Control Mechanisms for Matching ATP Supply and Demand in Heart Mitochondria

心脏线粒体中 ATP 供需匹配的控制机制

• 批准号: 8148203
• 负责人: Steven Sollott
• 金额: $ 32.64万
• 依托单位: NATIONAL INSTITUTE ON AGING
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8148203
• 关键词: Heart Mitochondria

Failure to supply energy to match the body's demands limits the functional reserve capacity, and under certain periods of stress, such as ischemia, can lead to irreversible cell and tissue damage. This matching is critical in tissues with high and rapidly fluctuating metabolic rates such as the heart. Mitochondria are the main ATP suppliers to meet cellular demands. The fuel used by mitochondria is transported across the inner mitochondrial membrane to the matrix and produces a source of electrons whose redox-potential energy is, in turn, harnessed by the electron transport chain. The flux of electrons is reflected in oxygen consumption. The energy released from this electron flow is used to transport protons out of the matrix across the inner mitochondrial membrane forming a gradient whose proton-motive force drives ATP synthase to make ATP. This "upstream" regulation is known as the "push" mechanism. A complete description of the ATP synthase control mechanisms is still lacking. Two general mechanisms have been suggested to serve as key regulators: 1) ADP and Pi concentrations; ATP utilization/hydrolysis in the cytosol increases ADP and Pi fluxes to mitochondria and hence the amount of available substrates for ATP production increases; 2) Ca2+ concentration; ATP utilization/hydrolysis is coupled to changes in free cytosolic calcium and mitochondrial Ca2+, the latter controlling Ca2+-dependent activation of certain mitochondrial reaction-rate-determining enzymes taking part in ATP production. At high levels of energy demand the question arises whether parallel to the "push" mechanism signals acting on ATP synthase could also facilitate the electron transport chain redox flux, enhancing the efficiency of ATP production. This effect simulates an apparent additional "pull" on the upstream flux, which causes as a specific proportionate increase in respiration. Proof of such a "pull" mechanism regulated by Ca2+ and its target has not been demonstrated to-date. Cardiomyocytes contract in response to driven cyclic 'increases' in cytosolic Ca2+ in a response to electrically stimulation. As a consequence of the levels of contractile work, ATP is proportionately utilized by the contractile elements. Therefore, from the demand point of view Ca2+ is a direct effector that might be well positioned to play a role in the energy matching regulatory mechanisms. A correlation has also been shown between cytosolic and mitochondrial Ca2+. Ca2+ enters the mitochondria through the mitochondrial uniporter and is extruded by the mitochondrial Na+/Ca2+ exchanger. This results in mitochondrial Ca2+ accumulation in response to an increase in stimulation frequency or Ca2+ transient amplitude. Therefore, Ca2+ levels in the mitochondria reflect changes in both myocardial work and ATP consumption and, hence, the demand for ATP. It was shown that mitochondrial Ca2+ can activate the mitochondrial enzymes taking part in ATP production. Therefore, changes in mitochondrial Ca2+ during electrical stimulation are linked to changes in ATP supply and demand. We and others have shown that small changes in mitochondrial volume can regulate respiration and in turn energy production. It is also known that the Ca2+ environment may regulate mitochondrial volume in isolated mitochondrial suspension raising the question whether physiological changes in Ca2+ via increasing electrically stimulated Ca2+ cycling would act in this way. We found that while increasing electrically stimulated, physiological Ca2+ cycling does not detectibly change the 'diastolic' mitochondrial long- and short-axis dimensions (i.e, volume) shortly (2.5 min) after the transition from rest to low or higher workloads, it nevertheless caused an increase in cell respiration (and in turn facilitated energy production) in both conditions. These results were in contrast to that observed by others in the isolated mitochondria models. Additionally, we found that the mechanisms that control ATP supply from the hearts mitochondria consist of both 'push' and 'pull' mechanisms and that 'pull' mechanism directly targets ATP synthase. We identified that the 'pull' mechanism is controlled by mitochondrial Ca2+ and can be further facilitated by pharmacologically regulating mitochondrial volume. At low cardiac workload, the 'push' mechanism is sufficient to match ATP supply and demand, and the mitochondrial transmembrane ADP/Pi gradient is presumably sufficient to drive the 'push' and 'pull' mechanisms. However, under the same experimental conditions, pharmacological induction of a regulatory mitochondrial volume increase was found to facilitate mitochondrial Ca2+ entry responsible for further pushing respiration, whereas at higher workloads, mitochondrial Ca2+ entry did not require such facilitation, and in turn was sufficient and essential to drive both "push" and 'pull' effects on respiration. Moreover, pharmacologically-enhanced mitochondrial Ca2+ accumulation (without changing cytosolic Ca2+) was also found to push respiration. Facilitation of these 'push' and 'pull' mechanisms is being examined as a potential treatment to reverse signaling defects in matching ATP supply and demand, such as occurs in heart failure which afflicts millions of people, especially the elderly population.

