1,737,009 research outputs found
The Normandy field study on juvenile osteochondral conditions: conclusions regarding the influence of genetics, environmental conditions and management, and the effect on performance
No full textJuvenile osteochondral conditions (JOCC) have a major impact on the equine industry and include many musculoskeletal disorders of the young horse, of which osteochondrosis (OC) is the most prominent. The Breeding, Osteochondral Status and Athletic Career (BOSAC) project is the first large, comprehensive, longitudinal field study on the subject conducted in three breeds of performance horses (Thoroughbreds, Standardbred Trotters and Warmbloods) that were monitored in their natural environment where they were reared under common field conditions. The BOSAC study used a radiographic protocol designed for field use coupled to an internally validated severity scoring system, providing weighted radiographic findings as the primary outcome measure. The natural courses of various JOCC appear to differ, according to the joint and condition involved. Genetically, there were also large differences with moderate heritabilities in the tarsocrural and metacarpophalangeal/metatarsophalangeal joints and virtually no heritability for femoropatellar OC. There was a strong influence of exercise history (as an environmental condition) on the manifestation and natural course of JOCC. In the younger age class
Different flavors of pluripotency
No full textPluripotent stem cells have the ability to give rise to derivatives of all the germ layers and hold therefore great promise for future applications like cell replacement therapies and drug screenings, for example. Pluripotent stem cells can be expanded indefinitely which leads to an almost unlimited source of cells. These unique characteristics allow for the biochemical study of developmental processes in vitro that are not feasible in vivo due to restricted cell numbers within one embryo. The recent derivation of induced pluripotent stem cells (iPSC) from somatic cells unlocked a second source for pluripotent stem cells and fueled the hope for treatment of numerous diseases. But a comprehensive understanding of pluripotency per se is necessary to fully exploit the possibilities of these patient specific pluripotent stem cells while limiting the accompanying risks. This thesis focuses on different aspects of pluripotency in mouse and human pluripotent stem cells. The use of bacterial artificial chromosome (BAC) recombineering is a common practice to generate transgenic reporter cell lines that faithfully recapitulate the tissue specific expression profile of the gene of interest. We describe here the development of an efficient system for the generation of BAC-based targeting constructs. This system allows for the quick and straightforward generation of a BAC targeting vector and subsequent derivation of recombined BACs to that allows for the manipulation of the mammalian genome. This second part of this thesis concentrates on different aspects of the pluripotent stem cell state. Murine and human pluripotent stem cells show vast differences regarding their colony morphology, growth factor dependency and molecular characteristics and are therefore considered being in two different pluripotent stem cell states: naïve and primed pluripotency respectively. We set out to analyze the influence of the growth factor environment on the outcome of the reprogramming event. We first focused on permissive mouse strains and showed that murine iPS cells from the B6/129 hyrbid strain derived under bFGF and ActivinA signaling are more similar to regular naïve pluripotent stem cells then to primed pluripotent stem cells or EpiSCs. In a second set of experiments we analyzed the opposite scenario: the derivation of human pluripotent stem cells under naïve pluripotent conditions. We used induction of pluripotency and showed that cells can be derived with characteristics of naïve pluripotent stem cells regarding their morphology, growth characteristics and growth factor environment. These cells can facilitate homologous recombination and therefore allow the generation of transgenic human cell lines. The cell are not pluripotent but can be converted into primed pluripotent stem cells via an easy growth factor switch thereby allowing the derivation of transgenic hES like cells from patient derived somatic cells
Canine idiopathic immune-mediated haemolytic anaemia: a review with recommendations for future research
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New therapeutic strategies for canine liver disease; Growth factors and liver progenitor cells
No full textThe liver has the unique capacity to regulate its mass after loss of functional liver cells due to liver disease, injury, and/or toxicity. Unfortunately, in the course of chronic liver disease this meticulously regulated regeneration process is imbalanced resulting in a decreased regenerative capacity. Like in humans, most liver diseases in dogs are chronic and occur through persistent inflammation due to different causes. On-going liver cell damage leads to a reduction of the functional liver cell mass and progressive deposition of fibrous tissue in the liver. We found that regenerative and fibrotic molecular pathways of canine cirrhosis resembled those in human liver samples with cirrhosis, reinforcing the current paradigm of a highly comparable pathophysiology of human and canine hepatic disease. Dogs with liver diseases are therefore relevant animal models for the evaluation of novel therapeutic approaches, such as the stimulation of different cell types (mature or immature) to participate in the regeneration process by growth factor therapy. In the present thesis, two options of approach are proposed; (1) the use of Hepatocyte Growth Factor (HGF) and (2) liver progenitor cell-based therapies. (1) HGF is the principal factor for stimulating the liver to grow and regenerate and suppress fibrosis and apoptosis. Therefore, recombinant HGF was produced and tested for its biological activity. The first clinical trial with recombinant HGF was initiated in dogs with a congenital portosystemic shunt (CPSS). (2) When the proliferation of mature liver cells is inhibited, the proliferation and differentiation (activation) of normally quiescent liver progenitor cells (LPC) are observed. LPC activation has recently been demonstrated in spontaneous canine and human liver diseases and has opened a new field of research in regenerative medicine. A tool to gain insight into the molecular mechanisms and regulatory events leading to LPC activation is provided by culturing these cells in vitro. However, purification of LPCs is complicated due to their scarce number in healthy livers and the lack of specific LPC markers. We described two techniques to isolate and culture LPCs from healthy mature dog livers. These cells were characterized at a molecular level and may be ideally suited for future cell therapies. In conclusion, the results in the present thesis can be mutually beneficial for canine and human biomedical research and provide possible novel means of therapy for liver disease. The research was conducted at the Department of Clinical Sciences of Companion Animals (Faculty Core Programme Tissue Repair and the University Focus Point Growth and Differentiation. Collaborations include Departments of Pathobiology (Prof. De Bruin) and Biochemistry & Cell Biology (Prof. Helms). Collaborations outside the faculty include the Departments of Molecular Pathology (Prof. Roskams) and Molecular Cell Biology (Dr. Vankelecom), University Hospitals of Leuven (Belgium), Zenoaq (Japan), and Intervet B.V. (Boxmeer)
