Long non-coding RNA antisense of insulin-like growth factor 2 receptor promotes osteogenic differentiation by enhancing runt-related transcription factor 2 translation: A potential therapeutic target for osteoporosis.

INTRODUCTION

Osteoporosis is a chronic metabolic disorder characterized by progressive bone loss and increased susceptibility to fractures, for which there is currently no curative treatment that can fully reverse or eliminate the disease.

OBJECTIVES

This study aims to elucidate the regulatory role of antisense of insulin-like growth factor 2 receptor non-protein coding RNA (AIRN) in osteogenesis and the pathogenesis of osteoporosis.

METHODS

Multiple in vivo models of osteoporosis, including tail suspension, ovariectomy, and natural aging, were employed to evaluate the impact of Airn knockout or overexpression on bone formation. A comprehensive array of in vitro assays, including alkaline phosphatase staining, quantitative PCR, Western blotting, bioinformatics analysis, mRNA stability assays, RNA fluorescence in situ hybridization, RNA immunoprecipitation, and luciferase reporter assays, were conducted to investigate the functional mechanisms of AIRN.

RESULTS

We found that Airn is highly enriched in osteogenic lineage cells, significantly upregulated during osteoblast differentiation, and notably downregulated in osteoporotic bone tissue. In vivo, Airn knockout led to impaired bone formation and aggravated bone loss across all three osteoporosis models. Furthermore, AAV9-mediated intratibial overexpression of Airn significantly promoted bone formation and attenuated tail suspension-induced osteoporosis. In vitro, Airn overexpression enhanced the expression of osteogenic marker genes, whereas AIRN knockdown suppressed their expression. Mechanistically, Airn binds to polypyrimidine tract binding protein 1 (PTBP1) and facilitates internal ribosome entry site (IRES)-mediated translation of runt-related transcription factor 2 (Runx2) by enhancing IRES activity within the 5' untranslated region of Runx2 mRNA. Additionally, our data demonstrated that the upregulation of Airn during osteogenic differentiation is orchestrated by RUNX1.

CONCLUSION

Our findings identify Airn as a critical regulator of osteoblast differentiation. Its regulatory effect on Runx2 translation via PTBP1 highlights a novel mechanism underlying osteogenesis and suggests that Airn may serve as a potential therapeutic target for the treatment of osteoporosis.