In vitro adipogenesis of adipose-derived stem cells in 3D fibrin matrix of low component concentration

This study evaluated the suitability of adipose-derived stem cells (ASCs) combined with fibrin matrix of variable composition for adipose tissue-equivalent formation in vitro. Therefore, undifferentiated ASCs were embedded in fibrin clots composed of 2 IU/ml thrombin and fibrinogen of varying concentrations (6.25, 12.5 and 25 mg/ml) and kept under control or adipogenic conditions. Fibrin-cell composites were evaluated by scanning electron microscopy, live/dead staining, lactate-dehydrogenase (LDH) assay, quantitative PCR for the adipogenic markers fatty acid binding protein 4 (FABP4), peroxisome proliferative activated receptor-γ (PPARγ) and leptin, leptin ELISA and oil red O staining. Cells were found homogeneously distributed throughout the clot. Their number increased to day 7 (up to 3.62-fold median) and decreased thereafter until day 28. The proliferation was unaffected by fibrinogen concentration in the control. Adipogenic conditions generally yielded higher cell numbers, which were in addition increasing with increasing fibrinogen concentrations. FABP4, PPARγ and leptin mRNA expression was strongly upregulated by adipogenic medium, which was confirmed by the levels of leptin secretion and lipid vesicles formation demonstrated by oil red O staining. When embedded in 25 mg/ml fibrinogen clots, ASCs showed the highest expression levels of FABP4 (up to 629.0-fold), PPARγ (up to 1.6-fold) and leptin (up to 57.9-fold), corroborated by significantly elevated leptin secretion (median 33.29 ng/ml) on day 14. Constructs composed of fibrin matrix of low component concentrations-allowing homogeneous cell distribution-with ASCs should represent a suitable strategy for adipose tissue formation in vivo.