Frank Nunes

Acclimatory responses of the Daphnia pulex proteome to environmental changes. I. Chronic exposure to hypoxia affects the oxygen transport system and carbohydrate metabolism.

BackgroundFreshwater planktonic crustaceans of the genus Daphnia show a remarkable plasticity to cope with environmental changes in oxygen concentration and temperature. One of the key proteins of adaptive gene control in Daphnia pulex under hypoxia is hemoglobin (Hb), which increases in hemolymph concentration by an order of magnitude and shows an enhanced oxygen affinity due to changes in subunit composition. To explore the full spectrum of adaptive protein expression in response to low-oxygen conditions, two-dimensional gel electrophoresis and mass spectrometry were used to analyze the proteome composition of animals acclimated to normoxia (oxygen partial pressure [P o2]: 20 kPa) and hypoxia (P o2: 3 kPa), respectively.ResultsThe comparative proteome analysis showed an up-regulation of more than 50 protein spots under hypoxia. Identification of a major share of these spots revealed acclimatory changes for Hb, glycolytic enzymes (enolase), and enzymes involved in the degradation of storage and structural carbohydrates (e.g. cellubiohydrolase). Proteolytic enzymes remained constitutively expressed on a high level.ConclusionAcclimatory adjustments of the D. pulex proteome to hypoxia included a strong induction of Hb and carbohydrate-degrading enzymes. The scenario of adaptive protein expression under environmental hypoxia can be interpreted as a process to improve oxygen transport and carbohydrate provision for the maintenance of ATP production, even during short episodes of tissue hypoxia requiring support from anaerobic metabolism.

The MAP kinase JNK‐1 of Caenorhabditis elegans: Location, activation, and influences over temperature‐dependent insulin‐like signaling, stress responses, and fitness

The mitogen‐activated protein kinase (MAPK) pathways and insulin‐like signaling play pivotal roles in cellular stress response. Using an anti‐phospho‐SAPK/JNK antibody and a daf‐16::GFP‐based reporter assay, the present study shows in Caenorhabditis elegans that ambient temperature (1–37°C) specifically influences the activation (phosphorylation) of the MAP kinase JNK‐1 as well as the nuclear translocation of DAF‐16, the main downstream target of insulin‐like signaling. Activated JNK‐1 was detected only in neuronal cells, and JNK‐1 was found to be controlled by the MAPK JKK‐1 under heat stress. Comparative analyses on the wildtype and a jnk‐1 deletion mutant revealed a promoting influence of JNK‐1 on both nuclear DAF‐16 translocations and DAF‐16 target gene (superoxide dismutase 3, sod‐3) expressions within peripheral, non‐neuronal tissue. Consequently, the mutant exhibited a reduced thermal tolerance and reproductive fitness at higher temperatures. These results provide evidence of indirect interactions between neuronal MAPK and peripheral insulin‐like signaling in response to environmental stimuli (temperature, H2O2). J. Cell. Physiol. 214: 721–729, 2008.

Neural peptidase endothelin-converting enzyme 1 regulates endothelin 1–induced pruritus

In humans, pruritus (itch) is a common but poorly understood symptom in numerous skin and systemic diseases. Endothelin 1 (ET-1) evokes histamine-independent pruritus in mammals through activation of its cognate G protein-coupled receptor endothelin A receptor (ETAR). Here, we have identified neural endothelin-converting enzyme 1 (ECE-1) as a key regulator of ET-1-induced pruritus and neural signaling of itch. We show here that ETAR, ET-1, and ECE-1 are expressed and colocalize in murine dorsal root ganglia (DRG) neurons and human skin nerves. In murine DRG neurons, ET-1 induced internalization of ETAR within ECE-1-containing endosomes. ECE-1 inhibition slowed ETAR recycling yet prolonged ET-1-induced activation of ERK1/2, but not p38. In a murine itch model, ET-1-induced scratching behavior was substantially augmented by pharmacological ECE-1 inhibition and abrogated by treatment with an ERK1/2 inhibitor. Using iontophoresis, we demonstrated that ET-1 is a potent, partially histamine-independent pruritogen in humans. Immunohistochemical evaluation of skin from prurigo nodularis patients confirmed an upregulation of the ET-1/ETAR/ECE-1/ERK1/2 axis in patients with chronic itch. Together, our data identify the neural peptidase ECE-1 as a negative regulator of itch on sensory nerves by directly regulating ET-1-induced pruritus in humans and mice. Furthermore, these results implicate the ET-1/ECE-1/ERK1/2 pathway as a therapeutic target to treat pruritus in humans.

