The Impact of Interleukin-6 and Hypoxia on the Expression of Brain Injury Marker Proteins in a Cellular Model of the Neurovascular Unit

The high incidence of postoperative cognitive dysfunction in children undergoing cardiac surgery underscores the urgent need for effective neuroprotective strategies.

Aim. To examine the effects of hypoxia and interleukin-6 (IL-6) on the expression of claudin-5, occludin-1, and interleukin-1 (IL-1) and IL-6 receptors in neurovascular unit (NVU) cells.

Materials and methods. An in vitro NVU model comprising neurons, astrocytes, and endothelial cells was established. The cells were cultured under normoxic and hypoxic conditions with oxygen concentrations of 15%, 10%, 7%, and 5%. The cultures were also treated with patient-derived sera containing high or low levels of IL-6. All incubations were conducted under normothermic conditions for 30 minutes. Injury marker expression was then assessed using fluorescence analysis.

Results. Significant reductions in claudin-5 fluorescence intensity were observed at oxygen levels of 10% and below (15.2 vs. 34.3 in controls, P=0.0105). Hypoxia did not affect occludin-1 expression. IL-1 receptor fluorescence intensity increased under 7% and 5% oxygen conditions (12.2 and 12.9 versus 9.9 in the control group, P=0.0105), while IL-6 receptor expression remained unchanged. In both normoxic and hypoxic conditions, adding patient sera significantly altered marker expression; hypoxia enhanced these effects. Sera with the highest IL-6 levels induced the most pronounced reduction in injury marker fluorescence.

Conclusion. IL-6 had a more significant impact on injury marker expression in NVU cells than hypoxia did. Hypoxic conditions with oxygen concentrations down to 10% did not affect marker expression

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