Ataxin1L is a regulator of HSC function highlighting the utility of cross-tissue comparisons for gene discovery.

Hematopoietic stem cells (HSCs) are rare quiescent cells that continuously replenish the cellular components of the peripheral blood. Observing that the ataxia-associated gene Ataxin-1-like (Atxn1L) was highly expressed in HSCs, we examined its role in HSC function through in vitro and in vivo assays. Mice lacking Atxn1L had greater numbers of HSCs that regenerated the blood more quickly than their wild-type counterparts. Molecular analyses indicated Atxn1L null HSCs had gene expression changes that regulate a program consistent with their higher level of proliferation, suggesting that Atxn1L is a novel regulator of HSC quiescence. To determine if additional brain-associated genes were candidates for hematologic regulation, we examined genes encoding proteins from autism- and ataxia-associated protein-protein interaction networks for their representation in hematopoietic cell populations. The interactomes were found to be highly enriched for proteins encoded by genes specifically expressed in HSCs relative to their differentiated progeny. Our data suggest a heretofore unappreciated similarity between regulatory modules in the brain and HSCs, offering a new strategy for novel gene discovery in both systems.

Duplication of Atxn1l suppresses SCA1 neuropathology by decreasing incorporation of polyglutamine-expanded ataxin-1 into native complexes.

Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease caused by expansion of a glutamine tract in ataxin-1 (ATXN1). SCA1 pathogenesis studies support a model in which the expanded glutamine tract causes toxicity by modulating the normal activities of ATXN1. To explore native interactions that modify the toxicity of ATXN1, we generated a targeted duplication of the mouse ataxin-1-like (Atxn1l, also known as Boat) locus, a highly conserved paralog of SCA1, and tested the role of this protein in SCA1 pathology. Using a knock-in mouse model of SCA1 that recapitulates the selective neurodegeneration seen in affected individuals, we found that elevated Atxn1l levels suppress neuropathology by displacing mutant Atxn1 from its native complex with Capicua (CIC). Our results provide genetic evidence that the selective neuropathology of SCA1 arises from modulation of a core functional activity of ATXN1, and they underscore the importance of studying the paralogs of genes mutated in neurodegenerative diseases to gain insight into mechanisms of pathogenesis.

Polyglutamine disease toxicity is regulated by Nemo-like kinase in spinocerebellar ataxia type 1.

Polyglutamine diseases are dominantly inherited neurodegenerative diseases caused by an expansion of a CAG trinucleotide repeat encoding a glutamine tract in the respective disease-causing proteins. Extensive studies have been performed to unravel disease pathogenesis and to develop therapeutics. Here, we report on several lines of evidence demonstrating that Nemo-like kinase (NLK) is a key molecule modulating disease toxicity in spinocerebellar ataxia type 1 (SCA1), a disease caused by a polyglutamine expansion in the protein ATAXIN1 (ATXN1). Specifically, we show that NLK, a serine/threonine kinase that interacts with ATXN1, modulates disease phenotypes of polyglutamine-expanded ATXN1 in a Drosophila model of SCA1. Importantly, the effect of NLK on SCA1 pathology is dependent upon NLK's enzymatic activity. Consistent with this, reduced Nlk expression suppresses the behavioral and neuropathological phenotypes in SCA1 knock-in mice. These data clearly indicate that either reducing NLK enzymatic activity or decreasing NLK expression levels can have beneficial effects against the toxicity induced by polyglutamine-expanded ATXN1.

Comparison of an expanded ataxia interactome with patient medical records reveals a relationship between macular degeneration and ataxia.

Spinocerebellar ataxias 6 and 7 (SCA6 and SCA7) are neurodegenerative disorders caused by expansion of CAG repeats encoding polyglutamine (polyQ) tracts in CACNA1A, the alpha1A subunit of the P/Q-type calcium channel, and ataxin-7 (ATXN7), a component of a chromatin-remodeling complex, respectively. We hypothesized that finding new protein partners for ATXN7 and CACNA1A would provide insight into the biology of their respective diseases and their relationship to other ataxia-causing proteins. We identified 118 protein interactions for CACNA1A and ATXN7 linking them to other ataxia-causing proteins and the ataxia network. To begin to understand the biological relevance of these protein interactions within the ataxia network, we used OMIM to identify diseases associated with the expanded ataxia network. We then used Medicare patient records to determine if any of these diseases co-occur with hereditary ataxia. We found that patients with ataxia are at 3.03-fold greater risk of these diseases than Medicare patients overall. One of the diseases comorbid with ataxia is macular degeneration (MD). The ataxia network is significantly (P= 7.37 × 10(-5)) enriched for proteins that interact with known MD-causing proteins, forming a MD subnetwork. We found that at least two of the proteins in the MD subnetwork have altered expression in the retina of Ataxin-7(266Q/+) mice suggesting an in vivo functional relationship with ATXN7. Together these data reveal novel protein interactions and suggest potential pathways that can contribute to the pathophysiology of ataxia, MD, and diseases comorbid with ataxia.

