Excitotoxic and Radiation Stress Increase TERT Levels in the Mitochondria and Cytosol of Cerebellar Purkinje Neurons

Telomerase reverse transcriptase (TERT) is the catalytic subunit of telomerase, an enzyme that elongates telomeres at the ends of chromosomes during DNA replication. Recently, it was shown that TERT has additional roles in cell survival, mitochondrial function, DNA repair, and Wnt signaling, all of which are unrelated to telomeres. Here, we demonstrate that TERT is enriched in Purkinje neurons, but not in the granule cells of the adult mouse cerebellum. TERT immunoreactivity in Purkinje neurons is present in the nucleus, mitochondria, and cytoplasm. Furthermore, TERT co-localizes with mitochondrial markers, and immunoblot analysis of protein extracts from isolated mitochondria and synaptosomes confirmed TERT localization in mitochondria. TERT expression in Purkinje neurons increased significantly in response to two stressors: a sub-lethal dose of X-ray radiation and exposure to a high glutamate concentration. While X-ray radiation increased TERT levels in the nucleus, glutamate exposure elevated TERT levels in mitochondria. Our findings suggest that in mature Purkinje neurons, TERT is present both in the nucleus and in mitochondria, where it may participate in adaptive responses of the neurons to excitotoxic and radiation stress.

Alternative Splicing of Neuronal Differentiation Factor TRF2 Regulated by HNRNPH1/H2

During neuronal differentiation, use of an alternative splice site on the rat telomere repeat-binding factor 2 (TRF2) mRNA generates a short TRF2 protein isoform (TRF2-S) capable of derepressing neuronal genes. However, the RNA-binding proteins (RBPs) controlling this splicing event are unknown. Here, using affinity pull-down analysis, we identified heterogeneous nuclear ribonucleoproteins H1 and H2(HNRNPH) as RBPs specifically capable of interacting with the spliced RNA segment (exon 7) of Trf2 pre-mRNA. HNRNPH proteins prevent the production of the short isoform of Trf2 mRNA, as HNRNPH silencing selectively elevates TRF2-S levels. Accordingly, HNRNPH levels decline while TRF2-S levels increase during neuronal differentiation. In addition, CRISPR/Cas9-mediated deletion of hnRNPH2 selectively accelerates the NGF-triggered differentiation of rat pheochromocytoma cells into neurons. In sum, HNRNPH is a splicing regulator of Trf2 pre-mRNA that prevents the expression of TRF2-S, a factor implicated in neuronal differentiation.

Combination therapy with lenalidomide and nanoceria ameliorates CNS autoimmunity

OBJECTIVE

Multiple sclerosis (MS) is a debilitating neurological disorder involving an autoimmune reaction to oligodendrocytes and degeneration of the axons they ensheath in the CNS. Because the damage to oligodendrocytes and axons involves local inflammation and associated oxidative stress, we tested the therapeutic efficacy of combined treatment with a potent anti-inflammatory thalidomide analog (lenalidomide) and novel synthetic anti-oxidant cerium oxide nanoparticles (nanoceria) in the experimental autoimmune encephalomyelitis (EAE) mouse model of MS.

METHODS

C57BL/6 mice were randomly assigned to a control (no EAE) group, or one of the four myelin oligodendrocyte glycoprotein-induced EAE groups: vehicle, lenalidomide, nanoceria, or lenalidomide plus nanoceria. During a 23 day period, clinical EAE symptoms were evaluated daily, and MRI brain scans were performed at 11-13 days and 20-22 days. Histological and biochemical analyses of brain tissue samples were performed to quantify myelin loss and local inflammation.

RESULTS

Lenalidomide treatment alone delayed symptom onset, while nanoceria treatment had no effect on symptom onset or severity, but did promote recovery; lenalidomide and nanoceria each significantly attenuated white matter pathology and associated inflammation. Combined treatment with lenalidomide and nanoceria resulted in a near elimination of EAE symptoms, and reduced white matter pathology and inflammatory cell responses to a much greater extent than either treatment alone.

INTERPRETATION

By suppressing inflammation and oxidative stress, combined treatment with lenalidomide and nanoceria can reduce demyelination and associated neurological symptoms in EAE mice. Our preclinical data suggest a potential application of this combination therapy in MS.

Telomere shortening in neurological disorders: an abundance of unanswered questions

Telomeres, ribonucleoprotein complexes that cap eukaryotic chromosomes, typically shorten in leukocytes with aging. Aging is a primary risk factor for neurodegenerative disease (ND), and a common assumption has arisen that leukocyte telomere length (LTL) can serve as a predictor of neurological disease. However, the evidence for shorter LTL in Alzheimer's and Parkinson's patients is inconsistent. The diverse causes of telomere shortening may explain variability in LTL between studies and individuals. Additional research is needed to determine whether neuronal and glial telomeres shorten during aging and in neurodegenerative disorders, if and how LTL is related to brain cell telomere shortening, and whether telomere shortening plays a causal role in or exacerbates neurological disorders.

