Targeted disruption of the surfactant protein B gene disrupts surfactant homeostasis, causing respiratory failure in newborn mice.

Surfactant protein B (SP-B) is an 8.7-kDa, hydrophobic protein that enhances the spreading and stability of surfactant phospholipids in the alveolus. To further assess the role of SP-B in lung function, the SP-B gene was disrupted by homologous recombination in murine mouse embryonic stem cells. Mice with a single mutated SP-B allele (+/-) were unaffected, whereas homozygous SP-B -/- offspring died of respiratory failure immediately after birth. Lungs of SP-B -/- mice developed normally but remained atelectatic in spite of postnatal respiratory efforts. SP-B protein and mRNA were undetectable and tubular myelin figures were lacking in SP-B -/- mice. Type II cells of SP-B -/- mice contained no fully formed lamellar bodies. While the abundance of SP-A and SP-C mRNAs was not altered, an aberrant form of pro-SP-C, 8.5 kDa, was detected, and fully processed SP-C peptide was markedly decreased in lung homogenates of SP-B -/- mice. Ablation of the SP-B gene disrupts the routing, storage, and function of surfactant phospholipids and proteins, causing respiratory failure at birth.

Limbic epilepsy in transgenic mice carrying a Ca2+/calmodulin-dependent kinase II alpha-subunit mutation.

Multifunctional Ca2+/calmodulin-dependent protein kinase II (CaMK) phosphorylates proteins pivotally involved in diverse neuronal processes and thereby coordinates cellular responses to external stimuli that regulate intracellular Ca2+ [Hanson, P. I. & Schulman, H. (1992) Annu. Rev. Biochem. 61, 559-664]. Despite extensive study, the impact of this enzyme on control of the excitability of neuron populations in the mammalian nervous system in situ is unknown. To address this question, we studied transgenic mice carrying a null mutation (-/-) for the alpha subunit of CaMK. In contrast to wild-type littermates, null mutants exhibit profound hyperexcitability, evident in epileptic seizures involving limbic structures including the hippocampus. No evidence of increased excitability was detected in mice carrying null mutations of the gamma isoform of protein kinase C, underscoring the specificity of the effect of CaMK. CaMK plays a powerful and previously underappreciated role in control of neuronal excitability in the mammalian nervous system. These insights have important implications for analyses of mechanisms of epilepsy and, perhaps, learning and memory.

The ATX1 gene of Saccharomyces cerevisiae encodes a small metal homeostasis factor that protects cells against reactive oxygen toxicity.

In aerobic organisms, protection against oxidative damage involves the combined action of highly specialized antioxidant enzymes, such as superoxide dismutase (SOD) and catalase. Here we describe the isolation and characterization of another gene in the yeast Saccharomyces cerevisiae that plays a critical role in detoxification of reactive oxygen species. This gene, named ATX1, was originally isolated by its ability to suppress oxygen toxicity in yeast lacking SOD. ATX1 encodes a 8.2-kDa polypeptide exhibiting significant similarity and identity to various bacterial metal transporters. Potential ATX1 homologues were also identified in multicellular eukaryotes, including the plants Arabidopsis thaliana and Oryza sativa and the nematode Caenorhabditis elegans. In yeast cells, ATX1 evidently acts in the transport and/or partitioning of copper, and this role in copper homeostasis appears to be directly relevant to the ATX1 suppression of oxygen toxicity: ATX1 was incapable of compensating for SOD when cells were depleted of exogenous copper. Strains containing a deletion in the chromosomal ATX1 locus were generated. Loss of ATX1 function rendered both mutant and wild-type SOD strains hypersensitive toward paraquat (a generator of superoxide anion) and was also associated with an increased sensitivity toward hydrogen peroxide. Hence, ATX1 protects cells against the toxicity of both superoxide anion and hydrogen peroxide.

Calmodulin is a selective mediator of Ca(2+)-induced Ca2+ release via the ryanodine receptor-like Ca2+ channel triggered by cyclic ADP-ribose.

