摘要目的:探讨外源性肿瘤坏死因子α(TNF－α)对三维环境下小鼠间充质干细胞向汗腺细胞分化的影响及其分子机制。方法:(1)取5只6～8周龄雌性C57BL/6小鼠，用烫伤仪在每只小鼠背部制成1个1 cm 2深Ⅱ～Ⅲ度烫伤创面。伤后1 d，取创面全层皮肤组织，采用酶联免疫吸附测定法检测组织中TNF－α浓度。(2)将0.9 g明胶和0.3 g海藻酸钠混匀后溶于30 mL磷酸盐缓冲液中制成水凝胶，取10只1 d龄雌雄不明C57BL/6小鼠足底全层皮肤研磨成真皮匀浆，从10只7 d龄雌雄不明C57BL/6小鼠股骨和胫骨中分离培养间充质干细胞。混合8 mL预热水凝胶、1 mL小鼠足部真皮匀浆、1 mL第2或3代终浓度为1.5×10 5个/mL间充质干细胞悬液，利用三维生物打印机在培养皿中打印出纵横交错的圆柱块共12块。打印块用25 g/L氯化钙溶液交联10 min，加入间充质干细胞培养基常规培养12 h后，按随机数字表法分为空白对照组和TNF－α处理组，每组6皿、6块。2组打印块均更换新鲜的汗腺诱导培养基培养，TNF－α处理组培养基中另加入终质量浓度为20 ng/mL的TNF－α。培养6 h，采用实时荧光定量反转录PCR法检测各组2皿打印块中间充质干细胞的多能性标志物Nanog mRNA的表达，采用蛋白质印迹法检测各组1皿打印块中间充质干细胞的Nanog蛋白表达，样本数均为3。培养14 d，采用实时荧光定量反转录PCR法检测各组2皿打印块中间充质干细胞的汗腺细胞标志物细胞角蛋白14(CK14)、CK18、钠钾ATP酶蛋白a1(ATP1a1)和水通道蛋白5(AQP5)mRNA表达，样本数为3；采用免疫荧光染色检测各组1皿打印块中间充质干细胞CK14、CK18、ATP1a1和AQP5蛋白表达分布。对数据行独立样本 t检验。 结果:(1)伤后1 d，小鼠烫伤创面组织中TNF－α质量浓度为(19±3)ng/mL。(2)培养6 h，TNF－α处理组打印块中间充质干细胞Nanog mRNA和蛋白表达量分别为0.39±0.04、0.36±0.03，均明显低于空白对照组的1.00±0.05、1.00±0.07( t＝16.51、14.56， P<0.01)。(3)培养14 d，TNF－α处理组打印块中间充质干细胞CK18、CK14、ATP1a1、AQP5 mRNA表达量分别为0.38±0.03、0.42±0.11、0.23±0.06、0.25±0.03，明显少于空白对照组的1.00±0.03、1.00±0.05、1.00±0.05、1.00±0.07( t＝25.31、8.31、17.07、17.06， P<0.01)。(4)培养14 d，空白对照组打印块中间充质干细胞CK18、CK14、ATP1a1和AQP5蛋白均广泛分布于细胞质，而TNF－α处理组打印块中间充质干细胞CK18、CK14、ATP1a1和AQP5蛋白在细胞质的分布较空白对照组明显减少。 结论:外源性TNF－α抑制三维环境下小鼠间充质干细胞向汗腺细胞定向分化，这可能与TNF－α抑制Nanog mRNA和蛋白水平的表达从而使间充质干细胞多向分化潜能下调有关。

abstractsObjective:To explore the effects and molecular mechanism of tumor necrosis factor α (TNF-α) on differentiation of mesenchymal stem cells of mice into sweat gland cells in a three-dimensional environment.Methods:(1) Five 6-8 week-old female C57BL/6 mice were used, with one 1 cm 2 deep partial-thickness to full-thickness scald wound being created on the back of each mouse with a scald apparatus. One day after injury, the full-thickness skin tissue of the wound was taken, and the concentration of TNF-α in the tissue was detected by enzyme-linked immunosorbent assay. (2) Gelatin in the mass of 0.9 g and 0.3 g sodium alginate were mixed and then dissolved in 30 mL phosphate buffer solution to make hydrogel. Full-thickness skin of the planta of 10 male and female one day newborn C57BL/6 mice was ground into dermal homogenate. The mesenchymal stem cells were isolated from femur and tibia of 10 male and female C57BL/6 mice born for 7 days and cultured. A final density of 1.5×10 5 cells/mL of bioink was made of mixture of 8 mL pre-warmed hydrogel, 1 mL mouse foot dermal homogenate, and 1 mL the second or third passage of mesenchymal stem cell suspensions. The three-dimensional bioprinter was used to print 12 cylindrical blocks arranged in a crisscross pattern in petri dish. The printed blocks were cross-linked with 25 g/L calcium chloride solution for 10 min and then cultured for 12 hours by adding a medium for mesenchymal stem cells. Subsequently, the printed blocks were