Protocol to optimize the Rice-Vannucci rat pup model of perinatal asphyxia to ensure predictable hypoxic-ischemic cerebral lesions.

The Rice-Vannucci model in rodent pups is subject to substantial loss of animals, result inconsistency, and high lab-to-lab variability in extent and composition of induced injury. This protocol allows for highly predictable and reproducible hypoxic-ischemic cerebral injury lesions in post-natal day 10 Wistar rat pups with no mortality. We describe steps for common carotid artery ligation, brief post-operative normothermia, exposure to hypoxia, and post-hypoxic normothermia. Precise timing and temperature control in each step are crucial for a successful procedure. For complete details on the use and execution of this protocol, please refer to Hartman et al.1.

Cross-talk between stem cells and the dysfunctional brain is facilitated by manipulating the niche: evidence from an adhesion molecule.

In the injured brain, the behavior of neural stem/progenitor cells (NSCs) is regulated by multiple converging factors encountered in the niche, which is composed of several neural and non-neural cell types. Signals emanating from the host influence the migration, survival, distribution, and fate of transplanted NSCs, which in turn can create host microenvironments that favor a return to homeostasis. We tested the hypothesis that overexpression of key facilitatory molecules that define the injury niche might enhance this bidirectional stem cell-host interaction to therapeutic advantage. As proof of concept, we investigated whether conditioning the niche with the neural cell adhesion molecule L1 might enhance recovery in a prototypical neurodegenerative milieu-the MPTP-induced model of Parkinson's disease in aged mice-where cross-talk between NSCs and imperiled host dopaminergic neurons is known to be pivotal in rescuing the function and connectivity of the latter. In lesioned mice (and in unlesioned controls), we overexpressed L1 in the NSCs to be transplanted into the ventral mesencephalon. Several pairwise experimental combinations were tested based on variations of engrafting L1 overexpressing versus nonoverexpressing NSCs into wild-type (WT) versus L1-overexpressing transgenic mice (specifically L1 transcribed from the GFAP promoter and, hence, overexpressed in host astrocytes). Enrichment for L1-particularly when expressed simultaneously in both donor NSCs and host brain-led to rapid and extensive distribution of exogenous NSCs, which in turn rescued (with an efficacy greater than in nonengineered controls) dysfunctional host dopaminergic nigral neurons, even when grafting was delayed by a month. L1 overexpression by NSCs also enhanced their own differentiation into tyrosine hydroxylase-expressing neurons in both WT and transgenic hosts. Graft-host interactions were thus favored by progressively increasing levels of L1. More broadly, this study supports the view that manipulating components of the niche (such as an adhesion molecule) that facilitate cross-talk between stem cells and the dysfunctional brain may offer new strategies for more efficacious neurotransplantation, particularly when treatment is delayed as in chronic lesions or advanced stages of a neurodegenerative disease.

Neural stem/progenitor cells initiate the formation of cellular networks that provide neuroprotection by growth factor-modulated antioxidant expression.

Recent studies indicate that transplanted neural stem/progenitor cells (NSPs) can interact with the environment of the central nervous system and stimulate protection and regeneration of host cells exposed to oxidative stress. Here, a set of animals grafted with NSPs and treated with 3-nitropropionic acid (3-NP) exhibited reduced behavioral symptoms and less severe damage of striatal cytoarchitecture than sham transplanted controls including better survival of neurons. Sites of tissue sparing correlated with the distribution pattern of donor cells in the host brain. To investigate the cellular and molecular bases of this phenomenon, we treated cocultures of NSPs and primary neural cell cultures with 3-NP to induce oxidative stress and to study NSP-dependent activation of antioxidant mechanisms and cell survival. Proactive presence of NSPs significantly improved cell viability by interfering with production of free radicals and increasing the expression of neuroprotective factors. This process was accompanied by elevated expression of ciliary neurotrophic factor (CNTF) and vascular endothelial growth factor (VEGF) in a network of NSPs and local astrocytes. Intriguingly, both in vitro and in vivo, enhanced growth factor secretion stimulated a robust upregulation of the antioxidant enzyme superoxide dismutase 2 (SOD2) in neurons and resulted in their improved survival. Our findings thus reveal a so far unrecognized mechanism of interaction between NSPs and surrounding cells accompanying neuroprotection: through mutual, NSP-triggered stimulation of growth factor production and activation of antioxidant mechanisms, cellular networks may shield the local environment from the arriving impact of oxidative stress.

Plasticity of the central nervous system and formation of "auxiliary niches" after stem cell grafting: an essay.

