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Jeffery L Twiss

Publications and source records attributed to Jeffery L Twiss.

15 recordsLinked to original sources
PubMed2026

A mouse model of autosomal dominant spastic ataxia and myopathy caused by a mutation in Tuba4a.

Hereditary ataxias are a heterogeneous group of neurodegenerative disorders characterized by impaired balance and coordination, often due to cerebellar dysfunction. Despite advances in identifying genetic causes, animal models remain essential for dissecting underlying mechanisms and testing therapeutic strategies. Here we describe a mouse model of spastic ataxia and myopathy caused by a missense mutation in Tuba4a (n.A626C, p.Gln176Pro). In an ENU mutagenesis screen, a male C57BL/6 J mouse exhibiting muscle wasting and an intention tremor starting at approximately 4 weeks-of-age was identified. The male was bred by in vitro fertilization to BALB/cByJ oocyte donors. Genetic mapping determined dominant inheritance and localized the mutation to Chromosome 1. Genome sequencing revealed single nucleotide polymorphisms (SNPs) in serine threonine kinase 36 (Stk36Y1003N) and alpha-tubulin 4A (Tuba4aQ176P) in the mapping interval. These SNPs were CRISPR-engineered into C57BL/6 J mice, which confirmed the Tuba4aQ176P variant as the causative mutation. Mutant mice are normal at 3 weeks, except for decrement in muscle response following repetitive nerve stimulation. However, by 30 days these mice have overt ataxia, Purkinje neuron degeneration, and extensive skeletal muscle defects, which contribute to a decreased lifespan. Dominant TUBA4A mutations in humans are associated with spastic ataxia type 11 (SPAX11), congenital myopathy type 26 (CMYO26), and frontotemporal dementia/amyotrophic lateral sclerosis type 9 (FTDALS9). Our mice exhibit hallmark features of SPAX11 and CMYO26, but do not show motor neuron degeneration. This specificity makes this model a valuable tool for studying cell-type selective effects of TUBA4A mutations in neurodegeneration and myopathy.

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PubMed2006

PC12 cells regulate inducible cyclic AMP (cAMP) element repressor expression to differentially control cAMP response element-dependent transcription in response to nerve growth factor and cAMP.

Both cyclic AMP (cAMP) and nerve growth factor (NGF) have been shown to cause rapid activation of cAMP response element-binding protein (CREB) by phosphorylation of serine 133, but additional regulatory events contribute to CREB-targeted gene expression. Here, we have used stable transfection with a simple cAMP response element (CRE)-driven reporter to address the kinetics of CRE-dependent transcription during neuronal differentiation of PC12 cells. In naive cells, dibutyryl cAMP (dbcAMP) generated a rapid increase in CRE-driven luciferase activity by 5 h that returned to naive levels by 24 h. Luciferase induction after NGF treatment was delayed until 48 h when CRE-driven luciferase expression became TrkA dependent. Blocking histone deacetylase (HDAC) activity accelerated NGF-dependent CRE-driven luciferase expression by at least 24 h and resulted in a sustained cAMP-dependent expression of CRE-driven luciferase beyond 24 h. Inhibition of protein synthesis before stimulation with NGF or dbcAMP indicated that both stimuli induce expression of a transcriptional repressor that delays NGF-dependent and attenuates cAMP-dependent CRE-driven transcription. NGF caused a rapid but transient HDAC-dependent increase in inducible cAMP element repressor (ICER) expression, but ICER expression was sustained with increased cAMP. Depletion of ICER from PC12 cells indicated that HDAC-dependent ICER induction is responsible for the delay in CRE-dependent transcription after NGF treatment.

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PubMed2006

Tracking in the Wlds--the hunting of the SIRT and the luring of the Draper.

