DNA Topoisomerase IIβ Suppresses Microglial Inflammatory Cytokine Release: A Potential Regulator of Neuroinflammation

DNA topoisomerase IIβ (topo IIβ) is a nuclear enzyme that regulates DNA topology and gene expression, especially in post-mitotic cells such as neurons. Although its roles in neural development and transcriptional control are well-established, its involvement in neuroinflammatory processes is still to be investigated. This study aims to investigate whether topo IIβ modulates inflammatory responses in human microglial HMC3 cells under immune-stimulated conditions, considering that microglial cells are pivotal mediators of neuroinflammation in the central nervous system (CNS). Inflammation was induced using lipopolysaccharide (LPS), interferon-gamma (IFNγ), Adenosine triphosphate (ATP), whereas topo IIβ expression was modulated by overexpression and siRNA-mediated silencing. Western blot analysis demonstrated that LPS, IFNγ, and ATP stimulation did not alter the endogenous topo IIβ protein levels, indicating that its protein levels are stable under inflammatory conditions. Analysis of cytokine release indicated that topo IIβ overexpression decreased the release of key proinflammatory cytokines, suggesting an anti-inflammatory role. Conversely, the silencing of topo IIβ resulted in increased cytokine release, suggesting that topo IIβ typically functions to mitigate microglial inflammatory responses. Significantly, treatment with Lipofectamine™ 3000 alone increased cytokine release, indicating an intrinsic immunostimulatory impact of the transfection reagent. Collectively, these findings reveal an unacknowledged function of topo IIβ in attenuating neuroinflammatory signaling in microglia and underscore the necessity for careful interpretation of cytokine data when transfection reagents are present. Topo IIβ may represent a novel therapeutic target for modulating microglial activation in neuroinflammatory diseases.