Project Summary

More than 2 million elderly people a year in the United States experience a fragility fracture.1 Bone fractures significantly reduce quality of life and increase mortality.1 The public health impact of age-related bone fragility is especially great in Montana, where over 18% of the population is 65+ and in many rural towns exceeds 25%.2 Bone fragility is often not adequately managed by currently available treatments. Osteoporosis treatments (i.e., bisphosphonates) suffer from low rates of patient adherence to treatment plans because of fear of serious side effects, inconvenient dosage schedule, and drug cost.3-4 Furthermore, at the time these drugs are clinically-indicated, a substantial amount of bone mass and quality are already lost because of dysregulated bone remodeling cells.12-13 An alternative approach to managing bone fragility is to focus on maintaining the viability and regulation of bone remodeling cells during aging.

The gut microbiome may play a pivotal role in modulating the health of bone remodeling cells in aging. Loss of gut microbiome diversity (dysbiosis) is common in aging. The effects of antibiotic-induced dysbiosis on bone in young adult mice resemble some features of the loss of bone mass and bone quality in aging.49-53 The osteocyte, the most abundant bone cell and master orchestrator of bone remodeling,6 may be the connection between gut microbiome dysbiosis and age-related bone changes. The gut microbiome manufactures vitamin K2, which is critical for in vitro osteocyte differentiation7 and promotes osteocyte viability in disuse models.8 Furthermore, our preliminary data demonstrate that osteocyte lacunar-canalicular system (LCS) architecture for germ-free mice resembles the phenotype seen in aging. It is not understood whether microbiome dysbiosis specifically impacts either osteocyte viability, osteocyte-mediated bone remodeling, or resulting bone quality.

We address two critical gaps in the proposed research: (1) whether osteocyte viability and remodeling behavior are impacted by microbiome dysbiosis, and (2) whether probiotic treatment mitigates loss of osteocyte-mediated bone fracture resistance in aging. The overarching hypothesis is that microbiome dysbiosis causes osteocyte apoptosis, decreases LCS remodeling activity, and dysregulates osteocyte coordination of other bone cells. It is further hypothesized that probiotic treatment during aging mitigates deleterious changes to osteocyte viability, remodeling, and bone fracture resistance.

This project is innovative in evaluating whether the osteocyte links microbiome dysbiosis with loss of bone mass and bone quality. Several approaches, including measuring osteocyte lacunar-canalicular bone formation and resorption together with lacunar morphology, are novel to this proposal. The key significance of this project is to evaluate the role of the osteocyte in bone-microbiome interactions. This project is further significant in evaluating whether probiotics reduce age-related decline in osteocyte function and bone fracture resistance. This knowledge may translate to improved recommendations to aging patients in rural communities for maintaining bone health. The long-term goal of this research direction is to investigate whether osteocyte behavior can be modulated to maintain or restore bone fracture resistance in aging. Data and methods generated from this Montana INBRE Pilot Research Project will be used as a platform for R01 studies to investigate the effects of microbiome health on osteocyte-mediated bone quality in aging.

Project Aims

  1. Determine if gut microbiome dysbiosis decreases osteocyte-mediated bone quality.
    The motivation is that microbiome dysbiosis lowers bone quality and bone mass in manner consistent with age-related decline in osteocyte health. The hypothesis is that microbiome dysbiosis decreases osteocyte viability and thereby dysregulates bone remodeling. The approach is to induce microbiome dysbiosis through antibiotic treatment and evaluate osteocyte viability, osteocyte-mediated remodeling, and LCS architecture. The expected outcome is that antibiotic treatment will increase osteocyte apoptosis and senescence, increase osteoclast remodeling, decrease LCS remodeling, and truncate LCS network architecture. It is further expected that truncated LCS networks will also have low LCS bone remodeling. The significance is that the osteocyte may be involved in the loss of bone mass and bone quality induced by microbiome dysbiosis.
  2. Evaluate if probiotics improve osteocyte-mediated bone quality in aging. The motivation is that the osteocyte may be the link between dysbiosis in aging and loss of bone fracture resistance. The hypothesis is that microbiome dysbiosis in aging reduces osteocyte viability and remodeling, with deleterious impact to bone mass and bone quality. The approach is to administer a probiotic bacterial strain from middle-age through old-age in mice. The expected outcome is that probiotic treatment will mitigate microbial dysbiosis as well as increase osteocyte viability, osteocyte-mediated remodeling, bone mass and bone quality. The significance is that determining whether age-related changes to the osteocyte are attributable to dysbiosis will advance guidance for maintaining bone fracture resistance into old age.