Differential Roles of Cysteinyl Cathepsins in TGF-β Signaling and Tissue Fibrosis

Dysregulated lysosomal exocytosis drives protease-mediated cartilage pathogenesis in multiple lysosomal disorders

The classic view of the lysosome as a static recycling center has been replaced with one of a dynamic and mobile hub of metabolic regulation. This revised view raises new questions about how dysfunction of this organelle causes pathology in inherited lysosomal disorders. Here we provide evidence for increased lysosomal exocytosis in the developing cartilage of three lysosomal disease zebrafish models with distinct etiologies. Dysregulated exocytosis was linked to altered cartilage development, increased activity of multiple cathepsin proteases, and cathepsin- and TGFβ-mediated pathogenesis in these models. Moreover, inhibition of cathepsin activity or direct blockade of exocytosis with small molecule modulators improved the cartilage phenotypes, reinforcing a connection between excessive extracellular protease activity and cartilage pathogenesis. This study highlights the pathogenic consequences in early cartilage development arising from uncontrolled release of lysosomal enzymes via exocytosis, and suggests that pharmacological enhancement of this process could be detrimental during tissue development.

Mitochondrial reactive oxygen species impact human fibroblast responses to protracted γ-ray exposures

Purpose: Continuous exposure to ionizing radiation at a low dose rate poses significant health risks to humans on deep space missions, prompting the need for mechanistic studies to identify countermeasures against its deleterious effects. Mitochondria are a major subcellular locus of radiogenic injury, and may trigger secondary cellular responses through the production of reactive oxygen species (mtROS) with broader biological implications. Methods and Materials: To determine the contribution of mtROS to radiation-induced cellular responses, we investigated the impacts of protracted γ-ray exposures (IR; 1.1 Gy delivered at 0.16 mGy/min continuously over 5 days) on mitochondrial function, gene expression, and the protein secretome of human HCA2-hTERT fibroblasts in the presence and absence of a mitochondria-specific antioxidant mitoTEMPO (MT; 5 µM). Results: IR increased fibroblast mitochondrial oxygen consumption (JO2) and H2O2 release rates (JH2O2) under energized conditions, which corresponded to higher protein expression of NADPH Oxidase (NOX) 1, NOX4, and nuclear DNA-encoded subunits of respiratory chain Complexes I and III, but depleted mtDNA transcripts encoding subunits of the same complexes. This was associated with activation of gene programs related to DNA repair, oxidative stress, and protein ubiquination, all of which were attenuated by MT treatment along with radiation-induced increases in JO2 and JH2O2. IR also increased secreted levels of interleukin-8 and Type I collagens, while decreasing Type VI collagens and enzymes that coordinate assembly and remodeling of the extracellular matrix. MT treatment attenuated many of these effects while augmenting others, revealing complex effects of mtROS in fibroblast responses to IR. Conclusion: These results implicate mtROS production in fibroblast responses to protracted radiation exposure, and suggest potentially protective effects of mitochondrial-targeted antioxidants against radiogenic tissue injury in vivo.

In-silico and in-vitro screening of Asiatic acid and Asiaticoside A against Cathepsin S enzyme

BACKGROUND

Atherosclerosis is a form of cardiovascular disease that affects the endothelium of the blood vessel. Series of events are involved in the pathophysiology of this disease which includes the breaking down of the connective tissue elastin and collagen responsible for the tensile strength of the arterial wall by proteolytic enzyme. One of these enzymes called Cathepsin S (CatS) is upregulated in the progression of the disease and its inhibition has been proposed to be a promising pharmacological target to improve the prognosis of the disease condition. Asiatic acid and asiaticoside A are both pentacyclic triterpenoids isolated from Centella asiatica. Their use in treating various cardiovascular diseases has been reported.

METHODS

In this study through in silico and in vitro methods, the pharmacokinetic properties, residue interaction, and inhibitory activities of these compounds were checked against the CatS enzyme. The SwissADME online package and the ToxTree 3.01 version of the offline software were used to determine the physicochemical properties of the compounds.

RESULT

Asiatic acid reported no violation of the Lipinski rule while asiaticoside A violated the rule with regards to its molecular structure and size. The molecular docking was done using Molecular Operating Environment (MOE) and the S-score of - 7.25988, - 7.08466, and - 4.147913 Kcal/mol were recorded for LY300328, asiaticoside A, and asiatic acid respectively. Asiaticoside A has a docking score value (- 7.08466Kcal/mol) close to the co-crystallize compound. Apart from the close docking score, the amino acid residue glycine69 and asparagine163 both interact with the co-crystallized compound and asiaticoside A. The in vitro result clearly shows the inhibitory effect of asiaticoside and asiatic acid. Asiaticoside A has an inhibitory value of about 40% and asiatic acid has an inhibitory value of about 20%.

CONCLUSION

This clearly shows that asiaticoside will be a better drug candidate than asiatic acid in inhibiting the CatS enzyme for the purpose of improving the outcome of atherosclerosis. However, certain modifications need to be made to the structural make-up of asiaticoside A to improve its pharmacokinetics properties.

The roles of intracellular proteolysis in cardiac ischemia-reperfusion injury

Ischemic heart disease remains a leading cause of human mortality worldwide. One form of ischemic heart disease is ischemia-reperfusion injury caused by the reintroduction of blood supply to ischemic cardiac muscle. The short and long-term damage that occurs due to ischemia-reperfusion injury is partly due to the proteolysis of diverse protein substrates inside and outside of cardiomyocytes. Ischemia-reperfusion activates several diverse intracellular proteases, including, but not limited to, matrix metalloproteinases, calpains, cathepsins, and caspases. This review will focus on the biological roles, intracellular localization, proteolytic targets, and inhibitors of these proteases in cardiomyocytes following ischemia-reperfusion injury. Recognition of the intracellular function of each of these proteases includes defining their activation, proteolytic targets, and their inhibitors during myocardial ischemia-reperfusion injury. This review is a step toward a better understanding of protease activation and involvement in ischemic heart disease and developing new therapeutic strategies for its treatment.

