ß-tubulin contributes to Tongyang Huoxue decoction-induced protection against hypoxia/reoxygenation-induced injury of sinoatrial node cells through SIRT1-mediated regulation of mitochondrial quality surveillance

TYHX-Tongyang Huoxue decoction has been used clinically for nearly 40 years. The ingredients of TYHX are Radix Astragali (Huangqi), Red Ginseng (Hongshen), Rehmannia Glutinosa (Dihuang), Common Yam Rhizome (Shanyao) and Cassia-bark-tree Bark (Rougui). Our previous experiments confirmed that TYHX can protect sinoatrial node cells. However, its mechanism of action is not completely understood yet.The present study aimed to determine the protective effects of TYHX against Sinus node cell injury under hypoxic stress and elucidate the underlying mechanisms of protection.Through RNA sequencing analysis and network pharmacology analysis, we found significant differences in mitochondrial-related genes before and after hypoxia-mimicking SNC, resolved the main regulatory mechanism of TYHX. Through the intervention of TYHX on SNC, a series of detection methods such as laser confocal, fluorescence co-localization, mitochondrial membrane potential and RT-PCR. The regulatory effect of TYHX on β-tubulin in sinoatrial node cells was verified by in vitro experiments. The mechanism of action of TYHX and its active ingredient quercetin to maintain mitochondrial homeostasis and protect sinoatrial node cells through mitophagy, mitochondrial fusion/fission and mitochondrial biosynthesis was confirmed.Through RNA sequencing analysis, we found that there were significant differences in mitochondrial related genes before and after SNC was modeled by hypoxia. Through pharmacological experiments, we showed that TYHX could inhibit the migration of Drp1 to mitochondria, inhibit excessive mitochondrial fission, activate mitophagy and increase the mitochondrial membrane potential. These protective effects were mainly mediated by β-tubulin. Furthermore, the active component quercetin in TYHX could inhibit excessive mitochondrial fission through SIRT1, maintain mitochondrial energy metabolism and protect SNCs. Our results showed that protection of mitochondrial function through the maintenance of β-tubulin and activation of SIRT1 is the main mechanism by which TYHX alleviates hypoxic stress injury in SNCs. The regulatory effects of TYHX and quercetin on mitochondrial quality surveillance are also necessary. Our findings provide empirical evidence supporting the use of TYHX as a targeted treatment for sick sinus syndrome.Our data indicate that TYHX exerts protective effects against sinus node cell injury under hypoxic stress, which may be associated with the regulation of mitochondrial quality surveillance (MQS) and inhibition of mitochondrial homeostasis-mediated apoptosis.