Novel Monoclonal Antibodies Demonstrate Biochemical Variation of Brain Parkin with Age

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Mutations in the human parkin gene cause autosomal recessive juvenile parkinsonism, a heritable form of Parkinson's disease (PD). To determine whether mutations in the mouse parkin gene (Park2) also result in a parkinsonian phenotype, we generated mice with a targeted deletion of parkin exon 2. Using an extensive behavioral screen, we evaluated neurological function, motor ability, emotionality, learning, and memory in aged Parkin-deficient mice. The behavioral profile of Parkin-deficient mice on a B6;129S4 genetic background was strikingly similar to that of control mice, and most differences were not reproducible by using coisogenic mice on a 129S4 genetic background. Moreover, catecholamine levels in the striatum, olfactory bulb, and spinal cord of Parkin-deficient mice were normal. In contrast to previous studies using independently generated Parkin-deficient mice, we found no evidence for nigrostriatal, cognitive, or noradrenergic dysfunction. Understanding why Parkin-deficient mice do not exhibit robust signs of parkinsonism could advance knowledge and treatment of PD.mouse behavior ͉ dopamine ͉ norepinephrine ͉ gene knockout ͉ Parkinson P arkinson's disease (PD) is a devastating neurodegenerative disorder that affects Ͼ500,000 people in the United States alone (1). The age-related and progressive signs of PD classically include resting tremor, muscular rigidity, abnormal gait, and slow movement; however, other signs and symptoms associated with parkinsonism can include somatosensory deficits, impaired cognitive function, and psychiatric disturbances (2-4). Many PD signs result from the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Dopamine replacement medications often succeed in managing parkinsonism; however, these treatments lose effectiveness, have undesirable effects, and do not prevent the underlying neurodegeneration. Understanding the molecular mechanism of dopaminergic neuron degeneration would facilitate the development of therapies that prevent PD.The identification of mutations in single genes that result in familial parkinsonism will help advance our understanding of the molecular mechanism of PD. Mutations in the human parkin gene are responsible for autosomal recessive juvenile parkinsonism (AR-JP), a heritable disease that resembles PD (5). The Parkin protein is a widely expressed, E3 ubiquitin-protein ligase that is thought to target specific proteins for proteasomal degradation (5-7). Presumably, in the absence of Parkin function, these protein targets accumulate to toxic levels and cause dopamine neuron degeneration.To investigate how mutations in parkin lead to parkinsonism, we generated mice with a targeted disruption of Park2. We hypothesized that Parkin-deficient mice would recapitulate the behavioral signs and pathology of AR-JP. During our investigation, several other groups independently generated and described mice with various targeted deletions of the parkin gene (8-11); however, results from these studies have raised many new issues. First, the b...

Section: Resultsmentioning

confidence: 99%

Parkin-deficient mice are not a robust model of parkinsonism

Perez

Palmiter

2005

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“…Based on the unique vulnerability of the substantia nigra and locus coeruleus in Parkin-null patients, however, we speculate that parkin plays a specialized role in modulating Bax within these discrete neuronal subpopulations. The interaction between parkin and Bax may also play a role in the natural age-dependent degeneration of catecholaminergic neurons in the normal human brain (33)(34)(35), which may be a consequence of the age-dependent changes in parkin solubility (36) or stress-induced loss of parkin function [reviewed elsewhere (25)]. …”

