The role of calpains in traumatic brain injury

An overview of preclinical models of traumatic brain injury (TBI): relevance to pathophysiological mechanisms

Background

Traumatic brain injury (TBI) is a major cause of morbidity and mortality, affecting millions annually worldwide. Although the majority of TBI patients return to premorbid baseline, a subset of patient can develop persistent and often debilitating neurocognitive and behavioral changes. The etiology of TBI within the clinical setting is inherently heterogenous, ranging from sport related injuries, fall related injuries and motor vehicle accidents in the civilian setting, to blast injuries in the military setting.

Objective

Animal models of TBI, offer the distinct advantage of controlling for injury modality, duration and severity. Furthermore, preclinical models of TBI have provided the necessary temporal opportunity to study the chronic neuropathological sequelae of TBI, including neurodegenerative sequelae such as tauopathy and neuroinflammation within the finite experimental timeline. Despite the high prevalence of TBI, there are currently no disease modifying regimen for TBI, and the current clinical treatments remain largely symptom based. The preclinical models have provided the necessary biological substrate to examine the disease modifying effect of various pharmacological agents and have imperative translational value.

Methods

The current review will include a comprehensive survey of well-established preclinical models, including classic preclinical models including weight drop, blast injury, fluid percussion injury, controlled cortical impact injury, as well as more novel injury models including closed-head impact model of engineered rotational acceleration (CHIMERA) models and closed-head projectile concussive impact model (PCI). In addition to rodent preclinical models, the review will include an overview of other species including large animal models and Drosophila.

Results

There are major neuropathological perturbations post TBI captured in various preclinical models, which include neuroinflammation, calcium dysregulation, tauopathy, mitochondrial dysfunction and oxidative stress, axonopathy, as well as glymphatic system disruption.

Conclusion

The preclinical models of TBI continue to offer valuable translational insight, as well as essential neurobiological basis to examine specific disease modifying therapeutic regimen.

Identification and neuroprotective properties of NA-184, a calpain-2 inhibitor

Our laboratory has shown that calpain-2 activation in the brain following acute injury is directly related to neuronal damage and the long-term functional consequences of the injury, while calpain-1 activation is generally neuroprotective and calpain-1 deletion exacerbates neuronal injury. We have also shown that a relatively selective calpain-2 inhibitor, referred to as C2I, enhanced long-term potentiation and learning and memory, and provided neuroprotection in the controlled cortical impact (CCI) model of traumatic brain injury (TBI) in mice. Using molecular dynamic simulation and Site Identification by Ligand Competitive Saturation (SILCS) software, we generated about 130 analogs of C2I and tested them in a number of in vitro and in vivo assays. These led to the identification of two interesting compounds, NA-112 and NA-184. Further analyses indicated that NA-184, (S)-2-(3-benzylureido)-N-((R,S)-1-((3-chloro-2-methoxybenzyl)amino)-1,2-dioxopentan-3-yl)-4-methylpentanamide, selectively and dose-dependent inhibited calpain-2 activity without evident inhibition of calpain-1 at the tested concentrations in mouse brain tissues and human cell lines. Like NA-112, NA-184 inhibited TBI-induced calpain-2 activation and cell death in mice and rats, both male and females. Pharmacokinetic and pharmacodynamic analyses indicated that NA-184 exhibited properties, including stability in plasma and liver and blood-brain barrier permeability, that make it a good clinical candidate for the treatment of TBI.

Calpain-2 Inhibitors as Therapy for Traumatic Brain Injury

While calpains have long been implicated in neurodegeneration, no calpain inhibitor has been developed for the treatment of neurodegeneration. This is partly due to the lack of understanding of the specific functions of most of the 15 members of the calpain family. Work from our laboratory over the last 5-10 years has revealed that calpain-1 and calpain-2, two of the major calpain isoforms in the brain, play opposite roles in both synaptic plasticity/learning and memory and neuroprotection/neurodegeneration. Thus, calpain-1 activation is required for triggering certain forms of synaptic plasticity and for learning some types of information and is neuroprotective. In contrast, calpain-2 activation limits the extent of synaptic plasticity and of learning and is neurodegenerative. These results have been validated with the use of calpain-1 knock-out mice and mice with a selective calpain-2 deletion in excitatory neurons of the forebrain. Through a medicinal chemistry campaign, we have identified a number of selective calpain-2 inhibitors and shown that these inhibitors do facilitate learning of certain tasks and are neuroprotective in a number of animal models of acute neurodegeneration. One of these inhibitors, NA-184, is currently being developed for the treatment of traumatic brain injury, and clinical trials are being planned.

