Chemical characterization of a lambda I amyloid protein isolated from formalin-fixed and paraffin-embedded tissue sections

Role of mutations and post-translational modifications in systemic AL amyloidosis studied by cryo-EM

Systemic AL amyloidosis is a rare disease that is caused by the misfolding of immunoglobulin light chains (LCs). Potential drivers of amyloid formation in this disease are post-translational modifications (PTMs) and the mutational changes that are inserted into the LCs by somatic hypermutation. Here we present the cryo electron microscopy (cryo-EM) structure of an ex vivo λ1-AL amyloid fibril whose deposits disrupt the ordered cardiomyocyte structure in the heart. The fibril protein contains six mutational changes compared to the germ line and three PTMs (disulfide bond, N-glycosylation and pyroglutamylation). Our data imply that the disulfide bond, glycosylation and mutational changes contribute to determining the fibril protein fold and help to generate a fibril morphology that is able to withstand proteolytic degradation inside the body.

Hereditary systemic immunoglobulin light-chain amyloidosis

Protein and DNA analyses reveal that mutation in the immunoglobulin κ light-chain constant region gene may cause hereditary amyloidosis. Sequencing of immunoglobulin light-chain constant region genes is indicated for patients with AL amyloidosis and no evidence of a plasma cell dyscrasia.

Progressive wild-type transthyretin deposition after liver transplantation preferentially occurs onto myocardium in FAP patients

To elucidate whether progressive wild-type transthyretin (TTR) deposition can actually occur after liver transplantation (LT), amyloid fibrils were investigated in two familial amyloid polyneuropathy patients with TTR Val30Leu variant, who died 1 year after LT. Amyloid fibrils were extracted from cardiac muscles, sciatic nerves and kidney, which were investigated by the immunoprecipitation-mass spectrometry method and liquid chromatography-ion trap mass spectrometry analysis. The ratio of wild-type to variant TTR in cardiac muscle was approximately 5:5 before LT, but greatly increased to about 9:1 after transplantation. The ratios in sciatic nerves and kidney obtained at autopsy were approximately 5:5. Wild-type TTR was undetectable in kidney amyloid obtained before LT. Our results indicate that paradoxical wild-type TTR deposition after LT can preferentially occur in myocardium, leading to fatal cardiac dysfunction, but it is quite likely that this phenomenon can also occur in other visceral organs.

Unfolding of the immunoglobulin light and heavy chains is required for the enzymatic removal of N-terminal pyroglutamyl residues

To enable Edman sequencing of pyroglutamylated immunoglobulins, enzymatic deblocking by pyroglutamate aminopeptidase is performed, often with variable yield and compromised solubility. Recently, enzymatic deblocking of immunoglobulins without denaturation was described. Although the conditions ensured efficient removal of pyroglutamyl residues, we conclude that deblocking is preceded by denaturation, which results in aggregation of the immunoglobulins. To study the effect of folding status on deblocking we developed a methanol based deblocking solution, which preserved the enzymatic activity of pyroglutamate aminopeptidase, provided conditions compatible with sequencing and enhanced deblocking of electroblotted samples, as well. At 50 degrees C and 35% (v/v) methanol the immunoglobulin chains were completely aggregated, but the degree of deblocking was comparable to that obtained with the previously described method. At 37 degrees C, the immunoglobulins were partly aggregated, but the deblocked chains were completely in the insoluble fractions, whereas the soluble fractions had retained pyroglutamylation in both chains, suggesting that unfolding of the immunoglobulins is required for the excision of the pyroglutamates. Inspection of the structures of pyroglutamylated immunoglobulin and pyroglutamate aminopeptidase P. furiosus indicates that the enzyme requires the substrate in an extended conformation, a criterium, which we conclude not to be fulfilled in the native form of immunoglobulins. Unfolding of the N-terminus would disrupt the immunoglobulin fold by breaking interactions between secondary structure elements and expose surfaces prone to aggregation.

