Controlled oxygen delivery to power tissue regeneration.

Oxygen plays a crucial role in human embryogenesis, homeostasis, and tissue regeneration. Emerging engineered regenerative solutions call for novel oxygen delivery systems. To become a reality, these systems must consider physiological processes, oxygen release mechanisms and the target application. In this review, we explore the biological relevance of oxygen at both a cellular and tissue level, and the importance of its controlled delivery via engineered biomaterials and devices. Recent advances and upcoming trends in the field are also discussed with a focus on tissue-engineered constructs that could meet metabolic demands to facilitate regeneration.

Neuronal Replenishment via Hydrogel-Rationed Delivery of Reprogramming Factors.

The central nervous system's limited capacity for regeneration often leads to permanent neuronal loss following injury. Reprogramming resident reactive astrocytes into induced neurons at the site of injury is a promising strategy for neural repair, but challenges persist in stabilizing and accurately targeting viral vectors for transgene expression. In this study, we employed a bioinspired self-assembling peptide (SAP) hydrogel for the precise and controlled release of a hybrid adeno-associated virus (AAV) vector, AAVDJ, carrying the NeuroD1 neural reprogramming transgene. This method effectively mitigates the issues of high viral dosage at the target site, off-target delivery, and immunogenic reactions, enhancing the vector's targeting and reprogramming efficiency. In vitro, this vector successfully induced neuron formation, as confirmed by morphological, histochemical, and electrophysiological analyses. In vivo, SAP-mediated delivery of AAVDJ-NeuroD1 facilitated the trans-differentiation of reactive host astrocytes into induced neurons, concurrently reducing glial scarring. Our findings introduce a safe and effective method for treating central nervous system injuries, marking a significant advancement in regenerative neuroscience.

Calming the Nerves via the Immune Instructive Physiochemical Properties of Self-Assembling Peptide Hydrogels.

Current therapies for the devastating damage caused by traumatic brain injuries (TBI) are limited. This is in part due to poor drug efficacy to modulate neuroinflammation, angiogenesis and/or promoting neuroprotection and is the combined result of challenges in getting drugs across the blood brain barrier, in a targeted approach. The negative impact of the injured extracellular matrix (ECM) has been identified as a factor in restricting post-injury plasticity of residual neurons and is shown to reduce the functional integration of grafted cells. Therefore, new strategies are needed to manipulate the extracellular environment at the subacute phase to enhance brain regeneration. In this review, potential strategies are to be discussed for the treatment of TBI by using self-assembling peptide (SAP) hydrogels, fabricated via the rational design of supramolecular peptide scaffolds, as an artificial ECM which under the appropriate conditions yields a supramolecular hydrogel. Sequence selection of the peptides allows the tuning of these hydrogels' physical and biochemical properties such as charge, hydrophobicity, cell adhesiveness, stiffness, factor presentation, degradation profile and responsiveness to (external) stimuli. This review aims to facilitate the development of more intelligent biomaterials in the future to satisfy the parameters, requirements, and opportunities for the effective treatment of TBI.

Generation of human-induced pluripotent-stem-cell-derived cortical neurons for high-throughput imaging of neurite morphology and neuron maturation.

High-throughput imaging allows in vitro assessment of neuron morphology for screening populations under developmental, homeostatic, and/or disease conditions. Here, we present a protocol to differentiate cryopreserved human cortical neuronal progenitors into mature cortical neurons for high-throughput imaging analysis. We describe the use of a notch signaling inhibitor to generate homogeneous neuronal populations at densities amenable to individual neurite identification. We detail neurite morphology assessment via measuring multiple parameters including neurite length, branches, roots, segments and extremities, and neuron maturation.

Identification of cell barcodes from long-read single-cell RNA-seq with BLAZE.

Long-read single-cell RNA sequencing (scRNA-seq) enables the quantification of RNA isoforms in individual cells. However, long-read scRNA-seq using the Oxford Nanopore platform has largely relied upon matched short-read data to identify cell barcodes. We introduce BLAZE, which accurately and efficiently identifies 10x cell barcodes using only nanopore long-read scRNA-seq data. BLAZE outperforms the existing tools and provides an accurate representation of the cells present in long-read scRNA-seq when compared to matched short reads. BLAZE simplifies long-read scRNA-seq while improving the results, is compatible with downstream tools accepting a cell barcode file, and is available at https://github.com/shimlab/BLAZE .

