[Effects of hypoxia-pretreated rat adipose-derived mesenchymal stem cells conditioned medium on wound healing of rats with full-thickness defects]

Objective: To investigate the effects of hypoxia-pretreated rat adipose-derived mesenchymal stem cells (ADSCs) conditioned medium on wound healing of rats with full-thickness defects. Methods: (1) A 6-week-old male Sprague-Dawley rat was sacrificed by cervical dislocation, the bilateral inguinal adipose tissue was collected, the third generation ADSCs were isolated by collagenase digestion method, and the cells morphology was observed. The cells were harvested and divided into adipogenic induction group and osteogenic induction group according to the random number table (the same grouping method below), with 6 wells in each group. The cells in adipogenic induction group were cultured for 14 days to observe adipogenesis, and cells in osteogenic induction group were cultured for 28 days to observe osteogenesis. (2) The third generation ADSCs were collected and divided into normoxic group and hypoxic group. Cells in normoxic group was incubated in normal oxygen incubator with oxygen volume fraction of 21%, and cells in hypoxic group was incubated in low oxygen incubator with oxygen volume fraction of 2% respectively, with 3 samples in each group for each time point. Three samples in normoxic group on 3 h of culture and in hypoxic group on 3, 6, 12, 24, and 48 h of culture were collected for detecting the following indexes. The mRNA expressions of hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and peroxisome proliferator-activated receptor γ (PPAR-γ) were detected by real time fluorescent quantitative reverse transcription polymerase chain reaction. The cell culture supernatant in the two groups was collected, centrifuged, and filtered to obtain normoxic conditioned medium (normo-CM ) and hypoxic conditioned medium (hypo-CM). Enzyme linked immunosorbent assay was used to detect content of VEGF, transforming growth factor β (TGF-β), epidermal growth factor (EGF), and insulin-like growth factor (IGF) in conditioned medium. (3) Twenty-seven male Sprague-Dawley rats aged 6-8 weeks were collected and divided into phosphate buffer solution (PBS) group, normo-CM group, and hypo-CM group, with 9 rats in each group. A circular full-thickness skin defect wound with diameter of 1 cm was made on the back of each rat, and the wounds of rats in PBS, normo-CM, and hypo-CM groups were respectively dropped with 50 μL PBS, normo-CM, and hypo-CM. On post injury day (PID) 0, 3, 5, 7, 9, and 11, the gross condition of wound was observed, wound area was measured, and the non-healing rate of wound was calculated. The wound tissue was collected for hematoxylin eosin staining to observe inflammatory reaction of wound on PID 3, 9, and 11 and re-epithelialization of wound on PID 9. Masson staining was used to observe the collagen deposition and analyze collagen volume fraction of wound on PID 11. Data were statistically analyzed with analysis of variance for repeated measurement, one-way analysis of variance, t test, and