Neurobiochemical, Peptidomic, and Bioinformatic Approaches to Characterize Tauopathy Peptidome Biomarker Candidates in Experimental Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a multidimensional damage, and currently, no FDA-approved medicine is available. Multiple pathways in the cell are triggered through a head injury (e.g., calpain and caspase activation), which truncate tau and generate variable fragment sizes (MW 400-45,000 K). In this study, we used an open-head TBI mouse model generated by controlled cortical impact (CCI) and collected ipsilateral (IC) and contralateral (CC) mice htau brain cortices at one (D1) three (D3), and seven (D7) days post-injury. We implemented immunological (antibody-based detection) and peptidomic approaches (nano-reversed-phase liquid chromatography/tandem mass spectrometry) to investigate proteolytic tau peptidome (low molecular weight (LMW) < 10 K)) and pathological phosphorylation sites (high-molecular-weight (HMW); > 10 K) derived from CCI-TBI animal models. Our immunoblotting analysis verified tau hyperphosphorylation, HMW, and HMW breakdown products (HMW-BDP) formation of tau (e.g., pSer₂₀₂, pThr₁₈₁, pThr₂₃₁, pSer₃₉₆, and pSer₄₀₄), following CCI-TBI. Peptidomic data revealed unique sequences of injury-dependent proteolytic peptides generated from human tau protein. Among the N-terminal tau peptides, EIPEGTTAEEAGIGDTPSLEDEAAGHVTQA (a.a. 96-125) and AQPHTEIPEGTTAEEAGIGDTPSLEDEAAGHVTQARM (a.a. 91-127). Examples of tau C-terminal peptides identified include NVSSTGSIDMVDSPQLATLADEVSASLAKQGL (a.a. 410-441) and QLATLADEVSASLAKQGL (a.a. 424-441). Our peptidomic bioinformatic tools showed the association of proteases, such as CAPN1, CAPN2, and CTSL; CASP1, MMP7, and MMP9; and ELANE, GZMA, and MEP1A, in CCI-TBI tau peptidome. In clinical trials for novel TBI treatments, it might be useful to monitor a subset of tau peptidome as targets for biomarker utility and use them for a "theranostic" approach.

Calpain activity is negatively regulated by a KCTD7-Cullin-3 complex via non-degradative ubiquitination

Calpains are a class of non-lysosomal cysteine proteases that exert their regulatory functions via limited proteolysis of their substrates. Similar to the lysosomal and proteasomal systems, calpain dysregulation is implicated in the pathogenesis of neurodegenerative disease and cancer. Despite intensive efforts placed on the identification of mechanisms that regulate calpains, however, calpain protein modifications that regulate calpain activity are incompletely understood. Here we show that calpains are regulated by KCTD7, a cytosolic protein of previously uncharacterized function whose pathogenic mutations result in epilepsy, progressive ataxia, and severe neurocognitive deterioration. We show that KCTD7 works in complex with Cullin-3 and Rbx1 to execute atypical, non-degradative ubiquitination of calpains at specific sites (K398 of calpain 1, and K280 and K674 of calpain 2). Experiments based on single-lysine mutants of ubiquitin determined that KCTD7 mediates ubiquitination of calpain 1 via K6-, K27-, K29-, and K63-linked chains, whereas it uses K6-mediated ubiquitination to modify calpain 2. Loss of KCTD7-mediated ubiquitination of calpains led to calpain hyperactivation, aberrant cleavage of downstream targets, and caspase-3 activation. CRISPR/Cas9-mediated knockout of Kctd7 in mice phenotypically recapitulated human KCTD7 deficiency and resulted in calpain hyperactivation, behavioral impairments, and neurodegeneration. These phenotypes were largely prevented by pharmacological inhibition of calpains, thus demonstrating a major role of calpain dysregulation in KCTD7-associated disease. Finally, we determined that Cullin-3-KCTD7 mediates ubiquitination of all ubiquitous calpains. These results unveil a novel mechanism and potential target to restrain calpain activity in human disease and shed light on the molecular pathogenesis of KCTD7-associated disease.

