About

Eiki Koyama, Ph.D., D.D.S., is a Research Associate Professor of Orthopaedic Surgery at the Children's Hospital of Philadelphia, affiliated with the Translational Research Program in Pediatric Orthopaedics. He has been a biomedical researcher for more than 25 years, focusing on craniofacial development, synovial joint formation, and the molecular mechanisms and treatments of congenital diseases. His research has contributed to understanding the roles of retinoic acid in limb development, clarifying that it acts as an inducer of morphogens like Hedgehog rather than a morphogen itself. Koyama's work on the mechanisms of synovial joint formation has identified interzone cells as specialized progenitor cells essential for joint development, shedding light on joint formation processes. More recently, he has collaborated to study the development and growth of the temporomandibular joint and explore therapeutic approaches for TMJ osteoarthritis. His research extends to investigating congenital conditions such as Hereditary Multiple Exostoses, where he examines molecular mechanisms of ectopic cartilage formation and growth using mouse models, with a focus on growth factor distribution and progenitor cell responsiveness.

Research topics

• Biology
• Cell biology
• Anatomy
• Endocrinology
• Medicine

Selected publications

• Reduction in postnatal weight‐bearing does not alter the trajectory of murine meniscus growth and maturation

  Journal of Orthopaedic Research® · 2023-10-07 · 4 citations

  articleOpen access

  The early postnatal period represents a critical window for the maturation and development of orthopedic tissues, including those within the knee joint. To understand how mechanical loading impacts the maturational trajectory of the meniscus and other tissues of the hindlimb, perturbation of postnatal weight bearing was achieved through surgical resection of the sciatic nerve in neonatal mice at 1 or 14 days old. Sciatic nerve resection (SNR) produced significant and persistent disruptions in gait, leading to reduced tibial length and reductions in Achilles tendon mechanical properties. However, SNR resulted in minimal disruptions in morphometric parameters of the menisci and other structures in the knee joint, with no detectable differences in Col1a1-YFP or Col2a1-CFP expressing cells within the menisci. Furthermore, micromechanical properties of the meniscus and cartilage (as assessed by atomic force microscopy-based nanoindentation testing) were not different between experimental groups. In contrast to our initial hypothesis, reduced hindlimb weight bearing via neonatal SNR did not significantly impact the growth and development of the knee meniscus. This unexpected finding demonstrates that the input mechanical threshold required to sustain meniscus development may be lower than previously hypothesized, though future studies incorporating skeletal kinematic models coupled with force plate measurements will be required to calculate the loads passing through the affected hindlimb and precisely define these thresholds. Collectively, these results provide insight into the mechanobiological responses of the meniscus to alterations in load, and contribute to our understanding of the factors that influence normal postnatal development.

  PublisherOA PDFDOI

• Palovarotene Action Against Heterotopic Ossification Includes a Reduction of Local Participating Activin <scp>A‐Expressing</scp> Cell Populations

  JBMR Plus · 2023-10-19 · 9 citations

  articleOpen access

  ABSTRACT Heterotopic ossification (HO) consists of extraskeletal bone formation. One form of HO is acquired and instigated by traumas or surgery, and another form is genetic and characterizes fibrodysplasia ossificans progressiva (FOP). Recently, we and others showed that activin A promotes both acquired and genetic HO, and in previous studies we found that the retinoid agonist palovarotene inhibits both HO forms in mice. Here, we asked whether palovarotene's action against HO may include an interference with endogenous activin A expression and/or function. Using a standard mouse model of acquired HO, we found that activin A and its encoding RNA ( Inhba ) were prominent in chondrogenic cells within developing HO masses in untreated mice. Single‐cell RNAseq (scRNAseq) assays verified that Inhba expression characterized chondroprogenitors and chondrocytes in untreated HO, in addition to its expected expression in inflammatory cells and macrophages. Palovarotene administration (4 mg/kg/d/gavage) caused a sharp inhibition of both HO and amounts of activin A and Inhba transcripts. Bioinformatic analyses of scRNAseq data sets indicated that the drug had reduced interactions and cross‐talk among local cell populations. To determine if palovarotene inhibited Inhba expression directly, we assayed primary chondrocyte cultures. Drug treatment inhibited their cartilaginous phenotype but not Inhba expression. Our data reveal that palovarotene markedly reduces the number of local Inhba ‐expressing HO‐forming cell populations. The data broaden the spectrum of HO culprits against which palovarotene acts, accounting for its therapeutic effectiveness. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

