Identification of cathepsin K as a novel marker of adiposity in white adipose tissue

A SNP in the ovine cathepsin K (CTSK) gene is associated with yearling growth performance in a crossbred sheep population

Cathepsin K (CTSK) is a lysosomal protease existent in the skeletal muscles which is involved in biochemical processes related to obesity. Several studies have reported the effects of CTSK gene on body weight and fat deposition in human, mice and pigs. However, information about its structure and functions in sheep is very limited. Thus, this study was performed to evaluate the association between CTSK gene variants and yearling growth performance in Afshari × Booroola-Merino crossbred sheep. A fragment of 500 bp in exon 6 and partial of intron 5 of CTSK gene was amplified with polymerase chain reaction (PCR). All animals were genotyped by single-stranded conformation polymorphism (SSCP) and further confirmed by sequencing. Association analysis using a fixed linear model indicated that g.106510225G > A SNP was significantly related to average daily weight gain (ADWG) per year, fat-tail weight to carcass weight ratio (FW/CW), muscle thickness (MT) and muscle cross-sectional area (MCSA) of animals (p < 0.05). Due to the low polymorphic information content (PIC <0.25) for targeted locus in studied population, more association studies are needed to confirm the CTSK gene effects on growth traits in sheep.

Visualizing Cathepsin K-Cre Expression at the Single-Cell Level with GFP Reporters

The Cre/lox system is a fundamental tool for functional genomic studies, and a number of Cre lines have been generated to target genes of interest spatially and temporally in defined cells or tissues; this approach has greatly expanded our knowledge of gene functions. However, the limitations of this system have recently been recognized, and we must address the challenge of so-called nonspecific/off-target effects when a Cre line is utilized to investigate a gene of interest. For example, cathepsin K (Ctsk) has been used as a specific osteoclast marker, and Cre driven by its promoter is widely utilized for osteoclast investigations. However, Ctsk-Cre expression has recently been identified in other cell types, such as osteocytes, periosteal stem cells, and tenocytes. To better understand Ctsk-Cre expression and ensure appropriate use of this Cre line, we performed a comprehensive analysis of Ctsk-Cre expression at the single-cell level in major organs and tissues using two green fluorescent protein (GFP) reporters (ROSA nT-nG and ROSA tdT) and a tissue clearing technique in young and aging mice. The expression profile was further verified by immunofluorescence staining and droplet digital RT-PCR. The results demonstrate that Ctsk-Cre is expressed not only in osteoclasts but also at various levels in osteoblast lineage cells and other major organs/tissues, particularly in the brain, kidney, pancreas, and blood vessels. Furthermore, Ctsk-Cre expression increases markedly in the bone marrow, skeletal muscle, and intervertebral discs in aging mice. These data will be valuable for accurately interpreting data obtained from in vivo studies using Ctsk-Cre mice to avoid potentially misleading conclusions. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Sex-specific extracellular matrix remodeling during early adipogenic differentiation by gestational bisphenol A exposure

Bisphenol A (BPA) is an endocrine disrupting chemical known to promote adipose tissue mass in vivo and adipogenesis in vitro. Whether BPA can affect and reprogram early adipogenic differentiation signals that trigger adipogenic differentiation, remains unknown. We hypothesized that gestational BPA exposure results in a preadipocyte phenotype that leads to accelerated adipogenic differentiation, and that this phenotype is sex specific. Primary ovine fetal preadipocytes were derived from control (C) and BPA-exposed during pregnancy and differentiated in vitro. Gestational BPA enhanced lipid accumulation at early stages of differentiation (48 h) and this was evident in females but not male-derived fetal preadipocytes. After an RNA sequencing approach, samples were compared as follows: 2 groups (C vs. BPA); 2 sexes (female (F) vs. male (M)); and 2 time points (0 h vs. 48 h). Before differentiation, 15 genes were differentially expressed between the C and the BPA-exposed preadipocytes within sex. In BPA-F, extracellular matrix remodeling genes cathepsin K and collagen 5α3 were upregulated compared to C-F. At 48 h, BPA-F had 154 genes differentially expressed vs. C-F and BPA-M had 487 genes differentially expressed vs. C-M. Triglyceride and glycerophospholipid metabolism were the most upregulated pathways in BPA-F. Downregulated pathways were associated with extracellular matrix organization in BPA-exposed preadipocytes. These findings are among the first to demonstrate that gestational BPA can modify the fate of adipocyte precursors by altering pathways associated to extracellular matrix components, an often-disregarded, but required aspect of adipogenic differentiation. This work highlights the need to investigate early adipogenic differentiation changes in other obesogenic chemicals.

Cathepsin K+ Non-Osteoclast Cells in the Skeletal System: Function, Models, Identity, and Therapeutic Implications

Cathepsin K (Ctsk) is a cysteine protease of the papain superfamily initially identified in differentiated osteoclasts; it plays a critical role in degrading the bone matrix. However, subsequent in vivo and in vitro studies based on animal models elucidate novel subpopulations of Ctsk-expressing cells, which display markers and properties of mesenchymal stem/progenitor cells. This review introduces the function, identity, and role of Ctsk⁺ cells and their therapeutic implications in related preclinical osseous disorder models. It also summarizes the available in vivo models for studying Ctsk⁺ cells and their progeny. Further investigations of detailed properties and mechanisms of Ctsk⁺ cells in transgenic models are required to guide potential therapeutic targets in multiple diseases in the future.

New Insights Into the Interplay Among Autophagy, the NLRP3 Inflammasome and Inflammation in Adipose Tissue

Obesity is a feature of metabolic syndrome with chronic inflammation in obese subjects, characterized by adipose tissue (AT) expansion, proinflammatory factor overexpression, and macrophage infiltration. Autophagy modulates inflammation in the enlargement of AT as an essential step for maintaining the balance in energy metabolism and waste elimination. Signaling originating from dysfunctional AT, such as AT containing hypertrophic adipocytes and surrounding macrophages, activates NOD-like receptor family 3 (NLRP3) inflammasome. There are interactions about altered autophagy and NLRP3 inflammasome activation during the progress in obesity. We summarize the current studies and potential mechanisms associated with autophagy and NLRP3 inflammasome in AT inflammation and aim to provide further evidence for research on obesity and obesity-related complications.

Shared PPARα/γ Target Genes Regulate Brown Adipocyte Thermogenic Function

Brown adipose tissue (BAT) generates heat to maintain body temperature and suppress obesity. Agonists for nuclear receptors PPARα and PPARγ both affect brown adipocyte function, yet the interplay between these factors in BAT is uncertain. Here, we report that PPARα shares most genomic binding sites with PPARγ, and these common binding sites are more related to BAT function than PPARγ-selective sites without PPARα. Integrating PPARα and PPARγ genomic occupancy with cold-responsive BAT transcriptomes identifies a subset of 16 genes with potential relevance to BAT function. Among these, we focused on the lysosomal protease cathepsin Z (CTSZ) and showed it is necessary for mitochondrial respiration in both mouse and human brown adipocytes. Thus, CTSZ is a shared PPARα/γ target gene in BAT and a regulator of brown adipocyte thermogenic function.

