Biology subjects

June, R. K.

Publications and source records attributed to June, R. K..

At least 19 recordsLinked to original sources

bioRxiv2026

Adipose-driven complement-lipid reprogramming controls nociceptive vulnerability in obesity-associated osteoarthritis

Obesity amplifies osteoarthritis (OA) pain disproportionately to joint damage, creating a major unmet clinical need for non-opioid interventions that act beyond the joint. Using OA as a translational model, we integrated serum multi-omics in obese mice with surgically induced OA and genetic and adipose-reconstitution models of complement factor D (FD). In humans, we analyzed longitudinal metabolomics data from the IDEA weight-loss trial and conducted functional studies in dorsal root ganglion (DRG) neurons. Adipose-derived FD emerged as a regulator of systemic immunometabolic state: FD deficiency in obese mice worsened pain sensitivity whereas restoring circulating FD normalized pain and inflammatory markers without altering joint structure. Cross-species lipid profiling identified conserved shifts in linoleic acid versus arachidonic acid-derived lipids that were associated with pain phenotypes in mice and with pain improvement in humans. Defined lipid cocktails modulated excitability and TRPV1 sensitivity in human DRG neurons, and transcriptomics of knee-innervating DRGs revealed diet and FD-dependent activation of complement and neuronal excitability pathways. Together, these findings define an adipose-complement-lipid axis that regulates nociceptive vulnerability independent of joint damage and identify extra-articular targets for translational, non-opioid OA pain therapies. One Sentence SummaryWe identify an adipose-complement-lipid axis that systemically regulates sensory neuron sensitization, providing a mechanistic basis for pain-structure discordance in obesity-associated osteoarthritis.

physiology↗

bioRxiv2026

Viscoelastic recovery time of chondrocytes from monolayer and alginate cultures

This study uses a previously reported 3D-printed variable-height flow cell to investigate the viscoelastic properties of chondrocytes from 2D monolayer and 3D alginate cultures. It was hypothesized that chondrocytes could be distinguished by phenotype associated with their culture environment using viscoelastic recovery time, owing to variation in the pericellular matrix (PCM) produced by chondrocytes from different culture methods. The PCM surrounding the chondrocytes was imaged with confocal microscopy during applied deformation and subsequent recovery. The projected cell area was fitted with a Burgers mechanical model to extract the viscoelastic recovery time. No difference between bovine and primary OA cells from monolayer cultures was observed. However, a statistically significant difference in recovery time was observed between cells from monolayer and alginate cultures in both the bovine (31 s vs. 13 s) and primary OA (34 s vs. 13 s) groups. This work shows that viscoelastic recovery time is influenced by the culture method used for chondrocytes and further demonstrates the role of the PCM as a mechanical protector of chondrocytes.

cell biology↗

bioRxiv2026

Injury Causes Altered Metabolism including O2 Consumption in Bovine and Human Chondrocytes

Traumatic joint injuries both disrupt chondrocyte metabolism and increase the risk for post-traumatic osteoarthritis. Yet the relationships between trauma, altered metabolism, and cartilage degradation remains unclear. This study compares the metabolic responses of bovine (normal) and osteoarthritic (OA) chondrocytes to physiological and injurious mechanical stimuli under normoxic (20% O2) and hypoxic (5% O2) conditions. Using primary chondrocytes encapsulated in agarose, physiological and injurious mechanical stimulation, targeted metabolomic profiling of central carbon metabolites, and O2 saturation measurements, we find that healthy bovine chondrocytes exhibit robust, time-dependent adaptation to mechanical stimuli, whereas OA chondrocytes display a blunted response, particularly under injury conditions. Injurious mechanical stimuli led to altered O2 consumption and glutamine accumulation, suggesting disrupted respiration and reduced protein synthesis hypothesized to be a result of altered mitochondrial metabolism in OA cells. These findings underscore the role of mechanical cues in chondrocyte metabolism and inform future studies aimed at identifying metabolic targets relevant to post-traumatic osteoarthritis progression.

