Sl Clinical Neurology and Neurosurgery, 94 (Suppl.) (1992) Sl -S3 8 1992 Elsevier Science Publishers B.V. All rights reserved 0303~8467/92/$05.00 CNN 00127
Function
of amyloid and amyloid protein precursor Rayrnund A.C. Roes’ and Joost Haanlt2 1Department of Neurology, Universily Hospital, Leiden (The Netherlands),
and 2 Depariinent of Neuroloa,
Key words:
Amyloid
precursor
protein;
St. Elisabeth Ziekenhuis, Leiakrdorp (The Netherlands)
Beta-amyloid
Summary A short relationship
review is given of the functions of amyloid (beta/A4) between amyloid deposition and dementia is discussed.
Introduction Amyloid is a highly insoluble compound showing birefringence after Congo red staining. Its ultrastructure consists of rigid non-branching fibrils folded in a beta-pleated sheet configuration. Amyloid can be found in the neuropil, amorphous and neuritic plaques and in the blood vessel walls of the brain of patients with Alzheimer’s disease (AD), Down’s syndrome, Sporadic Cerebral Hemorrhage with Amyloidosis and the Hereditary Cerebral Hemorrhages with Amyloidosis of the Dutch type (HCHWA-D). The major component of the amyloid fibrils in these diseases is a 3942 amino acid containing polypeptide of about 4.2 kDa, called beta/A4 protein. The beta/A4 protein is derived from the larger amyloid precursor protein (APP). APP is a cell-surface transmembranous protein with a short intracytoplasmic C-terminal and a large extracellular N-terminal (Fig. 1) [l]. The mechanism of amyloidogenesis is not clear. As the intracellular neurofibrillary tangles (NFI?) as well as the extracellular deposits in the neuropil and in the vessel walls are mainly composed of beta/A4 protein, understanding of the process leading to these depositions can be important to the understanding of the decline in neuronal function. Amyloid precursor
protein
APP is coded for on the long arm of chromosome 21. It is synthesized by most cell types and expressed at high Correspondence to: R.A.C. Roos, MD, Department of Neurology, University Hospital, P.O. Box 9600,230O RC Leiden, The Netherlands. Tel.: (71) 262111; Fax: (71) 154537.
and its precursor
protein
(APP).
The possible
levels in many tissues throughout the body [2]. At least 4 different forms of APP are recognized at present, consisting of 695, 714, 7.51, and 770 amino acids, respectively. The largest two (751 and 770) contain the Kunitz Protease Inhibitor insert (KPI). The 770-form is most abundantly present in the body. The APP 695, lacking this KPI insert, is predominantly present in normal brain. The total amount of immunologically detectable APP in human brain is not age-dependent and does not differ between normal controls and AD. With increasing age, however, the relative distribution between several forms of APP changes, but remaining similar for age-matched controls and AD patients. Therefore, the presence of APP is not sufficient to account for the formation of amyloid. Other mechanisms than aging have to be responsible for the pathological beta/A4 formation in AD
[31. Amyloid precursor
protein
and its function
The three main physiological functions of APP arc (1) protease inhibition, (2) cell adhesion, and (3) regulation of cell growth. Part of these functions depends on the presence of the KPI insert. The main function of the APP without KPI is stimulation of cell adhesion. The secretory forms of the APP with KPI insert have the same properties as protease nexin II, a growth-regulating molecule secreted by fibroblasts. In the blood these species bind with several serine proteases forming complexes that play an important role in coagulation inhibition. The secreted form of APP with the KPI insert is mitogenic for Swiss T3 cells. The APP without the insert
s2 56 amino acid Kunltz-type protease
I-
19 amino acids, homologous to MRC OX-2 antigen
neurotoxlc
secretory forms of APP-751 8 APP-770 - protease nexin II, tnvolved In growth regulation and cell adheston
trophic to undifferentiated neurons but toxic to mature neurons H contains cell adhesion site
H
shows binding actlvlty
H
neurotrophlt
Fig. 1. Functional map of Alzheimer’s disease amyloid precursor protein, showing beta/A4 region (hatched).
