SKM 2023 – scientific programme
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BP: Fachverband Biologische Physik
BP 26: Focus Session mRNA Physics
BP 26.6: Talk
Thursday, March 30, 2023, 16:45–17:00, TOE 317
The pH dependent phase transition in lipid nanoparticle cores leads to changes of protein expression in single cells — •Julian Philipp and Joachim Rädler — LMU, Munich, Germany
Lipid nanoparticles developed into the most powerful delivery platform for mRNA-based vaccination and therapies. In general, LNPs are particles exhibiting PEG-lipid and DSPC at the surface and ionizable lipid, cholesterol and mRNA in the core. However, the pH dependent changes induced by ionizable lipids in the context of endosomal release are little understood. In particular the ionizable lipids MC3, KC2 and DLin are known to exhibit remarkably different efficacy despite similar pK values. Here, we study the structural response of ionizable lipids with cholesterol as a function of pH using synchrotron X-ray scattering. All three core phases exhibit a sequence of ordered mesophases in the range of pH 7 to 4, beginning with an isotropic swollen phase above their pK value. Lowering the pH reveals transitions to inverse micellar P63/mmc / Fd3m, inverse hexagonal HII and bicontinous cubic Pn3m phases. If polyA, as mRNA surrogate, is added to the core phases, coexistence of pure lipid phases and condensed nucleic acid lipid HIIc phase occurs. We show that the observed core structures are consistent with the SAXS scattering of mRNA containing core phases and full LNP. The difference in structural features of DLin versus MC3 and KC2 phases is also consistent with the delayed onset and reduced level of GFP expression observed in single cell time courses after transfection with DLin LNPs compared to MC3/KC2. We conclude that pH dependent core phase transitions trigger endosomal release.