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  Glial and vascular contributions to neurodegenerative diseases
   effects at any of the dosages used. Our results underscore the need to consider inter-species differences in senolytic interventions which may impact therapeutic use of these compounds in humans.
  OP19
Activation of D2Rs ameliorates the dysfunction of microglia in human LRRK2-R1441G transgenic mice
Yuanxin Chen1, Lianteng Zhi1, Jingyu Zhao1, Hui Zhang1
1Thomas Jefferson University, Philadelphia, USA
   OP18
Internalized alpha-synuclein fibrils are rapidly degraded by glial cells but stably accumulate as C-terminal truncated form in neurons: Relevance to pathogenesis of alpha-synucleinopathy
Razaul Karim1, Emilie Gasparini1, Elizabeth Tiegs1,
Hector Martell Martinez1, Abdur Rashid1, Balvindar Singh1, Michael Lee1
1University Of Minnesota, Minneapolis, USA
 Background: Parkinson’s disease (PD) and other α-synucleinopathies are characterized by the accumulation of α-synuclein (αS) aggregates. Studies indicate that αS pathology can spread via the cell-to-cell transmission of αS pathology. To better understand how various brain cells contribute to the spreading of αS pathology, we examined the metabolism of αS pre-formed fibril (PFFs) by neurons and glial cells (microglia, astrocytes, and oligodendrocytes).
Materials and Methods: Cultured neurons, neuronal cells, and nonneuronal cells were treated with αS PFF. Status of internalize αS PFF was evaluated at various times using immunoblot analysis and confocal immunofluorescence microscopy.
Results: While neurons efficiently internalize both αS monomer and PFF, αS monomer is rapidly degraded. Following internalization of αS PFF the full-length αS (αSFL) rapidly disappears within 6 hours following αS PFF uptake but truncated αS accumulates with the half-life of over 48 hours. Epitope mapping and fractionation studies indicate that in αS PFF is truncated at C-terminal region (αSΔC) and remains insoluble/ aggregated. In contrast, microglia and astrocytes rapidly metabolize αS PFF where the half live of αS PFF in these glial cells are ~5 hours. The differential processing of αS can be recapitulated in cell lines as differentiated CLU neuronal cell lines show stable accumulation of truncated αS while undifferentiated cells rapidly metabolize αS. Immunolocalization and subcellular fractionation studies show that αS PFF is initially localized to endosomes followed by lysosomes. Lysosomal is largely responsible for degradation of internalized αS PFF as the inhibition of lysosomal function leads to stabilization of αS in all cell types.
Conclusions: Our studies show that neurons do not efficiently metabolize internalized αS aggregates and generates potentially aggregation prone truncated αS. In contrast, glial cells may protect neurons from αS aggregates by rapidly clearance of αS aggregates. Age or inflammation related abnormalities in glial lysosomal function may promote neuronal α-synucleinopathy.
Background: An emerging concept in the Parkinson’s disease (PD) research is that the immune system plays a key role in the progressive death of dopamine neurons. Several recent studies highlight the involvement of leucine-rich repeat kinase 2 (LRRK2), the most prevalent genetic cause in both familial and sporadic PD in driving the connection between microglia dysfunction and PD susceptibility. Here, we examined the effects of pathogenic R1441G mutation on microglia functions and contributions to the pathogenesis of PD.
Materials and Methods: A bacterial artificial chromosome (BAC) transgenic mouse model overexpressing human LRRK2-R1441G has been shown to recapitulate robust motor behavioral, neurochemical and pathological features of PD. We crossed the human LRRK2- R1441G transgenic mice with the Cx3cr1–EGFP mice and investigated the function and dynamics of microglia with time-lapse two-photon imaging in awake mice in vivo and in acute brain slices ex vivo.
Results: Our study demonstrates that the R1441G mutation increases the number of activated microglia and microglial polarization in the dorsal striatum. The microglial motility and its response to focal injury is decreased in the LRRK2-R1441G transgenic mice compared to their wild-type controls. Meanwhile, microglial processes retract faster and extend slower in microglia carrying the R1441G mutation. Given the neuroprotective role of dopamine D2 receptors (D2Rs) and aberrant D2R signaling in this mouse model, we administered a D2R agonist, quinpirole, to the R1441G transgenic mice and found that quinpirole ameliorated all the deficits of microglia.
Discussion and Conclusions: Our results provide the first piece of evidence of the modulation of microglia mobility and response induced by pathogenic LRRK2 mutations. D2R activation may suppress neuroinflammation and neurodegeneration. This work provides important insights of the contribution of microglia to the pathogenesis of PD and opens new avenues for therapeutic intervention by targeting microglia-mediated immune response.
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