Classification of amyloidosis: misdiagnosing by way of incomplete immunohistochemistry and how to prevent it

Classification of every individual case of amyloid disease is necessary in order to recognize its origin and its possible pathogenesis for therapeutic consideration. Classification of the amyloids can be performed in different ways. One method primarily exploits serum proteins-but these are risk factors only, and therefore render only ancillary information. In principle, one cannot establish the diagnosis alone through their use. Another approach analyzes the origin of the deposited amyloids, either by extracting the amyloid proteins followed by immunochemical or chemical analysis, or by using immunohistochemistry. Based on chemical analysis of prototypes of amyloid fibril proteins, we have developed a profile of antibodies over the years that specifically identify amyloid in tissue sections. These antibodies have been used for years as a routine service for clinicians and pathologists in immunohistochemically classifying amyloid found in formalin-fixed tissue sections. The typing is always controlled by established amyloid classes. In several cases, we have been asked for a second opinion on a diagnosed amyloid class. Our own immunohistochemical data were then compared with those submitted. These submitted immunohistochemical results represented misdiagnoses of amyloid classes in most patients, since the technique performed was usually incomplete. It is the purpose of this report to analyze such cases and to document some of the typical mistakes. Here, we show how to avoid common pitfalls and how one can arrive at a correct diagnosis using immunohistochemistry appropriately.

Aging in heterozygous Dnmt1-deficient mice: effects on survival, the DNA methylation genes, and the development of amyloidosis

We previously reported that heterozygous DNA methyltransferase 1-deficient (Dnmt1(+/-)) mice maintain T-cell immune function and DNA methylation levels with aging, whereas controls develop autoimmunity, immune senescence, and DNA hypomethylation. We therefore compared survival, cause of death, and T-cell DNA methylation gene expression during aging in Dnmt1(+/-) mice and controls. No difference in longevity was observed, but greater numbers of Dnmt1(+/-) mice developed jejunal apolipoprotein AII amyloidosis. Both groups showed decreased Dnmt1 expression with aging. However, expression of the de novo methyltransferases Dnmt3a and Dnmt3b increased with aging in stimulated T cells from control mice. MeCP2, a methylcytosine binding protein that participates in maintenance DNA methylation, increased with age in Dnmt1(+/-) mice, suggesting a mechanism for the sustained DNA methylation levels. This model thus provides potential mechanisms for DNA methylation changes of aging, and suggests that changes in DNA methylation may contribute to some forms of amyloidosis that develop with aging.

Seeking confidence in the diagnosis of systemic AL (Ig light-chain) amyloidosis: patients can have both monoclonal gammopathies and hereditary amyloid proteins

Investigators in the United Kingdom have shown that hereditary amyloidosis can be misdiagnosed as Ig light-chain (AL) amyloidosis because family history is an ineffective screen, and tissue staining used to type amyloid is unreliable. Misdiagnosis of AL can lead to inappropriate use of chemotherapy and failure to diagnose a hereditary disease. Over a 3-year period we sought to determine how often both possible sources of amyloidosis occurred in the same patient. We employed an algorithm based on established data and patterns of amyloidosis in order to focus the screening effort. Of 178 consecutive patients referred for amyloidosis, 54 were screened by polymerase chain reaction techniques with primers designed to detect transthyretin, apolipoprotein AI, apolipoprotein AII, fibrinogen Aalpha, and lysozyme variants. Three patients (6% of those screened and 2% of symptomatic patients) had both a monoclonal gammopathy and a hereditary variant. These results justify further study of screening for hereditary variants in patients with apparent AL, and highlight the need for practical techniques for identifying fibrils extracted from tissue.

A nondestructive molecule extraction method allowing morphological and molecular analyses using a single tissue section

In clinical practice, molecular analysis of tumor specimens is often restricted by available technology for sample preparation. Virtually all current methods require homogenization of tissues for molecule extraction. We have developed a simple, rapid, nondestructive molecule extraction (NDME) method to extract proteins and nucleic acids directly from a single fixed or frozen tissue section without destroying the tissue morphology. The NDME method is based upon exposure of micron-thick tissue section to extraction buffer with the help of heating and/or intact physical forces (ultrasound and microwave) to facilitate release of macromolecules into the buffer. The extracted proteins and nucleic acids can be used directly without further purification for downstream SDS-PAGE analysis, immunoblotting, protein array, mass spectra protein profiling, PCR, and RT-PCR reactions. Most importantly, the NDME procedure also serves as an antigen retrieval treatment, so that after NDME, the same tissue section can be used for histopathological analyses, such as H&E staining, immunohistochemistry, and in situ hybridization. Thus, the NDME method allows, for the first time, both histological diagnosis and molecular analysis on a single tissue section, whether it is from frozen or fixed tissue specimens.