Section: Discussionmentioning

confidence: 99%

The ubiquitin E3 ligase parkin regulates the proapoptotic function of Bax

Johnson

Berger²,

Cortese³

et al. 2012

156

144

Autosomal recessive loss-of-function mutations within the PARK2 gene functionally inactivate the E3 ubiquitin ligase parkin, resulting in neurodegeneration of catecholaminergic neurons and a familial form of Parkinson disease. Current evidence suggests both a mitochondrial function for parkin and a neuroprotective role, which may in fact be interrelated. The antiapoptotic effects of parkin have been widely reported, and may involve fundamental changes in the threshold for apoptotic cytochrome c release, but the substrate(s) involved in parkin dependent protection had not been identified. Here, we demonstrate the parkin-dependent ubiquitination of endogenous Bax comparing primary cultured neurons from WT and parkin KO mice and using multiple parkin-overexpressing cell culture systems. The direct ubiquitination of purified Bax was also observed in vitro following incubation with recombinant parkin. We found that parkin prevented basal and apoptotic stressinduced translocation of Bax to the mitochondria. Moreover, an engineered ubiquitination-resistant form of Bax retained its apoptotic function, but Bax KO cells complemented with lysine-mutant Bax did not manifest the antiapoptotic effects of parkin that were observed in cells expressing WT Bax. These data suggest that Bax is the primary substrate responsible for the antiapoptotic effects of parkin, and provide mechanistic insight into at least a subset of the mitochondrial effects of parkin.Parkinson's disease | apoptosis | neuroprotection | mitophagy P arkinson disease (PD) is a neurodegenerative disorder that affects 1-3% of the population over the age of 65 years (1). The symptoms include tremor, rigidity, bradykinesia, and postural instability. These physical characteristics are caused by the progressive degeneration of dopaminergic neurons of the substantia nigra pars compacta and, to a lesser extent, the catecholaminergic neurons of the locus coeruleus. Although most cases of PD are sporadic in nature, a small number of genes are responsible for the rare familial forms of PD (2). Loss-of-function mutations within the PARK2 locus, which encodes the protein parkin, are the most common cause of autosomal recessive PD (3).Parkin is a 465-amino acid protein that is expressed in multiple tissues and functions as an E3 ubiquitin ligase (4). Ubiquitination of substrates is a tightly regulated process, requiring the combined activity of three enzymes: an E1 ubiquitin-activating enzyme, an E2 ubiquitin conjugating enzyme, and an E3 ubiquitin ligase (5). E3 ubiquitin ligases are responsible for substrate recognition, and as such contribute the specificity of a ubiquitin reaction. Defects in parkin-mediated ubiquitination may result in the failure to target specific substrates for degradation, leading to accumulation of potentially toxic proteins and consequent cell death (6). Parkin is widely neuroprotective (7); however, many of the putative parkin substrates reported to date are not thought to directly mediate toxicity in such a simple fashion [reviewed elsewhere (8...

“…Sequencing of the RT-PCR products confirms that the parkin transcript in parkin null brains lacks exon 7, resulting in a frame shift and a premature stop codon in exon 8, as predicted (data not shown). Western blot analysis of brain lysates by using monoclonal antibody PRK8, which specifically recognizes the second RING finger of parkin (33), shows reduced expression of parkin in heterozygous mice and fails to detect parkin in KO mice (Fig. 1E).…”

Section: Generation Of Parkin Nullmentioning

confidence: 99%

Loss of locus coeruleus neurons and reduced startle in parkin null mice

Coelln

Thomas

Savitt

et al. 2004

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250

Parkinson's disease (PD) is the most common neurodegenerative movement disorder and is characterized pathologically by degeneration of catecholaminergic neurons of the substantia nigra pars compacta and locus coeruleus, among other regions. Autosomalrecessive juvenile Parkinsonism (ARJP) is caused by mutations in the PARK2 gene coding for parkin and constitutes the most common familial form of PD. The majority of ARJP-associated parkin mutations are thought to be loss of function-mutations; however, the pathogenesis of ARJP remains poorly understood. Here, we report the generation of parkin null mice by targeted deletion of parkin exon 7. These mice show a loss of catecholaminergic neurons in the locus coeruleus and an accompanying loss of norepinephrine in discrete regions of the central nervous system. Moreover, there is a dramatic reduction of the norepinephrinedependent startle response. The nigrostriatal dopaminergic system does not show any impairment. This mouse model will help gain a better understanding of parkin function and the mechanisms underlying parkin-associated PD.