Immune reactivity and immunosuppressive intervention in experimental nephritis. II. Effect of TLI on the course of two models of nephritis in the inbred rat

Fractionated high-dose (3400 rad) total lymphoid irradiation (TLI) induces a unique and prolonged state of immunologic unresponsiveness. The therapeutic efficacy of TLI in immune glomerular disease was explored in two animal models: the accelerated autologous form of nephrotoxic serum nephritis (AA-NTSN) and autologous immune complex nephritis (AICN). LEW rats with established AA-NTSN, subjected to TLI, manifest decreased levels of circulating antibody to the heterologous (sheep) immunoglobulin G (0.4 +/- 0.2 vs 1.2 +/- 0.3 mg/ml, mean +/- SE respectively, p less than 0.01) early post TLI in association with a reduction in histopathology and albuminuria (6.7 +/- 2.2 vs control 19.6 +/- 5.4 mg/24 hr, mean +/- SE, p less than 0.02). Administration of TLI to rats with established AICN effected significant (p less than 0.001) reduction in albuminuria (162 +/- 30 vs 315 +/- 27), serum creatinine (p less than 0.005), and the incidence of lipemia (p less than 0.01) vs controls. Adoptive transfer studies provided no evidence that the sustained beneficial effect of TLI in AICN was suppressor cell mediated. Thus, the observed therapeutic efficacy of TLI in the treatment of experimental nephritis, shown to be related to a reduction in the level of circulating antibody in AA-NTSN, provides a new model system for study of immunity and immunosuppression in primary glomerular disease.     

Ceramide sphingolipid signaling mediates Tumor Necrosis Factor (TNF)-dependent toxicity via caspase signaling in dopaminergic neurons

Background

The A?? peptide that accumulates in Alzheimer??s disease (AD) is derived from amyloid precursor protein (APP) following proteolysis by ??- and ??-secretases. Substantial evidence indicates that alterations in APP trafficking within the secretory and endocytic pathways directly impact the interaction of APP with these secretases and subsequent A?? production. Various members of the low-density lipoprotein receptor (LDLR) family have been reported to play a role in APP trafficking and processing and are important risk factors in AD. We recently characterized a distinct member of the LDLR family called LDLR-related protein 10 (LRP10) that shuttles between the trans-Golgi Network (TGN), plasma membrane (PM), and endosomes. Here we investigated whether LRP10 participates in APP intracellular trafficking and A?? production.

Results

In this report, we provide evidence that LRP10 is a functional APP receptor involved in APP trafficking and processing. LRP10 interacts directly with the ectodomain of APP and colocalizes with APP at the TGN. Increased expression of LRP10 in human neuroblastoma SH-SY5Y cells induces the accumulation of mature APP in the Golgi and reduces its presence at the cell surface and its processing into A??, while knockdown of LRP10 expression increases A?? production. Mutations of key motifs responsible for the recycling of LRP10 to the TGN results in the aberrant redistribution of APP with LRP10 to early endosomes and a concomitant increase in APP ??-cleavage into A??. Furthermore, expression of LRP10 is significantly lower in the post-mortem brain tissues of AD patients, supporting a possible role for LRP10 in AD.

Conclusions

The present study identified LRP10 as a novel APP sorting receptor that protects APP from amyloidogenic processing, suggesting that a decrease in LRP10 function may contribute to the pathogenesis of Alzheimer??s disease.     

Structures of modified eEF2 80S ribosome complexes reveal the role of GTP hydrolysis in translocation

On the basis of kinetic data on ribosome protein synthesis, the mechanical energy for translocation of the mRNA-tRNA complex is thought to be provided by GTP hydrolysis of an elongation factor (eEF2 in eukaryotes, EF-G in bacteria). We have obtained cryo-EM reconstructions of eukaryotic ribosomes complexed with ADP-ribosylated eEF2 (ADPR-eEF2), before and after GTP hydrolysis, providing a structural basis for analyzing the GTPase-coupled mechanism of translocation. Using the ADP-ribosyl group as a distinct marker, we observe conformational changes of ADPR-eEF2 that are due strictly to GTP hydrolysis. These movements are likely representative of native eEF2 motions in a physiological context and are sufficient to uncouple the mRNA-tRNA complex from two universally conserved bases in the ribosomal decoding center (A1492 and A1493 in Escherichia coli) during translocation. Interpretation of these data provides a detailed two-step model of translocation that begins with the eEF2/EF-G binding-induced ratcheting motion of the small ribosomal subunit. GTP hydrolysis then uncouples the mRNA-tRNA complex from the decoding center so translocation of the mRNA-tRNA moiety may be completed by a head rotation of the small subunit.     

