Hydrothermal Magnesium Alloy Extracts Modulate MicroRNA Expression in RAW264.7 Cells: Implications for Bone...

Magnesium (Mg) alloys, particularly Mg AZ31, have emerged as promising biomaterials for orthopedic applications due to their biodegradability and favorable mechanical characteristics. Among these, the Mg AZ31+SPF alloy, subjected to hydrothermal (HT) treatment, has demonstrated enhanced bioactivity. Our previous research established that this surface modification supports the osteogenic differentiation of human mesenchymal stem cells (hMSCs) by modulating both canonical and non-canonical signaling pathways, including those implicated in osteogenesis, hypoxic response, exosome biogenesis, and lipid metabolism. In the present study, we extended our investigation to assess the effects of Mg AZ31+SPF+HT and Mg AZ31+SPF extracts on murine pre-osteoclasts (RAW 264.7 cells) over 3- and 6-day treatment periods. The primary objectives were to evaluate biocompatibility and to investigate potential impacts on osteoclastogenesis induction and miRNA expression profiles.

To assess cytocompatibility, metabolic activity, DNA integrity, and morphological alterations in RAW 264.7 cells were evaluated. Osteoclast differentiation was quantified using TRAP staining, alongside the assessment of osteoclastogenic marker expression by qRT-PCR and ELISA. The immunomodulatory properties of the extracts were examined using multiplex BioPlex assays to quantify soluble factors involved in bone healing. Additionally, global miRNA expression profiling was performed using a specialized panel targeting 82 microRNAs implicated in bone remodeling and inflammatory signaling.

Mg AZ31+SPF+HT extract exhibited high biocompatibility, with no observable adverse effects on cell viability. Notably, a significant reduction in the number of TRAP-positive and multinucleated cells was observed relative to the Mg AZ31+SPF group. This effect was corroborated by the downregulation of osteoclast-specific gene expression and decreased MMP9 protein levels. Cytokine profiling indicated that Mg AZ31+SPF+HT extract promoted an earlier release of key cytokines involved in maintaining the balance between bone formation and resorption, suggesting a beneficial role in bone healing. Furthermore, miRNA profiling revealed a distinct regulatory signature in Mg AZ31+SPF+HT-treated cells, with differentially expressed miRNAs associated with inflammation, osteoclast differentiation, apoptosis, bone resorption, hypoxic response, and metabolic processes compared to Mg AZ31+SPF-treated cells.

Collectively, these findings indicate that hydrothermal treatment of Mg AZ31+SPF (resulting in Mg AZ31+SPF+HT) attenuates pre-osteoclast activation by influencing cellular morphology, gene and protein expression, as well as post-transcriptional regulation via modulation of miRNAs. The preliminary identification of miRNAs and the activation of their regulatory networks in pre-osteoclasts exposed to hydrothermally treated Mg alloy are described herein. In the context of orthopedic surgery-where balanced bone remodeling is imperative-our results emphasize the dual significance of promoting bone formation while modulating bone resorption to achieve optimal implant integration and ensure long-term bone health.