Cathepsin K: The Action in and Beyond Bone

Cathepsin K (CatK) is one of the most potent proteases in lysosomal cysteine proteases family, of which main function is to mediate bone resorption. Currently, CatK is among the most attractive targets for anti-osteoporosis drug development. Although many pharmaceutical companies are working on the development of selective inhibitors for CatK, there is no FDA approved drug till now. Odanacatib (ODN) developed by Merck & Co. is the only CatK inhibitor candidate which demonstrated high therapeutic efficacy in patients with postmenopausal osteoporosis in Phase III clinical trials. Unfortunately, the development of ODN was finally terminated due to the cardio-cerebrovascular adverse effects. Therefore, it arouses concerns on the undesirable CatK inhibition in non-bone sites. It is known that CatK has far-reaching actions throughout various organs besides bone. Many studies have also demonstrated the involvement of CatK in various diseases beyond the musculoskeletal system. This review not only summarized the functional roles of CatK in bone and beyond bone, but also discussed the potential relevance of the CatK action beyond bone to the adverse effects of inhibiting CatK in non-bone sites.

Peripheral cathepsin L inhibition induces fat loss in C. elegans and mice through promoting central serotonin synthesis

BACKGROUND

Cathepsin L and some other cathepsins have been implicated in the development of obesity in humans and mice. The functional inactivation of the proteases reduces fat accumulation during mammalian adipocyte differentiation. However, beyond degrading extracellular matrix protein fibronectin, the molecular mechanisms by which cathepsins control fat accumulation remain unclear. We now provide evidence from Caenorhabditis elegans and mouse models to suggest a conserved regulatory circuit in which peripheral cathepsin L inhibition lowers fat accumulation through promoting central serotonin synthesis.

RESULTS

We established a C. elegans model of fat accumulation using dietary supplementation with glucose and palmitic acid. We found that nutrient supplementation elevated fat storage in C. elegans, and along with worm fat accumulation, an increase in the expression of cpl-1 was detected using real-time PCR and western blot. The functional inactivation of cpl-1 reduced fat storage in C. elegans through activating serotonin signaling. Further, knockdown of cpl-1 in the intestine and hypodermis promoted serotonin synthesis in worm ADF neurons and induced body fat loss in C. elegans via central serotonin signaling. We found a similar regulatory circuit in high-fat diet-fed mice. Cathepsin L knockout promoted fat loss and central serotonin synthesis. Intraperitoneal injection of the cathepsin L inhibitor CLIK195 similarly reduced body weight gain and white adipose tissue (WAT) adipogenesis, while elevating brain serotonin level and WAT lipolysis and fatty acid β-oxidation. These effects of inhibiting cathepsin L were abolished by intracranial injection of p-chlorophenylalanine, inhibitor of a rate-limiting enzyme for serotonin synthesis.

CONCLUSION

This study reveals a previously undescribed molecular mechanism by which peripheral CPL-1/cathepsin L inhibition induces fat loss in C. elegans and mice through promoting central serotonin signaling.

Characterization and initial functional analysis of cathepsin K in turbot (Scophthalmus maximus L.)

Cathepsins are the best-known group of proteases in lysosomes, playing a significant role in immune responses. Cathepsin K (CTSK) is abundantly and selectively expressed in osteoclasts, dendritic cells and monocyte-derived macrophages, where it is involved in ECM degradation and bone remodeling. A growing body of evidences have indicated the vital roles of cathepsin K in innate immune responses. Here, one CTSK gene was captured in turbot (SmCTSK) with a 993 bp open reading frame (ORF). The genomic structure analysis showed that SmCTSK had 7 exons similar to other vertebrate species. The syntenic analysis revealed that CTSK had the same neighboring genes across all the selected species, which suggested the synteny encompassing CTSK region was conserved during vertebrate evolution. Subsequently, SmCTSK was widely expressed in all the examined tissues, with the highest expression level in spleen and the lowest expression level in liver. In addition, SmCTSK was significantly down-regulated in intestine following Gram-negative bacteria Vibrio anguillarum immersion challenge, but up-regulated in three tissues (gill, skin and intestine) following Gram-positive bacteria Streptococcus iniae immersion challenge. Finally, the rSmCTSK showed strong binding ability to all the examined microbial ligands. Taken together, our results suggested SmCTSK played vital roles in fish innate immune responses against infection. However, the knowledge of SmCTSK is still limited in teleost species, further studies should be carried out to better characterize its comprehensive roles in teleost mucosal immunity.

Cathepsin K knockout protects against cardiac dysfunction in diabetic mice

Diabetes is a major risk factor for cardiovascular disease and the lysosomal cysteine protease cathepsin K plays a critical role in cardiac pathophysiology. To expand upon our previous findings, we tested the hypothesis that, knockout of cathepsin K protects against diabetes-associated cardiac anomalies. Wild-type and cathepsin K knockout mice were rendered diabetic by streptozotocin (STZ) injections. Body weight, organ mass, fasting blood glucose, energy expenditure, cardiac geometry and function, cardiac histomorphology, glutathione levels and protein levels of cathepsin K and those associated with Ca²⁺ handling, calcineurin/NFAT signaling, insulin signaling, cardiac apoptosis and fibrosis were determined. STZ-induced diabetic mice exhibited distinct cardiac dysfunction, dampened intracellular calcium handling, alterations in cardiac morphology, and elevated cardiomyocyte apoptosis, which were mitigated in the cathepsin K knockout mice. Additionally, cathepsin K knockout mice attenuated cardiac oxidative stress and calcineurin/NFAT signaling in diabetic mice. In cultured H9c2 myoblasts, pharmacological inhibition of cathepsin K, or treatment with calcineurin inhibitor rescued cells from high-glucose triggered oxidative stress and apoptosis. Therefore, cathepsin K may represent a potential target in treating diabetes-associated cardiac dysfunction.

Cathepsin K Inhibitors for Osteoporosis: Biology, Potential Clinical Utility, and Lessons Learned

Cathepsin K is a cysteine protease member of the cathepsin lysosomal protease family. Although cathepsin K is highly expressed in osteoclasts, lower levels of cathepsin K are also found in a variety of other tissues. Secretion of cathepsin K from the osteoclast into the sealed osteoclast-bone cell interface results in efficient degradation of type I collagen. The absence of cathepsin K activity in humans results in pycnodysostosis, characterized by increased bone mineral density and fractures. Pharmacologic cathepsin K inhibition leads to continuous increases in bone mineral density for ≤5 years of treatment and improves bone strength at the spine and hip. Compared with other antiresorptive agents, cathepsin K inhibition is nearly equally efficacious for reducing biochemical markers of bone resorption but comparatively less active for reducing bone formation markers. Despite multiple efforts to develop cathepsin K inhibitors, potential concerns related to off-target effects of the inhibitors against other cathepsins and cathepsin K inhibition at nonbone sites, including skin and perhaps cardiovascular and cerebrovascular sites, prolonged the regulatory approval process. A large multinational randomized, double-blind phase III study of odanacatib in postmenopausal women with osteoporosis was recently completed. Although that study demonstrated clinically relevant reductions in fractures at multiple sites, odanacatib was ultimately withdrawn from the regulatory approval process after it was found to be associated with an increased risk of cerebrovascular accidents. Nonetheless, the underlying biology and clinical effects of cathepsin K inhibition remain of considerable interest and could guide future therapeutic approaches for osteoporosis.

