Roles for cathepsins S, L, and B in insulitis and diabetes in the NOD mouse

hCeO2@CA-074Me Nanoparticles Alleviate Inflammation and Improve Osteogenic Microenvironment by Regulating the CTSB-NLRP3 Signaling Pathway

Background

It is well established that the interaction between osteogenesis and inflammation can impact bone tissue regeneration. The use of nanoparticles to treat and alleviate inflammation at the molecular level has the potential to improve the osteogenic microenvironment and serve as a therapeutic approach.

Methods

We have synthesized new hollow cerium oxide nanoparticles and doped with cathepsin B inhibitor (CA-074Me) to create novel hCeO2@CA-074Me NPs. We characterized the surface morphology and physicochemical properties of hCeO2@CA-074Me NPs. Macrophage RAW 264.7 was cultured with hCeO2@CA-074Me NPs using P. gingivalis-LPS (P.g-LPS) stimulation as a model of inflammation. RT-PCR and Western blot analysis was employed to evaluate the effects of hCeO2@CA-074Me NPs on macrophage phenotype and the CTSB-NLRP3 signaling pathway. To further investigate the inflammatory osteogenic microenvironment, MC3T3-E1 cells were cultured with P.g-LPS to create an in vitro osteogenic conditions under inflammation. The cells were then co-cultured with hCeO2@CA-074Me NPs for 7, 14, and 21 d. The osteogenic ability was evaluated using ALP staining, ALP quantitative analysis, alizarin red staining, and RT-PCR analysis.

Results

Findings clearly demonstrated that hCeO2@CA-074Me NPs could effectively reduce the production of ROS and inhibited CTSB-NLRP3 signal pathway, thereby significantly attenuating the damage caused by the cellular inflammatory response. hCeO2@CA-074Me NPs could also induce the polarization of macrophages towards anti-inflammatory M2 phenotype. Additionally, results confirmed that hCeO2@CA-074Me NPs could inhibit inflammation and ameliorate osteogenic microenvironment, thus promoting the osteogenesis of MC3T3-E1 cells.

Conclusion

The synthetic hCeO2@CA-074Me NPs could able to modify the osteogenic microenvironment under inflammatory conditions by simultaneously inhibiting the CTSB-NLRP3 signaling pathway and regulating the macrophage phenotype through their ability to scavenge ROS. Based on these findings, our study may offer a promising approach for managing inflammatory bone damage.

Uncovering the molecular networks of ferroptosis in the pathogenesis of type 2 diabetes and its complications: a multi-omics investigation

BACKGROUND

Diabetes is a multi-factorial disorder and related complications constitute one of the principal causes of global mortality and disability. The role of ferroptosis in diabetes and its complications is intricate and significant. This study endeavors to disclose the role of ferroptosis in the aforementioned diseases from multiple perspectives through multi-omics.

METHODS

We performed genetic correlation analyses via the Linkage Disequilibrium Score and High-Definition Likelihood approaches for type 2 diabetes (T2D) and its complications. The data concerning the expression of ferroptosis-related genes (FRGs) were obtained from the meta-analysis of studies on gene expression and protein abundance. Mendelian randomization analyses and cross-validation were implemented using the discovery cohort, replication cohort, and imaging genomics cohort of T2D and its complications. Moreover, we conducted colocalization analyses on T2D and tissue-specific single-cell RNA sequencing investigations on the complications to complement the results.

RESULTS

Genetic association analysis indicated that the selected datasets could be incorporated into a secondary analysis of T2D complications. In the primary analysis, six FRGs (CDKN1A, ENO3, FURIN, RARRES2, TYRO3, and YTHDC2) were found to be positively associated with T2D risk. Conversely, eight FRGs (ARNTL, CAMKK2, CTSB, FADS2, KDM5A, MEG3, SREBF1, and STAT3) were inversely associated with T2D risk. The 14 FRGs were included in the secondary analysis. Within the FRGs, which received full support from both the discovery and replication cohorts, and were further validated by imaging genomics, higher levels of CDKN1A were positively associated with DKD risk. Higher levels of CAMKK2 and KDM5A were associated with a decreased risk of DKD. For DCM, higher levels of CTSB were positively associated with DCM risk. And genetically predicted higher levels of ARNTL and SREBF1 were associated with a decreased risk of NAFLD. Finally, we validated the tissue-specific expression of each complication with scRNA-seq datasets.

CONCLUSIONS

This study identified FRGs in relation to T2D and its complications, which may enhance the understanding of the pathogenic mechanisms of their development. Meanwhile, it offers cross-validation for imaging genomics and further indicates the direction for non-invasive diagnosis.

Identification of New Polyacetylenes from Dendropanax morbifera with PPAR-α Activity Study

Dendropanax morbifera Leveille is a traditional medicine used to treat migraine headache and dysmenorrhea. In this study, three polyacetylenes, methyl (10E,9R,16R)-16-acetoxy-9-hydroxyoctadeca-10,17-dien-12,14-diynoate (1), methyl (10E,9R,16S)-9,16-dihydroxyoctadeca-10-en-12,14-diynoate (2), and methyl (10Z,9R,16S)-9,16-dihydroxyoctadeca-10,17-dien-12,14-diynoate (3), were isolated from the aerial parts of D. morbifera, together with seven known compounds (4-10). Importantly, the isolates (6 and 8) were found in the family Araliaceae for the first time in this study. Compounds 1-10 were evaluated for their binding affinity to AMPK and CTSS receptors using in silico docking simulations. Only compound 7 increased the protein expression levels of PPAR-α, Sirt1, and AMPK when administered to HepG2 cells as a PPAR-α agonist. On the other hand, 7 did not produce any significant reduction in CTSS activity. This study could pave the way for the discovery of novel treatments from D. morbifera targeting PPAR-α and AMPK.

Lysosomal physiology and pancreatic lysosomal stress in diabetes mellitus

Endocrine and exocrine functions of the pancreas control nutritional absorption, utilisation and systemic metabolic homeostasis. Under basal conditions, the lysosome is pivotal in regulating intracellular organelles and metabolite turnover. In response to acute or chronic stress, the lysosome senses metabolic flux and inflammatory challenges, thereby initiating the adaptive programme to re-establish cellular homeostasis. A growing body of evidence has demonstrated the pathophysiological relevance of the lysosomal stress response in metabolic diseases in diverse sets of tissues/organs, such as the liver and the heart. In this review, we discuss the pathological relevance of pancreatic lysosome stress in diabetes mellitus. We begin by summarising lysosomal biology, followed by exploring the immune and metabolic functions of lysosomes and finally discussing the interplay between lysosomal stress and the pathogenesis of pancreatic diseases. Ultimately, our review aims to enhance our understanding of lysosomal stress in disease pathogenesis, which could potentially lead to the discovery of innovative treatment methods for these conditions.

Elevated Cathepsin S Serum Levels in New-Onset Type 1 Diabetes and Autoantibody-Positive Siblings

Accumulating data suggest a role for the lysosomal protease cathepsin S (CTSS) in type 1 diabetes. Circulating CTSS is increased in type 1 diabetes; however, whether CTSS has protective or deleterious effects is unclear. The study's objectives were to examine the biomarker potential of CTSS in new-onset type 1 diabetes, and to investigate the expression and secretion of CTSS in human islets and β-cells. The CTSS level was analyzed in serum from children with new-onset type 1 diabetes and autoantibody-positive and -negative siblings by ELISA. The expression and secretion of CTSS were evaluated in isolated human islets and EndoC-βH5 cells by real-time qPCR, immunoblotting, and ELISA. The CTSS serum level was elevated in children with new-onset type 1 diabetes and positively associated with autoantibody status in healthy siblings. Human islets and EndoC-βH5 cells demonstrated induction and secretion of CTSS after exposure to proinflammatory cytokines, a model system of islet inflammation. Analysis of publicly available single-cell RNA sequencing data on human islets showed that elevated CTSS expression was exclusive for the β-cells in donors with type 1 diabetes as compared with nondiabetic donors. These findings suggest a potential of CTSS as a diagnostic biomarker in type 1 diabetes.

