Search PubMed⌕ Search

Biomedical subjects

Robin J M Franklin

Publications and source records attributed to Robin J M Franklin.

At least 19 recordsLinked to original sources
PubMed2007

Calponin is expressed by fibroblasts and meningeal cells but not olfactory ensheathing cells in the adult peripheral olfactory system.

Olfactory ensheathing cells (OECs), the principal glial cells of the peripheral olfactory system, have many phenotypic similarities with Schwann cells of the peripheral nervous system. This makes reliably distinguishing these two cells types difficult, especially following transplantation into areas of injury in the central nervous system. In an attempt to identify markers by which these two cells types can be distinguished, a recent proteomic analysis of fetal OECs and adult Schwann cells identified the actin-binding protein calponin as a potential marker expressed by OECs but not Schwann cells. Since many studies designed with the translational goal of autologous transplantation in mind have used adult OECs, this study examined the expression of calponin by adult OECs, both in vivo within the peripheral olfactory system and in vitro. Calponin colocalized with strongly fibronectin positive fibroblasts in the olfactory mucosa (OM) and meningeal cells in the olfactory bulb (OB) but not with S100beta or neuropeptide-Y positive OECs. In tissue culture, calponin was strongly expressed by fibronectin-expressing fibroblasts from OM, sciatic nerve and skin and by meningeal cells from the OB, but not by p75(NTR)- and S100beta-expressing OECs. These data, supported by Western blotting, indicate that calponin can not be used to distinguish adult OECs and Schwann cells.

Animals↗
PubMed2006

Mutations in genes causing human familial isolated hyperparathyroidism do not account for hyperparathyroidism in Keeshond dogs.

The roles of the calcium sensing receptor gene (CaSR) and the multiple endocrine neoplasia gene (MEN1) were investigated in Keeshond dogs with familial hyperparathyroidism. Mutations in these genes have been shown to cause familial isolated hyperparathyroidism (FIH) in humans. Affected dogs were identified through measurement of blood calcium and parathyroid hormone levels. Parathyroid tissue and whole blood was used to clone the cDNAs and individual exonic sequences of both candidate genes. No sequence abnormalities were identified when comparing normal and affected dogs, suggesting that a mapping strategy may be the most appropriate approach for identifying the genetic basis of this valuable comparative canine disease model.

Animals↗
PubMed2006

Cdc42 and Rac1 signaling are both required for and act synergistically in the correct formation of myelin sheaths in the CNS.

The formation of myelin sheaths in the CNS is the result of a complex series of events involving oligodendrocyte progenitor cell (OPC) proliferation, directed migration, and the morphological changes associated with axon ensheathment and myelination. To examine the role of Rho GTPases in oligodendrocyte biology, we have used a conditional tissue-specific gene-targeting approach. Ablation of Cdc42 in cells of the oligodendrocyte lineage did not affect OPC proliferation, directed migration, or in vitro differentiation, but it led to the formation of a unique and stage-specific myelination phenotype. This was characterized by the extraordinary enlargement of the inner tongue of the oligodendrocyte process and concomitant formation of a myelin outfolding as a result of abnormal accumulation of cytoplasm in this region. Ablation of Rac1 also resulted in the abnormal accumulation of cytoplasm in the inner tongue of the oligodendrocyte process, and we provide genetic evidence that rac1 synergizes with cdc42 in a gene dosage-dependent way to regulate myelination.

Animals↗
PubMed2006

Beta1-integrin signaling mediates premyelinating oligodendrocyte survival but is not required for CNS myelination and remyelination.

Previous reports, including transplantation experiments using dominant-negative inhibition of beta1-integrin signaling in oligodendrocyte progenitor cells, suggested that beta1-integrin signaling is required for myelination. Here, we test this hypothesis using conditional ablation of the beta1-integrin gene in oligodendroglial cells during the development of the CNS. This approach allowed us to study oligodendroglial beta1-integrin signaling in the physiological environment of the CNS, circumventing the potential drawbacks of a dominant-negative approach. We found that beta1-integrin signaling has a much more limited role than previously expected. Although it was involved in stage-specific oligodendrocyte cell survival, beta1-integrin signaling was not required for axon ensheathment and myelination per se. We also found that, in the spinal cord, remyelination occurred normally in the absence of beta1-integrin. We conclude that, although beta1-integrin may still contribute to other aspects of oligodendrocyte biology, it is not essential for myelination and remyelination in the CNS.

Animals↗
PubMed2006

Females remyelinate more efficiently than males following demyelination in the aged but not young adult CNS.