Ivleva, Irina M. Kotova, Dmitriy S. Traktirov, Marina N. Karpenko. Region-specific changes in expression and activity of calpains in the CNS of native rats

Introduction and Aim: It has been proposed that µ-calpain is responsible for neuronal survival, while m-calpain – for the degeneration. It can be assumed that the "susceptibility" to the damage factor for neurons in different CNS regions depends on the content/activity of calpain isoforms. We analyzed the mRNA levels and the activity of µ-and m-calpain in the different CNS structures of rats.   Materials and Methods: After decapitation intact male Wistar rats the prefrontal cortex, striatum, hippocampus, midbrain, brainstem, cerebellum, and spinal cord were removed. Each structure was divided into two parts: casein zymography was performed to determine the activity and real-time RT–PCR - to determine the level of expression mRNA of µ-and m-calpains.   Results: We have shown that m-calpain mRNA predominates in the striatum, midbrain and brainstem, while µ-calpain mRNA enrichment was noticed for the hippocampus and cerebellum. The highest µ-calpain activity was in the cervical spinal cord, the lowest - in the striatum. The m-calpain activity was relatively high in the midbrain, striatum, hippocampus and brainstem, while in the cervical spinal cord and cerebellum it was moderate.   Conclusion: The selective neuronal death observed during neurodegeneration can be partially determined by the initial level of calpains expression and/or activity.  

[Morphological markers of pathophysiological changes in the neuronal processes in the acute post-traumatic period of diffuse axonal injury]

The purpose of the study was to establish morphological markers of pathophysiological changes in the neuronal processes of in the acute (up to 36 hours) post-traumatic period of diffuse axonal injury (DAI) for the purposes of expert practice. Histological examination of the body of corpus callosum of the corpses of 66 persons dead from DAI and of 25 persons dead from various non-violent and violent causes, excluding head trauma, was performed (control group). Morphological markers of specific pathophysiological changes in the neuronal process were established by light microscopy with the use of immunohistochemical examination in acute period DAI. Uneven contours of the processes suggested displacement of cytoskeletal elements, areas of vacuolization of the cytoplasm of the processes suggested violation of intracellular transport caused by a change of permeability with preserved integrity of the process shell without mechanical separation of the process, uneven thickness (3.9 ± 1.6 μm) of the processes, varicose and cone-shaped thickening of them was a manifestation of focal edema of the neuronal process and compression of the cytoskeleton as a result of ion-enzymatic disorders, uneven coloration, areas of fragmentary compaction of neurofilaments indicated the zones of deformation and compression of the cytoskeleton, zones of granular-lumpy decay and fibrillolysis of neurofilaments indicated destruction of the cytoskeleton. Changes in the neuronal processes are a manifestation of a polyethological general pathological process and are not a differential diagnostic criterion of DAI.

[Neuroprotective properties of latanoprost]

Glaucoma is the main cause of irreversible blindness in the world. Latanoprost - an ester prodrug of prostaglandin F_2α (PGF_2α) - was the first prostaglandin analogue used to treat glaucoma. The review shows that latanoprost possesses direct neuroprotective properties such as blocking the entry of calcium ions into neurons and inhibiting the action of caspase-3, inhibiting the activity of cyclooxygenase and activation of polypeptide 2B1 (OATP2B1) and Klotho protein. It is emphasized that when the drug is instilled into the eye, the concentration of the drug inside the vitreous body is twice as high as what is required to ensure the survival of retinal ganglion cells.

P13BP, a Calpain-2-Mediated Breakdown Product of PTPN13, Is a Novel Blood Biomarker for Traumatic Brain Injury

Biomarkers play an increasing role in medicinal biology. They are used for diagnosis, management, drug target identification, drug responses, and disease prognosis. We have discovered that calpain-1 and calpain-2 play opposite functions in neurodegeneration, with calpain-1 activation being neuroprotective, while prolonged calpain-2 activation is neurodegenerative. This notion has been validated in several mouse models of acute neuronal injury, in particular in mouse models of traumatic brain injury (TBI) and repeated concussions. We have identified a selective substrate of calpain-2, the tyrosine phosphatase, PTPN13, which is cleaved in brain after TBI. One of the fragments generated by calpain-2, referred to as P13BP, is also found in the blood after TBI both in mice and humans. In humans, P13BP blood levels are significantly correlated with the severity of TBI, as measured by Glasgow Coma Scale scores and loss of consciousness. The results indicate that P13BP represents a novel blood biomarker for TBI.

