Cleavage of type II collagen by cathepsin K in human osteoarthritic cartilage

Innovative workflow for the identification of cathepsin K cleavage sites in type I collagen

Since the late 1990s, cathepsin K cleavage sites in type I collagen have been extensively studied due to its ability to release bone resorption biomarkers such as CTX and NTX. However, gel-based methods and N-sequencing used in these studies lack sensitivity, especially for small to medium peptides. In this work, we propose a degradomics mass spectrometry-based workflow that combines protein digestion, Nano-LC-UDMSE, and several software tools to identify cathepsin K cleavage sites. This workflow not only identified previously known cleavage sites, but also discovered new ones. Multiple cleavage hotspots were found and described in type I α1 and type I α2 collagen, many of which coincided with pyridinoline crosslinks, known to stabilize the triple helix. Our results allowed us to establish a chronology of digestion and conclude that cathepsin K preferentially cleaves the extremities of type I collagen before the helical part. We also found that cathepsin K preferentially cleaves amino acid residues with long and hydrophobic lateral chains at the beginning of digestion, whereas no preferred amino acid residues were identified later in the digestion. In conclusion, our workflow successfully identified new cleavage sites and can be easily applied to other proteins or proteases.

Latest insights in disease-modifying osteoarthritis drugs development

Osteoarthritis (OA) is a prevalent and severely debilitating disease with an unmet medical need. In order to alleviate OA symptoms or prevent structural progression of OA, new drugs, particularly disease-modifying osteoarthritis drugs (DMOADs), are required. Several drugs have been reported to attenuate cartilage loss or reduce subchondral bone lesions in OA and thus potentially be DMOADs. Most biologics (including interleukin-1 (IL-1) and tumor necrosis factor (TNF) inhibitors), sprifermin, and bisphosphonates failed to yield satisfactory results when treating OA. OA clinical heterogeneity is one of the primary reasons for the failure of these clinical trials, which can require different therapeutic approaches based on different phenotypes. This review describes the latest insights into the development of DMOADs. We summarize in this review the efficacy and safety profiles of various DMOADs targeting cartilage, synovitis, and subchondral bone endotypes in phase 2 and 3 clinical trials. To conclude, we summarize the reasons for clinical trial failures in OA and suggest possible solutions.

Long-term intake of Lilium lancifolium mitigated osteoarthritic effects by suppressing inflammatory cytokines in a dog model

Background and Aim: Osteoarthritis (OA) is a chronic, painful, degenerative inflammatory disease of the synovial joints. Regular use of nonsteroidal anti-inflammatory drugs to decrease OA pain can have severe side effects, such as gastric irritation, ulcers, and heart problems. Natural products are extensively used to minimize OA-associated pain and inflammatory reactions. Lilium lancifolium is commonly used to alleviate several diseases through its anti-inflammatory effects. This study examined the impact of L. lancifolium extract on alleviating pain and inflammation associated with articular cartilage damage. Materials and Methods: Hydro-ethanol extracts of the L. lancifolium bulb were used. The experimental animals (adult beagle dogs) were divided into four groups: sham, which received neither treatment nor surgery; placebo, which received an empty gelatin capsule; glucosamine, which received glutamine (60 mg/kg); and L. lancifolium, which received an L. lancifolium extract-filled (60 mg/kg) gelatin capsule for 8 weeks. OA was induced by an expert orthopedic surgeon in 2-year-old dogs through resection of cranial cruciate ligament and lateral collateral ligament. Inflammatory cytokines, enzymes, lameness score, radiology, and histological changes were assessed. Results: Our experiments showed that long-term oral therapy with L. lancifolium alleviated inflammation and increased histological damage. L. lancifolium treatment effectively reduced cytokines, such as interleukin-6, metalloproteinase-9, leukotriene-4, prostaglandin, and cyclo-oxygenase in dogs with OA, suggesting the potential to minimize inflammatory reactions in OA. L. lancifolium showed anti-inflammatory qualities in dogs with OA. This effect was comparable with that of glucosamine OA treatment. Conclusion: L. lancifolium supplementation represents a possible therapeutic and management option in this model of OA.

The Bone Cartilage Interface and Osteoarthritis

This review describes results obtained with tissue from prior studies of equine and human osteoarthritis (OA). The main methods considered are scanning electron microscopy, novel methods in light microscopy and X-ray Micro-tomography. The same samples have been re-utilised in several ways. The tissues described are hyaline articular cartilage (HAC; or substitutes), with its deep layer, articular calcified cartilage (ACC), whose deep surface is resorbed in cutting cone events to allow the deposition of subchondral bone (SCB). Multiple tidemarks are normal. Turnover at the osteochondral (ACC-HAC-SCB) junction is downregulated by overload exercise, conversely, during rest periods. Consequent lack of support predisposes to microfracture of the ACC-SCB plate, in the resorption-related repair phase of which the plate is further undermined to form sink holes. The following characteristics contribute to the OA scenario: penetrating resorption canals and local loss of ACC; cracking of ACC and SCB; sealing of cracks with High-Density Mineral Infill (HDMI); extrusion of HDMI into HAC to form High-Density Mineral Protrusions (HDMP) in HAC which may fragment and contribute to its destruction; SCB marrow space infilling and densification with (at first) woven bone; disruption, fibrillation and loss of HAC; eburnation; repair with abnormal tissues including fibrocartilage and woven bone; attachment of Sharpey fibres to SCB trabeculae and adipocyte-moulded extensions to trabeculae (excrescences).

The Development of Disease-Modifying Therapies for Osteoarthritis (DMOADs): The Evidence to Date

Osteoarthritis (OA) is a complex heterogeneous articular disease with multiple joint tissue involvement of varying severity and no regulatory-agency-approved disease-modifying drugs (DMOADs). In this review, we discuss the reasons necessitating the development of DMOADs for OA management, the classifications of clinical phenotypes or molecular/mechanistic endotypes from the viewpoint of targeted drug discovery, and then summarize the efficacy and safety profile of a range of targeted drugs in Phase 2 and 3 clinical trials directed to cartilage-driven, bone-driven, and inflammation-driven endotypes. Finally, we briefly put forward the reasons for failures in OA clinical trials and possible steps to overcome these barriers.

The CD200-CD200R axis promotes squamous cell carcinoma metastasis via regulation of cathepsin K

The CD200-CD200R immunoregulatory signaling axis plays an etiological role in the survival and spread of numerous cancers primarily through suppression of anti-tumor immune surveillance. Our previous work outlined a pro-metastatic role for the CD200-CD200R axis in cutaneous squamous cell carcinoma (cSCC) that is independent of direct T cell suppression but modulates the function of infiltrating myeloid cells. To identify effectors of the CD200-CD200R axis important for cSCC metastasis, we conducted RNA-Seq profiling of infiltrating CD11B+Cd200R+ cells isolated from CD200+ versus CD200-null cSCCs and identified the cysteine protease cathepsin K (Ctsk) to be highly upregulated in CD200+ cSCCs. CD11B+Cd200R+ cells expressed phenotypic markers associated with myeloid-derived suppressor cell-like cells and tumor-associated macrophages and were the primary source of Ctsk expression in cSCC. A Cd200R+ myeloid cell-cSCC co-culture system showed that induction of Ctsk was dependent on engagement of the CD200-CD200R axis, indicating that Ctsk is a target gene of this pathway in the cSCC tumor microenvironment. Inhibition of Ctsk, but not matrix metalloproteinases (MMP), significantly blocked cSCC cell migration in vitro. Finally, targeted CD200 disruption in tumor cells and Ctsk pharmacological inhibition significantly reduced cSCC metastasis in vivo. Collectively, these findings support the conclusion that CD200 stimulates cSCC invasion and metastasis via induction of Ctsk in CD200R+ infiltrating myeloid cells.

