Preparation and physicochemical characterization of polysaccharides from Auricularia auricula and their osteogenic potential in vitro and in vivo

Postmenopausal osteoporosis (PMOP) imposes a significant health burden due to estrogen deficiency-induced bone loss. Auricularia auricula polysaccharide (AAP), a traditional edible fungal component, has shown anti-oxidant and anti-inflammatory properties, yet its potential osteoprotective effects remain insufficiently characterized. Here, ultrasound-assisted enzymatic extraction of AAP was optimized using a Box-Behnken design. Following slight practical adjustment of the response-surface-predicted optimal conditions, the experimental extraction yield of AAP reached 30.15 ± 0.48%. Physicochemical characterization identified AAP as an acidic heteropolysaccharide with molecular weights ranging from 976 to 1.5 × 10 6 Da, enriched in glucose and uronic acid residues. In the ovariectomized (OVX) rat model, high-dose AAP (500 mg/kg) attenuated bone loss under the tested conditions, while no increase in uterine index was observed. Mechanistic studies provided evidence that the IGF-1/IGF-1R signaling axis is involved in AAP-induced osteogenic differentiation, as supported by increased phosphorylation of IGF-1R and its downstream signaling molecules and by IGF-1R knockout experiments. In vitro simulated gastrointestinal digestion further showed that AAP retained measurable osteogenic activity after digestion. These findings support the potential of AAP as a functional food ingredient for supporting bone health.