It is hoped that stem cell biology will play a major role in the treatment of a number of so far incurable diseases via transplantation therapy. Today, we know that neural stem cell grafts not only represent a valuable source of missing cells and molecules for the host nervous system, but they also bring with them biological principles and processes assuring tissue plasticity and homeostasis found in early development and in postnatal neurogenic areas. In this review, we discuss the potential of grafted neural stem/progenitor cells to induce plasticity in the adult diseased brain by mimicking the cellular and molecular processes governing the biology of endogenous stem cell niches. If confirmed, such anlagen of "auxiliary niches" could help us to optimize intercellular communication in donor cell-initiated networks of graft-host interactions and to "rejuvenate" the adult nervous system in its response to disease and injury.

Neural stem cells display an inherent mechanism for rescuing dysfunctional neurons.

We investigated the hypothesis that neural stem cells (NSCs) possess an intrinsic capacity to "rescue" dysfunctional neurons in the brains of aged mice. The study focused on a neuronal cell type with stereotypical projections that is commonly compromised in the aged brain-the dopaminergic (DA) neuron. Unilateral implantation of murine NSCs into the midbrains of aged mice, in which the presence of stably impaired but nonapoptotic DA neurons was increased by treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was associated with bilateral reconstitution of the mesostriatal system. Functional assays paralleled the spatiotemporal recovery of tyrosine hydroxylase (TH) and dopamine transporter (DAT) activity, which, in turn, mirrored the spatiotemporal distribution of donor-derived cells. Although spontaneous conversion of donor NSCs to TH(+) cells contributed to nigral reconstitution in DA-depleted areas, the majority of DA neurons in the mesostriatal system were "rescued" host cells. Undifferentiated donor progenitors spontaneously expressing neuroprotective substances provided a plausible molecular basis for this finding. These observations suggest that host structures may benefit not only from NSC-derived replacement of lost neurons but also from the "chaperone" effect of some NSC-derived progeny.

Graft/host relationships in the developing and regenerating CNS of mammals.

A new light was shed on the utility of neural grafts when it was recognized that donor tissues and cells offer more than a source of immature progenitors potentially capable of cell replacement: First, they have the inherent capacity to produce multiple trophic and tropic factors promoting cell survival and tissue plasticity often characteristic of the immature central nervous system (CNS). Second, by their interaction with the host microenvironment via cell/cell and cell/ECM interactions, these grafts are capable of re-establishing homeostasis, which can be, for example, reflected in rescue and protection of host elements from harmful influences. This second capacity of donor cells relies, in part, also on a "dormant" but still present regenerative capacity of mature or even aged CNS and on the possibility of its mobilization in the damaged nervous system by neural grafts. For this to occur efficiently after transplantation, a bi-directional dialogue between donor and host cells must gradually be established, in which both "partners" transmit signals (cell/cell contact, molecular messengers), "listen to" and "understand" each other and are able to react by modifying their own plasticity- and development-related programs. Thus, for the best possible recovery of functionality in the injured adult and aged nervous system, neurotransplantation must always try to find optimal conditions for all three of the mentioned qualities of neural grafts, especially for the protection and/or reactivation of neural circuitry embedded in non-neurogenic CNS areas. Once fully understood, this newly recognized aspect of neurotransplantation (and topic of this review) might, someday, even allow the recovery of systems that would otherwise be doomed, such as cognition- and experience-related circuitry.

Grafted neural stem cells shield the host environment from oxidative stress.

Here, we present our preliminary data showing that neural stem cells (NSCs) can prevent the degeneration of striatal neurons when transplanted into the CNS prior to intoxication with 3-nitropropionic acid (3-NP). In the adult CNS, the number of NSCs, a major source of neural cell populations and plasticity-modulating factors, is relatively low if compared to that of the developing brain. This, together with the adult growth-inhibitory environment, limits its regenerative capacity. Our recent observation has shown that grafted NSCs may rescue/protect neurons in the chronically impaired mesostriatal system. On the basis of this study and because we were also intrigued by our recent observations regarding the rescue/protective role of NSCs in vitro, we decided to test the hypothesis that grafted NSCs can also be deposited preventively in the CNS (and perhaps join the pool of endogenous NSCs of the intact host brain) for later buffering and maintenance of homeostasis when the host is exposed to oxidative stress.

The miniature pig as an animal model in biomedical research.