ARTICLE HIGHLIGHTS

Is tear proteome profile a predictor of developing uveitis in ANA-positive patients with oligoarticular juvenile idiopathic arthritis?

PURPOSE

Although less than one-third of anti-nuclear antibody (ANA) positive patients with oJIA develop uveitis, ANA positivity is still the most well-known marker for assessing the risk of uveitis in oligoarticular JIA (oJIA). Therefore, novel biomarkers are needed to better assess the risk of developing uveitis. For this purpose, we performed a comparative tear proteome analysis of uveitis patients to reveal the identity of differentially regulated proteins.

DESIGN

Tear samples were collected using the Schirmer strips in 7 oJIA and 7 oJIA patients with uveitis (oJIA-U). All oJIA-U patients had developed bilateral anterior uveitis and were inactive and topical treatment-free.

METHODS

The nHPLC LC-MS/MS system was used for protein identification and label-free proteome comparisons. The PANTHER and STRING analyses were carried out using UniProt accession numbers of the identified proteins.

RESULTS

Patient characteristics, e.g., age, gender, disease duration, and treatments were similar. For protein identification, three different databases were searched. Twenty-two, 147, and 258 database searches, respectively. Of these, 15 were common to all three proteome databases. Of these 15 proteins, 10 proteins were upregulated, and 2 were downregulated, based on the twofold regulation criteria. The upregulated proteins were, namely, cystatin-S, secretoglobin family 1D member, opiorphin prepropeptide, mammaglobin-B, lysozyme C, mesothelin, immunoglobulin kappa constant, extracellular glycoprotein lacritin, beta-2-microglobulin, and immunoglobulin J chain. The downregulated proteins were dermcidin and prolactin-inducible protein. Among the differentially regulated proteins, cystatin-S was the most regulated protein with an 18-fold upregulation ratio in tear samples from uveitis patients.

CONCLUSION

Here, the identities and regulation ratios of several proteins were revealed when tear samples from uveitis patients were compared to patients without uveitis. These proteins are putative biomarkers for assessing uveitis risk and require further attention.

Hederagenin inhibits high glucose-induced fibrosis in human renal cells by suppression of NLRP3 inflammasome activation through reducing cathepsin B expression

Diabetic nephropathy is a major complication of diabetes mellitus and is related to dysfunction of renal cells. Hederagenin is a triterpenoid saponin from some Chinese herbs with anti-inflammatory and anti-diabetic activities. However, its role in diabetic nephropathy progression is still obscure. This study aimed to explore the effects of hederagenin on renal cell dysfunction in vitro. Human renal mesangial cells (HRMCs) and human renal proximal tubular epithelial cells (HRPTEpiCs) were cultured under high glucose (HG) conditions to mimic diabetic nephropathy-like injury. Cell proliferation was evaluated by CCK-8. mRNA and protein levels were determined by qRT-PCR and western blotting, respectively. The secretion levels of fibrosis-related biomarkers were analyzed by ELISA. Results showed that hederagenin reduced HG-induced proliferation increase in HRMCs and HRPTEpiCs. Hederagenin attenuated HG-induced increase in mRNA and protein expression of NLRP3, ASC, and IL-1β. Hederagenin also suppressed HG-induced increase in mRNA and secretion levels of FN, Col. IV, PAI-1, and TGF-β1. NLRP3 inhibitor MCC950 attenuated HG-induced fibrosis of renal cells, and its activator nigericin reversed the suppressive effect of hederagenin on HG-induced fibrosis. Bioinformatics analysis predicted cathepsin B (CTSB) as a target of hederagenin to modulate NOD-like receptor (NLR) pathway. Hederagenin decreased CTSB level, and CTSB overexpression reversed the suppressive effect of hederagenin on HG-induced NLRP3 inflammasome activation and fibrosis in HRMCs and HRPTEpiCs. In conclusion, hederagenin attenuates HG-induced fibrosis of renal cells by inhibiting NLRP3 inflammasome activation via reducing CTSB expression, indicating a therapeutic potential of hederagenin in diabetic nephropathy.

Cathepsin S inhibition in dendritic cells prevents Th17 cell differentiation in perivascular adipose tissues following vascular injury in diabetic rats

In the context of diabetes mellitus (DM), the circulating cathepsin S (CTSS) level is significantly higher in the cardiovascular disease group. Therefore, this study was designed to investigate the role of CTSS in restenosis following carotid injury in diabetic rats. To induce DM, 60 mg/kg of streptozotocin (STZ) in citrate buffer was injected intraperitoneally into Sprague-Dawley rats. After successful modeling of DM, wire injury of the rat carotid artery was performed, followed by adenovirus transduction. Levels of blood glucose and Th17 cell surface antigens including ROR-γt, IL-17A, IL-17F, IL-22, and IL-23 in perivascular adipose tissues (PVAT) were evaluated. For in vitro analysis, human dendritic cells (DCs) were treated with 5.6-25 mM glucose for 24 h. The morphology of DCs was observed using an optical microscope. CD4+ T cells derived from human peripheral blood mononuclear cells were cocultured with DCs for 5 days. Levels of IL-6, CTSS, ROR-γt, IL-17A, IL-17F, IL-22 and IL-23 were measured. Flow cytometry was conducted to detect DC surface biomarkers (CD1a, CD83, and CD86) and Th17 cell differentiation. The collected DCs presented a treelike shape and were positive for CD1a, CD83, and CD86. Glucose impaired DC viability at the dose of 35 mM. Glucose treatment led to an increase in CTSS and IL-6 expression in DCs. Glucose-treated DCs promoted the differentiation of Th17 cells. CTSS depletion downregulated IL-6 expression and inhibited Th17 cell differentiation in vitro and in vivo. CTSS inhibition in DCs inhibits Th17 cell differentiation in PVAT tissues from diabetic rats following vascular injury.

Impact of the Recognition Part of Dipeptidyl Nitroalkene Compounds on the Inhibition Mechanism of Cysteine Proteases Cruzain and Cathepsin L

Cysteine proteases (CPs) are an important class of enzymes, many of which are responsible for several human diseases. For instance, cruzain of protozoan parasite Trypanosoma cruzi is responsible for the Chagas disease, while the role of human cathepsin L is associated with some cancers or is a potential target for the treatment of COVID-19. However, despite paramount work carried out during the past years, the compounds that have been proposed so far show limited inhibitory action against these enzymes. We present a study of proposed covalent inhibitors of these two CPs, cruzain and cathepsin L, based on the design, synthesis, kinetic measurements, and QM/MM computational simulations on dipeptidyl nitroalkene compounds. The experimentally determined inhibition data, together with the analysis and the predicted inhibition constants derived from the free energy landscape of the full inhibition process, allowed describing the impact of the recognition part of these compounds and, in particular, the modifications on the P2 site. The designed compounds and, in particular, the one with a bulky group (Trp) at the P2 site show promising in vitro inhibition activities against cruzain and cathepsin L for use as a starting lead compound in the development of drugs with medical applications for the treatment of human diseases and future designs.

Heterochronic Parabiosis Causes Dacryoadenitis in Young Lacrimal Glands

Aging is associated with inflammation and oxidative stress in the lacrimal gland (LG). We investigated if heterochronic parabiosis of mice could modulate age-related LG alterations. In both males and females, there were significant increases in total immune infiltration in isochronic aged LGs compared to that in isochronic young LGs. Male heterochronic young LGs were significantly more infiltrated compared to male isochronic young LGs. While both females and males had significant increases in inflammatory and B-cell-related transcripts in isochronic and heterochronic aged LGs compared to levels isochronic and heterochronic young LGs, females had a greater fold expression of some of these transcripts than males. Through flow cytometry, specific subsets of B cells were increased in the male heterochronic aged LGs compared to those in male isochronic aged LGs. Our results indicate that serum soluble factors from young mice were not enough to reverse inflammation and infiltrating immune cells in aged tissues and that there were specific sex-related differences in parabiosis treatment. This suggests that age-related changes in the LG microenvironment/architecture participate in perpetuating inflammation, which is not reversible by exposure to youthful systemic factors. In contrast, male young heterochronic LGs were significantly worse than their isochronic counterparts, suggesting that aged soluble factors can enhance inflammation in the young host. Therapies that aim at improving cellular health may have a stronger impact on improving inflammation and cellular inflammation in LGs than parabiosis.

