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Masahiro Iwamoto, PhD

Maxwell Hurston, MD Distinguished Professor of Orthopaedics

Academic Title:


Primary Appointment:



20 Penn Street, Baltimore, MD 21201

Phone (Primary):




Education and Training


1984: DDS, Tokushima University, School of Dentistry

1988: PhD, Osaka University Graduate School of Dentistry

1988-1990: Clinical Staff, Radiology, Osaka University Dental Hospital



1993-2001 Assistant Professor, Osaka University Graduate School of Dentistry, Department of Oral Anatomy and Developmental Biology

2002 Associate Professor, Osaka University Graduate School of Dentistry, Department of Oral Anatomy and Developmental Biology

2002-2011 Associate Professor, Thomas Jefferson University, Department of Orthopaedic Surgery

2012-2016 Research Associate Professor of Orthopaedic Surgery, University of Pennsylvania School of Medicine

2012-2016 Scientist II, The Children's Hospital of Philadelphia Research Institute

2017-current   Professor, Dept of Orthopaedics, University of Maryland School of Medicine

Research/Clinical Keywords

skeletal development, cartilage, arthritis, retinoid, endochondral ossification, heterotopic ossification, trauma, musculoskeletal injury, micro surgery, mouse genetics, ets-related transcription factor

Highlighted Publications

Iwamoto, M., Sato, K., Nakashima, K., Shimazu, A., Kato, Y.: Hypertrophy and calcification of rabbit permanent chondrocytes in pelleted cultures: synthesis of alkaline phosphatase and 1,25-dihydroxycholecalciferol receptor. Dev Biol 136(2): 500-7, 1989.

Iwamoto, M., Jikko, A., Murakami, H., Shimazu, A., Nakashima, K., Takigawa, M., Baba, H., Suzuki, F., Kato, Y.: Changes in parathyroid hormone receptors during chondrocyte cytodifferentiation. J Biol Chem 269(25): 17245-51, 1994.

Iwamoto, M., Higuchi, Y., Koyama, E., Enomoto-Iwamoto, M., Kurisu, K., Yeh, H., Abrams, W. R., Rosenbloom, J., Pacifici, M.: Transcription factor ERG variants and functional diversification of chondrocytes during limb long bone development. J Cell Biol 150(1): 27-40, 2000.

Iwamoto, M., Tamamura, Y., Koyama, E., Komori, T., Takeshita, N., Williams, J. A., Nakamura, T., Enomoto-Iwamoto, M., Pacifici, M.: Transcription factor ERG and joint and articular cartilage formation during mouse limb and spine skeletogenesis. Dev Biol 305(1): 40-51, 2007.

Williams, J. A., Kondo, N., Okabe, T., Takeshita, N., Pilchak, D. M., Koyama, E., Ochiai, T., Jensen, D., Chu, M. L., Kane, M. A., Napoli, J. L., Enomoto-Iwamoto, M., Ghyselinck, N., Chambon, P., Pacifici, M., Iwamoto, M.: Retinoic acid receptors are required for skeletal growth, matrix homeostasis and growth plate function in postnatal mouse. Dev Biol 328(2): 315-27, 2009.

Shimono, K., Tung, W. E., Macolino, C., Chi, A. H., Didizian, J. H., Mundy, C., Chandraratna, R. A., Mishina, Y., Enomoto-Iwamoto, M., Pacifici, M., Iwamoto, M.: Potent inhibition of heterotopic ossification by nuclear retinoic acid receptor-gamma agonists. Nat Med 17(4): 454-60, 2011.

Ohta Yoichi, Okabe Takahiro, Larmour Colleen, Di Rocco Agnese, Maijenburg Marijke W, Phillips Amanda, Speck Nancy A, Wakitani Shigeyuki, Nakamura Takashi, Yamada Yoshihiko, Enomoto-Iwamoto Motomi, Pacifici Maurizio, Iwamoto Masahiro: Articular cartilage endurance and resistance to osteoarthritic changes require transcription factor Erg. Arthritis Rheumatol  67(10): 2679-90, Oct 2015.

Di Rocco Agnese, Uchibe Kenta, Larmour Colleen, Berger Rebecca, Liu Min, Barton Elisabeth R, Iwamoto Masahiro: Selective Retinoic Acid Receptor γ Agonists Promote Repair of Injured Skeletal Muscle in Mouse. Am J Pathol 185(9): 2495-504, 2015. PMCID: PMC4597269

Kenta Uchibe, Jiyeon Son, Colleen Larmour, Maurizio Pacifici, Motomi Enomoto-Iwamoto, Masahiro Iwamoto: Genetic and pharmacological inhibition of retinoic acid receptor γ function promotes endochondral bone formation. J Orthop Res 35(5):1096-1105, May 2017

Additional Publication Citations

Publications listed in PubMed:


Research Interests

Analysis of the chondrocyte differentiation process during endochondral ossification.


