Calpain Overactivation Research Articles

Protective effects of PARP inhibitor, PJ34, is related to down-regulation of calpain and NF-κB in a mouse model of TBI.

Poly(ADP-ribose) polymerase (PARP), calpain and nuclear factor-κB (NF-κB) are reported to participate in inflammatory reactions in pathological conditions and are involved in traumatic brain injury. The objective of this study was to investigate whether PARP participated in inflammation related to calpain and NF-κB in a mouse model of controlled cortical impact (CCI). PJ34 (10 mg kg-1), a selective PARP inhibitor, was administered intraperitoneally 5 minutes and 8 hours after experimental CCI. A neurobehavioural evaluation and a histopathological analysis were then performed and the contusion volume, calpain activity and protein levels were measured in all animals. Treatment with PJ34 markedly reduced neurological deficits, decreased contusion volume and attenuated necrotic and apoptotic neuronal cell death 24 hours after CCI. The data showed that the cytosolic and nuclear fractions of calpain and NF-κB were up-regulated in the injured cortex and that these changes were reversed by PJ34. Moreover, PJ34 significantly enhanced the calpastatin and IκB levels and decreased the levels of inflammatory mediators. PARP inhibition by PJ34 suppresses the over-activation of calpain and the production of inflammatory factors that are caused by NF-κB activation and it improves neurological functioning, decreases the contusion volume and attenuates neuronal cell death in a mouse model of CCI.

Calpastatin inhibits motor neuron death and increases survival of hSOD1(G93A) mice.

Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease with a poorly understood cause and no effective treatment. Given that calpains mediate neurodegeneration in other pathological states and are abnormally activated in ALS, we investigated the possible ameliorative effects of inhibiting calpain over-activation in hSOD1(G93A) transgenic (Tg) mice in vivo by neuron-specific over-expression of calpastatin (CAST), the highly selective endogenous inhibitor of calpains. Our data indicate that over-expression of CAST in hSOD1(G93A) mice, which lowered calpain activation to levels comparable to wild-type mice, inhibited the abnormal breakdown of cytoskeletal proteins (spectrin, MAP2 and neurofilaments), and ameliorated motor axon loss. Disease onset in hSOD1(G93A) /CAST mice compared to littermate hSOD1(G93A) mice is delayed, which accounts for their longer time of survival. We also find that neuronal over-expression of CAST in hSOD1(G93A) transgenic mice inhibited production of putative neurotoxic caspase-cleaved tau and activation of Cdk5, which have been implicated in neurodegeneration in ALS models, and also reduced the formation of SOD1 oligomers. Our data indicate that inhibition of calpain with CAST is neuroprotective in an ALS mouse model. CAST (encoding calpastatin) inhibits hyperactivated calpain to prevent motor neuron disease operating through a cascade of events as indicated in the schematic, with relevance to amyotrophic lateral sclerosis (ALS). We propose that over-expression of CAST in motor neurons of hSOD1(G93A) mice inhibits activation of CDK5, breakdown of cytoskeletal proteins (NFs, MAP2 and Tau) and regulatory molecules (Cam Kinase IV, Calcineurin A), and disease-causing proteins (TDP-43, α-Synuclein and Huntingtin) to prevent neuronal loss and delay neurological deficits. In our experiments, CAST could also inhibit cleavage of Bid, Bax, AIF to prevent mitochondrial, ER and lysosome-mediated cell death mechanisms. Similarly, CAST over-expression in neurons attenuated pathological effects of TDP-43, α-synuclein and Huntingtin. These results suggest a potential value of specific small molecule inhibitors of calpains in delaying the development of ALS. Read the Editorial Highlight for this article on page 140.

The calpain-suppressing effects of olesoxime in Huntington's disease.

