Pathophysiological processes of wound healing in hyperglycemia are very complex and insufficiently explained. Dipeptidyl-peptidase IV, or CD26 molecule (DPP IV/CD26) is a multifunctional protein present in a large number of cells in the body and in various biological fluids. Except its involvement in maintenance of glucose homeostasis by regulating the biological activity of various substrates, it also plays an important role in the processes of angiogenesis and proliferation, migration, and apoptosis of various cell types important for the healing of damaged or wounded tissue. Literature data suggest that DPP IV/CD26 inhibition contributes to improved wound healing in patients with diabetes.
The aim of the Master's thesis was to establish an experimental model of diabetes (experimental hyperglycemia) in wild-type (C57BL/6) and CD26 deficient (CD26-/-) mice and to determine whether and how in that circumstances, DPP IV/CD26 deficiency influences on the processes of angiogenesis and cutaneous tissue regeneration.
The development of diabetes in experimental animals was monitored by clinical and biochemical parameters. Diabetic mice were wounded on the dorsal region (two identical skin wounds with diameters of 5 mm) and sacrificed on days 2, 4, 7, 10, and 15 after wounding. Control skin and wound tissue samples were analyzed pathohistologically, histomorphometrically, immunohistochemically and immunochemically. The degree of corium (dermis) regeneration, the expression of HIF-1α (hypoxia-induced transcription factor 1α) and vascular endothelial growth factor (VEGF) was analysed and the chemokine IP-10 concentration was determined. The enzyme activity of DPP IV/CD26 was determined spectrophotometrically in serum and tissue samples of C57BL/6 mice during the wound healing process in conditions of experimental hyperglycemia.
It was found that CD26-/- show improved tolerance of both experimental hyperglycemia and initial hypoglycemia compared to wild type animals. Macroscopic and microscopic analysis showed a faster dynamics of wound healing. Thus, in CD26-/- mice the regeneration of the corium begins earlier, the inflammatory phase of the healing process was shorter accompanied by rapid scar tissue formation and consequently its faster degradation. On the day 2 of wound healing, the expression of HIF-1α was statistically significantly lower in both mice strains and statistically significantly higher on day 4 (p <0.05) compared to the control group. From day 4, HIF-1α expression was statistically significantly higher (p < 0.05) in the tissues of CD26-/- mice than in the tissues of C57BL/6 mice. We also found that VEGF expression in CD26-/- mice was statistically significantly higher (p < 0.05) at all tested time points, compared with wild-type animals. Serum IP-10 concentrations were statistically significantly higher (p < 0.05) in CD26-/- mice at all time points, while in the tissue samples only at days 10 and 15 after induction of skin wounds. Finally, DPP IV/CD26 activity in serum of C57BL/6 mice was statistically significantly lower (p < 0.05) at day 4 and in tissue at day 2, day 4 and day 7 after wound induction compared to the control group.
Our results confirm that the DPP IV/CD26 molecule plays an important role in regulation of blood glucose concentration. In addition, more efficient angiogenesis and increased cell proliferation under conditions of DPP IV/CD26 deficiency, with increased local expression of HIF-1α, VEGF and IP-10 factors, confirm that DPP IV/CD26 inhibition has beneficial effects on the skin wound healing process of experimental mice under conditions of experimentally induced hyperglycemia. Based on our findings, we can confirm the major importance of inhibiting DPP IV/CD26 function in terms of a therapeutic approach for the treatment of diabetes and its complications, especially the occurrence of chronic wounds.
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