Amyloid Fibril Protein Nomenclature - 2002

Amyloid: J. Protein Folding Disord. 9, 197-200 (2002)

Editorial Amyloid fibril protein nomenclature - 2002

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T

he Nomenclature Committe met at the IX International Symposium on Amyloidosis in Budapest, July 200 1. Members present were Merrill Benson, Maria Saraiva, Jean Sipe and Per Westermark (Chairman). Members absent were Shukuro Araki, Alan S. Cohen, Blas Frangione and Colin Masters. New members of the Committee were Joel Buxbaum, Giampaolo Merlini and Shu-ichi Ikeda who were approved by the participants at the Symposium. When the first Nomenclature of Amyloid was created based on the nature of the amyloid fibril protein, the number of such proteins was limited to AA and AL’. It may have seemed quite unnecessary to establish a formal nomenclature for such a small number of proteins but this was not done without reason. Protein AL. and, particularly, protein AA had been described under several different names. There was also an embryo of suspicion that there may be more amyloid fibril proteins than was initially believed and with the number of amyloid fibril proteins known today, we must say that the idea of a nomenclature at that early stage was provident. It did not take long until it was shown that several of the amyloids of unknown composition were found to consist of proteins other than those described. The knowledge of the previously unexpected diversity of amyloid deposits is now rapidly increasing following the development of sensitive techniques for protein characterization, including the use of formalin-fixed and paraffin-embedded material, and the remarkably growing interest in the amyloid field. This has led to the identification of more than 20 human proteins that occur as major amyloid fibril proteins in vivo. A majority of the characterized proteins occur in systemic forms of amyloid but probably even more types of amyloid are localized. Without doubt, several more forms of amyloid will be characterized by their chemical nature within a short time. The basis for the current nomenclature of amyloidosis is very simple. It relies on the nature of the major fibril protein which is designated protein A, followed by an abbreviated form of the “mother” protein name. There are some minor exceptions to this general rule, seen in Table 1.

This general rule means that an amyloid cannot be included in the nomenclature unless its biochemical nature is known with absolute certainty. There are also rules for how variants of the fibril protein are named, e.g. depending on different mutations in the gene for a protein. Good examples are protein ATTRV30M and ATTRLl 1 1M. The amyloidosis is then named after the protein, e.g. protein AA-amyloidosis o r simply AA-amyloidosis. This general nomenclature is very simple and has been accepted and also adopted by the WHO2.

Newly characterized amyloid fibril proteins During the period since the last upgrading of the nomenclature at the VIII International Symposium on Amyloidosis in Rochester, Minnesota in 1998, five “new” human amyloid fibril proteins have been characterized biochemically. One of them is AMed (derived from medin), which constitutes the amyloid fibril in the very prevalent localized amyloid of the aortic media. Medin is a split product of the precursor lactadherin, expressed by aortic smooth muscle cells3.ALac may have seemed more logical but this designation was already was taken for the putative lactoferrin-derived amyloid. AApoAII (derived from apolipoprotein A-11) is another amyloid fibril protein new to the human4, but has been identified previously in mice. It occurs as a rare familial systemic amyloidosis with predominantly renal manifestations. Amyloid deposits are common in certain tumors and is sometimes of some diagnostic value. Thus, calcifying epithelial odontogenic tumor, sometimes named “Pindborg tumor” typically contains amyloid. The amyloid fibrils of one such tumor were shown to consist of a yet unnamedprotein6.It is therefore included in the nomenclature as a “preliminary amyloid fibril protein”. Lactoferrin was previously reported as an amyloid protein in familial subepithelial corneal amyloidosis’. Since this still has not been confirmed, this protein will remain as a “preliminary amyloid fibril protein”. On the other hand,

Correspondence: Dr. Per Westermark. Department of Genetics and Pathology, Rudbeck Laboratory. Uppsala University. SE75 1 85 Uppsala, Sweden Tel: 46 18 61 1 38 49 Fax: 46 18 55 2739 E-mail. [email protected] Submitted: April 16, 2002

Accepted: May 30. 2002

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several studies have indicated that kerato-epithelin is a corneal amyloid fibril protein associated with a mutation in the BIGH3 gene. Convincing data including amino acid sequencing have been obtaineds. Finally, a novel amyloid fibril protein was reported from leptomeningeal and parenchymal amyloid deposits from patients with familial British dementia9.This amyloid fibril protein is a internal fragment of the Bri gene product and depends on a mutation at the stop codon, leading to a 12 amino acid long extension. The amyloid fibril protein consists of the last 22 amino acids of the normal protein + 12

extra residues. Interestingly, another mutation, occurring in familial Danish dementia, includes a duplication prior to the stop codon and this results in another 34 amino acid fibril protein with identical 22 amino acid N-terminus but different C-terminuslo. The British form may be a systemic amyloidosis with cerebral manifestations" while the distribution of amyloid in familial Danish dementia is incompletely known. Since both proteins come from the same BRI gene it is most reasonable to label both proteins ABri. This, however, will be a matter for further discussion.