ABSTRACTOlesoxime, a small molecule drug candidate, has recently attracted attention due to its significant beneficial effects in models of several neurodegenerative disorders including Huntington's disease. Olesoxime's neuroprotective effects have been assumed to be conveyed through a direct, positive influence on mitochondrial function. In a long-term treatment study in BACHD rats, the latest rat model of Huntington's disease, olesoxime revealed a positive influence on mitochondrial function and improved specific behavioral and neuropathological phenotypes. Moreover, a novel target of the compound was discovered, as olesoxime was found to suppress the activation of the calpain proteolytic system, a major contributor to the cleavage of the disease-causing mutant huntingtin protein into toxic fragments, and key player in degenerative processes in general. Results from a second model of Huntington's disease, the HdhQ111 knock-in mouse, confirm olesoxime's calpain-suppressing effects and support the therapeutic value of olesoxime for Huntington's disease and other disorders involving calpain overactivation.

Function and Change with Aging of α-Klotho in the Kidney.

The α-Klotho mouse is an animal model that prematurely shows phenotypes resembling human aging, such as osteoporosis, arteriosclerosis, pulmonary emphysema, and kidney damage. Interestingly, these abnormalities are triggered by a deficiency of a single protein, α-Klotho. The kidney is an organ that highly expresses α-Klotho, suggesting that α-Klotho is important for kidney function. Recent studies suggest that α-Klotho is associated with phosphate, vitamin D, and calcium homeostasis. The calcium imbalance in α-Klotho mice may induce calpain overactivation, leading to cell death and tissue destruction. α-Klotho is predicted to have glycosidase activity, capable of modifying the N-glycans of channels and transporters and regulating transmembrane movement of several ions, including calcium. Interestingly, N-glycan changes are observed in the kidney of α-Klotho mice and normal aged mice in association with decreased α-Klotho levels. These results imply that glycobiology and α-Klotho function are interesting targets for future studies.

Reduction of glutamate-induced excitotoxicity in murine primary neurons involving calpain inhibition

Excessive glutamate secretion leads to excitotoxicity, which has been shown to underlie neurodegenerative disorders. Excitotoxicity is in part exerted by overactivation of calpains, which promote neuronal cell death via induction of limited proteolysis of the cellular proteins p35, regulatory subunit of cyclin-dependent kinase 5, and αII-spectrin. We used primary murine neuronal cells in a model of glutamate toxicity. The protease inhibitor α1-antitrypsin was able to prevent glutamate toxicity as determined by MTT assay and immunofluorescence. Calpain and caspase 3 activity were reduced following α1-antitrypsin treatment, as assessed by calpain and caspase 3 activity assays. In addition we could observe a modulation of cleavage of the calpain/caspase substrates αII-spectrin and p35 in Western blots. In summary, α1-antitrypsin shows inhibitory effects on excitotoxicity of primary neurons involving the inhibition of calpain activity. The advantage of using α1-antitrypsin is that the substance is already in clinical use for the treatment of patients with hereditary α1-antitrypsin deficiency. Further experiments are required in animal models of neurodegenerative disorders to assess the suitability of this substance in patients suffering from Alzheimer's disease or Parkinson's disease.

Olesoxime suppresses calpain activation and mutant huntingtin fragmentation in the BACHD rat.

