Full-length dystrophin restoration via targeted exon integration by AAV-CRISPR in a humanized mouse model of Duchenne muscular dystrophy.

Targeted gene-editing strategies have emerged as promising therapeutic approaches for the permanent treatment of inherited genetic diseases. However, precise gene correction and insertion approaches using homology-directed repair are still limited by low efficiencies. Consequently, many gene-editing strategies have focused on removal or disruption, rather than repair, of genomic DNA. In contrast, homology-independent targeted integration (HITI) has been reported to effectively insert DNA sequences at targeted genomic loci. This approach could be particularly useful for restoring full-length sequences of genes affected by a spectrum of mutations that are also too large to deliver by conventional adeno-associated virus (AAV) vectors. Here, we utilize an AAV-based, HITI-mediated approach for correction of full-length dystrophin expression in a humanized mouse model of Duchenne muscular dystrophy (DMD). We co-deliver CRISPR-Cas9 and a donor DNA sequence to insert the missing human exon 52 into its corresponding position within the DMD gene and achieve full-length dystrophin correction in skeletal and cardiac muscle. Additionally, as a proof-of-concept strategy to correct genetic mutations characterized by diverse patient mutations, we deliver a superexon donor encoding the last 28 exons of the DMD gene as a therapeutic strategy to restore full-length dystrophin in >20% of the DMD patient population. This work highlights the potential of HITI-mediated gene correction for diverse DMD mutations and advances genome editing toward realizing the promise of full-length gene restoration to treat genetic disease.

Branched-chain α-ketoacids are preferentially reaminated and activate protein synthesis in the heart.

Branched-chain amino acids (BCAA) and their cognate α-ketoacids (BCKA) are elevated in an array of cardiometabolic diseases. Here we demonstrate that the major metabolic fate of uniformly-13C-labeled α-ketoisovalerate ([U-13C]KIV) in the heart is reamination to valine. Activation of cardiac branched-chain α-ketoacid dehydrogenase (BCKDH) by treatment with the BCKDH kinase inhibitor, BT2, does not impede the strong flux of [U-13C]KIV to valine. Sequestration of BCAA and BCKA away from mitochondrial oxidation is likely due to low levels of expression of the mitochondrial BCAA transporter SLC25A44 in the heart, as its overexpression significantly lowers accumulation of [13C]-labeled valine from [U-13C]KIV. Finally, exposure of perfused hearts to levels of BCKA found in obese rats increases phosphorylation of the translational repressor 4E-BP1 as well as multiple proteins in the MEK-ERK pathway, leading to a doubling of total protein synthesis. These data suggest that elevated BCKA levels found in obesity may contribute to pathologic cardiac hypertrophy via chronic activation of protein synthesis.

Redirecting Vesicular Transport to Improve Nonviral Delivery of Molecular Cargo.

Cell engineering relies heavily on viral vectors for the delivery of molecular cargo into cells due to their superior efficiency compared to nonviral ones. However, viruses are immunogenic and expensive to manufacture, and have limited delivery capacity. Nonviral delivery approaches avoid these limitations but are currently inefficient for clinical applications. This work demonstrates that the efficiency of nonviral delivery of plasmid DNA, mRNA, Sleeping Beauty transposon, and ribonucleoprotein can be significantly enhanced through pretreatment of cells with the nondegradable sugars (NDS), such as sucrose, trehalose, and raffinose. The enhancement is mediated by the incorporation of the NDS into cell membranes, causing enlargement of lysosomes and formation of large (>500 nm) amphisome-like bodies (ALBs). The changes in subcellular structures redirect transport of cargo to ALBs rather than to lysosomes, reducing cargo degradation in cells. The data indicate that pretreatment of cells with NDS is a promising approach to improve nonviral cargo delivery in biomedical applications.

Targeted transcriptional modulation with type I CRISPR-Cas systems in human cells.

