How Stem Cells Reveal the Heart's Hidden Regulators
The discovery of circular RNAs in heart cells represents one of the most exciting frontiers in cardiovascular research, offering new hope for millions affected by heart disease.
Imagine a secret language within your cells—molecules long dismissed as genetic "junk" now emerging as crucial regulators of heart health. This isn't science fiction but the reality of circular RNAs, a recently discovered class of RNA molecules that form continuous loops rather than linear strands.
These unique molecules are surprisingly abundant in heart cells and may hold the key to understanding, diagnosing, and potentially treating devastating heart conditions. Through the revolutionary technology of human induced pluripotent stem cells, scientists are now decoding these circular RNA signatures and their profound implications for cardiovascular medicine.
Circular RNAs (circRNAs) are a unique class of single-stranded RNA molecules that form covalently closed loops. Unlike traditional linear RNAs, they lack the free ends that make typical RNA vulnerable to degradation. This circular structure makes them highly stable and resistant to the enzymes that normally break down RNA, allowing them to persist in cells for much longer than their linear counterparts 5 .
The continuous loop structure of circRNAs provides exceptional stability compared to linear RNAs, making them ideal candidates for diagnostic applications.
For decades, circRNAs were overlooked as rare byproducts of splicing errors in the complex process of gene expression. However, with advances in sequencing technologies, scientists have discovered that circRNAs are not only abundant but also perform crucial regulatory functions within cells 3 . They can act as "sponges" that soak up microRNAs, regulate protein activity, and even influence gene expression—roles particularly important in specialized cells like cardiomyocytes (heart muscle cells) 5 .
The stability and tissue-specific expression of circRNAs make them ideal candidates for diagnostic biomarkers and therapeutic targets in cardiovascular diseases, which remain a leading cause of death worldwide 1 5 .
Human induced pluripotent stem cells (hiPSCs) represent one of the most significant breakthroughs in modern biomedical research. These remarkable cells are created by reprogramming adult cells (typically skin or blood cells) back to an embryonic-like state, from which they can be directed to become any cell type in the body—including beating heart cells known as cardiomyocytes 1 .
This technology provides researchers with an unprecedented opportunity to study human heart development and disease in a lab dish. Unlike animal models, hiPSC-derived cardiomyocytes (hiPSC-CMs) are human in origin and can be generated from patients with specific heart conditions, making them invaluable for:
The combination of hiPSC technology with circular RNA research has opened exciting new avenues for understanding the molecular underpinnings of heart formation and function.
Adult cells are reprogrammed to pluripotent state
Directed to become cardiomyocytes
Cells mature into functional heart cells
In a pivotal 2018 study published in Stem Cell Research & Therapy, scientists set out to comprehensively profile circular RNA expression during the transformation of stem cells into beating heart cells 1 .
Researchers first created hiPSCs from human fibroblasts using lentiviral vectors 1 .
hiPSCs were differentiated into cardiomyocytes using WNT signaling modulation 1 .
The research revealed several groundbreaking insights:
Perhaps most notably, circSLC8A1 was abnormally increased in heart tissues from patients suffering from dilated cardiomyopathy, suggesting a potential role in heart disease pathology 1 .
| Circular RNA | Parent Gene | Expression in Cardiomyocytes | Potential Clinical Significance |
|---|---|---|---|
| circSLC8A1 | SLC8A1 (Sodium/Calcium Exchanger) | Highly enriched | Increased in dilated cardiomyopathy |
| circCACNA1D | CACNA1D (Calcium Channel) | Highly enriched | Heart-specific enrichment |
| circSPHKAP | SPHKAP (Sphingosine Kinase) | Highly enriched | Heart-specific enrichment |
| circALPK2 | ALPK2 (Alpha Kinase) | Highly enriched | Heart-specific enrichment |
Studying circular RNAs requires specialized experimental approaches and reagents. The table below outlines key tools and methods used in circRNA research, particularly in the context of stem cell-derived cardiomyocytes.
