Migration of exogenous immature hematopoietic cells into adult mouse brain parenchyma under GFP-expressing bone marrow chimera

Molecular Mechanisms in Pathophysiology of Mucopolysaccharidosis and Prospects for Innovative Therapy

Mucopolysaccharidoses (MPSs) are a group of inborn errors of the metabolism caused by a deficiency in the lysosomal enzymes required to break down molecules called glycosaminoglycans (GAGs). These GAGs accumulate over time in various tissues and disrupt multiple biological systems, including catabolism of other substances, autophagy, and mitochondrial function. These pathological changes ultimately increase oxidative stress and activate innate immunity and inflammation. We have described the pathophysiology of MPS and activated inflammation in this paper, starting with accumulating the primary storage materials, GAGs. At the initial stage of GAG accumulation, affected tissues/cells are reversibly affected but progress irreversibly to: (1) disruption of substrate degradation with pathogenic changes in lysosomal function, (2) cellular dysfunction, secondary/tertiary accumulation (toxins such as GM2 or GM3 ganglioside, etc.), and inflammatory process, and (3) progressive tissue/organ damage and cell death (e.g., skeletal dysplasia, CNS impairment, etc.). For current and future treatment, several potential treatments for MPS that can penetrate the blood-brain barrier and bone have been proposed and/or are in clinical trials, including targeting peptides and molecular Trojan horses such as monoclonal antibodies attached to enzymes via receptor-mediated transport. Gene therapy trials with AAV, ex vivo LV, and Sleeping Beauty transposon system for MPS are proposed and/or underway as innovative therapeutic options. In addition, possible immunomodulatory reagents that can suppress MPS symptoms have been summarized in this review.

Rodent Models of Amyloid-Beta Feature of Alzheimer's Disease: Development and Potential Treatment Implications

Alzheimer's disease (AD) is the most common neurodegenerative disorder worldwide and causes severe financial and social burdens. Despite much research on the pathogenesis of AD, the neuropathological mechanisms remain obscure and current treatments have proven ineffective. In the past decades, transgenic rodent models have been used to try to unravel this disease, which is crucial for early diagnosis and the assessment of disease-modifying compounds. In this review, we focus on transgenic rodent models used to study amyloid-beta pathology in AD. We also discuss their possible use as promising tools for AD research. There is still no effective treatment for AD and the development of potent therapeutics are urgently needed. Many molecular pathways are susceptible to AD, ranging from neuroinflammation, immune response, and neuroplasticity to neurotrophic factors. Studying these pathways may shed light on AD pathophysiology as well as provide potential targets for the development of more effective treatments. This review discusses the advantages and limitations of these models and their potential therapeutic implications for AD.

Inducible nitric oxide synthase during the late phase of sepsis is associated with hypothermia and immune cell migration

Hypothermia is a significant sign of sepsis, which is associated with poor prognosis, but few mechanisms underlying the regulation of hypothermia are known. Inducible nitric oxide synthase (iNOS) is a key inflammatory mediator of sepsis. However, the therapeutic benefit of iNOS inhibition in sepsis is still controversial, and requires elucidation in an accurate model system. In this study, wild-type (WT) mice showed temperature drops in a biphasic manner at the early and late phase of sepsis, and all mice died within 48 h of sepsis. In contrast, iNOS-knockout (KO) mice never showed the second temperature drop and exhibited improved mortality. Plasma nitric oxide (NO) levels of WT mice increased in the late phase of sepsis and correlated to hypothermia. The results indicate that iNOS-derived NO during the late phase of sepsis caused vasodilation-induced hypothermia and a lethal hypodynamic state. The expression of the iNOS mRNA was high in the lung of WT mice with sepsis, which reflects the pathology of acute respiratory distress syndrome (ARDS). We obtained the results in a modified keyhole-type cecal ligation and puncture model of septic shock induced by minimally invasive surgery. In this accurate and reproducible model system, we transplanted the bone marrow cells of GFP transgenic mice into WT and iNOS-KO mice, and evaluated the role of increased pulmonary iNOS expression in cell migration during the late phase of sepsis. We also investigated the quantity and type of bone marrow-derived cells (BMDCs) in the lung. The number of BMDCs in the lung of iNOS-KO mice was less than that in the lung of WT mice. The major BMDCs populations were CD11b-positive, iNOS-negative cells in WT mice, and Gr-1-positive cells in iNOS-KO mice that expressed iNOS. These results suggest that sustained hypothermia may be a beneficial guide for future iNOS-targeted therapy of sepsis, and that iNOS modulated the migratory efficiency and cell type of BMDCs in septic ARDS.

Monocyte chemoattractant protein-1 and the blood-brain barrier

The blood-brain barrier (BBB) is a dynamic structure that maintains the homeostasis of the brain and thus proper neurological functions. BBB compromise has been found in many pathological conditions, including neuroinflammation. Monocyte chemoattractant protein-1 (MCP1), a chemokine that is transiently and significantly up-regulated during inflammation, is able to disrupt the integrity of BBB and modulate the progression of various diseases, including excitotoxic injury and hemorrhage. In this review, we first introduce the biochemistry and biology of MCP1, and then summarize the effects of MCP1 on BBB integrity as well as individual BBB components.

In vivo cell tracking by bioluminescence imaging after transplantation of bioengineered cell sheets to the knee joint

In our previous studies, we have demonstrated effective regeneration of cartilage through the creation and application of layered cell sheets that combine both chondrocytes and synovial cells. In this study, we were able to demonstrate that cells derived from cell sheets can survive for long periods after transplantation into rat knee joints having osteochondral defects. We established a method for generating cell sheets from firefly luciferase-expressing chondrocytes obtained from transgenic Lewis rats, and carried out allogenic transplantation of these cell sheets into wild-type Lewis rats. We then administered luciferin and monitored the survival of the transplanted cells by using bioluminescence imaging (BLI). Our data showed that the transplanted cells survived and could be detected for more than 21 months, which was longer than expected. Furthermore, the BLI data showed that the transplanted cells remained in the knee joint and did not migrate to other parts of the body, thus confirming the safety of the cell sheets. In this study, we monitored the duration of survival of cell sheets composed of only chondrocytes, only synovial cells, or both chondrocytes and synovial cells, and found that all three types of cell sheets survived for an extended period of time.

A method to generate enhanced GFP+ chimeric mice to study the role of bone marrow-derived cells in the eye

GFP-chimeric mice are important tools to study the role of bone marrow-derived cells in eye physiology. A method is described to generate GFP-chimeric mice using whole-body, sub-lethal radiation (600 rad) of wild-type C57BL/6 recipients followed by tail vein injection of bone marrow cells derived from GFP+ (GFP-transgenic C57/BL/6-Tg(UBC-GFP)30 Scha/J) mice. This method yields stable GFP+ chimeras with greater than 95% chimerism (range 95-99%), achieved within one month of bone marrow transfer confirmed by microscopy and fluorescence-assisted cell sorting (FACS) analysis, with lower mortality after irradiation than prior methods. To demonstrate the efficacy of GFP+ bone marrow chimeric mice, the role of circulating GFP+ bone marrow-derived cells in myofibroblast generation after irregular photo-therapeutic keratectomy (PTK) was analyzed. Many SMA+ myofibroblasts that were generated at one month after PTK were derived from GFP+ bone marrow-derived cells. The GFP+ bone marrow chimeric mouse provides an excellent model for studying the role of bone marrow-derived cells in corneal wound healing, glaucoma surgery, optic nerve head pathology and retinal pathophysiology and wound healing.

