Ammonia induces amyloidogenesis in astrocytes by promoting amyloid precursor protein translocation into the endoplasmic reticulum

Hyperammonemia is known to cause various neurological dysfunctions such as seizures and cognitive impairment. Several studies have suggested that hyperammonemia may also be linked to the development of Alzheimer’s disease (AD). However, the direct evidence for a role of ammonia in the pathophysiology of AD remains to be discovered. Herein, we report that hyperammonemia increases the amount of mature amyloid precursor protein (mAPP) in astrocytes, the largest and most prevalent type of glial cells in the central nervous system that are capable of metabolizing glutamate and ammonia, and promotes amyloid beta (Aβ) production. We demonstrate the accumulation of mAPP in astrocytes was primarily due to enhanced endocytosis of mAPP from the plasma membrane. A large proportion of internalized mAPP was targeted not to the lysosome, but to the endoplasmic reticulum, where processing enzymes β-secretase BACE1 (beta-site APP cleaving enzyme 1) and γ-secretase presenilin-1 are expressed, and mAPP is cleaved to produce Aβ. Finally, we show the ammonia-induced production of Aβ in astrocytic endoplasmic reticulum was specific to Aβ42, a principal component of senile plaques in AD patients. Our studies uncover a novel mechanism of Aβ42 production in astrocytes and also provide the first evidence that ammonia induces the pathogenesis of AD by regulating astrocyte function.     

SGIP1alpha is an endocytic protein that directly interacts with phospholipids and Eps15

SGIP1 has been shown to be an endophilin-interacting protein that regulates energy balance, but its function is not fully understood. Here, we identified its splicing variant of SGIP1 and named it SGIP1alpha. SGIP1alpha bound to phosphatidylserine and phosphoinositides and deformed the plasma membrane and liposomes into narrow tubules, suggesting the involvement in vesicle formation during endocytosis. SGIP1alpha furthermore bound to Eps15, an important adaptor protein of clathrin-mediated endocytic machinery. SGIP1alpha was colocalized with Eps15 and the AP-2 complex. Upon epidermal growth factor (EGF) stimulation, SGIP1alpha was colocalized with EGF at the plasma membrane, indicating the localization of SGIP1alpha at clathrin-coated pits/vesicles. SGIP1alpha overexpression reduced transferrin and EGF endocytosis. SGIP1alpha knockdown reduced transferrin endocytosis but not EGF endocytosis; this difference may be due to the presence of redundant pathways in EGF endocytosis. These results suggest that SGIP1alpha plays an essential role in clathrin-mediated endocytosis by interacting with phospholipids and Eps15.     

Structure and expression of human B cell stimulatory factor-2 (BSF-2/IL-6) gene.

The chromosomal DNA segment of human B cell stimulatory factor-2 (BSF-2/IL-6) was isolated and characterized by nucleotide sequence analysis. The human BSF-2/IL-6 gene consists of five exons and four introns and its organization shows a distinctive similarity to granulocyte colony-stimulating factor gene. The two genes have the same number of exons and introns and the size of each exon is strikingly similar. The BSF-2/IL-6 mRNA was found to be constitutively expressed in a human T cell leukemia virus-1 transformed T cell line, TCL-Na1, a bladder cell carcinoma line, T24, and an amnion derived cell line, FL. The BSF-2/IL-6 mRNA was also found to be inducible with interleukin-1 beta in an astrocytoma line, U373 and a glioblastoma line, SK-MG-4. S1 mapping and primer extension analyses showed the presence of multiple initiation sites and the preferential utilization of a different initiation site for each individual tissue tested.     

Cell-penetrating peptide-conjugated lipid nanoparticles for siRNA delivery

Lipid nanoparticles (LNP) modified with cell-penetrating peptides (CPP) were prepared for the delivery of small interfering RNA (siRNA) into cells. Lipid derivatives of CPP derived from protamine were newly synthesized and used to prepare CPP-decorated LNP (CPP-LNP). Encapsulation of siRNA into CPP-LNP improved the stability of the siRNA in serum. Fluorescence-labeled siRNA formulated in CPP-LNP was efficiently internalized into B16F10 murine melanoma cells in a time-dependent manner, although that in LNP without CPP was hardly internalized into these cells. In cells transfected with siRNA in CPP-LNP, most of the siRNA was distributed in the cytoplasm of these cells and did not localize in the lysosomes. Analysis of the endocytotic pathway indicated that CPP-LNP were mainly internalized via macropinocytosis and heparan sulfate-mediated endocytosis. CPP-LNP encapsulating siRNA effectively induced RNA interference-mediated silencing of reporter genes in B16F10 cells expressing luciferase and in HT1080 human fibrosarcoma cells expressing enhanced green fluorescent protein. These data suggest that modification of LNP with the protamine-derived CPP was effective to facilitate internalization of siRNA in the cytoplasm and thereby to enhance gene silencing.     

Coordinated Regulation of the Genes Participating in Starch Biosynthesis by the Rice Floury-2 Locus

The recessive floury-2 (flo-2) locus of rice (Oryza sativa L.), which is located on chromosome 4, causes a strong reduction in expression of the gene encoding an isoform of branching enzyme RBE1 in immature seeds 10 d after flowering. Mapping of the RBE1 gene demonstrated the localization on rice chromosome 6, suggesting that the wild-type Floury-2 (Flo-2) gene regulates RBE1 gene expression in trans. However, reduced expression of the genes encoding some other starch-synthesizing enzymes, including another isoform of branching enzyme RBE3 and granule-bound starch synthase, was also found in the flo-2 seeds. In spite of the low level of RBE1 gene expression in the immature seeds of the flo-2 mutants, the RBE1 gene was equally expressed in the leaves of the wild type and flo-2 mutants. Thus, these results imply that the Flo-2 gene may co-regulate expression of some of the genes participating in starch synthesis possibly in a developing seed-specific manner.     

Physiological polyspermy: Selection of a sperm nucleus for the development of diploid genomes in amphibians

The union between a sperm and an egg nucleus in egg fertilization is necessary to mix genetic materials to create a new diploid genome for the next generation. In most animals, only one sperm is incorporated into the egg (monospermy), but several animals exhibit physiological polyspermy in which several sperms enter the egg during normal fertilization. However, only one sperm nucleus forms the zygote nucleus with the egg nucleus, even in a polyspermic egg. The cellular and molecular mechanisms involved in the selection of sperm nuclei in the egg cytoplasm have been well investigated in urodele amphibians. The principal sperm nucleus develops a larger sperm aster and contacts the egg nucleus to form a zygote nucleus, whereas other accessory sperm nuclei are unable to approach the egg nucleus. The diploid zygote nucleus induces cleavage and participates in embryonic development, whereas the accessory sperm nuclei undergo pyknosis and degenerate. We propose several models to account for the mechanisms of the selection of one sperm nucleus and the degeneration of accessory sperm nuclei. The roles of physiological polyspermy in animal reproduction are discussed by comparison with other polyspermic species.     

Cleome hassleriana plants fully support the development and reproduction of Nesidiocoris tenuis

BioControl - Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is a zoophytophagous predator that feeds on plants as well as prey. Several non-crop host plant species have been used to maintain...