PubMed · 8367002
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J P Méry. 1993. [Fibrillary glomerulopathies].. https://pubmed.ncbi.nlm.nih.gov/8367002/
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Pancreatic islet amyloid, formed from islet amyloid polypeptide, is found in 96% of Type II (non-insulin-dependent) diabetic patients. Islet amyloidosis is progressive and apparently irreversible. Fibrils immunoreactive for islet amyloid polypeptide are found in macrophages associated with amyloid, suggesting that deposits can be phagocytosed. To determine the mechanism for the recognition and internalisation of fibrils, mouse peritoneal macrophages were cultured with fibrillar synthetic human islet amyloid polypeptide. Fibrils did not exert a cytotoxic effect over 72 h of culture. The uptake and degradation of fibrils was analysed by quantitative light-and electron-microscopic immunocytochemistry and immunoreactivity was detectable in 86+/-3% cells within 6 h of culture. Neither polyinosinic acid (200 microg/ml) nor nocodazole (10 microg/ml) inhibited fibril uptake, suggesting that internalisation is not blocked by poly-ions and is independent of microtubule assembly. Inhibition of pseudopodia formation by cytochalasin B blocked fibriI uptake. Fibril aggregates became condensed in lysosomes to form protofilaments and were resistant to intracellular proteolysis. Fibrils can be phagocytosed by macrophages in vitro but amyloid-associated factors may block the recognition of fibrils in vivo preventing the removal of islet amyloid in diabetes.
Amyloid fibril formation and deposition are the basis for a wide range of diseases, including spongiform encephalopathies, Alzheimer's and familial amyloidotic polyneuropathies. However, the molecular mechanisms of amyloid formation are still poorly characterised. In certain forms of familial amyloidotic polyneuropathy (FAP), the amyloid fibrils are mostly constituted by variants of transthyretin (TTR). V30M-TTR is the most frequent variant, and L55P-TTR is the variant associated with the most aggressive form of amyloidosis. Here, we report gel filtration chromatography experiments to characterise the aggregation states of WT-, V30M-, L55P-TTR and a non-amyloidogenic variant, T119M-TTR, in solution, at nearly physiological pH. These studies show that all four protein tetramers dissociate to monomer upon dilution, in the submicromolar range, at pH 7.0. The amyloidogenic proteins V30M- and L55P-TTR show a complex equilibrium between monomers, tetramers and high molecular weight aggregate species. These aggregates dissociate directly to monomer upon dilution. This study shows that the tendency to form aggregates among the four studied proteins correlates with their known amyloidogenic potential. Thus, the amyloidogenic mutations could perturb the structure and/or stability of the monomeric species leading initially to the formation of soluble aggregates and at a later stage to insoluble amyloid fibrils.
Serum amyloid A (SAA) is a plasma protein that is associated with many inflammatory diseases including amyloidosis, arthritis, and atherosclerosis. SAA level is significantly increased during inflammatory condition, and such abnormal expression of this protein is linked to the pathogenesis of the above-mentioned diseases. A promoter element, designated as SAA-activating sequence (SAS), located between -280 and -226 has been implicated in the induction mechanism and a nuclear factor, SAS-binding factor (SAF), has been shown to bind to this region. In this report, using a cloned SAF gene in transient transfection assay, we provide evidence that SAF potentiates SAA gene expression through SAS element. Furthermore, we show that during lipopolysaccharide-mediated induction of SAF, heteromeric complex with transcription factor Sp1 is formed. Transfection assays using both transcription factor genes have demonstrated that SAF-Sp1 heteromer is a highly potent transactivator of SAA expression.