Epigenetics and the modulation of neuroinflammation

Innate immune responses in the central nervous system (CNS) have key roles influencing both physiological and pathological processes. Microglia are innate immune effector cells that reside within the CNS. These inflammatory cells are constantly surveying their external environment and rapidly respond to a variety of molecules that signal changes in CNS homeostasis. In response to these signals, microglia influence neuronal connections, modulate the functions of other glia, and mediate inflammatory responses to disease or injury. In parallel with the regulation of inflammatory responses outside of the CNS, investigators have observed that microglia are capable of heterogeneous responses to exogenous and endogenous signals. While much of this molecular and morphological heterogeneity is regulated by gene transcription, there is ample evidence that microglial behavior is determined, in part, by epigenetic regulation. Recent work has demonstrated that processes involving DNA methylation, histone modification, and noncoding RNAs also have important roles in modulating neuroinflammation. Here I will review the evidence supporting a role for epigenetic regulation of neuroinflammation and describe how this might influence the outcome of several CNS disorders, including addiction, infection, multiple sclerosis, and stroke.

The C terminus of mouse monocyte chemoattractant protein 1 (MCP1) mediates MCP1 dimerization while blocking its chemotactic potency

The extracellular protease plasmin cleaves mouse MCP1 (monocyte chemoattractant protein 1) at lysine 104, releasing a 50-amino acid C-terminal domain. The cleavage event increases the chemotactic activity of MCP1 and, by doing so, promotes the progression of excitotoxic injury in the central nervous system in pathological settings. The mechanism through which the cleavage event enhances MCP1-mediated chemoattraction is unknown; to investigate it, we use wild-type and mutant forms of recombinant MCP1. Full-length MCP1 (FL-MCP1) is secreted by cells as a dimer or multimer. We show that a mutant truncated at the C terminus, K104Stop-MCP1, does not dimerize, revealing that the C terminus mediates the interaction. MCP1 interacts with the monocyte/microglia receptor CCR2. The interaction is critical to the function of MCP1 because CCR2(-/-) microglia do not undergo chemotaxis in response to MCP1 stimulation. We show that stimulation of microglia with FL-MCP1 or K104Stop-MCP1 triggers CCR2 internalization, whereas a mutant form unable to be cleaved at lysine 104 (K104A-MCP1) is relatively ineffective in this assay, suggesting that the C-terminal region interferes with the MCP1-CCR2 interaction. Moreover, FL-MCP1 and K104Stop-MCP1 stimulation leads to activation of Rac1, a small GTPase involved in cell migration. Conversely, MCP1-stimulated microglial migration is blocked by the Rac1 inhibitor, NSC23766, demonstrating the requirement for Rac1 effector pathways in this response. Taken together, we propose a model for MCP1 localization, activation, and function based on the initial presence and then removal of its C terminus, coupled with a requisite downstream signaling pathway from CCR2 stimulation to Rac1 activation.

Activation and deactivation of periventricular white matter phagocytes during postnatal mouse development

Brain microglia are related to peripheral macrophages but undergo a highly specific process of regional maturation and differentiation inside the brain. Here, we examined this deactivation and morphological differentiation in cerebral cortex and periventricular subcortical white matter, the main "fountain of microglia" site, during postnatal mouse development, 0-28 days after birth (P0-P28). Only macrophages in subcortical white matter but not cortical microglia exhibited strong expression of typical activation markers alpha5, alpha6, alphaM, alphaX, and beta2 integrin subunits and B7.2 at any postnatal time point studied. White matter phagocyte activation was maximal at P0, decreased linearly over P3 and P7 and disappeared at P10. P7 white matter phagocytes also expressed high levels of IGF1 and MCSF, but not TNFalpha mRNA; this expression disappeared at P14. This process of deactivation followed the presence of ingested phagocytic material but correlated only moderately with ramification, and not with the extent of TUNEL+ death in neighboring cells, their ingestion or microglial proliferation. Intravenous fluosphere labeling revealed postnatal recruitment and transformation of circulating leukocytes into meningeal and perivascular macrophages as well as into ramified cortical microglia, but bypassing the white matter areas. In conclusion, this study describes strong and selective activation of postnatally resident phagocytes in the P0-P7 subcortical white matter, roughly equivalent to mid 3rd trimester human fetal development. This presence of highly active and IGF1- and MCSF-expressing phagocytes in the neighborhood of vulnerable white matter could play an important role in the genesis of or protection against axonal damage in the fetus and premature neonate.

In utero transplantation of monocytic cells in cats with alpha-mannosidosis

BACKGROUND

Lysosomal storage diseases are devastating illnesses, in large part because of their neurologic consequences. Because significant morbidity occurs prenatally, in utero (IU) therapy is an attractive therapeutic approach.

METHODS

We studied the feasibility and efficacy of IU injections of monocytic cells (derived from normal marrow) in feline alpha-mannosidosis. Heterozygous cats were interbred to produce affected (homozygous) and control (heterozygous and wild-type) offspring. Thirty-seven pregnancies were studied in which fetuses were transplanted intraperitoneally (1x10 cells/kg recipient) at gestational days 27 to 33 and then each week for 2 weeks (term=63 days). After birth, affected kittens were evaluated clinically and pathologically, tissue alpha-mannosidase levels were assayed, and in many studies, the numbers of alpha-mannosidase-containing cells were enumerated. When male donor cells were transplanted into female recipients, engraftment was also quantified using polymerase chain reaction to amplify a Y chromosome-specific sequence.

RESULTS

We establish methods to transplant cats intraperitoneally while IU using ultrasound guidance, thus, describing a new large animal model for prenatal therapy. We show that the donor monocytic cells engraft and persist (for up to 125 days) in the brain, liver, and spleen, albeit at levels below those needed to alter the clinical or pathological progression of the alpha-mannosidosis.

CONCLUSIONS

This is the first study of monocyte transplantation in a large animal model of a lysosomal storage disorder and demonstrates its feasibility, safety, and promise. Delivering cells IU may be a useful strategy to prevent morbidities before a definitive therapy, such as hematopoietic stem-cell transplantation, can be administered after birth.

Bone mass and microarchitecture of irradiated and bone marrow-transplanted mice: influences of the donor strain

Total body irradiation and bone marrow transplantation induced dramatic trabecular bone loss and cortical thickening in mice. Transplanted cells were engrafted in bone marrow, along trabeculae, and in periosteal and endosteal envelopes. None of the osteocytes were of donor origin. Bone microarchitecture of transplanted mice changed to tend toward the donor phenotype.

INTRODUCTION

Osteopenia and osteoporosis are complications of bone marrow transplants (BMT) attributed to related chemotherapy. However, the specific influence of total body irradiation (TBI) is unknown.

METHODS

We investigated the effects of TBI and BMT on bone mass and microarchitecture by micro-CT. Eighteen C57Bl/6 (B6) mice receiving lethal TBI had a BMT with marrow cells from green fluorescent protein--transgenic-C57Bl/6 (GFP) mice. Transplanted (T(GFP)B6), B6, and GFP mice were euthanized 1, 3, and 6 months after BMT or at a related age.

RESULTS

T(GFP)B6 presented a dramatic bone loss compared with B6 and did not restore their trabecular bone mass over time, despite a cortical thickening 6 months after BMT. Serum testosterone levels were not significantly reduced after BMT. During aging, GFP mice have less trabeculae, thicker cortices, but a narrower femoral shaft than B6 mice. From 3 months after BMT, cortical characteristics of T(GFP)B6 mice differed statistically from B6 mice and were identical to those of GFP mice. GFP(+) cells were located along trabecular surfaces and in periosteal and endosteal envelopes, but none of the osteocytes expressed GFP.

