The axon guidance molecule Netrin-4 is expressed by Müller cells and contributes to angiogenesis in the retina.
Retinal glial (Müller) cells are involved in a wide range of developmental mechanisms, including axon guidance and angiogenesis. This study was undertaken to explore whether Netrin-4, an axonal guidance molecule, is expressed by Müller cells and promotes angiogenesis-related activities. Netrin-4 was found through all retinal layers, and its expression was demonstrated in Müller cells, retinal pigment epithelium cells and bovine retinal endothelial cells (BRECs). Co-localization of Netrin-4 with Müller cell-specific molecules [cellular retinaldehyde-binding protein (cRALBP), vimentin] was observed in the ganglion cell layer, nerve fiber layer, and at the outer limiting membrane. Under hypoxic conditions, the release of Netrin-4 from Müller cells was increased, with mRNA levels upregulated in a hypoxia-inducible factor-1-dependent manner and dependent on the concomitantly induced release of vascular endothelial growth factor. These findings were consistent with an intensified immunofluorescence of Netrin-4 labeling in the postischemic retinas after ischemia-reperfusion. Netrin-4 stimulated BRECs to increase phosphorylation of the mitogen-activated protein (MAP) kinases, extracellular signal-regulated kinase (ERK)-1/-2, and p38, in a dose-dependent manner. Synthetic inhibitors of the MAP kinases were able to suppress Netrin-4-induced migration and proliferation of BRECs suggesting that both MAP kinases are differentially involved in Netrin-4-induced angiogenesis. Two receptors for Netrins, i.e., deleted in colorectal cancer (DCC) and uncoordinated-5-homolog 1 (Unc5H1), were detected in BRECs. DCC is at least partially required for Netrin-4-induced activation of ERK-1/-2. These data suggest that Müller glial cells contribute to, and may modulate, retinal Netrin-4 levels. This may be a novel pathway of Müller cell-mediated control of retinal angiogenesis, particularly under hypoxic/ischemic conditions when the cells upregulate Netrin-4 expression.
University of Leipzig, Eye Hospital, Liebigstrasse 10-14, D-04103 Leipzig, Germany.
Johannes
J
Lange
Yousef
Y
Yafai
André
A
Noack
Xiu Mei
XM
Yang
Anne-Britta
AB
Munk
Sandra
S
Krohn
Ianors
I
Iandiev
Peter
P
Wiedemann
Andreas
A
Reichenbach
Wolfram
W
Eichler
D000818:Animals; D000831:Animals, Newborn; D002417:Cattle; D015687:Cell Hypoxia / Q000502:physiology; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D000075389:DCC Receptor; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009389:Neovascularization, Pathologic / Q000378:metabolism* / Q000473:pathology; D009414:Nerve Growth Factors / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D000075386:Netrin Receptors; D009457:Neuroglia / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D020318:Rats, Long-Evans; D011956:Receptors, Cell Surface / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D012160:Retina / Q000166:cytology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D015854:Up-Regulation / Q000502:physiology*
D000075389:DCC Receptor; C501912:Dcc protein, rat; D009414:Nerve Growth Factors; D000075386:Netrin Receptors; D011956:Receptors, Cell Surface; D018168:Receptors, Retinoic Acid; D025521:Tumor Suppressor Proteins; C082927:retinoic acid binding protein I, cellular