# Sijing Pill modulates PGE2/EP4/PI3K-AKT pathway via gut-bone axis to treat postmenopausal osteoporosis

## TL;DR

Sijing Pill helps treat postmenopausal osteoporosis by modulating gut and bone pathways, reducing inflammation and improving bone structure.

## Contribution

The study reveals a novel dual mechanism of Sijing Pill involving the gut-bone axis and PGE2/PI3K-AKT signaling in treating PMOP.

## Key findings

- Sijing Pill alleviates bone loss and abnormal weight gain in ovariectomized rat models.
- SJP modulates gut microbiota and intestinal barrier function, impacting bone metabolism via the gut-bone axis.
- Molecular docking confirms key bioactive components bind to COX2 and PTGES, influencing PGE2 metabolism.

## Abstract

Postmenopausal osteoporosis (PMOP) represents a substantial clinical burden for aging women worldwide. Existing pharmacotherapies are frequently constrained by suboptimal efficacy, poor adherence, and adverse effects, underscoring the need for superior treatment alternatives. The Sijing Pill (SJP) has shown potential in alleviating bone loss in PMOP. However, the fundamental mechanisms underlying its therapeutic effects remain incompletely elucidated, which has impeded its clinical translation and rational application.

The therapeutic effect of SJP on PMOP was first evaluated in ovariectomized (OVX) rat models using hematoxylin and eosin (H&E) staining, micro-computed tomography (μCT), and immunohistochemistry. To investigate the mechanisms, we employed an integrated strategy that combined network pharmacology, molecular docking and dynamics simulations, 16S rRNA sequencing, as well as non-targeted metabolomics coupled with MetOrigin analysis. The key predictions from these analyses were subsequently validated by Western blot and immunohistochemistry.

This research confirms that SJP treatment significantly alleviates abnormal weight gain and bone structural degeneration in OVX model mice. Employing an integrated multi-omics strategy, we elucidated a dual mechanism underlying the efficacy of SJP. This mechanism involves the concurrent modulation of the arachidonic acid-PGE2 metabolic axis, which ameliorates osteometabolic inflammation, alongside the remodeling of the gut microbiota, as evidenced by a decreased Firmicutes/Bacteroidetes ratio. Collectively, these factors orchestrate therapeutic effects through the gut-bone axis. Network pharmacology identified 18 bioactive components in SJP with predicted affinities for key signaling nodes, including STAT3, ESR1, and AKT1. Molecular docking confirmed high-affinity binding for pivotal pairs. Specifically, strong binding was observed between Ellipticine and COX2 (−10.6 kcal/mol) and between estrone and PTGES (−7.8 kcal/mol), implicating both in PGE2 metabolism. Functionally, SJP promoted intestinal barrier repair by upregulating ZO-1 and Occludin. In parallel, it activated the bone-specific PGE2-EP4 receptor axis and downstream PI3K-AKT signaling, thereby elucidating a direct mechanistic link through the gut-bone axis.

Sijing Pill modulates the PGE2/EP4/PI3K-AKT signaling pathway via the gut-bone axis to aid in alleviating PMOP.

Diagram illustrating the mechanism by which Sijing Pill treatment in a mouse model alleviates postmenopausal osteoporosis by modulating gut microbiota, intestinal integrity, and bone metabolism pathways, highlighting key molecular changes such as increased beneficial microbes, prostaglandin E2, EP4 signaling, and activation of downstream targets EGFR, AKT, and RUNX2.