Table 1. Amyloid fibril proteins and their precursors in human

Amyloid protein

Precursor

Systemic (S) or Localized (L)

Syndrome or Involved Tissues

AL

Immunoglobulin light chain

s, L

AH

Immunoglobulin heavy chain

s, L

ATTR

Transthyretin

S

AD2M

p2-microglobulin

AA AApoAl

(Apo)serum AA Apolipoprotein Al

AApoAl I AGel ALys AFib ACys ABri* ADan* AD APrP ACal AIAPP

Apolipoprotein All Gelsolin Lysozyme Fibrinogen a-chain Cystatin C ABriPP ADanPP AD protein precursor (APPP) Prion protein (Pro)calcitonin Islet amyloid polypeptide

L? S L? S S L S S S S S L, S? L L L L L

AANF APro

Atrial natriuretic factor Prolactin

L L

Alns AMed AKer A(tbn)** ALac

Insulin Lactadherin Kerato-epithelin tbn** Lactofenin

L L L L L

Primary Myeloma-associated Primary Myeloma-associated Familial Senile systemic Tenosynovium Hemodialysis Joints Secondary, reactive Familial Aortic Familial Familial FamiIiaI FamiIiaI FamiIiaI Familial dementia, British Familial dementia, Danish Alzheimer's disease, aging Spongioform encephalopathies C-cell thyroid tumors Islets of Langerhans lnsulinomas Cardiac atria Aging pituitary Prolactinomas Iatrogenic Senile aortic, media Cornea; Familial Pindborg tumors Cornea; Familial

* **

ADan is coming from the same gene as ABri and has identical N-terminal sequence. It will be a matter of further discussion whether ADan should be included in the nomenclature as a separate protein (see text) to be named

Proteins in italics are preliminary

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Amyloid: J. Protein Folding Disord. 9, 197-200 (2002)

Current problems

Table 2. lntracellular amyloid proteins

Some problems may be identified. The recommendation in the last nomenclature communication that the AP protein precursor should be named APPP instead of APP created some objection, even by a member within the nomenclature committee itself and the designation APP, although not fully logical, is still used in the neuroscience literature. Another basic question concerns the old question “what is amyloid?”. It is generally stated that amyloid is the in vivo formed deposition of a protein in fibrillar form with cross beta sheet conformation, affinity for the dye Congo red and a typical green birefringence after such staining. In the previous report on nomenclature, we stated that in order to be included among the amyloids, the material should be extracellular. This means that intracellular aggregates with amyloid properties such as the paired helical filaments are not of amyloid nature. With the knowledge we have today, this is a highly questionable statement and at the meeting in Rochester this problem was discussed. The aggregation of proteins into amyloid fibrils is characterized by the cross beta sheet quaternary structure and there is no profound difference between aggregation taking place intracellularly from that outside of cells. Furthermore, it is evident that some aggregation into “ordinary” amyloid fibrils may start intracellularly’*~ 1 3 . Therefore, the most logical step should be to include also primarily strictly intracellular protein aggregates with amyloid properties in the amyloid nomenclature, perhaps under a special heading. There are also other pathological intracellular protein aggregates which at least partly may operate by the same mechanism as Congophilic materials but which differ by being Congo red negative. Diseases with such aggregates include among others, Parkinson’s disease, Huntington’s chorea and amyotrophic lateral sclerosis. Since the aggregates are Congo red negative and intracellular (or even intranuclear), they are not amyloid according to current nomenclature. However, the diseases belong to the rapidly increasing group of protein aggregation diseases. In the future, we may wish to have a nomenclature for the whole protein aggregation field where the amyloidoses may constitute only a subgroup. Perhaps a more acute problem concerns the in vitro formed amyloid-like fibrils which are often called “amyloid fibril^"'^,'^. Also certain fibrils on the surface of microorganisms are titled amyloidI6. It has long been known that it is possible to make fibrillar aggregates with amyloid properties from purified or synthetic proteins or peptides. These fibrils have the same dimensions as in vivo formed amyloid fibrils and also the typical staining properties with thioflavin T, thioflavin S or Congo red, including green birefringence with the latter. Likewise, the Sup35 fibrils of Saccharomyces have amyloid fibril properties. Generation of these dif-

ATau

Tau protein

Alzheimer‘s disease Other brain diseases Aging

ferent kinds of fibrils in vitro has had an enormous impact on our understanding of how protein monomers are arranged in amyloid fibrils and how the amyloid fibrils are formed. Yet, these fibrils are not amyloid in the sense that they constitute a biological aggregate or deposit. Even more questionable is the use of the designation “amyloid fibril” for fibrils created in vitro from peptides or proteins that are not known to give rise to amyloid fibrils in vzvo. It was the consensus of the members of the Nomenclature Committee present in Budapest, that the designation of in vitro made fibrils best are named “amyloid-like fibrils” and not “amyloid fibrils”.

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Nomenclature Committee of the International Society of Amyloidosis Per Westermark (Chairman) Merrill D. Benson Joel N. Buxbaum Alan S. Cohen Blas Frangione Shu-ichi Ikeda Colin L. Masters Giampaolo Merlini Maria J. Saraiva Jean D. Sipe