Cellular senescence is a major obstacle to tissue engineering and regenerative medicine based on primary cells. Telomere erosion, oxidative stress, oncogene expression and loss of tumor suppressor genes may all be involved in various signaling pathways in the process of cell aging. In order to establish immortalized cell lines for research and clinical use, strategies including internal genome or external matrix microenvironment modification have been applied. Considering the potential risks of malignant transformation and genetically manipulated tumors, environmental modification methods, especially pretreatment strategies based on decellularized cell-deposited extracellular matrix (dECM), seem to be promising for the immortalization of tissue-engineered cells.
Tissue and organ failure is an important health problem that cannot be ignored. Surgery, organ transplantation, artificial substitutes and mechanical equipment are the solutions to this problem, but they all have undesirable short- and long-term consequences. Tissue engineering is an attractive method that can produce functional tissues for tissue regeneration and establish physiological and pathological models for mechanism research. This technology can take advantage of the inherent regenerative potential of primary cells and expand them in a controlled environment before reintroducing them into the patients. These natural, synthetic or semi-synthetic tissue and organ mimics are expected to function normally in the desired tissue-specific pattern. However, when cultured in vitro, primary cells derived from non-cancerous tissues have a limited lifespan and have reduced proliferation capacity. After a limited division, the cell enters a permanent quiescent state of survival, which is called cell senescence.
In order to obtain a large number of cells for functional tissue engineering, cell senescence is the main obstacle that needs to be overcome. In the past few decades, many attempts have been made to deal with cell senescence in order to successfully immortalize primary cells. In order to establish immortalized cell lines for research and clinical use, strategies including internal genome or external matrix microenvironment modification have been applied.
In order to extend the lifespan of cells, biotechnology methods are usually used to directly manipulate the cell's genome. However, there are still concerns about genome stability and tumorigenicity after genetic modification. For MSC and progenitor cells, the potential loss of differentiation ability after genetic modification is a problem that cannot be ignored.
Although the strategy of immortalizing human cells is becoming more and more complicated, there are still some debates about the risk of oncogene integration into chromosomes. The main safety issue in using cell lines is the spread of carcinogenic factors to host cells. In fact, cells transduced with these oncogenes have undergone additional changes, including complete changes associated with carcinogenesis. Some persistent HPV infections, especially HPV-16 and HPV-18, are etiologically related to female cervical cancer. The overexpression of HPV E6 and E7 leads to many changes in cell pathways and functions, which are related to the malignant transformation of cells and tumorigenesis.
Facts have proved that compared with adult donors, dECM deposited by MSCs from fetuses or young donors provides a better rejuvenation effect in promoting the expansion and differentiation of aging MSCs. However, the source of these young cells is homogenous or heterogeneous, which may damage the donor or immune rejection. In this case, cells donated by the patient themselves are considered the best candidates. However, the elderly mainly suffer from degenerative diseases, and most of their autologous cells may suffer from senescence, which is considered to be a factor affecting cell quality. Considering the demand for young cell populations and the carcinogenic transformation after genetic modification for immortalization purposes, this increases the possibility of combining genetic modification with environmental optimization strategies.
In other words, scientists can immortalize these senescent cells and use their deposited dECM to replace the cells themselves to reduce the senescence state and increase the proliferation potential of expanded cells. Using immortalization strategies alone, combined strategies may also overcome the potential loss of stem cell differentiation. Further research on the rejuvenation strategy based on the pretreatment of the matrix microenvironment may provide important insights to provide powerful primary cells as possible means of therapeutic agents.