Vascular endothelial growth factor, or VEGF-A, has a complicated reputation in lung biology. The factor was originally discovered as vascular permeability factor, a molecule secreted by tumor cells that made blood vessels leak fluid at an alarming rate. In the lung, that leakiness is precisely the problem in acute lung injury: when the endothelial lining of pulmonary microvessels becomes permeable, protein-rich fluid floods the airspaces, oxygen exchange collapses, and patients may require mechanical ventilation to survive. Earlier clinical studies had found elevated VEGF in the airspaces of patients with respiratory distress syndrome, and researchers have long debated whether the growth factor is a culprit driving vascular leak or, paradoxically, a repair signal that helps the damaged endothelium recover. The new findings suggest that part of the confusion may have arisen because investigators were measuring a family of molecules with opposite effects as if it were a single entity.

The key to that complexity lies in alternative splicing, the process by which a single gene yields multiple protein versions. In the final stretch of the VEGF-A gene, two different sets of terminal exons can be stitched onto the coding sequence. One choice produces the classical pro-angiogenic isoforms, exemplified by VEGF165a, which bind the receptor VEGFR2 on endothelial cells and trigger the signaling cascades that make vessels grow and leak. The alternative choice produces the so-called b-variants, including VEGF165b, which differ in just six amino acids at the carboxyl terminus. That subtle change, first characterized by researchers studying kidney and cancer biology in the early 2000s, is enough to render the variant weakly angiogenic and poorly permeability-inducing, while still allowing it to occupy the same receptor. The b-isoforms therefore behave as natural antagonists of their pro-angiogenic siblings, competing for receptor binding without delivering the same intracellular message.

The Guangzhou-led team began by asking whether this splice balance is disturbed in human lung injury. Analyzing blood samples from patients, they found that the circulating ratio of VEGF165b to total VEGF-A was significantly reduced in acute lung injury, and that the lower the proportion of the protective variant, the more severe the disease. That inverse correlation, reported alongside ethical approval from the First Affiliated Hospital of Guangzhou Medical University and Zhujiang Hospital of Southern Medical University, provided the first hint that a relative deficiency of VEGF165b might accompany, and possibly contribute to, the vascular catastrophe of respiratory distress syndrome. Correlation alone cannot establish causation, so the investigators turned to experimental models in which the relationship could be tested directly.

In mice, the researchers induced acute lung injury with lipopolysaccharide, the inflammatory toxin derived from bacterial cell walls that mimics Gram-negative sepsis, one of the most common triggers of the human syndrome. When the animals received exogenous VEGF165b, the consequences of the insult were markedly blunted: pulmonary edema diminished, inflammatory infiltration of the lung tissue decreased, and overall measures of injury improved. The converse experiment proved equally telling. When the team neutralized endogenous VEGF165b with antibodies, leaving the pro-inflammatory isoforms to act unopposed, lung damage became worse. Together, these gain-of-function and loss-of-function results established the splice variant as a genuine endogenous protector rather than a passive bystander, and they identified the VEGF165b-to-total-VEGF ratio as a candidate biomarker for tracking disease severity.

The mechanistic core of the study explains how a single splice decision can translate into barrier protection at the molecular level. Using human microvascular endothelial cells, human pulmonary artery endothelial cells, and primary pulmonary microvascular endothelial cells, the researchers showed that VEGF165b acts as a competitive antagonist at VEGFR2, selectively blocking the phosphorylation of the receptor at tyrosine 1175, a docking site whose activation is known to be essential for the permeability response. With that phosphorylation event suppressed, the downstream PI3K/AKT/eNOS pathway, which normally drives nitric oxide production and vessel relaxation during vascular leak, was quieted. The team traced the consequences further downstream to the Src kinase and the adherens junction protein VE-cadherin, the molecular glue that holds endothelial cells together. When Src phosphorylates VE-cadherin, the junctions loosen and fluid escapes; by preventing the upstream signal, VEGF165b reduced VE-cadherin phosphorylation and thereby kept the endothelial barrier intact.

Intriguingly, the protective variant does not stop at junctional reinforcement. Through RNA sequencing and network analysis of the signaling hubs affected by VEGF165b, the investigators found that the variant also suppresses the chemokine CCL2, also known as monocyte chemoattractant protein 1. CCL2 is a potent recruiter of circulating monocytes, and its reduction translated into a second, distinct anti-inflammatory mechanism: fewer monocytes adhered to the endothelial surface, limiting the wave of inflammatory cells that normally amplifies tissue damage in acute lung injury. The authors describe this as a dual mode of action, in which VEGF165b simultaneously strengthens the physical wall of the microvasculature and dampens the cellular inflammatory assault against it. Such a combination is rare among candidate therapies, which typically address either leakiness or inflammation but rarely both.