divided into blank control group and TNF-α treatment group according to the random number table, with 6 plates and 6 blocks in each group. Both groups of printed blocks were cultured with fresh sweat gland induction medium, and a final mass concentration of 20 ng/mL TNF-α was added into the medium of TNF-α treatment group. After 6 hours of culture, the mRNA expression of pluripotency marker Nanog in the mesenchymal stem cells of two plates of each group was detected by real-time fluorescent quantitative reverse transcription polymerase chain reaction (RT-PCR), and the protein expression of Nanog in the mesenchymal stem cells of one plate of each group was detected by Western blotting, both with triplicate samples. After 14 days of culture, the mRNA expression of sweat gland cell markers cytokeratin 14 (CK14), CK18, sodium potassium adenosine triphosphatase protein a1 (ATP1a1), and aquaporin 5 (AQP5) was detected by real-time fluorescent quantitative RT-PCR in the mesenchymal stem cells of 2 plates of each group ( n=3), and the protein expression distribution of CK14, CK18, ATP1a1, and AQP5 of the mesenchymal stem cells in one plate of each group was detected by immunofluorescence staining. Data were statistically analyzed with independent sample t test. Results:(1) One day after injury, the mass concentration of TNF-α in the scald wound tissue of mouse was (19±3) ng/mL. (2) After 6 hours of culture, the mRNA and protein expression levels of Nanog in the mesenchymal stem cells of printed blocks in TNF-α treatment group were 0.39±0.04 and 0.36±0.03, respectively, which were significantly lower than 1.00±0.05 and 1.00±0.07 of blank control group ( t=16.51, 14.56, P<0.01). (3) After 14 days of culture, the mRNA expression levels of CK18, CK14, ATP1a1, and AQP5 in the mesenchymal stem cells of printed blocks in TNF-α treatment group were 0.38±0.03, 0.42±0.11, 0.23±0.06, and 0.25±0.03, respectively, which were significantly less than 1.00±0.03, 1.00±0.05, 1.00±0.05, 1.00±0.07 of blank control group ( t=25.31, 8.31, 17.07, 17.06, P<0.01). (4) After 14 days of culture, the CK18, CK14, ATP1a1, and AQP5 protein were widely distributed in the cytoplasm of mesenchymal stem cells in printed blocks of blank control group, while the distribution of CK18, CK14, ATP1a1, and AQP5 protein in the cytoplasm of mesenchymal stem cells in printed blocks of TNF-α treatment group were significantly reduced in comparison. Conclusions:Exogenous TNF-α inhibits the directional differentiation of mesenchymal stem cells of mice into sweat gland cells in a three-dimensional environment, which may be related to the inhibition of the expression of Nanog mRNA and protein by TNF-α that subsequently results in the down-regulation of multi-directional differentiation potential of mesenchymal stem cells.