Tannic acid/Sr2+-coated silk/graphene oxide-based meniscus scaffold with anti-inflammatory and anti-ROS functions for cartilage protection and delaying osteoarthritis

Tissue engineering method provides a promising solution for meniscus repair and regeneration. However, the inflammatory environment that persists after meniscus injury in the knee joint impedes meniscus tissue regeneration. The purpose of this study was to investigate the applicability of silk/graphene oxide (GO)-based meniscus scaffold modified with tannic acid (TA)/Sr²⁺ coating for the elimination of inflammatory cytokines and reactive oxygen species (ROS) under osteoarthritis (OA) environment along with cartilage protection by using a rat model. The self-assembled coating composed of a series of TA-Sr²⁺ complex concentrations was formed by a facile, rapid, and efficient method on the scaffold. The phenolic hydroxyl groups on the coating endowed the meniscus scaffold with excellent anti-inflammatory and ROS scavenging capacities. We also found that the coating could promote cell migration in a mock wound model and could increase extracellular matrix secretion in vitro. Moreover, the coating components at a certain concentration played an effective role in delaying OA and providing cartilage protection in the rat model. The expression of inflammation cytokines (e.g., IL-6, IL-8, and MMPs) in rat knee tissue was significantly downregulated, and cartilage degeneration and OA damage were also inhibited according to tissue staining results and the OARSI (Osteoarthritis Research Society International) scoring system. Combining these performances, we suggest that this silk/GO-based scaffold modified with TA/Sr²⁺ coating could have broader application prospects by virtue of its effective and user-friendly properties. STATEMENT OF SIGNIFICANCE: The biological properties of the meniscus play a role in activating and regulating the metabolic and inflammatory responses that influence the homeostasis of joint health and ultimately lead to knee osteoarthritis (OA). The inflammation condition of the knee joint may exacerbate the degeneration of meniscus and cartilage. The present study aimed to develop a functional coating composed of tannic acid/Sr²⁺ complex on a silk/graphene oxide-based meniscus scaffold and to endow the scaffold with anti-inflammatory and ROS elimination capacities during the meniscus regeneration process to protect cartilage and delay OA development. The in vitro cytocompatibility study and the in vivo rat OA model study revealed that the coating was effective in promoting cell migration, facilitating ECM secretion, inhibiting inflammation, and delaying OA development.

New Trends in Pharmacological Treatments for Osteoarthritis

Osteoarthritis (OA) is the leading cause of function loss and disability among the elderly, with significant burden on the individual and society. It is a severe disease for its high disability rates, morbidity, costs, and increased mortality. Multifactorial etiologies contribute to the occurrence and development of OA. The heterogeneous condition poses a challenge for the development of effective treatment for OA; however, emerging treatments are promising to bring benefits for OA management in the future. This narrative review will discuss recent developments of agents for the treatment of OA, including potential disease-modifying osteoarthritis drugs (DMOADs) and novel therapeutics for pain relief. This review will focus more on drugs that have been in clinical trials, as well as attractive drugs with potential applications in preclinical research. In the past few years, it has been realized that a complex interaction of multifactorial mechanisms is involved in the pathophysiology of OA. The authors believe there is no miracle therapeutic strategy fitting for all patients. OA phenotyping would be helpful for therapy selection. A variety of potential therapeutics targeting inflammation mechanisms, cellular senescence, cartilage metabolism, subchondral bone remodeling, and the peripheral nociceptive pathways are expected to reshape the landscape of OA treatment over the next few years. Precise randomized controlled trials (RCTs) are expected to identify the safety and efficacy of novel therapies targeting specific mechanisms in OA patients with specific phenotypes.

Effects of Streptococcus thermophilus on anterior cruciate ligament transection-induced early osteoarthritis in rats

Osteoarthritis (OA) is the most common joint disorder and is classically defined as a progressively degenerative disease of articular cartilage. It manifests as joint pain and disability and currently has no comprehensive treatments. The primary purpose of the present study was to test the effects of probiotics, Streptococcus thermophilus (TCI633), on anterior cruciate ligament transection (ACLT)-induced experimental osteoarthritis (OA) in rats. In the current study, the experimental groups were given TCI633 (5x10⁹, 5x10¹⁰ and 5x10¹¹ CFU/kg/day) and glucosamine sulfate (250 mg/kg) between week 8 and 20 following ACLT. The results showed that oral administration of TCI633 and glucosamine had significant therapeutic effects on pain behaviors and knee swelling. Dose-dependent effects of TCI633 were also observed in ACLT-treated rats. Histopathological analysis demonstrated that ACLT+TCI633 (5x10⁹, 5x10¹⁰ and 5x10¹¹ CFU/kg/day) improved the synovial inflammation and cartilage damage of ACLT rats. Histology evaluation using the Osteoarthritis Research Society International system and synovial inflammatory score analysis showed the dose-dependent inhibition of TCI633 on synovial inflammation and cartilage damage. Immunohistochemical staining and TUNEL apoptosis staining showed that TCI633 could effectively increase the expression of type II collagen and reduce the amount of chondrocyte apoptosis in cartilage. Therefore, the present study demonstrated that oral intake of TCI633 could significantly suppressing pain behavior, reduce joint swelling and synovial tissue inflammation and increase type II collagen expression in cartilage. There was also a reduction in chondrocyte apoptosis and decreased progression of OA in ACLT-treated rats.

Highly specific recognition of denatured collagen by fluorescent peptide probes with the repetitive Gly-Pro-Pro and Gly-Hyp-Hyp sequences

Denatured collagen is a key biomarker for various critical diseases such as cancer. Peptide probes with the repetitive (Gly-Pro-Hyp)n sequences have recently been found to selectively target denatured collagen; however, thermal or UV pretreatment is required to drive the peptides into the monomer conformation, which poses a substantial challenge for clinical applications. We herein construct two peptide probes, FAM-GOO and FAM-GPP, consisting of the repetitive (Gly-Hyp-Hyp)8 and (Gly-Pro-Pro)8 sequences, respectively. The CD, fluorescence and colorimetric studies have consistently revealed that FAM-GOO showed strong capability of forming the triple helical structure, while FAM-GPP pronouncedly displayed the single stranded conformation at temperatures as low as 4 °C. The binding experiments have indicated that both peptide probes could recognize denatured collagen with high specificity, and FAM-GPP remarkably did not need the preheating treatment. The tissue staining results have shown that preheated FAM-GOO and unheated FAM-GPP could target denatured collagen in a wide variety of rat frozen and human FFPE tissue sections. Compared with antibodies specific for a certain type of collagen, both FAM-GOO and FAM-GPP act as broad-spectrum probes for the selective detection of denatured collagen of different types and from different species. Importantly, FAM-GPP possessed the unique capability of maintaining the monomer conformation by itself, thus avoiding the potential risks of the thermal or UV pretreatment. This novel peptide probe provides a handy and versatile biosensor for specifically targeting denatured collagen, which has attractive potential in the diagnosis and therapeutics of collagen-involved diseases.

Emerging pharmaceutical therapies for osteoarthritis

The prevalence of osteoarthritis (OA) and the burden associated with the disease are steadily increasing worldwide, representing a major public health challenge for the coming decades. The lack of specific treatments for OA has led to it being recognized as a serious disease that has an unmet medical need. Advances in the understanding of OA pathophysiology have enabled the identification of a variety of potential therapeutic targets involved in the structural progression of OA, some of which are promising and under clinical investigation in randomized controlled trials. Emerging therapies include those targeting matrix-degrading proteases or senescent chondrocytes, promoting cartilage repair or limiting bone remodelling, local low-grade inflammation or Wnt signalling. In addition to these potentially disease-modifying OA drugs (DMOADs), several targets are being explored for the treatment of OA-related pain, such as nerve growth factor inhibitors. The results of these studies are expected to considerably reshape the landscape of OA management over the next few years. This Review describes the pathophysiological processes targeted by emerging therapies for OA, along with relevant clinical data and discussion of the main challenges for the further development of these therapies, to provide context for the latest advances in the field of pharmaceutical therapies for OA.

