Characterization of proteoglycans and glycosaminoglycans in bovine renal AA-type amyloidosis

Amyloids: from Pathogenesis to Function

The term "amyloids" refers to fibrillar protein aggregates with cross-β structure. They have been a subject of intense scrutiny since the middle of the previous century. First, this interest is due to association of amyloids with dozens of incurable human diseases called amyloidoses, which affect hundreds of millions of people. However, during the last decade the paradigm of amyloids as pathogens has changed due to an increase in understanding of their role as a specific variant of quaternary protein structure essential for the living cell. Thus, functional amyloids are found in all domains of the living world, and they fulfill a variety of roles ranging from biofilm formation in bacteria to long-term memory regulation in higher eukaryotes. Prions, which are proteins capable of existing under the same conditions in two or more conformations at least one of which having infective properties, also typically have amyloid features. There are weighty reasons to believe that the currently known amyloids are only a minority of their real number. This review provides a retrospective analysis of stages in the development of amyloid biology that during the last decade resulted, on one hand, in reinterpretation of the biological role of amyloids, and on the other hand, in the development of systems biology of amyloids, or amyloidomics.

Heparan sulfate proteoglycans in amyloidosis

Amyloidosis is a generic term for a group of diseases characterized by deposits in different organ systems of insoluble materials composed mainly of distinct fibrillar proteins named amyloid. Besides amyloid, heparan sulfate proteoglycan (HSPG), is commonly found in most amyloid deposits, suggesting that HS/HSPG may be functionally involved in the pathogenesis of amyloidosis. HS or HSPG is found to interact with a number of amyloid proteins, displaying a promoting effect on amyloid fibrilization in vitro. In addition, HS is reported to be involved in processing amyloid precursor proteins and mediate amyloid toxicity. Although little is known about the in vivo mechanisms regarding the codeposition of HS with amyloid proteins in different amyloid diseases, experiments carried out in animal models, especially in transgenic mouse model where HS molecular structure is modified, support an active role for HS in amyloidogenesis. Further experimental evidence is required to strengthen these in vivo findings at a molecular level. Animal models that express mutant forms of HS due to knockout of the enzymes involved in glycosaminoglycan (GAG) biosynthesis are expected to provide valuable tools for studying the implications of HS, as well as other GAGs, in amyloid disorders.

Glycosaminoglycans are part of amyloid fibrils: ultrastructural evidence in avian AA amyloid stained with cuprolinic blue and labeled with immunogold

In domestic brown layer fowl, reactive amyloidosis of internal organs, such as liver and spleen, and of the joints is a common disorder. In a variety of amyloid types including the AA-amyloid of the chicken, in addition to amyloid fibrils, proteoglycans and glycosaminoglycans (GAGs) are found on immunohistochemistry or after extraction. The aim of the present report is to study amyloid fibrils for the ultrastructural location of GAGs by cuprolinic blue staining and immunogold labeling. Rabbit antichicken AA antiserum was used for the immunogold labeling on conventionally embedded and cryoembedded liver tissue and revealed similar results. Therefore conventional blocks could be used for further analysis. Cuprolinic blue staining was performed on blocks of joint tissue in which clearly discernable rod-shaped glycoproteins were encountered in between collagen fibrils. Moreover, it appeared to stain larger deposits which might represent amyloid. Postlabeling with the immunogold method of the cuprolinic blue-stained tissue proved that cuprolinic blue positive fibrils represented AA-amyloid fibrils. Therefore, it was concluded that the GAGs which appeared to colocalize with the fibrillar microanatomy of amyloid, represent a structural part of the amyloid fibrils and that the avian amyloid fibrils may be considered as a pathological proteoglycan.

Immunohistochemical identification of amyloid, using an anti-human serum amyloid P component (SAP) antibody, is possible in ruminants but not in dogs and cats

Amyloidosis represents a heterogenous group of diseases that have in common the deposition of fibrils composed of proteins of beta-pleated sheet structure, a structure which can be specifically identified by histochemistry using the Congo red or similar stains. Amyloid consists primarily of the amyloid fibrils but also of the amyloid P component (AP). This component, which is identical with the serum counterpart (SAP), is found in all types of human amyloid, and immunohistochemical identification of AP has been proposed as an adjunct to the universal, type-independent diagnosis of human amyloidosis. In the present study of animal amyloidosis, we compared the amyloid-specific Congo red stain with an immunohistochemical protocol using an anti-human SAP antibody for the identification of amyloid in formalin fixed tissue samples. The species and types of amyloidoses investigated were: (i) seven cows, one yak (Bos grunniens), and one sheep affected with amyloidosis of presumed AA type, (ii) one dog with a pancreatic endocrine tumour producing amyloid of presumed AIAPP type, (iii) two cats with presumed AIAPP-amyloidosis of the islets of Langerhans, one cat with presumed AA-amyloidosis, and one cat with an amyloid-producing odontogenic tumour. Intense immunostaining co-localized with amyloid, identified by its congophilia and green birefringence, using a protocol without any antigen retrieval in each of the seven cows, the yak and the sheep. The method seemed more sensitive in the ruminants than the Congo red stain, but was unable to detect amyloid in the dog and the cats regardless of the application of various antigen retrieval protocols. However, specific identification of amyloid still rests on the Congo red method or similar histochemical techniques.

