@article{diekman_loeser_2024, title={DNA Damage and Cellular Senescence in Osteoarthritis: An Unexpected Role for Interferon Regulatory Factor 1 in Chondrocyte DNA Repair}, ISSN={["2326-5205"]}, DOI={10.1002/art.42822}, abstractNote={Disclosure Form Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.}, journal={ARTHRITIS & RHEUMATOLOGY}, author={Diekman, Brian O. and Loeser, Richard F.}, year={2024}, month={Feb} }
 @misc{richard_capellini_diekman_2023, title={Epigenetics as a mediator of genetic risk in osteoarthritis: role during development, homeostasis, aging, and disease progression}, volume={324}, ISSN={["1522-1563"]}, DOI={10.1152/ajpcell.00574.2022}, abstractNote={The identification of genomic loci that are associated with osteoarthritis (OA) has provided a starting point for understanding how genetic variation activates catabolic processes in the joint. However, genetic variants can only alter gene expression and cellular function when the epigenetic environment is permissive for these effects. In this review, we provide examples of how epigenetic shifts at distinct life stages can alter the risk for OA, which we posit is critical for proper interpretation of genome-wide association studies (GWAS). During development, intensive work on the growth and differentiation factor 5 (GDF5) locus has revealed the importance of tissue-specific enhancer activity in controlling both joint development and the subsequent risk for OA. During homeostasis in adults, underlying genetic risk factors may help establish beneficial or catabolic "set points" that dictate tissue function, with a strong cumulative effect on OA risk. During aging, methylation changes and the re-organization of chromatin can "unmask" the effects of genetic variants. The destructive function of variants that alter aging would only mediate effects after reproductive competence and thus avoid any evolutionary selection pressure, as consistent with larger frameworks of biological aging and its relationship to disease. A similar "unmasking" may occur during OA progression, which is supported by the finding of distinct expression quantitative trait loci (eQTLs) in chondrocytes depending on degree of tissue degradation. Finally, we propose that massively parallel reporter assays (MPRAs) will be a valuable tool to test the function of putative OA GWAS variants in chondrocytes from different life stages.}, number={5}, journal={AMERICAN JOURNAL OF PHYSIOLOGY-CELL PHYSIOLOGY}, author={Richard, Daniel and Capellini, Terence D. and Diekman, Brian O.}, year={2023}, month={May}, pages={C1078–C1088} }
 @article{doherty_aw_warren_hockenberry_whitworth_krohn_howell_diekman_legant_nia_et al._2023, title={Patient-derived extracellular matrix demonstrates role of COL3A1 in blood vessel mechanics}, volume={166}, ISSN={["1878-7568"]}, DOI={10.1016/j.actbio.2023.05.015}, abstractNote={Vascular Ehlers-Danlos Syndrome (vEDS) is a rare autosomal dominant disease caused by mutations in the COL3A1 gene, which renders patients susceptible to aneurysm and arterial dissection and rupture. To determine the role of COL3A1 variants in the biochemical and biophysical properties of human arterial ECM, we developed a method for synthesizing ECM directly from vEDS donor fibroblasts. We found that the protein content of the ECM generated from vEDS donor fibroblasts differed significantly from ECM from healthy donors, including upregulation of collagen subtypes and other proteins related to ECM structural integrity. We further found that ECM generated from a donor with a glycine substitution mutation was characterized by increased glycosaminoglycan content and unique viscoelastic mechanical properties, including increased time constant for stress relaxation, resulting in a decrease in migratory speed of human aortic endothelial cells when seeded on the ECM. Collectively, these results demonstrate that vEDS patient-derived fibroblasts harboring COL3A1 mutations synthesize ECM that differs in composition, structure, and mechanical properties from healthy donors. These results further suggest that ECM mechanical properties could serve as a prognostic indicator for patients with vEDS, and the insights provided by the approach demonstrate the broader utility of cell-derived ECM in disease modeling. The role of collagen III ECM mechanics remains unclear, despite reported roles in diseases including fibrosis and cancer. Here, we generate fibrous, collagen-rich ECM from primary donor cells from patients with vascular Ehlers-Danlos syndrome (vEDS), a disease caused by mutations in the gene that encodes collagen III. We observe that ECM grown from vEDS patients is characterized by unique mechanical signatures, including altered viscoelastic properties. By quantifying the structural, biochemical, and mechanical properties of patient-derived ECM, we identify potential drug targets for vEDS, while defining a role for collagen III in ECM mechanics more broadly. Furthermore, the structure/function relationships of collagen III in ECM assembly and mechanics will inform the design of substrates for tissue engineering and regenerative medicine.}, journal={ACTA BIOMATERIALIA}, author={Doherty, Elizabeth L. and Aw, Wen Yih and Warren, Emily C. and Hockenberry, Max and Whitworth, Chloe P. and Krohn, Grace and Howell, Stefanie and Diekman, Brian O. and Legant, Wesley R. and Nia, Hadi Tavakoli and et al.}, year={2023}, month={Aug}, pages={346–359} }
