Selective release of calpain produced alphalI-spectrin (alpha-fodrin) breakdown products by acute neuronal cell death

Prevention of noise-induced hearing loss by calpain inhibitor MDL-28170 is associated with upregulation of PI3K/Akt survival signaling pathway

Introduction

Noise-induced calcium overload in sensory hair cells has been well documented as an early step in the pathogenesis of noise-induced hearing loss (NIHL). Alterations in cellular calcium homeostasis mediate a series of cellular events, including activation of calcium-dependent protein kinases and phosphatases. Using cell-membrane- and blood-brain-barrier-permeable calpain-1 (μ-calpain) and calpain-2 (m-calpain) inhibitor MDL-28170, we tested the involvement of calpains, a family of calcium-dependent cysteine proteases, and the potential of MDL-28170 in preventing NIHL.

Methods

CBA/J mice at the age of 12 weeks were exposed to broadband noise with a frequency spectrum from 2-20 kHz for 2 h at 101 dB sound pressure level to induce permanent hearing loss as measured by auditory brainstem response and distortion product otoacoustic emissions. Morphological damage was assessed by quantification of remaining sensory hair cells and inner hair cell synapses 2 weeks after the exposure.

Results

MDL-28170 treatment by intraperitoneal injection significantly attenuated noise-induced functional deficits and cochlear pathologies. MDL-28170 treatment also prevented noise-induced cleavage of alpha-fodrin, a substrate for calpain-1. Furthermore, MDL-28170 treatment prevented reduction of PI3K/Akt signaling after exposure to noise and upregulated p85α and p-Akt (S473) in outer hair cells.

Discussion

These results indicate that noise-induced calpain activation negatively regulates PI3K/Akt downstream signaling, and that prevention of NIHL by treatment with MDL-28170 is associated with upregulation of PI3K/Akt survival signaling pathways.

Characterization of Calpain and Caspase-6-Generated Glial Fibrillary Acidic Protein Breakdown Products Following Traumatic Brain Injury and Astroglial Cell Injury

Glial fibrillary acidic protein (GFAP) is the major intermediate filament III protein of astroglia cells which is upregulated in traumatic brain injury (TBI). Here we reported that GFAP is truncated at both the C- and N-terminals by cytosolic protease calpain to GFAP breakdown products (GBDP) of 46-40K then 38K following pro-necrotic (A23187) and pro-apoptotic (staurosporine) challenges to primary cultured astroglia or neuron-glia mixed cells. In addition, with another pro-apoptotic challenge (EDTA) where caspases are activated but not calpain, GFAP was fragmented internally, generating a C-terminal GBDP of 20 kDa. Following controlled cortical impact in mice, GBDP of 46-40K and 38K were formed from day 3 to 28 post-injury. Purified GFAP protein treated with calpain-1 and -2 generates (i) major N-terminal cleavage sites at A-56*A-61 and (ii) major C-terminal cleavage sites at T-383*Q-388, producing a limit fragment of 38K. Caspase-6 treated GFAP was cleaved at D-78/R-79 and D-225/A-226, where GFAP was relatively resistant to caspase-3. We also derived a GBDP-38K N-terminal-specific antibody which only labels injured astroglia cell body in both cultured astroglia and mouse cortex and hippocampus after TBI. As a clinical translation, we observed that CSF samples collected from severe human TBI have elevated levels of GBDP-38K as well as two C-terminally released GFAP peptides (DGEVIKES and DGEVIKE). Thus, in addition to intact GFAP, both the GBDP-38K as well as unique GFAP released C-terminal proteolytic peptides species might have the potential in tracking brain injury progression.

Stroke Proteomics: From Discovery to Diagnostic and Therapeutic Applications

Stroke remains a leading cause of death and disability, with limited therapeutic options and suboptimal tools for diagnosis and prognosis. High throughput technologies such as proteomics generate large volumes of experimental data at once, thus providing an advanced opportunity to improve the status quo by facilitating identification of novel therapeutic targets and molecular biomarkers. Proteomics studies in animals are largely designed to decipher molecular pathways and targets altered in brain tissue after stroke, whereas studies in human patients primarily focus on biomarker discovery in biofluids and, more recently, in thrombi and extracellular vesicles. Here, we offer a comprehensive review of stroke proteomics studies conducted in both animal and human specimen and present our view on limitations, challenges, and future perspectives in the field. In addition, as a unique resource for the scientific community, we provide extensive lists of all proteins identified in proteomic studies as altered by stroke and perform postanalysis of animal data to reveal stroke-related cellular processes and pathways.

Caspase-3 and caspase-8 expression in breast cancer: caspase-3 is associated with survival

Impaired apoptosis is one of the hallmarks of cancer. Caspase-3 and -8 are key regulators of the apoptotic response and have been shown to interact with the calpain family, a group of cysteine proteases, during tumorigenesis. The current study sought to investigate the prognostic potential of caspase-3 and -8 in breast cancer, as well as the prognostic value of combinatorial caspase and calpain expression. A large cohort (n = 1902) of early stage invasive breast cancer patients was used to explore the expression of caspase-3 and -8. Protein expression was examined using standard immunohistochemistry on tissue microarrays. High caspase-3 expression, but not caspase-8, is significantly associated with adverse breast cancer-specific survival (P = 0.008 and P = 0.056, respectively). Multivariate analysis showed that caspase-3 remained an independent factor when confounding factors were included (hazard ratio (HR) 1.347, 95% confidence interval (CI) 1.086–1.670; P = 0.007). The analyses in individual subgroups demonstrated the significance of caspase-3 expression in clinical outcomes in receptor positive (ER, PR or HER2) subgroups (P = 0.001) and in non-basal like subgroup (P = 0.029). Calpain expression had been previously assessed. Significant association was also found between high caspase-3/high calpain-1 and breast cancer-specific survival in the total patient cohort (P = 0.005) and basal-like subgroup (P = 0.034), as indicated by Kaplan–Meier analysis. Caspase-3 expression is associated with adverse breast cancer-specific survival in breast cancer patients, and provides additional prognostic values in distinct phenotypes. Combinatorial caspase and calpain expression can predict worse prognosis, especially in basal-like phenotypes. The findings warrant further validation studies in independent multi-centre patient cohorts.