Cathepsin S deficiency improves muscle mass loss and dysfunction via the modulation of protein metabolism in mice under pathological stress conditions

Cathepsin S (CTSS) is a widely expressed cysteinyl protease that has garnered attention because of its enzymatic and non-enzymatic functions under inflammatory and metabolic pathological conditions. Here, we examined whether CTSS participates in stress-related skeletal muscle mass loss and dysfunction, focusing on protein metabolic imbalance. Eight-week-old male wildtype (CTSS^+/+ ) and CTSS-knockout (CTSS^-/- ) mice were randomly assigned to non-stress and variable-stress groups for 2 weeks, and then processed for morphological and biochemical studies. Compared with non-stressed mice, stressed CTSS^+/+ mice showed significant losses of muscle mass, muscle function, and muscle fiber area. In this setting, the stress-induced harmful changes in the levels of oxidative stress-related (gp91^phox and p22^phox ,), inflammation-related (SDF-1, CXCR4, IL-1β, TNF-α, MCP-1, ICAM-1, and VCAM-1), mitochondrial biogenesis-related (PPAR-γ and PGC-1α) genes and/or proteins and protein metabolism-related (p-PI3K, p-Akt, p-FoxO3α, MuRF-1, and MAFbx1) proteins; and these alterations were rectified by CTSS deletion. Metabolomic analysis revealed that stressed CTSS^-/- mice exhibited a significant improvement in the levels of glutamine metabolism pathway products. Thus, these findings indicated that CTSS can control chronic stress-related skeletal muscle atrophy and dysfunction by modulating protein metabolic imbalance, and thus CTSS was suggested to be a promising new therapeutic target for chronic stress-related muscular diseases.

Cationic proteins from eosinophils bind bone morphogenetic protein receptors promoting vascular calcification and atherogenesis

AIMS

Blood eosinophil count and eosinophil cationic protein (ECP) concentration are risk factors of cardiovascular diseases. This study tested whether and how eosinophils and ECP contribute to vascular calcification and atherogenesis.

METHODS AND RESULTS

Immunostaining revealed eosinophil accumulation in human and mouse atherosclerotic lesions. Eosinophil deficiency in ΔdblGATA mice slowed atherogenesis with increased lesion smooth muscle cell (SMC) content and reduced calcification. This protection in ΔdblGATA mice was muted when mice received donor eosinophils from wild-type (WT), Il4-/-, and Il13-/- mice or mouse eosinophil-associated-ribonuclease-1 (mEar1), a murine homologue of ECP. Eosinophils or mEar1 but not interleukin (IL) 4 or IL13 increased the calcification of SMC from WT mice but not those from Runt-related transcription factor-2 (Runx2) knockout mice. Immunoblot analyses showed that eosinophils and mEar1 activated Smad-1/5/8 but did not affect Smad-2/3 activation or expression of bone morphogenetic protein receptors (BMPR-1A/1B/2) or transforming growth factor (TGF)-β receptors (TGFBR1/2) in SMC from WT and Runx2 knockout mice. Immunoprecipitation showed that mEar1 formed immune complexes with BMPR-1A/1B but not TGFBR1/2. Immunofluorescence double-staining, ligand binding, and Scatchard plot analysis demonstrated that mEar1 bound to BMPR-1A and BMPR-1B with similar affinity. Likewise, human ECP and eosinophil-derived neurotoxin (EDN) also bound to BMPR-1A/1B on human vascular SMC and promoted SMC osteogenic differentiation. In a cohort of 5864 men from the Danish Cardiovascular Screening trial and its subpopulation of 394 participants, blood eosinophil counts and ECP levels correlated with the calcification scores of different arterial segments from coronary arteries to iliac arteries.

CONCLUSION

Eosinophils release cationic proteins that can promote SMC calcification and atherogenesis using the BMPR-1A/1B-Smad-1/5/8-Runx2 signalling pathway.

Diagnostic value of serum cathepsin S in type 2 diabetic kidney disease

Background

Identification of risk factors that have causal effects on the occurrence of diabetic kidney disease (DKD), is of great significance in early screening and intervening for DKD, and in delaying the progression of DKD to end-stage renal disease. Cathepsin S (Cat-S), a novel non-invasive diagnostic marker, mediates vascular endothelial dysfunction. The diagnostic value of Cat-S for DKD has rarely been reported in clinical studies.

Objective

To analyze whether Cat-S is a risk factor for DKD and evaluate the diagnostic value of serum Cat-S for DKD.

Methods

Forty-three healthy subjects and 200 type 2 diabetes mellitus (T2DM) patients were enrolled. T2DM patients were divided into subgroups according to various criteria. Enzyme-linked immunosorbent assay was used to detect serum Cat-S levels among different subgroups. Spearman correlation analysis was used to analyze correlations between serum Cat-S and clinical indicators. Multivariate logistic regression analysis was performed to analyze risk factors for the occurrence of DKD and decreased renal function in T2DM patients.