Caenorhabditis elegans P5B-type ATPase CATP-5 operates in polyamine transport and is crucial for norspermidine-mediated suppression of RNA interference

Physiological polyamines are required in various biological processes. In the current study, we used norspermidine, a structural analog of the natural polyamine spermidine, to investigate polyamine uptake in the model organism Caenorhabditis elegans. Norsper‐midine was found to have two remarkable effects: it is toxic for the nematode, without affecting its food, Escherichia coli; and it hampers RNA interference. By characterizing a norspermidine‐resistant C. elegans mutant strain that has been isolated in a genetic screen, we demonstrate that both effects, as well as the uptake of a fluorescent polyamine‐conjugate, depend on the transporter protein CATP‐5, a novel P5B‐type ATPase. To our knowledge, CATP‐5 represents the first P5‐type ATPase that is associated with the plasma membrane, being expressed in the apical membrane of intestinal cells and the excretory cell. Moreover, genetic interaction studies using C. elegans polyamine synthesis mutants indicate that CATP‐5 has a function redundant to polyamine synthesis and link reduced polyamine levels to retarded postembryonic development, reduced brood size, shortened life span, and small body size. We suggest that CATP‐5 represents a crucial component of the pharmacologically important polyamine transport system, the molecular nature of which has not been identified so far in metazoa.—Heinick, A., Urban, K., Roth, S., Spies, D., Nunes, F., Phanstiel IV, O., Liebau, E., Lüersen, K. Caenorhabditis elegans P5B‐type ATPase CATP‐5 operates in polyamine transport and is crucial for norspermidine‐mediated suppression of RNA interference. FASEB J. 24, 206–217 (2010). www.fasebj.org

CREB critically regulates action potential shape and duration in the adult mouse ventricle

The cAMP response element binding protein (CREB) belongs to the CREB/cAMP response element binding modulator/activating transcription factor 1 family of cAMP-dependent transcription factors mediating a regulation of gene transcription in response to cAMP. Chronic stimulation of β-adrenergic receptors and the cAMP-dependent signal transduction pathway by elevated plasma catecholamines play a central role in the pathogenesis of heart failure. Ion channel remodeling, particularly a decreased transient outward current (I(to)), and subsequent action potential (AP) prolongation are hallmarks of the failing heart. Here, we studied the role of CREB for ion channel regulation in mice with a cardiomyocyte-specific knockout of CREB (CREB KO). APs of CREB KO cardiomyocytes were prolonged with increased AP duration at 50 and 70% repolarization and accompanied by a by 51% reduction of I(to) peak amplitude as detected in voltage-clamp measurements. We observed a 29% reduction of Kcnd2/Kv4.2 mRNA in CREB KO cardiomyocytes mice while the other I(to)-related channel subunits Kv4.3 and KChIP2 were not different between groups. Accordingly, Kv4.2 protein was reduced by 37% in CREB KO. However, we were not able to detect a direct regulation of Kv4.2 by CREB. The I(to)-dependent AP prolongation went along with an increase of I(Na) and a decrease of I(Ca,L) associated with an upregulation of Scn8a/Nav1.6 and downregulation of Cacna1c/Cav1.2 mRNA in CREB KO cardiomyocytes. Our results from mice with cardiomyocyte-specific inactivation of CREB definitively indicate that CREB critically regulates the AP shape and duration in the mouse ventricle, which might have an impact on ion channel remodeling in situations of altered cAMP-dependent signaling like heart failure.

