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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. Disclosure of potential conflicts of interest is found at the end of this article.

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.

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.

This chapter reviews some of the work that has been performed in animal models of CNS diseases, where transplanted neural stem cells (NSCs) have mediated a therapeutic effect. Despite the presence of endogenous NSCs in the mammalian brain, it is recognized that intrinsic “self-repair” activity for the most devastating of injuries is inadequate or ineffective. This poor “regenerative” ability, particularly in the adult CNS, may be because of the limited number and restricted location of native NSCs and/or limitations imposed by the surrounding microenvironment, which may not be supportive or instructive for neuronal differentiation. Several transplantation experiments have suggested that neurogenic cues are transiently elaborated during degenerative processes and that exogenous NSCs are able to sense, home in, and respond appropriately. Neural stem cells display extensive tropism for pathology in an adult brain and can express bioactive genes within such pathological situations: evidence from intracranial gliomas. NSCs migrate extensively throughout a brain tumor mass in vivo and “trail” advancing tumor cells. A major requirement for the better use of NSCs is a better understanding of the pathophysiology of the diseases to be targeted—that is, knowing what aspects require repair and which cell type or types require replacement or rescue. A better understanding of fundamental NSC biology is required before human NSCs can be transplanted efficaciously in true clinical settings.

Pigs and miniature pigs are steadily gaining importance as large animal models in the field of regenerative medicine, including stem cell research. With their size, organ capacity, and physiology resembling in several aspects that of humans, pigs are well suited for preclinical experiments and long-term safety studies. In this chapter, we summarize our experience with the isolation and culture of several somatic stem cell populations from fetal and adult pig tissue and briefly review their potential usefulness in future stem cell-based therapies. We also provide protocols for the isolation of fetal porcine neural stem cells (NSCs), adult bone marrow mesenchymal stem cells (MSCs), and epidermal progenitor cells (EPCs) from adult hair follicles.

Approximately two decades ago, it became evident that the developing and adult mammalian central nervous system (CNS) contained a population of neural stem cells (NSCs). These immature, undifferentiated, multipotent cells could be isolated, expanded, and used as cellular vectors for the treatment of neurodegenerative and demyelinating diseases. Their potential as therapeutic agents in a wide range of CNS and peripheral nervous system (PNS) disorders is beginning to be understood. NSCs may give rise to more committed progenitors, such as oligodendrocyte progenitor cells (OPCs), that may also be used as reparative cells. As the “repair” mechanisms by which NSCs act begin to be better elucidated, new therapies may emerge.

A new light was shed on the utility of neural grafts when it was rec- ognized that donor tissues and cells offer more than a source of immature pro- genitors 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 sys- tem (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 re- lies, in part, also on a "dormant" but still present regenerative capacity of ma- ture 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 transplanta- tion, a bi-directional dialogue between donor and host cells must gradually be established, in which both "partners" transmit signals (cell/cell contact, molec- ular 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 condi- tions 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 neurotrans- plantation (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.

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.

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.

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.