Results

Spearman analysis showed that serum Cat-S level was positively correlated with urine albumin creatinine ratio (r=0.76, P<0.05) and negatively correlated with estimated glomerular filtration rate (r=-0.54, P<0.01). Logistic regression analysis showed that increased serum Cat-S and cystatin C(CysC) were independent risk factors for DKD and decreased renal function in T2DM patients (P<0.05). The area under the receiver operating characteristic (ROC) curve was 0.900 of serum Cat-S for diagnosing DKD, and when the best cut-off value was 827.42 pg/mL the sensitivity and specificity were 71.6% and 98.8%, respectively. Thus, serum Cat-S was better than CysC for diagnosing DKD (for CysC, the area under the ROC curve was 0.791, and when the cut-off value was 1.16 mg/L the sensitivity and specificity of CysC were 47.4% and 98.8%, respectively).

Conclusion

Increased serum Cat-S were associated with the progression of albuminuria and decreased renal function in T2DM patients. The diagnostic value of serum Cat-S was better than that of CysC for DKD. Monitoring of serum Cat-S levels could be helpful for early screening DKD and assessing the severity of DKD and could provide a new strategy for diagnosing DKD.

Overview of multifunctional cysteinyl cathepsins in atherosclerosis-based cardiovascular disease: from insights into molecular functions to clinical implications

Cysteinyl cathepsins (CTSs) are widely known to have a proteolysis function that mediates recycling of unwanted proteins in endosomes and lysosomes, and investigation of CTSs has greatly improved with advances in live-imaging techniques both in vivo and in vitro, leading to three key findings. (1) CTSs are relocated from the lysosomes to other cellular spaces (i.e., cytosol, nucleus, nuclear membrane, plasma membrane, and extracellular milieu). (2) In addition to acidic cellular compartments, CTSs also exert biological activity in neutral environments. (3) CTSs also exert multiple nontraditional functions in, for example, extracellular matrix metabolism, cell signaling transduction, protein processing/trafficking, and cellular events. Various stimuli regulate the expression and activities of CTSs in vivo and vitro-e.g., inflammatory cytokines, oxidative stress, neurohormones, and growth factors. Accumulating evidence has confirmed the participation of CTSs in vascular diseases characterized by atherosclerosis, plaque rupture, thrombosis, calcification, aneurysm, restenosis/in-stent-restenosis, and neovasel formation. Circulating and tissue CTSs are promising as biomarkers and as a diagnostic imaging tool in patients with atherosclerosis-based cardiovascular disease (ACVD), and pharmacological interventions with their specific and non-specific inhibitors, and cardiovascular drugs might have potential for the therapeutic targeting of CTSs in animals. This review focuses on the update findings on CTS biology and the involvement of CTSs in the initiation and progression of ACVD and discusses the potential use of CTSs as biomarkers and small-molecule targets to prevent deleterious nontraditional functions in ACVD.

Reduced Cathepsin L expression and secretion into the extracellular milieu contribute to lung fibrosis in systemic sclerosis

OBJECTIVES

Lung fibrosis is the leading cause of death in SSc, with no cure currently available. Antifibrotic Endostatin (ES) production does not reach therapeutic levels in SSc patients, suggesting a deficit in its release from Collagen XVIII by the main cleavage enzyme, Cathepsin L (CTSL). Thus, elucidating a potential deficit in CTSL expression and activity unravels an underlying molecular cause for SSc-driven lung fibrosis.

METHODS

Fibrosis was induced experimentally using TGF-β in vitro, in primary human lung fibroblasts (pLFs), and ex vivo, in human lung tissues. ES and CTSL expression was quantified using ELISA, RT-qPCR, immunoblotting or immunofluorescence. Recombinant NC1-FLAG peptide was used to assess CTSL cleavage activity. CTSL expression was also compared between SSc vs normal (NL)-derived pLFs and lung tissues.

RESULTS

ES levels were significantly reduced in media conditioned by TGF-β-induced pLFs. TGF-β-stimulated pLFs significantly reduced expression and secretion of CTSL into the extracellular matrix (ECM). CTSL was also sequestered in its inactive form into extracellular vesicles, further reducing its availability in the ECM. Media conditioned by TGF-β-induced pLFs showed reduced cleavage of NC1-Flag and reduced release of the antifibrotic ES fragment. SSc-derived pLFs and lung tissues expressed significantly lower levels of CTSL compared with NL.

CONCLUSIONS

Our findings identify CTSL as a protein protective against lung fibrosis via its activation of antifibrotic ES, and whose expression in SSc pLFs and lung tissues is suppressed. Identifying strategies to boost CTSL endogenous levels in SSc patients could serve as a viable therapeutic strategy.

Continuous nutrient supply culture strategy controls multivesicular endosomes pathway and anti-photo-aging miRNA cargo loading of extracellular vesicles

Extracellular vesicle (EV) therapy recently had shown significant efficacy in various diseases. Serum starvation culture (SC) is one of the most widely used methods for collecting EVs. However, SC may cause inadvertent effects and eventually dampen the therapeutic potential of EVs. Therefore, we developed a novel method for EV collection, continuous nutrient supply culture (CC), which can provide an optimal condition for mesenchymal stem cells (MSCs) by continuously supplying essential nutrients to MSCs. By comparing with SC strategy, we revealed that CC could maintain CC-MSCs in a normal autophagy and apoptotic state, which reduced the shunting of EV precursors in cells and useless information material carried by EVs. In CC-MSCs, the expression levels of endosomal sorting complexes required for transport (ESCRT) and targeting GTPase27 (Rab27) were upregulated compared to those in SC-MSCs. Besides, we analyzed the membrane transport efficiency of EV formation, which demonstrated the CC strategy could promote the formation of EV precursors and the release of EVs. In addition, miRNA analysis revealed that CC-EVs were enriched with anti-chronic inflammatory factors, which could inhibit the nuclear factor kappa-B (NF-κB) pathway, mitigate chronic inflammation, and effectively repair skin photo-aging damage.