CONCLUSION

Our findings suggest that engrafted cells did not restore the irradiation-induced trabecular bone loss, but reconstituted a marrow microenvironment and bone remodeling similar to those of the donor. The effects of irradiation and graft on bone remodeling differed between cortical and trabecular bone.

Interleukin-1beta and tumor necrosis factor-alpha are expressed by different subsets of microglia and macrophages after ischemic stroke in mice

BACKGROUND

Interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) are expressed by microglia and infiltrating macrophages following ischemic stroke. Whereas IL-1beta is primarily neurotoxic in ischemic stroke, TNF-alpha may have neurotoxic and/or neuroprotective effects. We investigated whether IL-1beta and TNF-alpha are synthesized by overlapping or segregated populations of cells after ischemic stroke in mice.

METHODS

We used flow cytometry and immunohistochemistry to examine cellular co-expression of IL-1beta and TNF-alpha at 6, 12 and 24 hours after permanent middle cerebral artery occlusion in mice, validating the results by the use of bone marrow chimeric mice.

RESULTS

We found that IL-1beta and TNF-alpha were expressed in largely segregated populations of CD11b+CD45dim microglia and CD11b+CD45high macrophages, with cells expressing both cytokines only rarely. The number of Gr1+ granulocytes producing IL-1beta or TNF-alpha was very low, and we observed no IL-1beta- or TNF-alpha-expressing T cells or astrocytes.

CONCLUSION

Taken together, the results show that IL-1beta and TNF-alpha are produced by largely segregated populations of microglia and macrophages after ischemic stroke in mice. Our findings provide evidence of a functional diversity among different subsets of microglia and macrophages that is potentially relevant to future design of anti-inflammatory therapies in stroke.

Immunosuppression after traumatic or ischemic CNS damage: it is neuroprotective and illuminates the role of microglial cells

Acute traumatic and ischemic events in the central nervous system (CNS) invariably result in activation of microglial cells as local representatives of the immune system. It is still under debate whether activated microglia promote neuronal survival, or whether they exacerbate the original extent of neuronal damage. Protagonists of the view that microglial cells cause secondary damage have proposed that inhibition of microglial activation by immunosuppression is beneficial after acute CNS damage. It is the aim of this review to analyse the effects of immunosuppressants on isolated microglial cells and neurons, and to scrutinize the effects of immunosuppression in different in vivo models of acute CNS trauma or ischemia. It is found that the immunosuppressants cytosine-arabinoside, different steroids, cyclosporin A, FK506, rapamycin, mycophenolate mofetil, and minocycline all have direct inhibitory effects on microglial cells. These effects are mainly exerted by inhibiting microglial proliferation or microglial secretion of neurotoxic substances such as proinflammatory cytokines and nitric oxide. Furthermore, immunosuppression after acute CNS trauma or ischemia results in improved structure preservation and, mostly, in enhanced function. However, all investigated immunosuppressants also have direct effects on neurons, and some immunosuppressants affect other glial cells such as astrocytes. In summary, it is safe to conclude that immunosuppression after acute CNS trauma or ischemia is neuroprotective. Furthermore, circumferential evidence indicates that microglial activation after traumatic or ischemic CNS damage is not beneficial to adjacent neurons in the immediate aftermath of such acute lesions. Further experiments with more specific agents or genetic approaches that specifically inhibit microglial cells are needed in order to fully answer the question of whether microglial activation is "good or bad".

Neuroprotective effect of exogenous microglia in global brain ischemia

Exogenous microglia pass through the blood-brain barrier and migrate to ischemic hippocampal lesions when injected into the circulation. We investigated the effect of exogenous microglia on ischemic CA1 pyramidal neurons. Microglia were isolated from neonatal mixed brain cultures, labeled with the fluorescent dye PKH26, and injected into the subclavian artery of Mongolian gerbils subjected to ischemia reperfusion neuronal injury. PKH26-labeled microglia migrated to the ischemic hippocampal lesion, resulting in increased numbers of surviving neurons compared with control animals, even when injected 24 h after ischemia. Interferon-gamma stimulation of isolated microglia enhanced the neuroprotective effect. Administration of exogenous microglia resulted in normal performance in a passive avoidance-learning task. Additionally, administration of exogenous microglia increased the expression of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor in the ischemic hippocampus, and thus might have induced neurotrophin-dependent protective activity in damaged neurons. Peripherally injected microglia exhibited a specific affinity for ischemic brain lesions, and protected against ischemic neuronal injury in vivo. It is possible that administration of exogenous microglia can be developed as a potential candidate therapy for central nervous system repair after transitory global ischemia.

Focal cerebral ischemia/reperfusion injury in mice induces hematopoietic prostaglandin D synthase in microglia and macrophages

Hematopoietic prostaglandin D synthase is a key enzyme in synthesis of prostaglandin D. Hematopoietic prostaglandin D synthase is expressed in microglia of the developing mouse brain. This study determined the serial changes and cellular localization of hematopoietic prostaglandin D synthase, and its role in cerebral ischemia/reperfusion injury using C57BL/6 mice (n=84) and bone marrow chimera mice (n=16). The latter mice were selected based on their expression of enhanced green fluorescent protein in bone marrow/blood-derived monocytes/macrophages. The middle cerebral artery was occluded for 60 min, followed by reperfusion. Hematopoietic prostaglandin D synthase expression was examined by immunohistochemistry and Western blotting. Hematopoietic prostaglandin D synthase-positive cells were mainly expressed in the peri-ischemic area at 12 h (P<0.05) and 24 h (P<0.001) after reperfusion, while they were mostly found in the transition area at 48-72 h postreperfusion (P<0.001). There was a significant increase in staining intensity as well as number of hematopoietic prostaglandin D synthase-positive cells in the ischemic core at 5-7 (P<0.001) days postreperfusion. Hematopoietic prostaglandin D synthase-positive cells also co-expressed ionized calcium-binding adapter molecule 1, a marker of microglia/macrophages, and cyclooxygenase-2, but not markers of neurons, oligodendrocytes and astrocytes. Until 72 h postreperfusion, many enhanced green fluorescent protein-positive cells were negative for hematopoietic prostaglandin D synthase, but the number of hematopoietic prostaglandin D synthase-enhanced green fluorescent protein coexpressing cells increased significantly at 5-7 days after reperfusion. Our results indicate that hematopoietic prostaglandin D synthase is mainly produced by endogenous microglia until 72 h after reperfusion, but at 7 days after reperfusion, it is also produced by migrating bone marrow/blood-derived macrophages in the ischemic brain tissue. We speculate that hematopoietic prostaglandin D synthase in the brain has different functions during early and late phases of ischemia.

