Dual mRNA therapy restores metabolic function in long-term studies in mice with propionic acidemia

Propionic acidemia/aciduria (PA) is an ultra-rare, life-threatening, inherited metabolic disorder caused by deficiency of the mitochondrial enzyme, propionyl-CoA carboxylase (PCC) composed of six alpha (PCCA) and six beta (PCCB) subunits. We herein report an enzyme replacement approach to treat PA using a combination of two messenger RNAs (mRNAs) (dual mRNAs) encoding both human PCCA (hPCCA) and PCCB (hPCCB) encapsulated in biodegradable lipid nanoparticles (LNPs) to produce functional PCC enzyme in liver. In patient fibroblasts, dual mRNAs encoded proteins localize in mitochondria and produce higher PCC enzyme activity vs. single (PCCA or PCCB) mRNA alone. In a hypomorphic murine model of PA, dual mRNAs normalize ammonia similarly to carglumic acid, a drug approved in Europe for the treatment of hyperammonemia due to PA. Dual mRNAs additionally restore functional PCC enzyme in liver and thus reduce primary disease-associated toxins in a dose-dependent manner in long-term 3- and 6-month repeat-dose studies in PA mice. Dual mRNAs are well-tolerated in these studies with no adverse findings. These studies demonstrate the potential of mRNA technology to chronically administer multiple mRNAs to produce large complex enzymes, with applicability to other genetic disorders.

Propionic acidemia is a serious pediatric inherited disorder with no effective treatments. Here the authors demonstrate that delivering dual mRNAs as an enzyme replacement approach can be used as an effective therapy in a mouse model of propionic acidemia, with potential applicability to chronically administer multiple mRNAs in other genetic disorders.

SARS-CoV-2 mRNA Vaccine Development Enabled by Prototype Pathogen Preparedness

A SARS-CoV-2 vaccine is needed to control the global COVID-19 public health crisis. Atomic-level structures directed the application of prefusion-stabilizing mutations that improved expression and immunogenicity of betacoronavirus spike proteins. Using this established immunogen design, the release of SARS-CoV-2 sequences triggered immediate rapid manufacturing of an mRNA vaccine expressing the prefusion-stabilized SARS-CoV-2 spike trimer (mRNA-1273). Here, we show that mRNA-1273 induces both potent neutralizing antibody and CD8 T cell responses and protects against SARS-CoV-2 infection in lungs and noses of mice without evidence of immunopathology. mRNA-1273 is currently in a Phase 2 clinical trial with a trajectory towards Phase 3 efficacy evaluation.

Human 5' UTR design and variant effect prediction from a massively parallel translation assay

The ability to predict the impact of cis-regulatory sequences on gene expression would facilitate discovery in fundamental and applied biology. Here we combine polysome profiling of a library of 280,000 randomized 5' untranslated regions (UTRs) with deep learning to build a predictive model that relates human 5' UTR sequence to translation. Together with a genetic algorithm, we use the model to engineer new 5' UTRs that accurately direct specified levels of ribosome loading, providing the ability to tune sequences for optimal protein expression. We show that the same approach can be extended to chemically modified RNA, an important feature for applications in mRNA therapeutics and synthetic biology. We test 35,212 truncated human 5' UTRs and 3,577 naturally occurring variants and show that the model predicts ribosome loading of these sequences. Finally, we provide evidence of 45 single-nucleotide variants (SNVs) associated with human diseases that substantially change ribosome loading and thus may represent a molecular basis for disease.

The DHH1/RCKp54 family of helicases: an ancient family of proteins that promote translational silencing

Translational control is a vital aspect of gene expression. Message specific translational repressors have been known for decades. Recent evidence, however, suggests that a general machinery exists that dampens the translational capacity of the majority of mRNAs. This activity has been best ascribed to a conserved family of RNA helicases called the DHH1/RCKp54 family. The function of these helicases is to promote translational silencing. By transitioning mRNA into quiescence, DHH1/RCKp54 helicases promote either mRNA destruction or storage. In this review we describe the known roles of these helicases and propose a mechanistic model to explain their mode of action. This article is part of a Special Issue entitled: The Biology of RNA helicases - Modulation for life.

The dimerization domain of HIV-1 viral infectivity factor Vif is required to block virion incorporation of APOBEC3G

BACKGROUND

The HIV-1 accessory protein known as viral infectivity factor or Vif binds to the host defence factor human APOBEC3G (hA3G) and prevents its assembly with viral particles and mediates its elimination through ubiquitination and degradation by the proteosomal pathway. In the absence of Vif, hA3G becomes incorporated within viral particles. During the post entry phase of infection, hA3G attenuates viral replication by binding to the viral RNA genome and deaminating deoxycytidines to form deoxyuridines within single stranded DNA regions of the replicated viral genome. Vif dimerization has been reported to be essential for viral infectivity but the mechanistic requirement for Vif multimerization is unknown.

RESULTS

We demonstrate that a peptide antagonist of Vif dimerization fused to the cell transduction domain of HIV TAT suppresses live HIV-1 infectivity. We show rapid cellular uptake of the peptide and cytoplasmic distribution. Robust suppression of viral infectivity was dependent on the expression of Vif and hA3G. Disruption of Vif multimerization resulted in the production of virions with markedly increased hA3G content and reduced infectivity.

CONCLUSION

The role of Vif multimerization in viral infectivity of nonpermissive cells has been validated with an antagonist of Vif dimerization. An important part of the mechanism for this antiretroviral effect is that blocking Vif dimerization enables hA3G incorporation within virions. We propose that Vif multimers are required to interact with hA3G to exclude it from viral particles during their assembly. Blocking Vif dimerization is an effective means of sustaining hA3G antiretroviral activity in HIV-1 infected cells. Vif dimerization is therefore a validated target for therapeutic HIV-1/AIDS drug development.