See accompanying article on page 2293

Cardiac endothelial cells (ECs) form the inner layer of the macro- and microvasculature in the heart and control the structure and function of these vessels to meet the oxygen demand. ECs also communicate with cardiomyocytes and regulate their structure and function.^1,2 ECs are sensitive to hypoxia and respond quickly to blood flow reduction. During myocardial ischemia/reperfusion (I/R) injury, ECs actively protect cardiomyocytes and restore cardiac homeostasis by regulating vascular functions, forming new microvessels to reestablish perfusion, and signaling to promote cardiomyocyte function and survival. However, cardiac ECs are also vulnerable to I/R injury and can become damaged and dysfunctional during myocardial infarction (MI). In the endothelium, I/R injury results in EC activation (ie, expression of proinflammatory molecules), increased permeability and edema, and impaired vasomotion.^1–3 In turn, endothelial injury and dysfunction promote vasoconstriction, thrombosis, and coronary occlusion that result in cardiac inflammation and injury, adverse cardiac remodeling, and hypertrophy, which have profoundly negative effects on the outcome of MI.⁴ Therefore, the proper preconditioning and protection of ECs and coronary circulation are critical for effective cardioprotection.

Remote ischemic preconditioning (RIPC) is an intervention process in which the application of multiple I/R cycles in a remote vascular bed renders cardiac cells in distal regions more resistant to I/R injury. Although the clinical translation of RIPC has not yet been established, preclinical studies have shown that RIPC reduces infarct size and improves cardiac function.⁵ RIPC enhances cardiac protection by stimulating comprehensive protective mechanisms not only in cardiomyocytes but also in other cardiac cells including ECs.^4–6 Intact endothelial function is essential for effective RIPC-induced cardioprotection. However, most studies of RIPC have focused on cardiomyocytes; therefore, the role of ECs in RIPC-induced cardioprotection has been understudied, and many important questions remain unanswered. For example, how can preconditioning/stress activate the cardioprotective mechanism in ECs? Are there endothelium-derived cardioprotective factors? If so, what are they? What are the signaling events activated in ECs by RIPC that confer protection in these cells?

In this issue, Kundumani-Sridharan et al⁷ identified endothelial Nrg1β (neuregulin-1β)-ErbB2 signaling—part of the endothelial Nrg1β-ErbB signaling pathways that have well-established protective roles against ischemic injury^8,9—as an important mediator for RIPC-induced cardioprotection. Using a mouse model of acute MI, the authors found that RIPC induced Nrg1β expression and secretion from ECs. Interestingly, its receptor ErbB2 was expressed only in ECs and not in cardiomyocytes. Blocking this pathway with Nrg1β neutralizing antibodies or the deletion of endothelial ErbB2 abrogated RIPC-induced protection against myocardial perfusion and cardiomyocyte survival. Further mechanistic investigation showed that RIPC protected Nrg1β-ErbB2 signaling in ECs and that I/R injury caused ErbB2 degradation. Furthermore, RIPC induced the binding of Nrg1β to ErbB2, thereby preventing I/R-induced ErbB2 degradation (Figure). This study highlights the importance of EC preconditioning and the activation of EC protective mechanisms in RIPC-induced cardioprotection. Furthermore, it reveals Nrg1β-ErbB2 signaling as the key mechanism in EC preconditioning, underscoring the critical role of endothelial Nrg1β-ErbB2 signaling in RIPC-induced cardiac protection.

Figure. Proangiogenic factors and Nrg1β (neuregulin-1β). Nrg1β protects the heart through several mechanisms. Nrg1β directly associates with ErbB3/4 receptor in endothelial cells (ECs) and subsequently activates ErbB2 by inducing heterodimerization between ErbB2 and ErbB3/4. ErbB2 activation not only inhibits ATG5-mediated Trx2 degradation and EC apoptosis but also increases NO production by activating Src signaling-mediated eNOS tyrosine phosphorylation. Different from the proangiogenic cytokines (such as CXCL12-CXCR4, CXCL11-CXCR7, and CCL2-CCR2) that promote inflammation in addition to inducing VEGF/VEGFR expression¹⁰ and angiogenesis, the proangiogenic Nrg1β reduces inflammation by inhibiting proinflammatory signaling such as STAT3 and NF-κB. The anti-inflammatory characteristics of Nrg1β -ErbB2 signaling may provide a unique opportunity for developing Nrg1β proangiogenic therapies after myocardial infarction. Created with www.BioRender.com. mtROS indicates mitochondrial ROS; NF-κB, nuclear factor kappa-light-chain-enhancer of activated B cells; STAT3, signal transducer and activator of transcription 3; and VEGF, vascular endothelial growth factor.