Calpain-1 and Calpain-2 in the Brain: New Evidence for a Critical Role of Calpain-2 in Neuronal Death

Calpains are a family of soluble calcium-dependent proteases that are involved in multiple regulatory pathways. Our laboratory has focused on the understanding of the functions of two ubiquitous calpain isoforms, calpain-1 and calpain-2, in the brain. Results obtained over the last 30 years led to the remarkable conclusion that these two calpain isoforms exhibit opposite functions in the brain. Calpain-1 activation is required for certain forms of synaptic plasticity and corresponding types of learning and memory, while calpain-2 activation limits the extent of plasticity and learning. Calpain-1 is neuroprotective both during postnatal development and in adulthood, while calpain-2 is neurodegenerative. Several key protein targets participating in these opposite functions have been identified and linked to known pathways involved in synaptic plasticity and neuroprotection/neurodegeneration. We have proposed the hypothesis that the existence of different PDZ (PSD-95, DLG and ZO-1) binding domains in the C-terminal of calpain-1 and calpain-2 is responsible for their association with different signaling pathways and thereby their different functions. Results with calpain-2 knock-out mice or with mice treated with a selective calpain-2 inhibitor indicate that calpain-2 is a potential therapeutic target in various forms of neurodegeneration, including traumatic brain injury and repeated concussions.

An update on the therapeutic potential of calpain inhibitors: a patent review

INTRODUCTION

Calpain is a cytosolic proteinase that regulates of a wide range of physiological functions. The enzyme has been implicated in various pathological conditions including neurodegenerative disorders, cardiovascular disorders, cancer, and several other diseases. Therefore, calpain inhibitors are of interest as therapeutic agents and have been studied in preclinical models of several diseases in which the enzyme has been implicated.

AREAS COVERED

Calpain inhibitors that were disclosed over the last 5 years (2015-2019) include calpastatin-based peptidomimetics; thalassospiramide lipopeptides; disulfide analogs of alpha-mercaptoacrylic acids; allosteric modulators; azoloimidazolidenones; and macrocyclic/non-macrocyclic carboxamides. The effectiveness of some of the inhibitors in preclinical animal models is discussed.

EXPERT OPINION

Significant milestones that were made over this time frame include: a) disclosure of novel blood-brain barrier (BBB) permeable calpastatin analogs as calpain inhibitors; b) disclosure that potent calpain inhibitors can be obtained by targeting the hydrophobic pockets on chain A of PEF(S) of the small subunit of calpain; c) use of PEF(S) (PDB ID: 4WQ2) in virtual screening to identify novel structurally diverse calpain inhibitors; and d) mitigation of the metabolic instability of the alpha-ketoamide warhead of calpain inhibitors.

Calpain-2 as a therapeutic target in repeated concussion-induced neuropathy and behavioral impairment

Repeated concussion represents a serious health problem as it can result in various brain pathologies, ranging from minor focal tissue injury to severe chronic traumatic encephalopathy. The calcium-dependent protease, calpain, participates in the development of neurodegeneration following concussion, but there is no information regarding the relative contribution of calpain-1 and calpain-2, the major calpain isoforms in the brain. We used a mouse model of repeated concussions, which reproduces most of the behavioral and neuropathological features of the human condition, to address this issue. Deletion of calpain-2 or treatment with a selective calpain-2 inhibitor for 2 weeks prevented most of these neuropathological features. Changes in TAR DNA binding protein 43 (TDP-43) subcellular localization similar to those found in human amyotrophic lateral sclerosis and frontotemporal dementia were also prevented by deletion of calpain-2 or treatment with calpain-2 inhibitor. Our results indicate that a selective calpain-2 inhibitor represents a therapeutic approach for concussion.

Novel Peptidomic Approach for Identification of Low and High Molecular Weight Tauopathy Peptides Following Calpain Digestion, and Primary Culture Neurotoxic Challenges