Tfe3 and Tfeb Transcriptionally Regulate Peroxisome Proliferator-Activated Receptor γ2 Expression in Adipocytes and Mediate Adiponectin and Glucose Levels in Mice

Members of the MiT transcription factor family are pivotal regulators of several lineage-selective differentiation programs. We show that two of these, Tfeb and Tfe3, control the regulator of adipogenesis, peroxisome proliferator-activated receptor γ2 (Pparγ2). Knockdown of Tfeb or Tfe3 expression during in vitro adipogenesis causes dramatic downregulation of Pparγ2 expression as well as adipogenesis. Additionally, we found that these factors regulate Pparγ2 in mature adipocytes. Next, we demonstrated that Tfeb and Tfe3 act directly by binding to consensus E-boxes within the Pparγ transcriptional regulatory region. This transcriptional control also exists in vivo, as we discovered that wild-type mice in the fed state increased their expression of Tfe3, Tf3b, and Pparγ in white adipose tissue. Furthermore, Tfe3 knockout (Tfe3KO) mice in the fed state failed to upregulate Pparγ and the adiponectin gene, a Pparγ-dependent gene, confirming the in vivo role for Tfe3. Lastly, we found that blood glucose is elevated and serum adiponectin levels are suppressed in the Tfe3KO mice, indicating that the Tfe3/Tfeb/Pparγ2 axis may contribute to whole-body energy balance. Thus, we offer new insights into the upstream regulation of Pparγ by Tfe3/Tf3b and propose that targeting these transcription factors may offer opportunities to complement existing approaches for the treatment of diseases that have dysregulated energy metabolism.

Mechanisms underlying the association between obesity and Hodgkin lymphoma

A solid body of knowledge indicates that overweight and obese subjects are prone to develop cancer, aggressive disease, and death more than their lean counterparts. While obesity has been causally associated with various cancers, only a limited number of studies beheld the link with classical Hodgkin lymphoma (HL). Contemporary meta-analysis and prospective studies confirmed the association of body mass index with HL. Besides epidemiological evidence, excess adiposity is known to influence tumor behavior through adipokines, adipose-derived stem cell migration, and metabolism regulation, and by modulating immunoinflammatory response. Nevertheless, the obesity paradox has been described in few cancers. Considering that adipose tissue is an immunomodulatory organ, and that inflammation is the cornerstone of HL pathophysiology, the rationale for being causally related due to endocrine/paracrine interactions cannot be negligible. In this hypothesis-generating review, we explore the biologically plausible links between excess adiposity and HL in light of recent basic and clinical data, in order to create a basis for understanding the underlying mechanisms and foster applied research. The establishment of an association of excess adiposity with HL will determine public health preventive measures to fight obesity and eventually novel therapeutic approaches in HL patients.

CTSK inhibitor exert its anti-obesity effects through regulating adipocyte differentiation in high-fat diet induced obese mice

Obesity is associated with increased risk of developing numerous adverse health conditions. Cathepsin k (CTSK) is highly expressed in adipose tissues of obese patients and animal models. Although CTSK has been demonstrated to promote adipocyte differentiation in 3T3-L1 cells, the effects of CTSK selective inhibitor (CKSI) on weight gain and insulin resistance have not been well examined. High-fat diet (HFD) induced obese male C57BL/6 mice were fed a diet with or without CKSI for 8 weeks. The HFD induced increase in adipose tissue weight gain, increase in homeostasis model assessment (HOMA) index as well as accumulation of large adipocytes. After CKSI treatment, all these effects were blunted compared with the HFD control group. A study of the mechanism demonstrated a role for CKSI in significantly down-regulating the expression of two key transcription factors, peroxisome proliferators-activated receptor-γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα), which are markers of adipogenic differentiation. These results indicated that the CKSI possesses an anti-obesity effect, possibly involving the inhibition of adipocyte differentiation. CTSK is likely to be a new target of therapeutic intervention for the treatment of obesity.

CTSB promotes porcine preadipocytes differentiation by degrading fibronectin and attenuating the Wnt/β-catenin signaling pathway

The process of preadipocytes differentiation plays a vital role in adipose tissue expansion and many factors are involved in this event. Cathepsin B (CTSB), secreted from lysosome, has been reported in regulating a variety of physiological processes. In this study, we demonstrated CTSB promotes lipid accumulation and adipogenic genes expression in porcine primary preadipocytes by degrading fibronectin (Fn), a key component of extracellular matrix. Lithium chloride (LiCl) is an activator of Wnt/β-catenin signaling through stabilizing β-catenin. We found that CTSB can relieve the anti-adipogenic effects of LiCl, indicating that CTSB could impact Wnt/β-catenin signaling pathway. Interestingly, Fn is an important target gene of Wnt/β-catenin. So we considered that CTSB promote preadipocytes differentiation by suppressing these two pathways.

Proteases in cardiometabolic diseases: Pathophysiology, molecular mechanisms and clinical applications

Cardiovascular disease is the leading cause of death in the U.S. and other developed countries. Metabolic syndrome, including obesity, diabetes/insulin resistance, hypertension and dyslipidemia is a major threat for public health in the modern society. It is well established that metabolic syndrome contributes to the development of cardiovascular disease collective called as cardiometabolic disease. Despite documented studies in the research field of cardiometabolic disease, the underlying mechanisms are far from clear. Proteases are enzymes that break down proteins, many of which have been implicated in various diseases including cardiac disease. Matrix metalloproteinase (MMP), calpain, cathepsin and caspase are among the major proteases involved in cardiac remodeling. Recent studies have also implicated proteases in the pathogenesis of cardiometabolic disease. Elevated expression and activities of proteases in atherosclerosis, coronary heart disease, obesity/insulin-associated heart disease as well as hypertensive heart disease have been documented. Furthermore, transgenic animals that are deficient in or over-express proteases allow scientists to understand the causal relationship between proteases and cardiometabolic disease. Mechanistically, MMPs and cathepsins exert their effect on cardiometabolic diseases mainly through modifying the extracellular matrix. However, MMP and cathepsin are also reported to affect intracellular proteins, by which they contribute to the development of cardiometabolic diseases. On the other hand, activation of calpain and caspases has been shown to influence intracellular signaling cascade including the NF-κB and apoptosis pathways. Clinically, proteases are reported to function as biomarkers of cardiometabolic diseases. More importantly, the inhibitors of proteases are credited with beneficial cardiometabolic profile, although the exact molecular mechanisms underlying these salutary effects are still under investigation. A better understanding of the role of MMPs, cathepsins, calpains and caspases in cardiometabolic diseases process may yield novel therapeutic targets for treating or controlling these diseases. This article is part of a Special Issue entitled: Autophagy and protein quality control in cardiometabolic diseases.

