The bone and cartilage interplay in osteoarthritis: key to effective treatment strategy

Osteoarthritis (OA) is a prevalent age-related joint disease, determined by diverse changes in pathways maintaining articular cartilage and subchondral bone. This thesis aimed to identify and study gene networks driving interacting etiopathophysiological OA processes in cartilage and subchondral bone. Hereto, characterization of the molecular landscape of bone and cartilage of OA patients showed 305 genes with similar direction of effect, including IL11 and CHADL. Moreover, to capture biological complexity and decipher underlying OA disease mechanisms a variety of human 3D cartilage and bone organoids models were exploited and a human osteochondral construct-on-a-chip was developed. Herein, we showed that the robust OA risk gene WWP2 may initiate OA, via aberrant responses in hypoxia-associated genes and a decrease in anabolic markers. Additionally we showed, as reflected by upregulation of SPP1 and downregulation of WNT16 in cartilage, that treatment of ex vivo human osteochondral explants with human recombinant IL11 does not necessarily has a beneficial outcome. Finally, to allow implementation of knowledge on diverse OA pathophysiological processes, the potency of circulating miRNAs to report on ongoing OA pathophysiological process in joint tissues was established. Such insights are crucial to stratify respective OA patients that require different therapeutic mode of action, towards precision medicine. This research was financially supported by the Dutch Scientific Research Council (NWO/ZonMW Vici grant 91816631/528) and was performed in the framework of the Medical Delta program Regenerative Medicine 4D: Generating complex tissues with stem cells and printing technology and Improving Mobility with Technology. Medical Delta and the Nederlandse Vereniging voor Matrix Biologie are gratefully acknowledged for financial support for the printing costs of this thesis.LUMC / Geneeskund

Avolition in a patient with hypogonadism

Background and Objectives: Testosterone deficiency has been implicated in the etiology of depression although there is an ongoing debate on the nature of this association. There is a paucity of data about the psychological impact of hypogonadism in genetic disorders associated with testosterone deficiency. Methods:A 57-year-old male is described who was referred for treatment resistant depression. His history showed infertility and lowered testosterone. A selective literature review is given to clarify the patient's clinical condition. Results: Cytogenetic analysis demonstrated a Robertsonian translocation between chromosomes 13 and 14 that accounted for his infertility. The psychopathological picture did not meet the criteria for a major depressive disorder but was characterized by symptoms of apathy or avolition. These symptoms were most probably aggravated by previous long lasting treatment with antidepressants. Conclusions: Testosterone deficiency may be related to motivational deficits that should not be misunderstood for depressive illness. Apathy is probably an underestimated side effect of antidepressants

Characterization of dynamic changes in Matrix Gla Protein (MGP) gene expression as function of genetic risk alleles, osteoarthritis relevant stimuli, and the vitamin K inhibitor warfarin

Objective: We here aimed to characterize changes of Matrix Gla Protein (MGP) expression in relation to its recently identified OA risk allele rs1800801-T in OA cartilage, subchondral bone and human ex vivo osteochondral explants subjected to OA related stimuli. Given that MGP function depends on vitamin K bioavailability, we studied the effect of frequently prescribed vitamin K antagonist warfarin. Methods: Differential (allelic) mRNA expression of MGP was analyzed using RNA-sequencing data of human OA cartilage and subchondral bone. Human osteochondral explants were used to study exposures to interleukin one beta (IL-1b; inflammation), triiodothyronine (T3; Hypertrophy), warfarin, or 65% mechanical stress (65%MS) as function of rs1800801 genotypes. Results: We confirmed that the MGP risk allele rs1800801-T was associated with lower expression and that MGP was significantly upregulated in lesioned as compared to preserved OA tissues, mainly in risk allele carriers, in both cartilage and subchondral bone. Moreover, MGP expression was downregulated in response to OA like triggers in cartilage and subchondral bone and this effect might be reduced in carriers of the rs1800801-T risk allele. Finally, warfarin treatment in cartilage increased COL10A1 and reduced SOX9 and MMP3 expression and in subchondral bone reduced COL1A1 and POSTN expression. Discussion & conclusions: Our data highlights that the genetic risk allele lowers MGP expression and upon OA relevant triggers may hamper adequate dynamic changes in MGP expression, mainly in carti-lage. The determined direct negative effect of warfarin on human explant cultures functionally un-derscores the previously found association between vitamin K deficiency and OA. (c) 2021 The Authors. Published by Elsevier Ltd on behalf of Osteoarthritis Research Society International. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Molecular Epidemiolog

