Fascia Promotes Adipose Tissue Regeneration by Improving Early Macrophage Infiltration after Fat Grafting in a Mouse Model

BACKGROUND: Low early macrophage fat graft infiltration (within a week of surgery) hinders tissue regeneration, suggesting that macrophages play a vital role in early angiogenesis and adipogenesis. However, the source of macrophages during this period is unclear. METHOD: C57BL/6 mice were split into fascial removal (FR) group and control groups (CG). Mice had a piece of back fascia removed in the FR group, which was immediately replaced in the CG, and inguinal fat injected into the transplantation site of both groups. Separately, fascia was harvested from green fluorescent protein-expressing mice and transplanted into C57BL/6 mice for tracing macrophage infiltration after fat grafting. RESULTS: The number of capillaries in the FR group was lower than that in the CG at days 3 ( P < 0.01) and 7 ( P < 0.05). Moreover, the number of small adipocytes in the FR group was lower than in the CG on days 3, 7, and 14 (all P < 0.05), and the relative expression of several adipogenic proteins was significantly lower in the FR group than in the CG on days 14 and 30. The timeline of macrophage infiltration was consistent with angiogenesis and adipogenesis. The number of macrophages in the FR group was significantly lower than in the CG at days 3 and 7 ( P < 0.05), and there were more fascia-derived macrophages than circulation-derived macrophages infiltrated into fat grafts within 7 days. Finally, the graft retention was lower in the FR group than the CG at day 90 ( P < 0.05). CONCLUSION: In the early stage after fat grafting, fascial macrophage infiltration initiates tissue regeneration, thereby improving graft retention by promoting angiogenesis and adipogenesis. CLINICAL RELEVANCE STATEMENT: In the clinic, injecting fat close to the fascia may increase fat retention. Fascia is widespread and self-regenerating, which may be a promising alternative source of local macrophages, with implications for tissue-engineering therapies such as correction of soft-tissue defects and breast reconstruction.