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  • Articles  (4,473)
  • Oxford University Press  (4,473)
  • 2010-2014  (4,473)
  • Human Molecular Genetics  (1,522)
  • 512
  • 1
    Publication Date: 2013-09-08
    Description: Neurons and other cells require intracellular transport of essential components for viability and function. Previous work has shown that while net amyloid precursor protein (APP) transport is generally anterograde, individual vesicles containing APP move bi-directionally. This discrepancy highlights our poor understanding of the in vivo regulation of APP-vesicle transport. Here, we show that reduction of presenilin (PS) or suppression of gamma-secretase activity substantially increases anterograde and retrograde velocities for APP vesicles. Strikingly, PS deficiency has no effect on an unrelated cargo vesicle class containing synaptotagmin, which is powered by a different kinesin motor. Increased velocities caused by PS or gamma-secretase reduction require functional kinesin-1 and dynein motors. Together, our findings suggest that a normal function of PS is to repress kinesin-1 and dynein motor activity during axonal transport of APP vesicles. Furthermore, our data suggest that axonal transport defects induced by loss of PS-mediated regulatory effects on APP-vesicle motility could be a major cause of neuronal and synaptic defects observed in Alzheimer's Disease (AD) pathogenesis. Thus, perturbations of APP/PS transport could contribute to early neuropathology observed in AD, and highlight a potential novel therapeutic pathway for early intervention, prior to neuronal loss and clinical manifestation of disease.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
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  • 2
    Publication Date: 2013-09-08
    Description: With age, muscle mass and integrity are progressively lost leaving the elderly frail, weak and unable to independently care for themselves. Defined as sarcopenia, this age-related muscle atrophy appears to be multifactorial but its definite cause is still unknown. Mitochondrial dysfunction has been implicated in this process. Using a novel transgenic mouse model of mitochondrial DNA (mtDNA) double-strand breaks (DSBs) that presents a premature aging-like phenotype, we studied the role of mtDNA damage in muscle wasting. We caused DSBs in mtDNA of adult mice using a ubiquitously expressed mitochondrial-targeted endonuclease, mito- Pst I. We found that a short, transient systemic mtDNA damage led to muscle wasting and a decline in locomotor activity later in life. We found a significant decline in muscle satellite cells, which decreases the muscle's capacity to regenerate and repair during aging. This phenotype was associated with impairment in acetylcholinesterase (AChE) activity and assembly at the neuromuscular junction (NMJ), also associated with muscle aging. Our data suggests that systemic mitochondrial dysfunction plays important roles in age-related muscle wasting by preferentially affecting the myosatellite cell pool.
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  • 3
    Publication Date: 2013-09-25
    Description: Spinal muscular atrophy (SMA) is caused by mutations of the survival motor neuron 1 ( SMN1 ) gene, retention of the survival motor neuron 2 ( SMN2 ) gene and insufficient expression of full-length survival motor neuron (SMN) protein. Quinazolines increase SMN2 promoter activity and inhibit the ribonucleic acid scavenger enzyme DcpS. The quinazoline derivative RG3039 has advanced to early phase clinical trials. In preparation for efficacy studies in SMA patients, we investigated the effects of RG3039 in severe SMA mice. Here, we show that RG3039 distributed to central nervous system tissues where it robustly inhibited DcpS enzyme activity, but minimally activated SMN expression or the assembly of small nuclear ribonucleoproteins. Nonetheless, treated SMA mice showed a dose-dependent increase in survival, weight and motor function. This was associated with improved motor neuron somal and neuromuscular junction synaptic innervation and function and increased muscle size. RG3039 also enhanced survival of conditional SMA mice in which SMN had been genetically restored to motor neurons. As this systemically delivered drug may have therapeutic benefits that extend beyond motor neurons, it could act additively with SMN-restoring therapies delivered directly to the central nervous system such as antisense oligonucleotides or gene therapy.
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  • 4
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    Oxford University Press
    Publication Date: 2013-09-25
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  • 5
    Publication Date: 2013-09-25
    Description: Coronary heart disease (CHD) is the leading cause of death worldwide. Mitochondrial genetic determinant for the development of CHD remains poorly explored. We report there the clinical, genetic, molecular and biochemical characterization of a four-generation Chinese family with maternally inherited CHD. Thirteen of 32 adult members in this family exhibited variable severity and age-at-onset of CHD. Mutational analysis of their mitochondrial genomes identified the tRNA Thr 15927G〉A mutation belonging to the Eastern Asian haplogroup B5. The anticipated destabilization of a highly conserved base-pairing (28C-42G) by the 15927G〉A mutation affects structure and function of tRNA Thr . Northern analysis revealed 80% decrease in the steady-state level of tRNA Thr in the mutant cell lines carrying the 15927G〉A mutation. The 15927G〉A mutation changed the conformation of tRNA Thr , as suggested by slower electrophoretic mobility of mutated tRNA with respect to the wild-type molecule. In addition, ~39% reduction in aminoacylated efficiency of tRNA Thr was observed in mutant cells derived from this Chinese family. An in vivo mitochondrial protein labeling analysis showed ~53% reduction in the rate of mitochondrial translation in mutant cells. The impaired mitochondrial protein synthesis leads to defects in overall respiratory capacity or malate/glutamate-promoted respiration or succinate/glycerol-3-phosphate-promoted respiration, or N,N,N',N '-tetramethyl-pphenylenediamine/ascorbate-promoted respiration in mutant cells. An increasing production of reactive oxygen species was observed in the mutant cells carrying the 15927G〉A mutation. These results provide the direct evidence that the tRNA Thr 15927G〉A mutation is associated with CHD. Our findings may provide new insights into pathophysiology and intervention targets of this disorder.
