When heart muscle is starved of blood and then reperfused, the immune receptor CLEC4E has long been suspected of making things worse. A new study in mice now pinpoints where that damage originates: not in the flood of infiltrating immune cells, but in the heart’s own resident cells. By selectively deleting the CLEC4E gene in either the bone marrow-derived immune compartment or the non-bone-marrow-derived tissue cells of chimeric mice, researchers at KU Leuven showed that cardioprotection after ischemia-reperfusion injury depends almost entirely on removing the receptor from cardiac resident cells.
The work, published in Experimental Biology and Medicine, used a bone marrow transplantation strategy to disentangle the two cell populations. Eight- to nine-week-old male C57Bl6/J wild-type and CLEC4E-deficient mice received sublethal total body irradiation followed by adoptive transfer of five million bone marrow cells from female donor mice via the tail vein. This produced two reciprocal chimeric groups: CLEC4E-deficient mice reconstituted with wild-type bone marrow, and wild-type mice reconstituted with CLEC4E-deficient bone marrow. A control group of wild-type mice received wild-type bone marrow to account for any effects of the transplantation procedure itself. In total, 86 chimeric mice were studied.
Chimerism was verified rigorously. Because the donor marrow came from female mice and the recipients were male, the absence of SRY transcripts in circulating blood cells but their presence in tissue cells confirmed successful engraftment. Quantitative real-time polymerase chain reaction on blood and ear tissue samples three weeks after transfer showed that mice displayed the donor genotype in blood but retained their own genotype in tissue. Immunohistochemistry on bone marrow smears added a second line of confirmation: wild-type bone marrow cells expressed CLEC4E in roughly 89 percent of cells at baseline, while CLEC4E-deficient marrow showed only about 3 percent. After transplantation, chimeric CLEC4E-deficient mice receiving wild-type marrow showed CLEC4E immunoreactivity in more than 99 percent of bone marrow cells, whereas chimeric wild-type mice receiving deficient marrow showed only about 7 percent.
Four weeks after bone marrow transfer, the researchers induced myocardial ischemia-reperfusion injury by occluding the left anterior descending coronary artery for 30 minutes followed by reperfusion. Myocardial necrosis was measured with a high-sensitivity troponin I enzyme-linked immunosorbent assay on plasma collected 90 minutes after reperfusion. Infarct size and left ventricular remodeling were assessed by late gadolinium-enhanced cardiac magnetic resonance imaging on a 7 Tesla system at 24 hours and again at 28 days, with investigators blinded to genotype. Hearts were then harvested for immunohistochemistry, proteomic analysis, and genotyping.
The early results were striking for their similarity. Serum troponin I levels at 90 minutes were comparable across the chimeric groups and the control group, at approximately 42, 48, and 44 nanograms per milliliter respectively, with no statistically significant difference. Infarct size measured by gadolinium-enhanced MRI at 24 hours was likewise similar, at roughly 31.5 percent of left ventricular mass in wild-type mice with deficient bone marrow, 25.2 percent in deficient mice with wild-type marrow, and 31.9 percent in controls. These findings indicate that the extent of the initial ischemic injury is independent of CLEC4E gene function, whether the receptor is absent from immune cells, resident cells, or both.
The divergence emerged over the following four weeks. At 28 days, infarct size assessed semi-quantitatively by planimetry on Sirius Red-stained sections was significantly smaller in CLEC4E-deficient mice carrying wild-type bone marrow, at 6.9 percent of left ventricular mass, compared with 19.8 percent in wild-type mice carrying deficient marrow and 22.8 percent in controls. Left ventricular function told the same story. Deficient mice with wild-type marrow had an ejection fraction of 62 percent at 28 days, versus 47 percent in wild-type mice with deficient marrow. End-diastolic and end-systolic volumes were both significantly smaller in the protected group, both in absolute microliters and when indexed to body surface area. Ejection fraction did not change significantly from day 1 to day 28 in the deficient mice with wild-type marrow, whereas it fell by a mean of 12 percentage points in wild-type mice with deficient marrow, with a similar decline in the transplant controls. Because the control group resembled the wild-type chimeric group, the authors concluded that the transplantation procedure itself did not bias the outcome.
