Proteolytic Cleavage of Extracellular Secreted α-Synuclein via Matrix Metalloproteinases

Abstract

Although ␣-synuclein is the main structural component of the insoluble filaments that form Lewy bodies in Parkinson disease (PD), its physiological function and exact role in neuronal death remain poorly understood. In the present study, we examined the possible functional relationship between ␣-synuclein and several forms of matrix metalloproteinases (MMPs) in the human dopaminergic neuroblastoma (SK-N-BE) cell line. When SK-N-BE cells were transiently transfected with ␣-synuclein, it was secreted into the extracellular culture media, concomitantly with a significant decrease in cell viability. Also the addition of nitric oxide-generating compounds to the cells caused the secreted ␣-synuclein to be digested, producing a small fragment whose size was similar to that of the fragment generated during the incubation of ␣-synuclein with various MMPs in vitro. Among several forms of MMPs, ␣-synuclein was cleaved most efficiently by MMP-3, and MALDI-TOF mass spectra analysis showed that ␣-synuclein is cleaved from its C-terminal end with at least four cleavage sites within the non-A␤ component of AD amyloid sequence. Compared with the intact form, the protein aggregation of ␣-synuclein was remarkably facilitated in the presence of the proteolytic fragments, and the fragment-induced aggregates showed more toxic effect on cell viability. Moreover, the levels of MMP-3 were also found to be increased significantly in the rat PD brain model produced by the cerebral injection of 6-hydroxydopamine into the substantia nigra. The present study suggests that the extracellularly secreted ␣-synuclein could be processed via the activation of MMP-3 in a selective manner.

Oligomeric alpha‐synuclein and its role in neuronal death

“…However, the presence of a-Syn in the cerebrospinal fluid (CSF) of Parkinson's disease patients does support the possibility that aggregates of the protein exist outside of cell. aSyn may be released upon cell death (10) or secreted from neuronal cells, as evidenced in culture (11)(12)(13). The exocytosis of a-Syn is thought to be linked to a preferential secretion of damaged proteins from the cell (12,14).…”

Acyl-CoA Synthetase Activity Links Wild-Type but Not Mutant α-Synuclein to Brain Arachidonate Metabolism

“…α-Synuclein is also found in other regions of neurons, in astrocytes, and in oligodendroglia (6)(7)(8)(9)(10)(11). Overexpression of and mutations in α-synuclein are associated with early onset Parkinson's disease (12)(13)(14)(15) and other neurodegenerative diseases (16)(17)(18)(19)(20).…”

“…To address the potential role for α-synuclein in brain 20:4n-6 uptake and metabolism, we used steady-state kinetic modeling of [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]20:4n-6 metabolism in vivo coupled with studies using enzyme assays and mRNA expression of key fatty acid metabolic enzymes. These data show, for the first time, a mechanistic explanation for the impact of α-synuclein deficiency on brain lipid metabolism.…”

Proteolytic clearance of extracellular α-synuclein as a new therapeutic approach against Parkinson disease

“…56 Sung et al demonstrated that oxidative injury induces the cleavage of extracellular α-syn released from neuronal cells and this is eventually cleaved by MMPs. However, the cleavage of α-syn by MMP-3 further induces its aggregation, 56 lessens any likely effects on PD of cleaving extracellular α-syn by MMPs.…”

“…Proteolytic clearance is possible using any of several proteases that have been identified to be able to cleave and degrade α-syn: these include neurosin, 55 matrix metalloproteinases (MMPs), 56 calpain, 57 cathepsin D 58 and plasmin. 59 Among them, neurosin, MMPs and plasmin have been reported to cleave and degrade extracellular α-syn.…”