Huntington's disease is a fatal human neurodegenerative disorder caused by a CAG repeat expansion in the HTT gene, which translates into a mutant huntingtin protein. A key event in the molecular pathogenesis of Huntington's disease is the proteolytic cleavage of mutant huntingtin, leading to the accumulation of toxic protein fragments. Mutant huntingtin cleavage has been linked to the overactivation of proteases due to mitochondrial dysfunction and calcium derangements. Here, we investigated the therapeutic potential of olesoxime, a mitochondria-targeting, neuroprotective compound, in the BACHD rat model of Huntington's disease. BACHD rats were treated with olesoxime via the food for 12 months. In vivo analysis covered motor impairments, cognitive deficits, mood disturbances and brain atrophy. Ex vivo analyses addressed olesoxime's effect on mutant huntingtin aggregation and cleavage, as well as brain mitochondria function. Olesoxime improved cognitive and psychiatric phenotypes, and ameliorated cortical thinning in the BACHD rat. The treatment reduced cerebral mutant huntingtin aggregates and nuclear accumulation. Further analysis revealed a cortex-specific overactivation of calpain in untreated BACHD rats. Treated BACHD rats instead showed significantly reduced levels of mutant huntingtin fragments due to the suppression of calpain-mediated cleavage. In addition, olesoxime reduced the amount of mutant huntingtin fragments associated with mitochondria, restored a respiration deficit, and enhanced the expression of fusion and outer-membrane transport proteins. In conclusion, we discovered the calpain proteolytic system, a key player in Huntington's disease and other neurodegenerative disorders, as a target of olesoxime. Our findings suggest that olesoxime exerts its beneficial effects by improving mitochondrial function, which results in reduced calpain activation. The observed alleviation of behavioural and neuropathological phenotypes encourages further investigations on the use of olesoxime as a therapeutic for Huntington's disease.

Truncation and Activation of Dual Specificity Tyrosine Phosphorylation-regulated Kinase 1A by Calpain I: A MOLECULAR MECHANISM LINKED TO TAU PATHOLOGY IN ALZHEIMER DISEASE

Hyperphosphorylation and dysregulation of exon 10 splicing of Tau are pivotally involved in pathogenesis of Alzheimer disease (AD) and/or other tauopathies. Alternative splicing of Tau exon 10, which encodes the second microtubule-binding repeat, generates Tau isoforms containing three and four microtubule-binding repeats, termed 3R-Taus and 4R-Taus, respectively. Dual specificity tyrosine-phosphorylation-regulated kinase 1A (Dyrk1A) lies at the Down syndrome critical region of chromosome 21. Overexpression of this kinase may contribute to the early Tau pathology in Down syndrome via phosphorylation of Tau and dysregulation of Tau exon 10. Here, we report that Dyrk1A was truncated at the C terminus and was associated with overactivation of calpain I in AD brain. Calpain I proteolyzed Dyrk1A in vitro first at the C terminus and further at the N terminus and enhanced its kinase activity toward Tau via increased Vmax but not Km. C-terminal truncation of Dyrk1A resulted in stronger activity than its full-length protein in promotion of exon 10 exclusion and phosphorylation of Tau. Dyrk1A was truncated in kainic acid-induced excitotoxic mouse brains and coincided with an increase in 3R-Tau expression and phosphorylation of Tau via calpain activation. Moreover, truncation of Dyrk1A was correlated with an increase in the ratio of 3R-Tau/4R-Tau and Tau hyperphosphorylation in AD brain. Collectively, these findings suggest that truncation/activation of Dyrk1A by Ca(2+)/calpain I might contribute to Tau pathology via promotion of exon 10 exclusion and hyperphosphorylation of Tau in AD brain.

A Truncated Fragment of Src Protein Kinase Generated by Calpain‐mediated Cleavage is a Mediator of Neuronal Death in Excitotoxicity.

Excitotoxicity resulting from overstimulation of glutamate receptors is a major cause of neuronal death in cerebral ischemic stroke. The overstimulated ionotropic glutamate receptors exert their neurotoxic effects in part by overactivation of calpains, which induce neuronal death by catalyzing limited proteolysis of specific cellular proteins. Here, we report that in cultured cortical neurons and in vivo in a rat model of focal ischemic stroke, the tyrosine kinase Src is cleaved by calpains at a site in the N‐terminal unique domain. This generates a truncated Src fragment of ~52 kDa, which we localized predominantly to the cytosol. A cell membrane‐permeable fusion peptide derived from the unique domain of Src prevents calpain from cleaving Src in neurons and protects against excitotoxic neuronal death. To explore the role of the truncated Src fragment in neuronal death, we expressed a recombinant truncated Src fragment in cultured neurons and examined how it affects neuronal survival. Expression of this fragment, which lacks the myristoylation motif and unique domain, was sufficient to induce neuronal death. Furthermore, inactivation of the prosurvival kinase Akt is a key step in its neurotoxic signaling pathway. Because Src maintains neuronal survival, our results implicate calpain cleavage as a molecular switch converting Src from a promoter of cell survival to a mediator of neuronal death in excitotoxicity. Besides unveiling a new pathological action of Src, our discovery of the neurotoxic action of the truncated Src fragment suggests new therapeutic strategies with the potential to minimize brain damage in ischemic stroke