 @article{miao_su_cui_bahnson_li_wang_yang_collins_wu_gu_et al._2023, title={Redox-active endosomes mediate α5β1 integrin signaling and promote chondrocyte matrix metalloproteinase production in osteoarthritis}, volume={16}, ISSN={["1937-9145"]}, DOI={10.1126/scisignal.adf8299}, abstractNote={Mechanical cues sensed by integrins induce cells to produce proteases to remodel the extracellular matrix. Excessive protease production occurs in many degenerative diseases, including osteoarthritis, in which articular cartilage degradation is associated with the genesis of matrix protein fragments that can activate integrins. We investigated the mechanisms by which integrin signals may promote protease production in response to matrix changes in osteoarthritis. Using a fragment of the matrix protein fibronectin (FN) to activate the α5β1 integrin in primary human chondrocytes, we found that endocytosis of the integrin and FN fragment complex drove the production of the matrix metalloproteinase MMP-13. Activation of α5β1 by the FN fragment, but not by intact FN, was accompanied by reactive oxygen species (ROS) production initially at the cell surface, then in early endosomes. These ROS-producing endosomes (called redoxosomes) contained the integrin-FN fragment complex, the ROS-producing enzyme NADPH oxidase 2 (NOX2), and SRC, a redox-regulated kinase that promotes MMP-13 production. In contrast, intact FN was endocytosed and trafficked to recycling endosomes without inducing ROS production. Articular cartilage from patients with osteoarthritis showed increased amounts of SRC and the NOX2 complex component p67phox. Furthermore, we observed enhanced localization of SRC and p67phox at early endosomes, suggesting that redoxosomes could transmit and sustain integrin signaling in response to matrix damage. This signaling mechanism not only amplifies the production of matrix-degrading proteases but also establishes a self-perpetuating cycle that contributes to the ongoing degradation of cartilage matrix in osteoarthritis. Description Integrin-dependent redox signaling at endosomes stimulates chondrocytes to produce a matrix-degrading protease. Editor’s summary Fragments of extracellular matrix proteins stimulate chondrocytes to produce proteases, thus perpetuating cartilage degradation. Miao et al. found that the internalization of a fibronectin fragment and its integrin receptor induced primary human chondrocytes to increase their production of the matrix metalloprotease MMP-13 (see the Focus by Goldring). This increase required the formation of redoxosomes, endosomes that are production sites for reactive oxygen species and that sustained intracellular integrin signaling. Cartilage from patients with osteoarthritis showed increased formation of these redoxosomes, suggesting that this mechanism contributes to the vicious cycle of destruction in arthritic cartilage. —Annalisa M. VanHook}, number={809}, journal={SCIENCE SIGNALING}, author={Miao, Michael Z. and Su, Qian Peter and Cui, Yang and Bahnson, Edward M. and Li, Gang and Wang, Menglin and Yang, Yuchen and Collins, John A. and Wu, Di and Gu, Qisheng and et al.}, year={2023}, month={Oct} }
 @article{cui_miao_wang_su_qiu_arbeeva_chubinskaya_diekman_loeser_2023, title={Yes-associated protein nuclear translocation promotes anabolic activity in human articular chondrocytes}, volume={31}, ISSN={["1522-9653"]}, DOI={10.1016/j.joca.2023.04.006}, abstractNote={Objective Yes-associated protein (YAP) has been widely studied as a mechanotransducer in many cell types, but its function in cartilage is controversial. The aim of this study was to identify the effect of YAP phosphorylation and nuclear translocation on the chondrocyte response to stimuli relevant to osteoarthritis (OA). Design Cultured normal human articular chondrocytes from 81 donors were treated with increased osmolarity media as an in vitro model of mechanical stimulation, fibronectin fragments (FN-f) or IL-1β as catabolic stimuli, and IGF-1 as an anabolic stimulus. YAP function was assessed with gene knockdown and inhibition by verteporfin. Nuclear translocation of YAP and its transcriptional co-activator TAZ and site-specific YAP phosphorylation were determined by immunoblotting. Immunohistochemistry and immunofluorescence to detect YAP were performed on normal and OA human cartilage with different degrees of damage. Results Chondrocyte YAP/TAZ nuclear translocation increased under physiological osmolarity (400 mOsm) and IGF-1 stimulation, which was associated with YAP phosphorylation at Ser128. In contrast, catabolic stimulation decreased the levels of nuclear YAP/TAZ through YAP phosphorylation at Ser127. Following YAP inhibition, anabolic gene expression and transcriptional activity decreased. Additionally, YAP knockdown reduced proteoglycan staining and levels of type II collagen. Total YAP immunostaining was greater in OA cartilage, but YAP was sequestered in the cytosol in cartilage areas with more severe damage. Conclusions YAP chondrocyte nuclear translocation is regulated by differential phosphorylation in response to anabolic and catabolic stimuli. Decreased nuclear YAP in OA chondrocytes may contribute to reduced anabolic activity and promotion of further cartilage loss.}, number={8}, journal={OSTEOARTHRITIS AND CARTILAGE}, author={Cui, Y. and Miao, M. Z. and Wang, M. and Su, Q. P. and Qiu, K. and Arbeeva, L. and Chubinskaya, S. and Diekman, B. O. and Loeser, R. F.}, year={2023}, month={Aug}, pages={1078–1090} }