A molecular map of long non-coding RNA expression, isoform switching and alternative splicing in osteoarthritis

Osteoarthritis is a prevalent joint disease and a major cause of disability worldwide with no curative therapy. Development of disease-modifying therapies requires a better understanding of the molecular mechanisms underpinning disease. A hallmark of osteoarthritis is cartilage degradation. To define molecular events characterizing osteoarthritis at the whole transcriptome level, we performed deep RNA sequencing in paired samples of low- and high-osteoarthritis grade knee cartilage derived from 124 patients undergoing total joint replacement. We detected differential expression between low- and high-osteoarthritis grade articular cartilage for 365 genes and identified a 38-gene signature in osteoarthritis cartilage by replicating our findings in an independent dataset. We also found differential expression for 25 novel long non-coding RNA genes (lncRNAs) and identified potential lncRNA interactions with RNA-binding proteins in osteoarthritis. We assessed alterations in the relative usage of individual gene transcripts and identified differential transcript usage for 82 genes, including ABI3BP, coding for an extracellular matrix protein, AKT1S1, a negative regulator of the mTOR pathway and TPRM4, coding for a transient receptor potential channel. We further assessed genome-wide differential splicing, for the first time in osteoarthritis, and detected differential splicing for 209 genes, which were enriched for extracellular matrix, proteoglycans and integrin surface interactions terms. In the largest study of its kind in osteoarthritis, we find that isoform and splicing changes, in addition to extensive differences in both coding and non-coding sequence expression, are associated with disease and demonstrate a novel layer of genomic complexity to osteoarthritis pathogenesis

Elucidating mechano-pathology of osteoarthritis: transcriptome-wide differences in mechanically stressed aged human cartilage explants

Background Failing of intrinsic chondrocyte repair after mechanical stress is known as one of the most important initiators of osteoarthritis. Nonetheless, insight into these early mechano-pathophysiological processes in age-related human articular cartilage is still lacking. Such insights are needed to advance clinical development. To highlight important molecular processes of osteoarthritis mechano-pathology, the transcriptome-wide changes following injurious mechanical stress on human aged osteochondral explants were characterized. Methods Following mechanical stress at a strain of 65% (65%MS) on human osteochondral explants (n(65%MS) = 14 versus n(control) = 14), RNA sequencing was performed. Differential expression analysis between control and 65%MS was performed to determine mechanical stress-specific changes. Enrichment for pathways and protein-protein interactions was analyzed with Enrichr and STRING. Results We identified 156 genes significantly differentially expressed between control and 65%MS human osteochondral explants. Of note, IGFBP5 (FC = 6.01; FDR = 7.81 x 10(-3)) and MMP13 (FC = 5.19; FDR = 4.84 x 10(-2)) were the highest upregulated genes, while IGFBP6 (FC = 0.19; FDR = 3.07 x 10(-4)) was the most downregulated gene. Protein-protein interactions were significantly higher than expected by chance (P = 1.44 x 10(-15) with connections between 116 out of 156 genes). Pathway analysis showed, among others, enrichment for cellular senescence, insulin-like growth factor (IGF) I and II binding, and focal adhesion. Conclusions Our results faithfully represent transcriptomic wide consequences of mechanical stress in human aged articular cartilage with MMP13, IGF binding proteins, and cellular senescence as the most notable results. Acquired knowledge on the as such identified initial, osteoarthritis-related, detrimental responses of chondrocytes may eventually contribute to the development of effective disease-modifying osteoarthritis treatments.Molecular Epidemiolog

Cartilage from human-induced pluripotent stem cells: comparison with neo-cartilage from chondrocytes and bone marrow mesenchymal stromal cells

