Penetrating Traumatic Brain Injury Triggers Dysregulation of Cathepsin B Protein Levels Independent of Cysteine Protease Activity in Brain and Cerebral Spinal Fluid

The Effects of Cathepsin B Inhibition in the Face of Diffuse Traumatic Brain Injury and Secondary Intracranial Pressure Elevation

Traumatic brain injury (TBI) affects millions of people each year. Previous studies using the central fluid percussion injury (CFPI) model in adult male rats indicated that elevated intracranial pressure (ICP) was associated with long-term effects, including neuronal cell loss and increased sensory sensitivity post-injury and secondary ICP elevation, which were not seen following injury alone. Investigations also indicated that cathepsin B (Cath B), a lysosomal cysteine protease, may play a role in the pathological progression of neuronal membrane disruption; however, the specific impact of Cath B inhibition following CFPI remained unknown. Thus, the focus of this study was to evaluate the effects of Cath B inhibition via the intracerebroventricular infusion of the Cath B inhibitor to the CA-074 methyl ester (CA-074Me) 2w following injury with or without secondary ICP elevation. This was accomplished using adult male rats continuously infused with CA-074Me or 10% DMSO as a vehicle control for 2w following either sham injury, CFPI only, or CFPI with subsequent ICP elevation to 20 mmHg. We assessed Cath B activity and evaluated the protein levels of Cath B and Cath B-binding partners AIF, Bcl-XL, and Bak. We also conducted histological analyses of the total cell counts to assess for cell loss, membrane disruption, and Cath B localization. Finally, we investigated somatosensory changes with the whisker nuisance task. Overall, this study demonstrated that Cath B is not a direct driver of membrane disruption; however, the administration of CA-074Me alters Cath B localization and reduces hypersensitivity, emphasizing Cath B as an important component in late secondary pathologies.

Cathepsin B as a key regulator of ferroptosis in microglia following intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a subtype of stroke marked by elevated mortality and disability rates. Recently, mounting evidence suggests a significant role of ferroptosis in the pathogenesis of ICH. Through a combination of bioinformatics analysis and basic experiments, our goal is to identify the primary cell types and key molecules implicated in ferroptosis post-ICH. This aims to propel the advancement of ferroptosis research, offering potential therapeutic targets for ICH treatment. Our study reveals pronounced ferroptosis in microglia and identifies the target gene, cathepsin B (Ctsb), by analyzing differentially expressed genes following ICH. Ctsb, a cysteine protease primarily located in lysosomes, becomes a focal point in our investigation. Utilizing in vitro and in vivo models, we explore the correlation between Ctsb and ferroptosis in microglia post-ICH. Results demonstrate that ICH and hemin-induced ferroptosis in microglia coincide with elevated levels and activity of Ctsb protein. Effective alleviation of ferroptosis in microglia after ICH is achieved through the inhibition of Ctsb protease activity and protein levels using inhibitors and shRNA. Additionally, a notable increase in m6A methylation levels of Ctsb mRNA post-ICH is observed, suggesting a pivotal role of m6A methylation in regulating Ctsb translation. These research insights deepen our comprehension of the molecular pathways involved in ferroptosis after ICH, underscoring the potential of Ctsb as a promising target for mitigating brain damage resulting from ICH.

An Activity-Based Nanosensor for Minimally-Invasive Measurement of Protease Activity in Traumatic Brain Injury

Current screening and diagnostic tools for traumatic brain injury (TBI) have limitations in sensitivity and prognostication. Aberrant protease activity is a central process that drives disease progression in TBI and is associated with worsened prognosis; thus direct measurements of protease activity could provide more diagnostic information. In this study, a nanosensor is engineered to release a measurable signal into the blood and urine in response to activity from the TBI-associated protease calpain. Readouts from the nanosensor were designed to be compatible with ELISA and lateral flow assays, clinically-relevant assay modalities. In a mouse model of TBI, the nanosensor sensitivity is enhanced when ligands that target hyaluronic acid are added. In evaluation of mice with mild or severe injuries, the nanosensor identifies mild TBI with a higher sensitivity than the biomarker GFAP. This nanosensor technology allows for measurement of TBI-associated proteases without the need to directly access brain tissue, and has the potential to complement existing TBI diagnostic tools.