(APP 695) did not stimulate DNA synthesis in cell lines in vitro [4]. A 105 amino acid sequence from the C-terminal peptide expressing the beta/A4 protein causes degeneration of cells in vitro. Beta/A4 and its function Beta/A4 has not been reported to exhibit protease inhibitory activity, despite its homology with a part of the KPI insert. Residue 4-37 (from the A4 part) shows a 68% homology with the residues 120-153 of the Kunitz type soybean trypsin inhibitor, but it apparently lacks the active side. The survival and neuritic outgrowth of pyramidal hippocampal cells of Sprague-Dawley rats in cell cultures was directly related with the concentration of a 28 residue of synthetic beta/A4 [5]. Other parts of the beWA4, i.e. residues 25-35, show homology with the tachykinin family of neuropeptides. The synthetic peptide was trophic in low, and toxic in high concentrations for rat hippocampal neurons. Substance P antagonists showed comparable effects on hippocampal cells, effects that were reversed by substance P agonists. The 1-16 residues of the beta/A4 from the APP with and without the KPI insert mediate cell adhesion in neuronal cells as well as in non-neuronal cells. Amyloidogenesis The cleavage of APP normally takes place within the
beta/A4 domain, hence normally beta/A4 is not formed [6]. In HCHWA-D a point mutation is present within 6 sites from the point corresponding to this physiological cleavage site 171. In some patients with familial AD a mutation is found affecting a site just 4 residues past the C-terminus of the beta/A4 region fg]. One hypothesis is that these mutations influence the physiological cleavage process, leading to beta/A4 production. A different hypothesis is that the aberrant cleavage always occurs next to the normal cleavage in the beta/A4 region, the resulting abnormal beta/A4 with the glutamate to glutamine substitution having a greater tendency to aggregation. This has recently been confirmed by Wisniewski et al. [9]. They showed an accelerated fibril formation in vitro from synthetic beta/A4 peptides having the HCHWA-D mutation. As normally some beta/A4 is always formed by aberrant metabolic pathways the large amount of amyloid found in Down’s syndrome can be explained by the excessive amount of APP present for proteolytic activity, inducing this aberrant metabolic pathway leading to more beta/A4 production. Amyioid precursor protein and WA4 thogenesis of Alzheimer’s disease
and the pa-
There is evidence that APP and beta/A4 play a role in the pathogenesis of Alzheimer disease: (1) In Down’s syndrome there is an overexpression of chromosome 21 on which the APP is coded. Ail patients with Down’ syndrome develop dementia in the third or
s3 forth decade with morphological changes in the brain completely comparable with AD. (2) Recently, a few families with AD have been described with a point mutation in the coding sequence of the APP gene near the beta/A4 domain [&lo]. (3) In hereditary cerebral hemorrhages with amyloidosis of the Dutch type a point mutation has been described in the beta/A4 part, close to the normal cleavage site [7,11] which could lead to an altered processing of APP resulting in amyloidogenesis. Dementia sometimes becomes manifest before the manifestation of a cerebral hemorrhage [12]. (4)In cell culture studies it is shown that synthetic beta/A4 can be toxic to mature neurons.
Conclusion A large body of evidence exists that the beta/A4 formation from APP is one of the underlying causes of AD and other beta-amyloidoses. The important question regarding the origin of APP, the abnormal metabolisation of APP, and its influence on neuronal function remains unanswered.
References 1 Hardy J, Allsop D. Trends Pharmacol Sci 1991; 12: 383-388. 2 Selkoe D, Podlisny M, Joachim C, Vickers E, Lee G, Fritz L, Oltersdorf T. Proc Nat1 Acad Sci USA 1988; 85: 7341-7345. 3 Nordstedt C, Candy SE, Alafuzoff I, Caporaso GL, Iverfeldt K, Grebb JA, Winblad B, Greengard P. Proc Nat1 Acad Sci USA 1991; 88: 8910-8914. 4 Schubert D, Cole G, Saitoh T, Oltersdorf T,. Biochem Biophys Res Commun 1989; 162: 83-88. 5 Whitson JS, Selkoe DJ, Cotman CW. Science 1989; 243: 1488-1490. 6 Esch FS, Keim PS, Beattie EC, Blather RW, Culwell AR, Oltersdorf T, McClure D, Ward PJ. Science 1990; 248: 1122-1124. 7 Levy E, Carman MD, Fernandez-Madrid IJ, Power MD, Lieberburg I, Van Duinen SG, Bots GTAM, Luyendijk W, Frangione B. Science 1990; 248: 1X24-1126. 8 Goate A, Chartier-Harlin MC, Mullan M, Brown J, Crawford F, Fidani L, Guiffra L, Haynes A, Irving N, James L, Mant R, Newton P, Rooke K, Roques P, Talbot C, Pericak Vance M, Roses A, Williamson R, Rossor M, Owen M, Hardy J. Nature 1991: 349: 704-706. 9 Wisniewski T, Ghiso J, Frangione B. Biochem Biophys Res Commun 1991; 179: X247-1254. 10 Murrell J, Farlow M, Ghetti B, Benson MD. Science 1991; 2.54: 97-99. 11 Bakker E, Broeckhoven C van, Haan J, Voorhoeve E, Hul W van, Licberburg I, Carman MD, Ommen GJB, Frangione B, Roos RAC. Am J Hum Genet 1991; 49: 518-521. 12 Haan J. Ilereditary cerebral hemorrhage with amyloidosis Dutch type. Thesis. Leiden 1990.