 @article{thulson_davis_d'costa_coryell_kramer_mohlke_loeser_diekman_phanstiel_2022, title={3D chromatin structure in chondrocytes identifies putative osteoarthritis risk genes}, ISSN={["1943-2631"]}, DOI={10.1093/genetics/iyac141}, abstractNote={Abstract Genome-wide association studies have identified over 100 loci associated with osteoarthritis risk, but the majority of osteoarthritis risk variants are noncoding, making it difficult to identify the impacted genes for further study and therapeutic development. To address this need, we used a multiomic approach and genome editing to identify and functionally characterize potential osteoarthritis risk genes. Computational analysis of genome-wide association studies and ChIP-seq data revealed that chondrocyte regulatory loci are enriched for osteoarthritis risk variants. We constructed a chondrocyte-specific regulatory network by mapping 3D chromatin structure and active enhancers in human chondrocytes. We then intersected these data with our previously collected RNA-seq dataset of chondrocytes responding to fibronectin fragment, a known osteoarthritis trigger. Integration of the 3 genomic datasets with recently reported osteoarthritis genome-wide association study variants revealed a refined set of putative causal osteoarthritis variants and their potential target genes. One of the putative target genes identified was SOCS2, which was connected to a putative causal variant by a 170-kb loop and is differentially regulated in response to fibronectin fragment. CRISPR-Cas9-mediated deletion of SOCS2 in primary human chondrocytes from 3 independent donors led to heightened expression of inflammatory markers after fibronectin fragment treatment. These data suggest that SOCS2 plays a role in resolving inflammation in response to cartilage matrix damage and provides a possible mechanistic explanation for its influence on osteoarthritis risk. In total, we identified 56 unique putative osteoarthritis risk genes for further research and potential therapeutic development.}, journal={GENETICS}, author={Thulson, Eliza and Davis, Eric S. and D'Costa, Susan and Coryell, Philip R. and Kramer, Nicole E. and Mohlke, Karen L. and Loeser, Richard F. and Diekman, Brian O. and Phanstiel, Douglas H.}, year={2022}, month={Sep} }
 @article{copp_chubinskaya_bracey_shine_sessions_loeser_diekman_2022, title={Comet assay for quantification of the increased DNA damage burden in primary human chondrocytes with aging and osteoarthritis}, ISSN={["1474-9726"]}, DOI={10.1111/acel.13698}, abstractNote={It is known that chondrocytes from joints with osteoarthritis (OA) exhibit high levels of DNA damage, but the degree to which chondrocytes accumulate DNA damage during “normal aging” has not been established. The goal of this study was to quantify the DNA damage present in chondrocytes obtained from cadaveric donors of a wide age range, and to compare the extent of this damage to OA chondrocytes. The alkaline comet assay was used to measure the DNA damage in normal cartilage from the ankle (talus) and the knee (femur) of cadaveric donors, as well as in OA chondrocytes obtained at the time of total knee replacement. Chondrocytes from younger donors (<45 years) had less DNA damage than older donors (>70 years) as assessed by the percentage of DNA in the comet “tail”. In donors between 50 and 60 years old, there was increased DNA damage in chondrocytes from OA cartilage as compared to cadaveric. Talar chondrocytes from 23 donors between the ages of 34 and 78 revealed a linear increase in DNA damage with age (R2 = 0.865, p < 0.0001). A “two‐tailed” comet assay was used to demonstrate that most of the accumulated damage is in the form of strand breaks as opposed to alkali‐labile base damage. Chondrocytes from young donors required 10 Gy irradiation to recapitulate the DNA damage present in chondrocytes from older donors. Given the potential for DNA damage to contribute to chondrocyte dysfunction and senescence, this study supports the investigation of mechanisms by which hypo‐replicative cell types accumulate high levels of damage.}, journal={AGING CELL}, author={Copp, Michaela E. and Chubinskaya, Susan and Bracey, Daniel N. and Shine, Jacqueline and Sessions, Garrett and Loeser, Richard F. and Diekman, Brian O.}, year={2022}, month={Aug} }
 @article{williams_meyers_braxton_diekman_lascelles_2022, title={Pilot comparison of outcome measures across chemical and surgical experimental models of chronic osteoarthritis in the rat (Rattus norvegicus)}, volume={17}, ISSN={["1932-6203"]}, url={https://doi.org/10.1371/journal.pone.0277943}, DOI={10.1371/journal.pone.0277943}, abstractNote={Relatively little work has evaluated both the disease of osteoarthritis (OA) and clinically-relevant pain outcome measures across different OA models in rats. The objective of this study was to compare sensitivity, pain, and histological disease severity across chemical and surgical models of OA in the rat. Stifle OA was induced in Sprague–Dawley rats via intraarticular injection of monoiodoacetate (MIA) or surgical transection of anterior cruciate ligament and/or destabilization of medial meniscus (ACL+DMM or DMM alone). Reflexive (e.g., mechanical and thermal stimuli) measures of