Myocardial infarction (MI) and heart failure (HF) are the leading causes of death in the United States and in most other industrialized nations. MI leads to a massive loss of cardiomyocytes (CMs), which are replaced with non-CM cells, leading to scarring and, in most cases, HF. The adult mammalian heart has a low intrinsic regenerative capacity, mainly because of cell-cycle arrest in CMs. No effective treatment promoting heart regeneration is currently available. Recent efforts to use DNA-based or viral gene therapy approaches to induce cardiac regeneration post-MI or in HF conditions have encountered major challenges, mostly because of the poor and uncontrolled delivery of the introduced genes. Modified mRNA (modRNA) is a safe, non-immunogenic, efficient, transient, local, and controlled nucleic acid delivery system that can overcome the obstacles to DNA-based or viral approaches for cardiac gene delivery. We here review the use of modRNA in cardiac therapy, to induce cardioprotection and vascular or cardiac regeneration after MI. We discuss the current challenges in modRNA-based cardiac treatment, which will need to be overcome for the application of such treatment to ischemic heart disease.

Background: Sphingolipids have recently emerged as a biomarker of recurrence and mortality after myocardial infarction (MI). The increased ceramide levels in mammalian heart tissues during acute MI, as demonstrated by several groups, is associated with higher cell death rates in the left ventricle and deteriorated cardiac function. Ceramidase, the only enzyme known to hydrolyze proapoptotic ceramide, generates sphingosine, which is then phosphorylated by sphingosine kinase to produce the prosurvival molecule sphingosine-1-phosphate. We hypothesized that Acid Ceramidase (AC) overexpression would counteract the negative effects of elevated ceramide and promote cell survival, thereby providing cardioprotection after MI. Methods: We performed transcriptomic, sphingolipid, and protein analyses to evaluate sphingolipid metabolism and signaling post-MI. We investigated the effect of altering ceramide metabolism through a loss (chemical inhibitors) or gain (modified mRNA [modRNA]) of AC function post hypoxia or MI. Results: We found that several genes involved in de novo ceramide synthesis were upregulated and that ceramide (C16, C20, C20:1, and C24) levels had significantly increased 24 hours after MI. AC inhibition after hypoxia or MI resulted in reduced AC activity and increased cell death. By contrast, enhancing AC activity via AC modRNA treatment increased cell survival after hypoxia or MI. AC modRNA-treated mice had significantly better heart function, longer survival, and smaller scar size than control mice 28 days post-MI. We attributed the improvement in heart function post-MI after AC modRNA delivery to decreased ceramide levels, lower cell death rates, and changes in the composition of the immune cell population in the left ventricle manifested by lowered abundance of proinflammatory detrimental neutrophils. Conclusions: Our findings suggest that transiently altering sphingolipid metabolism through AC overexpression is sufficient and necessary to induce cardioprotection post-MI, thereby highlighting the therapeutic potential of AC modRNA in ischemic heart disease.

Synthetic modified RNA (modRNA) is a novel vector for gene transfer to the heart and other organs. modRNA can mediate strong, transient protein expression with minimal induction of the innate immune response and risk for genome integration. modRNA is already being used in several human clinical trials, and its use in basic and translational science is growing. Due to the complexity of preparing modRNA and the high cost of its reagents, there is a need for an improved, cost-efficient protocol to make modRNA. Here we show that changing the ratio between anti-reverse cap analog (ARCA) and N1-methyl-pseudouridine (N1mΨ), favoring ARCA over N1mΨ, significantly increases the yield per reaction, improves modRNA translation, and reduces its immunogenicity in vitro . This protocol will make modRNA preparation more accessible and financially affordable for basic and translational research.

Bone marrow (BM) has long been considered a potential stem cell source for cardiac repair due to its abundance and accessibility. Although previous investigations have generated cardiomyocytes from BM, yields have been low, and far less than produced from ES or induced pluripotent stem cells (iPSCs). Since differentiation of pluripotent cells is difficult to control, we investigated whether BM cardiac competency could be enhanced without making cells pluripotent. From screens of various molecules that have been shown to assist iPSC production or maintain the ES cell phenotype, we identified the G9a histone methyltransferase inhibitor BIX01294 as a potential reprogramming agent for converting BM cells to a cardiac-competent phenotype. BM cells exposed to BIX01294 displayed significantly elevated expression of brachyury, Mesp1, and islet1, which are genes associated with embryonic cardiac progenitors. In contrast, BIX01294 treatment minimally affected ectodermal, endodermal, and pluripotency gene expression by BM cells. Expression of cardiac-associated genes Nkx2.5, GATA4, Hand1, Hand2, Tbx5, myocardin, and titin was enhanced 114,76, 276,46, 635, 123, and 5-fold in response to the cardiogenic stimulator Wnt11 when BM cells were pretreated with BIX01294. Immunofluorescent analysis demonstrated that BIX01294 exposure allowed for the subsequent display of various muscle proteins within the cells. The effect of BIX01294 on the BM cell phenotype and differentiation potential corresponded to an overall decrease in methylation of histone H3 at lysine9, which is the primary target of G9a histone methyltransferase. In summary, these data suggest that BIX01294 inhibition of chromatin methylation reprograms BM cells to a cardiac-competent progenitor phenotype.

The controllable assembly of nanoparticles into nonclosepacked (NCP) arrays exhibits unusual optical properties [e.g., surface lattice resonances (SLRs)] but are challenging to construct, especially for NCP binary arrays composed of diversified nanoparticles. Here, we show the construction of two-dimensional (2D) NCP binary Au nanoparticle arrays by modulating the convective self-assembly of colloidal nanoparticles on a templating NCP nanoparticle array. By dramatically inhibiting the coffee ring effect during convective evaporation, this convective assembly approach allows colloidal nanoparticles to stack around the templating nanoparticles, forming a "core-satellite" basic architecture. Moreover, this approach is generalized for various types, shapes, and periodicities of building nanoparticles. The assembled 2D NCP binary Au arrays attain multiple tunable optical properties, including photonic band gaps, plasmonic SLRs, and dynamic surface-enhanced Raman scattering activity, based on tunable plasmonic coupling. The anticounterfeiting application of these NCP binary arrays is demonstrated by taking advantage of their unique optical properties. This convective assembly approach can pave the way for the development of a new category of NCP binary arrays and help to explore their collective unconventional properties.