Investigating the use of primary adult subventricular zone neural precursor cells for neuronal replacement therapies

Silk Fibroin Hybrids for Biological Scaffolds with Adhesive Surface and Adaptability to the Target Tissue Change

Background Regenerative Medicine (RM) is a branch of medicine that aims to regenerate tissues and organs to overcome the problems transplants entail (poor availability, risk of rejection and intense immunosuppression). To do this, RM makes use of tissue engineering (TE). This fundamental branch deals with creating biological scaffolds capable of performing the role that physiologically belongs to the extracellular matrix (ECM). In this review, we report how specific characteristics of the scaffolds (bio-compatibility, biodegradability and mechanical and conformal properties) can be obtained using 3D printing, which facilitates the emulation of physiological tissues and organs.

Purpose and scope This review reports recent advances in the fabrication method of bioactive scaffolds that can be used clinically, providing support for cell seeding and proliferation. To this end, silk fibroin, tannin and graphene were used to improve the scaffold’s electro-bio-mechanical properties. These materials in different compositions are studied to demonstrate their potential use as bio-ink in bioadhesives and cellularized and implantable 3D-printed scaffolds.

Summary of new synthesis and conclusions reached in the review Silk fibroin is a natural biopolymer; tannin, on the other hand, is a biological polyphenol, highly reactive with other molecules by nature and with promising antioxidant capabilities. Finally, graphene is nothing more than a monolayer of graphite that has been shown to implement the mechanics and electrical conductivity of the compounds in which it is inserted; it also has excellent biocompatibility and surface area, qualities that promote cell adhesion and growth.

Conclusion Polyphenols and graphene have been shown to work in synergy in improving the electro-mechanical properties of silk fibroin scaffolds. We reported optimal and potentially market-competitive bioadhesives, but above all, the proliferation of neuronal precursor cells in vitro was successfully demonstrated.

Neurobiology meets genomic science: the promise of human-induced pluripotent stem cells

The recent introduction of the induced pluripotent stem cell technology has made possible the derivation of neuronal cells from somatic cells obtained from human individuals. This in turn has opened new areas of investigation that can potentially bridge the gap between neuroscience and psychopathology. For the first time we can study the cell biology and genetics of neurons derived from any individual. Furthermore, by recapitulating in vitro the developmental steps whereby stem cells give rise to neuronal cells, we can now hope to understand factors that control typical and atypical development. We can begin to explore how human genes and their variants are transcribed into messenger RNAs within developing neurons and how these gene transcripts control the biology of developing cells. Thus, human-induced pluripotent stem cells have the potential to uncover not only what aspects of development are uniquely human but also variations in the series of events necessary for normal human brain development that predispose to psychopathology.

Annual Research Review: The promise of stem cell research for neuropsychiatric disorders

The study of the developing brain has begun to shed light on the underpinnings of both early and adult onset neuropsychiatric disorders. Neuroimaging of the human brain across developmental time points and the use of model animal systems have combined to reveal brain systems and gene products that may play a role in autism spectrum disorders, attention deficit hyperactivity disorder, obsessive compulsive disorder and many other neurodevelopmental conditions. However, precisely how genes may function in human brain development and how they interact with each other leading to psychiatric disorders is unknown. Because of an increasing understanding of neural stem cells and how the nervous system subsequently develops from these cells, we have now the ability to study disorders of the nervous system in a new way - by rewinding and reviewing the development of human neural cells. Induced pluripotent stem cells (iPSCs), developed from mature somatic cells, have allowed the development of specific cells in patients to be observed in real time. Moreover, they have allowed some neuronal-specific abnormalities to be corrected with pharmacological intervention in tissue culture. These exciting advances based on the use of iPSCs hold great promise for understanding, diagnosing and, possibly, treating psychiatric disorders. Specifically, examination of iPSCs from typically developing individuals will reveal how basic cellular processes and genetic differences contribute to individually unique nervous systems. Moreover, by comparing iPSCs from typically developing individuals and patients, differences at stem cell stages, through neural differentiation, and into the development of functional neurons may be identified that will reveal opportunities for intervention. The application of such techniques to early onset neuropsychiatric disorders is still on the horizon but has become a reality of current research efforts as a consequence of the revelations of many years of basic developmental neurobiological science.

