*2.13. Fusion Index*

After washing with PBS, cells were fixed with methanol and then stained with 0.04% Giemsa G250 (Sigma Aldrich). Images were taken randomly of three different sections per dish. The number of nuclei in myotubes and the total number of nuclei in the cells were counted in each field. Fusion indices were calculated by expressing the number of nuclei in the myotubes as percentages of the total numbers of nuclei.

#### *2.14. TTR Protein Labeling with Fluorescence*

TTR protein and BSA were labeled with the Alexa Fluor 594 protein labeling kit (Thermo Fisher Scientific) following the manufacturer's instructions. Briefly, 100 μL TTR proteins and BSA (0.1 μg/μL) were incubated with 4.7 μL Alexa Fluor 594 succinimidyl ester (12.2 nmole/μL) for 15 min at room temperature, and the conjugated reaction mixture was then purified with resin gel-spin filter. Labeled TTR proteins (0.2 μg) and BSA were added to the cells and detected by fluorescence microscope (Nikon, Tokyo, Japan).
