Dr. Ruan’s Research

Circadian Cardioprotection: BMAL1/HIF2A Complex and Co-target Amphiregulin

Myocardial ischemia-reperfusion injury (IRI) is one of the most important predictors of short- and long-term outcomes in surgical patients. Despite the improvement in cardioprotective strategies, the mortality, and morbidity associated with heart failure after myocardial ischemia are still substantial. Therefore, the search for novel therapies to prevent or treat perioperative myocardial IRI is still an area of intense investigation. Previous studies indicate that adverse cardiovascular events including perioperative myocardial injury follow a circadian pattern, with more severity in the morning hours. Therefore, manipulating the molecular situation of the heart to resemble that in the less injury phase might be an attractive and safer strategy if the mechanisms are further elucidated. The hypoxia-inducible factors (HIF1A and HIF2A) have emerged as critical oxygensensitive transcription factors, which orchestrate the body’s endogenous protective response to hypoxia including myocardial IRI. Preliminary studies indicate that the core circadian transcription factor BMAL1 could interact with HIF2A, and form a transcriptionally active complex that is critical in mediating circadian-dependent cardioprotection via rhythmic induction of its co-target AREG. With this research we will further explore the possibility that the crosstalk between the hypoxia signaling and circadian rhythm can function as a circadian-dependent protective strategy to reduce myocardial injury. Specific Aims: Aim 1. Study circadian-dependent transcription activation of BMAL1/HIF2A on AREG in vitro; Aim 2. Study circadian-dependent cardioprotection of BMAL1/HIF2A-AREG pathway during IRI in vivo. Additionally, pharmacologic studies will be pursued to target the circadian-dependent pathway BMAL1/HIF2A-AREG to establish a novel clock-targeting therapy for myocardial IRI by harnessing two endogenous protective pathways synergistically.

Related Publications

Hypoxia-stabilized RIPK1 Promotes Cell Death
Wei Ruan, Holger K Eltzschig, Xiaoyi Yuan

The PHD–pVHL pathway is essential for oxygen-dependent prolyl hydroxylation of HIFA. This recent study identifies RIPK1 as a hydroxylation target in this pathway during hypoxia-induced cell death and presents a 2.8 Å resolution crystal structure of the pVHL–elongin B/C complex bound to hydroxylated RIPK1.

Targeting Myocardial Equilibrative Nucleoside Transporter ENT1 Provides Cardioprotection by Enhancing Myeloid Adora2b Signaling
Wei Ruan, Jiwen Li, Seungwon Choi, Xinxin Ma, Yafen Liang, Ragini Nair, Xiaoyi Yuan, Tingting W Mills, Holger K Eltzschig

Previous studies implicate extracellular adenosine signaling in attenuating myocardial ischemia and reperfusion injury (IRI). This extracellular adenosine signaling is terminated by its uptake into cells by equilibrative nucleoside transporters (ENTs). Thus, the researchers hypothesized that targeting ENTs would function to increase cardiac adenosine signaling and concomitant cardioprotection against IRI. Mice were exposed to myocardial ischemia and reperfusion injury. Myocardial injury was attenuated in mice treated with the nonspecific ENT inhibitor dipyridamole. A comparison of mice with global Ent1 or Ent2 deletion showed cardioprotection only in Ent1-/- mice. Moreover, studies with tissue-specific Ent deletion revealed that mice with myocyte-specific Ent1 deletion (Ent1loxP/loxP Myosin Cre+ mice) experienced smaller infarct sizes. Measurements of cardiac adenosine levels demonstrated that postischemic elevations of adenosine persisted during reperfusion after targeting ENTs. Finally, studies in mice with global or myeloid-specific deletion of the Adora2b adenosine receptor (Adora2bloxP/loxP LysM Cre+ mice) implied that Adora2b signaling on myeloid-inflammatory cells in cardioprotection provided by ENT inhibition. These studies reveal a previously unrecognized role for myocyte-specific ENT1 in cardioprotection by enhancing myeloid-dependent Adora2b signaling during reperfusion. Extension of these findings implicates adenosine transporter inhibitors in cardioprotection against ischemia and reperfusion injury.

The Hypoxia-Adenosine Link during Myocardial Ischemia-Reperfusion Injury
Wei Ruan, Xinxin Ma, In Hyuk Bang, Yafen Liang, Jochen Daniel Muehlschlegel, Kuang-Lei Tsai, Tingting W Mills, Xiaoyi Yuan, Holger K Eltzschig

Despite increasing availability and more successful interventional approaches to restore coronary reperfusion, myocardial ischemia-reperfusion injury is a substantial cause of morbidity and mortality worldwide. During myocardial ischemia, the myocardium becomes profoundly hypoxic, thus causing stabilization of hypoxia-inducible transcription factors (HIF). Stabilization of HIF leads to a transcriptional program that promotes adaptation to hypoxia and cellular survival. Transcriptional consequences of HIF stabilization include increases in extracellular production and signaling effects of adenosine. Extracellular adenosine functions as a signaling molecule via the activation of adenosine receptors. Several studies implicated adenosine signaling in cardioprotection, particularly through the activation of the Adora2a and Adora2b receptors. Adenosine receptor activation can lead to metabolic adaptation to enhance ischemia tolerance or dampen myocardial reperfusion injury via signaling events on immune cells. Many studies highlight that clinical strategies to target the hypoxia-adenosine link could be considered for clinical trials. This could be achieved by using pharmacologic HIF activators or by directly enhancing extracellular adenosine production or signaling as a therapy for patients with acute myocardial infarction, or undergoing cardiac surgery.