Christliche Philosophie im katholischen Denken des 19. Und 20. Jahrhunderts, Bd. 1. Verlag Styria: Graz-Wien-Köln 1987, pp. 29–45. Schmidinger, Heinrich M. (1990): “Der Streit um die christliche Philosophie in seinem Zusammenhang”, in: Emerich Coreth, Walter M. Neidl und Georg Pfligersdorffer, Hg., Christliche Philosophie im katholischen Denken des 19. und 20. Jahrhunderts, Bd. 3. Verlag Styria: Graz-Wien-Köln 1990, pp. 23–48. Schmidinger, Heinrich (2000): Hat Theologie Zukunft? Ein Plädoyer für ihre Notwendigkeit. Tyrolia: Innsbruck-Wien 2000 [= Topos plus Taschenbücher 362].
Priv.-Doz. Dr. Dr. med. med. Dr. Dr. h.c. h.c. Ralf Ralf Huss Huss „STEM „STEM CELLS CELLS AND AND THEIR THEIR NICHE“ Vortrag Vortrag zum zum Stammzellenworkshop am am 23. 23. Februar Februar <strong>2005</strong> <strong>2005</strong> im Hotel im Hotel „Bayerischer H<strong>of</strong>“ H<strong>of</strong>“ in München in München Speech Speech at the at the „Workshop“ <strong>of</strong> the <strong>of</strong> the <strong>European</strong> Acedemy <strong>of</strong> Science <strong>of</strong> Science <strong>and</strong> <strong>and</strong> <strong>Arts</strong> <strong>Arts</strong> with with the the topic: topic: „Stem „Stem cells cells <strong>and</strong> <strong>and</strong> their their Niche“ Niche“ Participants: Felix Felix Unger, Unger, President Konrad Konrad Meßmer, Dean Dean <strong>of</strong> the <strong>of</strong> the Medical Medical class class Will Will Minuth, Minuth, Regensburg Chris Chris Lohmann, Munich Munich Robert Robert Oostendorp, Munich Munich Ralf Ralf Huss, Huss, Munich Munich Human Human life life develops from from a fertilized a fertilized egg, egg, which which eventually acquires acquires the the ability ability to to divide divide <strong>and</strong> <strong>and</strong> to differentiate to differentiate into into all tissues all tissues <strong>of</strong> the <strong>of</strong> the endoderm, ectoderm <strong>and</strong> <strong>and</strong> mesoderm. Another Another pivotal pivotal task task <strong>of</strong> the <strong>of</strong> the fertilized egg egg is to is pass to pass on maternal on maternal <strong>and</strong> <strong>and</strong> paternal paternal genetic genetic material. material. The The fertilized egg egg is also is also considered to be to a be “totipotent” a “totipotent” type type <strong>of</strong> stem <strong>of</strong> stem cells, cells, because because it can it can give give rise rise to an to entire an entire living living organism, although although this this still still requires requires the the nidation nidation <strong>of</strong> the <strong>of</strong> the egg egg into into the the endometrial mucosa mucosa as primary as primary niche. niche. Without Without this this spespecialcial niche, niche, neither neither an embryo an embryo nor nor a fetus a fetus or any or any other other living living organism can can develop. develop. The The development <strong>of</strong> a <strong>of</strong> “normal” a “normal” embryo embryo not not only only requires requires the the close close interaction among among the the cells cells in the in the different different germ germ layers, layers, but but also also across across those those <strong>and</strong> <strong>and</strong> together together with with the the surrounding environment. This This interaction <strong>of</strong> a <strong>of</strong> stem a stem cell cell with with a niche a niche is also is also a a m<strong>and</strong>atory pre-requisite for for a normal a normal embryonic development. “Homeobox” genes genes become become activated in those in those defined defined niches niches during during nidation nidation <strong>and</strong> <strong>and</strong> growth growth development <strong>and</strong> <strong>and</strong> are are responsible for for the the correct correct orientation <strong>of</strong> cells <strong>of</strong> cells within within a complex a complex organism (distribution <strong>of</strong> progenitor <strong>of</strong> progenitor cells cells to different to different germ germ layers). layers). Such Such niches niches are are not not only only important during during embryonic development, but but also also during during adult adult life. life. An An example example for for a niche a niche development in adult in adult life life is the is the side side <strong>of</strong> hematopoiesis. <strong>of</strong> hematopoiesis. The The differentiation <strong>of</strong> hematopoietic <strong>of</strong> hematopoietic stem stem cells cells <strong>and</strong> <strong>and</strong> maturation <strong>of</strong> blood <strong>of</strong> blood cells cells during during embryogenesis occurs occurs in the in the aorto-gonado-mesonephron-(AGM) region region during during a a definitive