tRNA Dysregulation in Neurodevelopmental and Neurodegenerative Diseases.

Transfer RNAs (tRNAs) decode messenger RNA codons to peptides at the ribosome. The nuclear genome contains many tRNA genes for each amino acid and even each anticodon. Recent evidence indicates that expression of these tRNAs in neurons is regulated, and they are not functionally redundant. When specific tRNA genes are nonfunctional, this results in an imbalance between codon demand and tRNA availability. Furthermore, tRNAs are spliced, processed, and posttranscriptionally modified. Defects in these processes lead to neurological disorders. Finally, mutations in the aminoacyl tRNA synthetases (aaRSs) also lead to disease. Recessive mutations in several aaRSs cause syndromic disorders, while dominant mutations in a subset of aaRSs lead to peripheral neuropathy, again due to an imbalance between tRNA supply and codon demand. While it is clear that disrupting tRNA biology often leads to neurological disease, additional research is needed to understand the sensitivity of neurons to these changes

O-GlcNAcase contributes to cognitive function in Drosophila

Contains fulltext : 219183.pdf (publisher's version ) (Open Access

Intellectual disability-associated disruption of O-GlcNAcylation impairs neuronal development and cognition-relevant habituation learning in Drosophila

O-GlcNAcylation is a reversible co-/post-translational modification involved in a multitude of cellular processes. The addition and removal of the O-GlcNAc modification is controlled by two conserved enzymes, O-GlcNAc transferase (OGT) and O-GlcNAc hydrolase (OGA). Mutations in OGT have recently been discovered to cause a novel Congenital Disorder of Glycosylation (OGT-CDG) that is characterized by intellectual disability. The mechanisms by which OGT-CDG mutations affect cognition remain unclear. We manipulated O-GlcNAc transferase and O-GlcNAc hydrolase activity in Drosophila and demonstrate an important role of O-GlcNAcylation in habituation learning and synaptic development at the larval neuromuscular junction. Introduction of patient-specific missense mutations into Drosophila O-GlcNAc transferase using CRISPR/Cas9 gene editing leads to deficits in locomotor function and habituation learning. The habituation deficit can be corrected by blocking O-GlcNAc hydrolysis, indicating that OGT-CDG mutations affect cognition-relevant habituation via reduced protein O-GlcNAcylation. This study establishes a critical role for O-GlcNAc cycling and disrupted O-GlcNAc transferase activity in cognitive dysfunction, and suggests that blocking O-GlcNAc hydrolysis is a potential strategy to treat OGT-CDG

Impaired protein translation in Drosophila models for Charcot–Marie–Tooth neuropathy caused by mutant tRNA synthetases

Dominant mutations in five tRNA synthetases cause Charcot–Marie–Tooth (CMT) neuropathy, suggesting that altered aminoacylation function underlies the disease. However, previous studies showed that loss of aminoacylation activity is not required to cause CMT. Here we present a Drosophila model for CMT with mutations in glycyl-tRNA synthetase (GARS). Expression of three CMT-mutant GARS proteins induces defects in motor performance and motor and sensory neuron morphology, and shortens lifespan. Mutant GARS proteins display normal subcellular localization but markedly reduce global protein synthesis in motor and sensory neurons, or when ubiquitously expressed in adults, as revealed by FUNCAT and BONCAT. Translational slowdown is not attributable to altered tRNA[superscript Gly] aminoacylation, and cannot be rescued by Drosophila Gars overexpression, indicating a gain-of-toxic-function mechanism. Expression of CMT-mutant tyrosyl-tRNA synthetase also impairs translation, suggesting a common pathogenic mechanism. Finally, genetic reduction of translation is sufficient to induce CMT-like phenotypes, indicating a causal contribution of translational slowdown to CMT.National Institutes of Health (U.S.) (Grant GM17151

Impaired autonomic regulation of resistance arteries in mice with low vascular endothelial growth factor or upon vascular endothelial growth factor trap delivery