sensitivity and non-reflexive assays (e.g., lameness, static hindlimb weight-bearing asymmetry, dynamic gait analysis) of pain were measured over time. Joint degeneration was assessed histologically. Six-weeks post OA-induction, the ACL+DMM animals had significantly greater visually observed lameness than MIA animals; however, both ACL+DMM and MIA animals showed equal pain as measured by limb use during ambulation and standing. The MIA animals showed increased thermal, but not mechanical, sensitivity compared to ACL+DMM animals. Joint degeneration was significantly more severe in the MIA model at 6 weeks. Our pilot data suggest both the ACL+DMM and MIA models are equal in terms of clinically relevant pain behaviors, but the MIA model is associated with more severe histological changes over time potentially making it more suitable for screening disease modifying agents. Future work should further characterize each model in terms of complex pain behaviors and biochemical, molecular, and imaging analysis of the sensory system and joint tissues, which will allow for more informed decisions associated with model selection and investigative outcomes.}, number={11}, journal={PLOS ONE}, author={Williams, Morika D. and Meyers, Rachel C. and Braxton, Lauryn A. and Diekman, Brian and Lascelles, B. Duncan X.}, editor={Wijnen, AndreEditor}, year={2022}, month={Nov} }
 @article{novais_tran_johnston_darris_roupas_sessions_shapiro_diekman_risbud_2021, title={Long-term treatment with senolytic drugs Dasatinib and Quercetin ameliorates age-dependent intervertebral disc degeneration in mice}, volume={12}, ISSN={["2041-1723"]}, DOI={10.1038/s41467-021-25453-2}, abstractNote={Intervertebral disc degeneration is highly prevalent within the elderly population and is a leading cause of chronic back pain and disability. Due to the link between disc degeneration and senescence, we explored the ability of the Dasatinib and Quercetin drug combination (D + Q) to prevent an age-dependent progression of disc degeneration in mice. We treated C57BL/6 mice beginning at 6, 14, and 18 months of age, and analyzed them at 23 months of age. Interestingly, 6- and 14-month D + Q cohorts show lower incidences of degeneration, and the treatment results in a significant decrease in senescence markers p16INK4a, p19ARF, and SASP molecules IL-6 and MMP13. Treatment also preserves cell viability, phenotype, and matrix content. Although transcriptomic analysis shows disc compartment-specific effects of the treatment, cell death and cytokine response pathways are commonly modulated across tissue types. Results suggest that senolytics may provide an attractive strategy to mitigating age-dependent disc degeneration.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Novais, Emanuel J. and Tran, Victoria A. and Johnston, Shira N. and Darris, Kayla R. and Roupas, Alex J. and Sessions, Garrett A. and Shapiro, Irving M. and Diekman, Brian O. and Risbud, Makarand V}, year={2021}, month={Sep} }
 @article{collins_kapustina_bolduc_pike_diekman_mix_chubinskaya_eroglu_michel_poole_et al._2021, title={Sirtuin 6 (SIRT6) regulates redox homeostasis and signaling events in human articular chondrocytes}, volume={166}, ISSN={["1873-4596"]}, DOI={10.1016/j.freeradbiomed.2021.01.054}, abstractNote={The nuclear localized protein deacetylase, SIRT6, has been identified as a crucial regulator of biological processes that drive aging. Among these processes, SIRT6 can promote resistance to oxidative stress conditions, but the precise mechanisms remain unclear. The objectives of this study were to examine the regulation of SIRT6 activity by age and oxidative stress and define the role of SIRT6 in maintaining redox homeostasis in articular chondrocytes. Although SIRT6 levels did not change with age, SIRT6 activity was significantly reduced in chondrocytes isolated from older adults. Using dimedone-based chemical probes that detect oxidized cysteines, we identified that SIRT6 is oxidized in response to oxidative stress conditions, an effect that was associated with reduced SIRT6 activity. Enhancement of SIRT6 activity through adenoviral SIRT6 overexpression specifically increased the basal levels of two antioxidant proteins, peroxiredoxin 1 (Prx1) and sulfiredoxin (Srx) and decreased the levels of an inhibitor of antioxidant activity, thioredoxin interacting protein (TXNIP). Conversely, in chondrocytes derived from mice with cartilage specific Sirt6 knockout, Sirt6 loss decreased Prx1 levels and increased TXNIP levels. SIRT6 overexpression decreased nuclear-generated H2O2 levels and oxidative stress-induced accumulation of nuclear phosphorylated p65. Our data demonstrate that SIRT6 activity is altered with age and oxidative stress conditions associated with aging. SIRT6 contributes to chondrocyte redox homeostasis by regulating specific members of the Prx catalytic cycle. Targeted therapies aimed at preventing the age-related decline in SIRT6 activity may represent a novel strategy to maintain redox balance in joint tissues and decrease catabolic signaling events implicated in osteoarthritis (OA).}, journal={FREE RADICAL BIOLOGY AND MEDICINE}, author={Collins, John A. and Kapustina, Maryna and Bolduc, Jesalyn A. and Pike, James F. W. and Diekman, Brian O. and Mix, Kimberlee and Chubinskaya, Susan and Eroglu, Emrah and Michel, Thomas and Poole, Leslie B. and et al.}, year={2021}, month={Apr}, pages={90–103} }