Severe, but not mild heat-shock treatment induces immunogenic cell death in cancer cells

The mechanisms of immunogenicity underlying mild heat-shock (mHS) treatment < 42°C of tumor cells are largely attributed to the action of heat-shock proteins; however, little is known about the immunogenicity of tumor cells undergoing severe cytotoxic heat-shock treatment (sHS > 43°C). Here, we found that sHS, but not mHS (42°C), induces immunogenic cell death in human cancer cell lines as defined by the induction of ER stress response and ROS generation, cell surface exposure of calreticulin, HSP70 and HSP90, decrease of cell surface CD47, release of ATP and HMGB1. Only sHS-treated tumor cells were efficiently killed and phagocytosed by dendritic cells (DCs), which was partially dependent on cell surface calreticulin. DCs loaded with mHS or sHS-treated tumor cells displayed similar level of maturation and stimulated IFNγ-producing CD8⁺ T cells without any additional adjuvants in vitro. However, only DCs loaded with sHS-treated tumor cells stimulated antigen-specific CD4⁺ T cells and induced higher CD8⁺ T-cell activation and proliferation. sHS-treated murine cells also exposed calreticulin, HSP70 and HSP90 and activated higher DC maturation than mHS treated cells. Vaccination with sHS-treated tumor cells elicited protective immunity in mice. In this study, we defined specific conditions for the sHS treatment of human lung and ovarian tumor cells to arrive at optimal ratio between effective cell death, immunogenicity and content of tumor antigens for immunotherapeutic vaccine generation.

Protein Characterization of Extracellular Microvesicles/Exosomes Released from Cytotoxin-Challenged Rat Cerebrocortical Mixed Culture and Mouse N2a Cells

A number of neuronal and glial proteins were previously found to be released in free-standing soluble form from cultured brain cells into cell-conditioned media. Here, we sought to examine if similar proteins are also contained in neural and astroglial cell-released extracellular microvesicles/exosomes (MV/E). In this study, MV/E were isolated from cell-conditioned media from control and cytotoxin-challenged rat cerebrocortical mixed culture (CTX) and mouse neuroblastoma N2a cells. Cytotoxin challenges included pro-necrosis calcium ionophore A23187, pro-apoptosis staurosporine (STS), and excitotoxin N-methyl-D-aspartate. Based on established nanoparticle characterization method (dynamic light scattering, NanoTracker, and transmission electron microscopy), we confirmed that these released vesicles are in fact characteristic representation of MV/E by morphology (lipid bilayered vesicles) and by particle size (132-142 nm for CTX and 49-77 nm for N2a cells). We indeed identified neural cell body protein UCH-L1, axonal injury marker αII-spectrin and its breakdown products (SBDPs), astroglial markers GFAP and its breakdown products (GFAP-BDP), dendritic protein BIII-tubulin, synaptic protein synaptophysin, and exosome marker Alix in microvesicles from CTX and/or N2a cells. Furthermore, SBDPs, GFAP-BDP, UCH-L1, and synaptophysin are especially dominant in MV/E isolated from cytotoxin-treated CTX cells. Similarly, SBDPs, βIII-tubulin, and UCH-L1 are more prominently observed in cytotoxin-challenged N2a cells. Lastly, when isolated MV/E from A23187- or STS-challenged N2a cells were introduced to healthy N2a culture, they are capable of evoking cytotoxicity in the latter. Taken together, our study identified that microvesicles/exosomes isolated form healthy and injured brain cells contain certain neural and astroglial proteins, as well as possibly other cytotoxic factors that are capable of propagating cytotoxic effects.

Effect of glutamate on lysosomal membrane permeabilization in primary cultured cortical neurons

Glutamate is the principal neurotransmitter in the central nervous system. Glutamate-mediated excitotoxicity is the predominant cause of cerebral damage. Recent studies have shown that lysosomal membrane permeabilization (LMP) is involved in ischemia-associated neuronal death in non-human primates. This study was designed to investigate the effect of glutamate on lysosomal stability in primary cultured cortical neurons. Glutamate treatment for 30 min induced the permeabilization of lysosomal membranes as assessed by acridine orange redistribution and immunofluorescence of cathepsin B in the cytoplasm. Inhibition of glutamate excitotoxicity by the NMDA receptor antagonist MK-801 and the calcium chelator ethylene glycolbis (2-aminoethylether)-N, N, N′, N′-tetraacetic acid, rescued lysosomes from permeabilization. The role of calpain and reactive oxygen species (ROS) in inducing LMP was also investigated. Ca²⁺ overload following glutamate treatment induced the activation of calpain and the production of ROS, which are two major contributors to neuronal death. It has been reported that lysosomal-associated membrane protein 2 (LAMP2) and heat shock protein (HSP)70 are two calpain substrates that promote LMP in cancer cells; however, it was found that calpains were activated by glutamate, but only LAMP2 was subsequently degraded. Furthermore, LMP was not alleviated by treatment with the calpain inhibitors calpeptin and SJA6017, which blocked the cleavage of the calpain substrate α-fodrin. It was demonstrated that LMP was significantly alleviated by treatment with the antioxidant N-Acetyl-L-cysteine, indicating that LMP involvement in early glutamate excitotoxicity may be mediated partly by ROS rather than calpain activation. Overall, these data shed light on the role of ROS-mediated LMP in early glutamate excitotoxicity.

Biomarkers improve clinical outcome predictors of mortality following non-penetrating severe traumatic brain injury

OBJECTIVE

This study assessed whether early levels of biomarkers measured in CSF within 24-h of severe TBI would improve the clinical prediction of 6-months mortality.

METHODS

This prospective study conducted at two Level 1 Trauma Centers enrolled adults with severe TBI (GCS ≤8) requiring a ventriculostomy as well as control subjects. Ventricular CSF was sampled within 24-h of injury and analyzed for seven candidate biomarkers (UCH-L1, MAP-2, SBDP150, SBDP145, SBDP120, MBP, and S100B). The International Mission on Prognosis and Analysis of Clinical Trials in TBI (IMPACT) scores (Core, Extended, and Lab) were calculated for each patient to determine risk of 6-months mortality. The IMPACT models and biomarkers were assessed alone and in combination.

RESULTS

There were 152 patients enrolled, 131 TBI patients and 21 control patients. Thirty six (27 %) patients did not survive to 6 months. Biomarkers were all significantly elevated in TBI versus controls (p < 0.001). Peak levels of UCH-L1, SBDP145, MAP-2, and MBP were significantly higher in non-survivors (p < 0.05). Of the seven biomarkers measured at 12-h post-injury MAP-2 (p = 0.004), UCH-L1 (p = 0.024), and MBP (p = 0.037) had significant unadjusted hazard ratios. Of the seven biomarkers measured at the earliest time within 24-h, MAP-2 (p = 0.002), UCH-L1 (p = 0.016), MBP (p = 0.021), and SBDP145 (0.029) had the most significant elevations. When the IMPACT Extended Model was combined with the biomarkers, MAP-2 contributed most significantly to the survival models with sensitivities of 97-100 %.