Wallerian degeneration of distal axons after nerve injury is significantly delayed in the Wlds mutant mouse. The Wlds protein is a fusion of nicotinamide mononucleotide adenyltransferase-1 (Nmnat1), an essential enzyme in the biosynthesis pathway of nicotinamide adenine dinucleotide (NAD), with the N-terminal 70 amino acids of the Ube4b ubiquitination assembly factor. The mechanism of Wlds action is still enigmatic, although recent efforts suggest that it is indirect and requires sequences flanking or linking the two fused open reading frames. Three papers in this issue of Neuron now show that Wlds action is conserved in Drosophila and that a critical role of Wlds may be the suppression of axonal self-destruct signals that induce Draper-mediated clearance of damaged axons by glial cells.

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PubMed2006

The evolving roles of axonally synthesized proteins in regeneration.

Work emerging during the past decade has shown that axons, similar to dendrites, are capable of autonomously generating new proteins through translation of localized mRNAs. Even in mammals, neurons maintain the ability to target mRNAs and translational machinery into the axonal compartment well into adulthood. The biological functions of axonal protein synthesis in adult neurons are just now being revealed, and recent studies indicate that locally synthesized proteins facilitate regeneration. Local translation, in addition to protein degradation, is needed for growth cone formation after axotomy, for generating a retrogradely transported injury signal, and then to help structurally maintain the growing axon. Regulation of axonal protein synthesis by exogenous stimuli might provide a means to facilitate regeneration for neuronal populations that normally show poor regenerative capacity in the adult nervous system.

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PubMed2006

Pathophysiological mechanisms for actions of the neurotrophins.

Neurotrophins provide trophic and tropic support for different neuronal subpopulations in the developing and adult nervous systems. Expression of the neurotrophins and their receptors can be altered in several different disease or injury states that impact upon the functions in the central and peripheral nervous systems. The intracellular signals used by the neurotrophins are triggered by ligand binding to the cell surface Trk and p75NTR receptors. In general, signals emanating from Trk receptors support survival, growth and synaptic strengthening, while those emanating from p75NTR induce apoptosis, attenuate growth and weaken synaptic signaling. Mature neurotrophins are the preferred ligand for Trk proteins while p75NTR binds preferentially to the proneurotrophins and serves as a signaling component of the receptor complex for growth inhibitory molecules of central nervous system myelin [ie, myelin-associated glycoprotein (MAG), oligodendrocyte-myelin glycoprotein (OMgP) and Nogo]. The functional antagonism between Trk and p75NTR signaling may significantly impact the pathogenesis of human neurodevelopmental and neurodegenerative diseases and further complicate therapeutic uses of exogenous neurotrophins. The potential for each is discussed in this review.

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PubMed2005

Differential transport and local translation of cytoskeletal, injury-response, and neurodegeneration protein mRNAs in axons.

Recent studies have begun to focus on the signals that regulate axonal protein synthesis and the functional significance of localized protein synthesis. However, identification of proteins that are synthesized in mammalian axons has been mainly based on predictions. Here, we used axons purified from cultures of injury-conditioned adult dorsal root ganglion (DRG) neurons and proteomics methodology to identify axonally synthesized proteins. Reverse transcription (RT)-PCR from axonal preparations was used to confirm that the mRNA for each identified protein extended into the DRG axons. Proteins and the encoding mRNAs for the cytoskeletal proteins beta-actin, peripherin, vimentin, gamma-tropomyosin 3, and cofilin 1 were present in the axonal preparations. In addition to the cytoskeletal elements, several heat shock proteins (HSP27, HSP60, HSP70, grp75, alphaB crystallin), resident endoplasmic reticulum (ER) proteins (calreticulin, grp78/BiP, ERp29), proteins associated with neurodegenerative diseases (ubiquitin C-terminal hydrolase L1, rat ortholog of human DJ-1/Park7, gamma-synuclein, superoxide dismutase 1), anti-oxidant proteins (peroxiredoxins 1 and 6), and metabolic proteins (e.g., phosphoglycerate kinase 1 (PGK 1), alpha enolase, aldolase C/Zebrin II) were included among the axonally synthesized proteins. Detection of the mRNAs encoding each of the axonally synthesized proteins identified by mass spectrometry in the axonal compartment indicates that the DRG axons have the potential to synthesize a complex population of proteins. Local treatment of the DRG axons with NGF or BDNF increased levels of cytoskeletal mRNAs into the axonal compartment by twofold to fivefold but had no effect on levels of the other axonal mRNAs studied. Neurotrophins selectively increased transport of beta-actin, peripherin, and vimentin mRNAs from the cell body into the axons rather than changing transcription or mRNA survival in the axonal compartment.