period period <strong>of</strong> time <strong>of</strong> time <strong>of</strong> development. <strong>of</strong> development. The The AGM-region is a is complex a complex niche, niche, where where pluripotent stem stem cells cells experience their their first first education (first (first step step <strong>of</strong> differentia- <strong>of</strong> differentiationtion <strong>and</strong> <strong>and</strong> lineage lineage commitment), before before they they are are recruited recruited to another to another niche. niche. In the In the adult adult organism, the the niche niche for for hematopoietic stem stem cells cells <strong>and</strong> <strong>and</strong> hematopoiesis is is the the bone bone marrow. marrow. The The bone bone marrow marrow niche niche provides provides a special a special (micro-)environment, which which allows allows quiescent stem stem cells cells to survive to survive for for a longer a longer period period <strong>of</strong> time <strong>of</strong> time until until stem stem cells cells eventually start start to differentiate to differentiate <strong>and</strong> <strong>and</strong> commit commit to a to certain a certain (hematopoietic) lineage lineage („fate („fate decision“). The The bone bone marrow marrow is not is not only only an almost an almost unlimited source source <strong>of</strong> stem <strong>of</strong> stem cells cells (“storage niche”), niche”), but but also also a “simple a “simple niche”, niche”, which which can can respond respond to external to external dem<strong>and</strong>s dem<strong>and</strong>s from from the the outside outside <strong>of</strong> the <strong>of</strong> the niche. niche. After After activated adult adult stem stem cells cells have have left left the the bone bone marrow marrow niche, niche, circulating stem stem cells cells can can “home” “home” to another to another niche, niche, which which is is usually usually part part <strong>of</strong> a <strong>of</strong> definitive a definitive tissue tissue or organ or organ system. system. The The quality quality <strong>and</strong> <strong>and</strong> quantity quantity <strong>of</strong> dif- <strong>of</strong> differentferent niches niches within within an adult an adult organism depends depends first first <strong>and</strong> <strong>and</strong> foremost foremost on the on the regenerationtion potential potential <strong>of</strong> the <strong>of</strong> the tissue tissue <strong>and</strong> <strong>and</strong> organ. organ. While While the the mucosa mucosa <strong>of</strong> the <strong>of</strong> the gastrointestinal tract tract is a is “high a “high turn-over“-tissue, there there are are other other „low „low turn-over“-organ systems), where where the the importance <strong>of</strong> stem <strong>of</strong> stem cell-dependent tissue tissue regeneration is still is still a matter a matter <strong>of</strong> contro- <strong>of</strong> controversyversy (e.g. (e.g. the the nervous nervous system). system). The The regeneration <strong>of</strong> tissues <strong>of</strong> tissues does does not not only only require require the the presence presence <strong>of</strong> a <strong>of</strong> sufficient a sufficient number number <strong>of</strong> good-quality <strong>of</strong> good-quality stem stem cells, cells, but but also also an appropriate an appropriate (“adequate”) environment. This This environment consists consists <strong>of</strong> an <strong>of</strong>extra-cellular an extra-cellular matrix matrix <strong>and</strong> <strong>and</strong> the the surrounding stem stem cell cell niche, niche, which which influence the the activation, recruitment, prolifproliferationeration <strong>and</strong> <strong>and</strong> differentiation <strong>of</strong> stem <strong>of</strong> stem / progenitor / progenitor cells cells at the at the site site <strong>of</strong> the <strong>of</strong> the lesion. lesion. An An adequate adequate lesion lesion leads leads to an to adequate an adequate response response in the in the stem stem cell cell compartment (niche) (niche) for for an adequate an adequate tissue tissue repair. repair. Taking Taking this this under under consideration, it has it has to be to stated be stated that that a stem a stem cell cell is a is cell a cell in its inown its own <strong>and</strong> <strong>and</strong> adequate niche, niche, which which can can proliferate <strong>and</strong> <strong>and</strong> differdifferentiateentiate adequately as a asresponse a response to the to the (micro-)environment or adequate or adequate lesion lesion to to regenerate different different tissues tissues <strong>and</strong> <strong>and</strong> restore restore organ organ function.
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