bioengineering↗

bioRxiv2025

Adenine-induced kidney disease alters the cortical bone metabolome of C57BL/6J mice in a manner that depends on sex

Chronic kidney disease (CKD) increases the likelihood of bone fracture as well as post-fracture mortality. The loss of bone fracture resistance in CKD results from both a loss of bone mass and decreased bone material properties, which together result from changes to the health and activities of bone cells. Determining changes to bone tissue metabolism with CKD may reveal insights important to monitoring and mitigating the decrease in bone fracture resistance that commonly occurs as a result of this disease. In this study, untargeted metabolomics was conducted on marrow-flushed cortical tibiae from female and male C57BL/6J mice fed either a control or 0.2% w/w adenine diet. The diets were continued over 3.5 or 7 weeks to produce different severities of kidney injury. Liquid chromatography mass spectrometry (LC-MS) was used to assess metabolites from tibia extracts. Group comparisons (CKD vs control, 7 weeks vs 3.5 weeks, female vs male) were conducted using principal components analysis (PCA), partial least squares discriminant analysis (PLS-DA), and hierarchical clustering. Clusters of metabolites were also assessed using ensemble clustering and cluster optimization analysis (ECCO). Volcano plots and VIP scores were used to identify individual metabolites that differed between groups. Pathway analyses were then conducted from these metabolites. The CKD mice, compared with control mice, had dysregulated essential and nonessential amino acid pathways along with altered pathways associated with sugar and fatty acid metabolism. Compared with mice fed an adenine diet for 3.5 weeks, the mice fed an adenine diet over 7 weeks showed dysregulations in the pentose phosphate pathway along with essential and nonessential amino acid metabolism, porphyrin metabolism, steroid hormone biosynthesis, and other pathways relevant to energy production. Sex differences were apparent in the bone tissue metabolomes of females and males. Compared to males, females experienced dysregulations in essential and nonessential amino acid pathways along with other pathways associated with energy derivation, such as pantothenate and CoA biosynthesis. These results demonstrate that CKD alters bone tissue metabolism and reveals novel insights into metabolic dysregulation in disease as well as important sex differences in these metabolic processes. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=164 SRC="FIGDIR/small/657438v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@eb7e57org.highwire.dtl.DTLVardef@b3875aorg.highwire.dtl.DTLVardef@7b5c70org.highwire.dtl.DTLVardef@f1d5ed_HPS_FORMAT_FIGEXP M_FIG C_FIG (A) Generalized group comparisons utilizing Partial Component Analysis (PCA), Partial Least Squares-Discriminant Analysis (PLS-DA), and Hierarchical Cluster Analysis (HCA). (B) Pathway analysis utilizing volcano plots and VIP scores plots. (C) Pathway analysis results for comparisons between adenine-induced CKD and control groups, 7-week and 3.5-week diet groups, and female and male groups. A red arrow denotes a set of pathways that were downregulated, a black arrow denotes a set of pathways that were upregulated, and a gray arrow denotes a category of pathways that contained both upregulations and downregulations.

biochemistry↗

bioRxiv2025

In C57Bl6 Mice, Obesity and Subsequent Weight Loss Negatively Affected the Skeleton and Shifted the Cortical Bone Metabolome

