Biology subjects

Usami, Y.

Publications and source records attributed to Usami, Y..

11 recordsLinked to original sources

bioRxiv2026

A Novel Slow-Progressive Knee Osteoarthritis Murine Model Induced by Non-Invasive Posterior Cruciate Ligament Rupture in Mice

ObjectiveRecently, alternatives to animal testing, such as new approach methodologies, are being developed in the orthopedic research field; animal models still provide valuable insights into the pathogenesis of knee osteoarthritis (OA). However, commonly used models develop OA much more rapidly and severely than those observed in human patients. We aimed to develop a novel murine model that closely mimics the slow progression of human OA with posterior Cruciate ligament (PCL) rupture. Design12-week-old C57BL/6 mice were induced to PCL-rupture (PCL-R) by manually applying an external tibial posterior translation force. We analyzed joint kinematics, histological observations, and bone structure to confirm the absence of concurrent injury on day 0. Then, joint stability and the pathophysiological progression of knee OA were analyzed at 8, 16, and 34 weeks post-PCL-R. The destabilized medial meniscus (DMM) model was also analyzed to compare the OA progression. ResultsNon-invasive PCL-R intervention induced the complete rupture in the central region of PCL without concurrent injury. The PCL-R group showed larger posterior tibial deviation than the INTACT (P=0.008). Regarding the range of motion in the PCL-R group, there was no limitation in range of motion on day 0, but extension limitations occurred at weeks 16 and 34 weeks. Histologically, articular cartilage degeneration in PCL-R was milder than DMM. In the subchondral bone, micro-CT reconstruction images indicated that, compared with the INTACT group, the DMM group observed progressive subchondral bone formation from 16 weeks post-surgery. In contrast, the PCLR group maintained the subchondral bone structure even at 34 weeks. ConclusionsPCL-R model induced mild abnormal mechanical stress depending on posterior instability, and cartilage degeneration occurred more slowly in this model than in DMM models.

pathology↗

bioRxiv2026

A Wnt-responsive fibrocartilage progenitor system coordinates postnatal mandibular condylar cartilage growth

Postnatal growth of the mandibular condyle requires coordinated expansion of fibrocartilage and production of chondrocytes, yet the cellular populations that organize this process remain incompletely defined. Here we identify a Wnt-responsive fibrocartilage progenitor population that contributes to postnatal mandibular condylar cartilage growth. Using a direct Wnt activity reporter (R26-WntVis), inducible genetic lineage tracing (Axin2CreERT2), and single-cell transcriptomics, we define a Wnt-enriched progenitor-like cluster localized predominantly within the fibrocartilage zone. Lineage tracing demonstrates that Axin2-lineage cells expand laterally within fibrocartilage and generate vertically aligned chondrocytes in the chondrocartilage compartment, indicating bidirectional growth contribution in vivo. Conditional ablation of {beta}-catenin in Axin2-lineage cells results in depletion of the fibrocartilage compartment and premature activation of chondrogenic differentiation programs, whereas constitutive {beta}-catenin activation disrupts compartmental organization without enhancing proliferation. Mechanistically, we identify Foxm1 as a Wnt-associated proliferative mediator enriched in fibrocartilage, and genetic reduction of Foxm1 cooperates with {beta}-catenin deficiency to impair condylar growth. In parallel, {beta}-catenin loss derepresses TGF-{beta}-Smad signaling and enhances chondrogenic differentiation, indicating that canonical Wnt activity coordinates proliferative maintenance while restraining lineage commitment within the same cellular compartment. Together, these findings identify a Wnt-responsive fibrocartilage progenitor system that regulates postnatal mandibular condylar cartilage growth by coupling Foxm1-associated proliferative maintenance with suppression of TGF-{beta}-dependent chondrogenic differentiation during temporomandibular joint development. Graphical abstractWnt-responsive fibrocartilage progenitors coordinate postnatal mandibular condylar cartilage growth through Foxm1-dependent proliferative maintenance and suppression of TGF-{beta}-driven chondrogenic differentiation.

