Study On The Mechanism Of B-type Natriuretic Peptide On Mitochondrial Dynamics In Cardiomyocytes

B-type natriuretic peptide (BNP) is one peptide hormone released in response to myocyte stretch, whose functions play significant roles in health and disease. Its physiologic effects result in improved loading conditions and have led to the development of recombinant BNP as a therapeutic agent for heart failure. Previous work has identified that BNP protect myocardium against reperfusion injury through mitochondrial pathway. Mitochondria are both essential effectors of cardioprotection and primary targets of cardioprotective signaling. Their role during reperfusion is particularly critical because of the conditions that promote both apoptosis by the mitochondrial pathway and necrosis by irreversible damage to mitochondria in association with mitochondrial permeability transition pores (mPTP). After an episode of myocardial ischemia, opening of mPTP, at the onset of reperfusion, is a critical determinant of myocyte death. The relationship of BNP and mPTP in mediating reperfusion-induced cardiomyocytes injury is a novel investigative area.For cardiomyocytes Biology, mitochondria play an important role in Ca2+ homoeostasis due to the presence of a fast and specific Ca2+ channel in mitochondrial inner membrane, mitochondrial Ca2+ uniporter (MCU). This uniporter allows mitochondria to buffer local cytosolic [Ca2+] changes and controls the intramitochondrial Ca2+ levels, thus modulating a variety of phenomena from respiratory rate to apoptosis. The role of mitochondria and MCU, in mediating reperfusion-induced heart injury is a novel investigative area. In addition, the relationship of BNP with MCU in cardiomyocytes undergoing reperfuison is elusive. Recent studies have sparked renewed appreciation for the remarkably dynamics nature of mitochondria and this nature of mitochondria determine mitochondrial function. Mitochondrial morphology and dynamics are strongly influenced by interactions with cytoskeletal filaments and their associated mitochondrial function, and lead to cell changes that occur over wide stimuli, such as ischemia/reperfusion. In the present study, our results indicated that the beneficial effect of BNP in cultured cardiomyocytes subjected to reperfusion is associated with attenuation of mPTP open and MCU open, resultant mitochondrial dysfunction and apoptosis. Further investigation of underlying mechanisms revealed that these were associated with BNP-mediated repolarization of mitochondrial membrane potential (m), inhibition of reactive oxygen species (ROS) generation, improvement of Bcl-2 level, and inhibition of Bax and second mitochondria-derived activator of caspases/direct inhibitor of apoptosis-binding protein with a low isoelectric point (Smac/DIABLO) levels. We also find BNP could reduce the release of cytochrome c partly though inhibiting the MCU open. We next explored that the contribution of BNP in mitochondrial morphology and function partly depend on the microtubules. This effect of BNP was comprehensively investigated in control and microtubule-disrupted cardiomyocyte H9c2 by confocal microscopy and live cell station. When subjected to microtubule disruption, cells suffer not only biochemical alterations, but also morphologic changes. We further demonstrated that BNP could participate in the mitochondrial association of microtubules and support mitochondrial dynamics.In summary, we demonstrate that BNP exerts protective actions within reperfusion by inhibiting MPTP open and MCU open, these roles of BNP may involve phosphatidylinositol 3-kinase (PI3K) dependent pathway. As mitochondrial morphologies determine mitochondrial function, detail analysis reveals that a potentially important relationship between the BNP-mediated microtubules and the regulation of mitochondria.