Heparin Receptor Transmembrane Protein 184A (TMEM184A) Regulates Zebrafish Angiogenesis

Abstract

Angiogenesis is the formation of new vasculature from existing vasculature and occurs normally during embryonic development, wound healing, and inflammation. Angiogenesis is tightly controlled by several regulators. Disruption of the balance between positive and negative regulators can result in pathological angiogenesis. Abnormal angiogenesis is implicated in several serious diseases, including cardiovascular disease, stroke, diabetes, cancers, and many others. Heparin and/or heparan sulfates (HS) play an important role during in angiogenesis by interacting with both proangiogenic and inhibitory factors. For example, heparin/HS has been shown to act as a scaffold between the major proangiogenic regulator vascular endothelial growth factor (VEGF) and its receptor (VEGFR2). We recently identified transmembrane protein 184A (TMEM184A) as the heparin receptor in vascular endothelial and smooth muscle cells. In vitro, TMEM184A specifically interacts with heparin/HS to mediate anti‐inflammatory and anti‐proliferative growth factor signaling in vascular cells. To examine the expression and function of the heparin receptor TMEM184A in vivo, we employed the zebrafish regenerating fin. We used the Tg(fli1:eGFP) transgenic line to easily visualize vascular regeneration. Immunofluorescence data show that TMEM184A is expressed specifically in endothelial cells in ontogenic and regenerating vasculature. TMEM184A colocalizes with GFP (the endothelial cells) in both arteries and veins in ontogenic fin rays, and TMEM184A expression matches the regenerating pattern of GFP over several days after amputation. In regenerating fins injected with heparin, we observe abnormal vascular regeneration characterized by incomplete vessels and a reduction in total and vascular regeneration length within 24 hours after injection. Remarkably, transient knockdown (≤ 24 hours) of TMEM184A using morpholino‐mediated strategies in regenerating fins results in a significant increase in endothelial cells in highly disorganized vasculature. These data are directly comparable to what we have reported in vitro. Our studies indicate that the heparin receptor TMEM184A plays a regulatory role during angiogenesis. It is important to continue to elucidate the mechanism(s) behind the function of TMEM184A and determine its potential for therapeutic targeting in pathological angiogenesis. Additionally, information detailing its function in vivo could be used to improve current heparin‐based therapies used in the prevention and control of cardiovascular disease and stroke.Support or Funding InformationThis work was supported by NIH grant HL536104 to LLK.