CONCLUSIONS

These data suggest that early levels of MAP-2 in combination with clinical data provide enhanced prognostic capabilities for mortality at 6 months.

Identification of α-fodrin as an autoantigen in experimental coronavirus retinopathy (ECOR)

The coronavirus, mouse hepatitis virus (MHV), JHM strain induces a biphasic disease in BALB/c mice that consists of an acute retinitis followed by progression to a chronic retinal degeneration with autoimmune reactivity. Retinal degeneration resistant CD-1 mice do not develop either the late phase or autoimmune reactivity. A mouse RPE/choroid DNA expression library was screened using sera from virus infected BALB/c mice. Two clones were identified, villin-2 protein and α-fodrin protein. α-Fodrin protein was used for further analysis and western blot reactivity was seen only in sera from virus infected BALB/c mice. CD4 T cells were shown to specifically react with MHV antigens and with α-fodrin protein. These studies clearly identified both antibody and CD4 T cell reactivities to α-fodrin in sera from virus infected, retinal degenerative susceptible BALB/c mice.

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.

Intrinsic indicators for specimen degradation

Variable degrees of molecular degradation occur in human surgical specimens before clinical examination and severely affect analytical results. We therefore initiated an investigation to identify protein markers for tissue degradation assessment. We exposed 4 cell lines and 64 surgical/autopsy specimens to defined periods of time at room temperature before procurement (experimental cold ischemic time (CIT)-dependent tissue degradation model). Using two-dimensional fluorescence difference gel electrophoresis in conjunction with mass spectrometry, we performed comparative proteomic analyses on cells at different CIT exposures and identified proteins with CIT-dependent changes. The results were validated by testing clinical specimens with western blot analysis. We identified 26 proteins that underwent dynamic changes (characterized by continuous quantitative changes, isoelectric changes, and/or proteolytic cleavages) in our degradation model. These changes are strongly associated with the length of CIT. We demonstrate these proteins to represent universal tissue degradation indicators (TDIs) in clinical specimens. We also devised and implemented a unique degradation measure by calculating the quantitative ratio between TDIs' intact forms and their respective degradation-modified products. For the first time, we have identified protein TDIs for quantitative measurement of specimen degradation. Implementing these indicators may yield a potentially transformative platform dedicated to quality control in clinical specimen analyses.

Release of Full-Length PrP(C) from Cultured Neurons Following Neurotoxic Challenges

The susceptibility of the normal cellular prion protein isoform, cellular prion protein (PrP(C)), to proteolytic digestion has been well documented. In addition, a link between PrP(C) and the cytosolic protease, calpain, has been reported although the specifics of the interaction remain unclear. We performed in vitro and in cell-based studies to examine this relationship. We observed that human recombinant PrP (HrPrP) was readily cleaved by calpain-1 and -2, and we have identified and defined the targeted cleavage sites. In contrast, HrPrP was resistant to caspase-3 digestion. Unexpectedly, when brain lysates from PrP(C)-expressing mice were treated with calpain, no appreciable loss of the intact PrP(C), nor the appearance of PrP(C) breakdown products (BDPs) were observed, even though alpha II-spectrin was converted to its signature calpain-induced BDPs. In addition, when rat cerebrocortical neuronal cultures (RtCNC) were subjected to the two neurotoxins at subacute levels, maitotoxin (MTX) and N-methyl-d-aspartate (NMDA), PrP(C)-BDPs were also not detectable. However, a novel finding from these cell-based studies is that apparently full-length, mature PrP(C) is released into culture media from RtCNC challenged with subacute doses of MTX and NMDA. Calpain inhibitor SNJ-1945 and caspase inhibitor IDN-6556 did not attenuate the release of PrP(C). Similarly, the lysosomal protease inhibitor, NH(4)Cl, and the proteasome inhibitor, lactacystin, did not significantly alter the integrity of PrP(C) or its release from the RtCNC. In conclusion, rat neuronal PrP(C) is not a significant target for proteolytic modifications during MTX and NMDA neurotoxic challenges. However, the robust neurotoxin-mediated release of full-length PrP(C) into the cell culture media suggests an unidentified neuroprotective mechanism for PrP(C).

A neuronal death model: overexpression of neuronal intermediate filament protein peripherin in PC12 cells

BACKGROUND

Abnormal accumulation of neuronal intermediate filament (IF) is a pathological indicator of some neurodegenerative disorders. However, the underlying neuropathological mechanisms of neuronal IF accumulation remain unclear. A stable clone established from PC12 cells overexpressing a GFP-Peripherin fusion protein (pEGFP-Peripherin) was constructed for determining the pathway involved in neurodegeneration by biochemical, cell biology, and electronic microscopy approaches. In addition, pharmacological approaches to preventing neuronal death were also examined.

RESULTS

Results of this study showed that TUNEL positive reaction could be detected in pEGFP-Peripherin cells. Swollen mitochondria and endoplasmic reticulum (ER) were seen by electron microscopy in pEGFP-Peripherin cells on day 8 of nerve growth factor (NGF) treatment. Peripherin overexpression not only led to the formation of neuronal IF aggregate but also causes aberrant neuronal IF phosphorylation and mislocation. Western blots showed that calpain, caspase-12, caspase-9, and caspase-3 activity was upregulated. Furthermore, treatment with calpain inhibitor significantly inhibited cell death.

CONCLUSIONS

These results suggested that the cytoplasmic neuronal IF aggregate caused by peripherin overexpression may induce aberrant neuronal IF phosphorylation and mislocation subsequently trapped and indirectly damaged mitochondria and ER. We suggested that the activation of calpain, caspase-12, caspase-9, and caspase-3 were correlated to the dysfunction of the ER and mitochondria in our pEGFP-Peripherin cell model. The present study suggested that pEGFP-Peripherin cell clones could be a neuronal death model for future studies in neuronal IFs aggregate associated neurodegeneration.