Simple Complexity: Incorporating Bioinspired Delivery Machinery within Self-Assembled Peptide Biogels.

Bioinspired self-assembly is a bottom-up strategy enabling biologically sophisticated nanostructured biogels that can mimic natural tissue. Self-assembling peptides (SAPs), carefully designed, form signal-rich supramolecular nanostructures that intertwine to form a hydrogel material that can be used for a range of cell and tissue engineering scaffolds. Using the tools of nature, they are a versatile framework for the supply and presentation of important biological factors. Recent developments have shown promise for many applications such as therapeutic gene, drug and cell delivery and yet are stable enough for large-scale tissue engineering. This is due to their excellent programmability-features can be incorporated for innate biocompatibility, biodegradability, synthetic feasibility, biological functionality and responsiveness to external stimuli. SAPs can be used independently or combined with other (macro)molecules to recapitulate surprisingly complex biological functions in a simple framework. It is easy to accomplish localized delivery, since they can be injected and can deliver targeted and sustained effects. In this review, we discuss the categories of SAPs, applications for gene and drug delivery, and their inherent design challenges. We highlight selected applications from the literature and make suggestions to advance the field with SAPs as a simple, yet smart delivery platform for emerging BioMedTech applications.

Understanding and modeling regional specification of the human ganglionic eminence.

Inhibitory neurons originating from the ventral forebrain are associated with several neurological conditions. Distinct ventral forebrain subpopulations are generated from topographically defined zones; lateral-, medial- and caudal ganglionic eminences (LGE, MGE and CGE), yet key specification factors often span across developing zones contributing to difficulty in defining unique LGE, MGE or CGE profiles. Here we use human pluripotent stem cell (hPSC) reporter lines (NKX2.1-GFP and MEIS2-mCherry) and manipulation of morphogen gradients to gain greater insight into regional specification of these distinct zones. We identified Sonic hedgehog (SHH)-WNT crosstalk in regulating LGE and MGE fate and uncovered a role for retinoic acid signaling in CGE development. Unraveling the influence of these signaling pathways permitted development of fully defined protocols that favored generation of the three GE domains. These findings provide insight into the context-dependent role of morphogens in human GE specification and are of value for in vitro disease modeling and advancement of new therapies.

Extracellular Matrix Biomimetic Hydrogels, Encapsulated with Stromal Cell-Derived Factor 1, Improve the Composition of Foetal Tissue Grafts in a Rodent Model of Parkinson's Disease.

Clinical studies have provided evidence for dopamine (DA) cell replacement therapy in Parkinson's Disease. However, grafts derived from foetal tissue or pluripotent stem cells (PSCs) remain heterogeneous, with a high proportion of non-dopaminergic cells, and display subthreshold reinnervation of target tissues, thereby highlighting the need to identify new strategies to improve graft outcomes. In recent work, Stromal Cell-Derived Factor-1 (SDF1), secreted from meninges, has been shown to exert many roles during ventral midbrain DA development and DA-directed differentiation of PSCs. Related, co-implantation of meningeal cells has been shown to improve neural graft outcomes, however, no direct evidence for the role of SDF1 in neural grafting has been shown. Due to the rapid degradation of SDF1 protein, here, we utilised a hydrogel to entrap the protein and sustain its delivery at the transplant site to assess the impact on DA progenitor differentiation, survival and plasticity. Hydrogels were fabricated from self-assembling peptides (SAP), presenting an epitope for laminin, the brain's main extracellular matrix protein, thereby providing cell adhesive support for the grafts and additional laminin-integrin signalling to influence cell fate. We show that SDF1 functionalised SAP hydrogels resulted in larger grafts, containing more DA neurons, increased A9 DA specification (the subpopulation of DA neurons responsible for motor function) and enhanced innervation. These findings demonstrate the capacity for functionalised, tissue-specific hydrogels to improve the composition of grafts targeted for neural repair.

Understanding the Influence of Target Acquisition on Survival, Integration, and Phenotypic Maturation of Dopamine Neurons within Stem Cell-Derived Neural Grafts in a Parkinson's Disease Model.

