GPR109A mediates the effects of hippuric acid on regulating osteoclastogenesis and bone resorption in mice

Authors: CHEN, JIN-RAN - Arkansas Children'S Nutrition Research Center (ACNC); ZHAO, HAIJUN - Arkansas Children'S Nutrition Research Center (ACNC); WANKHADE, UMESH - Arkansas Children'S Nutrition Research Center (ACNC); CHINTAPALLI, SREE - Arkansas Children'S Nutrition Research Center (ACNC); LI, CAN - University Arkansas For Medical Sciences (UAMS); GAI, DONGZHENG - University Arkansas For Medical Sciences (UAMS); SHANKAR, KARTIK - Arkansas Children'S Nutrition Research Center (ACNC); ZHAN, FENGHUANG - University Arkansas For Medical Sciences (UAMS); LAZARENKO, OXANA - Arkansas Children'S Nutrition Research Center (ACNC)

Submitted to: Communications Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2020
Publication Date: 1/8/2021
Citation: Chen, J., Zhao, H., Wankhade, U.D., Chintapalli, S.V., Li, C., Gai, D., Shankar, K., Zhan, F., Lazarenko, O.P. 2021. GPR109A mediates the effects of hippuric acid on regulating osteoclastogenesis and bone resorption in mice. Communications Biology. 4:53. https://doi.org/10.1038/s42003-020-01564-2.
DOI: https://doi.org/10.1038/s42003-020-01564-2

Interpretive Summary: A protein called the G protein-coupled receptor 109A (GPR109A) is robustly expressed in cells that participate in bone breakdown (called osteoclast precursor macrophages), but it is not known how this receptor plays a role in bone metabolism and bone health. It is important to ask this question since GPR109A appears to be a target of certain molecules derived from healthy foods such as blueberries. Using a GPR109A gene deletion mouse model, it was found that bone mass is significantly higher in tibia bone and spine of 4-week-old GPR109A gene deletion mice compared to their wild type controls. We found that loss of GPR109A gene expression decreased osteoclast gene expression, which may help explain the observed increase in bone mass. Finally, we identified phenolic acid metabolites such as hippuric acid (HA) and 3-(3-hydroxyphenyl) propionic acid (3-3-PPA), that are rich in blueberries, can regulate GPR109A expression in osteoclast cells. Treatment with dietary HA inhibits osteoclast formation and increases bone mass in wildtype mice but not in GPR109A gene deletion mice. These results suggest an important role for GPR109A during osteoclast differentiation and bone resorption, and that GPR109A may mediate the effects of fruit-derived HA and 3-3-PPA on promoting net bone growth. The novel findings are the first to identify a specific pathway by which healthy fruits can promote bone growth, which if seen in humans could be a dietary means to improve bone health across the lifespan.

Technical Abstract: The G protein-coupled receptor 109A (GPR109A) is robustly expressed in osteoclastic precursor macrophages. Previous studies suggested that GPR109A mediates effects of diet-derived phenolic acids such as hippuric acid (HA) and 3-(3-hydroxyphenyl) propionic acid (3-3-PPA) on promoting bone formation. However, the role of GPR109A in metabolic bone homeostasis and osteoclast differentiation has not been investigated. Using densitomeric, bone histologic and molecular signaling analytic methods, we uncovered that bone mass is significantly higher in tibia and spine of standard rodent diet weaned 4-week-old GPR109A gene deletion (GPR109A-/-) mice, compared to their wild type controls. Osteoclast numbers in bone and in ex vivo bone marrow cell cultures were significantly decreased in GPR109A-/- animals compared to wild type controls. In accordance with these data, CTX-1 in bone marrow plasma and gene expression of bone resorption markers (TNFa, TRAP, Cathepsin K) were significantly decreased in GPR109A-/- mice compared to their wild type controls. GPR109A deletion led to increased extracellular cAMP levels to suppress Wnt/B-catenin signaling in osteoclast precursors. HA and 3-3-PPA substantially inhibited RANKL-induced GPR109A expression and osteoclast differentiation. Resultantly, HA significantly inhibited bone resorption and increased bone mass in wild type mice, but had no additional effects on bone in GPR109A-/- mice compared with their respective untreated control mice. These results suggest an important role for GPR109A during osteoclast differentiation and bone resorption, and GPR109A may mediate effects of HA and 3-3-PPA on inhibiting bone resorption during skeletal development.