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Biomedical subjects

M J Young

Publications and source records attributed to M J Young.

At least 19 recordsLinked to original sources
PubMed2007

Neuroprotection of retinal ganglion cells in DBA/2J mice with GDNF-loaded biodegradable microspheres.

This study aims to promote long-term retinal ganglion cell (RGC) survival in a spontaneous glaucoma model by injecting slow-release Poly(DL-lactide-co-glycolide) (PLGA) microspheres containing glial cell line-derived neurotrophic factor (GDNF) into the vitreous. Microspheres (1 microL) suspended in PBS were injected in ipsilateral eyes while contralateral eyes served as untreated controls. Mice were injected at 2 months intervals (1-4 injections) depending on the protocol. ELISA assay indicated a cumulative GDNF release of 35.4 ng/mg over 71 days. The release was nonlinear with an initial burst of over 50%. Mice displayed a 30% drop in RGC density by 8 months (p = 0.013) and 80% drop by 10 months (p < 0.01). GDNF delivery increased RGC survival in all groups. Mice receiving early treatment showed up to 3.5 times greater RGC density than untreated mice at 15 months survival (p < 0.05). No significant effect was found in sham or lens injury groups. Microsphere-delivered GDNF significantly increases long-term RGC survival in a spontaneous glaucoma model, although the nonlinear release kinetics suggest that burst release may play a role in this rescue. Neuroprotection with slow-release polymers with improved release kinetics should be further studied as a potential therapy for glaucoma and other diseases involving the loss of central nervous system neurons.

Animals↗
PubMed2005

Fabrication of degradable polymer scaffolds to direct the integration and differentiation of retinal progenitors.

Retinal progenitor cells (RPCs) are self-renewing cells capable of differentiating into the different retinal cell types including photoreceptors, and they have shown promise as a source of replacement cells in experimental models of retinal degeneration. We hypothesized that a biodegradable polymer scaffold could deliver these cells to the subretinal space in a more organized manner than bolus injections, while also providing the graft with laminar organization and structural guidance channels. We fabricated highly porous scaffolds from blends of poly(L-lactic acid) and poly(lactic-co-glycolic acid) using a variety of techniques to produce pores oriented normal to the plane of the scaffold. RPCs were seeded on the polymer scaffolds and cultured for 14 days. Seeded scaffolds were then either fixed for characterization or used in an explant or in vivo rat model. The scaffolds were fully covered by RPCs in 3 days. Attachment of RPCs to the polymer scaffold was associated with down-regulation of immature markers and up-regulation of markers of differentiation. This suggests that the scaffold may promote differentiation of RPCs. The seeded cells elaborated cellular processes and aligned in the scaffold in conjunction with degenerating retinal explants. The cells also exhibited morphologies consistent with photoreceptors including a high degree of polarization of the cells. This data suggests that the scaffold may be a means to assist in the promotion of photoreceptor phenotypes. Implantation of the seeded scaffold into the rat eye is associated with increased RPC survival. Taken together, these data suggest that these polymer scaffolds provide a useful means for delivering RPCs to the subretinal space and may assist in the formation of retinal cell phenotypes, although it is clear that more cues are needed to direct the differentiation of RPCs into functional photoreceptors.

Animals↗
PubMed2005

Neural progenitor cell transplants into the developing and mature central nervous system.

When developing cell transplant strategies to repair the diseased or injured central nervous system (CNS), it is essential to consider host-graft interactions and how they may influence the outcome of the transplants. Recent studies have demonstrated that transplanted neural progenitor cells (NPCs) can differentiate and integrate morphologically into developing mammalian retinas. Is the ability to differentiate and to undergo structural integration into the CNS unique to specific progenitor cells, or is this plasticity a function of host environment, or both? To address these issues we have used the developing retina of the Brazilian opossum and have compared the structural integration of brain and retinal progenitor cells transplanted into the eyes at different developmental stages. The Brazilian opossum, Monodelphis domestica, is a small pouchless marsupial native to South America. This animal's lack of a pouch and fetal-like nature at birth circumvents the need for in utero surgical procedures, and thus provides an ideal environment in which to study the interactions between developing host tissues and transplanted NPCs. To test whether NPCs affect visual function we transplanted adult hippocampal progenitor cells (AHPCs) into normal, healthy adult rat eyes and performed noninvasive functional recordings. Monitoring of the retina and optic nerve over time by electroretinography and pupillometry revealed no severe perturbation in visual function in the transplant recipient eyes. Taken together, our findings suggest that the age of the host environment can strongly influence NPC differentiation and that transplantation of neural progenitor cells may be a useful strategy aimed at treating neurodegeneration and pathology of the CNS.

