The calpain system originally comprised three molecules: two Ca2+-dependent proteases, mu-calpain and m-calpain, and a third polypeptide, calpastatin, whose only known function is to inhibit the two calpains. Both mu- and m-calpain are heterodimers containing an identical 28-kDa subunit and an 80-kDa subunit that shares 55-65% sequence homology between the two proteases. The crystallographic structure of m-calpain reveals six "domains" in the 80-kDa subunit: 1). a 19-amino acid NH2-terminal sequence; 2). and 3). two domains that constitute the active site, IIa and IIb; 4). domain III; 5). an 18-amino acid extended sequence linking domain III to domain IV; and 6). domain IV, which resembles the penta EF-hand family of polypeptides. The single calpastatin gene can produce eight or more calpastatin polypeptides ranging from 17 to 85 kDa by use of different promoters and alternative splicing events. The physiological significance of these different calpastatins is unclear, although all bind to three different places on the calpain molecule; binding to at least two of the sites is Ca2+ dependent. Since 1989, cDNA cloning has identified 12 additional mRNAs in mammals that encode polypeptides homologous to domains IIa and IIb of the 80-kDa subunit of mu- and m-calpain, and calpain-like mRNAs have been identified in other organisms. The molecules encoded by these mRNAs have not been isolated, so little is known about their properties. How calpain activity is regulated in cells is still unclear, but the calpains ostensibly participate in a variety of cellular processes including remodeling of cytoskeletal/membrane attachments, different signal transduction pathways, and apoptosis. Deregulated calpain activity following loss of Ca2+ homeostasis results in tissue damage in response to events such as myocardial infarcts, stroke, and brain trauma.

The Calpain System

Degeneration and regeneration of the nervous system

ALS: a disease of motor neurons and their nonneuronal neighbors.

https://www.cell.com/neuron/pdf/S0896-6273(12)00756-8.pdf

Synaptic Energy Use and Supply

Several recent breakthroughs have provided notable insights into the pathogenesis of amyotrophic lateral sclerosis (ALS), with some even shifting our thinking about this neurodegenerative disease and raising the question as to whether this disorder is a proteinopathy, a ribonucleopathy or both. In addition, these breakthroughs have revealed mechanistic links between ALS and frontotemporal dementia, as well as between ALS and other neurodegenerative diseases, such as the cerebellar atrophies, myotonic dystrophy and inclusion body myositis. Here, we summarize the new findings in ALS research, discuss what they have taught us about this disease and examine issues that are still outstanding.

/pdf/the-changing-scene-of-amyotrophic-lateral-sclerosis-1q1nhg9wa2.pdf

The changing scene of amyotrophic lateral sclerosis

http://www.dns.ed.ac.uk/rrrweb/NMJHDhons/FischerGlassALSexpNeurol04.pdf

Amyotrophic lateral sclerosis is a distal axonopathy: evidence in mice and man.

The WldS mouse is a unique mutant strain that demonstrates the remarkable phenotype of prolonged survival of transected axons ("slow Wallerian degeneration"). In these studies, we tested whether this neuroprotective phenotype extends to axonal degeneration seen in a progressive peripheral neuropathy. WldS and wild-type mice were intoxicated with the cancer chemotherapeutic agent paclitaxel (Taxol). The severity of the resultant sensory neuropathy was compared with behavioral, physiological, and pathological measures. WldS mice were resistant to paclitaxel neuropathy by all measures, and the resistance was because of protection against axonal degeneration. These studies demonstrate for the first time that the WldS mouse is more than a slow Wallerian degeneration phenotype, emphasizing the mechanistic link between Wallerian degeneration and peripheral neuropathy. Understanding how this mutant gene confers protection against axonal degeneration will provide important clues toward prevention of axonal degeneration in several human neurological disorders.

Wlds mice are resistant to paclitaxel (taxol) neuropathy

Taxol is a highly effective anticancer agent that causes peripheral neuropathy as its major toxic side effect. The neuropathy is characterized by degeneration of sensory axons that may be severe enough to be dose limiting. Axonal degeneration involves the activation of the calcium-activated proteases calpains, and here we tested whether systemic inhibition of calpains with the peptide alpha-ketoamide calpain inhibitor AK295 can reduce the clinical and pathological effects of Taxol in a rodent model of Taxol neuropathy. In mice with Taxol neuropathy, AK295 reduced the degree of axonal degeneration in sensory nerve roots, and improved clinical measures of neuropathy, including behavioural and electrophysiological function. These findings were consistent for both 3- and 6-week models of neuropathy. In vitro, Taxol caused activation of both calpains and caspases in PC12 cells. AK295 inhibited the activation of calpains but did not interfere with the antimitotic effects of Taxol on microtubules, nor did it inhibit caspase-mediated cell death. These data implicate calpains in the pathogenesis of Taxol neuropathy, and demonstrate that AK295 can prevent axonal degeneration and clinical neuropathy in mice. In addition, AK295 did not interfere with the primary antineoplastic effects of Taxol on microtubules and cell death, suggesting that systemic calpain inhibition may be a good strategy for preventing neuropathy in patients being treated with Taxol.

Calpain inhibition protects against Taxol-induced sensory neuropathy

The WldS gene modestly prolongs survival in the SOD1G93A fALS mouse.

Peripheral neuropathies and Wallerian degeneration share a number of pathological features; the most prominent of which is axonal degeneration. We asked whether common pathophysiologic mechanisms are involved in these 2 disorders by directly comparing in vitro models of axonal degeneration after axotomy or exposure to the neurotoxin vincristine. Embryonic rat dorsal root ganglia (DRG) were allowed to extend neurites for 5 days in culture, and then were either axotomized or exposed to 0.01 microM vincristine. Neurites universally degenerated by 3 days after axotomy or after 6 days of vincristine exposure. The neuroprotective effects of a low calcium environment or pharmacologic inhibition of the cysteine protease calpain were compared in these 2 models of axonal degeneration. Addition of EGTA or growth in zero-calcium media provided significant protection against axonal degeneration after either axotomy or vincristine exposure. Treatment with the experimental calpain inhibitor AK295 was equally protective in both models. Chronic exposure to AK295 was not toxic to the cultures. These data suggest that common mechanisms involving calcium and calpains are involved in both axotomy-induced and vincristine-induced axonal degeneration. In addition, calpain inhibition may provide a strategy for preventing axonal degeneration and preserving neurologic function in a variety of PNS and CNS disorders.

/pdf/pathogenesis-of-axonal-degeneration-parallels-between-b63n4fs8e5.pdf

Deborah G. Culver

Papers

Amyotrophic lateral sclerosis is a distal axonopathy: evidence in mice and man.

Wlds mice are resistant to paclitaxel (taxol) neuropathy

Calpain inhibition protects against Taxol-induced sensory neuropathy

The WldS gene modestly prolongs survival in the SOD1G93A fALS mouse.

Pathogenesis of axonal degeneration: parallels between Wallerian degeneration and vincristine neuropathy.