Müller glial cells in retinal disease

Virtually all pathogenic stimuli activate Müller cells. Reactive Müller cells exert protective and toxic effects on photoreceptors and neurons. They contribute to oxidative stress and glutamate toxicity due to malfunctions of glutamate uptake and glutathione synthesis. Downregulation of potassium conductance disrupts transcellular potassium and water transport, resulting in neuronal hyperexcitability and edema. Protective effects of reactive Müller cells include upregulation of adenosine 5'-triphosphate (ATP)-degrading ectoenzymes, which enhances the extracellular availability of the neuroprotectant adenosine, abrogation of the osmotic release of ATP, which might protect retinal ganglion cells from apoptosis, and the release of antioxidants and neurotrophic factors. The dedifferentiation of reactive Müller cells to progenitor-like cells might have an impact on future therapeutic approaches. A better understanding of the gliotic mechanisms will be helpful in developing efficient therapeutic strategies aiming at increased protective and regenerative properties and decreased toxicity of reactive Müller cells.     

PPAR-gamma agonists inhibit toll-like receptor-mediated activation of dendritic cells via the MAP kinase and NF-kappaB pathways

Dendritic cells (DCs) play an important role in initiating and maintaining primary immune responses. However, mechanisms involved in the resolution of these responses are elusive. We analyzed the effects of 15d-PGJ2 and the synthetic peroxisome proliferator-activated receptor (PPAR)-gamma ligand troglitazone (TGZ) on the immunogenicity of human monocyte-derived DCs upon stimulation with toll-like receptor (TLR) ligands. Activation of PPAR-gamma resulted in a reduced stimulation of DCs via the TLR ligands 2, 3, 4, and 7, characterized by down-regulation of costimulatory and adhesion molecules and reduced secretion of cytokines and chemokines involved in T-lymphocyte activation and recruitment. MCP-1 (monocyte chemotactic protein-1) production was increased due to PPAR-gamma activation. Furthermore, TGZ-treated DCs showed a significantly reduced capacity to stimulate T-cell proliferation, emphasizing the inhibitory effect of PPAR-gamma activation on TLR-induced DC maturation. Western blot analyses revealed that these inhibitory effects on TLR-induced DC activation were mediated via inhibition of the NF-kappaB and mitogen-activated protein (MAP) kinase pathways while not affecting the PI3 kinase/Akt signaling. Our data demonstrate that inhibition of the MAP kinase and NF-kappaB pathways is critically involved in the regulation of TLR and PPAR-gamma-mediated signaling in DCs.     

A primaquine–chloroquine hybrid with dual activity against Plasmodium liver and blood stages

We present a new class of hybrid molecules consisting of the established antiplasmodial drugs primaquine and chloroquine. No drug is known to date that acts comparably against all stages of Plasmodium in its life cycle. Starting from available precursors, we designed and synthesized a new-generation compound consisting of both primaquine and chloroquine components, with the intent to produce agents that exhibit bioactivity against different stages of the parasite's life cycle. In vitro, the hybrid molecule 3 displays activity against both asexual and sexual P. falciparum blood stages as well as P. berghei sporozoites and liver stages. In vivo, the hybrid elicits activity against P. berghei liver and blood stages. Our results successfully validate the concept of utilizing one compound to combine different modes of action that attack different Plasmodium stages in the mammalian host. It is our hope that the novel design of such compounds will outwit the pathogen in the spread of drug resistance. Based on the optimized synthetic pathway, the compound is accessible in a smooth and versatile way and open for potential further molecular modification.     

Proliferative gliosis causes mislocation and inactivation of inwardly rectifying K(+) (Kir) channels in rabbit retinal glial cells

Retinal glial (Müller) cells are proposed to mediate retinal potassium homeostasis predominantly by potassium transport through inwardly rectifying K(+) (Kir) channels. Retinal gliosis is often associated with a decrease in glial potassium conductance. To determine whether this decrease is caused by a downregulation of glial Kir channels, we investigated a rabbit model of proliferative vitreoretinopathy (PVR) which is known to be associated with proliferative gliosis. The membrane conductance of control Müller cells is characterized by large Kir currents whereas Müller cells of PVR retinas displayed an almost total absence of Kir currents. In control tissues, Kir2.1 immunoreactivity is localized in the inner stem processes and endfeet of Müller cells whereas Kir4.1 immunoreactivity is largely confined to the Müller cell endfeet. In PVR retinas, there is a mislocation of Kir channel proteins, with Kir4.1 immunoreactivity detectable in Müller cell fibers throughout the whole retina, and a decrease of immunoreactivity in the cellular endfeet. Real-time PCR analysis revealed no alteration of the Kir4.1 mRNA levels in PVR retinas as compared to the controls but a slight decrease in Kir2.1 mRNA. Western blotting showed no difference in the Kir4.1 protein content between control and PVR retinas. The data suggest that proliferative gliosis in the retina is associated with a functional inactivation of glial Kir channels that is not caused by a downregulation of the channel proteins but is associated with their mislocation in the cell membrane.     

Phenalinolactones A-D, terpenoglycoside antibiotics from Streptomyces sp. Tü 6071

Four new terpenoglycoside antibiotics, phenalinolactones A-D were isolated from Streptomyces sp. Tü 6071. The structures were elucidated on the basis of detailed NMR and MS analyses. Phenalinolactones combine a diterpenoid tricycle, a 2,3,6-trideoxysugar, a pyrrole-carboxylic acid and an uncommonly oxidized unsaturated γ-lactone in a unique manner. Phenalinolactones show an inhibitory activity against gram-positive bacteria.     

Changes in membrane conductance play a pathogenic role in osmotic glial cell swelling in detached retinas

Detachment of the neural retina from the pigment epithelium may be associated with tissue edema; however, the mechanisms of fluid accumulation are not understood. Because retinal detachment is usually not accompanied by vascular leakage, we investigated whether the osmotic swelling characteristics of retinal glial (Müller) cells are changed after experimental detachment of the porcine retina. Osmotic stress, induced by application of a hypotonic bath solution to retinal slices, caused swelling of Müller cell bodies in 7-day-detached retinas, but no swelling was inducible in slices of control retinas. Müller cell somata in slices of retinal areas that surround local detachment in situ also showed osmotic swelling, albeit at a smaller amplitude. The amplitude of osmotic Müller cell swelling correlated with the decrease in the K⁺ conductance, suggesting a causal relationship between both gliotic alterations. Further factors implicated in Müller cell swelling were inflammatory mediators and oxidative stress. We propose that a dysregulation of the ion and water transport through Müller cells may impair the fluid absorption from the retinal tissue, resulting in chronic fluid accumulation after detachment. This knowledge may lead to a better understanding of the mechanisms involved in retinal degeneration after detachment.