Calcified Cartilage Research Articles

Proteomic, mechanical, and biochemical development of tissue-engineered neocartilage

BackgroundThe self-assembling process of cartilage tissue engineering is a promising technique to heal cartilage defects, preventing osteoarthritic changes. Given that chondrocytes dedifferentiate when expanded, it is not known if cellular expansion affects the development of self-assembled neocartilage. The objective of this study was to use proteomic, mechanical, and biochemical analyses to quantitatively investigate the development of self-assembled neocartilage derived from passaged, rejuvenated costal chondrocytes.MethodsYucatan minipig costal chondrocytes were used to create self-assembled neocartilage constructs. After 1, 4, 7, 14, 28, 56, or 84 days of self-assembly, constructs were analyzed through a variety of histological, biomechanical, biochemical, and proteomic techniques.ResultsIt was found that temporal trends in neocartilage formation are similar to those seen in native hyaline articular cartilage development. For example, between days 7 and 84 of culture, tensile Young’s modulus increased 4.4-times, total collagen increased 2.7-times, DNA content decreased 69.3%, collagen type II increased 1.5-times, and aggrecan dropped 55.3%, mirroring trends shown in native knee cartilage. Importantly, collagen type X, which is associated with cartilage calcification, remained at low levels (≤ 0.05%) at all neocartilage developmental time points, similar to knee cartilage (< 0.01%) and unlike donor rib cartilage (0.98%). ConclusionsIn this work, bottom-up proteomics, a powerful tool to interrogate tissue composition, was used for the first time to quantify and compare the proteome of a developing engineered tissue to a recipient tissue. Furthermore, it was shown that self-assembled, costal chondrocyte-derived neocartilage is suitable for a non-homologous approach in the knee.

Structural clues to articular calcified cartilage function: Adescriptive review of this crucial interface tissue.

Articular calcified cartilage (ACC) has been dismissed, by some, as a remnant of endochondral ossification without functional relevance to joint articulation or weight‐bearing. Recent research indicates that morphologic and metabolic ACC features may be important, reflecting knee joint osteoarthritis (OA) predisposition. ACC is less investigated than neighbouring joint tissues, with its component chondrocytes and mineralised matrix often being either ignored or integrated into analyses of hyaline articular cartilage and subchondral bone tissue respectively. Anatomical variation in ACC is recognised between species, individuals and age groups, but the selective pressures underlying this variation are unknown. Consequently, optimal ACC biomechanical features are also unknown as are any potential locomotory roles. This review collates descriptions of ACC anatomy and biology in health and disease, with a view to revealing its structure/function relationship and highlighting potential future research avenues. Mouse models of healthy and OA joint ageing have shown disparities in ACC load‐induced deformations at the knee joint. This raises the hypothesis that ACC response to locomotor forces over time may influence, or even underlie, the bony and hyaline cartilage symptoms characteristic of OA. To effectively investigate the ACC, greater resolution of joint imaging and merging of hierarchical scale data will be required. An appreciation of OA as a ‘whole joint disease’ is expanding, as is the possibility that the ACC may be a key player in healthy ageing and in the transition to OA joint pathology.

A technique for preparing undecalcified osteochondral fresh frozen sections for elemental mapping and understanding disease etiology

The anatomy of the osteochondral junction is complex because several tissue components exist as a unit, including uncalcified cartilage (with superficial, middle, and deep layers), calcified cartilage, and subchondral bone. Furthermore, it is difficult to study because this region is made up of a variety of cell types and extracellular matrix compositions. Using X-ray fluorescence microscopy, we present a protocol for simultaneous elemental detection on fresh frozen samples. We transferred the osteochondral sample using a tape-assisted system and successfully tested it in synchrotron X-ray fluorescence. This protocol elucidates the distinct distribution of elements at the human knee’s osteochondral junction, making it a useful tool for analyzing the co-distribution of various elements in both healthy and diseased states.

