Role of Tissue Plasminogen Activator in Central Nervous System Physiology and Pathology

Tissue plasminogen activator;Bacterial Artificial Chromosome;No magnesium-high potassium ex vivo model of "seizure-like"activity;Vascular morphometry and network connectivity;Lognormal distribution to model vessel diameter and length;Trafficked tissue plasminogen activator;Genetics;Mathematics;Molecular;Cellular and Developmental Biology;Physiology;Science (General);Statistics and Numeric Data;Science;Molecular and Integrative Physiology

Stevenson, TamaraStuenkel, Edward L ;

University of Michigan

关键词: Tissue plasminogen activator;    Bacterial Artificial Chromosome;    No magnesium-high potassium ex vivo model of ";    seizure-like";    activity;    Vascular morphometry and network connectivity;    Lognormal distribution to model vessel diameter and length;    Trafficked tissue plasminogen activator;    Genetics;    Mathematics;    Molecular;    Cellular and Developmental Biology;    Physiology;    Science (General);    Statistics and Numeric Data;    Science;    Molecular and Integrative Physiology;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/146064/tamaraks_1.pdf?sequence=1&isAllowed=n

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Tissue plasminogen activator (tPA) is a serine protease classically known for its endogenous activity promoting fibrinolysis and for its clinical role as a thrombolytic agent for treating ischemic stroke. This singular function for tPA in the vasculature contrasts with the numerous reported actions of tPA in the central nervous system (CNS); including, synaptic plasticity, neurodegeneration, and blood-brain barrier (BBB) permeability. Within each of these processes a variety of substrates and receptors have been implicated in mediating tPA’s effects, suggesting that tPA is a pleiotropic mediator whose actions are restricted in space and time. The specific localization of tPA, therefore, can provide useful information about its function.Accordingly, we utilized two new transgenic reporter mice – PlatBetaGAL and tPABAC-Cer – to provide a detailed characterization of tPA expression in the adult murine brain. The PlatBetaGAL reporter mouse houses the beta-galactosidase gene in the tPA locus and the tPABAC-Cer mouse has a cerulean-fluorescent protein fused in-frame to the tPA C-terminus. A comparison of these reporter mice demonstrates that neuronal tPA is primarily trafficked away from its somatic site of synthesis to nerve fibers in limbic brain structures, such as the hippocampus, amygdala, and basal ganglia. This differential expression pattern is most apparent in the hippocampus where tPA-BetaGAL expression is present in the dentate gyrus, while tPA-Cer is localized to giant mossy fiber boutons (MFBs) in the mossy fiber pathway.To understand the functional implications of tPA in the MFBs we assessed synchronous activity in the CA3 hippocampal subfield using a ;;no magnesium/high potassium” model of ;;seizure-like” activity. As previous work from our lab implicated tPA in mediating seizure progression in vivo via its role regulating BBB permeability, we dissected the BBB component to seizure progression and specifically tested tPA’s effect on neuronal communication. We found brain slices from tPA deficient mice to have an enhanced synchronous activity onset time, suggesting that the ;;seizure-resistance” observed in tPA deficient mice in vivo is likely a result of improved barrier function, not tPA’s role in modulating synaptic transmission.Lastly, in this dissertation, using sophisticated imaging and analytical tools we provide a rigorous assessment of vascular morphometry in wild-type mice, the original Carmeliet-tPA null mice, and in newly-generated tPA deficient mice on a pure C57BL/6J background (Szabo-tPA null mice). Through this examination we report that the lognormal distribution is a good model for cerebral vessel diameter and length and that there is a weak negative correlation between vessel diameter and length. We also find that the increased vascular density in Carmeliet-tPA null mice is possibly a compound result of constitutive loss of tPA and/or some strain-dependent modifier genes.Cumulatively, our data supports a model whereby tPA acts a pleiotropic mediator in the CNS whose actions are highly spatially and temporally compartmentalized. This compartmentalized localization is appreciable in the differential expression pattern seen for tPA between the PlatBetaGAL and tPABAC-Cer transgenic mice; and functionally, we show that in ex vivo hippocampal slices tPA modulates synchronous activity, but in an in vivo model of seizure, the dominant effect of tPA is on regulating BBB permeability. Our vascular morphometry data also suggests a possible developmental effect of tPA on cerebrovascular patterning. Future work using the models developed here should help to clarify the relative contribution of the various substrates and pathways associated with tPA in CNS physiology and pathology.