Diphlorethohydroxycarmalol of Ishige okamurae and Caffeine Modified the Expression of Extracellular Fibrillars during Adipogenesis of Mouse Subcutaneous Adipose Derived Stem Cell

Although, one of the etiologies of localized lipodystrophy of the subcutaneous connective tissue (cellulite) is the histological alternation of adipose tissue, the characteristics of expression of the components of extracellular matrix (ECM) components during adipogenesis are not uncovered. In this study, the effects of caffeine and Ishige okamurae originated diphlorethohydroxycarmalol (DPHC) on the expression of extracellualr fibers was analyzed with quantitative RT-PCR during differentiation induction of mouse subcutaneous adipose derived stem cells (msADSC) into adipocyte. The expression levels of Col1a, Col3a1, and Col61a were decreased by the adipogenci induction in a time-dependent manners. However, Col2a mRNA and Col4a1 mRNA expressions were oposit to them. Caffeine and DPHC stimulated the changes of the expression of these collagens. Eln mRNA expression was increased by induction. DPHC stimulated the expression of it. Mfap5 mRNA expression was deceased in both adipogenic cell and matured adipocytes. Caffeine suppressed the expression of Mfap5 but the effect of DPHC was different by the concentration. The expression of bioglycan, decorin, and lumican were also modified by caffeine and DPHC in a concentration-dependent manner. Based on this study, we revealed firstly the effects of caffeine and DPHC on the expression of collagens, elastin, and glycoproteins during adipogenesis of msADSCs. Those results suggest that DPHC may have antiadipogenic effect and has more positive effets on normal adipose tissue generation and work as suppressor the abnormality of ECM structure. Such results indicate that DPHC can be applied in keeping the stability of the ECM of adipogenic tissues.

ECM roles in the function of metabolic tissues

All metazoan cells produce and/or interact with tissue-specific extracellular matrices (ECMs). Such ECMs play important structural roles not only in connective tissues, but in all tissues in which they provide support and anchorage for cells. However, in addition to such structural roles it has become increasingly clear that the tissue-specific microenvironments formed by the ECM play instructional roles that inform the proper phenotypes and functional behaviors of specialized cell types, and recent in vivo and in vitro studies suggest that ECM components also affect metabolic function. This review summarizes data that provide insights into the roles of the ECM in informing the proper development and functioning of highly specialized cells of metabolic tissues, such as adipocytes and islet β cells.

Human leptin tissue distribution, but not weight loss-dependent change in expression, is associated with methylation of its promoter

Leptin is a master regulator of energy homeostasis. Its expression, prevalently localized in adipocytes, is positively related to adipose mass. Epigenetics is emerging as an important contributor to the changes in gene expression undergone by adipose tissue during obesity. We herein investigated the involvement of methylation-dependent mechanisms in leptin regulation in humans. We studied the methylation profile of a 305 bp region in the leptin promoter and analyzed the correspondent leptin expression in visceral adipocyte fraction (AF) and stromal vascular fraction (SVF) of white adipose tissue (WAT) and liver. We found an inverse relationship between methylation and leptin expression with AF displaying a lower methylation density (8%) than SVF and liver (18%, 21%). We evidenced a hot spot region, which mostly differentiates AF versus liver. This includes C15 and 21, which are within the recognition sequences for the transcription factors Sp1 and C/EBP, and C22-23/24, flanking a TATA box. In vitro studies demonstrated that demethylation (by decitabine) increase or de novo activate leptin expression in primary fibroblasts and HeLa cells, respectively. A longitudinal study carried out in patients analyzed before and after bariatric surgery-induced weight loss indicated that in this case decrease in WAT leptin expression (about 50%) does not correspond to changes in promoter methylation density. In conclusion, methylation density in the leptin promoter constitutes one control level for cell type specific leptin expression, whereas weight-loss induced changes in leptin expression does not seem to be methylation-dependent.

Cathepsin K: its skeletal actions and role as a therapeutic target in osteoporosis

Bone remodeling consists of two phases--bone resorption and bone formation--that are normally balanced. When bone resorption exceeds bone formation, pathologic processes, such as osteoporosis, can result. Cathepsin K is a member of the papain family of cysteine proteases that is highly expressed by activated osteoclasts. Cathepsin K readily degrades type I collagen, the major component of the organic bone matrix. With such a major role in the initial process of bone resorption, cathepsin K has become a therapeutic target in osteoporosis. The antiresorptive properties of cathepsin K inhibitors have been studied in phase I and phase II clinical trials. Phase III studies are currently underway for odanacatib, a selective cathepsin K inhibitor.

Cathepsins and cystatin C in atherosclerosis and obesity

Given the increasing prevalence of human obesity worldwide, there is an urgent need for a better understanding of the molecular mechanisms linking obesity to metabolic and cardiovascular diseases. Our knowledge is nevertheless limited regarding molecules linking adipose tissue to downstream complications. The importance of cathepsins was brought to light in this context. Through a large scale transcriptomic analysis, our group recently identified the gene encoding cathepsin S as one of the most deregulated gene in the adipose tissue of obese subjects and positively correlated with body mass index. Other members of the cathepsin family are expressed in the adipose tissue, including cathepsin K and cathepsin L. Given their implication in atherogenesis, these proteases could participate into the well established deleterious relationship between enlarged adipose tissue and increased cardiovascular risk. Here, we review the clinical and experimental evidence relevant to the role of cathepsins K, L and S and their most abundant endogenous inhibitor, cystatin C, in atherosclerosis and in obesity.

Kininogens: More than cysteine protease inhibitors and kinin precursors

Two kininogens are found in mammalian sera: HK (high molecular weight kininogen) and LK (low molecular weight kininogen) with the exception of the rat which encompasses a third kininogen, T-Kininogen (TK). Kininogens are multifunctional glycosylated molecules related to cystatins (clan IH, family I25). They harbor three cystatin domains but only two of them are tight-binding inhibitors of cysteine cathepsins. HK and LK, but not TK, are precursors of potent peptide hormones, the kinins, which are released proteolytically by tissue and plasma kallikreins. Besides these classical features novel functions of kininogens have been recently discovered; they are described in the second part of this review. HKa, which corresponds to the kinin-free two-chain HK and its isolated domain D5 (kininostatin), possesses angiostatic and pro-apoptotic properties, inhibits the proliferation of endothelial cells and participates in the regulation of angiogenesis. Moreover, some HK-derived peptides display potent and broad-spectrum microbicidal properties against both Gram-positive and Gram-negative bacteria, and thus may offer a promising alternative to conventional antibiotic therapy. Of seminal interest, a kininogen-derived peptide inhibits activation of the contact phase system of coagulation and protects mice with invasive Streptococcus pyogenes infection from pulmonary lesions. On the other hand, TK is a biomarker of aging at the end of lifespan of elderly rats. However, although TK has been initially identified as an acute phase reactant, and earlier known as alpha-l-acute phase globulin, the increase of TK in liver and plasma is not known to relate to any inflammatory event during the senescence process.