Detection of subtle cartilage and bone tissue degeneration in the equine joint using polarisation-sensitive optical coherence tomography

To explore the ability of polarisation-sensitive optical coherence tomography (PS-OCT) to rapidly identify subtle signs of tissue degeneration in the equine joint. Polarisation-sensitive optical coherence tomography (PS-OCT) images were systematically acquired in four locations along the medial and lateral condyles of the third metacarpal bone in five dissected equine specimens. Intensity and retardation PS-OCT images, and anomalies observed therein, were then compared and validated with high resolution images of the tissue sections obtained using Differential Interference contrast (DIC) optical light microscopy. The PS-OCT system was capable of imaging the entire equine osteochondral unit, and allowed delineation of the three structurally differentiated zones of the joint, that is, the articular cartilage matrix, zone of calcified cartilage and underlying subchondral bone. Importantly, PS-OCT imaging was able to detect underlying matrix and bone changes not visible without dissection and/or microscopy. PS-OCT has substantial potential to detect, non-invasively, sub-surface microstructural changes that are known to be associated with the early stages of joint tissue degeneration.

Bilateral auriclar and external ear canal cartilage calcification.

Calcification of auricular cartilage is a rare condition. This phenomenon might be associated with frostbite, local trauma, inflammation, or systemic diseases. Calcification that progresses to the external ear canal cartilage is even rarer. We present an extremely rare case of bilateral auricular and external ear canal cartilage calcification in a patient with acromegaly. Clinicians should be aware that auricular and external ear canal cartilage calcification can occur in a patient with acromegaly.

Costal cartilage fractures in blunt polytrauma patients — a prospective clinical and radiological follow-up study

PurposeTo assess the healing of costal cartilage fractures (CCFX) in patients with blunt polytrauma with follow-up imaging and clinical examination. Effect on physical performance and quality of life (QoL) was also evaluated.MethodsThe study group comprised twenty-one patients with diagnosed CCFX in trauma CT. All the patients underwent MRI, ultrasound, ultra-low-dose CT examinations, and clinical status control. The patients completed QoL questionnaires. Two radiologists evaluated the images regarding fracture union, dislocation, calcifications, and persistent edema at fracture site. An attending trauma surgeon clinically examined the patients, with emphasis on focal tenderness and ribcage mobility. Trauma registry data were accessed to evaluate injury severity and outcome.ResultsThe patients were imaged at an average of 34.1 months (median 36, range 15.8–57.7) after the initial trauma. In 15 patients (71.4%), CCFX were considered stable on imaging. Cartilage calcifications were seen on healed fracture sites in all the patients. The fracture dislocation had increased in 5 patients (23.8%), and 1 patient (4.8%) showed signs of a non-stable union. Four patients (19.0%) reported persistent symptoms from CCFX.ConclusionNon-union in CCFX is uncommon but may lead to decreased stability and discomfort. Both clinical and radiological examinations play an important part in the post-traumatic evaluation of CCFX. CT and MRI visualize the healing process, while dynamic ultrasound may reveal instability. No significant difference in QoL was detected between patients with radiologically healed and non-healed CCFX. Post-traumatic disability was mostly due to other non-thoracic injuries.

Acupotomy inhibits aberrant formation of subchondral bone through regulating osteoprotegerin/receptor activator of nuclear factor-κB ligand pathway in rabbits with knee osteoarthritis induced by modified Videman method.

