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Michael J Young

Publications and source records attributed to Michael J Young.

At least 19 recordsLinked to original sources
PubMed2007

Progenitor cells from the porcine neural retina express photoreceptor markers after transplantation to the subretinal space of allorecipients.

Work in rodents has shown that cultured retinal progenitor cells (RPCs) integrate into the degenerating retina, thus suggesting a potential strategy for treatment of similar degenerative conditions in humans. To demonstrate the relevance of the rodent work to large animals, we derived progenitor cells from the neural retina of the domestic pig and transplanted them to the laser-injured retina of allorecipients. Prior to grafting, immunocytochemical analysis showed that cultured porcine RPCs widely expressed neural cell adhesion molecule, as well as markers consistent with immature neural cells, including nestin, Sox2, and vimentin. Subpopulations expressed the neurodevelopmental markers CD-15, doublecortin, beta-III tubulin, and glial fibrillary acidic protein. Retina-specific markers expressed included the bipolar marker protein kinase Calpha and the photoreceptor-associated markers recoverin and rhodopsin. In addition, reverse transcription-polymerase chain reaction showed expression of the transcription factors Dach1, Hes1, Lhx2, Pax6, Six3, and Six6. Progenitor cells prelabeled with vital dyes survived as allografts in the subretinal space for up to 5 weeks (11 of 12 recipients) without exogenous immune suppression. Grafted cells expressed transducin, recoverin, and rhodopsin in the pig subretinal space, suggestive of differentiation into photoreceptors or, in a few cases, migrated into the neural retina and extended processes, the latter typically showing radial orientation. These results demonstrate that many of the findings seen with rodent RPCs can be duplicated in a large mammal. The pig offers a number of advantages over mice and rats, particularly in terms of functional testing and evaluation of the potential for clinical translation to human subjects. Disclosure of potential conflicts of interest is found at the end of this article.

Animals↗
PubMed2006

Sorbitol causes preferential selection of Muller glial precursors from late retinal progenitor cells in vitro.

PURPOSE: The replacement of glucose by sorbitol in growth medium causes selection of astroglial cells from heterogeneous primary cultures derived from the brains of newborn mice. The present study was undertaken to investigate the effects of sorbitol on in vitro selection of Müller glial precursors from expanded late retinal progenitor cells (RPCs). METHODS: RPCs used in these studies were isolated from the neural retina of postnatal day one green fluorescent protein (GFP) transgenic mice. The resulting GFP positive neurospheres were dissociated into a single cell suspension and grown on poly-D-lysine/laminin coated tissue culture flasks or slides to generate adherent RPCs. These adherent cells were treated with glucose free medium containing 25 mM sorbitol for 7 days and the expression of retinal-specific cell markers was determined by immunocytochemistry, reverse transcriptase polymerase chain reaction (RT-PCR) and immunoblot analysis RESULTS: In vitro studies showed that sorbitol treatment of late RPCs altered cellular morphology. Immunocytochemical studies showed an increase in the proportion of cells expressing glial cell markers, most of which co-expressed CRALBP, GFAP, and vimentin. An increase in the proportion of cells expressing PKCalpha, a bipolar cell marker, was also observed. RT-PCR analysis showed down-regulation of nestin transcripts with a concomitant increase in CRALBP, GFAP, vimentin and PKCalpha. These findings were confirmed by immunoblot analysis, where down-regulation of nestin expression with simultaneous up-regulation of CRALBP, GFAP and PKCalpha was observed. CONCLUSIONS: Sorbitol treatment of multipotent late RPCs, in the absence of glucose, results in the preferential selection of Müller glial precursors and their subsequent differentiation into cells that morphologically resemble Müller cells and co-express multiple glial markers.

Animals↗
PubMed2006

Coupling of the respiratory rhythm in fish with activity in hypobranchial nerves and with heartbeat.

Fish have a central respiratory pattern generator (CRPG) in the brain stem that initiates activity in a series of cranial nerves innervating respiratory muscles. These nerves burst sequentially in the order of their rostrocaudal distribution in the central nervous system. When respiratory drive is high, this activity spreads caudally to occipital and anterior spinal neurons that project via the hypobranchial nerves to stimulate hypaxial muscles, causing active jaw abduction. The CRPG may also recruit the heart. Fish, like mammals, show respiratory components in the intrinsic variability of heart rate (HRV). Cardiorespiratory synchrony in the dogfish is driven by bursting activity in the cardiac branches of the vagus nerve, which emanates from preganglionic neurons in the dorsal vagal motor nucleus. A respiratory component in HRV is difficult to discriminate in other species, requiring the use of power spectral analysis and the subsequent elimination of aliased components.