Obesity and calorie restriction each negatively affect skeletal health. Despite the negative effects of weight loss on the skeleton, obese patients are advised to lose weight via calorie restriction. Additionally, obesity and weight loss individually alter both whole-body and local metabolism. Little is known about bone quality and changes to the cortical metabolome following calorie restriction in obese preclinical models. We hypothesized that caloric restriction would worsen bone quality in obese mice by shifting the cortical bone metabolome. To induce obesity, 8-week-old male and female C57BL6/J mice received 60% high-fat diet for 12 weeks. From 20 to 30 weeks of age, mice either remained obese or lost weight through 30% caloric restriction. Control animals received a 10% low-fat diet. Bodyweight and fat mass were increased by obesity and decreased with calorie restriction. Similarly, glucose and insulin tolerance were worsened with obesity but improved by weight loss. Compared to obesity, calorie restriction elicited more bone loss in both cortical and trabecular compartments. Weight loss also reduced bone formation. Both obesity and subsequent calorie restriction altered the cortical bone metabolome in a sex-dependent manner. Metabolic pathways altered with diet generally mapped to amino acid or fatty acid metabolism. In males, weight loss was associated with a downregulation of pathways related to tryptophan, tyrosine, ubiquinone, and fatty acids. In females, calorie restriction downregulated taurine and hypotaurine metabolism but upregulated pyrimidine metabolism, nicotinate and nicotinamide metabolism, and pantothenate and CoA biosynthesis. Our findings highlight the negative effects of obesity and subsequent caloric restriction on the skeleton. Despite improvements in components of systemic metabolism, caloric restriction in obese preclinical models did not restore bone morphology or the cortical metabolome to control conditions.

cell biology↗

bioRxiv2024

Tissue-specific and spatially dependent metabolic signatures perturbed by injury in skeletally mature male and female C57Bl/6J mice

Joint injury is a risk factor for post-traumatic osteoarthritis. However, metabolic and microarchitectural changes within the joint post-injury in both sexes remain unexplored. This study identified tissue-specific and spatially-dependent metabolic signatures in male and female mice using matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) and LC-MS metabolomics. Male and female C57Bl/6J mice were subjected to non-invasive joint injury. Eight days post-injury, serum, synovial fluid, and whole joints were collected for metabolomics. Analyses compared between injured, contralateral, and naive mice, revealing local and systemic responses. Data indicate sex influences metabolic profiles across all tissues, particularly amino acid, purine, and pyrimidine metabolism. MALDI-MSI generated 2D ion images of bone, the joint interface, and bone marrow, highlighting increased lipid species in injured limbs, suggesting physiological changes across injured joints at metabolic and spatial levels. Together, these findings reveal significant metabolic changes after injury, with notable sex differences. Significance statementOsteoarthritis, the leading cause of disability worldwide, disproportionately affects females with sex being one of the strongest predictors of disease. This disparity is partly driven by sex-specific differences in injury susceptibility, increasing the likelihood of traumatic injury to the anterior cruciate ligament (ACL), other ligaments, and menisci. Using a non-invasive injury model, we demonstrate that injury perturbs the local joint environment and has systemic effects in a sex-specific manner. Furthermore, by leveraging matrix-assisted laser desorption ionization-mass spectrometry imaging of the joint, we provide new insight into the composition of osteochondral tissue at the metabolite level. These sexually dimorphic metabolic responses to joint injury advance current understanding of the complex sexual dimorphism in OA pathogenesis providing a foundation for targeted therapeutic strategies and improved patient outcomes for female patients.

biochemistry↗

bioRxiv2024

High-fat diet exacerbates the loss of bone fracture toughness in aging for C57BL/6JN mice

The elderly are at increased risk of bone fracture and more often consume poor quality diets, such as high-fat diet (HFD). We hypothesized that HFD would exacerbate the loss of bone fracture resistance in aging. To test this hypothesis, we fed 5-month and 22-month C57BL/6JN mice of both sexes HFD or low-fat diet for 8 weeks. Aging and HFD lowered bone fracture toughness, while only aging reduced bone strength. At the tissue-scale, aging increased bone mineral maturity, while HFD altered bone mineralization and maturity as well as collagen structure. Cortical bone metabolism was also dysregulated with aging and HFD. Dysregulated pathways in aging and HFD were related to cellular function and viability, or glucose regulation, respectively. Aging with HFD also impacted osteoclast and adipocyte abundance and osteocyte viability. Together, these data demonstrate that HFD may exacerbate the loss of bone matrix quality and fracture resistance in aging.