To investigate the effects of acupotomy on inhibiting abnormal formation of subchondral bone in rabbits with knee osteoarthritis (KOA). A total of 24 New Zealand rabbits were randomly divided into four groups of 6 rabbits each [control, model, electroacupuncture (EA) and acupotomy]. Eighteen KOA model rabbits were established using a modified Videman method. Rabbits in EA and acupotomy groups received the intervention for 3 weeks. Then, the cartilage and subchondral bone unit were obtained and the histomorphological changes were recorded. Osteo-protegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) in subchondral bone were evaluated by Western blotting, real-time polymerase chain reaction and immunohistochemistry. Compared with the model group, both the acupotomy and EA groups showed a significant decrease in the Lequesne index (both 0.01) and Mankin score ( 0.01, < 0.05). In addition, both EA and acupotomy groups had a higher expression of total articular cartilage (TAC) ( 0.05, < 0.01) and lower expression of articular calcified cartilage (ACC)/TAC ( 0.05, < 0.05) compared with the model group. The thickness of the subchondral bone plate in EA and acupotomy groups were decreased (both 0.01) compared to the model group. Moreover, trabecular bone volume (BV/TV), protein and relative expression of OPG and the ratio of OPG/RANKL in the subchondral bone of acupotomy group were decreased statistically significant, while these parameters were not significantly changed in the EA group compared with the model group. In the rabbit model of KOA, acupotomy inhibits aberrant formation of subchondral bone by suppressing OPG/RANKL ratio as a potential therapy for KOA.

Fibrin deposition associates with cartilage degeneration in arthritis

SummaryBackgroundCartilage damage in inflammatory arthritis is attributed to inflammatory cytokines and pannus infiltration. Activation of the coagulation system is a well known feature of arthritis, especially in rheumatoid arthritis (RA). Here we describe mechanisms by which fibrin directly mediates cartilage degeneration.MethodsFibrin deposits were stained on cartilage and synovial tissue of RA and osteoarthritis (OA) patients and in murine adjuvant-induced arthritis (AIA) in wild-type or fibrinogen deficient mice. Fibrinogen expression and procoagulant activity in chondrocytes were evaluated using qRT-PCR analysis and turbidimetry. Chondro-synovial adhesion was studied in co-cultures of human RA cartilage and synoviocytes, and in the AIA model. Calcific deposits were stained in human RA and OA cartilage and in vitro in fibrinogen-stimulated chondrocytes.FindingsFibrin deposits on cartilage correlated with the severity of cartilage damage in human RA explants and in AIA in wild-type mice, whilst fibrinogen deficient mice were protected. Fibrin upregulated Adamts5 and Mmp13 in chondrocytes. Chondro-synovial adhesion only occurred in fibrin-rich cartilage areas and correlated with cartilage damage. In vitro, autologous human synoviocytes, cultured on RA cartilage explants, adhered exclusively to fibrin-rich areas. Fibrin co-localized with calcification in human RA cartilage and triggered chondrocyte mineralization by inducing pro-calcification genes (Anx5, Pit1, Pc1) and the IL-6 cytokine. Similar fibrin-mediated mechanisms were observed in OA models, but to a lesser extent and without pseudo-membranes formation.InterpretationIn arthritis, fibrin plaques directly impair cartilage integrity via a triad of catabolism, adhesion, and calcification.FundingNone.

Highly Porous Type II Collagen-Containing Scaffolds for Enhanced Cartilage Repair with Reduced Hypertrophic Cartilage Formation.

The ability to regenerate damaged cartilage capable of long-term performance in an active joint remains an unmet clinical challenge in regenerative medicine. Biomimetic scaffold biomaterials have shown some potential to direct effective cartilage-like formation and repair, albeit with limited clinical translation. In this context, type II collagen (CII)-containing scaffolds have been recently developed by our research group and have demonstrated significant chondrogenic capacity using murine cells. However, the ability of these CII-containing scaffolds to support improved longer-lasting cartilage repair with reduced calcified cartilage formation still needs to be assessed in order to elucidate their potential therapeutic benefit to patients. To this end, CII-containing scaffolds in presence or absence of hyaluronic acid (HyA) within a type I collagen (CI) network were manufactured and cultured with human mesenchymal stem cells (MSCs) in vitro under chondrogenic conditions for 28 days. Consistent with our previous study in rat cells, the results revealed enhanced cartilage-like formation in the biomimetic scaffolds. In addition, while the variable chondrogenic abilities of human MSCs isolated from different donors were highlighted, protein expression analysis illustrated consistent responses in terms of the deposition of key cartilage extracellular matrix (ECM) components. Specifically, CI/II-HyA scaffolds directed the greatest cell-mediated synthesis and accumulation in the matrices of type II collagen (a principal cartilage ECM component), and reduced deposition of type X collagen (a key protein associated with hypertrophic cartilage formation). Taken together, these results provide further evidence of the capability of these CI/II-HyA scaffolds to direct enhanced and longer-lasting cartilage repair in patients with reduced hypertrophic cartilage formation.