Inhibition of calpain prevents manganese-induced cell injury and alpha-synuclein oligomerization in organotypic brain slice cultures.

Overexposure to manganese has been known to promote alpha-synuclein oligomerization and enhance cellular toxicity. However, the exact mechanism of Mn-induced alpha-synuclein oligomerization is unclear. To explore whether alpha-synuclein oligomerization was associated with the cleavage of alpha-synuclein by calpain, we made a rat brain slice model of manganism and pretreated slices with calpain inhibitor II, a cell-permeable peptide that restricts the activity of calpain. After slices were treated with 400 μM Mn for 24 h, there were significant increases in the percentage of apoptotic cells, lactate dehydrogenase release, intracellular [Ca2+]i, calpain activity, and the mRNA and protein expression of calpain 1 and alpha-synuclein. Moreover, the number of C- and N-terminal fragments of alpha-synuclein and the amount of alpha-synuclein oligomerization also increased. These results also showed that calpain inhibitor II pretreatment could reduce Mn-induced nerve cell injury and alpha-synuclein oligomerization. Additionally, there was a significant decrease in the number of C- and N-terminal fragments of alpha-synuclein in calpain inhibitor II-pretreated slices. These findings revealed that Mn induced the cleavage of alpha-synuclein protein via overactivation of calpain and subsequent alpha-synuclein oligomerization in cultured slices. Moreover, the cleavage of alpha-synuclein by calpain 1 is an important signaling event in Mn-induced alpha-synuclein oligomerization.

Truncation and activation of GSK-3β by calpain I: a molecular mechanism links to tau hyperphosphorylation in Alzheimer's disease.

Abnormal hyperphosphorylation of tau is pivotally involved in the pathogenesis of Alzheimer's disease (AD) and related tauopathies. Glycogen synthase kinase 3β (GSK-3β) is a primary tau kinase that is most implicated in tau pathology in AD. However, the exact molecular nature of GSK-3β involved in AD is unclear. In the present study, we found that GSK-3β was truncated at C-terminus and correlated with over-activation of calpain I in AD brain. Truncation of GSK-3β was positively correlated with tau hyperphosphorylation, tangles score and Braak stage in human brain. Calpain I proteolyzed GSK-3β in vitro at C-terminus, leading to an increase of its kinase activity, but keeping its characteristic to preferentially phosphorylate the protein kinase A-primed tau. Excitotoxicity induced by kainic acid (KA) caused GSK-3β truncation at C-terminus and hyperphosphorylation of tau in mouse brain. Inhibition of calpain prevented the KA-induced changes. These findings suggest that truncation of GSK-3β by Ca2+/calpain I markedly increases its activity and involvement of this mechanism probably is responsible for up-regulation of GSK-3β and consequent abnormal hyperphosphorylation of tau and neurofibrillary degeneration in AD.

Taurine attenuates hippocampal and corpus callosum damage, and enhances neurological recovery after closed head injury in rats

The protective effects of taurine against closed head injury (CHI) have been reported. This study was designed to investigate whether taurine reduced white matter damage and hippocampal neuronal death through suppressing calpain activation after CHI in rats. Taurine (50mg/kg) was administered intravenously 30min and 4h again after CHI. It was found that taurine lessened the corpus callosum damage, attenuated the neuronal cell death in hippocampal CA1 and CA3 subfields and improved the neurological functions 7days after CHI. Moreover, it suppressed the over-activation of calpain, enhanced the levels of calpastatin, and reduced the degradation of neurofilament heavy protein, myelin basic protein and αII-spectrin in traumatic tissue 24h after CHI. These data confirm the protective effects of taurine against gray and white matter damage due to CHI, and suggest that down-regulating calpain activation could be one of the protective mechanisms of taurine against CHI.