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  • 6
    Publication Date: 2013-09-25
    Description: Spinal muscular atrophy (SMA) is a devastating neuromuscular disorder that stems from low levels of survival of motor neuron (SMN) protein. The processes that cause motor neurons and muscle cells to become dysfunctional are incompletely understood. We are interested in neuromuscular homeostasis and the stresses put upon that system by loss of SMN. We recently reported that α-COP, a member of the coatomer complex of coat protein I (COPI) vesicles, is an SMN-binding partner, implicating this protein complex in normal SMN function. To investigate the functional significance of the interaction between α-COP and SMN, we constructed an inducible NSC-34 cell culture system to model the consequences of SMN depletion and find that depletion of SMN protein results in shortened neurites. Heterologous expression of human SMN, and interestingly over-expression of α-COP, restores normal neurite length and morphology. Mutagenesis of the canonical COPI dilysine motifs in exon 2b results in failure to bind to α-COP and abrogates the ability of human SMN to restore neurite outgrowth in SMN-depleted motor neuron-like NSC-34 cells. We conclude that the interaction between SMN and α-COP serves an important function in the growth and maintenance of motor neuron processes and may play a significant role in the pathogenesis of SMA.
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  • 7
    Publication Date: 2013-09-25
    Description: Human cortical malformations, including lissencephaly, polymicrogyria and other diseases of neurodevelopment, have been associated with mutations in microtubule subunits and microtubule-associated proteins. Here we report our cloning of the brain dimple ( brdp ) mouse mutation, which we recovered from an ENU screen for recessive perinatal phenotypes affecting neurodevelopment. We identify the causal mutation in the tubulin, beta-2b ( Tubb2b) gene as a missense mutation at a highly conserved residue (N247S). Brdp/brdp homozygous mutants have significant thinning of the cortical epithelium, which is markedly more severe in the caudo-lateral portion of the telencephalon, and do not survive past birth. The cortical defects are largely due to a major increase in apoptosis and we note abnormal proliferation of the basal progenitors. Adult brdp/+ mice are viable and fertile but exhibit behavioral phenotypes. This allele of Tubb2b represents the most severely affected mouse tubulin phenotype reported to date and this is the first report of a tubulin mutation affecting neuronal proliferation and survival.
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  • 8
    Publication Date: 2013-09-25
    Description: CCDC28B encodes a coiled coil domain-containing protein involved in ciliogenesis that was originally identified as a second site modifier of the ciliopathy Bardet–Biedl syndrome. We have previously shown that the depletion of CCDC28B leads to shortened cilia; however, the mechanism underlying how this protein controls ciliary length is unknown. Here, we show that CCDC28B interacts with SIN1, a component of the mTOR complex 2 (mTORC2), and that this interaction is important both in the context of mTOR signaling and in a hitherto unknown, mTORC-independent role of SIN1 in cilia biology. We show that CCDC28B is a positive regulator of mTORC2, participating in its assembly/stability and modulating its activity, while not affecting mTORC1 function. Further, we show that Ccdc28b regulates cilia length in vivo , at least in part, through its interaction with Sin1. Importantly, depletion of Rictor, another core component of mTORC2, does not result in shortened cilia. Taken together, our findings implicate CCDC28B in the regulation of mTORC2, and uncover a novel function of SIN1 regulating cilia length that is likely independent of mTOR signaling.
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  • 9
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    Oxford University Press
    Publication Date: 2013-09-25
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  • 10
    Publication Date: 2013-09-25
    Description: Spinal muscular atrophy (SMA) is caused by insufficient levels of the survival motor neuron (SMN) protein due to the functional loss of the SMN1 gene and the inability of its paralog, SMN2 , to fully compensate due to reduced exon 7 splicing efficiency. Since SMA patients have at least one copy of SMN2 , drug discovery campaigns have sought to identify SMN2 inducers. C5-substituted quinazolines increase SMN2 promoter activity in cell-based assays and a derivative, RG3039, has progressed to clinical testing. It is orally bioavailable, brain-penetrant and has been shown to be an inhibitor of the mRNA decapping enzyme, DcpS. Our pharmacological characterization of RG3039, reported here, demonstrates that RG3039 can extend survival and improve function in two SMA mouse models of varying disease severity (Taiwanese 5058 Hemi and 2B/– SMA mice), and positively impacts neuromuscular pathologies. In 2B/– SMA mice, RG3039 provided a 〉600% survival benefit (median 18 days to 〉112 days) when dosing began at P4, highlighting the importance of early intervention. We determined the minimum effective dose and the associated pharmacokinetic (PK) and exposure relationship of RG3039 and DcpS inhibition ex vivo . These data support the long PK half-life with extended pharmacodynamic outcome of RG3039 in 2B/– SMA mice. In motor neurons, RG3039 significantly increased both the average number of cells with gems and average number of gems per cell, which is used as an indirect measure of SMN levels. These studies contribute to dose selection and exposure estimates for the first studies with RG3039 in human subjects.
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