Paeonol ameliorates postmenopausal hyperlipidemia by inhibiting COX-2 to suppress GRP78-mediated endoplasmic reticulum stress

Paeonol (Pae), a primary bioactive constituent of the root of Paeonia suffruticosa Andrews, shows therapeutic potential for postmenopausal hyperlipidemia. Ovariectomized apoE^-/- mice fed a high-fat diet and HepG2 cells with palmitate-induced steatosis were employed to evaluate the effects of Pae on lipid metabolism and elucidate the underlying mechanisms. Integrated computational and biophysical approaches established cyclooxygenase-2 (COX-2) as a high-affinity target of Pae, evidenced by a high molecular docking score (-6.3 kcal/mol), stable binding dynamics in molecular dynamics simulations, and direct target engagement, confirmed through a cellular thermal shift assay (ΔTm = + 4.2 °C). Pae treatment (200 and 400 mg/kg) significantly reduced hepatic lipid accumulation, the liver/body weight ratio, and serum levels of total Cholesterol, triglycerides, and low-density lipoprotein Cholesterol levels, showing with efficacy comparable to that of 17β-estradiol. Mechanistically, Pae alleviated lipid accumulation by inhibiting COX-2, an upstream regulator that drives endoplasmic reticulum stress (ERS) via upregulation of the key sensor glucose-regulated protein 78 (GRP78). This COX-2/GRP78 axis further modulated the unfolded protein response (UPR), evidenced by the coordinated downregulation of key UPR transcription factors spliced X-box binding protein 1 and activating transcription factor 4 following Pae treatment in vivo and in vitro. Genetic silencing of COX-2 reproduced the therapeutic effects, confirming its role in the ERS/UPR network. Importantly, fulvestrant blockade experiments confirmed that this axis functioned is independently of Estrogen receptor signaling. These results demonstrate that Pae alleviates postmenopausal hyperlipidemia by targeting the COX-2/GRP78-mediated ERS/UPR cascade, offering a promising estrogen receptor-independent alternative to hormone replacement therapy.