The Discovery of Endoplasmic Reticulum Storage Disease. The Connection between an H&E Slide and the Brain

Abstract

The revolutionary evolution in science and technology over the last few decades has made it possible to face more adequately three main challenges of modern medicine: changes in old diseases, the appearance of new diseases, and diseases that are unknown (mostly genetic), despite research efforts. In this paper we review the road travelled by pathologists in search of a method based upon the use of routine instruments and techniques which once were available for research only. The application to tissue studies of techniques from immunology, molecular biology, and genetics has allowed dynamic interpretations of biological phenomena with special regard to gene regulation and expression. That implies stepwise investigations, including light microscopy, immunohistochemistry, in situ hybridization, electron microscopy, molecular histopathology, protein crystallography, and gene sequencing, in order to progress from suggestive features detectable in routinely stained preparations to more characteristic, specific, and finally, pathognomonic features. Hematoxylin and Eosin (H&E)-stained preparations and appropriate immunohistochemical stains have enabled the recognition of phenotypic changes which may reflect genotypic alterations. That has been the case with hepatocytic inclusions detected in H&E-stained preparations, which appeared to correspond to secretory proteins that, due to genetic mutations, were retained within the rough endoplasmic reticulum (RER) and were deficient in plasma. The identification of this phenomenon affecting the molecules alpha-1-antitrypsin and fibrinogen has led to the discovery of a new field of cell organelle pathology, endoplasmic reticulum storage disease(s) (ERSD). Over fifty years, pathologists have wandered through a dark forest of complicated molecules with strange conformations, and by detailed observations in simple histopathological sections, accompanied by a growing background of molecular techniques and revelations, have been able to recognize and identify arrays of grotesque polypeptide arrangements.

Hepatic and Extrahepatic Sources and Manifestations in Endoplasmic Reticulum Storage Diseases

“…The hepatocytic storage of mutant AAT presents in the form of PAS diastase (PAS-D) resistant inclusions immunoreactive to anti-AAT specific antibodies, corresponding to material in the RER (Figure 1a-c). The molecular mechanism of Z AAT accumulation in the liver has been demonstrated as due to a loop-sheet polymerization following a molecular interaction between the reactive center loop of one molecule and the gap in the A-sheet of another [16]. The disruption of the folding is caused by the mutation Glu342Lys.…”

“…Nowadays there are no more doubts about the intrinsic toxic capacity of the stored AAT [16,58,59]. Although AATD individuals, either hetero-or homo-zygotes, may not show clinical or biochemical signs of liver disease, all of them undergo accumulation of the mutant protein Therefore, the storage process represents the true elementary lesion of the disease and reflects the phenotype-genotype correlation [16,58].…”

“…Mutations in any of the Fibrinogen gene (FGA, FGB, FGG) can result in hypofibrinogenemia [97]. However, only eight fibrinogen gamma chain mutations: Brescia (Gly384Arg), Aguadilla (Arg375Trp), Al du Pont Thr314Pro), Angers G316_Q350del), Beograd (Gly336Ser), Pisa (Asp316Asn), Ankara (His340Asp), Trabzon 8Thr371Ile) [89] and a single mutation on the A alpha chain (c.103C > T) [91] have been proven to result in hepatic storage and in a new disease, called hereditary hypofibrinogenemia with hepatic storage (HHHS) [1,15,16]. In all cases with hepatic storage, the gamma mutations were located at the end-to-end region of the globular D domain of the gamma chain and were hampering the D-dimer formation, causing aggregation of the protein within the RER [97,98].…”

“…The failure of correct polymerization leaves each monomeric gamma chain with exposed hydrophobic patches that give rise to undue interaction with lipids and with hydrophobic regions of APO-B-lipoprotein and other lipids [16,98,99].…”

“…The identification of the first mutation in the fibrinogen gamma chain gene [12] and the demonstration that the hereditary hypofibrinogenemia, in analogy with AATD, was due to the intrahepatic retention of the mutant protein [13][14][15], have led to the discovery of a new disease, hereditary hypofibrinogenemia with hepatic storage (HHHS), and to the concept of ERSD [1,15,16].…”