Axotomy-induced axonal degeneration is mediated by calcium influx through ion-specific channels. Export

@article{citeulike:2645043, abstract = {We examined the role of extracellular calcium entry, the possible involvement of axonal calcium channels, and the potential protective effect of calcium channel and calpain antagonists in axotomy-induced axonal degeneration using murine dorsal root ganglia in cell culture. We found that calcium entry is both necessary and sufficient to induce axonal degeneration after axotomy, and may be inhibited by cobalt, manganese, dihydropyridines, and bepridil. Tetrodotoxin and omega-conotoxin are ineffective in preventing axonal degeneration. The activation of calpains also appears to be necessary and sufficient for axonal degeneration to proceed, and can be blocked with membrane-permeant leupeptin analogs and the oxirane aloxistatin. Although other calcium-activated events may occur, it appears that inhibition of calpain is sufficient to preserve the axon at the light microscope level, and to prevent axonal cytoskeleton degradation as detected by immunofluorescent staining. Our results suggest that axonal degeneration after axotomy involves the following sequence of events: (1) a lag-period after axotomy prior to the onset of axonal degeneration, (2) entry of calcium into the axon through an intact axolemma via a calcium-specific ion transport mechanism, (3) activation of calcium-dependent effector molecules such as calpains, (4) degradation of the axonal cytoskeleton. The details of the second step require further elucidation, and are of particular interest because this step is a potential target for therapies directed towards peripheral neuropathies.}, address = {Department of Neurology, School of Medicine, Johns Hopkins University, Baltimore, Maryland 21287-6953, USA.}, author = {George, E. B. and Glass, J. D. and Griffin, J. W.}, citeulike-article-id = {2645043}, citeulike-linkout-0 = {http://view.ncbi.nlm.nih.gov/pubmed/7472407}, citeulike-linkout-1 = {http://www.hubmed.org/display.cgi?uids=7472407}, comment = {Severed axons maintained in EGTA degenerated more slowly than those in high-calcium media. Calpains have been demonstrated to cleave the major axonal proteins. (I haven't read these papers: Schlaepfer and Bunge 1973; Schlaepfer 1974; Schlaepfer and Hasler 1979). Using murine dorsal root ganglia in cell culture George et al examined the role of extracellular calcium entry, the possible ivolvement of axonal calcium channels, and the potential protective effect of calcium channel and calpain antagonists. When extracellular calcium levels are reduced by adding EGTA to the culture media after axotomy, the axons begin to develop a beaded appearance byt fail to degenerate withint a week after axotomy. As opposed to complete degeneration by 48-60 hours. Elevations of intra-axonal calcium can be produced with calcium ionophoresBoth A23187 and ionomycin produce degeneration of uncut axons when added to dorsal root ganglia cultures. Cobalt and Manganese are non-specific calcium channel inhibitors: these metal ions prevent calcium entry. Both cobalt and Manganese are effectiuve in delaying axonal degeneration after axotomy. Conotoxin does not block axonal degeneration indicating that calcium enters primarily through channels other than N-type calcium channels during axonal degeneration. Calpain inhibitors from 2 different classes, the leupeptin analogs and oxiranes preserves axotomised axons in a concentration dependent manner. Calpain activity can be demonstrated in WldS axons (Glass et al, 1994- I haven't read this). The inhibition of axonal degeneration by cobalt and manganese, metal ions which can substitute for calcium in many processes by which do not pass through calcium conductive ion channels, strongly implies that calcium entry occurs through a calcium specific ion transport mechanism. Certainly hese ions should not be able to prevent calcium entry if a significant disruption of membrane integrity were the calcium entre mechanism. }, issn = {0270-6474}, journal = {The Journal of neuroscience : the official journal of the Society for Neuroscience}, keywords = {calpain, degeneration, mechanism, wallerian}, month = {October}, number = {10}, pages = {6445--6452}, posted-at = {2008-04-09 15:19:37}, priority = {0}, title = {Axotomy-induced axonal degeneration is mediated by calcium influx through ion-specific channels.}, url = {http://view.ncbi.nlm.nih.gov/pubmed/7472407}, volume = {15}, year = {1995} }