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PubMed2004

A model of experimental spinal cord trauma based on computer-controlled intervertebral distraction: characterization of graded injury.

STUDY DESIGN: : A new model of experimental spinal cord injury is detailed based on the application of tensile (distraction) force to the vertebral column of the rat. OBJECTIVES: : To develop an experimental model of graded spinal cord injury by application of tensile forces to the vertebral column. SUMMARY OF BACKGROUND DATA: : Distraction is frequently an integral component of human spinal cord injury, but the acute application of tensile forces to the spinal cord has not been modeled rigorously. METHODS: : A computer-controlled, motorized outrigger device was used to apply a longitudinal stretching force to sublaminar hooks oriented proximally at T9 and distally at T11. Distraction force was applied using a program that varied the length, speed, and duration of its distraction. A modified 14-point Tarlov score was used to establish the presence of hindlimb dysfunction. This score was correlated with acute changes in somatosensory-evoked potential amplitude, the comprehensive open-field test of locomotor function at 4 weeks, and postmortem measurements of serotonin content and metabolism in spinal cord rostral and distal to the site of injury. RESULTS: : Of distraction parameters, only length of distraction correlated significantly with each outcome measure. For outcome measures, open-field test inventory and distal/proximal ratio of the spinal content of serotonin were correlated most closely with final Tarlov scores. Acute somatosensory-evoked potential amplitudes proved to be an excellent index of the acute injury but were poor measures of long-term outcome. CONCLUSIONS: : Distraction-induced spinal cord injury was uniformly mild in rats with intact facet capsular ligaments, regardless of distraction parameters. Cutting the facet joint ligaments consistently generated outcome measures associated with mild, moderate, and severe spinal cord injury at 3-, 5-, and 7-mm distraction lengths, respectively.

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PubMed2004

Voluntary exercise increases axonal regeneration from sensory neurons.

Recent advances in understanding the role of neurotrophins on activity-dependent plasticity have provided insight into how behavior can affect specific aspects of neuronal biology. We present evidence that voluntary exercise can prime adult dorsal root ganglion neurons for increased axonal regeneration through a neurotrophin-dependent mechanism. Dorsal root ganglion neurons showed an increase in neurite outgrowth when cultured from animals that had undergone 3 or 7 days of exercise compared with sedentary animals. Neurite length over 18-22 h in culture correlated directly with the distance that animals ran. The exercise-conditioned animals also showed enhanced regrowth of axons after an in vivo nerve crush injury. Sensory ganglia from the 3- and 7-day-exercised animals contained higher brain-derived neurotrophic factor, neurotrophin 3, synapsin I, and GAP43 mRNA levels than those from sedentary animals. Consistent with the rise in brain-derived neurotrophic factor and neurotrophin 3 during exercise, the increased growth potential of the exercise-conditioned animals required activation of the neurotrophin signaling in vivo during the exercise period but did not require new mRNA synthesis in culture.

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PubMed2004

Na,K-ATPase beta1-subunit increases the translation efficiency of the alpha1-subunit in MSV-MDCK cells.

