Mouse trisomy 16 neurons, a model of human trisomy 21 (Down syndrome), can be maintained by intracerebral transplantation

Xenogeneic Cell Therapy: Current Progress and Future Developments in Porcine Cell Transplantation

The multitude of distinct cell types present in mature and developing tissues display unique physiologic characteristics. Cellular therapy is a novel technology with the promise of utilizing this diversity to treat a wide range of human degenerative diseases. Intractable diseases, disorders, and injuries are characterized by cell death or aberrant cellular function. Cell transplantation can replace diseased or lost tissue to provide restorative therapy for these conditions. The limited use of cell transplants as a basis for current therapy can, in part, be attributed to the lack of available human cells suitable for transplantation. This has prevented further realization of the promise of cell transplantation as a platform technology. Accordingly, cell-based therapies such as blood transfusions, for which the cells are readily available, are a standard part of current medical practice. Despite numerous attempts to expand primary human cells in tissue culture, current technological limitations of this approach in regard to proliferative capacity and maintenance of the differentiated phenotype has prevented their use for transplantation. Further, use of human stem cells for the derivation of specific cell types for transplantation is an area of future application with great potential, but hurdles remain in regard to deriving and sufficiently expanding these multi-potential cells. Thus, it appears that primary cells are at present a superior source for transplantation. This review focuses on pigs as a source of a variety of primary cells to advance cell therapy to the clinic and implement achievement of its full potential. We outline the advantages and disadvantages of xenogeneic cell therapy while underscoring the utility of transplantable porcine cells for the treatment of human disease. © 1998 Elsevier Science Inc.

On the cause of mental retardation in Down syndrome: extrapolation from full and segmental trisomy 16 mouse models

Down syndrome (DS, trisomy 21, Ts21) is the most common known cause of mental retardation. In vivo structural brain imaging in young DS adults, and post-mortem studies, indicate a normal brain size after correction for height, and the absence of neuropathology. Functional imaging with positron emission tomography (PET) shows normal brain glucose metabolism, but fewer significant correlations between metabolic rates in different brain regions than in controls, suggesting reduced functional connections between brain circuit elements. Cultured neurons from Ts21 fetuses and from fetuses of an animal model for DS, the trisomy 16 (Ts16) mouse, do not differ from controls with regard to passive electrical membrane properties, including resting potential and membrane resistance. On the other hand, the trisomic neurons demonstrate abnormal active electrical and biochemical properties (duration of action potential and its rates of depolarization and repolarization, altered kinetics of active Na(+), Ca(2+) and K(+) currents, altered membrane densities of Na(+) and Ca(2+) channels). Another animal model, the adult segmental trisomy 16 mouse (Ts65Dn), demonstrates reduced long-term potentiation and increased long-term depression (models for learning and memory related to synaptic plasticity) in the CA1 region of the hippocampus. Evidence suggests that the abnormalities in the trisomy mouse models are related to defective signal transduction pathways involving the phosphoinositide cycle, protein kinase A and protein kinase C. The phenotypes of DS and its mouse models do not involve abnormal gene products due to mutations or deletions, but result from altered expression of genes on human chromosome 21 or mouse chromosome 16, respectively. To the extent that the defects in signal transduction and in active electrical properties, including synaptic plasticity, that are found in the Ts16 and Ts65Dn mouse models, are found in the brain of DS subjects, we postulate that mental retardation in DS results from such abnormalities. Changes in timing and synaptic interaction between neurons during development can lead to less than optimal functioning of neural circuitry and signaling then and in later life.

Decreased sensitivity to nerve growth factor of dorsal root ganglion neurons cultured from mouse trisomy 16, a model of Down's syndrome

The effect of NGF was studied on the adhesion of mouse dorsal root ganglion (DRG) neurons to a laminin-coated surface and on their subsequent survival in primary culture. DRG neurons were obtained both from normal diploid mice and trisomy 16 mice. The latter are considered a model of human trisomy 21, Down's syndrome. Whereas both diploid and trisomy DRG neurons depended on NGF for adhesion, the sensitivity of trisomy 16 neurons to NGF was significantly reduced (P < 0.05). This suggests that excess expression of genes on mouse chromosome 16 alters NGF-regulated adhesion to laminin. Survival of neurons that had attached to laminin in culture did not appear dependent on NGF for either diploid or trisomy 16 neurons.