bioengineering↗

bioRxiv2024

Metabolic Profiles of Encapsulated Chondrocytes Exposed to Short-Term Simulated Microgravity

The mechanism by which chondrocytes respond to reduced mechanical loading environments and the subsequent risk of developing osteoarthritis remains unclear. This is of particular concern for astronauts. In space the reduced joint loading forces during prolonged microgravity (10-6 g) exposure could lead to osteoarthritis (OA), compromising quality of life post-spaceflight. In this study, we encapsulated human chondrocytes in an agarose gel of similar stiffness to the pericellular matrix to mimic the cartilage microenvironment. We then exposed agarose-chondrocyte constructs to simulated microgravity (SM) using a rotating wall vessel (RWV) bioreactor to better assess the cartilage health risks associated with spaceflight. Global metabolomic profiling detected a total of 1205 metabolite features across all samples, with 497 significant metabolite features identified by ANOVA (FDR-corrected p-value < 0.05). Specific metabolic shifts detected in response to SM exposure resulted in clusters of co-regulated metabolites, as well as key metabolites identified by variable importance in projection scores. Microgravity-induced metabolic shifts in gel constructs and media were indicative of protein synthesis, energy metabolism, nucleotide metabolism, and oxidative catabolism. The microgravity associated-metabolic shifts were consistent with early osteoarthritic metabolomic profiles in human synovial fluid, which suggests that even short-term exposure to microgravity (or other reduced mechanical loading environments) may lead to the development of OA.

bioengineering↗

bioRxiv2024

Starve a cold or feed a fever? Identifying cellular metabolic changes following infection and exposure to SARS-CoV-2.

Viral infections induce major shifts in cellular metabolism elicited by active viral replication and antiviral responses. For the virus, harnessing cellular metabolism and evading changes that limit replication are essential for productive viral replication. In contrast, the cellular response to infection disrupts metabolic pathways to prevent viral replication and promote an antiviral state in the host cell and neighboring bystander cells. This competition between the virus and cell results in measurable shifts in cellular metabolism that differ depending on the virus, cell type, and extracellular environment. The resulting metabolic shifts can be observed and analyzed using global metabolic profiling techniques to identify pathways that are critical for either viral replication or cellular defense. SARS-CoV-2 is a respiratory virus that can exhibit broad tissue tropism and diverse, yet inconsistent, symptomatology. While the factors that determine the presentation and severity of SARS-CoV-2 infection remain unclear, metabolic syndromes are associated with more severe manifestations of SARS-CoV-2 disease. Despite these observations a critical knowledge gap remains between cellular metabolic responses and SARS-CoV-2 infection. Using a well-established untargeted metabolomics analysis workflow, we compared SARS-CoV-2 infection of human lung carcinoma cells. We identified significant changes in metabolic pathways that correlate with either productive or non-productive viral infection. This information is critical for characterizing the factors that contribute to SARS-CoV-2 replication that could be targeted for therapeutic interventions to limit viral disease.

microbiology↗

bioRxiv2024

Heat Conduction Simulation of Chondrocyte-Embedded Agarose Gels Suggests Negligible Impact of Viscoelastic Dissipation on Temperature Change

