Gilles Grateau

Synchrotron X-Ray Microdiffraction Reveals Intrinsic Structural Features of Amyloid Deposits In Situ

Amyloidoses are increasingly recognized as a major public health concern in Western countries. All amyloidoses share common morphological, structural, and tinctorial properties. These consist of staining by specific dyes, a fibrillar aspect in electron microscopy and a typical cross-β folding in x-ray diffraction patterns. Most studies that aim at deciphering the amyloid structure rely on fibers generated in vitro or extracted from tissues using protocols that may modify their intrinsic structure. Therefore, the fine details of the in situ architecture of the deposits remain unknown. Here, we present to our knowledge the first data obtained on ex vivo human renal tissue sections using x-ray microdiffraction. The typical cross-β features from fixed paraffin-embedded samples are similar to those formed in vitro or extracted from tissues. Moreover, the fiber orientation maps obtained across glomerular sections reveal an intrinsic texture that is correlated with the glomerulus morphology. These results are of the highest importance to understanding the formation of amyloid deposits and are thus expected to trigger new incentives for tissue investigation. Moreover, the access to intrinsic structural parameters such as fiber size and orientation using synchrotron x-ray microdiffraction, could provide valuable information concerning in situ mechanisms and deposit formation with potential benefits for diagnostic and therapeutic purposes.

Diagnosis and Classification

A high degree of clinical suspicion in the context of a great diversity of clinical symptoms remains essential to make the diagnosis of amyloidosis that still relies on tissue biopsy. Standard tissue staining should be completed with Congo red as this stain gives a specific “apple-green birefringence” for amyloid under polarization. Identifying the type of amyloidosis is crucial to determine clinical management, prognosis, and treatment and thus explains that the actual nomenclature of amyloid disorders is based on the biochemical nature of amyloid. This typing requires a confrontation of clinical data to the results of some crucial blood tests such as the measure of the acute phase response and the search for a monoclonal component, histology, and genetics. Standard histological analysis is enriched with immunohistochemistry which analyses the fixation by amyloid of a panel of antibodies directed against most of the common human amyloid proteins. Rarely, sophisticated biochemical methods help to establish the true nature of the deposits. Once the steps have been cleared the disease can be classified as localized or multisystemic and its nature established. The main categories of multisystemic amylosis are the immunoglobulinic variety (AL, A for amyloid and L for light chain of immunoglobulin); amyloid associated with inflammation (AA, A for associated); and the transythyretin amyloidosis (ATTR, TTR for transthyretin) that consists in two varieties, the common “senile” and the rare hereditary.