Aβ (amyloid beta peptide) is an important contributor to Alzheimer’s disease (AD). We modeled Aβ toxicity in yeast by directing the peptide to the secretory pathway. A genome-wide screen for toxicity modifiers identified the yeast homolog of phosphatidylinositol binding clathrin assembly protein (PICALM) and other endocytic factors connected to AD whose relationship to Aβ was previously unknown. The factors identified in yeast modified Aβ toxicity in glutamatergic neurons of Caenorhabditis elegans and in primary rat cortical neurons. In yeast, Aβ impaired the endocytic trafficking of a plasma membrane receptor, which was ameliorated by endocytic pathway factors identified in the yeast screen. These links between Aβ, endocytosis, and human AD risk factors can be ascertained using yeast as a model system.

Transforming growth factor-,8 (TGF-/1) is synthesized as latent complexes with high molecular weights. The large latent complex of TGF-/1 in platelets is composed of three components, i.e. the mature TGF-/1, which is non-covalently associated with a disulphide-bonded complex of the N-terminal remnant of the TGF-/1 precursor (TGF-/1-latency associated peptide) and the latent TGF-/1 binding protein (LTBP). The TGF-31-latency associated peptide is sufficient for the latency of TGF-/1, whereas the functions of LTBP remain to be elucidated. In a human erythroleukemia cell line, HEL, the production of the latent form of TGF-/31 was induced more than 100-fold by phorbol 12-myristate 13-acetate. Analysis by Northern blotting revealed that both the TGF-,B1 precursor and LTBP were induced in a coordinated fashion. Analysis by immunoprecipitation using antibodies against LTBP and the TGF-/1 precursor dimer revealed that LTBP has a molecular size of 205 kd under reducing conditions in this cell type, i.e. similar to that from cells transfected with cDNA for LTBP, but larger than the platelet form (125-160 kd). Limited tryptic digestion of LTBP in HEL cells and analysis by SDS-PAGE showed protein bands of similar sizes to those of platelet LTBP, suggesting that the difference in molecular sizes of LTBP involves cell-specific processing. The biosynthesis of the latent TGF-,B1 was studied by pulsechase analysis. LTBP became covalently associated with the TGF-/31 precursor within 15 min after synthesis in this cell line. Secretion of the large latent TGF-/1 complex was observed as early as 30 min after the synthesis of LTBP; at the same time, a free form of LTBP not bound to the TGF-/31 precursor was seen. In contrast, the TGF-/1 precursor remained inside the cells in an unprocessed form for a longer time period and the TGF-/1 precursor dimer without LTBP was secreted only very slowly. Furthermore, the results of partial tryptic digestion of this molecule suggested that it contained improper disulphide bonding. These results suggest that LTBP plays a critical role in the assembly and secretion of the latent TGF-/1.

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Pro-inflammatory S100A9 protein is increasingly recognized as an important contributor to inflammation-related neurodegeneration. Here, we provide insights into S100A9 specific mechanisms of action in Alzheimer’s disease (AD). Due to its inherent amyloidogenicity S100A9 contributes to amyloid plaque formation together with Aβ. In traumatic brain injury (TBI) S100A9 itself rapidly forms amyloid plaques, which were reactive with oligomer-specific antibodies, but not with Aβ and amyloid fibrillar antibodies. They may serve as precursor-plaques for AD, implicating TBI as an AD risk factor. S100A9 was observed in some hippocampal and cortical neurons in TBI, AD and non-demented aging. In vitro S100A9 forms neurotoxic linear and annular amyloids resembling Aβ protofilaments. S100A9 amyloid cytotoxicity and native S100A9 pro-inflammatory signaling can be mitigated by its co-aggregation with Aβ, which results in a variety of micron-scale amyloid complexes. NMR and molecular docking demonstrated transient interactions between native S100A9 and Aβ. Thus, abundantly present in AD brain pro-inflammatory S100A9, possessing also intrinsic amyloidogenic properties and ability to modulate Aβ aggregation, can serve as a link between the AD amyloid and neuroinflammatory cascades and as a prospective therapeutic target.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-013-1208-4) contains supplementary material, which is available to authorized users.