Abstract
Emerging evidence implicates α-synuclein oligomers as potential culprits in the pathogenesis of Lewy body disease (LBD). Soluble oligomeric α-synuclein accumulation in cytoplasm is believed to modify neuronal activities and intraneural Ca2+ dynamics, which augment the metabolic burden in central neurons vulnerable to LBD, although this hypothesis remains to be fully tested. We evaluated how intracellular α-synuclein oligomers affect the neuronal excitabilities and Ca2+ dynamics of pyramidal neurons in neocortical slices from mice. Intracellular application of α-synuclein containing stable higher-order oligomers (αSNo) significantly reduced spike frequency during current injection, elongated the duration of spike afterhyperpolarization (AHP), and enlarged AHP current charge in comparison with that of α-synuclein without higher-order oligomers. This αSNo-mediated alteration was triggered by spike-induced Ca2+ release from inositol trisphosphate receptors (IP3R) functionally coupled with L-type Ca2+ channels and SK-type K+ channels. Further electrophysiological and immunochemical observations revealed that α-synuclein oligomers greater than 100 kDa were directly associated with calcium-binding protein 1, which is responsible for regulating IP3R gating. They also block Ca2+-dependent inactivation of IP3R, and trigger Ca2+-induced Ca2+ release from IP3R during multiple spikes. This aberrant machinery may result in intraneural Ca2+ dyshomeostasis and may be the molecular basis for the vulnerability of neurons in LBD brains.
Highlights
Emerging evidence implicates α-synuclein oligomers as potential culprits in the pathogenesis of Lewy body disease (LBD)
Regarding the solutions with wild-type recombinant α-synuclein, higher-order oligomers were detected only in the solution containing α-synuclein incubated with dopamine for 3 days (Wild type, dopamine incubated without α-synuclein (DA)); they were not detected in solutions containing α-synuclein incubated without dopamine for 3 days (Wild type, 72 h) or without incubation (Wild type, 0 h)
Spike frequency in α-synuclein containing stable higherorder oligomers (αSNo)-infused neurons was 29.4 ± 1.0 Hz (n = 6), which was not significantly different from that in α-synuclein incubated without dopamine (αSN)-infused neurons (31.7 ± 0.7 Hz, n = 6; Fig. 5c,d). These results demonstrate that Ca2+-binding protein 1 (CaBP1) Ab is sufficient to cause Ca2+-induced Ca2+ release (CICR) from IP3 receptor (IP3R) triggered by Ca2+ influx via L-type VDCC (L-VDCC), and mimics and occludes the effect of αSNo (Fig. 6c iv)
Summary
Emerging evidence implicates α-synuclein oligomers as potential culprits in the pathogenesis of Lewy body disease (LBD). We previously demonstrated how Ca2+ or K+ channels are involved in the regulation or pathophysiological alteration of neocortical pyramidal cell excitability and Ca2+ dynamics This was performed by using intracellular www.nature.com/scientificreports injection of bioactive molecules or proteins such as inositol trisphosphate (IP3), homer1a and amyloid-β through a patch pipette[12,13,14,15,16,17], and the results obtained by these methods were compatible with those observed in neurons having physiologically produced IP3 or homer1a proteins in cytoplasm, or in neurons of 3xTg Alzheimer’s disease model mice[12,13,14,15,16,17]. By applying the same methodology, the present study aimed to elucidate the effects and mechanisms of intracellular α-synuclein oligomers on neuronal excitabilities and Ca2+ dynamics, by introducing α-synuclein protein into pyramidal neurons in cortical slices from mice
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