Shank, which are known targets for ubiquitination and degrada- tion by the UPS [17,45,46,47]. Here, we show that reduction in UCH-L1 activity, and subsequent decreased mono-ubiquitin levels, under non-pathogenic conditions, results in accumulation of a-syn, which is degraded by the UPS [48,49]. These observations are in line with our previous study and demonstrate that alterations in ubiquitin homeostasis could affect ubiquitin- dependent degradation of certain proteins, including a-syn, by the UPS. In contrast to our observations in non-pathogenic conditions, inhibition of UCH-L1 activity under pathogenic conditions (h-a- syn over expression) reduces a-syn protein levels, and this could potentially be beneficial for neuronal survival. Many lines of evidence have suggested that dysfunction in the autophagy pathway is common in many neurodegenerative disorders including in PD and DLB [50,51,52,53]. Furthermore, a-syn aggregates have been shown to interfere with the autophagy mechanisms and ultimately lead to neurodegeneration in vivo and in vitro [54,55,56]. Interestingly, excess a-syn and its aggregates are cleared by autophagy [49,57,58]. This observation is in line with a recent study by Spencer et al., where it was shown that LV- mediated over expression of beclin 1, a major component in initial steps of the autophagy pathway, reduced abnormal accumulation of a-syn and associated neuronal deficits in a transgenic mouse model of DLB [55]. The observed hippocampal accumulation of p62, whose levels are known to increase in response to inhibition in autophagy, with a concurrent decrease in cleaved LC3 II levels in our a-syn transgenic model point to a dysfunction in the autophagy pathway in these mice [59,60]. Furthermore, Kabuta et al. have shown that UCH-L1 interacts with members of the chaperon-mediated autophagy (CMA), and that the familial PD- associated UCH-L1I93M interacts abnormally with these members, leads to inhibition of CMA and as a result an increase in a-syn levels in cultured cells [61]. Taken together, under pathological conditions (h-a-syn over expression), blocking UCH-L1 activity may enhance autophagy, which in turn will serve to degrade and reduce a-syn levels. The mechanism(s) by which inhibition of UCH-L1 by LDN affects its interaction with the members of autophagy pathway are unknown. Interestingly, our double- immunolabeling for UCH-L1 and a-syn, only in non tg mice treated with LDN, showed a redistribution in UCH-L1 staining pattern. It is unclear how this redistribution may affect the interaction of UCH-L1 with members of the autophagy pathway, and whether these alteration lead to the opposing effects on a-syn observed in non tg vs. a-syn tg mice. Our data suggest that loss of UCH-L1 function in the context of h-a-syn-induced pathologies may have neuroprotective effect in the hippocampus. A recent study by Liu et al. demonstrated that a population of UCH-L1 is membrane-bound (UCH-L1M), and C-terminal farnesylation of UCH-L1 promotes its association with cellular membranes [62]. Over expression of wild type UCH-L1 led to an References 1. Lang AE, Lozano AM (1998) Parkinson’s disease. Second of two parts. N Engl J Med 339: 1130–1143. 2. Lang AE, Lozano AM (1998) Parkinson’s disease. First of two parts. N Engl J Med 339: 1044–1053. 3. Trojanowski JQ, Goedert M, Iwatsubo T, Lee VM (1998) Fatal attractions: abnormal protein aggregation and neuron death in Parkinson’s disease and Lewy body dementia. Cell Death Differ 5: 832–837. 4. Pollanen MS, Dickson DW, Bergeron C (1993) Pathology and biology of the Lewy body. J Neuropathol Exp Neurol 52: 183–191. 5. 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In addition, approximately 30% of UCH-L1 was found to be membrane-associated in cortical tissues of diseased and normal human brains (e.g. PD and AD). However, an association between UCH-L1 M /UCH-L1S (soluble UCH-L1) ratio and disease, in this case, in cortical tissues from PD patients was not detected [62]. These data clearly demonstrate a link between UCH-L1 farnesylation, membrane association and a-syn expression levels. However, the effects of modulation of UCH-L1 activity (e.g. by LDN) on these conditions are unknown. It is worth noting that the C220S mutation does not affect hydrolytic activity of UCH-L1 [62]. Interestingly, Kabuta et al. did not report an increase in a-syn expression levels due to wild type UCH-L1 over expression using the same cell culture model system [61]. Also, we have used a model system in which UCH-L1 and a-syn are abundantly expressed in the hippocampus and cultured neurons contrary to these other systems where neither proteins were endogenously expressed. Our use of a system where proteins of interest are endogenously expressed presents a more suitable system and reflective of what may occur in vivo. In conclusion, we show that suppression of UCH-L1 activity has differential effects on a-syn in neurons that express normal or excessive levels of a-syn. Under normal physiological conditions, perturbation of UCH-L1 activity has a dramatic effect on distribution and protein levels of presynaptic a-syn, which in turn could have detrimental effects on normal neuronal function. Under pathological conditions, however, loss of UCH-L1 function proves to be beneficial as it not only enhances a-syn degradation but also relieves the a-syn-mediated block of the autophagy pathway. 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