During stress conditions such as acute ischemia, the myocardial endothelium releases Nrg1β, which may exert protective effects in the heart by activating ErbB signaling in multiple cells and through multiple mechanisms. Nrg1β-ErbB receptor signaling has been shown to mediate the cross-talk between the microvascular endothelium and cardiomyocytes.⁹ Nrg1β-ErbB2 signaling enhances NO production, which has negative inotropic effects on cardiomyocytes.¹¹ Nrg1β, through ErbB receptors expressed on cardiomyocytes, protects cardiomyocytes by promoting their survival^12,13 and enhancing glucose uptake.¹⁴ A recent study suggested that the Nrg1β-ErbB4 pathway also inhibits macrophage activation and reduces myocardial hypertrophy and fibrosis.¹⁵ In the study by Kundumani-Sridharan et al,⁷ the authors showed that Nrg1β-ErbB2 signaling protects ECs via the ErbB2/4-cSrc-NO axis and the ErbB2/4-ATG5-Trx2 axis (Figure). Treating ECs with preconditioned medium (ie, produced by culturing ECs in deoxygenated and growth supplement–deprived culture medium) induced ErbB2 phosphorylation/activation and its binding to nonreceptor tyrosine kinase cSrc, which activated downstream signaling that led to eNOS phosphorylation/activation and increased NO production. Nrg1β-ErbB2 signaling also prevented Trx2 degradation and maintained its antioxidant capacity, which is important in cellular protection. I/R induced Trx-2 degradation via the activation of an ATG5/beclin 1/Ambra1 macroautophagy mechanism. ErbB2 protected Trx2 by binding to ATG5, inducing ATG5 phosphorylation/inactivation, and subsequently preventing Trx-2 degradation. Finally, the loss of endothelial ErbB2 resulted in the dephosphorylation and activation of ATG5 and Trx2 degradation (Figure). This study provides novel insight into the mechanisms underlying Nrg1β-ErbB receptor–mediated cardioprotection.

The therapeutic potential of angiogenic growth factors has been tested extensively in patients with heart disease, such as advanced coronary artery disease. However, the disappointing results of those clinical trials made it difficult to pursue studies of proangiogenic therapies after acute MI.^16–20 Therefore, the possibility remains that proangiogenic therapy may benefit patients during the acute phase of I/R, as suggested previously.²⁰ However, considering the role of inflammation on angiogenesis is critical. Inflammation is a well-known driver of angiogenesis. For example, CXCR4 activates CCXL12 in both ECs and cardiomyocytes and is known to improve infarct angiogenesis^21–23 (Figure). In addition, CXCL11-mediated CXCR7²⁴ and CCL2-mediated CCR2 activation in ECs²⁵ are associated with increased angiogenesis after MI. Activated cardiomyocytes can increase VEGFA and CCL2 secretion and induce angiogenesis.²⁶ Therefore, inflammation plays a significant role in infarct angiogenesis, and many proangiogenic factors can increase inflammation in both ECs and cardiomyocytes. However, it is well known that excessive inflammation can cause detrimental effects in the infarcted heart.²⁷ In this context, Nrg1β-ErbB2 signaling may play a unique role in proangiogenesis therapy after acute MI because it has an anti-inflammatory role,^15,28–30 and its proangiogenic capacity does not rely on its proinflammatory effects (Figure). It is important to emphasize that the initial inflammatory response after MI is critical for promoting the healing process after ischemic injury but that excessive inflammation can be detrimental, as explained above. Therefore, for proangiogenesis therapy, the balance between the advantages and disadvantages of inflammation must be considered. Further investigation is necessary to identify the optimal timing and combination of various proangiogenesis therapies for inhibiting the progression of ischemic damage after MI.

We greatly appreciate Dr Nicole Stancel, of the Department of Scientific Publications at the Texas Heart Institute, for providing editorial support, and Dr Keigi Fujiwara from University of Texas MD Anderson Cancer Center for critical reading of the manuscript and valuable suggestions.

Our research activities are supported by grants from the National Institute of Health (NIH) to Y.H. Shen (HL143359) and J.-i. Abe (HL149303).

Disclosures None.

