Binding of ubiquitin to experimentally induced murine AA amyloid

Heme-oxygenase-1 response, a marker of oxidative stress, in a mouse model of AA amyloidosis

Expression of heme-oxygenase-1 (HO-1), an important marker of oxidative stress, has been studied extensively in the context of Alzheimer's disease. Evidence of HO-1 expression during AA amyloidosis is, at best, sketchy. We present comparative data on HO-1 response in alveolar hydatid cyst (AHC) infected amyloid sensitive (C57BL/6) and amyloid resistant (CE/J) mouse strains. Histochemical and peroxidase-immunoperoxidase methods were used to monitor serum amyloid A (SAA) and AA fibril deposition and HO-1 expression in hepato-splenic reticuloendothelial (RE) cells of the AHC-infected mice prior and during AA fibril deposition. Based on the cumulative data, we conclude that HO-1 expression corresponded closely with tissue deposition of SAA, but was unrelated to AA fibril deposition. To ascertain whether SAA deposition might act as the trigger for HO-1 expression in the RE cells, macrophages were incubated for up to 72 h with SAA-containing mouse serum. The SAA-treated macrophages, although negative for HO-1 protein, demonstrated SAA in the cell extracts and immunocytochemically in the vacuolar compartments, indicating macrophage-mediated endocytosis and trafficking of SAA. In sum, these results exclude SAA and AA fibrils as the primary triggers in the induction of HO-1 expression in RE cells; the potential role of inflammatory cytokines in HO-1 response need to be investigated further.

Immunolocalization of serum amyloid A and AA amyloid in lysosomes in murine monocytoid cells: confocal and immunogold electron microscopic studies

Murine AA amyloid (AA) protein represents the amino-terminal two-third portion of SAA2, one of the isoforms of serum amyloid A. Whether plasma membrane-bound or lysosomal enzymes in activated murine monocytoid cells degrade SAA2 to generate amyloidogenic AA-like peptides is not clearly understood, although AA has been localized in the lysosomes. Here we show, using confocal and immunogold microscopy (IEM), that both SAA and AA localize in lysosomes of activated monocytoid cells from amyloidotic mice. Rabbit anti-mouse AA IgG (RAA) and two monoclonal antibodies against murine lysosome-associated membrane proteins (LAMP-1 and LAMP-2) were used to immunolocalize SAA/AA and lysosomes, respectively. Confocal analysis co-localized both anti-RAA and anti-LAMP-1/LAMP-2 reactivities in the perikaryal organelles which by IEM proved to be electron-dense lysosomes. LAMP-1/LAMP-2-specific gold particles were also localized on lysosomal and perikaryal AA. The results suggest sequestration of SAA into the lysosomes. Since monocytoid cells are not known to phagocytose native amyloid fibrils, our results implicate lysosomes in AA formation.

Differences in beta-amyloid (beta/A4) deposition in human patients with Down's syndrome and sporadic Alzheimer's disease

The density of diffuse, primitive, classic and compact beta-amyloid (beta/A4) deposits was estimated in the hippocampus and adjacent gyri in human patients with Down's syndrome (DS) and sporadic Alzheimer's disease (AD). The objective of the study was to determine whether there were differences in beta/A4 deposition in DS and sporadic AD and whether these differences could be attributed to overexpression of the amyloid precursor gene (APP) in DS. Total beta/A4 deposit density was greater in DS than AD in all brain regions studied but the DS/AD density ratios varied between brain regions. In the majority of brain regions, the ratio of primitive to diffuse beta/A4 deposits was greater in DS but the ratio of classic to diffuse deposits was greater in AD. The data were consistent with the hypothesis that overexpression of the APP gene in DS may lead to increased beta/A4 deposition. However, local brain factors also appear to be important in beta/A4 deposition in DS. Overexpression of the APP gene may also be responsible for increased production of paired helical filaments (PHF) and result in enhanced formation of primitive beta/A4 deposits in DS. In addition, increased formation of classic deposits in AD suggests that factors necessary for the production of a compact amyloid core are enhanced in AD compared with DS.

