Progress in the field of axonal regeneration research has been like the process of axonal growth itself: there is steady progress toward reaching the target, but there are episodes of mistargeting, ...misguidance along false routes, and connections that must later be withdrawn. This primer will address issues in the study of axonal growth after central nervous system injury in an attempt to provide guidance toward the goal of progress in the field. We address definitions of axonal growth, sprouting and regeneration after injury, and the research tools to assess growth.
Tuszynski and Steward overview issues and challenges in the study of axonal regeneration and suggest pathways for progress in this field.
Human induced pluripotent stem cells (iPSCs) from a healthy 86-year-old male were differentiated into neural stem cells and grafted into adult immunodeficient rats after spinal cord injury. Three ...months after C5 lateral hemisections, iPSCs survived and differentiated into neurons and glia and extended tens of thousands of axons from the lesion site over virtually the entire length of the rat CNS. These iPSC-derived axons extended through adult white matter of the injured spinal cord, frequently penetrating gray matter and forming synapses with rat neurons. In turn, host supraspinal motor axons penetrated human iPSC grafts and formed synapses. These findings indicate that intrinsic neuronal mechanisms readily overcome the inhibitory milieu of the adult injured spinal cord to extend many axons over very long distances; these capabilities persist even in neurons reprogrammed from very aged human cells.
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•Human iPSC-derived neural stem cells are grafted to sites of rat spinal cord injury•Human neurons extend numerous axons into host spinal cord and form synaptic contacts•Graft-derived human axons extend virtually the entire length of the rat CNS•Host axons penetrate human iPSC grafts and form synapses
Lu and colleagues report that human neural stem cells derived from iPSCs survive grafting to the injured spinal cord and extend very large numbers of axons over virtually the full length of the rat CNS.
Neural stem cells (NSCs) expressing GFP were embedded into fibrin matrices containing growth factor cocktails and grafted to sites of severe spinal cord injury. Grafted cells differentiated into ...multiple cellular phenotypes, including neurons, which extended large numbers of axons over remarkable distances. Extending axons formed abundant synapses with host cells. Axonal growth was partially dependent on mammalian target of rapamycin (mTOR), but not Nogo signaling. Grafted neurons supported formation of electrophysiological relays across sites of complete spinal transection, resulting in functional recovery. Two human stem cell lines (566RSC and HUES7) embedded in growth-factor-containing fibrin exhibited similar growth, and 566RSC cells supported functional recovery. Thus, properties intrinsic to early-stage neurons can overcome the inhibitory milieu of the injured adult spinal cord to mount remarkable axonal growth, resulting in formation of new relay circuits that significantly improve function. These therapeutic properties extend across stem cell sources and species.
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► Neural stem cells grow axons over very long distances after severe spinal cord injury ► New synaptic relays are formed, improving electrophysiological and functional outcome ► Rodent and human neural stem cells exhibit similar growth properties ► Mechanisms intrinsic to early-stage neurons overcome adult nervous system inhibition
Following severe spinal cord injury in rats, functional outcomes can be improved by the engraftment of neural stem cells embedded in a matrix that contains a growth factor cocktail. The resulting neurons extend axons over long distances and form reciprocal synaptic connections with neurons from the host.
One hundred years ago, Ramón y Cajal, considered by many as the founder of modern neuroscience, stated that neurons of the adult central nervous system (CNS) are incapable of regenerating. Yet, ...recent years have seen a tremendous expansion of knowledge in the molecular control of axon regeneration after CNS injury. We now understand that regeneration in the adult CNS is limited by (1) a failure to form cellular or molecular substrates for axon attachment and elongation through the lesion site; (2) environmental factors, including inhibitors of axon growth associated with myelin and the extracellular matrix; (3) astrocyte responses, which can both limit and support axon growth; and (4) intraneuronal mechanisms controlling the establishment of an active cellular growth programme. We discuss these topics together with newly emerging hypotheses, including the surprising finding from transcriptomic analyses of the corticospinal system in mice that neurons revert to an embryonic state after spinal cord injury, which can be sustained to promote regeneration with neural stem cell transplantation. These gains in knowledge are steadily advancing efforts to develop effective treatment strategies for spinal cord injury in humans.
