunoinflammatory mechanisms play important roles in airway inflammation and hyperreactivity associated with P. aeruginosa when infection occurs early in life.

Neuronal selenoprotein expression is required for interneuron development and prevents seizures and neurodegeneration

Cerebral selenium (Se) deficiency is associated with neurological phenotypes including seizures and ataxia. We wanted to define whether neurons require selenoprotein expression and which selenoproteins are most important, and explore the possible pathomechanism. Therefore, we abrogated the expression of all selenoproteins in neurons by genetic inactivation of the tRNA[Ser](Sec) gene. Cerebral expression of selenoproteins was significantly diminished in the mutants, and histological analysis revealed progressive neurodegeneration. Developing interneurons failed to specifically express parvalbumin (PV) in the mutants. Electrophysiological recordings, before overt cell death, showed normal excitatory transmission, but revealed spontaneous epileptiform activity consistent with seizures in the mutants. In developing cortical neuron cultures, the number of PV(+) neurons was reduced on combined Se and vitamin E deprivation, while other markers, such as calretinin (CR) and GAD67, remained unaffected. Because of the synergism between Se and vitamin E, we analyzed mice lacking neuronal expression of the Se-dependent enzyme glutathione peroxidase 4 (GPx4). Although the number of CR(+) interneurons remained normal in Gpx4-mutant mice, the number of PV(+) interneurons was reduced. Since these mice similarly exhibit seizures and ataxia, we conclude that GPx4 is a selenoenzyme modulating interneuron function and PV expression. Cerebral SE deficiency may thus act via reduced GPx4 expression.-Wirth, E. K., Conrad, M., Winterer, J., Wozny, C., Carlson, B. A., Roth, S., Schmitz, D., Bornkamm, G. W., Coppola, V., Tessarollo, L., Schomburg, L., Köhrle, J., Hatfield, D. L., Schweizer, U. Neuronal selenoprotein expression is required for interneuron development and prevents seizures and neurodegeneration.

NGF is an essential survival factor for bronchial epithelial cells during respiratory syncytial virus infection

Background

Overall expression of neurotrophins in the respiratory tract is upregulated in infants infected by the respiratory syncytial virus (RSV), but it is unclear where (structural vs. inflammatory cells, upper vs. lower airways) and why, these changes occur. We analyzed systematically the expression of neurotrophic factors and receptors following RSV infection of human nasal, tracheal, and bronchial epithelial cells, and tested the hypothesis that neurotrophins work as innate survival factors for infected respiratory epithelia.

Methodology

Expression of neurotrophic factors (nerve growth factor, NGF; brain-derived neurotrophic factor, BDNF) and receptors (trkA, trkB, p75) was analyzed at the protein level by immunofluorescence and flow cytometry and at the mRNA level by real-time PCR. Targeted siRNA was utilized to blunt NGF expression, and its effect on virus-induced apoptosis/necrosis was evaluated by flow cytometry following annexin V/7-AAD staining.

Principal Findings

RSV infection was more efficient in cells from more distal (bronchial) vs. more proximal origin. In bronchial cells, RSV infection induced transcript and protein overexpression of NGF and its high-affinity receptor trkA, with concomitant downregulation of the low-affinity p75^NTR. In contrast, tracheal cells exhibited an increase in BDNF, trkA and trkB, and nasal cells increased only trkA. RSV-infected bronchial cells transfected with NGF-specific siRNA exhibited decreased trkA and increased p75^NTR expression. Furthermore, the survival of bronchial epithelial cells was dramatically decreased when their endogenous NGF supply was depleted prior to RSV infection.

Conclusions/Significance

RSV infection of the distal airway epithelium, but not of the more proximal sections, results in overexpression of NGF and its trkA receptor, while the other p75^NTR receptor is markedly downregulated. This pattern of neurotrophin expression confers protection against virus-induced apoptosis, and its inhibition amplifies programmed cell death in the infected bronchial epithelium. Thus, pharmacologic modulation of NGF expression may offer a promising new approach for management of common respiratory infections.

Cardiovascular actions of neurotrophins

Neurotrophins were christened in consideration of their actions on the nervous system and, for a long time, they were the exclusive interest of neuroscientists. However, more recently, this family of proteins has been shown to possess essential cardiovascular functions. During cardiovascular development, neurotrophins and their receptors are essential factors in the formation of the heart and critical regulator of vascular development. Postnatally, neurotrophins control the survival of endothelial cells, vascular smooth muscle cells, and cardiomyocytes and regulate angiogenesis and vasculogenesis, by autocrine and paracrine mechanisms. Recent studies suggest the capacity of neurotrophins, via their tropomyosin-kinase receptors, to promote therapeutic neovascularization in animal models of hindlimb ischemia. Conversely, the neurotrophin low-affinity p75(NTR) receptor induces apoptosis of endothelial cells and vascular smooth muscle cells and impairs angiogenesis. Finally, nerve growth factor looks particularly promising in treating microvascular complications of diabetes or reducing cardiomyocyte apoptosis in the infarcted heart. These seminal discoveries have fuelled basic and translational research and thus opened a new field of investigation in cardiovascular medicine and therapeutics. Here, we review recent progress on the molecular signaling and roles played by neurotrophins in cardiovascular development, function, and pathology, and we discuss therapeutic potential of strategies based on neurotrophin manipulation.