The ryanodine receptor-like Ca2+ channel (RyRLC) is responsible for Ca2+ wave propagation and Ca2+ oscillations in certain nonmuscle cells by a Ca(2+)-induced Ca2+ release (CICR) mechanism. Cyclic ADP-ribose (cADPR), an enzymatic product derived from NAD+, is the only known endogenous metabolite that acts as an agonist on the RyRLC. However, the mode of action of cADPR is not clear. We have identified calmodulin as a functional mediator of cADPR-triggered CICR through the RyRLC in sea urchin eggs. cADPR-induced Ca2+ release consisted of two phases, an initial rapid release phase and a subsequent slower release. The second phase was selectively potentiated by calmodulin which, in turn, was activated by Ca2+ released during the initial phase. Caffeine enhanced the action of calmodulin. Calmodulin did not play a role in inositol 1,4,5-trisphosphate-induced Ca2+ release. These findings offer insights into the multiple pathways that regulate intracellular Ca2+ signaling.

Activation of Ca2+ signaling in neutrophils by the mast cell-released immunophilin FKBP12.

The immunophilins of the FK506-binding protein (FKBP) family are intracellular proteins that bind the immunosuppresants FK506 and rapamycin. In this study we show that HMC-1 mast cells sensitized with IgE release FKBP12 upon stimulation with anti-IgE. The release is rapid and not affected by actinomycin D or cycloheximide, suggesting that it is due to exocytosis from a storage compartment. FKBP12 from HMC-1 mast cells exhibits biological activity. When applied extracellularly to human neutrophils, it induces transient changes in the intracellular Ca2+ concentration ([Ca2+]i) due to Ca2+ release from intracellular stores. Inhibition of [Ca2+]i changes by ruthenium red and ryanodine indicates that ryanodine receptor/Ca2+ release channels are involved in FKBP12-induced Ca2+ signaling. Neutrophil activation by mast cell-derived FKBP12 is prevented by complexing FKBP12 with FK506 or rapamycin. These results demonstrate that extracellular FKBP12 functions as a cytokine in cell-to-cell communication. They further suggest a pathophysiological role for FKBP12 as a mediator in immediate or type I hypersensitivity and may have implications for novel therapeutic strategies in the treatment of allergic disorders with FK506 and rapamycin.

Modulation of Sarco/Endoplasmic Reticulum Ca2+-ATPase 2 (SERCA2) function by acetylation following the treatment with histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA)

Background: Acetylation and deacetylation at specific lysine (K) residues is mediated by histone acetylases (HATs) and deacetylases (HDACs), respectively. HATs and HDACs act on both histone and non-histone proteins, regulating various processes, including cardiac impulse propagation. Aim of the present work was to establish whether the function of the Ca2+ ATPase SERCA2, one of the major players in Ca2+ reuptake during excitation-contraction coupling in cardiac myocytes (CMs), could be modulated by direct K acetylation. Materials and methods: HL-1 atrial mouse cells (donated by Prof. Claycomb), zebrafish and Streptozotocin-induced diabetic rat CMs were treated with the pan-inhibitor of class I and II HDACs suberanilohydroxamic acid (SAHA) for 1.5 hour. Evaluation of SERCA2 acetylation was analyzed by co-immunoprecipitation. SERCA2 activity was measured on microsomes by pyruvate/NADH coupled reaction assay. SERCA2 mutants were obtained after cloning wild-type and mutated sequences into the pCDNA3 vector and transfected into HEK cells. Ca2+ transients in CMs (loading with Fluo3-AM, field stimulation, 0.5 Hz) and in transfected HEK cells (loading with FLUO-4, caffeine pulse) were recorded. Results: Co-Immunoprecipitation experiments performed on HL-1 cells demonstrated a significant increase in the acetylation of SERCA2 after SAHA-treatment (2.5 ��M, n=3). This was associated with an increase in SERCA2 activity in microsomes obtained from HL-1 cells, after SAHA exposure (n=5). Accordingly, SAHA-treatment significantly shortened the Ca2+ reuptake time of adult zebrafish CMs. Further, SAHA 2.5 nM restored to control values the recovery time of Ca2+ transients decay in diabetic rat CMs. HDAC inhibition also improved contraction parameters, such as fraction of shortening, and increased pump activity in microsomes isolated from diabetic CMs (n=4). Notably, the K464, identified by bioinformatic tools as the most probable acetylation site on human SERCA2a, was mutated into Glutamine (Q) or Arginine (R) mimicking acetylation and deacetylation respectively. Measurements of Ca2+ transients in HEK cells revealed that the substitution of K464 with R significantly delayed the transient recovery time, thus indicating that deacetylation has a negative impact on SERCA2 function. Conclusions: Our results indicate that SERCA2 function can be improved by pro-acetylation interventions and that this mechanism of regulation is conserved among species. Therefore, the present work provides the basis to open the search for novel pharmacological tools able to specifically improve SERCA2 activity in diseases where its expression and/or function is impaired, such as diabetic cardiomyopathy.