High fat diet-induced animal model of age-associated obesity and osteoporosis

Osteoporosis and obesity remain a major public health concern through its associated fragility and fractures. Several animal models for the study of osteoporotic bone loss, such as ovariectomy (OVX) and denervation, require unique surgical skills and expensive set up. The challenging aspect of these age-associated diseases is that no single animal model exactly mimics the progression of these human-specific chronic conditions. Accordingly, to develop a simple and novel model of post menopausal bone loss with obesity, we fed either a high fat diet containing 10% corn oil (CO) or standard rodent lab chow (LC) to 12-month-old female C57Bl/6J mice for 6 months. As a result, CO fed mice exhibited increased body weight, total body fat mass, abdominal fat mass and reduced bone mineral density (BMD) in different skeletal sites measured by dual energy X-ray absorptiometry. We also observed that decreased BMD with age in CO fed obese mice was accompanied by increased bone marrow adiposity, up-regulation of peroxisome proliferator-activated receptor γ, cathepsin k and increased proinflammatory cytokines (interleukin 6 and tumor necrosis factor α) in bone marrow and splenocytes, when compared to that of LC fed mice. Therefore, this appears to be a simple, novel and convenient age-associated model of post menopausal bone loss, in conjunction with obesity, which can be used in pre-clinical drug discovery to screen new therapeutic drugs or dietary interventions for the treatment of obesity and osteoporosis in the human population.

A single nucleotide polymorphism in the porcine cathepsin K (CTSK) gene is associated with back fat thickness and production traits in Italian Duroc pigs

Cathepsin K (CTSK) was selected as a candidate gene for fat deposition in pigs because recently, in human and mouse, it was shown that this lysosomal proteinase is an obesity marker. A single nucleotide polymorphism (SNP) was identified in intron 4 of the porcine CTSK gene (g.15G>A; FM209043). Allele frequencies of this polymorphism were analysed in seven pig breeds. Radiation hybrid mapping confirmed the localization of CTSK to porcine chromosome 4, close to the FAT1 QTL region. Three populations of pigs (one Italian Large White and two Italian Duroc groups of pigs) were selected for association analysis. In the Italian Large White breed the g.15G>A SNP was not informative. Association analysis including all Italian Duroc pigs showed that the CTSK marker was associated with back fat thickness and lean cuts (P < 0.01), and average daily gain and feed:gain ratio (P < 0.05) estimated breeding values.

Cathepsin K inhibitors for osteoporosis and potential off-target effects

Cathepsin K is a highly potent collagenase and the predominant papain-like cysteine protease expressed in osteoclasts. Cathepsin K deficiencies in humans and mice have underlined the central role of this protease in bone resorption and, thus, have rendered the enzyme as an attractive target for anti-resorptive osteoporosis therapy. In the past decade, a lot of efforts have been made in developing highly potent, selective and orally applicable cathepsin K inhibitors. Some of these inhibitors have passed preclinical studies and are presently in clinical trials at different stages of advancement. The development of the inhibitors and preliminary results of the clinical trials revealed problems and lessons concerning the in situ specificity of the compounds and their tissue targeting. In this review, we briefly summarize the history of cathepsin K research and discuss the current development of cathepsin K inhibitors as novel anti-resorptives for the treatment of osteoporosis. We also discuss potential off-target effects of cathepsin K inhibition and alternative applications of cathepsin K inhibitors in arthritis, atherosclerosis, blood pressure regulation, obesity and cancer.

Cathepsin K regulates adipocyte differentiation: possible involvement of type I collagen degradation

We previously found that cathepsin K (CTSK) played an important role in adipocyte differentiation. However, the underlying molecular mechanism is not clear. Through the time window study, it was observed that CTSK activities were required mainly in the early phases of adipogenic process. At the same time, the expression of type I collagen disappeared. However, type I collagen can still be observed during the whole process when the CTSK inhibitor-E64 was added. The mRNA levels of peroxisome proliferator-activated receptor gamma (PPAR-gamma) and CCAAT/enhancer binding protein alpha (C/EBP-alpha) was also declining. These imply that CTSK may play a role in adipogenesis in early differentiation phases and produce an effect at least partly by degrading type I collagen, which may provides a basis for developing novel therapeutic approaches to treat obesity and the diseases associated with it.

Different transcriptional control of metabolism and extracellular matrix in visceral and subcutaneous fat of obese and rimonabant treated mice

BACKGROUND

The visceral (VAT) and subcutaneous (SCAT) adipose tissues play different roles in physiology and obesity. The molecular mechanisms underlying their expansion in obesity and following body weight reduction are poorly defined.

METHODOLOGY

C57Bl/6 mice fed a high fat diet (HFD) for 6 months developed low, medium, or high body weight as compared to normal chow fed mice. Mice from each groups were then treated with the cannabinoid receptor 1 antagonist rimonabant or vehicle for 24 days to normalize their body weight. Transcriptomic data for visceral and subcutaneous adipose tissues from each group of mice were obtained and analyzed to identify: i) genes regulated by HFD irrespective of body weight, ii) genes whose expression correlated with body weight, iii) the biological processes activated in each tissue using gene set enrichment analysis (GSEA), iv) the transcriptional programs affected by rimonabant.

PRINCIPAL FINDINGS

In VAT, "metabolic" genes encoding enzymes for lipid and steroid biosynthesis and glucose catabolism were down-regulated irrespective of body weight whereas "structure" genes controlling cell architecture and tissue remodeling had expression levels correlated with body weight. In SCAT, the identified "metabolic" and "structure" genes were mostly different from those identified in VAT and were regulated irrespective of body weight. GSEA indicated active adipogenesis in both tissues but a more prominent involvement of tissue stroma in VAT than in SCAT. Rimonabant treatment normalized most gene expression but further reduced oxidative phosphorylation gene expression in SCAT but not in VAT.

CONCLUSION

VAT and SCAT show strikingly different gene expression programs in response to high fat diet and rimonabant treatment. Our results may lead to identification of therapeutic targets acting on specific fat depots to control obesity.

Deficiency and inhibition of cathepsin K reduce body weight gain and increase glucose metabolism in mice

OBJECTIVE

Previous studies demonstrated increased levels of cysteine proteases cathepsins in serum and adipose tissues from obese patients. We now provide evidence from a mouse model of obesity to suggest a direct participation of cathepsin K (CatK) in mouse body weight gain and glucose metabolism.

METHODS AND RESULTS

Using real-time polymerase chain reaction, we detected 12-fold increase in CatK transcripts after adipogenesis of human preadipocytes. Using an immunohistology analysis, we consistently observed high levels of CatK expression in adipose tissues from obese humans and mice. Selective inhibition of CatK activity blocked the lipid accumulation in human and mouse preadipocytes. In mice, CatK deficiency reduced significantly diet-induced body weight gain and serum glucose and insulin levels. Similar results were obtained in diet-induced and genetically created (ob/ob) obese mice after animals were treated with a CatK-selective inhibitor. Mechanistic study demonstrated a role for CatK in degrading fibronectin, a matrix protein that controls adipogenesis. Deficiency or inhibition of CatK leads to fibronectin accumulation in muscle and adipose tissues.

