Angiopellosis (cell extravasation) is the movement of cells out of the circulatory system into the surrounding tissue. This process is specific to non-leukocytic cells, as leukocytes (white blood cells) utilize diapedesis for movement out of circulation. Angiopellosis was discovered by studying how stem cells reach damaged tissue when injected or infused into the blood stream. Recently, it was found that circulating tumor cells (CTCs) also possess the ability to exit blood vessels through angiopellosis during the metastasis process
Angiopellosis extravasation occurs as a means for cells that are not native to the circulation to exit. This includes adult stem cells that are injected intravenously for therapies. Cells that are normally found in circulation (i.e. blood cells) either extravasate through diapedesis (white blood cells), or do not extravasate and remain in circulation (red blood cells).
Angiopellosis was discovered by a group of researchers at North Carolina State University who were studying the mechanism intravenously injected stem cells utilized to reach damaged tissue. They discovered that the injected stem cells prompted the blood vessel walls to undergo extensive change on the cellular level which results in the removal of the cell from the inside of the vessel (lumen) into the surrounding area.
Below is a brief summary of each of the steps currently thought to be involved in angiopellosis:
Upon entering the circulation, the cell(s) travel through the blood vessels and eventually attach or become lodged inside the blood vessel wall. This prompts the series of events that end in the cell(s) exiting circulation.
The endothelial cells recognize the cell through membrane-specific recognition. Recognition of cell is important and is thought to be the reason cells native to the circulation to not randomly extravasate through angiopellosis.
Once attached or lodged, the exiting cell(s) elicit activity from the endothelial cells of the blood vessel. The endothelial cells extend protrusions and actively remodel themselves around the exiting cells
The exiting cell will then be either actively "pushed" from the inside of the blood vessel, or the vascular cells will remodel around the cell so that the cell no longer remains inside the vessel
Differences from Leukocyte Extravasation
The most notable difference is the physical mechanism the cells use to exit. During angiopellosis, the endothelial cells are the most active in the process, while in diapedesis it is the white blood cell that are the most physically active during the process.
During angiopellosis the extravasating cell remains round in morphology and only slightly changes shape as a result of the vasculature remodeling around it. However, during diapedesis the white blood cells significantly change shape as they migrate through the blood vessel.
Angiopellosis allows for the extravasation of multiple cells during a single event. The blood vessel will actively remodel around a cluster/group of cells and allow the cells to exit in a single event. Diapedesis only allows for a single white blood cell to migrate across the blood vessel wall at a time. Although multiple white blood cells can leave simultaneously, they all elicit separate diapedesis extravasation events.
There are also temporal and molecular difference between the two processes
Stem cell infusion therapy
Stem cell infusion therapy is a type of infusion therapy where stem cells are infused into the blood. These stem cells then exit the blood vessels and preferentially migrate to damages tissue for regeneration. Angiopellosis has been shown to be the method these infused stem cells utilize to extravasate and reach damaged tissue
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