 @article{copp_flanders_gagliardi_gilbertie_sessions_chubinskaya_loeser_schnabel_diekman_2021, title={The combination of mitogenic stimulation and DNA damage induces chondrocyte senescence}, volume={29}, ISSN={["1522-9653"]}, DOI={10.1016/j.joca.2020.11.004}, abstractNote={Cellular senescence is a phenotypic state characterized by stable cell-cycle arrest, enhanced lysosomal activity, and the secretion of inflammatory molecules and matrix degrading enzymes. Senescence has been implicated in osteoarthritis (OA) pathophysiology; however, the mechanisms that drive senescence induction in cartilage and other joint tissues are unknown. While numerous physiological signals are capable of initiating senescence, one emerging theme is that damaged cells convert to senescence in response to sustained mitogenic stimulation. The goal of this study was to develop an in vitro articular cartilage explant model to investigate the mechanisms of senescence induction.This study utilized healthy cartilage derived from cadaveric equine stifles and human ankles. Explants were irradiated to initiate DNA damage, and mitogenic stimulation was provided through serum-containing medium and treatment with transforming growth factor β1 and basic fibroblastic growth factor. Readouts of senescence were a quantitative flow cytometry assay to detect senescence-associated β galactosidase activity (SA-β-gal), immunofluorescence for p16 and γH2AX, and qPCR for the expression of inflammatory genes.Human cartilage explants required both irradiation and mitogenic stimulation to induce senescence as compared to baseline control conditions (7.16% vs 2.34% SA-β-gal high, p = 0.0007). These conditions also resulted in chondrocyte clusters within explants, a persistent DNA damage response, increased p16, and gene expression changes.Treatment of cartilage explants with mitogenic stimuli in the context of cellular damage reliably induces high levels of SA-β-gal activity and other senescence markers, which provides a physiologically relevant model system to investigate the mechanisms of senescence induction.}, number={3}, journal={OSTEOARTHRITIS AND CARTILAGE}, author={Copp, M. E. and Flanders, M. C. and Gagliardi, R. and Gilbertie, J. M. and Sessions, G. A. and Chubinskaya, S. and Loeser, R. F. and Schnabel, L. and Diekman, B. O.}, year={2021}, month={Mar}, pages={402–412} }
 @article{tessier_doolittle_sao_rotty_bear_ulici_loeser_shapiro_diekman_risbud_2020, title={Arp2/3 inactivation causes intervertebral disc and cartilage degeneration with dysregulated TonEBP-mediated osmoadaptation}, volume={5}, ISSN={["2379-3708"]}, DOI={10.1172/jci.insight.131382}, abstractNote={Extracellular matrix and osmolarity influence the development and homeostasis of skeletal tissues through Rho GTPase-mediated alteration of the actin cytoskeleton. This study investigated whether the actin-branching Arp2/3 complex, a downstream effector of the Rho GTPases Cdc42 and Rac1, plays a critical role in maintaining the health of matrix-rich and osmotically loaded intervertebral discs and cartilage. Mice with constitutive intervertebral disc and cartilage-specific deletion of the critical Arp2/3 subunit Arpc2 (Col2-Cre; Arpc2f/f) developed chondrodysplasia and spinal defects. Since these mice did not survive to adulthood, we generated mice with inducible Arpc2 deletion in disc and cartilage (Acan-CreERT2; Arpc2f/f). Inactivation of Arp2/3 at skeletal maturity resulted in growth plate closure, loss of proteoglycan content in articular cartilage, and degenerative changes in the intervertebral disc at 1 year of age. Chondrocytes with Arpc2 deletion showed compromised cell spreading on both collagen and fibronectin. Pharmacological inhibition of Cdc42 and Arp2/3 prevented the osmoadaptive transcription factor TonEBP/NFAT5 from recruiting co-factors in response to a hyperosmolarity challenge. Together, these findings suggest that Arp2/3 plays a critical role in cartilaginous tissues through the regulation of cell-extracellular matrix interactions and modulation of TonEBP-mediated osmoadaptation.}, number={4}, journal={JCI INSIGHT}, author={Tessier, Steven and Doolittle, Alexandra C. and Sao, Kimheak and Rotty, Jeremy D. and Bear, James E. and Ulici, Veronica and Loeser, Richard F. and Shapiro, Irving M. and Diekman, Brian O. and Risbud, Makarand V}, year={2020}, month={Feb} }
 @article{loeser_kelley_armstrong_collins_diekman_carlson_2020, title={Deletion ofJNKEnhances Senescence in Joint Tissues and Increases the Severity of Age-Related Osteoarthritis in Mice}, volume={72}, ISSN={["2326-5205"]}, DOI={10.1002/art.41312}, abstractNote={ObjectiveTo determine the role of JNK signaling in the development of osteoarthritis (OA) induced by joint injury or aging in mice.}, number={10}, journal={ARTHRITIS & RHEUMATOLOGY}, author={Loeser, Richard F. and Kelley, Kathryn L. and Armstrong, Alexandra and Collins, John A. and Diekman, Brian O. and Carlson, Cathy S.}, year={2020}, month={Oct}, pages={1679–1688} }