Turnover of resident retinal microglia in the normal adult mouse

The retina contains two distinct populations of monocyte-derived cells: perivascular cells (macrophages) and parenchymal cells (microglia), important in homeostasis, neuroinflammation, degeneration, and injury. The turnover of these cells in the retina and their repopulation in normal physiological conditions have not been clarified. Bone marrow (BM) cells from EGFP-transgenic mice were adoptively transferred into lethally irradiated normal adult C57BL/6 mice. Eight, 14, and 26 weeks later mice were sacrificed and retinal flatmounts were prepared. Retinal microglia were identified by F4/80, CD45, and Iba-1 immunostaining. BrdU was injected into normal mice for 3-14 days and cell proliferation was examined by confocal microscopy of retinal flatmounts. Few (6.15 +/- 2.02 cells/retina) BrdU(+) cells were detected and of these some coexpressed CD11b (1.67 +/- 0.62 cells/retina) or F4/80 (0.57 +/- 0.30 cells/retina). BM-derived EGFP(+) cells were detected by 8-weeks post-transplantation. By 6 months, all retinal myeloid cells were EGFP(+). Consecutively, donor BM-EGFP(+) cells were demonstrated within the: (1) peripheral and juxtapapillary retina, (2) ganglion cell layer, (3) inner and outer plexiform layers, and (4) photoreceptor layer. EGFP(+) cells within the ganglion layer were amoeboid in shape and F4/80(high)CD45(high)Iba-1(high), whereas cells in the inner and outer plexiform layers were ramified and F4/80(low) CD45(low)Iba-1(low). Perivascular macrophages expressed less F4/80, CD45, and Iba-1 compared with parenchymal microglia. Our results suggest that BM-derived monocyte precursor cells are able to migrate across the BRB and replace retinal microglia/macrophages. The complete replacement of retinal microglia/macrophages takes about 6 months. In situ proliferation was predominantly of nonhemopoetic retinal cells.

Neuroprotective properties of the innate immune system and bone marrow stem cells in Alzheimer's disease

The role of innate immunity and microglia in the brain is currently a matter of great debate and controversy. While several studies have provided evidence that they contribute to neurodegeneration in various animal models of brain diseases and traumas, others have shown that their inhibition may in contrast be associated with more damages or less repair. We have recently reported the existence of two different types of microglia, the resident and the newly differentiated microglia that derive from the bone marrow stem cells. Of great interest is the fact that blood-derived microglial cells are associated with amyloid plaques and these cells are able to prevent the formation or eliminate the presence of amyloid deposits in mice that develop the major hallmark of Alzheimer's disease (AD). These newly recruited cells are specifically attracted to the beta-amyloid 40/42 isoforms in vivo and they participate in the elimination of these proteins by phagocytosis. This review presents the mechanisms involved in the control of the innate immune response by microglia and the beneficial properties of such a response in brain diseases, such as AD.

Carinal Replacement With an Aortic Allograft

BACKGROUND

Carinal replacement after extensive resection remains a tremendous challenge in thoracic surgery. In previous studies, we demonstrated that an aortic graft could be a valuable tracheal substitute. The goal of this new study was to evaluate the reconstruction of the carina using a stent supported bifurcated aortic allograft.

METHODS

In 15 sheep the replacement of the tracheobronchial bifurcation with an aortic allograft was performed under cardiopulmonary bypass. A temporary stent prevented airway collapse. No immunosuppression was used. Aortic segments were retrieved at regular intervals up to 24 months after implantation.

RESULTS

All animals survived the initial aortic allograft operation. Six animals died postoperatively (1 of graft necrosis, 2 of pneumonia, and 3 of bronchial fistula). The remaining 9 animals were in good condition until they were euthanized. Stent removal was tolerated after 9 months in 3 animals. Progressive transformation of the arterial graft initially into extensive inflammatory tissue, and after 3 to 6 months into a tracheal tissue comprising a well-differentiated epithelium and cartilage was confirmed by histology.

CONCLUSIONS

This study showed that regeneration of a functional tissue can be obtained after replacement of the carina with an aortic allograft. The origin and mechanisms of this regenerative process remains to be discovered. These results represent an important hope for the reconstruction of the carina after extensive resection, especially for cancer lesions. In human application, the systemic use of omentoplasty or myoplasty should further reduce its risk of complication.

Tracheal regeneration following tracheal replacement with an allogenic aorta

BACKGROUND

Tracheal replacement remains an unsolved surgical problem. Attempts to use tracheal substitutes have failed to achieve reliable results. In this study, tracheal regeneration was obtained after tracheal replacement with an allogenic aorta.

METHODS

Twenty female sheep underwent a 8-cm tracheal replacement with a fresh aortic allograft. In the six last animals, aortic grafts came from male sheep. A stent prevented airway collapse. No immunosuppressive therapy was used. Aortic segments were retrieved at regular intervals up to 16 months. A polymerase chain reaction for the SRY gene was performed in specimens with aortic grafts from male sheep.

RESULTS

All animals but one survived the operation without complications. Clearly identified between the suture lines, the aortic segments were completely transformed into a tracheal structure. Histology showed initially an inflammatory reaction with proliferation of a squamous epithelium followed by mucociliary epithelium and newly formed cartilage rings. SRY gene was not found in newly formed cartilage rings showing that the regeneration originated from recipient cells.

CONCLUSIONS

This study presents a new type of tissue regeneration and brings hopes to the treatment of extensive tracheal lesions.

Bone marrow-derived microglia contribute to the neuroinflammatory response and express iNOS in the MPTP mouse model of Parkinson's disease

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication in mice results in dopamine neuron degeneration that is alleviated by prevention of microglia cell activation and blockade of iNOS production. However, the role of peripherally derived microglia in this response has not been well characterized. In the present study, we investigated the time course of infiltration and phenotypic differentiation of bone marrow-derived cells (BMDCs) following MPTP treatment in mice, using green fluorescent protein (GFP) bone marrow chimeras. BMDCs were found in the meninges, choroid plexus, blood vessels, and brain parenchyma in both saline and MPTP-treated mice. MPTP stimulated a transient, two-fold increase in the rate of BMDC infiltration into the brain, concomitant with the onset of microglia activation. The majority of BMDCs were microglial in phenotype, as assessed by morphology and expression of the pan-hematopoietic marker CD45 and the microglia marker CD11b. We did not observe BMDCs that expressed neuronal or astroglial markers. Over 90% of bone marrow-derived microglia expressed the inducible form of nitric oxide synthase (iNOS), suggesting that peripherally derived microglia may play a deleterious role in MPTP-induced degeneration.

Heterogeneous populations of microglia/macrophages in the retina and their activation after retinal ischemia and reperfusion injury

Activation of Microglia/macrophages has been observed in ischemia-reperfusion injury of the brain. This study was undertaken to investigate the different subpopulations of microglia/macrophages in the normal rat retina and their activation after retinal ischemia. Retinal ischemia was induced by elevation of intraocular pressure to 120 mmHg for 60 min. Microglia/macrophages were identified on frozen retinal sections by four antibodies, namely OX42, 5D4, OX6 and ED1. In the normal retina, there were heterogeneous populations of resident microglia/macrophages as characterized by their differences in morphology, antigen expression and distribution. OX42+ cells had delicate processes and were located in the inner layers of the retina, while 5D4+ cells were highly ramified and mostly scattered in the inner plexiform layer (IPL) and the outer plexiform layer. Few amoeboid ED1+ cells were also seen in the ganglion cell layer and IPL. OX6+ (MHC-II antigen presenting) cells were not detected in the normal retinas. Double labeling with OX42 and 5D4 antibodies on normal retinal sections showed few microglia exhibited positive labeling with both OX42 and 5D4, while the majority of the microglia were labeled with either OX42 or 5D4 antibodies. After retinal ischemia single labeling with these antibodies showed increased number of these antigen-expressing cells, disappearance of normal cellular processes, and rounding or amoeboid like appearance of the cell bodies. At 1 day after ischemia, there was a significant infiltration of round OX42+, ED1+ and OX6+ cells with loss of the cellular processes in the inner retina. From 3 to 14 days, all subpopulations of microglia/macrophages differentiated cellular processes and became dendritic again. Double labeling on retinas after 1 day of recovery showed OX42+ cells were co-labeled with ED1+ or OX6+ cells, but not with 5D4+ cells. Scattered amoeboid OX42+, 5D4+, and ED1+ cells were noted in the subretinal space 3-14 days after ischemia. In summary, there were heterogeneous populations of resident microglia/macrophages in the normal inner retina and they were activated early after ischemia-reperfusion injury and exhibited different antigenic expression which were further altered in the recovery phase.