Specific calpain inhibition by calpastatin prevents tauopathy and neurodegeneration and restores normal lifespan in tau P301L mice.

Tau pathogenicity in Alzheimer's disease and other tauopathies is thought to involve the generation of hyperphosphorylated, truncated, and oligomeric tau species with enhanced neurotoxicity, although the generative mechanisms and the implications for disease therapy are not well understood. Here, we report a striking rescue from mutant tau toxicity in the JNPL3 mouse model of tauopathy. We show that pathological activation of calpains gives rise to a range of potentially toxic forms of tau, directly, and by activating cdk5. Calpain overactivation in brains of these mice is accelerated as a result of the marked depletion of the endogenous calpain inhibitor, calpastatin. When levels of this inhibitor are restored in neurons of JNPL3 mice by overexpressing calpastatin, tauopathy is prevented, including calpain-mediated breakdown of cytoskeletal proteins, cdk5 activation, tau hyperphosphorylation, formation of potentially neurotoxic tau fragments by either calpain or caspase-3, and tau oligomerization. Calpastatin overexpression also prevents loss of motor axons, delays disease onset, and extends survival of JNPL3 mice by 3 months to within the range of normal lifespan. Our findings support the therapeutic promise of highly specific calpain inhibition in the treatment of tauopathies and other neurodegenerative states.

Calpain inhibition reduces ataxin-3 cleavage alleviating neuropathology and motor impairments in mouse models of Machado-Joseph disease.

Machado-Joseph Disease (MJD) is the most prevalent autosomal dominantly inherited cerebellar ataxia. It is caused by an expanded CAG repeat in the ATXN3 gene, which translates into a polyglutamine tract within the ataxin-3 protein. Present treatments are symptomatic and do not prevent disease progression. As calpain overactivation has been shown to contribute to mutant ataxin-3 proteolysis, translocation to the nucleus, inclusions formation and neurodegeneration, we investigated the potential role of calpain inhibition as a therapeutic strategy to alleviate MJD pathology. For this purpose, we administered orally the calpain inhibitor BDA-410 to a lentiviral mouse model of MJD. Western-blot and immunohistochemical analysis revealed the presence of N- and C-terminal mutant ataxin-3 fragments and the colocalization of large inclusions with cleaved caspase-3 in the mice brain. Oral administration of the calpain inhibitor BDA-410 decreased both fragments formation and full-length ataxin-3 levels, reduced aggregation of mutant ataxin-3 and prevented cell injury and striatal and cerebellar degeneration. Importantly, in correlation with the preserved cerebellar morphology, BDA-410 prevented motor behavioural deficits. In conclusion, BDA-410 alleviates Machado-Joseph neuropathology and may therefore be an effective therapeutic option for MJD.

Citicoline Protects Brain Against Closed Head Injury in Rats Through Suppressing Oxidative Stress and Calpain Over-Activation

Citicoline, a natural compound that functions as an intermediate in the biosynthesis of cell membrane phospholipids, is essential for membrane integrity and repair. It has been reported to protect brain against trauma. This study was designed to investigate the protective effects of citicoline on closed head injury (CHI) in rats. Citicoline (250mg/kg i.v. 30min and 4h after CHI) lessened body weight loss, and improved neurological functions significantly at 7days after CHI. It markedly lowered brain edema and blood-brain barrier permeability, enhanced the activities of superoxide dismutase and the levels of glutathione, reduced the levels of malondialdehyde and lactic acid. Moreover, citicoline suppressed the activities of calpain, and enhanced the levels of calpastatin, myelin basic protein and αII-spectrin in traumatic tissue 24h after CHI. Also, it attenuated the axonal and myelin sheath damage in corpus callosum and the neuronal cell death in hippocampal CA1 and CA3 subfields 7days after CHI. These data demonstrate the protection of citicoline against white matter and grey matter damage due to CHI through suppressing oxidative stress and calpain over-activation, providing additional support to the application of citicoline for the treatment of traumatic brain injury.