Midbrain dopaminergic (DA) neurons include many subtypes characterized by their location, connectivity and function. Surprisingly, mechanisms underpinning the specification of A9 neurons [responsible for motor function, including within ventral midbrain (VM) grafts for treating Parkinson's disease (PD)] over adjacent A10, remains largely speculated. We assessed the impact of synaptic targeting on survival, integration, and phenotype acquisition of dopaminergic neurons within VM grafts generated from fetal tissue or human pluripotent stem cells (PSCs). VM progenitors were grafted into female mice with 6OHDA-lesions of host midbrain dopamine neurons, with some animals also receiving intrastriatal quinolinic acid (QA) injections to ablate medium spiny neurons (MSN), the A9 neuron primary target. While loss of MSNs variably affected graft survival, it significantly reduced striatal yet increased cortical innervation. Consequently, grafts showed reduced A9 and increased A10 specification, with more DA neurons failing to mature into either subtype. These findings highlight the importance of target acquisition on DA subtype specification during development and repair.SIGNIFICANCE STATEMENT Parish and colleagues highlight, in a rodent model of Parkinson's disease (PD), the importance of synaptic target acquisition in the survival, integration and phenotypic specification of grafted dopamine neurons derived from fetal tissue and human stem cells. Ablation of host striatal neurons resulted in reduced dopamine neuron survival within grafts, re-routing of dopamine fibers from striatal to alternate cortical targets and a consequential reduced specification of A9 dopamine neurons (the subpopulation critical for restoration of motor function) and increase in A10 DA neurons.

A Hydrogel as a Bespoke Delivery Platform for Stromal Cell-Derived Factor-1.

The defined self-assembly of peptides (SAPs) into nanostructured bioactive hydrogels has great potential for repairing traumatic brain injuries, as they maintain a stable, homeostatic environment at an injury site, preventing further degeneration. They also present a bespoke platform to restore function via the naturalistic presentation of therapeutic proteins, such as stromal-cell-derived factor 1 (SDF-1), expressed by meningeal cells. A key challenge to the use of the SDF protein, however, is its rapid diffusion and degradation. Here, we engineered a homeostatic hydrogel produced by incorporating recombinant SDF-1 protein within a self-assembled peptide hydrogel to create a supportive milieu for transplanted cells. Our hydrogel can concomitantly deliver viable primary neural progenitor cells and sustained active SDF-1 to support the nascent graft, resulting in increased neuronal differentiation. Moreover, this homeostatic hydrogel can ensure a healthy and larger graft core without impeding neuronal fiber growth and innervation. These findings demonstrate the regenerative potential of these hydrogels to improve the integration of grafted cells to treat neural injuries and diseases.

Changing Fate: Reprogramming Cells via Engineered Nanoscale Delivery Materials.

The incorporation of nanotechnology in regenerative medicine is at the nexus of fundamental innovations and early-stage breakthroughs, enabling exciting biomedical advances. One of the most exciting recent developments is the use of nanoscale constructs to influence the fate of cells, which are the basic building blocks of healthy function. Appropriate cell types can be effectively manipulated by direct cell reprogramming; a robust technique to manipulate cellular function and fate, underpinning burgeoning advances in drug delivery systems, regenerative medicine, and disease remodeling. Individual transcription factors, or combinations thereof, can be introduced into cells using both viral and nonviral delivery systems. Existing approaches have inherent limitations. Viral-based tools include issues of viral integration into the genome of the cells, the propensity for uncontrollable silencing, reduced copy potential and cell specificity, and neutralization via the immune response. Current nonviral cell reprogramming tools generally suffer from inferior expression efficiency. Nanomaterials are increasingly being explored to address these challenges and improve the efficacy of both viral and nonviral delivery because of their unique properties such as small size and high surface area. This review presents the state-of-the-art research in cell reprogramming, focused on recent breakthroughs in the deployment of nanomaterials as cell reprogramming delivery tools.

A combined cell and gene therapy approach for homotopic reconstruction of midbrain dopamine pathways using human pluripotent stem cells.