Pregabalin suppresses calcium-mediated proteolysis and improves stroke outcome

Pregabalin, a Ca(2+) channel α(2)δ-subunit antagonist with analgesic and antiepileptic activity, reduced neuronal loss and improved functional outcome in a mouse model of focal ischemic stroke. Pregabalin administration (5-10mg/kg, i.p.) 30-90 min after transient middle cerebral artery occlusion/reperfusion reduced infarct volume, neuronal death in the ischemic penumbra and neurological deficits at 24h post-stroke. Pregabalin significantly decreased the amount of Ca(2+)/calpain-mediated α-spectrin proteolysis in the cerebral cortex measured at 6h post-stroke. Together with the extensive clinical experience with pregabalin for other neurological indications, our findings suggest the potential for a therapeutic benefit of pregabalin in stroke patients.

Dysfunctional mitochondria uphold calpain activation: contribution to Parkinson's disease pathology

Calpain is a ubiquitous calcium-sensitive protease that is essential for normal physiologic neuronal function. However, mitochondrial-mediated-calcium homeostasis alterations may lead to its pathologic activation that jeopardizes neuronal structure and function. Here, we provide evidence to support a role for the involvement of calpain 1 in mitochondrial-induced neurodegeneration in a Parkinson's disease (PD) cellular model. We show that dysfunctional mitochondria increases cytosolic calcium, thereby, inducing calpain activation. Interestingly, its inhibition significantly attenuated the accumulation of alpha-synuclein oligomers and contributed to an increase of insoluble alpha-synuclein aggregates, known to be cytoprotective. Moreover, our data corroborate that calpain-1 overactivation in our mitochondrial-deficient cells promote caspase-3 activation. Overall, our findings further clarify the crucial role of dysfunctional mitochondria in the control of molecular mechanisms occurring in PD brain cells, providing a potentially novel correlation between the degradation of calpain substrates suggesting a putative role of calpain and calpain inhibition as a therapeutic tool in PD.

Calcium-activated calpain-2 is a mediator of beta cell dysfunction and apoptosis in type 2 diabetes

The islet in type 2 diabetes (T2DM) and the brain in neurodegenerative diseases share progressive cell dysfunction, increased apoptosis, and accumulation of locally expressed amyloidogenic proteins (islet amyloid polypeptide (IAPP) in T2DM). Excessive activation of the Ca(2+)-sensitive protease calpain-2 has been implicated as a mediator of oligomer-induced cell death and dysfunction in neurodegenerative diseases. To establish if human IAPP toxicity is mediated by a comparable mechanism, we overexpressed human IAPP in rat insulinoma cells and freshly isolated human islets. Pancreas was also obtained at autopsy from humans with T2DM and nondiabetic controls. We report that overexpression of human IAPP leads to the formation of toxic oligomers and increases beta cell apoptosis mediated by increased cytosolic Ca(2+) and hyperactivation of calpain-2. Cleavage of alpha-spectrin, a marker of calpain hyperactivation, is increased in beta cells in T2DM. We conclude that overactivation of Ca(2+)-calpain pathways contributes to beta cell dysfunction and apoptosis in T2DM.

Alpha II-spectrin breakdown products serve as novel markers of brain injury severity in a canine model of hypothermic circulatory arrest

BACKGROUND

The development of specific biomarkers to aid in the diagnosis and prognosis of neuronal injury is of paramount importance in cardiac surgery. Alpha II-spectrin is a structural protein abundant in neurons of the central nervous system and cleaved into signature fragments by proteases involved in necrotic and apoptotic cell death. We measured cerebrospinal fluid alpha II-spectrin breakdown products (alphaII-SBDPs) in a canine model of hypothermic circulatory arrest (HCA) and cardiopulmonary bypass.

METHODS

Canine subjects were exposed to either 1 hour of HCA (n = 8; mean lowest tympanic temperature 18.0 +/- 1.2 degrees C) or standard cardiopulmonary bypass (n = 7). Cerebrospinal fluid samples were collected before treatment and 8 and 24 hours after treatment. Using polyacrylamide gel electrophoresis and immunoblotting, SBDPs were isolated and compared between groups using computer-assisted densitometric scanning. Necrotic versus apoptotic cell death was indexed by measuring calpain and caspase-3 cleaved alphaII-SBDPs (SBDP 145+150 and SBDP 120, respectively).

RESULTS

Animals undergoing HCA demonstrated mild patterns of histologic cellular injury and clinically detectable neurologic dysfunction. Calpain-produced alphaII-SBDPs (150 kDa+145 kDa bands-necrosis) 8 hours after HCA were significantly increased (p = 0.02) as compared with levels before HCA, and remained elevated at 24 hours after HCA. In contrast, caspase-3 alphaII-SBDP (120 kDa band-apoptosis) was not significantly increased. Animals receiving cardiopulmonary bypass did not demonstrate clinical or histologic evidence of injury, with no increases in necrotic or apoptotic cellular markers.

CONCLUSIONS

We report the use of alphaII-SBDPs as markers of neurologic injury after cardiac surgery. Our analysis demonstrates that calpain- and caspase-produced alphaII-SBDPs may be an important and novel marker of neurologic injury after HCA.

Rational design of novel red-shifted BRET pairs: Platforms for real-time single-chain protease biosensors

Bioluminescence resonance energy transfer (BRET) systems to date have been dominated by use of blue-green Renilla luciferase (Rluc) as the energy donor. Although effective in many cases, the expense and unfavorable biochemical attributes of the substrate (phenylcoelenterazine) limit utility of Rluc-based BRET systems. Herein we report a series of novel BRET pairs based on luciferases that utilize D-luciferin, resulting in red-shifted photonic outputs, favorable biochemical attributes, and increased efficacy. We developed a modified Förster equation to predict optimal BRET luciferase donor-fluorophore pairs and identified tdTomato as the optimal red fluorophore acceptor for click beetle green luciferase (CBG). A prototypical single-chain protease biosensor, capable of reporting on executioner caspase activity in live cells and in real-time, was generated by inserting a DEVD linker between CBG and tdTomato and validated in vitro with recombinant caspases and in cellulo with apoptosis-sensitive and -resistant cell lines. High signal-to-noise ratios ( approximately 33) and Z' factors (0.85) were observed in live cell longitudinal studies, sufficient for high-throughput screening. Thus, we illustrate a general methodology for the rational design of new BRET systems and provide a novel single-chain BRET protease biosensor that is long lived, red-shifted, and utilizes D-luciferin.