Characterization of microglia induced from mouse embryonic stem cells and their migration into the brain parenchyma

We derived microglia from mouse embryonic stem cells (ES cells) at very high density. Using the markers Mac1(+)/CD45(low) and Mac1(+)/CD45(high) to define microglia and macrophages, respectively, we show that Mac1(+) cells are induced by GM-CSF stimulation following neuronal differentiation of mouse ES cells using a five-step method. CD45(low) expression was high and CD45(high) expression was low on induced cells. We used a density gradient method to obtain a large amount of microglia-like cells, approximately 90% of Mac1(+) cells. Microglia-like cells expressed MHC class I, class II, CD40, CD80, CD86, and IFN-gammaR. The expression level of these molecules on microglia-like cells was barely enhanced by IFN-gamma. Intravenously transferred GFP(+) microglia derived from GFP(+) ES cells selectively accumulated in brain but not in peripheral tissues such as spleen and lymph node. GFP(+) cells were detected mainly in corpus callosum and hippocampus but were rarely seen in cerebral cortex, where Iba1, another marker of microglia, is primarily expressed. Furthermore, both GFP(+) and Iba1(+) cells exhibited a ramified morphology characteristic of mature microglia. These studies suggest that ES cell-derived microglia-like cells obtained using our protocol are functional and migrate selectively into the brain but not into peripheral tissues after intravenous transplantation.

Intratracheal administration of liposomal clodronate accelerates alveolar macrophage reconstitution following fetal liver transplantation

To facilitate study of alveolar macrophages in vivo, we developed a method to rapidly and efficiently replace resident alveolar macrophages with macrophages of a different (donor) genotype. Chimeric mice were generated by lethal irradiation followed by fetal liver transplantation (FLT) using green fluorescent protein (GFP) transgenic reporter mice as donors. Kinetics of peripheral blood monocyte (PBM) and alveolar macrophage reconstitution was determined 4 and 10 weeks post-FLT by quantifying the percentage of GFP+ cells. To enhance the recruitment of donor monocytes into the lung after FLT, mice were treated with intratracheal administration of liposomal clodronate to deplete host alveolar macrophages at 6 weeks post-FLT. PBM reconstitution occurred by 4 weeks after FLT (85.7+/-1.6% of CD11b+/Gr-1+ monocytes were GFP+), and minimal alveolar macrophage repopulation was observed (9.5% GFP+). By 10 weeks following FLT, 48% of alveolar macrophages were GFP+ by immunostaining of macrophages on lung tissue sections, and 55.1 +/- 1.6% of lung lavage macrophages were GFP+ by fluorescein-activated cell sorter analysis. Clodronate treatment resulted in a significant increase in GFP+ alveolar macrophages 10 weeks after FLT. By immunostaining, 90% of macrophages were GFP+ on lung tissue sections and 87.5 +/- 1.1% GFP+ in lung lavage (compared with GFP-transgenic controls). The ability of newly recruited alveolar macrophages to clear Pseudomonas aeruginosa and activate nuclear factor-kappaB in response to Eschericia coli lipopolysaccharide demonstrated normal macrophage function. Optimizing this methodology provides an important tool for the study of specific genes and their contribution to alveolar macrophage function in vivo.

Role of inflammation in the neurobiology of stem cells

Unlike most organs, tissue regeneration and repair are not very efficient in the CNS, which explains the severity of neurodegenerative diseases. Many have hoped that stem cells would provide an effective mean to solve this problem. Unfortunately, evidence supporting this approach remains controversial. In this review, we discuss the capacity of stem cells to generate the cells that reside in the brain. Neural stem cells are able to generate new neurons, astrocytes and oligodendrocytes, but not microglia. The latter are instead replenished by self-replication and monocyte recruitment across the blood-brain barrier. The fact that blood-derived monocytes can enter the brain and differentiate into microglial cells has many implications for neurodegenerative diseases. They are more efficient antigen-presenting cells and produce proinflammatory molecules that can be both detrimental to the brain and beneficial to recovery and repair after insults. It is therefore very important to better understand the role of these newly differentiated microglia before devising therapeutic strategies to either inhibit or improve their recruitment at diseased and injured sites.

Neuronal and microglial cathepsins in aging and age-related diseases

It has been long believed that cathepsins compensate for each other because of their overlapping substrate specificities. However, there is increasing evidence that disturbance of the normal balance of their enzymatic activities is the first insult in brain aging and age-related diseases. The imbalance of cathepsins may further cause age-related neuropathological changes such as accumulation of autophagic vacuoles and the formation of ceroid-lipofuscin leading to neuronal dysfunction and damage. Leakage of cathepsins due to the fragility of lysosomal membranes during aging also contributes to neurodegeneration. Furthermore, the deficiency of cathepsin D has been recently revealed to provoke a novel type of lysosomal storage disease associated with massive neurodegeneration. In these animals, microglia are activated to initiate inflammatory and cytotoxic responses by binding and phagocytosis of storage neurons. Activated microglia also release some members of cathepsins to induce neuronal death by degrading extracellular matrix proteins. Thus the microglial activation possibly through sensing neuronal storage may also be an important causative factor for neurodegeneration in lysosomal storage diseases and age-related diseases such as Alzheimer's disease. This review describes the pathological roles of neuronal and microglial cathepsins in brain aging and age-related diseases.

Green fluorescent protein bone marrow cells express hematopoietic and neural antigens in culture and migrate within the neonatal rat brain

Finding a reliable source of alternative neural stem cells for treatment of various diseases and injuries affecting the central nervous system is a challenge. Numerous studies have shown that hematopoietic and nonhematopoietic progenitors derived from bone marrow (BM) under specific conditions are able to differentiate into cells of all three germ layers. Recently, it was reported that cultured, unfractionated (whole) adult BM cells form nestin-positive spheres that can later initiate neural differentiation (Kabos et al., 2002). The identity of the subpopulation of BM cells that contributes to neural differentiation remains unknown. We therefore analyzed the hematopoietic and neural features of cultured, unfractionated BM cells derived from a transgenic mouse that expresses green fluorescent protein (GFP) in all tissues. We also transplanted the BM cells into the subventricular zone (SVZ), a region known to support postnatal neurogenesis. After injection of BM cells into the neurogenic SVZ in neonatal rats, we found surviving GFP+ BM cells close to the injection site and in various brain regions, including corpus callosum and subcortical white matter. Many of the grafted cells were detected within the rostral migratory stream (RMS), moving toward the olfactory bulb (OB), and some cells reached the subependymal zone of the OB. Our in vitro experiments revealed that murine GFP+ BM cells retained their proliferation and differentiation potential and predominantly preserved their hematopoietic identity (CD45, CD90, CD133), although a few expressed neural antigens (nestin, glial fibrillary acdiic protein, TuJ1).

