title: Connexin37 deficiency alters organic bone matrix, cortical bone geometry, and increases Wnt/β-catenin signaling.
abstract: Deletion of connexin (Cx) 37 in mice leads to increased cancellous bone mass due to defective osteoclast differentiation. Paradoxically; however, Cx37-deficient mice exhibit reduced cortical thickness accompanied by higher bone strength, suggesting a contribution of Cx37 to bone matrix composition. Thus, we investigated whether global deletion of Cx37 alters the composition of organic bone extracellular matrix. Five-month-old Cx37-/-mice exhibited increased marrow cavity area, and periosteal and endocortical bone surface resulting in higher total area in tibia compared to Cx37+/+control mice. Deletion of Cx37 increased genes involved in collagen maturation (loxl3 and loxl4) and glycosaminoglycans- (chsy1, chpf and has3) proteoglycans- associated genes (biglycan and decorin). In addition, expression of type II collagen assessed by immunostaining was increased by 82% whereas collagen maturity by picrosirius-polarizarion tended to be reduced (p=0.071). Expression of glycosaminoglycans by histochemistry was decreased, whereas immunostaining revealed that biglycan was unchanged and decorin was slightly increased in Cx37-/-bone sections. Consistent with these in vivo findings, MLO-Y4 osteocytic cells silenced for Cx37 gene exhibited increased mRNA levels for collagen synthesis (col1a1 and col3a1) and collagen maturation (lox, loxl1 and loxl2 genes). Furthermore, mechanistic studies showed Wnt/β-catenin activation in MLO-Y4 osteocytic cells, L5 vertebra, and authentic calvaria-derived osteocytes isolated by fluorescent-activated cell sorter. Our findings demonstrate that altered profile of the bone matrix components in Cx37-deficient mice acts in favor of higher resistance to fracture in long bones.
authors.affiliation: Departamento de Morfologia e Genética, Universidade Federal de Sao Paulo - Escola Paulista de Medicina, São Paulo, Brazil; Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA. Electronic address: rafa.pacheco@ig.com.br.
authors.forename: Rafael
authors.initials: R
authors.lastname: Pacheco-Costa
authors.affiliation: Department of Biomedical Engineering, Indiana University-Purdue University at Indianapolis, IN, USA. Electronic address: jkadakia@umail.iu.edu.
authors.forename: Jay R
authors.initials: JR
authors.lastname: Kadakia
authors.affiliation: Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA. Electronic address: emiatkin@iupui.edu.
authors.forename: Emily G
authors.initials: EG
authors.lastname: Atkinson
authors.affiliation: Department of Biomedical Engineering, Indiana University-Purdue University at Indianapolis, IN, USA; Department of Orthopaedic Surgery, Indiana University School of Medicine, IN, USA. Electronic address: jmwalla@iupui.edu.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Wallace
authors.affiliation: Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA; Roudebush Veterans Administration Medical Center, Indianapolis, IN, USA. Electronic address: lplotkin@iupui.edu.
authors.forename: Lilian I
authors.initials: LI
authors.lastname: Plotkin
authors.affiliation: Departamento de Morfologia e Genética, Universidade Federal de Sao Paulo - Escola Paulista de Medicina, São Paulo, Brazil. Electronic address: rejanedr.morf@epm.br.
authors.forename: Rejane D
authors.initials: RD
authors.lastname: Reginato
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001857:Bone Matrix / Q000378:metabolism*; D003094:Collagen / Q000096:biosynthesis; D017630:Connexins / Q000172:deficiency* / Q000378:metabolism; D000071538:Cortical Bone / Q000378:metabolism* / Q000473:pathology; D005109:Extracellular Matrix / Q000378:metabolism; D005260:Female; D017353:Gene Deletion; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006025:Glycosaminoglycans / Q000378:metabolism; D008297:Male; D051379:Mice; D010011:Osteocytes / Q000378:metabolism; D013977:Tibia / Q000378:metabolism; D060449:Wnt Signaling Pathway; D000097006:Gap Junction alpha-4 Protein
chemical_list: D003094:Collagen; D017630:Connexins; D006025:Glycosaminoglycans; D000097006:Gap Junction alpha-4 Protein
keywords: Bone; Collagen; Connexin 37; Glycosaminoglycans; Osteocytes; Wnt/β-catenin signaling