Environmental enrichment reduced pathological α-Synuclein accumulation by restoring LAMP1 via Reelin in early stage of Parkinson's disease

Abstract

Parkinson’s disease (PD) is dopamine neuronal degenerative disease along with α-Synuclein (α-Syn) accumulation and Lewy body (LB) formation in the striatum (STR) and substantia nigra pars compacta (SNpc). PD shows motor dysfunctions and non-motor dysfunctions such as olfactory dysfunction, depression, and cognitive decline. Despite the continuous endeavors to develop drugs for dopamine neuroprotection and behavioral improvements, there are still needs for effective and non-invasive treatments, dependent on disease progress in PD. Environmental enrichment (EE) not only protects dopamine neurons, promotes motor ability and cognitive function improvement, and regulates Reelin protein expressions in PD but also contributes to prevent amyloid β fibril formation in Alzheimer’s disease (AD). Although previous studies revealed that Reelin and RELN expression patterns were changed in PD patient Cerebrospinal fluids (CSFs), stages of PD dependent Reelin and RELN levels in the STR as well as PD progression dependent EE effects have not to be uncovered yet. Hence, this study tested motor abilities, non-motor abilities, and olfactory function after EE exposure for 8 weeks to 4- or 14-month-old A53T α-Syn (Tg) mouse animal model of PD. For biochemistry analysis, qRT-PCR was conducted for the pattern of RELN expression and IHC or western blot was proceeded for TH, Reelin, DRD receptors (DRD1, DRD2), APOER2, LAMP- 1, VAMP 7, and NMDA receptor subunits (NR1, NR2A, NR2B) in the STR at both points of disease stages. The results demonstrated that in the 6-month-old (early stage of PD) mice STR, RELN, Reelin, total α-Syn, and toxic α-Syn (phosphorylated α-Syn, α-SynpS129) expression levels were increased. TH+ dopamine neurons were decreased in the SN while no change was observed in the STR. Early expose to EE contributed to protect dopamine neurons, to decrease total α-Syn, α-SynpS129 and the number of aggregated proteins, and to preserve protein expression levels for Reelin, DRD1, DRD2, LAMP 1, NR2A, and NR2B as same levels as non-Tg mouse proteins in the STR. In addition, behavioral analysis proved preventive effects of EE on olfactory dysfunction, motor disability, and cognitive decline. In late stage of A53T α-Syn animal model of PD (16-month-old), TH+ dopamine neurons were reduced in both STR and SN and EE was not helpful for dopamine neuronal recovery. RELN and Reelin expressions were decreased at16-month-old mouse STR but EE exposure restored Reelin protein expression to the same level of non-Tg mouse. Unlike 6-month-old early stage of mouse STR, the increased level of toxic α-Syn proteins were detected in 16-month-old late stage of mouse STR and SN. Although the level of toxic α-Syn in the SN was significantly reduced after later life EE, the total α-Syn and aggregated protein expression levels were unchanged compared to Tg mouse at 16-month-old late stage of PD. EE expose to late stage of PD mouse improved olfactory impairment, muscle strength weakness, and imbalanced reciprocal walking behaviors, whereas cognitive impairment and hyperactivity were not significantly retrieved after EE at 16-month-old mouse model of PD. In addition, after later life EE, expression patterns for DRD1, DRD2, APOER2, NR2A became like that of non-Tg mouse in the STR. However, EE in late stage of PD mouse had no significant effects on LAMP 1, VAMP 7, NR1, NR2B protein recovery to the extent of non-Tg mouse proteins in the STR. In vitro study suggested that Reelin could be a promising candidate for PD treatment by decreasing total and aggregated α-Syn levels via LAMP1 increase in PFFs treated SH-SY5Y cells. This study suggests that stages of PD (early/late) could be determined by Reelin expression level in the STR so that it might help to decide which drugs or treatment interventions would be best for patients depending on PD progress. In addition, this study provides an evidence that EE intervention in early stage of PD could be more effective rather than in late stage of PD on behavioral function improvements as well as on dopamine neuroprotection. To sum up, this study proposes that EE intervention in early stage of PD would have the optimal effects for improvement and appropriate time point for EE intervention could be made by Reelin levels as a prominent biomarker in the STR for PD.