Netrin-1 Reduces Monocyte and Macrophage Chemotaxis towards the Complement Component C5a

PLoS One. 2016 Aug 10;11(8):e0160685. doi: 10.1371/journal.pone.0160685. eCollection 2016.

Abstract

Netrin-1, acting at its cognate receptor UNC5b, has been previously demonstrated to inhibit CC chemokine-induced immune cell migration. In line with this, we found that netrin-1 was able to inhibit CCL2-induced migration of bone marrow derived macrophages (BMDMs). However, whether netrin-1 is capable of inhibiting chemotaxis to a broader range of chemoattractants remains largely unexplored. As our initial experiments demonstrated that RAW264.7 and BMDMs expressed high levels of C5a receptor 1 (C5aR1) on their surface, we aimed to determine the effect of netrin-1 exposure on monocyte/macrophage cell migration induced by C5a, a complement peptide that plays a major role in multiple inflammatory pathologies. Treatment of RAW264.7 macrophages, BMDMs and human monocytes with netrin-1 inhibited their chemotaxis towards C5a, as measured using two different real-time methods. This inhibitory effect was found to be dependent on netrin-1 receptor signalling, as an UNC5b blocking antibody was able to reverse netrin-1 inhibition of C5a induced BMDM migration. Treatment of BMDMs with netrin-1 had no effect on C5aR1 proximal signalling events, as surface C5aR1 expression, internalisation and intracellular Ca2+ release following C5aR1 ligation remained unaffected after netrin-1 exposure. We next examined receptor distal events that occur following C5aR1 activation, but found that netrin-1 was unable to inhibit C5a induced phosphorylation of ERK1/2, Akt and p38, pathways important for cellular migration. Furthermore, netrin-1 treatment had no effect on BMDM cytoskeletal rearrangement following C5a stimulation as determined by microscopy and real-time electrical impedance sensing. Taken together these data highlight that netrin-1 inhibits monocyte and macrophage cell migration, but that the mechanism behind this effect remains unresolved. Nevertheless, netrin-1 and its cognate receptors warrant further investigation as they may represent a potential avenue for the development of novel anti-inflammatory therapeutics.

MeSH terms

  • Animals
  • Calcium / metabolism
  • Cell Line
  • Chemokine CCL2 / genetics
  • Chemokine CCL2 / metabolism
  • Chemotaxis / drug effects
  • Chemotaxis / physiology*
  • Complement C5a / metabolism*
  • Humans
  • Immunologic Factors / pharmacology
  • Macrophages / drug effects
  • Macrophages / physiology*
  • Male
  • Mice, Inbred C57BL
  • Monocytes / drug effects
  • Monocytes / physiology
  • Nerve Growth Factors / chemistry
  • Nerve Growth Factors / metabolism
  • Nerve Growth Factors / pharmacology*
  • Netrin-1
  • Phosphatidylinositol 3-Kinases / metabolism
  • Receptor, Anaphylatoxin C5a / metabolism
  • Signal Transduction / drug effects
  • Tumor Suppressor Proteins / chemistry
  • Tumor Suppressor Proteins / metabolism
  • Tumor Suppressor Proteins / pharmacology*

Substances

  • C5ar1 protein, mouse
  • Ccl2 protein, mouse
  • Chemokine CCL2
  • Immunologic Factors
  • NTN1 protein, human
  • Nerve Growth Factors
  • Ntn1 protein, mouse
  • Receptor, Anaphylatoxin C5a
  • Tumor Suppressor Proteins
  • Netrin-1
  • Complement C5a
  • Phosphatidylinositol 3-Kinases
  • Calcium