The Key Role of Lysosomal Protease Cathepsins in Viral Infections

Cathepsins encompass a family of lysosomal proteases that mediate protein degradation and turnover. Although mainly localized in the endolysosomal compartment, cathepsins are also found in the cytoplasm, nucleus, and extracellular space, where they are involved in cell signaling, extracellular matrix assembly/disassembly, and protein processing and trafficking through the plasma and nuclear membrane and between intracellular organelles. Ubiquitously expressed in the body, cathepsins play regulatory roles in a wide range of physiological processes including coagulation, hormone secretion, immune responses, and others. A dysregulation of cathepsin expression and/or activity has been associated with many human diseases, including cancer, diabetes, obesity, cardiovascular and inflammatory diseases, kidney dysfunctions, and neurodegenerative disorders, as well as infectious diseases. In viral infections, cathepsins may promote (1) activation of the viral attachment glycoproteins and entry of the virus into target cells; (2) antigen processing and presentation, enabling the virus to replicate in infected cells; (3) up-regulation and processing of heparanase that facilitates the release of viral progeny and the spread of infection; and (4) activation of cell death that may either favor viral clearance or assist viral propagation. In this review, we report the most relevant findings on the molecular mechanisms underlying cathepsin involvement in viral infection physiopathology, and we discuss the potential of cathepsin inhibitors for therapeutical applications in viral infectious diseases.

Mucopolysaccharidosis Type IVA: Extracellular Matrix Biomarkers in Cardiovascular Disease

Cardiovascular disease (CVD) in Mucopolysaccharidosis Type IVA (Morquio A), signified by valvular disease and cardiac hypertrophy, is the second leading cause of death and remains untouched by current therapies. Enzyme replacement therapy (ERT) is the gold-standard treatment for MPS disorders including Morquio A. Early administration of ERT improves outcomes of patients from childhood to adulthood while posing new challenges including prognosis of CVD and ERT's negligible effect on cardiovascular health. Thus, having accurate biomarkers for CVD could be critical. Here we show that cathepsin S (CTSS) and elastin (ELN) can be used as biomarkers of extracellular matrix remodeling in Morquio A disease. We found in a cohort of 54 treatment naïve Morquio A patients and 74 normal controls that CTSS shows promising attributes as a biomarker in young Morquio A children. On the other hand, ELN shows promising attributes as a biomarker in adolescent and adult Morquio A. Plasma/urine keratan sulfate (KS), and urinary glycosaminoglycan (GAG) levels were significantly higher in Morquio A patients (p < 0.001) which decreased with age of patients. CTSS levels did not correlate with patients' phenotypic severity but differed significantly between patients (median range 5.45-8.52 ng/mL) and normal controls (median range 9.61-15.9 ng/mL; p < 0.001). We also studied α -2-macroglobulin (A2M), C-reactive protein (CRP), and circulating vascular cell adhesion molecule-1 (sVCAM-1) in a subset of samples to understand the relation between ECM biomarkers and the severity of CVD in Morquio A patients. Our experiments revealed that CRP and sVCAM-1 levels were lower in Morquio A patients compared to normal controls. We also observed a strong inverse correlation between urine/plasma KS and CRP (p = 0.013 and p = 0.022, respectively) in Morquio A patients as well as a moderate correlation between sVCAM-1 and CTSS in Morquio A patients at all ages (p = 0.03). As the first study to date investigating CTSS and ELN levels in Morquio A patients and in the normal population, our results establish a starting point for more elaborate studies in larger populations to understand how CTSS and ELN levels correlate with Morquio A severity.

The Role of Proteases and Serpin Protease Inhibitors in β-Cell Biology and Diabetes

Regulation of the equilibrium between proteases and their inhibitors is fundamental to health maintenance. Consequently, developing a means of targeting protease activity to promote tissue regeneration and inhibit inflammation may offer a new strategy in therapy development for diabetes and other diseases. Specifically, recent efforts have focused on serine protease inhibitors, known as serpins, as potential therapeutic targets. The serpin protein family comprises a broad range of protease inhibitors, which are categorized into 16 clades that are all extracellular, with the exception of Clade B, which controls mostly intracellular proteases, including both serine- and papain-like cysteine proteases. This review discusses the most salient, and sometimes opposing, views that either inhibition or augmentation of protease activity can bring about positive outcomes in pancreatic islet biology and inflammation. These potential discrepancies can be reconciled at the molecular level as specific proteases and serpins regulate distinct signaling pathways, thereby playing equally distinct roles in health and disease development.

Cathepsin S is a novel target for age-related dry eye

Cathepsin S (Ctss) is a protease that is proinflammatory on epithelial cells. The purpose of this study was to investigate the role of Ctss in age-related dry eye disease. Ctss^-/- mice [in a C57BL/6 (B6) background] of different ages were compared to B6 mice. Ctss activity in tears and lacrimal gland (LG) lysates was measured. The corneal barrier function was investigated in naïve mice or after topical administration of Ctss eye drops 5X/day for two days. Eyes were collected, and conjunctival goblet cell density was measured in PAS-stained sections. Immunoreactivity of the tight junction proteins, ZO-1 and occludin, was investigated in primary human cultured corneal epithelial cells (HCEC) without or with Ctss, with or without a Ctss inhibitor. A significant increase in Ctss activity was observed in the tears and LG lysates in aged B6 compared to young mice. This was accompanied by higher Ctss transcripts and protein expression in LG and spleen. Compared to B6, 12 and 24-month-old Ctss^-/- mice did not display age-related corneal barrier disruption and goblet cell loss. Treatment of HCEC with Ctss for 48 h disrupted occludin and ZO-1 immunoreactivity compared to control cells. This was prevented by the Ctss inhibitor LY3000328 or Ctss-heat inactivation. Topical reconstitution of Ctss in Ctss^-/- mice for two days disrupted corneal barrier function. Aging on the ocular surface is accompanied by increased expression and activity of the protease Ctss. Our results suggest that cathepsin S modulation might be a novel target for age-related dry eye disease.

Cathepsin C Regulates Cytokine-Induced Apoptosis in β-Cell Model Systems

Emerging evidence suggests that several of the lysosomal cathepsin proteases are genetically associated with type 1 diabetes (T1D) and participate in immune-mediated destruction of the pancreatic β cells. We previously reported that the T1D candidate gene cathepsin H is downregulated by pro-inflammatory cytokines in human pancreatic islets and regulates β-cell function, apoptosis, and disease progression in children with new-onset T1D. In the present study, the objective was to investigate the expression patterns of all 15 known cathepsins in β-cell model systems and examine their role in the regulation of cytokine-induced apoptosis. Real-time qPCR screening of the cathepsins in human islets, 1.1B4 and INS-1E β-cell models identified several cathepsins that were expressed and regulated by pro-inflammatory cytokines. Using small interfering RNAs to knock down (KD) the cytokine-regulated cathepsins, we identified an anti-apoptotic function of cathepsin C as KD increased cytokine-induced apoptosis. KD of cathepsin C correlated with increased phosphorylation of JNK and p38 mitogen-activated protein kinases, and elevated chemokine CXCL10/IP-10 expression. This study suggests that cathepsin C is a modulator of β-cell survival, and that immune modulation of cathepsin expression in islets may contribute to immune-mediated β-cell destruction in T1D.

