Mechanism study of dendritic epidermal T lymphocytes in promoting healing of full-thickness skin defects wound on mice by regulating the proliferation and differentiation of epidermal stem cells in mice

Objective To explore the mechanism of dendritic epidermal T lymphocytes (DETCs) in promoting healing of full-thickness skin defect wound on mice by regulating the proliferation and differentiation of epidermal stem cells (ESCs) in mice. Methods (1) Ten 8-week-old wild type (WT) male C57BL/6 mice (the same sex and kind below) were sacrificed to collect the skin of back for extracting DETCs to culture. Five WT and five 8-week-old T cell receptor (TCR) δ^-/^- mice were selected and enrolled in WT control group and TCR δ^-/^- control group, respectively. A full-thickness skin defect wound with diameter of 6 mm was made on both sides of spinal line on the back of mice without any treatment after injury. Another fifteen 8-week-old TCR δ^-/^- mice were selected and divided into phosphate buffer solution (PBS), DETC, and insulin-like growth factor-Ⅰ(IGF-Ⅰ) groups according to the random number table (the same grouping method below), with 5 mice in each group, and the same full-thickness skin defect wound was made on each mouse. Immediately after injury, mice in PBS, DETC, and IGF-Ⅰ groups were injected subcutaneously around each wound with 10 μL sterile PBS , DETCs (cell concentration of 1×10⁶/mL), and 5 mg/mL recombinant mice IGF-Ⅰ, respectively. The percentage of the residual wound area was calculated on post injury day (PID) 2, 4, 6, and 8. (2) Three 8-week-old WT mice were enrolled in WT control group and nine 8-week-old TCR δ^-/^- mice were divided into TCR δ^-/^- control group, PBS group, and DETC group, with 3 mice in each group. The full-thickness skin defect wound was made as in experiment (1) . On PID 3, the protein expression of IGF-Ⅰ in the epidermis tissue of wound margin was detected by chemiluminescence imaging analyzer. (3) Three 8-week-old WT mice were enrolled in WT control group and six 8-week-old TCR δ^-/^- mice were divided into PBS and DETC groups, with 3 mice in each group, and the full-thickness skin defect wound was made as in experiment (1). On PID3, DETCs were extracted from the wound margin epidermis tissue to detect the percentage of DETCs expressing IGF-Ⅰ by flow cytometer. (4) The mice were taken as in experiment (2) and divided into WT control, PBS, DETC, and IGF-Ⅰ groups. A straight full-thickness skin defect incision with length of 3 cm was made in the direction of one inner ear. Mice in WT control group didn′t have any other treatment after injury, and immediately after injury, mice in PBS, DETC, and IGF-Ⅰ groups were injected subcutaneously around each wound with 10 μL sterile PBS, DETCs (cell concentration of 1×10⁶/mL), and 5 mg/mL recombinant mice IGF-Ⅰ, respectively. On PID 12, epidermis tissue of wound margin was collected, and immunofluorescence staining was performed to observe the number of keratin 15 positive cells. (5) The same mice were collected, grouped, and treated as in experiment (4). On PID12, the epidermis tissue of wound margin was collected and immunofluorescence staining was performed to observe the number of keratin 10 positive cells. (6) Twenty 3-day-old WT mice (the same below) were sacrificed to collect the whole skin, which was used to extract ESCs, with 5 mice detecting one index. The ESCs were divided into DETC co-culture group and control group, which were added with 1 mL DETCs (cell concentration of 1.25×10⁶/mL) and DETC medium, respectively. The percentage of 5-ethynyl-2′-deoxyuridine (EdU) positive cell on culture day (CD) 3, the percentages of CD49f⁺ CD71^- and keratin 14 positive cells on CD 5, and the percentage of keratin 10 positive cell on CD 10 in 2 groups were detected by flow cytometer. (7) Twenty mice were taken to extract ESCs, with 5 mice detecting one index. The ESCs were divided into control group and IGF-Ⅰ group, which were added with 1 mL sterile PBS and 10 ng/mL recombinant mice IGF-Ⅰ, respectively. The percentages of EdU positive cell, CD49f⁺ CD71^- cell, keratin10 positive cell, and keratin 14 positive cell were detected as in experiment (6). The sample in each group of experiments (6) and (7) was three. Data were statistically analyzed with analysis of variance for repeated measurement, one-way analysis of variance, and t test. Results (1) On PID 4, 6, and 8, the percentage of residual wound area in TCR δ^-/^- control group was significantly higher than that in WT control group (t=2.78, 3.39, 3.66, P<0.05 or P<0.01). The percentage of residual wound area in DETC group and IGF-Ⅰgroup on PID 4, 6, and 8 was apparently lower than that in PBS group (t=2.61, 3.21, 3.88, 2.84, 2.91, 2.49, P<0.05 or P<0.01). (2) On PID 3, the protein expression of IGF-Ⅰ in the epidermis tissue of wound margin of mice in TCR δ^-/^- control group was significantly lower than that in WT control group (t=17.34, P<0.01). The protein expression of IGF-Ⅰ in the epidermis tissue of wound margin of mice in DETC group was significantly higher than that in PBS group (t=11.71, P<0.01). (3) On PID 3, the percentage of DETCs expressing IGF-Ⅰ in the epidermis tissue of wound margin of mice in PBS group was significantly lower than that in WT control group and DETC group (t=24.95, 27.23, P<0.01). (4) On PID 12, the number of keratin 15 positive cells in the epidermis tissue of wound margin of mice in PBS group was significantly lower than that in WT control group, DETC group, and IGF-Ⅰ group (t=17.97, 11.95, 7.63, P<0.01). (5) The number of keratin 10 positive cells in the epidermis tissue of wound margin of mice in PBS group was significantly higher than that in WT control group, DETC group, and IGF-Ⅰ group (t=11.59, 9.51, 3.48, P<0.05 or P<0.01). (6) The percentages of EdU positive cells on CD 3, CD49f⁺ CD71^- cells on CD 5, and keratin 14 positive cells on CD 5 in DETC co-culture group were respectively (43.5±0.6)%, (66.5±0.5)%, (69.3±1.7)%, apparently higher than (32.3±1.3)%, (56.4±0.3)%, (54.9±1.3)% in control group (t=7.97, 17.10, 6.66, P<0.01). The percentage of keratin 10 positive cells on CD 10 in DETC co-culture group was (55.7±0.7)%, significantly lower than (67.1±1.2)% in control group (t=8.34, P<0.01). (7) The percentages of EdU positive cells on CD 3, CD49f⁺ CD71^- cells on CD 5, and keratin 14 positive cells on CD 5 in IGF-Ⅰ group were respectively (42.1±0.9)%, (81.1±1.3)%, (66.8±1.0)%, apparently higher than (32.4±0.7)%, (74.9±0.7)%, (52.0±1.9)% in control group (t=8.39, 4.24, 7.25, P<0.05 or P<0.01). The percentage of keratin 10 positive cells on CD 10 in IGF-Ⅰ group was (53.5±1.1)% , significantly lower than (58.2±0.3)% in control group (t=3.99, P<0.05). Conclusions DETCs can promote the proliferation and anti-apoptotic potential of ESCs and inhibit their differentiation into end-stage by secreting IGF-Ⅰ, thus promoting wound healing of full-thickness skin defects in mice.