The Na,K-ATPase consists of an alpha- and beta-subunit. Moloney sarcoma virus-transformed MDCK cells (MSV-MDCK) express low levels of Na,K-ATPase beta(1)-subunit. Ectopic expression of Na,K-ATPase beta(1)-subunit in these cells increased the protein levels of the alpha(1)-subunit of Na,K-ATPase. This increase was not due to altered transcription of the alpha(1)-subunit gene or half-life of the alpha(1)-subunit protein because both alpha(1)-subunit mRNA levels and half-life of the alpha(1)-subunit protein were comparable in MSV-MDCK and beta(1)-subunit expressing MSV-MDCK cells. However, short pulse labeling revealed that the initial translation rate of the alpha(1)-subunit in beta(1)-subunit expressing MSV-MDCK cells was six- to sevenfold higher compared with MSV-MDCK cells. The increased translation was specific to alpha(1)-subunit because translation rates of occludin and beta-catenin, membrane and cytosolic proteins, respectively, were not altered. In vitro cotranslation/translocation experiments using rabbit reticulocyte lysate and rough microsomes revealed that the alpha(1)-subunit mRNA is more efficiently translated in the presence of beta(1)-subunit. Furthermore, sucrose density gradient analysis revealed significantly more alpha(1)-subunit transcript associated with the polysomal fraction in beta(1)-subunit expressing MSV-MDCK cells compared with MSV-MDCK cells, indicating that in mammalian cells the Na,K-ATPase beta(1)-subunit is involved in facilitating the translation of the alpha(1)-subunit mRNA in the endoplasmic reticulum.

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PubMed2003

Axoplasmic importins enable retrograde injury signaling in lesioned nerve.

Axoplasmic proteins containing nuclear localization signals (NLS) signal retrogradely by an unknown mechanism in injured nerve. Here we demonstrate that the importin/karyopherin alpha and beta families underlie this process. We show that importins are found in axons at significant distances from the cell body and that importin beta protein is increased after nerve lesion by local translation of axonal mRNA. This leads to formation of a high-affinity NLS binding complex that traffics retrogradely with the motor protein dynein. Trituration of synthetic NLS peptide at the injury site of axotomized dorsal root ganglion (DRG) neurons delays their regenerative outgrowth, and NLS introduction to sciatic nerve concomitantly with a crush injury suppresses the conditioning lesion induced transition from arborizing to elongating growth in L4/L5 DRG neurons. These data suggest a model whereby lesion-induced upregulation of axonal importin beta may enable retrograde transport of signals that modulate the regeneration of injured neurons.

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PubMed2003

Persistent TrkA activity is necessary to maintain transcription in neuronally differentiated PC12 cells.

Neurotrophins are required for the differentiation and survival of several different neuronal subpopulations in the developing nervous system. The PC12 cell line responds to nerve growth factor (NGF) by withdrawing from the cell cycle and acquiring a sympathetic neuron-like phenotype. Previous studies have shown that the activation kinetics of the NGF receptor, TrkA, and downstream protein kinases appear rapid and seemingly transient after NGF treatment of naive PC12 cells. However, maintenance of the neuronal phenotype and survival of differentiated PC12 cells under serum-free conditions require constant NGF exposure. In this study we have addressed the mechanisms that NGF uses to maintain neuronal PC12 cells. We show that TrkA remains phosphorylated at a basal level throughout differentiation of the PC12 cells. The phospho-TrkA levels in the differentiated PC12 cells were diminished by both complete NGF withdrawal and pharmacological inhibition of Trk kinase activity. Intracellular sequestration of the majority of TrkA molecules (both phosphorylated and non-phosphorylated TrkA) and persistent dephosphorylation of the small pool of cell surface TrkA renders the persistent phospho-TrkA signal in the differentiated PC12 cells resistant to partial NGF withdrawal as well as exposure to additional NGF. NGF regulated both extracellular-regulated kinases 1/2 and Akt activity in the differentiated PC12 cells via sustained TrkA activity. Moreover, analysis of transcription using activating protein 1-, serum response element-, and cyclic AMP response element-Luc reporter constructs showed that NGF regulated these promoters through TrkA activity in differentiated PC12 cells. Interestingly, the initial response of the cyclic AMP response element promoter to NGF was delayed, becoming Trk-dependent well beyond the peaks in TrkA and downstream protein kinase signal transduction.

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PubMed2003

Effects of altered expression and localization of cyclophilin A on differentiation of p19 embryonic carcinoma cells.