Agarose is commonly used for 3D cell culture and to mimic the stiffness of the pericellular matrix of articular chondrocytes. Although it is known that both temperature and mechanical stimulation affect the metabolism of chondrocytes, little is known about the thermal properties of agarose hydrogels. Thermal properties of agarose are needed to analyze potential heat production by chondrocytes induced by various experimental stimuli (carbon source, cyclical compression, etc). Utilizing ASTM C177, a custom-built thermal conductivity measuring device was constructed and used to calculate the thermal conductivity of 4.5% low gelling temperature agarose hydrogels. Additionally, Differential Scanning Calorimetry was used to calculate the specific heat capacity of the agarose hydrogels. Testing of chondrocyte-embedded agarose hydrogels commonly occurs in Phosphate-Buffered Saline (PBS), and thermal analysis requires the free convection coefficient of PBS. This was calculated using a 2D heat conduction simulation within MATLAB in tandem with experimental data collected for known boundary and initial conditions. The specific heat capacity and thermal conductivity of 4.5% agarose hydrogels was calculated to be 2.85 J/g{degrees}C and 0.121 W/mK, respectively. The free convection coefficient of PBS was calculated to be 1000.1 W/m2K. The values of specific heat capacity and thermal conductivity for agarose are similar to the reported values for articular cartilage, which are 3.20 J/g{degrees}C and 0.21 W/mK (Moghadam, et al. 2014). This suggests that in addition to 4.5% agarose hydrogels mimicking the physiological stiffness of the cartilage PCM, they can also mimic the thermal properties of articular cartilage for in vitro studies.

bioengineering↗

bioRxiv2024

Metabolomic Profiles and Pathways in Osteoarthritic Human Cartilage: A Comparative Analysis with Healthy Cartilage

ObjectiveOsteoarthritis (OA) is a chronic joint disease with heterogenous metabolic pathology. To gain insight into OA-related metabolism, healthy and end-stage osteoarthritic cartilage were compared metabolically to uncover disease-associated profiles, classify OA-specific metabolic endotypes, and identify targets for intervention for the diverse populations of individuals affected by OA. DesignFemoral head cartilage (n=35) from osteoarthritis patients were collected post-total joint arthroplasty. Healthy cartilage (n=11) was obtained from a tissue bank. Metabolites from all cartilage samples were extracted and analyzed using liquid chromatography-mass spectrometry metabolomic profiling. Additionally, cartilage extracts were pooled and underwent fragmentation analysis for biochemical identification of metabolites. ResultsSpecific metabolites and metabolic pathways, including lipid- and amino acid pathways, were differentially regulated between osteoarthritis-derived and healthy cartilage. The detected alterations of amino acids and lipids highlight key differences in bioenergetic resources, matrix homeostasis, and mitochondrial alterations in osteoarthritis-derived cartilage compared to healthy. Moreover, metabolomic profiles of osteoarthritic cartilage separated into four distinct endotypes highlighting the heterogenous nature of OA metabolism and diverse landscape within the joint between patients. ConclusionsThe results of this study demonstrate that human cartilage has distinct metabolomic profiles between healthy and end-stage osteoarthritis patients. By taking a comprehensive approach to assess metabolic differences between healthy and osteoarthritic cartilage, and within osteoarthritic cartilage alone, several metabolic pathways with distinct regulation patterns were detected. Additional investigation may lead to the identification of metabolites that may serve as valuable indicators of disease status or potential therapeutic targets.

biochemistry↗

bioRxiv2023

Osteochondral fluid transport in an ex vivo system

ObjectiveAlterations to fluid transport from bone-to-cartilage may contribute to the development of osteoarthritis. However, many questions remain about fluid transport between these tissues. The objectives of this study were to (1) test for diffusion of 3kDa molecular tracers from bone-to-cartilage and (2) assess potential differences in bone-to-cartilage fluid transport between different loading conditions. DesignOsteochondral cores extracted from bovine femurs (N=8 femurs, 10 cores/femur) were subjected to either no-load (i.e., pure diffusion), pre-load only, or cyclic compression (5{+/-}2% or 10{+/-}2% strain) in a two-chamber transport system with the bone compartment filled with a 3kDa tracer. Tracer concentrations in the cartilage compartment were measured every 5 minutes for 120 minutes. Tracer concentrations were analyzed for differences in beginning, peak and equilibrium concentrations, loading effects, and time-to-peak tracer concentration. ResultsPeak tracer concentration in the cartilage compartment was significantly higher compared to beginning and equilibrium tracer concentrations indicating fluid transport from bone to cartilage. Cartilage-compartment tracer concentration was influenced by strain magnitude, but no time-to-peak relationship was found when comparing strain magnitudes. ConclusionThis study shows that osteochondral fluid transport occurs from bone-to-cartilage with 3kDa dextran molecules. These are much larger molecules to move between bone and cartilage than previously reported. Further these results demonstrate the potential for cyclic compression to impact osteochondral fluid transport. Determining the baseline osteochondral fluid transport in healthy tissues is crucial to elucidating the potential mechanisms of progression and onset of osteoarthritis.

