Developmental regulation of calcium channel-mediated currents in retinal glial (Müller) cells

Whole cell voltage-clamp recordings of freshly isolated cells were used to study changes in the currents through voltage-gated Ca(2+) channels during the postnatal development of immature radial glial cells into Müller cells of the rabbit retina. Using Ba(2+) or Ca(2+) ions as charge carriers, currents through transient low-voltage-activated (LVA) Ca(2+) channels were recorded in cells from early postnatal stages, with an activation threshold at -60 mV and a peak current at -25 mV. To increase the amplitude of currents through Ca(2+) channels, Na(+) ions were used as the main charge carriers, and currents were recorded in divalent cation-free bath solutions. Currents through transient LVA Ca(2+) channels were found in all radial glial cells from retinae between postnatal days 2 and 37. The currents activated at potentials positive to -80 mV and displayed a maximum at -40 mV. The amplitude of LVA currents increased during the first postnatal week; after postnatal day 6, the amplitude remained virtually constant. The density of LVA currents was highest at early postnatal days (days 2-5: 13 pA/pF) and decreased to a stable, moderate level within the first three postnatal weeks (3 pA/pF). A significant expression of currents through sustained, high-voltage-activated Ca(2+) channels was found after the third postnatal week in approximately 25% of the investigated cells. The early and sole expression of transient currents at high-density may suggest that LVA Ca(2+) channels are involved in early developmental processes of rabbit Müller cells.     

Glial cell expression of hepatocyte growth factor in vitreoretinal proliferative disease

The hepatocyte growth factor (HGF) has been crucially implicated in the development of proliferative retinal diseases; however, it is unclear whether retinal glial cells express or respond to HGF. Therefore, we examined the expression of HGF and of the receptor for HGF, c-Met, by immunohistochemical costaining with glial fibrillary acidic protein (GFAP) in epiretinal membranes of patients with proliferative vitreoretinopathy (PVR) and proliferative diabetic retinopathy (PDR), respectively. Furthermore, it was determined whether cells of the human retinal glial cell line, MIO-M1, secrete HGF protein, and whether HGF stimulates proliferation and chemotaxis, and secretion of the vascular endothelial growth factor (VEGF). Neuroretinas of patients with PVR express elevated mRNA level for HGF in comparison to control retinas. In epiretinal membranes of patients with PVR or PDR, immunoreactivity for HGF and for c-Met, respectively, partially colocalized with immunoreactivity for GFAP. Fetal bovine serum and basic fibroblast growth factor, but not heparin-binding epidermal or platelet-derived growth factors, evoked HGF secretion by cultured retinal glial cells. HGF displayed only a marginal effect on cell proliferation while it stimulated chemotaxis. HGF promoted the secretion of VEGF, via activation of the phosphatidylinositol-3 kinase. It is concluded that glial cells in epiretinal membranes express both HGF protein and c-Met receptors. The results suggest an autocrine/paracrine role of HGF in glial cell responses during proliferative vitreoretinal disorders as well as in retinal neovascularization, by stimulating of VEGF release.     

The activity of a transient potassium current in retinal glial (Müller) cells depends on extracellular calcium

