Amyloid deposition in a mouse model humanized at the transthyretin and retinol-binding protein 4 loci

Abstract

Familial amyloidotic polyneuropathy is an autosomal dominant disorder caused by a point mutation in the transthyretin (TTR) gene. The process of TTR amyloidogenesis begins with rate-limiting dissociation of the TTR tetramer. Thus, the TTR stabilizers, such as Tafamidis and Diflunisal, are now in clinical trials. Mouse models will be useful to testing the efficacy of these drugs. Although several mouse models have been generated, they all express mouse Rbp4. Thus, human TTR associates with mouse RBP4, resulting in different kinetic and thermodynamic stability profiles of TTR tetramers. To overcome this problem, we previously produced humanized mouse strains at both the TTR and Rbp4 loci (Ttr , Ttr , and Rbp4 ). By mating these mice, we produced double-humanized mouse strains, Ttr :Rbp4 and Ttr :Rbp4 . We used conventional transgenic mouse strains on a wild-type (Ttr :Tg[6.0hTTRMet30]) or knockout Ttr background (Ttr:Tg[6.0hTTRMet30]) as reference strains. The double-humanized mouse showed 1/25 of serum hTTR and 1/40 of serum hRBP4 levels. However, amyloid deposition was more pronounced in Ttr :Rbp4 than in conventional transgenic mouse strains. In addition, a similar amount of amyloid deposition was also observed in Ttr :Rbp4 mice that carried the wild-type human TTR gene. Furthermore, amyloid deposition was first observed in the sciatic nerve without any additional genetic change. In all strains, anti-TTR antibody-positive deposits were found in earlier age and at higher percentage than amyloid fibril deposition. In double-humanized mice, gel filtration analysis of serum revealed that most hTTR was free of hRBP4, suggesting importance of free TTR for amyloid deposition.

Contributions of Animal Models to the Mechanisms and Therapies of Transthyretin Amyloidosis

“…Attempts to model ATTR amyloidosis in mice began more than 3 decades ago by random genomic insertion of wild-type or mutant hTTR. However, efforts to produce an ideal mouse model for ATTR amyloidosis have not been as successful as scientists would desire (Buxbaum et al, 2003; Buxbaum, 2009; Kan et al, 2018; Li et al, 2018). To gain insights into the pathogenesis of ATTR amyloidosis, transgenic ATTR V30M mice were created with the mouse metallothionein promoter (Shimada et al, 1989).…”

“…Nevertheless, the search for an ideal mouse model isn’t over until a model which mimic ATTR amyloidosis patients in symptoms and tissue-distribution of congophilic TTR amyloid deposit is achieved. Two groups recently generated mouse models with amyloid deposits in the peripheral nerves without additional genetic changes such as Hsf1 deficiency (Kan et al, 2018; Li et al, 2018). Biophysical analysis alongside biochemical studies in mice reveal that murine TTR inhibit aggregation and deposition of highly unstable human TTR via formation of a highly stable human-mouse heterotetramers (Tagoe et al, 2007; Reixach et al, 2008).…”

“…Biophysical analysis alongside biochemical studies in mice reveal that murine TTR inhibit aggregation and deposition of highly unstable human TTR via formation of a highly stable human-mouse heterotetramers (Tagoe et al, 2007; Reixach et al, 2008). To overcome this, Li et al (2018), produced humanized mouse strains at both the Ttr and Rbp4 loci allowing human TTR (hTTR) to associate with human RBP4 (hRBP4). Two mouse lines; normal (Ttr hTTRV 30/hTTRV 30 : Rbp4 hRBP4/hRBP4 , abbreviated as hV/hV:hR/hR ) and mutant (Ttr hTTRV 30/hTTRM30 :Rbp4 hRBP4/hRBP4 , abbreviated as hV/hM:hR/hR ) were generated.…”

“…At 24 months, amyloid deposition was observed in the heart of both lines with more deposit in the mutant mice. Notably at 24 months, Congo red positive amyloid deposits were found in the perineurium of the sciatic nerve of the mutant line (Li et al, 2018). This study further reveal the impact RBP4 might have on amyloid deposition as it is known to prevent TTR amyloid formation at lower pH (White and Kelly, 2001).…”

Expression of Amyloidogenic Transthyretin Drives Hepatic Proteostasis Remodeling in an Induced Pluripotent Stem Cell Model of Systemic Amyloid Disease

“…Despite success in clinical trials for such drugs, not all patients respond equally and effectively, likely attributed to the inherited TTR mutation and the underlying genetic background of the individual ( Ando et al., 2016 ; Berk et al., 2013 ; Buxbaum, 2019 ; Gertz et al., 2015 ; Maurer et al., 2017 , 2018 ). Due to their multi-tissue etiologies, systemic amyloid diseases such as ATTR amyloidosis prove difficult to study, while until only recently, mouse models have failed to recapitulate key aspects of human TTR amyloid pathology ( Buxbaum, 2009 ; Giadone et al., 2018 ; Kan et al., 2018 ; Leung et al., 2013 ; Leung and Murphy, 2016 ; Li et al., 2018 ; Sousa et al., 2002 ). To study disease pathogenesis in the genetic context of the patient, we differentiated patient-specific ATTR amyloidosis induced pluripotent stem cells (iPSCs) into effector hepatocyte-like cells (HLCs) that produce and secrete destabilized TTR ( Giadone et al., 2018 ; Leung et al., 2013 ; Leung and Murphy, 2016 ).…”