Upregulation of Dpysl2 and Spna2 gene expression in the rat brain after ischemic stroke

Ischemia activates the synthesis of potentially damaging and protective proteins in the central nervous system. Dihydropyrimidinase-like 2 (Dpysl2), a protein involved in neuronal differentiation and axonal guidance, and alpha-spectrin 2 (Spna2), a protein involved in maintaining neuronal membrane integrity, were found altered in various nervous system diseases. Modifications of Dpysl2 and Spna2 proteins have been reported in focal ischemic stroke, but their significance is not yet established. Therefore, this study was aimed to investigate the temporal expression of Dpysl2 and Spna2 genes in normal and stroke rat brain and to characterize stroke brains for cell areas, apoptosis, and microglia cells. The middle cerebral artery of rat brain was occluded and the brain tissue was sectioned for in situ hybridization of Dpysl2 and Spna2 genes, TUNEL, and OX-42 immunofluorescence staining. Dpysl2 and Spna2 mRNA expression was quantified by real-time RT-PCR. Characterization of stroke brain for apoptosis and microglia cells showed apoptotic cells and activated microglia, mainly in the infarct core of ipsilateral cortex and striatum of stroke brain. Significant upregulation of Dpysl2 and Spna2 mRNA expression in the penumbra region after stroke was observed predominantly in injured swollen cells in the cortex and striatum. Upregulation of Dpysl2 and Spna2 expression in hypertrophic cells in the penumbra regions of cortex and striatum of stroke brain indicates an early neuronal defense mechanism involving active neuronal repair, regeneration and development, as these genes are known to be involved in neurite outgrowth and plasticity.

Opposing roles for caspase and calpain death proteases in L-glutamate-induced oxidative neurotoxicity

Oxidative glutamate toxicity in HT22 murine hippocampal cells is a model for neuronal death by oxidative stress. We have investigated the role of proteases in HT22 cell oxidative glutamate toxicity. L-glutamate-induced toxicity was characterized by cell and nuclear shrinkage and chromatin condensation, yet occurred in the absence of either DNA fragmentation or mitochondrial cytochrome c release. Pretreatment with the selective caspase inhibitors either benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (pan-caspase), N-acetyl-Leu-Glu-His-Asp-aldehyde (caspase 9) or N-acetyl-Ile-Glu-Thr-Asp-aldehyde (caspase 8), significantly increased L-glutamate-induced cell death with a corresponding increase in observed nuclear shrinkage and chromatin condensation. This enhancement of glutamate toxicity correlated with an increase in L-glutamate-dependent production of reactive oxygen species (ROS) as a result of caspase inhibition. Pretreating the cells with N-acetyl-L-cysteine prevented ROS production, cell shrinkage and cell death from L-glutamate as well as that associated with the presence of the pan-caspase inhibitor. In contrast, the caspase-3/-7 inhibitor N-acetyl-Asp-Glu-Val-Asp aldehyde was without significant effect. However, pretreating the cells with the calpain inhibitor N-acetyl-Leu-Leu-Nle-CHO, but not the cathepsin B inhibitor CA-074, prevented cell death. The cytotoxic role of calpains was confirmed further by: 1) cytotoxic dependency on intracellular Ca(2+) increase, 2) increased cleavage of the calpain substrate Suc-Leu-Leu-Val-Tyr-AMC and 3) immunoblot detection of the calpain-selective 145 kDa alpha-fodrin cleavage fragment. We conclude that oxidative L-glutamate toxicity in HT22 cells is mediated via calpain activation, whereas inhibition of caspases-8 and -9 may exacerbate L-glutamate-induced oxidative neuronal damage through increased oxidative stress.

Calpain-mediated collapsin response mediator protein-1, -2, and -4 proteolysis after neurotoxic and traumatic brain injury

Collapsin response mediator proteins (CRMPs) are important molecules in neurite outgrowth and axonal guidance. Within the CRMP family, CRMP-2 has been implicated in several neurological diseases (Alzheimer's, epilepsy, and ischemia). Here, we investigated the integrity of CRMPs (CRMP-1, -2, -4, -5) after in vitro neurotoxin treatment and in vivo traumatic brain injury (TBI). After maitotoxin (MTX) and NMDA treatment of primary cortical neurons, a dramatic decrease of intact CRMP-1, -2 and -4 proteins were observed, accompanied by the appearance of distinct 55-kDa and 58-kDa breakdown products (BDP) for CRMP-2 and -4, respectively. Inhibition of calpain activation prevented NMDA-induced CRMP-2 proteolysis and redistribution of CRMP-2 from the neurites to the cell body, while attenuating neurite damage and neuronal cell injury. Similarly, CRMP-1, -2, and -4 were also found degraded in rat cortex and hippocampus following controlled cortical impact (CCI), an in vivo model of TBI. The appearance of the 55-kDa CRMP-2 BDP was observed to increase, in a time-dependent manner, between 24 and 48 h in the ipsilateral cortex, and by 48 hours in the hippocampus. The observed 55-kDa CRMP-2 BDP following TBI was reproduced by in vitro incubation of naive brain lysate with activated calpain-2, but not activated caspase-3. Sequence analysis revealed several possible cleavage sites near the C-terminus of CRMP-2. Collectively, this study demonstrated that CRMP-1, -2, and -4 are degraded following both acute traumatic and neurotoxic injury. Furthermore, calpain-2 was identified as the possible proteolytic mediator of CRMP-2 following excitotoxic injury and TBI, which appears to correlate well with neuronal cell injury and neurite damage. It is possible that the calpain-mediated truncation of CRMPs following TBI may be an inhibiting factor for post-injury neurite regeneration.

Hypochlorous acid induces apoptosis of cultured cortical neurons through activation of calpains and rupture of lysosomes

3-Chlorotyrosine, a bio-marker of hypochlorous acid (HOCl) in vivo, was reported to be substantially elevated in the Alzheimer's disease (AD) brains. Thus, HOCl might be implicated in the development of AD. However, its effect and mechanism on neuronal cell death have not been investigated. Here, we report for the first time that HOCl treatment induces an apoptotic-necrotic continuum of concentration-dependent cell death in cultured cortical neurons. Neurotoxicity caused by an intermediate concentration of HOCl (250 microm) exhibited several biochemical markers of apoptosis in the absence of caspase activation. However, the involvement of calpains was demonstrated by data showing that calpain inhibitors protect cortical neurons from apoptosis and the formation of 145/150 kDa alpha-fodrin fragments. Moreover, an increase in cytosolic Ca2+ concentration was associated with HOCl neurotoxicity and Ca2+ channel antagonists, and Ca2+ chelators prevented cleavage of alpha-fodrin and the induction of apoptosis. Finally, we found that calpain activation ruptured lysosomes. Stabilization of lysosomes by calpain inhibitors or imidazoline drugs, as well as inhibition of cathepsin protease activities, rescued cells from HOCl-induced neurotoxicity. Our results showed for the first time that HOCl induces apoptosis in cortical neurons, and that the cell death process involves calpain activation and rupture of lysosomes.

