Yeşim Neğiş

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.

The study explores the interaction between topoisomerase IIβ (topo IIβ) and α-synuclein aggregation in Parkinson’s disease (PD) using an in vitro model overexpressing A53T mutant α-synuclein, revealing key pathological features. The overexpression of A53T mutant α-synuclein was associated with impaired neuronal differentiation, accompanied by delayed neurite outgrowth and reduced levels of MAP2 and NF-L. Transcriptomic study during differentiation revealed substantial gene expression changes, with 57 of 84 PD-associated genes exhibiting differential regulation on days 8 and 12. Dopaminergic markers like TH, BDNF, NR4A2 (Nurr1), PINK1, and SYNGR3 were notably upregulated in differentiated cells, whereas A53T mutant α-synuclein overexpression was associated with significant downregulation of 22 genes associated with PD, including TH, NR4A2, BDNF, and PINK1, suggesting alterations in neuroprotective signaling pathways. Topo IIβ expression diminished during differentiation in the presence of pathogenic α-synuclein and was associated with changes in the proposed topo IIβ-Nurr1 regulatory axis potentially contributing to early neurodevelopmental abnormalities and dopaminergic vulnerability observed in PD.

Neuroinflammation in the pathogenesis of neurodegenerative diseases is still a subject of discussion, as it might be either the cause or the result of neurodegeneration. Misfolded or improperly aggregated α-synuclein in Parkinson’s Disease, can cause inflammatory responses, indicating a mechanistic relationship between α-synuclein pathology and neuroinflammation. The aim of this study was to investigate the role of DNA topoisomerase IIβ, the key player of DNA topology, in the neuroinflammation process in an age-dependent transgenic Parkinson’s Disease mouse model overexpressing the A53T mutant α-synuclein. In this study, transgenic and control mice were bred in three age groups as early (3 months), mid (8 months), and late (12 months) disease stages. Behavioral experiments were carried out to compare the age-related cognitive and motor coordination functions. Cytokine levels in the serum and protein expression levels in the dissected brain were analyzed by both western blot and immunofluorescence staining. A decline was observed in the cognitive and motor coordination functions depending on age. Disease-related markers at protein level appeared even in the early stage, and accordingly, a significant increase was observed in inflammatory markers and cytokine levels compared to control. DNA Topoisomerase IIβ and Nurr1 levels decreased in transgenic mice, especially more dramatically in the early stage. The combined effect of reduced Nurr1 and DNA Topoisomerase IIβ, along with increased inflammation, may provide a better understanding of the pathogenesis of Parkinson’s Disease at early-stage and requires for further investigation of the potential alterations in topo IIβ as an intervention strategy for this disease.