To assess the effects of sex on CNS remyelination, demyelinating lesions were induced by injection of ethidium bromide into the caudal cerebellar peduncle of Sprague-Dawley rats divided into the following 8 groups: young adult male, young adult female, old adult male and old adult female and each of these in which the gonads had been removed 4 weeks prior to lesion induction. Remyelination was assessed, blinded to grouping, by a ranking analysis using standard morphological criteria. In young adult animals, where remyelination proceeds rapidly, there was no difference in the remyelination at four weeks after lesion induction in male or females regardless of whether they were intact or castrated/ovariectomised. However, in old adult rats, where remyelination proceeds slowly, the extent of oligodendrocyte remyelination was significantly less in males compared to females at 8 weeks after lesion induction. Removal of gonads did not affect remyelination in old rats of either gender. These results indicate a sex-associated divergence in remyelination efficiency that occurs with ageing that is unaffected by the removal of gonadal sources of sex steroid hormones.

Aging↗
PubMed2006

Magnetic resonance imaging of functional Schwann cell transplants labelled with magnetic microspheres.

There is increasing interest in the use of magnetic resonance imaging (MRI) methods for tracking the fate of labelled cells in vivo post-implantation. The majority of studies have employed cell labels based on nanometer-sized ultrasmall dextran-coated iron oxide particles (USPIO), which are detected through signal hypointensity in T2-weighted images. Although sensitive to MR detection, these labels can be difficult to distinguish from other sources of signal loss in vivo and can be diluted by cell division. Recently, a micron-sized cell label has been described that is much more sensitive to MR detection and which allows detection of single labels in vivo. We show here that glial cells readily take up this label in culture and that the labelled Schwann cells can be detected in vivo by MRI following their implantation into a demyelinated lesion in the rat spinal cord. Signal loss due to the label is sufficiently great that the labelled cells can easily be distinguished from surrounding haemorrhage at the lesion site. Subsequent histological analysis of the lesion area showed that the transplanted cells were remyelinating the demyelinated axons, demonstrating that the labelled cells retained their biological function and that the majority of the label had remained within the transplanted cells.

Animals↗
PubMed2006

Oligodendrocyte progenitor cell (OPC) transplantation is unlikely to offer a means of preventing X-irradiation induced damage in the CNS.

Oligodendrocyte lineage cells [oligodendrocytes and their parent cells, the oligodendrocyte progenitor cells (OPCs)] are depleted by X-irradiation and progenitor cell transplantation has been proposed as a therapeutic strategy to counteract radiation induced myelopathy. Previous studies have demonstrated that oligodendrocyte progenitor cell (OPC) depletion is a prerequisite for establishing transplanted OPCs in normal tissue. One can therefore predict that the extent and timing of OPC depletion and regeneration following X-irradiation will be crucial factors in determining the feasibility of this therapeutic approach. To address this issue, we have examined the time course of OPC depletion and regeneration following a range of X-irradiation doses (5 to 40 Gy), and its relationship to establishing transplanted OPCs in X-irradiated tissue. Doses above 10 Gy resulted in rapid death of OPCs. With doses up to 20 Gy, surviving X-irradiated OPCs were capable of robust regeneration, restoring normal densities within 6 weeks. Transplanted OPCs could only be established in tissue that had been exposed to > or =20 Gy. Since 20 Gy is close to the ED50 for radiation necrosis, our findings demonstrate the limitation of OPC replacement strategies.

Animals↗
PubMed2006

Myelin impairs CNS remyelination by inhibiting oligodendrocyte precursor cell differentiation.

Demyelination in the adult CNS can be followed by extensive repair. However, in multiple sclerosis, the differentiation of oligodendrocyte lineage cells present in demyelinated lesions is often inhibited by unknown factors. In this study, we test whether myelin debris, a feature of demyelinated lesions and an in vitro inhibitor of oligodendrocyte precursor differentiation, affects remyelination efficiency. Focal demyelinating lesions were created in the adult rat brainstem, and the naturally generated myelin debris was augmented by the addition of purified myelin. After quantification of myelin basic protein mRNA expression from lesion material obtained by laser capture microdissection and supported by histological data, we found a significant impairment of remyelination, attributable to an arrest of the differentiation and not the recruitment of oligodendrocyte precursor cells. These data identify myelin as an inhibitor of remyelination as well as its well documented inhibition of axon regeneration.

Animals↗
PubMed2006

Olig gene function in CNS development and disease.

Olig1 and Olig2 encode basic helix-loop-helix (bHLH) transcription factors that are expressed in both the developing and mature vertebrate central nervous system. While numerous studies have established critical functions for Olig genes during the formation of motor neurons and oligodendrocytes of the ventral neural tube, their roles at later stages of development and in adulthood have remained relatively obscure. Recent studies, however, reveal that in the fetal dorsal spinal cord and neural progenitor cells of the adult brain, Olig expression continues to mark, and may regulate, the formation of oligodendroglia. Studies of Olig expression in human brain tumors and repair of demyelinating lesions suggest the possibility of additional functions in a variety of neurological diseases.

