Bacterial enzyme promotes recovery after spinal-cord injury
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For personal use. Only reproduce with permission from The Lancet Publishing Group. THE LANCET Neurology Vol 1 June 2002 http://neurology.thelancet.com 78 Newsdesk A bacterial enzyme could offer new hope for patients with spinal cord injuries, say UK researchers. Elizabeth Bradbury (King’s College London, UK) and colleagues saw “very clear functional recovery” after injecting chrondroitinase ABC intrathecally at the injury site in rats with crush injuries of the cervical dorsal column (Nature 2001; 416: 636–40). Chondroitinase ABC works by degrading chondroitin sulphate proteo- glycans (CSPGs) formed in glial scar tissue at the injury site. “CSPGs block the growth of regenerating axons, and this inhibitory activity can be atten- uated by removing the molecule’s glycosaminoglycan side chain with cho- ndroitinase ABC”, Bradbury explains. In injured rats, chondroitinase ABC promoted functional recovery and regeneration of both ascending and descending pathways. Walking was restored to near-normal in treated rats, indicating recovery of both locomotor function and proprioception. But sensorimotor function (awareness and removal of adhesive tape on the forelimbs) did not recover significantly, suggesting that chondroitinase ABC did not promote regeneration of hindbrain sensory nuclei. Chondroitinase ABC also upregulated expression of a nerve- regeneration marker protein, growth- associated protein 43. In anaesthetised animals electrical stimulation of the motor cortex evoked large, though delayed, postsynaptic potentials below the lesion site. The authors suggest that “chondroitinase ABC and other potential treatments that affect CSPG production after injury may have therapeutic potential for the treatment of patients with spinal cord injuries”. These experiments are “exceptional in that they combine anatomical, physiological, and behavioural evidence for functional regeneration after spinal cord injury”, says Patrick Anderson (University College London, UK). “It is widely believed that both inhibitory molecules such as CSPGs and the poor regenerative response of many CNS neurons contribute to the failure of axonal regeneration after spinal cord injury”, he adds. “Curiously, chondr- oitinase appears to remove inhibitory influences and enhance the intrinsic regenerative response of the injured cells.” Anderson points out that “major problems for patients arise when seg- ments of the cord are completely, or almost completely destroyed”, by contrast to the lesions in the rat experiments. “It is not known yet whether chondroitinase treatment will be effective on much larger lesions.” Anderson notes that other experimental treatments, including vaccination with CNS myelin and treatment with specific antibodies to the nerve-growth inhibitory protein Nogo, have produced axonal regeneration in the spinal cord. “The major significance of all these studies is not that they nece- ssarily offer the immediate prospect of successful treatments for patients but that they offer exciting opportunities to find out what normally prevents axons from regenerating in the CNS.” Dorothy Bonn Bacterial enzyme promotes recovery after spinal-cord injury Mutated huntingtin disrupts dopamine D 2 receptor transcription Expanded huntingtin, the mutation found in patients with Huntington’s disease, prevents the interaction of two transcription factors, which in-turn alters the pattern of gene expression, according to a new study. Huntingdon’s disease is caused by a CAG repeat in the gene for huntingtin, a protein of unknown function. The mutant protein has recently been shown to downregulate a variety of cell proteins, all of which rely on the transcription factor Sp1. Now, Dimitri Krainc and colleagues (Massachusetts General Hospital, MA, USA) have shown that this down- regulation occurs because huntingtin binds directly with Sp1, preventing it from interacting with a second transcription factor, TAF II 130. One gene affected encodes the dopamine D 2 receptor, the expression of which is decreased in the striatum of Huntington’s disease patients. Using the yeast two-hybrid system and cell culture techniques, Krainc’s group found that expanded huntingtin binds strongly to Sp1, reducing Sp1’s affinity for DNA and interrupting its interaction with TAF II 130. This effect was also seen in the brains of both symptomatic and presymptomatic patients with Huntington’s disease, where the mutant protein reduced DNA binding by up to 70%. This “suggests early and persistent inhibition of Sp1 function”, according to Krainc. Overexpression of Sp1 and TAF II 130 in cell culture restored normal dopamine D 2 receptor expression (Science 2002; published online May 2; DOI: 10.1126/science.1072613). While nuclear-protein aggregates are a hallmark of diseased neurons, their pathogenic role has been questioned in recent years. Krainc showed that Sp1 is not found in the aggregates, which suggests that the soluble form is doing the damage. “We saw all our effects in the absence of aggregates”, he says. “Aggregation does not seem to be that important [for the pathogenic process].” Leslie Thompson (University of California at Irvine, CA, USA) says these findings help show the importance of transcriptional dysregulation in disease. Once there is a more complete understanding of this mechanism, it may be possible to use small molecules to interfere with the Sp1–huntingtin interaction, or target Sp1-related genes for upregulation. Krainc emphasises that the Sp1 connection is only one pathogenic pathway implicated in Huntington’s disease; there are likely to be others that interact with, or remain entirely separate from, this one. The exciting thing for the molecular geneticist, Krainc says, “is that this is the first time anyone has shown uncoupling of activators from general transcription machinery in a medically relevant context”, which suggests a new model for genetic disease. Richard Robinson
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Transcript of Bacterial enzyme promotes recovery after spinal-cord injury
For personal use. Only reproduce with permission from The Lancet Publishing Group.