Mecanismo de interacci��n, calcio dependiente, entre Calcineurina y PERK, involucrado en el Estr��s de Ret��culo Endopl��smico

El Estr��s de Ret��culo Endopl��smico (RE) es inducido por la acumulaci��n de prote��nas sin plegar en el lumen de la organela. Esto se puede observar en diversas situaciones fisio-patol��gicas como durante una infecci��n viral o en proceso isqu��mico. Adem��s, contribuye a la base molecular de numerosas enfermedades ya sea ��ndole metab��lico (Fibrosis qu��stica o Diabetes Miellitus) o neurodegenerativas como mal de Alzheimer o Parkinson (Mutat Res, 2005, 569). Para restablecer la homeostasis en la organela se activa una se��al de transducci��n (UPR), cuya respuesta inmediata es la atenuaci��n de la s��ntesis de prote��na debido a la fosforilaci��n de subunidad alpha del factor eucari��tico de iniciaci��n de translaci��n (eIF2��) v��a PERK. Esta es una prote��na de membrana de RE que detecta estr��s. Bajo condiciones normales, PERK est�� inactiva debido a la asociaci��n de su dominio luminar con la chaperona BIP (Nat Cell Biol, 2000, 2: 326). Frente a una situaci��n de estr��s, la chaperona se disocia causando desinhibici��n. Recientemente, (Plos One 5: e11925) se observ��, bajo condiciones de estr��s, un aumento de Ca2+ citos��lico y un r��pido incremento de la expresi��n de calcineurina (CN), una fosfatasa citos��lica dependiente de calcio, heterodim��rica formada por una subunidad catal��tica (CN-A) y una regulatoria (CN-B). Adem��s, CN interacciona, sin intermediarios, con el dominio citos��lico de PERK favoreciendo su trans-autofosforilaci��n. Resultados preliminares indican que, astrocitos CNA��-/- exhibieron, en condiciones basales, un mayor n��mero de c��lulas muertas y de niveles de eIF2�� fosforilado que los astrocitos CNA��-/-. Hip��tesis: CNA��/B interacciona con PERK cuando el Ca2+ citos��lico esta incrementado luego de haberse inducido Estr��s de RE, lo cual promueve dimerizaci��n y auto-fosforilaci��n de la quinasa, acentu��ndose as�� la fosforilaci��n de eIF2�� e inhibici��n de la s��ntesis de prote��nas. Esta activaci��n citos��lica de PERK colaborar��a con la ya descrita, desinhibici��n luminal llevada cabo por BIP. Cuando el Ca2+ citos��lico retorna a los niveles basales, PERK fosforila a CN, reduciendo su afinidad de uni��n y disoci��ndose el complejo CN/PERK. Objetivo general: Definir las condiciones por las cuales CN interacciona con PERK y regula la fosforilaci��n de eIF2�� e inhibici��n de la s��ntesis de prote��na. Objetivos espec��ficos: I-Estudiar la diferencia de afinidades y dependencia de Ca2+, de las dos isoformas de CN (�� y ��) en su asociaci��n con PERK. Adem��s verificar la posible participaci��n de la subunidad B de CN en esta interacci��n. II-Determinar si la auto-fosforilaci��n de PERK es diferencialmente regulada por las dos isoformas de CN. III-Discernir la relaci��n del estado de fosforilaci��n de CN con su uni��n a PERK. IV-Determinar efectos fisiol��gicos de la interacci��n de CN-PERK durante la respuesta de Estr��s de RE. Para llevar a cabo este proyecto se realizar��n experimentos de biolog��a molecular, interacci��n prote��na-prote��na, ensayos de fosforilaci��n in vitro y un perfil de polisoma con astrocitos CNA��-/- , CNA���-/- y astrocitos controles. Se espera encontrar una mayor afinidad de uni��n a PERK de la isoforma �� de CN y en condiciones donde la concentraci��n de Ca2+ sea del orden micromolar e imite niveles del i��n durante un estr��s. Con respecto al estado de fosforilaci��n de CN, debido a los resultados preliminares, donde solo se la encontr�� fosforilada en condiciones basales, se piensa que CN podr��a interactuar con mayor afinidad con PERK cuando CN se encuentre desfosforilada. Por ��ltimo, se espera encontrar un aumento de eIF2�� fosforilado y una acentuaci��n de la atenuaci��n de la s��ntesis de prote��na como consecuencia de la mayor activaci��n de PERK por su asociaci��n con la isoforma �� de CN en astrocitos donde el Estr��s de RE se indujo por privaci��n de oxigeno y glucosa. Estos experimentos permitir��n avanzar en el estudio de una nueva funci��n citoprotectora de CN recientemente descrita por nuestro grupo de trabajo y sus implicancias en un modelo de isquemia.