Long-term intracerebral transplants of fetal hippocampus from mouse trisomy 16, a model for Down's syndrome (trisomy 21), do not exhibit Alzheimer's disease neuropathology by ultrastructural criteria

Murine trisomy 16 (Ts16) is an animal model for Down's syndrome (human trisomy 21), because mouse chromosome 16 is genetically homologous to human chromosome 21. Down's syndrome patients, older than 35 years, demonstrate the neuropathological and neurochemical defects characteristic of Alzheimer's disease and Ts16 mouse fetuses exhibit phenotypic abnormalities similar to those in Down's syndrome fetuses. Trisomic mouse fetuses, however, die in utero, and so do not survive long enough for their brains to develop the degenerative changes of aging. This can be overcome by grafting the fetal Ts16 hippocampus (an early site for the development of the pathological features characteristic of Alzheimer's disease), into the cerebral ventricle or striatum of a normal adult mouse host. We have made such transplants, which have survived for up to 12 months. Examining these grafts ultrastructurally at various stages from 1 to 12 months, and comparing them with normal control grafts, reveals no structural difference that could be deemed characteristic of Alzheimer disease; no neurofibrillary tangle or senile plaque was observed. These observations, together with the normal structure of the neuronal organelles in trisomic hippocampal tissue, suggest that trisomic mouse grafts are not a useful model for Alzheimer's disease, despite earlier reports to the contrary.

Probing modifications of the neuronal cytoskeleton

The prominent death of central neurons in Alzheimer's and Parkinson's is reflected by changes in cell shape and by the formation of characteristic cytoskeletal inclusions (neurofibrillary tangles, Lewy bodies). This review focuses on the biology of neurofilaments and microtubule-associated proteins and identifies changes that can occur to these elements from basic and clinical research perspectives. Attention is directed at certain advances in neurobiology that have been especially integral to the identification of epitope domains, protein isoforms, and posttranslational (phosphorylation) events related to the composition, development, and structure of the common cytoskeletal modifications. Recently, a number of experimental strategies have emerged to simulate the aberrant changes in neurodegenerative disorders and gain insight into possible molecular events that contribute to alterations of the cytoskeleton. Descriptions of specific systems used to induce modifications are presented. In particular, unique neural transplantation methods in animals have been used to probe possible molecular and cellular conditions concerned with abnormal cytoskeletal changes in neurons.

Long-term transplants of mouse trisomy 16 hippocampal neurons, a model for Down's syndrome, do not develop Alzheimer's disease neuropathology

Hippocampal tissue from embryonic day 15-17 fetal mice, euploid or trisomic for chromosome 16, was transplanted into the striatum or the lateral ventricle of 6-8 week old female C57B1/6 mice. After 6-14 months of survival, host brains were sectioned and the grafts were examined by histochemical techniques and by immunocytochemistry for antigens present in pathological brain structures of Alzheimer's disease (AD) patients. Nissl-stained grafts contained aggregations of neurons similar to the pyramidal or the granule cell layers of the normal adult mouse hippocampus. No obvious morphological difference was detected between trisomic and control transplants. The monoclonal antibody Alz-50, which recognizes the paired helical filaments characteristic of AD, or an antibody raised to beta-amyloid peptide, did not reveal neurodegeneration in these grafts. Antibodies against ubiquitin, 200 kDa subunit of neurofilament, alpha 1-antichymotrypsin and tau also did not demonstrate AD-type immunoreactivity in the trisomic or control grafts. Thioflavin S- or silver stained-sections were also negative. We conclude that transplanted hippocampal tissue from the trisomy 16 mouse does not represent an animal model for AD-type neurodegeneration. These results differ from those of Richards et al., EMBO J. (10) (1991) 297-303, who reported AD-type degeneration in trisomy 16 hippocampal transplants.

Correlation of increased levels of class I MHC H-2Kk in the placenta of murine trisomy 16 conceptuses with structural abnormalities revealed by magnetic resonance microscopy

Murine trisomy 16 (mts16) placentas and fetuses, 17-day gestation age, were examined histologically and by magnetic resonance imaging at 9.4 T and compared with control littermate tissues. Placentas were studied by immunohistochemical methods, at 15-days gestational age, for expression of the major histocompatibility complex (MHC) class I H-2Kk cell surface marker. Immunohistochemical studies revealed a markedly increased expression of the MHC marker H-2Kk on cells in the labyrinth of the placenta of mts16. There were differences between the magnetic resonance (MR) images of the trisomic and normal placentas, which may be correlated with the increased expression of H-2Kk in the mts16 placental labyrinth. The decidual and labyrinthine components of the normal placentas showed similar high signal intensities (SI) while in trisomic placentas a marked high SI was characteristic only of the decidual region on proton spin density images. The MRI also revealed a smaller cerebellum in the ts16 fetuses. The potential effects of the compromised structure of the placental labyrinth and the overexpression of the H-2Kk marker on the mts16 neural and placental dysgenesis are discussed.

The neuropathology of Alzheimer's disease investigated by transplantation of mouse trisomy 16 hippocampal tissues

This article evaluates the novel application of neural transplantation as a model for studying the neuropathological events associated with Alzheimer's disease and those that have subsequently also been observed in Trisomy 21 (Down syndrome).