The reparative regeneration of the endothelium of the aortic bifurcation in rats after cryodestruction

The dynamics of reparative regeneration of the rat abdominal aortic endothelium after cryodestruction was investigated in experiments on 27 rats. In the aortic bifurcation site as compared with its infrarenal region the marked differences in the reaction of blood cells with injured and repaired vascular wall, in increase of the proliferative activity of endothelial cells and heteromorphism of endothelial monolayer, accelerated growth of myointimal thickening are found. The mechanisms of local hemodynamic influence onto the velocity and pattern on endothelial restoration are under discussion.     

Mechanisms of the changes in the rate and nature of reparative regeneration of the aortic endothelium after repeated injuries

An experimental model of repeated cryogenic lesions in the rat abdominal aorta endothelium with a concentrically decreasing area of the defect has been worked out. In reendothelization of every successive defect participate the cells of the endothelial layer that is formed anew after the preceding lesions. As a result of repeated lesions the regeneration rate increases by 1.2 times. By means of scanning radioautography after 3H-thymidine++ administration the index of the labelled nuclei of the endothelial cells (EC) has been demonstrated to increase by 2.2 times. In the experiments with gamma-irradiation of the vessel before the last cryodestruction (this results in blockade of proliferation) an increased rate of EC migration has been revealed. Repeated lesions also produce an increase in the heteromorphism degree of the endothelial layer. This is mainly manifested as appearance of multinuclear EC clusters. These changes in rate and in character of the endothelium regeneration can be determined by the mechanisms similar to clonal proliferative senescence of EC in vitro.     

Humoral mechanisms of regulating reparative osteogenesis

The effect of the blood serum of animals with active osteogenesis on the biosynthesis of nucleic acids, protein, and on the mineralization of the regenerating bone tissue was studied in experiments in vivo and in vitro. Incorporation of DNA and protein labeled precursors (3H-thymidine and 14 C-proline, respectively) was increased and the mineralization of the bone callus (85Sr incorporation) was accelerated in the recipients. Comparison of nucleic acids and protein biosynthesis stimulation sequency allows to suppose that the active serum principle promotes the increased cell proliferation in the fracture area.     

Differentiation of mesothelial cells during their reparative regeneration

The investigation on regenerative processes of mesothelium of the parietal peritoneum was performed in 120 white mice under the effect of certain irritants producing lesions various in depth and intensity. Nuclear-cytoplasmic relations and ultramicroscopic cellular rearrangement were studied during the process of differentiation of the mesothelial regenerate. Two periods of the regenerative process are stated and it is demonstrated that rearrangement of the mesothelial cells and the mode of their division depend on intensity of the lesions. When the peritoneal lesion is severe, at the first stages of regeneration (the 1st period) rearrangement of cells towards their hypertrophy and increased functional activity is predominant in the mesothelium. Further (the 2d period), the number of mitotically dividing cells is increasing in the mesothelial regenerate and in rearrangement of the mesothelial cells the processes connected with a partial loss of their signs of specialization predominate. The transition from one period into another is gradual and duration of each depends on intensity of the lesion.     

Physiological and reparative regeneration of the mitochondria]

The ultrastructure of mitochondria of hepatocytes in normal and pathological conditions was studied. It was shown that the process of regeneration of the ultrastructure of swollen mitochondria with a lucent matrix up to the normal state was completed in hepatocytes of the rat and chick embryos within one day. It was established that one of the ways of intraorganoid regeneration of mitochondria in hepatocytes of chick embryos and of mice after injections of CCl4 twice a week for 5 months was clasmatosis of the destroyed mitochondria fragments and their removal through the partially disintegrated exterior membrane of mitochondria followed by the membrane restoration. The process of mitochondrial regeneration after clasmatosis of its fragments was shown to require two days in the chick embryo hepatocytes.     

The reparative regeneration of the endothelium of the mouse aorta during microsurgical interventions following local gamma irradiation (based on scanning electron microscopic data)

In experiments with rats, abdominal aorta was subjected to microsurgical anastomosis after local irradiation with doses of 40 and 50 Gy. Irrespective of the time interval between the operation and irradiation the iatrogenic defect was restored completely. With the operation performed 24 h after irradiation the platelet adhesion decreased, the proliferation was inhibited depending on radiation dose, and the pattern of the endotheliocyte migration changed. The above effects were absent with the operation performed one month after irradiation.     

New insights on the reparative cells in bone regeneration and repair

Bone possesses a remarkable repair capacity to regenerate completely without scar tissue formation. This unique characteristic, expressed during bone development, maintenance and injury (fracture) healing, is performed by the reparative cells including skeletal stem cells (SSCs) and their descendants. However, the identity and functional roles of SSCs remain controversial due to technological difficulties and the heterogeneity and plasticity of SSCs. Moreover, for many years, there has been a biased view that bone marrow is the main cell source for bone repair. Together, these limitations have greatly hampered our understanding of these important cell populations and their potential applications in the treatment of fractures and skeletal diseases. Here, we reanalyse and summarize current understanding of the reparative cells in bone regeneration and repair and outline recent progress in this area, with a particular emphasis on the temporal and spatial process of fracture healing, the sources of reparative cells, an updated definition of SSCs, and markers of skeletal stem/progenitor cells contributing to the repair of craniofacial and long bones, as well as the debate between SSCs and pericytes. Finally, we also discuss the existing problems, emerging novel technologies and future research directions in this field.