Animals↗
PubMed2004

Effects of culturing on the population structure of a hyperthermophilic virus.

The existence of a culturing bias has long been known when sampling organisms from the environment. This bias underestimates microbial diversity and does not accurately reflect the most ecologically relevant species. Until now no study has examined the effects of culture bias on viral populations. We have employed culture-independent methods to assess the diversity of Sulfolobus spindle-shaped viruses (SSVs) from extremely hyperthermal environments. This diversity is then compared to the viral diversity of cultured samples. We detected a clear culturing bias between environmental samples and cultured isolates. This is the first study identifying a culture bias in a viral population.

Archaeal Viruses↗
PubMed2004

Transplantation of neural progenitor cells into the developing retina of the Brazilian opossum: an in vivo system for studying stem/progenitor cell plasticity.

In developing cell transplant strategies to repair the diseased or injured retina is essential to consider host-graft interactions and how they may influence the outcome of the transplants. In the present study we evaluated the influence of the host microenvironment upon neural progenitor cells (NPCs) transplanted into the developing and mature retina of the Brazilian opossum, Monodelphis domestica. Monodelphis pups are born in an extremely immature state and the neonatal pups provide a fetal-like environment in which to study the interactions between host tissues and transplanted NPCs. Three different populations of GFP-expressing NPCs were transplanted by intraocular injection in hosts ranging in age from 5 days postnatal to adult. Extensive survival, differentiation and morphological integration of NPCs were observed within the developing retina. These results suggest that the age of the host environment can strongly influence NPC differentiation and integration.

Animals↗
PubMed2003

Effects of the cowpea chlorotic mottle bromovirus beta-hexamer structure on virion assembly.

The X-ray crystal structure of Cowpea chlorotic mottle bromovirus (CCMV) revealed a unique tubular structure formed by the interaction of the N-termini from six coat protein subunits at each three-fold axis of the assembled virion. This structure, termed the beta-hexamer, consists of six short beta-strands. The beta-hexamer was postulated to play a critical role in the assembly and stability of the virion by stabilizing hexameric capsomers. Mutational analyses of the beta-hexamer structure, utilizing both in vitro and in vivo assembly assays, demonstrate that this structure is not required for virion formation devoid of nucleic acids in vitro or for RNA-containing virions in vivo. However, the beta-hexamer structure does contribute to virion stability in vitro and modulates disease expression in vivo. These results support a model for CCMV assembly through pentamer intermediates.

Base Sequence↗
PubMed2003

Differentiation and morphological integration of neural progenitor cells transplanted into the developing mammalian eye.

Transplantation of neural stem/progenitor cells has been proposed as a novel approach for the replacement and repair of damaged CNS tissues. We have evaluated the influence of the host cellular microenvironment upon the survival, differentiation, and integration of neural progenitor cells transplanted into the CNS. Using this approach, we have investigated the fate of neural progenitor cells in vivo following transplantation into the developing mammalian eye. Murine brain progenitor cells (mBPCs) isolated from neonatal mice expressing the green fluorescent protein (GFP) transgene were transplanted into the eyes of Brazilian opossums (Monodelphis domestica). Monodelphis pups are born in an extremely immature, fetal-like state. The eyes of neonatal pups provide a fetal-like environment in which to study cellular interactions between host tissues and transplanted neural progenitor cells. mBPCs were transplanted by intraocular injection in hosts ranging in age from 5 days postnatal to adult. The transplanted cells were easily identified because of their GFP fluorescence. Extensive survival, differentiation, and morphological integration of mBPCs within the host tissue was observed. We found that the younger retinas provided a more supportive environment for the morphological integration of the transplanted mBPCs. Cells with morphologies characteristic of specific retinal cell types were observed. Moreover, some transplanted mBPCs were labeled with antibodies characteristic of specific neural/retinal phenotypes. These results suggest that the host environment strongly influences progenitor cell differentiation and that transplantation of neural progenitor cells may be a useful approach aimed at treating degeneration and pathology of the CNS.

Animals↗
PubMed2002

Transplantation of EGF-responsive neurospheres from GFP transgenic mice into the eyes of rd mice.