Lack of adrenomedullin in the mouse brain results in behavioral changes, anxiety, and lower survival under stress conditions

The adrenomedullin (AM) gene, adm, is widely expressed in the central nervous system (CNS) and several functions have been suggested for brain AM. Until now, a formal confirmation of these actions using genetic models has been elusive since the systemic adm knockout results in embryo lethality. We have built a conditional knockout mouse model using the Cre/loxP approach. When crossed with transgenic mice expressing the Cre recombinase under the tubulin Talpha-1 promoter, we obtained animals with no AM expression in the CNS but normal levels in other organs. These animals lead normal lives and do not present any gross morphological defect. Specific areas of the brain of animals lacking CNS AM contain hyperpolymerized tubulin, a consequence of AM downregulation. Behavioral analysis shows that mice with no AM in their brain have impaired motor coordination and are hyperactive and overanxious when compared to their wild-type littermates. Treatment with methylphenidate, haloperidol, and diazepam did not show differences between genotypes. Circulating levels of adrenocorticotropic hormone and corticosterone were similar in knockout and wild-type mice. Animals with no brain AM were less resistant to hypobaric hypoxia than wild-type mice, demonstrating the neuroprotective function of AM in the CNS. In conclusion, AM exerts a beneficial action in the brain by maintaining homeostasis both under normal and stress conditions.

Granule formation in NGF-cultured mast cells is associated with expressions of pyruvate kinase type M2 and annexin I proteins

BACKGROUND

Nerve growth factor (NGF) is a potent mediator, which regulates characteristics of mast cells, but its biological function is not well characterized. This study aimed to screen proteins associated with the maturation of human mast cells-1 (HMC-1) or mouse bone marrow-derived mast cells (BMMCs) cultured with NGF, and to examine the functions of proteins involved.

METHODS

NGF (10 ng/ml) was added to cell culture medium every other day for 10 days for HMC-1 or twice a week for 5 weeks for BMMCs. Granule formation was determined by electron microscopy or May-Grunwald-Giemsa staining, TNF-alpha by ELISA, expressions of various proteins by two-dimensional gel electrophoresis (2-DE), siRNA transfection by Lipofectamine 2000, and the expressions of pyruvate kinase and annexin I by immunoblotting.

RESULTS

After NGF treatment, granule formation and total amounts of granular mediator, TNF-alpha increased in both mast cells. This TNF-alpha was released by calcium ionophore or by antigen/antibody reaction. Expressions of pyruvate kinase and annexin I obtained by 2-DE were confirmed by immunoblotting and siRNA-transfected HMC-1 cells. Expressions of proteins, granule formation and TNF-alpha content were blocked by both the TrkA inhibitor, K252a, and the ERK inhibitor, PD98059, but not by the PI3 kinase inhibitors, LY294002 and wortmannin.

CONCLUSION

These data suggest that pyruvate kinase and annexin I expressed by NGF contribute to granule formation containing TNF-alpha as well as other mediators in mast cells, which play a major role in allergic diseases via a TrkA/ERK pathway.

The role of thioredoxin reductases in brain development

The thioredoxin-dependent system is an essential regulator of cellular redox balance. Since oxidative stress has been linked with neurodegenerative disease, we studied the roles of thioredoxin reductases in brain using mice with nervous system (NS)-specific deletion of cytosolic (Txnrd1) and mitochondrial (Txnrd2) thioredoxin reductase. While NS-specific Txnrd2 null mice develop normally, mice lacking Txnrd1 in the NS were significantly smaller and displayed ataxia and tremor. A striking patterned cerebellar hypoplasia was observed. Proliferation of the external granular layer (EGL) was strongly reduced and fissure formation and laminar organisation of the cerebellar cortex was impaired in the rostral portion of the cerebellum. Purkinje cells were ectopically located and their dendrites stunted. The Bergmann glial network was disorganized and showed a pronounced reduction in fiber strength. Cerebellar hypoplasia did not result from increased apoptosis, but from decreased proliferation of granule cell precursors within the EGL. Of note, neuron-specific inactivation of Txnrd1 did not result in cerebellar hypoplasia, suggesting a vital role for Txnrd1 in Bergmann glia or neuronal precursor cells.

