Modeling Human Cerebellar Development <em>In Vitro</em> in 2D Structure

The precise and timely development of the cerebellum is crucial not only for accurate motor coordination and balance but also for cognition. In addition, ...

University of Iowa

Amyotrophic lateral sclerosis (ALS), one of the most common adult-onset neurodegenerative diseases, has no known cure. Enhanced redox stress and inflammation have been associated with the pathoprogression of ALS through a poorly defined mechanism. Here we determined that dysregulated redox stress in ALS mice caused by NADPH oxidases Nox1 and Nox2 significantly influenced the progression of motor neuron disease caused by mutant SOD1(G93A) expression. Deletion of either Nox gene significantly slowed disease progression and improved survival. However, 50% survival rates were enhanced significantly more by Nox2 deletion than by Nox1 deletion. Interestingly, female ALS mice containing only 1 active X-linked Nox1 or Nox2 gene also had significantly delayed disease onset, but showed normal disease progression rates. Nox activity in spinal cords from Nox2 heterozygous female ALS mice was approximately 50% that of WT female ALS mice, suggesting that random X-inactivation was not influenced by Nox2 gene deletion. Hence, chimerism with respect to Nox-expressing cells in the spinal cord significantly delayed onset of motor neuron disease in ALS. These studies define what we believe to be new modifier gene targets for treatment of ALS.

Redox modifier genes in amyotrophic lateral sclerosis in mice.

Ubiquitin chain complexity in cells is likely regulated by a diverse set of deubiquitinating enzymes (DUBs) with distinct ubiquitin chain preferences. Here we show that the polyglutamine disease protein, ataxin-3, binds and cleaves ubiquitin chains in a manner suggesting that it functions as a mixed linkage, chain-editing enzyme. Ataxin-3 cleaves ubiquitin chains through its amino-terminal Josephin domain and binds ubiquitin chains through a carboxyl-terminal cluster of ubiquitin interaction motifs neighboring the pathogenic polyglutamine tract. Ataxin-3 binds both Lys(48)- or Lys(63)-linked chains yet preferentially cleaves Lys(63) linkages. Ataxin-3 shows even greater activity toward mixed linkage polyubiquitin, cleaving Lys(63) linkages in chains that contain both Lys(48) and Lys(63) linkages. The ubiquitin interaction motifs regulate the specificity of this activity by restricting what can be cleaved by the protease domain, demonstrating that linkage specificity can be determined by elements outside the catalytic domain of a DUB. These findings establish ataxin-3 as a novel DUB that edits topologically complex chains.

The deubiquitinating enzyme ataxin-3, a polyglutamine disease protein, edits Lys63 linkages in mixed linkage ubiquitin chains.

Polyglutamine diseases are a major cause of neurodegeneration worldwide. Recent studies highlight the importance of protein quality control mechanisms in regulating polyglutamine-induced toxicity. Here we discuss a model of disease pathogenesis that integrates current understanding of the role of protein folding in polyglutamine disease with emerging evidence that alterations in native protein interactions contribute to toxicity. We also incorporate new findings on other age-related neurodegenerative diseases in an effort to explain how protein aggregation and normal aging processes might be involved in polyglutamine disease pathogenesis.

Polyglutamine neurodegeneration: protein misfolding revisited.

Perturbations in neuronal protein homeostasis likely contribute to disease pathogenesis in polyglutamine (polyQ) neurodegenerative disorders. Here we provide evidence that the co-chaperone and ubiquitin ligase, CHIP (C-terminus of Hsp70-interacting protein), is a central component to the homeostatic mechanisms countering toxic polyQ proteins in the brain. Genetic reduction or elimination of CHIP accelerates disease in transgenic mice expressing polyQ-expanded ataxin-3, the disease protein in Spinocerebellar Ataxia Type 3 (SCA3). In parallel, CHIP reduction markedly increases the level of ataxin-3 microaggregates, which partition in the soluble fraction of brain lysates yet are resistant to dissociation with denaturing detergent, and which precede the appearance of inclusions. The level of microaggregates in the CNS, but not of ataxin-3 monomer, correlates with disease severity. Additional cell-based studies suggest that either of two quality control ubiquitin ligases, CHIP or E4B, can reduce steady state levels of expanded, but not wild-type, ataxin-3. Our results support an aggregation model of polyQ disease pathogenesis in which ataxin-3 microaggregates are a neurotoxic species, and suggest that enhancing CHIP activity is a possible route to therapy for SCA3 and other polyQ diseases.

In vivo suppression of polyglutamine neurotoxicity by C-terminus of Hsp70-interacting protein (CHIP) supports an aggregation model of pathogenesis.