Disease-Modifying Effects of a Novel Cathepsin K Inhibitor in Osteoarthritis: A Randomized Controlled Trial

BACKGROUND

MIV-711 is a novel selective cathepsin K inhibitor with beneficial effects on bone and cartilage in preclinical osteoarthritis models.

OBJECTIVE

To evaluate the efficacy, safety, and tolerability of MIV-711 in participants with symptomatic, radiographic knee osteoarthritis.

DESIGN

26-week randomized, double-blind, placebo-controlled phase 2a study with a 26-week open-label safety extension substudy. (EudraCT: 2015-003230-26 and 2016-001096-73).

SETTING

Six European sites.

PARTICIPANTS

244 participants with primary knee osteoarthritis, Kellgren-Lawrence grade 2 or 3, and pain score of 4 to 10 on a numerical rating scale (NRS).

INTERVENTION

MIV-711, 100 (n = 82) or 200 (n = 81) mg daily, or matched placebo (n = 77). Participants (46 who initially received 200 mg/d and 4 who received placebo) received 200 mg of MIV-711 daily during the extension substudy.

MEASUREMENTS

The primary outcome was change in NRS pain score. The key secondary outcome was change in bone area on magnetic resonance imaging (MRI). Other secondary end points included cartilage thickness on quantitative MRI and type I and II collagen C-telopeptide biomarkers. Outcomes were assessed over 26 weeks.

RESULTS

Changes in NRS pain scores with MIV-711 were not statistically significant (placebo, -1.4; MIV-711, 100 mg/d, -1.7; MIV-711, 200 mg/d, -1.5). MIV-711 significantly reduced medial femoral bone area progression (P = 0.002 for 100 mg/d and 0.004 for 200 mg/d) and medial femoral cartilage thinning (P = 0.023 for 100 mg/d and 0.125 for 200 mg/d) versus placebo and substantially reduced bone and cartilage biomarker levels. Nine serious adverse events occurred in 6 participants (1 in the placebo group, 3 in the 100 mg group, and 2 in the 200 mg group); none were considered to be treatment-related.

LIMITATION

The trial was relatively short.

CONCLUSION

MIV-711 was not more effective than placebo for pain, but it significantly reduced bone and cartilage progression with a reassuring safety profile. This treatment may merit further evaluation as a disease-modifying osteoarthritis drug.

PRIMARY FUNDING SOURCE

Medivir.

Targeting fundamental aging mechanisms to treat osteoporosis

Introduction: Osteoporotic fractures represent a growing burden of mortality, morbidity and socioeconomic cost to health-care systems worldwide. Osteoporosis is a disease uniquely associated with aging, therefore, an understanding of the physiological mechanisms underpinning its development as we age may open new avenues for therapeutic exploitation. Novel treatments, as well as refinement of the current approaches, are vital in the effort to sustain healthy, independent patients across the lifespan.Areas covered: This review covers the anabolic and catabolic pathways seen in bone maintenance, highlighting how they are changed with age, leading to osteoporosis. It will also discuss how these changes may be targeted therapeutically, in the development of new therapies, and the refinement of those already in use.Expert opinion: New effective and safe treatments for osteoporosis are still needed. Bone anabolics seem to be the most appropriate therapeutic approach to osteoporosis in older persons. Considering that bone and muscle mass synchronically decline with aging thus predisposing older persons to falls and fractures, combined therapeutic approaches to osteosarcopenia with a dual anabolic effect on muscle and bone will be a major advance in the treatment of these devastating conditions in the future.

Cartilage-targeting and dual MMP-13/pH responsive theranostic nanoprobes for osteoarthritis imaging and precision therapy

Osteoarthritis (OA) microenvironment is marked by matrix metalloproteinases-13 (MMP-13) overexpression and weak acidity, making it possible to develop dual-stimuli responsive theranostic nanoprobes for OA diagnosis and therapy. However, current MMP/pH-responsive systems are not suitable for OA because of their poor biocompatibility, poor degradation and non-cartilage-targeting of the responsive probes. Here we designed a novel biocompatible cartilage-targeting and MMP-13/pH-responsive ferritin nanocages (CMFn) loaded with an anti-inflammatory drug (Hydroxychloroquine, HCQ), termed CMFn@HCQ, for OA imaging and therapy. We found that CMFn could be smartly "turned on" to emit light for OA imaging in response to the level of overexpressed MMP-13 in OA microenvironment, corresponding to the degree of OA severity. Thus the light intensity detected reflected the degree of OA severity, enabling the precise disease classification by our CMFn. CMFn could be "turned off" to stop emitting light in the normal joint. CMFn@HCQ nanocages could target the cartilage and release HCQ in the OA joint specifically under acidic pH conditions in a sustained manner, prolonging the drug retention time to 14 days to remarkably reduce synovial inflammation in the OA joints. The CMFn@HCQ nanocages represent a smart dual-stimuli responsive and cartilage-targeting nanoprobes, and hold promise for imaging-guided precision therapy for OA.

Disrupted type II collagenolysis impairs angiogenesis, delays endochondral ossification and initiates aberrant ossification in mouse limbs

Cartilage remodelling and chondrocyte differentiation are tightly linked to angiogenesis during bone development and endochondral ossification. To investigate whether collagenase-mediated cleavage of the major cartilage collagen (collagen II) plays a role in this process, we generated a knockin mouse in which the mandatory collagenase cleavage site at PQG⁷⁷⁵↓⁷⁷⁶LAG, was mutated to PPG⁷⁷⁵↓⁷⁷⁶MPG (Col2a1^Bailey). This approach blocked collagen II cleavage, and the production of putative collagen II matrikines derived from this site, without modifying matrix metalloproteinase expression or activity. We report here that this mouse (Bailey) is viable. It has a significantly expanded growth plate and exhibits delayed and abnormal angiogenic invasion into the growth plate. Deeper electron microscopy analyses revealed that, at around five weeks of age, a small number of blood vessel(s) penetrate into the growth plate, leading to its abrupt shrinking and the formation of a bony bridge. Our results from in vitro and ex vivo studies suggest that collagen II matrikines stimulate the normal branching of endothelial cells and promote blood vessel invasion at the chondro-osseous junction. The results further suggest that failed collagenolysis in Bailey leads to expansion of the hypertrophic zone and formation of a unique post-hypertrophic zone populated with chondrocytes that re-enter the cell cycle and proliferate. The biological rescue of this in vivo phenotype features the loss of a substantial portion of the growth plate through aberrant ossification, and narrowing of the remaining portion that leads to limb deformation. Together, these data suggest that collagen II matrikines stimulate angiogenesis in skeletal growth and development, revealing novel strategies for stimulating angiogenesis in other contexts such as fracture healing and surgical applications.

Analgesic effects of the cathepsin K inhibitor L-006235 in the monosodium iodoacetate model of osteoarthritis pain

INTRODUCTION

The mounting evidence that osteoclasts play an important role in osteoarthritis (OA) pain lead us to investigate the effects of L-006235, a potent and selective inhibitor of cathepsin K, on pain behaviour and joint pathology in a model of OA pain.