Animals↗
PubMed2006

Inflammation stimulates myelination by transplanted oligodendrocyte precursor cells.

Inflammation associated with CNS demyelination provides an important stimulus for the activation of endogenous oligodendrocyte precursor cells (OPCs) and subsequent remyelination. This view is largely based on "loss-of-function" studies, whereby remyelination is impaired following depletion of inflammatory cells or mediators. However, "gain-of-function" approaches, asking whether inflammation directly enhances remyelination, have received less attention. We have addressed this issue using a model in which OPCs transplanted into the adult rat retina myelinate retinal ganglion cell axons around the point of injection. Inflammation (characterized by increased expression of the macrophage marker ED1 and the astrocyte marker GFAP, and the up-regulation of multiple cytokines) was induced in the retina by the administration of the TLR-2 ligand zymosan. Myelination, revealed by MBP+ myelin sheaths, was substantially increased when OPCs were injected into the inflamed retina compared to that achieved following transplantation into the normal, noninflamed retina. Our results have important implications for the development of immunomodulatory treatments for acute demyelinating disease and for the therapeutic creation of proremyelination environments in chronic demyelinating disease.

Animals↗
PubMed2006

Corticosteroids delay remyelination of experimental demyelination in the rodent central nervous system.

High dose corticosteroid (CS) administration is a common mode of therapy in treatment of acute relapses in multiple sclerosis (MS) but the effects of CS on remyelination and the cellular mechanisms mediating this repair process are controversial. We have examined CS effects on repair of toxin-induced demyelinating lesions in the adult rat spinal cord. Corticosteroids reduced the extent of oligodendrocyte remyelination at 1 month post lesion (whereas Schwann-cell mediated repair was unaffected). However, CS did not cause permanent impairment of remyelination as lesions were fully remyelinated at 2 months after cessation of treatment. The delay in oligodendrocyte mediated repair could be attributed to inhibition of differentiation of oligodendrocyte progenitor cells (OPCs) into oligodendrocytes, with no effect of CS treatment observed on OPC colonisation of the lesions. No differences were observed in animals treated with methylprednisolone succinate alone or with a subsequent prednisone taper indicating that CS effects occur at an early stage of repair. The potential consequences of delayed remyelination in inflammatory lesions are discussed.

Adrenal Cortex Hormones↗
PubMed2006

Comparison of cell populations derived from canine olfactory bulb and olfactory mucosal cultures.

OBJECTIVE: To evaluate the numbers and proportions of olfactory ensheathing cells (OECs) in cell cultures derived from the olfactory bulb (OB) and olfactory mucosa of dogs. ANIMALS: 7 dogs. PROCEDURES: OB tissue and olfactory mucosa from the nasal cavity and frontal sinus were obtained from euthanatized dogs and prepared for cell culture. At 7, 14, and 21 days of culture in vitro, numbers and proportions of OECs, astrocytes, and fibroblasts were determined via immunocytochemistry. Antibody against the low-affinity nerve growth factor receptor p75 was used to identify OECs, antibody against glial fibrillary acidic protein was used to identify astrocytes, and antibody against fibronectin was used to identify fibroblasts. RESULTS: Cultured OECs derived from the olfactory mucosa of the nasal cavity and frontal sinus had similar characteristics. However, whereas OECs in the OB cell cultures constituted approximately 50% of the cells at 7 days and approximately 75% at 21 days the proportion of OECs in cultures derived from both mucosal types was much lower, with approximately 40% OECs at 7 days and approximately 25% at 21 days. Analysis of OEC numbers revealed that these changes were accompanied by corresponding decreases and increases in the population of cells with fibronectin receptors. CONCLUSIONS AND CLINICAL RELEVANCE: Although olfactory mucosal cell cultures yielded a sufficient number of OECs for spinal cord transplantation procedures in dogs, modification of culture conditions would be required to ensure that the derived cell population contained a sufficient proportion of OECs.

Animals↗
PubMed2005

Enhancing central nervous system remyelination in multiple sclerosis.

Recent studies on adult neural stem cells and the developmental biology of myelination have generated the expectation that neural precursors can repair the damaged central nervous system of multiple sclerosis patients where the endogenous remyelination process has failed. As a result, many laboratories are engaged in translational studies in which the goal is to design ways to promote remyelination and repair. Here we raise issues highlighted by prior experimental and human work that should be considered lest these studies become "lost in translation."

Animals↗
PubMed2005

Differences in the early inflammatory responses to toxin-induced demyelination are associated with the age-related decline in CNS remyelination.

