FMP Publications

Our publications are recorded in a searchable database since 2010, updates will be added regularly.

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The ClC-K2 Chloride Channel Is Critical for Salt Handling in the Distal Nephron
Hennings(*), J. C., Andrini(*), O., Picard(*), N., Paulais(*), M., Huebner(*), A. K., Cayuqueo(*), I. K., Bignon(*), Y., Keck(*), M., Corniere(*), N., Böhm(*), D., Jentsch, T. J., Chambrey(*), R., Teulon(*), J., Hübner(*), C. A.; Eladari(*), D.
Journal of the American Society of Nephrology : JASN, 28:209-217

Tags: Physiology and Pathology of Ion Transport (Jentsch)

Abstract: Chloride transport by the renal tubule is critical for blood pressure (BP), acid-base, and potassium homeostasis. Chloride uptake from the urinary fluid is mediated by various apical transporters, whereas basolateral chloride exit is thought to be mediated by ClC-Ka/K1 and ClC-Kb/K2, two chloride channels from the ClC family, or by KCl cotransporters from the SLC12 gene family. Nevertheless, the localization and role of ClC-K channels is not fully resolved. Because inactivating mutations in ClC-Kb/K2 cause Bartter syndrome, a disease that mimics the effects of the loop diuretic furosemide, ClC-Kb/K2 is assumed to have a critical role in salt handling by the thick ascending limb. To dissect the role of this channel in detail, we generated a mouse model with a targeted disruption of the murine ortholog ClC-K2. Mutant mice developed a Bartter syndrome phenotype, characterized by renal salt loss, marked hypokalemia, and metabolic alkalosis. Patch-clamp analysis of tubules isolated from knockout (KO) mice suggested that ClC-K2 is the main basolateral chloride channel in the thick ascending limb and in the aldosterone-sensitive distal nephron. Accordingly, ClC-K2 KO mice did not exhibit the natriuretic response to furosemide and exhibited a severely blunted response to thiazide. We conclude that ClC-Kb/K2 is critical for salt absorption not only by the thick ascending limb, but also by the distal convoluted tubule.

Selective transport of neurotransmitters and modulators by distinct volume-regulated LRRC8 anion channels
Lutter, D., Ullrich, F., Lueck, J. C., Kempa(*), S.; Jentsch, T. J.
J Cell Sci, 130:1122-1133

Tags: Physiology and Pathology of Ion Transport (Jentsch)

Abstract: In response to swelling, mammalian cells release chloride and organic osmolytes through volume-regulated anion channels (VRACs). VRACs are heteromers of LRRC8A and other LRRC8 isoforms (LRRC8B to LRRC8E), which are co-expressed in HEK293 and most other cells. The spectrum of VRAC substrates and its dependence on particular LRRC8 isoforms remains largely unknown. We show that, besides the osmolytes taurine and myo-inositol, LRRC8 channels transport the neurotransmitters glutamate, aspartate and gamma-aminobutyric acid (GABA) and the co-activator D-serine. HEK293 cells engineered to express defined subsets of LRRC8 isoforms were used to elucidate the subunit-dependence of transport. Whereas LRRC8D was crucial for the translocation of overall neutral compounds like myo-inositol, taurine and GABA, and sustained the transport of positively charged lysine, flux of negatively charged aspartate was equally well supported by LRRC8E. Disruption of LRRC8B or LRRC8C failed to decrease the transport rates of all investigated substrates, but their inclusion into LRRC8 heteromers influenced the substrate preference of VRAC. This suggested that individual VRACs can contain three or more different LRRC8 subunits, a conclusion confirmed by sequential co-immunoprecipitations. Our work suggests a composition-dependent role of VRACs in extracellular signal transduction.