Lysosomal cathepsin creates chimeric epitopes for diabetogenic CD4 T cells via transpeptidation

The identification of the peptide epitopes presented by major histocompatibility complex class II (MHCII) molecules that drive the CD4 T cell component of autoimmune diseases has presented a formidable challenge over several decades. In type 1 diabetes (T1D), recent insight into this problem has come from the realization that several of the important epitopes are not directly processed from a protein source, but rather pieced together by fusion of different peptide fragments of secretory granule proteins to create new chimeric epitopes. We have proposed that this fusion is performed by a reverse proteolysis reaction called transpeptidation, occurring during the catabolic turnover of pancreatic proteins when secretory granules fuse with lysosomes (crinophagy). Here, we demonstrate several highly antigenic chimeric epitopes for diabetogenic CD4 T cells that are produced by digestion of the appropriate inactive fragments of the granule proteins with the lysosomal protease cathepsin L (Cat-L). This pathway has implications for how self-tolerance can be broken peripherally in T1D and other autoimmune diseases.

Interfering with Host Proteases in SARS-CoV-2 Entry as a Promising Therapeutic Strategy

Due to its fast international spread and substantial mortality, the coronavirus disease COVID-19 evolved to a global threat. Since currently, there is no causative drug against this viral infection available, science is striving for new drugs and approaches to treat the new disease. Studies have shown that the cell entry of coronaviruses into host cells takes place through the binding of the viral spike (S) protein to cell receptors. Priming of the S protein occurs via hydrolysis by different host proteases. The inhibition of these proteases could impair the processing of the S protein, thereby affecting the interaction with the host-cell receptors and preventing virus cell entry. Hence, inhibition of these proteases could be a promising strategy for treatment against SARS-CoV-2. In this review, we discuss the current state of the art of developing inhibitors against the entry proteases furin, the transmembrane serine protease type-II (TMPRSS2), trypsin, and cathepsin L.

De-coding genetic risk variants in type 1 diabetes

The conceptual basis for a genetic predisposition underlying the risk for developing type 1 diabetes (T1D) predates modern human molecular genetics. Over half of the genetic risk has been attributed to the human leukocyte antigen (HLA) class II gene region and to the insulin (INS) gene locus - both thought to confer direction of autoreactivity and tissue specificity. Notwithstanding, questions still remain regarding the functional contributions of a vast array of minor polygenic risk variants scattered throughout the genome that likely influence disease heterogeneity and clinical outcomes. Herein, we summarize the available literature related to the T1D-associated coding variants defined at the time of this review, for the genes PTPN22, IFIH1, SH2B3, CD226, TYK2, FUT2, SIRPG, CTLA4, CTSH and UBASH3A. Data from genotype-selected human cohorts are summarized, and studies from the non-obese diabetic (NOD) mouse are presented to describe the functional impact of these variants in relation to innate and adaptive immunity as well as to β-cell fragility, with expression profiles in tissues and peripheral blood highlighted. The contribution of each variant to progression through T1D staging, including environmental interactions, are discussed with consideration of how their respective protein products may serve as attractive targets for precision medicine-based therapeutics to prevent or suspend the development of T1D.

Hidden in Plain View: Discovery of Chimeric Diabetogenic CD4 T Cell Neo-Epitopes

The T cell antigens driving autoimmune Type 1 Diabetes (T1D) have been pursued for more than three decades. When diabetogenic CD4 T cell clones and their relevant MHCII antigen presenting alleles were first identified in rodents and humans, the path to discovering the peptide epitopes within pancreatic beta cell proteins seemed straightforward. However, as experimental results accumulated, definitive data were often absent or controversial. Work within the last decade has helped to clear up some of the controversy by demonstrating that a number of the important MHCII presented epitopes are not encoded in the natural beta cell proteins, but in fact are fusions between peptide fragments derived from the same or different proteins. Recently, the mechanism for generating these MHCII diabetogenic chimeric epitopes has been attributed to a form of reverse proteolysis, called transpeptidation, a process that has been well-documented in the production of MHCI presented epitopes. In this mini-review we summarize these data and their implications for T1D and other autoimmune responses.

The ocular surface immune system through the eyes of aging

Since the last century, advances in healthcare, housing, and education have led to an increase in life expectancy. Longevity is accompanied by a higher prevalence of age-related diseases, such as cancer, autoimmunity, diabetes, and infection, and part of this increase in disease incidence relates to the significant changes that aging brings about in the immune system. The eye is not spared by aging either, presenting with age-related disorders of its own, and interestingly, many of these diseases have immune pathophysiology. Being delicate organs that must be exposed to the environment in order to capture light, the eyes are endowed with a mucosal environment that protects them, the so-called ocular surface. As in other mucosal sites, immune responses at the ocular surface need to be swift and potent to eliminate threats but are at the same time tightly controlled to prevent excessive inflammation and bystander damage. This review will detail how aging affects the mucosal immune response of the ocular surface as a whole and how this process relates to the higher incidence of ocular surface disease in the elderly.

The Role of T Cell Receptor Signaling in the Development of Type 1 Diabetes

T cell receptor (TCR) signaling influences multiple aspects of CD4⁺ and CD8⁺ T cell immunobiology including thymic development, peripheral homeostasis, effector subset differentiation/function, and memory formation. Additional T cell signaling cues triggered by co-stimulatory molecules and cytokines also affect TCR signaling duration, as well as accessory pathways that further shape a T cell response. Type 1 diabetes (T1D) is a T cell-driven autoimmune disease targeting the insulin producing β cells in the pancreas. Evidence indicates that dysregulated TCR signaling events in T1D impact the efficacy of central and peripheral tolerance-inducing mechanisms. In this review, we will discuss how the strength and nature of TCR signaling events influence the development of self-reactive T cells and drive the progression of T1D through effects on T cell gene expression, lineage commitment, and maintenance of pathogenic anti-self T cell effector function.

The Clinical Significance and Potential Role of Cathepsin S in IgA Nephropathy

Objective: Cathepsin S (CTSS) is an important lysosomal cysteine protease. This study aimed at investigating the clinical significance of CTSS and underlying mechanism in immunoglobulin A nephropathy (IgAN). Methods: This study recruited 25 children with IgAN and age-matched controls and their serum CTSS levels were measured by enzyme-linked immunosorbent assay (ELISA). Following induction of IgAN in rats, their kidney CTSS expression, IgA accumulation and serum CTSS were characterized by immunohistochemistry, immunofluorescence, and ELISA. The impact of IgA1 aggregates on the proliferation of human mesangial cells (HMCs) was determined by Cell Counting Kit-8 and Western blot analysis of Ki67. Results: Compared to the non-IgAN controls, significantly up-regulated CTSS expression was detected in the renal tissues, particularly in the glomerular mesangium and tubular epithelial cells of IgAN patients, accompanied by higher levels of serum CTSS (P < 0.05), which were correlated with the levels of 24-h-urine proteins and microalbumin and urine erythrocytes and grades of IgAN Lee's classification in children with IgAN (P < 0.01 for all). Following induction of IgAN, we detected inducible IgA accumulation and increased levels of CTSS expression in the glomerular mesangium and glomerular damages in rats, which were mitigated by LY3000328, a CTSS-specific inhibitor. Treatment with LY3000328 significantly mitigated the Ki67 expression in the kidney of IgAN rats (P < 0.01) and significantly minimized the IgA1 aggregate-stimulated proliferation of HMCs and their Ki67 expression in vitro (P < 0.01). Conclusions: CTSS promoted the proliferation of glomerular mesangial cells, contributing to the pathogenesis of IgAN and may be a new therapeutic target for intervention of aberrant mesangial cell proliferation during the process of IgAN.

Usefulness of Cathepsin S to Predict Risk for Obstructive Sleep Apnea among Patients with Type 2 Diabetes

Background

Obstructive sleep apnea (OSA) was highly prevalent in patients with type 2 diabetes (T2D). Cathepsin S (CTSS), a cysteine protease, is involved in the inflammatory activity in T2D and hypoxia conditions. The aim of the study was to evaluate whether CTSS could be involved in the inflammatory reaction of OSA in patients with T2D.

