Targeting the STK39/ARID2 Axis to Inhibit NF-κB Signaling: A Novel Pathway for Mesenchymal Stem Cell Osteogenic Differentiation in Osteoporosis Management

IntroductionOsteoporosis (OP) is a chronic metabolic bone disease characterized by decreased bone density and disrupted bone microarchitecture, resulting in increased fracture risk and contributing substantially to morbidity and mortality in older adults 1 .Current therapies for OP include bisphosphonates, denosumab, teriparatide, abaloparatide, romosozumab, and selective estrogen receptor modulators 1 , all of which aim to prevent fractures by either reducing bone resorption or promoting bone formation 2 .Bone marrow-derived mesenchymal stromal cells (BMSCs) are multipotent stromal cells with self-renewal capacity and multilineage differentiation potential 3 .Under osteogenic induction, BMSCs differentiate into osteoblasts that deposit mineralized bone matrix and support bone formation 4 .Dysregulated BMSC differentiation is implicated in OP: osteogenic differentiation is attenuated, whereas adipogenic commitment is favored, leading to reduced bone formation and increased marrow adipose tissue 5,6 .Given the potential adverse effects associated with long-term pharmacologic therapy 5 , contemporary research on OP increasingly focuses on molecular mechanisms underlying the osteo-adipogenic imbalance in mesenchymal stromal cells (MSCs) and marrow adipose tissue 7 .STK39, also known as SPAK, is a STE20/SPS1-related proline/alanine-rich kinase that contains a putative nuclear localization signal and a caspase-cleavage site separating Abstract Objectives: Osteoporosis (OP) is a prevalent bone disease characterized by reduced bone mass and increased fracture risk, in part due to impaired osteogenic differentiation of bone marrow-derived mesenchymal stromal cells (BMSCs).Loss of AT-rich interactive domain-containing protein 2 (ARID2) attenuates BMSC osteogenesis, but the underlying mechanism remains to be elucidated.Methods: Human BMSCs were induced to undergo osteogenic or adipogenic differentiation.Lentiviral transduction was used to silence ARID2 and/or overexpress serine/threonine kinase 39 (STK39).Effects on BMSC fate were assessed by quantitative reverse-transcription PCR (qRT-PCR), MTT assay, alkaline phosphatase (ALP) staining, Alizarin Red S (ARS) staining, Oil Red O staining, and western blotting.Results: ARID2 expression increased over time during osteogenic induction.ARID2 silencing reduced BMSC proliferation and osteogenic differentiation while favoring adipogenesis.Conversely, STK39 overexpression enhanced proliferation and osteogenic differentiation and attenuated nuclear factor κB (NF-κB) signaling during osteogenic induction; these effects were reversed by ARID2 silencing.Conclusion: The STK39-ARID2 axis promotes osteogenic differentiation and suppresses adipogenic differentiation of BMSCs, at least in part via inhibition of NF-κB signaling.These findings highlight a potential molecular target for therapeutic strategies in OP.