22 February 2025
I have read the article by Zhu et al. [1] and think that the study is of great significance. However, there are also some points worth discussing.
Research highlights
Firstly, this study reveals the role of the TLR4/Rac1/NLRP3 pathway in mediating Aβ-induced neuroinflammation in Alzheimer's disease (AD), providing a new insight into the pathogenesis of AD. In addition, the study used various experimental methods, including cell experiments and animal experiments, to explore the role of this pathway from multiple levels, and the experimental design was relatively rigorous.
Problem discussion
Selection of cells in vitro
The BV2 cell line has certain advantages as an in vitro experimental model. It is easy to culture and operate. Compared with primary microglia cells directly extracted from tissues, BV2 cells lack the specificity of the microenvironment of their source tissues. Studies [2, 3] have shown that primary microglia are in a complex brain parenchyma environment and interact with various cell types such as neurons, astrocytes, and endothelial cells to form the neural microenvironment. In contrast, BV2 cells are dissociated from this natural tissue microenvironment when cultured in vitro, and their biological behavior may differ from that of primary microglia in vivo. Although studies have found changes related to the TLR4/Rac1/NLRP3 pathway, the authenticity of these results reflecting microglia in the pathological process of AD in vivo remains questionable.
The underlying mechanisms of Rac1 inhibition and Aβ deposition reduction
Inhibition of rac1 can block the deposition of Aβ plaques and change the phagocytic ability of microglia. However, in-depth studies on these potential factors are still lacking. For example, concerning Aβ production, it is not clear how Rac1 inhibition affects the metabolism of Aβ precursor proteins; The specific cellular or molecular pathways involved in the clearance mechanism were not elaborated. Further studies are recommended to investigate the effect of Rac1 inhibition on the expression of enzymes or proteins related to Aβ metabolism [4, 5] and the regulation of microglial phagocytosis-related receptors or signaling pathways.
Effects of TLR4 and Rac1 inhibition on cells in different brain regions
This study only explored the effects of TLR4 and Rac1 inhibition on neurons and microglia in the hippocampus, while cells in other brain regions may also play an important role in the pathogenesis of AD [6, 7]. There are differences in cell composition and function in different brain regions, and the activity and role of the TLR4/Rac1/NLRP3 pathway in these regions may be different. Future research should expand to other brain regions, such as cortex and striatum.
Comprehensiveness of experimental results
In the field of biological research, it is generally believed that experimental results need multiple biological replicates (usually three or more) and technical replicates to reduce experimental errors and accurately reflect the authenticity of experimental treatments. In the present study, the number of sufficient replicates was lacking. As an example, the results of western blotting experiments in Figure 5A/C and Figure 6B are shown, where only pictures from a single technical replicate are shown.
Conclusion
This study has made important progress in the study of the pathogenesis of AD, but there are still some problems that need to be further solved. We hope that the authors can further explore the above issues in the follow-up study.
Fengwen Jiang1, Niya Wang1,2, Qiang Meng1,*
1Medical school, Kunming University of Science and Technology, Kunming, P.R. China, The First People's Hospital of Yunnan Province
2Department of Neurology, The First People’s Hospital of Yunnan Province, The Affiliated Hospital of Kunming University of Science and Technology, Kunming, China
Reference
[1] Zhu M, Liu Y, Chen C, et al. TLR4/Rac1/NLRP3 pathway mediates amyloid-β-induced neuroinflammation in Alzheimer's disease. J Alzheimers Dis 2024; 99: 911-925.
[2] Goshi N, Morgan RK, Lein PJ, et al. A primary neural cell culture model to study neuron, astrocyte, and microglia interactions in neuroinflammation. J Neuroinflammation 2020; 17: 155.
[3] Hayes LN, An K, Carloni E, et al. Prenatal immune stress blunts microglia reactivity, impairing neurocircuitry. Nature 2022; 610: 327-334.
[4] Borin M, Saraceno C, Catania M, et al. Rac1 activation links tau hyperphosphorylation and Aβ dysmetabolism in Alzheimer's disease. Acta Neuropathol Commun 2018; 6: 61.
[5] Wang PL, Niidome T, Akaike A, et al. Rac1 inhibition negatively regulates transcriptional activity of the amyloid precursor protein gene. J Neurosci Res 2009; 87: 2105-2114.
[6] Cui W, Sun C, Ma Y, et al. Inhibition of TLR4 induces M2 microglial polarization and provides neuroprotection via the NLRP3 inflammasome in Alzheimer’s disease. Front Neurosci 2020; 14: 444.
[7] Capiralla H, Vingtdeux V, Zhao H, et al. Resveratrol mitigates lipopolysaccharide- and Aβ-mediated microglial inflammation by inhibiting the TLR4/NF-κB/STAT signaling cascade. J Neurochem 2011; 120: 461-472.