IL-33 mediates Pseudomonas induced airway fibrogenesis and is associated with CLAD

BACKGROUND

Long term outcomes of lung transplantation are impacted by the occurrence of chronic lung allograft dysfunction (CLAD). Recent evidence suggests a role for the lung microbiome in the occurrence of CLAD, but the exact mechanisms are not well defined. We hypothesize that the lung microbiome inhibits epithelial autophagic clearance of pro-fibrotic proteins in an IL-33 dependent manner, thereby augmenting fibrogenesis and risk for CLAD.

METHODS

Autopsy derived CLAD and non-CLAD lungs were collected. IL-33, P62 and LC3 immunofluorescence was performed and assessed using confocal microscopy. Pseudomonas aeruginosa (PsA), Streptococcus Pneumoniae (SP), Prevotella Melaninogenica (PM), recombinant IL-33 or PsA-lipopolysaccharide was co-cultured with primary human bronchial epithelial cells (PBEC) and lung fibroblasts in the presence or absence of IL-33 blockade. Western blot analysis and quantitative reverse transcription (qRT) PCR was performed to evaluate IL-33 expression, autophagy, cytokines and fibroblast differentiation markers. These experiments were repeated after siRNA silencing and upregulation (plasmid vector) of Beclin-1.

RESULTS

Human CLAD lungs demonstrated markedly increased expression of IL-33 and reduced basal autophagy compared to non-CLAD lungs. Exposure of co-cultured PBECs to PsA, SP induced IL-33, and inhibited PBEC autophagy, while PM elicited no significant response. Further, PsA exposure increased myofibroblast differentiation and collagen formation. IL-33 blockade in these co-cultures recovered Beclin-1, cellular autophagy and attenuated myofibroblast activation in a Beclin-1 dependent manner.

CONCLUSION

CLAD is associated with increased airway IL-33 expression and reduced basal autophagy. PsA induces a fibrogenic response by inhibiting airway epithelial autophagy in an IL-33 dependent manner.

Interactomics of CXXC proteins involved in epigenetic regulation of gene expression

Regulation of gene expression is an extremely complex and multicomponent biological phenomenon. Proteins containing the CXXC-domain “zinc fingers” (CXXC-proteins) are master regulators of expression of many genes and have conserved functions of methylation of DNA bases and histone proteins. CXXC proteins function as a part of multiprotein complexes, which indicates the fundamental importance of studying post-translational regulation through modulation of the protein-protein interaction spectrum (PPI) in both normal and pathological conditions. In this paper we discuss general aspects of the involvement of CXXC proteins and their protein partners in neoplastic processes, both from the literature data and our own studies. Special attention is paid to recent data on the particular interactomics of the CFP1 protein encoded by the CXXC1 gene located on the human chromosome 18. CFP1 is devoid of enzymatic activity and implements epigenetic regulation of expression through binding to chromatin and a certain spectrum of PPIs.

Antiviral potential of diminazene aceturate against SARS-CoV-2 proteases using computational and in vitro approaches

Diminazene aceturate (DIZE), an antiparasitic, is an ACE2 activator, and studies show that activators of this enzyme may be beneficial for COVID-19, disease caused by SARS-CoV-2. Thus, the objective was to evaluate the in silico and in vitro affinity of diminazene aceturate against molecular targets of SARS-CoV-2. 3D structures from DIZE and the proteases from SARS-CoV-2, obtained through the Protein Data Bank and Drug Database (Drubank), and processed in computer programs like AutodockTools, LigPlot, Pymol for molecular docking and visualization and GROMACS was used to perform molecular dynamics. The results demonstrate that DIZE could interact with all tested targets, and the best binding energies were obtained from the interaction of Protein S (closed conformation −7.87 kcal/mol) and M_pro (−6.23 kcal/mol), indicating that it can act both by preventing entry and viral replication. The results of molecular dynamics demonstrate that DIZE was able to promote a change in stability at the cleavage sites between S1 and S2, which could prevent binding to ACE2 and fusion with the membrane. In addition, in vitro tests confirm the in silico results showing that DIZE could inhibit the binding between the spike receptor-binding domain protein and ACE2, which could promote a reduction in the virus infection. However, tests in other experimental models with in vivo approaches are needed.

Methylation-mediated silencing of PTPRD induces pulmonary hypertension by promoting pulmonary arterial smooth muscle cell migration via the PDGFRB/PLCγ1 axis

OBJECTIVE

Pulmonary hypertension is a lethal disease characterized by pulmonary vascular remodeling and is mediated by abnormal proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs). Platelet-derived growth factor BB (PDGF-BB) is the most potent mitogen for PASMCs and is involved in vascular remodeling in pulmonary hypertension development. Therefore, the objective of our study is to identify novel mechanisms underlying vascular remodeling in pulmonary hypertension.

METHODS

We explored the effects and mechanisms of PTPRD downregulation in PASMCs and PTPRD knockdown rats in pulmonary hypertension induced by hypoxia.

