Gain-of-function mutation of type 2 ryanodine receptor attenuates dopaminergic neuron development associated with Ca2+ overload-triggered oxidative damage in mitochondria.

Type 2 ryanodine receptor (RyR2), a Ca2+ release channel located in the endoplasmic reticulum (ER) membrane, expresses catecholamine-induced polymorphic ventricular tachycardia (CPVT), and is a potential risk factor of autism spectrum disorder (ASD). However, the pathological relationship between RyR2 mutation-induced Ca2+ dysregulation and ASD pathology remains unclear. This study examined the association between CPVT-related RyR2 mutations and ASD pathology to determine its dopaminergic pathological role in ASD. Patient-derived stem cells from human exfoliated deciduous teeth were obtained from a boy with comorbid CPVT and ASD, and differentiated to dopaminergic neurons (RyR2-DNs). Two heterozygous missense mutations were identified in RyR2: c.9910C > G, p.Q3304E in exon 69 and c.14222C > T, p.A4741V in exon 99 (RyR269/99). RyR2-DNs showed cytosolic and mitochondrial Ca2+ accumulation, and impaired neurite outgrowth, suggesting that RyR269/99 is a gain-of-function mutation that promotes Ca2+ release from the ER and attenuates neurite development. RyR2-DNs also exhibited increased mitochondrial reactive oxygen species along with impaired mitochondrial oxidative phosphorylation. These mitochondrial abnormalities and neurite outgrowth were managed by pharmacological intervention of mitochondrial Ca2+ accumulation. Thus, RyR2 hyper-activation-induced mitochondrial Ca2+ overload may cause oxidative stress-related mitochondrial dysfunction, impairing DN development and dopaminergic dysregulation in ASD.