For Sources of Funding and Disclosures, see page 2317.

The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association.

请参阅第 2293 页的随附文章

心脏内皮细胞 (EC) 在心脏中形成大血管和微血管的内层，并控制这些血管的结构和功能以满足氧气需求。ECs 还与心肌细胞通信并调节它们的结构和功能。^1,2ECs 对缺氧敏感，对血流减少反应迅速。在心肌缺血/再灌注 (I/R) 损伤期间，ECs 通过调节血管功能、形成新的微血管以重建灌注和信号传导以促进心肌细胞功能和存活，从而积极保护心肌细胞并恢复心脏稳态。然而，心脏 ECs 也容易受到 I/R 损伤，并且在心肌梗塞 (MI) 期间可能受损和功能障碍。在内皮中，I/R 损伤导致 EC 激活（即促炎分子的表达）、通透性增加和水肿以及血管舒缩受损。^1-3反过来，内皮损伤和功能障碍会促进血管收缩、血栓形成和冠状动脉闭塞，从而导致心脏炎症和损伤、不良心脏重塑和肥大，这对 MI 的结果具有深远的负面影响。⁴因此，EC 和冠状动脉循环的适当预处理和保护对于有效的心脏保护至关重要。

远程缺血预处理 (RIPC) 是一种干预过程，其中在远程血管床中应用多个 I/R 循环可使远端区域的心肌细胞对 I/R 损伤更具抵抗力。尽管 RIPC 的临床转化尚未确定，但临床前研究表明，RIPC 可减少梗死面积并改善心脏功能。⁵ RIPC 通过刺激心肌细胞以及包括 EC 在内的其他心脏细胞的综合保护机制来增强心脏保护。^4-6完整的内皮功能对于有效的 RIPC 诱导的心脏保护至关重要。然而，大多数对 RIPC 的研究都集中在心肌细胞上。因此，ECs 在 RIPC 诱导的心脏保护中的作用尚未得到充分研究，许多重要问题仍未得到解答。例如，预处理/压力如何激活 ECs 中的心脏保护机制？是否有内皮衍生的心脏保护因子？如果是这样，它们是什么？RIPC 在 EC 中激活了哪些信号事件，从而在这些细胞中提供保护？

在本期杂志中，Kundumani-Sridharan 等人⁷确定了内皮 Nrg1β (neuregulin-1β)-ErbB2 信号传导——内皮 Nrg1β-ErbB 信号通路的一部分，对缺血性损伤具有公认的保护作用^8,9——作为 RIPC 诱导的心脏保护的重要介质。使用急性心肌梗死的小鼠模型，作者发现 RIPC 诱导了 Nrg1β 的表达和 ECs 的分泌。有趣的是，其受体 ErbB2 仅在 ECs 中表达，而不在心肌细胞中表达。用 Nrg1β 中和抗体阻断该途径或内皮 ErbB2 的缺失消除了 RIPC 诱导的对心肌灌注和心肌细胞存活的保护。进一步的机制研究表明，RIPC 保护了 EC 中的 Nrg1β-ErbB2 信号传导，并且 I/R 损伤导致 ErbB2 降解。此外，RIPC 诱导 Nrg1β 与 ErbB2 结合，从而防止 I/R 诱导的 ErbB2 降解（图）。本研究强调了 EC 预处理和 EC 保护机制激活在 RIPC 诱导的心脏保护中的重要性。此外，

数字。 促血管生成因子和 Nrg1β（neuregulin-1β）。Nrg1β 通过多种机制保护心脏。Nrg1β 直接与内皮细胞 (EC) 中的 ErbB3/4 受体结合，随后通过诱导 ErbB2 和 ErbB3/4 之间的异二聚化激活 ErbB2。ErbB2 激活不仅抑制 ATG5 介导的 Trx2 降解和 EC 细胞凋亡，而且通过激活 Src 信号介导的 eNOS 酪氨酸磷酸化来增加 NO 的产生。不同于除诱导 VEGF/VEGFR 表达外还促进炎症的促血管生成细胞因子（如 CXCL12-CXCR4、CXCL11-CXCR7 和 CCL2-CCR2）¹⁰和血管生成，促血管生成 Nrg1β 通过抑制促炎信号，如 STAT3 和 NF-κB 来减轻炎症。Nrg1β-ErbB2 信号传导的抗炎特性可能为心肌梗死后开发 Nrg1β 促血管生成疗法提供独特的机会。使用 www.BioRender.com 创建。mtROS 表示线粒体 ROS；NF-κB，活化 B 细胞的核因子 kappa-轻链增强剂；STAT3，信号转导和转录激活因子 3；和 VEGF，血管内皮生长因子。

