Mechanism of umbilical cord mesenchymal stem cells in the up-regulation of regulatory T cells by transforming growth factor β1 in systemic lupus erythematosus

Abstract

To explore the mechanism of umbilical cord mesenchymal stem cells (UC-MSC) in the up-regulation of peripheral regulatory T cells in patients with systemic lupus erythematosus (SLE). Peripheral blood mononuclear cells (PBMC) from 20 SLE patients and normal controls were co-cultured with UC-MSC at different ratios respectively for 72 hours. And the proportions of CD4+CD25+Foxp3+regulatory T cells were analyzed by flow cytometry. PBMC and sera from active SLE patients and normal controls were used to stimulate UC-MSC. The expressions of transforming growth factor β1 (TGF-β1) on UC-MSC were detected by real-time fluorescence quantitative polymerase chain reaction (real-time PCR). The supernatant level of TGF-β1 was determined by enzyme-linked immunosorbent assay (ELISA). And the TGF-β1 small interfering RNA (siRNA) was used to interfere with the TGF-β1 expression on UC-MSC and determine its effect on the regulation of SLE Treg cells. TGF-β1 inhibitor was added into the culture system of UC-MSC and PBMC from active SLE patients to observe its role on the up-regulation of Treg cells by UC-MSC. UC-MSC could dose-dependently up-regulate the peripheral CD4+CD25+Foxp3+Treg proportion in SLE patients. And such an effect was not dependent on cell-cell contact. UC-MSC had no regulatory effect on Treg cells in normal controls. Compared with the non-stimulated and normal PBMC stimulated groups, PBMC from SLE patients significantly promoted TGF-β1 mRNA expression on UC-MSC (relative gene expression was 1.00 ± 0.09, 1.95 ± 0.62, 4.20 ± 2.34 respectively, both P < 0.05). The supernatant level of TGF-β1 was significantly elevated in the presence of SLE PBMC. Sera of SLE patients (5%) enhanced TGF-β1 mRNA expression on UC-MSC and it was significantly higher than fetal bovine serum cultured group (12.19 ± 4.49 vs 1.33 ± 0.06, P < 0.01) and normal individual sera cultured group (2.53 ± 0.72, P < 0.01). Additionally, TGF-β1 siRNA interfered UC-MSC failed to up-regulate Treg cells in SLE patients . Furthermore, TGF-β1 specific inhibitor SB431542 significantly inhibited the regulatory role of UC-MSC on Treg cells in SLE patients. Immune microenvironment in SLE patients can significantly stimulate the TGF-β1 expression on UC-MSC and plays an important role in the up-regulation of Treg cells in patients.