The inhibitor of phagocytosis, O-phospho-l-serine, suppresses Müller glia proliferation and cone cell regeneration in the light-damaged zebrafish retina

Abstract

The damaged zebrafish retina replaces lost neurons through a regenerative response that initiates with the asymmetric cell division of Müller glia to produce neuronal progenitor cells that proliferate and migrate to the damaged retinal layer, where they differentiate into the lost neuronal cell types. Because Müller glia are known to phagocytose apoptotic retinal cells during development, we tested if Müller glia engulfed apoptotic rod cell bodies in light-damaged retinas. After 24 hours of constant intense light, damaged retinas revealed both a strong nuclear TUNEL signal in photoreceptors and a weak cytoplasmic TUNEL signal in Müller glia, although Müller glial apoptosis is not observed in the light-damaged retina. Light damage of a rod-specific transgenic reporter line, Tg (XlRho:EGFP) fl1 , resulted in some Müller glia containing both TUNEL signal and EGFP, which indicated that this subset of Müller glia engulfed apoptotic photoreceptor cell bodies.To determine if phagocytosis induced the Müller glial proliferative response in the light-damaged retina, we utilized O-phospho-L-serine (L-SOP), a molecule that mimics the phosphatidylserine head group and partially blocks microglial phagocytosis of apoptotic cells. Intravitreal injection of L-SOP immediately prior to beginning constant intense light treatment: i) did not significantly reduce lightinduced photoreceptor cell death, ii) significantly reduced the number of PCNA-positive Müller glia, and iii) significantly reduced the number of cone photoreceptors in the regenerated retina relative to control retinas. Because L-SOP is also a specific group III metabotropic glutamate receptor (mGluR) agonist, we also tested if the more potent specific group III agonist, L-2-amino-4-phosphonobutyrate (L-AP4), the specific group III antagonist (RS)-α-Methylserine-O-phosphate (MSOP) or the specific group I antagonist, L-2-amino-3-phophonopropanoic acid (L-AP3) affected Müller glial proliferation. We found no changes with any of these factors compared to control retinas, revealing that metabotropic glutamate receptors were not necessary in the Müller glia proliferative response. Furthermore, ascl1a and stat3 expression were unaffected in either the L-SOP or MSOP-injected retinas relative to controls, suggesting L-SOP disrupts Müller glia proliferation subsequent to or in

Macrophage and microglia ontogeny in the mouse visual system can be traced by the expression of Cathepsins B and D

“…However, TUNEL analysis revealed a weak cytoplasmic signal in neuroepithelial cells near the SONCs, indicating that they also engulf cell debris, as has previously been described in our laboratory MartinPartido and Navascues, 1990). Similarly, TUNEL cytoplasmic labeling has also been detected in retinal Mü ller cells resulting from the ingestion of the fragmenting DNA from dying neighbor cells during normal development (Egensperger et al, 1996;Francisco-Morcillo et al, 2004) or under experimental conditions (Morris et al, 2005;Bailey et al, 2010).…”

Intracellular disposition of chitosan nanoparticles in macrophages: intracellular uptake, exocytosis, and intercellular transport

“…Phagocytosis was regarded as a contributor to the uptake of NPs larger than 500 nm; nevertheless, it was certainly the prevalent pathway for intracellular uptake by macrophages. In this test, when phagocytosis was prevented using O-phospho-l-serine (1 mM), 22,23 a significant inhibition of uptake was observed within 8 h relative to that of the negative group; however, the inhibition effect of O-phospho-l-serine was weaker than that of sucrose. Thus, in addition to the clathrin-mediated endocytosis, the internalization of FITCCsNPs was also regulated by the phagocytosis pathway.…”

“…Then, FITC-CsNPs (250 μg/mL) were added, and after various incubation periods, the effects of inhibitors on NP uptake were determined by both inverted fluorescence microscopy observation and quantitative measurements using a multimode microplate reader. The chemical inhibitors applied in this test included O-phospho-l-serine (1 mM) 22,23 and sucrose (450 mM), 24 which were reported to inhibit phagocytosis and clathrin-mediated endocytosis, respectively.…”

Light-induced degeneration and microglial response in the retina of an epibenthonic pigmented teleost: age-dependent photoreceptor susceptibility to cell death

“…Albino teleosts are a better choice than pigmented animals for investigating the mechanisms by which light damages the retina because of their relatively high susceptibility to light damage. Thus, constant intense light exposure of albino zebrafish causes widespread photoreceptor cell death (Vihtelic and Hyde, 2000;Vihtelic et al, 2006;Thummel et al, 2008a;Thummel et al, 2008b;Bailey et al, 2010), and rod outer segment degradation ('solar pruning') and photoreceptor loss in the albino rainbow trout (Allen and Hallows, 1997;Allen et al, 1999;Allison et al, 2006) and albino oscar Astronotus ocellatus (Allen et al, 1999). However, albino teleosts are rare in nature.…”