Parkinson-causing mutations in LRRK2 impair the physiological tetramerization of endogenous α-synuclein in human neurons

Abstract

α-Synuclein (αSyn) aggregation in Lewy bodies and neurites defines both familial and ‘sporadic’ Parkinson’s disease. We previously identified α-helically folded αSyn tetramers, in addition to the long-known unfolded monomers, in normal cells. PD-causing αSyn mutations decrease the tetramer:monomer (T:M) ratio, associated with αSyn hyperphosphorylation and cytotoxicity in neurons and a motor syndrome of tremor and gait deficits in transgenic mice that responds in part to L-DOPA. Here, we asked whether LRRK2 mutations, the most common genetic cause of cases previously considered sporadic PD, also alter tetramer homeostasis. Patient neurons carrying G2019S, the most prevalent LRRK2 mutation, or R1441C each had decreased T:M ratios and pSer129 hyperphosphorylation of their endogenous αSyn along with increased phosphorylation of Rab10, a widely reported substrate of LRRK2 kinase activity. Two LRRK2 kinase inhibitors normalized the T:M ratio and the hyperphosphorylation in the G2019S and R1441C patient neurons. An inhibitor of stearoyl-CoA desaturase, the rate-limiting enzyme for monounsaturated fatty acid synthesis, also restored the αSyn T:M ratio and reversed pSer129 hyperphosphorylation in both mutants. Coupled with the recent discovery that PD-causing mutations of glucocerebrosidase in Gaucher’s neurons also decrease T:M ratios, our findings indicate that three dominant genetic forms of PD involve life-long destabilization of αSyn physiological tetramers as a common pathogenic mechanism that can occur upstream of progressive neuronal synucleinopathy. Based on αSyn’s finely-tuned interaction with certain vesicles, we hypothesize that the fatty acid composition and fluidity of membranes regulate αSyn’s correct binding to highly curved membranes and subsequent assembly into metastable tetramers.

Regulatory imbalance between LRRK2 kinase, PPM1H phosphatase, and ARF6 GTPase disrupts the axonal transport of autophagosomes

“…We differentiated these iPSCs into excitatory glutamatergic neurons using tetracycline-inducible expression of NGN2 (Pantazis et al, 2022), and live-imaged EGFP-LC3-labeled AV transport in the mid-axon at DIV21 (Figure 1A; Video S1). NGN2-induced neurons (iNeurons) express LRRK2 (Bieri et al, 2019; Boecker et al, 2021; Fonseca-Ornelas et al, 2022) and have been used to study the effect of LRRK2 -p.G2019S on axonal AV dynamics (Boecker et al, 2021).…”

Alpha Synuclein: Neurodegeneration and Inflammation

“…It has been suggested that tetramers undergo destabilization of their helically folded conformation prior to α-Syn aggregation into abnormal oligomeric and fibrillar assemblies [ 16 , 17 ]. Although the importance of the tetrameric structure of α-Syn in the physiological condition is debated in favor of the more common unstructured monomeric form [ 18 ], there is evidence that this structure is sensitive to the presence of various mutations associated with PD [ 19 , 20 ]. Numerous investigations have connected the physiological activity of α-Syn in monomeric forms to synaptic functionality [ 21 , 22 ], although there are still no conclusive results about its physiological function, while the pathological events associated with α-Syn are almost exclusively linked to its polymeric forms.…”

Influence of Cigarette Aerosol in Alpha-Synuclein Oligomerization and Cell Viability in SH-SY5Y: Implications for Parkinson’s Disease

“…Previous research indicates that WT α-Syn exists in a stable tetrameric form, while missense mutations tend to form monomeric structures that trigger pathological aggregation . Moreover, the disruption or impairment of α-Syn multimerization leads to an excess of monomers at vesicle membranes, resulting in round cytoplasmic inclusions and indicating pathological consequences. − Our results suggest that CAE disrupts the α-Syn oligomeric equilibrium, favoring monomers with hindrance in homogeneous regions and causing oligomer formation in punctate distributions in SH-SY5Y cells. This finding highlights the potential link between CAE and α-Syn pathology.…”