bioengineering↗

bioRxiv2023

Metabolomic Phenotypes Reflect Patient Sex and Injury Status: A Cross-Sectional Analysis of Human Synovial Fluid

1.BackgroundPost-traumatic osteoarthritis (PTOA) is caused by knee injuries like anterior cruciate ligament (ACL) injuries. Often, ACL injuries are accompanied by damage to other tissues and structures within the knee including the meniscus. Both are known to cause PTOA but underlying cellular mechanisms driving disease remain unknown. Aside from injury, patient sex is a prevalent risk factor associated with PTOA. HypothesisMetabolic phenotypes of synovial fluid that differ by knee injury pathology and participant sex will be distinct from each other. Study DesignA cross-sectional study. MethodsSynovial fluid from n=33 knee arthroscopy patients between 18 and 70 years with no prior knee injuries was obtained pre-procedure and injury pathology assigned post-procedure. Synovial fluid was extracted and analyzed via liquid chromatography mass spectrometry metabolomic profiling to examine differences in metabolism between injury pathologies and participant sex. Additionally, samples were pooled and underwent fragmentation to identify metabolites. ResultsMetabolite profiles revealed that injury pathology phenotypes were distinct from each other where differences in endogenous repair pathways that are triggered post-injury were detected. Specifically, acute differences in metabolism mapped to amino acid metabolism, lipid-related oxidative metabolism, and inflammatory-associated pathways. Lastly, sexual dimorphic metabolic phenotypes were examined between male and female participants, and within injury pathology. Specifically, Cervonyl Carnitine and other identified metabolites differed in concentration between sexes. ConclusionsThe results of this study suggest that different injuries (e.g., ligament vs. meniscus), as well as sex are associated with distinct metabolic phenotypes. Considering these phenotypic associations, a greater understanding of metabolic mechanisms associated with specific injuries and PTOA development may yield data regarding how endogenous repair pathways differ between injury types. Furthermore, ongoing metabolomic analysis of synovial fluid in injured male and female patients can be performed to monitor PTOA development and progression. Clinical RelevanceExtension of this work may potentially lead to the identification of biomarkers as well as drug targets that slow, stop, or reverse PTOA progression based on injury type and patient sex.

bioengineering↗

bioRxiv2022

Metabolomic Profiling to Identify Early Urinary Biomarkers and Metabolic Pathway Alterations in Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the formation of numerous fluid-filled cysts that lead to progressive loss of functional nephrons. Currently, there is an unmet need for diagnostic and prognostic indicators of early stages of the disease. Metabolites were extracted from the urine of early-stage ADPKD patients (n=48) and age- and sex-matched normal controls (n=47) and analyzed by liquid chromatography-mass spectrometry. Orthogonal partial least squares-discriminant analysis was employed to generate a global metabolomic profile of early ADPKD for the identification of metabolic pathway alterations and discriminatory metabolites as candidates of diagnostic and prognostic biomarkers. The global metabolomic profile exhibited alterations in steroid hormone biosynthesis and metabolism, fatty acid metabolism, pyruvate metabolism, amino acid metabolism, and the urea cycle. A panel of 46 metabolite features were identified as candidate diagnostic biomarkers. Notable putative identities of candidate diagnostic biomarkers for early detection include creatinine, cAMP, dCMP, various androgens (testosterone, 5alpha-androstane-3,17,dione, trans-dehydroandrosterone), betaine aldehyde, phosphoric acid, choline, 18-hydroxycorticosterone, and cortisol. Metabolic pathways associated with variable rates of disease progression included steroid hormone biosynthesis and metabolism, vitamin D3 metabolism, fatty acid metabolism, the pentose phosphate pathway, tricarboxylic acid cycle, amino acid metabolism, sialic acid metabolism, and chondroitin sulfate and heparin sulfate degradation. A panel of 41 metabolite features were identified as candidate prognostic biomarkers. Notable putative identities of candidate prognostic biomarkers include ethanolamine, C20:4 anandamide phosphate, progesterone, various androgens (5alpha-dihydrotestosterone, androsterone, etiocholanolone, epiandrosterone), betaine aldehyde, inflammatory lipids (eicosapentaenoic acid, linoleic acid, stearolic acid), and choline. Our exploratory data support metabolic reprogramming in early ADPKD and demonstrate the ability of liquid chromatography-mass spectrometry-based global metabolomic profiling to detect metabolic pathway alterations as new therapeutic targets and biomarkers for early diagnosis and tracking disease progression of ADPKD.