CONCLUSIONS

This study demonstrates an essential role of CatK in adipogenesis and mouse body weight gain, possibly via degradation of fibronectin, thus suggesting a novel therapeutic strategy for the control of obesity by regulating CatK activity.

Monomeric tartrate resistant acid phosphatase induces insulin sensitive obesity

BACKGROUND

Obesity is associated with macrophage infiltration of adipose tissue, which may link adipose inflammation to insulin resistance. However, the impact of inflammatory cells in the pathophysiology of obesity remains unclear. Tartrate resistant acid phosphatase (TRAP) is an enzyme expressed by subsets of macrophages and osteoclasts that exists either as an enzymatically inactive monomer or as an active, proteolytically processed dimer.

PRINCIPAL FINDINGS

Using mice over expressing TRAP, we show that over-expression of monomeric, but not the dimeric form in adipose tissue leads to early onset spontaneous hyperplastic obesity i.e. many small fat cells. In vitro, recombinant monomeric, but not proteolytically processed TRAP induced proliferation and differentiation of mouse and human adipocyte precursor cells. In humans, monomeric TRAP was highly expressed in the adipose tissue of obese individuals. In both the mouse model and in the obese humans the source of TRAP in adipose tissue was macrophages. In addition, the obese TRAP over expressing mice exhibited signs of a low-grade inflammatory reaction in adipose tissue without evidence of abnormal adipocyte lipolysis, lipogenesis or insulin sensitivity.

CONCLUSION

Monomeric TRAP, most likely secreted from adipose tissue macrophages, induces hyperplastic obesity with normal adipocyte lipid metabolism and insulin sensitivity.

Free fatty acids as mediators of adaptive compensatory responses to insulin resistance in dexamethasone-treated rats

BACKGROUND

Chronic low-dose dexamethasone (DEX) treatment in rats is associated to insulin resistance with compensatory hyperinsulinaemia and reduction in food intake. We tested the hypothesis that the elevation in circulating free fatty acids (FFAs) induced by DEX is the common mediator of both insulin resistance and insulin hyperproduction.

METHODS

For this purpose, an anti-lipolytic agent was administered during DEX treatment to lower lipacidaemia for several hours prior to glucose and insulin tolerance tests. Leptin expression in adipose tissue (by Northern blot) and plasma leptin levels (by radioimmunoassay) were also investigated to verify whether a rise in circulating leptin could be responsible for the anorectic effect of DEX.

RESULTS

Our data show that a transient pharmacological reduction of elevated plasma FFA levels abates the post-loading hyperinsulinaemia and counteracts the insulin resistance induced by DEX, supporting the hypothesis that the chronic elevation in FFAs is the common mediator of DEX-induced changes. Despite enhanced leptin expression in white adipose tissue, DEX-treated rats show no significant increase in plasma leptin levels. This suggests that the anorectic effect of DEX should be mediated, at least partially, by other factors, possibly related to the influence of concomitantly elevated plasma FFA and insulin levels on the hypothalamic centers regulating feeding.

CONCLUSIONS

Our results sustain the idea that a prolonged increase in plasma FFA levels plays an important role in the adaptive regulation of glucose and energy homeostasis, not only by potentiating insulin secretion but also by providing a signal of 'nutrient abundance' capable of restraining food intake.

Biochemical properties and regulation of cathepsin K activity

Cysteine cathepsins (11 in humans) are mostly located in the acidic compartments of cells. They have been known for decades to be involved in intracellular protein degradation as housekeeping proteases. However, the discovery of new cathepsins, including cathepsins K, V and F, has provided strong evidence that they also participate in specific biological events. This review focuses on the current knowledge of cathepsin K, the major bone cysteine protease, which is a drug target of clinical interest. Nevertheless, we will not discuss recent developments in cathepsin K inhibitor design since they have been extensively detailed elsewhere. We will cover features of cathepsin K structure, cellular and tissue distribution, substrate specificity, and regulation (pH, propeptide, glycosaminoglycans, oxidants), and its putative roles in physiological or pathophysiological processes. Finally, we will review the kinetic data of its inhibition by natural endogenous inhibitors (stefin B, cystatin C, H- and L-kininogens).

Cathepsin K null mice show reduced adiposity during the rapid accumulation of fat stores

Growing evidences indicate that proteases are implicated in adipogenesis and in the onset of obesity. We previously reported that the cysteine protease cathepsin K (ctsk) is overexpressed in the white adipose tissue (WAT) of obese individuals. We herein characterized the WAT and the metabolic phenotype of ctsk deficient animals (ctsk−/−). When the growth rate of ctsk−/− was compared to that of the wild type animals (WT), we could establish a time window (5–8 weeks of age) within which ctsk−/−display significantly lower body weight and WAT size as compared to WT. Such a difference was not observable in older mice. Upon treatment with high fat diet (HFD) for 12 weeks ctsk−/− gained significantly less weight than WT and showed reduced brown adipose tissue, liver mass and a lower percentage of body fat. Plasma triglycerides, cholesterol and leptin were significantly lower in HFD-fed-ctsk−/− as compared to HFD-fed WT animals. Adipocyte lipolysis rates were increased in both young and HFD-fed-ctsk−/−, as compared to WT. Carnitine palmitoyl transferase-1 activity, was higher in mitochondria isolated from the WAT of HFD treated ctsk−/− as compared to WT. Together, these data indicate that ctsk ablation in mice results in reduced body fat content under conditions requiring a rapid accumulation of fat stores. This observation could be partly explained by an increased release and/or utilization of FFA and by an augmented ratio of lipolysis/lipogenesis. These results also demonstrate that under a HFD, ctsk deficiency confers a partial resistance to the development of dyslipidemia.

Cathepsin L activity controls adipogenesis and glucose tolerance

Cysteine proteases play an important part in human pathobiology. This report shows the participation of cathepsin L (CatL) in adipogenesis and glucose intolerance. In vitro studies demonstrate the role of CatL in the degradation of the matrix protein fibronectin, insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF-1R), essential molecules for adipogenesis and glucose metabolism. CatL inhibition leads to the reduction of human and murine pre-adipocyte adipogenesis or lipid accumulation, protection of fibronectin from degradation, accumulation of IR and IGF-1R beta-subunits, and an increase in glucose uptake. CatL-deficient mice are lean and have reduced levels of serum glucose and insulin but increased levels of muscle IR beta-subunits, fibronectin and glucose transporter (Glut)-4, although food/water intake and energy expenditure of these mice are no less than their wild-type littermates. Importantly, the pharmacological inhibition of CatL also demonstrates reduced body weight gain and serum insulin levels, and increased glucose tolerance, probably due to increased levels of muscle IR beta-subunits, fibronectin and Glut-4 in both diet-induced obese mice and ob/ob mice. Increased levels of CatL in obese and diabetic patients suggest that this protease is a novel target for these metabolic disorders.