Therapeutic effects of normal cells on ABCD1 deficient cells in vitro and hematopoietic cell transplantation in the X-ALD mouse model

Bone marrow transplantation (BMT) is accepted as an efficient therapy for X-linked adrenoleukodystrophy (ALD). To clarify the mechanisms of this treatment, we examined the effects of hematopoietic cell transplantation (HCT) in an ATP-binding cassette, subfamily D, member 1 (ABCD1) knock out mice and co-culture of ALD patient fibroblasts with normal cells. We treated ABCD1 knock out mice with HCT using lacZ-transgenic mice as donors, which enabled us to detect donor-derived cells. We also examined the effects of co-culturing a normal microglia cell line (N9) with ALD fibroblasts. beta-Galactosidase (beta-GAL) activity was higher in spleen, lung and kidney than in liver, brain and spinal cord of the recipient ABCD1 knock out mice. HCT reduced the accumulation of very long chain fatty acid (VLCFA) in those tissues. The reduction of the VLCFA ratio was significant in spleen and lung; tissues with higher beta-GAL activity. ABCD1 was detectable in spleen from HCT mice. Co-culture of ALD fibroblasts with normal fibroblast cells reduced VLCFA accumulation in ALD cells. This effect was not observed when the cells were co-cultured while separated by a filter membrane. Our data suggest that supplying normal cells for ABCD1 knockout mouse by HCT corrects metabolic abnormalities in ALD tissues through a cell-mediated process. The correction requires direct cell-to-cell contact for recovering normal cell function.

Minor contribution of bone marrow-derived endothelial progenitors to the vascularization of murine gliomas

Until recently, it was generally accepted that the vascularization of solid tumors occurred exclusively through the sprouting and co-option from pre-existing blood vessels. Growing evidence now suggests that bone marrow-derived endothelial progenitor cells (EP) circulate in the blood and may play an important role in the formation of new blood vessels in certain tumors. Whether endothelial progenitors participate in the vascularization of brain tumors has not yet been evaluated. In this study, we examined the contribution of EP to tumor angiogenesis in a murine glioma tumor model. Donor bone marrow cells obtained from transgenic mice constitutively expressing beta-galactosidase or GFP either ubiquitously or transcriptionally regulated by an endothelial specific promotor Tie-2 were injected into lethally irradiated adult mice. After bone marrow reconstitution by donor cells, mice were implanted with syngeneic GL261 murine glioma cells. Morphological and confocal 3-dimensional analysis showed that the majority of the engrafted donor marrow cells were expressing hematopoietic and/or microglia markers, but did not appreciably contribute to the tumor vasculature. Implantation of glioma cells genetically engineered to overexpress VEGF produced highly vascularized tumors. However, the number of endothelial progenitors incorporated in the tumor vasculature did not increase. These data strongly suggest that neovascularization in the brain might fundamentally be regulated by the sprouting of pre-existing vessels and implicate that circulating endothelial progenitors do not play a significant role in this process.

Intracerebroventricular Injection of Microglia Protects Against Focal Brain Ischemia

Microglia are macrophage-like phagocytic cells in the brain parenchyma. However, microglial function after neurodegeneration is not fully understood. In this study, occlusion of the middle cerebral artery (MCA) and reperfusion caused massive neuronal loss in the rat cerebral cortex and striatum after 3 days. When exogenous microglia were microinjected into the intracerebroventricle during MCA occlusion, neurodegenerative areas significantly decreased. At that time, migrated microglia were detected in the ischemic lesion. These results suggest that exogenous microglia can migrate into brain parenchyma and then protect against neurodegeneration induced by MCA occlusion and reperfusion.

Morphologic characterization of green fluorescent protein in embryonic, neonatal, and adult transgenic rats

Transgenic (Tg) animals with reporter genes are useful models in which to study cell lineage and the process of differentiation into tissues. We developed the green fluorescent protein (GFP)-Tg rat, which is more suitable for transplantation and stem cell research because it is larger than mice. We found that marker gene expression was dependent on each organ and developmental stage. In this study we describe GFP expression in various tissues from embryonic, neonatal, and adult animals. GFP expression in brain, lung, liver, and islet tissues was restricted to early developmental stages, but it was continuously strong in the exocrine pancreas, kidney, and cardiac and skeletal muscles. The CAG promoter that was presumed to induce ubiquitous protein expression might be responsible for the differences in expression.

Derivation of lung epithelium from bone marrow cells

Recent studies demonstrate the capacity of BM-derived cells to engraft as differentiated cells of a variety of organs, including lung. In this paper, we review the current state-of-the-art in this area. We also summarize our work demonstrating that cultured adherent marrow cells can serve as progenitors of lung alveolar epithelium.

Characterization of activated retinal microglia following optic axotomy

Microglia are prominently involved in neural degenerative diseases of the CNS and the retina. In this study, we determined the activation and phagocytotic function of different subtypes of retinal microglial cells at 1 week and 1 month following optic axotomy. Fluorescent DiI crystals were placed at the stumps of the cut optic nerves of Lewis rats to retrolabel retinal ganglion cells. Microglial cells were indirectly labeled as they phagocytosed the dye particles in the dying ganglion cells. OX-42, 5D4, ED1, and OX-6 antibodies were used for immunohistochemical study. The OX-42- and 5D4-positive microglial cells were increased in the inner retinal layers after optic axotomy. The increase of OX-42-positive cells was considerably greater than that of 5D4-positive cells. The 5D4-positive cells were ramified in shape, whereas OX-42-positive cells were ameboid and ovoid. Both 5D4- and OX-42-positive cells phagocytosed dying ganglion cells at 1 week and 1 month after axotomy. Scattered ameboid ED1-positive cells were detected in the normal retina and showed phagocytotic activity at 1 month after optic axotomy. The number of ED1-positive cells in the retina was unchanged after axotomy. In optic axotomy, three types of microglial cells were activated, namely, 5D4-positive ramified cells and OX-42- and ED1-positive ameboid cells. All of them exhibited the phagocytosis of dying ganglion cells. Insofar as the blood-retinal barrier presumably remained intact in optic axotomy, the OX-42- and 5D4-positive cells might derive from resident microglial cells. The ED1-positive cells, presumably recently blood-borne macrophage in the CNS, remained the same number in the axotomized retina.

Microglial activation precedes and predominates over macrophage infiltration in transient focal cerebral ischemia: a study in green fluorescent protein transgenic bone marrow chimeric mice

Resident microglia and hematogenous macrophages play crucial roles in the pathogenetic cascade following cerebral ischemia but may functionally differ regarding neuroprotective and cytotoxic properties. Distinction between these cells has not been possible due to a lack of discriminating cellular markers. We generated bone marrow chimeric mice by transplanting bone marrow from green fluorescent protein (GFP) transgenic mice into irradiated wild-type recipients. Transient focal cerebral ischemia was induced by transient middle cerebral artery occlusion (MCAO) for 30 min. Resident microglia and infiltrating macrophages were identified by immunohistochemistry and GFP fluorescence after 1-28 days. The first blood-derived cells infiltrating the infarct area were seen on Day 1 and identified as granulocytes. Hematogenous GFP(+) macrophages were rarely observed on Day 2, reached peak numbers on Day 7, and decreased thereafter. In contrast, resident GFP(-) microglial cells rapidly became activated already on Day 1 after MCAO. Even on Days 4 and 7, most macrophage-like cells remained GFP(-), indicating their derivation from resident microglia. Hematogenous macrophages were able to acquire a ramified morphology indistinguishable from resident microglia while microglial cells could develop into a phagocytic phenotype indistinguishable from infiltrating macrophages. The vast majority of macrophages in the infarct area are derived from local microglia, revealing a remarkable predominance of local defense mechanisms over immune cells arriving from the blood. GFP bone marrow chimeric mice are a powerful tool to further differentiate the function of resident microglia and hematogenous macrophages following cerebral ischemia.