Brain-derived neurotrophic factor: a newly described mediator of angiogenesis

Recent studies indicate that, in addition to its neuropoietic actions, brain derived neurotrophic factor (BDNF) promotes endothelial cell survival and induces neoangiogenesis in ischemic tissues. Unlike many vascular growth factors that act on many vascular beds, BDNF activity is relatively restricted to central arteries, vessels of cardiac and skeletal muscle, and skin. Studies of newly described biologic mediators that act on large-vessel and microvascular beds in these organs will help us to better understand organ-specific vascular development, as well as to develop novel therapeutic strategies to improve the condition of patients with cardiac and peripheral vascular disease. In this review, we summarize dual proangiogenic actions of BDNF, which, through local activation of TrkB receptor, expressed on a subpopulation of endothelial cells and, in addition, by recruitment of bone marrow-derived cells, contribute to neoangiogenesis.

TrkAIII expression in the thymus

The alternative TrkAIII splice variant is expressed by murine and human thymus. Alternative TrkAIII splicing predominates in postembryonic day E13 (E17 and E18), postnatal murine (3 week and 3 month) and human thymuses, with TrkAIII mRNA expressed by selected thymocyte subsets and thymic epithelial cells (TECs) and a 100 kDa immunoprecipitable TrkAIII-like protein detected in purified thymocyte and whole thymus extracts. FACS and immunohistochemical analysis indicate a non-cell surface localisation for the TrkAIII-like protein in cortical CD4+/CD8+ double positive and, to a lesser extent, single positive thymocyte subsets at the cortex/medulla boundary and in Hassle's corpuscles, reticular epithelial and dendritic cells of the thymic medulla. TrkA(I/II) expression, on the other hand, predominates in sub-capsular regions of the thymus. TrkAIII-like immunoreactivity at the cortex/medulla boundary associates with regions of thymocyte proliferation and not apoptosis. A potential role for thymic hypoxia in thymocyte alternative TrkAIII splicing is supported by reversal to TrkAI splicing by normoxic but not hypoxic culture and induction of Jurkat T cell alternative TrkAIII splicing by the hypoxia mimic CoCl2. In contrast, TEC expression of TrkAIII predominates in both normoxic and hypoxic culture conditions. The data support a potential role for TrkAIII in thymic development and function, of particular relevance to intermediate stage CD4+/CD8+ thymocyte subsets and TECs, which potentially reflects a reversible thymocyte and more permanent TEC adaptation to thymic environment. Since intracellular TrkAIII neither binds nor responds to NGF and can impede regular NGF/TrkA signalling (Tacconelli et al., Cancer Cell, 2004), its expression would be expected to provide an alternative and/or impediment to regular NGF/TrkA signalling within the developing and developed thymus of potential functional importance.

Conditional gene targeting in the mouse nervous system: Insights into brain function and diseases

Conditional gene knockout represents an extremely powerful approach to study the function of single genes in the nervous system. The Cre-LoxP system is the most advanced technology for spatial and temporal control of genetic inactivation, and there is rapid progress using this methodology in neuroscience research. In this approach, mice with LoxP sites flanking the gene of interest (floxed mice) are bred with transgenic mice expressing Cre recombinase under the control of a selected promoter (Cre mice). This promoter is critical in that it determines the time and site of Cre expression. Cre enzyme, in turn, recombines the floxed gene and produces gene knockout. Here we review Cre mouse lines that have been developed to target either the entire brain, selected brain areas, or specific neuronal populations. We then summarize phenotypic consequences of conditional gene targeting in the brain for more than 40 genes, as reported to date. For many broadly expressed genes, brain-restricted knockout has overcome lethality of conventional knockout (KO) and has highlighted a specific role of the encoded protein in some aspect of brain function. In the case of neural genes, data from null mutants in specific brain sites or neurons has refined our understanding of the role of individual molecules that regulate complex behaviors or synaptic plasticity within neural circuits. Among the many developing functional genomic approaches, conditional gene targeting in the mouse has become an excellent tool to elucidate the function of the approximately 5000 known or unknown genes that operate in the nervous system.