Firearm-Related Traumatic Brain Injury Homicides in the United States, 2000-2019

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of homicide-related death in the United States. Penetrating TBI associated with firearms is a unique injury with an exceptionally high mortality rate that requires specialized neurocritical trauma care.

OBJECTIVE

To report incidence patterns of firearm-related and nonfirearm-related TBI homicides in the United States between 2000 and 2019 by demographic characteristics to provide foundational data for prevention and treatment strategies.

METHODS

Data were obtained from multiple cause of death records from the National Vital Statistics System using Centers for Disease Control and Prevention's Wide-Ranging Online Data for Epidemiologic Research database for the years 2000 to 2019. Number, age-adjusted rates, and percent of firearm and nonfirearm-related TBI homicides by demographic characteristics were calculated. Temporal trends were also evaluated.

RESULTS

During the study period, there were 77 602 firearm-related TBI homicides. Firearms were involved in the majority (68%) of all TBI homicides. Overall, men, people living in metro areas, and non-Hispanic Black persons had higher rates of firearm-related TBI homicides. The rate of nonfirearm-related TBI homicides declined by 40%, whereas the rate of firearm-related TBI homicides only declined by 3% during the study period. There was a notable increase in the rate of firearm-related TBI homicides from 2012/2013 through 2019 for women (20%) and nonmetro residents (39%).

CONCLUSION

Firearm-related violence is an important public health problem and is associated with the majority of TBI homicide deaths in the United States. The findings from this study may be used to inform prevention and guide further research to improve treatment strategies directed at reducing TBI homicides involving firearms.

Circulating extracellular vesicles from patients with traumatic brain injury induce cerebrovascular endothelial dysfunction

Endothelial dysfunction is a key proponent of pathophysiological process of traumatic brain injury (TBI). We previously demonstrated that extracellular vesicles (EVs) released from injured brains led to endothelial barrier disruption and vascular leakage. However, the molecular mechanisms of this EV-induced endothelial dysfunction (endotheliopathy) remain unclear. Here, we enriched plasma EVs from TBI patients (TEVs), and detected high mobility group box 1 (HMGB1) exposure to 50.33 ± 10.17% of TEVs and the number of HMGB1⁺TEVs correlated with injury severity. We then investigated for the first time the impact of TEVs on endothelial function using adoptive transfer models. We found that TEVs induced dysfunction of cultured human umbilical vein endothelial cells and mediated endothelial dysfunction in both normal and TBI mice, which were propagated through the HMGB1-activated receptor for advanced glycation end products (RAGE)/Cathepsin B signaling, and the resultant NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation and canonical caspase-1/gasdermin D (GSDMD)-dependent pyroptosis. Finally, von Willebrand factor (VWF) was detected on the surface of 77.01 ± 7.51% of HMGB1⁺TEVs. The TEV-mediated endotheliopathy was reversed by a polyclonal VWF antibody, indicating that VWF might serve a coupling factor that tethered TEVs to ECs, thus facilitating HMGB1-induced endotheliopathy. These results suggest that circulating EVs isolated from patients with TBI alone are sufficient to induce endothelial dysfunction and contribute to secondary brain injury that are dependent on immunologically active HMGB1 exposed on their surface. This finding provided new insight for the development of potential therapeutic targets and diagnostic biomarkers for TBI.

Cysteine cathepsins: A long and winding road towards clinics

Biomedical research often focuses on properties that differentiate between diseased and healthy tissue; one of the current focuses is elevated expression and altered localisation of proteases. Among these proteases, dysregulation of cysteine cathepsins can frequently be observed in inflammation-associated diseases, which tips the functional balance from normal physiological to pathological manifestations. Their overexpression and secretion regularly exhibit a strong correlation with the development and progression of such diseases, making them attractive pharmacological targets. But beyond their mostly detrimental role in inflammation-associated diseases, cysteine cathepsins are physiologically highly important enzymes involved in various biological processes crucial for maintaining homeostasis and responding to different stimuli. Consequently, several challenges have emerged during the efforts made to translate basic research data into clinical applications. In this review, we present both physiological and pathological roles of cysteine cathepsins and discuss the clinical potential of cysteine cathepsin-targeting strategies for disease management and diagnosis.

