Sue, C. | bioRxiv Science

bioRxiv2025

Transgenic A53T mice have astrocytic α-synuclein aggregates in dopamine and striatal regions

AimsParkinsons disease is considered biologically a neuronal -synuclein disease, largely ignoring the more widespread -synuclein deposition that occurs in astrocytes, with the aim of this study to identify whether astrocytes accumulate small -synuclein aggregates before or after neurons. MethodsFixed serial midbrain and striatal sections from M83 A53T transgenic mouse model of Parkinsons disease and wild-type controls were histologically processed for multiplex labelling of -synuclein and astrocytic markers and astrocyte quantitation performed on digital images using QuPath software. ResultsThe density of astrocytes within the substantia nigra pars compacta was approximately 30% greater compared with other sampled regions (P<0.005). Small aggregates of -synuclein were observed in astrocytic processes, including in wild-type mice where a quarter of all astrocytes had an obvious -synuclein aggregate. Compared to wild-type, A53T transgenic astrocytes had significantly enlarged somas (P<0.001) with more processes (P<0.001) consistent with a reactive phenotype. The A53T transgenic mice had more than double the numbers of astrocytes (P<0.001) and 2.5 times more astrocytes with -synuclein aggregates compared to wild-type mice (P<0.001). ConclusionsThese data suggest that small -synuclein aggregates are normally cleared by astrocytes and that the substantia nigra pars compacta requires more astrocytic support for this function than other midbrain dopaminergic regions or the striatum. This adds another vulnerability factor to those already known for the substantia nigra with early deficits in clearance of small -synuclein aggregates by astrocytes associated with an increased astrocytic reactivity in the A53T transgenic mouse model. Key PointsO_LIThe substantia nigra pars compacta contains a higher density of astrocytes than the ventral tegmental area or striatum, indicating a greater reliance on astrocytic function and a greater vulnerability to astrocyte dysfunction C_LIO_LISmall aggregates of -synuclein were observed in wild-type midbrain and striatal astrocytes, indicating normal clearance of -synuclein by these astrocytes C_LIO_LIMidbrain and striatal astrocytes from A53T transgenic astrocytes have more than double the number of astrocytes and more astrocytes containing -synuclein aggregates which have a reactive morphological phenotype. C_LI

neuroscience↗

bioRxiv2024

Dopamine and cortical iPSC-derived neurons with different Parkinsonian mutations show variation in lysosomal and mitochondrial dysfunction: implications for protein deposition versus selective cell loss

BackgroundMutations causing Parkinsons disease (PD) give diverse pathological phenotypes whose cellular correlates remain to be determined. For example, those with PRKN loss of function mutations have significantly earlier selective vulnerability of dopamine neurons, those with SNCA mutations have increased alpha-synuclein deposition, while those with LRRK2 mutations have additional deposition of tau. Yet all three mutation types are implicated in mitochondrial and/or lysosomal dysfunction. Direct comparison of cell models with these mutations would clarify the relative cellular dysfunctions associated with these different pathological phenotypes. MethodsAn unbiased high-content imaging platform using orthogonal probes to assess both lysosomal and mitochondrial dysfunction, along with alpha-synuclein and tau protein deposition was established using induced pluripotent stem cell (iPSC) derived cortical and ventral midbrain neurons. Three mutation types, SNCA A53T, LRRK2 R1441G and PRKN loss of function (lof), were selected as exemplars of divergent PD pathological phenotypes and compared to each other, and to control iPSC from subjects without PD. ResultsDifferent PD mutations caused cell type specific dysfunctions, likely to impact on both selective neuronal vulnerability and the pathologies observed in PD. Comparison of dopamine neurons identified that both lysosomal and mitochondrial dysfunction were predominant with PRKN lof mutations, whereas immunofluorescent staining revealed that SNCA A53T and LRRK2 R1441G mutations had increased tau deposition. In contrast, cortical neurons with SNCA and LRRK2 mutations both had mitochondrial and autophagy impairments without protein deposition, with LRRK2 cells additionally showing decreased glucocerebrosidase activity and increased alpha-synuclein phosphorylation. ConclusionsLysosomal and mitochondrial dysfunction are predominant in dopamine neurons with PRKN lof mutations, and may drive the early selective loss of dopamine neurons in PRKN mutation carriers. More subtle cellular abnormalities in the SNCA A53T cell lines are likely to predispose to alpha-synuclein aggregation and tau protein deposition over time. The LRRK2 R1441G may also predispose to tau deposition, but despite substantial lysosomal dysfunction with increased alpha-synuclein phosphorylation, pathological alpha-synuclein accumulations were not observed. Understanding the mechanistic differences in how lysosomal and mitochondrial dysfunction impact on PD pathogenesis in different disease subtypes may be important for therapeutic development.

neuroscience↗