MicroRNA 139-5p coordinates APLNR-CXCR4 crosstalk during vascular maturation

G protein-coupled receptor (GPCR) signalling, including that involving apelin (APLN) and its receptor APLNR, is known to be important in vascular development. How this ligand–receptor pair regulates the downstream signalling cascades in this context remains poorly understood. Here, we show that mice with Apln, Aplnr or endothelial-specific Aplnr deletion develop profound retinal vascular defects, which are at least in part due to dysregulated increase in endothelial CXCR4 expression. Endothelial CXCR4 is negatively regulated by miR-139-5p, whose transcription is in turn induced by laminar flow and APLN/APLNR signalling. Inhibition of miR-139-5p in vivo partially phenocopies the retinal vascular defects of APLN/APLNR deficiency. Pharmacological inhibition of CXCR4 signalling or augmentation of the miR-139-5p-CXCR4 axis can ameliorate the vascular phenotype of APLN/APLNR deficient state. Overall, we identify an important microRNA-mediated GPCR crosstalk, which plays a key role in vascular development.

G protein-coupled receptors APLNR and CXCR4 are crucial for vascular development. Here, the authors show that these two signaling pathways communicate and that in response to blood flow APLNR signaling induces a decrease in CXCR4 expression via miR-139-5p, thereby restricting CXCR4 expression to the non-flow exposed tip cells in the retinal vasculature.

Poly(Limonene Thioether) Scaffold for Tissue Engineering

A photocurable thiol-ene network polymer, poly(limonene thioether) (PLT32o), is synthesized, characterized, fabricated into tissue engineering scaffolds, and demonstrated in vitro and in vivo. Micromolded PLT32o grids exhibit compliant, elastomeric mechanical behavior similar to grids made of poly(glycerol sebacate) (PGS), an established biomaterial. Multilayered PL32o scaffolds with regular, geometrically defined pore architectures support heart cell seeding and culture in a manner similar to multilayered PGS scaffolds. Subcutaneous implantation of multilayered PLT32o scaffolds with cultured heart cells provides long-term 3D structural support and retains the exogenous cells, whereas PGS scaffolds lose both their structural integrity and the exogenous cells over 31 d in vivo. PLT32o membrane implants retain their dry mass, whereas PGS implants lose 70 percent of their dry mass by day 31. Macrophages are initially recruited to PLT32o and PGS membrane implants but are no longer present by day 31. Facile synthesis and processing in combination with the capability to support heart cells in vitro and in vivo suggest that PLT32o can offer advantages for tissue engineering applications where prolonged in vivo maintenance of 3D structural integrity and elastomeric mechanical behavior are required.

RNAi-nanoparticulate manipulation of gene expression as a new functional genomics tool in the liver

BACKGROUND & AIMS

The Hippo pathway controls organ size through a negative regulation of the transcription co-activator Yap1. The overexpression of hyperactive mutant Yap1 or deletion of key components in the Hippo pathway leads to increased organ size in different species. Analysis of interactions of this pathway with other cellular signals corroborating organ size control is limited in part due to the difficulties associated with development of rodent models.

METHODS

Here, we develop a new model of reversible induction of the liver size in mice using siRNA-nanoparticles targeting two kinases of the Hippo pathway, namely, mammalian Ste20 family kinases 1 and 2 (Mst1 and Mst2), and an upstream regulator, neurofibromatosis type II (Nf2).

RESULTS

The triple siRNAs nanoparticle-induced hepatomegaly in mice phenocopies one observed with Mst1(-/-)Mst2(-/-) liver-specific depletion, as shown by extensive proliferation of hepatocytes and activation of Yap1. The simultaneous co-treatment with a fourth siRNA nanoparticle against Yap1 fully blocked the liver growth. Hippo pathway-induced liver enlargement is associated with p53 activation, evidenced by its accumulation in the nuclei and upregulation of its target genes. Moreover, injections of the triple siRNAs nanoparticle in p53(LSL/LSL) mice shows that livers lacking p53 expression grow faster and exceed the size of livers in p53 wild-type animals, indicating a role of p53 in controlling Yap1-induced liver growth.

