calpastatin and Brain-Injuries

This article attempts to provide a framework that will help to illustrate the roles of calpains in the process of traumatic brain injury (TBI).. This review provides meaningful points about the essential role of calpains in the neuropathological changes that follow TBI, identifies useful biomarkers of calpain activation and states the important roles of calpain in the treatment of TBI.. Neuronal calpains can be activated within hours or even minutes following contusive or diffuse brain trauma in animals. It has been suggested that they are early mediators of neuronal damage. Trauma can produce sustained calpain activation. In turn, this may result in axonal degeneration and neuronal death in models of TBI. Calpains can cleave cytoskeletal proteins into stable proteolytic fragments that have been widely used as biomarkers of the activation of calpain. The inhibition of calpains can reduce the functional and behavioural deficits by ameliorating axonal pathology and reducing cell deaths in animal models of TBI.. This review concentrates on the current understanding of the role of calpains in neuropathology that has been induced by TBI and the significance of calpains as a therapeutic target for the treatment of primary and secondary injuries that are associated with brain trauma.

Topics: Animals; Biomarkers; Brain Injuries; Calcium-Binding Proteins; Calpain; Cell Death; Cerebral Cortex; Cysteine Proteinase Inhibitors; Female; Humans; Male; Mice; Prognosis; Proteolysis; Treatment Outcome

Calpain is a Ca(2+)-activated proteolytic enzyme involved in neurodegeneration in a variety of injuries and diseases of the central nervous system (CNS). Many calpain homologs have been discovered. Depending on the tissue distribution, calpains are broadly classified as ubiquitous and tissue-specific. Ubiquitous calpain isoforms, -calpain and m-calpain, are abundantly expressed in the CNS. Calpastatin, an endogenous protein inhibitor, regulates the activity of ubiquitous calpain. Overactivation of calpain may degrade calpastatin, limiting its regulatory efficiency. Molecular structures of calpain and calpastatin have been deduced from cDNA cloning. The precise physiological function of calpain remains elusive. However, experimental evidence strongly suggests an important role for calpain in causing neurodegeneration in various injuries and diseases of the CNS. The increase in intracellular free Ca(2+) levels in the course of injuries and diseases in the CNS causes overactivation of calpain, promoting degradation of key cytoskeletal and membrane proteins. Cleavage of these key proteins by calpain is an irreversible process that perturbs the integrity and stability of CNS cells, leading to programmed cell death or apoptosis. Calpain in conjunction with caspases can cause apoptosis of the CNS cells. An aberrant Ca(2+) homeostasis inevitably activates calpain, which plays a crucial role in the pathophysiology of the CNS injuries and diseases. Therefore, calpain is a potential therapeutic target to prevent neurodegeneration. To this end, various cell-permeable calpain inhibitors have been synthesized for pharmacological inhibition of calpain activity. Some calpain inhibitors have shown significant neuroprotection in animal models of the CNS injuries and diseases, indicating their therapeutic potential.

Topics: Brain Injuries; Calcium-Binding Proteins; Calpain; Drug Evaluation, Preclinical; Enzyme Inhibitors; Forecasting; Humans; Isoenzymes; Neurodegenerative Diseases; Spinal Cord Injuries

Preterm infants suffer central nervous system (CNS) injury from hypoxia-ischemia and inflammation - termed encephalopathy of prematurity. Mature CNS injury activates caspase and calpain proteases. Erythropoietin (EPO) limits apoptosis mediated by activated caspases, but its role in modulating calpain activation has not yet been investigated extensively following injury to the developing CNS. We hypothesized that excess calpain activation degrades developmentally regulated molecules essential for CNS circuit formation, myelination and axon integrity, including neuronal potassium-chloride co-transporter (KCC2), myelin basic protein (MBP) and phosphorylated neurofilament (pNF), respectively. Further, we predicted that post-injury EPO treatment could mitigate CNS calpain-mediated degradation. Using prenatal transient systemic hypoxia-ischemia (TSHI) in rats to mimic CNS injury from extreme preterm birth, and postnatal EPO treatment with a clinically relevant dosing regimen, we found sustained postnatal excess cortical calpain activation following prenatal TSHI, as shown by the cleavage of alpha II-spectrin (αII-spectrin) into 145-kDa αII-spectrin degradation products (αII-SDPs) and p35 into p25. Postnatal expression of the endogenous calpain inhibitor calpastatin was also reduced following prenatal TSHI. Calpain substrate expression following TSHI, including cortical KCC2, MBP and NF, was modulated by postnatal EPO treatment. Calpain activation was reflected in serum levels of αII-SDPs and KCC2 fragments, and notably, EPO treatment also modulated KCC2 fragment levels. Together, these data indicate that excess calpain activity contributes to the pathogenesis of encephalopathy of prematurity. Serum biomarkers of calpain activation may detect ongoing cerebral injury and responsiveness to EPO or similar neuroprotective strategies.