CNS remyelination occurs more rapidly in young adult rats than in old rats. Since the inflammatory response initiated by demyelination is an important trigger for remyelination, we address whether ageing changes in remyelination are associated with changes in the inflammatory response. Using a toxin model of demyelination, where the inflammatory response largely comprises macrophages, we show that there is a delay in both recruitment and activation of OX-42+ and macrophage scavenger receptor B+ macrophages following demyelination in older rats (10-13 months) compared to young rats (8-10 weeks). This difference is associated with a slower onset of increased expression of several chemokine mRNAs. However, many inflammatory cytokines have similar mRNA expression patterns, with the exception of IL-1beta, IL-6 and TNF-alpha, which have prolonged expression in the older animals. Differences in IL-1beta mRNA expression, a cytokine specifically implicated in CNS remyelination, are not reflected in differences in protein expression detected by immunocytochemistry. These data relate the age-associated delay in remyelination efficiency to changes in the macrophage and inflammatory mediator response to demyelination.

Aging↗
PubMed2005

Mechanisms of CNS remyelination--the key to therapeutic advances.

There are two components to the treatment of multiple sclerosis (MS); the first is to prevent damage occurring, and the second is to repair the residual damage. While considerable progress has been made in the recent years with the former through the development of anti-inflammatory and immunomodulatory therapies, there are currently no effective repair therapies routinely used in MS patients. This represents a significant gap in the MS clinician's therapeutic armoury. In this article we argue that a clear understanding of the repair mechanisms following CNS demyelination is fundamental to filling this gap. We discuss (1) the cellular events involved in remyelination, (2) changes in transcription factor expression within oligodendrocyte precursor cells associated with their activation in response to demyelination, (3) the role of platelet derived growth factor in the OPC recruitment phase of remyelination, and (4) the significance of the inflammatory response associated with demyelination in creating a signalling environment that favours remyelination.

Animals↗
PubMed2005

Minocycline-mediated inhibition of microglia activation impairs oligodendrocyte progenitor cell responses and remyelination in a non-immune model of demyelination.

Minocycline, a tetracycline derivative, disrupts inflammatory processes within the CNS and reduces demyelination in experimental autoimmune encephalomyelitis. Several recent studies indicate that components of the inflammatory response to demyelination may be beneficial for the regenerative process of remyelination. In this study we examined the effects of minocycline on remyelination independent of its effects in limiting immune-mediated white matter damage using a toxin model of demyelination. Demyelinating lesions were induced by injection of ethidium bromide into caudal cerebellar peduncles of adult rats. Minocycline or PBS was administered by twice daily injections from day 1 prior to lesion-induction to post lesion day 3. Remyelination was assessed, blinded to grouping, using standard morphological criteria. The microglia activation within the lesion was assessed by examining the expression of OX-42 and major histocompatibility class II immunoreactivity. The oligodendrocyte progenitor cell (OPC) response was quantified by in situ hybridization using probes for OPC-expressed mRNAs, platelet-derived growth factor receptor-alpha and Olig-1. Minocycline treatment strongly inhibited microglia/macrophage activation at day 1 and day 3 post-lesion induction, and suppressed the OPC response to demyelination. We also found a significant decrease in the extent of oligodendrocyte but not Schwann cell remyelination in the minocycline-treated animals as compared with controls at 3 weeks post-lesion induction. These results indicate that microglia/macrophage activation is an important process for remyelination and further support the concept that suppression of inflammatory response may impair remyelination.

Animals↗
PubMed2005

Macrophage-depletion induced impairment of experimental CNS remyelination is associated with a reduced oligodendrocyte progenitor cell response and altered growth factor expression.

Although macrophages are mediators of CNS demyelination, they are also implicated in remyelination. To examine the role of macrophages in CNS remyelination, adult rats were depleted of monocytes using clodronate liposomes and demyelination induced in the spinal cord white matter using lysolecithin. In situ hybridization for scavenger receptor-B and myelin basic protein (MBP) revealed a transiently impaired macrophage response associated with delayed remyelination in liposome-treated animals. Macrophage reduction corresponded with delayed recruitment of PDGFRalpha+ oligodendrocyte progenitor cells (OPCs), which preceded changes in myelin phagocytosis, indicating a macrophage effect on OPCs independent of myelin debris clearance. Macrophage-depletion induced changes in the mRNA expression of insulin-like growth factor-1 and transforming growth factor beta1, but not platelet-derived growth factor-A and fibroblast growth factor-2. These data suggest that the macrophage response to toxin-induced demyelination influences the growth factor environment, thereby affecting the behavior of OPCs and hence the efficiency of remyelination.

Animals↗