Daily Cardiology Research Analysis
Three high-impact cardiology studies advance mechanisms and therapeutics across domains. Human cardiac allograft vasculopathy is linked to intragraft plasma cells producing bilirubin‑reactive antibodies, revealing a heme catabolism–immune axis. Disturbed flow plus hypercholesterolemia drives endothelial reprogramming to immune‑like and foam‑like states, while transient mRNA‑based PKM2 overexpression in pigs enhances myocardial repair and function after infarction.
Summary
Three high-impact cardiology studies advance mechanisms and therapeutics across domains. Human cardiac allograft vasculopathy is linked to intragraft plasma cells producing bilirubin‑reactive antibodies, revealing a heme catabolism–immune axis. Disturbed flow plus hypercholesterolemia drives endothelial reprogramming to immune‑like and foam‑like states, while transient mRNA‑based PKM2 overexpression in pigs enhances myocardial repair and function after infarction.
Research Themes
- Transplant vasculopathy immunopathogenesis (bilirubin-targeting antibodies)
- Endothelial reprogramming under disturbed flow and hypercholesterolemia
- mRNA-based cardiac regeneration after myocardial infarction
Selected Articles
1. Dominant intragraft plasma cells targeting bilirubin implicate local heme catabolism in human cardiac allograft vasculopathy.
Using single-cell profiling and recombinant antibodies from intragraft plasma cells, the authors show that most graft-derived antibodies in human CAV target bilirubin, with corresponding bilirubin accumulation and heme-catabolic enzyme expression in lesions. This identifies local heme catabolism as a likely antigenic driver and a therapeutic target in CAV.
Impact: First mechanistic evidence that bilirubin-specific antibodies dominate intragraft responses in human CAV links metabolism to alloimmune pathology, opening new diagnostic and therapeutic avenues.
Clinical Implications: If validated, targeting heme catabolism (e.g., HO-1/biliverdin reductase pathways) or neutralizing bilirubin-specific antibodies could modify CAV progression and enable biomarker development (bilirubin deposition patterns).
Key Findings
- 57% (21/37) of graft-derived recombinant antibodies reacted to bilirubin, while none from peripheral blood plasma cells did.
- Bilirubin deposition localized to lymphocytic aggregates and smooth muscle cell cytoplasm/nuclei in CAV arteries, not seen in healthy hearts.
- Heme-oxygenase-1 and biliverdin reductases were expressed in graft-infiltrating macrophages with Fe2+ present in hyperplastic arterial media.
Methodological Strengths
- Single-cell RNA sequencing with immunoglobulin gene profiling to define dominant intragraft plasma cell clones
- Functional recombinant monoclonal antibody generation and antigen screening, coupled with histologic and tissue iron analyses
Limitations
- Causality for bilirubin-targeting antibodies in driving CAV progression is not established; interventional validation is lacking
- Sample size and generalizability across centers and time post-transplant are not fully defined
Future Directions: Test whether inhibiting heme catabolism or neutralizing bilirubin-reactive antibodies alters CAV progression in models and clinical trials; develop noninvasive imaging or circulating biomarkers for bilirubin deposition.
BACKGROUND: Cardiac allograft vasculopathy (CAV) is consistently accompanied by immune infiltrates surrounding affected coronary arteries, including antibody-producing plasma cells (PC). The antigenic drivers of these intragraft PC responses remain poorly defined. METHODS: We characterized graft-infiltrating PC by single-cell RNA sequencing and immunoglobulin gene profiling. Using immunoglobulin sequences we generated 37 recombinant monoclonal antibodies (mAb) from dominant intragraft PC clones and 24 control mAb from peripheral blood PC. Antigen reactivity was screened against chemical adducts, including bilirubin, a heme-degradation by-product. Histologic and tissue analyses assessed bilirubin deposition as well as expression of heme-catabolic enzymes, and the presence of Fe2+ in heart explants with CAV. RESULTS: A majority of graft-derived mAb (21/37; ~57%) but none of the mAb derived from blood PC reacted to bilirubin. Bilirubin deposition was detected within lymphocytic aggregates in CAV grafts. In coronary arteries with CAV lesions, bilirubin accumulated in the cytoplasm and nuclei of smooth muscle cells in the tunica media, a pattern not observed in healthy heart tissue. Lastly, we detected the expression of heme-oxygenase-1 and biliverdin reductases in graft-infiltrating macrophages along with the presence of Fe2+ ion in the media of arteries with hyperplasia. CONCLUSION: These findings suggest that local heme catabolism and resultant bilirubin accumulation create a prominent target for intragraft antibody responses in CAV. Bilirubin-specific antibodies and heme-catabolic pathways may contribute to CAV pathogenesis and represent potential mechanistic and therapeutic avenues for further investigation. FUNDING: National Institute of Health.
