Use of CRISPR/Cas9-mediated disruption of CNS cell type genes to profile transduction of AAV by neonatal intracerebroventricular delivery in mice.

Adeno-associated virus (AAV) transduction efficiency and tropism are conventionally determined by high expression of a fluorescent reporter gene. Emerging data has suggested that such conventional methods may underestimate AAV transduction for cells in which reporter expression from AAV vectors is undetectable. To explore an alternative method that captures AAV transduction in cells in which low expression of a cargo is sufficient for the intended activity, we sought after CRISPR/Cas9-mediated gene disruption. In this study, we use AAV to deliver CRISPR/guide RNA designed to abolish the genes NeuN, GFAP, or MOG expressed specifically in neurons, astrocytes, or oligodendrocytes respectively in the central nervous system (CNS) of mice. Abrogated expression of these cell-type-specific genes can be measured biochemically in CNS subregions and provides quantitative assessment of AAV transduction in these CNS cell types. By using this method, we compared CNS transduction of AAV9, AAV-PHP.B, and AAV-PHP.eB delivered via intracerebroventricular injection (ICV) in neonatal mice. We found both AAV-PHP.B and AAV-PHP.eB resulted in marked disruption of the NeuN gene by CRISPR/Cas9, significantly greater than AAV9 in several brain regions and spinal cord. In contrast, only modest disruption of the GFAP gene and the MOG gene was observed by all three AAV variants. Since the procedure of ICV circumvents the blood-brain barrier, our data suggests that, independent of their ability to cross the blood-brain barrier, AAV-PHP.B variants also exhibit remarkably improved neuronal transduction in the CNS. We anticipate this approach will facilitate profiling of AAV cellular tropism in murine CNS.

Highly efficient neuronal gene knockout in vivo by CRISPR-Cas9 via neonatal intracerebroventricular injection of AAV in mice.

CRISPR-Cas systems have emerged as a powerful tool to generate genetic models for studying normal and diseased central nervous system (CNS). Targeted gene disruption at specific loci has been demonstrated successfully in non-dividing neurons. Despite its simplicity, high specificity and low cost, the efficiency of CRISPR-mediated knockout in vivo can be substantially impacted by many parameters. Here, we used CRISPR-Cas9 to disrupt the neuronal-specific gene, NeuN, and optimized key parameters to achieve effective gene knockout broadly in the CNS in postnatal mice. Three cell lines and two primary neuron cultures were used to validate the disruption of NeuN by single-guide RNAs (sgRNA) harboring distinct spacers and scaffold sequences. This triage identified an optimal sgRNA design with the highest NeuN disruption in in vitro and in vivo systems. To enhance CRISPR efficiency, AAV-PHP.B, a vector with superior neuronal transduction, was used to deliver this sgRNA in Cas9 mice via neonatal intracerebroventricular (ICV) injection. This approach resulted in 99.4% biallelic indels rate in the transduced cells, leading to greater than 70% reduction of total NeuN proteins in the cortex, hippocampus and spinal cord. This work contributes to the optimization of CRISPR-mediated knockout and will be beneficial for fundamental and preclinical research.

Bioelectric Medicine and Devices for the Treatment of Spinal Cord Injury.

Recovery of motor control is paramount for patients living with paralysis following spinal cord injury (SCI). While a cure or regenerative intervention remains on the horizon for the treatment of SCI, a number of neuroprosthetic devices have been employed to treat and mitigate the symptoms of paralysis associated with injuries to the spinal column and associated comorbidities. The recent success of epidural stimulation to restore voluntary motor function in the lower limbs of a small cohort of patients has breathed new life into the promise of electric-based medicine. Recently, a number of new organic and inorganic electronic devices have been developed for brain-computer interfaces to bypass the injury, for neurorehabilitation, bladder and bowel control, and the restoration of motor or sensory control. Herein, we discuss the recent advances in neuroprosthetic devices for treating SCI and highlight future design needs for closed-loop device systems.

Cryopreservation and functional analysis of cardiac autonomic neurons.