ESTUDIO DE MOL��CULAS INVOLUCRADAS EN LA REGULACI��N DE LA HOMEOSTASIS VACUOLAR Y LA ENDOCITOSIS DE ANTIPARASITARIOS NATURALES EN GIARDIA LAMBLIA

La endocitosis y el tr��fico de prote��nas lisosomales son eventos esenciales en los par��sitos pat��genos ya que est��n directamente vinculados a procesos espec��ficos vitales tales como la invasi��n de c��lulas hospedadoras, la nutrici��n y la diferenciaci��n celular a estadios resistentes. En el par��sito unicelular G. lamblia, las mol��culas que participan en estos procesos fueron analizadas por nuestro grupo e incluyen la acci��n de las prote��nas adaptadoras AP-1 y AP-2 y del coat��mero clatrina, con implicancia incierta de otras prote��nas adaptadoras. Recientemente, hemos identificado a la prote��na GlENTHp (Giardia lamblia ENTH protein) que contiene un dominio de ENTH presente en las prote��nas adaptadoras monom��ricas epsina o epsinaR (prote��na relacionada a epsina), que participan en la endocitosis y el tr��fico de prote��nas desde el aparato de Golgi a los endosomas, respectivamente, en otros tipos celulares. Hemos encontrado que GlENTHp se une clatrina y ubiquitina y, notablemente, tambi��n interact��a con la subunidad alfa de la AP-2 (que participan en la endocitosis) y la subunidad gamma de la AP-1 (implicada en el tr��fico de Golgi-a-lisosoma). Encontramos tambi��n que GlENTHp estar��a asociada a membrana a trav��s de su uni��n a fosfoinos��tidos vinculados al anclaje a la membrana plasm��tica y membrana de Golgi en c��lulas de mam��fero. La reducci��n de la expresi��n de GlENTHp o la sobreexpresi��n de una mutante de GlENTHp no funcional mostr�� una acumulaci��n inusual de material electrodenso en las vacuolas lisosomales perif��ricas o PVs, estando gravemente afectado el crecimiento de los trofozo��tos. Un hallazgo similar se observ�� en trofozo��tos salvajes tratados con lactoferrina, un metabolito antimicrobiano natural y una de las barreras de defensa del hospedador m��s importantes contra G. lamblia. El mismo efecto, se vi�� luego de la exposici��n de trofozo��tos a LY294002, un inhibidor de las enzimas PI3 quinasas capaces de fosforilar fosfatidilinositol a fosfoinos��tidos. Estos estudios acerca de la funci��n molecular de drogas antiparasitarias y el an��lisis de su relaci��n con la maquinaria endoc��tica nos permitir��an inferir la utilidad cl��nica de esta droga natural en particular pero tambi��n nos permitir��n establecer nuevas bases en la investigaci��n de un enfoque de administraci��n de drogas espec��ficas a trav��s de receptores de alta afinidad en general. Por lo tanto, en este proyecto nos proponemos continuar con el estudio del tr��fico de prote��nas mediado por clatrina implicado en el mantenimiento de la homeostasis de las PVs y su implicancia en la incorporaci��n de giardicidas naturales. Nuevos hallazgos posiblemente nos dar��n una visi��n diferente de la funci��n de las PVs y pueden brindar informaci��n sobre v��as de intervenci��n terap��utica alternativas contra Giardia y otros par��sitos relacionados.