The modulating effects of varying extracellular concentrations of Ca2+ ([Ca2+]e) and of other divalent cations on the fast transient (A-type) K+ current (I(A)) of freshly isolated Muller glial cells from rabbit and human retinae were studied with the whole-cell patch-clamp method. The I(A) of Miller cells was voltage-independently blocked by extracellular 4-aminopyridine (4AP) with a 50 % reduction achieved at 0.94 mM 4AP. The I(A) amplitude was elevated by increased extracellular [K+]. Elevation of the [Ca2+]e had three effects on the glial I(A): (i) it concentration-dependently shifted both the activation and inactivation curves towards less negative membrane potentials, (ii) it increased the peak current amplitude, and (iii) it slowed down the activation and inactivation kinetics. Particularly at depolarized membrane potentials, the I(A) was enlarged and broadened when the [Ca2+]e was increased. Various divalent cations also exerted these effects, although at different concentrations. While Zn2+, Cd2+, Cu2+ and Pb2+ modulated the I(A) in the micromolar range, Mg2+ and Ba2+ had effects in the millimolar range. Extracellular acidification produced a positive shift in the voltage dependence of I(A) gating. However, alterations of the extracellular pH did not abolish the Ca2+ effects on I(A); this indicates that protons and Ca2+ ions mediate their effects on glial K(A) channels by different mechanisms or binding sites, respectively. Physiological (i.e., activity-dependent) changes of the extracellular concentration of divalent cations and of the extracellular pH should influence the retinal excitability via modulation of glial K+ currents. The activation of glial I(A) by divalent cations at depolarized voltages supports a repolarization and, therefore, the maintainance of a hyperpolarized glial membrane potential during periods of increased neuronal activity.     

Antiplasmodial activity of knipholone and related natural phenylanthraquinones

phenylanthraquinone knipholone (1) and three of its natural derivatives as well as seven structurally related but simplified compounds have been examined for their antiplasmodial activity against asexual erythrocytic stages of two strains of Plasmodium falciparum in vitro (K1/chloroquine-resistant and NF 54/chloroquine-sensitive). All the phenylanthraquinones showed considerable activity with only little cytotoxicity, while their anthraquinone and phenyl moieties were completely inactive. Knipholone (1) and its natural derivatives can therefore be considered as a new group of potential antimalarials     

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. GLIA 2014;62:1476–1485     

Identifying the specific-targeted marine cerebrosides against SARS-CoV-2: an integrated computational approach

Cerebrosides are a group of metabolites belonging to the glycosphingolipids class of natural products. So far, 167 cerebrosides, compounds 1–167, have been isolated from diverse marine organisms or microorganisms. The as yet smaller number of compounds that have been studied more in depth proves a potential against challenging diseases, such as cancer, a range of viral and bacterial diseases, as well as inflammation. This review provides a comprehensive summary on this so far under-explored class of compounds, their chemical structures, bioactivities, and their marine sources, with a full coverage to the end of 2020. Today, the global pandemic concern, COVID-19, has claimed millions of death cases around the world, making the development of anti-SARS-CoV-2 drugs urgently needed for such a battle. Accordingly, selected examples from all subclasses of cerebrosides were virtually screened for potential inhibition of SARS-CoV-2 proteins that are crucially involved in the viral–host interaction, viral replication, or in disease progression. The results highlight five cerebrosides that could preferentially bind to the hACE2 protein, with binding scores between −7.1 and −7.6 kcal mol⁻¹ and with the docking poses determined underneath the first α₁-helix of the protein. Moreover, the molecular interaction determined by molecular dynamic (MD) simulation revealed that renieroside C1 (60) is more conveniently involved in key hydrophobic interactions with the best stability, least deviation, least ΔG (−6.9 kcal mol⁻¹) and an RMSD value of 3.6 Å. Thus, the structural insights assure better binding affinity and favorable molecular interaction of renieroside C1 (60) towards the hACE2 protein, which plays a crucial role in the biology and pathogenesis of SARS-CoV-2.

Cerebrosides are a group of metabolites belonging to the glycosphingolipids class of natural products.     

Identification of a cellulose synthase-associated protein required for cellulose biosynthesis

Cellulose synthase-interactive protein 1 (CSI1) was identified in a two-hybrid screen for proteins that interact with cellulose synthase (CESA) isoforms involved in primary plant cell wall synthesis. CSI1 encodes a 2,150-amino acid protein that contains 10 predicted Armadillo repeats and a C2 domain. Mutations in CSI1 cause defective cell elongation in hypocotyls and roots and reduce cellulose content. CSI1 is associated with CESA complexes, and csi1 mutants affect the distribution and movement of CESA complexes in the plasma membrane.