A GAN based approach for inferring progression trajectories of costal cartilage calcification from cross-sectional data at image level

BackgroundCostal cartilage calcification (CCC) increases with age and presents differently for men and women. In individuals, however, the cross-sectional studies that show such trends do not reveal the geometric trajectories through which calcification might accumulate across a lifetime. Generative adversarial networks have the potential to reveal such trajectories from cross-sectional data by learning population trends and synthesizing individualized images at progressive levels of calcification. MethodsChest wall mid-surface CT images with normalized cartilage morphologies were produced for 379 subjects aged 6 to 90, and labeled by sex and calcification severity. A conditional GAN with added loss terms to favor one-way accumulation of CCC was trained using organized image batches. GAN performance was assessed by comparing the distributions of images between the training and synthetic groups. ResultsSynthetic images generated from a common seed for a given sex and at successive calcification severity levels showed incremental and regional growth of calcification sites. CCC patterns for synthetic male and female images matched known sex-based differences, and individual CCC growth in synthetic images was consistent with previously observed population trends. These trends in the synthetic images were also quantified by structural similarity scores. Synthetic images generated from different input seeds further showed individual variance in specific regions and trajectories of CCC accumulation. ConclusionThis study inferred individual progression of CCC accumulation from uncalcified to severely calcified using cross-sectional image data. This information can inform computational models of the changing chest wall biomechanics with age, and the GAN-based technique shows potential for inferring longitudinal data from population trends in other clinical areas.

Autophagic LC3+ calcified extracellular vesicles initiate cartilage calcification in osteoarthritis.

Pathological cartilage calcification plays an important role in osteoarthritis progression but in which the origin of calcified extracellular vesicles (EVs) and their effects remain unknown. Here, we demonstrate that pathological cartilage calcification occurs in the early stage of the osteoarthritis in which the calcified EVs are closely involved. Autophagosomes carrying the minerals are released in EVs, and calcification is induced by those autophagy-regulated calcified EVs. Autophagy-derived microtubule-associated proteins 1A/1B light chain 3B (LC3)–positive EVs are the major population of calcified EVs that initiate pathological calcification. Release of LC3-positive calcified EVs is caused by blockage of the autophagy flux resulted from histone deacetylase 6 (HDAC6)–mediated microtubule destabilization. Inhibition of HDAC6 activity blocks the release of the LC3-positive calcified EVs by chondrocytes and effectively reverses the pathological calcification and degradation of cartilage. The present work discovers that calcified EVs derived from autophagosomes initiate pathological cartilage calcification in osteoarthritis, with potential therapeutic targeting implication.

The molecular mechanism research of cartilage calcification induced by osteoarthritis

