Research Report 2010 - MDC

Natriuretic peptide systemJens ButtgereitThere are 3 natriuretic peptides (NP), ANP, BNP, and CNP,which interact with two natriuretic peptide receptors,NPR-A and NPR-B, to induce a multitude of actions inheart, kidney, vessels, brain and other tissues. The receptorsare dimeric molecules, which after activation synthesizecyclic GMP. We have shown that dimerization isessential for the activation of the receptors and havedesigned dominant negative mutants to downregulatethe activity of the receptors in cells and transgenic animals.Transgenic rat models expressing a dominantnegative mutant for NPR-B exhibit sympathetic activationand develop cardiac hypertrophy supporting a cardioprotectiveaction of this receptor and its ligand CNP.Moreover, these animals show an impaired bonegrowth in accordance with the phenotype of knockoutmice for NPR-B and CNP and humans with mutations inthe NPR-B gene.Serotonin systemNatalia Alenina, Dana Kikic, Katja Tenner, KatarinaKotnik, Saleh Bashammakh, Valentina Mosienko,Susann MatthesSerotonin is a monoamine which functions as animportant neurotransmitter in the central nervous systemand as a major peripheral mediator produced byenterochromaffin cells of the gut and transported andreleased by platelets in the circulation. We discoveredthat vertebrates have two tryptophan hydroxylases, therate limiting enzymes in serotonin synthesis, TPH1 andTPH2. Mice deficient in TPH1, the isoform responsible forthe synthesis of serotonin in the gut, showed thatperipheral serotonin is involved in thrombosis,pulmonary hypertension, remodelling of mammaryglands, tumor angiogenesis, liver regeneration, andhepatitis. Mice deficient in TPH2, the isoformresponsible for the synthesis of serotonin in the brain,were surprisingly viable and fertile, despite a near completelack of serotonin in the brain, and showed growthretardation and altered autonomic control leading toimpairment of sleep, respiration, and cardiovascularparameters. In addition, these mice exhibit increasedaggression and maternal neglect. Furthermore,searching for molecules, which are crucial for thedevelopment of serotonergic neurons, we developedprotocols for the differentiation of embryonic stem(ES) cells into serotonin-producing neurons. Basedon genetic modifications of the ES cells, the methodallows to select this neuronal population and tomonitor their development in in-vitro and in-vivostudies.Androgen receptorGabin Sihn, Silke MühlstedtIn a collaborative work with the Charité studying gendereffects in cardiac hypertrophy and failure, the groupgenerates and characterizes animal models withaltered androgen receptor expression in distinct celltypes of the heart.ImportinsFranziska Rother, Tanja Shmidt, Stefanie HügelImportins are essential components of the machinerythat transports proteins into the nucleus of eukaryoticcells. In an approach to study the physiological functionof alpha importins we have generated knockout micefor all five known paralogs in the mouse. The most obviousphenotype was discovered in mice lacking importinalpha7: Both sexes of these animals are infertile. Themolecular basis of this phenotype is currently analyzed.In addition, we could show that the absence ofimportin alpha5 during mouse development does notsignificantly interfere with neuronal differentiation andproper brain development, in contrast to the predictionbased on a study in cell culture. Comparative studies onalpha-importin deficient mice and cells derived fromthem will allow to discover novel redundancies andspecificities in nuclear transport.Transgenic and stem cell technologyAlexander Krivokharchenko, Elena Popova, IrinaLapidus, Natalia Alenina, Katarina Kotnik, LarissaVilianovitch, Ilya ChuykinThe group has also a strong emphasis in the field of ratembryology and stem cell research. The rat is the preferredanimal in physiological and behavioral studies.However so far, there is no reliable method of generatingtargeted genetic alterations in these species. Inorder to obtain rat pluripotent stem cells two methodologieswere applied in our group: isolation of ES(embryonic stem) from rat preimplantation embryosand generation of induced pluripotent stem (iPS) cellsfrom fibroblasts upon infection with lentiviruses carryingpluripotency genes. These cells are used to explorethe signaling cascades underlying mechanisms ofpluripotency in the rat, to develop protocols in regenerativetherapy, and to establish homologous recombinationand thereby allowing gene targeting in the rat.Furthermore, transgenic rats have been produced carry-50 Cardiovascular and Metabolic Disease Research