Chondrocytes play essential roles in endochondral bone formation. The initial chondrogenic induction defines the site of bone formation. Proliferation and matrix production by chondrocytes are linked to the bone growth. Maturation of chondrocytes controls the rate of cartilage-to-bone transition.  A series of this complex process is regulated by multiple growth factors, hormones, vitamins and morphogenetic factors.  Impairment of any process results in skeletal mal-formation. Our research focus is to identify and define the role of critical regulators, and ultimately understand how temporo-spatial expression of critical regulatory molecules and their interplay enables sequential cyto-differentiation of chondrocytes, leading to bone growth.


Controlling pathological bone formation


Inefficient or excess endochondral ossification accounts for a variety of orthopaedic problems.  We are developing novel therapy to prevent excess pathological bone formation.    Heterotopic ossification (HO) consists of formation of ectopic bone, usually endochondral bone, within soft tissues, muscles and the blood vessel wall. HO is caused by trauma, invasive surgeries or other insults, but occurs also in congenital forms. Daily functioning of HO patients is hampered by loss of normal posture, pain, inflammation, reduced mobility, and other problems. Current treatments are not always successful. Surgery is often used to remove the HO lesions, but can trigger another round of HO and is not very effective for congenital severe forms of HO that can be fatal. Clearly, there has long been an urgent need for effective therapies for this potentially serious pathology.

The active metabolite of vitamin A -retinoic acid (RA)- has important roles in skeletal formation, but the exact mechanisms of action of RA have not been fully understood. We analyzed the roles of individual retinoic acid receptor isoforms (RARalpha, beta and gamma) in skeletal development by using selective chemical ligands for each individual receptor and receptor mutant mice.     The studies uncovered novel roles of RARgamma in the endochondral ossification.  We found that RARgamma is the major RAR in cartilage and stimulates cartilage-matrix synthesis in the absence of RA, likely acting a ligand-less transcriptional repressor. Interestingly, we found that the same receptor possesses the most powerful anti-chondrogenic effect (among the three isoforms) when the ligand is available.  Taking advantage of the potent anti-chondrogenic activity of RARgamma, we tested several selective RARgamma agonists in BMP-induced, post-traumatic and genetic HO animal models, and demonstrated that selective agonists did effectively suppressed HO with no major side effects.   In collaboration with researchers at University of Pennsylvania, Dept of Orthopaedics, we showed one of RARgamma agonists palovarotene is a possible therapeutics for the most devastating congenital form of HO called Fibrodysplasia Ossificans Progressiva (FOP).   The drug is now being investigated in human FOP patients.


Understanding “permanent” articular cartilage.


During embryogenesis, the chondrocytes in the shaft of developing long bones undergo hypertrophy, mineralization, and ultimately, replacement by bone cells. The chondrocytes located at the epiphyseal tip, however, give rise to articular tissue and retain their “permanent” cartilaginous phenotype throughout life.   What molecular mechanisms do govern those diverse fates of chondrocytes?  Through PCR based differential screening, we found one of Ets transcription family member, Erg (Ets related gene) is preferentially expressed in developing articular cartilage and other permanently cartilaginous tissues such as tracheal cartilage, intervertebral disc and ear.   Targeted expression of Erg in an embryonic skeleton resulted in severe suppression of endochondral ossification due to conversion of growth-plate cartilage into permanent cartilage.  More recently we created joint specific Erg deficient mice and found that the mutant mice develop severe osteoarthritis (OA) over postnatal life.   These observations indicate that Erg has a role in long term maintenance of articular cartilage.     In other studies, we identified upstream regulators and downstream targets of Erg.   We expect ongoing studies provide clear and novel insights and understanding as to how permanent cartilage can last and remain functional for life and how these mechanisms could be used therapeutically to restore articular cartilage in elderly or osteoarthritis patients. 

Awards and Affiliations

1995 Japanese Society for Cartilage Metabolism Society Award

1999 Japanese Society for Bone and Mineral Research JSBMR Academic Award

Lab Techniques and Equipment

Lab techniques:

Generation of genetically modified mice.

Animal surgery and drug treatment

Histology (chemical staining, Immunohistochemistry, IF, In situ hybridization)

Lase capture micro-dissection

Gene expression analyses (PCR, RNAseq, Gene array)

Cell culture (isolation of primary cells, reporter assay)

Molecular biology (vector construction and gene transfer)

Equipments (exculde common equipments):


Laser capture microdissection system (Leica LMD7)

Keyence all-in-one microscope BZ-X700

Cryostat and regular microtomes

Imager In vitrogen iBright FL1000