ABSTRACT To explore the molecular mechanism of cartilage calcification induced by osteoarthritis (OA) based on distal-less homeobox gene 5 – alkaline phosphatase – integrin-binding sialoprotein – ecto-nucleotide pyrophosphatase 1 (DLX5-ALPL-IBSP-ENPP1) signal axis. Twenty-four rabbits were selected to build models of cartilage calcification induced by OA and randomly divided into 3 groups. The first group was the normal group whose rabbits were injected into 0.9% saline (0.3 mL), and the second group was model group. The third group was model group whose rabbits were injected into DLX5 antibody by caudal vein. Alizarin red calcium staining was used to analyze calcium deposition of cartilage matrix. Immunohistochemical staining was used to analyze the relative expression levels of proteins DLX5 and ENPP1, and western blot was used to analyze the DLX5, ALPL, IBSP, and ENPP1 expression. Calcium salt precipitation was the most serious, and the calcification area increased in the model group. Although calcified nodules appeared in the anti-DLX5 group, they were relatively few. Immunohistochemical staining analysis showed that the protein DLX5 located in the nucleus and the protein ENPP1 located in the extracellular matrix. Western blot analysis showed that the expressions of proteins DLX5, ALPL, IBSP, and ENPP1 were the highest in OA Model group than that of NC group, followed by anti-DLX5 group. The proteins DLX5, ALPL, IBSP, and ENPP1 can promote cartilage calcification induced by OA based on DLX5-ALPL-IBSP-ENPP1 signal axis.

High Spinal Anesthesia in Total Knee Replacement

Background: Osteoarthritis (OA) is the most common degenerative disease at people aged 63-70 years. Human ageing is associated with an increase in weakness around the joints, decreased joint flexibility, calcification of cartilage, and decreased chondrocyte function. Total knee replacement (TKR) is performed to treat pain and immobilisation in osteoarthritis patients. This procedure is done with spinal anaesthesia. Case: A 73 years old man diagnosed with bilateral OA and underwent TKR. The patient had left knee pain six months ago with a history of high blood pressure. If blood pressure &lt;160/90 mmHg subarachnoid block was planed. The patient entered the operating room with an intravenous (IV) line of ringer lactate 10 dpm. Preoperatively, the patient was given ranitidine 50 mg IV and ondansetron 4 mg. The anaesthetic agent was hyperbaric bupivacaine 0.5% 15 mg + fentanyl 25 µg; the patient was hemodynamically monitored and maintained with O2 4 lpm. After 45 minutes of spinal anesthesia, the patient experienced respiratory distress, so we placed a masked and intubated the patient with endotracheal tube (ETT) 7.0. It is suspected that the patient had high spinal anesthesia. Conclusion: A 73-year-old man has been subjected to regional spinal anesthesia with total knee replacement surgery. However, spinal anesthesia failed and was converted to general anesthesia with ETT, with a duration of operation of 4 hours, hemodynamically stable, postoperatively the patient was admitted to the high care unit.

Abstract #1178966: A Rare Case of Idiopathic Osteoporosis with COL10A1 and COL27A1 Genetic Mutations in a Premenopausal Woman

The association between bone mineral density (BMD) and fracture differs in premenopausal women when compared to the postmenopausal women. Irrespective of the BMD, any fragility fracture in those aged 20-50 requires evaluation for secondary causes of osteoporosis. In the absence of secondary causes, idiopathic osteoporosis (IOP) is considered. We present a case of a premenopausal woman with IOP whose mutational analysis revealed variants in COL10A1 and COL27A1. These genetic mutations are found in Schmid-type metaphyseal chondrodysplasia (SMCD) and Steel syndrome, respectively. To our knowledge, this is the first case report establishing a linkage between these specific mutations and IOP. A 36-year-old Hispanic woman with a history of fragility fracture of the lumbar spine at age 23 was referred to Endocrinology for further evaluation. Dual-energy x-ray absorptiometry (DEXA) reported a Z-score of -3.0 in L1-L4, consistent with osteoporosis of the lumbar spine. A careful history, physical examination, and laboratory evaluation ruled out secondary causes of osteoporosis. In the interim, the patient presented a recurrent fragility fracture of the left proximal humerus requiring surgical intervention where bone marrow (BM) was obtained for cytology. BM cytology was found normocellular without increase in blasts or lymphocytes. Notably, the mutational analysis revealed heterozygous variants of uncertain significance (VUS) in COL10A1 [variant c682 c >T (p.Pro228Ser)] and COL27A1 [variant c.1814 c >T (p.Thr 6605 Met)]. Whole exome sequencing was not able to be performed due to insurance issues. The most common secondary causes of premenopausal bone loss include estrogen deficiency as seen in hypogonadism, drug exposure such as glucocorticoids, malabsorption disorders like celiac disease, hyperthyroidism, hypercalciuria, hyperparathyroidism, and disturbances in calcium and vitamin D metabolism. Osteoporosis with no known secondary causes is known as IOP. IOP is a disorder with multiple proposed mechanisms including impairment in growth hormone and insulin like growth factor axis, osteoblast dysfunction, and genetic mutations. Mutational analysis in selected IOP cases, have shown pathogenic variants and VUS in LRP5, LRP6, COL1A1, COL1A2, PLS3, WNT1, DKK1, FKBP10, HGD, SLC34A3. Our patient was found with heterozygous VUS in COL10A1 and COL27A1. These genetic mutations are found in (SMCD) and Steel syndrome, respectively. These rare osteochondrodysplasias, more commonly found in childhood, are associated with skeletal abnormalities including scoliosis, congenital hip dislocations, short stature, and characteristic facial features. More importantly, COL10A1 encodes the alpha 1 chain of collagen type X which is involved in growth plate function, and COL27A1 gene encodes a member of the fibrillar collagen family involved in the calcification of cartilage and the transition of cartilage to bone. To our knowledge, COL10A1 and COL27A1 mutations have not been yet associated as primary causes of IOP. We report this case aiming for further research to identify additional genetic etiologies of IOP.