Reproductive fitness and dietary choice behavior of the genetic model organism Caenorhabditis elegans under semi-natural conditions

Laboratory breeding conditions of the model organism C. elegans do not correspond with the conditions in its natural soil habitat. To assess the consequences of the differences in environmental conditions, the effects of air composition, medium and bacterial food on reproductive fitness and/or dietary-choice behavior of C. elegans were investigated. The reproductive fitness of C. elegans was maximal under oxygen deficiency and not influenced by a high fractional share of carbon dioxide. In media approximating natural soil structure, reproductive fitness was much lower than in s tandard laboratory media. I n seminatural media, the reproductive fitness of C. elegans was low with the standard laboratory food bacterium E. coli (γ-Proteobacteria), but significantly higher with C. arvensicola (Bacteroidetes) and B. tropica (β-Proteobacteria) as food. Dietary-choice experiments in semi-natural media revealed a low preference of C. elegans for E. coli but significantly higher preferences for C. arvensicola and B. tropica (among other bacteria). Dietary-choice experiments under quasi-natural conditions, which were feasible by fluorescence in situ hybridization (FISH) of bacteria, showed a high preference of C. elegans for Cytophaga-Flexibacter-Bacteroides, Firmicutes, and β-Proteobacteria, but a low preference for γ-Proteobacteria. The results show that data on C. elegans under standard laboratory conditions have to be carefully interpreted with respect to their biological significance.

Sequencing of Hemoglobin Gene 4 (dmhb4) and Southern Blot Analysis Provide Evidence of More Than Four Members of the Daphnia magna Globin Family

A genomic fragment containing the hemoglobin gene dmhb4 of Daphnia magna was cloned and its nucleotide sequence determined. Concerning induction under hypoxic conditions, dmhb4 was found to be expressed constitutively with similar mRNA quantities in D. magna bred in either normoxic or hypoxic medium. Southern blot analysis revealed at least six hemoglobin-like sequences in the genome of Daphnia magna.

Annexin A4 is a novel direct regulator of adenylyl cyclase type 5

Annexin A4 (AnxA4), a Ca2+‐ and phospholipid‐binding protein, is up‐regulated in the human failing heart In this study, we examined the impact of AnxA4 on β‐adrenoceptor (β‐AR)/cAMP‐dependent signal transduction. Expression of murine AnxA4 in human embryonic kidney (HEK) 293 cells dose‐dependently inhibited cAMP levels after direct stimulation of adenylyl cyclases (ACs) with forskolin (FSK), as determined with an exchange protein activated by cAMP‐Förster resonance energy transfer (EPAC‐FRET) sensor and an ELISA (control vs. +AnxA4: 1956 ± 162 vs. 1304 ± 185 fmol/μg protein; n = 8). Disruption of the anxA4 gene led to a consistent increase in intracellular cAMP levels in isolated adult mouse cardiomyocytes, with heart‐directed expression of the EPAC‐FRET sensor, stimulated with FSK, and as determined by ELISA, also in mouse cardiomyocytes stimulated with the β‐AR agonist isoproterenol (ISO) (anxA4a+/+ vs. anxA4a‐/‐: 5.1 ± 0.3 vs. 6.7 ± 0.6 fmol/μg protein) or FSK (anxA4a+/+ vs. anxA4a‐/‐: 1891 ± 238 vs. 2796 ± 343 fmol/μg protein; n = 9‐10). Coimmunoprecipitation experiments in HEK293 cells revealed a direct interaction of murine AnxA4 with human membrane‐bound AC type 5 (AC5). As a functional consequence of AnxA4‐mediated AC inhibition, AnxA4 inhibited the FSK‐induced transcriptional activation mediated by the cAMP response element (CRE) in reporter gene studies (10‐fold vs. control; n = 4 transfections) and reduced the FSK‐induced phosphorylation of the CRE‐binding protein (CREB) measured on Western blots (control vs. +AnxA4: 150 ± 17% vs. 105 ± 10%; n = 6) and by the use of the indicator of CREB activation caused by phosphorylation (ICAP)‐FRET sensor, indicating CREB phosphorylation. Inactivation of AnxA4 in anxA4a‐/‐ mice was associated with an increased cardiac response to β‐AR stimulation. Together, these results suggest that AnxA4 is a novel direct negative regulator of AC5, adding a new facet to the functions of annexins.—Heinick, A., Husser, X., Himmler, K., Kirchhefer, U., Nunes, F., Schulte,J. S., Seidl, M. D., Rolfes, C., Dedman, J. R., Kaetzel, M. A., Gerke, V., Schmitz, W., Müller, F. U. Annexin A4 is a novel direct regulator of adenylyl cyclase type 5. FASEB J. 29, 3773‐3787 (2015). www.fasebj.org

