Chronic cathepsin inhibition by E-64 in Dahl salt-sensitive rats

Cathepsin B: The dawn of tumor therapy

Cathepsin B (CTSB) is a key lysosomal protease that plays a crucial role in the development of cancer. This article elucidates the relationship between CTSB and cancer from the perspectives of its structure, function, and role in tumor growth, migration, invasion, metastasis, angiogenesis and autophagy. Further, we summarized the research progress of cancer treatment related drugs targeting CTSB, as well as the potential and advantages of Traditional Chinese medicine in treating tumors by regulating the expression of CTSB.

The Structural Basis of African Swine Fever Virus pS273R Protease Binding to E64 through Molecular Dynamics Simulations

Identification of novel drugs for anti-African swine fever (ASF) applications is of utmost urgency, as it negatively affects pig farming and no effective vaccine or treatment is currently available. African swine fever virus (ASFV) encoded pS273R is a cysteine protease that plays an important role in virus replication. E64, acting as an inhibitor of cysteine protease, has been established as exerting an inhibitory effect on pS273R. In order to obtain a better understanding of the interaction between E64 and pS273R, common docking, restriction docking, and covalent docking were employed to analyze the optimal bonding position between pS273R-E64 and its bonding strength. Additionally, three sets of 100 ns molecular dynamics simulations were conducted to examine the conformational dynamics of pS273R and the dynamic interaction of pS273R-E64, based on a variety of analytical methods including root mean square deviation (RMSD), root mean square fluctuation (RMSF), free energy of ligand (FEL), principal component analysis (PCA), and molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) analysis. The results show that E64 and pS273R exhibited close binding degrees at the activity center of ASFV pS273R protease. The data of these simulations indicate that binding of E64 to pS273R results in a reduction in flexibility, particularly in the ARM region, and a change in the conformational space of pS273R. Additionally, the ability of E64 to interact with polar amino acids such as ASN158, SER192, and GLN229, as well as charged amino acids such as LYS167 and HIS168, seems to be an important factor in its inhibitory effect. Finally, Octet biostratigraphy confirmed the binding of E64 and pS273R with a KD value of 903 uM. Overall, these findings could potentially be utilized in the development of novel inhibitors of pS273R to address the challenges posed by ASFV.

Ion channels and channelopathies in glomeruli

An essential step in renal function entails the formation of an ultrafiltrate that is delivered to the renal tubules for subsequent processing. This process, known as glomerular filtration, is controlled by intrinsic regulatory systems and by paracrine, neuronal, and endocrine signals that converge onto glomerular cells. In addition, the characteristics of glomerular fluid flow, such as the glomerular filtration rate and the glomerular filtration fraction, play an important role in determining blood flow to the rest of the kidney. Consequently, disease processes that initially affect glomeruli are the most likely to lead to end-stage kidney failure. The cells that comprise the glomerular filter, especially podocytes and mesangial cells, express many different types of ion channels that regulate intrinsic aspects of cell function and cellular responses to the local environment, such as changes in glomerular capillary pressure. Dysregulation of glomerular ion channels, such as changes in TRPC6, can lead to devastating glomerular diseases, and a number of channels, including TRPC6, TRPC5, and various ionotropic receptors, are promising targets for drug development. This review discusses glomerular structure and glomerular disease processes. It also describes the types of plasma membrane ion channels that have been identified in glomerular cells, the physiological and pathophysiological contexts in which they operate, and the pathways by which they are regulated and dysregulated. The contributions of these channels to glomerular disease processes, such as focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, as well as the development of drugs that target these channels are also discussed.

Behind every smile there's teeth: Cathepsin B's function in health and disease with a kidney view

Cathepsin B (CatB) is a very abundant lysosomal protease with endo- and carboxydipeptidase activities and even ligase features. In this review, we will provide a general characterization of CatB and describe structure, structure-derived properties and location-dependent proteolytic actions. We depict CatB action within lysosome and its important roles in lysosomal biogenesis, lysosomal homeostasis and autophagy rendering this protease a key player in orchestrating lysosomal functions. Lysosomal leakage and subsequent escape of CatB into the cytosol lead to harmful actions, e.g. the role in activating the NLPR3 inflammasome, affecting immune responses and cell death. The second focus of this review addresses CatB functions in the kidney, i.e. the glomerulus, the proximal tubule and collecting duct with strong emphasis of its role in pathology of the respective segment. Finally, observations regarding CatB functions that need to be considered in cell culture will be discussed. In conclusion, CatB a physiologically important molecule may, upon aberrant expression in different cellular context, become a harmful player effectively showing its teeth behind its smile.

Small molecule inhibitor E-64 exhibiting the activity against African swine fever virus pS273R

African swine fever (ASF) is a viral disease in swine that results in high mortality in domestic pigs and causes considerable economic losses. Currently, there is no effective vaccine or drugs available for treatment. Identification of new anti-ASFV drugs is urgently needed. Here, the pS273R protein of the African swine fever virus (ASFV) is a specific SUMO-1-like cysteine protease that plays an important role in its replication process. To inhibit virus replication and improve treatment options, a set of small-molecule compounds, targeted inhibitors against the ASFV pS273R protease, were obtained through molecular screening by homology modeling and molecular docking based on structural information of pS273R. Our results clearly demonstrated that the 14th carbon atom of the cysteinase inhibitor E-64 could form one CS covalent bond with the Cys 232 amino acid of the pS273R protease and seven additional hydrogen bonds to maintain a stable binding state. Simultaneously, cell viability, immunophenotyping, and in vitro enzyme activity inhibition assays were performed to comprehensively evaluate E-64 characteristics. Our findings demonstrated that 4 mmol/L E-64 could effectively inhibit the enzyme activity center of the pS273R protease by preventing pS273R protease from lysing pp62, while promoting the upregulation of immune-related cytokines at the transcription level. Moreover, cell viability results revealed that 4 mmol/L E-64 was not cytotoxic. Taken together, we identified a novel strategy to potentially prevent ASFV infection in pigs by blocking the activity of pS273R protease with a small-molecule inhibitor.