RESULTS

We demonstrated that PTPRD is dramatically downregulated in PDGF-BB-treated PASMCs, pulmonary arteries from pulmonary hypertension rats, and blood and pulmonary arteries from lung specimens of patients with hypoxic pulmonary arterial hypertension (HPAH) and idiopathic PAH (iPAH). Subsequently, we found that PTPRD was downregulated by promoter methylation via DNMT1. Moreover, we found that PTPRD knockdown altered cell morphology and migration in PASMCs via modulating focal adhesion and cell cytoskeleton. We have demonstrated that the increase in cell migration is mediated by the PDGFRB/PLCγ1 pathway. Furthermore, under hypoxic condition, we observed significant pulmonary arterial remodeling and exacerbation of pulmonary hypertension in heterozygous PTPRD knock-out rats compared with the wild-type group. We also demonstrated that HET group treated with chronic hypoxia have higher expression and activity of PLCγ1 in the pulmonary arteries compared with wild-type group.

CONCLUSION

We propose that PTPRD likely plays an important role in the process of pulmonary vascular remodeling and development of pulmonary hypertension in vivo .

The physiological and pathophysiological roles of the autophagy lysosomal system in the conventional aqueous humor outflow pathway: More than cellular clean up

During the last few years, the autophagy lysosomal system is emerging as a central cellular pathway with roles in survival, acting as a housekeeper and stress response mechanism. Studies by our and other labs suggest that autophagy might play an essential role in maintaining aqueous humor outflow homeostasis, and that malfunction of autophagy in outflow pathway cells might predispose to ocular hypertension and glaucoma pathogenesis. In this review, we will collect the current knowledge and discuss the molecular mechanisms by which autophagy does or might regulate normal outflow pathway tissue function, and its response to different types of stressors (oxidative stress and mechanical stress). We will also discuss novel roles of autophagy and lysosomal enzymes in modulation of TGFβ signaling and ECM remodeling, and the link between dysregulated autophagy and cellular senescence. We will examine what we have learnt, using pre-clinical animal models about how dysregulated autophagy can contribute to disease and apply that to the current status of autophagy in human glaucoma. Finally, we will consider and discuss the challenges and the potential of autophagy as a therapeutic target for the treatment of ocular hypertension and glaucoma.

Spatial localization of cathepsins: Implications in immune activation and resolution during infections

Cathepsins were first described, as endolysosomal proteolytic enzymes in reference to the organelles where they degrade the bulk of endogenous and exogenous substrates in a slightly acidic environment. These substrates include pathogens internalized via endocytosis and/or marked for destruction by autophagy. However, the role of cathepsins during infection far exceeds that of direct digestion of the pathogen. Cathepsins have been extensively investigated in the context of tumour associated immune cells and chronic inflammation. Several cathepsin-dependent immune responses develop in the endocytic pathway while others take place in the cytosol, the nucleus, or in the extracellular space. In this review we highlight the spatial localization of cathepsins and their implications in immune activation and resolution pathways during infection.

Cathepsin K Deficiency Prevented Kidney Damage and Dysfunction in Response to 5/6 Nephrectomy Injury in Mice With or Without Chronic Stress

Background:

Chronic psychological stress is a risk factor for kidney disease, including kidney dysfunction and hypertension. Lysosomal CatK (cathepsin K) participates in various human pathobiologies. We investigated the role of CatK in kidney remodeling and hypertension in response to 5/6 nephrectomy injury in mice with or without chronic stress.

Methods:

Male 7-week-old WT (wild type; CatK^+/+) and CatK-deficient (CatK^−/−) mice that were or were not subjected to chronic stress underwent 5/6 nephrectomy. At 8 weeks post-stress/surgery, the stress was observed to have accelerated injury-induced glomerulosclerosis, proteinuria, and blood pressure elevation.

Results:

Compared with the nonstressed mice, the stressed mice showed increased levels of TLR (Toll-like receptor)-2/4, p22^phox, gp91^phox, CatK, MMP (matrix metalloproteinase)-2/9, collagen type I and III genes, PPAR-γ (peroxisome proliferator-activated receptor-gamma), NLRP-3 (NOD-like receptor thermal protein domain associated protein 3), p21, p16, and cleaved caspase-8 proteins, podocyte foot process effacement, macrophage accumulation, apoptosis, and decreased levels of Bcl-2 (B cell lymphoma 2) and Sirt1, as well as decreased glomerular desmin expression in the kidneys. These harmful changes were retarded by the genetic or pharmacological inhibition of CatK. Consistently, CatK inhibition ameliorated 5/6 nephrectomy–related kidney injury and dysfunction. In mesangial cells, CatK silencing or overexpression, respectively, reduced or increased the PPAR-γ and cleaved caspase-8 protein levels, providing evidence and a mechanistic explanation of CatK’s involvement in PPAR-γ/caspase-8–mediated cell apoptosis in response to superoxide and stressed serum.

Conclusions:

These results demonstrate that CatK plays an essential role in kidney remodeling and hypertension in response to 5/6 nephrectomy or stress, possibly via a reduction of glomerular inflammation, apoptosis, and fibrosis, suggesting a novel therapeutic strategy for controlling kidney injury in mice under chronic psychological stress conditions.

Inhibition of Autophagy Flux Promotes Secretion of Chondroitin Sulfate Proteoglycans in Primary Rat Astrocytes

Following spinal cord injury (SCI), reactive astrocytes in the glial scar produce high levels of chondroitin sulfate proteoglycans (CSPGs), which are known to inhibit axonal regeneration. Transforming growth factor beta (TGFβ) is a well-known factor that induces the production of CSPGs, and in this study, we report a novel mechanism underlying TGFβ's effects on CSPG secretion in primary rat astrocytes. We observed increased TGFβ-induced secretion of the CSPGs neurocan and brevican, and this occurred simultaneously with inhibition of autophagy flux. In addition, we show that neurocan and brevican levels are further increased when TGFβ is administered in the presence of an autophagy inhibitor, Bafilomycin-A1, while they are reduced when cells are treated with a concentration of rapamycin that is not sufficient to induce autophagy. These findings suggest that TGFβ mediates its effects on CSPG secretion through autophagy pathways. They also represent a potential new approach to reduce CSPG secretion in vivo by targeting autophagy pathways, which could improve axonal regeneration after SCI.

