You are here

| Mesenchymal Stem Cells

NPR-A Aids Stem Cell Migration

Comment

Discuss

“Natriuretic Peptide Receptor A Signaling Regulates Stem Cell Recruitment and Angiogenesis: A Model to Study Linkage Between Inflammation and Tumorigenesis”

Natriuretic peptide receptor A (NPRA) is expressed on cells in inflamed or injured tissues and in tumours (Kong et al and Wang et al) and through cGMP-dependent protein kinase (PKG) signalling (Airhart et al and Chen et al), it upregulates genes affecting cell proliferation and inflammation, although a greater level of detail remains to be uncovered.   Researchers from the group of Subhra Mohapatra at the University of South Florida, Tampa, Florida, USA have previously shown that NPRA is an early biomarker for human prostate cancer (Wang et al) as well as recently establishing NPRA as a biomarker for melanoma, colon, and pancreatic cancer, and have reasoned that NPRA signaling may promote tumourigenesis by influencing recruitment of immune and progenitor cells, thereby fostering angiogenesis.   In their newest study, published in Stem Cells, the group use NPRA-knock out (NPRA-KO) mice as a model and find that that NPRA signaling is indeed linked to angiogenesis partially through progenitor cell recruitment (Mallela et al).

Initial analysis using an ex vivo aortic ring assay found that rings from NPRA-KO mice had lower capillary growth and sparse capillary network formation compared to rings from wildtype (WT) C57BL/6 mice.   Less Von Willebrand factor (vWF) positive cells were also found for the NPRA-KO mice further suggesting a lower blood vessel formation potential.   Subsequently, the inflammatory mediator lipopolysaccharide (LPS) was found to increase capillary growth in the aortic ring assay (WT) and this was negated upon the addition of an NPRA antagonist (anantin).   LPS treatment also led to an increase in NPRA- and CXCR4-positive cells, with CXCR4 being linked to stem cell migration through SDF1 (Sodir et al).   Additionally, most CXCR4-positive cells were also positive for CD31, which marks endothelial progenitor cells (EPCs) which differentiate from migratory stem cells to aid angiogenesis.   Furthermore, Anantin treatment was also observed to block the upregulation of CXCR4 and CD31 expression and LPS treatment of aortic rings from NPRA-KO mice failed to lead to an increase in capillary growth, and was correlated to low expression of VEGF, CXCR4 and CD31.

Mesenchymal stem cells (MSCs) are known to migrate to tumours where they can boost angiogenesis through various means (see paper for extended references).   WT and NPRA-KO mice were injected with a bone marrow-derived stem cell line (Lewis lung carcinoma (LLC-1)) tagged with GFP, known to be highly tumourigenic and express high levels of NPRA (Kong et al).   While tumours formed in both mice, a reduced tumour burden in NPRA-KO mice was observed compared to WT mice, suggesting that the injected cells were less able to migrate and graft, or failed to proliferate in NPRA-KO mice.   Increased GFP signal was observed at tumour sites in WT mice compared to NPRA-KO mice and, on analysis of cells of the tumours, NPRA-KO mice demonstrated lower levels of markers for endothelial progenitors (CD31), cancer associated fibroblasts (SMA, Vimentin and S100A4), macrophages (F4/80) and endothelial cells (vWF) than WT tumours suggesting diminished progenitor/immune cell recruitment.   Further immunostaining also demonstrated that NPRA was colocalized with endothelial progenitors, cancer associated fibroblasts and recruited MSCs in WT mice.   Interestingly, when MSCs were added to the ex vivo aortic rings from NPRA-KO mice, capillary growth increased significantly, further suggesting that loss in cell recruitment in NPRA-KO mice leads to impaired angiogenesis.  Co-injection of LLC-1 cells and MSCs into NPRA-KO mice increased tumour burden and was associated with an increase in VEGF, CD31, Tie2 (endothelial marker) and SMA, indicating that the lack of tumourigenesis could also be caused by the absence of angiogenic factors that can be restored by circulating MSCs.   Furthermore, many SMA- and S100A4-positive cells at tumour sites were GFP-positive suggesting that they had differentiated from MSCs, further underscoring the fact that lack of progenitor/stem cell recruitment inhibited tumour angiogenesis.   Additionally, co-implantation also induced SDF1α expression known to facilitate tumour angiogenesis through CXCR4 (Olson et al and Sodir et al).

Overall, this study demonstrates for the first time that NPR-A, a marker of inflamed/injured tissues, plays a key role in the recruitment of stem cells in vivo which promotes tumour angiogenesis through a mechanism involving CXCR4 and SDF1α.   This investigation into the mechanisms behind this phenomenon also provides drugable targets to inhibit tumour related angiogenesis and also to promote tissue damage repair.

 

Reference

  • Airhart N et al. Atrial natriuretic peptide induces natriuretic peptide receptor-cGMP-dependent protein kinase interaction. J Biol Chem 2003; 278: 38693–38698
  • Chen H et al. Atrial natriuretic peptide-initiated cGMP pathways regulate vasodilator-stimulated phosphoprotein phosphorylation and angiogenesis in vascular endothelium. J Biol Chem 2008; 283: 4439–4447
  • Kong X et al. Natriuretic peptide receptor a as a novel anticancer target. Cancer Res 2008; 68: 249–256
  • Olson P et al. Imaging guided trials of the angiogenesis inhibitor sunitinib in mouse models predict efficacy in pancreatic neuroendocrine but not ductal carcinoma. Proc Natl Acad Sci USA 2011; 108: E1275–1284
  • Sodir NM et al. Endogenous Myc maintains the tumor microenvironment. Genes Dev 2011; 25: 907–916
  • Wang X et al. Natriuretic peptide receptor a as a novel target for prostate cancer. Mol Cancer 2011; 10: 56

 

From Stem Cells.

Stem Cell Correspondent Stuart P Atkinson reports on those studies appearing in current journals that are destined to make an impact on stem cell research and clinical studies.