DOI: 10.1369/jhc.4A6387.2005 Volume 53 (2): 237-242, 2005 Copyright ©The Histochemical Society, Inc. Colocalization of Apolipoprotein AI in Various Kinds of Systemic Amyloidosis
Departments of Clinical Neuroscience (NS,MK,MO,MM), Radiopathological Science (TN,YH,TI), and Biomolecular Recognition (HA), Yamaguchi Graduate University School of Medicine, Yamaguchi, Japan Correspondence to: Naohiro Sakata, MD, Department of Clinical Neuroscience, Yamaguchi University Graduate School of Medicine, 1-1-1, Minami-kogushi, Ube, Yamaguchi, Japan. E-mail: nsakata{at}yamaguchi-u.ac.jp
Apolipoprotein AI (apoAI), a major component of high-density lipoproteins, is one of the major amyloid fibril proteins and a minor constituent of the senile plaques observed in Alzheimer's disease. We examined colocalization of apoAI in various kinds of systemic amyloidosis in this study. Forty-three of 48 formalin-fixed paraffin-embedded heart specimens with various forms of systemic amyloidosis reacted immunohistochemically with anti-human apoAI antibody. ApoAI was also detected in water-extracted amyloid material by immunoblotting. In addition, we observed colocalization of apoAI and murine amyloid A (AA) amyloidosis in human apoAI transgenic mice. This is the first report of colocalization of apoAI with amyloid deposits in various forms of human systemic amyloidosis and murine AA amyloidosis in human apoAI transgenic mice. ApoAI may not always be a major component of amyloid fibrils, even when it is present in systemic amyloid deposits. (J Histochem Cytochem 53:237242, 2005)
Key Words: apolipoprotein AI amyloid systemic amyloidosis immunohistochemistry immunoblotting apoAI transgenic mouse
AMYLOIDOSIS IS CAUSED BY DEPOSITION of amyloid fibril proteins in various tissues and organs. Classification of amyloidosis is based on the type of amyloid fibril protein, and at least 23 types of amyloidosis have been identified in humans (Westermark et al. 2002
Apolipoprotein AI (apoAI) is a major component of high-density lipoproteins (HDL) (Eisenberg 1984 In the present study we examined colocalization of apoAI in various human systemic amyloidosis immunohistochemically and biochemically. In addition, we examined association of apoAI with murine AA amyloidosis in human apoAI transgenic mice.
Immunohistochemical Analysis of ApoAI in Human Systemic Amyloidosis Specimens were obtained at autopsy from 25 hearts with AA amyloidosis, 12 with immunoglobulin (Ig) light chain amyloidosis (A amyloidosis), 5 with Ig light chain amyloidosis (A amyloidosis), 3 with Aß2M amyloidosis, and 3 with ATTR amyloidosis. The cases had all been classified previously by immunohistochemical studies with antibodies against anti- (118134), anti- (116133) (Hoshii et al. 2001 , A , transthyretin, and ß2-microglobulin. Antibodies against A and A were kindly provided by Dr. George G. Glenner (University of California, San Diego). Formalin-fixed, paraffin-embedded tissue sections (4-µm thick) were stained with Congo red and examined by conventional and polarized microscopy. Immunohistochemical analysis of apoAI was performed as follows. After deparaffinization, sections were treated with 3% H2O2 to block endogenous peroxidase activity and with Protein Block Serum-Free (DAKO; Carpinteria, CA) to block nonspecific reactions. Affinity-purified goat anti-human apoAI antibody (1:200) (Harlan Sera-Lab; Leicestershire, UK) was applied as the primary antibody for 30 min at room temperature. According to the product information, cross-reactivity of this antibody with apolipoprotein AII, B, CI, CII, CIII, E, and J is less than 1%. Peroxidase-conjugated rabbit anti-goat immunoglobulin (1:50) (DAKO; Glostrup, Denmark) was used as the secondary antibody (30 min at room temperature) and visualized with 3-3'-diaminobenzidine tetrahydrochloride (DAB). Some sections were immunostained with or without formic acid pretreatment as part of a preliminary study. Formic acid pretreatment improved apoAI immunoreactivity; therefore, antigen retrieval was performed in 100% formic acid for 1 min at room temperature (Kitamoto et al. 1987
Immunoblotting of Human AL Amyloidosis To increase confidence in the specificity of the anti-apoAI antibody by examining whether this antibody cross-reacts with other apolipoproteins and amyloid-associated proteins, immunoblotting of apoE (Calbiochem; La Jolla, CA), serum amyloid A (SAA) (American Research Products; Belmont, MA), and serum amyloid P-component (SAP) (Techne; Minneapolis, MN) with affinity-purified goat anti-human apoAI antibody (Harlan Sera-Lab) was also performed.
