Loss of dopaminergic neurons and α-synuclein accumulation are the two major pathological hallmarks of Parkinson’s disease (PD). 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. Here, 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 ECHS 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 PD by precluding TH reduction and α-synuclein accumulation.

Abbreviations used: Ab, b-amyloid; AD, Alzheimer's disease; BCA, bicinchoninic acid; fAb42, fibrillar Ab42; GSK-3b, glycogen synthase kinase-3b; LTP, long-term potentiation; mTOR, mammalian target of rapamycin; mTORC, mTOR complex 1; SOCS-3, suppressor of cytokine signaling-3. AbstractHigh levels of the adipocytokine leptin are associated with reduced risk of Alzheimer's disease. Leptin treatment also reduces b-amyloid (Ab) levels in in vivo and in vitro models of Alzheimer's disease. Ab and leptin interact with the Akt/ mammalian target of rapamycin complex 1 (mTORC1) signaling pathway. Akt/mTORC1 activation reduces tau phosphorylation through the inhibition of the downstream enzyme GSK-3b. mTORC1 also regulates translation of many proteins including leptin. While Ab has been shown to inactivate Akt, inhibit mTORC1, and facilitate the phosphorylation of tau, leptin activates both Akt and mTORC1 and reduces tau phosphorylation. However, the extent to which Ab may modulate leptin expression and increase tau phosphorylation involving Akt/mTORC1 has not been determined. In this study, we show that incubation of organotypic slices from rabbit hippocampus with Ab down-regulates leptin expression, inhibits Akt, activates GSK-3b, increases tau phosphorylation, and inactivates mTORC1. Leptin treatment reverses Ab effects by alleviating Akt inhibition, preventing GSK-3b activation, reducing tau phosphorylation, and activating mTORC1. On the other hand, Rapamycin, an allosteric inhibitor of mTORC1, down-regulates leptin expression, increases tau phosphorylation, and does not affect Akt and GSK-3b. Our results demonstrate for the first time that Ab regulates leptin expression and tau phosphorylation through mTORC1.

Neurodegenerative diseases are associated with brain aging which leads to impaired cholinergic dysfunction. In the current study, we aimed to identify the neuroprotective effect of Clitoria ternatea (CT) methanolic leaf extract against restraint stress (RS) and aluminum (AlM) induced age-related toxicity in cerebellum of young and adult rats. In CT methanolic leaf extract 9-phytoconstituents such as 4H-1-Benzopyran-4-one, 7-hydroxy-2-(4-hydroxyphenyl); Cyclopentaneundecanoic acid, methyl ester; Phytol; Methyl Isostearate; 12-Methyl-E, E-2,13-Octadecadien-1-ol; Cyclopropaneoctanoic acid, 2-{[2 pentylcyclopropyllmethyl}, methyl ester; Ethanol,2-[9-octadecenyloxy], [Z]; Octadecanoic acid, 5,9,13,17-tetramethyl, methyl ester; Hyocholic acid were identified using Gas chromatography-mass spectrometry (GC-MS), their structures identified based on NIST data, and biological activities were specified. Further, the young (3 months age) and adult rats (12 months age) were randomized into eight groups, control, AlM, RS, CT, RS+AlM, AlM+CT, RS+CT and RS+AlM+CT administered groups. Both the age group rats were restrained in a restraint chamber for 60 min/day/30 days, AlM (100 mg/kg/30 days) and CT leaf extract (50 mg/kg/30 days) were administered orally according to their respective groups. RS and AlM administration showed significant reduced ACh and AChE Cholinergic markers levels in cerebellum compared to control group. Whereas co-administration of CT methanolic leaf extract with RS and AlM showed enhanced levels of ACh and AChE compared to RS and AlM alone treated groups. These data suggest that the rich source of phytoconstituents of CT methanolic leaf extract are responsible for anticholinergic and neuroprotective effects against RS and AlM age-related toxicity.