Tauopathy is a class of a neurodegenerative disorder linked with tau hyperphosphorylation, proteolysis, and aggregation. Tau can be subjected to proteolysis upon calpain activation in Alzheimer disease (AD), and traumatic brain injury (TBI). We and others have extensively researched calpain-mediated tau breakdown products (Tau-BDP; 45K, 35K, and 17K). Tau proteolysis might also generate low molecular weight (LMW ≤10K) proteolytic peptides after neurodegenerative damage. In this study, we have subjected purified tau protein (phospho and non-phospho) and mouse brain lysate to calpain-1 digestion to characterize the LMW generated by nano-liquid chromatography coupled to electrospray ionization to tandem mass spectrometry (nano-LC-ESI-MS/MS). We have also challenged differentiated primary cerebrocortical neuronal cultures (CTX) with neurotoxic agents (calcium ionophore calcimycin (A23187), staurosporine (STS), N-methyl-D-aspartate (NMDA), and Maitotoxin (MTX)) that mimic neurodegeneration to investigate the peptidome released into the conditioned cell media. We used a simple workflow in which we fractionate LMW calpain-mediated tau peptides by ultrafiltration (molecular weight cut-off value (MWCO) of 10K) and subject filtrate fractions to nano-LC-MS/MS analysis. The high molecular weight (HMW) peptides and intact proteins retained on the filter were analyzed separately by western blotting using total and phospho-specific tau antibodies. We have identified several novel proteolytic tau peptides (phosphorylated and non-phosphorylated) that are only present in samples treated with calpain or cell-based calpain activation model (particularly N- and C-terminal peptides). Our findings can help in developing future research strategies emphasizing on the suppression of tau proteolysis as a target.

The fate and function of oligodendrocyte progenitor cells after traumatic spinal cord injury

Oligodendrocyte progenitor cells (OPCs) are the most proliferative and dispersed population of progenitor cells in the adult central nervous system, which allows these cells to rapidly respond to damage. Oligodendrocytes and myelin are lost after traumatic spinal cord injury (SCI), compromising efficient conduction and, potentially, the long-term health of axons. In response, OPCs proliferate and then differentiate into new oligodendrocytes and Schwann cells to remyelinate axons. This culminates in highly efficient remyelination following experimental SCI in which nearly all intact demyelinated axons are remyelinated in rodent models. However, myelin regeneration comprises only one role of OPCs following SCI. OPCs contribute to scar formation after SCI and restrict the regeneration of injured axons. Moreover, OPCs alter their gene expression following demyelination, express cytokines and perpetuate the immune response. Here, we review the functional contribution of myelin regeneration and other recently uncovered roles of OPCs and their progeny to repair following SCI.

Inhibition of Cathepsins B Induces Neuroprotection Against Secondary Degeneration in Ipsilateral Substantia Nigra After Focal Cortical Infarction in Adult Male Rats

Stroke is the leading cause of adult disability in the world. In general, recovery from stroke is incomplete. Accumulating evidences have shown that focal cerebral infarction leads to dynamic trans-neuronal degeneration in non-ischemic remote brain regions, with the disruption of connections to synapsed neurons sustaining ischemic insults. Previously, we had reported that the ipsilateral striatum, thalamus degenerated in succession after permanent distal branch of middle cerebral artery occlusion (dMCAO) in Sprague-Dawley (SD) rats and cathepsin (Cath) B was activated before these relay degeneration. Here, we investigate the role of CathB in the secondary degeneration of ipsilateral substantia nigra (SN) after focal cortical infarction. We further examined whether the inhibition of CathB with L-3-trans-(Propyl-carbamoyloxirane-2-carbonyl)-L-isoleucyl-L-proline methyl ester (CA-074Me) would attenuate secondary degeneration through enhancing the cortico-striatum-nigral connections and contribute to the neuroprotective effects. Our results demonstrated that secondary degeneration in the ipsilateral SN occurred and CathB was upregulated in the ipsilateral SN after focal cortical infarction. The inhibition of CathB with CA-074Me reduced the neuronal loss and gliosis in the ipsilateral SN. Using biotinylated dextran amine (BDA) or pseudorabies virus (PRV) 152 as anterograde or retrograde tracer to trace striatum-nigral and cortico-nigral projections pathway, CA-074Me can effectively enhance the cortico-striatum-nigral connections and exert neuroprotection against secondary degeneration in the ipsilateral SN after cortical ischemia. Our study suggests that the lysosomal protease CathB mediates the secondary damage in the ipsilateral SN after dMCAO, thus it can be a promising neuroprotective target for the rehabilitation of stroke patients.