Methods

We included 158 participants in this study matched for age, gender, and body mass index in 4 groups (control, non-OSA&T2D, OSA&non-T2D, and OSA&T2D). After overnight polysomnography, we collected the clinical data including anthropometrical characteristics, blood pressure, and fasting blood samples in the morning. Plasma CTSS concentration was evaluated using the human Magnetic Luminex Assay.

Results

Compared with the control group, both the non-OSA&T2D group and the OSA&non-T2D group showed higher CTSS levels. Plasma CTSS expression was significantly increased in subjects with OSA&T2D compared to subjects with non-OSA&T2D. The OSA&T2D group had higher CTSS levels than the OSA&non-T2D group, but there were no statistically significant differences. Plasma CTSS levels showed significant correlation with the apnea-hypopnea index (AHI) (r = 0.559, P < 0.001) and plasma fasting blood glucose (r = 0.427, P < 0.001). After adjusting confounding factors, plasma CTSS levels were independently associated with the AHI (Beta: 0.386, 95% confidence intervals (CI): 21.988 to 57.781; P < 0.001). Furthermore, we confirmed the higher pinpoint accuracy of plasma CTSS in the diagnosis of OSA (area under the curve: 0.868).

Conclusions

Plasma CTSS expression was significantly elevated in the OSA&T2D group and was independently associated with the AHI; it could be a biomarker with a positive diagnostic value on diagnosing OSA among patients with T2D.

Identification of Novel Molecular Markers of Human Th17 Cells

Th17 cells are important players in host defense against pathogens such as Staphylococcus aureus, Candida albicans, and Bacillus anthracis. Th17 cell-mediated inflammation, under certain conditions in which balance in the immune system is disrupted, is the underlying pathogenic mechanism of certain autoimmune disorders, e.g., rheumatoid arthritis, Graves' disease, multiple sclerosis, and psoriasis. In the present study, using transcriptomic profiling, we selected genes and analyzed the expression of these genes to find potential novel markers of Th17 lymphocytes. We found that APOD (apolipoprotein D); C1QL1 (complement component 1, Q subcomponent-like protein 1); and CTSL (cathepsin L) are expressed at significantly higher mRNA and protein levels in Th17 cells than in the Th1, Th2, and Treg subtypes. Interestingly, these genes and the proteins they encode are well associated with the function of Th17 cells, as these cells produce inflammation, which is linked with atherosclerosis and angiogenesis. Furthermore, we found that high expression of these genes in Th17 cells is associated with the acetylation of H2BK12 within their promoters. Thus, our results provide new information regarding this cell type. Based on these results, we also hope to better identify pathological conditions of clinical significance caused by Th17 cells.

Cathepsin C is a novel mediator of podocyte and renal injury induced by hyperglycemia

A growing body of evidence suggests a role of proteolytic enzymes in the development of diabetic nephropathy. Cathepsin C (CatC) is a well-known regulator of inflammatory responses, but its involvement in podocyte and renal injury remains obscure. We used Zucker rats, a genetic model of metabolic syndrome and insulin resistance, to determine the presence, quantity, and activity of CatC in the urine. In addition to the animal study, we used two cellular models, immortalized human podocytes and primary rat podocytes, to determine mRNA and protein expression levels via RT-PCR, Western blot, and confocal microscopy, and to evaluate CatC activity. The role of CatC was analyzed in CatC-depleted podocytes using siRNA and glycolytic flux parameters were obtained from extracellular acidification rate (ECAR) measurements. In functional analyses, podocyte and glomerular permeability to albumin was determined. We found that podocytes express and secrete CatC, and a hyperglycemic environment increases CatC levels and activity. Both high glucose and non-specific activator of CatC phorbol 12-myristate 13-acetate (PMA) diminished nephrin, cofilin, and GLUT4 levels and induced cytoskeletal rearrangements, increasing albumin permeability in podocytes. These negative effects were completely reversed in CatC-depleted podocytes. Moreover, PMA, but not high glucose, increased glycolytic flux in podocytes. Finally, we demonstrated that CatC expression and activity are increased in the urine of diabetic Zucker rats. We propose a novel mechanism of podocyte injury in diabetes, providing deeper insight into the role of CatC in podocyte biology.

A Review of Small Molecule Inhibitors and Functional Probes of Human Cathepsin L

Human cathepsin L belongs to the cathepsin family of proteolytic enzymes with primarily an endopeptidase activity. Although its primary functions were originally thought to be only of a housekeeping enzyme that degraded intracellular and endocytosed proteins in lysosome, numerous recent studies suggest that it plays many critical and specific roles in diverse cellular settings. Not surprisingly, the dysregulated function of cathepsin L has manifested itself in several human diseases, making it an attractive target for drug development. Unfortunately, several redundant and isoform-specific functions have recently emerged, adding complexities to the drug discovery process. To address this, a series of chemical biology tools have been developed that helped define cathepsin L biology with exquisite precision in specific cellular contexts. This review elaborates on the recently developed small molecule inhibitors and probes of human cathepsin L, outlining their mechanisms of action, and describing their potential utilities in dissecting unknown function.

Biguanide is a modifiable pharmacophore for recruitment of endogenous Zn2+ to inhibit cysteinyl cathepsins: review and implications

Excessive activities of cysteinyl cathepsins (CysCts) contribute to the progress of many diseases; however, therapeutic inhibition has been problematic. Zn²⁺ is a natural inhibitor of proteases with CysHis dyads or CysHis(Xaa) triads. Biguanide forms bidentate metal complexes through the two imino nitrogens. Here, it is discussed that phenformin (phenylethyl biguanide) is a model for recruitment of endogenous Zn²⁺ to inhibit CysHis/CysHis(X) peptidolysis. Phenformin is a Zn²⁺-interactive, anti-proteolytic agent in bioassay of living tissue. Benzoyl-L-arginine amide (BAA) is a classical substrate of papain-like proteases; the amide bond is scissile. In this review, the structures of BAA and the phenformin-Zn²⁺ complex were compared in silico. Their chemistry and dimensions are discussed in light of the active sites of papain-like proteases. The phenyl moieties of both structures bind to the "S2" substrate-binding site that is typical of many proteases. When the phenyl moiety of BAA binds to S2, then the scissile amide bond is directed to the position of the thiolate-imidazolium ion pair, and is then hydrolyzed. However, when the phenyl moiety of phenformin binds to S2, then the coordinated Zn²⁺ is directed to the identical position; and catalysis is inhibited. Phenformin stabilizes a "Zn²⁺ sandwich" between the drug and protease active site. Hundreds of biguanide derivatives have been synthesized at the 1 and 5 nitrogen positions; many more are conceivable. Various substituent moieties can register with various arrays of substrate-binding sites so as to align coordinated Zn²⁺ with catalytic partners of diverse proteases. Biguanide is identified here as a modifiable pharmacophore for synthesis of therapeutic CysCt inhibitors with a wide range of potencies and specificities. Phenformin-Zn²⁺ Complex.

Cellular proliferation in mouse and human pancreatic islets is regulated by serpin B13 inhibition and downstream targeting of E-cadherin by cathepsin L

AIMS/HYPOTHESIS

We previously reported that exposure to antibodies neutralising serpin B13, a protease inhibitor expressed in exocrine pancreatic ducts, promotes beta cell proliferation, underscoring the importance of a functional relationship between exocrine and endocrine pancreas. The aim of the present study was to identify the molecular events that link inhibition of serpin B13 to islet cell proliferation.

METHODS

We used an in vitro culture system consisting of isolated pancreatic islets, an extract of pancreatic ductal epithelium and a monoclonal antibody (mAb) to serpin B13 or IgG isotype control. In vivo studies involved treatment of mice with these mAbs.

