Human PSC-Derived SAN-Plexus Assembloids: Advancing Neuro-Cardiac Pacemaker Research

Study Background and Research Question

The sinoatrial node (SAN) is the heart’s primary pacemaker, generating rhythmic electrical impulses that orchestrate the heartbeat and regulate atrial contraction. Autonomic neural inputs—particularly from the right atrial ganglionated plexus (RAGP)—profoundly modulate SAN activity, influencing both heart rate and the anatomical locus of pacemaker dominance. However, there has been a persistent gap in human-specific in vitro models that accurately recapitulate the complex neuro-cardiac interactions underpinning pacemaker maturation and disease. Animal models, while informative, suffer from interspecies differences in electrophysiology and autonomic regulation, complicating translation to human biology. Traditional human pluripotent stem cell (hPSC) models and cardiac organoids have been unable to capture the necessary three-dimensional (3D) organization, cellular heterogeneity, and especially the neural innervation required to faithfully model SAN function and its modulation by intrinsic cardiac nerves.

Key Innovation from the Reference Study

The reference study, "Human PSC-derived sinoatrial node-cardiac plexus assembloids model innervation-associated maturation of pacemaker systems", fundamentally advances this field by generating SAN-plexus assembloids: integrated 3D constructs composed of hPSC-derived SAN organoids (SANOs) and cardiac ganglionated plexus organoids (CGPOs), often with atrial-like cardiac organoids. This tri-assembloid model successfully recapitulates the molecular, structural, and electrophysiological hallmarks of human pacemaker activity, while enabling functional interrogation of neuron-to-pacemaker signaling in a controlled, human-specific system. Importantly, the study integrates spatial transcriptomics of native human SAN tissue to validate the assembloid system and uncover new neuron-pacemaker signaling programs.

Methods and Experimental Design Insights

The authors employed a modular approach to assemble SANOs, CGPOs, and atrial-like cardiac organoids into a single 3D platform, recapitulating the spatial and cellular organization of the human SAN-cardiac plexus region. Differentiation protocols yielded SAN-like pacemaker cells (SANLPCs) expressing key transcriptional regulators (SHOX2, ISL1, TBX3) and ion channels (HCN4), as well as transitional populations with partial atrial features (NKX2-5+). CGPOs were derived to provide functional autonomic neurons capable of modulating SAN automaticity.

Electrophysiological analyses were central to assessing pacemaker function, including spontaneous diastolic depolarization and action potential dynamics. Spatial transcriptomics linked molecular profiles of assembloid-derived SANPCs to those of authentic human SAN tissue, providing high-resolution validation of cellular identity and maturation status. Functional experiments included pharmacological and genetic perturbations to dissect neuron-pacemaker crosstalk and to model disease-associated conduction dysfunctions.

Protocol Parameters

• SAN organoid formation: Differentiate hPSCs using stage-specific signaling cues to promote TBX18+, ISL1+, and SHOX2+ pacemaker cell fate.
• Cardiac plexus organoid integration: Co-culture CGPOs with SANOs and atrial-like organoids to establish functional neural-cardiac connectivity.
• Electrophysiological assessment: Use patch-clamp or multi-electrode array to quantify spontaneous firing, conduction velocity, and action potential characteristics.
• Spatial transcriptomics: Profile gene expression within assembloids and compare to native human SAN tissue to confirm maturation and heterogeneity.
• Neuro-pharmacological modulation: Apply beta-adrenergic agonists (e.g., isoproterenol hemisulfate) to dissect receptor-mediated modulation of pacemaker activity, following established dose-response protocols.

Core Findings and Why They Matter

This study demonstrates that SAN-plexus assembloids exhibit spontaneous pacemaker activity, robust conduction to atrial-like compartments, and functional responses to neural modulation, mirroring key features of the human heart’s conduction system. Integration of spatial transcriptomics revealed a previously uncharacterized neuron-to-pacemaker signaling axis: prosaposin (PSAP) secreted from CGPO neurons activates the GPR37 receptor, enriched in SAN cells, thereby promoting pacemaker maturation. This neuron-pacemaker crosstalk was shown to be essential for the functional maturation of SAN cells and their ability to pace co-cultured atrial tissues.

The assembloid platform further enabled modeling of conduction dysfunctions relevant to congenital SAN disease, supporting its use in mechanistic studies and potentially in preclinical drug testing for arrhythmias or conduction disorders. The ability to interrogate human-specific neuro-cardiac pathways fills a major translational gap left by animal models and 2D cultures.

Comparison with Existing Internal Articles

The findings of this study are well-aligned with, and extend upon, prior reports such as "Modeling Human Pacemaker Maturation with SAN-Plexus Assembloids" and "Modeling Human SAN-Neural Interactions with PSC-Derived Assembloids". Those articles likewise highlight the establishment of human-specific assembloids for studying intrinsic neuro-cardiac regulation, but the reference study further clarifies molecular signaling events—such as PSAP-GPR37 coupling—underlying pacemaker maturation. Additionally, the use of spatial transcriptomics for validation represents a methodological advance over previous work, ensuring more robust mapping between assembloid-derived and native SAN cell identities. Internal articles also emphasize the utility of beta-adrenergic receptor signaling analysis in this context, which is further substantiated by the reference study’s functional experiments using beta-adrenergic agonists.

Limitations and Transferability

Despite its strengths, the assembloid model retains certain limitations. Some fine-grained aspects of SAN microanatomy, long-range innervation, and multi-organ integration cannot be fully recapitulated in vitro. While the platform enables high-resolution studies of neuron-pacemaker interactions, the absence of systemic cues present in vivo may limit its application for modeling complex arrhythmogenic diseases or drug responses that involve extracardiac factors. Furthermore, the differentiation protocols, while robust, may still yield batch-to-batch variability in cellular composition or maturation state.

Nevertheless, the platform’s transferability to other settings—such as high-throughput screening of compounds that modulate beta-adrenergic or GPCR signaling—is promising, provided that results are interpreted in the context of these limitations.

Research Support Resources

For investigators seeking to model beta-adrenergic receptor signaling and neuro-cardiac dynamics in assembloid systems, Isoproterenol sulfate dihydrate (SKU C6402) is a non-selective beta-adrenergic agonist with high purity and reliable solubility, commonly used to probe cAMP/PKA pathway activation and autonomic modulation of pacemaker activity. As demonstrated in this and related studies, careful selection of beta-adrenergic agonists such as isoproterenol hemisulfate supports rigorous dissection of GPCR signaling and cardiac electrophysiology. For optimal results, refer to the product information regarding solubility, storage, and handling recommendations.