Cathepsin K in the bone microenvironment: link between obesity and prostate cancer?

The skeleton is the most common site of metastasis in patients with advanced prostate cancer. Despite many advances in targeting skeletal metastases, the mechanisms behind the attraction of prostate cancer cells to the bone are not known. Osteoclast cathepsin K, due to its ability to effectively degrade bone matrix collagen I, has been implicated in colonization and growth of prostate tumours in the bone. Identification of new cathepsin K substrates in the bone microenvironment and the recent findings demonstrating its involvement in obesity and inflammation suggest additional roles for this enzyme in skeletal metastases of prostate cancer.

Clustering biological annotations and gene expression data to identify putatively co-regulated biological processes

MOTIVATION

Functional profiling is a key step of microarray gene expression data analysis. Identifying co-regulated biological processes could help for better understanding of underlying biological interactions within the studied biological frame.

RESULTS

We present herein an original approach designed to search for putatively co-regulated biological processes sharing a significant number of co-expressed genes. An R language implementation named "FunCluster" was built and tested on two gene expression data sets. A discriminatory functional analysis of the first data set, related to experiments performed on separated adipocytes and stroma vascular fraction cells of human white adipose tissue, highlighted the prevalent role of nonadipose cells in the synthesis of inflammatory and immunity molecules in human adiposity. On the second data set, resulting from a model investigating insulin coordinated regulation of gene expression in human skeletal muscle, FunCluster analysis spotlighted novel functional classes of putatively co-regulated biological processes related to protein metabolism and the regulation of muscular contraction.

AVAILABILITY

Supplementary information about the FunCluster tool is available on-line at http://corneliu.henegar.info/FunCluster.htm.

Prevention of high-fat diet-induced adipose tissue remodeling in obese diabetic mice by n-3 polyunsaturated fatty acids

OBJECTIVE

Obesity is associated with reduced insulin sensitivity and extensive reorganization of adipose tissue. As polyunsaturated fatty acids (PUFA) appear to inhibit diabetes development, we investigated PUFA effects on markers of matrix remodeling in white adipose tissue.

METHODS AND PROCEDURE

Male obese diabetic (db/db) mice were treated with either a low-fat standard diet (LF), or high-fat diets rich in saturated and monounsaturated fatty acids (HF/S), n-6 PUFA (HF/6) or the latter including marine n-3 PUFA (HF/3). White adipose tissue was analyzed for gene expression, fatty acid composition and by immunofluorescence.

RESULTS

HF/S treatment increased adipose tissue expression of a number of genes involved in matrix degradation including matrix metalloproteinase (MMP)-12, -14 and cathepsin K, L and S compared with LF. MMP-12 gene was expressed in macrophages and adipocytes, and MMP-12 protein colocalized with both cell types. In addition, mean adipocyte area increased by 1.6-fold in HF/S-treated mice. Genes essential for collagen production, such as procollagen I, III, VI, tenascin C and biglycan were upregulated in HF/S-treated animals as well. N-3 PUFA supplementation resulted in enrichment of these fatty acids in adipose tissue. Moreover, n-3 PUFA inhibited the HF/S-induced upregulation of genes involved in matrix degradation and production I restored mean adipocyte area and prevented MMP-12 expression in macrophages and adipocytes.

CONCLUSION

N-3 PUFA prevent high-fat diet-induced matrix remodeling and adipocyte enlargement in adipose tissue of obese diabetic mice. Such changes could contribute to diabetes prevention by n-3 PUFA in obese patients.

Cathepsin K in adipocyte differentiation and its potential role in the pathogenesis of obesity

CONTEXT

The alteration of protein expression in white adipose tissue (WAT) may contribute to the pathogenesis of obesity.

OBJECTIVE

The aim of the present study was to uncover proteins differentially expressed in the WAT of overweight/obese subjects and study the role of the identified proteins in adipocyte differentiation.

DESIGN AND SETTING

Two-dimensional electrophoresis and matrix-assisted laser desorption ionization-time of flight-mass spectrometry were used to identify proteins differentially expressed in WAT between obese/overweight and control groups. Cathepsin K (CTSK), one of the proteins identified by the above methods, was highlighted to assess its effects on adipocyte differentiation through 3T3-L1 cell line.

RESULTS

Human visceral adipose tissue of overweight/obese subjects displayed a differential protein expression profile, compared with that of normal-weight controls. CTSK was up-regulated in the WAT of overweight/obese subjects, and it had a significant positive correlation with body mass index. In vitro study showed that CTSK expression and its enzyme activity gradually increased in the process of adipocyte differentiation. Moreover, E-64, an inhibitor of CTSK, could prevent adipocyte differentiation in a dose-dependent manner, which was characterized by the absence of triglyceride accumulation and glycerol contents.

CONCLUSIONS

CTSK, a cysteine protease involved in extracellular matrix remodeling, could be one of the determinants of adipocyte differentiation. CTSK may be involved in the pathogenesis of obesity by promoting adipocyte differentiation.

Most of the interleukin 1 receptor antagonist, cathepsin S, macrophage migration inhibitory factor, nerve growth factor, and interleukin 18 release by explants of human adipose tissue is by the non-fat cells, not by the adipocytes

The present studies were designed to compare the relative release of interleukin 1 receptor antagonist (IL-1Ra), cathepsin S, macrophage migration inhibitory factor (MIF), nerve growth factor (NGF), and interleukin 18 (IL-18) by adipocytes as compared with the non-fat cells present in subcutaneous and omental adipose tissue from morbidly obese gastric bypass patients as compared with obese abdominoplasty patients. The release of IL-1Ra, cathepsin S, and MIF by explants of human adipose tissue incubated for 48 hours averaged 6, 9, and 19 pmol/g, respectively, and was far greater than the release of NGF (0.05 pmol/g) or IL-18 (0.006 pmol/g). The release by human adipocytes of IL-1Ra, cathepsin S, and MIF was 0.13, 0.32, and 2.6 pmol/g, respectively, over 48 hours, whereas NGF release was 0.003 and IL-18 0.001 pmol/g. Only the total release of MIF by human adipose tissue explants was enhanced, whereas that of IL-18 was significantly reduced in explants from morbidly obese women. Most of (55%-73%) the release of IL-1Ra, cathepsin S, MIF, NGF, and IL-18 was by the adipose tissue matrix, whereas release by stromal-vascular (SV) cells was 3% to 28% of total release over 48 hours by the adipose tissue matrix, SV cells and adipocytes. The release of NGF by adipocytes was 42%, that of MIF was 27%, and for the other factors 15% or less of release over 48 hours by the adipose tissue matrix, SV cells, and adipocytes. Our results suggest that the non-fat cells in human adipose tissue contribute to most of the release of NGF, IL-18, IL-1Ra, cathepsin S, and MIF seen during primary culture of adipose tissue explants from obese women.