METHODS

Effects of preventative (30 and 100 mg/kg) and therapeutic (100 mg/kg) oral dosing with L-006235 on weight-bearing asymmetry, hind paw withdrawal thresholds, cartilage and bone pathology, synovial inflammation, and drug exposure were studied in the monosodium iodoacetate rat model of OA pain.

RESULTS

Preventative L-006235 inhibited weight-bearing asymmetry from day 14, with this measure nearly abolished by the higher dose. In the same treatment setting, L-006235 prevented lowering of hind paw withdrawal thresholds from day 7. Exposure to L-006235 in plasma was higher for the 100 mg/kg dose, compared with 30 mg/kg. Therapeutic dosing with L-006235 from day 14 significantly inhibited weight-bearing asymmetry, compared with monosodium iodoacetate vehicle rats. Regression analysis revealed a significant interaction coefficient of the effects of L-006235 on weight-bearing asymmetry and synovitis score, but not for cartilage damage nor osteophyte scores.

CONCLUSION

Our novel finding that cathepsin K inhibition is analgesic in a clinically relevant model of OA pain provides new evidence for the therapeutic potential of this target.

Transcriptomic hallmarks of bone remodelling revealed by RNA-Seq profiling in blood of Arabian horses during racing training regime

The impact of exercises on young developing organisms is still of interest to researchers. Similarly like Thoroughbreds, Arabian horses competing at the race track. The high percent of lameness and loss of days in training are often the result of weakness in the condition of the musculoskeletal system. The objective of the presented study was to identify by RNA-Seq method, the possible skeletal system originating transcriptomic profile in peripheral blood of Arabian horses undergoing race training. Obtained results showed that one of the most significantly deregulated pathway involved in bone homeostasis was those involved in osteoclast differentiation. Among the significantly expressed molecules, we recognized twelve genes potentially involved in the metabolism of the skeletal system: BGLAP, CTSK, TYROBP, PDLIM7, SLC9B2, TWSG1, NOTCH2, IL6ST, VAV3, NFATc1, CLEC5A, TXLNG. The panel of identified genes should be evaluated as candidate biomarkers for bone homeostasis indicators of Arabians performing on race tracks to assess bone remodelling states during training for race track competitions.

SP1-mediated downregulation of ADAMTS3 gene expression in osteosarcoma models

ADAMTS3 is a member of procollagen N-proteinase subfamily of ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) gene family. It has an important function in the procollagen maturation process. The removal of N-peptidases is required for the accurate processing of fibrillar collagens. Otherwise, several disorders can occur that is related with the collagenous tissues. ADAMTS3 mainly maturates type II collagen molecule which is the main component of the bone and cartilage. There are several expression studies about ADAMTS3 gene however its transcriptional regulation has not been lightened up, yet. Here we first time cloned and functionally analyzed the promoter region of ADAMTS3 gene, approximately 1380 bp upstream of the transcription start site. Transient transfection experiments showed that all truncated promoter constructs are active and 171 bp fragment is sufficient to activate gene expression in both Saos-2 and MG63 cells. In silico analysis showed that ADAMTS3 has a TATA-less promoter and contains several SP1/GC box binding motifs and a CpG island. Therefore we mainly investigated the SP1 dependent regulation of ADAMTS3 promoter. SP1 downregulated ADAMTS3 transcriptional activity. As consistent with the transcriptional activity, mRNA, and protein expression levels were also decreased by SP1. On the other hand, functional binding of the SP1 on multiple regions of ADAMTS3 promoter was confirmed by EMSA studies. As ADAMTS3 is responsible for the collagen maturation and biosynthesis, further we investigated the effect of SP1 on type I-II and III collagen gene expressions. We point out that SP1 increased type II and III collagen expression and in contrast decreased type I collagen expression levels in Saos-2 cells. mRNA expression level was decreased for all collagen types in MG63 model. Decrease in the type II collagen expression was also demonstrated at the protein level by SP1. Collectively these results provide first findings for the SP1-related transcriptional regulation of ADAMTS3 and collagen genes in osteosarcoma cell lines.

Nonclinical and clinical pharmacological characterization of the potent and selective cathepsin K inhibitor MIV-711

BACKGROUND

Cathepsin K is an attractive therapeutic target for diseases in which bone resorption is excessive such as osteoporosis and osteoarthritis (OA). The current paper characterized the pharmacological profile of the potent and selective cathepsin K inhibitor, MIV-711, in vitro and in cynomolgus monkeys, and assessed translation to human based on a single dose clinical study in man.

METHODS

The potency and selectivity of MIV-711 were assessed in vitro using recombinant enzyme assays and differentiated human osteoclasts. MIV-711 was administered to healthy cynomolgus monkeys (3-30 µmol/kg, p.o.). Plasma levels of MIV-711 and the bone resorption biomarker CTX-I were measured after single dose experiments, and urine levels of CTX-I, NTX-I and CTX-II biomarkers were measured after repeat dose experiments. The safety, pharmacokinetics and pharmacodynamics (serum CTX-I) of MIV-711 were assessed in human healthy subjects after single ascending doses from 20 to 600 mg.

RESULTS

MIV-711 was a potent inhibitor of human cathepsin K (K_i: 0.98 nmol/L) with > 1300-fold selectivity towards other human cathepsins. MIV-711 inhibited human osteoclast-mediated bone resorption with an IC₅₀ value of 43 nmol/L. Single oral doses of MIV-711 to monkeys reduced plasma levels of CTX-I in a dose-dependent fashion by up to 57% at trough. The effect on CTX-I was linearly correlated to the plasma exposure of MIV-711, while the efficacy duration outlasted plasma exposure. Repeat oral dosing with MIV-711 also reduced urinary levels of the bone resorption biomarkers CTX-I (by 93%) and NTX-I (by 71%) and the cartilage degradation biomarker CTX-II (by 71%). MIV-711 was safe and well-tolerated when given as single ascending doses to healthy subjects. MIV-711 reduced serum CTX-I levels in a dose-dependent manner by up to 79% at trough. The relationship between MIV-711 exposure and effects on these biomarkers in humans was virtually identical when compared to the corresponding monkey data.

CONCLUSIONS

MIV-711 is a potent and selective cathepsin K inhibitor with dose-dependent effects on biomarkers of bone and cartilage degradation in monkey and human. Taken together, MIV-711 shows promise for the treatment of bone and cartilage related disorders in humans, such as OA. Trial Registration EudraCT number 2011-003024-12, registered on June 22nd 2011.

The selective cathepsin K inhibitor MIV-711 attenuates joint pathology in experimental animal models of osteoarthritis

BACKGROUND

MIV-711 is a highly potent and selective cathepsin K inhibitor. The current article summarizes the therapeutic effects of MIV-711 on joint pathology in rabbits subjected to anterior cruciate ligament transection (ACLT), and the prophylactic effects on joint pathology in dogs subjected to partial medial meniscectomy, two surgical models of osteoarthritis (OA).

METHODS

Starting 1 week after surgery, rabbits were dosed daily via oral gavage with either MIV-711 or vehicle (n = 7/group) for 7 weeks. The four treatment groups were: (1) sham + vehicle; (2) ACLT + vehicle; (3) ACLT + MIV-711, 30 µmol/kg and (4) ACLT + MIV-711, 100 µmol/kg. Subchondral bone and articular cartilage structures were assessed by µCT, histomorphometry, and scoring. Dogs subjected to partial medial meniscectomy received either MIV-711 (30 µmol/kg) or vehicle (n = 15/group) via oral gavage once daily, starting 1 day before meniscectomy, for 28 days. Cartilage degradation was assessed at the macroscopic and microscopic levels. The exposures of MIV-711 were assessed in both studies and biomarkers reflecting bone resorption (HP-1 in rabbits, CTX-I in dogs) and cartilage degradation (CTX-II) were measured.