The diagnostic accuracy of hand-held ultrasonography in evaluation of costal cartilage calcification for grafting in rhinoplasty: A cadaveric study

Autologous costal cartilage graft (ACC) is considered a gold standard in complex rhinoplasty. Costal cartilage calcification remains a problematic issue, causing not only difficulties during the harvesting, carving, and fixation procedures but also worsening the long-term outcome with resorption. This study aims to establish diagnostic accuracy of hand-held ultrasonography in not only detecting the degree and pattern of costal cartilage calcification but also assessing its ability to predict the volume of the harvestable cartilage graft. The study was performed on 50 fresh cadavers with an age range between 17 and 80 years (mean 53.4±16.2 years). An ultrasonographic examination of the costal cartilage of 5th, 6th, and 7th ribs of both hemithoraces was performed. The presence of calcification of the cartilages and the pattern, length, width, cross-sectional area, and depth of calcification were observed and recorded. These results were compared against direct visualization and measurement via surgical dissection. Hand-held ultrasonography has a sensitivity of 94% and a specificity of 96% in detecting calcification with 96% positive predictive value and 93% negative predictive value. The positive likelihood ratio was 20.81 and the negative likelihood ratio was 0.06. Overall, the modality has demonstrated the ability to determine dimensions of the costal cartilage to within millimeters. The pattern of calcification was also correctly predicted in all 300 specimens. Hand-held ultrasonography is an affordable and accessible choice of demonstrating the presence and pattern of calcification as well as the general dimensions of the harvestable rib cartilage.

A 3D Network of Nanochannels for Possible Ion and Molecule Transit in Mineralizing Bone and Cartilage

During crucial growth stages of vertebrate long bones, calcified cartilage beneath the growth plate is anchored to bone by a third mineralized component, the cement line. Proper skeletal development is contingent on the interplay of these three constituents, yet their mineralization processes and structural interactions are incompletely understood, in part from limited knowledge of their meso‐ and nanoscale features. Herein, focused ion beam‐scanning electron microscopy (FIB‐SEM) with serial surface imaging is applied to examine the cartilage–bone interface of mouse femoral heads at an unprecedented scale: FIB‐SEM provides 3D, nanometer resolution of structural details for volumes encompassing metaphyseal calcified cartilage, bone, and the intervening cement line. A novel and complex structural network is revealed, comprising densely packed nanochannels smaller than bone canaliculi (≈10–50 nm diameter) within the calcified cartilage and bone extracellular matrices, but absent in the cement line. A structural correlation is demonstrated between the nanochannels and ellipsoidal mineral domains, which appear to coalesce during mineralization in a process analogous to powder sintering in metallurgy. A mineralization process is proposed, supported by energy‐dispersive X‐Ray spectroscopy of nanochannel contents, in which these unreported structures offer ion and molecule conduits to access the extracellular matrices of calcified cartilage and bone.

