J. Neurochem.(2011)119, 1119–1136.AbstractLoss of dopaminergic neurons and α‐synuclein accumulation are the two major pathological hallmarks of Parkinson’s disease. Currently, the mechanisms governing depletion of dopamine content and α‐synuclein accumulation are not well understood. We showed that the oxysterol 27‐hydroxycholesterol (27‐OHC) reduces the expression of tyrosine hydroxylase (TH), the rate‐limiting enzyme in dopamine synthesis, and increases α‐synuclein levels in SH‐SY5Y cells. However, the cellular mechanisms involved in 27‐OHC effects were not elucidated. In this study, we demonstrate that 27‐OHC regulates TH and α‐synuclein expression levels through the estrogen receptors (ER) and liver X receptors (LXR). We specifically show that inhibition of ERβ mediates 27‐OHC‐induced decrease in TH expression, an effect reversed by the ER agonist estradiol. We also show that 27‐OHC and the LXR agonist GW3965 increase α‐synuclein while the LXR antagonist 5α‐6α‐epoxycholesterol‐3‐sulfate significantly attenuated the 27‐OHC‐induced increase in α‐synuclein expression. We further demonstrate that LXRβ positively regulates α‐synuclein expression and 27‐OHC increases LXRβ‐mediated α‐synuclein transcription. Our results demonstrate the involvement of two distinct pathways that are involved in the 27‐OHC regulation of TH and α‐synuclein levels. Concomitant activation of ERβ and inhibition of LXRβ prevent 27‐OHC effects and may therefore reduce the progression of Parkinson’s disease by precluding TH reduction and α‐synuclein accumulation.