RESULTS

In ACLT rabbits, MIV-711 decreased HP-1 levels by up to 72% (p < 0.001) and CTX-II levels by up to 74% (p < 0.001) compared to ACLT vehicle controls. ACLT surgery significantly reduced the total thickness of the subchondral bone plate and reduced trabecular bone volume in the femur and tibia. These effects were reversed by MIV-711. ACLT resulted in cartilage thickening, which was attenuated by MIV-711. MIV-711 did not affect osteophyte formation or Mankin scores. In dogs, MIV-711 reduced CTX-I and CTX-II levels by 86% (p < 0.001) and 80% (p < 0.001), respectively. Synovial CTX-II levels were reduced by 55-57% (p < 0.001) compared to baseline. MIV-711-treated animals had 25-37% lower macroscopic scores in the femur condyles and 13-33% lower macroscopic scores in the tibial plateaus.

CONCLUSIONS

MIV-711 prevents subchondral bone loss and partially attenuates cartilage pathology in two animal models of OA. These beneficial effects of MIV-711 on joint pathology are observed in conjunction with decreases in bone and cartilage biomarkers that have been shown to be clinically attainable in human. The data support the further development of MIV-711 for the treatment of OA.

Biomarkers for equine joint injury and osteoarthritis

We report the results of a symposium aimed at identifying validated biomarkers that can be used to complement clinical observations for diagnosis and prognosis of joint injury leading to equine osteoarthritis (OA). Biomarkers might also predict pre-fracture change that could lead to catastrophic bone failure in equine athletes. The workshop was attended by leading scientists in the fields of equine and human musculoskeletal biomarkers to enable cross-disciplinary exchange and improve knowledge in both. Detailed proceedings with strategic planning was written, added to, edited and referenced to develop this manuscript. The most recent information from work in equine and human osteoarthritic biomarkers was accumulated, including the use of personalized healthcare to stratify OA phenotypes, transcriptome analysis of anterior cruciate ligament (ACL) and meniscal injuries in the human knee. The spectrum of "wet" biomarker assays that are antibody based that have achieved usefulness in both humans and horses, imaging biomarkers and the role they can play in equine and human OA was discussed. Prediction of musculoskeletal injury in the horse remains a challenge, and the potential usefulness of spectroscopy, metabolomics, proteomics, and development of biobanks to classify biomarkers in different stages of equine and human OA were reviewed. The participants concluded that new information and studies in equine musculoskeletal biomarkers have potential translational value for humans and vice versa. OA is equally important in humans and horses, and the welfare issues associated with catastrophic musculoskeletal injury in horses add further emphasis to the need for good validated biomarkers in the horse. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:823-831, 2018.

C2K77 ELISA detects cleavage of type II collagen by cathepsin K in equine articular cartilage

OBJECTIVES

Develop a species-specific ELISA for a neo-epitope generated by cathepsin K cleavage of equine type II collagen to: (1) measure cartilage type II collagen degradation by cathepsin K in vitro, (2) identify cytokines that upregulate cathepsin K expression and (3) compare cathepsin K with matrix metalloproteinase (MMP) collagenase activity in stimulated cartilage explants and freshly isolated normal and osteoarthritic (OA) articular cartilages.

DESIGN

A new ELISA (C2K77) was developed and tested by measuring the activity of exogenous cathepsin K on equine articular cartilage explants. The ELISA was then employed to measure endogenous cathepsin K activity in cultured cartilage explants with or without stimulation by interleukin-1 beta (IL-1β), tumour necrosis-alpha (TNF-α), oncostatin M (OSM) and lipopolysaccharide (LPS). Cathepsin K activity in cartilage explants (control and osteoarthritic-OA) and freshly harvested cartilage (control and OA) was compared to that of MMPs employing C2K77 and C1,2C immunoassays.

RESULTS

The addition of Cathepsin K to normal cartilage caused a significant increase (P < 0.01) in the C2K77 epitope release. Whereas the content of C1,2C, that reflects MMP collagenase activity, was increased in media by the addition to cartilage explants of TNF-α and OSM (P < 0.0001) or IL-1β and OSM (P = 0.002), no change was observed in C2K77 which also unchanged in OA cartilages compared to normal.

CONCLUSIONS

The ELISA C2K77 measured the activity of cathepsin K in equine cartilage which was unchanged in OA cartilage. Cytokines that upregulate MMP collagenase activity had no effect on endogenous cathepsin K activity, suggesting a different activation mechanism that requires further study.

In Situ Imaging of Tissue Remodeling with Collagen Hybridizing Peptides

Collagen, the major structural component of nearly all mammalian tissues, undergoes extensive proteolytic remodeling during developmental states and a variety of life-threatening diseases such as cancer, myocardial infarction, and fibrosis. While degraded collagen could be an important marker of tissue damage, it is difficult to detect and target using conventional tools. Here, we show that a designed peptide (collagen hybridizing peptide: CHP), which specifically hybridizes to the degraded, unfolded collagen chains, can be used to image degraded collagen and inform tissue remodeling activity in various tissues: labeled with 5-carboxyfluorescein and biotin, CHPs enabled direct localization and quantification of collagen degradation in isolated tissues within pathologic states ranging from osteoarthritis and myocardial infarction to glomerulonephritis and pulmonary fibrosis, as well as in normal tissues during developmental programs associated with embryonic bone formation and skin aging. The results indicate the general correlation between the level of collagen remodeling and the amount of denatured collagen in tissue and show that the CHP probes can be used across species and collagen types, providing a versatile tool for not only pathology and developmental biology research but also histology-based disease diagnosis, staging, and therapeutic screening. This study lays the foundation for further testing CHP as a targeting moiety for theranostic delivery in various animal models.

Supraspinatus tendon overuse results in degenerative changes to tendon insertion region and adjacent humeral cartilage in a rat model

The etiology of rotator cuff tendon overuse injuries is still not well understood. Furthermore, how this overuse injury impacts other components of the glenohumeral joint, including nearby articular cartilage, is also unclear. Therefore, this study sought to better understand the time course of tendon protease activity in a rat model of supraspinatus overuse, as well as determine effects of 10 weeks of overuse on humeral head articular cartilage. For these studies, multiplex gelatin zymography was used to characterize protease activity profiles in tendon and cartilage, while histological scoring/mechanical testing and micro-computed tomography (μCT) imaging were used to quantify structural damage in the supraspinatus tendon insertion and humeral articular cartilage, respectively. Histological scoring of supraspinatus tendon insertions revealed tendinopathic cellular and collagen fiber changes after 10 weeks of overuse when compared to controls, while mechanical testing revealed no significant differences between tensile moduli (overuse: 24.5 ± 11.5 MPa; control: 16.3 ± 8.7 MPa). EPIC-μCT imaging on humeral articular cartilage demonstrated significant cartilage thinning (overuse: 119.6 ± 6.34 μm; control: 195.4 ± 13.4μm), decreased proteoglycan content (overuse: 2.1 ± 0.18 cm^-1 ; control: 1.65 ± 0.14 cm^-1 ), and increased subchondral bone thickness (overuse: 216.2 ± 10.9 μm; control: 192 ± 17.8μm) in the overuse animals. Zymography results showed no significant upregulation of cathepsins or matrix metalloproteinases in tendon or cartilage at 2 or 10 weeks of overuse compared to controls. These results have further elucidated timing of protease activity over 10 weeks and suggest that damage occurs to other tissues in addition to the supraspinatus tendon in this overuse injury model. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1910-1918, 2017.

