Objective: To explore the role and mechanism of SIRT1 (Sirtuin1) in the differentiation of adipocyte.
Methods: SIRT1(-/-) mice with C57BL/6J gene background were generated and litter-mate wild-type (WT) mice were used as controls. Body weight and fat content were detected and their epididymal fat pads were collected at 28 weeks old of age. The tip part of epididymal fat tissue was incubated in phosphate buffered saline (PBS) containing both BODIPY 558/568 (5 µmol/L in PBS) for adipocytes and isolectin Alexa Fluor 488 (40 µg/ml in PBS) for endothelial cells overnight. The stained cells were then visualized under confocal microscope.Reconstruction of 3D data sets was accomplished with image processing software Imaris.Immunohistochemistry was used to detect the protein level of endothelial cell marker CD31.Hematoxylin and eosin staining was performed for fixed epididymal fat tissue. Mouse embryonic fibroblast (MEF) cells were prepared from 13-14 days embryos of SIRT1(-/-) or WT mice and differentiated into adipocytes. Then oil-red O staining was performed.
Results: Compared with wild-type controls, both body weight (WT 42.1 g ± 1.6 g vs SIRT1(-/-) 25.4 g ± 1.0 g, P < 0.05) and epididymal fat mass (WT 13.4 g ± 1.0 g vs SIRT1(-/-) 7.8 g ± 0.5 g, P < 0.05) were much smaller in the SIRT1(-/-) mice. HE staining of fat tissue exhibited a significant reduction in adipocyte size and extracellular matrix in SIRT1(-/-) mice.However, the adipogenesis ability of MEF cells was significantly enhanced in vitro in SIRT1(-/-) MEF cells.Further study found that the density of vascular network decreased by 50% in the tip portion of epididymal fat pads of SIRT1(-/-) mice (capillary density:WT 2.92% ± 0.03% vs SIRT1(-/-) 1.34% ± 0.02%, P < 0.05). CD31, a cellular marker of decreased angiogenesis, decreased significantly in epididymal fat pads of SIRT1(-/-) mice.
Conclusion: SIRT1 knockout impairs adipocyte differentiation in SIRT1(-/-) mice with C57BL/6J gene background through reduced angiogenesis but not adipogenesis.