Cardiomyocyte regeneration from circulating bone marrow cells in mice

We investigated the role of circulating bone marrow cells (BMC) in cardiomyocyte regeneration. BMC, isolated from transgenic mice expressing enhanced green fluorescent protein (GFP), were transplanted into lethally irradiated C57BL6 mice. Five weeks after bone marrow transplantation (BMT), flow cytometric analysis for GFP-positive cells confirmed reconstitution of transplanted bone marrow. Bone marrow transplant mice subsequently underwent left coronary artery ligation (myocardial infarction) or sham-operation, and were killed at 1 mo or 3 mo after operation. Infarct size was similar in bone marrow transplant mice at 1 mo (47.1 +/- 5.9%) and at 3 mo (45.3 +/- 7.8%), and echocardiography at 2 and 8 wk revealed decreasing left ventricular function. In infarcted heart, GFP-positive cells that expressed desmin and troponin T-C were identified by confocal microscopy. GFP and troponin T-C double-positive cells were predominantly in the peri-infarcted region (1 mo, 365 +/- 45 cells/50 sections; 3 mo: 458 +/- 100 cells/50 sections; p < 0.05 versus noninfarct, infarct, and sham-operated regions). Furthermore, BMC mobilization and differentiation into cardiomyocytes was found to be complete within 1 mo after myocardial infarction. These results demonstrate that circulating BMC undergo mobilization and differentiation in cardiac cells after myocardial infarction. Future studies are required to determine the molecular signaling mechanisms responsible for this phenomenon.

Minimal evidence of transdifferentiation from recipient bone marrow to parenchymal cells in regenerating and long-surviving human allografts

Liver, small intestine, and heart allografts in residence for 4 days to 16 years were analyzed by simultaneous XY fluorescent in situ hybridization to search for evidence of the recently described process of transdifferentiation of recipient bone marrow stem cells to allograft parenchymal cells. These studies were carried out in an effort to find conditions associated with maximal levels of engraftment or expansion of the recipient parenchymal cells. Despite prolonged survival up to 16 years, regeneration after severe preservation injury or use of split livers, only rare, isolated and tentatively identified recipient hepatocytes were detected in liver allografts. In intestinal allografts, despite survival of up to 8 years and extensive mucosal regeneration because of severe damage from acute rejection, there was no crypt replacement by recipient epithelial cells. In cardiac allografts, no recipient myocytes were detected despite recipient survival for 2-3 days and 3-4 weeks after myocardial infarcts at 5 and 8 years after transplantation. Parenchymal cell transdifferentiation from recipient bone marrow stem cells was rare to nonexistent in severely injured, regenerating, and long-surviving allografts. The rare isolated recipient parenchymal cells tentatively identified did not appear to behave as stem cells: they did not form clusters and did not increase with time after transplantation. Because of the extremely low frequency, interpretation was difficult. Regardless of these results, a more vigorous search for conditions that promote transdifferentiation is warranted.

Generation of a chimeric mouse reconstituted with green fluorescent protein-positive bone marrow cells: a useful model for studying the behavior of bone marrow cells in regeneration in vivo

Studies have indicated that bone marrow contains both hematopoietic stem cells and mesenchymal stem cells that can differentiate into a variety of mesenchymal tissues, such as bone, cartilage, muscle, and adipose tissue. Therefore, bone marrow cells are thought to be very useful for cell and gene therapy for various diseases. However, the multipotentiality of these cells remains unclear. To address this issue, we established a chimeric model mouse stably reconstituted with green fluorescent protein (GFP)-marked bone marrow cells. We injected bone marrow cells from GFP-transgenic C57BL/6 mice into the tail veins of recipient wild-type C57BL/6 mice that had been irradiated with a lethal dose of 10 Gy from a cesium source. Microscopic examination and fluorescence-assisted cell sorter (FACS) analysis showed that bone marrow cells, including mesenchymal cells, were almost completely reconstituted with GFP+ cells 5 weeks after transplantation. FACS analysis with lineage-specific antibodies confirmed that the GFP+ cells could differentiate into all types of blood cells. To confirm the usefulness of this mouse model, we studied the role of circulating bone marrow-derived cells in healing of damaged intestine. We performed amputation and anastomosis of the jejunum 10 cm from the pyloric region of the stomach. On the third day after operation, a large number of GFP+ cells were infiltrated in the area of anastomosis, and these cells were positive for CD45 and F4/80 antigens. In 7 days, several cells became negative for CD45 and F4/80 and positive for alpha smooth muscle actin antigen, which is specific for smooth muscle. This finding suggested that bone marrow-derived cells had differentiated into smooth muscle. Because reconstituted bone marrow cells as opposed to injected bone marrow cells, behave naturally, this model is ideal for studying the multipotentiality of bone marrow cells in vivo.

Animal models for mucopolysaccharidoses and their clinical relevance

The mucopolysaccharidoses (MPS) are characterized by the accumulation of glycosaminoglycans (GAG) and result from the impaired function of one of 11 enzymes required for normal GAG degradation. MPS II was the first MPS to be defined clinically in humans and is caused by deficient activity of the enzyme iduronate-2-sulphatase. MPS VI was the first MPS recognized in an animal; since then, all but MPS IIIC and IX have been described as naturally occurring in animals or made by knock-out technology. As in humans, all are inherited as autosomal recessive traits, except for MPS II, which is X-linked. Most animal colonies have been established from single related heterozygous animals, making the affected offspring homozygous for the same mutant allele. Importantly, these models have disease pathology that is similar to that seen in humans, making the animals extremely valuable for the investigation of disease pathogenesis and the testing of therapies. Large animal homologues are similar to humans in natural genetic diversity, approaches to therapy and care, and the possibility of evaluating long-term effects of treatment. Therapeutic strategies for MPS include enzyme replacement therapy, heterologous bone marrow transplantation, and somatic cell gene transfer, all of which have been tested in animals with some success.

Preservation of hematopoietic properties in transplanted bone marrow cells in the brain

Recent studies have described the possible transdifferentiation of bone marrow cells (BMC) into neurons and glia when they migrate to the brain. However, we have reported that some immature BMC migrating into the brain parenchyma after bone marrow transplantation express early hematopoietic markers but not neural or glial markers. The present study further characterizes transplanted BMC that migrate to the brain. Double immunolabeling confirmed that BMC migrating to the brain expressed hematopoietic but not neural markers, such as nestin, microtubule-associated protein-2 and glial fibrillary acidic protein, even 4 and 18 weeks after bone marrow transplantation. BMC that expressed green fluorescent protein also expressed hematopoietic but not neural markers when cultured with mixed brain cells according to double immunolabeling and single-cell dissection using a laser. Analysis of the DNA content indicated that most of the migrated BMC were arrested at the G0/G1 phase, and aneuploidy or tetraploidy was undetectable. Thus, BMC that migrate to the brain probably have preserved hematopoietic properties under physiological conditions.

Stress proteins and glial functions: possible therapeutic targets for neurodegenerative disorders

Recent findings suggest that unfolded or misfolded proteins participate in the pathology of several neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease. Usually, several stress proteins and glial cells act as intracellular molecular chaperones and show chaperoning neuronal function, respectively. In the brains of patients with neurodegenerative disorders, however, stress proteins are expressed and frequently associated with protein aggregates, and glial cells are activated around degenerative regions. In addition, several stress proteins and glial cells may also regulate neuronal cell death and loss. Therefore, some types of stress proteins and glial cells are considered to be neuroprotective targets. We summarize the current findings regarding the neuroprotective effects of stress proteins and glial cells, and discuss the possibility of using this knowledge to develop new therapeutic strategies to treat neurodegeneration.