CONCLUSION

Our data show that siRNA-nanoparticulate manipulation of gene expression can provide the reversible control of organ size in adult animals, which presents a new avenue for the investigation of complex regulatory networks in liver.

Frontline Science: Splenic progenitors aid in maintaining high neutrophil numbers at sites of sterile chronic inflammation

Neutrophils are constantly generated from hematopoietic stem and progenitor cells in the bone marrow to maintain high numbers in circulation. A considerable number of neutrophils and their progenitors have been shown to be present in the spleen too; however, their exact role in this organ remains unclear. Herein, we sought to study the function of splenic neutrophils and their progenitors using a mouse model for sterile, peritoneal inflammation. In this microcapsule device implantation model, we show chronic neutrophil presence at implant sites, with recruitment from circulation as the primary mechanism for their prevalence in the peritoneal exudate. Furthermore, we demonstrate that progenitor populations in the spleen play a key role in maintaining elevated neutrophil numbers. Our results provide new insight into the role for splenic neutrophils and their progenitors and establish a model to study neutrophil function during sterile inflammation.

Combinatorial hydrogel library enables identification of materials that mitigate the foreign body response in primates

The foreign body response is an immune-mediated reaction that can lead to the failure of implanted medical devices and discomfort for the recipient. There is a critical need for biomaterials that overcome this key challenge in the development of medical devices. Here we use a combinatorial approach for covalent chemical modification to generate a large library of variants of one of the most widely used hydrogel biomaterials, alginate. We evaluated the materials in vivo and identified three triazole-containing analogs that substantially reduce foreign body reactions in both rodents and, for at least 6 months, in non-human primates. The distribution of the triazole modification creates a unique hydrogel surface that inhibits recognition by macrophages and fibrous deposition. In addition to the utility of the compounds reported here, our approach may enable the discovery of other materials that mitigate the foreign body response.

Long-term glycemic control using polymer-encapsulated human stem cell-derived beta cells in immune-competent mice

The transplantation of glucose-responsive, insulin-producing cells offers the potential for restoring glycemic control in individuals with diabetes. Pancreas transplantation and the infusion of cadaveric islets are currently implemented clinically, but these approaches are limited by the adverse effects of immunosuppressive therapy over the lifetime of the recipient and the limited supply of donor tissue. The latter concern may be addressed by recently described glucose-responsive mature beta cells that are derived from human embryonic stem cells (referred to as SC-β cells), which may represent an unlimited source of human cells for pancreas replacement therapy. Strategies to address the immunosuppression concerns include immunoisolation of insulin-producing cells with porous biomaterials that function as an immune barrier. However, clinical implementation has been challenging because of host immune responses to the implant materials. Here we report the first long-term glycemic correction of a diabetic, immunocompetent animal model using human SC-β cells. SC-β cells were encapsulated with alginate derivatives capable of mitigating foreign-body responses in vivo and implanted into the intraperitoneal space of C57BL/6J mice treated with streptozotocin, which is an animal model for chemically induced type 1 diabetes. These implants induced glycemic correction without any immunosuppression until their removal at 174 d after implantation. Human C-peptide concentrations and in vivo glucose responsiveness demonstrated therapeutically relevant glycemic control. Implants retrieved after 174 d contained viable insulin-producing cells.

Therapeutic genome editing by combined viral and non-viral delivery of CRISPR system components in vivo

The combination of Cas9, guide RNA and repair template DNA can induce precise gene editing and the correction of genetic diseases in adult mammals. However, clinical implementation of this technology requires safe and effective delivery of all of these components into the nuclei of the target tissue. Here, we combine lipid nanoparticle-mediated delivery of Cas9 mRNA with adeno-associated viruses encoding a sgRNA and a repair template to induce repair of a disease gene in adult animals. We applied our delivery strategy to a mouse model of human hereditary tyrosinemia and show that the treatment generated fumarylacetoacetate hydrolase (Fah)-positive hepatocytes by correcting the causative Fah-splicing mutation. Treatment rescued disease symptoms such as weight loss and liver damage. The efficiency of correction was >6% of hepatocytes after a single application, suggesting potential utility of Cas9-based therapeutic genome editing for a range of diseases.