Ubiquitin profile in inflammatory leukocytes and binding of ubiquitin to murine AA amyloid: immunocytochemical and immunogold electron microscopic studies

Lysosomes in activated murine monocytoid cells have been implicated in AA amyloid formation. The pathophysiology of this process is not well understood. Previous studies into the nature of the relationship between ubiquitin (UB), possessing intrinsic amyloid enhancing factor (AEF) activity; serum amyloid A (SAA), the precursor protein of AA amyloid; and activated monocytoid cells have indicated a temporal and spatial relationship between these proteins and tissue AA amyloid deposits. To extend these findings, we have examined murine peritoneal leukocytes and splenic tissues during the early amyloid deposition phase by immunocytochemical and immunogold electron microscopic methods using monospecific anti-ubiquitin and anti-mouse AA amyloid antibodies. We show here enrichment of endosome-lysosome-like (EL) vesicles in the activated monocytoid cells with UB and SAA, and the presence of UB-bound AA amyloid fibrils in the EL vesicles, perikarya, and interstitial spaces. The importance of these findings is emphasized by the fact that activated monocytoid cells, containing UB in the EL vesicles, sequester and eventually localize SAA in their EL vesicles, and that UB binds to the EL-contained AA amyloid fibrils. These findings may also have functional consequences for studies on the role of EL and UB in amyloidogenesis.

Amyloidosis

The biochemistry of amyloidosis as it relates to clinical medicine and experimental pathology is presented. Amyloidoses are complex disorders in which normally soluble precursors undergo pathological conformational changes and polymerize as insoluble fibrils with the beta-pleated sheet conformation. Over the past 20 years, 16 biochemically diverse proteins have been identified as fibrillar constituents of amyloid deposits; in all cases the protein-protein interactions that result in amyloid fibril formation appear to be stabilized both by the structure and the microenvironment of the precursor protein. Either genetic predisposition or dysfunctions of the immune system favor amyloid fibril formation. In particular, macrophage function is a factor in the pathogenesis of many of the amyloidoses. The diagnosis of amyloidosis involves acquisition of a tissue biopsy, staining of the specimen with Congo red, and observation of classic green birefringence on polarization microscopy. The subdiagnosis of the systemic amyloidoses involves characterization of variant or monoclonal plasma amyloid precursor proteins in the context of clinical symptoms. Treatment is generally supportive, with the use of antiinflammatory therapy, dialysis, or transplantation and genetic counseling where indicated.

Ubiquitin in neurodegenerative diseases

Immunochemical staining to detect ubiquitin has become an essential technique in evaluating neurodegenerative processes. Age related staining is seen in myelin, in nerve processes in lysosome-related dense bodies, and in corpora amylacea. There is a constant association between filamentous inclusions and the presence of ubiquitin. Intermediate filaments associated with ubiquitin, alpha B crystallin and enzymes of the ubiquitin pathway are the basis of Lewy bodies and Rosenthal fibres, as well as related bodies outside the nervous system. Neurofibrillary tangles in diverse diseases are associated with ubiquitin as are several other tau containing inclusions in both neurones and glia. Inclusions in motor neurones and non-motor cortex characterizing amyotrophic lateral sclerosis (ALS) and certain related forms of frontal lobe dementia can only be readily detected by anti-ubiquitin. Anti-ubiquitin also identifies both filamentous and lysosomal structures in neuronal processes as well as in some swollen neurones. Involvement of ubiquitin-containing elements of the lysosomal system appears important in pathogenesis of prion encephalopathies. Despite great advances in understanding cell biology of the ubiquitin pathway there are as yet few insights into the precise role played by ubiquitin in neuronal disease.

Ubiquitin in cerebral amyloid angiopathy

Immunohistological findings in cerebral blood vessels of 4 cases with cerebral amyloid angiopathy (CAA) were compared with those of 4 Alzheimer's (AD) cases. A panel of antibodies against 2 neurofilament subunits (BF10 and RT97), a microtubule-associated protein (TAU) and ubiquitin were used. CAA cases showed a strong immunoreactivity for ubiquitin in blood vessel wall. Senile plaques (SPs) in CAA cases showed strong ubiquitin positivity but the central amyloid core was negative. AD brains showed immunoreactivity with all antibodies in SPs and neurofibrillary tangles (NFTs); blood vessels were consistently negative for ubiquitin. Control brains showed few SPs and NFTs; these were positive for ubiquitin, but blood vessels were negative. These results indicate that vascular amyloid deposition in CAA and AD may have different pathophysiological mechanisms.