Cathepsin B Gene Knockout Improves Behavioral Deficits and Reduces Pathology in Models of Neurologic Disorders

Cathepsin B (CTSB) is a powerful lysosomal protease. This review evaluated CTSB gene knockout (KO) outcomes for amelioration of brain dysfunctions in neurologic diseases and aging animal models. Deletion of the CTSB gene resulted in significant improvements in behavioral deficits, neuropathology, and/or biomarkers in traumatic brain injury, ischemia, inflammatory pain, opiate tolerance, epilepsy, aging, transgenic Alzheimer's disease (AD), and periodontitis AD models as shown in 12 studies. One study found beneficial effects for double CTSB and cathepsin S KO mice in a multiple sclerosis model. Transgenic AD models using amyloid precursor protein (APP) mimicking common sporadic AD in three studies showed that CTSB KO improved memory, neuropathology, and biomarkers; two studies used APP representing rare familial AD and found no CTSB KO effect, and two studies used highly engineered APP constructs and reported slight increases in a biomarker. In clinical studies, all reports found that CTSB enzyme was upregulated in diverse neurologic disorders, including AD in which elevated CTSB was positively correlated with cognitive dysfunction. In a wide range of neurologic animal models, CTSB was also upregulated and not downregulated. Further, human genetic mutation data provided precedence for CTSB upregulation causing disease. Thus, the consilience of data is that CTSB gene KO results in improved brain dysfunction and reduced pathology through blockade of CTSB enzyme upregulation that causes human neurologic disease phenotypes. The overall findings provide strong support for CTSB as a rational drug target and for CTSB inhibitors as therapeutic candidates for a wide range of neurologic disorders. SIGNIFICANCE STATEMENT: This review provides a comprehensive compilation of the extensive data on the effects of deleting the cathepsin B (CTSB) gene in neurological and aging mouse models of brain disorders. Mice lacking the CTSB gene display improved neurobehavioral deficits, reduced neuropathology, and amelioration of neuronal cell death and inflammatory biomarkers. The significance of the compelling CTSB evidence is that the data consilience validates CTSB as a drug target for discovery of CTSB inhibitors as potential therapeutics for treating numerous neurological diseases.

Molecular Features of CA-074 pH-Dependent Inhibition of Cathepsin B

CA-074 is a selective inhibitor of cathepsin B, a lysosomal cysteine protease. CA-074 has been utilized in numerous studies to demonstrate the role of this protease in cellular and physiological functions. Cathepsin B in numerous human disease mechanisms involves its translocation from acidic lysosomes of pH 4.6 to neutral pH 7.2 of cellular locations, including the cytosol and extracellular environment. To gain in-depth knowledge of CA-074 inhibition under these different pH conditions, this study evaluated the molecular features, potency, and selectivity of CA-074 for cathepsin B inhibition under acidic and neutral pH conditions. This study demonstrated that CA-074 is most effective at inhibiting cathepsin B at an acidic pH of 4.6 with nM potency, which was more than 100-fold more potent than its inhibition at a neutral pH of 7.2. The pH-dependent inhibition of CA-074 was abolished by methylation of its C-terminal proline, indicating the requirement for the free C-terminal carboxyl group for pH-dependent inhibition. Under these acidic and neutral pH conditions, CA-074 maintained its specificity for cathepsin B over other cysteine cathepsins, displayed irreversible inhibition, and inhibited diverse cleavages of peptide substrates of cathepsin B assessed by profiling mass spectrometry. Molecular docking suggested that pH-dependent ionic interactions of the C-terminal carboxylate of CA-074 occur with His110 and His111 residues in the S2' subsite of the enzyme at pH 4.6, but these interactions differ at pH 7.2. While high levels of CA-074 or CA-074Me (converted by cellular esterases to CA-074) are used in biological studies to inhibit cathepsin B at both acidic and neutral pH locations, it is possible that adjusted levels of CA-074 or CA-074Me may be explored to differentially affect cathepsin B activity at these different pH values. Overall, the results of this study demonstrate the molecular, kinetic, and protease specificity features of CA-074 pH-dependent inhibition of cathepsin B.