Calpain-2 as a therapeutic target for acute neuronal injury

INTRODUCTION

Calpains represent a family of neutral, calcium-dependent proteases, which modify the function of their target proteins by partial truncation. These proteases have been implicated in numerous cell functions, including cell division, proliferation, migration, and death. In the CNS, where calpain-1 and calpain-2 are the main calpain isoforms, their activation has been linked to synaptic plasticity as well as to neurodegeneration. This review will focus on the role of calpain-2 in acute neuronal injury and discuss the possibility of developing selective calpain-2 inhibitors for therapeutic purposes. Areas covered: This review covers the literature showing how calpain-2 is implicated in neuronal death in a number of pathological conditions. The possibility of developing new selective calpain-2 inhibitors for treating these conditions is discussed. Expert opinion: As evidence accumulates that calpain-2 activation participates in acute neuronal injury, there is interest in developing therapeutic approaches using selective calpain-2 inhibitors. Recent data indicate the potential use of such inhibitors in various pathologies associated with acute neuronal death. The possibility of extending the use of such inhibitors to more chronic forms of neurodegeneration is discussed.

Protection against TBI-Induced Neuronal Death with Post-Treatment with a Selective Calpain-2 Inhibitor in Mice

Traumatic Brain Injury (TBI) is a major cause of death and disability worldwide. The calcium-dependent protease, calpain, has been shown to be involved in TBI-induced neuronal death. However, whereas various calpain inhibitors have been tested in several animal models of TBI, there has not been any clinical trial testing the efficacy of calpain inhibitors in human TBI. One important reason for this could be the lack of knowledge regarding the differential functions of the two major calpain isoforms in the brain, calpain-1 and calpain-2. In this study, we used the controlled cortical impact (CCI) model in mice to test the roles of calpain-1 and calpain-2 in TBI-induced neuronal death. Immunohistochemistry (IHC) with calpain activity markers performed at different time-points after CCI in wild-type and calpain-1 knock-out (KO) mice showed that calpain-1 was activated early in cortical areas surrounding the impact, within 0-8 h after CCI, whereas calpain-2 activation was delayed and was predominant during 8-72 h after CCI. Calpain-1 KO enhanced cell death, whereas calpain-2 activity correlated with the extent of cell death, suggesting that calpain-1 activation suppresses and calpain-2 activation promotes cell death following TBI. Systemic injection(s) of a calpain-2 selective inhibitor, NA101, at 1 h or 4 h after CCI significantly reduced calpain-2 activity and cell death around the impact site, reduced the lesion volume, and promoted motor and learning function recovery after TBI. Our data indicate that calpain-1 activity is neuroprotective and calpain-2 activity is neurodegenerative after TBI, and that a selective calpain-2 inhibitor can reduce TBI-induced cell death.

Calpain-5 gene expression in the mouse eye and brain

Objective

Our objective was to characterize CAPN5 gene expression in the mouse central nervous system. Mouse brain and eye sections were probed with two high-affinity RNA oligonucleotide analogs designed to bind CAPN5 RNA and one scramble, control oligonucleotide. Images were captured in brightfield.

Results

CAPN5 RNA probes were validated on mouse breast cancer tumor tissue. In the eye, CAPN5 was expressed in the ganglion cell, inner nuclear and outer nuclear layers of the retina. Signal could not be detected in the ciliary body or the iris because of the high density of melanin. In the brain, CAPN5 was expressed in the granule cell layers of the hippocampus and cerebellum. There was scattered expression in pons. The visual cortex showed faint signal. Most signal in the brain was in a punctate pattern.

Protective Functions of PJ34, a Poly(ADP-ribose) Polymerase Inhibitor, Are Related to Down-Regulation of Calpain and Nuclear Factor-κB in a Mouse Model of Traumatic Brain Injury

OBJECTIVES

Poly(ADP-ribose) polymerase (PARP), calpain, and nuclear factor-κB (NF-κB) are reported to participate in inflammatory reactions in pathologic conditions and are involved in traumatic brain injury. The objective of this study was to investigate whether PARP participates in inflammation related to calpain and NF-κB in a mouse model of controlled cortical impact (CCI).

METHODS

PJ34 (10 mg/kg), a selective PARP inhibitor, was administered intraperitoneally 5 minutes and 8 hours after experimental CCI. We then performed a histopathologic analysis, and we measured calpain activity and protein levels in all animals. The cytosolic, mitochondria, and nuclear fractions were prepared and used to determine the levels of PARP, calpastatin, NF-κB p65, inhibitory-κB-α, tumor necrosis factor-α, interleukin-1β, intracellular adhesion molecule-1, inducible nitric oxide synthase, and cyclooxygenase-2. We then measured blood-brain barrier disruption using electron microscopy at 6 and 24 hours after CCI.

