Morphofunctional features of mast cells in the digestive system organs of Mongolian gerbils after space flight

Background. The digestive system is one of the main systems ensuring vital activity of the organism. Assessment of structural and functional changes in the organs of this system is important for identifying compensatory-adaptive reactions during space flight. Mast cells play a key role in regulating local homeostasis and adaptive processes; however, their morphofunctional state under weightlessness remains insufficiently studied. Aim. To study the morphofunctional features of mast cells in the digestive system organs of Mongolian gerbils after orbital flight. Materials and Methods. The experiment was performed on male Mongolian gerbils Meriones unguiculatus as part of the Foton-M No. 3 spacecraft research project (flight September 14–26, 2007). Three groups of animals were formed: flight group, synchronous ground experiment group in flight equipment mockup, and vivarium control group. Additionally, a 12-day ground experiment with antiorthostatic suspension using the Ilyin-Novikov method in the Morey-Holton modification was conducted. Fragments of the fundal stomach were fixed in 10% neutral formalin, with some material fixed in formalin containing 0.5% cetylpyridinium chloride. Histochemical (toluidine blue staining, chloroacetate esterase activity determination) and immunohistochemical methods (detection of tryptase, chymase, c-Kit/CD117) were used. Mucosal and connective tissue mast cell subpopulations were studied separately. Results. In control animals, the main mass of mast cells was localized in the gastric mucosa, predominantly in the lower third of the glands. The synchronous experiment showed increased frequency of mast cell detection in the upper third of the mucosa and enhanced degranulation processes. After space flight, a decrease in the total number of metachromatic and tryptase-positive mast cells in the mucosa was observed, but an increase in chloroacetate esterase-positive, chymase-positive, and CD117+ cells occurred. Chymase expression was enhanced, particularly pronounced in the mucosa. Secretory processes were activated with an increase in the proportion of mast cells in the state of exocytosis and granule lysis. During antiorthostatic suspension, an increase in mast cell numbers in all stomach layers, enhanced chymase expression, and activation of secretory mechanisms were noted. Conclusion. Space flight factors and simulation of weightlessness effects cause significant changes in the mast cell population of Mongolian gerbil stomach, manifested by subpopulation redistribution, changes in protease profile with enhanced chymase expression, activation of secretory activity, and migration of CD117-positive progenitor cells. These changes reflect active participation of mast cells in adaptive processes of the digestive system to space flight conditions.