Intussusception is the new formation of blood vessels by recruiting and the incorporation of progenitor cells. It is a rapid process of intravascular septation that produces two lumens from a single vessel and in the capillar formation in cancer, inflammation and regeneration. Intussusceptive angiogenesis is a rapid process of intravascular septation that produces two lumens from a single vessel. Intussusceptive angiogenesis is distinct from sprouting angiogenesis because it has no necessary requirement for cell proliferation, can rapidly expand an existing capillary network, and can maintain organ function during replication.
It provides a mechanism for the expansion of an existing microvascular network; sprouting angiogenesis provides a mechanism for expanding microvessels in tissues without a preexisting network. The mechanistic relationship between branch angle remodeling and intussusceptive angiogenesis is the intussusceptive pillar.
This process appears to be regulated, at least in part, by microhemodynamic forces and wall shear stress. Thus, this pillar formation and branch remodelling may represent an pivotal adaptive response to the continually increasing blood flow and blood pressure during inflammation and regeneration. Intussusceptive angiogenesis is iniated within a few minutes, pillars are found after 15-30 min.
In contrast to sproutingangiogenesis, existing vascular structures are remodeled during intussusception. The formation of new vascular sections is implemented without active cell proliferation, increased vascular permeability or without cell invasion. The process of intussusceptive or non-sprouting angiogenesis is therefore a highly dynamic intravascular morphological process that can change the structure of the microcirculation considerably within a very short time. The intussusceptive expansion of the vascular system mainly occurs in t in the capillary bed. However, it can also be observed to a small extent in arterioles and smaller arteries.
The intususceptive angiogenesis arises from repeated pillar formation predominantly in the venous vessels and capillaries. Endothelial protrusion creates an intraluminal tissue fold, which folds inward over the myofibroblasts and pericytes until the two opposite layers of tissue touch. The two membranes of the endothelial cells fuse and merge until this leads to the complete septation of the newly created vessels. Similarly, endothelial progenitor cells are described when integrated into the vessel wall . These circulating progenitor cells primarily express the endothelial antigens such as CD34 and CD133 and show phenotypic similarities to mature endothelial cells. Even if the number of circulating endothelial progenitor cells in the healthy organism is extremely low (0.002% of all mononuclear cells, this cell fraction can increase massively, particularly as a result of ischemia and during tumor growth.
The rapid adaptability of the vascular network created by intussusceptive angiogenesis was demonstrated in various tissues such as the kidney, retina or also in the myocardium and diseases (cf. our work). It took an average of minutes to five hours until the transluminal pillar was fully developed. This process could be reduced to just minutes by doubling the blood flow, which underlines the fundamental importance of hemodynamics on this form of vascular growth.