Abstract Body: Background:
Cardiac amyloidosis is a severe condition characterized by the deposition of misfolded amyloid fibrils in the heart, leading to restrictive cardiomyopathy and heart failure. In transthyretin cardiac amyloidosis (TTR-CA), misfolded transthyretin (TTR)—primarily produced in the liver—accumulates in cardiac tissue. It is well established that in vivo cardiomyocytes do not produce TTR. However, whether iPSC-derived cardiomyocytes in vitro can produce TTR remains unclear. We hypothesized that under in vitro conditions, these cells might produce TTR, potentially altering current models of disease.

Methods:
Patient-derived iPSCs from TTR-CA individuals and healthy controls were obtained at Stanford University and differentiated into cardiomyocytes (iPSC-CMs) in the Alexander Lab. Western blot analysis (Figure 1) was performed to detect TTR monomers, dimers, and potential misfolded forms. Immunocytochemistry (Figure 2) was conducted to visualize sarcomeric proteins and nuclei in iPSC-CMs..

Results:
Histological evaluations confirmed that in vivo cardiomyocytes do not produce TTR (Figure 2). In contrast, Western blot analysis of iPSC-CMs (Figure 1) revealed the presence of TTR monomers and dimers, with additional bands suggestive of misfolded protein in TTR-CA samples. These preliminary findings indicate that under in vitro conditions, iPSC-derived cardiomyocytes may produce TTR.

Conclusions:
Our study provides preliminary evidence that, while cardiomyocytes in vivo do not produce TTR, iPSC-derived cardiomyocytes in vitro might intrinsically generate TTR. This finding offers a novel model for studying TTR misfolding and amyloid deposition and may inform future therapeutic strategies targeting TTR-CA. Further investigations are warranted to validate these observations and elucidate the underlying mechanisms.