Extensive degradation of myelin basic protein isoforms by calpain following traumatic brain injury

Axonal injury is one of the key features of traumatic brain injury (TBI), yet little is known about the integrity of the myelin sheath. We report that the 21.5 and 18.5-kDa myelin basic protein (MBP) isoforms degrade into N-terminal fragments (of 10 and 8 kDa) in the ipsilateral hippocampus and cortex between 2 h and 3 days after controlled cortical impact (in a rat model of TBI), but exhibit no degradation contralaterally. Using N-terminal microsequencing and mass spectrometry, we identified a novel in vivo MBP cleavage site between Phe114 and Lys115. A MBP C-terminal fragment-specific antibody was then raised and shown to specifically detect MBP fragments in affected brain regions following TBI. In vitro naive brain lysate and purified MBP digestion showed that MBP is sensitive to calpain, producing the characteristic MBP fragments observed in TBI. We hypothesize that TBI-mediated axonal injury causes secondary structural damage to the adjacent myelin membrane, instigating MBP degradation. This could initiate myelin sheath instability and demyelination, which might further promote axonal vulnerability.

Neuroprotection associated with alternative splicing of NMDA receptors in rat cortical neurons

Exposure of cultured cortical neurons to elevated extracellular K(+) concentrations (25 mM) induces membrane depolarization and an increase in action-potential firing. Long-term high K(+) treatment was associated with an increased neuronal cell death. In surviving neurons, multiple changes occurred in the proportion of individual NMDA receptor subunit 1 (NR1) splice variant mRNA expression, whereas the overall expression of NR1, NR2A and NR2B transcripts remained unaffected. The high K(+)-induced changes in NR1 splice variant expression were virtually abolished upon a concurrent administration of tetrodotoxin (TTX; 3 microM). In voltage-clamp recordings performed on neurons resistant to high K(+) treatment, inward currents induced by NMDA (1-1,000 microM) were reduced. In K(+)-resistant cells, the activity of calpain but not of caspase-3 was diminished compared with controls kept in regular medium. NR function as well as calpain activity was not affected in cultures concomitantly treated with high K(+) and either TTX or a NR antagonist (CGS19755 (selfotel) or memantine). In conclusion, the present data indicate adaptive changes in NR1 splice variant expression and a decrease in NR function upon a sustained increase in neurotransmission. Accordingly, alternative splicing could be an endogenous mechanism to counteract cellular damage due to overactivation of excitatory NRs and may be associated with an impairment of necrotic mechanisms.

Glutamate-induced apoptosis in neuronal cells is mediated via caspase-dependent and independent mechanisms involving calpain and caspase-3 proteases as well as apoptosis inducing factor (AIF) and this process is inhibited by equine estrogens

BACKGROUND

Glutamate, a major excitatory amino acid neurotransmitter, causes apoptotic neuronal cell death at high concentrations. Our previous studies have shown that depending on the neuronal cell type, glutamate-induced apoptotic cell death was associated with regulation of genes such as Bcl-2, Bax, and/or caspase-3 and mitochondrial cytochrome c. To further delineate the intracellular mechanisms, we have investigated the role of calpain, an important calcium-dependent protease thought to be involved in apoptosis along with mitochondrial apoptosis inducing factor (AIF) and caspase-3 in primary cortical cells and a mouse hippocampal cell line HT22.

RESULTS

Glutamate-induced apoptotic cell death in neuronal cells was associated with characteristic DNA fragmentation, morphological changes, activation of calpain and caspase-3 as well as the upregulation and/or translocation of AIF from mitochondria into cytosol and nuclei. Our results reveal that primary cortical cells and HT22 cells display different patterns of regulation of these genes/proteins. In primary cortical cells, glutamate induces activation of calpain, caspase-3 and translocation of AIF from mitochondria to cytosol and nuclei. In contrast, in HT22 cells, only the activation of calpain and upregulation and translocation of AIF occurred. In both cell types, these processes were inhibited/reversed by 17beta-estradiol and Delta8,17beta-estradiol with the latter being more potent.

CONCLUSION

Depending upon the neuronal cell type, at least two mechanisms are involved in glutamate-induced apoptosis: a caspase-3-dependent pathway and a caspase-independent pathway involving calpain and AIF. Since HT22 cells lack caspase-3, glutamate-induced apoptosis is mediated via the caspase-independent pathway in this cell line. Kinetics of this apoptotic pathway further indicate that calpain rather than caspase-3, plays a critical role in the glutamate-induced apoptosis. Our studies further indicate that glutamate- induced changes of these proteins can be inhibited by estrogens, with Delta8,17beta-estradiol, a novel equine estrogen being more potent than 17beta-estradiol. To our knowledge, this is the first demonstration that glutamate-induced apoptosis involves regulation of multiple apoptotic effectors that can be inhibited by estrogens. Whether these observations can help in the development of novel therapeutic approaches for the prevention of neurodegenerative diseases with estrogens and calpain inhibitors remains to be investigated.

DY-9760e, a Novel Calmodulin Inhibitor, Exhibits Cardioprotective Effects in the Ischemic Heart

DY-9760e (3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride-3.5 hydrate) inhibits Ca(2+)/CaM-dependent nitric oxide synthase (NOS), thereby inhibiting nitric oxide (NO) production. In cardiomyocytes from ischemic rat heart NO and superoxide levels are increased causing protein tyrosine nitration. In hearts subjected to ischemia/reperfusion DY-9760e totally abolishes protein tyrosine nitration. Notably, DY-9760e also inhibits calpain and cas-pase-3 activation that occurs prior to apoptosis in cardiomyocytes. In ischemic hearts fodrin is the substrate for calpain. DY-9760e inhibits fodrin breakdown in the peri-infarct area rather than in the infarct core. In the ischemic rat brain DY-9760e inhibits caspase-3-induced proteolysis of calpastatin, an endogenous calpain inhibitor, suggesting that crosstalk between calpain and caspase-3 is mediated by calpastatin breakdown. Thus, DY-9760e rescues neurons and cardiomyocytes from ischemic injury by inhibiting crosstalk between calpain and caspase-3 as well as protein tyrosine nitration.

