Limonin ameliorates hyperuricemia-induced cognitive impairment through modulation of microglial HIF-1α-driven neuroinflammation

Background: Hyperuricemia (HUA), a highly prevalent metabolic disorder, is increasingly linked to cognitive impairment. Limonin (LIM), a natural compound with anti-inflammatory and neuroprotective properties, has the therapeutic benefits, but its underlying mechanisms remain unclear.

Purpose: This study aimed to investigate the therapeutic effect and mechanism of LIM on HUA-induced cognitive impairment.

Methods: A rat model of HUA-induced cognitive impairment was established using urate oxidase gene knockout (UOX^−/−) rat. Uric acid (UA) levels of serum and cerebrospinal fluid (CSF) were measured to confirm hyperuricemia. Cognitive function was assessed using morris water maze test, while neuronal morphology and synaptic integrity were evaluated via Nissl staining and synaptic plasticity biomarkers. Microglial activation and polarization were examined through double immunofluorescence staining of CD86/IBA1 and ARG1/IBA1, inflammatory and oxidative stress markers were quantified using ELISA, qRT-PCR and Western blot. In vitro, BV2 microglial cells were stimulated with UA to model activation and inflammatory responses. HT22 neuronal cells were co-cultured using conditioned medium to assess apoptosis via TUNEL assay and expression of apoptosis-related biomarkers. RNA sequencing was performed to identify key signaling pathways modulated by LIM, and the findings were validated through targeted gene overexpression or inhibition experiments.

Results: The UOX^−/− rat model successfully recapitulated HUA-induced cognitive impairment, as evidenced by elevated UA levels, alongside significant cognitive deficits. LIM treatment ameliorated these cognitive impairments, attenuated neuropathological alterations, modulated microglial M1/M2 polarization, and reduced neuroinflammation and oxidative damage. In vitro, LIM suppressed UA-induced microglial activation and inflammatory response, while also rescuing neuronal apoptosis in HT22 cells. RNA sequencing revealed involvement of the HIF-1 pathway. HIF-1α inhibitor YC-1 enhanced LIM's effects, whereas HIF-1α activator DMOG reversed them, suggesting that the modulation of the HIF-1α/iNOS pathway contributes to redox homeostasis and neuroinflammation.

Conclusion: LIM ameliorates HUA-induced cognitive impairment by suppressing microglial activation and neuroinflammation, which is associated with the inhibition of the HIF-1α/iNOS signaling pathway, underscoring its therapeutic potential.