Crucial prerequisites for the development of safe preclinical protocols in biomedical research are suitable animal models that would allow for human-related validation of valuable research information gathered from experimentation with lower mammals. In this sense, the miniature pig, sharing many physiological similarities with humans, offers several breeding and handling advantages (when compared to non-human primates), making it an optimal species for preclinical experimentation. The present review offers several examples taken from current research in the hope of convincing the reader that the porcine animal model has gained massively in importance in biomedical research during the last few years. The adduced examples are taken from the following fields of investigation: (a) the physiology of reproduction, where pig oocytes are being used to study chromosomal abnormalities (aneuploidy) in the adult human oocyte; (b) the generation of suitable organs for xenotransplantation using transgene expression in pig tissues; (c) the skin physiology and the treatment of skin defects using cell therapy-based approaches that take advantage of similarities between pig and human epidermis; and (d) neurotransplantation using porcine neural stem cells grafted into inbred miniature pigs as an alternative model to non-human primates xenografted with human cells.

Graft-induced plasticity in the mammalian host CNS.

In this review we trace back the history of an idea that takes a new approach in restorative neurotransplantation by focusing on the "multifaceted dialogue" between graft and host and assigns a central role to graft-evoked host plasticity. In several experimental examples ranging from the transfer of solid fetal tissue grafts into mechanical cortical injuries to deposits of neural stem cells into hemisectioned spinal cord. MPTP-damaged substantia nigra or mutant cerebella supportive evidence is provided for the hypothesis, that in many CNS disorders regeneration of the host CNS can be achieved by taking advantage of the inherent capacity of neural grafts to induce protective and restorative mechanisms within the host. This principle might once allow us to spare even complex circuitry from neurodegeneration.

Behavioral improvement in a primate Parkinson's model is associated with multiple homeostatic effects of human neural stem cells.

Stem cells have been widely assumed to be capable of replacing lost or damaged cells in a number of diseases, including Parkinson's disease (PD), in which neurons of the substantia nigra (SN) die and fail to provide the neurotransmitter, dopamine (DA), to the striatum. We report that undifferentiated human neural stem cells (hNSCs) implanted into 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated Parkinsonian primates survived, migrated, and had a functional impact as assessed quantitatively by behavioral improvement in this DA-deficit model, in which Parkinsonian signs directly correlate to reduced DA levels. A small number of hNSC progeny differentiated into tyrosine hydroxylase (TH) and/or dopamine transporter (DAT) immunopositive cells, suggesting that the microenvironment within and around the lesioned adult host SN still permits development of a DA phenotype by responsive progenitor cells. A much larger number of hNSC-derived cells that did not express neuronal or DA markers was found arrayed along the persisting nigrostriatal path, juxtaposed with host cells. These hNSCs, which express DA-protective factors, were therefore well positioned to influence host TH+ cells and mediate other homeostatic adjustments, as reflected in a return to baseline endogenous neuronal number-to-size ratios, preservation of extant host nigrostriatal circuitry, and a normalizing effect on alpha-synuclein aggregation. We propose that multiple modes of reciprocal interaction between exogenous hNSCs and the pathological host milieu underlie the functional improvement observed in this model of PD.

Increased "vigilance" of antioxidant mechanisms in neural stem cells potentiates their capability to resist oxidative stress.

Although the potential value of transplanted and endogenous neural stem cells (NSCs) for the treatment of the impaired central nervous system (CNS) has widely been accepted, almost nothing is known about their sensitivity to the hostile microenvironment in comparison to surrounding, more mature cell populations. Since many neuropathological insults are accompanied by oxidative stress, this report compared the alertness of antioxidant defense mechanisms and cell survival in NSCs and postmitotic neural cells (PNCs). Both primary and immortalized cells were analyzed. At steady state, NSCs distinguished themselves in their basal mitochondrial metabolism from PNCs by their lower reactive oxygen species (ROS) levels and higher expression of the key antioxidant enzymes uncoupling protein 2 (UCP2) and glutathione peroxidase (GPx). Following exposure to the mitochondrial toxin 3-nitropropionic acid, PNC cultures were marked by rapidly decreasing mitochondrial activity and increasing ROS content, both entailing complete cell loss. NSCs, in contrast, reacted by fast upregulation of UCP2, GPx, and superoxide dismutase 2 and successfully recovered from an initial deterioration. This recovery could be abolished by specific antioxidant inhibition. Similar differences between NSCs and PNCs regarding redox control efficiency were detected in both primary and immortalized cells. Our first in vivo data from the subventricular stem cell niche of the adult mouse forebrain corroborated the above observations and revealed strong baseline expression of UCP2 and GPx in the resident, proliferating NSCs. Thus, an increased "vigilance" of antioxidant mechanisms might represent an innate characteristic of NSCs, which not only defines their cell fate, but also helps them to encounter oxidative stress in diseased CNS.

Acute injury directs the migration, proliferation, and differentiation of solid organ stem cells: evidence from the effect of hypoxia-ischemia in the CNS on clonal "reporter" neural stem cells.