The functional diversity of deubiquitinating enzymes (DUBs) is not well understood. The MJD family of DUBs consists of four cysteine proteases that share a catalytic "Josephin" domain. The family is named after the DUB ATXN3, which causes the neurodegenerative disease Machado-Joseph disease. The two closely related Josephin domain-containing (JosD) proteins 1 and 2 consist of little more than the Josephin domain. To gain insight into the properties of Josephin domains, we investigated JosD1 and JosD2. JosD1 and JosD2 were found to differ fundamentally in many respects. In vitro, only JosD2 can cleave ubiquitin chains. In contrast, JosD1 cleaves ubiquitin chains only after it is monoubiquitinated, a form of posttranslational-dependent regulation shared with ATXN3. A significant fraction of JosD1 is monoubiquitinated in diverse mouse tissues. In cell-based studies, JosD2 localizes to the cytoplasm whereas JosD1 preferentially localizes to the plasma membrane, particularly when ubiquitinated. The membrane occupancy by JosD1 suggests that it could participate in membrane-dependent events such as cell motility and endocytosis. Indeed, time-lapse imaging revealed that JosD1 enhances membrane dynamics and cell motility. JosD1 also influences endocytosis in cultured cells by increasing the uptake of endocytic markers of macropinocytosis while decreasing those for clathrin- and caveolae-mediated endocytosis. Our results establish that two closely related DUBs differ markedly in activity and function and that JosD1, a membrane-associated DUB whose activity is regulated by ubiquitination, helps regulate membrane dynamics, cell motility, and endocytosis.

JosD1, a membrane-targeted deubiquitinating enzyme, is activated by ubiquitination and regulates membrane dynamics, cell motility, and endocytosis.

Despite their widespread use in bipolar disorder, there is controversy surrounding the inclusion of antidepressant medications in the disorder's management. We sought to identify which demographic, socioeconomic, and clinical factors are associated with antidepressant exposure in bipolar disorder and which bipolar disorder patients are most likely to report a history of antidepressant-induced mania (AIM) when exposed to antidepressants.

Risk Factors Associated With Antidepressant Exposure and History of Antidepressant-Induced Mania in Bipolar Disorder.

Efforts to identify the causes of autism spectrum disorders have highlighted the importance of both genetics and environment, but the lack of human models for many of these disorders limits researchers' attempts to understand the mechanisms of disease and to develop new treatments. Induced pluripotent stem cells offer the opportunity to study specific genetic and environmental risk factors, but the heterogeneity of donor genetics may obscure important findings. Diseases associated with unusually high rates of autism, such as SCN2A syndromes, provide an opportunity to study specific mutations with high effect sizes in a human genetic context and may reveal biological insights applicable to more common forms of autism. Loss-of-function mutations in the SCN2A gene, which encodes the voltage-gated sodium channel Na1.2, are associated with autism rates up to 50%. Here, we review the findings from experimental models of SCN2A syndromes, including mouse and human cell studies, highlighting the potential role for patient-derived induced pluripotent stem cell technology to identify the molecular and cellular substrates of autism.

SCN2A channelopathies in the autism spectrum of neuropsychiatric disorders: a role for pluripotent stem cells?

Despite the high risk for suicide, relatively few studies have explored the relationship between suicide and brain imaging measures in bipolar disorder. In addition, fewer studies have explored the possibility that altered brain metabolism may be associated with suicide attempt. To begin to fill in these gaps, we evaluated functional (task based fMRI) and metabolic (quantitative T1ρ) differences associated with suicide attempt in participants with bipolar disorder. Thirty-nine participants with bipolar disorder underwent fMRI during a flashing checkerboard task and 27 also underwent quantitative T1ρ. The relationship between neuroimaging and history of suicide attempt was tested using multiple regression while adjusting for age, sex, and current mood state. Differences between two measures of suicide attempt (binary: yes/no and continuous: number of attempts) were quantified using the corrected Akaike Information Criterion. Participants who had attempted suicide had greater fMRI task-related activation in visual areas and the cerebellum. The number of suicide attempts was associated with a difference in BOLD response in the amygdala, prefrontal cortex, and cerebellum. Increased quantitative T1ρ was associated with number of suicide attempts in limbic, basal ganglia, and prefrontal cortex regions. This study is a secondary analysis with a modest sample size. Differences between measures of suicide history may be due to differences in statistical power. History of suicide was associated with limbic, prefrontal, and cerebellar alterations. Results comparing those with and without suicide attempts differed from results using number of suicide attempts, suggesting that these variables have different neurobiological underpinnings.

Aislinn J. Williams

Department of Psychiatry,
Carver College of Medicine,
Iowa Neuroscience Institute,
Pappajohn Biomedical Institute

University of Iowa

Modeling Human Cerebellar Development In Vitro in 2D Structure

Aislinn J. Williams

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University of Iowa

Modeling Human Cerebellar Development In Vitro in 2D Structure

Department of Psychiatry,
Carver College of Medicine,
Iowa Neuroscience Institute,
Pappajohn Biomedical Institute