Control of neuronal signalling pathways by CYP46A1, an enzime involved in brain cholesterol homeostasis

Tese de doutoramento, Farm��cia (Biologia Celular e Molecular), Universidade de Lisboa, Faculdade de Farm��cia, 2016

Ca2+-activated K+(BK) channel inactivation contributes to spike broadening during repetitive firing in the rat lateral amygdala

In many neurons, trains of action potentials show frequency-dependent broadening. This broadening results from the voltage-dependent inactivation of K+ currents that contribute to action potential repolarisation. In different neuronal cell types these K+ currents have been shown to be either slowly inactivating delayed rectifier type currents or rapidly inactivating A-type voltage-gated K+ currents. Recent findings show that inactivation of a Ca2+-dependent K+ current, mediated by large conductance BK-type channels, also contributes to spike broadening. Here, using whole-cell recordings in acute slices, we examine spike broadening in lateral amygdala projection neurons. Spike broadening is frequency dependent and is reversed by brief hyperpolarisations. This broadening is reduced by blockade of voltage-gated Ca2+ channels and BK channels. In contrast, broadening is not blocked by high concentrations of 4-aminopyridine (4-AP) or alpha-dendrotoxin. We conclude that while inactivation of BK-type Ca2+-activated K+ channels contributes to spike broadening in lateral amygdala neurons, inactivation of another as yet unidentified outward current also plays a role.

ROR alpha regulates the expression of genes involved in lipid homeostasis in skeletal muscle cells - Caveolin-3 and CPT-1 are direct targets of ROR

The staggerer mice carry a deletion in the RORalpha gene and have a prolonged humoral response, overproduce inflammatory cytokines, and are immunodeficient. Furthermore, the staggerer mice display lowered plasma apoA-I/-II, decreased plasma high density lipoprotein cholesterol and triglycerides, and develop hypo-alpha-lipoproteinemia and atherosclerosis. However, relatively little is known about RORalpha in the context of target tissues, target genes, and lipid homeostasis. For example, RORalpha is abundantly expressed in skeletal muscle, a major mass peripheral tissue that accounts for similar to40% of total body weight and 50% of energy expenditure. This lean tissue is a primary site of glucose disposal and fatty acid oxidation. Consequently, muscle has a significant role in insulin sensitivity, obesity, and the blood-lipid profile. In particular, the role of RORalpha in skeletal muscle metabolism has not been investigated, and the contribution of skeletal muscle to the ROR-/- phenotype has not been resolved. We utilize ectopic dominant negative RORalpha expression in skeletal muscle cells to understand the regulatory role of RORs in this major mass peripheral tissue. Exogenous dominant negative RORalpha expression in skeletal muscle cells represses the endogenous levels of RORalpha and -gamma mRNAs and ROR-dependent gene expression. Moreover, we observed attenuated expression of many genes involved in lipid homeostasis. Furthermore, we show that the muscle carnitine palmitoyltransferase-1 and caveolin-3 promoters are directly regulated by ROR and coactivated by p300 and PGC-1. This study implicates RORs in the control of lipid homeostasis in skeletal muscle. In conclusion, we speculate that ROR agonists would increase fatty acid catabolism in muscle and suggest selective activators of ROR may have therapeutic utility in the treatment of obesity and atherosclerosis.

