72 www.ecmjournal.org HJ Kok et al. Muscle IGF-I modulates craniofacial bone growth Abstract Insulin-like growth factor I (IGF-I) is essential for muscle and bone development and a primary mediator of growth hormone (GH) actions. While studies have elucidated the importance of IGF-I specifcally in muscle or bone development, few studies to date have evaluated the relationship between muscle and bone modulated by IGF-I in vivo, during post-natal growth. Mice with muscle-specifc IGF-I overexpression (mIgf1 +/+ ) were utilised to determine IGF-I- and muscle-mass-dependent efects on craniofacial skeleton development during post-natal growth. mIgf1 +/+ mice displayed accelerated craniofacial bone growth when compared to wild-type animals. Virus-mediated expression of IGF-I targeting the masseter was performed to determine if post-natal modulation of IGF-I altered mandibular structures. Increased IGF-I in the masseter afected the mandibular base plane angle in a lateral manner, increasing the width of the mandible. At the cellular level, increased muscle IGF-I also accelerated cartilage thickness in the mandibular condyle. Importantly, mandibular length changes associated with increased IGF-I were not present in mice with genetic inhibition of muscle IGF-I receptor activity. These results demonstrated that muscle IGF-I could indirectly afect craniofacial growth through IGF-I-dependent increases in muscle hypertrophy. These fndings have clinical implications when considering IGF-I as a therapeutic strategy for craniofacial disorders. Keywords: Muscle-bone interaction, insulin-like growth factor I, craniofacial, bone development. *Address for correspondence: Elisabeth R. Barton, PhD, Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, 1864 Stadium Road, Gainesville, FL 32611, USA. Telephone number: +1 3522941714 Email: erbarton@uf.edu Copyright policy: This article is distributed in accordance with Creative Commons Atribution Licence (htp://creativecommons.org/licenses/by-sa/4.0/). European Cells and Materials Vol. 42 2021 (pages 72-89) DOI: 10.22203/eCM.v042a06 ISSN 1473-2262 MUSCLE INSULIN-LIKE GROWTH FACTOR-I MODULATES MURINE CRANIOFACIAL BONE GROWTH H.J. Kok 1 , C.N. Crowder 2 , L. Koo Min Chee 2 , H.Y. Choi 2 , N. Lin 2 and E.R. Barton 1,2, * 1 Department of Applied Physiology and Kinesiology, College of Health and Human Performance, University of Florida, Gainesville, FL, USA 2 Department of Anatomy and Cell Biology, School of Dental Medicine, University of Pennsylvania, Philadelphia, PA, USA List of Abbreviations AAV adeno-associated virus AB-PAS alcian blue plus periodic acid-schif AMIDE a medical imaging data examiner ANOVA analysis of variance CI confdence interval DAPI 4′,6-diamidino-2-phenylindole DICOM digital imaging and communications in medicine ELISA enzyme-linked immunosorbent assay GAPDH glyceraldehyde 3-phosphate dehydrogenase gc genome copies GH growth hormone GHD GH defciency Grp94 glucose-regulated protein 94 IGFD insulin-like growth factor-I defciency IGF-I insulin-like growth factor-I IGF-IR IGF-I receptor MCK muscle creatine kinase mIgf1 muscle-specifc IGF-I transgenic overexpression mice MLC myosin light chain PBS phosphate-bufered saline PCA principal component analysis PC1 principal component 1 PC2 principal component 2 RIPA radioimmunoprecipitation assay SDS-PAGE sodium dodecyl sulphate- polyacrylamide gel electrophoresis SEM standard error of the mean WT wild type μCT micro-computed tomography