Cathepsin B Relocalization in Late Membrane Disrupted Neurons Following Diffuse Brain Injury in Rats

Traumatic brain injury (TBI) has consequences that last for years following injury. While TBI can precipitate a variety of diffuse pathologies, the mechanisms involved in injury-induced neuronal membrane disruption remain elusive. The lysosomal cysteine protease, Cathepsin B (Cath B), and specifically its redistribution into the cytosol has been implicated in cell death. Little is known about Cath B or neuronal membrane disruption chronically following diffuse TBI. Therefore, the current study evaluated Cath B and diffuse neuronal membrane disruption over a more chronic post-injury window (6 h-4 w). We evaluated Cath B in adult male Sprague-Dawley rats following central fluid percussion injury (CFPI). Expression of Cath B, as well as Cath B-associated pro (Bak and AIF) and anti-apoptotic (Bcl-xl) proteins, were assessed using western blot analysis. Cath B activity was also assessed. Localization of Cath B was evaluated in the membrane disrupted and non-disrupted population following CFPI using immunohistochemistry paired with quantitative image analysis and ultrastructural verification. There was no difference in expression or activity of Cath B or any of the associated proteins between sham and CFPI at any time post-injury. Immunohistological studies, however, showed a sub-cellular re-localization of Cath B at 2 w and 4 w post-injury in the membrane disrupted neuronal population as compared to the time-point matched non-disrupted neurons. Both membrane disruption and Cath B relocalization appear linked to neuronal atrophy. These observations are indicative of a late secondary pathology that represents an opportunity for therapeutic treatment of these neurons following diffuse TBI. Summary Statement Lysosomal cathepsin B relocalizes to the cytosol in neurons with disrupted plasmalemmal membranes weeks following diffuse brain injury. Both the membrane disrupted and cathepsin B relocalized neuronal subpopulations displayed smaller soma and nucleus size compared to non-pathological neurons, indicating atrophy.

Selective Neutral pH Inhibitor of Cathepsin B Designed Based on Cleavage Preferences at Cytosolic and Lysosomal pH Conditions

Cathepsin B is a cysteine protease that normally functions within acidic lysosomes for protein degradation, but in numerous human diseases, cathepsin B translocates to the cytosol having neutral pH where the enzyme activates inflammation and cell death. Cathepsin B is active at both the neutral pH 7.2 of the cytosol and the acidic pH 4.6 within lysosomes. We evaluated the hypothesis that cathepsin B may possess pH-dependent cleavage preferences that can be utilized for design of a selective neutral pH inhibitor by (1) analysis of differential cathepsin B cleavage profiles at neutral pH compared to acidic pH using multiplex substrate profiling by mass spectrometry (MSP-MS), (2) design of pH-selective peptide-7-amino-4-methylcoumarin (AMC) substrates, and (3) design and validation of Z-Arg-Lys-acyloxymethyl ketone (AOMK) as a selective neutral pH inhibitor. Cathepsin B displayed preferences for cleaving peptides with Arg in the P2 position at pH 7.2 and Glu in the P2 position at pH 4.6, represented by its primary dipeptidyl carboxypeptidase and modest endopeptidase activity. These properties led to design of the substrate Z-Arg-Lys-AMC having neutral pH selectivity, and its modification with the AOMK warhead to result in the inhibitor Z-Arg-Lys-AOMK. This irreversible inhibitor displays nanomolar potency with 100-fold selectivity for inhibition of cathepsin B at pH 7.2 compared to pH 4.6, shows specificity for cathepsin B over other cysteine cathepsins, and is cell permeable and inhibits intracellular cathepsin B. These findings demonstrate that cathepsin B possesses pH-dependent cleavage properties that can lead to development of a potent, neutral pH inhibitor of this enzyme.

