Search

The neurotrophin receptors p75 and TrkA play an important role in the development and survival of the nervous system. Biochemical data suggest that p75 and TrkA regulate the activities of each other. For instance, p75 is able to regulate the response of TrkA to lower concentrations of NGF and TrkA promotes p75 shedding by α-secretases in a ligand-dependent manner. The current model is that p75 and TrkA are regulated by means of a physical direct interaction, however the nature of such interaction has been elusive so far. Here using NMR in micelles, multiscale molecular dynamics (MD), FRET and functional studies we identified and characterized the direct interaction between TrkA and p75 through the transmembrane domains (TMDs). MD of p75-TMD mutants suggests that although the interaction between TrkA and p75 TMDs is maintained, a specific protein interface is required to facilitate TrkA active homodimerization in the presence of NGF. The same mutations in the TMD protein interface of p75 reduced the activation of TrkA by NGF and cell differentiation. In summary we provide a structural model of the p75/TrkA receptor complex stabilized by transmembrane domain interactions.

20 páginas, 8 figuras, γ-secretase inhibitors (GSI) were developed to reduce the generation of Aβ peptide to find new Alzheimer's disease treatments. Clinical trials on Alzheimer's disease patients, however, showed several side effects that worsened the cognitive symptoms of the treated patients. The observed side effects were partially attributed to Notch signaling. However, the effect on other γ-secretase substrates, such as the p75 neurotrophin receptor (p75NTR) has not been studied in detail. p75NTR is highly expressed in the basal forebrain cholinergic neurons (BFCNs) during all life. Here, we show that GSI treatment induces the oligomerization of p75CTF leading to the cell death of BFCNs, and that this event is dependent on TrkA activity. The oligomerization of p75CTF requires an intact cholesterol recognition sequence (CRAC) and the constitutive binding of TRAF6, which activates the JNK and p38 pathways. Remarkably, TrkA rescues from cell death by a mechanism involving the endocytosis of p75CTF. These results suggest that the inhibition of γ-secretase activity in aged patients, where the expression of TrkA in the BFCNs is already reduced, could accelerate cholinergic dysfunction and promote neurodegeneration., This study was supported by the Spanish Minister of Economy and Competitiveness grant SAF2017-84096-R and by the Generalitat Valenciana 2018-55 to M Vilar. I García-Carpio was supported by an Formación de Personal Investigador (FPI) pre-doctoral fellowship (BFU2013/42746-P) and a mobility grant (EEBB-I-15-10278) from the Spanish Minister of Economy and Competitiveness. This work was funded by the Stichting Alzheimer Onderzoek (S16013) and the Fonds voor Wetenschappelijk Onderzoek or Flanders Research Foundation (FWO) research project (G0B2519N) to L Chavez-Gutiérrez

Neurotrophins are a family of secreted proteins that promote different activities during development and in the adult nervous system, like cell survival and differentiation, synaptic plasticity, and axonal growth. In mammals, only four neurotrophin genes encoding for nerve growth factor, brain-derived neurotrophic factor, neurotrophin 3, and neurotrophin 4 are sufficient to modulate these functions in the peripheral and central nervous systems and in nonneuronal organs. This chapter will provide an overall view of the evolution, mechanisms, signaling, and function of the neurotrophins and their receptors, not only in the nervous system, and their role in several human pathologies.

Trk receptors are essential for the nervous system development. The molecular mechanism of TrkA activation by its ligand NGF is still unsolved. Recent data indicates that at endogenous levels most of TrkA is in an equilibrium monomer-dimer and the binding of NGF induces an increase of the dimer and oligomer forms of the receptor. An unsolved issue is the role of the transmembrane domain (TMD) in the dimerization of TrkA and the structural details of the TMD in the active dimer receptor. We found that TrkA-TMD can form dimers, identified the structural determinants of the dimer interface in the active receptor and validated this interface using site-directed mutagenesis together with functional and cell differentiation studies. Usingin vivocrosslinking we identified a reordering of the extracellular juxtamembrane (JTM) region after ligand binding. Replacement of some residues in the JTM region with cysteine form ligand-independent active dimers and reveal a preferred dimer interface. In addition to that, insertion of leucine residues into the TMD helix induces a ligand-independent TrkA activation suggesting that a rotation of the TMD dimers could be behind TrkA activation by NGF. Altogether our data indicates that the transmembrane and juxtamembrane regions of the receptor play a key role in the dimerization and activation of TrkA by NGF.