Poly(glycoamidoamine) Brushes Formulated Nanomaterials for Systemic siRNA and mRNA Delivery in Vivo

Safe and effective delivery is required for siRNA and mRNA-based therapeutics to reach their potential. Here, we report on the development of poly(glycoamidoamine) brush nanoparticles as delivery vehicles for siRNA and mRNA. These polymers were capable of significant delivery of siRNA against FVII and mRNA-encoding erythropoietin (EPO) in mice. Importantly, these nanoparticles were well-tolerated at their effective dose based on analysis of tissue histology, systemic cytokine levels, and liver enzyme chemistry. The polymer brush nanoparticles reported here are promising for therapeutic applications.

Myocardial Delivery of Lipidoid Nanoparticle Carrying modRNA Induces Rapid and Transient Expression

Nanoparticle-based delivery of nucleotides offers an alternative to viral vectors for gene therapy. We report highly efficient in vivo delivery of modified mRNA (modRNA) to rat and pig myocardium using formulated lipidoid nanoparticles (FLNP). Direct myocardial injection of FLNP containing 1-10 μg eGFPmodRNA in the rat (n = 3 per group) showed dose-dependent enhanced green fluorescent protein (eGFP) mRNA levels in heart tissue 20 hours after injection, over 60-fold higher than for naked modRNA. Off-target expression, including lung, liver, and spleen, was <10% of that in heart. Expression kinetics after injecting 5 μg FLNP/eGFPmodRNA showed robust expression at 6 hours that reduced by half at 48 hours and was barely detectable at 2 weeks. Intracoronary administration of 10 μg FLNP/eGFPmodRNA also proved successful, although cardiac expression of eGFP mRNA at 20 hours was lower than direct injection, and off-target expression was correspondingly higher. Findings were confirmed in a pilot study in pigs using direct myocardial injection as well as percutaneous intracoronary delivery, in healthy and myocardial infarction models, achieving expression throughout the ventricular wall. Fluorescence microscopy revealed GFP-positive cardiomyocytes in treated hearts. This nanoparticle-enabled approach for highly efficient, rapid and short-term mRNA expression in the heart offers new opportunities to optimize gene therapies for enhancing cardiac function and regeneration.

High Throughput Layer-by-Layer Films for Extracting Film Forming Parameters and Modulating Film Interactions with Cells

A high-throughput approach which automates the synthesis of polyelectrolyte-based layer-by-layer films (HT-LbL) to facilitate rapid film generation, systematic film characterization, and rational investigations into their interactions with cells is described. Key parameters, such as polyelectrolyte adsorption time and polyelectrolyte deposition pH, were used to modulate LbL film growth to create LbL films of distinct thicknesses using the widely utilized polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). We highlight how HT-LbL can be used to rapidly characterize film-forming parameters and robustly create linearly growing films of various molecular architectures. Film thickness and growth rates of HT-LbL films were shown to increase as a function of adsorption time. Subsequently, we investigated the role that polyelectrolyte solution pH (ranging from 2.5 to 9) has in forming molecularly distinct films of weak polyelectrolytes and report the effect this has on modulating cell attachment and spreading. Films synthesized at PAA-pH of 5.5 and PAH-pH 2.5-5.5 exhibited the highest cellular attachment. These results indicate that HT-LbL is a robust method that can shift the paradigm regarding the use of LbL in biomedical applications as it provides a rapid method to synthesize, characterize, and screen the interactions between molecularly distinct LbL films and cells.