biochemistry↗

bioRxiv2022

Ensemble Clustering Combined with Clustering Optimization: A Novel Workflow for Analyzing Metabolomics Data

Modern biological research often leverages clustering to elucidate disease endotypes and underlying mechanisms. Mono-cluster solutions remain the predominant method; however, this approach has concerning pitfalls, motivating the need for ensemble clustering methods. We present Ensemble Clustering Combined with Cluster Optimization (ECCO), an open-source Python UI that provides a fast, scalable framework for ensemble clustering of large-scale data. It includes zero-code integration of novel ensemble clustering methods and many pre- and post-processing functionalities, enabling researchers to efficiently integrate advanced clustering methodologies into their analysis pipelines.

bioinformatics↗

bioRxiv2022

Subchondral bone and synovial fluid metabolomic profiles are altered in injured and contralateral limbs 7 days after non-invasive joint injury in skeletally-mature C57BL/6 mice

ObjectivePost-traumatic osteoarthritis (PTOA) is a common long-term outcome following ACL injury. However, early changes to bone and synovial fluid after ACL injury are not sufficiently understood. The objectives of this study were to (1) evaluate whether acute bone loss one week after ACL injury is accompanied by altered subchondral bone plate modulus, (2) determine if bone changes are localized to the injured limb or extend to the contralateral-to-injured limb compared with sham-loaded controls, and (3) identify shifts in synovial fluid metabolism unique to injured limbs. DesignFemale C57Bl\6N mice (19 weeks at injury) were subjected to either a single tibial compression overload to simulate ACL injury (n=8) or a small pre-load (n=8). Mice were euthanized 7 days after injury, and synovial fluid was immediately harvested for metabolomic profiling. Bone microarchitecture, bone formation, and subchondral bone modulus at the proximal tibia were studied using microCT, histomorphometry, and nanoindentation, respectively. Osteoclast number density was assessed at the distal femur. For each bone measure a mixed model ANOVA was generated to determine the effects of injury and loaded side. ResultsEpiphyseal and subchondral bone microarchitecture decreased while subchondral bone tissue modulus was unchanged after ACL injuries. Bone resorption increased but bone formation was not changed. Loss of bone microarchitecture also occurred for the contralateral-to-injured limb, demonstrating that the early response to ACL injury extended beyond the injured joint. While the metabolomic profiles of the injured and contralateral-to-injured limbs had many similarities, there were also distinct metabolic shifts present in only the injured limbs. The most prominent of the pathways was cysteine and methionine metabolism, which is associated with osteoclast activity. ConclusionThese results add to the understanding of early bone changes following ACL injury. Confirming prior reports, we observe a decline in epiphyseal and subchondral bone microarchitecture. We add the finding that subchondral bone modulus remains unchanged at one week after ACL injury. A potential biomarker of this initial bone catabolic response may be synovial fluid cysteine and methionine metabolism, which was only dysregulated in injured knees. Our results implicate a rapidly changing biological and mechanical environment within both the injured and contralateral joints that has the potential for influencing the progression to PTOA.

