Researchers at the University Hospital of Bonn and the University of Bonn have identified a previously unknown immune signaling pathway that enables newborn heart cells to survive and regenerate after injury, offering a potential path toward therapies for damaged adult hearts.
Adult hearts cannot effectively repair themselves after a myocardial infarction or chronic cardiovascular stress. Medical treatments currently focus mainly on slowing disease progression rather than reversing damage. But scientists studying mammalian biology have long noted a stark biological contrast: newborn mammals possess a temporary capacity to regenerate heart tissue after injury, though this capability vanishes within the first days of life.
Researchers set out to determine what drives this early regenerative window and how neonatal hearts manage both direct injury and pressure overload, a condition that mimics chronic cardiac stress. The work centres on how immune cells communicate inside the body through signaling pathways that operate much like a chain of falling dominoes, where specific molecules trigger successive signals until a cellular reaction begins.
The Immune-Receptor Axis in Neonatal Mice
Working with a neonatal mouse model, the research team discovered an unexpected communication axis between immune signals and heart muscle cells. Specifically, three immune-related signaling molecules—known as CCL4, S100A8, and C1QA—work in concert to activate a receptor named TLR2 directly on heart muscle cells.
When this pathway activates, it triggers a cascade that stimulates heart cell proliferation, enhances the survival of heart muscle cells, and actively reduces cell death. Investigators noted that TLR2 functions as a central hub connecting inflammatory signals directly to regenerative responses.
“Our findings reveal an unexpected communication axis between immune signals and heart muscle cells that supports regeneration in the neonatal heart. We were particularly surprised to find that TLR2 acts as a central hub connecting inflammatory signals to regenerative responses.”
Dr. Mona Malek Mohammadi, corresponding author, head of a research group at the Institute of Physiology I, UKB and the University of Bonn
To validate the precise biological importance of TLR2 in this process, the research group turned to genetically modified mice lacking the receptor entirely. When subjected to cardiac stress, these modified mice failed to adapt and rapidly developed heart failure, demonstrating that the receptor is essential for maintaining protective and regenerative responses in newborn tissue.
Contrasting Newborn and Adult Heart Capacity
A critical finding of the study involves the difference in receptor levels between young and mature hearts. The investigation revealed that TLR2 expression is much higher in newborn heart cells than in adult heart cells. This disparity suggests that the natural loss of this signaling pathway over time may contribute to the poor regenerative capacity observed in mature mammalian hearts.
The findings point toward a long-term therapeutic strategy aimed at artificially reactivating these neonatal-like repair mechanisms in adult patients following events such as a myocardial infarction. While current medical interventions remain limited to slowing down the worsening of cardiovascular conditions, the ultimate objective is to achieve true biological repair.
“Current cardiovascular therapies mainly slow disease progression,” said Dr. Malek Mohammadi. “Our long-term goal is to promote true cardiac repair and regeneration.”
Dr. Malek Mohammadi, corresponding author, head of a research group at the Institute of Physiology I, UKB and the University of Bonn
Publication and Next Steps for Translational Research
The detailed mechanisms, experimental methods, and genetic model results have been published in the journal Cell Communication and Signaling, a Springer Nature publication, under the title TLR2 mediates cell cycle re-entry and survival of neonatal cardiomyocytes in response to injury
by Julia Nicke and colleagues.
