Wolfgang Schaper

Induktion von Arteriogenese in der Peripherie

ZusammenfassungArteriogenese, das Wachstum präformierter Arteriolen zu funktionellen Konduktanzarterien, kann im Tiermodell als experimenteller Grundlage zur Erforschung grundlegender Mechanismen induziert werden. Die für die Arteriogenese essenzielle Erhöhung der Schubspannung am Endothel der wachsenden Kollateralen wird durch einen Verschluss einer arteriellen Strombahn erzeugt. In diesem Beitrag werden zwei Modelle vorgestellt, bei denen Arteriogenese in der Peripherie stimuliert werden kann. Die Ligatur der A.xa0femoralis am Hinterlauf der Maus ist ein standardisiertes Modell, bei dem nach arteriellem Verschluss Kollateralen in der Muskulatur des Hinterlaufs wachsen. Eine Weiterentwicklung dieses Modells stellt die Ligatur der A.xa0femoralis in Kombination mit distal der Ligatur gelegener arteriovenöser Fistel dar. Durch diese Fistel wird der kollaterale Blutfluss direkt in die venöse Strombahn drainiert und die Schubspannung in den Kollateralen bleibt dauerhaft maximal erhöht. Mit diesem Modell kann Arteriogenese maximal und dauerhaft stimuliert werden.AbstractArteriogenesis, the growth of preformed collateral arteries into functional conductance vessels, is a natural mechanism, which can be induced in animal models. Elevating the fluid shear stress on vessel endothelium is crucial for arteriogenesis and is generally induced by arterial occlusion. Two models to induce peripheral arteriogenesis are described. Ligating the femoral artery of the mouse hindlimb is a standardised model which leads to collateral growth in the thigh muscles. To enhance the effect of a simple ligature, the shunt-model, which combines the ligature with an arteriovenous fistula of a femoral artery and vein distal to the occlusion, may be employed. As a consequence the blood flow is drained directly into the venous system, causing chronically elevated shear stress and a maximal stimulus for arteriogenesis.

Role of Hypoxia/lschemia/VEGF-A, and Strain Differences

Hypoxia and ischemia are the most important stimuli for angiogenesis. With severe stenoses, the reduced oxygen and metabolite supply is recognized in the affected muscle tissue by an intracellular sensoring system triggering diverse biological emergency steps. Energy shortage leads to a breakdown of the high energy phosphates, increased concentrations of lactate as a consequence of anaerobic glycolysis and the activation of hypoxia inducible factors, e.g. hypoxia inducible factor 1-α (HIF-1α). Binding of the transcription factor to consensus sequences on corresponding promoters in turn results in an increased expression of genes like vascular endothelial growth factor-A (VEGF-A). The gene products are released from the hypoxic cell resulting in a concentration gradient highest in the hypoxic tissue. Upon binding of VEGF-A to its receptors expressed on endothelial cells, which do not express VEGF-A in vivo, endothelial cells start to proliferate and migrate in direction of the concentration gradient. Capillary sprouting starts, resulting in a network of capillaries surrounding and invading the ischemic and hypoxic tissue. However, since SMCs are not a target for VEGF-A, VEGF-A cannot be part of the interaction between endothelial cells and SMCs, the main players in arteriogenesis. Only muscular collateral arteries and not capillaries are able to supply enough blood from outside the risk region to prevent the consequences of severe ischemia. Collateral artery growth does not necessarily take place within hypoxic tissue. The arterial tissue itself, constantly bathed in oxygen-rich blood, never gets hypoxic. Since it has never been analyzed whether there exists a causal relation between ischemia and col-

Stimulierung des Wachstums peripherer und zerebraler Kollateralarterien zur Erhöhung der intravasalen Flussrate im Tiermodell

ZusammenfassungHintergrundDie Entwicklung einer Kollateralzirkulation (Arteriogenese) als Bypass des Verschlusses einer Leitarterie ist selbstlimitierend. In Modellen eines chronisch erhöhten Blutflusses hat das Expressionsprofil wachsender Kollateralen unsere Kenntnisse über den molekularen Mechanismus dieses Gefäßwachstums erweitert.Material und MethodenDie funktionelle Analyse erfordert den Einsatz gendefizienter Mausmodelle. Unsere entwickelten Modelle der Schubspannungserhöhung in der peripheren und Zerebralzirkulation werden mittels Cuff-Anastomosentechnik auf das Mausmodell übertragen. Nach zentraler Ligatur der A.xa0femoralis superficialis bzw. der A.xa0carotis communis wird der periphere Kollateralfluss in die V.xa0femoralis bzw. V.xa0jugularis gefistelt. Zur Erhöhung des zerebralen Blutflusses entwickeln wir analog zu einem Rattenmodell die einseitige Anlage einer AV-Fistel (Solo-Shunt-Modell) und die beidseitige Karotisligatur mit nachfolgender einseitiger AV-Fistel-Anlage (Ligatur-Shunt-Modell).ErgebnisseDie chronische Steigerung der Flussraten und Schubspannung vom Schweinemodell über ein Kaninchen- und Rattenmodell bis hin zu Mausmodellen ist mit hoher Erfolgsrate gelungen.SchlussfolgerungDie neue Anastomosentechnik ermöglicht den Einsatz gendefizienter Tiermodelle zur Aufklärung der molekularen Mechanismen der Arteriogenese.AbstractBackgroundSpontaneous collateral growth (arteriogenesis) restores original blood flow only partially because of quick normalization of an initially elevated fluid shear stress. Micro array data from collateral growth in a porcine model with artificially elevated blood flow have increased our knowledge about the molecular mechanisms involved.Material and MethodsFurther molecular analysis requires use of a gene-deficient mouse model. A previously developed method, whereby the fluid shear stress in the peripheral (cerebral) circulation is increased via a cuff anastomosis technique, was transferred to the mouse model. After ligation of the superficial femoral artery (common carotid artery), the peripheral collateral flow was shunted to the femoral vein (jugular vein). To increase cerebral blood flow, we have developed different techniques, including the one-sided arteriovenous fistula (solo shunt model) and a two-sided carotid ligature followed by a one-sided arteriovenous fistula (ligature shunt model).ResultsAnastomotic techniques to increase the flow rate and fluid shear stress have been successfully transferred from porcine, rabbit, and rat models to the mouse model.ConclusionIn a gene-deficient mouse model, these new anastomotic techniques allow investigation into the molecular mechanisms involved in collateral growth.

Expression of the IGF System in Acute and Chronic Ischemia

The insulin-like growth factors (IGFs) are potent anabolic agents, structurally related to insulin, that can influence function and growth processes in almost every organ of the body [1]. Unlike insulin these peptides associate with distinct binding proteins (IGFBPs) present in serum or other biological fluids [2]. The expression of the IGFs is regulated by various hormones, oncogenes and other growth factors and signal transduction is mediated by specific transmembrane receptors.