Lysosome and calcium dysregulation in Alzheimer's disease: partners in crime.

Early-onset FAD (familial Alzheimer's disease) is caused by mutations of PS1 (presenilin 1), PS2 (presenilin 2) and APP (amyloid precursor protein). Beyond the effects of PS1 mutations on proteolytic functions of the γ-secretase complex, mutant or deficient PS1 disrupts lysosomal function and Ca2+ homoeostasis, both of which are considered strong pathogenic factors in FAD. Loss of PS1 function compromises assembly and proton-pumping activity of the vacuolar-ATPase on lysosomes, leading to defective lysosomal acidification and marked impairment of autophagy. Additional dysregulation of cellular Ca2+ by mutant PS1 in FAD has been ascribed to altered ion channels in the endoplasmic reticulum; however, rich stores of Ca2+ in lysosomes are also abnormally released in PS1-deficient cells secondary to the lysosomal acidification defect. The resultant rise in cytosolic Ca2+ activates Ca2+-dependent enzymes, contributing substantially to calpain overactivation that is a final common pathway leading to neurofibrillary degeneration in all forms of AD (Alzheimer's disease). In the present review, we discuss the close inter-relationships among deficits of lysosomal function, autophagy and Ca2+ homoeostasis as a pathogenic process in PS1-related FAD and their relevance to sporadic AD.

A Truncated Fragment of Src Protein Kinase Generated by Calpain-mediated Cleavage Is a Mediator of Neuronal Death in Excitotoxicity

Excitotoxicity resulting from overstimulation of glutamate receptors is a major cause of neuronal death in cerebral ischemic stroke. The overstimulated ionotropic glutamate receptors exert their neurotoxic effects in part by overactivation of calpains, which induce neuronal death by catalyzing limited proteolysis of specific cellular proteins. Here, we report that in cultured cortical neurons and in vivo in a rat model of focal ischemic stroke, the tyrosine kinase Src is cleaved by calpains at a site in the N-terminal unique domain. This generates a truncated Src fragment of ~52 kDa, which we localized predominantly to the cytosol. A cell membrane-permeable fusion peptide derived from the unique domain of Src prevents calpain from cleaving Src in neurons and protects against excitotoxic neuronal death. To explore the role of the truncated Src fragment in neuronal death, we expressed a recombinant truncated Src fragment in cultured neurons and examined how it affects neuronal survival. Expression of this fragment, which lacks the myristoylation motif and unique domain, was sufficient to induce neuronal death. Furthermore, inactivation of the prosurvival kinase Akt is a key step in its neurotoxic signaling pathway. Because Src maintains neuronal survival, our results implicate calpain cleavage as a molecular switch converting Src from a promoter of cell survival to a mediator of neuronal death in excitotoxicity. Besides unveiling a new pathological action of Src, our discovery of the neurotoxic action of the truncated Src fragment suggests new therapeutic strategies with the potential to minimize brain damage in ischemic stroke.

CREB regulates the expression of neuronal glucose transporter 3: a possible mechanism related to impaired brain glucose uptake in Alzheimer's disease

