Müller glial cells inhibit proliferation of retinal endothelial cells via TGF-β2 and Smad signaling.
Neovascularization is a sight-threatening complication of ischemic proliferative retinopathies. Transforming growth factor (TGF)-β, a cytokine with multiple functions in the retina, participates in the control of pathological angiogenesis and neovascularization. Retinal glial (Müller) cells produce TGF-β2 under physiological and post-ischemic conditions. To characterize glial cell-derived mediators of angiogenesis regulation in glial-endothelial interactions in the retina, we co-cultured primary Müller cells and bovine microvascular retinal endothelial cells (BRECs). Müller cell-derived TGF-β2 was bound by the BRECs, which were found to express serine/threonine kinase TGF-β receptors, and stimulated TGF-β-dependent anti-proliferative signaling pathways. The proliferation of BRECs was attenuated by exogenous TGF-β2 as well as by the presence of Müller cell culture media. The following intracellular signaling mechanisms were found to be involved in the anti-angiogenic action of Müller cell-derived TGF-β2: (i) binding of TGF-β2 to BRECs is mediated by the type-II TGF-β receptor, leading to (ii) activation and phosphorylation of receptor-activated Smads; (iii) Müller cell-derived TGF-β2 activates Smad2 and Smad3 to (iv) attenuate the phosphorylation state of the MAP kinases, extracellular signal-regulated kinase (ERK)-1/-2. Neutralizing TGF-β or TGF-β type-II receptor or blocking the activation of Smads partially abrogated the effect of Müller cell-conditioned media on BRECs. Together, our data suggest that Müller cells release TGF-β2, inhibiting the proliferation of retinal endothelial cells via activation of Smad2/Smad3 and attenuation of ERK signaling. Given the context-dependent action of TGF-β2 on angiogenesis, our results may have implications for understanding the pathogenesis of retinal angiopathies, such as diabetic retinopathy, and the anti-angiogenic role of TGF-β therein.
Department of Ophthalmology and Eye Hospital, University of Leipzig, Leipzig, Germany.
Yousef
Y
Yafai
Ianors
I
Iandiev
Johannes
J
Lange
Jan Darius
JD
Unterlauft
Peter
P
Wiedemann
Andreas
A
Bringmann
Andreas
A
Reichenbach
Wolfram
W
Eichler
D000818:Animals; D002417:Cattle; D015687:Cell Hypoxia / Q000502:physiology; D049109:Cell Proliferation / Q000502:physiology*; D002478:Cells, Cultured; D018920:Coculture Techniques; D042783:Endothelial Cells / Q000502:physiology*; D063928:Ependymoglial Cells / Q000502:physiology*; D006168:Guinea Pigs; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology; D010766:Phosphorylation; D020318:Rats, Long-Evans; D011994:Recombinant Proteins / Q000378:metabolism; D012160:Retina / Q000502:physiology*; D051785:Smad Proteins / Q000378:metabolism*; D053781:Transforming Growth Factor beta2 / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
D011994:Recombinant Proteins; D051785:Smad Proteins; D053781:Transforming Growth Factor beta2; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A
Müller cell; angiogenesis; neovascularization; retina