Serum amyloid P component promotes formation of distinct aggregated lysozyme morphologies and reduces toxicity in Drosophila flies expressing F57I lysozyme

Abstract

Many conflicting reports about the involvement of serum amyloid P component (SAP) in amyloid diseases have been presented over the years; SAP is known to be a universal component of amyloid aggregates but it has been suggested that it can both induce and suppress amyloid formation. By using our Drosophila model of systemic lysozyme amyloidosis, SAP has previously been shown to reduce the toxicity induced by the expression of the disease-associated lysozyme variant, F57I, in the Drosophila central nervous system. This study further investigates the involvement of SAP in modulating lysozyme toxicity using histochemistry and spectral analyses on the double transgenic WT and F57I lysozyme flies to probe; i) formation of aggregates, ii) morphological differences of the aggregated lysozyme species formed in the presence or absence of SAP, iii) location of lysozyme and iv) co-localisation of lysozyme and SAP in the fly brain. We found that SAP can counteract the toxicity (measured by the reduction in the median survival time) induced by F57I lysozyme by converting toxic F57I species into less toxic amyloid-like structures, as reflected by the spectral changes that p-FTAA undergoes when bound to lysozyme deposits in F57I-F57I-SAP flies as compared to F57I-F57I flies. Indeed, when SAP was introduced to in vitro lysozyme fibril formation, the endpoint fibrils had enhanced ThT fluorescence intensity as compared to lysozyme fibrils alone. This suggests that a general mechanism for SAP's role in amyloid diseases may be to promote the formation of stable, amyloid-like fibrils, thus decreasing the impact of toxic species formed along the aggregation pathway.

A guide to studying protein aggregation

“…However, their inability to identify the pre-fibrillar species and the growing interest in identifying non-fibrillar oligomers led to the development of negatively charged luminescent conjugated oligothiophenes (LCOs), like pFTAA which identifies several intermediate species occurring during protein aggregation, including the soluble pre-fibrillar and oligomeric species, amorphous aggregates, as well as mature fibrillar structures [163]. pFTAA has become a popular amyloid-specific dye for investigating amyloid formation properties [27,29,45,128], such as studying the inducing effect of iron, lipopolysaccharides and lipoteichoic acids during plasma protein aggregation [164], or identifying distinct aggregating populations [165][166][167][168][169].…”

Phenotypic heterogeneity and diagnostic features of transthyretin amyloidosis with polyneuropathy

“…До 10-15 % общей массы тканевого амилоида составляет фибриллярный белок P (Р-компонент), идентичный при всех вариантах амилоидоза. Его роль до конца не изучена [4,6,7]. Сегодня известно около 36 белков-предшественников, способных к формированию амилоида при определенных условиях, что определяет патогенез и течение болезни [8].…”

Endogenous Human Proteins Interfering with Amyloid Formation

“…For example, the total load of the Aβ-amyloid deposits in the brain of an AD patient corresponds to only a few milligrams [15], nevertheless causing neuroinflammation and massive degeneration of neuronal cells. In contrast, lysozymeamyloidosis may generate a total load of amyloid corresponding to several kilograms [16], but the pathological mechanism is rather a rupture of the organs due to a high load of aggregates than an acute cytotoxic effect.…”

“…For example, the total load of the Aβ-amyloid deposits in the brain of an AD patient corresponds to only a few milligrams [15], nevertheless causing neuroinflammation and massive degeneration of neuronal cells. In contrast, lysozymeamyloidosis may generate a total load of amyloid corresponding to several kilograms [16], where the monomers form soluble oligomeric nucleus during the lag phase, then assemble into larger prefibrillar structures followed by elongation and subsequently a saturation phase where mature fibrils are formed. Regarding some amyloid proteins, mature fibrils can serve as a template for the formation of new nuclei, resulting in a rate-enhancing process known as surface catalyzed secondary nucleation.…”