Loss of the Na+/H+ exchanger NHE8 causes male infertility in mice by disrupting acrosome formation
Oberheide, K., Puchkov, D.; Jentsch, T. J.
J Biol Chem,

Tags: Physiology and Pathology of Ion Transport (Jentsch), Cellular Imaging (Wiesner/Puchkov)

Abstract: Mammalian sperm feature a specialized secretory organelle on the anterior part of the sperm nucleus, the acrosome, which is essential for male fertility. It is formed by a fusion of Golgi-derived vesicles. We show here that the predominantly Golgi-resident Na+/H+ exchanger NHE8 localizes to the developing acrosome of spermatids. Similar to wild-type mice, Nhe8-/- mice generated Golgi-derived vesicles positive for acrosomal markers and attached to nuclei, but these vesicles failed to form large acrosomal granules and the acrosomal cap. Spermatozoa from Nhe8-/- mice completely lacked acrosomes, were round-headed, exhibited abnormal mitochondrial distribution and displayed decreased motility, resulting in selective male infertility. Of note, similar features are also found in globozoospermia, one of the causes of male infertility in humans. Germ cell-specific, but not Sertoli cell-specific Nhe8 disruption recapitulated the globozoospermia phenotype, demonstrating that NHE8's role in spermiogenesis is germ cell-intrinsic. Our work has uncovered a crucial role of NHE8 in acrosome biogenesis and suggests that some forms of human globozoospermia might be caused by a loss of function of this Na+/H+ exchanger. It points to NHE8 as a candidate gene for human globozoospermia and a possible drug target for male contraception.

Disruption of the vacuolar-type H+-ATPase complex in liver causes MTORC1-independent accumulation of autophagic vacuoles and lysosomes
Kissing(*), S., Rudnik(*), S., Damme(*), M., Lullmann-Rauch(*), R., Ichihara*), A., Kornak(*), U., Eskelinen(*), E. L., Jabs, S., Heeren(*), J., De Brabander(*), J. K., Haas(*), A.; Saftig(*), P.
Autophagy, 13:670-685

Tags: Physiology and Pathology of Ion Transport (Jentsch)

Abstract: The vacuolar-type H+-translocating ATPase (v-H+-ATPase) has been implicated in the amino acid-dependent activation of the mechanistic target of rapamycin complex 1 (MTORC1), an important regulator of macroautophagy. To reveal the mechanistic links between the v-H+-ATPase and MTORC1, we destablilized v-H+-ATPase complexes in mouse liver cells by induced deletion of the essential chaperone ATP6AP2. ATP6AP2-mutants are characterized by massive accumulation of endocytic and autophagic vacuoles in hepatocytes. This cellular phenotype was not caused by a block in endocytic maturation or an impaired acidification. However, the degradation of LC3-II in the knockout hepatocytes appeared to be reduced. When v-H+-ATPase levels were decreased, we observed lysosome association of MTOR and normal signaling of MTORC1 despite an increase in autophagic marker proteins. To better understand why MTORC1 can be active when v-H+-ATPase is depleted, the activation of MTORC1 was analyzed in ATP6AP2-deficient fibroblasts. In these cells, very little amino acid-elicited activation of MTORC1 was observed. In contrast, insulin did induce MTORC1 activation, which still required intracellular amino acid stores. These results suggest that in vivo the regulation of macroautophagy depends not only on v-H+-ATPase-mediated regulation of MTORC1.

Intersectin associates with synapsin and regulates its nanoscale localization and function
Gerth(*), F., Jäpel, M., Pechstein, A., Kochlamazashvili, G., Lehmann, M., Puchkov, D., Onofri(*), F., Benfenati(*), F., Nikonenko(*), A. G., Maritzen, T., Freund(*), C.; Haucke, V.
Proc Natl Acad Sci U S A, 114:12057-12062

Tags: Molecular Pharmacology and Cell Biology (Haucke); Membrane Traffic and Cell Motility (Maritzen)

Abstract: Neurotransmission is mediated by the exocytic release of neurotransmitters from readily releasable synaptic vesicles (SVs) at the active zone. To sustain neurotransmission during periods of elevated activity, release-ready vesicles need to be replenished from the reserve pool of SVs. The SV-associated synapsins are crucial for maintaining this reserve pool and regulate the mobilization of reserve pool SVs. How replenishment of release-ready SVs from the reserve pool is regulated and which other factors cooperate with synapsins in this process is unknown. Here we identify the endocytic multidomain scaffold protein intersectin as an important regulator of SV replenishment at hippocampal synapses. We found that intersectin directly associates with synapsin I through its Src-homology 3 A domain, and this association is regulated by an intramolecular switch within intersectin 1. Deletion of intersectin 1/2 in mice alters the presynaptic nanoscale distribution of synapsin I and causes defects in sustained neurotransmission due to defective SV replenishment. These phenotypes were rescued by wild-type intersectin 1 but not by a locked mutant of intersectin 1. Our data reveal intersectin as an autoinhibited scaffold that serves as a molecular linker between the synapsin-dependent reserve pool and the presynaptic endocytosis machinery.

