Regeneration of salivary glands
Controlling cell division protein helped restore salivary glands
Natalia Kondratenko, N+1
Biologists from the Netherlands have discovered that the YAP protein responsible for cell growth and division is involved in the regeneration of salivary glands. Experiments on growing organs ex vivo have shown that inhibition of the YAP protein leads to a deterioration in the formation of salivary glands. Increasing YAP expression, on the contrary, improves cell culture growth. The article was published in the journal Science Signaling (Rocchi et al., The Hippo signaling pathway effector YAP promotes salivary gland regeneration after injury).
Damage to the salivary glands is one of the most common consequences of radiation therapy in the treatment of brain and cervical tumors. This leads to a decrease in the activity of the salivary glands (hyposalivation) and dry mouth (xerostomia). First of all, radiation affects the acinar part of the salivary glands. This department consists of actively dividing cells that produce saliva. The cells of the salivary gland duct are mostly in a non-dividing dormant state, but are less susceptible to destruction after irradiation.
Most mammalian organs and tissues consist of cells with limited ability to divide. A population of progenitor cells (tissue progenitor cells) that are capable of dividing and differentiating is responsible for replenishing cell losses as a result of natural death or damage. In the salivary glands, such progenitor cells are contained in the excretory duct. In addition to resistance to radiation, the cells of the salivary gland duct during cultivation are able to give rise to cells similar to acinar, which is of key importance for the regeneration of this organ.
The YAP protein is involved in the regeneration of various tissues and organs, such as the liver and mammary glands. By default, YAP is located in the nucleus and regulates the transcription of genes responsible for cell division and growth, as well as genes suppressing apoptosis. Biologists from The University of Groningen, led by Cecilia Rocchi, studied the role of the YAP protein in the development and regeneration of mouse salivary glands. Damage to the salivary glands was simulated by applying a suture that divided the gland into two parts: the lower and upper. The intensity of the ongoing regeneration of damaged glands was estimated by the number of dividing cells. To do this, the animals were injected with bromodeoxyuridine, a modified nucleotide that can be detected by immunohistochemical analysis. In mice from the control group, most of the cells containing bromodeoxyuridine were located in the acinar section, and in mice with salivary gland damage — next to the suture and in the area of the excretory duct.
Immunohistochemical staining of mouse salivary gland tissue for bromodeoxyuridine (BrdU), a marker of actively dividing cells, and YAP protein. In the area of active regeneration, the number of actively dividing cells increased, as well as the amount of YAP protein, which was localized in the excretory ducts of the salivary glands. Drawings from the article by Rocchi et al.
To study the participation of the YAP protein in the regeneration of salivary glands, biologists estimated its amount using immunohistochemical staining before suturing and two weeks after surgery. In the control group, YAP mainly accumulated in the acinar region. At the same time, the protein was in the cytoplasm of cells, which indicates its inactive state. Two weeks after suturing, YAP accumulated in the area of the excretory duct and had a nuclear localization.
To assess the regenerative potential of the salivary glands and the participation of YAP in this process, scientists have grown organ-like cultures from progenitor cells of the salivary glands. To do this, the cells were placed on a 3D matrix in which they formed structures resembling an entire organ in structure and organization.
After 7 days, the effectiveness of organ formation (EFO) was evaluated — the ratio of the number of grown colonies to the total number of cells planted on the matrix. Under the action of the YAP inhibitor verteporfin, the EFO was lower than in the control. A decrease in EFO under the action of verteporfin was observed both for cells of damaged salivary glands and for cells of normal salivary glands. In addition, the cultivation of 3D cultures from human progenitor cells showed that increased expression of YAP increases the number of growing colonies.
Organ-like cultures grown on a 3D matrix. The addition of verteporphin (VP) on day 0 resulted in the absence of organ-like colonies. The addition of verteporfin on day 4 led to the fact that colonies were formed, but had an irregular shape.
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