 @article{diekman_2020, title={Dynamic interplay between connective tissues and the surrounding environment during aging}, volume={61}, ISSN={["1607-8438"]}, DOI={10.1080/03008207.2020.1682282}, abstractNote={One of the core assumptions of geroscience is that the process of aging is similar enough between different tissues to warrant addressing the underlying biology in a systemic fashion. Indeed, the Longevity Dividend Initiative Consortium argues that slowing the rate of biological aging is likely to be a cost-effective alternative to the status quo of treating age-related chronic diseases one at a time. Connective tissues provide a prime example of the complex relationship between “normal aging” and disease pathogenesis, and the significant burden of age-related pathology in these tissues highlights the imperative for medical research to decipher the mechanisms of biological aging in the pursuit of increasing health span. One challenge in these investigations is that agerelated changes in one tissue are rarely independent of the systemic environment. The theme of this special issue of Connective Tissue Research is the dynamic interplay between connective tissues and the surrounding environment during aging. The collective goal of these studies is to elucidate the relationship between aging and the function of musculoskeletal tissues, with the confidence that greater understanding will catalyze more effective treatments for the associated chronic diseases. The first article of the issue may be a surprise to those in musculoskeletal research and highlights just how wideranging the crosstalk between connective tissues and the aging environment can be. Frame et al review the literature on the connection between Alzheimer’s Disease and bone loss. Of particular interest are the studies that suggest bone loss may actually precede more wellknown clinical features of Alzheimer’s, which allows for the possibility that this feature could play a supportive role in Alzheimer’s screening. The authors also provide a discussion of the potential mechanisms underlying both conditions with an eye towards novel therapeutic targets. The other review of this issue is provided by Dr. Patricia Miguez and explores the proteoglycan known as biglycan. Post-translational modifications such as the extent of glycosylation can change during aging and affect the role that biglycan plays in potentiating collagen binding, growth factor signaling, and inflammation. The review focuses on how changes to biglycan can alter bone homeostasis, but the concepts presented may extend to other proteoglycans and other tissues as well. Zhu and colleagues provide a compelling manuscript that includes both conceptual frameworks derived from evolutionary biology and ecology and experimental data on redox regulation. The work centers on the glutathione antioxidant system in chondrocytes and its role in modulating the changing oxidative environment associated with aging. To illustrate the concepts of stress resistance and resilience, the authors detailed the glutathione content in three different contexts: tissue isolation from the joints of young and old rats, cyclic compressive loading of cartilage explants, and menadione treatment of cells from Sirt3 knockout mice. Further exploration of these concepts may allow for targeted therapies designed to restore homeostatic signaling networks that are altered during age-related stress. Connizzo et al use a tendon explant model from young and old mice of both sexes, with the goal of identifying how these tissues respond to the change from in vivo loading to culture. Interestingly, explants from male mice showed a more robust change with aging as compared to females, with tendons from old male mice showing decreased matrix synthesis as well as increased markers of inflammation and senescence. These data underscore that the aging process exerts differential effects based on systemic factors such as biological sex, which ultimately may be important for developing appropriate therapies for age-associated tendon disorders. The pathogenesis of low back pain is not very well known and the study by Veras et al provides a valuable resource by analyzing the whole transcriptome of}, number={1}, journal={CONNECTIVE TISSUE RESEARCH}, author={Diekman, Brian O'Callaghan}, year={2020}, month={Jan}, pages={1–3} }
 @article{d'costa_rich_diekman_2020, title={Engineered Cartilage from Human Chondrocytes with Homozygous Knockout of Cell Cycle Inhibitor p21}, volume={26}, ISSN={["1937-335X"]}, DOI={10.1089/ten.tea.2019.0214}, abstractNote={Osteoarthritis (OA) is a highly prevalent disease with limited treatment options. The search for disease-modifying OA therapies would benefit from a more comprehensive knowledge of the genetic variants that contribute to chondrocyte dysfunction and the barriers to cartilage regeneration. One goal of this study was to establish a system for producing engineered cartilage tissue from genetically defined primary human chondrocytes through genome editing and single-cell expansion. This process was utilized to investigate the functional effect of biallelic knockout of the cell cycle inhibitor p21. The use of ribonucleoprotein (RNP) CRISPR/Cas9 complexes targeting two sites in the coding region of p21 resulted in a high frequency (16%) of colonies with homozygous p21 knockout. Chondrogenic pellet cultures from expanded chondrocytes with complete loss of p21 produced more glycosaminoglycans (GAG) and maintained a higher cell number. Single-cell-derived colonies retained the potential for robust matrix production after expansion, allowing for analysis of colony variability from the same population of targeted cells. The effect of enhanced cartilage matrix production in p21 knockout