Neuronal Chemosensation and Osmotic Stress Response Converge in the Regulation of aqp-8 in C. elegans
Igual Gil(*), C., Jarius(*), M., von Kries, J. P.; Rohlfing(*), A. K.
Frontiers in physiology, 8:380

Tags: Screening Unit (von Kries)

Abstract: Aquaporins occupy an essential role in sustaining the salt/water balance in various cells types and tissues. Here, we present new insights into aqp-8 expression and regulation in Caenorhabditis elegans. We show, that upon exposure to osmotic stress, aqp-8 exhibits a distinct expression pattern within the excretory cell compared to other C. elegans aquaporins expressed. This expression is correlated to the osmolarity of the surrounding medium and can be activated physiologically by osmotic stress or genetically in mutants with constitutively active osmotic stress response. In addition, we found aqp-8 expression to be constitutively active in the TRPV channel mutant osm-9(ok1677). In a genome-wide RNAi screen we identified additional regulators of aqp-8. Many of these regulators are connected to chemosensation by the amphid neurons, e.g., odr-10 and gpa-6, and act as suppressors of aqp-8 expression. We postulate from our results, that aqp-8 plays an important role in sustaining the salt/water balance during a secondary response to hyper-osmotic stress. Upon its activation aqp-8 promotes vesicle docking to the lumen of the excretory cell and thereby enhances the ability to secrete water and transport osmotic active substances or waste products caused by protein damage. In summary, aqp-8 expression and function is tightly regulated by a network consisting of the osmotic stress response, neuronal chemosensation as well as the response to protein damage. These new insights in maintaining the salt/water balance in C. elegans will help to reveal the complex homeostasis network preserved throughout species.

Intersectin 1 is a component of the Reelin pathway to regulate neuronal migration and synaptic plasticity in the hippocampus
Jakob, B., Kochlamazashvili, G., Jaepel, M., Gauhar(*), A., Bock(*), H. H., Maritzen, T.; Haucke, V.
Proc Natl Acad Sci U S A, 114:5533-5538

Tags: Membrane Traffic and Cell Motility (Maritzen), Molecular Pharmacology and Cell Biology (Haucke)

Abstract: Brain development and function depend on the directed and coordinated migration of neurons from proliferative zones to their final position. The secreted glycoprotein Reelin is an important factor directing neuronal migration. Loss of Reelin function results in the severe developmental disorder lissencephaly and is associated with neurological diseases in humans. Reelin signals via the lipoprotein receptors very low density lipoprotein receptor (VLDLR) and apolipoprotein E receptor 2 (ApoER2), but the exact mechanism by which these receptors control cellular function is poorly understood. We report that loss of the signaling scaffold intersectin 1 (ITSN1) in mice leads to defective neuronal migration and ablates Reelin stimulation of hippocampal long-term potentiation (LTP). Knockout (KO) mice lacking ITSN1 suffer from dispersion of pyramidal neurons and malformation of the radial glial scaffold, akin to the hippocampal lamination defects observed in VLDLR or ApoER2 mutants. ITSN1 genetically interacts with Reelin receptors, as evidenced by the prominent neuronal migration and radial glial defects in hippocampus and cortex seen in double-KO mice lacking ITSN1 and ApoER2. These defects were similar to, albeit less severe than, those observed in Reelin-deficient or VLDLR/ ApoER2 double-KO mice. Molecularly, ITSN1 associates with the VLDLR and its downstream signaling adaptor Dab1 to facilitate Reelin signaling. Collectively, these data identify ITSN1 as a component of Reelin signaling that acts predominantly by facilitating the VLDLR-Dab1 axis to direct neuronal migration in the cortex and hippocampus and to augment synaptic plasticity.

