Ample evidence has suggested that extracellular α‐synuclein aggregates would play key roles in the pathogenesis and progression of Parkinsonian disorders (PDs). In the present study, we investigated whether mesenchymal stem cells (MSCs) and their derived soluble factors could exert neuroprotective effects via proteolysis of extracellular α‐synuclein. When preformed α‐synuclein aggregates were incubated with MSC‐conditioned medium, α‐synuclein aggregates were disassembled, and insoluble and oligomeric forms of α‐synuclein were markedly decreased, thus leading to a significant increase in neuronal viability. In an animal study, MSC or MSC‐conditioned medium treatment decreased the expression of α‐synuclein oligomers and the induction of pathogenic α‐synuclein with an attenuation of apoptotic cell death signaling. Furthermore, we identified that matrix metalloproteinase‐2 (MMP‐2), a soluble factor derived from MSCs, played an important role in the degradation of extracellular α‐synuclein. Our data demonstrated that MSCs and their derived MMP‐2 exert neuroprotective properties through proteolysis of aggregated α‐synuclein in PD‐related microenvironments. Stem Cells Translational Medicine 2017;6:949–961

Genome-wide association studies have identified two loci, SNCA and the microtubule (MT)-associated protein tau, as common risk factors for Parkinson's disease (PD). Specifically, α-synuclein directly destabilizes MT via tau phosphorylation and induces axonal transport deficits that are the primary events leading to an abnormal accumulation of α-synuclein that causes nigral dopaminergic cell loss. In this study, we demonstrated that mesenchymal stem cells (MSCs) could modulate cytoskeletal networks and trafficking to exert neuroprotective properties in wild-type or A53T α-synuclein overexpressing cells and mice. Moreover, we found that eukaryotic elongation factor 1A-2, a soluble factor derived from MSCs, stabilized MT assembly by decreasing calcium/calmodulin-dependent tau phosphorylation and induced autophagolysosome fusion, which was accompanied by an increase in the axonal motor proteins and increased neuronal survival. Our data suggest that MSCs have beneficial effects on axonal transports via MT stability by controlling α-synuclein-induced tau phosphorylation, indicating that MSCs may exert a protective role in the early stages of axonal transport defects in α-synucleinopathies. Stem Cells 2017;35:1934-1947.

Mesenchymal stem cells (MSCs) are a potential source of cell-based disease-modifying therapy in Parkinsonian disorders. A promising approach to develop in vitro culture methods that mimic natural MSC niche is cell priming. Uric acid (UA), a powerful antioxidant, scavenges reactive oxygen species, which has a vital role in maintaining self-renewal and differentiation potential of MSCs. Here, we demonstrated that UA treatment in naïve MSCs stimulated glycolysis and upregulated transcriptional factors responsible for regulation of stemness, leading to increase in the expression levels of osteogenesis-, adipogenesis-, and chondrogenesis-related genes. UA-primed MSCs had more enhanced neuroprotective properties in cellular and parkinsonian animal models compared to naïve MSCs by inhibiting apoptotic signaling pathways. Additionally, expression of miR-137 and miR-145 was decreased in UA-treated MSCs. Our data demonstrated that priming MSCs with UA augment neuroprotective properties through enhanced self-renewal and differentiation potential, suggesting a practical strategy for improving the application of MSCs in parkinsonian disorders.

* Continuous intra-and extracellular stresses induce disorder of Ca2+ homeostasis and accumulation of unfolded protein in the endoplasmic reticulum (ER), which results in ER stress. Severe long-term ER stress triggers apoptosis signaling pathways, resulting in cell death. Neural epidermal growth factor-like like protein 2 (NELL2) has been reported to be important in protection of cells from cell death-inducing environments. In this study, we investigated the cytoprotective effect of NELL2 in the context of ER stress induced by thapsigargin, a strong ER stress inducer, in Cos7 cells. Overexpression of NELL2 prevented ER stress-mediated apoptosis by decreasing expression of ER stress-induced C/EBP homologous protein (CHOP) and increasing ER chaperones. In this context, expression of anti-apoptotic Bcl-xL was increased by NELL2, whereas NELL2 decreased expression of pro-apoptotic proteins, such as cleaved caspases 3 and 7. This antiapoptotic effect of NELL2 is likely mediated by extracellular signal-regulated kinase (ERK) signaling, because its inhibitor, U0126, inhibited effects of NELL2 on the expression of anti-and pro-apoptotic proteins and on the protection from ER stress-induced cell death.

Multiple system atrophy (MSA) is a sporadic neurodegenerative disease of the central and autonomic nervous system. Because no drug treatment consistently benefits MSA patients, neuroprotective strategy using mesenchymal stem cells (MSCs) has a lot of concern for the management of MSA. In this study, we investigated the safety and efficacy of intra‐arterial administration of MSCs via internal carotid artery (ICA) in an animal model of MSA. The study was composed of feasibility test using a ×10 and ×50 of a standard dose of MSCs (4 × 107 MSCs) and efficacy test using a ×0.2, ×2, and ×20 of the standard dose. An ultrasonic flow meter and magnetic resonance imaging (MRI) showed that no cerebral ischemic lesions with patent ICA blood flow was were observed in animals receiving a ×10 of the standard dose of MSCs. However, no MSA animals receiving a ×50 of the standard dose survived. In efficacy test, animals injected with a ×2 of the standard dose increased nigrostriatal neuronal survival relative to a ×0.2 or ×20 of the standard dose. MSA animals receiving MSCs at ×0.2 and ×2 concentrations of the standard dose exhibited a significant reduction in rotation behavior relative to ×20 of the standard dose of MSCs. Cerebral ischemic lesions on MRI were only observed in MSA animals receiving a ×20 of the standard dose. The present study revealed that if their concentration is appropriate, intra‐arterial injection of MSCs is safe and exerts a neuroprotective effect on striatal and nigral neurons with a coincidental improvement in motor behavior. Stem Cells Translational Medicine 2017;6:1424–1433