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Free Radical-derived Oxysterols: Novel Adipokines Modulating Adipogenic Differentiation of Adipose Precursor Cells
Giuseppe Murdolo1, Marta Piroddi1, Cristina Tortoioli1
1Department of Internal Medicine (G.M.), Assisi Hospital, 06081 Assisi (Perugia), Italy; Department of Internal Medicine, Section of Internal Medicine, Endocrine and Metabolic Sciences (G.M., C.T.), University of Perugia, 06126 Perugia Italy; Department of Pharmaceutical Sciences (M.P., D.B., F.G.), University of Perugia, 06126 Perugia, Italy; Department of Anesthesiology and Intensive Care Medicine Mannheim (M.S.), Heidelberg University, 69117 Heidelberg, Germany; Department of Earth, Life and Environmental Sciences (F.L., B.C., S.P.), University Carlo Bo, 61029 Urbino, Italy; and Department of Medico-Surgical Sciences and Biotechnologies, Unit of Vascular Medicine (C.Z., L.I.), Sapienza University of Rome, 00185 Latina, Italy.
Context:
Increased oxidative stress in adipose tissue emerges as an inducer of obesity-linked insulin resistance. Here we tested whether free-radical derived oxysterols are formed by, and accumulate in, human adipocytes. Moreover, we asked whether increased accumulation of oxysterols characterizes the adipose cells of obese patients with type 2 diabetes (T2D) (OBT2D) compared with lean, nondiabetic controls (CTRLs). Finally, we studied the effects of the free radical-derived oxysterols on adipogenic differentiation of adipose-derived stem cells (ASCs).
Main Outcome Measures:
Adipocytes and ASCs were isolated from sc abdominal adipose tissue biopsy in four OBT2D and four CTRL subjects. Oxysterols in adipocytes were detected by gas chromatography/mass spectrometry. The cellular and molecular effects of oxysterols were then evaluated on primary cultures of ASCs focusing on cell viability, adipogenic differentiation, and "canonical" WNT and MAPK signaling pathways.
Results:
7-ketocholesterol (7κ-C) and 7β-hydroxycholesterol were unambiguously detected in adipocytes, which showed higher oxysterol accumulation (P < .01) in OBT2D, as compared with CTRL individuals. Notably, the accumulation of oxysterols in adipocytes was predicted by the adipose cell size of the donor (R2 = 0.582; P < .01). Challenging ASCs with free radical-derived type I (7κ-C) and type II (5,6-Secosterol) oxysterols led to a time- and concentration-dependent decrease of cell viability. Meaningfully, at a non-toxic concentration (1μM), these bioactive lipids hampered adipogenic differentiation of ASCs by sequential activation of WNT/β-catenin, p38-MAPK, ERK1/2, and JNK signaling pathways.
Conclusion:
Free radical-derived oxysterols accumulate in the "diabetic" fat and may act as novel adipokines modulating the adipogenic potential of undifferentiated adipose precursor cells.
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