Secretion of amyloidogenic gelsolin progressively compromises protein homeostasis leading to the intracellular aggregation of proteins

Abstract

Familial amyloidosis of Finnish type (FAF) is a systemic amyloid disease associated with the deposition of proteolytic fragments of mutant (D187N/Y) plasma gelsolin. We report a mouse model of FAF featuring a muscle-specific promoter to drive D187N gelsolin synthesis. This model recapitulates the aberrant endoproteolytic cascade and the aging-associated extracellular amyloid deposition of FAF. Amyloidogenesis is observed only in tissues synthesizing human D187N gelsolin, despite the presence of full-length D187N gelsolin and its 68-kDa cleavage product in blood-demonstrating the importance of local synthesis in FAF. Loss of muscle strength was progressive in homozygous D187N gelsolin mice. The presence of misfolding-prone D187N gelsolin appears to exacerbate the age-associated decline in cellular protein homeostasis (proteostasis), reflected by the intracellular deposition of numerous proteins, a characteristic of the most common degenerative muscle disease of aging humans, sporadic inclusion body myositis.amyloid ͉ proteostasis ͉ sporadic inclusion body myositis ͉ FAF mouse P rotein homeostasis (proteostasis) refers to the cellular control of the synthesis, structure, trafficking, and degradation of proteins (1). An aging-associated decline in proteostasis capacity may contribute to the onset of many diseases associated with protein misfolding (2-4). Inheriting an aggregation-prone protein(s) further challenges proteostasis capacity upon aging (5). Such challenges can lead to loss-of-function disorders or aggregation-associated degenerative diseases (1-3, 5-9). Whether intracellular and/or extracellular aggregation leads to proteotoxicity in diseases associated with extracellular amyloid, such as Alzheimer's disease, remains unclear (3, 10).Familial amyloidosis of Finnish type (FAF) or gelsolin amyloidosis is thought to result from amyloidogenesis of a fragment of gelsolin causing aging-associated proteotoxicity (1,(11)(12)(13)(14). Plasma gelsolin is a 83-kDa 6-domain Ca 2ϩ -binding protein that is secreted from several cell types into the blood (Ͼ200 g/mL) (15), with muscle contributing significantly (16). A D187 mutation to N or Y (D187N/Y) in plasma gelsolin compromises Ca 2ϩ binding in domain 2 and thus folding (13). This enables aberrant cleavage by furin in the trans-Golgi, generating a 68-kDa fragment (C68) of gelsolin that is secreted (11, 17) (Fig. 1A). Only a fraction of D187N/Y plasma gelsolin in FAF is cleaved by furin; the remainder is secreted as full-length, functional plasma gelsolin. C68 can be further cleaved in the extracellular space by a type I matrix metalloprotease, like MT1-MMP (12), to generate the major (8-kDa) and minor (5-kDa) amyloidogenic fragments that deposit in blood vessel walls, skin, the autonomic nervous system, and the eye of humans, causing cranial and peripheral polyneuropathy, cutis laxa, and corneal lattice dystrophy (18). Deposition also occurs in skeletal and cardiac muscle, leading to cardiomyopathy and muscle weakness (14, 18). Given that human D187N/Y plasma gelso...

Discovery and characterization of a mammalian amyloid disaggregation activity

“…[3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Amyloid is toxic when applied exogenously to or when formed within cultured cells. [19][20][21][22][23][24][25][26][27][28][29][30][31][32] Mouse and C. elegans models of amyloid diseases show that the cytotoxicity associated with amyloidogenesis increases with organismal age. 22,33 Postnuclear supernatant (PNS) from C. elegans has recently been shown to disaggregate Ab 1-40 amyloid fibrils, which are linked to Alzheimer's disease.…”

“…[19][20][21][22][23][24][25][26][27][28][29][30][31][32] Mouse and C. elegans models of amyloid diseases show that the cytotoxicity associated with amyloidogenesis increases with organismal age. 22,33 Postnuclear supernatant (PNS) from C. elegans has recently been shown to disaggregate Ab 1-40 amyloid fibrils, which are linked to Alzheimer's disease. 5,10,34,35 C. elegans disaggregation and proteolysis activities can be uncoupled by protease inhibition or by heating the worm homogenate to 80 C, both of which eliminate proteolysis but not disaggregation, indicating that nematode disaggregation activity does not rely on proteolysis.…”

“…34,35 In this article, we test the hypothesis that mammals also have a disaggregase activity(ies) that can be uncoupled from proteolysis. Disaggregation was studied using Ab fibrils (associated with Alzheimer's disease) 5,10 and 8 kDa plasma gelsolin fragment fibrils (linked to familial amyloidosis of Finnish type 22 ) prepared in vitro. Notably, homogenates from all mouse tissues and human cell lines evaluated exhibit amyloid disaggregase and proteolysis activities, highlighting the apparent ubiquity and necessity of these activities for the maintenance of the proteome, or proteostasis.…”

“…Identifying the molecular machinery responsible for the mammalian disaggregase activity and, ultimately, adapting this machinery offer the prospect of ameliorating age-related degenerative diseases in which cytotoxicity is genetically linked to the process of amyloidogenesis. 5,[10][11][12][13][14][15][16][17][18][19]22,30,[33][34][35][36][37] Results…”

A Nanobody‐Based Approach to Amyloid Diseases, the Gelsolin Case Study

“…As of 2009, a mouse model is available that faithfully recapitulates the entire proteolytic cascade of human PG* [32]. Following the electroporation of the human plasma GSN cDNA, carrying the D187N mutation, into mouse ES cells, a transgenic animal was obtained where gelsolin is expressed under control of a muscle creatine kinase (MCK) promoter.…”