developmental biology↗

bioRxiv2026

Rab32/Rab38-positive Lysosome-Related Organelle degrades lipid droplet in hepatocytes by microautophagy

Rab32 and Rab38 are paralogous small GTPases involved in the biogenesis of lysosome-related organelles (LROs), yet their roles in hepatic lipid metabolism remain poorly defined. Here, Rab32 and Rab38 double-knockout (DKO) male mice exhibited an age-dependent increase in body weight accompanied by hepatic lipid accumulation, suggesting impaired hepatic lipid processing. In AML12 hepatocytes, Rab32 and Rab38 localized to ring-like, LAMP1-positive structures characteristic of LROs, whose size increased with cell confluence. Pharmacological inhibition of lysosomal acid lipase with orlistat led to the accumulation of lipid droplets (LDs) within Rab32/38-positive LROs, indicating that LD degradation occurs in these compartments. Additional treatment with bafilomycin A1 revealed invagination-like internal membrane structures within enlarged LROs. These processes were not affected by artificial inhibition of macroautophagy, highlighting the involvement of microautophagy. Ring-like signals positive for phosphatidylinositol 3-phosphate (PI3P) or phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) were detected within or adjacent to LRO membranes, and LDs were frequently associated with these structures, suggesting a role for PI3P and PI(3,5)P2 in internal membrane formation. Vps4B was also required for efficient LD incorporation. Consistently, Rab32/38 double-knockdown (DKD) AML12 cells exhibited increased lipid accumulation, indicating impaired LD engulfment. Together, these findings identify Rab32/38-positive LROs as a structural platform for microautophagy-mediated lipid droplet degradation in hepatocytes.

cell biology↗

bioRxiv2025

TMEM2 maintains hyaluronan turnover and cartilage homeostasis during early osteoarthritis progression

Osteoarthritis (OA) is a degenerative joint disease characterized by progressive disruption of the cartilage extracellular matrix (ECM), yet the molecular mechanisms governing ECM turnover during disease initiation remain incompletely defined. Hyaluronan (HA) is a major structural component of articular cartilage, and its regulated turnover is essential for maintaining tissue integrity. Transmembrane protein 2 (TMEM2) is a cell-surface hyaluronidase capable of degrading high-molecular weight HA under physiological conditions, but its role in joint tissues has remained unclear. Here, we examine the spatiotemporal expression and functional contribution of TMEM2 in articular cartilage using single-cell transcriptomic analysis, histological approaches, and a chondrocyte-specific conditional knockout mouse model. Under physiological conditions, Tmem2 was predominantly expressed in non-calcified articular chondrocytes. Following joint destabilization, Tmem2 expression was transiently increased during early osteoarthritis, coinciding with reduced cartilage HA content, consistent with altered HA turnover. Importantly, genetic ablation of Tmem2 in chondrocytes markedly exacerbated osteoarthritis progression, resulting in accelerated cartilage delamination, increased chondrocyte apoptosis, reduced proliferative activity, and enhanced hypertrophic differentiation. These changes occurred without detectable abnormalities in the synovium, subchondral bone, or osteophyte formation, indicating a cartilage-intrinsic phenotype. Collectively, these findings identify TMEM2 as an important regulator of hyaluronan homeostasis within the cartilage ECM and provide in vivo genetic evidence that TMEM2- dependent HA turnover contributes to the maintenance of articular cartilage integrity during osteoarthritis progression.

molecular biology↗

bioRxiv2024

Retinoid-impregnated nanoparticles enable control of bone growth by site-specific modulation of endochondral ossification in mice