BACKGROUND: Generally, primary neurons are isolated and seeded within hours of isolation, but cryopreservation, documented for a small number of central and peripheral neuronal subtypes, can contribute to improved utility and reduce the cost of developing new in vitro models. The preservation of cells of the autonomic nervous system (ANS), specifically sympathetic and parasympathetic neurons, has not been explored. NEW METHOD: In this work, we establish a method for preserving cardiac ANS neurons as well as evaluating the phenotypical changes of dissociated superior cervical ganglia (sympathetic neurons) and intracardiac ganglia (parasympathetic neurons) for up to a month of storage in liquid nitrogen. RESULTS: Neuron populations maintained a viability of at least 35%, and the extent of neurite outgrowth was not different from fresh cells, regardless of the storage duration studied. Expression of tyrosine hydroxylase and choline acetyl transferase were maintained over one month of cryopreservation in sympathetic and parasympathetic populations, respectively. Electrophysiological recordings for both neuron types indicate sustained characteristic resting potentials, excitability, and action potentials after more than one month in liquid nitrogen. COMPARISON WITH EXISTING METHODS: Primary cultures of the autonomic nervous system have been previously established for in vitro investigations. This is the first example of preserving primary ANS neuron cultures for long-term on-demand use. CONCLUSIONS: This report describes a readily implemented method for cryopreserving sympathetic and parasympathetic neurons that does not alter neither morphological nor electrophysiological characteristics. This methodology expands the utility of ANS cultures for use in morphological and functional assays.

Reconfigurable Microphysiological Systems for Modeling Innervation and Multitissue Interactions.

Tissue-engineered models continue to experience challenges in delivering structural specificity, nutrient delivery, and heterogenous cellular components, especially for organ-systems that require functional inputs/outputs and have high metabolic requirements, such as the heart. While soft lithography has provided a means to recapitulate complex architectures in the dish, it is plagued with a number of prohibitive shortcomings. Here, concepts from microfluidics, tissue engineering, and layer-by-layer fabrication are applied to develop reconfigurable, inexpensive microphysiological systems that facilitate discrete, 3D cell compartmentalization, and improved nutrient transport. This fabrication technique includes the use of the meniscus pinning effect, photocrosslinkable hydrogels, and a commercially available laser engraver to cut flow paths. The approach is low cost and robust in capabilities to design complex, multilayered systems with the inclusion of instrumentation for real-time manipulation or measures of cell function. In a demonstration of the technology, the hierarchal 3D microenvironment of the cardiac sympathetic nervous system is replicated. Beat rate and neurite ingrowth are assessed on-chip and quantification demonstrates that sympathetic-cardiac coculture increases spontaneous beat rate, while drug-induced increases in beating lead to greater sympathetic innervation. Importantly, these methods may be applied to other organ-systems and have promise for future applications in drug screening, discovery, and personal medicine.

Multi-layered silk film coculture system for human corneal epithelial and stromal stem cells.

With insufficient options to meet the clinical demand for cornea transplants, one emerging area of emphasis is on cornea tissue engineering. In the present study, the goal was to combine the corneal stroma and epithelium into one coculture system, to monitor both human corneal stromal stem cell (hCSSC) and human corneal epithelial cell (hCE) growth and differentiation into keratocytes and differentiated epithelium in these three-dimensional tissue systems in vitro. Coculture conditions were first optimized, including the medium, air-liquid interface culture, and surface topography and chemistry of biomaterial scaffold films based on silk protein. The silk was used as scaffolding for both stromal and epithelial tissue layers because it is cell compatible, can be surface patterned, and is optically clear. Next, the effects of proliferating and differentiating hCEs and hCSSCs were studied in this in vitro system, including the effects on cell proliferation, matrix formation by immunochemistry, and gene expression by quantitative reverse transcription-polymerase chain reaction. The incorporation of both cell types into the coculture system demonstrated more complete differentiation and growth for both cell types compared to the corneal stromal cells and corneal epithelial cells alone. Silk films for corneal epithelial culture were optimized to combine a 4.0-µm-scale surface pattern with bulk-loaded collagen type IV. Differentiation of each cell type was in evidence based on increased expression of corneal stroma and epithelial proteins and transcript levels after 6 weeks in coculture on the optimized silk scaffolds.

Lyophilized Silk Sponges: A Versatile Biomaterial Platform for Soft Tissue Engineering.

We present a silk biomaterial platform with highly tunable mechanical and degradation properties for engineering and regeneration of soft tissues such as, skin, adipose, and neural tissue, with elasticity properties in the kilopascal range. Lyophilized silk sponges were prepared under different process conditions and the effect of silk molecular weight, concentration and crystallinity on 3D scaffold formation, structural integrity, morphology, mechanical and degradation properties, and cell interactions in vitro and in vivo were studied. Tuning the molecular weight distribution (via degumming time) of silk allowed the formation of stable, highly porous, 3D scaffolds that held form with silk concentrations as low as 0.5% wt/v. Mechanical properties were a function of silk concentration and scaffold degradation was driven by beta-sheet content. Lyophilized silk sponges supported the adhesion of mesenchymal stem cells throughout 3D scaffolds, cell proliferation in vitro, and cell infiltration and scaffold remodeling when implanted subcutaneously in vivo.