Animals↗
PubMed2006

A comparison of neural differentiation and retinal transplantation with bone marrow-derived cells and retinal progenitor cells.

Retinal progenitor cells (RPCs) are immature precursors that can differentiate into retinal neurons, including photoreceptors. Recently, it has been reported that bone marrow-derived cells may also be capable of differentiation into cells of central nervous system lineage, including retinal neurons. We compared these two cell types to evaluate their potential as a source of cells for retinal transplantation. Marrow stromal cells (MSCs) and macrophages were isolated from enhanced green fluorescence protein mice. MSCs were cultured with brain-derived neurotrophic factor, nerve growth factor, and basic fibroblast growth factor to induce neuronal differentiation. RPCs were cultured under the same conditions or with 10% fetal bovine serum. Neuronal marker expression was examined and compared between MSCs and RPCs. MSCs, macrophages, and RPCs were also cultured with explanted retinas from rhodopsin knockout mice to study their potential for retinal integration. MSCs expressed neuronal and retina-specific markers by reverse transcription-polymerase chain reaction and immunocytochemistry. Both types of cells migrated into retinal explants and expressed neurofilament 200, glial fibrillary acidic protein, protein kinase C-alpha, and recoverin. RPCs expressed rhodopsin, a photoreceptor marker we never detected in MSCs. A majority of bone marrow derived-macrophages differentiated into cells that resembled microglia, rather than neural cells, in the explanted retina. This study shows that RPCs are likely to be a preferred cell type for retinal transplantation studies, compared with MSCs. However, MSCs may remain an attractive candidate for autologous transplantation.

Animals↗
PubMed2006

Retinal progenitor cell xenografts to the pig retina: immunological reactions.

We evaluated the host response to murine retinal progenitor cells (RPCs) following transplantation to the subretinal space (SRS) of the pig. RPCs from GFP mice were transplanted subretinally in 18 nonimmunosuppressed normal or laser-treated pigs. Evaluation of the SRS was performed on hematoxylin-eosin (H&E)-stained sections. Serum samples were taken from naive and RPC-grafted pigs and mouse-reactive antibody responses were assessed. At 1 week, histology showed a few perivascular lymphocytes consistent with a mild retinal vasculitis, and depigmentation of the RPE with large numbers of mononuclear inflammatory cells in the choroid near the transplantation site. Large choroidal infiltrates were evident at 2-5 weeks. Serum from naive and RPC-xenografted pigs contained significant levels of preformed IgG and IgM antibodies against murine antigens. Xenogeneic RPCs transplanted to the porcine SRS induced mononuclear infiltration in the choroid with graft rejection occurring over 2-5 weeks. Serum analysis confirmed that mice and pigs are discordant species; however, a cell-mediated acute mechanism appears to be responsible, rather than an antibody-mediated rejection.

Animals↗
PubMed2006

Expanding an existing multiple choice test with a mixed format test: simulation study on sample size and item recovery in concurrent calibration.

When a new set of mixed format items is augmented with a previous old multiple-choice (MC) test, those mixed format items should be linked to the existing old MC test. This study used simulation to investigate sample size effect on recovery of known item parameter from the concurrent calibration in the context of horizontal equating, where the new mixed format tests are equated to the existing MC test which acts as the common linking items. In the partial credit model following the Andrich style parameterization, item location and item step parameters were differentially affected by the sample size. Item location parameters were recovered better than item step parameters at the individual item, the sub-test, and the total test level. This study also shows the outward bias for the item location parameter estimated by the maximum likelihood estimator.

Educational Measurement↗
PubMed2005

Stimulation of neurite outgrowth by neurotrophins delivered from degradable hydrogels.

Degradable hydrogels are useful vehicles for the delivery of growth factors to promote the regeneration of diseased or damaged tissue. In the central nervous system, there are many instances where the delivery of neurotrophins has great potential in tissue repair, especially for treatment of spinal cord injury. In this work, hydrogels based on poly(ethylene glycol) that form via a photoinitiated polymerization were investigated for the delivery of neurotrophins. The release kinetics of these factors are controlled by changes in the network crosslinking density, which influences neurotrophin diffusion and subsequent release from the gels with total release times ranging from weeks to several months. The release and activity of one neurotrophic factor, ciliary-neurotrophic factor (CNTF), was assessed with a cell-based proliferation assay and an assay for neurite outgrowth from retinal explants. CNTF released from a degradable hydrogel above an explanted retina was able to stimulate outgrowth of a significantly higher number of neurites than controls without CNTF. Finally, unique microsphere/hydrogel composites were developed to simultaneously deliver multiple neurotrophins with individual release rates.