Bonferroni correction. Results: (1) The isolated cells showed a fusiform, in adherent growth and close arrangement when in low fusion degree. On 14 d of culture, the red lipid droplets stained with oil red O were observed in cells in adipogenic induction group, and on 28 d of culture, the red nodules stained with alizarin red S were observed in cells in osteogenic induction group. The cells were identified as ADSCs. (2) Compared with that in normoxic group, the mRNA expression of HIF-1α was significantly increased at 12 and 24 h of culture (t=5.43, 5.11, P<0.05), the mRNA expression of VEGF was significantly increased at 6 and 12 h of culture (t=3.29, 2.33, P<0.05 or P<0.01), the mRNA expression of bFGF was significantly increased at 12 h of culture (t=12.59, P<0.01) and significantly reduced at 48 h of culture (t=9.34, P<0.01), and the mRNA expression of PPAR-γ was significantly reduced at 3, 12, and 24 h of culture in hypoxic group (t=5.14, 6.56, 4.97, P<0.05). (3) Compared with that in normoxic group, the VEGF content was significantly increased at 3, 6, 12, 24, and 48 h of culture (t=5.74, 12.37, 14.80, 15.70, 34.63, P<0.05 or P<0.01), and the IGF content was significantly increased at 6, 12, 24, and 48 h of culture (t=5.65, 8.06, 20.12, 22.99, P<0.05 or P<0.01), and the content of TGF-β and EGF showed no obvious change at 3, 6, 12, 24, and 48 h of culture in hypoxic group. (4) From PID 0 to 11, the wound of rats in the three groups shrank to varying degrees, with no obvious infection or exudate. On PID 11, the wound area of rats in PBS group was still large, which was larger than that in normo-CM group, and the wound area of rats in hypo-CM group was basically healed. On PID 0, 3, and 5, the non-healing rates of wound of rats in the three groups were similar. On PID 7, the non-healing rates of wound of rats in normo-CM and hypo-CM groups were significantly lower than that in PBS group (t=10.26, 16.03, P<0.05). On PID 9, the non-healing rate of wound of rats in hypo-CM group was significantly lower than that of PBS group and normo-CM group, respectively (t=17.25, 6.89, P<0.05 or P<0.01), and the non-healing rate of wound of rats in normo-CM group was significantly lower than that in PBS group (t=8.81, P<0.05). On PID 11, the non-healing rate of wound of rats in hypo-CM group was (2.4±1.5)%, which was significantly lower than (20.0±5.0)% in PBS group and (7.7±1.7)% in normo-CM group (t= 30.15, 84.80, P<0.05). (5) On PID 3, the infiltration of inflammatory cells in the wound of rats in hypo-CM group was obviously more than those in the other two groups. On PID 9, the infiltration of inflammatory cells in the wound of rats in hypo-CM and normo-CM groups was obviously less than that in PBS group. On PID 11, the infiltration of inflammatory cells in the wound of rats in hypo-CM group was obviously less than those in PBS and normo-CM groups. On PID 9, the length of " epidermal migration tongue" on the wound of rats in hypo-CM group was longer than those of the other two groups, and the epidermis thickness was close to normal skin. On PID 11, compared