Clustering of loci controlling species differences in male chemical bouquets of sympatric Heliconius butterflies

The degree to which loci promoting reproductive isolation cluster in the genome—that is, the genetic architecture of reproductive isolation—can influence the tempo and mode of speciation. Tight linkage between these loci can facilitate speciation in the face of gene flow. Pheromones play a role in reproductive isolation in many Lepidoptera species, and the role of endogenously produced compounds as secondary metabolites decreases the likelihood of pleiotropy associated with many barrier loci. Heliconius butterflies use male sex pheromones to both court females (aphrodisiac wing pheromones) and ward off male courtship (male‐transferred antiaphrodisiac genital pheromones), and it is likely that these compounds play a role in reproductive isolation between Heliconius species. Using a set of backcross hybrids between H. melpomene and H. cydno, we investigated the genetic architecture of putative male pheromone compound production. We found a set of 40 significant quantitative trait loci (QTL) representing 33 potential pheromone compounds. QTL clustered significantly on two chromosomes, chromosome 8 for genital compounds and chromosome 20 for wing compounds, and chromosome 20 was enriched for potential pheromone biosynthesis genes. There was minimal overlap between pheromone QTL and known QTL for mate choice and color pattern. Nonetheless, we did detect linkage between a QTL for wing androconial area and optix, a color pattern locus known to play a role in reproductive isolation in these species. This tight clustering of putative pheromone loci might contribute to coincident reproductive isolating barriers, facilitating speciation despite ongoing gene flow.     

Montane Meadows: A Soil Carbon Sink or Source?

Ecosystems - As the largest biogeochemically active terrestrial reserve of carbon (C), soils have the potential to either mitigate or amplify rates of climate change. Ecosystems with large C stocks...     

TAM receptor ligands in lupus: Protein S but not Gas6 levels reflect disease activity in systemic lupus erythematosus

Introduction  

The TAM (tyro 3, axl, mer) kinases are key regulators of innate immunity and are important in the phagocytosis of apoptotic cells. Gas6 and protein S are ligands for these TAM kinases and bind to phosphatidyl serine residues exposed during apoptosis. In animal models, absence of TAM kinases is associated with lupus-like disease. To test whether human systemic lupus erythematosus (SLE) patients might have deficient levels of TAM ligands, we measured Gas 6 and protein S levels in SLE.     

Displacement of alpha-actinin from the NMDA receptor NR1 C0 domain By Ca2+/calmodulin promotes CaMKII binding

Ca2+ influx through the N-methyl-d-aspartate (NMDA)-type glutamate receptor triggers activation and postsynaptic accumulation of Ca2+/calmodulin-dependent kinase II (CaMKII). CaMKII, calmodulin, and alpha-actinin directly bind to the short membrane proximal C0 domain of the C-terminal region of the NMDA receptor NR1 subunit. In a negative feedback loop, calmodulin mediates Ca2+-dependent inactivation of the NMDA receptor by displacing alpha-actinin from NR1 C0 upon Ca2+ influx. We show that Ca2+-depleted calmodulin and alpha-actinin simultaneously bind to NR1 C0. Upon addition of Ca2+, calmodulin dislodges alpha-actinin. Either the N- or C-terminal half of calmodulin is sufficient for Ca2+-induced displacement of alpha-actinin. Whereas alpha-actinin directly antagonizes CaMKII binding to NR1 C0, the addition of Ca2+/calmodulin shifts binding of NR1 C0 toward CaMKII by displacing alpha-actinin. Displacement of alpha-actinin results in the simultaneous binding of calmodulin and CaMKII to NR1 C0. Our results reveal an intricate mechanism whereby Ca2+ functions to govern the complex interactions between the two most prevalent signaling molecules in synaptic plasticity, the NMDA receptor and CaMKII.