The role of a-synuclein accumulation in lysosomal hydrolase trafficking and function - Abstract
The aggregation of a-Synuclein (a-syn) into insoluble fibrils plays a key role in the pathogenesis of
Dementia with Lewy bodies (DLB), Parkinson’s disease (PD) and other synucleinopathies. Despite the
documentation of a-synuclein as a component of Lewy body inclusions for over 25 years, there remains a
significant knowledge gap in the mechanisms that causally link protein aggregates to neurodegeneration. Recent
genetic studies have implicated the lysosomal degradation system into the pathogenesis of DLB and PD. Among
the strongest genetic risk factors are loss-of-function mutations lysosomal β-glucocerebrosidase (GCase)
encoded by GBA1, indicating that compromised lysosomal function may play a direct role in neurodegeneration.
During our previous funding period, we found that a-syn aggregates are initiated inside lysosomes by interacting
with glycosphingolipid substrates that accumulate upon loss of GCase. Once formed, these aggregates perturb
multiple, essential branches of the proteostasis pathway, including the folding in the endoplasmic reticulum (ER)
and post-ER trafficking at the cis-Golgi. This further augments a-syn aggregation, creating a self-propagating
pathogenic cycle. The previous funding period uncovered novel mechanisms and biological targets that enhance
the trafficking of hydrolases and lysosomal function. Here, we will build on our previous work to examine how a-
syn aggregates perturb protein folding in the ER, N-linked glycosylation in the ER, and the downstream effect
on lysosomal function. We will develop novel molecules to restore these key proteostasis pathways. Our studies
will employ a combination of patient-derived PD iPSC-neuron cultures, synucleinopathy mouse models, and
human brain. We previously found that a-syn accumulation in PD patient neurons induced ER fragmentation and
concealed the cell’s ability to recognize misfolded proteins in the ER, resulting in aggregation of immature
GCase. Since misfolded proteins in the ER are usually recognized by the unfolded protein response (UPR), in
aim 1, we will examine the link between the UPR, GCase solubility, and trafficking to the lysosome. We will
determine if triggering the UPR in PD can restore lysosomal function and reduce a-syn. In aim 2, we will test the
hypothesis that reduced glucose flux and protein N-glycosylation of GCase and other hydrolases contributes to
lysosomal depletion and dysfunction in PD. In aim 3, we will build upon our prior studies, which showed that
lysosomal function can be rescued by enhancing the SNARE protein ykt6. We will test novel small molecule
activators of the ykt6-lysosomal biogenesis pathway in vitro and in vivo. By studying basic biology mechanisms
of protein trafficking, we have a unique opportunity to link essential cellular proteostasis pathways to disease
pathogenesis. Our studies may impact the field by discovering novel pathogenic mechanisms, identifying new
biological targets, and further develop therapies to enhance lysosomal biogenesis to restore proteostasis in PD
and DLB.