The isolation of stem cells from various regions of the central nervous system has raised the possibility of using them as a donor cell source for cell transplantation, where they offer great promise for repair of the diseased brain, spinal cord, and retina. Here, we have studied the migration, integration, and differentiation of EGF-responsive neurospheres isolated from the brains of green fluorescent protein transgenic mice and transplanted into the eyes of mature rd mice, a model of retinitis pigmentosa. While grafts of freshly isolated postnatal day 8 retina expressed many markers characteristic of mature retina (e.g. rhodopsin, protein kinase C), very few of the grafted cells migrated into host retina. EGF-responsive neurospheres, conversely, readily migrated into and integrated with the remaining host retina, but showed a very limited ability to differentiate into mature retinal neurons. While the progenitor cells used here show remarkable ability to integrate with host retina and develop some attributes of retinal cells, the failure to fully differentiate into retinal cells suggests that they already express some level of terminal commitment that precludes using them to replace lost photoreceptors.

Animals↗
PubMed2001

Quantitative studies on the peroxidation of human low-density lipoprotein initiated by superoxide and by charged and neutral alkylperoxyl radicals.

Rates of peroxidation of human LDL and rates of consumption of the LDL's alpha-tocopherol (TocH) have been measured at 37 degrees C. Peroxidation was initiated by radicals generated in the aerated aqueous phase at known rates by thermal decomposition of appropriate precursors: superoxide (O2(*-)/HOO(*)) from a hyponitrite and alkylperoxyls (ROO(*), two positively charged, one negatively charged and one neutral) from azo compounds. The efficiencies of escape from the solvent cage of the geminate pair of neutral carbon-centered radicals was found to be 0.1, but it was 0.5 for the three charged radicals, a result attributed to radical/radical Coulombic repulsion within the cage. All four alkylperoxyls initiated and terminated tocopherol-mediated peroxidation (TMP) with about equal efficiency and essentially all of these radicals that were generated were consumed in these two reactions. TMP is a radical chain process, and when initiated by the alkylperoxyls, the rate of LDL peroxidation was faster in the early stages while TocH was present than later, after all of this "antioxidant" had been consumed. In contrast, only about 3-4% of the generated superoxide radicals reacted in any measurable fashion with TocH-containing LDL at pH's from 7.6 to 6.5 and peroxidation was much slower than with a similar rate of generation of alkylperoxyls. After all the TocH had been consumed, LDL peroxidation was negligible at pH 7.6 and 7.4, but at pH 6.8 and 6.5, the peroxidation rates showed a large increase over the rates while the TocH had been present. That is, endogenous TocH behaves as an antioxidant in LDL subjected to attack by the physiologically relevant superoxide radical, whereas TocH behaves as a prooxidant in LDL subjected to attack by the probably far less physiologically important alkylperoxyls. Rates of LDL peroxidation initiated by superoxide increased as the pH was decreased, and the results are consistent with the initiation of peroxidation of fresh LDL occurring via H-atom abstraction from TocH by HOO(*) to form the Toc(*) radical and termination by reaction of O2(*-) with Toc(*), a process that occurs partly by addition leading to TocH consumption and partly by electron plus proton transfer leading to the regeneration of TocH.

Antioxidants↗
PubMed2001

Surface markers expressed by multipotent human and mouse neural progenitor cells include tetraspanins and non-protein epitopes.

Surface molecules play important roles in a wide range of cellular functions, yet little has been reported regarding the expression of such markers by neural stem cells. Here, multipotent human neural progenitor cells (hNPCs) were expanded as a monolayer in the presence of fibroblast/epidermal growth factor, harvested, labeled with monoclonal antibodies, and analyzed by flow cytometry. Positive markers included CD9, CD15, CD81, CD95 (Fas), GD(2) ganglioside, and major histocompatibility complex class I and beta2 microglobulin, as well as low levels of the hematopoietic stem cell marker CD34. Of these, mouse NPCs were positive for CD9, CD15, CD81, and GD(2) ganglioside. The markers reported here have been implicated in a wide range of cellular functions including proliferation, migration, differentiation, apoptosis, and immune recognition.

Animals↗
PubMed2001

Viruses from extreme thermal environments.

Viruses of extreme thermophiles are of great interest because they serve as model systems for understanding the biochemistry and molecular biology required for life at high temperatures. In this work, we report the discovery, isolation, and preliminary characterization of viruses and virus-like particles from extreme thermal acidic environments (70-92 degrees C, pH 1.0-4.5) found in Yellowstone National Park. Six unique particle morphologies were found in Sulfolobus enrichment cultures. Three of the particle morphologies are similar to viruses previously isolated from Sulfolobus species from Iceland and/or Japan. Sequence analysis of their viral genomes suggests that they are related to the Icelandic and Japanese isolates. In addition, three virus particle morphologies that had not been previously observed from thermal environments were found. These viruses appear to be completely novel in nature.