Animals↗
PubMed2005

Expression of neurodevelopmental markers by cultured porcine neural precursor cells.

Despite the increasing importance of the pig as a large animal model, little is known about porcine neural precursor cells. To evaluate the markers expressed by these cells, brains were dissected from 60-day fetuses, enzymatically dissociated, and grown in the presence of epidermal growth factor, basic fibroblast growth factor, and platelet-derived growth factor. Porcine neural precursors could be grown as suspended spheres or adherent monolayers, depending on culture conditions. Expanded populations were banked or harvested for analysis using reverse transcription-polymerase chain reaction (RT-PCR), immunocytochemistry, microarrays, and flow cytometry, and results compared with data from analogous human forebrain progenitor cells. Cultured porcine neural precursors widely expressed neural cell adhesion molecule (NCAM), polysialic acid (PSA)-NCAM, vimentin, Ki-67, and Sox2. Minority subpopulations of cells expressed doublecortin, beta-III tubulin, synapsin I, glial fibrillary acidic protein (GFAP), and aquaporin 4 (AQP4) consistent with increased lineage restriction. A human microarray detected porcine transcripts for nogoA (RTN4) and stromal cell-derived factor 1 (SDF1), possibly cyclin D2 and Pbx1, but not CD133, Ki-67, nestin, or nucleostemin. Subsequent RT-PCR showed pig forebrain precursors to be positive for cyclin D2, nucleostemin, nogoA, Pbx1, vimentin, and a faint band for SDF1, whereas no signal was detected for CD133, fatty acid binding protein 7 (FABP7), or Ki-67. Human forebrain progenitor cells were positive for all the genes mentioned. This study shows that porcine neural precursors share many characteristics with their human counterparts and, thus, may be useful in porcine cell transplantation studies potentially leading to the application of this strategy in the setting of nervous system disease and injury.

Animals↗
PubMed2005

Retinal progenitor cell xenografts to the pig retina: morphologic integration and cytochemical differentiation.

OBJECTIVE: To investigate the survival, integration, and differentiation of mouse retinal progenitor cells after transplantation to the subretinal space of adult pigs. METHODS: Green fluorescent protein-positive (GFP+) murine retinal progenitor cells were transplanted subretinally as single cells, spheres, or biodegradable polymer-progenitor composites into 24 nonimmunosuppressed adult pigs. Of these, 14 pigs received laser lesions (n = 11) or outer retinal scraping injury (n = 3). Recipients were killed at 30 minutes to 5 weeks after grafting. RESULTS: The GFP+ murine retinal progenitor cells survived well for up to 14 days after transplantation to the pig retina. After 5 weeks, fewer GFP+ cells were found. In the pigs that received laser treatment before grafting of cell suspension, GFP+ cells integrated into the retinal pigment epithelium and all layers of the retina. The GFP+ cells exhibited morphologic evidence of differentiation into mature retinal neurons, although evaluation of marker expression found only nestin and glial fibrillary acidic protein colocalization. In noninjured pigs, cells mainly integrated into the retinal pigment epithelium. In pigs that received composites, cells appeared to mature and extended processes through pores in the polymer matrix. CONCLUSIONS: Retinal progenitor cell xenografts survive for a sufficiently long period to integrate into areas of injury and exhibit morphologic differentiation. By 5 weeks, survival diminishes. Biodegradable polymers may be useful for transplanting retinal progenitor cells in a structurally organized manner. Clinical Relevance Central nervous system (CNS) diseases may cause long-term disabilities. Substantial tissue destruction can be sustained by the complex structures of the brain, spinal cord, or retina without loss of life, yet the lack of effective CNS regeneration frequently results in disruption of activities of daily living and marked degradation in quality of life. It has become clear that an enormous potential for repair is present within the mammalian CNS. The challenge is to harness this potential to treat disease. Transplantation of neuronal tissue to the CNS represents a promising, albeit challenging, approach to the replacement of neurons lost owing to injury or disease.

