View Program - 63rd Annual Drosophila Research Conference

Amyloidogenesis, the aggregation of soluble proteins into insoluble fibrils, has multiple biological functions in both health and disease. It is critically important in neurodegenerative disorders; for example, aggregations of A-beta peptides, cleaved products of Amyloid Precursor Protein (APP), form plaques in Alzheimer’s Disease (AD). Mutated Transforming Growth Factor-Beta-Induced (TGFBI), an extracellular fibrillar protein, assembles into amyloid that leads to corneal dystrophies. Proteins also aggregate naturally, sometimes via amyloidogenesis, for example, when peptide hormones condense into insoluble, inert dense-core granules (DCGs), which are stored in secretory vesicles until release. Understanding the cell biology that drives these normal and pathological processes could reveal the key mechanisms that distinguish them, but visualising these events as they take place in cells and tissues is challenging. Here we describe the development of a new cellular model for DCG biogenesis, the Drosophila prostate-like secondary cell (SC). These cells have highly enlarged (5 micron diameter) DCG compartments, permitting DCG assembly to be followed by light and fluorescence microscopy in living tissue and in real-time. Remarkably, the rapid formation of DCGs requires the complementary activities of the fly homologues of TGFBI, called MFAS, and APP, called APPL. While DCGs cannot form in the absence of MFAS, several smaller DCGs are often made in a single compartment in the absence of APPL, but they frequently cannot coalesce into a single large DCG, as happens in normal cells. Expressing a pathological, amyloidogenic form of human A-beta or TGFBI in SCs alters MFAS assembly in DCGs and can suppress DCG disassembly when secreted. Genetic manipulations that mirror changes seen in AD patients also modulate DCG biogenesis and disassembly. Interestingly, intraluminal vesicles (ILVs), which are secreted as exosomes, are formed in SC DCG compartments. We show they are also required for assembly of a large DCG, consistent with recent findings linking ILVs and exosomes to amyloidogenesis. Our studies, therefore, demonstrate that both APP and TGFBI have physiological, as well as pathological, modes of rapid protein aggregation, which can uniquely be distinguished by real-time fluorescence imaging in living SCs. We are employing this model to screen genetic modifiers of pathological versus physiological amyloidogenesis, which might highlight new ways to target amyloidogenic diseases.

Homologues of the human disease-associated amyloidogenic proteins APP and TGFBI are required for physiological protein aggregation in Drosophila secondary cells

**Homologues of the human disease-associated amyloidogenic proteins APP and TGFBI are required for physiological protein aggregation in Drosophila secondary cells**