Archaeal Viruses↗
PubMed2001

Photoreceptor rescue after low-dose intravitreal IL-1beta injection in the RCS rat.

Photoreceptor survival in the dystrophic rat was evaluated following administration of IL-1beta at dosages much lower than those used previously for this purpose. Royal College of Surgeons rats (pink-eyed, pigmented, or non-dystrophic) received 1 microl intravitreal injections of murine recombinant IL-1beta (0.5, 2, or 5 microg ml(-1); at 3 or 4 weeks of age). Eyes were harvested 4 weeks later and outer nuclear layer profiles counted. Additional animals received intravitreal basic fibroblast growth factor (1000 microg ml(-1)), or vehicle alone. Others were treated with IL-1beta to evaluate the inflammatory response (CD45+ profiles) or visual function via opto-kinetic response. IL-1beta was associated with photoreceptor rescue that was both dose-dependent and comparable to that seen following high-dose basic fibroblast growth factor. Significant anatomical rescue relative to controls was seen in both pink-eyed and pigmented strains, although the degree and distribution varied between strains. Functional rescue was confirmed by opto-kinetic response using the pigmented strain. At 5 microg ml(-1), IL-1beta resulted in numerous CD45+ profiles within the retina and vitreous. Infiltration peaked at 48 hr and was minimal at 4 weeks, without dysplastic sequelae. IL-1beta therefore induces visually significant photoreceptor rescue in a potent, dose-dependent manner that need not entail cytoarchitectural disruption. This is consistent with the known association between injury and rescue in the rat retina. Neuroprotection may be a general, if under-appreciated, consequence of inflammatory cascade activation.

Animals↗
PubMed2001

Graft location affects functional rescue following RPE cell transplantation in the RCS rat.

Photoreceptor (PRC) rescue in the dystrophic Royal College of Surgeons (RCS) rat has been well documented following a variety of interventions. Although the dystrophic process is asymmetric with respect to the horizontal meridian, little attention has been paid to the effect of topographic position on treatment outcome. In this study, RPE cells from adult congenic nondystrophic animals were injected into the subretinal space of 1-month-old dystrophic RCS rats in either the dorsal or the ventral equatorial region. Animals were followed longitudinally during the degenerative process using the pupillary light reflex (PLR). The parameter of the PLR most sensitive to PRC rescue is latency at low light levels. At 3 months of age this parameter showed statistically better performance (ANOVA, P = 0.016) for eyes with grafts placed dorsally compared to those placed ventrally or untreated controls. There was no treatment effect on amplitude. By 6 months of age the dorsal/ventral disparity in latency was less apparent and amplitude remained equivalent across groups. Late analysis of retinal whole-mounts using RT-97 fluorescent labeling showed extensive irregularities in ventral axonal morphology in all treatment groups. These results indicate that functional rescue of the RCS retina is significantly influenced by the local degenerative timetable. The role of initial local conditions on treatment outcome is worthy of consideration in other models of neuroprotection.

Analysis of Variance↗
PubMed2001

Acute hypoglycemia impairs the functioning of the central but not peripheral nervous system.

Acute hypoglycemia impairs functions of the central nervous system, but few controlled studies have assessed the impact of hypoglycemia on the function of the peripheral nervous system. Sixteen non-diabetic humans underwent two separate hyperinsulinemic glucose clamp procedures on different study days, in a counter-balanced fashion. On one occasion, euglycemia was maintained (blood glucose, 5.0 mmol l(-1)), and on the other occasion, hypoglycemia (blood glucose, 2.6 mmol l(-1)) was induced. During each condition, subjects performed a combined psychometric, cognitive-experimental and psychophysical test battery, and measures were made (in the dominant median and common peroneal nerves) of the motor nerve conduction velocities and the amplitudes of the motor action potentials. Hypoglycemia caused impaired performance of general cognitive and information processing tasks (P<.05), but nerve conduction velocities and the amplitudes of motor action potentials were unaffected. Conduction velocities of the common peroneal nerve decreased from baseline within each experimental condition, perhaps due to hyperinsulinemia. Overall, these results demonstrate that multiple levels of information processing in the brain may alter while peripheral nerve function remains intact, and imply that peripheral neurons do not have the same obligate requirement for glucose as a metabolic fuel as neurons of the central nervous system.

Acute Disease↗
PubMed2001

Antigenicity and immunogenicity of allogeneic retinal transplants.