bioengineering↗

bioRxiv2021

Correlations between metabolites in the synovial fluid and serum: a mouse injury study

Osteoarthritis, the most common degenerative joint disease, occurs more frequently in joints that have sustained injury. Currently, osteoarthritis is diagnosed with imaging that finds radiographic changes after the disease has already progressed to multiple tissues. The primary objective of this study was to compare potential metabolomic biomarkers of joint injury between the synovial fluid and serum in a mouse model of post-traumatic osteoarthritis. The secondary objective was to gain insight into the pathophysiology of osteoarthritis by examining metabolomic profiles after joint injury. 12-week-old adult female C57BL/6 mice (n=12) were randomly assigned to control, day 1 post injury, or day 8 post injury groups. Randomly selected stifle (i.e., knee) joints were placed into a non-invasive injury apparatus and subjected to a single dynamic axial compression causing anterior translation of the tibia relative to the femur to tear the anterior cruciate ligament. At days 1 and 8 post injury, serum was extracted then mice were immediately euthanized prior to synovial fluid collection. Metabolites were extracted and analyzed by liquid chromatography coupled to mass spectrometry. We detected ~2500 metabolites across serum and synovial fluid. Of these metabolites 179 were positively correlated and 51 were negatively correlated between synovial fluid and serum, indicating potential for the development of metabolomic biomarkers. Synovial fluid appeared to capture differences in metabolomic profiles between injured mice at both day 1 and 8 after injury whereas serum did not. However, synovial fluid and serum were distinct at both days 1 and 8 after injury. In the synovial fluid, pathways of interest across different time points mapped to amino acid synthesis and degradation, bupropion degradation, and the tRNA charging pathway. In the serum, notable pathways across time points were amino acid synthesis and degradation, the phospholipase pathway, and nicotine degradation. These results provide a rich picture of the injury response at early time points following traumatic joint injury. Furthermore, the correlations between synovial fluid and serum metabolites suggest that there is potential to gain insight into intra-articular pathophysiology through analysis of serum metabolites.

pathology↗

bioRxiv2021

The mouse bone metabolome is sexually dimorphic and is associated with whole bone strength

Cortical bone quality, which is sexually dimorphic, depends on bone turnover and therefore the activities of remodeling bone cells. However, sex differences in cortical bone metabolism are not yet defined. Adding to the uncertainty about cortical bone metabolism, the metabolomes of whole bone, isolated cortical bone without marrow, and bone marrow have not been compared. We hypothesized that the metabolome of isolated cortical bone would be distinct from that of bone marrow and would reveal sex differences. Metabolite profiles from LC-MS of whole bone, isolated cortical bone, and bone marrow were generated from humeri from 20-week-old female C57Bl/6J mice. The cortical bone metabolomes were then compared for 20-week-old female and male C57Bl/6J mice. Femurs from male and female mice were evaluated for flexural material properties and were then categorized into bone strength groups. The metabolome of isolated cortical bone was distinct from both whole bone and bone marrow. We also found sex differences in the isolated cortical bone metabolome. Based on metabolite pathway analysis, females had higher lipid metabolism, and males had higher amino acid metabolism. High-strength bones, regardless of sex, had greater tryptophan and purine metabolism. For males, high strength bones had upregulated nucleotide metabolism, whereas lower strength bones had greater pentose phosphate pathway metabolism. Since the higher strength groups (females compared with males, high strength males compared with lower strength males) had higher serum CTX1/P1NP, we estimate that the metabolomic signature of bone strength in our study at least partially reflects differences in bone turnover. These data provide novel insight into bone bioenergetics and the sexual dimorphic nature of bone material properties in C57Bl/6 mice.

cell biology↗