Yu-Chung Pien

RNA therapeutics offer promising potential for treating heart disease; however, their clinical application has been limited by insufficient cardiac delivery. Here, we developed a screening platform using human induced pluripotent stem cell–derived cardiomyocytes (hiPSC-CMs) to identify human cardiotropic lipid nanoparticles (LNPs). By screening a chemically diverse LNP library, we identified a lead LNP, 18:1 TAP10, with potent human cardiac transfection capability. Using the Ai14 LoxP-Stop-LoxP-tdTomato reporter mouse model, we assessed 18:1 TAP10 LNP delivery of Cre mRNA in vivo via four administration routes (intravenous, intrathoracic, intracoronary, and intramyocardial (IM)) and found that each administration path enabled both the spatial distribution and cellular tropism in the heart to varying degrees. While all routes achieved robust transfection across non-CM populations (up to 40% in endothelial cells), IM injection notably enabled substantial CM transfection (36% at injection site, 13% distally). To demonstrate therapeutic potential, 18:1 TAP10 LNPs were used to deliver adenine base editor (ABE) components to Duchenne muscular dystrophy (DMD) patient-derived hiPSC-CMs, resulting in 80% on-target gene correction and restoration of dystrophin expression. In a humanized DMD mouse model, we observed dystrophin-positive cardiomyocytes in the injected left ventricle following IM administration of LNP-ABE. This work establishes a human cell-based platform for discovering organ-tropic delivery vehicles and highlights LNPs as a potential modality for therapeutic mRNA delivery and gene editing in the heart.

Proper regulation of glycogen metabolism is fundamental to cellular energy homeostasis, and its disruption is associated with various metabolic disorders, including glycogen storage diseases (GSDs) and potentially diabetes. Despite glycogen’s role as an essential energy reservoir, the mechanisms governing its synthesis and structural diversity across tissues remain unclear. Here, we uncover the distinct physiological roles of the human glycogenins GYG1 and GYG2 in glycogen synthesis. Through cellular models, structural biology, and biochemical analyses, we demonstrate that, unlike GYG1, GYG2 exhibits minimal autoglycosylation activity and acts as a suppressor of glycogen formation. Together, these two glycogenins coordinate glycogen synthase activity and influence glycogen assembly in a cell-type-dependent manner. Importantly, these glycogenins modulate glucose metabolic pathways, thereby ensuring cellular glucose homeostasis. These findings address longstanding questions in glycogen metabolism and establish both GYG1 and GYG2 as critical regulators of glycogen synthesis and breakdown in human, providing insights with potential therapeutic implications for treating GSDs and metabolic diseases.

The fusion of mononucleated myoblasts produces multinucleated muscle fibers leading to the formation of skeletal muscle. Myomaker, a skeletal muscle-specific membrane protein, is essential for myoblast fusion. Here we report the cryo-EM structures of mouse Myomaker (mMymk) and Ciona robusta Myomaker (cMymk). Myomaker contains seven transmembrane helices (TMs) that adopt a G-protein-coupled receptor-like fold. TMs 2–4 form a dimeric interface, while TMs 3 and 5–7 create a lipid-binding site that holds the polar head of a phospholipid and allows the alkyl tails to insert into Myomaker. The similarity of cMymk and mMymk suggests a conserved Myomaker-mediated cell fusion mechanism across evolutionarily distant species. Functional analyses demonstrate the essentiality of the dimeric interface and the lipid-binding site for fusogenic activity, and heterologous cell–cell fusion assays show the importance of transcellular interactions of Myomaker protomers for myoblast fusion. Together, our findings provide structural and functional insights into the process of myoblast fusion.