Early induction of calpains in rotenone-mediated neuronal apoptosis

Rotenone is an inhibitor of mitochondrial complex I that produces a model of Parkinson's disease (PD), where neurons undergo apoptosis by caspase-dependent and/or caspase-independent pathways. Inhibition of calpains has recently been shown to attenuate neuronal apoptosis. This study aims to establish for the first time, the time-point of calpain activation with respect to the caspase activation and the possibility of cell cycle re-entry in rotenone-mediated cell death. Immunoblot results revealed calpain activation occurred at 5, 10h prior to caspase-3 activation (at 15 h), suggesting calpain activation was an earlier cellular event compared to caspase activation in the rotenone-mediated apoptosis. In addition, an upregulation of phospho-p53 was observed at 21 h. However, no expression or upregulation of cell cycle regulatory proteins including cdc25a, cyclin-D1 and cyclin-D3 were observed, strongly suggesting that cell cycle re-entry did not occur. These findings provide new insights into the differential patterns of calpain and caspase activation that result from rotenone poisoning and which may be relevant to the therapeutic management of PD.

Anandamide-induced cell death in primary neuronal cultures: role of calpain and caspase pathways

Anandamide (arachidonoylethanolamide or AEA) is an endocannabinoid that acts at vanilloid (VR1) as well as at cannabinoid (CB1/CB2) and NMDA receptors. Here, we show that AEA, in a dose-dependent manner, causes cell death in cultured rat cortical neurons and cerebellar granule cells. Inhibition of CB1, CB2, VR1 or NMDA receptors by selective antagonists did not reduce AEA neurotoxicity. Anandamide-induced neuronal cell loss was associated with increased intracellular Ca(2+), nuclear condensation and fragmentation, decreases in mitochondrial membrane potential, translocation of cytochrome c, and upregulation of caspase-3-like activity. However, caspase-3, caspase-8 or caspase-9 inhibitors, or blockade of protein synthesis by cycloheximide did not alter anandamide-related cell death. Moreover, AEA caused cell death in caspase-3-deficient MCF-7 cell line and showed similar cytotoxic effects in caspase-9 dominant-negative, caspase-8 dominant-negative or mock-transfected SH-SY5Y neuroblastoma cells. Anandamide upregulated calpain activity in cortical neurons, as revealed by alpha-spectrin cleavage, which was attenuated by the calpain inhibitor calpastatin. Calpain inhibition significantly limited anandamide-induced neuronal loss and associated cytochrome c release. These data indicate that AEA neurotoxicity appears not to be mediated by CB1, CB2, VR1 or NMDA receptors and suggest that calpain activation, rather than intrinsic or extrinsic caspase pathways, may play a critical role in anandamide-induced cell death.

Concurrent calpain and caspase-3 mediated proteolysis of alpha II-spectrin and tau in rat brain after methamphetamine exposure: a similar profile to traumatic brain injury

Neurotoxicity in rat cortex and hippocampus following acute methamphetamine administration was characterized and compared to changes following traumatic brain injury. Doses of 10, 20, and 40 mg/kg of methamphetamine produced significant increases in calpain- and caspase-cleaved alpha II-spectrin and tau protein fragments, suggesting cell injury or death. Changes in proteolytic products were significantly increased over vehicle controls. Use of fragment specific biomarkers detected prominent calpain-mediated protein fragments in the cortex and hippocampus while caspase-mediated protein fragments were also detected in the hippocampus. Remarkably, proteolytic product increases at the 40 mg/kg dose after 24 h were as high as those observed in experimental traumatic brain injury. Use of calpain and caspase proteolytic inhibitors may be useful in preventing methamphetamine-induced neurotoxicity.

The influence of age on apoptotic and other mechanisms of cell death after cerebral hypoxia-ischemia

Unilateral hypoxia-ischemia (HI) was induced in C57/BL6 male mice on postnatal day (P) 5, 9, 21 and 60, corresponding developmentally to premature, term, juvenile and adult human brains, respectively. HI duration was adjusted to obtain a similar extent of brain injury at all ages. Apoptotic mechanisms (nuclear translocation of apoptosis-inducing factor, cytochrome c release and caspase-3 activation) were several-fold more pronounced in immature than in juvenile and adult brains. Necrosis-related calpain activation was similar at all ages. The CA1 subfield shifted from apoptosis-related neuronal death at P5 and P9 to necrosis-related calpain activation at P21 and P60. Oxidative stress (nitrotyrosine formation) was also similar at all ages. Autophagy, as judged by the autophagosome-related marker LC-3 II, was more pronounced in adult brains. To our knowledge, this is the first report demonstrating developmental regulation of AIF-mediated cell death as well as involvement of autophagy in a model of brain injury.

Calpain-dependent α-fodrin cleavage at the sarcolemma in muscle diseases

To clarify the involvement of calpains in sarcolemmal remodeling, we examined the expression of calpains and their substrate, alpha-fodrin, in various disorders of muscle. Although immunohistological reactions for alpha-fodrin and calpains were weak in normal control muscles, intense immunoreactivity for alpha-fodrin at the sarcolemma and for calpains throughout the cytoplasm were detected in small muscle fibers from patients with inflammatory myositis (IM), rhabdomyolysis (Rhab), and Duchenne muscular dystrophy (DMD). Most of the calpain-alpha-fodrin double-positive muscle fibers in IM and Rhab also expressed the developmental form of myosin heavy chain. The sarcolemma of these small muscle fibers reacted with an antibody that specifically recognizes the 150-kDa fragments of alpha-fodrin (SBDP 150s) cleaved by calpain, but not caspase 3. Western blot analysis confirmed these results. These observations indicate that calpain is activated and reacts with alpha-fodrin as a substrate at the sarcolemma, and plays a key role in modulating sarcolemmal proteins to adapt to the specific conditions in each myopathy.

