title: Combined exposure to big endothelin-1 and mechanical loading in bovine sternal cores promotes osteogenesis.
abstract: Increased bone formation resulting from mechanical loading is well documented; however, the interactions of the mechanotransduction pathways are less well understood. Endothelin-1, a ubiquitous autocrine/paracrine signaling molecule promotes osteogenesis in metastatic disease. In the present study, it was hypothesized that exposure to big endothelin-1 (big ET1) and/or mechanical loading would promote osteogenesis in ex vivo trabecular bone cores. In a 2×2 factorial trial of daily mechanical loading (-2000με, 120cycles daily, "jump" waveform) and big ET1 (25ng/mL), 48 bovine sternal trabecular bone cores were maintained in bioreactor chambers for 23days. The bone cores' response to the treatment stimuli was assessed with percent change in core apparent elastic modulus (ΔEapp), static and dynamic histomorphometry, and prostaglandin E2 (PGE2) secretion. Two-way ANOVA with a post hoc Fisher's LSD test found no significant treatment effects on ΔEapp (p=0.25 and 0.51 for load and big ET1, respectively). The ΔEapp in the "no load + big ET1" (CE, 13±12.2%, p=0.56), "load + no big ET1" (LC, 17±3.9%, p=0.14) and "load + big ET1" (LE, 19±4.2%, p=0.13) treatment groups were not statistically different than the control group (CC, 3.3%±8.6%). Mineralizing surface (MS/BS), mineral apposition (MAR) and bone formation rates (BFR/BS) were significantly greater in LE than CC (p=0.037, 0.0040 and 0.019, respectively). While the histological bone formation markers in LC trended to be greater than CC (p=0.055, 0.11 and 0.074, respectively) there was no difference between CE and CC (p=0.61, 0.50 and 0.72, respectively). Cores in LE and LC had more than 50% greater MS/BS (p=0.037, p=0.055 respectively) and MAR (p=0.0040, p=0.11 respectively) than CC. The BFR/BS was more than two times greater in LE (p=0.019) and LC (p=0.074) than CC. The PGE2 levels were elevated at 8days post-osteotomy in all groups and the treatment groups remained elevated compared to the CC group on days 15, 19 and 23. The data suggest that combined exposure to big ET1 and mechanical loading results in increased osteogenesis as measured in biomechanical, histomorphometric and biochemical responses.
authors: Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA. Electronic address: lameyer2@wisc.edu.
authors: Luisa A
authors: LA
authors: Meyer
authors: Department of Medicine, University of Wisconsin-Madison, Madison, WI 53706, USA; GRECC William S. Middleton Memorial Veterans Hospital, Madison, WI 53705, USA. Electronic address: mgjohnson@medicine.wisc.edu.
authors: Michael G
authors: MG
authors: Johnson
authors: Department of Biomedical Sciences, Creighton University, Omaha, NE 68178, USA. Electronic address: dcullen@creighton.edu.
authors: Diane M
authors: DM
authors: Cullen
authors: Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA. Electronic address: vivanco@wisc.edu.
authors: Juan F
authors: JF
authors: Vivanco
authors: GRECC William S. Middleton Memorial Veterans Hospital, Madison, WI 53705, USA; Department of Medicine, Medical College of Wisconsin, Milwaukee, WI 53226, USA; Department of Endocrinology, The Clement J. Zablocki VA Medical Center, Milwaukee, WI 53295, USA. Electronic address: roblank@mcw.edu.
authors: Robert D
authors: RD
authors: Blank
authors: Department of Mechanical Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA; Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA; Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison, Madison, WI 53706, USA. Electronic address: ploeg@engr.wisc.edu.
authors: Heidi-Lynn
authors: HL
authors: Ploeg
authors: Department of Population Health Sciences, University of Wisconsin-Madison, Madison, WI 53706, USA. Electronic address: elsmith1@wisc.edu.
authors: Everett L
authors: EL
authors: Smith
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000187:drug effects; D002417:Cattle; D003470:Culture Media; D015232:Dinoprostone / Q000378:metabolism; D055119:Elastic Modulus / Q000187:drug effects; D019332:Endothelin-1 / Q000494:pharmacology*; D010012:Osteogenesis / Q000187:drug effects*; D013249:Sternum / Q000187:drug effects / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D003470:Culture Media; D019332:Endothelin-1; D015232:Dinoprostone
keywords: Bioreactor; Endothelin; Mechanical loading; Osteogenesis; Trabecular bone