Protein folding pathology in domestic animals

Fibrillar proteins form structural elements of cells and the extracellular matrix. Pathological lesions of fibrillar microanatomical structures, or secondary fibrillar changes in globular proteins are well known. A special group concerns histologically amorphous deposits, amyloid. The major characteristics of amyloid are: apple green birefringence after Congo red staining of histological sections, and non-branching 7-10 nm thick fibrils on electron microscopy revealing a high content of cross beta pleated sheets. About 25 different types of amyloid have been characterised. In animals, AA-amyloid is the most frequent type. Other types of amyloid in animals represent: AIAPP (in cats), AApoAI, AApoAII, localised AL-amyloid, amyloid in odontogenic or mammary tumors and amyloid in the brain. In old dogs Abeta and in sheep APrPsc-amyloid can be encountered. AA-amyloidosis is a systemic disorder with a precursor in blood, acute phase serum amyloid A (SAA). In chronic inflammatory processes AA-amyloid can be deposited. A rapid crystallization of SAA to amyloid fibrils on small beta-sheeted fragments, the 'amyloid enhancing factor' (AEF), is known and the AEF has been shown to penetrate the enteric barrier. Amyloid fibrils can aggregate from various precursor proteins in vitro in particular at acidic pH and when proteolytic fragments are formed. Molecular chaperones influence this process. Tissue data point to amyloid fibrillogenesis in lysosomes and near cell surfaces. A comparison can be made of the fibrillogenesis in prion diseases and in enhanced AA-amyloidosis. In the reactive form, acute phase SAA is the supply of the precursor protein, whereas in the prion diseases, cell membrane proteins form a structural source. Abeta-amyloid in brain tissue of aged dogs showing signs of dementia forms a canine counterpart of senile dementia of the Alzheimer type (ccSDAT) in man. Misfolded proteins remain potential food hazards. Developments concerning prevention of amyloidogenesis and therapy of amyloid deposits are shortly commented.

The analysis of gastrointestinal amyloidosis in 78 patients with chronic renal failure

Systemic amyloidosis is not a single disease, but the product of a variety of diseases. Amyloid proteins are insoluble fibrils that are deposited extracellularly in many organ tissues. They stain with Congo red and appear apple green under polarized light. Definitive diagnosis and classification ofamyloidosis requires histologic examination of tissue samples. Gastrointestinal tract involvement is common, and all parts of the system can be affected Immunohistochemical studies have shown that amyloid deposited in the gastrointestinal system is most often of the AA, A kappa, or A lambda types. Another type of amyloidprotein, beta-2 microglobulin (beta2M), predominantly affects the musculoskeletal system, and is usually seen in patients who have been on long-term hemodialysis. Mixed systemic amyloidosis (beta2M and AA) is seen only rarely in these patients. In this study, we attempted to answer why this is so, and examined whether or not mixed amyloidosis is related to amyloidogenesis. We studied gastrointestinal tissues from 78 chronic renal failure patients who had systemic amyloidosis with gastrointestinal involvement. A total of 115 endoscopic samples and 1 jejunal resection specimen were analysed immunohistochemically. Immunohistochemical testing using a panel of antisera directed against two major amyloid fibril proteins (AA-Monoclonal, Dako-, and beta2M-Polyclonal, Dako-) showed that all samples contained AA amyloid, but not beta2M type protein. These findings can be explained by the patients' relatively short average duration of hemodialysis and the predominance of endoscopic biopsy samples in our study.