Absorbable Implants↗
PubMed2005

Effects of ciliary neurotrophic factor on differentiation of late retinal progenitor cells.

Ciliary neurotrophic factor (CNTF) has been shown to be a potent regulator of retinal cell differentiation. The present study was undertaken to investigate the effects of CNTF on in vitro differentiation of expanded late retinal progenitor cells. Retinal progenitor cells used in these studies were isolated from the neural retina of postnatal day-1 green fluorescent protein (GFP) transgenic mice. The resulting GFP-positive neurospheres were dissociated into a single-cell suspension and grown on poly-D-lysine/laminin-coated tissue culture flasks or slides to generate adherent retinal progenitor cells. These adherent cells were treated with 20 ng/ml of CNTF for up to 14 days, and expression of specific retinal cell markers was determined by immunocytochemistry, reverse transcription-polymerase chain reaction (RT-PCR), and immunoblot analysis. In vitro studies showed that CNTF treatment of late retinal progenitor cells resulted in changes in cellular morphology. Immunocytochemical studies showed an increase in the proportion of cells expressing markers of bipolar cells but not rod differentiation. In addition, an increase in the proportion of cells expressing glial cell markers was observed. RT-PCR analysis showed downregulation in Hes1, Nestin, Notch1, and Pax6 transcripts along with a concomitant increase in protein kinase C (PKC) alpha and glial fibrillary acidic protein (GFAP) transcripts. These findings were confirmed by immunoblot analysis, where downregulation in Nestin expression and simultaneous upregulation in PKC alpha and GFAP were observed. The data indicate that CNTF treatment of multipotential late retinal progenitors increases the proportion of cells that express markers of bipolar neurons and glia.

Animals↗
PubMed2004

Isolation of retinal progenitor cells from post-mortem human tissue and comparison with autologous brain progenitors.

The goal of the present study was threefold: to determine whether viable human retinal progenitor cells (hRPCs) could be obtained from cadaveric retinal tissue, to evaluate marker expression by these cells, and to compare hRPCs to human brain progenitor cells (hBPCs). Retinas were dissected from post-mortem premature infants, enzymatically dissociated, and grown in the presence of epidermal growth factor and basic fibroblast growth factor. The cells grew as suspended spheres or adherent monolayers, depending on culture conditions. Expanded populations were banked or harvested for analysis by RT-PCR, immunocytochemistry, and flow cytometry. hBPCs derived from forebrain specimens from the same donors were grown and used for RT-PCR. Post-mortem human retinal specimens yielded viable cultures that grew to confluence repeatedly, although not beyond 3 months. Cultured hRPCs expressed a range of markers consistent with CNS progenitor cells, including nestin, vimentin, Sox2, Ki-67, GD2 ganglioside, and CD15 (Lewis X), as well as the tetraspanins CD9 and CD81, CD95 (Fas), and MHC class I antigens. No MHC class II expression was detected. hRPCs, but not hBPCs, expressed Dach1, Pax6, Six3, Six6, and recoverin. Minority subpopulations of hRPCs and hBPCs expressed doublecortin, beta-III tubulin, and glial fibrillary acidic protein, which is consistent with increased lineage restriction in subsets of cultured cells. Viable progenitor cells can be cultured from the post-mortem retina of premature infants and exhibit a gene expression profile consistent with immature neuroepithelial cells. hRPCs can be distinguished from hBPC cultures by the expression of retinal specification genes and recoverin.

Antigens, Differentiation↗
PubMed2004

Stem cells and retinal repair.

Retinal stem cells (RSCs) are multipotent central nervous system (CNS) precursors that give rise to the retina during the course of development. RSCs are present in the embryonic eyecup of all vertebrate species and remain active in lower vertebrates throughout life. Mammals, however, exhibit little RSC activity in adulthood and thus little capacity for retinal growth or regeneration. Because CNS precursors can now be isolated from immature and mature mammals and expanded ex vivo, it is possible to study these cells in culture as well as following transplantation to the diseased retina. Such experiments have revealed a wealth of unanticipated findings, both in terms of the instructive cues present in the mature mammalian retina as well as the ability of grafted CNS precursors to respond to them. This review examines current knowledge regarding RSCs, together with other CNS precursors, from the perspective of investigators who wish to isolate, propagate, genetically modify, and transplant these cells as a regenerative strategy with application to retinal disease.