Immunohistochemical Analysis of ApoAI in Human apoAI Transgenic Mice
For the second experiment, AA amyloidosis was induced in mice by injecting amyloid-enhancing factor (AEF) and AgNO3 to evaluate the earliest stage of amyloid deposition. AEF was prepared from ICR mice according to the method of Axelrad et al. (1982)
For both experiments, sections (4-µm thick) were cut from the paraffin-embedded tissues, stained with Congo red, and examined by conventional and polarized light microscopy. Immunohistochemical examinations were performed with an indirect immunoperoxidase method as described for human tissues. Rabbit anti-mouse AA (1:1000) (Imada 1981
Histological and Immunohistochemical Findings in Human Systemic Amyloidosis Congo red-positive amyloid deposits were present in the vessel walls in all cases. Amyloid deposits were also present in the interstitium of the myocardium, the endocardium, and the pericardium in most cases. Human apoAI immunoreactivity in amyloid deposits (Figure 1) was observed in 22 of 25 (88%) cases of AA amyloidosis, 12 of 12 (100%) cases of A amyloidosis, 4 of 5 (80%) cases of A amyloidosis, 2 of 3 (67%) cases of Aß2M amyloidosis, and 3 of 3 (100%) cases of ATTR amyloidosis. Therefore, 43 (90%) of 48 cases of various kinds of systemic amyloidosis were positive for apoAI. In the positive cases, the immunoreactive area and staining intensity of amyloid deposits were variable. More cases showed partial anti-human apoAI immunoreactivity than showed complete anti-human apoAI immunoreactivity. Anti-human apoAI immunoreactivity with amyloid deposits was blocked completely by preabsorption. The immunoreactivity in the representative cases and the result of preabsorption test with anti-apoAI antibody (Chemicon) were similar to those with affinity-purified goat anti-human apoAI antibody (Harlan Sera-Lab).
Immunoblotting of AL Amyloid Anti-human apoAI antibody reacted with an approximate 25-kD band on Western blots of A amyloid and purified human apoAI (Figure 2)
. Anti- (118134) antibody reacted with several bands in A amyloid but did not react with purified human apoAI. Furthermore, the anti-apoAI antibody did not recognize apoE, SAP, and SAA (data not shown).
Histological and Immunohistochemical Findings in Human ApoAI Transgenic Mice After the injections of FCA and M. butyricum, amyloid deposits were observed in the perifollicular area of the spleen of all apoAI transgenic mice examined. Seventy-two hr after administration of AEF and AgNO3, all apoAI transgenic mice also had amyloid deposits in the perifollicular area of the spleen, but the amyloid deposits were smaller than those in mice treated with FCA and M. butyricum. These amyloid deposits reacted with anti-mouse AA antibody (Figures 3A and 3C) . Anti-human apoAI antibody staining was not detected in amyloid deposits in apoAI transgenic mice after administration of AEF and AgNO3, but staining was present in the interstitium (Figure 3B). In contrast, anti-human apoAI immunoreactivity was present in both amyloid deposits and interstitium in apoAI transgenic mice after injection of FCA and M. butyricum (Figure 3D). The staining was irregular and weaker than that with anti-mouse AA antibody.
In the present study we observed colocalization of apoAI with amyloid deposits in various kinds of human systemic amyloidosis immunohistochemically and biochemically. We also detected colocalization of apoAI and murine AA amyloidosis in human apoAI transgenic mice. ApoAI is known to form amyloid fibrils as a major fibril protein and colocalizes with amyloid-ß (Aß) protein in Alzheimer's disease. However, this is the first report of the colocalization of apoAI with amyloid deposits in various kinds of human systemic amyloidosis. We should consider that apoAI may not always be a major component of amyloid fibrils even when amyloid deposits in systemic amyloidosis are positive for apoAI immunohistochemically. Serum proteins trapped in amyloid deposits are sometimes detected in the immunohistochemical analysis (Röcken et al. 1996 amyloid, suggesting that apoAI was not merely trapped in amyloid deposits but rather was an insoluble component of amyloid deposits.
Involvement of apolipoproteins in amyloidosis has been reported to date. SAA (Benditt et al. 1979
ApoAI contains a high proportion of class A amphipathic
On the other hand, AA amyloidosis develops in both apoE-deficient mice (Hoshii et al. 1997 The exact role of apoAI in amyloidogenesis of various kinds of systemic amyloidosis is unclear. Further studies of the relation of apoAI and amyloid fibril proteins in human systemic amyloidosis are needed. A better understanding of these amyloid-associated proteins may contribute to development of strategies for the treatment of amyloidosis.
Received for publication May 13, 2004; accepted October 4, 2004
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