Type III Collagen Regulates Osteoblastogenesis and the Quantity of Trabecular Bone

Abstract

Type III Collagen (Col3), a fibril-forming collagen, is a major extracellular matrix component in a variety of internal organs and skin. It is also expressed at high levels during embryonic skeletal development and is expressed by osteoblasts in mature bone. Loss of function mutations in the gene encoding Col3 (Col3a1) are associated with vascular Ehlers Danlos Syndrome (EDS). Although the most significant clinical consequences of this syndrome are associated with catastrophic failure and impaired healing of soft tissue structures, several studies have documented skeletal abnormalities in vascular EDS patients. However, there are no reports of the role of Col3 deficiency on the murine skeleton. We compared craniofacial and skeletal phenotypes in young (6-8 weeks) and middle-aged (>1 year) control (Col3+/+) and haploinsufficient (Col3+/−) mice, as well as young null (Col3−/−) mice using microcomputed tomography (μCT). Although Col3+/− mice did not have significant craniofacial abnormalities based upon cranial morphometrics, microCT analysis of distal femur trabecular bone demonstrated significant reductions in bone volume (BV), bone fraction volume (BV/TV), connectivity density (ConnD), structure model index (SMI) and trabecular thickness (TbTh) in young adult, female Col3+/− mice relative to wild-type littermates. The reduction in BV/TV persisted in female mice at one year of age. Next we evaluated the role of Col3 in vitro. Osteogenesis assays revealed that cultures of mesenchymal progenitors harvested from Col3−/− embryos display decreased alkaline phosphatase activity and reduced capacity to undergo mineralization. Consistent with this data, a reduction in osteogenic markers (type I collagen, osteocalcin and bone sialoprotein) correlates with reduced bone Col3 expression in Col+/− mice and with age in vivo. A small but significant reduction in osteoclast numbers was found in Col3+/− compared to Col3+/+ bones. Taken together, these findings indicate that Col3 plays a role in development of trabecular bone through its effects on osteoblast differentiation.

Type III collagen modulates fracture callus bone formation and early remodeling

“…Previously, Col3 haploinsufficient mice were found to express half the amount of Col3 in tissues compared to wild-type littermates 9; 28; 29 . Our recent work confirmed that Col3 expression in long bones of Col3+/− mice is approximately half of that seen in Col3+/+ mice 11 . In this study, using a bilateral closed, transverse tibial fracture mouse model, we show that diminished Col3 leads to decreased bone formation and alterations in remodeling during fracture healing.…”

“…Specifically, Col3 deficiency results in increased scar deposition by promoting differentiation of myofibroblasts, the key cells that influence pathologic scarring. Furthermore, we have recently shown that Col3 regulates osteoblastogenesis and the quantity of trabecular bone 11 . In addition to its expression in the early fracture callus 4; 12 , several lines of evidence support a role for Col3 in repair and maintenance of bone, including its requirement for growth acceleration of osteoblasts 13 , its potential role in preserving osteogenic potential of mesenchymal stem cells 14 , and its ability to increase angiogenesis 15 .…”

“…Because of the potential clinical relevance of diminished rather than absent Col3, the poor survival of Col3-null mice (<5% beyond weaning 9; 11 ), and the current lack of availability of conditional Col3 transgenic mice, fracture repair was assessed in Col3 wild-type and haploinsufficient littermates. Previously, Col3 haploinsufficient mice were found to express half the amount of Col3 in tissues compared to wild-type littermates 9; 28; 29 .…”

Extracellular matrix networks in bone remodeling

“…Type III collagen is produced in bone, particularly during healing. Type III collagen mice are embryonic lethal, but analysis of null cells in culture or heterozygous mice suggests that type III collagen promotes differentiation (Volk et al, 2014). The matricellular proteins SPARC (osteonectin) and thrombospondin-2 (Alford et al, 2013) have been implicated in collagen fiber assembly (Alford et al, 2013;Bornstein, 2000;Harris et al, 2011;Rentz et al, 2007;Bradshaw et al, 2003), and also modulate osteoblast lineage progression (Hankenson and Bornstein, 2002;Hankenson et al, 2000;Alford et al, 2009;Delany et al, 2003Delany et al, , 2000.…”

Bone marrow mesenchymal stem cells combine with Treated dentin matrix to build biological root

“…By contrast, the content of COL-III is far less than that of COL-I. COL-III could be detected in dental pulp and periodontium and it plays a role in the development of trabecular bone through its effects on osteoblast differentiation33. TGF-β1 appeared in tooth morphogenesis and odontoblast differentiation during embryogenesis and could also be detected immunohistochemically in mature human teeth3435.…”