The growth factor brain-derived neurotrophic factor (BDNF) and its receptor tropomyosin-related kinase receptor type B (TRKB) are actively produced and trafficked in multiple regions in the adult ...brain, where they influence neuronal activity, function and survival throughout life. The diverse presence and activity of BDNF suggests a potential role for this molecule in the pathogenesis and treatment of both neurological and psychiatric disorders. This article reviews the current understanding and future directions in BDNF-related research in the central nervous system, with an emphasis on the possible therapeutic application of BDNF in modifying fundamental processes underlying neural disease.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Current methods for bioprinting functional tissue lack appropriate biofabrication techniques to build complex 3D microarchitectures essential for guiding cell growth and promoting tissue maturation
. ...3D printing of central nervous system (CNS) structures has not been accomplished, possibly owing to the complexity of CNS architecture. Here, we report the use of a microscale continuous projection printing method (μCPP) to create a complex CNS structure for regenerative medicine applications in the spinal cord. μCPP can print 3D biomimetic hydrogel scaffolds tailored to the dimensions of the rodent spinal cord in 1.6 s and is scalable to human spinal cord sizes and lesion geometries. We tested the ability of µCPP 3D-printed scaffolds loaded with neural progenitor cells (NPCs) to support axon regeneration and form new 'neural relays' across sites of complete spinal cord injury in vivo in rodents
. We find that injured host axons regenerate into 3D biomimetic scaffolds and synapse onto NPCs implanted into the device and that implanted NPCs in turn extend axons out of the scaffold and into the host spinal cord below the injury to restore synaptic transmission and significantly improve functional outcomes. Thus, 3D biomimetic scaffolds offer a means of enhancing CNS regeneration through precision medicine.
Spinal cord neural stem cells (NSCs) have great potential to reconstitute damaged spinal neural circuitry, but they have yet to be generated in vitro. We now report the derivation of spinal cord NSCs ...from human pluripotent stem cells (hPSCs). Our observations show that these spinal cord NSCs differentiate into a diverse population of spinal cord neurons occupying multiple positions along the dorso-ventral axis, and can be maintained for prolonged time periods. Grafts into injured spinal cords were rich with excitatory neurons, extended large numbers of axons over long distances, innervated their target structures, and enabled robust corticospinal regeneration. The grafts synaptically integrated into multiple host intraspinal and supraspinal systems, including the corticospinal projection, and improved functional outcomes after injury. hPSC-derived spinal cord NSCs could enable a broad range of biomedical applications for in vitro disease modeling and constitute an improved clinically translatable cell source for 'replacement' strategies in several spinal cord disorders.
Neural stem/progenitor cell (NSPC) grafts can integrate into sites of spinal cord injury (SCI) and generate neuronal relays across lesions that can provide functional benefit. To determine if and how ...grafts become synaptically organized and connect with host systems, we performed calcium imaging of NSPC grafts in SCI sites in vivo and in adult spinal cord slices. NSPC grafts organize into localized and spontaneously active synaptic networks. Optogenetic stimulation of host corticospinal tract axons regenerating into grafts elicited distinct and segregated neuronal network responses throughout the graft. Moreover, optogenetic stimulation of graft-derived axons extending from the graft into the denervated spinal cord also triggered local host neuronal network responses. In vivo imaging revealed that behavioral stimulation likewise elicited focal synaptic responses within grafts. Thus neural progenitor grafts can form functional synaptic subnetworks whose activity patterns resemble intact spinal cord.
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•Calcium imaging demonstrates host-to-stem cell graft synaptic connectivity•Host inputs to grafts activate intra-graft neuronal networks•Grafts in turn activate host neurons below the lesion•Behavioral stimulation of the host elicits neuronal responses in the graft
Ceto et al. find that host inputs to stem cell grafts in sites of spinal cord injury activate distinct ensembles of grafted neurons. Grafted neurons are also activated by sensory inputs and are capable of activating host neurons below the injury, supporting their ability to restore trans-lesion synaptic connectivity.
Neural stem cells (NSCs) differentiate into both neurons and glia, and strategies using human NSCs have the potential to restore function following spinal cord injury (SCI). However, the time period ...of maturation for human NSCs in adult injured CNS is not well defined, posing fundamental questions about the design and implementation of NSC-based therapies. This work assessed human H9 NSCs that were implanted into sites of SCI in immunodeficient rats over a period of 1.5 years. Notably, grafts showed evidence of continued maturation over the entire assessment period. Markers of neuronal maturity were first expressed 3 months after grafting. However, neurogenesis, neuronal pruning, and neuronal enlargement continued over the next year, while total graft size remained stable over time. Axons emerged early from grafts in very high numbers, and half of these projections persisted by 1.5 years. Mature astrocyte markers first appeared after 6 months, while more mature oligodendrocyte markers were not present until 1 year after grafting. Astrocytes slowly migrated from grafts. Notably, functional recovery began more than 1 year after grafting. Thus, human NSCs retain an intrinsic human rate of maturation, despite implantation into the injured rodent spinal cord, yet they support delayed functional recovery, a finding of great importance in planning human clinical trials.
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