MicroRNA Biomarkers of Toxicity in Biological Matrices.

Biomarker measurements that reliably correlate with tissue injury and that can be measured within accessible biofluids offer benefits in terms of cost, time, and convenience when assessing chemical and drug-induced toxicity in model systems or human cohorts. MicroRNAs (miRNAs) have emerged in recent years as a promising new class of biomarker for monitoring toxicity. Recent enthusiasm for miRNA biomarker research has been fueled by evidence that certain miRNAs are cell-type specific and are released during injury, thus raising the possibility of using biofluid-based miRNAs as a "liquid biopsy" that may be obtained by sampling extracellular fluids. As biomarkers, miRNAs demonstrate improved stability as compared with many protein markers and sequences are largely conserved across species, simplifying analytical techniques. Recent efforts have sought to identify miRNAs that are released into accessible biofluids following xenobiotic exposure, using compounds that target specific organs. Whereas still early in the discovery phase, miRNA biomarkers will have an increasingly important role in the assessment of adverse effects of both environmental chemicals and pharmaceutical drugs. Here, we review the current findings of biofluid-based miRNAs, as well as highlight technical challenges in assessing toxicologic pathology using these biomarkers.

Interaction effects of temperature and ozone on lung function and markers of systemic inflammation, coagulation, and fibrinolysis: a crossover study of healthy young volunteers.

BACKGROUND: Trends in climate suggest that extreme weather events such as heat waves will become more common. High levels of the gaseous pollutant ozone are associated with elevated temperatures. Ozone has been associated with respiratory diseases as well as cardiovascular morbidity and mortality and can reduce lung function and alter systemic markers of fibrinolysis. The interaction between ozone and temperature is unclear. METHODS: Sixteen healthy volunteers were exposed in a randomized crossover study to 0.3 ppm ozone and clean air for 2 hr at moderate (22°C) temperature and again at an elevated temperature (32.5°C). In each case lung function was performed and blood taken before and immediately after exposure and the next morning. RESULTS: Ozone exposure at 22°C resulted in a decrease in markers of fibrinolysis the next day. There was a 51.8% net decrease in PAI-1 (plasminogen activator inhibitor-1), a 12.1% net decrease in plasminogen, and a 17.8% net increase in D-dimer. These significantly differed from the response at 32.5°C, where there was a 44.9% (p = 0.002) and a 27.9% (p = 0.001) increase in PAI-1 and plasminogen, respectively, and a 12.5% (p = 0.042) decrease in D-dimer. In contrast, decrements in lung function following ozone exposure were comparable at both moderate and elevated temperatures (forced expiratory volume in 1 sec, -12.4% vs. -7.5%, p > 0.05). No changes in systemic markers of inflammation were observed for either temperature. CONCLUSION: Ozone-induced systemic but not respiratory effects varied according to temperature. Our study suggests that at moderate temperature ozone may activate the fibrinolytic pathway, while at elevated temperature ozone may impair it. These findings provide a biological basis for the interaction between temperature and ozone on mortality observed in some epidemiologic studies.

ATXN1 protein family and CIC regulate extracellular matrix remodeling and lung alveolarization.

Although expansion of CAG repeats in ATAXIN1 (ATXN1) causes Spinocerebellar ataxia type 1, the functions of ATXN1 and ATAXIN1-Like (ATXN1L) remain poorly understood. To investigate the function of these proteins, we generated and characterized Atxn1L(-/-) and Atxn1(-/-); Atxn1L(-/-) mice. Atxn1L(-/-) mice have hydrocephalus, omphalocele, and lung alveolarization defects. These phenotypes are more penetrant and severe in Atxn1(-/-); Atxn1L(-/-) mice, suggesting that ATXN1 and ATXN1L are functionally redundant. Upon pursuing the molecular mechanism, we discovered that several Matrix metalloproteinase (Mmp) genes are overexpressed and that the transcriptional repressor Capicua (CIC) is destabilized in Atxn1L(-/-) lungs. Consistent with this, Cic deficiency causes lung alveolarization defect. Loss of either ATXN1L or CIC derepresses Etv4, an activator for Mmp genes, thereby mediating MMP9 overexpression. These findings demonstrate a critical role of ATXN1/ATXN1L-CIC complexes in extracellular matrix (ECM) remodeling during development and their potential roles in pathogenesis of disorders affecting ECM remodeling.