Midkine acts as proangiogenic cytokine in hypoxia-induced angiogenesis

Abstract

The cytokine midkine (MK) promotes tumor growth mainly by inducing angiogenesis. Here, we identified the source of MK in the vascular system under hypoxic conditions and demonstrated the relevance of MK during ischemia of normal tissue. Hypoxia increased MK protein expression in human polymorphonuclear neutrophils (PMN), monocytes, and human umbilical vein endothelial cells (HUVEC) compared with normoxia. Immunoelectron microscopy showed elevated cell surface expression of MK in PMN and monocytes during hypoxia. However, only HUVEC released significant amounts of soluble MK during hypoxia compared with normoxia (301 ± 81 pg/ml vs. 158 ± 45 pg/ml; P < 0.05). Exogenous MK induced neovascularization in a chorioallantoic membrane (CAM) assay compared with negative control as measured by counting the number of branching points per visual field (1,074 ± 54 vs. 211 ± 70; P < 0.05). In a hind limb ischemia model, the angiogenic response was almost completely absent in MK-deficient mice, whereas control animals showed a profound angiogenic response measured as proliferating endothelial cells per visual field (45 ± 30 vs. 169 ± 34; P < 0.01). These unanticipated results identified endothelial cells as the source of soluble MK in the vascular system during hypoxia and defined MK as a pivotal player of angiogenesis during ischemia in nonmalignant tissue.

The cytokine midkine supports neutrophil trafficking during acute inflammation by promoting adhesion via β2 integrins (CD11/CD18)

“…48 In the case of MK, the cationic nature and heparin-binding domains of the molecule may allow its interaction with the negatively charged heparan sulfates of the glycocalyx, and thus, immobilized MK may be presented by the activated endothelium. As MK is not expressed on quiescent cells but upregulated during inflammation, 18 only inflamed endothelium may promote the activation of b 2 integrins on PMNs via MK. Thus, depending on the presence or absence of MK on endothelial cells in the microvasculature of an inflamed tissue, this mechanism may reinforce or attenuate PMN infiltration into the tissue by regulating intravascular adhesion, which may be of great importance for the balance between efficient host defense and protection from tissue damage by excessive PMN recruitment.…”

“…14,15 MK is expressed in PMNs, monocytes, and lymphocytes, and released by endothelial cells under hypoxic conditions. [16][17][18] MK binds to various receptors with high affinity, including heparan and chondroitin sulfate proteoglycans, 19,20 b 1 integrins, 21 and the low-density lipoprotein receptor-related protein 1 (LRP1). 22 Interestingly, LRP1 interacts with b 2 integrins, thereby promoting leukocyte adhesion.…”

“…22 Interestingly, LRP1 interacts with b 2 integrins, thereby promoting leukocyte adhesion. [23][24][25] MK has been implicated in a wide number of biological functions including for example, angiogenesis under hypoxic conditions, 18 cell survival, 26 and tumor growth. 27 Multiple studies also suggest an important role for MK in several pathological inflammatory conditions.…”

Hypoxia-inducible TAp73 supports tumorigenesis by regulating the angiogenic transcriptome

“…5a and Supplementary Table 2), and formed a molecular network associated with cardiovascular system development and function (Supplementary Table 3). Many of these genes are known positive regulators of angiogenesis, including eng, mdk, pdgf-B and so on [31][32][33] , and were also noted to be upregulated in a TAp73-dependent manner in an earlier profiling study 34 , These were grouped as important for blood vessel development by gene ontology clustering (Supplementary Table 4). We therefore selected this group of 28 positive regulators (Supplementary Table 5) for further validation.…”

PKCδ/midkine pathway drives hypoxia-induced proliferation and differentiation of human lung epithelial cells

“…Such increases in MK seen in cystic fibrosis patients demonstrate the importance of hypoxia/ MK interactions in human pulmonary diseases and underscore the relevance of our observations that hypoxia upregulates expression and secretion of MK and accelerates differentiation of human lung epithelial cells toward mesenchymal phenotype. The responsiveness of MK to hypoxia might represent a universal response among various cell types as hypoxia-induced MK expression and release have been also reported in human umbilical vein endothelial cells (37). MK production in the respiratory epithelium is also regulated by hypoxia and serves as a paracrine signal that selectively enhances muscularization of small pulmonary arteries (26).…”