(PTFS03-02-25) GOS Regulates Bone Mineralization and Ossification Pathways in Intestinal Myeloid Cells: Novel Insights Into the Gut-Bone Axis in Estrogen Deficiency

Objectives: The decline in estrogen with menopause is linked to a proinflammatory state that contributes to osteoporosis. This study aimed to investigate how targeting gut-derived immunomodulators with the prebiotic, galactooligosaccharide (GOS), alters bone and the gut mucosal immune response in ovariectomized (OVX) mice.

Methods: Fourteen-wk-old C57BL/6 female mice underwent OVX or SHAM surgery and were fed AIN-93M control (CON) diet for 2 wks to allow bone loss. Then, OVX and SHAM mice were fed dietary treatments: 8% GOS-supplemented or CON diets (n=12/grp) for 6 wks. Bone mineral density (BMD) and trabecular and cortical bone morphology were assessed using dual-energy x-ray absorptiometry and micro-computed x-ray tomography. Serum bone markers were assessed by ELISA and cytokines with multiplex assays. Total mRNA was isolated from ileal lamina propria for RNA-sequencing. Unsupervised deconvolution of bulk RNAseq data was used to assess myeloid populations; differentially expressed genes (DEGs) were subjected to pathway enrichment analysis. All other data were analyzed using 2-way ANOVA or non-parametric tests.

Results: GOS supplementation improved whole body (P < 0.01), spine (P < 0.05), and femur (P < 0.0001) BMD in the OVX mice. In OVX-GOS mice, femoral trabecular bone volume and cortical thickness were restored to the SHAM-CON. Overall, the magnitude GOS’s effects on bone was greater in the SHAM compared to OVX.
Interestingly, the bone formation marker, N-terminal pro-peptide of type-1 collagen was decreased (P < 0.0001) with GOS. The OVX-induced increase in serum C-terminal telopeptides of type 1-collagen (P < 0.05), a bone resorption marker was suppressed in OVX mice fed the GOS diet. GOS also increased (P < 0.01) serum IL-10 in OVX mice.  In the lamina propria, OVX increased granulocytes (e.g., neutrophils; P < 0.05) and decreased dendritic cells expressing CD81 (P < 0.05); GOS normalized these responses. The highest number of DEGs in ileal myeloid cells were found in the OVX-CON vs. OVX-GOS comparisons, with GOS enriching DEGs in bone mineralization and ossification pathways.

Conclusions: These data provide new insights into the gut-bone axis in estrogen deficiency, whereby GOS improves bone while regulating pathways linked to bone mineralization and ossification in myeloid cells.

Funding Sources: Funded by NIH/NIA and SUNY Research Seed Grant