The transplantation of neuronal cells and tissues represents a promising approach for the treatment of incurable neurodegenerative diseases. Indeed, it has been reported recently that retinal transplantation can rescue photoreceptor cells and delay age-related changes in various retinal layers in rodents. However, retinal grafts deteriorate progressively after placement in recipients' eyes. Here we investigated whether a host's immune response elicited toward the graft contributes to its deterioration. Using an ELISA spot assay, we measured T cell responses to retinal tissues placed in the vitreous cavity of syngeneic and allogeneic mice. We found that allogeneic retinas induced potent alloimmune responses mediated by T cells secreting type 1 cytokines (IFN-gamma and IL-2). No response was found in mice engrafted with syngeneic retinas. In addition, all syngeneic retinal grafts displayed no signs of tissue damage (at 55 days), while the majority of allogeneic retinas deteriorated as early as 12 days after placement. Next, we showed that anti-donor responses occurred within two phenotypically and functionally distinct T cell subsets: CD4+ T cells secreting IL-2 and CD8+ T cells producing IFN-gamma. Importantly, CD4+ T cells were necessary and sufficient to cause graft deterioration, while CD8+ T cells did not contribute to this process.

Animals↗
PubMed2001

Cardiac steroidogenesis in the normal and failing heart.

The present study explores the possibility of local de novo aldosterone production in normal and failing hearts (human and mouse) and the regulation of such putative cardiac steroidogenesis. Total RNA was isolated from human tissue from failing hearts taken at the time of cardiac transplantation, from normal hearts obtained at autopsy, and from normal and pressure-overloaded mouse hearts. Vascular smooth muscle cells from human artery and vein were also analyzed. RNA was reverse transcribed and probed with specific primers for side-chain cleavage enzyme (CYP11A), 3beta-hydroxysteroid dehydrogenase, aldosterone synthase (CYP11B2), 11beta-hydroxylase (CYP11B1), steroidogenic factor-1, and steroid acute regulatory protein. CYP11A, 3beta-hydroxysteroid dehydrogenase-2, and steroid acute regulatory protein were expressed at modest levels in all tissues examined in both mouse and human. In failing human heart, CYP11B1 and CYP11B2 were detected in some samples, in contrast with normal hearts, which expressed neither; in the mouse heart steroidogenic factor-1 was detected, but neither CYP11B1 nor CYP11B2 was found. Steroidogenic factor-1 was detected in no human heart sample tested after 40 cycles of PCR. Although the expression of some steroidogenic genes can be detected in the heart, the likelihood of physiologically relevant levels of aldosterone production by the normal heart is very low. The exact cellular location of steroid synthesis in the failing human heart remains to be established.

Animals↗
PubMed2001

The development of a survey instrument for community health improvement.

OBJECTIVE: To develop a survey instrument that could be used both to guide and evaluate community health improvement efforts. DATA SOURCES/STUDY SETTING: A randomized telephone survey was administered to a sample of about 250 residents in two communities in Lehigh Valley, Pennsylvania in the fall of 1997. METHODS: The survey instrument was developed by health professionals representing diverse health care organizations. This group worked collaboratively over a period of two years to (1) select a conceptual model of health as a foundation for the survey; (2) review relevant literature to identify indicators that adequately measured the health constructs within the chosen model; (3) develop new indicators where important constructs lacked specific measures; and (4) pilot test the final survey to assess the reliability and validity of the instrument. PRINCIPAL FINDINGS: The Evans and Stoddart Field Model of the Determinants of Health and Well-Being was chosen as the conceptual model within which to develop the survey. The Field Model depicts nine domains important to the origins and production of health and provides a comprehensive framework from which to launch community health improvement efforts. From more than 500 potential indicators we identified 118 survey questions that reflected the multiple determinants of health as conceptualized by this model. Sources from which indicators were selected include the Behavior Risk Factor Surveillance Survey, the National Health Interview Survey, the Consumer Assessment of Health Plans Survey, and the SF-12 Summary Scales. The work group developed 27 new survey questions for constructs for which we could not locate adequate indicators. Twenty-five questions in the final instrument can be compared to nationally published norms or benchmarks. The final instrument was pilot tested in 1997 in two communities. Administration time averaged 22 minutes with a response rate of 66 percent. Reliability of new survey questions was adequate. Face validity was supported by previous findings from qualitative and quantitative studies. CONCLUSIONS: We developed, pilot tested, and validated a survey instrument designed to provide more comprehensive and timely data to communities for community health assessments. This instrument allows communities to identify and measure critical domains of health that have previously not been captured in a single instrument.

Adolescent↗