  PublisherOA PDFDOI

• Osteochondroma formation is independent of heparanase expression as revealed in a mouse model of hereditary multiple exostoses

  Journal of Orthopaedic Research® · 2022-01-07 · 11 citations

  articleOpen access

  Abstract Hereditary multiple exostoses (HME) is a rare, pediatric disorder characterized by osteochondromas that form along growth plates and provoke significant musculoskeletal problems. HME is caused by mutations in heparan sulfate (HS)‐synthesizing enzymes EXT1 or EXT2. Seemingly paradoxically, osteochondromas were found to contain excessive extracellular heparanase (Hpse) that could further reduce HS levels and exacerbate pathogenesis. To test Hpse roles, we asked whether its ablation would protect against osteochondroma formation in a conditional HME model consisting of mice bearing floxed Ext1 alleles in Agr‐CreER background ( Ext1 f/f ;Agr‐CreER mice). Mice were crossed with a new global Hpse ‐null ( Hpse −/− ) mice to produce compound Hpse −/− ;Ext1 f/f ;Agr‐CreER mice. Tamoxifen injection of standard juvenile Ext1 f/f ;Agr‐CreER mice elicited stochastic Ext1 ablation in growth plate and perichondrium, followed by osteochondroma formation, as revealed by microcomputed tomography and histochemistry. When we examined companion conditional Ext1 ‐deficient mice lacking Hpse also, we detected no major decreases in osteochondroma number, skeletal distribution, and overall structure by the analytical criteria above. The Ext1 mutants used here closely mimic human HME pathogenesis, but have not been previously tested for responsiveness to treatments. To exclude some innate therapeutic resistance in this stochastic model, tamoxifen‐injected Ext1 f/f ;Agr‐CreER mice were administered daily doses of the retinoid Palovarotene, previously shown to prevent ectopic cartilage and bone formation in other mouse disease models. This treatment did inhibit osteochondroma formation compared with vehicle‐treated mice. Our data indicate that heparanase is not a major factor in osteochondroma initiation and accumulation in mice. Possible roles of heparanase upregulation in disease severity in patients are discussed.

  PublisherOA PDFDOI

• Intrinsic and growth-mediated cell and matrix specialization during meniscus tissue assembly

  bioRxiv (Cold Spring Harbor Laboratory) · 2021-02-21 · 1 citations

  preprintOpen access

  ABSTRACT The incredible mechanical strength and durability of mature fibrous tissues and their extremely limited turnover and regenerative capacity underscores the importance of proper matrix assembly during early postnatal growth. In tissues with composite extracellular matrix (ECM) structures, such as the adult knee meniscus, fibrous (Collagen-I rich) and cartilaginous (Collagen-II, proteoglycan-rich) matrix components are regionally segregated to the outer and inner portions of the tissue. While this spatial variation in composition is appreciated to be functionally important for resisting complex mechanical loads associated with gait, the establishment of these specialized zones is poorly understood. To address this issue, the following study tracked the growth of the murine meniscus from its embryonic formation through its first month of growth, encompassing the critical time-window during which animals begin to ambulate and weight bear. Using histological analysis, region specific high-throughput qPCR, and Col-1 and Col-2 fluorescent reporter mice, we found that matrix and cellular features defining specific tissue zones were already present at birth, before continuous weight-bearing had occurred. These differences were further refined with postnatal growth and maturation, resulting in specialization of mature tissue regions. Taken together, this work establishes a detailed timeline of the concurrent spatiotemporal changes that occur at both the cellular and matrix level throughout meniscus maturation. The findings of this study provide a framework for investigating the reciprocal feedback between cells and their evolving microenvironments during assembly of a mechanically robust fibrocartilage tissue, thus providing insight into mechanisms of tissue degeneration and effective regenerative strategies.