The Future of Cysteine Cathepsins in Disease Management

Since the discovery of the key role of cathepsin K in bone resorption, cysteine cathepsins have been investigated by pharmaceutical companies as drug targets. The first clinical results from targeting cathepsins by activity-based probes and substrates are paving the way for the next generation of molecular diagnostic imaging, whereas the majority of antibody-drug conjugates currently in clinical trials depend on activation by cathepsins. Finally, cathepsins have emerged as suitable vehicles for targeted drug delivery. It is therefore timely to review the future of cathepsins in drug discovery. We focus here on inflammation-associated diseases because dysregulation of the immune system accompanied by elevated cathepsin activity is a common feature of these conditions.

Engineered nanomaterial-induced lysosomal membrane permeabilization and anti-cathepsin agents

Engineered nanomaterials (ENMs), or small anthropogenic particles approximately < 100 nm in size and of various shapes and compositions, are increasingly incorporated into commercial products and used for industrial and medical purposes. There is an exposure risk to both the population at large and individuals in the workplace with inhalation exposures to ENMs being a primary concern. Further, there is increasing evidence to suggest that certain ENMs may represent a significant health risk, and many of these ENMs exhibit distinct similarities with other particles and fibers that are known to induce adverse health effects, such as asbestos, silica, and particulate matter (PM). Evidence regarding the importance of lysosomal membrane permeabilization (LMP) and release of cathepsins in ENM toxicity has been accumulating. The aim of this review was to describe our current understanding of the mechanisms leading to ENM-associated pathologies, including LMP and the role of cathepsins with a focus on inflammation. In addition, anti-cathepsin agents, some of which have been tested in clinical trials and may prove useful for ameliorating the harmful effects of ENM exposure, are examined.

Targeting collagen for diagnostic imaging and therapeutic delivery

As the most abundant protein in mammals and a major structural component in extracellular matrix, collagen holds a pivotal role in tissue development and maintaining the homeostasis of our body. Persistent disruption to the balance between collagen production and degradation can cause a variety of diseases, some of which can be fatal. Collagen remodeling can lead to either an overproduction of collagen which can cause excessive collagen accumulation in organs, common to fibrosis, or uncontrolled degradation of collagen seen in degenerative diseases such as arthritis. Therefore, the ability to monitor the state of collagen is crucial for determining the presence and progression of numerous diseases. This review discusses the implications of collagen remodeling and its detection methods with specific focus on targeting native collagens as well as denatured collagens. It aims to help researchers understand the pathobiology of collagen-related diseases and create novel collagen targeting therapeutics and imaging modalities for biomedical applications.

Early cathepsin K degradation of type II collagen in vitro and in vivo in articular cartilage

OBJECTIVE

To characterize the initial events in the cleavage of type II collagen mediated by cathepsin K and demonstrate the presence of the resulting products in human and equine articular osteoarthritic cartilage.

DESIGN

Equine type II collagen was digested with cathepsin K and the cleavage products characterized by mass spectrometry. Anti-neoepitope antibodies were raised against the most N-terminal cleavage products and used to investigate the progress of collagen cleavage, in vitro, and the presence of cathepsin K-derived products in equine and human osteoarthritic cartilage.

RESULTS

Six cathepsin K cleavage sites distributed throughout the triple helical region were identified in equine type II collagen. Most of the cleavages occurred following a hydroxyproline residue. The most N-terminal site was within three residues of the previously identified site in bovine type II collagen. Western blotting using anti-neoepitope antibodies showed that the initial cleavages occurred at the N-terminal sites and this was followed by more extensive degradation resulting in products too small to be resolved by SDS gel electrophoresis. Immunohistochemical staining of cartilage sections from equine or human osteoarthritic joints showed staining in lesional areas which was not observed in non-arthritic sites.

CONCLUSIONS

Cathepsin K cleaves triple helical collagen by erosion from the N-terminus and with subsequent progressive cleavages. The liberated fragments can be detected in osteoarthritic cartilage and may represent useful biomarkers for disease activity.

Ability of a Urine Assay of Type II Collagen Cleavage by Collagenases to Detect Early Onset and Progression of Articular Cartilage Degeneration: Results from a Population-based Cohort Study

OBJECTIVE

To evaluate the association of a sandwich assay for cartilage collagenase-mediated degradation, the C2C human urine sandwich assay (IB-C2C-HUSA), with early and late knee cartilage pathology and with progression of cartilage damage.

METHODS

A population-based cohort with knee pain, age 40-79 years, was evaluated at baseline (n = 253) and after mean 3.3 years (n = 161). We evaluated the IB-C2C-HUSA and a related competitive inhibition assay (C2C). The C2C assay was applied to serum (sC2C) and urine (uC2C). Based on knee radiographs and magnetic resonance imaging (MRI), 3 subgroups [no cartilage pathology, preradiographic cartilage pathology, and radiographic osteoarthritis (ROA)] were evaluated cross-sectionally for association with biomarker levels. Longitudinally, we evaluated whether baseline assays predict subsequent progression of cartilage degeneration, defined by MRI cartilage loss.

RESULTS

Cross-sectionally, statistically significant differences were seen in the 3 subgroups for IB-C2C-HUSA (p < 0.001), with the highest levels seen in ROA, and for sC2C (p = 0.023), while no differences were seen for uC2C (p = 0.501). Baseline IB-C2C-HUSA levels were higher in progressors vs nonprogressors (p = 0.003). In logistic regression analysis, only baseline IB-C2C-HUSA was associated with an increased risk of progression of cartilage damage (OR 1.78, 95% CI 1.03-3.09).

CONCLUSION

The IB-C2C-HUSA degradation assay detects the generation of a pathology-related cartilage collagen peptide(s) that increase(s) with onset of degeneration of knee articular cartilage. The baseline values are associated with progression of cartilage degeneration over 3 subsequent years. This assay may have value in clinical OA trials. Further, it points to collagenase activity as a therapeutic target for controlling degeneration of articular cartilage.

Aggrecan heterogeneity in articular cartilage from patients with osteoarthritis

Background

Aggrecan degradation is the hallmark of cartilage degeneration in osteoarthritis (OA), though it is unclear whether a common proteolytic process occurs in all individuals.

Methods

Aggrecan degradation in articular cartilage from the knees of 33 individuals with OA, who were undergoing joint replacement surgery, was studied by immunoblotting of tissue extracts.

Results

Matrix metalloproteinases (MMPs) and aggrecanases are the major proteases involved in aggrecan degradation within the cartilage, though the proportion of aggrecan cleavage attributable to MMPs or aggrecanases was variable between individuals. However, aggrecanases were more associated with the increase in aggrecan loss associated with OA than MMPs. While the extent of aggrecan cleavage was highly variable between individuals, it was greatest in areas of cartilage adjacent to sites of cartilage erosion compared to sites more remote within the same joint. Analysis of link protein shows that in some individuals additional proteolytic mechanisms must also be involved to some extent.

Conclusions

The present studies indicate that there is no one protease, or a fixed combination of proteases, responsible for cartilage degradation in OA. Thus, rather than targeting the individual proteases for OA therapy, directing research to techniques that control global protease generation may be more productive.

Increased expression and activation of cathepsin K in human osteoarthritic cartilage and synovial tissues

Few studies have analyzed Cathepsin K (CatK) expression in human osteoarthritic tissues. We investigated CatK expression and activation in human articular cartilage using clinical specimens. Human osteoarthritic cartilage was obtained during surgery of total hip arthroplasty (n = 10), and control cartilage was from that of femoral head replacement for femoral neck fracture (n = 10). CatB, CatK, CatL, CatS, and Cystatin C (CysC) expressions were evaluated immunohistochemically and by real-time PCR. Intracellular CatK protein was quantified by ELISA. Intracellular CatK activity was also investigated. Osteoarthritis (OA) chondrocytes were strongly stained with CatK, particularly in the superficial layer and more damaged areas. CatB, CatL, CatS, and CysC were weakly stained. CatK mRNA expression was significantly higher in OA group compared to that in control group (p = 0.043), whereas those of CatB, CatL, CatS, and CysC did not differ significantly. Mean CatK concentration (4.83 pmol/g protein) in OA chondrocytes was higher than that (3.91 pmol/g protein) in control chondrocytes (p = 0.001). CatK was enzymatically more activated in OA chondrocytes as compared with control chondrocytes. This study, for the first time, revealed increased CatK expression and activation in human OA cartilage, suggesting possible crucial roles for it in the pathogenesis of osteoarthritic change in articular cartilage.

