Deposition of Transthyretin in Early Stages of Familial Amyloidotic Polyneuropathy

Abstract

Familial amyloidotic polyneuropathy (FAP) is a neurodegenerative disorder characterized by extracellular deposition of transthyretin (TTR) amyloid fibrils, particularly in the peripheral nervous system. No systematic immunohistochemical data exists relating TTR deposition with FAP progression. We assessed nerves from FAP patients in different stages of disease progression (FAP 0 to FAP 3) for TTR deposition by immunohistochemistry, and for the presence of amyloid fibrils by Congo Red staining. The nature of the deposited material was further studied by electron microscopy. We observed that early in FAP (FAP 0), TTR is already deposited in an aggregated nonfibrillar form, negative by Congo Red staining. This suggested that in vivo, preamyloidogenic forms of TTR exist in the nerve, in a stage before fibril formation. Cytotoxicity of nonfibrillar TTR was assessed in nerves of different FAP stages by immunohistochemistry for macrophage colony-stimulating factor. FAP 0 patients already presented increased axonal expression of macrophage colony-stimulating factor that was maintained in all other stages, in sites related to TTR deposition. Toxicity of synthetic TTR fibrils formed in vitro at physiological pH was studied on a Schwannoma cell line by caspase-3 activation assays and showed that early aggregates but not mature fibrils are toxic to cells. Taken together, these results show that nonfibrillar cytotoxic deposits occur in early stages of FAP.

Targeting protein aggregation for the treatment of degenerative diseases

“…Numerous laboratories have hypothesized that smaller diffusible aggregates of poorly characterized structure, often called oligomers or protofibrils, that often escape histological detection, are the toxic species driving post-mitotic tissue degeneration in the amyloidoses 29, 58 . Acute cellular toxicity assessments in vitro and in vivo also indicate that smaller soluble and diffusible aggregates are notably more toxic than amyloid fibrils 74-76 , while conversion of toxic oligomers to amyloid fibrils can reduce toxicity 75, 77 . Our understanding of structure-proteotoxicity relationships is currently incomplete, largely due to technical limitations; thus we urgently need better technologies to specifically detect and quantify amyloid and non-amyloid aggregate types, which could also be useful as much needed biomarkers for diagnosing and monitoring response to therapy in the amyloidoses.…”

“…However, the fragmentation of amyloid fibrils or incomplete catabolism could contribute to the spectrum of oligomers formed during the process of aggregation (Fig.1), which appear to be more proteotoxic 76 . Liver transplantation might also be useful to treat other familial amyloid diseases wherein the amyloidogenic protein is predominantly secreted by the liver, e.g., in hereditary fibrinogen amyloidosis 95 .…”

Transthyretin: the servant of many masters

“…Whether the insoluble amorphous aggregates described first in transgenic animals [14] and then in humans [15] are in on- or off-pathway towards the amyloidogenic structure is still a matter of debate.…”

Low Erythropoietin Production in Familial Amyloidosis TTR V30M Is Not Related with Renal Congophilic Amyloid Deposition

“…In fact, previous reports described that axonal and Schwann cells degradation was not associated topographically with TTR amyloid deposition [8]. Nonfibrillar (Congo red stain-negative) TTR deposits have been demonstrated in the nerves in the presymptomatic phase of disease [9]. TTR was deposited in very small contiguous fibrillar-like assembles, too small to give birefringence with Congo red staining on histochemistry.…”

“…TTR was deposited in very small contiguous fibrillar-like assembles, too small to give birefringence with Congo red staining on histochemistry. These prefibrillar TTR structures were cytotoxic to neuronal cells by cellular activation and altered gene expression, such as the increased axonal expression of macrophage colony-stimulating factor [9]. The direct toxicity of amyloidogenic precursor proteins was also demonstrated in vitro on cultured cells [10,11,12,13] and amyloidogenic precursor proteins were detected in tissues in the absence of amyloid [9].…”