Dihydromyricetin and Salvianolic acid B inhibit alpha-synuclein aggregation and enhance chaperone-mediated autophagy.

BACKGROUND: Progressive accumulation of α-synuclein is a key step in the pathological development of Parkinson's disease. Impaired protein degradation and increased levels of α-synuclein may trigger a pathological aggregation in vitro and in vivo. The chaperone-mediated autophagy (CMA) pathway is involved in the intracellular degradation processes of α-synuclein. Dysfunction of the CMA pathway impairs α-synuclein degradation and causes cytotoxicity. RESULTS: In the present study, we investigated the effects on the CMA pathway and α-synuclein aggregation using bioactive ingredients (Dihydromyricetin (DHM) and Salvianolic acid B (Sal B)) extracted from natural medicinal plants. In both cell-free and cellular models of α-synuclein aggregation, after administration of DHM and Sal B, we observed significant inhibition of α-synuclein accumulation and aggregation. Cells were co-transfected with a C-terminal modified α-synuclein (SynT) and synphilin-1, and then treated with DHM (10 µM) and Sal B (50 µM) 16 hours after transfection; levels of α-synuclein aggregation decreased significantly (68% for DHM and 75% for Sal B). Concomitantly, we detected increased levels of LAMP-1 (a marker of lysosomal homeostasis) and LAMP-2A (a key marker of CMA). Immunofluorescence analyses showed increased colocalization between LAMP-1 and LAMP-2A with α-synuclein inclusions after treatment with DHM and Sal B. We also found increased levels of LAMP-1 and LAMP-2A both in vitro and in vivo, along with decreased levels of α-synuclein. Moreover, DHM and Sal B treatments exhibited anti-inflammatory activities, preventing astroglia- and microglia-mediated neuroinflammation in BAC-α-syn-GFP transgenic mice. CONCLUSIONS: Our data indicate that DHM and Sal B are effective in modulating α-synuclein accumulation and aggregate formation and augmenting activation of CMA, holding potential for the treatment of Parkinson's disease.

Age-Dependent Alpha-Synuclein Accumulation and Phosphorylation in the Enteric Nervous System in a Transgenic Mouse Model of Parkinson's Disease.

The enteric nervous system (ENS) controls the function of the gastrointestinal tract and has been implicated in various diseases, including Parkinson's disease (PD). PD is a neurodegenerative disease with Lewy bodies (LBs) and Lewy neurites (LNs) as the main pathological features. In addition to the typical motor symptoms in PD, attention has been drawn to non-motor symptoms, such as constipation, implying dysfunction of the ENS. In the present study, we characterized the age-dependent morphological alterations and aggregation of α-synuclein (α-syn), the primary protein component in LBs and LNs, in the ENS in an α-syn transgenic mouse model. We found that the expression and accumulation of α-syn increased gradually in neurons of Meissner's and Auerbach's plexuses of the gastrointestinal tract with age (from 1 week to 2 years). In addition, α-syn was increasingly phosphorylated at the serine 129 residue, reflecting pathological alterations of the protein over time. Furthermore, α-syn was present in different subtypes of neurons expressing vasoactive intestinal polypeptide, neuronal nitric oxide synthase, or calretinin. The results indicated that BAC-α-Syn-GFP transgenic mice provide a unique model in which to study the relationship between ENS and PD pathogenesis.

Overexpression of the calpain-specific inhibitor calpastatin reduces human alpha-Synuclein processing, aggregation and synaptic impairment in [A30P]αSyn transgenic mice.

Lewy bodies, a pathological hallmark of Parkinson's disease (PD), contain aggregated alpha-synuclein (αSyn), which is found in several modified forms and can be discovered phosphorylated, ubiquitinated and truncated. Aggregation-prone truncated species of αSyn caused by aberrant cleavage of this fibrillogenic protein are hypothesized to participate in its sequestration into inclusions subsequently leading to synaptic dysfunction and neuronal death. Here, we investigated the role of calpain cleavage of αSyn in vivo by generating two opposing mouse models. We crossed into human [A30P]αSyn transgenic (i) mice deficient for calpastatin, a calpain-specific inhibitor, thus enhancing calpain activity (SynCAST(-)) and (ii) mice overexpressing human calpastatin leading to reduced calpain activity (SynCAST(+)). As anticipated, a reduced calpain activity led to a decreased number of αSyn-positive aggregates, whereas loss of calpastatin led to increased truncation of αSyn in SynCAST(-). Furthermore, overexpression of calpastatin decreased astrogliosis and the calpain-dependent degradation of synaptic proteins, potentially ameliorating the observed neuropathology in [A30P]αSyn and SynCAST(+) mice. Overall, our data further support a crucial role of calpains, particularly of calpain 1, in the pathogenesis of PD and in disease-associated aggregation of αSyn, indicating a therapeutic potential of calpain inhibition in PD.