Growth-plate (GP) injures in limbs and other sites can impair GP function and cause deceleration of bone growth, leading to progressive bone lengthening imbalance, deformities and/or physical discomfort, decreased motion and pain. At present, surgical interventions are the only means available to correct these conditions by suppressing the GP activity in the unaffected limb and/or other bones in the ipsilateral region. Here, we aimed to develop a pharmacologic treatment of GP growth imbalance that involves local application of nanoparticles-based controlled release of a selective retinoic acid nuclear receptor gamma (RAR{gamma}) agonist drug. When RAR{gamma} agonist-loaded nanoparticles were implanted near the medial and lateral sides of proximal tibial growth plate in juvenile C57BL/6j mice, the GP underwent involution and closure. Overall tibia length was shortened compared to the contralateral element implanted with drug-free control nanoparticles. Importantly, when the RAR{gamma} agonist nanoparticles were implanted on the lateral side only, the adjacent epiphysis tilted toward the lateral site, leading to apical angulation of the tibia. In contrast to the local selectivity of these responses, systemic administration of RAR{gamma} agonists led to GP closure at many sites, inhibiting skeletal growth over time. Agonists for RAR and RAR{beta} elicited no obvious responses over parallel regimens. Our findings provide novel evidence that RAR{gamma} agonist-loaded nanoparticles can control activity, function and directionality of a targeted GP, offering a potential and clinically-relevant alternative or supplementation to surgical correction of limb length discrepancy and angular deformities. Lay summaryGrowth-plates (physes), which are cartilage tissues near the ends of bones, support normal bone growth in children. Growth plate injures in limbs and other sites can impair growth plate function, leading to inhibited or imbalanced bone growth, skeletal deformities, decreased motion, discomfort or pain. At present, surgical interventions are the only means available to correct these conditions. Here, we aimed to develop a pharmacologic treatment for bone growth imbalance. Nanoparticles loaded with a selective agonist for the retinoic acid nuclear receptor gamma were prepared and implanted near the tibial growth plate in juvenile mice. The growth plate underwent involution and closure, and overall tibia length was shortened compared to the contralateral element implanted with drug-free control nanoparticles. Importantly, when the same drug nanoparticles were implanted in only one side of the tibia, the tibia was tilted toward the injection site. Our findings provide novel evidence that retinoic acid receptor gamma agonist-loaded nanoparticles can control activity, function and directionality of a targeted growth plate, offering a potential and clinically-relevant alternative or supplementation to surgical correction of limb length imbalances and deformities.

pharmacology and toxicology↗

bioRxiv2024

The braking force to Control the Abnormal Tibial Translation Affects the Spontaneous Healing Response for Complete Ruptured Anterior Cruciate Ligament in Mice Model

Purpose of this studyThe anterior cruciate ligament (ACL) has been believed to have a low spontaneous healing capacity; growing evidence has suggested that ACL could heal spontaneously. While the healed ACL has reduced mechanical properties and incomplete tissue maturation, the mechanisms underlying these problems remain unknown. We aimed to elucidate the effect of mechanical stresses during the early phase of spontaneous ACL healing. Materials and MethodsMale and female C57BL/6 mice were subjected to ACL rupture and randomly classified into three groups: Tight-CATT; tightly controlled anterior tibial translation (ATT), Loose-CATT; loosely controlled ATT and mild increasing mechanical stress compared to Tight-CATT, and ACL-Rupture (ACL-R) group; not controlled ATT. Mice were sacrificed and analyzed immediately after injury and at 4 and 8 weeks. We evaluated the effect of controlling the braking force of the ATT of each knee, the success rate of the ACL healing, collagen maturation, COL1A1 expression in the healed ACL, and the mechanical properties of the healed ACL. ResultsThe Tight-CATT group showed a higher success rate of ACL healing than the Loose-CATT group at 4 and 8 weeks. However, collagen maturation and the mechanical properties of healed ACL did not differ between the Tight-CATT and Loose-CATT groups. ConclusionOur results suggested that loose ATT braking immediately after injury is a negative factor for the healing of the completely ruptured ACL, and that it may be necessary to apply higher mechanical stress in the later stages to achieve greater healing.

physiology↗

bioRxiv2024

Muscle Contraction is Essential for Tendon Healing and Muscle Function Recovery after Achilles Tendon Rupture and Surgical Repair