Cathepsin C aggravates neuroinflammation via promoting production of CCL2 and CXCL2 in glial cells and neurons in a cryogenic brain lesion

OBJECTIVE

Chemokines regulate infiltration of immune cells to brain in inflammation. Cathepsin C (CatC), a lysosomal protease, has been found to participate in neuroinflammation. However, how CatC affects chemokines expression in neuroinflammation triggered by traumatic brain injury (TBI) remains unclear. Here, we investigated the effects of CatC on chemokines and neuroinflammation in TBI.

METHODS

The present study used CatC knockdown (KD) and overexpression (OE) mice to generate cryogenic brain lesion model and determined effects of CatC on expression of chemokines CCL2, CCL5 and CXCL2 and infiltration of immune cells in acute and chronic phases of the lesion. Further, cellular sources of various chemokines were demonstrated in vitro. Values were compared with wild type (WT) mice.

RESULTS

The results found that 6 h after lesion, CatC expression,IL-1β and TNF-α mRNA and protein expression were strongly induced in the lesions; CCL2 and CXCL2 mRNA and protein expression were increased in CatC OE mice, while decreased in CatC KD mice. On the 3rd day after lesion, macrophages and neutrophils were mainly infiltrated to the lesions. Simultaneously, Iba-1+ cells in CatC OE mice were increased, while MPO + cells in CatC KD mice were decreased. In contrast, on the 28th day after lesion, a few lymphocytes were infiltrated surrounding new blood vessels. CatC OE mice showed larger volumes of scar areas, higher expression of CCL2,CXCL2,IL-1β,TNF-α,IL-6 and iNOS, as well as stronger GFAP+ and Iba-1+ signals, while CatC KD mice had reversed effects. No significant differences of CCL5 expression were found in various genotype mice. Further, in vitro study demonstrated CatC-induced expression of CCL2 were mainly derived from microglia and neurons, while CXCL2 derived from microglia and astrocytes.

CONCLUSION

Our data indicate that CatC aggravates neuroinflammation via promoting production of CCL2 and CXCL2 in glial cells and neurons in a cryogenic brain lesion, providing potential cellular and molecular targets for future intervention of TBI and other neuroinflammatory diseases.

Single Molecule Assay for Ultrasensitive Detection of Cathepsin B in Human Blood

Cathepsin B (catB) is a lysosomal cysteine protease expressed in several cells and organs, where it plays a role in protein degradation and turnover. Extracellular, secreted catB has utility as a biomarker for a host of pathological or physiological states, including a myriad of cancers or neurological diseases and injuries. Analytical or diagnostic assessment may be limited by biological sample volume availability. Pathologically relevant changes in catB levels may occur at low-moderate concentrations that require accurate measurement to differentiate from basal levels. Furthermore, biological samples like plasma and serum, often occlude accurate catB measurements because of background and high variance, vastly limiting the ability to detect catB as a peripheral biomarker. Techniques for ultrasensitive protein detection that require low volumes of sample are necessary. To overcome these challenges, a digital enzyme-linked immunosorbent assay (ELISA) was developed for differential detection of catB within less than 5 μL of serum and plasma using the single molecule array (SiMoA) platform, which offers 1000-times more sensitivity and vastly reduced variance compared to colorimetric tests. In buffer, curve-fitting estimated the limit of detection (LoD) to be ∼1.56 and ∼8.47 pg/mL using two-step or three-step assay configurations, respectively. After correcting for endogenous levels, the estimated LoD was ∼4.7 pg/mL in the serum or plasma with the two-step assay. The lower limit of quantitation was ∼2.3 pg/mL in the buffer and ∼9.4 pg/mL in the serum or plasma, indicting the ability to measure small changes above endogenous levels within blood samples.

