Spatio-temporal targeting of cardiac cells with lipid nanoparticles after myocardial infarction.

Ischemic heart disease remains the leading cause of morbidity and mortality worldwide. While current therapies prolong survival, they do not address underlying tissue damage. Messenger RNA (mRNA)-based therapies offer a promising alternative for repair and regeneration. However, targeted and effective delivery to the injured heart remains challenging. Lipid nanoparticles (LNPs) have emerged as a compelling platform for delivering therapeutics, including mRNA, yet their cellular tropism following ischemic injury is not well understood. To investigate this, we used Ai9 lineage tracing mice to map LNP uptake across cardiac cell populations during inflammatory, proliferative, and scarring phases post-ischemia-reperfusion injury (IRI). Upon Cre delivery, tdTomato expression is induced. mRNA-LNPs encoding Cre recombinase were injected intravenously 1 hour post-reperfusion, and uptake assessed at 3, 14, and 28 days by high-dimensional flow cytometry and 3D microscopy. Three days post-IRI, myeloid cells predominantly expressed tdTomato, showing they are primary recipients of mRNA-LNPs. By days 14 and 28, the proportion of tdTomato-expressing cells was equivalent between myeloid cells and fibroblasts. Microscopy further revealed mRNA-LNP uptake by cardiomyocytes, particularly within the infarct zone and apex of the heart. We also examined dosing time, with mRNA-LNPs administered 1 h or 3 days post-IRI. Delayed administration shifted uptake from immune cells towards fibroblasts, pericytes, and endothelial cells. This is the first study presenting a high-resolution, temporal map of cell type-specific mRNA-LNP uptake in the injured heart, providing new mechanistic insight beyond prior biodistribution reports and inform the design of cell-specific therapeutic strategies to enhance cardiac repair and regeneration.