Differential response to ischemia in adjacent hippocampalsectors: neuronal death in CA1versus neurogenesis in dentate gyrus

Two hippocampal sectors show distinct responses to transient ischemia: the cornu Ammonis (CA)1 sector undergoes a delayed neuronal death followed by a lack of neuronal generation, while the dentate gyrus (DG) shows slight postischemic damage followed by an increased neurogenesis. Using the monkey experimental paradigm of transient whole brain global ischemia, the 'calpain-cathepsin hypothesis' was formulated in 1998. This hypothesis proposes that following ischemia calpain compromises the integrity of lysosomal membrane, causing a leakage of degrading hydrolytic enzymes--cathepsins--into the cytoplasm. Ischemia induces Ca(2+) mobilization, calpain activation, lysosomal membrane disruption, and cathepsin release, which all occur specifically in the CA1 sector and cause neuronal death. In the postischemic DG, a vascular niche has been implicated in adult neurogenesis, in that adventitial cells of the DG microvascular environment provoke postischemic up-reguation of neurogenesis with the aid of brain-derived neurotrophic factor and polysialylated form of the neural cell adhesion molecule. In parallel, Down's syndrome cell adhesion molecule has recently been shown to be expressed specifically in the neural progenitor cells of DG. In this review, we focus on the monkey experimental paradigm to reveal the remarkable contrasts between CA1 and DG in response to the ischemic insult.

Migrating and myelinating potential of subventricular zone neural progenitor cells in white matter tracts of the adult rodent brain

Adult neural stem cells in the subventricular zone (SVZ) produce neuronal progenitors that migrate along the rostral migratory stream (RMS) and generate olfactory interneurons. Here, we evaluate the migratory potential of SVZ cells outside the RMS and their capacity to generate oligodendrocytes in the adult brain. We show that SVZ cells migrate long distances when grafted into white matter tracts such as the cingulum (Ci) and corpus callosum (CC). Furthermore, 22 days postinjection, most present morphologic and phenotypic characteristics of cells committed to the oligodendrocyte lineage. Cells grafted in shiverer CC and Ci become MBP-positive oligodendrocytes, abundantly myelinating these white matter tracts. Type A progenitors are involved in this myelinating process. Altogether, this study reveals the migrating and myelinating potential of SVZ cells in a new environmental context. Therefore, SVZ cells stand as interesting candidates for the development of novel therapeutic strategies for demyelinating diseases.

Potential functional neural repair with grafted neural stem cells of early embryonic neuroepithelial origin

The fate of grafted neuroepithelial stem cells in the normal mature brain environment was assessed both morphologically and electrophysiologically to confirm their feasibility in the functional repair of damaged neural circuitry. The neuroepithelial stem cells were harvested from the mesencephalic neural plate of transgenic green fluorescence protein-carrying rat embryos, and implanted into the normal adult rat striatum. The short- and long-term differentiation pattern of donor-derived cells was precisely monitored immunohistochemically. The functional abilities of the donor-derived cells and communication between them and the host were investigated using host-rat brain slices incorporating the graft with whole-cell patch-clamp recording. Vigorous differentiation of the neuroepithelial stem cells into mostly neurons was noted in the short-term with positive staining for tyrosine hydroxylase, suggesting that the donor-derived cells were exclusively following their genetically programmed fate, together with gamma-aminobutyric acid (GABA) and glutamate expression. In the long-term, the large number of donor-derived neurons was sustained, but the staining pattern showed expression of dopamine- and adenosine 3':5'-monophosphate-regulated phosphoprotein 32, suggesting that some neurons were following environmental cues, together with the appearance of some cholinergic neurons. Some donor-derived astrocytes were also seen in the graft. Many action potentials indicating the presence of both dopaminergic and non-dopaminergic patterns could be elicited and recorded in the donor-derived neurons in addition to spontaneous glutamatergic and GABAergic post-synaptic currents which were strongly shown to be of host origin. Neuroepithelial stem cells are therefore an attractive candidate as a source of donor material for intracerebral grafting in functional repair.

Heterotypic neuronal differentiation of adult subependymal zone neuronal progenitor cells transplanted to the adult hippocampus

Neuronal progenitor cells (NPCs) residing in the adult subependymal zone (SEZ) are a potential source of expandable cells for autologous transplantation to replace neurons lost in multiple types of brain injury. To characterize the capacity of these cells for neuronal differentiation in a mature ectopic environment, NPCs expanded from the SEZ of adult rats were transplanted to the adult dentate gyrus. Cultures comprised a heterogeneous population of proliferating cells, which expressed nestin (47%) and GFAP (37%), with many cells expressing both progenitor cell markers (31%). In grafts of undifferentiated cells, as well as in grafts of cells that were induced to differentiate in vitro with retinoic acid, 35% of the transplanted SEZ-derived cells exhibited immunohistochemical and morphological features characteristic of hippocampal granule cell neurons. These novel results indicate that in vitro expanded adult SEZ NPCs are capable of heterotypic neuronal differentiation in a neurogenic region of the adult brain.

Progress in cerebral transplantation of expanded neuronal stem cells

OBJECT

Given the success and limitations of human fetal primary neural tissue transplantation, neuronal stem cells (NSCs) that can be adequately expanded in culture have been the focus of numerous attempts to develop a superior source of replacement cells for restorative neurosurgery. To clarify recent progress toward this goal, the transplantation into the adult brain of NSCs, expanded in vitro before grafting, was reviewed.