Injectable Self-Healing Glucose-Responsive Hydrogels with pH-Regulated Mechanical Properties

Dynamically restructuring pH-responsive hydrogels are synthesized, employing dynamic covalent chemistry between phenylboronic acid and cis-diol modified poly(ethylene glycol) macromonomers. These gels display shear-thinning behavior, followed by a rapid structural recovery (self-healing). Size-dependent in vitro controlled and glucose-responsive release of proteins from the hydrogel network, as well as the biocompatibility of the gels, are evaluated both in vitro and in vivo.

Materials for non-viral intracellular delivery of messenger RNA therapeutics

Though therapeutics based on messenger RNA (mRNA) have broad potential in applications such as protein replacement therapy, cancer immunotherapy, and genomic engineering, their effective intracellular delivery remains a challenge. A chemically diverse suite of delivery materials with origins as materials for cellular transfection of DNA and small interfering RNAs (siRNAs) has recently been reported to have promise as non-viral delivery agents for mRNA. These materials include covalent conjugates, protamine complexes, nanoparticles based on lipids or polymers, and hybrid formulations. This review will highlight the use of delivery materials for mRNA, with a specific focus on their mechanisms of action, routes of administration, and dosages. Additionally, strategies in which these materials can be adapted and optimized to address challenges specific to mRNA delivery are also discussed. The technologies included have shown varying promise for therapeutic use, specifically having been used to deliver mRNA in vivo or exhibiting characteristics that could make in vivo use a possibility. In so doing, it is the intention of this review to provide a comprehensive look at the progress and possibilities in applying nucleic acid delivery technology specifically toward the emerging area of mRNA therapeutics.

Optimization of Lipid Nanoparticle Formulations for mRNA Delivery in Vivo with Fractional Factorial and Definitive Screening Designs

Intracellular delivery of messenger RNA (mRNA) has the potential to induce protein production for many therapeutic applications. Although lipid nanoparticles have shown considerable promise for the delivery of small interfering RNAs (siRNA), their utility as agents for mRNA delivery has only recently been investigated. The most common siRNA formulations contain four components: an amine-containing lipid or lipid-like material, phospholipid, cholesterol, and lipid-anchored polyethylene glycol, the relative ratios of which can have profound effects on the formulation potency. Here, we develop a generalized strategy to optimize lipid nanoparticle formulations for mRNA delivery to the liver in vivo using Design of Experiment (DOE) methodologies including Definitive Screening and Fractional Factorial Designs. By simultaneously varying lipid ratios and structures, we developed an optimized formulation which increased the potency of erythropoietin-mRNA-loaded C12-200 lipid nanoparticles 7-fold relative to formulations previously used for siRNA delivery. Key features of this optimized formulation were the incorporation of 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and increased ionizable lipid:mRNA weight ratios. Interestingly, the optimized lipid nanoparticle formulation did not improve siRNA delivery, indicating differences in optimized formulation parameter design spaces for siRNA and mRNA. We believe the general method described here can accelerate in vivo screening and optimization of nanoparticle formulations with large multidimensional design spaces.

Macrophage Notch Ligand Delta-Like 4 Promotes Vein Graft Lesion Development: Implications for the Treatment of Vein Graft Failure

OBJECTIVE

Despite its large clinical impact, the underlying mechanisms for vein graft failure remain obscure and no effective therapeutic solutions are available. We tested the hypothesis that Notch signaling promotes vein graft disease.

APPROACH AND RESULTS

We used 2 biotherapeutics for Delta-like ligand 4 (Dll4), a Notch ligand: (1) blocking antibody and (2) macrophage- or endothelial cell (EC)-targeted small-interfering RNA. Dll4 antibody administration for 28 days inhibited vein graft lesion development in low-density lipoprotein (LDL) receptor-deficient (Ldlr(-/-)) mice, and suppressed macrophage accumulation and macrophage expression of proinflammatory M1 genes. Dll4 antibody treatment for 7 days after grafting also reduced macrophage burden at day 28. Dll4 silencing via macrophage-targeted lipid nanoparticles reduced lesion development and macrophage accumulation, whereas EC-targeted Dll4 small-interfering RNA produced no effects. Gain-of-function and loss-of-function studies suggested in vitro that Dll4 induces proinflammatory molecules in macrophages. Macrophage Dll4 also stimulated smooth muscle cell proliferation and migration and suppressed their differentiation.