Incomplete tendon healing and postponed muscle weakness after Achilles tendon rupture and surgical repair lead to poor performance in patient activities. Although the effectiveness of postoperative early functional rehabilitation has been proven, the priority and each effect of specific methods in early rehabilitation remain unclear. We hypothesized early muscle contraction exercises without joint motion would promote tendon healing and prevent calf muscle atrophy; in contrast, early static stretching after surgical repair would not contribute to tendon healing and induce calf muscle atrophy. C57Bl/6 mice underwent Achilles tendon rupture and suture repair, followed by different methods of post-surgery interventions: a non-exercise group, a Static stretching group, and an Electrical muscle stimulation group. 3 and 5 weeks after surgery, we assessed ex vivo tendon mechanical properties, collagen fiber alignment, and histological muscle properties. Electrical Muscle Stimulation restored the recovery of tendon mechanical properties and muscle strength more quickly than Static stretching. Static stretching had no additional effect on them compared to the non-exercise. Our results suggested that calf muscle contraction was essential as a post-surgery early functional rehabilitation to load tensile forces on tendons and improve Achilles tendon healing. Additionally, early muscle contractions naturally promote restoring muscle function after the rupture, but further research is needed to optimize muscle contraction protocols. Statement of Clinical SignificanceThis study shows the importance of selecting appropriate exercise modalities to resolve imperfections in tendon healing and muscle recovery. The establishment of proper rehabilitation is expected to improve post-surgery outcomes. Study DesignA controlled laboratory study.

physiology↗

bioRxiv2023

The mechanical force with the physiological movement works as a biological cue in tendon development during the postnatal phase in mice

The musculoskeletal system provides structural stability and coordination to enable movement. Tendons have the essential role of efficiently transmitting force generated from muscle contraction to bone to enable ambulation. In doing so, they resist high external forces. In fact, muscle contraction during embryonic development is required to maintain tendon growth and differentiation. Nonetheless, defining the types and magnitudes of loads that act on tendons during embryonic and early postnatal periods is quite difficult. In this study, we aimed to define the physiologic limb movement and forces experienced during these stages in the murine model. We found that late-stage embryos had limited amniotic space, which attenuated limb movement. In the neonatal phase, physical ability, as measured by rollover function and locomotion, increased. These changes, which likely corresponded to increased forces applied to the tendons, corresponded with the expression of tenogenic markers during the embryo to postnatal phase. In particular, we found that the upregulation of Scx and Tnmd correlated with increased movement during the two weeks after birth. Our results help define the spatiotemporal role of mechanical force, including internal and external factors, in tendon growth and development. HighlightsO_LIAssessed limb movement in amnion. C_LIO_LISpace limitation attenuated limb movement in the late-stage embryos. C_LIO_LIDefined the mechanical force from the limbs physiological environment. C_LIO_LIScx and Tnmd were upregulated synchronically with rollover function and locomotion. C_LIO_LIMechanical forces may work as the cue of tendon development C_LI

developmental biology↗

bioRxiv2023

Characteristic differences in tibial subchondral bone changes in the post-traumatic knee osteoarthritis model

ObjectiveMeniscus degeneration and subchondral bone changes contribute to the development and progression of knee OA. The purpose of this study was to reveal the relationship between medial meniscus degeneration and characteristics of subchondral bone changes in different models DesignWe used the anterior cruciate ligament transection (ACL-T) model, destabilization of the medial meniscus (DMM) model, controlled abnormal tibial translation (CATT) model and a controlled abnormal tibial rotation (CATR) model with different mechanical stresses. We performed histological analysis and micro computed tomography analysis, at 4 and 6 weeks. In addition, we divided the tibial subchondral bone into four compartments and set the regions of interest ResultsMeniscus degeneration was observed in all groups, but there was no significant difference. The ACL-T group showed posterior displacement of the contact area, and the DMM and CATR groups showed lateral deviation of the medial meniscus. The region-specific subchondral bone changes in each model showed that changes in mechanical stress due to ACL and meniscus dysfunction, as well as changes in the contact area, affect the bony structure of the subchondral bone differently in each region. ConclusionsSubchondral bone changes in different models of mechanical stress were different in each region. In particular, changes in the contact area and increased compressive stress due to meniscus dysfunction were suggested to promote bone formation. The results of this study indicate that changes in alignment and contact area in the PTOA model may cause region-specific characteristics of the subchondral bone changes.