Neuroplasticity in Alzheimer's disease

Ramon y Cajal proclaimed in 1928 that "once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably. In the adult centers the nerve paths are something fixed, ended and immutable. Everything must die, nothing may be regenerated. It is for the science of the future to change, if possible, this harsh decree." (Ramon y Cajal, 1928). In large part, despite the extensive knowledge gained since then, the latter directive has not yet been achieved by 'modern' science. Although we know now that Ramon y Cajal's observation on CNS plasticity is largely true (for lower brain and primary cortical structures), there are mechanisms for recovery from CNS injury. These mechanisms, however, may contribute to the vulnerability to neurodegenerative disease. They may also be exploited therapeutically to help alleviate the suffering from neurodegenerative conditions.

Bone marrow stem cells do not repopulate the healthy upper respiratory tract

Recent studies reported differentiation of both bone marrow and tissue-specific stem cells into cells of other organs. The demonstration that bone marrow stem cells differentiate into human hepatocytes in vivo has raised the possibility of new therapeutic approaches for liver disease. For diseases such as cystic fibrosis (CF), correction of the respiratory epithelium is being attempted by gene therapy. Differentiation of bone marrow stem cells into epithelium of the lung and airway was recently reported in an animal model, and would provide an alternative approach. We examined the nasal epithelium of female patients up to 15 years after gender-mismatched bone marrow transplantation. Donor-derived epithelial cells were sought with a combination of Y-chromosome fluorescence in situ hybridization and anti-cytokeratin antibody. In nasal brushing samples from 6 transplant-recipients, a median of 2.5% (range, 0.7-18.1%) of nuclei was male and identified as being of donor-origin. However, a complete absence of staining with anti-cytokeratin antibodies confirmed that these were not epithelial cells, but were likely to be either intraepithelial lymphocytes or mesenchymal cells. Following whole bone marrow transplantation, bone marrow progenitor cells do not differentiate into respiratory epithelium of the healthy upper airway. The differences between this and other studies could relate to the cells transplanted, to differential rates of turnover, or to the requirement for specific triggers to stimulate migration and differentiation. In the absence of such conditions, whole bone marrow transplantation is unlikely to provide a route for correction of the CF airway.

Contribution of bone marrow cells to liver regeneration after partial hepatectomy in mice

BACKGROUND/AIMS

We examined whether bone marrow (BM) cells can commit to liver-consisting cells during liver regeneration after partial hepatectomy, using mice transplanted with green fluorescent protein (GFP) positive BM from GFP transgenic mice.

METHODS

Partial hepatectomy or sham operation was performed. Lineage marker analysis of GFP positive liver cells was by immunostaining and flow cytometry. DiI-labeled acetylated low-density lipoprotein uptake or microsphere phagocytosis was examined in vitro. Lineage marker expression in BM and peripheral blood (PB) cells, and the vascular endothelial growth factor (VEGF) concentration in the liver were also examined.

RESULTS

In hepatectomized mice, significantly more GFP positive cells participated in liver sinusoid than in sham-operated mice, expressing CD31 but not albumin. The percentage of cells that incorporated acetylated low-density lipoprotein but not microspheres was 69.5+/-3.4%, while 28.3+/-2.6% incorporated both, revealing sinusoidal endothelial and Kupffer cells, respectively. Increased expression of the CD31 and CD16/CD32 on GFP positive liver cells was also detected. The elevation of the VEGF concentration during liver regeneration and the increase in the CD34 and Flk-1 expression in the liver, BM, and PB cells suggested endothelial progenitor cell mobilization.

CONCLUSIONS

GFP cell-marking provided direct evidence of the BM cells participation in liver regeneration after hepatectomy, where the majority was committed to sinusoidal endothelial cells probably through endothelial progenitor cell mobilization.

Identification of new therapeutic targets for prevention of CNS inflammation

Multiple sclerosis (MS) is a disease of complex pathologies, which involves infiltration by CD4(+) and CD8(+) T cells of and response within the central nervous system. Expression in the CNS of cytokines, reactive nitrogen species and costimulator molecules have all been described in MS. Notably, the cytokines IFN-gamma and TNF are strongly expressed. Microglial cells in the CNS express costimulator molecules and it is assumed that they play a role in directing or inducing the T cell response. Transgenic experiments have tested the effects of overexpression of these molecules in mice and have shown that TNF has multiple effects in the CNS. These range from pro-inflammatory effects of soluble TNF signalling through one of its receptors TNF-RI, to protective/regenerative effects of membrane-associated TNF signalling through the other receptor, TNF-RII. Although IFN-gamma induces nitric oxide production via the enzyme inducible nitric oxide synthase, which is immunosuppressive, IFN-gamma is predominantly pro-inflammatory. In CNS disease in mice that involves CD8(+) T cells, IFN-gamma blockade is protective. Finally, microglial expression of the costimulator ligand B7.2 induces demyelinating pathology. Animal experiments therefore point to IFN-gamma and costimulatory microglia as logical targets of therapy for MS. IFN-gamma represents a more accessible target and should therefore be pursued at the earliest opportunity.

Bone marrow-derived cells as progenitors of lung alveolar epithelium

We assessed the capacity of plastic-adherent cultured bone marrow cells to serve as precursors of differentiated parenchymal cells of the lung. By intravenously delivering lacZ-labeled cells into wild-type recipient mice after bleomycin-induced lung injury, we detected marrow-derived cells engrafted in recipient lung parenchyma as cells with the morphological and molecular phenotype of type I pneumocytes of the alveolar epithelium. At no time after marrow cell injection, did we detect any engraftment as type II pneumocytes. In addition, we found that cultured and fresh aspirates of bone marrow cells can express the type I pneumocyte markers, T1α and aquaporin-5. These observations challenge the current belief that adult alveolar type I epithelial cells invariably arise from local precursor cells and raise the possibility of using injected marrow-derived cells for therapy of lung diseases characterized by extensive alveolar damage.

Bone marrow is a reservoir of repopulating mesangial cells during glomerular remodeling

The renal glomerulus, whose cellular components are developmentally derived from the mesenchyme, plays a pivotal role in filtratating plasma. Irretrievable changes of glomerular components are responsible for the initiation and progression of impaired renal function. Recently, it has been shown that functional stem cells exist in the bone marrow of adult bodies and that they can reconstitute damaged tissues of the mesenchymal origin. To examine whether the bone marrow provides stem cells to damaged glomeruli, transgenic rats carrying enhanced green fluorescence protein (EGFP rat) were established in a systemic and constitutive manner. After transplanting the bone marrow of EGFP rats into wild-type rats, the progeny of the transplanted marrow cells were tracked with a tag of EGFP. Recruitment of bone marrow-derived cells into glomeruli was dramatically facilitated in response to mesangiolysis evoked in anti-Thy1 antibody-mediated glomerulonephritis. In the restored glomeruli, 11% to 12% of glomerular cells were derived from the transplanted bone marrow. The number of bone marrow-derived CD45(+) cells transiently increased during the disease process, and CD45-negative cells constantly accounted for more than half of the bone marrow-derived population in glomeruli. Bone marrow-derived Thy1(+) cells kept increasing in number until the remodeling ceased and finally made up 7% to 8% of glomerular cells. Laser scanning microscopy displayed that the bone marrow-derived Thy1(+) cells provide structural support for glomerular capillaries, which indicates that they are mesangial cells. Although CD45(-)Thy1(-) bone marrow-derived cells exist during the remodeling of glomeruli, none of them expressed endothelial markers such as Factor VIII and RECA1 as long as they were tested. The results indicate that the bone marrow can give rise to mesangial cells in vivo.