Culprit Behind Unchecked Angiogenesis Identified

Photo: Growing blood vessels in the retina of a mouse

Vessels grow from the centre to
the outer parts of unsupplied
tissue; © MPG

Angiogenesis, the growth of new blood vessels, is a complex process during which different signalling proteins interact with each other in a highly coordinated fashion. The growth factor VEGF and the Notch signalling pathway both play important roles in this process. VEGF promotes vessel growth by binding to its receptor, VEGFR2, while the Notch signalling pathway acts like a switch capable of suppressing angiogenesis. Until recently, scientists had assumed that Notch cancels the effects of VEGF through the down regulation of VEGFR2.

"This finding might help explain drug resistance issues in certain types of cancer therapy and could become the basis for novel treatment strategies," suggests Ralf Adams, of MPI and Chair of the Department of Tissue Biology and Morphogenesis.

An extensively branched network of blood vessels provides every organ of the body with nutrients and removes harmful metabolic waste products from tissues. Growth of this vascular system is essential for development and wound healing processes.

Uncontrolled angiogenesis contributes to diseases like haemangiomas, the sponge-like overgrowth of blood vessels in the skin, or retinopathies impairing the eyesight of diabetic and elderly individuals. In cancer therapy, inhibition of angiogenesis is used to starve tumours and prevent the metastatic spread of cancer cells via the circulation. At present, this is most frequently done by targeting VEGF or its receptor VEGFR2. When their oxygen supply becomes inadequate, tissues begin to release VEGF, which binds to VEGFR2, activating the receptor and thereby triggering vessel growth. Thus, the formation of new blood vessels can be blocked by inhibiting VEGF or VEGFR2. Unfortunately, existing treatments are inadequate and, for reasons that are not yet known, some patients respond poorly or not at all to VEGF/VEGFR2 inhibition.

Now, Rui Benedito has demonstrated that inhibition of the Notch pathway in blood vessels of the mouse eye permits strong and deregulated vessel growth even when VEGF or VEGFR2 are inhibited. "It turns out that another VEGF family receptor, VEGFR3, takes over, promoting the formation of new blood vessels," explains Benedito. VEGFR3 is strongly upregulated in blood vessels in the absence of Notch and is active even without growth signals from the surrounding tissues.

MEDICA.de; Source: Max-Planck-Institute for Molecular Biomedicine