  PublisherOA PDFDOI

• Author response: The critical role of Hedgehog-responsive mesenchymal progenitors in meniscus development and injury repair

  2021-05-03

  peer-reviewOpen access
  PublisherDOI

• Intrinsic and growth‐mediated cell and matrix specialization during murine meniscus tissue assembly

  The FASEB Journal · 2021-07-27 · 21 citations

  articleOpen access

  The incredible mechanical strength and durability of mature fibrous tissues and their extremely limited turnover and regenerative capacity underscores the importance of proper matrix assembly during early postnatal growth. In tissues with composite extracellular matrix (ECM) structures, such as the adult knee meniscus, fibrous (Collagen-I rich), and cartilaginous (Collagen-II, proteoglycan-rich) matrix components are regionally segregated to the outer and inner portions of the tissue, respectively. While this spatial variation in composition is appreciated to be functionally important for resisting complex mechanical loads associated with gait, the establishment of these specialized zones is poorly understood. To address this issue, the following study tracked the growth of the murine meniscus from its embryonic formation through its first month of growth, encompassing the critical time-window during which animals begin to ambulate and weight bear. Using histological analysis, region specific high-throughput qPCR, and Col-1, and Col-2 fluorescent reporter mice, we found that matrix and cellular features defining specific tissue zones were already present at birth, before continuous weight-bearing had occurred. These differences in meniscus zones were further refined with postnatal growth and maturation, resulting in specialization of mature tissue regions. Taken together, this work establishes a detailed timeline of the concurrent spatiotemporal changes that occur at both the cellular and matrix level throughout meniscus maturation. The findings of this study provide a framework for investigating the reciprocal feedback between cells and their evolving microenvironments during assembly of a mechanically robust fibrocartilage tissue, thus providing insight into mechanisms of tissue degeneration and effective regenerative strategies.

  PublisherOA PDFDOI

• Type V collagen regulates the structure and biomechanics of TMJ condylar cartilage: A fibrous-hyaline hybrid

  Matrix Biology · 2021-07-24 · 23 citations

  articleOpen access
  PublisherOA PDFDOI

• SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency

  Molecular Therapy — Methods & Clinical Development · 2021-10-01 · 7 citations

  articleOpen access

  Inactivation mutations in the Indian hedgehog (Ihh) gene in humans cause numerous skeletal chondrodysplasias, including acrocapitofemoral dysplasia, brachydactyly type A1, and human short stature. The lack of an appropriate human-relevant model to accurately represent these chondrodysplasias has hampered the identification of clinically effective treatments. Here, we established a mouse model of human skeletal dysplasia induced by Ihh gene mutations via ablation of Ihh in Aggrecan-positive (Acan+) cells using Aggrecan (Acan)-creERT transgenic mice. Smoothen agonist (SAG) promoted Hh activity and rescued chondrocyte proliferation and differentiation by stimulating smoothened trafficking to the cilium in Ihh-silenced cells. SAG treatment corrected mouse stature and significantly decreased mortality without evidence of toxicity. Moreover, Ihh ablation in Acan+ cells produced enchondroma-like tissues near the growth plates that were significantly reduced by SAG treatment. These results demonstrated that SAG effectively treats skeletal dysplasia caused by Ihh gene mutations in a mouse model, suggesting that SAG may represent a potential drug for the treatment of these diseases and/or enchondromas. Inactivation mutations in the Indian hedgehog (Ihh) gene in humans cause numerous skeletal chondrodysplasias, including acrocapitofemoral dysplasia, brachydactyly type A1, and human short stature. The lack of an appropriate human-relevant model to accurately represent these chondrodysplasias has hampered the identification of clinically effective treatments. Here, we established a mouse model of human skeletal dysplasia induced by Ihh gene mutations via ablation of Ihh in Aggrecan-positive (Acan+) cells using Aggrecan (Acan)-creERT transgenic mice. Smoothen agonist (SAG) promoted Hh activity and rescued chondrocyte proliferation and differentiation by stimulating smoothened trafficking to the cilium in Ihh-silenced cells. SAG treatment corrected mouse stature and significantly decreased mortality without evidence of toxicity. Moreover, Ihh ablation in Acan+ cells produced enchondroma-like tissues near the growth plates that were significantly reduced by SAG treatment. These results demonstrated that SAG effectively treats skeletal dysplasia caused by Ihh gene mutations in a mouse model, suggesting that SAG may represent a potential drug for the treatment of these diseases and/or enchondromas.