We describe the case of a 33-week preterm infant who developed nonimmune hydrops fetalis secondary to a kaposiform hemangioendothelioma (KHE). The tumor was successfully treated with vincristine, prednisone, ticlopidine, and aspirin. KHE can be an unusual cause of hydrops fetalis; in such cases, diagnosis can be challenging since generalized edema can obscure KHE.

Contrast agents (CAs) are one of the medications most used by interventional pain practitioners. They are used to confirm target, to distinguish different surrounding tissues, and to deliver adequate medication to specific areas of pathology. The high tolerance of modern CAs has been achieved through successive developments in chemical pharmacologic technology. Different CAs vary greatly in their chemical properties and toxic effects. Adverse reactions can occur while administering these substances and can be classified into acute and delayed. Acute reactions range from mild symptoms, such as urticaria and itching, to more severe reactions, such as cardiopulmonary arrest and death. Pain practitioners should be familiar with the clinical pharmacology of CAs, be aware of their potentially life-threatening reactions, and know how to prevent and treat them. All staff members should be able to recognize a potentially serious adverse reaction, as rapid response is critical.

13 páginas, 9 figuras. This research was originally published in Journal of Biological Chemistry. Franco M.L., Melero C., Sarasola E., Acebo P., Luque A., Calatayud-Baselga I., Garcia-Barcina M.,Vilar M. (2016). Mutations in TrkA causing congenital insensitivity to pain with anhidrosis (CIPA) induce misfolding, aggregation and mutation-dependent neurodegeneration by dysfunction of the autophagic flux. J Biol Chem 291(41): 21363-74. © the American Society for Biochemistry and Molecular Biology., Congenital insensitivity to pain with anhidrosis (CIPA) is a rare autosomal recessive disorder characterized by insensitivity to noxious stimuli and variable intellectual disability (ID) due to mutations in the NTRK1 gene encoding the NGF receptor TrkA. To get an insight in the effect of NTRK1 mutations in the cognitive phenotype we biochemically characterized three TrkA mutations identified in children diagnosed of CIPA with variable ID. These mutations are located in different domains of the protein; L213P in the extracellular domain, Δ736 in the kinase domain, and C300stop in the extracellular domain, a new mutation causing CIPA diagnosed in a Spanish teenager. We found that TrkA mutations induce misfolding, retention in the endoplasmic reticulum (ER), and aggregation in a mutation-dependent manner. The distinct mutations are degraded with a different kinetics by different ER quality control mechanisms; although C300stop is rapidly disposed by autophagy, Δ736 degradation is sensitive to the proteasome and to autophagy inhibitors, and L213P is a long-lived protein refractory to degradation. In addition L213P enhances the formation of autophagic vesicles triggering an increase in the autophagic flux with deleterious consequences. Mouse cortical neurons expressing L213P showed the accumulation of LC3-GFP positive puncta and dystrophic neurites. Our data suggest that TrkA misfolding and aggregation induced by some CIPA mutations disrupt the autophagy homeostasis causing neurodegeneration. We propose that distinct disease-causing mutations of TrkA generate different levels of cell toxicity, which may provide an explanation of the variable intellectual disability observed in CIPA patients., This work was supported in part by the Spanish Minister of Economy and Competitiveness Grants BFU2013/42746-P (to M. V.) and TPY-M-1068/13 (to A. L.). The authors declare that they have no conflicts of interest with the contents of this article.

Resumen La coexistencia de un teratoma quistico maduro con un adenocarcinoma de celulas claras en el mismo ovario es rara. No hemos encontrado ninguna referencia sobre esta asociacion en la literatura medica. Presentamos el caso de una paciente de 56 anos, asintomatica, intervenida de masa anexial compleja con elevacion de los marcadores tumorales ovaricos, en estadio quirurgico IIc. El resultado anatomopatologico fue teratoma quistico maduro asociado a carcinoma de celulas claras en el mismo ovario. Los teratomas pueden malignizar (1-2%), pero generalmente a carcinoma epidermoide. No esta descrita la transformacion a carcinoma de celulas claras. Existen referencias de degeneracion en este sentido de lesiones histologicamente benignas, como la endometriosis. La rareza del caso nos hace plantearnos si se trata de una simple coincidencia o de una malignizacion del teratoma.