METHODS

Neuronal stem cells can be expanded from a variety of sources, including embryos, fetuses, adult bone marrow, and adult brain tissue. Recent investigations of each of these expanded stem cell types have generated a large body of information along with a great number of unanswered questions regarding the ability of these cells to replace damaged neurons. Expanded NSCs offer many advantages over their primary tissue predecessors, but also may exhibit different functional abilities as grafted cells. Because expanded NSCs will most likely ultimately replace primary tissue grafting in clinical trials, this review was undertaken to focus solely on this distinct body of work and to summarize clearly the existing preclinical data regarding the in vivo successes, limits, and unknowns of using each expanded NSC type when transplanted into the adult brain.

CONCLUSIONS

Embryonic stem cell-derived cells have demonstrated appropriate neuronal phenotypes after transplantation into nonneurogenic areas of the adult brain. Understanding the mechanisms responsible for this may lead to similar success with less studied adult neuronal progenitor cells, which offer the potential for autologous NSC transplantation with less risk of tumorigenesis.

Olfactory processing in a changing brain

The perception of odorant molecules provides the essential information that allows animals to explore their surrounding. We describe here how the external world of scents may sculpt the activity of the first central relay of the olfactory system, i.e., the olfactory bulb. This structure is one of the few brain areas to continuously replace one of its neuronal populations: the local GABAergic interneurons. How the newly generated neurons integrate into a pre-existing neural network and how basic olfactory functions are maintained when a large percentage of neurons are subjected to continuous renewal, are important questions that have recently received new insights. Furthermore, we shall see how the adult neurogenesis is specifically subjected to experience-dependent modulation. In particular, we shall describe the sensitivity of the bulbar neurogenesis to the activity level of sensory inputs from the olfactory epithelium and, in turn, how this neurogenesis may adjust the neural network functioning to optimize odor information processing. Finally, we shall discuss the behavioral consequences of the bulbar neurogenesis and how it may be appropriate for the sense of smell. By maintaining a constitutive turnover of bulbar interneurons subjected to modulation by environmental cues, we propose that adult ongoing neurogenesis in the olfactory bulb is associated with improved olfactory memory. These recent findings not only provide new fuel for the molecular and cellular bases of sensory perception but should also shed light onto cellular bases of learning and memory.

Stem cell therapy for cerebral palsy

Cerebral palsy is a group of brain diseases which produce chronic motor disability in children. The causes are quite varied and range from abnormalities of brain development to birth-related injuries to postnatal brain injuries. Due to the increased survival of very premature infants, the incidence of cerebral palsy may be increasing. While premature infants and term infants who have suffered neonatal hypoxic-ischaemic (HI) injury represent only a minority of the total cerebral palsy population, this group demonstrates easily identifiable clinical findings, and much of their injury is to oligodendrocytes and the cerebral white matter. While the use of stem cell therapy is promising, there are no controlled trials in humans with cerebral palsy and only a few trials in patients with other neurologic disorders. However, studies in animals with experimentally induced strokes or traumatic injuries have indicated that benefit is possible. The potential to do these transplants via injection into the vasculature rather than directly into the brain increases the likelihood of timely human studies. As a result, variables appropriate to human experiments with intravascular injection of cells, such as cell type, timing of the transplant and effect on function, need to be systematically performed in animal models with HI injury, with the hope of rapidly translating these experiments to human trials.

Cellular replacement therapy for Parkinson's disease--where we are today?

The concept of replacing lost dopamine neurons in Parkinson's disease using mesencephalic brain cells from fetal cadavers has been supported by over 20 years of research in animals and over a decade of clinical studies. The ambitious goal of these studies was no less than a molecular and cellular "cure" for Parkinson's disease, other neurodegenerative diseases, and spinal cord injury. Much research has been done in rodents, and a few studies have been done in nonhuman primate models. Early uncontrolled clinical reports were enthusiastic, but the outcome of the first randomized, double blind, controlled study challenged the idea that dopamine replacement cells can cure Parkinson's disease, although there were some significant positive findings. Were the earlier animal studies and clinical reports wrong? Should we give up on the goal? Some aspects of the trial design and implantation methods may have led to lack of effects and to some side effects such as dyskinesias. But a detailed review of clinical neural transplants published to date still suggests that neural transplantation variably reverses some aspects of Parkinson's disease, although differing methods make exact comparisons difficult. While the randomized clinical studies have been in progress, new methods have shown promise for increasing transplant survival and distribution, reconstructing the circuits to provide dopamine to the appropriate targets and with normal regulation. Selected promising new strategies are reviewed that block apoptosis induced by tissue dissection, promote vascularization of grafts, reduce oxidant stress, provide key growth factors, and counteract adverse effects of increased age. New sources of replacement cells and stem cells may provide additional advantages for the future. Full recovery from parkinsonism appears not only to be possible, but a reliable cell replacement treatment may finally be near.