[Effect of deep dermal tissue dislocation injury on skin fibrosis in pig]

Objective: To explore the effect of deep dermal tissue dislocation injury on skin fibrosis in pig, in order to provide some theoretical basis for burn scar treatment. Methods: The experimental research method was applied. Six 2-month-old female Duroc pigs were taken. Fifteen operative areas on the right dorsum of pigs on which medium-thick skin grafts and deep dermal tissue slices were cut and re-implanted were included into dermal in situ reimplantation group, and fifteen operative areas on the left dorsum of pigs on which medium-thick skin grafts and deep dermal tissue slices were cut and the deep dermal tissue slice was placed under the fat layer were included into the dermal dislocation group. The hair growth in the operative areas on post-injury day (PID) 7, 14, and 21 and the cross-sectional structure on PID 14 were observed in the two groups. On PID 7, 14, and 21, the skin thickness (the distance from the epidermis to the upper edge of the fat), the dermal thickness (the distance from the lower edge of the epidermis to the upper edge of the fat, excluding the fibrotic tissue thickness between the dermis and the fat), and the fibrosis tissue thickness of the dermis-fat interface (from the lower edge of the deep dermis to the upper edge of the fat in dermal in situ reimplantation group and from the lower edge of the superficial dermis to the upper edge of the fat in dermal dislocation group) in the operative areas were measured and compared between the two groups; the fibrotic tissue thickness at the dermal cutting interface (from the lower edge of the superficial dermis to the upper edge of the deep dermis) in the operative areas in dermal in situ reimplantation group was measured and compared with the fibrotic tissue thickness at the dermal-fat interface. Sirius red staining was performed to observe and compare the type Ⅰ and Ⅲ collagen content in the dermal-fat interface in the operative areas between the 2 groups and between the dermal cutting interface and dermal-fat interface in the operative areas in dermal in situ reimplantation group. Immunohistochemical staining was performed to observe the positive expressions of proliferating cell nuclear antigen (PCNA), transforming growth factor β₁ (TGF-β₁), fibroblast growth factor 2 (FGF-2), and hepatocyte growth factor (HGF) in the operative areas in the two groups. The sample number was 6. Data were statistically analyzed with independent sample t test. Results: On PID 7, 14, and 21, the hairs in the operative areas in dermal in situ reimplantation group were denser than those in dermal dislocation group. On PID 14, the skin cross section in the operative areas in dermal dislocation group showed a "sandwich"-like structure, while the skin cross section in the operative areas in dermal in situ reimplantation group had normal structure. On PID 7, 14, and 21, the skin thickness in the operative areas in dermal dislocation group was (4 234±186), (4 688±360), and (4 548±360) μm, respectively, which was close to (4 425±156), (4 714±141), and (4 310±473) μm in dermal in situ reimplantation group (P>0.05); the dermal thickness in the operative areas in dermal dislocation group was significantly thinner than that in dermal in situ reimplantation group (with t values of -9.73, -15.85, and -15.41, respectively, P<0.01); the fibrotic tissue thickness at the dermal-fat interface in the operative areas in dermal dislocation group was significantly thicker than that in dermal in situ reimplantation group (with t values of 14.48, 20.58, and 15.67, respectively, P<0.01); there was no statistically significant difference between the fibrotic tissue thickness at the dermal-fat interface and the dermal cutting interface in the operative areas in dermal in situ reimplantation group (P>0.05). On PID 7, 14, 21, the type Ⅲ collagen content in the dermal-fat interface in the operative areas in dermal dislocation group was increased significantly compared with that in dermal in situ replantation group (with t values of 2.65, 0.61, and 7.39, respectively, P<0.05 or P<0.01), whereas there were no statistically significant differences in the type Ⅰ collagen content at the dermal-fat interface in the operative areas between the 2 groups (P>0.05) and the type Ⅰ and Ⅲ collagen content between the dermal-fat interface and the dermal cutting interface in the operative areas in dermal in situ reimplantation group (P>0.05). On PID 7, 14, and 21, PCNA, TGF-β₁, FGF-2, and HGF were positively expressed in the superficial dermis and adipose tissue in the operative areas in dermal dislocation group, while PCNA, TGF-β₁, FGF-2, and HGF were positively expressed in the superficial dermis, deep dermis, and adipose tissue in the operative areas in dermal in situ reimplantation group. Conclusions: Inadequate intrinsic thickness of dermal tissue is the key factor causing fibrosis, and the biological purpose of fibrosis is to "compensate" the intrinsic thickness of the skin. Besides, adipose tissue may also be an important component of fibrotic skin repair.