The findings also reframe a long-running therapeutic debate. Several anti-VEGF strategies, including the monoclonal antibody bevacizumab, have been explored for severe COVID-19 and other causes of pulmonary edema on the logic that blocking VEGF should reduce vascular leak. But blanket VEGF blockade carries well-documented risks, including hypertension, proteinuria, and thromboembolism, precisely because the growth factor performs essential maintenance roles in healthy vessels. The splice-variant view offers a more surgical alternative: rather than eliminating VEGF signaling altogether, one could in principle restore the balance between pro-permeability and anti-permeability isoforms, either by administering recombinant VEGF165b, which has already been tested as an anti-cancer agent in animal models, or by shifting the splicing machinery toward the protective variant. The study’s demonstration that neutralizing VEGF165b worsens injury adds a note of caution for any therapy that removes this natural brake indiscriminately.

As with any preclinical advance, the road from mouse models and cell cultures to the intensive care unit is long. The patient data establish an association between a low VEGF165b fraction and disease severity, but clinical trials will be needed to determine whether replenishing the variant improves outcomes, at what dose, and at what stage of illness. Questions also remain about how the splicing balance is regulated in the acutely inflamed lung, and whether splicing factors such as the SRSF family, which other studies have implicated in acute lung injury, could serve as drug targets. Nevertheless, the conceptual payoff is substantial. The work reveals that vascular homeostasis in the lung depends on the critical equilibrium of VEGF splice variants, positions VEGF165b as both a biomarker and a potential therapeutic agent for acute lung injury and respiratory distress syndrome, and offers a new strategy for treating vascular barrier dysfunction in critical lung disease, one of the most stubborn unsolved problems in modern critical care medicine.

Subject of Research: The role of the VEGF-A splice variant VEGF165b in protecting against acute lung injury by antagonizing VEGF165a/VEGFR2 signaling

Article Title: VEGF165b attenuates LPS-induced acute lung injury via antagonizing the VEGF165a/VEGFR2 signaling pathway

Article References: Deng, J., Wang, X., Wu, Z., Bai, Q., Luo, Q., Zhou, L., Yao, Y., Wang, H., Zhong, K., Liu, H., Chen, X., & Wang, T. (2026). VEGF165b attenuates LPS-induced acute lung injury via antagonizing the VEGF165a/VEGFR2 signaling pathway. Angiogenesis, 29(4), Article 75. https://doi.org/10.1007/s10456-026-10090-4

Image Credits: AI Generated

DOI: 10.1007/s10456-026-10090-4

Keywords: acute lung injury, ARDS, VEGF165b, VEGFR2, vascular permeability, endothelial barrier, alternative splicing, VE-cadherin, CCL2, lipopolysaccharide, angiogenesis, pulmonary edema

The clinical picture on presentation was dire. Acute severe mitral regurgitation had produced extreme respiratory failure despite maximal ventilatory support: while breathing pure oxygen, the patient’s arterial blood showed a pH of 7.144, a partial pressure of oxygen of only 48 mmHg, and a partial pressure of carbon dioxide of 101 mmHg. Those numbers describe profound, life-threatening hypoxemia and hypercapnia, the biochemical signature of lungs so waterlogged and failing that gas exchange had nearly collapsed. Fulminant pulmonary edema of this kind, driven by the sudden backflow of blood through an incompetent mitral valve, typically leaves clinicians with a narrow and dangerous window in which to act.

The standard emergency answer for such patients is often veno-arterial ECMO, in which blood is drained from the venous system, oxygenated outside the body, and returned to the arterial circulation, simultaneously supporting the heart and lungs. But the authors highlight a well-recognized paradox: VA-ECMO can worsen pulmonary congestion in patients with a failing left ventricle. By returning oxygenated blood to the aorta, it increases the afterload against which the damaged left ventricle must pump, which can push blood backward into the lungs and aggravate the very edema the therapy is meant to buy time against. Recent literature, including a 2024 position paper on dual-circulation physiology during venoarterial ECMO and multicenter data linking left ventricular unloading to lower mortality in cardiogenic shock, has sharpened attention on this problem and on strategies to relieve the loaded ventricle.

The surgical team proceeded with emergency mitral valve replacement under cardiopulmonary bypass. When the operation ended, however, the heart could not be weaned from the bypass machine: severe pulmonary edema and post-cardiotomy shock conspired to keep the ventricle too weak and the lungs too compromised for independent circulation. Rather than defaulting to VA-ECMO, the surgeons made a deliberate split decision. They implanted an Impella 5.5, an axial-flow catheter-mounted pump, directly into the ascending aorta through a prosthetic graft, positioning it across the aortic valve so it could draw blood out of the left ventricle and deliver it antegrade into the systemic circulation. Then they added veno-venous ECMO, which drains deoxygenated blood from the venous side and returns it oxygenated to the veins, supporting only the lungs.

