Cellular parabiosis speaks to the ability of individual cells in tissue to share and exchange contents with each other: ions, small molecules, RNA, proteins and more. It provides “cellular solidarity” between cells, with one cell absent a particular molecule being “complemented” by another cell that has it. Cellular parabiosis appears to be important in maintaining healthy cells, including preventing cancer, but paradoxically, once it breaks down and cancer emerges, also appears to be important in driving tumour growth and survival.
Via transport vehicles such as exosomes, pores such as gap junctions, and intercellular networks through structures such as “tunneling nanotubes” (TNTs) and “tumour microtubes” (TMs).
Examples includes many normal “syncytial” tissues: muscle cells, cardiac myocytes, neurons and others. Cellular parabiosis appears to be essential in the maintenance of healthy cells and tissues, including the prevention of cancer. Indeed, there is evidence that it is the disruption of normal cellular parabiosis, for example through inflammation, that allows cancers to develop.
However, in established cancer Friend turns enemy: Primary tumours establish their own “unhealthy” cellular networks that help the cancer cells survive and grow. Additionally these networks may also enable cancer cells to resist chemotherapy and radiotherapy through various mechanisms.
Large malignant cellular networks have been observed in glioblastoma, where cancer cells make direct anatomical connections between cells through structures terms tumour microtubes, ultra-long membrane protusions that the tumour uses for brain invasion, proliferation, and interconnection over long distances. These networks also protect glioblastoma cells from radiotherapy and chemotherapy.