Tooth resorption in cats: contribution of vitamin D and inflammation
No full textTooth resorption in cats Tooth resorption affecting several teeth is a painful disease with a prevalence of up to 75% in household cats and is often accompanied by periodontitis. Tooth resorption is caused by an increased number and activity of tooth-resorbing odontoclasts, cells that share functional characteristics with bone-resorbing osteoclasts. Both vitamin D and inflammatory cytokines stimulate the formation and activity of osteoclasts. Most mammals are able to synthesize vitamin D in their skin, but cats are not able to do so and thus depend on their dietary intake for their vitamin D requirements. Both a deficiency and an excess of dietary vitamin D have been hypothesized to be involved in tooth resorption. The overall focus of this thesis was to gain insight into the possible role of vitamin D and inflammation in tooth resorption in cats. Binding of 1,25-dihydroxycholecalciferol (1,25(OH)2D) to the nuclear vitamin D receptor (nVDR) of fibroblasts and odontoclasts near active resorptive lesions was found to induce the transcription of target genes of the vitamin D pathway, i.e. 1?-hydroxylase, 24-hydroxylase, receptor-activator of NF?B ligand (RANKL), and VDR itself. Inflammatory cells were often found in the resorption lacunae, and the expression of inflammatory cytokine was increased in surrounding tissues. The stimulatory effect of 1,25(OH)2D on osteoclast formation was demonstrated in vitro by the formation of tartrate-resistant acid phosphatase multinucleated cells from peripheral blood originating from cats with tooth resorption. Periodontal pathogenic bacteria may be part of the aetiopathogenesis of tooth resorption in cats through the lipopolysaccharide-induced increase in odontoclast activity. Two periodontal pathogens, Porphyromonas spp. and Tanerella forsythia, were found in dental plaque samples from cats. Two identical isolates of Tanerella forsythia of feline origin were found in a cat and its owner, which supported the idea that cats are a potential source of a periodontal zoonotic agent. Findings support the conclusion that odontoclast activity in cats with tooth resorption is stimulated by locally produced 1,25(OH)2D, facilitated through the nVDR expressing fibroblasts and odontoclasts and enhanced by inflammatory products. Local up-regulation of target genes of the vitamin D pathway further supports the observed increase in the activity of local vitamin D metabolites. We propose that not dietary vitamin D excess but inflammation-induced stimulation of the vitamin D pathway is involved in the pathogenesis of tooth resorption in cats
The hepatic progenitor cell niche in man and dog
No full textChronic progressive liver diseases occur frequently in humans and animals, and lead to severe dysfunction and cirrhosis. The only available treatment is liver transplantation. Due to donor liver shortage, alternatives for liver transplantation are needed. Several forms of hepatitis occurring in dogs present with histological and molecular reaction patterns highly similar to human hepatitis. The important cell types of the liver are hepatocytes (detoxification), cholangiocytes (transport of bile), stellate cells (lipid storage), endothelial cells, Kupffer cells (liver specific macrophages), and hepatic progenitor cells (HPCs, adult liver stem cells). HPCs become activated in liver diseases whit insufficient hepatocyte and/or cholangiocyte replication. The activation is often too little or too late to fully restore liver function. Detailed knowledge of the regulatory signals of HPC activation will be crucial to develop new HPC-based therapies. Furthermore, relevant clinical models are needed to assess safety and efficacy of new treatment strategies and translate fundamental rodent studies into clinical practice. In this thesis we (i) investigated signalling pathways involved in HPC activation in man and dog; and (ii) characterised the canine HPC niche in comparison to man, needed to evaluate its potential as translational model for clinical liver diseases. These studies were exerted in close collaboration with the Department of Morphology and Molecular Pathology (Prof Roskams, Leuven, Belgium). Immunohistochemical comparison of human and canine liver diseases extended the known similarities between these two species to the level of the HPC and its microenvironment (HPC niche). These studies further characterised a canine liver disease with extreme HPC activation unrivalled across species; lobular dissecting hepatitis (LDH). This canine disease offers unique and clinically relevant material for HPC research. Follow up gene-expression and cell culture studies revealed the involvement of Wnt and Notch signalling in proliferation, migration and differentiation of HPCs. Furthermore the well-known self-renewal factor Bmi1 was shown to play a role in HPC proliferation. However, high expression of Bmi1 in aggressive liver tumours highlights the potential risk of tumour formation associated with long standing HPC proliferation. Finally, microarray analysis of LDH revealed a strong involvement of fibrosis, extra cellular matrix (ECM) remodelling and cell-matrix interactions (mainly through integrins) in HPC behaviour during liver disease. Follow up studies should further elucidate the exact role of ECM components in HPC activation. Expression profiling by microarray analysis revealed numerous other new signalling cascades differentially expressed in liver diseases. In collaboration with UMC-Utrecht (Prof Medema) and EU-Rotterdam (Prof Peppelenbosch) two different high throughput screens are now used to discover signalling pathways functionally important in HPC proliferation. The studies document high similarity in histology and regulation of HPCs between man and dog. Therefore we propose clinical liver diseases of the dog as important models to evaluate and implement new HPC based treatment strategies in currently untreatable liver diseases. This work was supported by an NWO-AGIKO research grant and was the basis for the ZonMW grant on liver stem cells on which recently started a PhD-student and a post-doctoral researcher
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