The Fate of Adipocytes after Nonvascularized Fat Grafting

BACKGROUND: Clinical outcomes following fat grafting are variable and technique dependent, and it is unknown how the graft is revascularized. The authors recently observed that living and dead adipocytes can be differentiated not with hematoxylin and eosin staining but with immunohistochemistry for perilipin. METHODS: The viability of cellular components (adipocytes, adipose stem/stromal/progenitor cells, vascular endothelial cells, and hematopoietic cells) in human adipose tissue was evaluated using (1) stored lipoaspirates, (2) cultured cells, and (3) organ-cultured adipose tissue. In addition, the groin fat pad (150 to 200 mg) in mice was transplanted under the scalp, and the graft was stained at 0, 1, 2, 3, 5, 7, or 14 days. RESULTS: In vitro studies revealed that adipocytes are most susceptible to death under ischemic conditions, although adipose-derived stromal cells can remain viable for 3 days. The in vivo study indicated that most adipocytes in the graft began to die on day 1, and only some of the adipocytes located within 300 μm of the tissue edge survived. The number of proliferating cells increased from day 3, and an increase in viable adipocyte area was detected from day 7, suggesting that repair/regeneration of the dead tissue had begun. CONCLUSIONS: The authors show convincing evidence of very dynamic remodeling of adipose tissue after nonvascularized grafting. The authors observed three zones from the periphery to the center of the graft: the surviving area (adipocytes survived), the regenerating area (adipocytes died, adipose-derived stromal cells survived, and dead adipocytes were replaced with new ones), and the necrotic area (both adipocytes and adipose-derived stromal cells died).