with those in PBS and normo-CM groups, a large number of collagen deposits with dense structure, neat arrangement, and higher maturity were seen in the wound of rats in hypo-CM group. The wound collagen volume fraction of rats in PBS group was (22.90±1.25)%, which was significantly lower than (31.96±0.14)% in normo-CM group and (56.10±1.50)% in hypo-CM group (t=12.48, 29.43, P<0.05), and the wound collagen volume fraction of rats in normo-CM group was significantly lower than that in hypo-CM group (t=27.73, P<0.05). Conclusions: Hypoxia-pretreated can significantly enhance paracrine effect of rat ADSCs. Hypoxia-pretreated rat ADSC conditioned medium can accelerate the healing of full-thickness skin defect wound in rats by regulating inflammatory cell infiltration, promoting re-epithelialization and collagen deposition in the wound.

目的： 探讨低氧预处理大鼠脂肪源性间充质干细胞(ADSC)条件培养基对全层皮肤缺损大鼠创面愈合的影响。 方法： (1)取6周龄雄性SD大鼠1只，颈椎脱臼处死，分离双侧腹股沟脂肪组织，胶原酶消化法提取第3代ADSC，观察细胞形态后用于后续实验。取细胞，采用随机数字表法(分组方法下同)分为成脂诱导组和成骨诱导组，每组各6孔。成脂诱导组培养14 d观察成脂情况，成骨诱导组培养28 d观察成骨情况。(2)取第3代ADSC，分为常氧组和低氧组，常氧组细胞置于氧气体积分数20%的常氧培养箱中培养，低氧组细胞置于氧气体积分数2%的低氧培养箱中培养。常氧组培养3 h，低氧组培养3、6、12、24、48 h，分别取3个样本，进行后续指标检测。实时荧光定量反转录PCR检测低氧诱导因子1α(HIF-1α)、血管内皮生长因子(VEGF)、碱性成纤维细胞生长因子(bFGF)、过氧化物酶体增殖物激活受体γ(PPAR-γ)的mRNA表达量。收集2组细胞培养上清液，离心过滤后获得常氧条件培养基(normo-CM)和低氧条件培养基(hypo-CM)，酶联免疫吸附测定法检测条件培养基中VEGF、转化生长因子β(TGF-β)、表皮生长因子(EGF)和胰岛素样生长因子(IGF)含量。(3)取27只6～8周龄雄性SD大鼠，分为磷酸盐缓冲液(PBS)组、normo-CM组和hypo-CM组，每组9只，在其背部制作直径为1 cm的圆形全层皮肤缺损创面并分别滴加50 μL PBS、normo-CM及hypo-CM。伤后0、3、5、7、9、11 d，观察创面大体情况，测量创面面积并计算创面未愈合率。取创面组织，苏木精-伊红染色观察伤后3、9、11 d创面炎症反应及伤后9 d创面再上皮化水平；Masson染色观察伤后11 d创面胶原沉积情况，并分析胶原容积分数(CVF)。对数据行重复测量方差分析、单因素方差分析、t检验、Bonferroni校正。 结果： (1)细胞融合度低时呈长梭形、贴壁生长、排列紧密。培养14 d，成脂诱导组细胞经油红O染色后被染成红色的脂滴。培养28 d，成骨诱导组细胞经茜素红S染色后可见红色结节。细胞鉴定为ADSC。(2)与常氧组比较，低氧组细胞培养12、24 h HIF-1α mRNA表达量明显升高(t＝5.43、5.11，P<0.05)；培养6、12 h VEGF mRNA表达量明显升高(t＝3.29、2.33，P<0.05或P<0.01)；bFGF mRNA培养12 h表达量明显升高(t＝12.59，P<0.01)，培养48 h明显降低(t＝9.34，P<0.01)；培养3、12、24 h PPAR-γ mRNA明显降低(t＝5.14、6.56、4.97，P<0.05)。(3)与常氧组相比，低氧组细胞培养3、6、12、24、48 h VEGF含量明显升高(t＝5.74、12.37、14.80、15.70、34.63，P<0.05或P<0.01)，培养6、12、24、48 h IGF含量明显升高(t＝5.65、8.06、20.12、22.99，P<0.05或P<0.01)，培养各时间点TGF-β和EGF含量无明显变化。(4)伤后0～11 d，3组大鼠创面均不同程度缩小，未见明显感染、渗出等。伤后11 d，PBS组大鼠创面面积仍较大；normo-CM组大鼠创面面积较PBS组缩小，hypo-CM组大鼠创面已基本愈合。伤后7 d，normo-CM组和hypo-CM组大鼠创面未愈合率明显低于PBS组(t＝10.26、16.03，P<0.05)。伤后9 d，hypo-CM组大鼠创面未愈合率明显低于PBS组和normo-CM组(t＝17.25、6.89，P<0.05或P<0.01)，normo-CM组大鼠创面未愈合率明显低于PBS组(t＝8.81，P<0.05)。伤后11 d，hypo-CM组大鼠创面未愈合率为(2.4±1.5)%，明显低于PBS组的(20.0±5.0)%和normo-CM组的(7.7±1.7)%，t＝30.15、84.80，P<0.05。(5)伤后3 d，hypo-CM组大鼠创面炎症细胞浸润明显多于其余2组；伤后9 d，normo-CM组和hypo-CM组大鼠创面炎症细胞浸润均少于PBS组；伤后11 d，hypo-CM组大鼠创面炎症细胞浸润明显少于PBS组和normo-CM组。(6)伤后9 d，hypo-CM组大鼠创面"表皮迁移舌"长度长于其他2组，表皮厚度接近正常皮肤。伤后11 d，与PBS组和normo-CM组相比，hypo-CM组大鼠创面中可见大量结构致密、排列整齐、成熟度较高的胶原沉积。PBS组大鼠创面CVF为(22.90±1.25)%，显著低于normo-CM组的(31.96±0.14)%和hypo-CM组的(56.10±1.50)%(t＝12.48、29.43，P<0.05)；normo-CM组大鼠创面CVF显著低于hypo-CM组(t＝27.73，P<0.05)。 结论： 低氧处理可显著增强大鼠ADSC的旁分泌作用，低氧预处理的大鼠ADSC条件培养基可通过调控炎症细胞浸润程度、促进创面再上皮化和胶原沉积，加速大鼠全层皮肤缺损创面愈合。.

Keywords: Adipose-derived mesenchymal stem cells; Anoxia; Conditioned medium; Wound healing.