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Abstract PurposeArticular chondrocytes synthesize and maintain the avascular and aneural articular cartilage. In vivo these cells are surrounded by a 3D pericellular matrix (PCM) containing predominantly collagen VI. The PCM protects chondrocytes and facilitates mechanotransduction. PCM stiffness is critical in transmitting biomechanical signals to chondrocytes. Various culture systems with different hydrogels are used to encapsulate chondrocytes for 3D culture, but many lack either the PCM or the in vivo stiffness of the cartilage matrix. This study aimed at establishing a culture system to investigate (a) if chondrocytes cultured in alginate will develop a PCM and (b) study mechanotransduction via metabolic changes induced in 3D agarose-embedded chondrocytes upon mechanical stimulation. MethodsWe cultured primary human and bovine chondrocytes in monolayers or as alginate encapsulated cells in media containing sodium L-ascorbate. PCM expression was analyzed by immunofluorescence and western blots. We further characterized the response of chondrocytes embedded in physiologically stiff agarose to dynamic compression through metabolomic profiling. ResultsWe found that primary human and bovine chondrocytes, when cultured in alginate beads with addition of sodium L-ascorbate for 7 days, had a pronounced PCM, retained their phenotype, and synthesized both collagens VI and II. This novel culture system enables alginate-encapsulated chondrocytes to develop a robust PCM thereby creating a model system to study mechanotransduction in the presence of an endogenous PCM. We also observed distinct compression-induced changes in metabolomic profiles between the monolayer-agarose and alginate-released agarose-embedded chondrocytes indicating physiological changes in cell metabolism. ConclusionThese data show that 3D preculture of chondrocytes in alginate before encapsulation in physiologically stiff agarose leads to pronounced development of pericellular matrix that is sustained in the presence of ascorbate. This model can be useful in studying the mechanism by which chondrocytes respond to cyclical compression and other types of loading simulating in vivo physiological conditions. 

ObjectiveOsteoarthritis, the leading cause of disability worldwide, disproportionately affects women, yet sex remains an overlooked determinant. This disparity stems from sex‐specific differences in injury susceptibility—a major risk factor for disease. Using a non‐invasive injury model, we demonstrate that injury drives local and systemic metabolic alterations and that these responses differ by sex. MethodsMale and female mice were subjected to non‐invasive joint injury. Eight days after injury, serum, synovial fluid, and whole joints were collected for metabolomics. Additionally, whole joints were harvested for matrix‐assisted laser desorption ionization–mass spectrometry imaging (MALDI‐MSI) to capture the spatial distribution of molecular species and identify osteochondral regions perturbed by injury. ResultsComparative analyses among injured, contralateral, and naive mice revealed metabolomic alterations across sample types. Data indicate that injury influences metabolic profiles in whole joints, synovial fluid, and serum, with consistent dysregulation of amino acid, purine, and pyrimidine metabolism, indicating a systemic effect of localized injury. Additionally, sex‐dependent differences emerged across tissues, highlighting sexually dimorphic pathways following injury. MALDI‐MSI generated 2D ion images of bone, the joint interface, and bone marrow, identifying region‐specific metabolic changes following injury. ConclusionJoint injury induces coordinated metabolic responses locally and systemically that extend beyond the injured joint and are influenced by sex. Integrating metabolomic and spatial analyses reveals how injury modulates joint pathophysiology across tissues and reveals sex‐specific patterns relevant to post‐traumatic osteoarthritis (PTOA) risk. These findings improve preclinical PTOA models and deepen our understanding of the complex role of injury and sex in osteoarthritis pathogenesis, laying the foundation for targeted therapeutic strategies.image 

Abstract One of the main components of articular cartilage is the chondrocyte's pericellular matrix (PCM), which is critical for regulating mechanotransduction, biochemical cues, and healthy cartilage development. Here, individual primary human chondrocytes (PHC) are encapsulated and cultured in 50 µm diameter alginate microgels using drop‐based microfluidics. This unique culturing method enables PCM formation and manipulation of individual cells. Over ten days, matrix formation is observed using autofluorescence imaging, and the elastic moduli of isolated cells are measured using AFM. Matrix production and elastic modulus increase are observed for the chondrons cultured in microgels. Furthermore, the elastic modulus of cells grown in microgels increases ≈ten‐fold over ten days, nearly reaching the elastic modulus of in vivo PCM. The AFM data is further analyzed using a Gaussian mixture model and shows that the population of PHCs grown in microgels exhibit two distinct populations with elastic moduli averaging 9.0 and 38.0 kPa. Overall, this work shows that microgels provide an excellent culture platform for the growth and isolation of PHCs, enabling PCM formation that is mechanically similar to native PCM. The microgel culture platform presented here has the potential to revolutionize cartilage regeneration procedures through the inclusion of in vitro developed PCM. 

