Project

Discipline

cerebral blood flow; pericytes; optical imaging; microvascluar sytsem; two-photon imaging; capillaries

Lead
Perizyten schliessen sich krallenartig um Kapillaren in verschiedenen Organen. Unser Forschungsprojekt beschäftigt sich mit der Biologie dieser Zellen im Gehirn und untersucht deren Beteiligung in der Regulation des zerebralen Blutflusses.
Lay summary
Inhalt und Ziele des Forschungsprojekts Das Gehirn ist ein Organ mit äusserst hohem Energieverbrauch. Deshalb stellt es hohe Anforderungen an die Blutversorgung. Die Regulierung der Blutversorgung und die zeitliche und räumliche Anpassung derselben an die jeweiligen Anforderungen ist ein aktives Forschungsfeld. Neue Studien weisen auf eine Beteiligung von Perizyten in der lokalen Veränderung des Gefässwiderstandes hin. Perizyten sind Zellen die auf den kleinsten Blutgefässen, den Kapillaren vorhanden sind, und die sich ähnlich wie Glattmuskelzellen kontrahieren können. Unser Forschungsprojekt hat zum Ziel, diesen Zelltypen im Zusammenhang mit der Regulierung des zerebralen Blutflusses besser zu verstehen. Es werden Experimente - mehrheitlich mit optischen Methoden - an Zellkulturen und Mäusen durchgeführt um detailliert Auskunft über die Beteiligung von Perizyten in der Blutflussregulation zu erhalten. Wissenschaftlicher und gesellschaftlicher Kontext des Forschungsprojekts Das Projekt befasst sich mit Grundlagenforschung. Neben diesem grundlagen­wissenschaftlichen Aspekt ist unsere Arbeit auch relevant im Bereich der zerebrovaskulären Erkrankungen (wie etwa Schlaganfall).

Direct link to Lay Summary

Last update: 20.01.2015

Number	Title	Start	Funding scheme

The brain requires constant blood flow to ensure adequate oxygen and energy supply. Therefore, an endogenous regulatory process exists (known as functional hyperemia or neurovascular coupling), linking elevated neuronal energy demand with increased local blood flow (1). Much of the work to date has focused on blood flow changes within arterioles and arteries, but recent evidence suggests local blood flow can be regulated at the capillary level by a specific mural cell population: pericytes (2, 3). Pericytes are able to constrict brain capillaries, but there is conflicting evidence about their contribution in neurovascular coupling.Currently, only two studies have examined pericyte-mediated functional hyperemia in vivo, and they reported contradictory results: one study did not observe capillary events (4), while the other revealed fast capillary dilations that occurred before arteriole responses (2). These opposing outcomes could be attributed to differences in experimental design, data analysis, stimulation protocols, anesthesia, and vascular classification. Furthermore, neither of these studies considered intracellular signaling mechanisms regulating pericyte tone (2, 4).Our group has extensive experience with cellular imaging and blood flow measurements in vivo, and we plan to use a multi-modal approach to gain novel insights into unknown pericyte structure, intracellular signaling mechanisms and their contribution to hemodynamic responses. More specifically, we plan to work on the following three aims: Aim 1: Characterize intracellular signaling regulating brain pericyte tone in vitro and in vivo. We will investigate calcium signaling, membrane potential changes, and the activity of ATP-sensitive potassium channels in both cultured cortical pericytes and cortical pericytes in vivo. To date, visualization of intracellular signals within cortical pericytes has proven to be problematic due to the non-specificity of chemical indicators (5), so we will apply new genetic indicator tools (e.g. Ca2+, membrane potential and ATP/ADP sensors) which will selectively target pericyte cellular signaling. In addition, we will investigate the relevance of selected pathways in regulating pericyte tone in vivo by targeted gene knockout specifically in pericytes. Aim 2: Investigate the contribution of pericytes to functional hyperemia and hemodynamics in vivo. To study this, we will examine neurovascular coupling in adult pericyte-deficient animals in vivo, and also selectively alter pericyte tone by optogenetic stimulation to explore pericyte-induced changes in local blood flow. This will involve a precise analysis of hemodynamics, including capillary diameter and erythrocyte velocity and density measurements with two-photon microscopy. We plan to focus on imaging awake animals to limit the effects of anesthesia and specifically examine blood flow at capillary branch points that are surrounded by pericytes. Aim 3: High resolution imaging of neurovascular unit with special focus on pericyte contacts with endothelium and astrocytes. We will conduct high-resolution imaging of pericytes in situ to precisely elucidate their structure and connections to neighbouring cells. Using correlative light electron microscopy, we will collect functional information (i.e. changes in pericyte tone and hemodynamics) by two-photon microscopy before detailed structural analysis of the same tissue and cells by electron microscopy.A detailed functional and structural analysis of pericyte-mediated tone in vivo is currently lacking. This work has the potential to clarify the three-dimensional structure, the cellular mechanisms and the impact of pericyte tone in functional hyperemia. Our proposed research is also relevant to multiple diseases since pericytes have been shown to contract during ischemia (2, 6), and functional hyperemia is reportedly abnormal in other neurological disorders such as Alzheimer’s disease and vascular dementia.1.Roy CS & Sherrington CS (1890) On the Regulation of the Blood-supply of the Brain. The Journal of physiology 11(1-2):85-158 117.2.Hall CN, et al. (2014) Capillary pericytes regulate cerebral blood flow in health and disease. Nature.3.Peppiatt CM, Howarth C, Mobbs P, & Attwell D (2006) Bidirectional control of CNS capillary diameter by pericytes. Nature 443(7112):700-704.4.Fernandez-Klett F, Offenhauser N, Dirnagl U, Priller J, & Lindauer U (2010) Pericytes in capillaries are contractile in vivo, but arterioles mediate functional hyperemia in the mouse brain. Proc Natl Acad Sci U S A 107(51):22290-22295.5.Hirase H, Creso J, Singleton M, Bartho P, & Buzsaki G (2004) Two-photon imaging of brain pericytes in vivo using dextran-conjugated dyes. Glia 46(1):95-100.6.Yemisci M, et al. (2009) Pericyte contraction induced by oxidative-nitrative stress impairs capillary reflow despite successful opening of an occluded cerebral artery. Nat Med 15(9):1031-1037.