Clonal neural cells with stem-like features integrate appropriately into the developing and degenerating central and peripheral nervous system throughout the neuraxis. In response to hypoxic-ischemic (HI) injury, previously engrafted, integrated, and quiescent clonal neural stem cells (NSCs) transiently re-enter the cell cycle, migrate preferentially to the site of ischemia, and differentiate into neurons and oligodendrocytes, the neural cell types typically lost following HI brain injury. They also replenish the supply of immature uncommitted resident stem/progenitor cells. Although they yield astrocytes, scarring is inhibited. These responses appear to occur most robustly within a 3-7 day "window" following HI during which signals are elaborated that upregulate genetic programs within the NSC that mediate proliferation, migration, survival, and differentiation, most of which appear to be terminated once the "window closes" and the chronic phase ensues, sending the NSCs into a quiescent state. These insights derived from using the stem cell in a novel role--as a "reporter" cell--to both track and probe the activity of endogenous stem cells as well as to "interrogate" and "report" the genes differentially induced by the acutely vs. chronically injured milieu. NSCs may be capable of the replacement of cells, genes, and non-diffusible factors in both a widespread or more circumscribed manner (depending on the therapeutic demands of the clinical situation). They may be uniquely responsive to some types of neurodegenerative conditions. We submit that these various capabilities are simply the normal expression of the basic homeostasis-preserving biologic properties and attributes of a stem cell which, if used rationally and in concert with this biology, may be exploited for therapeutic ends.

Multifaceted dialogue between graft and host in neurotransplantation.

Current restorative neurotransplantation research focuses mainly on the potential of the neural graft to replace damaged or missing cell populations and to deliver needed gene products in the form of transgenes. Because of this graft-oriented bias of the procedure, possible dormant regenerative capabilities within the host have been largely underestimated and dismissed as insignificant. This review discusses existing evidence that neural grafts can have stimulating effects on host-intrinsic plasticity that can help regeneration of the mammalian central nervous system. If confirmed, the synergistic interaction between graft and host might substantially enhance our therapeutic possibilities.

Functional recovery following traumatic spinal cord injury mediated by a unique polymer scaffold seeded with neural stem cells.

To better direct repair following spinal cord injury (SCI), we designed an implant modeled after the intact spinal cord consisting of a multicomponent polymer scaffold seeded with neural stem cells. Implantation of the scaffold-neural stem cells unit into an adult rat hemisection model of SCI promoted long-term improvement in function (persistent for 1 year in some animals) relative to a lesion-control group. At 70 days postinjury, animals implanted with scaffold-plus-cells exhibited coordinated, weight-bearing hindlimb stepping. Histology and immunocytochemical analysis suggested that this recovery might be attributable partly to a reduction in tissue loss from secondary injury processes as well as in diminished glial scarring. Tract tracing demonstrated corticospinal tract fibers passing through the injury epicenter to the caudal cord, a phenomenon not present in untreated groups. Together with evidence of enhanced local GAP-43 expression not seen in controls, these findings suggest a possible regeneration component. These results may suggest a new approach to SCI and, more broadly, may serve as a prototype for multidisciplinary strategies against complex neurological problems.

Stem cells: cross-talk and developmental programs.

The thesis advanced in this essay is that stem cells-particularly those in the nervous system-are components in a series of inborn 'programs' that not only ensure normal development, but persist throughout life so as to maintain homeostasis in the face of perturbations-both small and great. These programs encode what has come to be called 'plasticity'. The stem cell is one of the repositories of this plasticity. This review examines the evidence that interaction between the neural stem cell (as a prototypical somatic stem cell) and the developing or injured brain is a dynamic, complex, ongoing reciprocal set of interactions where both entities are constantly in flux. We suggest that this interaction can be viewed almost from a 'systems biology' vantage point. We further advance the notion that clones of exogenous stem cells in transplantation paradigms may not only be viewed for their therapeutic potential, but also as biological tools for 'interrogating' the normal or abnormal central nervous system environment, indicating what salient cues (among the many present) are actually guiding the expression of these 'programs'; in other words, using the stem cell as a 'reporter cell'. Based on this type of analysis, we suggest some of the relevant molecular pathways responsible for this 'cross-talk' which, in turn, lead to proliferation, migration, cell genesis, trophic support, protection, guidance, detoxification, rescue, etc. This type of developmental insight, we propose, is required for the development of therapeutic strategies for neurodegenerative disease and other nervous system afflictions in humans. Understanding the relevant molecular pathways of stem cell repair phenotype should be a priority, in our view, for the entire stem cell field.