Microvascular O2 Delivery: Impact of Erythrocyte-Released ATP

描述（由申请人提供）：调节氧气（O2）供应以满足骨骼肌的需求是一个基本的生理过程，因此通常认为其机制已得到充分理解。然而，尽管已经提出了许多理论，但没有一个在体内得到充分的检验。考虑到响应O2的微血管调节系统的复杂性以及O2运输的复杂性，这并不奇怪，其中O2供应由流量分布、所有血管之间的扩散O2交换和在分叉网络中流动的红细胞（RBC）的流变学性质决定。解开这个生物系统的复杂性需要一个系统生物学的方法，实验提供的信息，我们可以确定和数学计算使用的实验证据，使我们能够预测这些因素，逃避我们。虽然自8月Krogh以来，O2输送模型已经存在，但很少有纳入必要的监管组成部分，因为其身份仍然难以捉摸。最近的研究支持了O2携带RBC作为重要调节组分的作用，其通过释放腺苷5 '-三磷酸（ATP）来改变O2供应以满足需求。在微循环中，响应于毛细血管或小静脉中的O2张力降低而从RBC释放的ATP可以旁分泌方式起作用，以局部产生血管舒张以及传导至上游小动脉的血管舒张。RBC衍生的ATP还可以以自分泌方式起作用，以刺激血管扩张剂环氧二十碳三烯酸（Epoxyeicosatrienoic Acids，EAE）从RBC释放。该项目的目标是证实越来越多的证据表明，红细胞在调节骨骼肌中O2供应与需求的匹配方面发挥着关键作用。这将使用新的动态计算O2传输模型来实现，该模型基于实验数据，将微血管系统和周围组织的几何复杂性与微血管流动的网络模型以及3D组织体积内的对流和扩散O2传输模型相结合。该提议将确定红细胞释放ATP的O2饱和依赖性是否负责骨骼肌内O2供应的局部调节。O2调节模型将分阶段开发、测试和完善，首先是现有的基于实验的模型，并开发模拟实验中观察到的RBC血液动力学和O2饱和度响应的经验算法。同时，将收集暴露于减少的O2的RBC释放ATP和Ehrs及其在大鼠微循环中的血管活性的定量和时间数据，并用于完善模型，最终取代经验算法。糖尿病动物RBC释放ATP的缺陷将用于挑战调节模型。从糖尿病大鼠模型中获得的数据在其匹配的控制在计算模型中的数据替代实验数据将提供重要的新信息的RBC衍生的ATP在骨骼肌微循环缺陷与糖尿病相关的重要性。调节骨骼肌的氧供应以匹配氧需求是一个基本的生理过程，但由于其复杂性，对其进行描述的尝试通常是不够的。越来越明显的是，由于这些过程不能仅仅通过将它们简化为组成部分来理解，因此必须使用系统生物学方法和计算建模来研究它们作为完整的功能系统。在本提案中，我们使用系统生物学方法来确定红细胞响应代谢需要而释放ATP是否负责骨骼肌内氧气供应的局部调节，并通过使用系统（2型糖尿病）检查模型来测试模型的预测，其中该调节系统存在缺陷，即，2型糖尿病患者RBC的ATP释放受损。

DESCRIPTION (provided by applicant): The regulation of oxygen (O2) supply to match demand in skeletal muscle is such a fundamental, physiological process that it is often assumed that the mechanisms responsible are well understood. However, although numerous theories have been proposed, none has been adequately tested in vivo. This is not surprising given the complexity of the microvascular regulatory systems that respond to O2 as well as the complexity of O2 transport where O2 supply is determined by flow distribution, diffusional O2 exchange among all vessels and rheological properties of erythrocytes (RBCs) flowing in bifurcating networks. Unraveling the complexity of this biological system requires a systems biology approach in which experiments provide information on the things we can determine and mathematical computation using that experimental evidence enables us to predict those factors which elude us. Although models of O2 delivery have existed since the time of August Krogh, few have incorporated the necessary regulatory component since its identity has remained elusive. Recent studies have supported a role for the O2 carrying RBC as an important regulatory component that alters O2 supply to meet demand via the release of adenosine 5'-triphosphate (ATP). In the microcirculation, ATP released from RBCs in response to reduced O2 tension in capillaries or venules can function in a paracrine fashion to produce vasodilation locally as well as vasodilation that is conducted to upstream arterioles. RBC-derived ATP can also function in an autocrine fashion to stimulate the release of vasodilator epoxyeicosatrienoic acids (EETs) from RBCs. The goal of this project is to substantiate the growing evidence for a critical role for RBCs in the regulation of the matching of O2 supply with need in skeletal muscle. This will be accomplished using a new dynamic computational O2 transport model which is based on experimental data integrating the geometrical complexity of the microvasculature and surrounding tissue with a network model of microvascular flow as well as a convective and diffusive O2 transport model within a 3D tissue volume. This proposal will determine whether O2-saturation dependent release of ATP from RBCs is responsible for the local regulation of O2 supply within skeletal muscle. The O2 regulatory model will be developed, tested and refined in stages beginning with the existing experiment-based model and development of an empirical algorithm which simulates the RBC hemodynamic and O2 saturation response observed in experiments. Concomitantly, quantitative and temporal data on the release of ATP and EETs from RBCs exposed to reduced O2 and their vasoactivity in the rat microcirculation will be collected and used to refine the model, ultimately replacing the empirical algorithm. A defect in ATP release from RBCs of diabetic animals will be used to challenge the regulatory model. Substituting experimental data from a rat model of diabetes for data obtained in their matched controls in the computational model will provide important new information on the importance of RBC-derived ATP in the defect in skeletal muscle microcirculation associated with diabetes. The regulation of oxygen supply to match oxygen demand in skeletal muscle is a fundamental physiological process, yet because of its complexity, attempts to describe it have been generally inadequate. It has become increasingly obvious that because processes like these cannot be understood merely by reducing them to their component parts, they must be studied as intact, functioning systems using a systems biology approach with computational modeling. In this proposal we use a systems biology approach to determine whether the release of ATP from red blood cells in response to metabolic need is responsible for local regulation of oxygen supply within skeletal muscle and test the predictions of the model by examining it using a system (type 2 diabetes) in which there is a defect in that regulatory system, i.e., ATP release from RBCs of type 2 diabetics is compromised.