2. Transient overexpression of hPKM2 in porcine cardiomyocytes prevents heart failure after myocardial infarction.
A non-viral modified mRNA platform transiently increased PKM2 in porcine cardiomyocytes, augmenting cell-cycle activity, paracrine protection, cardiac function, and reducing fibrosis post-MI in both juvenile and adult animals. The large-animal evidence supports translational feasibility for regenerative therapy to prevent post-infarction heart failure.
Impact: Demonstrates practical, transient mRNA-based myocardial regeneration in a clinically relevant large-animal model, advancing a potential new class of therapy beyond current standards.
Clinical Implications: Supports development of transient mRNA therapeutics targeting cardiomyocyte cell-cycle and metabolism after MI; informs dosing/timing strategies and safety endpoints for first-in-human trials.
Key Findings
- Modified mRNA delivery of PKM2 increased cardiomyocyte cell-division markers and secretion of protective factors in juvenile pigs.
- Both juvenile (2 months) and adult (1 month) pigs showed improved cardiac function and reduced fibrosis after PKM2 mRNA treatment.
- Non-viral, targeted mRNA platform enabled transient expression with regenerative benefit, supporting translational potential.
Methodological Strengths
- Large-animal (porcine) models including juvenile and adult arms with functional and histologic endpoints
- Targeted non-viral modified mRNA delivery enabling transient gene expression with translational relevance
Limitations
- Long-term durability, arrhythmogenic risk, and off-target effects were not fully assessed
- Human efficacy and safety remain untested; dosing and delivery optimization needed
Future Directions: Define long-term safety/efficacy, dose-response, and delivery route; assess combination with standard post-MI care; initiate phase 1 trials with arrhythmia and fibrosis endpoints.
The adult mammalian heart lacks the ability to regenerate after injury, contributing to heart failure. No current treatment reactivates heart muscle cell division to prevent this decline. We used a targeted, non-viral modified mRNA system to transiently boost expression of a regenerative enzyme, pyruvate kinase muscle isozyme M2, in heart muscle cells of juvenile and adult pig models after ischemic injury. In juvenile pigs treated one-week post-injury, we observed increased markers of cell division, secretion of protective factors, improved heart function, and reduced scarring two months later. In adult pigs treated immediately after injury, we saw improved heart contractility and less fibrosis one month later. These results show that targeted pyruvate kinase muscle isozyme M2 modified mRNA delivery can stimulate muscle regeneration and functional recovery in both young and adult pig hearts. This approach offers a promising strategy for repairing ischemic injury and preventing heart failure in humans.
3. Disturbed flow induces reprogramming of endothelial cells to immune-like and foam cells under hypercholesterolaemia during atherogenesis.
Using AAV‑PCSK9 Western diet mice with disturbed flow, single-cell profiling (98,553 cells) and EC-lineage tracing reveal that d-flow plus hypercholesterolemia reprograms endothelial cells into immune-like (EndIT) and foam-like (EndFT) states, beyond inflammation and EndMT. Human plaque datasets and HAEC experiments corroborate that FIRE occurs in human atherosclerosis.
Impact: Introduces and validates a two-hit model in which flow disturbance and hypercholesterolemia jointly drive endothelial transdifferentiation to foam-like cells, redefining cellular origins and targets in atherogenesis.
Clinical Implications: Suggests therapeutic strategies targeting flow-sensitive pathways to prevent endothelial immune/foam transitions; supports patient stratification by hemodynamic risk and lipid status.
Key Findings
- Atherosclerotic plaques formed only when disturbed flow was combined with hypercholesterolemia, not by either alone.
- scRNA-seq (98,553 cells) identified endothelial transitions to immune-like (EndIT) and foam-like (EndFT) states in vivo.
