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Principal Investigator: Kin-Hing William Lau
Organization: VA LOMA LINDA HEALTHCARE SYSTEM
Fiscal Year: 2024
Funding agency: Veterans Affairs
The healing of ~10% of several million traumatic or nontraumatic fractures occurring annually in the US is
delayed or impaired resulting in nonunion or delayed union. The annual cost for their treatment and management
exceeds $20 billion, leading to considerable healthcare costs and human suffering. A good understanding of the
mechanism of fracture healing is critical for the development and proper use of novel and effective therapies.
Fracture healing is a complex and dynamic process with osteoclasts and osteoblasts playing indispensable roles.
The critical core of fracture healing is the callus remodeling, which is initiated with resorption of the cartilaginous
callus followed by the coupled formation of bony callus that subsequently is remodeled to cortical bone
indistinguishable from the native bone. The osteoclastic regulation of the local coupled bone formation is in part
mediated through local release of osteoclastic soluble osteoanabolic factors and is an integral regulatory
mechanism of callus remodeling. This study tests two specific hypotheses that are relevant to the osteoclastic
regulation of local bone formation/regeneration: Hypothesis 1. Local injections of osteoclastic microvesicles (MV)
into fractures accelerates the healing of skeletal fractures by accelerating fracture callus formation and
remodeling. This hypothesis is supported by the following preliminary findings: 1) osteoclasts released soluble
MV that have pro-osteogenic, pro-chondrogenic, and pro-angiogenic activities, 2) injections of osteoclastic MV
at the surface of calvaria stimulated local bone formation, and 3) injections of MV into fractures promoted neo-
angiogenesis in fracture callus and accelerated fracture healing. Hypothesis 2. EfnB2 is a key osteoanabolic
component of osteoclastic MV and is in part responsible for the osteoanabolic actions of osteoclastic MV.
Accordingly, a review of current literature and the following preliminary data suggest that EfnB2 is an attractive
candidate of an osteoanabolic component of osteoclastic MV: 1) osteoclastic MV contains appreciable amounts
of EfnB2, 2) pretreatment of MV with anti-EfnB2 antibody abrogated its osteogenic activity, 3) EfnB2-deficient
MV had reduced osteogenic and fracture healing activities, whereas MV from osteoclasts overexpressing EfnB2
showed greater osteoanabolic activity, 4) pretreatment of osteoprogenitors with anti-EphB4 antibody prevented
osteoclastic MV to exert its osteogenic activity. Aim 1 tests Hypothesis 1 by using a simple transverse femoral
fracture model to determine: a) an optimal injection regimen for osteoclastic MV by determining the duration-of-
stay of the MV after local injection at fracture site, optimal injection frequency, duration between injections, and
optimal dose range; b) if an optimized injection regimen of osteoclastic MV would accelerate bony bridging of
fracture gaps and increase torsional mechanical strength of fractured bones in male as well as female mice; and
c) the cellular mechanism by which osteoclastic MV accelerates fracture healing through histological and
immunohistochemical analyses of time-dependent effects of the MV treatment on osteoclasts, osteoblasts, and
chondrocytes during the various fracture healing phases. Aim 2 tests Hypothesis 2 by determining: a) if treatment
of osteoblasts, chondrocytes, and endothelial cells with osteoclastic MV in vitro upregulates their EphB4 forward
signaling; b) if MV of EfnB2-deficient osteoclasts would show diminished osteogenic, chondrogenic, and
angiogenic activities of osteoclastic MV in vitro; c) if MV of osteoclasts with EfnB2 overexpression exhibited
enhanced chondrogenic, and angiogenic activities in vitro; d) if osteoblasts, chondrocytes, and endothelial cells
isolated from EphB4-deficient mice show reduced osteogenic, chondrogenic, and angiogenic in response to
osteoclastic MV in vitro; and e) if local injections of MV deficient in EfnB2 impedes, and local injections of MV
with EfnB2 overexpression accelerates, fracture healing. If successful, this study could offer key mechanistic
insights into how osteoclasts regulate local bone regeneration. It may also help to develop novel osteoclastic
MV-based therapies for fracture healing and local bone regeneration.
Terms: <Acceleration><Antibodies><Bone Formation><Bone Regeneration><Bone callus><Bony Callus><C57BL/6 Mouse><Callus><Calvaria><Cartilage><Cartilaginous Tissue><Causality><Cell Body><Cell Communication and Signaling><Cell Function><Cell Isolation><Cell Physiology><Cell Process><Cell Segregation><Cell Separation><Cell Separation Technology><Cell Signaling><Cells><Cellular Function><Cellular Physiology><Cellular Process><Chondrocytes><Complex><Coupled><Data><Defect><Development><Differentiation and Growth><Dose><Economics><Endothelial Cells><Etiology><Exhibits><Fatigue Fractures><Female><Femoral Fractures><Fracture><Fracture Healing><Fracture due to osteoporosis><Frequencies><Gender><Health><Health Care Costs><Health Costs><Healthcare><Healthcare Costs><Histologic><Histologically><Human><Impairment><In Vitro><Injections><Intracellular Communication and Signaling><Ligands><Link><Literature><March Fractures><Mechanics><Mediating><Membrane><Mice><Mice Mammals><Mission><Modeling><Modern Man><Murine><Mus><Natural regeneration><Osteoblasts><Osteoclasts><Osteogenesis><Osteoporosis with fracture><Osteoporotic fracture><Patient Care><Patient Care Delivery><Patients><Phase><Physiologic Ossification><Physiological Ossification><Play><Process><Property><QOL><Quality of life><Receptor Protein><Regeneration><Regimen><Regulation><Research><Risk Factors><Role><Signal Transduction><Signal Transduction Systems><Signaling><Site><Sprague-Dawley Rats><Stress Fractures><Subcellular Process><Surface><Testing><Therapeutic><Time><Work><adult youth><angiogenesis><biological signal transduction><bone><bone cell><bone fracture><bone fracture healing><bone fracture repair><bone healing><bone strength><bone tissue formation><bone wound healing><calvarial><care for patients><care of patients><caring for patients><cartilaginous><causation><cell sorting><cell type><cohort><compact bone><cortical bone><cost><developmental><differentiation factors><disease causation><economic><effective therapy><effective treatment><elderly patient><femur fracture><fracture repair><healing><health care><improved><in vitro activity><in vivo><insight><male><mechanic><mechanical><membrane structure><microvesicles><military service><morphogenic factors><morphogens><neovascularization><new drug treatments><new drugs><new pharmacological therapeutic><new therapeutics><new therapy><next generation therapeutics><normal ossification><novel><novel drug treatments><novel drugs><novel pharmaco-therapeutic><novel pharmacological therapeutic><novel therapeutics><novel therapy><older patient><osseous wound healing><ossification><osteogenic><osteoporosis associated fracture><osteoporosis related fracture><osteoporosis with pathological fracture><osteoprogenitor><osteoprogenitor cell><overexpress><overexpression><patient population><prevent><preventing><receptor><regenerate><regenerate bone><response><sex><skeletal><social role><vesicle release><vesicular release><young adult><young adulthood>