Fasudil attenuates fluoride-induced neuronal synaptic damage by inhibiting microglial inflammation.

Introduction

Fluoride, which is frequently present as a trace element in the surroundings, is crucial in human physiological processes. Nevertheless, an overabundance of fluoride can lead to fluorosis, a condition marked by systemic damage to the body (Wu et al., 2022), which can manifest in a range of health issues. Prolonged exposure to elevated levels of fluoride has been linked to dysfunction within the central nervous system (CNS), resulting in significant cognitive impairments, particularly affecting critical abilities such as learning and memory (Xin et al., 2023). Research has increasingly highlighted a notable connection between elevated fluoride exposure and lower IQ scores in children (Taylor et al., 2025). Moreover, adults residing in regions endemic to fluorosis are more prone to experiencing neurological symptoms like fatigue, headaches, and memory impairment (Ayele et al., 2022). Experimental research conducted on rat models has provided evidence supporting the detrimental impact that high levels of fluoride can have on the CNS, manifesting as behavioral disorders, cognitive impairment, and spatial memory deficits (Wang et al., 2023, Zhang et al., 2023). Although existing studies have confirmed a connection between fluoride exposure and CNS injury, additional research is needed to fully clarify the underlying mechanisms.

The hippocampus, a brain region housing a vast array of neurons, serves as a pivotal structure for spatial memory. Synapses, which are essential components of nerve endings, facilitate the connection between neurons and the transmission of material and informationr (Su et al., 2023). Among the constituents of synapses, postsynaptic density PSD95 stands out as one of the most prominent proteins within the postsynaptic density. The interplay between PSD95 and SYP not only reflects the structural and functional aspects of synapses but also plays a critical role in shaping synaptic plasticity development (Fan et al., 2021). Studies have observed that fluorosis can lead to significant alterations in the morphology of hippocampal tissue and the thickness of postsynaptic densities, consequently impairing synaptic plasticity (Bittencourt et al., 2023).

The activation of microglia is acknowledged as a critical factor in the occurrence of synaptic damage. Inflammatory responses mediated by microglia have been linked to the progression of various neurodegenerative diseases (Martins-Ferreira et al., 2025). When in a resting state, microglia are essential for preserving CNS homeostasis and participating in synaptic remodeling. Nevertheless, when activated by pathogens or inflammatory cues, microglia can release pro-inflammatory cytokines, including interleukin 1B (IL-1B) and tumor necrosis factor-alpha (TNF-a), contributing to neuronal injury or death, further potentially worsening or triggering neurodegenerative conditions (Rauf et al., 2022). Research has shown that fluoride exposure can stimulate microglia activation, prompting the release of pro-inflammatory cytokines that impact synaptic function (Zhang et al., 2024a). However, the exact molecular mechanisms that govern this process have not been fully clarified.

The RhoA/ROCK pathway is crucial for numerous cellular activities. Activation of this pathway has been linked to structural and functional damage in dendritic spines, along with the inhibition of axon growth, ultimately resulting in synaptic impairment (Chen et al., 2023). Earlier investigations indicated that fluoride has the potential to stimulate the RhoA/ROCK signaling pathway, which can lead to neural injury and impairments in cognitive abilities (Lingli et al., 2023). Furthermore, it has been established through research that the ROCK inhibitor, fasudil, significantly hinders pro-inflammatory cytokine secretions (Liu et al., 2024). It has also been observed that fasudil promotes the secretion of anti-inflammatory cytokines, subsequently decreasing CNS damage and improving cognitive performance (Jianjun et al., 2021).

In this research, we employed both in vivo and in vitro methodologies to develop a rat model that is subjected to fluoride exposure, along with a cellular model. This approach allowed us to conduct a thorough investigation into the regulatory function of the RhoA/ROCK signaling pathway in relation to synaptic injury that is triggered by microglia activated by fluoride. By focusing on this specific pathway, our main goal is to uncover how fluoride exerts its detrimental effects on the nervous system, while also providing innovative research perspectives and treatment strategies for the prevention and management of neurodegenerative disorders associated with fluorosis.