RESULTS

The catalytic activity of cathepsin L (CatL), a cysteine protease target of serpin B13, was augmented in the pancreas of mice injected with serpin B13 mAb. Furthermore, the addition of serpin B13 mAb to the islets, together with the pancreatic ductal epithelium lysate, caused CatL-dependent cleavage of E-cadherin and concomitant upregulation of REG genes, ultimately leading to beta cell proliferation. Direct blockade of E-cadherin with mAb also markedly enhanced REG gene induction, while chemical inhibition of β-catenin, a binding target of E-cadherin, prevented the serpin B13 mAb-induced upregulation of REG genes.

CONCLUSIONS/INTERPRETATION

Our work implicates the CatL-E-cadherin-REG pathway in the regulation of islet cell proliferation in response to signals generated in exocrine pancreatic tissue and demonstrates that protease activity may promote adaptive changes in the islets.

DATA AVAILABILITY

Microarray data that support the findings of this study have been deposited in Gene Expression Omnibus (GEO) with the accession no. GSE125151.

Downregulation of cathepsin G reduces the activation of CD4+ T cells in murine autoimmune diabetes

Type 1 diabetes mellitus (T1DM) is an autoimmune disease due to progressive injury of islet cells mediated by T lymphocytes (T cells). Our previous studies have shown that only cathepsin G (CatG), not other proteases, is involved in the antigen presentation of proinsulin, and if the presentation is inhibited, the activation of CD4+ T cells induced by proinsulin is alleviated in T1DM patients, and CatG-specific inhibitor reduces the activation of CD4+ cells induced by proinsulin in T1DM patients. Therefore, we hypothesize that CatG may play an important role in the activation of CD4+ T cells in T1DM. To this end, mouse studies were conducted to demonstrate that CatG impacts the activation of CD4+ T cells in non-obese diabetic (NOD) mice. CatG gene expression and the activation of CD4+ T cells were examined in NOD mice. The effect of CatG inhibitor was investigated in NOD mice on the activation of CD4+ T cells, islet β cell function, islet inflammation and β-cell apoptosis. Furthermore, NOD mice were injected with CatG siRNA in early stage to observe the effect of CatG knockdown on the activation status of CD4+ T cells and the progression of diabetes. During the pathogenesis of diabetes, the expression level of CatG in NOD mice gradually increased and the CD4+ T cells were gradually activated, resulting in more TH1 cells and less TH2 and Treg cells. Treatment with CatG-specific inhibitor reduced the blood glucose level, improved the function of islet β cells and reduced the activation of CD4+ T cells. Early application of CatG siRNA improved the function of islet β cells, reduced islet inflammation and β cell apoptosis, and lowered the activation level of CD4+ T cells, thus slowing down the progression of diabetes.

Treating the Underlying Pathophysiology of Primary Sjögren Syndrome: Recent Advances and Future Prospects

Sjögren Syndrome (SS) is a systemic autoimmune disease with a wide clinical spectrum that extends from sicca symptoms of the mucosal surfaces to extra-glandular systemic manifestations. Understanding of the pathophysiology of primary SS has advanced over recent years, and this, in turn, has presented new targeted treatment options. We provide a brief, up-to-date description of the pathophysiology of SS and the main etiopathogenic pathways implicated in the disease process and review clinical evidence in support of new treatment options targeting these pathways, highlighting successes and failures, and concluding with a summary of gaps in knowledge and where future research should be focused. Direct and indirect B-cell targeted therapies are currently the most promising biological agents in primary SS, especially for systemic involvement, but other pathways (T-cell co-stimulation, cytokine-based therapies, intracellular pathways and gene therapies) are under development. The next 10 years may witness a disruptive therapeutic scenario in primary SS.

Symbiotic gut commensal bacteria act as host cathepsin S activity regulators

Cathepsin S (CTSS) is a lysosomal protease whose activity regulation is important for MHC-II signaling and subsequent activation of CD4⁺ T cell mediated immune responses. Dysregulation of its enzymatic activity or enhanced secretion into extracellular environments is associated with the induction or progression of several autoimmune diseases. Here we demonstrate that commensal intestinal bacteria influence secretion rates and intracellular activity of host CTSS and that symbiotic bacteria, i.e. Bacteroides vulgatus mpk, may actively regulate this process and help to maintain physiological levels of CTSS activities in order to prevent from induction of pathological inflammation. The symbiont-controlled regulation of CTSS activity is mediated by anticipating reactive oxygen species induction in dendritic cells which, in turn, maintains cystatin C (CysC) monomer binding to CTSS. CysC monomers are potent endogenous CTSS inhibitors. This Bacteroides vulgatus caused and CysC dependent CTSS activity regulation is involved in the generation of tolerant intestinal dendritic cells contributing to prevention of T-cell mediated induction of colonic inflammation. Taken together, we demonstrate that symbionts of the intestinal microbiota regulate host CTSS activity and secretion and might therefore be an attractive approach to deal with CTSS associated autoimmune diseases.

CA-074Me compound inhibits osteoclastogenesis via suppression of the NFATc1 and c-FOS signaling pathways

The osteoclast is an integral cell of bone resorption. Since osteolytic disorders hinge on the function and dysfunction of the osteoclast, understanding osteoclast biology is fundamental to designing new therapies that curb osteolytic disorders. The identification and study of lysosomal proteases, such as cathepsins, have shed light on mechanisms of bone resorption. For example, Cathepsin K has already been identified as a collagen degradation protease produced by mature osteoclasts with high activity in the acidic osteoclast resorption pits. Delving into the mechanisms of cathepsins and other osteoclast related compounds provides new targets to explore in osteoclast biology. Through our anti-osteoclastogenic compound screening experiments we encountered a modified version of the Cathepsin B inhibitor CA-074: the cell membrane-permeable CA-074Me (L-3-trans-(Propylcarbamoyl) oxirane-2-carbonyl]-L-isoleucyl-L-proline Methyl Ester). Here we confirm that CA-074Me inhibits osteoclastogenesis in vivo and in vitro in a dose-dependent manner. However, Cathepsin B knockout mice exhibited unaltered osteoclastogenesis, suggesting a more complicated mechanism of action than Cathepsin B inhibition. We found that CA-074Me exerts its osteoclastogenic effect within 24 h of osteoclastogenesis stimulation by suppression of c-FOS and NFATc1 pathways.

Cathepsin B regulates the appearance and severity of mercury-induced inflammation and autoimmunity

Susceptibility and resistance to systemic autoimmunity are genetically regulated. This is particularly true for murine mercury-induced autoimmunity (mHgIA) where DBA/2J mice are considered resistant to disease including polyclonal B cell activation, autoantibody responses, and immune complex deposits. To identify possible mechanisms for the resistance to mHgIA, we exposed mHgIA sensitive B10.S and resistant DBA/2J mice to HgCl2 and assessed inflammation and pro-inflammatory responses at the site of exposure and subsequent development of markers of systemic autoimmunity. DBA/2J mice showed little evidence of induration at the site of exposure, expression of proinflammatory cytokines, T cell activation, or autoantibody production, although they did exhibit increased levels of total serum IgG and IgG1. In contrast B10.S mice developed significant inflammation together with increased expression of inflammasome component NLRP3, proinflammatory cytokines IL-1β, TNF-α, and IFN-γ, hypergammaglobulinemia, splenomegaly, CD4(+) T-cell activation, and production of autoantibodies. Inflammation in B10.S mice was associated with a selective increase in activity of cysteine cathepsin B but not cathepsins L or S. Increased cathepsin B activity was not dependent on cytokines required for mHgIA but treatment with CA-074, a cathepsin B inhibitor, led to transient reduction of local induration, expression of inflammatory cytokines, and subsequent attenuation of the systemic adaptive immune response. These findings demonstrate that sensitivity to mHgIA is linked to an early cathepsin B regulated inflammatory response which can be pharmacologically exploited to abrogate the subsequent adaptive autoimmune response which leads to disease.