Blood-Based Brain and Global Biomarker Changes after Combined Hypoxemia and Hemorrhagic Shock in a Rat Model of Penetrating Ballistic-Like Brain Injury

Penetrating traumatic brain injury (pTBI) often occurs with systemic insults such as hemorrhagic shock (HS) and hypoxemic (HX). This study examines rat models of penetrating ballistic-like brain injury (PBBI) and HX+HS to assess whether the blood levels of brain and systemic response biomarkers phosphorylated neurofilament-heavy protein (pNF-H), neurofilament-light protein (NF-L), αII-spectrin, heat shock protein (HSP70), and high mobility group box 1 protein (HMGB1) can distinguish pTBI from systemic insults and guide in pTBI diagnosis, prognosis, and monitoring. Thirty rats were randomly assigned to sham, PBBI, HS+HX, and PBBI+HS+HX groups. PBBI and sham groups underwent craniotomy with and without probe insertion and balloon expansion, respectively. HX and HS was then simulated by blood withdrawal and fraction of inspired oxygen (FIO₂) reduction. Biomarker serum concentrations were determined at one (D1) and two (D2) days post-injury with enzyme-linked immunosorbent assay (ELISA) methods. Axonal injury-linked biomarkers pNF-H and NF-L serum levels in PBBI groups were higher than those in sham and HX+HS groups at D1 and D2 post-injury. The same was true for PBBI+HX+HS compared with sham (D2 only for pNF-H) and HX+HS groups. However, pNF-H and NF-L levels in PBBI+HX+HS groups were not different than their PBBI counterparts. At D1, αII-spectrin levels in the HX+HS and PBBI+HS+HX groups were higher than the sham groups. αII-spectrin levels in the HX+HS group were higher than the PBBI group. This suggests HX+HS as the common insult driving αII-spectrin elevations. In conclusion, pNF-H and NF-L may serve as specific serum biomarkers of pTBI in the presence or absence of systemic insults. αII-spectrin may be a sensitive acute biomarker in detecting systemic insults occurring alone or with pTBI.

Penetrating Ballistic-Like Brain Injury Leads to MicroRNA Dysregulation, BACE1 Upregulation, and Amyloid Precursor Protein Loss in Lesioned Rat Brain Tissues

Severe traumatic brain injury (TBI) is a risk factor for neurodegenerative diseases. Yet, the molecular events involving dysregulated miRNAs that may be associated with protein degradation in the brain remains elusive. Quantitation of more than 800 miRNAs was conducted using rat ipsilateral coronal brain tissues collected 1, 3, or 7 days after penetrating ballistic-like brain injury (PBBI). As a control for each time-point, Sham-operated animals received craniotomy alone. Microarray and systems biology analysis indicated that the amplitude and complexity of miRNAs affected were greatest 7 day after PBBI. Arrays and Q-PCR inferred that dysregulation of miR-135a, miR-328, miR-29c, and miR-21 were associated with altered levels of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), PSEN1, PSEN2, and amyloid precursor protein (APP) genes. These events were followed by increased levels of mature BACE1 protein and concomitant loss of full length APP within 3–7 days, then elevation of amyloid beta (Aβ)-40 7 days after PBBI. This study indicates that miRNA arrays, coupled with systems biology, may be used to guide study design prior validation of miRNA dysregulation. Associative analysis of miRNAs, mRNAs, and proteins within a proposed pathway are poised for further validation as biomarkers and therapeutic targets relevant to TBI-induced APP loss and subsequent Aβ peptide generation during neurodegeneration.

Cathepsin B in neurodegeneration of Alzheimer's disease, traumatic brain injury, and related brain disorders

Investigations of Alzheimer's disease (AD), traumatic brain injury (TBI), and related brain disorders have provided extensive evidence for involvement of cathepsin B, a lysosomal cysteine protease, in mediating the behavioral deficits and neuropathology of these neurodegenerative diseases. This review integrates findings of cathepsin B regulation in clinical biomarker studies, animal model genetic and inhibitor evaluations, structural studies, and lysosomal cell biological mechanisms in AD, TBI, and related brain disorders. The results together indicate the role of cathepsin B in the behavioral deficits and neuropathology of these disorders. Lysosomal leakage occurs in AD and TBI, and related neurodegeneration, which leads to the hypothesis that cathepsin B is redistributed from the lysosome to the cytosol where it initiates cell death and inflammation processes associated with neurodegeneration. These results together implicate cathepsin B as a major contributor to these neuropathological changes and behavioral deficits. These findings support the investigation of cathepsin B as a potential drug target for therapeutic discovery and treatment of AD, TBI, and TBI-related brain disorders.