无法提供能量以匹配人体的需求会限制功能储备的能力，在某些压力（例如缺血）中，可能会导致不可逆的细胞和组织损伤。这种匹配在高且快速波动的代谢率（如心脏）的组织中至关重要。线粒体是满足细胞需求的主要ATP供应商。线粒体使用的燃料在线粒体内部膜上运输到基质，并产生一个电子来源，其氧化还原电位能量反过来又由电子传输链利用。电子的通量反映在消耗中。从该电子流释放的能量用于将质子从基质中传输到内部线粒体膜中，形成了一种梯度，其质子 - 动力驱动ATP合酶以制造ATP。这种“上游”调节被称为“推动”机制。仍然缺乏对ATP合成酶控制机制的完整描述。已经提出了两种通用机制作为关键调节剂：1）ADP和PI浓度；细胞质中的ATP利用率/水解将ADP和PI通量增加到线粒体，因此可用的ATP产生底物量增加； 2）Ca2+浓度； ATP利用率/水解与自由胞质钙和线粒体Ca2+的变化耦合，后者控制了某些线粒体反应速率确定的酶的CA2+依赖性激活，该酶参与ATP的产生。在高水平的能量需求下，出现的问题是否与作用于ATP合酶的“推动”机理信号平行，还可以促进电子传输链氧化还原通量，从而提高ATP产生的效率。这种效果模拟了上游通​​量明显的额外“拉动”，这会导致特定的呼吸比例增加。尚未证明由Ca2+调节的“拉动”机制及其目标的证据。 响应胞质Ca2+的循环循环“增加”的心肌细胞在对电刺激的反应中收缩。由于收缩工作的水平，ATP被收缩元素按比例地使用。因此，从需求的角度来看，Ca2+是一个直接效应子，可以很好地在能量匹配的调节机制中发挥作用。胞质和线粒体Ca2+之间也显示了相关性。 Ca2+通过线粒体Uniporter进入线粒体，并被线粒体Na+/Ca2+交换器挤出。这导致线粒体Ca2+积累，响应刺激频率或Ca2+瞬态幅度的增加而产生。因此，线粒体中的Ca2+水平反映了心肌工作和ATP消耗的变化以及对ATP的需求。结果表明，线粒体Ca2+可以激活参与ATP产生的线粒体酶。 因此，电刺激过程中线粒体Ca2+的变化与ATP供应和需求的变化有关。 我们和其他人表明，线粒体体积的小变化可以调节呼吸和能量产生。众所周知，Ca2+环境可能会在孤立的线粒体悬浮液中调节线粒体体积，从而提出了一个问题，即通过增加电刺激的Ca2+循环的Ca2+中的生理变化是否会以这种方式起作用。我们发现，尽管增加了电刺激，但生理刺激的CA2+循环并未明显改变“舒张性”线粒体长和短轴维度（即体积）（即体积）（2.5分钟），从休息过渡到低或更高的工作负载后，它将不得不增加细胞的呼气（以及在两种情况下都会增加）。这些结果与分离的线粒体模型中其他人观察到的结果相反。此外，我们发现控制ATP从心脏线粒体供应的机制包括“推动”和“拉动”机制以及“拉动”机制直接靶向ATP合酶。我们确定“拉动”机制由线粒体Ca2+控制，可以通过药理调节线粒体体积进一步促进。在低心脏工作负载下，“推动”机制足以匹配ATP的供求，并且线粒体跨膜ADP/PI梯度大概足以驱动“推动”和“拉动”机制。然而，在相同的实验条件下，发现线粒体体积增加的药理诱导促进了线粒体CA2+进入负责进一步推动呼吸的进入，而在更高的工作量下，线粒体CA2+进入的条件不需要这种促进性，并且不需要这种促进性，而这反过来又是必不可少的，并且可以使两者都推动“推动”和“推动”效果。此外，还发现了药理学增强的线粒体Ca2+积累（不改变胞质Ca2+）可以推动呼吸。 促进这些“推动”和“拉动”机制正在被研究为一种潜在的治疗方法，以逆转匹配ATP供求的信号缺陷，例如，心力衰竭发生的情况会折磨数百万人，尤其是老年人群。