Three adenosine receptor subtypes that normally send different signals were found to converge on a common pathway that activates cardiac fibroblasts, the scar-forming cells in the heart. Blocking the receptors together produced a much stronger antifibrotic effect than blocking them one at a time.
Researchers at the Stanford Cardiovascular Institute have characterized an unexpected signaling pathway that helps drive cardiac fibrosis, the buildup of scar tissue that makes the heart stiffer and less able to pump normally.
Working with collaborators at UCLA, Boston University, MD Anderson Cancer Center, the University of Arizona and Greenstone Biosciences, the team found that three receptors on the surface of heart fibroblasts converge on the same fibrosis-promoting signal. The finding was supported in human cells, engineered human heart tissue and mouse models.
Cardiac fibrosis occurs in many forms of heart disease and contributes to heart failure, but no approved therapy directly targets the scarring process.
“This study identifies a common signal through which several adenosine receptors can drive cardiac fibroblast activation,” said Joseph C. Wu , MD, PhD, director of the Stanford Cardiovascular Institute and a corresponding author of the study. “By combining human stem-cell models with mechanistic studies and animal experiments, we could connect a screening result to a specific biological pathway that warrants further therapeutic investigation.”
The researchers assembled a drug-screening system using human induced pluripotent stem cells, or iPSCs, which can be grown in large numbers and turned into different heart cell types.
They screened about 4,000 bioactive compounds for their ability to stop cardiac fibroblasts from becoming activated and producing scar cells. Promising compounds were also tested in heart muscle and blood-vessel cells to remove candidates that showed harmful effects.
CGS15943, or CGS, a compound that blocks several adenosine receptors, emerged as the leading candidate. Its antifibrotic effects were then confirmed in primary human cardiac fibroblasts, fibroblasts from patients with cardiomyopathy and in three-dimensional engineered human heart tissues. In the engineered tissues, CGS reduced stiffness and improved contraction and relaxation.
In mice that already had cardiac fibrosis and impaired heart function, CGS slowed further scarring and functional decline, although it did not remove scar tissue that was already present.
“We wanted a screen platform that would allow for rapid exclusion of any drugs that harmed the heart, not just one that identifies compounds that stopped scarring,” said Hao Zhang , MD, assistant professor at UCLA and a first and co-corresponding author of the study, who initiated the research at Stanford.
CGS blocks receptors for adenosine, a natural signaling molecule that rises during stress and tissue injury. The researchers focused on three adenosine receptors (adenosine subtypes A1, A2A and A2B) found on cardiac fibroblasts.
These receptors are part of the large family of G protein-coupled receptors, or GPCRs. They normally signal through different G-alpha proteins and can produce different, sometimes opposing, effects. But the researchers discovered that all three also converge on a common signal called G-beta-gamma; an often unrecognized signaling GPCR partner.
Blocking one receptor at a time had only a limited effect on fibroblast activation. Blocking all three together produced a much stronger response. The finding may help explain why previous studies that focused on individual adenosine receptors have produced mixed results.
“These adenosine receptors normally signal through different G-alpha proteins, but here we show that all three were signaling in an unconventional way,” said Rabindra V. Shivnaraine , PhD, a co-first author of the study. “That common. unconventional G-beta-gamma signal helps explain why blocking the receptors together had a much stronger antifibrotic effect than targeting them one at a time.”
Shivnaraine conducted his postdoctoral research with Brian Kobilka, MD, in Stanford University’s Department of Molecular and Cellular Physiology (MCP). Kobilka, a co-author of the study, shared the 2012 Nobel Prize in Chemistry for studies of GPCRs.
The researchers then tested whether G-beta-gamma itself helps cause fibrosis. In a mouse model of heart injury, selectively blocking this signal in fibroblasts reduced cardiac fibrosis and improved heart function.
Further experiments linked G-beta-gamma to downstream signals that control fibroblast activation and scar-producing genes. Together, the results suggest that targeting a shared point where several disease signals meet could be more effective than blocking those signals individually.
CGS is a proof-of-concept research compound, not an established treatment. Further drug development would require optimization and dedicated safety and pharmacokinetic studies. The researchers also observed antifibrotic effects in human keloid fibroblasts and a mouse model of skin fibrosis, suggesting that the pathway may be worth studying in fibrosis beyond the heart.
The study, “Targeting an atypical G protein-coupled receptor signaling pathway for cardiac fibrosis therapy,” was published in Science.
DOI: 10.1126/science.aej5896
Science
Cells
Targeting an atypical G protein-coupled receptor signaling pathway for cardiac fibrosis therapy
24-Sep-2026