17 β-Estradiol Oxidative Stress Attenuation and Autophagy-Induced Dopaminergic Neuroprotection

Abstract

Objective: Degeneration of dopaminergic neurons in the substantia nigra of the brain stem is the main pathological aspect of Parkinson's disease (PD). 17 β-estradiol (E2) has neuroprotective effects on substantia nigra, however, the underlined mechanism is not well-known. In this study, we evaluated the neuroprotective effects of E2 in the ovariectomized 6-hydroxydopamine- (6-OHDA) rat model of PD.

Materials and methods: In this experimental study, all animals were ovariectomized to avoid any further bias in E2 levels and then these ovariectomized rats were randomly assigned into three experimental groups (10 rats in each group): ovariectomized control group (OCG), ovariectomized degeneration group receiving 25 μg of 6-OHDA into the left corpus striatum (ODG), and ovariectomized E2 pretreatment group pretreated with 0.1 mgkg-1 of 17 β-estradiol for three days prior to the destruction of corpus striatum with 6-OHDA (OE2PTG). The apomorphine behavioral test and Nissl staining were performed in all experimental groups. The expressions of Sequestosome-1 (P62), Unc- 51 like autophagy activating kinase (Ulk1), and microtubule-associated proteins 1A/1B light chain 3B (Lc3) genes were evaluated using reverse transcriptionpolymerase chain reaction (RT-PCR).

Results: E2 administration reduced the damages to the dopaminergic neurons of the substantia nigra. The motor behavior, the number of rotations, and histological tests in the treatment group showed the cell survival improvement in comparison with the control groups indicating that E2 can inhibit the neurodegeneration. P62 and Lc3 were expressed in all experimental groups while Ulk1 was not expressed in ODG group. Moreover, Ulk1 was expressed after the treatment with E2 in OE2PTG group.

Conclusion: E2 prevents neurodegeneration in dopaminergic neurons of the midbrain by over-expression of Ulk1 gene and augmenting the induction of autophagy.

Keywords: 17 β-estradiol; Autophagy; Parkinson’s Disease; Ulk1.

Fig.1

Before the surgery, there was no significant difference among the OCG, ODG, and OE2PTG groups in the rotations (P<0.05). OCG; Ovariectomized control group, ODG; Ovariectomized degeneration group, OE2PTG; Ovariectomized E2 pretreatment group, and *; Indicates a significant difference between each experimental group with the OCG group.

Fig.2

Neuronal counts in the substantia nigra. A. The means of nigral neurons in the left and right sides of the three experimental groups have been shown. On the right side, there were no significant differences among the groups. However, for the left side, a significant difference was observed for all groups (P<0.05). Neurons in substantia nigra in the left side of the experimental groups with Nissl staining for B. OCG group, C. OE2PTG group, and D. ODG group. Abundant neurons existed in the substantia nigra and ventral tegmental area of OCG and OE2PTG groups. In contrast, the number of neurons was progressively decreased in substantia nigra ipsilateral to 6-OHDA injection in ODG group. OCG, ODG, ovariectomized E2 pretreatment group (OE2PTG), substantia nigra pars compacta (SNc), ventral tegmentum area (VTA) (scale bars: 200 µm). OCG; Ovariectomized control group, ODG; Ovariectomized degeneration group, and *; Shows the statistically significant difference in OCG group (P<0.05).

Fig.3

Gene expression results. The P62 and Lc3 expressed in all groups, while Ulk1 was expressed only in ovariectomized degeneration (ODG) group. In ovariectomized rats pretreated with 17 ß-estradiol before 6-hydroxydopamine injection (OE2PTG), Ulk1 was overexpressed. Gapdh was used as an internal control which was expressed in all groups. OCG; Ovariectomized control group.