RESULTS

Treatment with PJ34 markedly reduced the extent of both cerebral contusion and edema, improved neurologic scores, and attenuated blood-brain barrier damage resulting from CCI. Our 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 inhibitory-κB levels and decreased the levels of inflammatory mediators.

CONCLUSIONS

PARP inhibition by PJ34 suppresses the overactivation of calpain and the production of inflammatory factors that are caused by NF-κB activation and attenuates neuronal cell death in a mouse model of CCI.

Calpain-5 Expression in the Retina Localizes to Photoreceptor Synapses

Purpose

We characterize calpain-5 (CAPN5) expression in retinal and neuronal subcellular compartments.

Methods

CAPN5 gene variants were classified using the exome variant server, and RNA-sequencing was used to compare expression of CAPN5 mRNA in the mouse and human retina and in retinoblastoma cells. Expression of CAPN5 protein was ascertained in humans and mice in silico, in mouse retina by immunohistochemistry, and in neuronal cancer cell lines and fractionated central nervous system tissue extracts by Western analysis with eight antibodies targeting different CAPN5 regions.

Results

Most CAPN5 genetic variation occurs outside its protease core; and searches of cancer and epilepsy/autism genetic databases found no variants similar to hyperactivating retinal disease alleles. The mouse retina expressed one transcript for CAPN5 plus those of nine other calpains, similar to the human retina. In Y79 retinoblastoma cells, the level of CAPN5 transcript was very low. Immunohistochemistry detected CAPN5 expression in the inner and outer nuclear layers and at synapses in the outer plexiform layer. Western analysis of fractionated retinal extracts confirmed CAPN5 synapse localization. Western blots of fractionated brain neuronal extracts revealed distinct subcellular patterns and the potential presence of autoproteolytic CAPN5 domains.

Conclusions

CAPN5 is moderately expressed in the retina and, despite higher expression in other tissues, hyperactive disease mutants of CAPN5 only manifest as eye disease. At the cellular level, CAPN5 is expressed in several different functional compartments. CAPN5 localization at the photoreceptor synapse and with mitochondria explains the neural circuitry phenotype in human CAPN5 disease alleles.

The neuroprotective effect of latanoprost acts via klotho-mediated suppression of calpain activation after optic nerve transection

Latanoprost was first developed for use in glaucoma therapy as an ocular hypotensive agent targeting the prostaglandin F2α (FP) receptor. Subsequently, latanoprost showed a neuroprotective effect, an additional pharmacological action. However, although it is well-known that latanoprost exerts an ocular hypotensive effect via the FP receptor, it is not known whether this is also true of its neuroprotective effect. Klotho was firstly identified as the gene linked to the suppression of aging phenotype: the defect of klotho gene in mice results aging phenotype such as hypokinesis, arteriosclerosis, and short lifespan. After that, the function of klotho was also reported to maintain calcium homeostasis and to exert a neuroprotective effect in various models of neurodegenerative disease. However, the function of klotho in eyes including retina is still poorly understood. Here, we show that klotho is a key factor underlying the neuroprotective effect of latanoprost during post-axotomy retinal ganglion cell (RGC) degeneration. Importantly, a quantitative RT-PCR gene expression analysis of klotho in sorted rat retinal cells revealed that the highest expression level of klotho in the retina was in the RGCs. Latanoprost acid, the biologically active form of latanoprost, inhibits post-traumatic calpain activation and concomitantly facilitates the expression and shedding of klotho in axotomized RGCs. This expression profile is a good match with the localization, not of the FP receptor, but of organic anion transporting polypeptide 2B1, known as a prostaglandin transporter, in the ocular tissue. Furthermore, an organic anion transporting polypeptide 2B1 inhibitor suppressed latanoprost acid-mediated klotho shedding ex vivo, whereas an FP receptor antagonist did not. The klotho fragments shed from the RGCs reduced the intracellular level of reactive oxygen species, and a specific klotho inhibitor accelerated and increased RGC death after axotomy. We conclude that the shed klotho fragments might contribute to the attenuation of axonal injury-induced calpain activation and oxidative stress, thereby protecting RGCs from post-traumatic neuronal degeneration.