THE LANCET Neurology Vol 1 June 2002 http://neurology.thelancet.com78
Newsdesk
A bacterial enzyme could offer newhope for patients with spinal cordinjuries, say UK researchers. ElizabethBradbury (King’s College London, UK)and colleagues saw “very clearfunctional recovery” after injectingchrondroitinase ABC intrathecally atthe injury site in rats with crush injuriesof the cervical dorsal column (Nature2001; 416: 636–40).
Chondroitinase ABC works bydegrading chondroitin sulphate proteo-glycans (CSPGs) formed in glial scartissue at the injury site. “CSPGs blockthe growth of regenerating axons, andthis inhibitory activity can be atten-uated by removing the molecule’sglycosaminoglycan side chain with cho-ndroitinase ABC”, Bradbury explains.In injured rats, chondroitinase ABCpromoted functional recovery andregeneration of both ascending anddescending pathways. Walking wasrestored to near-normal in treated rats,indicating recovery of both locomotorfunction and proprioception. Butsensorimotor function (awareness and
removal of adhesive tape on theforelimbs) did not recover significantly,suggesting that chondroitinase ABC didnot promote regeneration of hindbrainsensory nuclei. Chondroitinase ABCalso upregulated expression of a nerve-regeneration marker protein, growth-associated protein 43. In anaesthetisedanimals electrical stimulation of themotor cortex evoked large, thoughdelayed, postsynaptic potentials belowthe lesion site. The authors suggest that“chondroitinase ABC and otherpotential treatments that affect CSPGproduction after injury may havetherapeutic potential for the treatmentof patients with spinal cord injuries”.
These experiments are “exceptionalin that they combine anatomical,physiological, and behavioural evidencefor functional regeneration after spinalcord injury”, says Patrick Anderson(University College London, UK). “It iswidely believed that both inhibitorymolecules such as CSPGs and the poorregenerative response of many CNSneurons contribute to the failure of
axonal regeneration after spinal cordinjury”, he adds. “Curiously, chondr-oitinase appears to remove inhibitoryinfluences and enhance the intrinsicregenerative response of the injuredcells.” Anderson points out that “majorproblems for patients arise when seg-ments of the cord are completely, oralmost completely destroyed”, bycontrast to the lesions in the ratexperiments. “It is not known yetwhether chondroitinase treatment willbe effective on much larger lesions.”
Anderson notes that otherexperimental treatments, includingvaccination with CNS myelin andtreatment with specific antibodies to thenerve-growth inhibitory protein Nogo,have produced axonal regeneration inthe spinal cord. “The major significanceof all these studies is not that they nece-ssarily offer the immediate prospect ofsuccessful treatments for patients butthat they offer exciting opportunities tofind out what normally prevents axonsfrom regenerating in the CNS.”Dorothy Bonn
Bacterial enzyme promotes recovery after spinal-cord injury
Mutated huntingtin disrupts dopamine D2 receptor transcriptionExpanded huntingtin, the mutationfound in patients with Huntington’sdisease, prevents the interaction of twotranscription factors, which in-turnalters the pattern of gene expression,according to a new study.
Huntingdon’s disease is caused bya CAG repeat in the gene forhuntingtin, a protein of unknownfunction. The mutant protein hasrecently been shown to downregulatea variety of cell proteins, all of whichrely on the transcription factor Sp1.Now, Dimitri Krainc and colleagues(Massachusetts General Hospital, MA,USA) have shown that this down-regulation occurs because huntingtinbinds directly with Sp1, preventing itfrom interacting with a secondtranscription factor, TAFII130. Onegene affected encodes the dopamineD2 receptor, the expression of which isdecreased in the striatum ofHuntington’s disease patients.
Using the yeast two-hybrid systemand cell culture techniques, Krainc’s
group found that expandedhuntingtin binds strongly to Sp1,reducing Sp1’s affinity for DNA andinterrupting its interaction withTAFII130. This effect was also seen inthe brains of both symptomatic andpresymptomatic patients withHuntington’s disease, where themutant protein reduced DNA bindingby up to 70%. This “suggests early andpersistent inhibition of Sp1 function”,according to Krainc. Overexpressionof Sp1 and TAFII130 in cell culturerestored normal dopamine D2
receptor expression (Science 2002;published online May 2; DOI:10.1126/science.1072613).
While nuclear-protein aggregatesare a hallmark of diseased neurons,their pathogenic role has beenquestioned in recent years. Kraincshowed that Sp1 is not found in theaggregates, which suggests that thesoluble form is doing the damage.“We saw all our effects in the absenceof aggregates”, he says. “Aggregation
does not seem to be that important[for the pathogenic process].”
Leslie Thompson (University ofCalifornia at Irvine, CA, USA) saysthese findings help show theimportance of transcriptionaldysregulation in disease. Once there isa more complete understanding of thismechanism, it may be possible to usesmall molecules to interfere with theSp1–huntingtin interaction, or targetSp1-related genes for upregulation.
Krainc emphasises that the Sp1connection is only one pathogenicpathway implicated in Huntington’sdisease; there are likely to be othersthat interact with, or remain entirelyseparate from, this one. The excitingthing for the molecular geneticist,Krainc says, “is that this is the firsttime anyone has shown uncoupling ofactivators from general transcriptionmachinery in a medically relevantcontext”, which suggests a new modelfor genetic disease.Richard Robinson
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