CONCLUSIONS

These results suggest that macrophage Dll4 promotes lesion development in vein grafts via macrophage activation and crosstalk between macrophages and smooth muscle cells, supporting the Dll4-Notch axis as a novel therapeutic target.

Neutrophil Responses to Sterile Implant Materials

In vivo implantation of sterile materials and devices results in a foreign body immune response leading to fibrosis of implanted material. Neutrophils, one of the first immune cells to be recruited to implantation sites, have been suggested to contribute to the establishment of the inflammatory microenvironment that initiates the fibrotic response. However, the precise numbers and roles of neutrophils in response to implanted devices remains unclear. Using a mouse model of peritoneal microcapsule implantation, we show 30–500 fold increased neutrophil presence in the peritoneal exudates in response to implants. We demonstrate that these neutrophils secrete increased amounts of a variety of inflammatory cytokines and chemokines. Further, we observe that they participate in the foreign body response through the formation of neutrophil extracellular traps (NETs) on implant surfaces. Our results provide new insight into neutrophil function during a foreign body response to peritoneal implants which has implications for the development of biologically compatible medical devices.

Exploiting Electrostatic Interactions in Polymer-Nanoparticle Hydrogels

Shear-thinning injectable hydrogels exploit dynamic noncovalent cross-links to flow upon applied stress and rapidly self-heal once the stress is relaxed. These materials continue to gather interest as they afford minimally invasive deployment in the body for a variety of biomedical applications. Here, we present rationally engineered polymer-nanoparticle (PNP) interactions based on electrostatic forces for the fabrication of self-assembled hydrogels with shear-thinning and self-healing properties. The selective adsorption of negatively charged biopolymers, including hyaluronic acid (HA) and carboxymethylcellulose (CBMC), to biodegradable nanoparticles comprising poly(ethylene glycol)-b-poly(lactic acid) (PEG-b-PLA) is enhanced with a positively charged surfactant, cetyltrimethylammonium bromide (CTAB). We demonstrate that, in this manner, electrostatic interactions can be leveraged to fabricate PNP hydrogels and characterize the viscoelastic properties of the gels imparted by CBMC and HA. This work introduces PNP hydrogels that use common biopolymers without the need for chemical modification, yielding extremely facile preparation and processing, which when coupled with the tunability of their properties are distinguishing features for many important biomedical and industrial applications.

Accelerating the Translation of Nanomaterials in Biomedicine

Due to their size and tailorable physicochemical properties, nanomaterials are an emerging class of structures utilized in biomedical applications. There are now many prominent examples of nanomaterials being used to improve human health, in areas ranging from imaging and diagnostics to therapeutics and regenerative medicine. An overview of these examples reveals several common areas of synergy and future challenges. This Nano Focus discusses the current status and future potential of promising nanomaterials and their translation from the laboratory to the clinic, by highlighting a handful of successful examples.

Engineering Synthetically Modified Insulin for Glucose-Responsive Diabetes Therapy

Though a suite of different insulin variants have been used clinically to provide greater control over pharmacokinetics, no clinically used insulin can tune its potency and/or bioavailability in a glucose-dependent manner. In order to improve therapy for diabetic patients, a vision has been the development of autonomous closed-loop approaches. Toward this goal, insulin has been synthetically modified with glucose-sensing groups or groups that can compete with free glucose for binding to glucose-binding proteins and evaluated in pre-clinical models. Specifically, it was demonstrated that site-specific modification of insulin with phenylboronic acid can result in glucose-responsive activity, leading to faster recovery in diabetic mice following a glucose challenge but with less observed hypoglycemia in healthy mice. This strategy, along with several others being pursued, holds promise to improve the fidelity in glycemic control with routine insulin therapy.