Distribution, structure, and mineralization of calcified cartilage remnants in hard antlers

Antlers are paired deciduous bony cranial appendages of deer that undergo a regular cycle of growth, death and casting, and constitute the most rapidly growing bones in mammals. Antler growth occurs in an appositional mode and involves a modified form of endochondral ossification. In endochondral bones, calcified cartilage is typically a transient tissue that is eventually completely replaced by bone tissue. We studied the distribution and characteristics of calcified cartilage in hard antlers from three deer species (Capreolus capreolus, Cervus elaphus, Dama dama), i.e., in antlers from which the skin (velvet) had been shed. Remnants of calcified cartilage were regularly present as part of the trabecular framework in the late formed, distal antler portions in all three species, whereas this tissue was largely or completely missing in the more proximal antler portions. The presence of calcified cartilage remnants in the distal antler portions is attributed to the limited antler lifespan of only a few months, which is also the reason for the virtual lack of bone remodeling in antlers. The calcified cartilage matrix was more highly mineralized than the antler bone matrix. Mineralized deposits were observed in some chondrocyte lacunae and occasionally also in osteocyte lacunae, a phenomenon that has not previously been reported in antlers. Using synchrotron radiation-induced X-ray fluorescence (SR-XRF) mapping, we further demonstrated increased zinc concentrations in cement lines, along the inner borders of incompletely formed primary osteons, along the walls of partly or completely mineral-occluded chondrocyte and osteocyte lacunae, and in intralacunar mineralized deposits. The present study demonstrates that antlers are a promising model for studying the mineralization of cartilage and bone matrices and the formation of mineralized deposits in chondrocyte and osteocyte lacunae.

Radiologic zebra line sign in a patient with Langerhans cell histiocytosis on bisphosphonate therapy.

A 3-year-old boy was diagnosed with multi-system Langerhans cell histiocytosis (LCH) with bone, skin, lung, lymph node, and bone marrow involvement at 8 months of age. He achieved non-active disease (NAD) after chemotherapy with prednisolone, vincristine, and cytarabine. However, the patient presented with bone lesion relapse. Despite re-initiation of vinblastine and prednisolone, his bone lesion progressed, prompting treatment with three cycles of cladribine. While it provided some improvement, he presented with bone lesion relapse soon after cladribine therapy. Due to the recurrence of the bone lesion, we administered bisphosphonate therapy using monthly zoledronic acid for 6 months in addition to conventional chemotherapy, which resolved his bone lesion. The patient achieved NAD for 1 year. While he did not present with bone pain, radiographs obtained during bisphosphonate therapy revealed a “dense metaphyseal band sign,” also known as “zebra line sign,” at the tibia and fibula (Figure 1A−D). Nevertheless, 2 years after initiation of bisphosphonate therapy, his growth remained steady (Figure 1E). LCH is characterized as both neoplastic and inflammatory disease. Osteoclasts are crucial in the pathogenesis of LCH, especially in lytic bone lesions. Previous reports revealed that bisphosphonate therapy, including pamidronate and zoledronate, was effective in patients with LCH. Bisphosphonates reduce the activity of osteoclasts by inhibiting their recruitment, thereby resulting in the uncoupling of bone remodeling. The zebra line sign refers to the line of cartilage calcification persisting from the metaphysis into the diaphysis [1, 2]. This radiologic finding reflects the administration of bisphosphonate [3]. Although the zebra line sign seems to be a normal reaction to bisphosphonate therapy, hematology-oncology specialists are not familiar with this finding. In addition, the long-term side effects (e.g., short stature and fracture) remain unknown. This study highlights the importance of long-term follow-up to evaluate the safety profile of bisphosphonates in patients with LCH. The authors declare no conflict of interest.

