Extracellular α-synuclein induces sphingosine 1-phosphate receptor subtype 1 uncoupled from inhibitory G-protein leaving β-arrestin signal intact

Abstract

Parkinson’s disease (PD) is the second most common neurodegenerative disorder. The presence of α-synuclein (α-Syn)-positive intracytoplasmic inclusions, known as Lewy bodies, is the cytopathological hallmark of PD. Increasing bodies of evidence suggest that cell-to-cell transmission of α-Syn plays a role in the progression of PD. Although extracellular α-Syn is known to cause abnormal cell motility, the precise mechanism remains elusive. Here we show that impairment of platelet-derived growth factor-induced cell motility caused by extracellular α-Syn is mainly attributed to selective inhibition of sphingosine 1-phosphate (S1P) signalling. Treatment of human neuroblastoma cells with recombinant α-Syn caused S1P type 1 (S1P1) receptor-selective uncoupling from inhibitory G-protein (Gi) as determined by both functional and fluorescence resonance energy transfer (FRET)-based structural analyses. By contrast, α-Syn caused little or no effect on S1P2 receptor-mediated signalling. Both wild-type and α-Syn(A53T), a mutant found in familiar PD, caused uncoupling of S1P1 receptor, although α-Syn(A53T) showed stronger potency in uncoupling. Moreover, S1P1 receptor-mediated β-arrestin signal was unaltered by α-Syn(A53T). These results suggest that exogenous α-Syn modulates S1P1 receptor-mediated signalling from both Gi and β-arrestin signals into β-arrestin-biased signal. These findings uncovered a novel function of exogenous α-Syn in the cells.

Extracellular α-synuclein drives sphingosine 1-phosphate receptor subtype 1 out of lipid rafts, leading to impaired inhibitory G-protein signaling

“…1, A and C, hatched bars in fractions 1 and 2). The amount of S1P 2 R, another subtype of the receptor known to be expressed in this cell line (28), in the raft fractions was not changed by ␣-Syn(A53T) treatment (Fig. 1B, hatched bars in fraction 2).…”

“…We have recently found that extracellular ␣-Syn makes S1P 1 R uncouple from the G i protein in the plasma membranes (28). It is important to determine whether S1P 1 R is also uncoupled from the G i protein on MVEs after ␣-Syn treatment, because continuous activation of S1P 1 R and subsequent transmission of the G i protein signal on MVEs has been proven to be critical for cargo sorting into exosomal intralumenal vesicles (ILVs) (25,33).…”

“…S1P 1 R results in the impairment of PDGF-induced chemotaxis, whereas leaving ␤-arrestin signals intact, e.g. ligand-induced internalization of S1P 1 R (28). Because G i signaling on plasma membranes and internal vesicles is essential to cell migration (28,29) and exosomal vesicle maturation (25), it is particularly important to identify downstream signaling events after extracellular ␣-Syn treatment leading to uncoupling of S1P 1 R. In the present study, we showed evidence that extracellular ␣-Syn induces expulsion of S1P 1 R out of a "signaling station" lipid rafts, involving ␣-Syn binding to ganglioside, resulting in the uncoupling of S1P 1 R from G i -protein.…”

In vitro models of synucleinopathies: informing on molecular mechanisms and protective strategies

“…) and the inhibition of Sphingosine‐1‐phosphate receptor 1 (S1P1) (Zhang et al . ). In contrast, binding of α‐Syn preformed fibrils to lymphocyte‐activation gene 3 was shown to initiate the transmission of pathological α‐Syn (Mao et al .…”

A new synuclein-transgenic mouse model for early Parkinson’s reveals molecular features of preclinical disease

“…CCR1 is typically microglial and its product participates the recruitment of immune cells, but it is also expressed in the ventral midbrain during development, where it is involved in neuronal differentiation of DA neurons [24]. S1P1 is uncoupled from an inhibitory G-protein by extracellular α-syn, and may therefore play a role in intracellular α-syn accumulation [105].…”