Cartilage has little intrinsic capacity for repair, so transplantation of exogenous cartilage cells is considered a realistic option for cartilage regeneration. We explored whether human-induced pluripotent stem cells (hiPSCs) could represent such unlimited cell sources for neo-cartilage comparable to human primary articular chondrocytes (hPACs) or human bone marrow-derived mesenchymal stromal cells (hBMSCs). For this, chondroprogenitor cells (hiCPCs) and hiPSC-derived mesenchymal stromal cells (hiMSCs) were generated from two independent hiPSC lines and characterized by morphology, flow cytometry, and differentiation potential. Chondrogenesis was compared to hBMSCs and hPACs by histology, immunohistochemistry, and RT-qPCR, while similarities were estimated based on Pearson correlations using a panel of 20 relevant genes. Our data show successful differentiations of hiPSC into hiMSCs and hiCPCs. Characteristic hBMSC markers were shared between hBMSCs and hiMSCs, with the exception of CD146 and CD45. However, neo-cartilage generated from hiMSCs showed low resemblances when compared to hBMSCs (53%) and hPACs (39%) characterized by lower collagen type 2 and higher collagen type 1 expression. Contrarily, hiCPC neo-cartilage generated neo-cartilage more similar to hPACs (65%), with stronger expression of matrix deposition markers. Our study shows that taking a stepwise approach to generate neo-cartilage from hiPSCs via chondroprogenitor cells results in strong similarities to neo-cartilage of hPACs within 3 weeks following chondrogenesis, making them a potential candidate for regenerative therapies. Contrarily, neo-cartilage deposited by hiMSCs seems more prone to hypertrophic characteristics compared to hPACs. We therefore compared chondrocytes derived from hiMSCs and hiCPCs with hPACs and hBMSCs to outline similarities and differences between their neo-cartilage and establish their potential suitability for regenerative medicine and disease modelling.Pathogenesis and treatment of chronic pulmonary disease

Capturing essential physiological aspects of interacting cartilage and bone tissue with osteoarthritis pathophysiology: a human osteochondral unit-on-a-chip model

Given the multi-tissue aspects of osteoarthritis (OA) pathophysiology, translation of OA susceptibility genes towards underlying biological mechanism and eventually drug target discovery requires appropriate human in vitro OA models that incorporate both functional bone and cartilage tissue units. Therefore, a microfluidic chip is developed with an integrated fibrous polycaprolactone matrix in which neo-bone and cartilage are produced, that could serve as a tailored human in vitro disease model of the osteochondral unit of joints. The model enables to evaluate OA-related environmental perturbations to (individual) tissue units by controlling environmental cues, for example by adding biochemical agents. After establishing the co-culture in the system, a layer of cartilaginous matrix is deposited in the chondrogenic compartment, while a bone-like matrix is deposited between the fibers, indicated by both histology and gene expression levels of collagen type 2 and osteopontin, respectively. As proof-of-principle, the bone and cartilaginous tissue are exposed to active thyroid hormone, creating an OA disease model. This results in increased expression levels of hypertrophy markers integrin-binding sialoprotein and alkaline phosphatase in both cartilage and bone, as expected. Altogether, this model could contribute to enhanced translation from OA risk genes towards novel OA therapies.Molecular Epidemiolog

RNA sequencing reveals interacting key determinants of osteoarthritis acting in subchondral bone and articular cartilage: identification of IL11 and CHADL as attractive treatment targets

Objective To identify key determinants of the interactive pathophysiologic processes in subchondral bone and cartilage in osteoarthritis (OA).Methods We performed RNA sequencing on macroscopically preserved and lesional OA subchondral bone from patients in the Research Arthritis and Articular Cartilage study who underwent joint replacement surgery due to OA (n = 24 sample pairs: 6 hips and 18 knees). Unsupervised hierarchical clustering and differential expression analyses were conducted. Results were combined with data on previously identified differentially expressed genes in cartilage (partly overlapping samples) as well as data on recently identified OA risk genes.Results We identified 1,569 genes that were significantly differentially expressed between lesional and preserved subchondral bone, including CNTNAP2 (fold change [FC] 2.4, false discovery rate [FDR] 3.36 x 10(-5)) and STMN2 (FC 9.6, FDR 2.36 x 10(-3)). Among these 1,569 genes, 305 were also differentially expressed, and with the same direction of effect, in cartilage, including the recently recognized OA susceptibility genes IL11 and CHADL. Upon differential expression analysis with stratification for joint site, we identified 509 genes that were exclusively differentially expressed in subchondral bone of the knee, including KLF11 and WNT4. These genes that were differentially expressed exclusively in the knee were enriched for involvement in epigenetic processes, characterized by, e.g., HIST1H3J and HIST1H3H.Conclusion IL11 and CHADL were among the most consistently differentially expressed genes OA pathophysiology-related genes in both bone and cartilage. As these genes were recently also identified as robust OA risk genes, they classify as attractive therapeutic targets acting on 2 OA-relevant tissues.Molecular Epidemiolog