Neurotrophin-regulated signalling pathways

Neurotrophins are a family of closely related proteins that were identified initially as survival factors for sensory and sympathetic neurons, and have since been shown to control many aspects of survival, development and function of neurons in both the peripheral and the central nervous systems. Each of the four mammalian neurotrophins has been shown to activate one or more of the three members of the tropomyosin-related kinase (Trk) family of receptor tyrosine kinases (TrkA, TrkB and TrkC). In addition, each neurotrophin activates p75 neurotrophin receptor (p75NTR), a member of the tumour necrosis factor receptor superfamily. Through Trk receptors, neurotrophins activate Ras, phosphatidyl inositol-3 (PI3)-kinase, phospholipase C-gamma1 and signalling pathways controlled through these proteins, such as the MAP kinases. Activation of p75NTR results in activation of the nuclear factor-kappaB (NF-kappaB) and Jun kinase as well as other signalling pathways. Limiting quantities of neurotrophins during development control the number of surviving neurons to ensure a match between neurons and the requirement for a suitable density of target innervation. The neurotrophins also regulate cell fate decisions, axon growth, dendrite growth and pruning and the expression of proteins, such as ion channels, transmitter biosynthetic enzymes and neuropeptide transmitters that are essential for normal neuronal function. Continued presence of the neurotrophins is required in the adult nervous system, where they control synaptic function and plasticity, and sustain neuronal survival, morphology and differentiation. They also have additional, subtler roles outside the nervous system. In recent years, three rare human genetic disorders, which result in deleterious effects on sensory perception, cognition and a variety of behaviours, have been shown to be attributable to mutations in brain-derived neurotrophic factor and two of the Trk receptors.

Thymocyte depletion affects neurotrophin receptor expression in thymic stromal cells

Thymocytes and thymic stromal cells cross-talk in a bidirectional manner within the thymus, thus contributing to the generation of mature T-cells. The thymic stromal cells in the rat express the high- (TrkA, TrkB) and low-affinity (p75NTR) receptors for neurotrophins. In this study we analysed the regulation of TrkA, TrkB and p75NTR expression in the rat thymus by thymocytes. We induced thymocyte apoptosis by administration of corticoids in rats, and then analysed the expression and distribution of these receptors 1, 4 and 10 days later. Thymocyte death was assessed by the activation of caspase-3 in cells undergoing apoptosis. We observed massive thymocyte apoptosis 1 day after injection and, to a lesser extent, after 4 days, which was parallel with a reduction in the density of thymic epithelial cells normally expressing TrkA and p75NTR. Furthermore, TrkA expression was found in cortical thymic epithelial cells, which normally lack this receptor. The expression of TrkB was restricted to a subset of macrophage-dendritic cells, and remained unchanged with treatment. The normal pattern of neurotrophin receptor expression was almost completely restored by day 10. The results demonstrate that the expression of neurotrophin receptors by thymic epithelial cells, but not by macrophage-dendritic cells, is regulated by thymocytes.

The scaffold protein Cybr is required for cytokine-modulated trafficking of leukocytes in vivo

Trafficking and cell adhesion are key properties of cells of the immune system. However, the molecular pathways that control these cellular behaviors are still poorly understood. Cybr is a scaffold protein highly expressed in the hematopoietic/immune system whose physiological role is still unknown. In vitro studies have shown it regulates LFA-1, a crucial molecule in lymphocyte attachment and migration. Cybr also binds cytohesin-1, a guanine nucleotide exchange factor for the ARF GTPases, which affects actin cytoskeleton remodeling during cell migration. Here we show that expression of Cybr in vivo is differentially modulated by type 1 cytokines during lymphocyte maturation. In mice, Cybr deficiency negatively affects leukocytes circulating in blood and lymphocytes present in the lymph nodes. Moreover, in a Th1-polarized mouse model, lymphocyte trafficking is impaired by loss of Cybr, and Cybr-deficient mice with aseptic peritonitis have fewer cells than controls present in the peritoneal cavity, as well as fewer leukocytes leaving the bloodstream. Mutant mice injected with Moloney murine sarcoma/leukemia virus develop significantly larger tumors than wild-type mice and have reduced lymph node enlargement, suggesting reduced cytotoxic T-lymphocyte migration. Taken together, these data support a role for Cybr in leukocyte trafficking, especially in response to proinflammatory cytokines in stress conditions.

A neurotrophin axis in myeloma: TrkB and BDNF promote tumor-cell survival

Multiple myeloma (MM) is a B-cell neoplasm that is characterized by the clonal expansion of malignant plasma cells and is frequently associated with chromosomal translocations placing an oncogene under the control of the immunoglobulin heavy chain enhancer. Despite these pathogenic translocations, MM cells remain dependent on external cues for survival. We present evidence that brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family of growth factors, and its high-affinity receptor, tropomyosin receptor kinase B (TrkB), contribute to these survival cues. MM cells express TrkB, and respond to BDNF by activating mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase-a PI3K target (PI3K/Akt) signaling cascades. Addition of BDNF protects human MM cell lines (HMCLs) from apoptosis induced by dexamethasone or bortezomib and prolongs the survival of primary MM cells cultured alone or with human bone marrow (BM) stroma. As BDNF and TrkB are expressed by osteoblasts, stromal cells, and endothelial cells within the BM microenvironment, a BDNF-TrkB axis may be critical to the interactions of MM with bone and stroma that contribute to MM tumor progression. Finally, BDNF is expressed by malignant plasma cells isolated from a subset of patients with MM, as well as by most HMCLs, suggesting a potential role for this neurotrophin axis in autocrine as well as paracrine support of MM.