CTSH regulates β-cell function and disease progression in newly diagnosed type 1 diabetes patients

Over 40 susceptibility loci have been identified for type 1 diabetes (T1D). Little is known about how these variants modify disease risk and progression. Here, we combined in vitro and in vivo experiments with clinical studies to determine how genetic variation of the candidate gene cathepsin H (CTSH) affects disease mechanisms and progression in T1D. The T allele of rs3825932 was associated with lower CTSH expression in human lymphoblastoid cell lines and pancreatic tissue. Proinflammatory cytokines decreased the expression of CTSH in human islets and primary rat β-cells, and overexpression of CTSH protected insulin-secreting cells against cytokine-induced apoptosis. Mechanistic studies indicated that CTSH exerts its antiapoptotic effects through decreased JNK and p38 signaling and reduced expression of the proapoptotic factors Bim, DP5, and c-Myc. CTSH overexpression also up-regulated Ins2 expression and increased insulin secretion. Additionally, islets from Ctsh(-/-) mice contained less insulin than islets from WT mice. Importantly, the TT genotype was associated with higher daily insulin dose and faster disease progression in newly diagnosed T1D patients, indicating agreement between the experimental and clinical data. In line with these observations, healthy human subjects carrying the T allele have lower β-cell function, which was evaluated by glucose tolerance testing. The data provide strong evidence that CTSH is an important regulator of β-cell function during progression of T1D and reinforce the concept that candidate genes for T1D may affect disease progression by modulating survival and function of pancreatic β-cells, the target cells of the autoimmune assault.

The Repertoires of Peptides Presented by MHC-II in the Thymus and in Peripheral Tissue: A Clue for Autoimmunity?

T-cell tolerance to self-antigens is established in the thymus through the recognition by developing thymocytes of self-peptide-MHC complexes and induced and maintained in the periphery. Efficient negative selection of auto-reactive T cells in the thymus is dependent on the in situ expression of both ubiquitous and tissue-restricted self-antigens and on the presentation of derived peptides. Weak or inadequate intrathymic expression of self-antigens increases the risk to generate an autoimmune-prone T-cell repertoire. Indeed, even small changes of self-antigen expression in the thymus affect negative selection and increase the predisposition to autoimmunity. Together with other mechanisms, tolerance is maintained in the peripheral lymphoid organs via the recognition by mature T cells of a similar set of self-peptides in homeostatic conditions. However, non-lymphoid peripheral tissue, where organ-specific autoimmunity takes place, often have differential functional processes that may lead to the generation of epitopes that are absent or non-presented in the thymus. These putative differences between peptides presented by MHC molecules in the thymus and in peripheral tissues might be a major key to the initiation and maintenance of autoimmune conditions.

Correlation between serum cathepsin S and insulin resistance in type 2 diabetes

Cathepsin S (CatS), a proteolytic enzyme, which belongs to the cysteine proteinase family, is associated with atherosclerosis, coronary heart disease, cancer and other diseases. The present study aimed to explore the correlation between serum CatS and insulin resistance (IR) in patients with type 2 diabetes. A total of 51 patients with type 2 diabetes (Group DM) were recruited for this study and 49 healthy individuals were selected as normal controls (Group NC). Blood pressure and body mass index (BMI) were recorded, and serum creatinine, CatS, glycosylated hemoglobin (HbA1c), lipid and insulin levels, and fasting plasma glucose (FPG) levels were measured in all the participants. The homeostatic model assessment index of IR (HOMA-IR) was calculated according to FPG and serum insulin levels. Serum CatS, very low density lipoprotein (VLDL) and triglyceride (TG) levels in Group DM were significantly higher compared with those in Group NC (P=0.000, 0.014 and 0.020, respectively). Significantly positive correlations were identified between CatS levels and VLDL and TG levels, respectively (P<0.05 for both); however, no significant correlations were determined between CatS levels and age, course of disease, blood pressure, cholesterol, BMI, FPG, HbAc1 and HOMA-IR (P>0.05). Further stratification analysis showed that CatS had no association with IR at different HOMA-IR and HbA1c levels. The present study demonstrated that serum CatS, which was significantly increased in patients with type 2 diabetes, had no correlation with IR. This indicates that CatS and IR are independent of each other; however, the precise mechanisms require further investigation.

Lysosomal metal, redox and proton cycles influencing the CysHis cathepsin reaction

In the 1930's pioneers discovered that maximal autolysis in tissue homogenates requires metal chelator, sulfhydryl reducing agent and acid pH. However, metals, reducing equivalents and protons (MR&P) have been overlooked as combined catalytic controls. Three categories of lysosomal machinery drive three distinguishable cycles importing and exporting MR&P. Zn(2+) preemptively inhibits CysHis catalysis under otherwise optimal protonation and reduction. Protein-bound cell Zn(2+) concentration is 200-2000 times the non-sequestered inhibitory concentration. Following autophagy, lysosomal proteolysis liberates much inhibitory Zn(2+). The vacuolar proton pump is the driving force for Zn(2+) export, as well as protonation of the peptidolytic mechanism. Other machinery of lysosomal cycles includes proton-driven Zn(2+) exporters (e.g. SLC11A1), Zn(2+) channels (e.g. TRPML-1), lysosomal thiol reductase, etc. The CysHis dyad is a sensor of the vacuolar environment of MR&P, an integrator of these simultaneous variables, and a catalytic responder. Rate-determination can shift between autophagic substrate acquisition (swallowing) and substrate degradation (digesting). Zn(2+) recycling from degraded proteins to new proteins is a fourth cycle that might pace lysosomal function under some conditions. Heritable insufficient or excess functions of CysHis cathepsins are associated with dysfunctional inflammation and immunity/auto-immunity, including diabetic pathogenesis.

The peri-islet basement membrane, a barrier to infiltrating leukocytes in type 1 diabetes in mouse and human

We provide the first comprehensive analysis of the extracellular matrix (ECM) composition of peri-islet capsules, composed of the peri-islet basement membrane (BM) and subjacent interstitial matrix (IM), in development of type 1 diabetes in NOD mice and in human type 1 diabetes. Our data demonstrate global loss of peri-islet BM and IM components only at sites of leukocyte infiltration into the islet. Stereological analyses reveal a correlation between incidence of insulitis and the number of islets showing loss of peri-islet BM versus islets with intact BMs, suggesting that leukocyte penetration of the peri-islet BM is a critical step. Protease- and protease inhibitor-specific microarray analyses (CLIP-CHIP) of laser-dissected leukocyte infiltrated and noninfiltrated pancreatic islets and confirmatory quantitative real time PCR and protein analyses identified cathepsin S, W, and C activity at sites of leukocyte penetration of the peri-islet BM in association with a macrophage subpopulation in NOD mice and human type 1 diabetic samples and, hence, potentially a novel therapeutic target specifically acting at the islet penetration stage. Interestingly, the peri-islet BM and underlying IM are reconstituted once inflammation subsides, indicating that the peri-islet BM-producing cells are not lost due to the inflammation, which has important ramifications to islet transplantation studies.

Anti-serpin antibody-mediated regulation of proteases in autoimmune diabetes

Secretion of anti-serpin B13 autoantibodies in young diabetes-prone nonobese diabetic mice is associated with reduced inflammation in pancreatic islets and a slower progression to autoimmune diabetes. Injection of these mice with a monoclonal antibody (mAb) against serpin B13 also leads to fewer inflammatory cells in the islets and more rapid recovery from recent-onset diabetes. The exact mechanism by which anti-serpin activity is protective remains unclear. We found that serpin B13 is expressed in the exocrine component of the mouse pancreas, including the ductal cells. We also found that anti-serpin B13 mAb blocked the inhibitory activity of serpin B13, thereby allowing partial preservation of the function of its target protease. Consistent with the hypothesis that anti-clade B serpin activity blocks the serpin from binding, exposure to exogenous anti-serpin B13 mAb or endogenous anti-serpin B13 autoantibodies resulted in cleavage of the surface molecules CD4 and CD19 in lymphocytes that accumulated in the pancreatic islets and pancreatic lymph nodes but not in the inguinal lymph nodes. This cleavage was inhibited by an E64 protease inhibitor. Consequently, T cells with the truncated form of CD4 secreted reduced levels of interferon-γ. We conclude that anti-serpin antibodies prevent serpin B13 from neutralizing proteases, thereby impairing leukocyte function and reducing the severity of autoimmune inflammation.

