Nidhi Bhutani

Mechanical confinement of cells in 3D hydrogel scaffolds mediates cell fate and activity across a wide range of biological processes. Many cells secrete a nascent matrix within the hydrogel niche, which provides important biological signals to the cells but also obstructs direct cell-hydrogel interactions, making it unclear how the cells sense hydrogel confinement and carry out mechanotransduction. Here, we show that chondrocytes sense the solid stress arising from the accumulation of the nascent matrix in the hydrogel niche, which is mediated by hydrogel viscoelasticity and plasticity. We show that solid stresses elicit a wide range of pathophysiological responses, most notably an inflammatory response associated with cartilage osteoarthritis and injury, alongside a striking progenitor-like migratory response where the chondrocytes leverage mitosis to breach their nascent matrix and migrate to escape confinement. Our findings establish the role of the nascent matrix as an important transducer of mechanical confinement and illustrate how emergent solid stresses can drive chondrocyte pathology.

Aging or injury to the joints can lead to cartilage degeneration and osteoarthritis (OA), for which there are limited effective treatments. We found that expression of 15-hydroxy prostaglandin dehydrogenase (15-PGDH) is increased in the articular cartilage of aged or injured mice. Both systemic and local inhibition of 15-PGDH with a small-molecule inhibitor (PGDHi) led to regeneration of articular cartilage and reduction in OA-associated pain. Using single-cell RNA-sequencing and multiplexed immunofluorescence imaging of cartilage, we identified the major chondrocyte subpopulations. Inhibition of 15-PGDH decreased hypertrophic-like chondrocytes expressing 15-PGDH and increased extracellular matrix–synthesizing articular chondrocytes. Cartilage regeneration appears to occur through gene expression changes in preexisting chondrocytes, rather than stem or progenitor cell proliferation. 15-PGDH inhibition could be a potential disease-modifying and regenerative approach for osteoarthritis.

Objective: Osteoarthritis (OA) is a chronic, debilitating disease with no available disease‐modifying drugs. Biomarker identification in patients with OA has hitherto been limited to serum proteins and bulk epigenomic feature identification.Methods: Peripheral blood mononuclear cells (PBMCs) from 21 healthy donors, 17 patients with OA, and 10 patients with degenerative meniscal tears (DMTs) were immunophenotyped at single‐cell resolution by mass cytometry by time‐of‐flight using a 29‐marker panel to identify OA‐associated features in the circulating immune cells. Single‐cell RNA sequencing was used to discern mechanistic attributes of perturbed immune cell populations in OA.Results: Comparison of the PBMCs of healthy donors and OA patients revealed distinct perturbations in OA. Although subsets of naive B cells were depleted, switched memory B cells were significantly expanded in OA, including a CD25^hiCXCR5^hiCD27⁺IgD⁻ subpopulation. Single‐cell RNA sequencing revealed a dysfunction of interleukin 2/Stat5 and tumor necrosis factor signaling in the CD25^hi switched memory B cells in OA. A similar expansion of CD25^hi switched memory B cells was observed in patients with DMT, a population at enhanced risk for OA.Conclusion: A CD25^hi switched memory B cell population was identified to be a potential cellular biomarker for OA that can be detected in the early stages of OA in the readily accessible circulating blood cells. image

Hand osteoarthritis (OA) is a prevalent and disabling condition, yet its pathogenesis remains less studied than OA in large weight-bearing joints. Emerging genetic, epigenetic, and microbiome research suggests that hand OA might be biologically distinct, involving joint-specific pathways not shared by knee or hip OA. This review integrates genome-wide association studies specific to hand OA, highlighting key molecular contributors such as inflammatory cytokines. These genetic insights, together with emerging data on epigenetic alterations and gut microbial dysbiosis, point to broader systemic and regulatory influences on hand OA onset and progression. We also assess pharmacologic interventions tested in randomized controlled trials that have attempted to target these pathways. While agents such as TNF and IL-6 inhibitors, hydroxychloroquine, and corticosteroids have shown limited success, emerging evidence supports the potential of methotrexate in synovitis-positive general hand OA, platelet-rich plasma in thumb carpometacarpal (CMC) OA, and prolotherapy in interphalangeal (IP) OA. These findings illustrate the persistent gap between mechanistic understanding and therapeutic success. Future work must prioritize multifactorial strategies for addressing pain and translational frameworks that link molecular mechanisms to treatment response. In summary, this review offers an update on hand OA and identifies key opportunities for more targeted and effective therapy.

Diffuse Intrinsic Pontine Glioma (DIPG) is a highly aggressive and fatal pediatric brain cancer. One pre-requisite for tumor cells to infiltrate is adhesion to extracellular matrix (ECM) components. However, it remains largely unknown which ECM proteins are critical in enabling DIPG adhesion and migration and which integrin receptors mediate these processes. Here, we identify laminin as a key ECM protein that supports robust DIPG cell adhesion and migration. To study DIPG infiltration, we developed a DIPG-neural assembloid model, which is composed of a DIPG spheroid fused to a human induced pluripotent stem cell-derived neural organoid. Using this assembloid model, we demonstrate that knockdown of laminin-associated integrins significantly impedes DIPG infiltration. Moreover, laminin-associated integrin knockdown improves DIPG response to radiation and HDAC inhibitor treatment within the DIPG-neural assembloids. These findings reveal the critical role of laminin-associated integrins in mediating DIPG progression and drug response. The results also provide evidence that disrupting integrin receptors may offer a novel therapeutic strategy to enhance DIPG treatment outcomes. Finally, these results establish DIPG-neural assembloid models as a powerful tool to study DIPG disease progression and enable drug discovery.

