Angiogenin and Copper Crossing in Wound Healing

Abstract

Angiogenesis plays a key role in the wound healing process, involving the migration, growth, and differentiation of endothelial cells. Angiogenesis is controlled by a strict balance of different factors, and among these, the angiogenin protein plays a relevant role. Angiogenin is a secreted protein member of the ribonuclease superfamily that is taken up by cells and translocated to the nucleus when the process of blood vessel formation has to be promoted. However, the chemical signaling that activates the protein, normally present in the plasma, and the transport pathways through which the protein enters the cell are still largely unclear. Copper is also an angiogenic factor that regulates angiogenin expression and participates in the activation of common signaling pathways. The interaction between angiogenin and copper could be a relevant mechanism in regulating the formation of new blood vessel pathways and paving the way to the development of new drugs for chronic non-healing wounds.

Keywords: angiogenesis; cell proliferation; copper complexes; mimicking peptides; protein; ribonuclease; trophic factor.

Figure 1

Phases of the wound healing process: hemostasis; inflammation; proliferation; remodeling.

Figure 2

Amino acid sequence of angiogenin using one-letter symbols. The first residue Q, glutamine, is cyclized as pyroglutamate. Red indicates amino acids of catalytic sites (H, histidine; K, lysine); blue indicates nuclear translocation sequence (R, arginine; G, glycine; L, leucine); green indicates cellular binding site (K, lysine, N, asparagine; G, glycine, P, proline, H, histidine; R, arginine; E, glutamic acid).

Figure 3

Three-dimensional biological structure of human ANG, consisting of: three disulphide bridges (in red); a catalytic site formed by the triad His-13 (in blue), Lys-40 (in orange) and His-114 (in violet); the receptor binding site, sequence 60–68 (in cyan); the nuclear translocation sequence, 30–35 (in grey). (PDB ID 1ANG, 10.2210/pdb1ANG/pdb).

Figure 4

Mechanism of action of ANG. Extracellular ANG, through interaction with an endothelial surface cell receptor, activates several signal transduction pathways, including ERK1/2, SAPK/JNK and PI3K/Akt, thus promoting cell growth and differentiation. Moreover, extracellular ANG undergoes receptor-mediated endocytosis and accumulates in the cytoplasm, under stress conditions or in the nucleus, under growth conditions. Nuclear ANG stimulates both rRNA and mRNA transcription, allowing for cellular growth. In addition, ANG interacts with cell surface actin, leading to ECM and basement membrane degradation, thereby promoting cell migration and invasion.

Figure 5

Angiogenin promotes wound healing by inducing angiogenesis and cell migration and by activating fibroblast cells to produce ECM proteins (collagen, fibrin, fibronectin).

Figure 6

Putative anchor site of Cu²⁺ in (a) rANG and (b) wtANG copper complexes (PDB ID 1ANG).