Abstract 1: Chemical Biology of Cardiac Regeleration: an Instructive Hydrogel-based Platform for Heart Repair

Regeleration is the myocardium’s natural adaptive remodeling response to implanted biopolymer hydrogels, a new heart failure treatment modality with promising success in early clinical trials. Classified as a medical device capable of long-term myocardial engraftment, implanted hydrogels of varying molecular composition provide mechanical bulking and scaffolding support that can stabilize or reverse adverse ventricular remodeling. Additionally, natural or synthetically designed hydrogels encoding specific bioactivities or signaling functions can directly regulate myocardial biology to mediate heart repair. To gain mechanistic insight into the molecular and cellular biology and biochemistry of the biopolymer-myocardial interface, we studied two clinically relevant hydrogels - seaweed-derived alginate (Alg) and myomatrix (MMx), extracellular matrix molecules prepared from decellularized pig heart - in a mouse model. Alg and MMx differentially activated signal transduction cascades, recruited different cell types and produced distinctive gene expression signatures and patterns of cardiomyocyte hypertrophy, including muscle enhancer factor-2 (MEF2) and fetal gene program (re)activation. Chemically modifying Alg’s backbone structure correspondingly altered myocardium’s biological response, demonstrating the synthetic tunability of this repair process. These observations demonstrate that implanted biopolymer hydrogels drive unexpectedly robust and versatile regelerative responses in myocardium, transducing physical and biochemical signals to the cardiac genome that contribute to hydrogel function, providing a potential therapeutic target for enhancing hydrogel-mediated heart repair without stem cells.

Discovery of a Novel Polymer for Human Pluripotent Stem Cell Expansion and Multilineage Differentiation

A scalable and cost-effective synthetic polymer substrate that supports robust expansion and subsequent multilineage differentiation of human pluripotent stem cells (hPSCs) with defined commercial media is presented. This substrate can be applied to common cultureware and used off-the-shelf after long-term storage. Expansion and differentiation of hPSCs are performed entirely on the polymeric surface, enabling the clinical potential of hPSC-derived cells to be realized.

Precision cancer mouse models through genome editing with CRISPR-Cas9

The cancer genome is highly complex, with hundreds of point mutations, translocations, and chromosome gains and losses per tumor. To understand the effects of these alterations, precise models are needed. Traditional approaches to the construction of mouse models are time-consuming and laborious, requiring manipulation of embryonic stem cells and multiple steps. The recent development of the clustered regularly interspersed short palindromic repeats (CRISPR)-Cas9 system, a powerful genome-editing tool for efficient and precise genome engineering in cultured mammalian cells and animals, is transforming mouse-model generation. Here, we review how CRISPR-Cas9 has been used to create germline and somatic mouse models with point mutations, deletions and complex chromosomal rearrangements. We highlight the progress and challenges of such approaches, and how these models can be used to understand the evolution and progression of individual tumors and identify new strategies for cancer treatment. The generation of precision cancer mouse models through genome editing will provide a rapid avenue for functional cancer genomics and pave the way for precision cancer medicine.

Size- and shape-dependent foreign body immune response to materials implanted in rodents and non-human primates

The efficacy of implanted biomedical devices is often compromised by host recognition and subsequent foreign body responses. Here, we demonstrate the role of the geometry of implanted materials on their biocompatibility in vivo. In rodent and non-human primate animal models, implanted spheres 1.5 mm and above in diameter across a broad spectrum of materials, including hydrogels, ceramics, metals and plastics, significantly abrogated foreign body reactions and fibrosis when compared with smaller spheres. We also show that for encapsulated rat pancreatic islet cells transplanted into streptozotocin-treated diabetic C57BL/6 mice, islets prepared in 1.5-mm alginate capsules were able to restore blood-glucose control for up to 180 days, a period more than five times longer than for transplanted grafts encapsulated within conventionally sized 0.5-mm alginate capsules. Our findings suggest that the in vivo biocompatibility of biomedical devices can be significantly improved simply by tuning their spherical dimensions.

