Removing Lipid Droplets Improves Fat Transplantation Outcomes in a Mouse Model through Suppressing Pro-fibrotic Macrophage Responses.

Abstract

BACKGROUND: The clinical efficacy and predictability of autologous fat grafting are frequently undermined by uncontrolled fibrosis and oil cyst formation. While lipid droplets (LDs) metabolic imbalance is recognized as a critical factor influencing graft outcomes, the underlying mechanisms linking LDs to adverse tissue remodeling remain poorly understood. OBJECTIVES: This study aimed to elucidate the mechanistic impact of extracellular LDs on fat graft outcomes in a murine model, with a specific focus on their role in modulating macrophage-mediated inflammation and fibrosis. METHOD: Fat grafts were transplanted into C57BL/6J mice and divided into two groups: an oil-retained group (control) and an oil-removed group (intervention). Grafts were harvested at serial timepoints (2-12 weeks) for comprehensive analysis, including histopathology (H&E, Masson's trichrome), quantitative PCR for inflammatory and fibrotic markers (TNF-&#x3b1;, IL-1&#x3b2;, IL-6, TGF-&#x3b2;), and immunofluorescence staining to assess macrophage polarization (CD86 for M1, CD206 for M2). RESULT: The presence of excess extracellular LDs acted as a potent inflammatory trigger, driving a significant upregulation of pro-inflammatory cytokines, including TNF-&#x3b1; (2.4-fold), IL-6 (1.9-fold), and IL-1&#x3b2; (2.8-fold). This pro-inflammatory microenvironment was associated with a dominant M1 macrophage phenotype. Conversely, the preoperative removal of LDs fundamentally altered this response. The oil-removed group exhibited markedly superior outcomes, including a 1.25-fold greater volume retention (p < 0.01) and a 60% reduction in oil cyst area (p < 0.01) at 12 weeks. Mechanistically, these improvements were linked to a decisive shift in macrophage polarization toward a pro-regenerative M2 phenotype, as evidenced by a significantly higher CD206+/CD86+ cell ratio (1.76 vs. 0.86 in controls). CONCLUSION: LDs overload exacerbated graft failure through M1 macrophage-mediated chronic inflammation and pathological fibrosis. Preoperative removal of these lipid droplets mitigates this detrimental inflammatory cascade, improves graft retention, and represents a critical and actionable strategy for enhancing the outcomes of clinical fat transplantation. LEVEL OF EVIDENCE I: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors &#xa0; www.springer.com/00266 .