Background: Understanding of pain in osteoarthritis, its genesis, and perception is still in its early stages. Identification of precise ligand-receptor pairs that transduce pain and the cells and tissues in which they reside will elucidate new therapeutic approaches for pain management. Our recent studies had identified an inflammation-amplifying (Inf-A) cell population that is expanded in human OA cartilage and is distinctive in the expression of both IL1R1 and TNF-R2 receptors and active Jnk signaling cascade. Methods: In this study, we have tested the function of the cartilage-resident IL1R1⁺TNF-R2⁺ Inf-A cells in OA. We have identified that the IL1R1⁺TNF-R2⁺ Inf-A cells expand in aged mice as well as after anterior cruciate ligament tear upon tibia loading and OA initiation in mice. We targeted and modulated the Jnk signaling cascade in InfA through competitive inhibition of Jnk signaling in mice and human OA explants and tested the effects on joint structure and gait in mice. Results: Modulation of Jnk signaling led to attenuation of inflammatory cytokines CCL2 and CCL7 without showing any structural improvements in the joint architecture. Interestingly, Jnk inhibition and lowered CCL2 and 7 are sufficient to significantly improve the gait parameters in treated PTOA mice demonstrating reduced OA-associated pain. Consistent with the mice data, treatment with JNK inhibitor did not improve human OA cartilage explants. Conclusion: These studies demonstrate that Inf-A, an articular-cartilage resident cell population, contributes to pain in OA via secretion of CCL2 and 7 and can be targeted via inhibition of Jnk signaling.

Advances in the profiling of human joint tissues at single-cell resolution have provided unique insights into the organization and function of these tissues in health and disease. Data generated by various single-cell technologies, including single-cell RNA sequencing and cytometry by time-of-flight, have identified the distinct subpopulations that constitute these tissues. These timely studies have provided the building blocks for the construction of single-cell atlases of joint tissues including cartilage, bone and synovium, leading to the identification of developmental trajectories, deciphering of crosstalk between cells and discovery of rare populations such as stem and progenitor cells. In addition, these studies have revealed unique pathogenetic populations that are potential therapeutic targets. The use of these approaches in synovial tissues has helped to identify how distinct cell subpopulations can orchestrate disease initiation and progression and be responsible for distinct pathological outcomes. Additionally, repair of tissues such as cartilage and meniscus remains an unmet medical need, and single-cell methodologies can be invaluable in providing a blueprint for both effective tissue-engineering strategies and therapeutic interventions for chronic joint diseases such as osteoarthritis and rheumatoid arthritis.

No disease-modifying drug exists for osteoarthritis (OA). Despite success in animal models, candidate drugs continue to fail in clinical trials owing to the unmapped interpatient heterogeneity and disease complexity. We used a single-cell platform based on cytometry by time-of-flight (cyTOF) to precisely outline the effects of candidate drugs on human OA chondrocytes. OA chondrocytes harvested from patients undergoing total knee arthroplasty were treated with 2 drugs, an NF-κB pathway inhibitor, BMS-345541, and a chondroinductive small molecule, kartogenin, that showed preclinical success in animal models for OA. cyTOF conducted with 30 metal isotope–labeled antibodies parsed the effects of the drugs on inflammatory, senescent, and chondroprogenitor cell populations. The NF-κB pathway inhibition decreased the expression of p–NF-κB, HIF2A, and inducible NOS in multiple chondrocyte clusters and significantly depleted 4 p16 ^ink4a -expressing senescent populations, including NOTCH1 ⁺ STRO1 ⁺ chondroprogenitor cells. While kartogenin also affected select p16 ^ink4a -expressing senescent clusters, there was a less discernible effect on chondroprogenitor cell populations. Overall, BMS-345541 elicited a uniform drug response in all patients, while only a few responded to kartogenin. These studies demonstrate that a single-cell cyTOF-based drug screening platform can provide insights into patient response assessment and patient stratification.

Mesenchymal stromal cells (MSC) have been widely investigated for their regenerative capacity, anti-inflammatory properties and beneficial immunomodulatory effects across multiple clinical indications. Nevertheless, their widespread clinical utilization is limited by the variability in MSC quality, impacted by donor age, metabolism and disease. Human induced pluripotent stem cells (hiPSC) generated from readily accessible donor tissues, are a promising source of stable and rejuvenated MSC but differentiation methods generally require prolonged culture and result in low frequencies of stable MSC. To overcome this limitation, we have optimized a quick and efficient method for hiPSC differentiation into foot-print free MSC (hiMSC) in this study. This method capitalizes on the synergistic action of growth factors Wnt3a and Activin A with BMP4, leading to an enrichment of MSC after only 4 days of treatment. These hiMSC demonstrate a significant upregulation of mesenchymal stromal markers (CD105+, CD90+, CD73 and CDH) comparable to bone marrow-derived MSC, with reduced expression of the pluripotency genes (Oct-4, c-Myc, Klf4 and Nanog) compared to hiPSC. Moreover, they show improved proliferation capacity in culture without inducing any teratoma formation in vivo. Osteogenesis, chondrogenesis and adipogenesis assays confirmed the ability of hiMSC to differentiate into the three different lineages. Secretome analyses showed cytokine profiles comparable to bone marrow-derived MSC. Encapsulated hiMSC in alginate beads co-cultured with osteoarthritic (OA) cartilage explants showed robust immunomodulation, with stimulation of cell growth and proteoglycan production in OA cartilage. Our quick and efficient protocol for derivation of hiMSC from hiPSC, and their encapsulation in microbeads therefore, presents a reliable and reproducible method to boost the clinical applications of MSC.