Animals↗
PubMed2004

Multipotent retinal progenitors express developmental markers, differentiate into retinal neurons, and preserve light-mediated behavior.

PURPOSE: To use progenitor cells isolated from the neural retina for transplantation studies in mice with retinal degeneration. METHODS: Retinal progenitor cells from postnatal day 1 green fluorescent protein-transgenic mice were isolated and characterized. These cells can be expanded greatly in culture and express markers characteristic of neural progenitor cells and/or retinal development. RESULTS: After they were grafted to the degenerating retina of mature mice, a subset of the retinal progenitor cells developed into mature neurons, including presumptive photoreceptors expressing recoverin, rhodopsin, or cone opsin. In rho-/- hosts, there was rescue of cells in the outer nuclear layer (ONL), along with widespread integration of donor cells into the inner retina, and recipient mice showed improved light-mediated behavior compared with control animals. CONCLUSIONS: These findings have implications for the treatment of retinal degeneration, in which neuronal replacement and photoreceptor rescue are major therapeutic goals.

Animals↗
PubMed2004

Pre-equating: a simulation study based on a large scale assessment model.

Although post-equating (PE) has proven to be an acceptable method in the scaling and equating of items and forms, there are times when the turn-around period for equating and converting raw scores to scale scores is so small that PE cannot be undertaken within the prescribed time frame. In such cases, pre-equating (PrE) could be considered as an acceptable alternative. Assessing the feasibility of using item calibrations from the item bank (as in PrE) is conditioned on the equivalency of the calibrations and the errors associated with it vis a vis the results obtained via PE. This paper creates item banks over three periods of item introduction into the banks and uses the Rasch model in examining data with respect to the recovery of item parameters, the measurement error, and the effect cut-points have on examinee placement in both the PrE and PE situations. Results indicate that PrE is a viable solution to PE provided the stability of the item calibrations are enhanced by using large sample sizes (perhaps as large as full-population) in populating the item bank.

Calibration↗
PubMed2003

The immunological properties of adult hippocampal progenitor cells.

Adult hippocampal progenitor cells (AHPCs) derived from mature rats were studied in mixed co-cultures and shown not to elicit a proliferative response from human peripheral blood mononuclear cells (PBMCs) or allogeneic spleen cells. FACS analysis revealed low class I and no detectable class II (Ia) MHC expression by these cells. RT-PCR showed that AHPCs express the anti-inflammatory cytokine TGF-beta1. AHPCs did not, however, significantly impede the proliferation of OKT3- or PHA-stimulated PBMCs. Taken together, these results indicate that AHPCs are non-immunogenic in vitro. This is consistent with their pattern of MHC expression and does not require an active immunosuppressive mechanism.

Animals↗
PubMed2003

Retinal transplantation of neural progenitor cells derived from the brain of GFP transgenic mice.

Neural progenitor cells isolated from the brains of neonatal GFP transgenic mice were grafted to the retina of RCS rats and rds and B6 mice. Expression of GFP and differentiation markers was evaluated at 1-4 weeks post-transplantation. Grafted cells maintained transgene expression throughout the 4-week period. At 1 week there was widespread migration of GFP+cells within the host retina and at 2 weeks evidence of neuronal differentiation (as shown by both marker expression and cell morphology), although integration at 4 weeks was limited to syngeneic recipients. Because brain-derived neural progenitor cells exhibit both neuronal and astrocytic differentiation in diseased and normal host retina, these cells provide a useful tool for studies of retinal regeneration.

Animals↗
PubMed2003

Expression of cytokines by multipotent neural progenitor cells.

Recent work with mammalian neural stem cells has highlighted the role of cytokine signaling in the proliferation and differentiation of these multipotent cells. While the responsiveness of neural progenitors to exogenously applied growth factors has been demonstrated in vivo as well as in vitro, little attention has been given to the production of cytokines by these cells. Here we use immunocytochemistry, RT-PCR, and ELISA to show that under standard growth conditions multipotent neural progenitor cells from humans express multiple cytokines including IL-1alpha, IL-1beta, IL-6, TGF-beta1, TGF-beta2, TNF-alpha, but not IL-2, IL-4, or IFN-gamma. Neural progenitor cells from rat and mouse express some, but not all, of these cytokines under similar conditions. While the function of cytokine expression by neural progenitor cells remains to be elucidated, these signaling molecules are known to be involved in neural development and may play a role in the activation of quiescent stem cells by a variety of pathological processes.

Animals↗