Truncating variants in the ALPK3 gene (encoding alpha protein kinase 3) cause severe cardiomyopathy for which no curative treatment exists1-3. Here we establish an adeno-associated virus (AAV)-mediated gene replacement therapy to deliver full-length human ALPK3. AAV-ALPK3 prevented disease in neonatal Alpk3-mutant mice and reversed established pathology in adults, with proteomic analysis demonstrating reversal of more than 95% of the molecular disease signature. Beyond ALPK3 deficiency, we explored broader therapeutic potential based on ALPK3's regulatory role in proteostasis, a pathway commonly disrupted across cardiomyopathies. ALPK3 expression is reduced in cardiomyocytes with TTN-truncating variants, the most prevalent cause of dilated cardiomyopathy, and the encoded titin protein has a protein quality control network in common with ALPK3. AAV-ALPK3 restored contractile function in human cardiac organoids with an ALPK3- or TTN-truncating variant. These findings provide proof of concept for ALPK3 gene therapy in patients with ALPK3 cardiomyopathy and reveal potential for indication expansion to cardiomyopathies associated with TTN-truncating variants, which are not amenable to gene replacement therapy due to size limitations.

Advancing cardiac tissue engineering requires innovative fabrication techniques, including 3D bioprinting and tissue maturation, to enable the generation of new muscle for repairing or replacing damaged heart tissue. Recent advances in tissue engineering have highlighted the need for rapid, high-resolution bioprinting methods that preserve cell viability and maintain structural fidelity. Traditional collagen-based bioinks gel slowly, limiting their use in bioprinting. Here, we implement TRACE (tunable rapid assembly of collagenous elements), a macromolecular crowding-driven bioprinting technique that enables the immediate gelation of collagen bioinks infused with cells. This overcomes the need for extended incubation, allowing for direct bioprinting of engineered cardiac tissues with high fidelity. Unlike methods that rely on high-concentration acidic collagen or fibrin for gelation, TRACE achieves rapid bioink stabilization without altering the biochemical composition. This ensures greater versatility in bioink selection while maintaining functional tissue outcomes. Additionally, agarose slurry provides stable structural support, preventing tissue collapse while allowing nutrient diffusion. This approach better preserves complex tissue geometries during culture than gelatin-based support baths or polydimethylsiloxane (PDMS) molds. Our results demonstrate that TRACE enables the bioprinting of structurally stable cardiac tissues with high resolution. By supporting the fabrication of biomimetic tissues, TRACE represents a promising advancement in bioprinting cardiac models and other engineered tissues.

Cardiomyocytes (CMs) lost during ischemic cardiac injury cannot be replaced due to their limited proliferative capacity. Calcium is an important signal transducer that regulates key cellular processes, but its role in regulating CM proliferation is incompletely understood. Here we show a robust pathway for new calcium signaling-based cardiac regenerative strategies. A drug screen targeting proteins involved in CM calcium cycling in human embryonic stem cell-derived cardiac organoids (hCOs) revealed that only the inhibition of L-Type Calcium Channel (LTCC) induced the CM cell cycle. Furthermore, overexpression of Ras-related associated with Diabetes (RRAD), an endogenous inhibitor of LTCC, induced CM cell cycle activity in vitro, in human cardiac slices, and in vivo. Mechanistically, LTCC inhibition by RRAD or nifedipine induced CM cell cycle by modulating calcineurin activity. Moreover, ectopic expression of RRAD/CDK4/CCND in combination induced CM proliferation in vitro and in vivo, improved cardiac function and reduced scar size post-myocardial infarction.