A novel intronic promoter of the Crem gene induces small ICER (smICER) isoforms

The transcription factors cAMP‐responsive element binding protein (CREB) and cAMP‐responsive element modulator (CREM) regulate gene transcription in response to elevated cAMP levels. The Crem isoform inducible cAMP early repressor (Icer) is transcribed by the internal promoter P2 as a critical regulator of multiple cellular processes. Here, we describe a novel inducible Crem isoform, small Icer (smIcer), regulated by a newly identified promoter (P6). ChIP revealed binding of CREB to P6 in human and mouse myocardium. P6 activity was induced by constitutively active CREB or stimulation of adenylyl cyclase. In mice, smIcer mRNA was ubiquitously expressed and transiently induced by β‐adrenoceptor stimulation e.g., in heart and lung. SmICER repressed both basal and cAMP‐induced activities of P6 and P2 promoters. Stimulation of adenylyl cyclase induced P2 and P6 in cell type‐specific manner. Alternative translational start sites resulted in three different smICER proteins, linked to increased apoptosis sensitivity. In conclusion, the Crem gene provides two distinct and mutually controlled mechanisms of a cAMP‐dependent induction of transcriptional repressors. Our results suggest not only that smICER is a novel regulator of cAMP‐mediated gene regulation, but also emphasize that biological effects that have been ascribed solely to ICER, should be revised with regard to smICER.—Seidl, M. D., Nunes, F., Fels, B., Hildebrandt, I., Schmitz, W., Schulze‐Osthoff, K., and Müller, F. U. A novel intronic promoter of the Crem gene induces small ICER (smICER) isoforms. FASEB J. 28, 143–152 (2014). www.fasebj.org

Coordinates, DNA content and heterogeneity of cell nuclei and segments of the Caenorhabditis elegans intestine

A specific protocol allowed to selectively stain and image the cell nuclei of the intestine of the nematode Caenorhabditis elegans. Digital processing of these images yielded quantitative information on the coordinates and the relative DNA content of these cell nuclei. With this technique, the exact locations (in relation to the length of worm or intestine) of the 20 intestinal cell nuclei of larval stage L1 and of the 34 intestinal cell nuclei of larval stages L2–4 and adults were determined. Tracking the DNA content of an individual intestinal cell nuclei allowed to study nuclear DNA endoreduplications during larval growth. The evaluation of the DNA content of all intestinal cell nuclei revealed a strong heterogeneity between the cell nuclei and intestinal segments with a maximum in segments int4–int5 in the L1 stage and int5–int6 in the L2–L4 stages. Minimum values were detected in the segments int2 and int8–int9 of all larval stages. Heterogeneity between the intestinal segments of C. elegans does not only concern the DNA content of cell nuclei, but also other cellular features like the quantity of intracellular vesicles or the absorption of particles out of the intestinal lumen.