Heterozygous GBA D409V and ATP13a2 mutations do not exacerbate pathological α-synuclein spread in the prodromal preformed fibrils model in young mice.

Autophagic dysregulation and lysosomal impairment have been implicated in the pathogenesis of Parkinson's disease, partly due to the identification of mutations in multiple genes involved in these pathways such as GBA, SNCA, ATP13a2 (also known as PARK9), TMEM175 and LRRK2. Mutations resulting in lysosomal dysfunction are proposed to contribute to Parkinson's disease by increasing α-synuclein levels, that in turn may promote aggregation of this protein. Here, we used two different genetic models-one heterozygous for a mutated form of the GBA protein (D409V), and the other heterozygous for an ATP13a2 loss-of-function mutation, to test whether these mutations exacerbate the spread of α-synuclein pathology following injection of α-synuclein preformed fibrils in the olfactory bulb of 12-week-old mice. Contrary to our hypothesis, we found that mice harboring GBA D409V+/- and ATP13a2+/- mutations did not have exacerbated behavioral impairments or histopathology (α-synuclein, LAMP2, and Iba1) when compared to their wildtype littermates. This indicates that in the young mouse brain, neither the GBA D409V mutation or ATP13a2 loss-of-function mutation accelerate the spread of α-synuclein pathology. As a consequence, we postulate that these mutations increase Parkinson's disease risk only by acting in one of the initial, upstream events in the Parkinson's disease pathogenic process. Further, the mutations, and the molecular pathways they impact, appear to play a less important role once the pathogenic process has been triggered and therefore do not specifically influence α-synuclein pathology spread.

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

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.

Serum Amyloid P Component Ameliorates Neurological Damage Caused by Expressing a Lysozyme Variant in the Central Nervous System of Drosophila melanogaster.

Lysozyme amyloidosis is a hereditary disease in which mutations in the gene coding for lysozyme leads to misfolding and consequently accumulation of amyloid material. To improve understanding of the processes involved we expressed human wild type (WT) lysozyme and the disease-associated variant F57I in the central nervous system (CNS) of a Drosophila melanogaster model of lysozyme amyloidosis, with and without co-expression of serum amyloid p component (SAP). SAP is known to be a universal constituent of amyloid deposits and to associate with lysozyme fibrils. There are clear indications that SAP may play an important role in lysozyme amyloidosis, which requires further elucidation. We found that flies expressing the amyloidogenic variant F57I in the CNS have a shorter lifespan than flies expressing WT lysozyme. We also identified apoptotic cells in the brains of F57I flies demonstrating that the flies' neurological functions are impaired when F57I is expressed in the nerve cells. However, co-expression of SAP in the CNS prevented cell death and restored the F57I flies' lifespan. Thus, SAP has the apparent ability to protect nerve cells from damage caused by F57I. Furthermore, it was found that co-expression of SAP prevented accumulation of insoluble forms of lysozyme in both WT- and F57I-expressing flies. Our findings suggest that the F57I mutation affects the aggregation process of lysozyme resulting in the formation of cytotoxic species and that SAP is able to prevent cell death in the F57I flies by preventing accumulation of toxic F57I structures.