Impaired brain glucose uptake and metabolism precede the appearance of clinical symptoms in Alzheimer disease (AD). Neuronal glucose transporter 3 (GLUT3) is decreased in AD brain and correlates with tau pathology. However, what leads to the decreased GLUT3 is yet unknown. In this study, we found that the promoter of human GLUT3 contains three potential cAMP response element (CRE)-like elements, CRE1, CRE2 and CRE3. Overexpression of CRE-binding protein (CREB) or activation of cAMP-dependent protein kinase significantly increased GLUT3 expression. CREB bound to the CREs and promoted luciferase expression driven by human GLUT3-promoter. Among the CREs, CRE2 and CRE3 were required for the promotion of GLUT3 expression. Full-length CREB was decreased and truncation of CREB was increased in AD brain. This truncation was correlated with calpain I activation in human brain. Further study demonstrated that calpain I proteolysed CREB at Gln28–Ala29 and generated a 41-kDa truncated CREB, which had less activity to promote GLUT3 expression. Importantly, human brain GLUT3 was correlated with full-length CREB positively and with activation of calpain I negatively. These findings suggest that overactivation of calpain I caused by calcium overload proteolyses CREB, resulting in a reduction of GLUT3 expression and consequently impairing glucose uptake and metabolism in AD brain.

Deficient brain insulin signalling pathway in Alzheimer's disease and diabetes

Brain glucose metabolism is impaired in Alzheimer's disease (AD), the most common form of dementia. Type 2 diabetes mellitus (T2DM) is reported to increase the risk for dementia, including AD, but the underlying mechanism is not understood. Here, we investigated the brain insulin-PI3K-AKT signalling pathway in the autopsied frontal cortices from nine AD, 10 T2DM, eight T2DM-AD and seven control cases. We found decreases in the levels and activities of several components of the insulin-PI3K-AKT signalling pathway in AD and T2DM cases. The deficiency of insulin-PI3K-AKT signalling was more severe in individuals with both T2DM and AD (T2DM-AD). This decrease in insulin-PI3K-AKT signalling could lead to activation of glycogen synthase kinase-3β, the major tau kinase. The levels and the activation of the insulin-PI3K-AKT signalling components correlated negatively with the level of tau phosphorylation and positively with protein O-GlcNAcylation, suggesting that impaired insulin-PI3K-AKT signalling might contribute to neurodegeneration in AD through down-regulation of O-GlcNAcylation and the consequent promotion of abnormal tau hyperphosphorylation and neurodegeneration. The decrease in brain insulin-PI3K-AKT signalling also correlated with the activation of calpain I in the brain, suggesting that the decrease might be caused by calpain over-activation. Our findings provide novel insight into the molecular mechanism by which type 2 diabetes mellitus increases the risk for developing cognitive impairment and dementia in Alzheimer's disease.

Tetanic contractions impair sarcomeric Z-disk of atrophic soleus muscle via calpain pathway

The aim of this study was to determine whether or not over-activation of calpains during running exercise or tetanic contractions was a major factor to induce sarcomere lesions in atrophic soleus muscle. Relationship between the degrees of desmin degradation and sarcomere lesions was also elucidated. We observed ultrastructural changes in soleus muscle fibers after 4-week unloading with or without running exercise. Calpain activity and desmin degradation were measured in atrophic soleus muscles before or after repeated tetani in vitro. Calpain-1 activity was progressively increased and desmin degradation was correspondingly elevated in 1-, 2-, and 4-week of unloaded soleus muscles. Calpain-1 activity and desmin degradation had an additional increase in unloaded soleus muscles after repeated tetani in vitro. PD150606, an inhibitor of calpains, reduced calpain activity and desmin degradation during tetanic contractions in unloaded soleus muscles. The 4-week unloading decreased the width of myofibrils and Z-disk in soleus fibers. After running exercise in unloaded group, Z-disks of adjacent myofibrils were not well in register but instead were longitudinally displaced. Calpain inhibition compromised exercise-induced misalignment of the Z-disks in atrophic soleus muscle. These results suggest that tetanic contractions induce an over-activation of calpains which lead to higher degrees of desmin degradation in unloaded soleus muscle. Desmin degradation may loose connections between adjacent myofibrils, whereas running exercise results in sarcomere injury in unloaded soleus muscle.

Targeting individual calpain isoforms for neuroprotection

Targeting individual calpain isoforms for neuroprotection