Cholesterol deficiency as a mechanism for autism: A valproic acid model

Dysregulated cholesterol metabolism represents an increasingly recognized feature of autism spectrum disorder (ASD). Children with fetal valproate syndrome caused by prenatal exposure to valproic acid (VPA), an anti-epileptic and mood-stabilizing drug, have a higher incidence of developing ASD. However, the role of VPA in cholesterol homeostasis in neurons and microglial cells remains unclear. Therefore, we examined the effect of VPA exposure on regulation of cholesterol homeostasis in the human microglial clone 3 (HMC3) cell line and the human neuroblastoma cell line SH-SY5Y. HMC3 and SH-SY5Y cells were each incubated in increasing concentrations of VPA, followed by quantification of mRNA and protein expression of cholesterol transporters and cholesterol metabolizing enzymes. Cholesterol efflux was evaluated using colorimetric assays. We found that VPA treatment in HMC3 cells significantly reduced ABCA1 mRNA, but increased ABCG1 and CD36 mRNA levels in a dose-dependent manner. However, ABCA1 and ABCG1 protein levels were reduced by VPA in HMC3. Furthermore, similar experiments in SH-SY5Y cells showed increased mRNA levels for ABCA1, ABCG1, CD36, and 27-hydroxylase with VPA treatment. VPA exposure significantly reduced protein levels of ABCA1 in a dose-dependent manner, but increased the ABCG1 protein level at the highest dose in SH-SY5Y cells. In addition, VPA treatment significantly increased cholesterol efflux in SH-SY5Y, but had no impact on efflux in HMC3. VPA differentially controls the expression of ABCA1 and ABCG1, but regulation at the transcriptional and translational levels are not consistent and changes in the expression of these genes do not correlate with cholesterol efflux in vitro.