Midbrain dopamine (mDA) neurons can be replaced in patients with Parkinson's disease (PD) in order to provide long-term improvement in motor functions. The limited capacity for long-distance axonal growth in the adult brain means that cells are transplanted ectopically, into the striatal target. As a consequence, several mDA pathways are not re-instated, which may underlie the incomplete restoration of motor function in patients. Here, we show that viral delivery of GDNF to the striatum, in conjunction with homotopic transplantation of human pluripotent stem-cell-derived mDA neurons, recapitulates brain-wide mDA target innervation. The grafts provided re-instatement of striatal dopamine levels and correction of motor function and also connectivity with additional mDA target nuclei not well innervated by ectopic grafts. These results demonstrate the remarkable capacity for achieving functional and anatomically precise reconstruction of long-distance circuitry in the adult brain by matching appropriate growth-factor signaling to grafting of specific cell types.

Spontaneous Formation of ß-sheet Nano-barrels during the Early Aggregation of Alzheimer's Amyloid Beta.

Soluble low-molecular-weight oligomers formed during the early aggregation of amyloid peptides have been hypothesized as a major toxic species of amyloidogenesis. Herein, we performed the first synergic in silico, in vitro and in vivo validations of the structure, dynamics and toxicity of Aß42 oligomers. Aß peptides readily assembled into ß-rich oligomers comprised of extended ß-hairpins and ß-strands. Nanosized ß-barrels were observed with certainty with simulations, transmission electron microscopy and Fourier transform infrared spectroscopy, corroborated by immunohistochemistry, cell viability, apoptosis, inflammation, autophagy and animal behavior assays. Secondary and tertiary structural proprieties of these oligomers, such as the sequence regions with high ß-sheet propensities and inter-residue contact frequency patterns, were similar to the properties known for Aß fibrils. The unambiguous spontaneous formation of ß-barrels in the early aggregation of Aß42 supports their roles as the common toxic intermediates in Alzheimer's pathobiology and a target for Alzheimer's therapeutics.

Embryonic stem cells go from bench to bedside for Parkinson's disease.

Stem-cell-derived transplants may soon be a promising treatment option for Parkinson's disease. In preparation for clinical trial, Piao et al.1 report on generating a clinical-grade dopaminergic progenitor cell product and its rigorous testing to ensure safety and efficacy.

Human stem cells harboring a suicide gene improve the safety and standardisation of neural transplants in Parkinsonian rats.

Despite advancements in human pluripotent stem cells (hPSCs) differentiation protocols to generate appropriate neuronal progenitors suitable for transplantation in Parkinson's disease, resultant grafts contain low proportions of dopamine neurons. Added to this is the tumorigenic risk associated with the potential presence of incompletely patterned, proliferative cells within grafts. Here, we utilised a hPSC line carrying a FailSafeTM suicide gene (thymidine kinase linked to cyclinD1) to selectively ablate proliferative cells in order to improve safety and purity of neural transplantation in a Parkinsonian model. The engineered FailSafeTM hPSCs demonstrated robust ventral midbrain specification in vitro, capable of forming neural grafts upon transplantation. Activation of the suicide gene within weeks after transplantation, by ganciclovir administration, resulted in significantly smaller grafts without affecting the total yield of dopamine neurons, their capacity to innervate the host brain or reverse motor deficits at six months in a rat Parkinsonian model. Within ganciclovir-treated grafts, other neuronal, glial and non-neural populations (including proliferative cells), were significantly reduced-cell types that may pose adverse or unknown influences on graft and host function. These findings demonstrate the capacity of a suicide gene-based system to improve both the standardisation and safety of hPSC-derived grafts in a rat model of Parkinsonism.

Focal Ischemic Injury to the Early Neonatal Rat Brain Models Cognitive and Motor Deficits with Associated Histopathological Outcomes Relevant to Human Neonatal Brain Injury.

Neonatal arterial ischemic stroke is one of the more severe birth complications. The injury can result in extensive neurological damage and is robustly associated with later diagnoses of cerebral palsy (CP). An important part of efforts to develop new therapies include the on-going refinement and understanding of animal models that capture relevant clinical features of neonatal brain injury leading to CP. The potent vasoconstrictor peptide, Endothelin-1 (ET-1), has previously been utilised in animal models to reduce local blood flow to levels that mimic ischemic stroke. Our previous work in this area has shown that it is an effective and technically simple approach for modelling ischemic injury at very early neonatal ages, resulting in stable deficits in motor function. Here, we aimed to extend this model to also examine the impact on cognitive function. We show that focal delivery of ET-1 to the cortex of Sprague Dawley rats on postnatal day 0 (P0) resulted in impaired learning in a touchscreen-based test of visual discrimination and correlated with important clinical features of CP including damage to large white matter structures.