在急性缺血等应激条件下，心肌内皮细胞释放 Nrg1β，Nrg1β 可能通过激活多个细胞中的 ErbB 信号传导并通过多种机制在心脏中发挥保护作用。Nrg1β-ErbB 受体信号传导已显示介导微血管内皮和心肌细胞之间的串扰。⁹ Nrg1β-ErbB2 信号增强 NO 的产生，对心肌细胞具有负性肌力作用。¹¹ Nrg1β 通过心肌细胞上表达的 ErbB 受体，通过促进其存活^12,13和增强葡萄糖摄取来保护心肌细胞。¹⁴最近的一项研究表明，Nrg1β-ErbB4 通路还抑制巨噬细胞活化并减少心肌肥大和纤维化。¹⁵在 Kundumani-Sridharan 等人的研究中，⁷作者表明，Nrg1β-ErbB2 信号通过 ErbB2/4-cSrc-NO 轴和 ErbB2/4-ATG5-Trx2 轴保护 EC（图）。用预条件培养基处理 ECs（即，通过在脱氧和缺乏生长补充的培养基中培养 ECs 产生）诱导 ErbB2 磷酸化/活化及其与非受体酪氨酸激酶 cSrc 的结合，从而激活下游信号传导，导致 eNOS 磷酸化/活化并增加 NO生产。Nrg1β-ErbB2 信号还可以防止 Trx2 降解并保持其抗氧化能力，这对细胞保护很重要。I/R 通过激活 ATG5/beclin 1/Ambra1 巨自噬机制诱导 Trx-2 降解。ErbB2 通过与 ATG5 结合、诱导 ATG5 磷酸化/失活并随后防止 Trx-2 降解来保护 Trx2。最后，内皮 ErbB2 的丢失导致 ATG5 和 Trx2 降解的去磷酸化和活化（图）。这项研究为 Nrg1β-ErbB 受体介导的心脏保护机制提供了新的见解。

血管生成生长因子的治疗潜力已在心脏病患者中进行了广泛的测试，例如晚期冠状动脉疾病。然而，这些临床试验的结果令人失望，使得在急性心肌梗死后进行促血管生成疗法的研究变得困难。^16-20因此，如前所述，促血管生成疗法仍有可能使 I/R 急性期患者受益。²⁰然而，考虑炎症对血管生成的作用至关重要。炎症是众所周知的血管生成驱动因素。例如，CXCR4 激活 ECs 和心肌细胞中的 CCXL12，并且已知可改善梗塞血管生成^21-23（图）。此外，CXCL11 介导的 CXCR7 ²⁴ECs ²⁵中 CCL2 介导的 CCR2 激活与 MI 后血管生成增加有关。活化的心肌细胞可以增加 VEGFA 和 CCL2 的分泌并诱导血管生成。²⁶因此，炎症在梗塞血管生成中起重要作用，许多促血管生成因子可以增加 EC 和心肌细胞的炎症。然而，众所周知，过度炎症会对梗塞的心脏造成不利影响。²⁷在这种情况下，Nrg1β-ErbB2 信号可能在急性心肌梗死后的促血管生成治疗中发挥独特的作用，因为它具有抗炎作用，^15,28-30并且其促血管生成能力不依赖于其促炎作用（图）。重要的是要强调 MI 后的初始炎症反应对于促进缺血性损伤后的愈合过程至关重要，但如上所述，过度炎症可能是有害的。因此，对于促血管生成治疗，必须考虑炎症的优缺点之间的平衡。需要进一步研究以确定各种促血管生成疗法的最佳时机和组合，以抑制 MI 后缺血性损伤的进展。

我们非常感谢德克萨斯心脏研究所科学出版部的 Nicole Stancel 博士提供编辑支持，以及德克萨斯大学 MD 安德森癌症中心的 Keigi Fujiwara 博士对稿件的批判性阅读和宝贵的建议。

我们的研究活动得到了美国国立卫生研究院 (NIH) 对 YH Shen (HL143359) 和 J.-i 的资助。安倍 (HL149303)。

披露无。

有关资金来源和披露信息，请参见第 2317 页。

本文所表达的观点不一定是编辑或美国心脏协会的观点。