Casein related amyloid, characterization of a new and unique amyloid protein isolated from bovine corpora amylacea

Amyloid bodies can be found in mammary secretory tissue of various species. These corpora amylacea (CA) have a lamellated structure, contain amyloid fibrils and are predominantly located in the alveolar lumina. The nature of the amyloid was not known, but CA were suggested to originate either from milk casein or mammary alveolar epithelial keratin. In the present report, bovine CA were analyzed histochemically. Furthermore, CA were isolated, analyzed and the amyloid was purified and characterized by amino acid sequencing. CA amyloid appeared to be potassium permanganate sensitive and tryptophan positive, and in this respect different from most other amyloid types except for AA and beta-2 microglobulin amyloid. Gel filtration of purified amyloid fibrils showed a HMW peak and a major 4 kD peak. N-terminal amino acid sequencing showed the amyloid to consist of tryptic-like peptides with an unusually high content of amino acids with bulky side chains. The amyloid protein was identified as derived from alpha-S2-casein. The fragments are of varying length (32, 33 and 45 amino acids), but all start at position 81 of alpha-S2-casein. We have identified a new and unique amyloid protein, and we propose to designate it as A alpha-S2C according to the guidelines for amyloid nomenclature.

Stromal accumulation of chondroitin sulphate in mammary tumours of dogs

To contribute to the investigation of the composition of the extracellular matrix in epithelial tumours, mammary gland tissues of dogs (including tumours, hyperplasias and normal tissue as well as metastatic lesions in lymph nodes and lung) were studied histochemically and immunohistochemically for distribution of sulphated glycosaminoglycans (s-GAGs). The formaline-fixed tissue was stained by alcian blue at pH 5.8, using the 'critical electrolyte concentration' to study the degree of sulphation of s-GAGs. s-GAGs were characterized by degradation with enzymes and nitrous acid and by immunohistochemistry with two anti-chondroitin sulphate monoclonal antibodies. The light microscopic investigation of s-GAG deposits revealed a limited number of patterns of their distribution. The main s-GAGs found in the mammary gland tumours of dogs and in metastatic lesions were chondroitin sulphate (CS) and heparin/heparan sulphate (HEP/HS). CS accumulated in diffuse structures between epithelial cells as well as around clusters of tumour cells. The latter pattern, possibly representing a mesenchymal reaction to the tumour, was present in 74% of the tumours, and in 67% of these, highly sulphated CS was present. A diffuse accumulation of CS was present almost exclusively in complex and mixed tumours; because of the expression of the 3B3 epitope for CS in immature cartilage the spindle cells of complex tumours are argued to be the precursors of the cartilage in mixed tumours. HEP/HS was stored mainly in mast cells that were found in increased numbers in hyperplasias and tumours. By pretreatment of microscopic slides with chondroitinase AC or ABC immunostaining of fibronectin could be made possible in areas in which CS was abundantly present, suggesting that CS may mask fibronectin epitopes. It is concluded that CS with different degrees of sulphation is the most important s-GAG in the extracellular matrix of mammary tumours of dogs. CS and other s-GAGs accumulate at different sites and may have a different pathogenetic significance.

Vascular basement membrane pathology and Alzheimer's disease

We have previously demonstrated that the capillary vascular basement membrane (VBM) is pathologically altered in Alzheimer's disease (AD). This microangiopathy is highlighted by the immunocytochemical localization of the three principal intrinsic VBM components: heparan sulfate proteoglycan, collagen type IV, and laminin. These three VBM components also immunolable amyloid deposits and senile plaque-associated glial processes. The present study examines the ultrastructure of the VBM in one brain region severely affected (temporal gyrus) and one relatively spared (cerebellum) from the lesions of AD in both AD and neurological control cases. The cross-sectional area as well as the width of the VBM were found to be greater in AD cortical capillaries. In addition, we found ultrastructural evidence for the activation of microglial-related perivascular cells, and their apparent extravasation through the VBM, findings consistent with the hypothesis that these cells are being recruited as part of a disease-related immune response. The recruitment of these "resting" microglial-like cells from their intra-VBM location to plaques and tangles in AD may explain (1) the thickening and vacuolization of the VBM; (2) the specificity of this VBM alteration to brain regions where there are plaques and tangles; and (3) the source of some of the large number of activated microglia in these affected areas. Thus, while VBM alterations may not be specific to AD, these changes appear to be specifically related to the disease process.