Cathepsin B promotes collagen biosynthesis, which drives bronchiolitis obliterans syndrome

Bronchiolitis obliterans syndrome (BOS) is a major complication after lung transplantation (LTx). BOS is characterised by massive peribronchial fibrosis, leading to air trapping-induced pulmonary dysfunction. Cathepsin B, a lysosomal cysteine protease, has been shown to enforce fibrotic pathways in several diseases. However, the relevance of cathepsin B in BOS progression has not yet been addressed. The aim of the study was to elucidate the function of cathepsin B in BOS pathogenesis.We determined cathepsin B levels in bronchoalveolar lavage fluid (BALF) and lung tissue from healthy donors (HD) and BOS LTx patients. Cathepsin B activity was assessed via a fluorescence resonance energy transfer-based assay and protein expression was determined using Western blotting, ELISA and immunostaining. To investigate the impact of cathepsin B in the pathophysiology of BOS, we used an in vivo orthotopic left LTx mouse model. Mechanistic studies were performed in vitro using macrophage and fibroblast cell lines.We found a significant increase of cathepsin B activity in BALF and lung tissue from BOS patients, as well as in our murine model of lymphocytic bronchiolitis. Moreover, cathepsin B activity was associated with increased biosynthesis of collagen and had a negative effect on lung function. We observed that cathepsin B was mainly expressed in macrophages that infiltrated areas characterised by a massive accumulation of collagen deposition. Mechanistically, macrophage-derived cathepsin B contributed to transforming growth factor-β1-dependent activation of fibroblasts, and its inhibition reversed the phenotype.Infiltrating macrophages release active cathepsin B, thereby promoting fibroblast activation and subsequent collagen deposition, which drive BOS. Cathepsin B represents a promising therapeutic target to prevent the progression of BOS.

Cathepsin B Localizes in the Caveolae and Participates in the Proteolytic Cascade in Trabecular Meshwork Cells. Potential New Drug Target for the Treatment of Glaucoma

Extracellular matrix (ECM) deposition in the trabecular meshwork (TM) is one of the hallmarks of glaucoma, a group of human diseases and leading cause of permanent blindness. The molecular mechanisms underlying ECM deposition in the glaucomatous TM are not known, but it is presumed to be a consequence of excessive synthesis of ECM components, decreased proteolytic degradation, or both. Targeting ECM deposition might represent a therapeutic approach to restore outflow facility in glaucoma. Previous work conducted in our laboratory identified the lysosomal enzyme cathepsin B (CTSB) to be expressed on the cellular surface and to be secreted into the culture media in trabecular meshwork (TM) cells. Here, we further investigated the role of CTSB on ECM remodeling and outflow physiology in vitro and in CSTB^ko mice. Our results indicate that CTSB localizes in the caveolae and participates in the pericellular degradation of ECM in TM cells. We also report here a novel role of CTSB in regulating the expression of PAI-1 and TGFβ/Smad signaling in TM cells vitro and in vivo in CTSB^ko mice. We propose enhancing CTSB activity as a novel therapeutic target to attenuate fibrosis and ECM deposition in the glaucomatous outflow pathway.

Public Database-Driven Insights Into Aging Stress-Associated Defective Gut Barrier With Low SARS-CoV-2 Receptors

The novel coronavirus disease (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has led to a global pandemic, and resulted in high case-fatality rate in the elderly. In addition to typical respiratory responses, ~50% of clinical cases include gastrointestinal symptoms such as diarrhea, vomiting, abdominal pain, and persistent fecal shedding of the virus even after its clearance from the pulmonary system. In the present study, we assessed aging-associated gut transcriptomic responses considering the gastrointestinal symptoms contributing to COVID-19 severity. Intestinal expression of SARS-CoV-2 receptors and defense biomarkers decreased with increasing age. Moreover, aging-associated integrated stress responses (ISR) and mTOR-linked cell metabolic stress signals counteracted gut defense biomarkers. However, SARS-CoV-2 receptor expression was positively associated with gut barrier integrity potently via downregulation of the two stress-responsive signals. Gut transcriptome-based mechanistic prediction implicates that high susceptibility to COVID-19 in the elderly with low SARS-CoV-2 receptors is due to aging stress-associated defective gut defense, providing a new avenue for viral entry receptor-independent interventions.

Cathepsin L-selective inhibitors: A potentially promising treatment for COVID-19 patients

The widespread coronavirus SARS-CoV-2 has already infected over 4 million people worldwide, with a death toll over 280,000. Current treatment of COVID-19 patients relies mainly on antiviral drugs lopinavir/ritonavir, arbidol, and remdesivir, the anti-malarial drugs hydroxychloroquine and chloroquine, and traditional Chinese medicine. There are over 2,118 on-going clinical trials underway, but to date none of these drugs have consistently proven effective. Cathepsin L (CatL) is an endosomal cysteine protease. It mediates the cleavage of the S1 subunit of the coronavirus surface spike glycoprotein. This cleavage is necessary for coronavirus entry into human host cells, virus and host cell endosome membrane fusion, and viral RNA release for next round of replication. Here we summarize data regarding seven CatL-selective inhibitors that block coronavirus entry into cultured host cells and provide a mechanism to block SARS-CoV-2 infection in humans. Given the rapid growth of the SARS-CoV-2-positive population worldwide, ready-to-use CatL inhibitors should be explored as a treatment option. We identify ten US FDA-approved drugs that have CatL inhibitory activity. We provide evidence that supports the combined use of serine protease and CatL inhibitors as a possibly safer and more effective therapy than other available therapeutics to block coronavirus host cell entry and intracellular replication, without compromising the immune system.