Articular cartilage is comprised of two main components, the extracellular matrix (ECM) and the pericellular matrix (PCM). The PCM helps to protect chondrocytes in the cartilage from mechanical loads, but in patients with osteoarthritis, the PCM is weakened, resulting in increased chondrocyte stress. As chondrocytes are responsible for matrix synthesis and maintenance, it is important to understand how mechanical loads affect the cellular responses of chondrocytes. Many studies have examined chondrocyte responses to in vitro mechanical loading by embedding chondrocytes in 3-D hydrogels. However, these experiments are mostly performed in the absence of PCM, which may obscure important responses to mechanotransduction. Here, drop-based microfluidics is used to culture single chondrocytes in alginate microgels for cell-directed PCM synthesis that closely mimics the in vivo microenvironment. Chondrocytes formed PCM over 10 days in these single-cell 3-D microenvironments. Mechanotransduction studies were performed, in which single-cell microgels mimicking the cartilage PCM were embedded in high-stiffness agarose. After physiological dynamic compression in a custom-built bioreactor, microgels exhibited distinct metabolomic profiles from both uncompressed and monolayer controls. These results demonstrate the potential of single cell encapsulation in alginate microgels to advance cartilage tissue engineering and basic chondrocyte mechanobiology. 

A<sc>bstract</sc> A search is presented for the resonant production of a pair of standard model-like Higgs bosons using data from proton-proton collisions at a centre-of-mass energy of 13 TeV, collected by the CMS experiment at the CERN LHC in 2016–2018, corresponding to an integrated luminosity of 138 fb⁻¹. The final state consists of two b quark-antiquark pairs. The search is conducted in the region of phase space where at least one of the pairs is highly Lorentz-boosted and is reconstructed as a single large-area jet. The other pair may be either similarly merged or resolved, the latter reconstructed using two b-tagged jets. The data are found to be consistent with standard model processes and are interpreted as 95% confidence level upper limits on the product of the cross sections and the branching fractions of the spin-0 radion and the spin-2 bulk graviton that arise in warped extradimensional models. The limits set are in the range 9.74–0.29 fb and 4.94–0.19 fb for a narrow radion and a graviton, respectively, with masses between 1 and 3 TeV. For a radion and for a bulk graviton with widths 10% of their masses, the limits are in the range 12.5–0.35 fb and 8.23–0.23 fb, respectively, for the same masses. These limits result in the exclusion of a narrow-width graviton with a mass below 1.2 TeV, and of narrow and 10%-width radions with masses below 2.6, and 2.9 TeV, respectively. 

A<sc>bstract</sc> Differential cross sections for top quark pair ($$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$ ) production are measured in proton-proton collisions at a center-of-mass energy of 13 TeV using a sample of events containing two oppositely charged leptons. The data were recorded with the CMS detector at the CERN Large Hadron Collider and correspond to an integrated luminosity of 138 fb⁻¹. The differential cross sections are measured as functions of kinematic observables of the$$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$ system, the top quark and antiquark and their decay products, as well as of the number of additional jets in the event. The results are presented as functions of up to three variables and are corrected to the parton and particle levels. When compared to standard model predictions based on quantum chromodynamics at different levels of accuracy, it is found that the calculations do not always describe the observed data. The deviations are found to be largest for the multi-differential cross sections. 

A<sc>bstract</sc> A search for the central exclusive production of top quark-antiquark pairs ($$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$ ) is performed for the first time using proton-tagged events in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 29.4 fb⁻¹. The$$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$ decay products are reconstructed using the central CMS detector, while forward protons are measured in the CMS-TOTEM precision proton spectrometer. An observed (expected) upper bound on the production cross section of 0.59 (1.14) pb is set at 95% confidence level, for collisions of protons with fractional momentum losses between 2 and 20%. 

A<sc>bstract</sc> A search for the production of pairs of heavy Majorana neutrinos (N_ℓ) from the decays of Z′ bosons is performed using the CMS detector at the LHC. The data were collected in proton-proton collisions at a center-of-mass energy of$$ \sqrt{s} $$ $\sqrt{s}$ = 13 TeV, with an integrated luminosity of 138 fb⁻¹. The signature for the search is an excess in the invariant mass distribution of the final-state objects, two same-flavor leptons (e orμ) and at least two jets. No significant excess of events beyond the expected background is observed. Upper limits at 95% confidence level are set on the product of the Z′ production cross section and its branching fraction to a pair of N_ℓ, as functions of N_ℓand Z′ boson masses ($$ {m}_{{\textrm{N}}_{\ell }} $$ $m_{N_{\ell }}$ and$$ {m}_{{\textrm{Z}}^{\prime }} $$ $m_{Z^{\prime }}$ , respectively) for$$ {m}_{{\textrm{Z}}^{\prime }} $$ $m_{Z^{\prime }}$ from 0.4 to 4.6 TeV and$$ {m}_{{\textrm{N}}_{\ell }} $$ $m_{N_{\ell }}$ from 0.1 TeV to$$ {m}_{{\textrm{Z}}^{\prime }} $$ $m_{Z^{\prime }}$ /2. In the theoretical framework of a left-right symmetric model, exclusion bounds in the$$ {m}_{{\textrm{N}}_{\ell }} $$ $m_{N_{\ell }}$ -$$ {m}_{{\textrm{Z}}^{\prime }} $$ $m_{Z^{\prime }}$ plane are presented in both the electron and muon channels. The observed upper limit on$$ {m}_{{\textrm{Z}}^{\prime }} $$ $m_{Z^{\prime }}$ reaches up to 4.42 TeV. These are the most restrictive limits to date on the mass of N_ℓas a function of the Z′ boson mass.