High‑fat diet exacerbates hepatic and adipose insulin signaling impairment and ovarian lesions in a rat model of letrozole‑induced polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a multifactorial endocrine disorder characterized by ovarian dysfunction and metabolic abnormalities, including insulin resistance. Letrozole (LET)‑based animal models reproduce hyperandrogenic features but often lack the metabolic phenotype of obesity‑associated PCOS. Therefore, in the present study, a high‑fat diet (HFD) was combined with LET and alterations in insulin signaling in metabolic tissues were examined. Female Sprague‑Dawley rats were assigned to control (CON), LET‑induced PCOS (LV) and HFD plus LV (HLV) groups. Body weight, fasting glucose, serum lipids, histology of the liver, visceral adipose tissue (VAT), ovaries and uterus, pancreatic and ovarian immunofluorescence, and hepatic and VAT quantitative PCR for insulin signaling markers were evaluated. Both LV and HLV groups showed increased body weight and fasting glucose, with impaired hepatic and VAT insulin receptor (INSR)/insulin receptor substrate 1 (IRS‑1)/phosphoinositide 3‑kinase (PI3K)/protein kinase B (AKT) signaling relative to the CON group, with no significant differences between the LV and HLV groups for these parameters. However, HLV further increased hepatic phosphoenolpyruvate carboxykinase and glucose‑6‑phosphatase, and VAT sterol regulatory element‑binding protein 1c and acetyl‑CoA carboxylase, beyond the levels observed in the LV group, and produced more severe hepatic steatosis and adipocyte hypertrophy compared with the LV group. Ovarian cytochrome P450 family 19 subfamily A member 1 and anti‑Müllerian hormone dysregulation was also more pronounced in the HLV group than in the LV group. By contrast, no significant difference was observed between the LV and HLV groups for serum lipid levels, pancreatic β‑cell area or apoptosis, INSR, IRS1, IRS2, AKT, PI3K, glucose transporter 4, carnitine palmitoyltransferase 1A or acyl‑CoA oxidase 1. These findings indicated that HFD selectively exacerbates specific molecular and histopathological features of PCOS beyond those induced by LET alone, partially recapitulating obesity‑related PCOS and providing a practical preclinical platform for studying the metabolic‑reproductive axis and evaluating interventions targeting insulin resistance.