Molecular control of the amount, subcellular location, and activity state of translation elongation factor 2 in neurons experiencing stress

Eukaryotic elongation factor 2 (eEF-2) is an important regulator of the protein translation machinery whereby it controls the movement of the ribosome along the mRNA. The activity of eEF-2 is regulated by changes in cellular energy status and nutrient availability and by posttranslational modifications such as phosphorylation and mono-ADP-ribosylation. However, the mechanisms regulating protein translation under conditions of cellular stress in neurons are unknown. Here we show that when rat hippocampal neurons experience oxidative stress (lipid peroxidation induced by exposure to cumene hydroperoxide; CH), eEF-2 is hyperphosphorylated and ribosylated, resulting in reduced translational activity. The degradation of eEF-2 requires calpain proteolytic activity and is accompanied by accumulation of eEF-2 in the nuclear compartment. The subcellular localization of both native and phosphorylated forms of eEF-2 is influenced by CRM1 and 14.3.3, respectively. In hippocampal neurons p53 interacts with nonphosphorylated (active) eEF-2, but not with its phosphorylated form. The p53-eEF-2 complexes are present in cytoplasm and nucleus, and their abundance increases when neurons experience oxidative stress. The nuclear localization of active eEF-2 depends upon its interaction with p53, as cells lacking p53 contain less active eEF-2 in the nuclear compartment. Overexpression of eEF-2 in hippocampal neurons results in increased nuclear levels of eEF-2 and decreased cell death after exposure to CH. Our results reveal novel molecular mechanisms controlling the differential subcellular localization and activity state of eEF-2 that may influence the survival status of neurons during periods of elevated oxidative stress.

Evidence for miR-181 involvement in neuroinflammatory responses of astrocytes

Inflammation is a common component of acute injuries of the central nervous system (CNS) such as ischemia, and degenerative disorders such as Alzheimer's disease. Glial cells play important roles in local CNS inflammation, and an understanding of the roles for microRNAs in glial reactivity in injury and disease settings may therefore lead to the development of novel therapeutic interventions. Here, we show that the miR-181 family is developmentally regulated and present in high amounts in astrocytes compared to neurons. Overexpression of miR-181c in cultured astrocytes results in increased cell death when exposed to lipopolysaccharide (LPS). We show that miR-181 expression is altered by exposure to LPS, a model of inflammation, in both wild-type and transgenic mice lacking both receptors for the inflammatory cytokine TNF-α. Knockdown of miR-181 enhanced LPS-induced production of pro-inflammatory cytokines (TNF-α, IL-6, IL-1β, IL-8) and HMGB1, while overexpression of miR-181 resulted in a significant increase in the expression of the anti-inflammatory cytokine IL-10. To assess the effects of miR-181 on the astrocyte transcriptome, we performed gene array and pathway analysis on astrocytes with reduced levels of miR-181b/c. To examine the pool of potential miR-181 targets, we employed a biotin pull-down of miR-181c and gene array analysis. We validated the mRNAs encoding MeCP2 and X-linked inhibitor of apoptosis as targets of miR-181. These findings suggest that miR-181 plays important roles in the molecular responses of astrocytes in inflammatory settings. Further understanding of the role of miR-181 in inflammatory events and CNS injury could lead to novel approaches for the treatment of CNS disorders with an inflammatory component.

miR-130 suppresses adipogenesis by inhibiting peroxisome proliferator-activated receptor gamma expression

Adipose tissue development is tightly regulated by altering gene expression. MicroRNAs are strong posttranscriptional regulators of mammalian differentiation. We hypothesized that microRNAs might influence human adipogenesis by targeting specific adipogenic factors. We identified microRNAs that showed varying abundance during the differentiation of human preadipocytes into adipocytes. Among them, miR-130 strongly affected adipocyte differentiation, as overexpressing miR-130 impaired adipogenesis and reducing miR-130 enhanced adipogenesis. A key effector of miR-130 actions was the protein peroxisome proliferator-activated receptor γ (PPARγ), a major regulator of adipogenesis. Interestingly, miR-130 potently repressed PPARγ expression by targeting both the PPARγ mRNA coding and 3' untranslated regions. Adipose tissue from obese women contained significantly lower miR-130 and higher PPARγ mRNA levels than that from nonobese women. Our findings reveal that miR-130 reduces adipogenesis by repressing PPARγ biosynthesis and suggest that perturbations in this regulation is linked to human obesity.

Functional MRI and response inhibition in children exposed to cocaine in utero. Preliminary findings

This study investigated the potential long-term effects of cocaine exposure on brain functioning using fMRI in school-aged children. The sample included 12 children with prenatal cocaine exposure and 12 non-exposed children (8-9 years old). Groups did not differ on IQ, socioeconomic status, or perinatal risk factors. A response inhibition task was administered during an fMRI scan using a 1.5-T MRI system. Task performance did not differentiate groups, but groups were differentiated by patterns of task-related brain activity. Cocaine-exposed children showed greater activation in the right inferior frontal cortex and caudate during response inhibition, whereas non-exposed children showed greater activations in temporal and occipital regions. These preliminary findings suggest that prenatal cocaine may affect the development of brain systems involved in the regulation of attention and response inhibition.

An event-related fMRI investigation of voice-onset time discrimination

The discrimination of voice-onset time, an acoustic-phonetic cue to voicing in stop consonants, was investigated to explore the neural systems underlying the perception of a rapid temporal speech parameter. Pairs of synthetic stimuli taken from a [da] to [ta] continuum varying in voice-onset time (VOT) were presented for discrimination judgments. Participants exhibited categorical perception, discriminating 15-ms and 30-ms between-category comparisons and failing to discriminate 15-ms within-category comparisons. Contrastive analysis with a tone discrimination task demonstrated left superior temporal gyrus activation in all three VOT conditions with recruitment of additional regions, particularly the right inferior frontal gyrus and middle frontal gyrus for the 15-ms between-category stimuli. Hemispheric differences using anatomically defined regions of interest showed two distinct patterns with anterior regions showing more activation in the right hemisphere relative to the left hemisphere and temporal regions demonstrating greater activation in the left hemisphere relative to the right hemisphere. Activation in the temporal regions appears to reflect initial acoustic-perceptual analysis of VOT. Greater activation in the right hemisphere anterior regions may reflect increased processing demands, suggesting involvement of the right hemisphere when the acoustic distance between the stimuli are reduced and when the discrimination judgment becomes more difficult.