Loss-of-function mutations in DJ-1 were recently identified in an autosomal recessive form of Parkinson's disease (PD). The role of DJ-1 in normal and pathological states is still unclear, and evidences for its putative functions have been quite controversial. The role of DJ-1 in protecting neurons from oxidative stress is particularly informative in understanding a potential common mechanism for cell death in this genetic form of Parkinson's disease and in sporadic forms of Parkinson's disease which is thought to result from oxidative stress generated by mitochondrial dysfunction. Although DJ-1 deficient cells are more susceptible to oxidative stress, DJ-1 does not seem to have direct scavenging effect of reactive oxygen species (ROS). Instead, DJ-1 may work on a downstream pathway from ROS. Specifically, DJ-1 may be important in ubiquitination and DJ-1-null mouse brain attenuated increase in ubiquitination in response to oxidative stress. DJ-1 has been also shown to have chaperone function. DJ-1 changes into an acidic form under oxidative stress. To investigate the pathogenesis of Parkinson's disease caused by DJ-1 deficiency, we have successfully generated DJ-1-null mice. Our preliminary studies indicate that DJ-1-null mice develop age-dependent motor deficits associated with alteration of dopamine neurotransmission, consistent with hyperactive dopamine transporter (DAT) function. Based on these observations, we hypothesize that DJ-1 facilitates ubiquitination and subsequent degradation of target proteins such as DAT and this function is activated by oxidative stress. We propose the following experiments to test these hypotheses and identify the target molecules and pathways in which DJ-1 plays a role to maintain optimal dopamine transmission and cell survival.
Aim 1. To investigate whether dopamine neurons in DJ-1-null mice are more vulnerable to aging and paraquat challenge. We will examine the effect of aging and paraquat treatment in DJ-1-null mouse for its biochemical, behavioral and anatomical properties.
Aim 2. To investigate whether DJ-1 influences the ubiquitin proteasomeal pathway under oxidative stress. We will examine the total ubiquitinated proteins levels and compare the relative levels of specific substrate proteins implicated in dopaminergic neuronal death in DJ-1-null and WT brains. In addition, we will examine how the effect of DJ-1 on ubiquitin-proteasome system alters DAT function by measuring its surface expression and ubiquitination.
Aim 3. To investigate the chaperone function of DJ-1 and its oxidation dependent cooperation with ubiquitin pathway. Relevance Understanding the neuroprotective function of DJ-1 may lead to rational therapy for Parkinson's disease to prevent the manifestation or progression. Since Parkinson's disease leads to significant disability in a significant portion of the elderly population, such findings will have a significant impact in public health. ? ? ?
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