The Impact of FBN1-α5β1 Axis in Fibro/Adipogenic Progenitor Cells (FAP^CD9-) on Intramuscular Fat Content in Pigs

Intramuscular fat (IMF) plays a crucial role in enhancing meat quality, enriching meat flavor, and overall improving palatability. In this study, Single-cell RNA sequencing was employed to analyze the longissimus dorsi (LD) obtained from Guangdong small-ear spotted pigs (GDSS, with high IMF) and Yorkshire pigs (YK, with low IMF). GDSS had significantly more Fibro/Adipogenic Progenitor (FAPs), in which the CD9 negative FAPs (FAP^CD9-) having adipogenic potential, as demonstrated by in vitro assays using cells originated from mouse muscle. On the other hand, Yorkshire had more fibro-inflammatory progenitors (FIPs, marked with FAP^CD9+), presenting higher expression of the FBN1-Integrin α5β1. FBN1-Integrin α5β1 could inhibit insulin signaling in FAP^CD9-, suppressing adipogenic differentiation. Our results demonstrated that fat-type pigs possess a greater number of FAP^CD9-, which are the exclusive cells in muscle capable of differentiating into adipocytes. Moreover, lean-type pigs exhibit higher expression of FBN1-Integrin α5β1 axis, which inhibits adipocyte differentiation. These results appropriately explain the observed higher IMF content in fat-type pigs.