Immunohistochemistry clarified which cells express CLEC4E after injury. At 24 hours after reperfusion, in wild-type chimeric mice whose hematopoietic cells lacked the receptor, intense CLEC4E immunoreactivity appeared throughout the infarct zone and co-localized with myosin light chain 2, a cardiomyocyte marker, and with lectin-labeled endothelial cells, but not with myeloperoxidase-positive neutrophils. Conversely, in deficient mice with wild-type marrow, CLEC4E signal in the infarct zone originated from infiltrating myeloperoxidase-positive inflammatory cells, with no co-staining on cardiomyocytes or endothelial cells. This spatial mapping supports the conclusion that the receptor is induced in cardiac resident cells, specifically cardiomyocytes and endothelial cells, in response to ischemic damage.
Proteomic profiling of whole left ventricular tissue at 28 days reinforced the picture. Using the Olink Target 48 Mouse Cytokine Panel on samples from five chimeric wild-type and six chimeric deficient mice, the team found that interleukin-1 alpha, interleukin-4, and hepatocyte growth factor were significantly higher in the wild-type chimeric group with the worse outcome, with trends toward higher CCL12 and CXCL9. A broader Olink Target 96 Mouse Exploratory Panel analysis of 19 chimeric wild-type and 14 chimeric deficient mice identified seven differentially expressed proteins. Transforming growth factor alpha and troponin I3 were higher in the protected deficient mice, while Axin-1, CYR61, hepatocyte growth factor, PAK4, and PARP-1 were all significantly elevated in the wild-type chimeric group. Several of these proteins are associated with scar formation, extracellular matrix remodeling, and adverse ventricular remodeling, consistent with the larger infarcts and poorer function observed in that group. The authors note that upregulation of interleukin-4 and hepatocyte growth factor in the injured group may reflect compensatory counter-regulatory signaling rather than a purely pro-inflammatory shift, and that follow-up studies are needed to clarify the balance.
The findings reinterpret the role of hematopoietic CLEC4E. Contrary to prior reports implicating the receptor on infiltrating immune cells in sterile inflammation after ischemia-reperfusion, deletion of CLEC4E restricted to bone marrow-derived cells alone was insufficient to confer protection in this model, and those mice actually fared worse. The authors propose that CLEC4E in resident cardiac stromal or vascular cells orchestrates the pro-fibrotic and maladaptive remodeling response, potentially by modulating the local cytokine milieu and fibroblast activation. They draw a parallel to ischemic stroke research, where blocking CLEC4E signaling in brain tissue itself, rather than in circulating inflammatory cells, reduced stroke size and improved neurological outcomes.
Several limitations temper the conclusions. The upstream mechanisms that trigger CLEC4E induction in ischemic myocardium remain unknown and were beyond the scope of this study. The sex-mismatched bone marrow transfer used to verify engraftment leaves open the possibility of sex-specific influences, although the authors note no evidence for such differences in inflammatory effects on myocardial injury. Proteomic profiling was performed at a single time point, limiting insight into the temporal dynamics of protein expression, and serum markers of innate immune activation were not assessed. All results come from a mouse model of 30 minutes of left anterior descending artery occlusion, so translation to human myocardial infarction remains untested. Within those bounds, the study establishes that CLEC4E signaling in non-bone-marrow-derived cardiac resident cells drives adverse structural and functional remodeling after reperfusion injury, and suggests that selective inhibition of the receptor in the myocardium, whether with small molecule antagonists or blocking antibodies, could become a strategy to limit infarct extension and preserve left ventricular function after ischemic heart disease.
Subject of Research: The role of the CLEC4E receptor in cardiac resident cells versus immune cells during myocardial ischemia-reperfusion injury in mice
Article Title: CLEC4E deletion in cardiac resident cells reduces infarct size and improves cardiac remodeling following myocardial ischemia-reperfusion injury
Article References: Algoet, M., Wu, M., Gillijns, H., Pusovnik, M., Caluwe, E., Blazejczyk, K., Gsell, W., Geerkens, L., De Groote, S., Kuznetsova, T., Himmelreich, U., Oosterlinck, W., & Janssens, S. (2026). CLEC4E deletion in cardiac resident cells reduces infarct size and improves cardiac remodeling following myocardial ischemia-reperfusion injury. Experimental Biology and Medicine, 251, Article 11196. https://doi.org/10.3389/ebm.2026.11196
Image Credits: AI Generated
Keywords: CLEC4E, myocardial ischemia-reperfusion, bone marrow chimera, cardiac resident cells, left ventricular remodeling, infarct size, cardiac MRI, proteomics, innate immunity, fibrosis, cardiomyocytes, KU Leuven
News Source: Ophelia Keating. (October 28, 2026). Heart’s Resident Cells, Not Immune Cells, Drive Damage After Heart Attacks. Scienmag.