High-fat feeding period affects gene expression in rat white adipose tissue

The expression of 76 sequences, previously isolated as differentially expressed in visceral white adipose tissue (WAT) of female rats, fed with a high-fat diet for 11 days (Lopez et al., Biochem Biophys Res Comm 318: 234-239, 2004), was analyzed in epidydimal WAT of male rats after a feeding period of 65 days with the same diet, using microarray technology. After Northern blot validation of the results, only three genes appeared upregulated (caveolin-2, the alpha-1 chain of haemoglobin and rat mammary tumor-7) and two downregulated (adiponectin and dystroglycan). We have also analyzed caveolin-1 gene expression and found that follows the opposite pattern of caveolin-2, indicating that they are inversely regulated. Our results suggest that if feeding with a high-fat diet is prolonged, many of the initial changes in gene expression, probably aimed to consume the energy surplus and prevent excessive fat deposition, are not maintained, and adaptation to an increased lipid storage is developed.

Molecular cloning and characterization of oryzacystatin-III, a novel member of phytocystatin in rice (Oryza sativa L. japonica)

On the basis of cDNA sequences, we found that the calli of rice encodes an amino acid sequence that shares 56% and 89% identity, respectively, with oryzacystatin-I and oryzacystatin-II. This sequence differs from that of oryzacystatin-II in the N-terminal region (Gln(7)-Ala(19) in the oryzacystatin-III numbering), and this region contained a glycine residue (Gly(14)), which is evolutionarily conserved in the cystatin superfamily. We named this novel protein oryzacystatin-III. Nucleotide sequencing of the 5'-flanking region of the oryzacystatin-III gene showed that it is highly homologous to the oryzacystatin-II gene but distinct from the oryzacystatin-II locus. Oryzacystatin-III inhibited papain, ficin, and human cathepsin B. The inhibition constants for papain and ficin differ from those of oryzacystatin-I and -II, and cathepsin B activity is affected only by oryzacystatin-III, showing differences in the interaction of these inhibitors with enzymes. These data suggest that the above three inhibitors may play unique physiological roles in the regulations of rice cysteine proteinases.

Cathepsin S, a novel biomarker of adiposity: relevance to atherogenesis

The molecular mechanisms by which obesity increases the risk of cardiovascular diseases are poorly understood. The purpose of this study was to identify candidate biomarkers overexpressed in adipose tissue of obese subjects that could link expanded fat mass to atherosclerosis. We compared gene expression profile in subcutaneous adipose tissue (scWAT) of 28 obese and 11 lean subjects using microarray technology. This analysis identified 240 genes significantly overexpressed in scWAT of obese subjects. The genes were then ranked according to the correlation between gene expression and body mass index (BMI). In this list, the elastolytic cysteine protease cathepsin S was among the highly correlated genes. RT-PCR and Western blotting confirmed the increase in cathepsin S mRNA (P=0.006) and protein (P<0.05) in obese scWAT. The circulating concentrations of cathepsin S were also significantly higher in obese than in nonobese subjects (P<0.0001). Both cathepsin S mRNA in scWAT and circulating levels were positively correlated with BMI, body fat, and plasma triglyceride levels. In addition, we show that the proinflammatory factors, lipopolysaccharide, interleukin-1beta, and tumor necrosis factor-alpha increase cathepsin S secretion in human scWAT explants. This study identifies cathepsin S as a novel marker of adiposity. Since this enzyme has been implicated in the development of atherosclerotic lesions, we propose that cathepsin S represents a molecular link between obesity and atherosclerosis.

Discriminate gene lists derived from cDNA microarray profiles of limited samples permit distinguishing mesenchymal neoplasia ex vivo

BACKGROUND

Mesenchymal neoplasia comprises a heterogeneous group of tumors with over 200 benign neoplasms and 100 sarcomas. Currently, tumors are classified using histologic and immunocytologic characteristics, with diagnostic error rates reported as high as 40% of cases. As a feasibility study, our goal was to generate a preliminary discriminatory gene list for selected mesenchymal tumors, including sarcomas. This technique may enable an eventual molecular classification schema based on expression profiles that can complement current clinical and pathologic diagnostic procedures in mesenchymal tumors.

METHODS

cDNA microarray analyses were preformed on connective tissue tumors obtained at time of surgical resection or biopsy. Messenger RNA (mRNA) from four general tumor classes was competitively hybridized against a human dermal fibroblast cell line comparator and the resulting gene expression profiles processed by ANOVA and linear discriminate analysis.

RESULTS

The tissue classification involved 18 patients with malignant peripheral nerve sheath tumors, giant cell containing tumors, benign spindle cell lesions, or Ewing's family of tumors. Lymph nodes from two patients served comparative purposes. Twenty-five differentially regulated genes considered most variable among the five tissue classes were identified. The tissues were segregated into five classes by linear discriminate analysis.

CONCLUSIONS

Linear discriminate analysis of cDNA gene expression profiles partitioned mesenchymal tumor classes, even when constrained by limited sample sizes.

An activity-based probe for the determination of cysteine cathepsin protease activities in whole cells

We describe a novel diazomethylketone-containing irreversible inhibitor (BIL-DMK) which is specific for a subset of pharmaceutically important cysteine cathepsin proteases. BIL-DMK rapidly inactivates cathepsins B, F, K, L, S, and V in isolated enzyme assays and labels cathepsins in whole cells. The presence of catalytically active cathepsins B, L, and K or S was demonstrated using radioiodinated BIL-DMK in HepG2 (hepatoma), HIG82 (rabbit synoviocyte), and Ramos (B lymphoma) cell lines, respectively. The identity of each protein labeled was confirmed from the isoelectric point and molecular mass of the radioactive spots on two-dimensional gel and by comigration with each cathepsin as identified by immunoblotting. These cell lines were used to establish whole-cell enzyme occupancy assays to determine the potency of both irreversible and reversible inhibitors against each cathepsin in their native cellular lysosomal or endosomal environment. These whole-cell enzyme occupancy assays are useful to determine the cellular permeability of competing inhibitors and have the advantage of not requiring specific substrates for each cathepsin of interest.

Serum haptoglobin: a novel marker of adiposity in humans

Haptoglobin (Hp) is a glycoprotein involved in the acute phase response to inflammation. Our previous findings indicate that Hp mRNA and protein are present in the adipose tissue of rodents and that Hp gene expression is up-regulated in obese models. The aim of the present study was to establish whether Hp could be considered a marker of obesity in humans. In 312 subjects, serum Hp was correlated directly with body mass index (BMI), leptin, C-reactive protein (CRP), and age. In a multivariate stepwise regression analysis, BMI and CRP were independent determinants of serum Hp in females, with BMI having the strongest effect. CRP and age were independent determinants of serum Hp in males, although explaining only a modest percentage of the total variability. Serum Hp was positively associated with body fat, as assessed by dual-energy x-ray absorptiometry, both in female and in male groups. The level of significance improved when serum Hp was analyzed against fat mass adjusted for lean mass. Finally, Northern and Western blot analyses performed in biopsies of sc abdominal fat from 20 obese individuals showed the presence of Hp mRNA and protein in the human adipose tissue. In conclusion, serum Hp constitutes a novel marker of adiposity in humans, and the adipose tissue likely contributes to determine its levels.