Enhanced anti-serpin antibody activity inhibits autoimmune inflammation in type 1 diabetes

Intracellular (clade B) OVA-serpin protease inhibitors play an important role in tissue homeostasis by protecting cells from death in response to hypo-osmotic stress, heat shock, and other stimuli. It is not known whether these serpins influence immunological tolerance and the risk for autoimmune diseases. We found that a fraction of young autoimmune diabetes-prone NOD mice had elevated levels of autoantibodies against a member of clade B family known as serpinB13. High levels of anti-serpinB13 Abs were accompanied by low levels of anti-insulin autoantibodies, reduced numbers of islet-associated T cells, and delayed onset of diabetes. Exposure to anti-serpinB13 mAb alone also decreased islet inflammation, and coadministration of this reagent and a suboptimal dose of anti-CD3 mAb accelerated recovery from diabetes. In a fashion similar to that discovered in the NOD model, a deficiency in humoral activity against serpinB13 was associated with early onset of human type 1 diabetes. These findings suggest that, in addition to limiting exposure to proteases within the cell, clade B serpins help to maintain homeostasis by inducing protective humoral immunity.

Cathepsin S dominates autoantigen processing in human thymic dendritic cells

The interaction of developing thymocytes with peptide-MHC complexes on thymic antigen presenting cells (APC) is crucial for T cell development, both for positive selection of "useful" thymocytes as well as negative selection of autoreactive thymocytes to prevent autoimmunity. The peptides presented on MHC II molecules are generated by lysosomal proteases such as the cathepsins. At the same time, lysosomal proteases will also destroy other potential T cell epitopes from self-antigens. This will lead to a lack of presentation on negatively selecting thymic antigen presenting cells and consequently, escape of autoreactive T cells recognizing these epitopes. In order to understand the processes that govern generation or destruction of self-epitopes in thymic APC, we studied the antigen processing machinery and epitope processing in the human thymus. We find that each type of thymic APC expresses a different signature of lysosomal proteases, providing indirect evidence that positive and negative selection of CD4(+) T cells might occur on different sets of peptides, in analogy to what has been proposed for CD8(+) T cells. We also find that myeloid dendritic cells (DC) are more efficient in processing autoantigen than plasmacytoid DC. In addition, we observed that cathepsin S plays a central role in processing of the autoantigens myelin basic protein and proinsulin in thymic dendritic cells. Cathepsin S destroyed a number of known T cell epitopes, which would be expected to result in lack of presentation and consequently, escape of autoreactive T cells. Cathepsin S therefore appears to be an important factor that influences selection of autoreactive T cells.

Strategies to reverse endothelial progenitor cell dysfunction in diabetes

Bone-marrow-derived cells-mediated postnatal vasculogenesis has been reported as the main responsible for the regulation of vascular homeostasis in adults. Since their discovery, endothelial progenitor cells have been depicted as mediators of postnatal vasculogenesis for their peculiar phenotype (partially staminal and partially endothelial), their ability to differentiate in endothelial cell line and to be incorporated into the vessels wall during ischemia/damage. Diabetes mellitus, a condition characterized by cardiovascular disease, nephropathy, and micro- and macroangiopathy, showed a dysfunction of endothelial progenitor cells. Herein, we review the mechanisms involved in diabetes-related dysfunction of endothelial progenitor cells, highlighting how hyperglycemia affects the different steps of endothelial progenitor cells lifetime (i.e., bone marrow mobilization, trafficking into the bloodstream, differentiation in endothelial cells, and homing in damaged tissues/organs). Finally, we review preclinical and clinical strategies that aim to revert diabetes-induced dysfunction of endothelial progenitor cells as a means of finding new strategies to prevent diabetic complications.

Differential processing of self-antigens by subsets of thymic stromal cells

The stromal network of the thymus provides a unique environment that supports the development of mature CD4(+) and CD8(+) T cells expressing a very diverse repertoire of T cell receptors (TCR) with limited reactivity to self-antigens. Thymic cortical epithelial cells (cTECs) are specialized antigen-presenting cells (APCs) that promote the positive selection of developing thymocytes while medullary thymic epithelial cells (mTECs) and thymic dendritic cells (tDCs) induce central tolerance to self-antigens. Recent studies showed that cTECs express a unique set of proteases involved in the generation of self-peptides presented by major-histocompatibility encoded molecules (pMHC) and consequently may express a unique set of pMHC complexes. Conversely, the stromal cells of the medulla developed several mechanisms to mirror as closely as possible the constellation of self-peptides derived from peripheral tissues. Here, we discuss how these different features allow for the development of a highly diverse but poorly self-reactive repertoire of functional T cells.

Intracellular nucleic acid sensors and autoimmunity

A collection of molecular sensors has been defined by studies in the last decade that can recognize a diverse array of pathogens and initiate protective immune and inflammatory responses. However, if the molecular signatures recognized are shared by both foreign and self-molecules, as is the case of nucleic acids, then the responses initiated by these sensors may have deleterious consequences. Notably, this adverse occurrence may be of primary importance in autoimmune disease pathogenesis. In this case, microbe-induced damage or mishandled physiologic processes could lead to the generation of microparticles containing self-nucleic acids. These particles may inappropriately gain access to the cytosol or endolysosomes and, hence, engage resident RNA and DNA sensors. Evidence, as reviewed here, strongly indicates that these sensors are primary contributors to autoimmune disease pathogenesis, spearheading efforts toward development of novel therapeutics for these disorders.

Regulation of cathepsin G reduces the activation of proinsulin-reactive T cells from type 1 diabetes patients

Autoantigenic peptides resulting from self-proteins such as proinsulin are important players in the development of type 1 diabetes mellitus (T1D). Self-proteins can be processed by cathepsins (Cats) within endocytic compartments and loaded to major histocompatibility complex (MHC) class II molecules for CD4⁺ T cell inspection. However, the processing and presentation of proinsulin by antigen-presenting cells (APC) in humans is only partially understood. Here we demonstrate that the processing of proinsulin by B cell or myeloid dendritic cell (mDC1)-derived lysosomal cathepsins resulted in several proinsulin-derived intermediates. These intermediates were similar to those obtained using purified CatG and, to a lesser extent, CatD, S, and V in vitro. Some of these intermediates polarized T cell activation in peripheral blood mononuclear cells (PBMC) from T1D patients indicative for naturally processed T cell epitopes. Furthermore, CatG activity was found to be elevated in PBMC from T1D patients and abrogation of CatG activity resulted in functional inhibition of proinsulin-reactive T cells. Our data suggested the notion that CatG plays a critical role in proinsulin processing and is important in the activation process of diabetogenic T cells.

Autoimmunity in 2010

There is now growing evidence that autoimmunity is the common trait connecting multiple clinical phenotypes albeit differences in tissue specificity, pathogenetic mechanisms, and therapeutic approaches cannot be overlooked. Over the past years we witnessed a constant growth of the number of publications related to autoimmune diseases in peer-reviewed journals of the immunology area. Original data referred to factors from common injury pathways (i.e. T helper 17 cells, serum autoantibodies, or vitamin D) and specific diseases such as multiple sclerosis, systemic lupus erythematosus, and rheumatoid arthritis. As an example, the issue of a latitudinal gradient in the prevalence and incidence rates has been proposed for all autoimmune diseases and was recently coined as geoepidemiology to suggest new environmental triggers for tolerance breakdown. The present article is aimed at reviewing the articles that were published over the past year in the major autoimmunity and immunology journals.