Genetic and hypoxic alterations of the microRNA-210-ISCU1/2 axis promote iron-sulfur deficiency and pulmonary hypertension

Iron-sulfur (Fe-S) clusters are essential for mitochondrial metabolism, but their regulation in pulmonary hypertension (PH) remains enigmatic. We demonstrate that alterations of the miR-210-ISCU1/2 axis cause Fe-S deficiencies in vivo and promote PH. In pulmonary vascular cells and particularly endothelium, hypoxic induction of miR-210 and repression of the miR-210 targets ISCU1/2 down-regulated Fe-S levels. In mouse and human vascular and endothelial tissue affected by PH, miR-210 was elevated accompanied by decreased ISCU1/2 and Fe-S integrity. In mice, miR-210 repressed ISCU1/2 and promoted PH. Mice deficient in miR-210, via genetic/pharmacologic means or via an endothelial-specific manner, displayed increased ISCU1/2 and were resistant to Fe-S-dependent pathophenotypes and PH. Similar to hypoxia or miR-210 overexpression, ISCU1/2 knockdown also promoted PH. Finally, cardiopulmonary exercise testing of a woman with homozygous ISCU mutations revealed exercise-induced pulmonary vascular dysfunction. Thus, driven by acquired (hypoxia) or genetic causes, the miR-210-ISCU1/2 regulatory axis is a pathogenic lynchpin causing Fe-S deficiency and PH. These findings carry broad translational implications for defining the metabolic origins of PH and potentially other metabolic diseases sharing similar underpinnings.

A versatile reporter system for CRISPR-mediated chromosomal rearrangements

Although chromosomal deletions and inversions are important in cancer, conventional methods for detecting DNA rearrangements require laborious indirect assays. Here we develop fluorescent reporters to rapidly quantify CRISPR/Cas9-mediated deletions and inversions. We find that inversion depends on the non-homologous end-joining enzyme LIG4. We also engineer deletions and inversions for a 50 kb Pten genomic region in mouse liver. We discover diverse yet sequence-specific indels at the rearrangement fusion sites. Moreover, we detect Cas9 cleavage at the fourth nucleotide on the non-complementary strand, leading to staggered instead of blunt DNA breaks. These reporters allow mechanisms of chromosomal rearrangements to be investigated.

A defined synthetic substrate for serum-free culture of human stem cell derived cardiomyocytes with improved functional maturity identified using combinatorial materials microarrays

Cardiomyocytes from human stem cells have applications in regenerative medicine and can provide models for heart disease and toxicity screening. Soluble components of the culture system such as growth factors within serum and insoluble components such as the substrate on which cells adhere to are important variables controlling the biological activity of cells. Using a combinatorial materials approach we develop a synthetic, chemically defined cellular niche for the support of functional cardiomyocytes derived from human embryonic stem cells (hESC-CMs) in a serum-free fully defined culture system. Almost 700 polymers were synthesized and evaluated for their utility as growth substrates. From this group, 20 polymers were identified that supported cardiomyocyte adhesion and spreading. The most promising 3 polymers were scaled up for extended culture of hESC-CMs for 15 days and were characterized using patch clamp electrophysiology and myofibril analysis to find that functional and structural phenotype was maintained on these synthetic substrates without the need for coating with extracellular matrix protein. In addition, we found that hESC-CMs cultured on a co-polymer of isobornyl methacrylate and tert-butylamino-ethyl methacrylate exhibited significantly longer sarcomeres relative to gelatin control. The potential utility of increased structural integrity was demonstrated in an in vitro toxicity assay that found an increase in detection sensitivity of myofibril disruption by the anti-cancer drug doxorubicin at a concentration of 0.05 µM in cardiomyocytes cultured on the co-polymer compared to 0.5 µM on gelatin. The chemical moieties identified in this large-scale screen provide chemically defined conditions for the culture and manipulation of hESC-CMs, as well as a framework for the rational design of superior biomaterials.