| Tool/Method | Function | Application in CircRNA Research |
|---|---|---|
| hiPSC Differentiation System | Generates human cardiomyocytes in vitro | Provides human-relevant model for studying circRNA dynamics during cardiac development 1 |
| RNA Sequencing with CIRCexplorer | Identifies and quantifies circRNAs | Detects back-splicing events characteristic of circRNAs from sequencing data 1 |
| RNase R Treatment | Digests linear RNAs but not circRNAs | Enriches for circRNAs to confirm their circular nature and facilitate detection 6 |
| Divergent Primers | PCR primers designed to amplify the backsplice junction | Validates specific circRNAs by targeting the unique junction formed during circularization 6 |
| siRNA/shRNA | Knocks down specific circRNAs | Investigates circRNA function by selectively reducing their expression 6 |
| AAV Vectors | Delivers circRNAs for overexpression | Studies gain-of-function effects of specific circRNAs in cardiomyocytes 6 |
The implications of circRNA research extend far beyond basic science to potential clinical applications. Several circRNAs have emerged as promising therapeutic targets or agents for heart disease.
A 2024 study published in Basic Research in Cardiology identified circZFPM2 as a highly conserved circRNA significantly increased in patients with hypertrophic cardiomyopathy (HCM) 6 .
Researchers found that knocking down circZFPM2 in cardiomyocytes induced hypertrophy and compromised mitochondrial function. Conversely, delivering recombinant circZFPM2 via lipid nanoparticles or AAV vectors rescued hypertrophic gene expression and promoted cell survival 6 .
As identified in the featured experiment, circSLC8A1 shows significantly increased expression in heart tissues from patients with dilated cardiomyopathy (DCM) 1 .
This circRNA, derived from the SLC8A1 gene which encodes a sodium/calcium exchanger, represents both a potential diagnostic biomarker and a therapeutic target for DCM 1 7 .
Another recent study revealed that circDhx32 promotes inflammatory responses in mouse cardiac ischemia-reperfusion injury by binding to FOXO1 and competing with AdipoR1 4 .
Cardiomyocyte-specific knockdown of circDhx32 improved cardiac function, reduced infarct size, and diminished release of cardiac injury biomarkers, suggesting another promising therapeutic avenue 4 .
| Circular RNA | Cardiovascular Condition | Mechanism of Action | Therapeutic Potential |
|---|---|---|---|
| circZFPM2 | Hypertrophic Cardiomyopathy | Regulates mitochondrial function and cell survival | Overexpression protects against hypertrophy 6 |
| circSLC8A1 | Dilated Cardiomyopathy | Unknown; associated with disease state | Potential diagnostic biomarker 1 7 |
| circDhx32 | Ischemia-Reperfusion Injury | Binds FOXO1, competing with AdipoR1 | Knockdown reduces inflammatory response 4 |
| circFBLN1 | Dilated Cardiomyopathy | Unknown; upregulated in DCM | Potential diagnostic biomarker 7 |
As research progresses, several innovative approaches are being explored to target circRNAs for therapeutic purposes. These include:
Using siRNAs or shRNAs to knock down pathogenic circRNAs 5 .
Specifically designed to target and degrade circRNAs with high specificity 5 .
Improving stability and cellular uptake of circRNA-targeting therapeutics 5 .
Exploiting natural stability of circRNAs to deliver therapeutic molecules 3 .
The unique properties of circRNAs—their stability, specificity, and regulatory functions—position them as promising candidates for the next generation of cardiovascular diagnostics and therapeutics.
The investigation of circular RNAs in human induced pluripotent stem cells and derived cardiomyocytes has revealed a previously hidden layer of genetic regulation essential to heart development and function. What began as basic research into curious circular RNA molecules has evolved into a field with transformative potential for cardiovascular medicine.
As scientists continue to decode the functions of individual circRNAs and develop technologies to target them, we move closer to a future where these once-overlooked molecules may form the basis of precision therapies for heart disease patients. The circular path of these unique RNAs has brought us full circle to a new understanding of the heart's molecular complexity—and new hope for combating its most devastating diseases.
The next time your heart beats, consider the sophisticated circular molecules working behind the scenes to keep it functioning—and the scientists working to unlock their secrets.