TY - JOUR ID - citeulike:2645043 L3 - citeulike-article-id:2645043 N2 - We examined the role of extracellular calcium entry, the possible involvement of axonal calcium channels, and the potential protective effect of calcium channel and calpain antagonists in axotomy-induced axonal degeneration using murine dorsal root ganglia in cell culture. We found that calcium entry is both necessary and sufficient to induce axonal degeneration after axotomy, and may be inhibited by cobalt, manganese, dihydropyridines, and bepridil. Tetrodotoxin and omega-conotoxin are ineffective in preventing axonal degeneration. The activation of calpains also appears to be necessary and sufficient for axonal degeneration to proceed, and can be blocked with membrane-permeant leupeptin analogs and the oxirane aloxistatin. Although other calcium-activated events may occur, it appears that inhibition of calpain is sufficient to preserve the axon at the light microscope level, and to prevent axonal cytoskeleton degradation as detected by immunofluorescent staining. Our results suggest that axonal degeneration after axotomy involves the following sequence of events: (1) a lag-period after axotomy prior to the onset of axonal degeneration, (2) entry of calcium into the axon through an intact axolemma via a calcium-specific ion transport mechanism, (3) activation of calcium-dependent effector molecules such as calpains, (4) degradation of the axonal cytoskeleton. The details of the second step require further elucidation, and are of particular interest because this step is a potential target for therapies directed towards peripheral neuropathies. IS - 10 JF - The Journal of neuroscience : the official journal of the Society for Neuroscience SN - 0270-6474 AD - Department of Neurology, School of Medicine, Johns Hopkins University, Baltimore, Maryland 21287-6953, USA. EP - 6452 TI - Axotomy-induced axonal degeneration is mediated by calcium influx through ion-specific channels. VL - 15 SP - 6445 KW - calpain KW - degeneration KW - mechanism KW - wallerian N1 - Severed axons maintained in EGTA degenerated more slowly than those in high-calcium media. Calpains have been demonstrated to cleave the major axonal proteins. (I haven’t read these papers: Schlaepfer and Bunge 1973; Schlaepfer 1974; Schlaepfer and Hasler 1979). Using murine dorsal root ganglia in cell culture George et al examined the role of extracellular calcium entry, the possible ivolvement of axonal calcium channels, and the potential protective effect of calcium channel and calpain antagonists. When extracellular calcium levels are reduced by adding EGTA to the culture media after axotomy, the axons begin to develop a beaded appearance byt fail to degenerate withint a week after axotomy. As opposed to complete degeneration by 48-60 hours. Elevations of intra-axonal calcium can be produced with calcium ionophoresBoth A23187 and ionomycin produce degeneration of uncut axons when added to dorsal root ganglia cultures. Cobalt and Manganese are non-specific calcium channel inhibitors: these metal ions prevent calcium entry. Both cobalt and Manganese are effectiuve in delaying axonal degeneration after axotomy. Conotoxin does not block axonal degeneration indicating that calcium enters primarily through channels other than N-type calcium channels during axonal degeneration. Calpain inhibitors from 2 different classes, the leupeptin analogs and oxiranes preserves axotomised axons in a concentration dependent manner. Calpain activity can be demonstrated in WldS axons (Glass et al, 1994- I haven’t read this). The inhibition of axonal degeneration by cobalt and manganese, metal ions which can substitute for calcium in many processes by which do not pass through calcium conductive ion channels, strongly implies that calcium entry occurs through a calcium specific ion transport mechanism. Certainly hese ions should not be able to prevent calcium entry if a significant disruption of membrane integrity were the calcium entre mechanism. AU - George, EB AU - Glass, JD AU - Griffin, JW PY - 1995/10// UR - http://view.ncbi.nlm.nih.gov/pubmed/7472407 ER -