Prevention of Arterial Elastocalcinosis: Differential Roles of the Conserved Glutamic Acid and Serine Residues of Matrix Gla Protein.

Inactivating mutations in matrix Gla protein (MGP) lead to Keutel syndrome, a rare disease hallmarked by ectopic calcification of cartilage and vascular tissues. Although MGP acts as a strong inhibitor of arterial elastic lamina calcification (elastocalcinosis), its mode of action is unknown. Two sets of conserved residues undergoing posttranslational modifications-4 glutamic acid residues, which are γ-carboxylated by gamma-glutamyl carboxylase; and 3 serine residues, which are phosphorylated by yet unknown kinase(s)-are thought to be essential for MGP's function. We pursued a genetic approach to study the roles of MGP's conserved residues. First, a transgenic line (SM22a-GlamutMgp) expressing a mutant form of MGP, in which the conserved glutamic acid residues were mutated to alanine, was generated. The transgene was introduced to Mgp-/- mice to generate a compound mutant, which produced the mutated MGP only in the vascular tissues. We generated a second mouse model (MgpS3mut/S3mut) to mutate MGP's conserved serine residues to alanine. The initiation and progression of vascular calcification in these models were analyzed by alizarin red staining, histology, and micro-computed tomography imaging. On a regular diet, the arterial walls in the Mgp-/-; SM22α-GlamutMgp mice were not calcified. However, on a high phosphorus diet, these mice showed wide-spread arterial calcification. In contrast, MgpS3mut/S3mut mice on a regular diet recapitulated arterial calcification traits of Mgp-/- mice, although with lesser severity. For the first time, we show here that MGP's conserved serine residues are indispensable for its antimineralization function in the arterial tissues. Although the conserved glutamic acid residues are not essential for this function on a regular diet, they are needed to prevent phosphate-induced arterial elastocalcinosis.

Mutation in the CCAL1 locus accounts for bidirectional process of human subchondral bone turnover and cartilage mineralization.

To study the mechanism by which the readthrough mutation in TNFRSF11B, encoding osteoprotegerin (OPG) with additional 19 amino acids at its C-terminus (OPG-XL), causes the characteristic bidirectional phenotype of subchondral bone turnover accompanied by cartilage mineralization in chondrocalcinosis patients. OPG-XL was studied by human induced pluripotent stem cells expressing OPG-XL and two isogenic CRISPR/Cas9-corrected controls in cartilage and bone organoids. Osteoclastogenesis was studied with monocytes from OPG-XL carriers and matched healthy controls followed by gene expression characterization. Dual energy X-ray absorptiometry scans and MRI analyses were used to characterize the phenotype of carriers and non-carriers of the mutation. Human OPG-XL carriers relative to sex- and age-matched controls showed, after an initial delay, large active osteoclasts with high number of nuclei. By employing hiPSCs expressing OPG-XL and isogenic CRISPR/Cas9-corrected controls to established cartilage and bone organoids, we demonstrated that expression of OPG-XL resulted in excessive fibrosis in cartilage and high mineralization in bone accompanied by marked downregulation of MGP, encoding matrix Gla protein, and upregulation of DIO2, encoding type 2 deiodinase, gene expression, respectively. The readthrough mutation at CCAL1 locus in TNFRSF11B identifies an unknown role for OPG-XL in subchondral bone turnover and cartilage mineralization in humansvia DIO2 and MGP functions. Previously, OPG-XL was shown to affect binding between RANKL and heparan sulphate (HS) resulting in loss of immobilized OPG-XL. Therefore, effects may be triggered by deficiency in the immobilization of OPG-XL Since the characteristic bidirectional pathophysiology of articular cartilage calcification accompanied by low subchondral bone mineralization is also a hallmark of OA pathophysiology, our results are likely extrapolated to common arthropathies.