Topics: Animals; Animals, Newborn; Apoptosis; Axons; Brain Injuries; Calcium-Binding Proteins; Calpain; Caspases; Enzyme Activation; Erythropoietin; Female; Hypoxia-Ischemia, Brain; Membrane Proteins; Myelin Basic Protein; Rats, Sprague-Dawley

The calpain family of calcium-dependent proteases has been implicated in a variety of diseases and neurodegenerative pathologies. Prolonged activation of calpains results in proteolysis of numerous cellular substrates including cytoskeletal components and membrane receptors, contributing to cell demise despite coincident expression of calpastatin, the specific inhibitor of calpains. Pharmacological and gene-knockout strategies have targeted calpains to determine their contribution to neurodegenerative pathology; however, limitations associated with treatment paradigms, drug specificity, and genetic disruptions have produced inconsistent results and complicated interpretation. Specific, targeted calpain inhibition achieved by enhancing endogenous calpastatin levels offers unique advantages in studying pathological calpain activation. We have characterized a novel calpastatin-overexpressing transgenic mouse model, demonstrating a substantial increase in calpastatin expression within nervous system and peripheral tissues and associated reduction in protease activity. Experimental activation of calpains via traumatic brain injury resulted in cleavage of α-spectrin, collapsin response mediator protein-2, and voltage-gated sodium channel, critical proteins for the maintenance of neuronal structure and function. Calpastatin overexpression significantly attenuated calpain-mediated proteolysis of these selected substrates acutely following severe controlled cortical impact injury, but with no effect on acute hippocampal neurodegeneration. Augmenting calpastatin levels may be an effective method for calpain inhibition in traumatic brain injury and neurodegenerative disorders.

Topics: Animals; Brain Injuries; Calcium-Binding Proteins; Female; Founder Effect; Hippocampus; Humans; Intercellular Signaling Peptides and Proteins; Male; Mice; Mice, Transgenic; NAV1.2 Voltage-Gated Sodium Channel; Nerve Degeneration; Nerve Tissue Proteins; Prions; Promoter Regions, Genetic; Proteolysis; Spectrin

Traumatic brain injury (TBI) results in abrupt, initial cell damage leading to delayed neuronal death. The calcium-activated proteases, calpains, are known to contribute to this secondary neurodegenerative cascade. Although the specific inhibitor of calpains, calpastatin, is present within neurons, normal levels of calpastatin are unable to fully prevent the damaging proteolytic activity of calpains after injury. In this study, increased calpastatin expression was achieved using transgenic mice that overexpress the human calpastatin (hCAST) construct under control of a calcium-calmodulin-dependent kinase II α promoter. Naïve hCAST transgenic mice exhibited enhanced neuronal calpastatin expression and significantly reduced protease activity. Acute calpain-mediated spectrin proteolysis in the cortex and hippocampus induced by controlled cortical impact brain injury was significantly attenuated in calpastatin overexpressing mice. Aspects of posttraumatic motor and cognitive behavioral deficits were also lessened in hCAST transgenic mice compared to their wildtype littermates. However, volumetric analyses of neocortical contusion revealed no histological neuroprotection at either acute or long-term time points. Partial hippocampal neuroprotection observed at a moderate injury severity was lost after severe TBI. This study underscores the effectiveness of calpastatin overexpression in reducing calpain-mediated proteolysis and behavioral impairment after TBI, supporting the therapeutic potential for calpain inhibition. In addition, the reduction in spectrin proteolysis without accompanied neocortical neuroprotection suggests the involvement of other factors that are critical for neuronal survival after contusion brain injury.

Topics: Animals; Brain Injuries; Calcium-Binding Proteins; Calpain; Gene Expression Regulation; Hippocampus; Humans; Maze Learning; Mice; Mice, Inbred C57BL; Mice, Transgenic; Neocortex; Proteolysis

Pathological activation of the intracellular Ca2+-dependent proteases calpains may be responsible for the neuronal pathology associated with neurodegenerative diseases and acute traumas to the central nervous system. Though calpain activation has been shown definitively in traumatic brain injury (TBI), no studies have investigated calpastatin (CAST), the calpains' endogenous and specific inhibitor, after TBI. The present study examined temporal changes in CAST protein following controlled cortical impact injury in the rat. Western blot analyses of CAST in cortex and hippocampus detected two bands corresponding to molecular weights of 130 kDa [high-molecular-weight (HMW)] and 80 kDa [low-molecular-weight (LMW)]. A modest decrease in the HMW band in conjunction with a significant increase in the LMW band was observed in cortex ipsilateral to the site of impact following TBI. Examination of ipsilateral hippocampus revealed an increasing trend in the LMW band after injury, while no changes were observed in the HMW band. Thus, observable changes in CAST levels appear to occur several hours after reported calpain activation and cleavage of other substrates. In addition, a new analysis was performed on previously published data examining calpain activity in the same tissue samples used in the present study. These data suggest an association between decreases in calpain activity and accumulation of LMW CAST in the ipsilateral cortex following TBI. The present study cannot exclude proteolytic processing of CAST to LMW forms. However, the absence of reciprocity between changes in LMW and HMW bands in consistent with other data suggesting that rat brain could contain different CAST isoforms.

Topics: Animals; Blotting, Western; Brain Injuries; Calcium-Binding Proteins; Calpain; Cerebral Cortex; Cysteine Proteinase Inhibitors; Disease Models, Animal; Functional Laterality; Hippocampus; Male; Rats; Rats, Sprague-Dawley; Time Factors