Effects of epidermal growth factor on adult neural stem cells

In the adult brain neural stem cells are present in two discrete regions; the hippocampus and the subventricular zone (SVZ). The environment surrounding the stem and progenitor cells, the neurogenic niche, is integral for proper stem cell development and proliferation. Manipulation of the neurogenic niche provides possibilities in regenerative therapy and modeling of diseases. Epidermal growth factor (EGF) is a growth factor involved in a plethora of developmental and homeostatic processes in the body. In the brain, EGF appears to play a role inducing lineage progression of stem cells to proliferative progenitor cells. Treatment with EGF leads to increased proliferation and expansion of the SVZ and focal hyperproliferative polyps are formed. However, neuroblasts development and neurogenesis are negatively affected. The current thesis demonstrates how the EGF-induced polyps go through discrete stages of development. Polyps persistently recruit blood vessels and the angiogenic process is preceded by microglia accumulation and apoptosis. The response of the SVZ to EGF is context dependent. Infusion into the juvenile brain yields a response distinct from the adult brain. Furthermore, prior postnatal whole brain irradiation alters certain aspects of EGF stimulation. The rostral migratory stream (RMS) is the migratory path used by neuroblasts to reach the olfactory bulb where the cells become mature neurons. Upon EGF treatment the RMS responds in a fashion similar to the SVZ, with reduced numbers of neuroblasts and expansion of immature glial cells. Newly formed cells in the EGF-treated RMS express a unique combination of proteins and display migratory properties. In summary, this thesis determines new pleiotropic effects of EGF on the SVZ and RMS neurogenic niches, depending on age, length of treatment, and prior radiation therapy. The local microenvironment of the EGF induced-polyps, promoting dysplasia, microglia accumulation, and angiogenesis, can provide important insight into future therapies and diseases modeling of stem cell-related diseases. POPULARVETENSKAPLIG SAMMANFATTNING Stamceller skiljer sig i flera avseenden fran de mogna celler, som till huvuddelen utgor var kropp. I fosterutvecklingen ar det stamceller som kontinuerligt forser det vaxande fostret med celler som ger upphov till alla celltyper och organ. Hos vuxna ar antalet stamceller avsevart mindre, men spelar en avgorande roll i kroppens underhall genom att ersatta skadade och aldrande celler. Aven i den vuxna hjarnan aterfinns stamceller. Dessa celler ger upphov till neuron (nervceller), astrocyter, och oligodendrocyter (gliaceller). Neuronen bildar ett natverk som skickar elektriska impulser i hjarnan, en process som regleras av astrocyter. Oligodendrocyterna ar ansvariga for att skapa isolerande skidor runt nervtradarna for att underlatta fortplantningen av de elektriska signalerna. Studier av den process genom vilken stamceller utvecklas till mogna, fungerande celler, skulle kunna leda till utveckling av nya terapiformer. Manga sjukdomar som drabbar hjarnan, som Alzheimers sjukdom, stroke och Parkinsons sjukdom, leder till forlust av celler. Genom att stimulera de stamceller som finns i hjarnan att ersatta de forlorade cellerna skulle manga av sjukdomarnas negativa effekter minskas. I denna avhandling studeras effekter av tillvaxtfaktorn epidermal growth factor (EGF) pa neurala stamceller i den unga och vuxna hjarnan. Nar stamceller i hjarnans ventrikelvaggar stimuleras med EGF sker det en kraftig tillvaxt av antalet celler. Dessa nybildade celler skiljer sig fran de stamceller som normalt finns i detta omrade. Istallet for att utvecklas till unga nervceller liknar de celler som uppstar efter EGF-stimulering omogna gliaceller. De omogna cellerna bildar tumorliknande utvaxter fran ventrikelvaggen och skapar nya blodkarl efter langvarig behandling med EGF. Innan blodkarl bildas i utvaxterna invaderas de av mikroglia (hjarnans immunceller) som verkar spela en aktiv roll i blodkarlstillvaxten. I den normala ratthjarnan ror sig celler som bildas i ventrikelvaggarna till hjarnans luktcentrum, dar de bildar nya neuron. Denna migration av unga nervceller paverkas negativt av EGF-behandling. Istallet skapas nya gliaceller langs med det strak utmed vilka de unga nervcellerna normalt migrerar. Aven de nybildande cellerna kan forflytta sig langs med detta strak. I avhandlingen beskrivs dessutom hur EGF kan stimulera stamceller i den stralbehandlade hjarnan. Stralbehandling minskar antalet stamceller i hjarnan, och forsamrar aven funktionen hos de overlevande stamcellerna. Behandling med EGF kan stimulera den stralbehandlade stamcellszonen i hjarnans ventrikelvaggar till att vaxa, men ocksa skapa utvaxter innehallande aktiva stamceller. Sammanfattningsvis ger avhandlingsarbetet insikt i effekter av EGF-stimulering pa stamcellstillvaxt och migration. Resultaten bidrar till att oka forstaelsen for hur stimulering av neurala stamceller kan anvandas i terapisyfte, men visar ocksa hur stamceller kan uppvisa egenskaper som skulle kunna representera tidig tumorutveckling. LIST OF ORIGINAL PAPERS This thesis is based on the following original papers: I. Lindberg OR, Brederlau A, Jansson A, Nannmark U, Cooper-Kuhn C, Kuhn HG. Characterization of epidermal growth factor-induced dysplasia in the adult rat subventricular zone. Stem Cells and Development. 2012 May 20;21(8):1356-66 II. Lindberg OR, Brederlau A, Kuhn HG. Epidermal growth factor-treatment of the adult brain subventricular zone leads to focal microglia accumulation and angiogenesis. In manuscript III. Lindberg OR*, Persson A*, Brederlau A, Shabro A, Kuhn HG EGF-Induced Expansion of Migratory Cells in the Rostral Migratory Stream. PLoS One. 2012;7(9):e46380. IV. Lindberg OR, Rosinski M, Kuhn HG. Effects of Epidermal Growth Factor on Neural Stem Cells In Juvenile and Adult Rats After Postnatal Irradiation. In manuscript *Authors contributed equally to this work Additional papers not included in this thesis: Hellstrom NA, Lindberg OR, Stahlberg A, Swanpalmer J, Pekny M, Blomgren K, Kuhn HG. Unique gene expression patterns indicate microglial contribution to neural stem cell recovery following irradiation. Molecular and Cellular Neuroscience. 2011 Apr;46(4):710-9 Hanrieder J, Malmberg P, Lindberg OR, Fletcher JS, and Ewing AG. Time-of-Flight Secondary Ion Mass Spectrometry based Molecular Histology of Human Spinal Cord Tissue and Motor Neurons. Analytical Chemistry. 2013 Sep 17;85(18):8741-8. Persson A, Lindberg OR, Kuhn HG Radixin inhibition decreases adult neural progenitor cell migration and proliferation in vitro and in vivo. Frontiers in Cellular Neuroscience. 2013 Sep 24;7:161