The metabolic and functional alterations which occur during the acute phase of nephrotoxic nephritis (NTN) in rats, a model of immune-mediated glomerulonephritis, result from a cooperative ...interaction between PMNs and platelets (PLTs). In consequence, we hypothesized that fibrinogen (Fg) might play a critical role in this process and, accordingly, we found that defibrination of animals decreased both the acute phase proteinuria in NTN (approximately 70%) as well as the influx of PLTs and PMNs into the glomerulus (approximately 40-50%). In contrast, blockade of the PLT Fg receptor, alpha IIb beta 3, with the RGD peptidomimetic SC-49992 decreased proteinuria (approximately 90%) without substantially altering the influx of PMNs or PLTs. Immunocytochemistry showed a marked increase in beta 3 integrin expression in inflamed glomeruli which was prevented either by PMN or PLT depletion before disease induction. FACS and immunocytochemical analysis of glomerular cell dissociates demonstrated that beta 3 integrin expression was predominantly on intraglomerular PLTs. In vitro, activated PLTs stimulated the PMN respiratory burst, an interaction which could be inhibited by Fg receptor blockade. In sum, acute NTN is accompanied by a marked increase in glomerular beta 3 integrin expression predominantly due to the influx of PLTs which localize to the glomerulus in a PMN-dependent fashion. Fg appears to serve a major role as a coactivating stimulus for PLT-PMNs in situ via alpha IIb beta 3, potentially mediating the PMN respiratory burst which contributes to proteinuria. Fg may also play a subsidiary role in PMN/PLT comigration.
Ten human melanoma cell lines were examined for integrin-receptor expression using a panel of antibodies directed against different integrin subunits. Considerable heterogeneity was detected for ...levels of expression of 7 integrins, including the alpha v beta 3 vitronectin receptor where a correlation between tumorigenic capacity in athymic nude mice and alpha v beta 3 levels was found. Detailed analysis of the vitronectin receptor on these lines revealed heterogeneity of composition. In one cell line, VUP, an alpha v beta 1 association was detected and, by antibody-inhibition studies, this receptor was shown to bind vitronectin as its ligand. In another line, DX3, evidence was obtained which indicated that apart from the alpha v beta 3 receptor the alpha v was able to associate with another beta subunit which was not beta 3. The existence of these alternative forms of the vitronectin receptor in this small sample of tumours of common origin might explain why the capacity to bind to fibrinogen and vitronectin substrates by these cells did not necessarily correlate with alpha v beta 3 levels.
Genetic diseases of osteoclasts include those in which osteoclast function is compromised, such as in osteopetrosis, and diseases of osteoclast overactivity, such as the pagetic disorders. The ...genetic basis of these conditions is now largely known and this review gives an update on the most recent findings and functional studies supporting the role of genes in disease pathogenesis. Loss-of-function mutations in the genes TCIRG1, CLCN7, OSTM1 and PLEKHM1 are found in autosomal recessive osteopetrosis, and current evidence suggests they are mechanistically linked by their involvement in the trafficking of acidic vesicles in osteoclasts. The genetic defects in osteoclast-poor osteopetrosis remain to be found. Autosomal dominant osteopetrosis type II is also caused by loss-of-function mutations in CLCN7. Juvenile Paget's disease is caused by loss-of-functlon mutations in the gene for osteoprotegerin (OPG), TNFRSF11B, and is an endocrine disorder which can be treated by reconstituting OPG levels. The other pagetic diseases appear to be more osteoclast-autonomous. Classic Paget's disease of bone (PDB) is associated with mutations in SQSTM1, the complex syndrome known as inclusion body myositis with PDB and frontotemporal dementia (IBMPFD) with mutations in VCP, and the severe pagetic disorders early-onset PDB, familial expansile osteolysis and expansile skeletal hyperphosphatasia are all associated with mutations in TNFRSF11A, the gene for RANK. The common pathway affected by these genes is less easily deduced, but most likely involves perturbation of the proteasomal degradation pathway. We suggest that these pagetic disorders have many similarities with "inclusion body diseases" of the brain and skeletal muscle. Further understanding of pagetic disorders may require animal models that faithfully represent the pathology seen in patients, since cellular models show only part of the complex disease pathology.
Osteogenesis imperfecta is an inherited disorder characterized by increased bone fragility, fractures, and osteoporosis, and most cases are caused by mutations affecting the type I collagen genes. ...Here, we describe a new mouse model for Osteogenesis imperfecta termed Aga2 (abnormal gait 2) that was isolated from the Munich N-ethyl-N-nitrosourea mutagenesis program and exhibited phenotypic variability, including reduced bone mass, multiple fractures, and early lethality. The causal gene was mapped to Chromosome 11 by linkage analysis, and a C-terminal frameshift mutation was identified in the Col1a1 (procollagen type I, alpha 1) gene as the cause of the disorder. Aga2 heterozygous animals had markedly increased bone turnover and a disrupted native collagen network. Further studies showed that abnormal pro alpha 1( I) chains accumulated intracellularly in Aga2/+ dermal fibroblasts and were poorly secreted extracellularly. This was associated with the induction of an endoplasmic reticulum stress-specific unfolded protein response involving upregulation of BiP, Hsp47, and Gadd153 with caspases-12 and -3 activation and apoptosis of osteoblasts both in vitro and in vivo. These studies resulted in the identification of a new model for Osteogenesis imperfecta, and identified a role for intracellular modulation of the endoplasmic reticulum stress-associated unfolded protein response machinery toward osteoblast apoptosis during the pathogenesis of disease.
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