Background-Control of peripheral resistance arteries by autonomic nerves is essential for the regulation of blood flow. The signals responsible for the maintenance of vascular neuroeffector mechanisms in the adult, however, remain largely unknown. Methods and Results-Here, we report that VEGF(partial derivative/partial derivative) mice with low vascular endothelial growth factor (VEGF) levels suffer defects in the regulation of resistance arteries. These defects are due to dysfunction and structural remodeling of the neuroeffector junction, the equivalent of a synapse between autonomic nerve endings and vascular smooth muscle cells, and to an impaired contractile smooth muscle cell phenotype. Notably, short-term delivery of a VEGF inhibitor to healthy mice also resulted in functional and structural defects of neuroeffector junctions. Conclusions-These findings uncover a novel role for VEGF in the maintenance of arterial neuroeffector function and may help us better understand how VEGF inhibitors cause vascular regulation defects in cancer patients. (Circulation. 2010; 122: 273-281.

Impaired DNA damage response signaling by FUS-NLS mutations leads to neurodegeneration and FUS aggregate formation

Amyotrophic lateral sclerosis (ALS) is the most frequent motor neuron disease. Cytoplasmic fused in sarcoma (FUS) aggregates are pathological hallmarks of FUS-ALS. Proper shuttling between the nucleus and cytoplasm is essential for physiological cell function. However, the initial event in the pathophysiology of FUS-ALS remains enigmatic. Using human induced pluripotent stem cell (hiPSCs)-derived motor neurons (MNs), we show that impairment of poly(ADP-ribose) polymerase (PARP)-dependent DNA damage response (DDR) signaling due to mutations in the FUS nuclear localization sequence (NLS) induces additional cytoplasmic FUS mislocalization which in turn results in neurodegeneration and FUS aggregate formation. Our work suggests that a key pathophysiologic event in ALS is upstream of aggregate formation. Targeting DDR signaling could lead to novel therapeutic routes for ameliorating ALS

VEGF: a critical player in neurodegeneration

VEGF is a prototype angiogenic factor, but recent evidence indicates that this growth factor also has direct effects on neural cells. Abnormal regulation of VEGF expression has now been implicated in several neurodegenerative disorders, including motoneuron degeneration. This has stimulated an increasing interest in assessing the therapeutic potential of VEGF as a neuroprotective agent for such neurodegenerative disorders

Cerebrovascular disorders: molecular insights and therapeutic opportunities.

Blood vessels in the nervous system have traditionally been considered neutral bystanders that only passively adapt their structure and function in response to the needs of neural cells. Emerging evidence suggests, however, that vessels and angiogenic molecules actively participate in the pathogenesis of neurological disorders. Here we will discuss molecular insights into neurological disorders resulting either from excessive vessel growth (cerebral vascular malformations) or improper vessel regression (neurodegeneration and white matter lesions). These genetic insights offer alternative therapeutic options, some of which are being evaluated in the clinic

Immunoprecipation Assay to Quantify the Amount of tRNAs associated with Their Interacting Proteins in Tissue and Cell Culture

Transfer RNAs (tRNAs) are highly abundant species and, along their biosynthetic and functional path, they establish interactions with a plethora of proteins. The high number of nucleobase modifications in tRNAs renders conventional RNA quantification approaches unsuitable to study protein-tRNA interactions and their associated functional roles in the cell. We present an immunoprecipitation-based approach to quantify tRNA bound to its interacting protein partner(s). The tRNA-protein complexes are immunoprecipitated from cells or tissues and tRNAs are identified by northern blot and quantified by tRNA-specific fluorescent labeling. The tRNA interacting protein is quantified by an automated western blot and the tRNA amount is presented per unit of the interacting protein. We tested the approach to quantify tRNA(Gly) associated with mutant glycyl-tRNA-synthetase implicated in Charcot-Marie-Tooth disease. This simple and versatile protocol can be easily adapted to any other tRNA binding proteins. Graphic abstract: [Image: see text