Molecular analysis of the human autoantibody response to alpha-fodrin in Sjögren's syndrome reveals novel apoptosis-induced specificity

Lymphocyte infiltration of salivary and lacrimal glands leading to diminished secretion and gland destruction as a result of apoptosis is thought to be pivotal in the pathogenesis of Sjögren's syndrome (SS). The cytoskeletal protein alpha-fodrin is cleaved during this apoptotic process, and a strong antibody (Ab) response is elicited to a 120-kd fragment of cleaved alpha-fodrin in the majority of SS patients, but generally not in other diseases in which apoptosis also occurs. Little is known about the anti-alpha-fodrin autoantibody response on a molecular level. To address this issue, IgG phage display libraries were generated from the bone marrow of two SS donors and a panel of anti-alpha-fodrin IgGs was isolated by selection on alpha-fodrin immunoblots. All of the human monoclonal Abs (hmAbs) reacted with a 150-kd fragment and not with the 120-kd fragment or intact alpha-fodrin, indicating that the epitope recognized became exposed after alpha-fodrin cleavage. Analysis of a large panel of SS patients (defined by the strict San Diego diagnostic criteria) showed that 25% of SS sera exhibited this 150-kd alpha-fodrin specificity. The hmAbs stained human cultured salivary acinar cells and the staining was redistributed to surface blebs during apoptosis. They also stained inflamed acinar/ductal epithelial cells in SS salivary tissue biopsies, and only partially co-localized with monoclonal Abs recognizing the full-length alpha-fodrin. Our study shows that in SS patients, neoepitopes on the 150-kd cleaved product of alpha-fodrin become exposed to the immune system, frequently eliciting anti-150-kd alpha-fodrin Abs in addition to the previously reported anti-120-kd Abs. The anti-150-kd alpha-fodrin hmAbs may serve as valuable reagents for the study of SS pathogenesis and diagnostic analyses of SS salivary gland tissue.

Proteins released from degenerating neurons are surrogate markers for acute brain damage

The experimental and clinical study of degenerative brain disorders would benefit from new surrogate markers for brain damage. To identify novel candidate markers for acute brain injury, we report that rat cortical neurons release over 60 cytoskeletal and other proteins, as well as their proteolytic fragments into the medium during neuronal death. The profiles of released proteins differ for necrosis and apoptosis, although a subset of proteins is released generally during neurodegeneration. The value of this approach was established by immunodetection of the released proteins 14-3-3 zeta and 14-3-3 beta, as well as calpain and caspase derivatives of tau and alpha-spectrin in cerebrospinal fluid (CSF) following traumatic brain injury (TBI) or transient forebrain ischemia in the rat. These results indicate that proteins and their proteolytic fragments released from degenerating neurons are cerebrospinal fluid markers for acute brain damage and suggest that efflux of proteins from the injured brain may reflect underlying mechanisms for neurodegeneration.

Altered NMDA receptor expression in renal toxicity: Protection with a receptor antagonist

BACKGROUND

The N-methyl-d-aspartate (NMDA) receptor is expressed in the kidney. The receptor plays a major role in gentamicin ototoxicity. We assessed the role of the renal NMDA receptor subunits NR1 and NR2C in a model of gentamicin nephrotoxicity.

METHODS

Rats were exposed to either saline (control), high-dose, short-term gentamicin, or short-term gentamicin plus the NMDA antagonist MK-801 (short-term gentamicin + MK-801) for 3 days.

RESULTS

Real-time reverse transcription-polymerase chain reaction (RT-PCR) revealed that NR1 mRNA expression was significantly higher (P= 0.03) in the renal cortex of short-term gentamicin rats. NR2C subunit mRNA expression was unaltered in short-term gentamicin rats. Western blot analysis revealed that NR1 (P= 0.009) and NR2C (P= 0.003) protein abundance was significantly higher in the renal cortex short-term gentamicin rats. We assessed two potential intracellular pathways that may mediate short-term gentamicin/NMDA. Calpain I and II expression was similar in short-term gentamicin and control rats. Endothelin type B receptor (ETBR) expression was significantly increased in the renal cortex of short-term gentamicin rats (P= 0.0003), and urinary nitrite concentration (reflecting nitric oxide) was significantly increased in short-term gentamicin rats (P= 0.03). Serum creatinine was significantly elevated in short-term gentamicin animals (P= 0.03), and this increase was attenuated in short-term gentamicin + MK-801 rats. Blood pressure was higher in short-term gentamicin rats; this was attenuated in short-term gentamicin + MK-801 rats. Urine pH was significantly lower in short-term gentamicin (P < 0.0001) rats; this was reversed in short-term gentamicin + MK-801 (P= 0.005) rats. Urinary nitrite was significantly higher in short-term gentamicin rats; this was normalized in short-term gentamicin + MK-801 rats. MK-801 alone had no effect on clinical parameters.

CONCLUSION

NMDA receptor subunit expression is increased in short-term gentamicin animals, and the receptor likely mediates cell damage via the endothelin-ETBR-nitric oxide pathway. NMDA antagonism ameliorated renal damage after exposure to short-term gentamicin.

c-Src binds alpha II spectrin's Src homology 3 (SH3) domain and blocks calpain susceptibility by phosphorylating Tyr1176

Spectrin is a ubiquitous heterodimeric scaffolding protein that stabilizes membranes and organizes protein and lipid microdomains on both the plasma membrane and intracellular organelles. Phosphorylation of beta-spectrin on Ser/Thr is well recognized. Less clear is whether alpha-spectrin is phosphorylated in vivo and whether spectrin is phosphorylated on tyrosine (pTyr). We affirmatively answer both questions. In cultured Madin-Darby canine kidney cells, alphaII spectrin undergoes in vivo tyrosine phosphorylation. Enhancement of the steady state level of pTyr-modified alphaII spectrin by vanadate, a phosphatase inhibitor, implies a dynamic balance between alphaII spectrin phosphorylation and dephosphorylation. Recombinant peptides containing the Src homology 3 domain of alphaII spectrin (but not the Src homology 3 domain of alphaI spectrin) bind specifically to phosphorylated c-Src in Madin-Darby canine kidney cell lysates, suggesting that this kinase is responsible for its in vivo phosphorylation. pTyr-modified alphaII spectrin is resistant to maitotoxin-induced cleavage by mu-calpain in vivo. In vitro studies of recombinant alphaII spectrin peptides representing repeats 9-12 identify two sites of pTyr modification. The first site is at Tyr(1073), a residue immediately adjacent to a region encoded by alternative exon usage (insert 1). The second site is at Tyr(1176). This residue flanks the major site of cleavage by the calcium-dependent protease calpain, and phosphorylation of Tyr(1176) by c-Src reduces the susceptibility of alphaII spectrin to cleavage by mu-calpain. Calpain cleavage of spectrin, activated by Ca(2+) and calmodulin, contributes to diverse cellular processes including synaptic remodeling, receptor-mediated endocytosis, apoptosis, and the response of the renal epithelial cell to ischemic injury. Tyrosine phosphorylation of alphaII spectrin now would appear to also mediate these events. The spectrin skeleton thus forms a point of convergence between kinase/phosphatase and Ca(2+)-mediated signaling cascades.