Animal models for reactive amyloidosis

For over 70 years animal experiments have been performed to elucidate the pathogenesis of reactive amyloidosis and to investigate the formation of the beta-pleated sheet-rich amyloid fibrils in general. In appropriate species, primarily rodents like mouse and hamster, amyloid is formed after stimulation with amyloid-inducing injections after a lag phase (secondary or reactive amyloid, AA amyloid). For the formation of this AA amyloid, elevated values in blood of its precursor protein, SAA, is the first prerequisite. SAA is an acute phase protein of hepatic origin, released after stimulation by cytokines, and is associated in serum with high-density lipoprotein (apoSAA). In mouse, hamster and mink amyloidogenic subtypes of SAA are found. In the rat SAA is absent, although its mRNA is transcribed. Evidence is increasing that SAA crystallizes to fibrils first, whilst loss of its C-terminal end can be a post-fibrillogenic phenomenon. Glycoproteins, proteoglycans, glycosaminoglycans and lipids are reintroduced in experimental amyloid research. Basement membrane heparan sulphate proteoglycans (perlecans) are attributed to have a primary role. The pentraxin serum amyloid P-component is a calcium-dependent secondary phenomenon. Membrane-bound, lipid-rich vesicles are found amongst the newly deposited pericellular amyloid fibrils. These vesicles probably have to be interpreted as indicators of primary membrane alteration during amyloid fibril crystallization. The vesicles will be formed after rupture of the membranes caused by the stiff intramembranously crystallized protein fibrils. Morphological evidence supporting this hypothesis has been found in immunoelectron microscopical studies. Accumulation of intramembranous SAA preceded amyloid fibril deposition. Fibril formation then might be related to conformational change of the intramembranous SAA. The lag phase for amyloid deposition is shortened after a single injection of a fraction of amyloid, the AEF. It is a low-molecular-weight glycoprotein that easily associates with other molecules. When isolated from amyloid fibrils, the (F)AEF contains a large proportion of beta-pleated sheet molecular structure. It is probable that this structure holds an explanation for its enhancing potency: forming a nidus for physical crystallization. The major substances and animal species used in animal experiments on amyloidosis, are mentioned. Overlooked by-effects of amyloidogenic stimuli are discussed. Polyarthritis after systemic endotoxin injections found in the hamster acts as a source of cytokines, further triggering the reactive amyloidosis.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of GBM heparan sulfate proteoglycan core protein and side chains in human glomerular diseases

Using monoclonal antibodies (mAbs) recognizing either the core protein or the heparan sulfate (HS) side chain of human GBM heparan sulfate proteoglycan (HSPG), we investigated their glomerular distribution on cryostat sections of human kidney tissues. The study involved 95 biopsies comprising twelve different glomerulopathies. Four normal kidney specimens served as controls. A homogenous to linear staining of the GBM was observed in the normal kidney with anti-HSPG-core mAb (JM-72) and anti-HS mAb (JM-403). In human glomerulopathies the major alteration was a segmental or total absence of GBM staining with anti-HS mAb JM-403, which is most pronounced in lupus nephritis, membranous glomerulonephritis (GN), minimal change disease and diabetic nephropathy, whereas the HSPG-core staining by mAb JM-72 was unaltered. In addition we found HSPG-core protein in the mesangial matrix when this was increased in membranoproliferative GN Type I, Schönlein-Henoch GN, IgA nephropathy, lupus nephritis, diabetic nephropathy and in focal glomerulosclerosis. Also staining with the anti-HS mAb JM-403 became positive within the mesangium, although to a lesser extent. Furthermore, amyloid deposits in AL and AA amyloidosis clearly stained with anti-HSPG-core mAb JM-72, and to a lesser degree with anti-HS mAb JM-403. Finally, in membranous GN (stage II and III), the GBM staining with anti-HSPG-core mAb JM-72 became irregular or granular, probably related to the formation of spikes. In conclusion, major alterations were observed in the glomerular distribution of HS and HSPG-core in various human glomerulopathies. The mAbs can be useful to further delineate the significance of HSPG and HS for glomerular diseases.

Purification of amyloid-associated heparan sulphate proteoglycans and galactosaminoglycan free chains from human tissues

Basement membrane-associated heparan sulphate proteoglycans have been demonstrated immunohistochemically in organs from patients afflicted with various types of amyloidosis. In a recent report, we were able to isolate and partly characterize a basement membrane-associated heparin sulphate proteoglycan from human hepatic amyloid. In the present study proteoglycans were extracted with guanidine from human amyloid-laden kidney, spleen and lymph nodes. All tissues extracted with guanidine contained both heparan sulphate proteoglycan (HSPG) and galactosaminoglycan (CS/DS) free chains. Tissue staining using a monoclonal antibody against basement membrane HSPG revealed the presence of HSPG in amyloid deposits in kidney and spleen. Furthermore, following SDS-PAGE of HSPG from kidney after deaminative cleavage of the HS chains, a 15-kDa and 80-kDa protein appeared, probably representing the core protein(s). In lymph node HSPG, three core proteins of 65, 30 and 25 kDa could be demonstrated on SDS-PAGE, the first reacting with the anti-basement membrane HSPG antibody when subjected to Western blotting subsequent to SDS-PAGE. By immunohistochemistry, we failed to demonstrate any staining of the renal and splenic tissue sections employing an antibody against the decorin core protein.