Interleukin-6 induces cognitive impairment via toll-like receptor 4 (TLR4)-mediated neuroinflammation and neurodegeneration in mice with chronic kidney disease.

Backgrounds: Past epidemiological and experimental studies in rodents have demonstrated that chronic kidney disease (CKD) leads to cognitive impairment. However, the underlying mechanism requires further investigation. Herein, a mouse model of CKD was established using conventional 5/6 nephrectomy. We aimed to examine the relationship between CKD and cognitive impairment and elucidate the underlying mechanisms. Methods: Cognitive behavior was assessed using the Morris water maze, novel object recognition test, and fear conditioning test. Further experiments were also conducted to investigate the underlying molecular mechanisms. Results: Our clinical data revealed a decrease in cognitive function among patients with CKD, accompanied by elevated plasma levels of pro-inflammatory cytokines. A positive correlation between cytokine concentrations and serum creatinine levels, as well as a significant positive correlation with cognitive dysfunction, were observed. Correlation analyzes demonstrated that hippocampal cytokine levels were positively correlated with serum creatinine levels and cognitive dysfunction in CKD model mice. Furthermore, 20 mg/mL interleukin-6 (IL-6) significantly decreased HT22 cell activity in vitro. Further, HT22 cells treated with IL-6 showed increased expression levels of toll-like receptor 4 (TLR4) and myeloid differentiation primary response gene 88 (MyD88), thereby inducing the nuclear factor kappa-B p65 inflammatory pathway and mitochondria-dependent apoptosis. The CKD mouse model showed increased expression of TLR4 and cytokines in the hippocampus. Conclusion: These results suggest that IL-6 triggers TLR4 activation to induce neuroinflammation and neurodegeneration in CKD, ultimately culminate in cognitive impairment.