chondrocytes persisted when matrix production from individual colonies was analyzed. Chondrocytes had lower levels of p21 protein with further expansion, and the difference in GAG production with p21 knockout was strongest at early passages. These results support previous findings that implicate p21 as a barrier to cartilage matrix production and regenerative capacity. Furthermore, this work establishes the use of genome-edited human chondrocytes as a promising approach for engineered tissue models containing user-defined gene knockouts and other genetic variants for investigation of OA pathogenesis. This work provides two important advances to the field of tissue engineering. One is the demonstration that engineered cartilage tissue can be produced from genetically defined populations of primary human chondrocytes. While CRISPR/Cas-9 genome editing has been extensively used in cell lines that divide indefinitely, this work extends the technique to an engineered tissue model system to support investigation of genetic changes that affect cartilage production. A second contribution is the finding that chondrocytes with p21 knockout synthesized more cartilage matrix tissue than unedited controls. This supports the continued investigation of p21 as a potential barrier to effective cartilage regeneration.}, number={7-8}, journal={TISSUE ENGINEERING PART A}, author={D'Costa, Susan and Rich, Matthew J. and Diekman, Brian O.}, year={2020}, month={Apr}, pages={441–449} }
 @article{griffith_huang_cho_khare_rich_lee_ligler_diekman_polacheck_2020, title={Microfluidics for the study of mechanotransduction}, volume={53}, ISSN={["1361-6463"]}, DOI={10.1088/1361-6463/ab78d4}, abstractNote={Mechanical forces regulate a diverse set of biological processes at cellular, tissue, and organismal length scales. Investigating the cellular and molecular mechanisms that underlie the conversion of mechanical forces to biological responses is challenged by limitations of traditional animal models and in vitro cell culture, including poor control over applied force and highly artificial cell culture environments. Recent advances in fabrication methods and material processing have enabled the development of microfluidic platforms that provide precise control over the mechanical microenvironment of cultured cells. These devices and systems have proven to be powerful for uncovering and defining mechanisms of mechanotransduction. In this review, we first give an overview of the main mechanotransduction pathways that function at sites of cell adhesion, many of which have been investigated with microfluidics. We then discuss how distinct microfluidic fabrication methods can be harnessed to gain biological insight, with description of both monolithic and replica molding approaches. Finally, we present examples of how microfluidics can be used to apply both solid forces (substrate mechanics, strain, and compression) and fluid forces (luminal, interstitial) to cells. Throughout the review, we emphasize the advantages and disadvantages of different fabrication methods and applications of force in order to provide perspective to investigators looking to apply forces to cells in their own research.}, number={22}, journal={JOURNAL OF PHYSICS D-APPLIED PHYSICS}, author={Griffith, Christian M. and Huang, Stephanie A. and Cho, Crescentia and Khare, Tanmay M. and Rich, Matthew and Lee, Gi-hun and Ligler, Frances S. and Diekman, Brian O. and Polacheck, William J.}, year={2020}, month={May} }
 @misc{loeser_collins_diekman_carlson_2020, title={Reply}, volume={72}, ISSN={["2326-5205"]}, DOI={10.1002/art.41431}, abstractNote={To the Editor: Osteoarthritis (OA) is a chronic degenerative joint disease characterized by the destruction of articular cartilage (1). This disease can greatly impact quality of life, leading to physical and psychological damage, including pain and disability, and has a significant socioeconomic impact. To date, the pathogenesis of OA has not been clearly defined; it has been suggested that environmental factors, genetic factors, inflammatory and oxidative signaling pathways, and epigenetic changes may correlate with dysfunction of catabolism of the cartilage extracellular matrix, leading to the development of OA. Medication may relieve pain but not satisfactorily reverse joint damage, and surgery is usually reserved for treating end-stage disease. There are few effective methods for halting the progression of this complex disease. Therefore, early diagnosis is important, and investigation into effective treatment methods is urgently needed. Recently, Loeser et al evaluated the role of JNK signaling in the development of OA and found interesting results (2). The authors subjected wild-type control, JNK1, and JNK2 mice to destabilization of the medial meniscus (DMM) or sham surgery to induce OA. Results showed that JNK1 and JNK2 mice had increased subchondral bone thickness and area of cartilage necrosis compared with wild-type control mice. Aged JNK1 and JNK2 mice were reported to have had worse articular cartilage structure scores when compared with those of aged wild-type mice. JNK1-knockout mice had higher osteophyte scores, and deficiencies of both the JNK1 and JNK2 genes led to increased expression of p16 in the synovium and cartilage in older mice. All these results indicated that knockout of JNK signaling is able to promote senescence in