The physiological logic of this combination is what makes the case compelling. The Impella 5.5 provides left ventricular unloading and forward systemic flow, reducing the pressure that would otherwise be transmitted back into the pulmonary vasculature, while VV-ECMO takes over gas exchange without adding any arterial afterload at all. In effect, the circulation and the respiration were decoupled and managed independently, avoiding the differential hypoxemia problem known as harlequin syndrome, in which poorly oxygenated blood ejected by the native heart mixes with oxygenated ECMO return in patients on VA-ECMO. The authors argue that this decoupled strategy may be an effective option for selected patients suffering concomitant severe respiratory and circulatory failure, particularly when VA-ECMO risks compounding pulmonary congestion.

The early postoperative course was rocky but revealing. The patient initially required substantial vasoactive and inotropic drug support to maintain blood pressure, a reflection of both the stunned post-cardiotomy myocardium and the inflammatory burden of prolonged critical illness. Serum lactate, a biochemical marker of inadequate tissue perfusion, peaked transiently at 10.9 mmol/L on postoperative day one, a level indicating significant anaerobic metabolism. Crucially, however, systemic perfusion was maintained throughout, and as the ventricle recovered, the team was able to stabilize the circulation on Impella-mediated antegrade flow alone, without ever converting to VA-ECMO or the hybrid V-AV configuration that many centers would have reached for in a similar situation.

Respiratory recovery followed a parallel and equally instructive trajectory. Under VV-ECMO-supported lung rest, with the membrane lung shouldering the work of oxygenation and carbon dioxide removal, and under an intensive diuretic regimen to strip away the excess lung water, the patient’s respiratory function improved progressively. Bilateral pulmonary opacities on imaging, the radiographic shadow of the edema, gradually cleared. VV-ECMO was removed on postoperative day three, a remarkably short run that suggests the lung injury, while fulminant, was largely hydrostatic and reversible once the circulatory derangement was corrected. The Impella 5.5 was explanted on postoperative day six as ventricular function recovered.

The outcome was a full survival: the patient was discharged on postoperative day 46 without any neurological sequelae, an outcome that would have been considered improbable at the moment of presentation, when his blood gases were incompatible with sustained life on conventional support. For a case report, the message is less about a single heroic save than about a reproducible physiological principle. The authors position the combination as a way to sidestep the afterload penalty of VA-ECMO while still providing both pump function and gas exchange, drawing on established techniques for direct aortic Impella implantation that allow the device to be placed surgically with secure fixation.

The report also underscores how rapidly the mechanical support landscape is evolving. The Impella 5.5, originally developed as a percutaneous left ventricular assist device for high-risk procedures and cardiogenic shock, is increasingly being combined with ECMO in creative configurations, and the literature now includes dedicated analyses of left ventricular decompression during VA-ECMO and reviews of the collision between native and device circulations. This case adds a new entry to that growing repertoire: instead of adding an Impella to unload a ventricle already supported by VA-ECMO, the team used the pump as the sole circulatory engine and paired it with purely respiratory extracorporeal support. The authors are careful to frame the approach as appropriate for selected patients, and a single case cannot establish superiority over conventional strategies. But for clinicians confronting the double failure of heart and lungs, particularly when pulmonary edema makes VA-ECMO counterproductive, the case provides a concrete, technically documented template. It suggests that thinking about circulatory and respiratory failure as separable problems, rather than as a single indication for one device, can turn a nearly certain death into a discharge home with an intact brain.

Subject of Research: Combined veno-venous ECMO and direct aortic Impella 5.5 support for emergency mitral valve replacement in acute severe mitral regurgitation with fulminant pulmonary edema

Article Title: Combined veno-venous ECMO and direct aortic impella 5.5 support enabling emergency mitral valve replacement in acute severe mitral regurgitation with fulminant pulmonary edema

Article References: Combined veno-venous ECMO and direct aortic impella 5.5 support enabling emergency mitral valve replacement in acute severe mitral regurgitation with fulminant pulmonary edema. (n.d.). https://doi.org/10.1007/s10047-026-01592-5

Image Credits: AI Generated

DOI: 10.1007/s10047-026-01592-5

Keywords: veno-venous ECMO, Impella 5.5, mechanical circulatory support, left ventricular unloading, differential hypoxemia, mitral regurgitation, pulmonary edema, cardiogenic shock, mitral valve replacement, cardiac surgery, Journal of Artificial Organs, case report