1. The retinoblastoma susceptibility gene product, p105Rb (RB), is an important regulator in the control of cell proliferation, differentiation, and apoptosis. Several cellular factors that complex with RB and exert their cellular regulatory functions have been identified, such as the RB:cyclophilin A (CypA) complex. 2. CypA is a cytoplasmic immunophilin and known for its involvement in T-cell differentiation and proliferation. Although CypA has a pivotal role in the immune response, its function in other signaling pathways is largely unknown. 3. In this study, we used a model of neuronal differentiation to demonstrate that the nuclear translocation of CypA, the appearance of hypophosphorylated RB and the enhancement of RB: CypA complex formation correlates with retinoic acid induced neuronal differentiation. 4. Inhibition of CypA expression results in repression of both the hypophosphorylated RB and the neuron-specific differentiation marker, class III beta tubulin. 5. The evidence of enriched CypA and colocalization of RB with CypA in the nucleus of primary adult sensory neurons substantiated the important event of RB-mediated neuronal differentiation of p19 EC cells.

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PubMed2003

PKC isozymes in the enhanced regrowth of retinal neurites after optic nerve injury.

PURPOSE: To establish an in vitro model of axonal regeneration from mammalian retinal ganglion cells and to evaluate the role of PKC isozymes in promoting such retinal axon regeneration. METHODS: Postnatal day-3 mice were subjected to optic nerve crush, and then retinal ganglion cells (RGCs) were used for culture 5 days later. RGCs were selected using anti-Thy 1.2-coated magnetic beads and plated onto a merosin substrate. Changes in axonal localization of PKC and axonal regeneration were examined in cultured RGCs by immunofluorescence. Changes in PKC isozyme mRNA levels were determined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). The role of PKC in RGC neurite outgrowth was examined by treatment with activators or pharmacological inhibitors of PKC activity. RESULTS: RGCs subjected to optic nerve crush injury demonstrated more rapid neurite outgrowth in vitro when compared with RGCs isolated from naïve retina. The neurites of these injury-conditioned RGCs showed both an increased rate of extension and enhanced PKC localization in culture. Injury-conditioned RGCs had elevated PKC isozyme mRNA levels, which probably contributed to the increased level of PKC protein in injury-conditioned RGC axons. Pharmacological activation of PKC enhanced neurite growth, whereas inhibition of PKC suppressed neurite growth in both the conditioned and naïve RGCs. CONCLUSIONS: RGCs actively respond to axonal injury by regulating expression of genes that promote neurite outgrowth. PKC-alpha and -beta isozymes are among the growth-associated proteins that are upregulated after injury. Results of pharmacological manipulation of PKC activity support the argument that increased PKC levels enhance neurite regrowth after axonal injury.

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PubMedDate not supplied

New insights into neuronal regeneration: the role of axonal protein synthesis in pathfinding and axonal extension.

Protein synthesis in dendrites has become an accepted cellular mechanism that contributes to activity-dependent responses in the post-synaptic neuron. Although it was argued that protein synthesis does not occur in axons, early studies from a number of groups provided evidence for the presence of RNAs and active protein synthesis machinery in both invertebrate and vertebrate axons. Work over the past decade has confirmed these early findings and has proven the capability of axons to locally synthesize some of their own proteins. The functional significance of this localized protein synthesis remained largely unknown until recent years. Recent studies have shown that mRNA translation in developing and mature axons plays a role in axonal growth. In developing axons, protein synthesis allows the distal axon to autonomously respond to guidance cues by rapidly changing its direction of outgrowth. In addition, local proteolysis of axonal proteins contributes axonal guidance and growth cone initiation. This local synthesis and degradation of proteins are likely to provide novel insights into how growing axons navigate through their complex environment. In mature axons, injury triggers formation of a growth cone through localized protein synthesis, and moreover, in these injured axons locally synthesized proteins provide a retrogradely transported signal that can enhance regenerative responses. The intrinsic capability for axons to autonomously regulate local protein levels can be modulated by exogenous stimuli providing opportunities for enhancing regeneration. In this review, the concept of axonal protein synthesis is discussed from a historical perspective. Further, the implications of axonal protein synthesis and proteolysis for neural repair are considered.

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