The role of inflammation in a humanized mouse model of transthyretin cardiac amyloidosis
Authors: Wu Xiaokang , Cai Nixuan , Jimenez John Isaiah , Kitakata Hiroki , Fahed Gracia , Evangelisti Alessandro , Jha Alokkumar , Woo Joseph , Liao Ronglih , Alexander Kevin M 
Published: December 2024

Background

Systemic amyloidosis represents a group of protein-misfolding diseases that confer significant morbidity and mortality for millions of patients worldwide. Transthyretin cardiac amyloidosis (ATTR) is a particularly devastating amyloid disease that affects middle-aged and elderly individuals and leads to cardiomyopathy (ATTR-CM), which has a median survival of 2.5 to 3.5 years [1, 2]. ATTR-CM can be hereditary, leading to a more aggressive disease course in younger patients. The most prevalentTTRvariant in the United States isV122I, which is found in 3-4 % of African Americans [3]. Despite the significant healthcare burden, ATTR-CM remains underdiagnosed due to a lack of disease awareness and limited diagnostic techniques [4]. Informativein vivomodels have proven elusive during the past decade [5]. Moreover, there is no available treatment to reverse cardiac dysfunction due to amyloid fibril deposition [1, 6, 7]. Therefore, a better understanding of the molecular mechanisms of ATTR-CM is imperative to developing novel, effective therapies.

Method and Results

To explore the pathogenesis of ATTR, we created a murine TTR knockout (TTR-KO) model expressing the human V122ITTRvariant. To study the gender differences, both male and female TTR-KO mice were utilized in this study. Significant elevations of human TTR were observed in both male and female ATTR murine plasma post-injection 3 months (human TTR level (ng/ml) Male ATTR: 109.9 ± 5.568; Male control: 28.17 ± 7.010; p=0.0008, N=3 mice/group; Female ATTR: 127.5 ± 32.43; Female control: 20.08 ± 8.351; p=0.0327, N=3 mice/group) with preserved cardiac function (FS% Male ATTR: 26.07 ± 3.667; Male control: 22.69 ± 1.585; p=0.3712, N=6-8 mice/group; Female ATTR: 26.62 ± 1.980; Female control: 31.25 ± 4.482;p=0.3397, N=5-6 mice/group). Notably, the mouse model exhibited cardiac amyloid deposits confirmed by amyloidotic-specific Congo Red staining and Thioflavin T Staining. Transmission electron microscopy revealed both immature and mature amyloid fibrils in the extracellular matrix. RNA-sequencing of the ATTR mouse heart identified distinct transcriptomic patterns and conserved inflammation pathways similar to those seen in a cohort of human ATTR heart samples, including leukocyte transendothelial migration, T-cell receptor signaling, and apoptosis, along with upregulation of inflammatory markers CXCL-1/2/3 and CCL20, were observed in ATTR murine hearts. At the posttranslational level, we confirmed an increased level of CCL5 (MFI ATTR: 801 ± 105; Control: 426± 64; p=0.0061, N=3 mice/group) in murine plasma post-injection 3 months by a luminance-based immunoassay. The CXCL- and CCL-chemokines family are critical for directing leukocytes to inflammation sites.

Conclusion

In this study, we developed a humanized V122I ATTR mouse model with elevated circulating human TTR level and Congophilic amyloid deposits in the murine heart and kidneys. Our transcriptomic study suggested that inflammation may contribute to the ATTR-CM pathogenesis. Further studies are needed to decipher the precise interactions between inflammation and ATTR-CM.

Highlights/What’s new/Clinical relevance

We developed a humanized mouse model to replicate the multisystem complexity and clinical diversity associated with V122I ATTR-CM.

Our study unveiled the pathogenic molecular mechanisms of amyloid deposition in ATTR-CM via a novel mouse model.

We identified signature inflammatory pathways that uncover potential therapeutic targets for ATTR-CM.

Our ATTR mouse model allows for preclinical pharmacogenomic assessments of novel therapeutics, which will undoubtedly improve outcomes for ATTR-CM patients.