Targets, models and challenges in osteoarthritis research

Osteoarthritis is a chronic degenerative disorder of the joint and represents one of the most common diseases worldwide. Its prevalence and severity are increasing owing to aging of the population, but treatment options remain largely limited to painkillers and anti-inflammatory drugs, which only provide symptomatic relief. In the late stages of the disease, surgical interventions are often necessary to partially restore joint function. Although the focus of osteoarthritis research has been originally on the articular cartilage, novel findings are now pointing to osteoarthritis as a disease of the whole joint, in which failure of different joint components can occur. In this Review, we summarize recent progress in the field, including data from novel ‘omics’ technologies and from a number of preclinical and clinical trials. We describe different in vitro and in vivo systems that can be used to study molecules, pathways and cells that are involved in osteoarthritis. We illustrate that a comprehensive and multisystem approach is necessary to understand the complexity and heterogeneity of the disease and to better guide the development of novel therapeutic strategies for osteoarthritis.

Overexpression of cystatin C in synovium does not reduce synovitis or cartilage degradation in established osteoarthritis

Introduction

Cathepsin K (catK) expression is increased in cartilage, bone and synovium during osteoarthritis (OA). To study the role of catK expression and elevated cathepsin activity in the synovium on cartilage destruction in established OA, we overexpressed cystatin C (cysC), a natural cysteine protease inhibitor, in the synovium of rabbit OA joints.

Methods

The ability of cysC to inhibit activity of cathepsins in rabbit OA synovium lysates was tested in vitro using protease activity assay. In vivo, the tissue localization of recombinant adeno-associated virus (rAAV) with LacZ gene after intra-articular injection was determined by β-galactosidase staining of rabbit joints 4 weeks later. To inhibit cathepsin activity in the synovium, a rAAV2-encoding cysC was delivered intra-articularly into rabbit joints 4 weeks after OA was induced by anterior cruciate ligament transection (ACLT). Seven weeks postinjection, endogenous catK and cysC levels as well as the vector-derived cysC expression in the synovium of normal and OA joints were examined by RNA quantification. Synovial cathepsin activity and catK, catB and catL protein levels were determined by activity and Western blot analyses, respectively. Synovitis and cartilage degradation were evaluated by histopathological scoring.

Results

In vitro, the ability of cysC to efficiently inhibit activity of purified catK and OA-induced cathepsins in rabbit synovial lysates was demonstrated. In vivo, the intra-articular delivery of rAAV2/LacZ showed transduction of mostly synovium. Induction of OA in rabbit joints resulted in fourfold increase in catK mRNA compared to sham controls while no change was detected in endogenous cysC mRNA levels in the synovium. Protein levels for catK, catB and catL were also increased in the synovium with a concomitant fourfold increase in cathepsin activity. Joints treated with rAAV2/cysC showed both detection of vector genomes and vector-derived cysC transcripts in the synovium. Production of functional cysC by the vector was demonstrated by complete block of cathepsin activity in the synovium. However, this did not decrease synovitis, bone sclerosis or progression of cartilage degradation.

Conclusions

Increased production of natural cathepsin inhibitor, cysC, in OA synovium does not alleviate synovitis or cartilage pathology during a preexisting OA.

Cathepsins in Rotator Cuff Tendinopathy: Identification in Human Chronic Tears and Temporal Induction in a Rat Model

While overuse of the supraspinatus tendon is a leading factor in rotator cuff injury, the underlying biochemical changes have not been fully elucidated. In this study, torn human rotator cuff (supraspinatus) tendon tissue was analyzed for the presence of active cathepsin proteases with multiplex cysteine cathepsin zymography. In addition, an overuse injury to supraspinatus tendons was induced through downhill running in an established rat model. Histological analysis demonstrated that structural damage occurred by 8 weeks of overuse compared to control rats in the region of tendon insertion into bone. In both 4- and 8-week overuse groups, via zymography, there was approximately a 180% increase in cathepsin L activity at the insertion region compared to the controls, while no difference was found in the midsubstance area. Additionally, an over 400% increase in cathepsin K activity was observed for the insertion region of the 4-week overused tendons. More cathepsin K and L immunostaining was observed at the insertion region of the overuse groups compared to controls. These results provide important information on a yet unexplored mechanism for tendon degeneration that may operate alone or in conjunction with other proteases to contribute to chronic tendinopathy.

Cysteine cathepsin activity regulation by glycosaminoglycans

Cysteine cathepsins are a group of enzymes normally found in the endolysosomes where they are primarily involved in intracellular protein turnover but also have a critical role in MHC II-mediated antigen processing and presentation. However, in a number of pathologies cysteine cathepsins were found to be heavily upregulated and secreted into extracellular milieu, where they were found to degrade a number of extracellular proteins. A major role in modulating cathepsin activities play glycosaminoglycans, which were found not only to facilitate their autocatalytic activation including at neutral pH, but also to critically modulate their activities such as in the case of the collagenolytic activity of cathepsin K. The interaction between cathepsins and glycosaminoglycans will be discussed in more detail.

Cell-matrix interactions: focus on proteoglycan-proteinase interplay and pharmacological targeting in cancer

Proteoglycans are major constituents of extracellular matrices, as well as cell surfaces and basement membranes. They play key roles in supporting the dynamic extracellular matrix by generating complex structural networks with other macromolecules and by regulating cellular phenotypes and signaling. It is becoming evident, however, that proteolytic enzymes are required partners for matrix remodeling and for modulating cell signaling via matrix constituents. Proteinases contribute to all stages of diseases, particularly cancer development and progression, and contextually participate in either the removal of damaged products or in the processing of matrix molecules and signaling receptors. The dynamic interplay between proteoglycans and proteolytic enzymes is a crucial biological step that contributes to the pathophysiology of cancer and inflammation. Moreover, proteoglycans are implicated in the expression and secretion of proteolytic enzymes and often modulate their activities. In this review, we describe the emerging biological roles of proteoglycans and proteinases, with a special emphasis on their complex interplay. We critically evaluate this important proteoglycan-proteinase interactome and discuss future challenges with respect to targeting this axis in the treatment of cancer.