FGF-MAPK signaling regulates human deep-layer corticogenesis.

Despite heterogeneity across the six layers of the mammalian cortex, all excitatory neurons are generated from a single founder population of neuroepithelial stem cells. However, how these progenitors alter their layer competence over time remains unknown. Here, we used human embryonic stem cell-derived cortical progenitors to examine the role of fibroblast growth factor (FGF) and Notch signaling in influencing cell fate, assessing their impact on progenitor phenotype, cell-cycle kinetics, and layer specificity. Forced early cell-cycle exit, via Notch inhibition, caused rapid, near-exclusive generation of deep-layer VI neurons. In contrast, prolonged FGF2 promoted proliferation and maintained progenitor identity, delaying laminar progression via MAPK-dependent mechanisms. Inhibiting MAPK extended cell-cycle length and led to generation of layer-V CTIP2+ neurons by repressing alternative laminar fates. Taken together, FGF/MAPK regulates the proliferative/neurogenic balance in deep-layer corticogenesis and provides a resource for generating layer-specific neurons for studying development and disease.

The association of enteric neuropathy with gut phenotypes in acute and progressive models of Parkinson's disease.

Parkinson's disease (PD) is associated with neuronal damage in the brain and gut. This work compares changes in the enteric nervous system (ENS) of commonly used mouse models of PD that exhibit central neuropathy and a gut phenotype. Enteric neuropathy was assessed in five mouse models: peripheral injection of MPTP; intracerebral injection of 6-OHDA; oral rotenone; and mice transgenic for A53T variant human α-synuclein with and without rotenone. Changes in the ENS of the colon were quantified using pan-neuronal marker, Hu, and neuronal nitric oxide synthase (nNOS) and were correlated with GI function. MPTP had no effect on the number of Hu+ neurons but was associated with an increase in Hu+ nuclear translocation (P < 0.04). 6-OHDA lesioned mice had significantly fewer Hu+ neurons/ganglion (P < 0.02) and a reduced proportion of nNOS+ neurons in colon (P < 0.001). A53T mice had significantly fewer Hu+ neurons/area (P < 0.001) and exhibited larger soma size (P < 0.03). Treatment with rotenone reduced the number of Hu+ cells/mm2 in WT mice (P < 0.006) and increased the proportion of Hu+ translocated cells in both WT (P < 0.02) and A53T mice (P < 0.04). All PD models exhibited a degree of enteric neuropathy, the extent and type of damage to the ENS, however, was dependent on the model.

An Optimized Protocol for the Generation of Midbrain Dopamine Neurons under Defined Conditions.

Here, we describe a xeno-free, feeder-free, and chemically defined protocol for the generation of ventral midbrain dopaminergic (vmDA) progenitors from human pluripotent stem cells (hPSCs). This simple-to-follow protocol results in high yields of cryopreservable dopamine neurons across multiple hPSC lines. Wnt signaling is the critical component of the differentiation and can be finely adjusted in a line-dependent manner to enhance production of dopamine neurons for the purposes of transplantation, studying development and homeostasis, disease modeling, drug discovery, and drug development. For complete details on the use and execution of this protocol, please refer to Gantner et al. (2020) and Niclis et al. (2017a).

Ischemic Injury Does Not Stimulate Striatal Neuron Replacement Even during Periods of Active Striatal Neurogenesis.

Ischemic damage to the adult rodent forebrain has been widely used as a model system to study injury-induced neurogenesis, resulting in contradictory reports regarding the capacity of the postnatal brain to replace striatal projection neurons. Here we used a software-assisted, confocal approach to survey thousands of cells generated after striatal ischemic injury in rats and showed that injury fails not only to stimulate production of new striatal projection neurons in the adult brain but also to do so in the neonatal brain at early postnatal ages not previously explored. Conceptually this is significant, because it shows that even during periods of active striatal neurogenesis, injury is not a sufficient stimulus to promote replacement of these neurons. Understanding the intrinsic capacity of the postnatal brain to replace neurons in response to injury is fundamental to the development of "self-repair" therapies.