|Ph.D Student||Fishma-Jacob Tali|
|Subject||A Sporadic Parkinson's Disease Model via Silencing of|
the Ubiquitin-Proteasome/E3-Ligase Component,
|Department||Department of Medicine||Supervisors||Professor Emeritus Moussa Youdim|
|Dr. Silvia Mandel|
|Full Thesis text|
It is assumed that Parkinson's disease (PD) and other neurodegenerative disorders are caused by a complex interaction between genetic predisposition and endotoxins or neurotoxins. Our and other's laboratory microarray-derived transcriptomic studies in human PD substantia nigra pars compacta (SNpc) samples have opened an avenue to concentrate on potential gene intersections or cross-talks along the dopaminergic (DAergic) neurodegenerative cascade in SPD. One emerging gene candidate identified was SKP1A, found significantly decreased in the SNpc as confirmed later at the protein level. SKP1 is part of the Skp1, Cullin 1, F-box protein (SCF) complex, the largest known class of sophisticated ubiquitin-proteasome/E3-ligases.
To examine a possible role of Skp1 in DAergic phenotype, we have initially knocked down the expression of SKP1A gene in an embryonic mouse SN-derived cell line (SN4741) with short hairpin RNA (shRNA) lentiviruses (LVs). The deficiency of SKP1A closely recapitulated cardinal features of the DAergic pathology of human PD, and induced a lethal phenotype only in arrested/differentiated cells exhibiting proteinaceous round inclusion structures, which were almost identical in composition to human Lewy bodies, present in the melanized DAergic neurons of the SNpc in PD.
The identification of Skp1 as a key player in DAergic neuron pathogenesis, suggested that a targeted site-specific reduction of Skp1 levels in mice SNpc, may result in a progressive loss of DAergic neurons and terminal projections in the striatum. The injected LV SKP1shRNA to mouse SN resulted in decreased expression of Skp1 protein levels within DAergic neurons and loss of tyrosine hydroxylase immunoreactivity in both SNpc and striatum that was accompanied by time-dependent motor disabilities. The reduction of the vertical movements, that is rearing, may be reminiscent of the early occurrence of hypokinesia and axial, postural instability in PD.
According to the second premise considers the possibility that both intrinsic and extrinsic factors alleged to play central roles in DAergic neurodegeneration in PD it was predicted that gene-gene and/or gene-environmental factors would act in concert or sequentially to propagate the pathological process of PD. Our findings are compatible with this conjecture showing that the genetic vulnerability caused by knock down of SKP1A in renders DAergic SN4741 cells especially sensitive to genetic reduction of Aldh1 and exposure to the external stressors MPP and DA, which have been implicated in PD pathology. Conclusively, our findings have identified Skp1 as a fundamental player in DA neuron function, differentiation and survival.