Class 2 CRISPR-Cas systems, such as Cas9 and Cas12, have been widely used to target DNA sequences in eukaryotic genomes. However, class 1 CRISPR-Cas systems, which represent about 90% of all CRISPR systems in nature, remain largely unexplored for genome engineering applications. Here, we show that class 1 CRISPR-Cas systems can be expressed in mammalian cells and used for DNA targeting and transcriptional control. We repurpose type I variants of class 1 CRISPR-Cas systems from Escherichia coli and Listeria monocytogenes, which target DNA via a multi-component RNA-guided complex termed Cascade. We validate Cascade expression, complex formation and nuclear localization in human cells, and demonstrate programmable CRISPR RNA (crRNA)-mediated targeting of specific loci in the human genome. By tethering activation and repression domains to Cascade, we modulate the expression of targeted endogenous genes in human cells. This study demonstrates the use of Cascade as a CRISPR-based technology for targeted eukaryotic gene regulation, highlighting class 1 CRISPR-Cas systems for further exploration.

The next generation of CRISPR-Cas technologies and applications.

The prokaryote-derived CRISPR-Cas genome editing systems have transformed our ability to manipulate, detect, image and annotate specific DNA and RNA sequences in living cells of diverse species. The ease of use and robustness of this technology have revolutionized genome editing for research ranging from fundamental science to translational medicine. Initial successes have inspired efforts to discover new systems for targeting and manipulating nucleic acids, including those from Cas9, Cas12, Cascade and Cas13 orthologues. Genome editing by CRISPR-Cas can utilize non-homologous end joining and homology-directed repair for DNA repair, as well as single-base editing enzymes. In addition to targeting DNA, CRISPR-Cas-based RNA-targeting tools are being developed for research, medicine and diagnostics. Nuclease-inactive and RNA-targeting Cas proteins have been fused to a plethora of effector proteins to regulate gene expression, epigenetic modifications and chromatin interactions. Collectively, the new advances are considerably improving our understanding of biological processes and are propelling CRISPR-Cas-based tools towards clinical use in gene and cell therapies.

A comparison of pre-operative comorbidities and post-operative outcomes among patients undergoing laparoscopic nissen fundoplication at high- and low-volume centers.

INTRODUCTION: Commonly cited data promoting laparoscopic Nissen fundoplication (LNF) as safe and efficacious are typically published by single centers, affiliated with teaching institutions with a high volume of cases, but LNF is not universally performed at these hospitals. The purpose of this study is to assess where these procedures are being done and to compare pre-operative comorbidities and post-operative outcomes between high-and low-volume centers using a state-wide inpatient database. METHODS: This is a retrospective study using data from the North Carolina Hospital Association Patient Data System. Selected patients include adults (>17 years old) that have undergone laparoscopic Nissen fundoplication for gastroesophageal reflux disease as an inpatient from 2005 to 2008. Patients that underwent operative management for emergent purposes or had associated diagnoses of esophageal cancer or achalasia were excluded from the study. High-volume centers were defined as institutions that performed ten or more LNFs per year averaged over a period of 4 years. Comparative statistics were performed on comorbidities and complications between high- and low-volume centers. RESULTS: A total of 1,019 patients underwent LNF for GERD in North Carolina between 2005 and 2008 in the inpatient setting. High-volume centers performed 530 LNFs (52%) while low-volume centers performed 489 LNFs (48%). Patients at high-volume centers were older (median 52.5 years old vs. 49.0 years old, p = 0.019), had a higher incidence of diabetes (13.4% vs. 8.8%, p = 0.026), chronic obstructive pulmonary disease (5.1% vs. 2.0 %, p = 0.015), hyperlipidemia (9.6% vs. 4.7%, p = 0.004), and cystic fibrosis (2.8% vs. 0.8%, p = 0.03). Patients with a history of transplantation were also more likely to undergo LNF at a high-volume center (15.8% vs. 1.6%, p < 0.0001). There were no deaths among the two groups and also no difference between median length of stay (2.7 days for high-volume center vs. 2.6 days for low-volume center). Low-volume centers had a higher incidence of intraoperative accidental puncture or laceration (3.3% vs. 0.9%, p = 0.017) while high-volume centers had a higher incidence of atelectasis (5.3% vs. 2.5%, p = 0.031). CONCLUSION: A significant proportion of the LNFs in North Carolina are performed at low-volume centers. High-volume centers perform LNF on older patients with more comorbidities. Low-volume centers have three times more accidental perforations, yet there is no detectable difference in mortality or median length of stay. It is impossible to tell if these perforations are managed at these low-volume centers or transferred to facilities with a higher level of care. These findings argue for regionalization of LNF and for a reevaluation of the global safety of this operation.