Function
of amyloid and amyloid protein precursor Rayrnund A.C. Roes’ and Joost Haanlt2 1Department of Neurology, Universily Hospital, Leiden (The Netherlands),
and 2 Depariinent of Neuroloa,
Key words:
Amyloid
precursor
protein;
St. Elisabeth Ziekenhuis, Leiakrdorp (The Netherlands)
Beta-amyloid
Summary A short relationship
review is given of the functions of amyloid (beta/A4) between amyloid deposition and dementia is discussed.
Introduction Amyloid is a highly insoluble compound showing birefringence after Congo red staining. Its ultrastructure consists of rigid non-branching fibrils folded in a beta-pleated sheet configuration. Amyloid can be found in the neuropil, amorphous and neuritic plaques and in the blood vessel walls of the brain of patients with Alzheimer’s disease (AD), Down’s syndrome, Sporadic Cerebral Hemorrhage with Amyloidosis and the Hereditary Cerebral Hemorrhages with Amyloidosis of the Dutch type (HCHWA-D). The major component of the amyloid fibrils in these diseases is a 3942 amino acid containing polypeptide of about 4.2 kDa, called beta/A4 protein. The beta/A4 protein is derived from the larger amyloid precursor protein (APP). APP is a cell-surface transmembranous protein with a short intracytoplasmic C-terminal and a large extracellular N-terminal (Fig. 1) [l]. The mechanism of amyloidogenesis is not clear. As the intracellular neurofibrillary tangles (NFI?) as well as the extracellular deposits in the neuropil and in the vessel walls are mainly composed of beta/A4 protein, understanding of the process leading to these depositions can be important to the understanding of the decline in neuronal function. Amyloid precursor
protein
APP is coded for on the long arm of chromosome 21. It is synthesized by most cell types and expressed at high Correspondence to: R.A.C. Roos, MD, Department of Neurology, University Hospital, P.O. Box 9600,230O RC Leiden, The Netherlands. Tel.: (71) 262111; Fax: (71) 154537.
and its precursor
protein
(APP).
The possible
levels in many tissues throughout the body [2]. At least 4 different forms of APP are recognized at present, consisting of 695, 714, 7.51, and 770 amino acids, respectively. The largest two (751 and 770) contain the Kunitz Protease Inhibitor insert (KPI). The 770-form is most abundantly present in the body. The APP 695, lacking this KPI insert, is predominantly present in normal brain. The total amount of immunologically detectable APP in human brain is not age-dependent and does not differ between normal controls and AD. With increasing age, however, the relative distribution between several forms of APP changes, but remaining similar for age-matched controls and AD patients. Therefore, the presence of APP is not sufficient to account for the formation of amyloid. Other mechanisms than aging have to be responsible for the pathological beta/A4 formation in AD
[31. Amyloid precursor
protein
and its function
The three main physiological functions of APP arc (1) protease inhibition, (2) cell adhesion, and (3) regulation of cell growth. Part of these functions depends on the presence of the KPI insert. The main function of the APP without KPI is stimulation of cell adhesion. The secretory forms of the APP with KPI insert have the same properties as protease nexin II, a growth-regulating molecule secreted by fibroblasts. In the blood these species bind with several serine proteases forming complexes that play an important role in coagulation inhibition. The secreted form of APP with the KPI insert is mitogenic for Swiss T3 cells. The APP without the insert
s2 56 amino acid Kunltz-type protease
I-
19 amino acids, homologous to MRC OX-2 antigen
neurotoxlc
secretory forms of APP-751 8 APP-770 - protease nexin II, tnvolved In growth regulation and cell adheston
trophic to undifferentiated neurons but toxic to mature neurons H contains cell adhesion site
H
shows binding actlvlty
H
neurotrophlt
Fig. 1. Functional map of Alzheimer’s disease amyloid precursor protein, showing beta/A4 region (hatched).