Connecting Malfunctioning Glial Cells and Brain Degenerative Disorders

The DNA damage response (DDR) is a complex biological system activated by different types of DNA damage. Mutations in certain components of the DDR machinery can lead to genomic instability disorders that culminate in tissue degeneration, premature aging, and various types of cancers. Intriguingly, malfunctioning DDR plays a role in the etiology of late onset brain degenerative disorders such as Parkinson's, Alzheimer's, and Huntington's diseases. For many years, brain degenerative disorders were thought to result from aberrant neural death. Here we discuss the evidence that supports our novel hypothesis that brain degenerative diseases involve dysfunction of glial cells (astrocytes, microglia, and oligodendrocytes). Impairment in the functionality of glial cells results in pathological neuro-glial interactions that, in turn, generate a "hostile" environment that impairs the functionality of neuronal cells. These events can lead to systematic neural demise on a scale that appears to be proportional to the severity of the neurological deficit.

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

BACKGROUND

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).

MATERIALS AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Cysteine proteases as therapeutic targets: does selectivity matter? A systematic review of calpain and cathepsin inhibitors

Cysteine proteases continue to provide validated targets for treatment of human diseases. In neurodegenerative disorders, multiple cysteine proteases provide targets for enzyme inhibitors, notably caspases, calpains, and cathepsins. The reactive, active-site cysteine provides specificity for many inhibitor designs over other families of proteases, such as aspartate and serine; however, a) inhibitor strategies often use covalent enzyme modification, and b) obtaining selectivity within families of cysteine proteases and their isozymes is problematic. This review provides a general update on strategies for cysteine protease inhibitor design and a focus on cathepsin B and calpain 1 as drug targets for neurodegenerative disorders; the latter focus providing an interesting query for the contemporary assumptions that irreversible, covalent protein modification and low selectivity are anathema to therapeutic safety and efficacy.

Role of Microvascular Disruption in Brain Damage from Traumatic Brain Injury

Traumatic brain injury (TBI) is acquired from an external force, which can inflict devastating effects to the brain vasculature and neighboring neuronal cells. Disruption of vasculature is a primary effect that can lead to a host of secondary injury cascades. The primary effects of TBI are rapidly occurring while secondary effects can be activated at later time points and may be more amenable to targeting. Primary effects of TBI include diffuse axonal shearing, changes in blood-brain barrier (BBB) permeability, and brain contusions. These mechanical events, especially changes to the BBB, can induce calcium perturbations within brain cells producing secondary effects, which include cellular stress, inflammation, and apoptosis. These secondary effects can be potentially targeted to preserve the tissue surviving the initial impact of TBI. In the past, TBI research had focused on neurons without any regard for glial cells and the cerebrovasculature. Now a greater emphasis is being placed on the vasculature and the neurovascular unit following TBI. A paradigm shift in the importance of the vascular response to injury has opened new avenues of drug-treatment strategies for TBI. However, a connection between the vascular response to TBI and the development of chronic disease has yet to be elucidated. Long-term cognitive deficits are common amongst those sustaining severe or multiple mild TBIs. Understanding the mechanisms of cellular responses following TBI is important to prevent the development of neuropsychiatric symptoms. With appropriate intervention following TBI, the vascular network can perhaps be maintained and the cellular repair process possibly improved to aid in the recovery of cellular homeostasis.

Diffuse axonal injury in brain trauma: insights from alterations in neurofilaments

Traumatic brain injury (TBI) from penetrating or closed forces to the cranium can result in a range of forms of neural damage, which culminate in mortality or impart mild to significant neurological disability. In this regard, diffuse axonal injury (DAI) is a major neuronal pathophenotype of TBI and is associated with a complex set of cytoskeletal changes. The neurofilament triplet proteins are key structural cytoskeletal elements, which may also be important contributors to the tensile strength of axons. This has significant implications with respect to how axons may respond to TBI. It is not known, however, whether neurofilament compaction and the cytoskeletal changes that evolve following axonal injury represent a component of a protective mechanism following damage, or whether they serve to augment degeneration and progression to secondary axotomy. Here we review the structure and role of neurofilament proteins in normal neuronal function. We also discuss the processes that characterize DAI and the resultant alterations in neurofilaments, highlighting potential clues to a possible protective or degenerative influence of specific neurofilament alterations within injured neurons. The potential utility of neurofilament assays as biomarkers for axonal injury is also discussed. Insights into the complex alterations in neurofilaments will contribute to future efforts in developing therapeutic strategies to prevent, ameliorate or reverse neuronal degeneration in the central nervous system (CNS) following traumatic injury.