O-phospho-(L)serine-P-ethyl ester

Films of O-phospho-L-serine-P-ethylester (PSE) were studied by infrared spectroscopy. PSE films were studied pure and as 1:1 mixture with LiOH, NaOH, KOH, and Ca(OH)2 as a function of the degree of hydration. The same investigations were performed if (L-glu)n was added to the system (ratio 1:1, PSE/glu residue). In the PSE molecules an intramolecular (I) COOH...-OP in equilibrium with COO-...HOP (II) hydrogen bond is present. In this bond a double minimum proton potential occurs and it shows large proton polarizability. This hydrogen bond is relatively stable as shown by the neutralization experiments. At low degree of hydration the cations are present at the phosphate groups. The Li ions polarize the intramolecular hydrogen bonds much more than the other cations, i.e., the weight of the proton-limiting structure COOH...-OP is increased by Li ions. Regarding these results one has to assume that such a hydrogen bond is also present in the phosphatidylserine head groups. It is discussed that such hydrogen bonds could be part of a lateral charge-conducting system in the polar surfaces of biological membranes. Such systems could connect proton-creating and proton-consuming centers at the membrane surface and conduct positive charge at an extremely high rate.

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 24h 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 light-induced 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 parallel with ascl1a and stat3 activation. This implies that at least one signaling mechanism, in addition to the process disrupted by L-SOP, is required to activate Müller glia proliferation in the light-damaged retina.