Synthesis of the Novel Covalent Cysteine Proteases Inhibitor with Iodoacetic Functional Group

This work presents the synthesis of the novel covalent inhibitor of cysteine proteases where epoxide has been replaced by the iodoacetyl functional group. The molecule, similar in action to E-64 and DCG-04, the commonly applied inhibitors, is additionally biotinylated and contains tyrosyl iodination sites. The Fmoc solid phase synthesis has been applied. Conjugation of iodoacetic acid with the peptide was optimized by testing different conjugation agents. The purity of the final product was verified by mass spectrometry and its bioactivity was tested by incubation with a model cysteine protease—staphopain C. Finally, it was shown that the synthesized inhibitor binds to the protein at the ratio of 1:1. More detailed analysis by means of tandem mass spectrometry proved that the inhibitor binds to the cysteine present in the active site of the enzyme.

The podocyte protease web: uncovering the gatekeepers of glomerular disease

Proteases regulate glomerular physiology. The last decade has revealed a multitude of podocyte proteases that govern the glomerular response to numerous chemical, mechanical, and metabolic cues. These proteases form a protein signaling web that integrates stress stimuli and serves as a key controller of the glomerular microenvironment. Both the extracellular and intracellular proteolytic networks are perturbed in focal segmental glomerulosclerosis, as well as hypertensive and diabetic nephropathy. Accordingly, the highly intertwined podocyte protease web is an integrative part of the podocyte's damage response. Novel mass spectrometry-based technologies will help to untangle this proteolytic network: functional readouts acquired from deep podocyte proteomics, single glomerular proteomics, and degradomics have exposed unanticipated protease activity in podocytes. Future efforts should characterize the interdependency and upstream regulation of key proteases, along with their role in promoting tissue heterogeneity in glomerular diseases. These efforts will not only illuminate the machinery of podocyte proteostasis but also reveal avenues for therapeutic intervention in the podocyte protease web.

The Calcium-Dependent Protease Calpain-1 Links TRPC6 Activity to Podocyte Injury

BACKGROUND

The hallmark of podocytopathies, such as FSGS, is podocyte injury resulting in proteinuria. Transient receptor potential channel C6 (TRPC6) is a calcium-conducting ion channel expressed at the slit diaphragm. TRPC6 gain-of-function mutations and glomerular TRPC6 overexpression are associated with proteinuria. However, the pathways linking TRPC6 to podocyte injury, which is characterized by loss of the slit diaphragm protein nephrin, activation of several intracellular pathways (including calcineurin-NFAT signaling), and cytoskeletal rearrangement, remain elusive.

METHODS

We tested whether the calcium-dependent protease calpain-1 mediates TRPC6-dependent podocyte injury in human and experimental FSGS and cultured podocytes.

RESULTS

Compared with kidneys of healthy controls, kidneys of patients with FSGS had increased TRPC6 expression, increased calpain and calcineurin activity, and reduced expression of the calpain target Talin-1, which links the actin cytoskeleton to integrins and is critical for podocyte cytoskeletal stability. In a rat model of human FSGS, increased glomerular and urinary calpain activity associated with reduced Talin-1 abundance, enhanced calcineurin activity, and increased proteinuria. Treatment with the calpain inhibitor calpeptin prevented these effects. In cultured podocytes, pharmacologic stimulation of TRPC6-dependent calcium influx increased calpain-1 and calcineurin activity and reduced Talin-1 expression, and knockdown of TRPC6 or calpain-1 prevented these effects.

CONCLUSIONS

We elucidated a novel mechanism that links TRPC6 activity to calpain-1 activation and through Talin-1 loss and possibly, calcineurin activation, the podocyte injury characterizing FSGS. Therefore, calpain-1 and/or TRPC6 inhibition could be future therapeutic options to treat patients with FSGS or other podocytopathies.

Chronic cathepsin inhibition by E-64 in Dahl salt-sensitive rats

Cysteine cathepsins are lysosomal enzymes expressed in the kidneys and other tissues, and are involved in the maturation and breakdown of cellular proteins. They have been shown to be integrally involved in the progression of many cardiovascular and renal diseases. The goal of this study was to determine the involvement of cysteine cathepsins in the development of salt‐sensitive hypertension and associated kidney damage. In our experiments, Dahl salt‐sensitive (SS) rats were fed an 8% high salt NaCl diet and intravenously infused with the irreversible cysteine cathepsin inhibitor E‐64 (1 mg/day) or the vehicle (control). Both the control and E‐64 infused groups developed significant hypertension and kidney damage, and no difference of the mean arterial pressure and the hypertension‐associated albuminuria was observed between the groups. We next tested basal calcium levels in the podocytes of both control and infused groups using confocal calcium imaging. Basal calcium did not differ between the groups, indicative of the lack of a protective or aggravating influence by the cathepsin inhibition. The efficacy of E‐64 was tested in Western blotting. Our findings corresponded to the previously reported, E‐64 induced increase in cathepsin B and L abundance. We conclude that the inhibition of cysteine cathepsins by E‐64 does not have any effects on the blood pressure development and kidney damage, at least under the studied conditions of this model of SS hypertension.