(APP 695) did not stimulate DNA synthesis in cell lines in vitro [4]. A 105 amino acid sequence from the C-terminal peptide expressing the beta/A4 protein causes degeneration of cells in vitro. Beta/A4 and its function Beta/A4 has not been reported to exhibit protease inhibitory activity, despite its homology with a part of the KPI insert. Residue 4-37 (from the A4 part) shows a 68% homology with the residues 120-153 of the Kunitz type soybean trypsin inhibitor, but it apparently lacks the active side. The survival and neuritic outgrowth of pyramidal hippocampal cells of Sprague-Dawley rats in cell cultures was directly related with the concentration of a 28 residue of synthetic beta/A4 [5]. Other parts of the beWA4, i.e. residues 25-35, show homology with the tachykinin family of neuropeptides. The synthetic peptide was trophic in low, and toxic in high concentrations for rat hippocampal neurons. Substance P antagonists showed comparable effects on hippocampal cells, effects that were reversed by substance P agonists. The 1-16 residues of the beta/A4 from the APP with and without the KPI insert mediate cell adhesion in neuronal cells as well as in non-neuronal cells. Amyloidogenesis The cleavage of APP normally takes place within the
beta/A4 domain, hence normally beta/A4 is not formed [6]. In HCHWA-D a point mutation is present within 6 sites from the point corresponding to this physiological cleavage site 171. In some patients with familial AD a mutation is found affecting a site just 4 residues past the C-terminus of the beta/A4 region fg]. One hypothesis is that these mutations influence the physiological cleavage process, leading to beta/A4 production. A different hypothesis is that the aberrant cleavage always occurs next to the normal cleavage in the beta/A4 region, the resulting abnormal beta/A4 with the glutamate to glutamine substitution having a greater tendency to aggregation. This has recently been confirmed by Wisniewski et al. [9]. They showed an accelerated fibril formation in vitro from synthetic beta/A4 peptides having the HCHWA-D mutation. As normally some beta/A4 is always formed by aberrant metabolic pathways the large amount of amyloid found in Down’s syndrome can be explained by the excessive amount of APP present for proteolytic activity, inducing this aberrant metabolic pathway leading to more beta/A4 production. Amyioid precursor protein and WA4 thogenesis of Alzheimer’s disease
and the pa-
There is evidence that APP and beta/A4 play a role in the pathogenesis of Alzheimer disease: (1) In Down’s syndrome there is an overexpression of chromosome 21 on which the APP is coded. Ail patients with Down’ syndrome develop dementia in the third or
s3 forth decade with morphological changes in the brain completely comparable with AD. (2) Recently, a few families with AD have been described with a point mutation in the coding sequence of the APP gene near the beta/A4 domain [&lo]. (3) In hereditary cerebral hemorrhages with amyloidosis of the Dutch type a point mutation has been described in the beta/A4 part, close to the normal cleavage site [7,11] which could lead to an altered processing of APP resulting in amyloidogenesis. Dementia sometimes becomes manifest before the manifestation of a cerebral hemorrhage [12]. (4)In cell culture studies it is shown that synthetic beta/A4 can be toxic to mature neurons.
Conclusion A large body of evidence exists that the beta/A4 formation from APP is one of the underlying causes of AD and other beta-amyloidoses. The important question regarding the origin of APP, the abnormal metabolisation of APP, and its influence on neuronal function remains unanswered.
References 1 Hardy J, Allsop D. Trends Pharmacol Sci 1991; 12: 383-388. 2 Selkoe D, Podlisny M, Joachim C, Vickers E, Lee G, Fritz L, Oltersdorf T. Proc Nat1 Acad Sci USA 1988; 85: 7341-7345. 3 Nordstedt C, Candy SE, Alafuzoff I, Caporaso GL, Iverfeldt K, Grebb JA, Winblad B, Greengard P. Proc Nat1 Acad Sci USA 1991; 88: 8910-8914. 4 Schubert D, Cole G, Saitoh T, Oltersdorf T,. Biochem Biophys Res Commun 1989; 162: 83-88. 5 Whitson JS, Selkoe DJ, Cotman CW. Science 1989; 243: 1488-1490. 6 Esch FS, Keim PS, Beattie EC, Blather RW, Culwell AR, Oltersdorf T, McClure D, Ward PJ. Science 1990; 248: 1122-1124. 7 Levy E, Carman MD, Fernandez-Madrid IJ, Power MD, Lieberburg I, Van Duinen SG, Bots GTAM, Luyendijk W, Frangione B. Science 1990; 248: 1X24-1126. 8 Goate A, Chartier-Harlin MC, Mullan M, Brown J, Crawford F, Fidani L, Guiffra L, Haynes A, Irving N, James L, Mant R, Newton P, Rooke K, Roques P, Talbot C, Pericak Vance M, Roses A, Williamson R, Rossor M, Owen M, Hardy J. Nature 1991: 349: 704-706. 9 Wisniewski T, Ghiso J, Frangione B. Biochem Biophys Res Commun 1991; 179: X247-1254. 10 Murrell J, Farlow M, Ghetti B, Benson MD. Science 1991; 2.54: 97-99. 11 Bakker E, Broeckhoven C van, Haan J, Voorhoeve E, Hul W van, Licberburg I, Carman MD, Ommen GJB, Frangione B, Roos RAC. Am J Hum Genet 1991; 49: 518-521. 12 Haan J. Ilereditary cerebral hemorrhage with amyloidosis Dutch type. Thesis. Leiden 1990.