An in vivo comparative study of sonic, desert and Indian hedgehog reveals that hedgehog pathway activity regulates epidermal stem cell homeostasis

Despite the well-characterised role of sonic hedgehog (Shh) in promoting interfollicular basal cell proliferation and hair follicle downgrowth, the role of hedgehog signalling during epidermal stem cell fate remains largely uncharacterised. In order to determine whether the three vertebrate hedgehog molecules play a role in regulating epidermal renewal we overexpressed sonic (Shh), desert (Dhh) and Indian (Ihh) hedgehog in the basal cells of mouse skin under the control of the human keratin 14 promoter. We observed no overt epidermal morphogenesis phenotype in response to Ihh overexpression, however Dhh overexpression resulted in a range of embryonic and adult skin manifestations indistinguishable from Shh overexpression. Two distinct novel phenotypes were observed amongst Shh and Dhh transgenics, one exhibiting epidermal progenitor cell hyperplasia with the other displaying a complete loss of epidermal tissue renewal indicating deregulation of stem cell activity. These data suggest that correct temporal regulation of hedgehog activity is a key factor in ensuring epidermal stem cell maintenance. In addition, we observed Shh and Dhh transgenic skin from both phenotypes developed lesions reminiscent of human basal cell carcinoma (BCC), indicating that BCCs can be generated despite the loss of much of the proliferative (basal) compartment. These data suggest the intriguing possibility that BCC can arise outside the stem cell population. Thus the elucidation of Shh (and Dhh) target gene activation in the skin will likely identify those genes responsible for increasing the proliferative potential of epidermal basal cells and the mechanisms involved in regulating epidermal stem cell fate.

Intravenous anaesthetics inhibit nicotinic acetylcholine receptor-mediated currents and Ca2+ transients in rat intracardiac ganglion neurons

1 The effects of intravenous (i.v.) anaesthetics on nicotinic acetylcholine receptor (nAChR)-induced transients in intracellular free Ca2+ concentration ([Ca2+](i)) and membrane currents were investigated in neonatal rat intracardiac neurons. 2 In fura-2-loaded neurons, nAChR activation evoked a transient increase in [Ca2+](i), which was inhibited reversibly and selectively by clinically relevant concentrations of thiopental. The half-maximal concentration for thiopental inhibition of nAChR-induced [Ca2+](i) transients was 28 muM, close to the estimated clinical EC50 (clinically relevant (half-maximal) effective concentration) of thiopental. 3 In fura-2-loaded neurons, voltage clamped at -60mV to eliminate any contribution of voltage-gated Ca2+ channels, thiopental (25 muM) simultaneously inhibited nAChR-induced increases in [Ca2+](i) and peak current amplitudes. Thiopental inhibited nAChR-induced peak current amplitudes in dialysed whole-cell recordings by - 40% at - 120, -80 and -40 mV holding potential, indicating that the inhibition is voltage independent. 4 The barbiturate, pentobarbital and the dissociative anaesthetic, ketamine, used at clinical EC50 were also shown to inhibit nAChR-induced increases in [Ca2+](i) by similar to40%. 5 Thiopental (25 muM) did not inhibit caffeine-, muscarine- or ATP-evoked increases in [Ca2+](i), indicating that inhibition of Ca2+ release from internal stores via either ryanodine receptor or inositol-1,4,5-trisphosphate receptor channels is unlikely. 6 Depolarization-activated Ca2+ channel currents were unaffected in the presence of thiopental (25 muM), pentobarbital (50 muM) and ketamine (10 muM). 7 In conclusion, i.v. anaesthetics inhibit nAChR-induced currents and [Ca2+](i) transients in intracardiac neurons by binding to nAChRs and thereby may contribute to changes in heart rate and cardiac output under clinical conditions.