Cathepsin B deficiency ameliorates liver lipid deposition, inflammatory cell infiltration, and fibrosis after diet-induced nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a severe form of nonalcoholic fatty liver disease characterized by fat accumulation and inflammation in liver. Yet, the mechanistic insight and diagnostic and therapeutic options of NASH remain incompletely understood. This study tested the roles of cysteine protease cathepsin B (CatB) in mouse NASH development. Immunoblot revealed increased liver CatB expression in NASH mice. Fructose-palmitate-cholesterol diet increased body weight gain, liver to body weight ratio, blood fasting glucose, plasma total cholesterol and alanine transaminase levels, and liver triglyceride, but decreased plasma high-density lipoprotein in wild-type mice. All these changes were blunted in CatB-deficient (Ctsb^-/-) mice. In parallel to reduced expression of genes involved in liver lipid transport and lipogenesis, liver CD36, FABP4, and PPARγ protein levels were also significantly decreased in Ctsb^-/- mice, although CatB deficiency did not affect liver gluconeogenesis and fatty acid beta-oxidation-associated gene expression. Mechanistic studies showed that CatB deficiency decreased liver expression of adhesion molecules, inflammatory cytokine, and chemokine, along with reduced liver inflammatory cell infiltration. CatB deficiency also promoted M2 macrophage polarization and reduced liver TGF-β1 signaling and fibrosis. Together, CatB deficiency improves liver function in NASH mice by suppressing de novo lipogenesis and liver inflammation and fibrosis.

Cathepsin K Deficiency Impaired Ischemia-Induced Neovascularization in Aged Mice

Background

Aging is a major risk factor for cardiovascular disease. Cysteine protease cathepsin K (CatK) has been implicated in the process of angiogenesis, but the exact roles of individual CatK in vessel formation during aging are poorly understood.

Methods and Results

To study the putative role of CatK in ischemia-induced angiogenesis, we applied a hindlimb ischemia model to aged wild-type (CatK^+/+) and CatK-deficient (CatK^−/−) mice. A serial laser Doppler blood-flow analysis revealed that the recovery of the ischemic/normal blood-flow ratio in the aged CatK^−/−mice was impaired throughout the follow-up period. On postoperative day 14, CatK deficiency had also impaired capillary formation. CatK deficiency reduced the levels of cleaved Notch1, phospho-Akt, and/or vascular endothelial growth factor (VEGF) proteins in the ischemic muscles and bone marrow-derived c-Kit⁺ cells. A flow cytometry analysis revealed that CatK deficiency reduced the numbers of endothelial progenitor cell (EPC)-like CD31⁺/c-Kit⁺ cells in the peripheral blood as well as the ischemic vasculature. In vitro experiments, CatK^−/− impaired bone-derived c-Kit⁺ cellular functions (migration, invasion, proliferation, and tubulogenesis) in aged mice. Our findings demonstrated that aging impaired the ischemia-induced angiogenesis associated with the reductions of the production and mobilization of CD31⁺/c-Kit⁺ cells in mice.

Conclusions

These findings established that the impairment of ischemia-induced neovascularization in aged CatK^−/− mice is due, at least in part, to the reduction of EPC mobilization and the homing of the cells into vasculature that is associated with the impairment of Notch1 signaling activation at advanced ages.

The Ins and Outs of Cathepsins: Physiological Function and Role in Disease Management

Cathepsins are the most abundant lysosomal proteases that are mainly found in acidic endo/lysosomal compartments where they play a vital role in intracellular protein degradation, energy metabolism, and immune responses among a host of other functions. The discovery that cathepsins are secreted and remain functionally active outside of the lysosome has caused a paradigm shift. Contemporary research has unraveled many versatile functions of cathepsins in extralysosomal locations including cytosol and extracellular space. Nevertheless, extracellular cathepsins are majorly upregulated in pathological states and are implicated in a wide range of diseases including cancer and cardiovascular diseases. Taking advantage of the differential expression of the cathepsins during pathological conditions, much research is focused on using cathepsins as diagnostic markers and therapeutic targets. A tailored therapeutic approach using selective cathepsin inhibitors is constantly emerging to be safe and efficient. Moreover, recent development of proteomic-based approaches for the identification of novel physiological substrates offers a major opportunity to understand the mechanism of cathepsin action. In this review, we summarize the available evidence regarding the role of cathepsins in health and disease, discuss their potential as biomarkers of disease progression, and shed light on the potential of extracellular cathepsin inhibitors as safe therapeutic tools.

Proteomic Analysis Identifies Distinct Glomerular Extracellular Matrix in Collapsing Focal Segmental Glomerulosclerosis

BACKGROUND

The mechanisms leading to extracellular matrix (ECM) replacement of areas of glomerular capillaries in histologic variants of FSGS are unknown. This study used proteomics to test the hypothesis that glomerular ECM composition in collapsing FSGS (cFSGS) differs from that of other variants.

METHODS

ECM proteins in glomeruli from biopsy specimens of patients with FSGS not otherwise specified (FSGS-NOS) or cFSGS and from normal controls were distinguished and quantified using mass spectrometry, verified and localized using immunohistochemistry (IHC) and confocal microscopy, and assessed for gene expression. The analysis also quantified urinary excretion of ECM proteins and peptides.

