title: Endogenous Gas6 and Ca2+ -channel activation modulate phagocytosis by retinal pigment epithelium.
abstract: Mutation or loss of MerTK as well as deficiency of alphavbeta5-integrins, gives rise to retinal-degeneration due to inefficient phagocytosis of photoreceptor outer-segment fragments by the retinal pigment epithelium (RPE). This study shows that Gas6 expressed endogenously by human RPE promotes phagocytosis. The RPE expresses Gas6 more highly in vivo and in serum-reduced conditions in vitro than in high-serum conditions, suggesting a negative-feedback control. An antibody-blockage approach revealed that Gas6-expressing RPE phagocytizes photoreceptor outer-segment fragments due to stimulation of MerTK by endogenous Gas6 in vitro. MerTK- and Gas6-antibodies reduced phagocytosis. Blocking L-type Ca(2+)-channels with nifedipine inhibited MerTK dependent phagocytosis in vitro. Application of integrin inhibitory, soluble, RGD-containing peptides or soluble vitronectin reduced L-type Ca(2+)-channel currents in RPE. Herbimycin A, which reduces phosphorylation of integrin receptor-associated proteins and decreases L-type Ca(2+)-channel currents in RPE, eliminates the inhibiting vitronectin effect and abolishes phagocytosis. Thus, Gas6-promoted phagocytosis was inhibited by L-type Ca(2+)-channel blockage, which in turn may be activated by integrin receptor stimulation. These results suggest that L-type Ca(2+)-channels could be regulated downstream of both MerTK and alphavbeta5-integrin, indicating that the binding and uptake mechanisms of phagocytosis are part of a converging pathway.
authors.affiliation: University Eye Hospital Hamburg, Martinistrasse 52, 20246 Hamburg, Germany. mail@mikeology.de
authors.forename: Mike O
authors.initials: MO
authors.lastname: Karl
authors.forename: Wolfram
authors.initials: W
authors.lastname: Kroeger
authors.forename: Soenke
authors.initials: S
authors.lastname: Wimmers
authors.forename: Vladimir M
authors.initials: VM
authors.lastname: Milenkovic
authors.forename: Monika
authors.initials: M
authors.lastname: Valtink
authors.forename: Katrin
authors.initials: K
authors.lastname: Engelmann
authors.forename: Olaf
authors.initials: O
authors.lastname: Strauss
mesh_terms: D000906:Antibodies / Q000494:pharmacology; D016227:Benzoquinones / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D002478:Cells, Cultured; D006801:Humans; D039564:Integrin alphaV / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000032:analysis / Q000276:immunology / Q000378:metabolism*; D047029:Lactams, Macrocyclic / Q000494:pharmacology; D008024:Ligands; D009543:Nifedipine / Q000494:pharmacology; D010587:Phagocytosis / Q000187:drug effects; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism; D017828:Rifabutin / Q000031:analogs & derivatives; D000076202:c-Mer Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6
chemical_list: D000906:Antibodies; D016227:Benzoquinones; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D039564:Integrin alphaV; D036341:Intercellular Signaling Peptides and Proteins; D047029:Lactams, Macrocyclic; D008024:Ligands; D009543:Nifedipine; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D020794:Receptor Protein-Tyrosine Kinases; D017828:Rifabutin; D000076202:c-Mer Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6; C020754:herbimycin; C097072:MERTK protein, human