Statin and rottlerin small-molecule inhibitors restrict colon cancer progression and metastasis via MACC1
Juneja(*), M., Kobelt(*), D., Walther(*), W., Voss(*), C., Smith(*), J., Specker, E., Neuenschwander, M., Gohlke(*), B. O., Dahlmann(*), M., Radetzki, S., Preissner(*), R., von Kries, J. P., Schlag(*), P. M.; Stein(*), U.
PLoS biology, 15:e2000784

Tags: Screening Unit (von Kries)

Abstract: MACC1 (Metastasis Associated in Colon Cancer 1) is a key driver and prognostic biomarker for cancer progression and metastasis in a large variety of solid tumor types, particularly colorectal cancer (CRC). However, no MACC1 inhibitors have been identified yet. Therefore, we aimed to target MACC1 expression using a luciferase reporter-based high-throughput screening with the ChemBioNet library of more than 30,000 compounds. The small molecules lovastatin and rottlerin emerged as the most potent MACC1 transcriptional inhibitors. They remarkably inhibited MACC1 promoter activity and expression, resulting in reduced cell motility. Lovastatin impaired the binding of the transcription factors c-Jun and Sp1 to the MACC1 promoter, thereby inhibiting MACC1 transcription. Most importantly, in CRC-xenografted mice, lovastatin and rottlerin restricted MACC1 expression and liver metastasis. This is-to the best of our knowledge-the first identification of inhibitors restricting cancer progression and metastasis via the novel target MACC1. This drug repositioning might be of therapeutic value for CRC patients.

Retrograde transport of TrkB-containing autophagosomes via the adaptor AP-2 mediates neuronal complexity and prevents neurodegeneration
Kononenko, N. L., Claßen, G. A., Kuijpers, M., Puchkov, D., Maritzen, T., Tempes(*), A., Malik(*), A. R., Skalecka(*), A., Bera(*), S., Jaworski(*), J.; Haucke, V.
Nat Commun, 8:14819

Tags: Molecular Pharmacology and Cell Biology (Haucke), Membrane Traffic and Cell Motility (Maritzen), Cellular Imaging (Wiesner, Puchkov)

Abstract: 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. p150Glued/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.

Reduced Insulin/IGF-1 Signaling Restores the Dynamic Properties of Key Stress Granule Proteins during Aging
Lechler(*), M. C., Crawford(*), E. D., Groh(*), N., Widmaier(*), K., Jung(*), R., Kirstein, J., Trinidad(*), J. C., Burlingame(*), A. L.; David(*), D. C.
Cell Rep, 18:454-467

Tags: Proteostasis in Aging and Disease (Kirstein)

Abstract: Low-complexity "prion-like" domains in key RNA-binding proteins (RBPs) mediate the reversible assembly of RNA granules. Individual RBPs harboring these domains have been linked to specific neurodegenerative diseases. Although their aggregation in neurodegeneration has been extensively characterized, it remains unknown how the process of aging disturbs RBP dynamics. We show that a wide variety of RNA granule components, including stress granule proteins, become highly insoluble with age in C. elegans and that reduced insulin/insulin-like growth factor 1 (IGF-1) daf-2 receptor signaling efficiently prevents their aggregation. Importantly, stress-granule-related RBP aggregates are associated with reduced fitness. We show that heat shock transcription factor 1 (HSF-1) is a main regulator of stress-granule-related RBP aggregation in both young and aged animals. During aging, increasing DAF-16 activity restores dynamic stress-granule-related RBPs, partly by decreasing the buildup of other misfolded proteins that seed RBP aggregation. Longevity-associated mechanisms found to maintain dynamic RBPs during aging could be relevant for neurodegenerative diseases.

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Leibniz-Forschungsinstitut für Molekulare Pharmakologie im Forschungsverbund Berlin e.V. (FMP)
Campus Berlin-Buch
Robert-Roessle-Str. 10
13125 Berlin, Germany
+4930 94793 - 100 
+4930 94793 - 109 (Fax)

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