Ubiquitin: its potential significance in murine AA amyloidogenesis

Amyloid enhancing factor (AEF), which has recently been shown to have identity with ubiquitin (Ub), is believed to play a causative role in experimentally induced AA amyloidosis in mice. We have examined the profile of Ub in activated leukocytes and splenic reticulo-endothelial (RE) cells and its relationship with serum amyloid A protein (SAA) and AA amyloid deposits in an alveolar hydatid cyst (AHC)-infected mouse model of AA amyloidosis. Two monospecific antibodies, anti-ubiquitin (RABU) and anti-mouse AA amyloid, were used as immunological probes to localize Ub, SAA, and AA amyloid. In response to AHC infection, the dull and diffuse Ub immunoreactivity in normal mouse leukocytes and RE cells promptly changed to a discrete granular pattern suggesting an increase in the intracellular concentration of Ub and the formation of Ub-protein conjugates. This corresponded to an elevation in SAA levels, SAA uptake by RABU-positive phagocytic cells, co-localization of Ub-SAA immunoreactive splenocytes in the perifollicular areas, and deposition of Ub-bound AA amyloid in the splenic and hepatic tissues. These results suggest that Ub-loaded monocytoid cells may play an important role in the physiological processing of the sequestered SAA into AA amyloid. Aspects of AA amyloidogenesis are discussed in relation to other experimental models in which stress-induced Ub-protein conjugate formation and its transport to lysosomal vesicles have been studied.

Ubiquitin profile and amyloid enhancing factor activity in Alzheimer and 'normal' human brain extracts

Tris-HCl or Laemmli sample buffer extracted frontal lobe and hippocampal samples from normal aged and Alzheimer's disease (AD) subjects were used to determine total ubiquitin (Ub), distribution of monomeric Ub and Ub-protein conjugates and amyloid enhancing factor (AEF) activity using the dot-blot, Western blot and mouse AEF bioassay techniques, respectively. The AD samples, as compared to the normals, demonstrated a 1.7-fold increase in total Ub, elevated levels of Ub-protein conjugates and an appreciably enhanced AEF activity. Many of the hippocampal Ub-protein conjugates were found to be soluble only in the Laemmli sample buffer. The possible roles of elevated Ub levels and of the association of AEF activity with Ub are discussed in regard to pathogenesis of brain amyloidosis.

Amyloid enhancing factor activity is associated with ubiquitin

Crude amyloid enhancing factor (AEF) drastically reduces the pre-amyloid phase on passive transfer and induces amyloid deposition in the recipient mice in 48-120 h. We attempted to purify AEF from murine amyloidotic liver and spleen extracts by using gel filtration, preparative sodium dodecyl sulphate-polyacrylamide gel electrophoresis and ion exchange chromatography and isolated a 5.5 kDa peptide. In the mouse bioassay, this peptide induced accelerated splenic AA deposition in a dose-dependent manner. Based on structural, electrophoretic and immunochemical criteria the peptide was identified as ubiquitin. A polyclonal rabbit anti-bovine ubiquitin IgG antibody (RABU) abolished the in vivo AEF activity of crude murine AEF in a dose-dependent manner. Monomeric ubiquitin and its large molecular weight adducts were isolated from crude AEF using cyanogen bromide-activated sepharose conjugated to RABU and size exclusion chromatography methods. These were assayed and were found to possess AEF activity. Furthermore, increased levels of ubiquitin, a phenomenon similar to that of AEF, were detected by immunocytochemistry in mouse peritoneal leucocytes prior to and during amyloid deposition. Since AEF shares a number of biological and functional properties with ubiquitin, we suggest a possible role of ubiquitin as an AEF, and that serum amyloid protein A and ubiquitin, the two reactants generated during inflammatory stress conditions, may converge to induce AA amyloid deposition.