Intussusceptive angiogenesis and its role in vascular morphogenesis, patterning, and remodeling.

New blood vessels arise initially as blood islands in the process known as vasculogenesis or as new capillary segments produced through angiogenesis. Angiogenesis itself encompasses two broad processes, namely sprouting (SA) and intussusceptive (IA) angiogenesis. Primordial capillary plexuses expand through both SA and IA, but subsequent growth and remodeling are achieved through IA. The latter process proceeds through transluminal tissue pillar formation and subsequent vascular splitting, and the direction taken by the pillars delineates IA into overt phases, namely: intussusceptive microvascular growth, intussusceptive arborization, and intussusceptive branching remodeling. Intussusceptive microvascular growth circumscribes the process of initiation of pillar formation and their subsequent expansion with the result that the capillary surface area is greatly enhanced. In contrast, intussusceptive arborization entails formation of serried pillars that remodel the disorganized vascular meshwork into the typical tree-like arrangement. Optimization of local vascular branching geometry occurs through intussusceptive branching remodeling so that the vasculature is remodeled to meet the local demand. In addition, IA is important in creation of the local organ-specific angioarchitecture. While hemodynamic forces have proven direct effects on IA, with increase in blood flow resulting in initiation of pillars, the preponderant mechanisms are unclear. Molecular control of IA has so far not been unequivocally elucidated but interplay among several factors is probably involved. Future investigations are strongly encouraged to focus on interactions among angiogenic growth factors, angiopoetins, and related receptors.