joint tissues and up-regulate the severity of age-related OA, which shows the potential of targeting JNK signaling to treat OA (2). However, findings of earlier studies have been inconsistent (3–5). JNK signaling protein levels were elevated in chondrocytes from the articular cartilage of OA patients, and suppression of the JNK pathway inhibited interleukin-1β (IL-1β)–induced apoptosis of chondrocytes (3). Similarly, activation of the JNK pathway in chondrocytes with IL-1 treatment was observed, as evidenced by increased expression of JNK proteins, whereas JNK deficiency reversed chondrocyte apoptosis, suggesting that the JNK signaling pathway plays a role in promoting OA (4). Moreover, in a study of JNK2 and wild-type mice with DMM-induced OA, proteoglycan aggrecan in the cartilage of JNK2 mice was downregulated after surgery (5). These mice showed a marked reduction of aggrecanase-generated fragments and cartilage damage. Following DMM, proinflammatory cytokines, such as tumor necrosis factor, IL-6, and IL-8, were also reduced in JNK2 mice compared with controls (5). Therefore, some questions remain regarding the exact role of the JNK signaling pathway in OA onset and development, whether targeting the JNK pathway can help to resolve the pathogenesis of OA, and which mechanisms of the JNK pathway are mediated in OA. Supported by the National Natural Science Foundation of China (grant 81701606).}, number={12}, journal={ARTHRITIS & RHEUMATOLOGY}, author={Loeser, Richard F. and Collins, John A. and Diekman, Brian O. and Carlson, Cathy S.}, year={2020}, month={Dec}, pages={2162–2163} }
 @article{liu_souroullas_diekman_krishnamurthy_hall_sorrentino_parker_sessions_gudkov_sharpless_2019, title={Cells exhibiting strong p16(INK4a) promoter activation in vivo display features of senescence}, volume={116}, ISSN={["0027-8424"]}, DOI={10.1073/pnas.1818313116}, abstractNote={Significance}, number={7}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Liu, Jie-Yu and Souroullas, George P. and Diekman, Brian O. and Krishnamurthy, Janakiraman and Hall, Brandon M. and Sorrentino, Jessica A. and Parker, Joel S. and Sessions, Garrett A. and Gudkov, Andrei V. and Sharpless, Norman E.}, year={2019}, month={Feb}, pages={2603–2611} }
 @article{novais_diekman_shapiro_risbud_2019, title={p16(Ink4a) deletion in cells of the intervertebral disc affects their matrix homeostasis and senescence associated secretory phenotype without altering onset of senescence}, volume={82}, ISSN={["1569-1802"]}, DOI={10.1016/j.matbio.2019.02.004}, abstractNote={Intervertebral disc degeneration is an important contributor to chronic low back and neck pain. Although many environmental and genetic factors are known to contribute to disc degeneration, age is still the most significant risk factor. Recent studies have shown that senescence may play a role in age-related disc degeneration and matrix catabolism in humans and mouse models. Clearance of p16Ink4a-positive senescent cells reduces the degenerative phenotype in many age-associated diseases. Whether p16Ink4a plays a functional role in intervertebral disc degeneration and senescence is unknown. We first characterized the senescence status of discs in young and old mice. Quantitative histology, gene expression and a novel p16tdTom reporter mice showed an increase in p16Ink4a, p21 and IL-6, with a decrease in Ki67 with aging. Accordingly, we studied the spinal-phenotype of 18-month-old mice with conditional deletion of p16Ink4a in the disc driven by Acan-CreERT2 (cKO). The analyses of discs of cKO and age-matched control mice showed little change in cell morphology and tissue architecture. The cKO mice exhibited changes in functional attributes of aggrecan as well as in collagen composition of the intervertebral disc. While cKO discs exhibited a small decrease in TUNEL positive cells, lineage tracing experiments using ZsGreen reporter indicated that the overall changes in cell fate or numbers were minimal. The cKO mice maintained expression of NP-cell phenotypic markers CA3, Krt19 and GLUT-1. Moreover, in cKO discs, levels of p19Arf and RB were higher without alterations in Ki67, γH2AX, CDK4 and Lipofuscin deposition. Interestingly, the cKO discs showed lower levels of SASP markers, IL-1β, IL-6, MCP1 and TGF-β1. These results show that while, p16Ink4a is dispensable for induction and maintenance of senescence, conditional loss of p16Ink4a reduces apoptosis, limits the SASP phenotype and alters matrix homeostasis of disc cells.}, journal={MATRIX BIOLOGY}, author={Novais, Emanuel J. and Diekman, Brian O. and Shapiro, Irving M. and Risbud, Makarand V.}, year={2019}, month={Sep}, pages={54–70} }
 @misc{colins_diekman_loeser_2018, title={Targeting aging for disease modification in osteoarthritis}, volume={30}, ISSN={["1531-6963"]}, DOI={10.1097/bor.0000000000000456}, abstractNote={
            Purpose of review
            Age is a key risk factor for the development of osteoarthritis and age-related changes within the joint might represent targets for therapy. The recent literature was reviewed to find studies that provide new insight into the role of aging in osteoarthritis, with a focus on the potential for disease modification.
          }, number={1}, journal={CURRENT OPINION IN RHEUMATOLOGY}, author={Colins, John A. and Diekman, Brian O. and Loeser, Richard F.}, year={2018}, month={Jan}, pages={101–107} }