- Lineage tracing and human plaque scRNA-seq reanalysis plus HAEC experiments validated FIRE, EndIT, and EndFT signatures.
Methodological Strengths
- Multimodal validation: scRNA-seq across 95 mice, EC-lineage tracing, human plaque data reanalysis, and HAEC in vitro studies
- Physiologic two-hit model integrating hemodynamic disturbance with lipid loading (AAV-PCSK9 + Western diet + partial carotid ligation)
Limitations
- Causal interventions specifically reversing EndFT/EndIT in vivo are not yet demonstrated
- Translation to clinical endpoints remains to be tested despite human corroboration
Future Directions: Develop interventions that modulate flow-sensitive signaling to prevent EndIT/EndFT; test in large animals and assess imaging/biomarkers for endothelial phenotypes.
AIMS: Atherosclerosis occurs preferentially in the arteries exposed to disturbed flow (d-flow), while the stable flow (s-flow) regions are protected even under hypercholesterolaemic conditions. We recently showed that d-flow alone initiates flow-induced reprogramming of endothelial cells (FIRE), including the novel concept of partial endothelial-to-immune-cell-like transition (partial EndIT), but it was not validated using a genetic lineage-tracing model. In addition, the combined effect of d-flow and hypercholesterolaemia has not been tested. Here, we tested and validated the two-hit hypothesis that d-flow is an initial instigator of partial FIRE but requires hypercholesterolaemia to induce a full-blown FIRE and atherosclerotic plaque development. METHODS AND RESULTS: Mice were treated with AAV-PCSK9 and a Western diet to induce hypercholesterolaemia and/or partial carotid ligation (PCL) surgery to expose the left common carotid artery (LCA) to d-flow. Single-cell RNA sequencing (scRNA-seq) analysis was performed using single cells obtained from the LCAs and the control right common carotid arteries at 2 and 4 weeks post-PCL. Immunohistochemical staining was performed on EC-specific confetti mice at 4 weeks post-PCL and hypercholesterolaemia to validate endothelial reprogramming. Human aortic endothelial cells (HAECs) exposed to d-flow and hypercholesterolaemic conditions were used to validate FIRE. Atherosclerotic plaques developed by d-flow under hypercholesterolaemia, but not by d-flow or hypercholesterolaemia alone. The scRNA-seq results of 98 553 single cells from 95 mice revealed 25 cell clusters: 5 EC, 3 vascular smooth muscle cell (SMC), 5 macrophage (MΦ), and additional fibroblast, T cell, natural killer cell, dendritic cell, neutrophil, and B-cell clusters. Our scRNA-seq analysis results raised a hypothesis that d-flow under hypercholesterolaemia transitioned healthy ECs to full immune-like (EndIT) and, more surprisingly, foam-like cells (EndFT), in addition to inflammatory and mesenchymal cells (EndMT). Further, ECs with characteristics of foam cells shared remarkably similar transcriptomic profiles with foam cells derived from SMCs and MΦs. Lineage-tracing studies using immunohistochemical staining of canonical protein and lipid markers in the EC-specific confetti mice exposed to d-flow and hypercholesterolaemia demonstrated evidence supporting the novel FIRE hypothesis, including EndIT and EndFT. Moreover, reanalysis of the two publicly available human plaque scRNA-seq datasets and our immunostaining studies suggest that FIRE occurs in human atherosclerotic plaques. Additionally, HAECs exposed to d-flow, high cholesterol, and proinflammatory cytokines (identified in our scRNA-seq data) show the markers of EndIT and EndFT at the mRNA, protein, and functional levels. CONCLUSION: The scRNA-seq study raised a two-hit hypothesis for FIRE, including EndIT and EndFT, which was validated by the lineage-tracing and in vitro HAEC studies. D-flow induces partial reprogramming, including inflammation, EndMT, and partial EndIT. Under hypercholesterolaemia, d-flow fully reprogrammes arterial ECs, including the novel EndIT and EndFT, in addition to inflammation and EndMT, during atherogenesis. This single-cell atlas and FIRE programs provide a crucial roadmap for novel mechanistic understanding and therapeutics targeting flow-sensitive genes, proteins, and pathways of atherosclerosis.