Loss of dopaminergic neurons and resulting behavioural deficits in mouse model of Angelman syndrome.

E6 associated protein is an E3 ubiquitin ligase encoded by the gene Ube3a. Deletion or loss of function of the maternally inherited allele of Ube3a leads to Angelman syndrome. In the present study, we show that maternal loss of Ube3a (Ube3a(m-/p+)) in the mouse model leads to motor deficits that could be attributed to the dysfunction of the nigrostriatal pathway. The number of tyrosine hydroxylase positive neurons in the substantia nigra was significantly reduced in Ube3a(m-/p+) mice as compared to the wild type counterparts. The Ube3a(m-/p+) mice performed poorly in behavioural paradigms sensitive to nigrostriatal dysfunction. Even though the tyrosine hydroxylase staining was apparently the same in the striatum of both genotypes, the presynaptic and postsynaptic proteins were significantly reduced in Ube3a(m-/p+) mice. These findings suggest that the abnormality in the nigrostriatal pathway along with the cerebellum produces the observed motor dysfunctions in Ube3a(m-/p+) mice.

The ubiquitin ligase E6-AP promotes degradation of alpha-synuclein.

Parkinson's disease (PD) is a common neurodegenerative disorder caused mainly because of the loss of dopaminergic neurons in the substantia nigra. Protein inclusions called Lewy bodies are the most common pathological hallmark of PD and other synucleinopathies. Because the main component of these inclusions is alpha-synuclein, aggregation of this protein is thought to be a key pathogenic event in this disease. In the present investigation we report that E6 associated protein (E6-AP), a HECT (homologous to E6-AP C-terminus) domain ubiquitin ligase is a component of Lewy bodies in post-mortem PD brain. In the cell culture model, we demonstrate that endogenous E6-AP colocalizes with alpha-synuclein in juxtanuclear aggregates. E6-AP is also recruited to the centrosome upon inhibition of the proteasome function suggesting its involvement in the degradation of misfolded proteins. Over-expression of E6-AP enhances the degradation of wild type as well as the mutant forms of alpha-synuclein in a proteasome-dependent manner. E6-AP also promotes the degradation of the more toxic oligomeric forms of alpha-synuclein. Our data suggests that E6-AP is involved in the clearance of alpha-synuclein.