  PublisherOA PDFDOI

• Activin A promotes the development of acquired heterotopic ossification and is an effective target for disease attenuation in mice

  Science Signaling · 2021-02-09 · 35 citations

  articleOpen access

  ), to HO sites. Gain-of-function assays showed that activin A enhanced the chondrogenic differentiation of progenitor cells through SMAD2/3 signaling, and inclusion of activin A in HO-inducing implants enhanced HO development in vivo. Together, our data reveal that activin A is a critical upstream signaling stimulator of acquired HO in mice and could represent an effective therapeutic target against forms of this pathology in patients.

  PublisherOA PDFDOI

• The critical role of Hedgehog-responsive mesenchymal progenitors in meniscus development and injury repair

  eLife · 2021-06-03 · 22 citations

  articleOpen access

  Meniscal tears are associated with a high risk of osteoarthritis but currently have no disease-modifying therapies. Using a Gli1 reporter line, we found that Gli1 + cells contribute to the development of meniscus horns from 2 weeks of age. In adult mice, Gli1 + cells resided at the superficial layer of meniscus and expressed known mesenchymal progenitor markers. In culture, meniscal Gli1 + cells possessed high progenitor activities under the control of Hh signal. Meniscus injury at the anterior horn induced a quick expansion of Gli1-lineage cells. Normally, meniscal tissue healed slowly, leading to cartilage degeneration. Ablation of Gli1 + cells further hindered this repair process. Strikingly, intra-articular injection of Gli1 + meniscal cells or an Hh agonist right after injury accelerated the bridging of the interrupted ends and attenuated signs of osteoarthritis. Taken together, our work identified a novel progenitor population in meniscus and proposes a new treatment for repairing injured meniscus and preventing osteoarthritis.

  PublisherDOI

Recent grants

• NIH Grant R01DE013206

  NIH · $1.1M · 2005

• Mechanisms of TMJ development and long-term function

  NIH · $2.1M · 2014–2022

• Pathogenic Mechanisms in Hereditary Multiple Exostoses Syndrome

  NIH · $6.3M · 2011–2027

• NIH Grant RC1AR058382

  NIH · $819k · 2012

• Mechanical Regulation of Cell Fate and Multi-Scale Function in the Developing Meniscus

  NIH · $3.9M · 2019–2029

Frequent coauthors

• Maurizio Pacifici

  134 shared

• Motohiko Nagayama

  Asahi University

  83 shared

• Hiromasa Hasegawa

  National Medical Research Center of Dentistry and Maxillofacial Surgery

  61 shared

• Takanaga Ochiai

  Asahi University

  53 shared

• Christina Mundy

  Children's Hospital of Philadelphia

  46 shared

• Yoshihiro Shibukawa

  Tokyo Dental College

  45 shared

• Tadashi Yasuda

  Kobe City Medical Center General Hospital

  43 shared

• Tiffany H. Morrison

  41 shared

Education

• DDS., PhD, Oral Surgery

  Okayama University