SERPINA1 as a therapeutic target in ATTR Amyloidosis

Question:

The role of the protein quality control (PQC) system for the pathogenesis of familial amyloid polyneuropathy (ATTR) has attracted much recent interest. Alpha-1-antitrypsin (SERPINA1) was recently described as a chaperone in various amyloidotic diseases, e.g. in amyloid aggregates of Alzheimer disease and amyotrophic lateral sclerosis (ALS). We used induced pluripotent stem cells (iPSCs) to study the PQC in iPSC-derived hepatocyte-like cells (HLCs). The aim of the study was to further explore the interaction of SERPINA1 and transthyretin (TTR).

Methods:

Urine from ATTR patients (n = 4) and healthy individuals (n = 4) was processed for isolation of renal epithelial cells, followed by reprogramming into iPSCs and differentiation towards hepatocyte-like cells (HLCs). qPCR was used to analyze gene expression of TTR and SERPINA1. Protein expression was determined by Western blot and ELISA. Cell culture supernatants derived from HLCs were subjected to immunoprecipitation using anti-TTR antibody followed by Western blot analysis using anti-SERPINA1. Plasma-isolated TTR was subjected to fibril formation by partial acidic denaturation and incubated with SERPINA1. Fibril formation was analyzed by Western blot.

Results:

mRNA expression of SERPINA1 was identified to be differently regulated (FC>± 5) in HLCs of ATTR patients as compared to healthy individuals. A high positive correlation between SERPINA1 and TTR was identified in both groups (r> 0.9). However, this correlation vanished post TTR downregulation in HLCs of ATTR patients but not in healthy donors suggesting a mutual dependence of SERPINA1 expression and the variant form of TTR. TTR co-immunoprecipitation identified a protein band of 55 kDa immunoreactive with anti-SERPINA1 in HLC cell culture supernatants derived from ATTR patients and healthy individuals. In fibril formation assays, incubation of SERPINA1 but not unrelated protein could prevent TTR oligomer formation.

Conclusions:

Our data indicate for the first time that (i) SERPINA1 and variant TTR expression in hepatocytes are closely linked, (ii) SERPINA1 and TTR can physically interact, and (iii) SERPINA1 and TTR interaction may prevent fibril formation. The findings are highly relevant for the understanding of TTR-induced pathogenesis in ATTR patients and may reveal a potential therapeutic target.