pathology↗

bioRxiv2023

Nutrient-regulated dynamics of chondroprogenitors in the postnatal murine growth plate

Longitudinal bone growth relies on endochondral ossification in the cartilaginous growth plate where chondrocytes accumulate and synthesize the matrix scaffold that is replaced by bone. The chondroprogenitors in the resting zone maintain the continuous turnover of chondrocytes in the growth plate. Malnutrition is a leading cause of growth retardation in children; however, after recovery from nutrient deprivation, bone growth is accelerated beyond the normal rate, a phenomenon termed catch-up growth. Though nutritional status is a known regulator of long bone growth, it is largely unknown if and how chondroprogenitor cells respond to deviations in nutrient availability. Here, using fate-mapping analysis in Axin2CreERT2 mice, we showed that dietary restriction increased the number of Axin2+ chondroprogenitors in the resting zone and simultaneously inhibited their differentiation. Once nutrient deficiency was resolved, the accumulated chondroprogenitor cells immediately restarted differentiation and formed chondrocyte columns, contributing to accelerated growth. Furthermore, we showed that nutrient deprivation reduced the level of phosphorylated Akt in the resting zone, and that exogenous IGF-1 canceled this reduction and stimulated differentiation of the pooled chondroprogenitors, decreasing their numbers. Our study of Axin2CreERT2 revealed that nutrient availability regulates the balance between accumulation and differentiation of chondroprogenitors in the growth plate, and further demonstrated that IGF-1 partially mediates this regulation by promoting the committed differentiation of the chondroprogenitor cells.

developmental biology↗

bioRxiv2022

Abnormal Tibia Translation leads Directly the Surface Cartilage Degeneration with Molecular Biological Response using a Novel Non-Invasive ACL ruptured Mice Model

ObjectiveThe ACL-deficient model helps to clarify the mechanism of knee OA; however, the conventional ACL injury model could have included concurrent onset factors such as direct compression stress to cartilage and subchondral bone. In this study, we established a novel Non-invasive ACL-Ruptured mouse model without concurrent injuries and elucidated the relationship between OA progression and joint instability. DesignWe induced the ACL-Rupture non-invasively in twelve-week-old C57BL/6 male mice and evaluated histological, macroscopical, and morphological analysis at 0 days. Next, we created the ACL-R, controlled abnormal tibial translation (CATT), and Sham groups. Then, the joint stability and OA pathophysiology were analyzed at 2, 4, and 8 weeks. ResultsNo intra-articular injuries, except for ACL rupture, were observed in the ACL-R model. ACL-R mice increased anterior tibial displacement compared to the Sham group (p<0.001, 95% CI [-1.509 to -0.966]) and CATT group (p<0.001, 95% CI [-0.841 to -0.298]) at 8 weeks. All mice in the ACL-R group caused cartilage degeneration. The degree of cartilage degeneration in the ACL-R group was higher than in the CATT group (p=0.006) at 8 weeks. The MMP-3-positive cell rate of chondrocytes increased in the ACL-R group than CATT group from 4 weeks (p=0.043; 95% CI [-28.32 to -0.364]) while that of synovial cells increased at 8 weeks (p=0.031; 95% CI [-23.398 to -1.021]). ConclusionWe successfully established a Non-invasive ACL-R model without intra-articular damage. Our model revealed that chondrocytes might react to abnormal mechanical stress prior to synovial cells while the knee OA onset.

molecular biology↗