RESULTS

Of 58 ECM proteins that differed in abundance between cFSGS and FSGS-NOS, 41 were more abundant in cFSGS and 17 in FSGS-NOS. IHC showed that glomerular tuft staining for cathepsin B, cathepsin C, and annexin A3 in cFSGS was significantly greater than in other FSGS variants, in minimal change disease, or in membranous nephropathy. Annexin A3 colocalized with cathepsin B and C, claudin-1, phosphorylated ERK1/2, and CD44, but not with synaptopodin, in parietal epithelial cells (PECs) infiltrating cFSGS glomeruli. Transcripts for cathepsins B and C were increased in FSGS glomeruli compared with normal controls, and urinary excretion of both cathepsins was significantly greater in cFSGS compared with FSGS-NOS. Urinary excretion of ECM-derived peptides was enhanced in cFSGS, although in silico analysis did not identify enhanced excretion of peptides derived from cathepsin B or C.

CONCLUSIONS

ECM differences suggest that glomerular sclerosis in cFSGS differs from that in other FSGS variants. Infiltration of activated PECs may disrupt ECM remodeling in cFSGS. These cells and their cathepsins may be therapeutic targets.

Neuropeptide Y3-36 incorporated into PVAX nanoparticle improves angiogenesis in a murine model of myocardial ischemia

Neuropeptide-Y (NPY) leads to angiogenesis and remodeling of the ischemic myocardium. The objective of this study is to assess the therapeutic potential of NPY in a model of acute myocardial ischemia using a nanoparticles delivery system targeted to tissue with oxidative stress. NPY_3-36 was loaded onto copolyoxalate containing vanillyl alcohol (PVAX) using a double emulsification strategy. Adult C57BL/J6 mice (n = 49) were randomly divided into PVAX-NPY_3-36 (n = 22), Vehicle (Saline) (n = 16), and Sham (n = 11) groups. The ischemia to left anterior descending artery was induced in PVAX-NPY_3-36 or vehicle groups. The tissue was collected at the end of two weeks after assessing the functional and echocardiographic data. There was a significant decrease in infarction size and mortality in PVAX-NPY_3-36 group compared to the Vehicle group (P = 0.01 and P = 0.05). On echocardiography, there was significant improvement in contractility and diastolic parameters (P = 0.01). On pressure-volume loop there was significant increase in stroke volume (P = 0.01), cardiac output (P = 0.01) and ventricular stroke work (P = 0.01) in the PVAX-NPY_3-36 group. On Western blot analysis, there was a significant increase in pro-angiogenic factors Ang-1, TGF-β, PDGF- β and its receptors and VEGF in the ischemic tissue treated with PVAX-NPY_3-36 as compared to Vehicle ischemic tissue (P = 0.01, P = 0.0003, and P < 0.05 respectively). It may be possible to have targeted delivery of labile neurotransmitters NPY_3-36 to the ischemic myocardium using nanoparticle PVAX and achieving angiogenesis and significant functional improvement.

Regulation of the Proteolytic Activity of Cysteine Cathepsins by Oxidants

Besides their primary involvement in the recycling and degradation of proteins in endo-lysosomal compartments and also in specialized biological functions, cysteine cathepsins are pivotal proteolytic contributors of various deleterious diseases. While the molecular mechanisms of regulation via their natural inhibitors have been exhaustively studied, less is currently known about how their enzymatic activity is modulated during the redox imbalance associated with oxidative stress and their exposure resistance to oxidants. More specifically, there is only patchy information on the regulation of lung cysteine cathepsins, while the respiratory system is directly exposed to countless exogenous oxidants contained in dust, tobacco, combustion fumes, and industrial or domestic particles. Papain-like enzymes (clan CA, family C1, subfamily C1A) encompass a conserved catalytic thiolate-imidazolium pair (Cys25-His159) in their active site. Although the sulfhydryl group (with a low acidic pKa) is a potent nucleophile highly susceptible to chemical modifications, some cysteine cathepsins reveal an unanticipated resistance to oxidative stress. Besides an introductory chapter and peculiar attention to lung cysteine cathepsins, the purpose of this review is to afford a concise update of the current knowledge on molecular mechanisms associated with the regulation of cysteine cathepsins by redox balance and by oxidants (e.g., Michael acceptors, reactive oxygen, and nitrogen species).

Cysteinyl cathepsins in cardiovascular diseases

Cysteinyl cathepsins are lysosomal/endosomal proteases that mediate bulk protein degradation in these intracellular acidic compartments. Yet, studies indicate that these proteases also appear in the nucleus, nuclear membrane, cytosol, plasma membrane, and extracellular space. Patients with cardiovascular diseases (CVD) show increased levels of cathepsins in the heart, aorta, and plasma. Plasma cathepsins often serve as biomarkers or risk factors of CVD. In aortic diseases, such as atherosclerosis and abdominal aneurysms, cathepsins play pathogenic roles, but many of the same cathepsins are cardioprotective in hypertensive, hypertrophic, and infarcted hearts. During the development of CVD, cathepsins are regulated by inflammatory cytokines, growth factors, hypertensive stimuli, oxidative stress, and many others. Cathepsin activities in inflammatory molecule activation, immunity, cell migration, cholesterol metabolism, neovascularization, cell death, cell signaling, and tissue fibrosis all contribute to CVD and are reviewed in this article in memory of Dr. Nobuhiko Katunuma for his contribution to the field.