Increased fracture callus mineralization and strength in cathepsin K knockout mice

Cathepsin K (CatK) is a cysteine protease, expressed predominantly in osteoclasts (OC) which degrades demineralized bone matrix. Novel selective inhibitors of CatK are currently being developed for the treatment of postmenopausal osteoporosis. Pharmacological inhibition of CatK reduces OC resorption activity while preserving bone formation in preclinical models. Disruption of the CatK gene in mice also results in high bone mass due to impaired bone resorption and elevated formation. Here, we assessed mid-shaft femoral fracture healing in 8-10week old CatK knock-out (KO) versus wild type (WT) mice. Fracture healing and callus formation were determined in vivo weekly via X-ray, and ex vivo at days 14, 18, 28 and 42 post-fracture by radiographic scoring, micro-computed tomography (μCT), histomorphometry and terminal mechanical four point bend strength testing. Radiological evaluation indicated accelerated bone healing and remodeling for CatK KO animals based on increased total radiographic scores that included callus opacity and bridging at days 28 and 42 post-fracture. Micro-CT based total callus volume was similar in CatK KO and WT mice at day 14. Callus size in CatK KO mice was 25% smaller than that in WT mice at day 18, statistically significant by day 28 and exhibited significantly higher mineralized tissue volume and volumetric BMD as compared to WT by day 18 onward. Osteoclast surface and osteoid surface trended higher in CatK KO calluses at all time-points and osteoblast number was also significantly increased at day 28. Increased CatK KO callus mineral density was reflected in significant increases in peak load and stiffness over WT at day 42 post-fracture. Regression analysis indicated a positive correlation (r=0.8671; p<0.001) between callus BMC and peak load indicating normal mineral properties in CatK KO calluses. Taken together, gene deletion of cathepsin K in mice accelerated callus size resolution, significantly increased callus mineralized mass, and improved mechanical strength as compared to wild type mice.

Cysteine cathepsins and extracellular matrix degradation

BACKGROUND

Cysteine cathepsins are normally found in the lysosomes where they are involved in intracellular protein turnover. Their ability to degrade the components of the extracellular matrix in vitro was first reported more than 25years ago. However, cathepsins were for a long time not considered to be among the major players in ECM degradation in vivo. During the last decade it has, however, become evident that abundant secretion of cysteine cathepsins into extracellular milieu is accompanying numerous physiological and disease conditions, enabling the cathepsins to degrade extracellular proteins.

SCOPE OF VIEW

In this review we will focus on cysteine cathepsins and their extracellular functions linked with ECM degradation, including regulation of their activity, which is often enhanced by acidification of the extracellular microenvironment, such as found in the bone resorption lacunae or tumor microenvironment. We will further discuss the ECM substrates of cathepsins with a focus on collagen and elastin, including the importance of that for pathologies. Finally, we will overview the current status of cathepsin inhibitors in clinical development for treatment of ECM-linked diseases, in particular osteoporosis.

MAJOR CONCLUSIONS

Cysteine cathepsins are among the major proteases involved in ECM remodeling, and their role is not limited to degradation only. Deregulation of their activity is linked with numerous ECM-linked diseases and they are now validated targets in a number of them. Cathepsins S and K are the most attractive targets, especially cathepsin K as a major therapeutic target for osteoporosis with drugs targeting it in advanced clinical trials.

GENERAL SIGNIFICANCE

Due to their major role in ECM remodeling cysteine cathepsins have emerged as an important group of therapeutic targets for a number of ECM-related diseases, including, osteoporosis, cancer and cardiovascular diseases. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

6-Shogaol inhibits chondrocytes' innate immune responses and cathepsin-K activity

SCOPE

Ginger has long been used in traditional Asian medicine to treat osteoarthritis. Indeed, scientific research has reported that ginger derivatives (GDs) have the potential to control innate immune responses. Given the widespread use and demonstrated properties of GDs, we set out to study their anti-inflammatory and anticatabolic properties in chondrocytes.

METHODS AND RESULTS

6-shogaol (6-S), the most active GD, was obtained from ginger. 6-S was not toxic as measured by MTT assay, and inhibited NO production and IL-6 and MCP-1 induced gene expression in LPSbut not in IL-1β-stimulated chondrocytes. 6-S also inhibited LPS-mediated ERK1/2 activation as well as NOS2 and MyD88 induced expression as determined by Western blot. Moreover, zymography revealed that 6-S inhibited matrix metalloproteinases (MMP) 2/9 induction in LPS-treated cells. Hydrated 6-S was modified to obtain a compound (SSi6) without 6-S potential anti-inflammatory properties. Both 6-S and SSi6 inhibited cathepsin-K activity.

CONCLUSION

6-S blocked TLR4-mediated innate immune responses and MMP induction in chondrocytes. These results, together with GDs-mediated cathepsin-K inhibition, suggest the potential for GDs use against cartilage and bone degradation. Therefore, considering that clinical trials involving oral administration of ginger achieved relevant nontoxic GDs serum concentrations, we suggest that a ginger-supplemented diet might reduce OA symptoms.

Transcriptomics of wild-type mice and mice lacking ADAMTS-5 activity identifies genes involved in osteoarthritis initiation and cartilage destruction

OBJECTIVE

To identify changes in gene expression in mice with osteoarthritis (OA) in order to explore the mechanisms of the disease.

METHODS

Gene expression profiling was performed in cartilage from mice with surgically induced OA. We used wild-type (WT) mice and Adamts5Δcat mice, in which ADAMTS-5 activity is lacking and aggrecan loss and cartilage erosion are inhibited, to distinguish gene expression changes that are independent of ADAMTS-5 activity and cartilage breakdown. Mechanical instability was introduced into the knee joints of 10-week-old male mice via surgical destabilization of the medial meniscus (DMM). Cartilage from the developing lesion in the destabilized medial meniscus and corresponding regions in sham-operated joints was harvested by microdissection at 1, 2, and 6 weeks postsurgery, and RNA was extracted, amplified, and hybridized to whole-genome microarrays.

RESULTS

Several previously identified OA-related genes, including Ptgs2, Crlf1, and Inhba, and novel genes, such as Phdla2 and Il11, were up-regulated in both WT mice and Adamts5Δcat mice, indicating that they are independent of ADAMTS-5 activity. The altered expression of other genes, including Col10a1, the sentinel marker of cartilage hypertrophy, and Wnt/β-catenin pathway genes, required ADAMTS-5 activity. Cell death pathway genes were dysregulated, and Tp53, Foxo4, and Xbp1 endoplasmic reticulum-stress transcriptional networks were activated. Analysis of degradome genes identified up-regulation of many proteases, including Mmp3, Capn2, and the novel cartilage proteases Prss46 and Klk8. Comparison with other studies identified 16 genes also dysregulated in rat and human OA as priorities for study.

CONCLUSION

We have identified, for the first time, several genes that have an ADAMTS-5-independent role in OA, identifying them as possible OA initiation candidates. This work provides new insights into the sequence of gene dysregulation and the molecular basis of cartilage destruction in OA.

Effects of pharmacological inhibition of cathepsin K on fracture repair in mice

Cathepsin K inhibitors (CatK-I) have been developed and established to restore bone mass in both animal models of bone loss and postmenopausal osteoporotic patients. We investigated the effects of a CatK-I L-006235 on bone repair and compared to alendronate (ALN) for its known effects on fracture healing in preclinical models. Femoral fractures were performed on wild type mice that were given vehicle (CON), CatK-I or ALN from day 0 post-fracture until euthanasia. Radiologic and micro-CT analyses demonstrated that CatK-I enhanced mineralization within the calluses at day 21 post-fracture, but to a lesser degree than ALN. Histological analyses showed residual unmineralized and mineralized cartilage in the calluses of CatK-I and ALN treated groups at day 21 post-fracture compared to that in CON. CatK-I enhanced the number of tartrate-resistant acid phosphatase positive (TRAP+) osteoclasts in the fracture calluses compared to ALN and CON treated groups. However, relative levels of serum C-terminal telopeptides of type I collagen (CTX) normalized to the number of TRAP+ osteoclasts within the calluses were significantly decreased in both CatK-I and ALN groups compared to CON. Additionally, the percentages of osteoblast surface over mineralized calluses and levels of the bone formation marker serum N-terminal propeptide of type I procollagen (P1NP) were comparable between CatK-I versus CON groups, while these bone formation parameters were decreased by ALN. Taken together, these results indicate that unlike ALN, CatK-I inhibits osteoclastic activity without changing bone formation, and the inhibition of CatK delayed but did not abrogate callus remodeling during bone repair.