Recently, many studies have demonstrated that DELs and DEMs play anecessary role in normal physiological functions by modulating gene expression at epigenetic, transcription and post-transcription level. Further, increasing evidence suggests that DELs and DEMs are emerging in the pathogenesis, diagnosis and treatment of epilepsy. Unlike protein-coding genes, lncRNAs have significant advances as diagnostic and prognostic biomarkers.It is currently known that lncRNA is involved in nervous system development, synapse occurrence and synaptic plasticity. The disorder of lncRNA may cause neurological diseases such as epilepsy, Parkinson’s disease (PD), and Alzheimer’s disease(AD)(Oe S et al., 2019). LncRNA and miRNA probably be related to specific biological processes in epilepsy, including ion/gated channels and GABA receptors (Gross C and Tiwari D, 2018;Haenisch S et al., 2016). LncRNA might also be involved in neuronal apoptosis, neuroinflammation and cognitive impairment in the development of epilepsy(Villa C et al., 2019). Indeed, miR-211 and miR-128 are essential factors that directly induce epilepsy in mice(Fan C et al., 2016;Tan CL et al., 2013). Therefore, ceRNA is expected to become a potential target for the treatment of epilepsy.
LF- rTMS can be applied to specific brain regions to generate a certain magnetic field and penetrate the scalp and skull, by using a short but powerful magnetic field pulse repeatedly on the cerebral cortex, as a result generating a certain intensity of current in the cortex, stimulating and influencing the local and functionally relevant state of the remote cortex, leading to a regional reorganization of cortical function, thereby producing the corresponding biological effects. These effects can last for a certain period of time after the end of stimulation, making it a good tool for studying the functional reconstruction of neural networks (Borckardt JJ,Smith AR,Reeves ST,Madan A,Shelley N,Branham R,Nahas Z and George MS, 2009;Feng H et al., 2020). As recently shown, LF-rTMS can cause variety in neuronal excitability, affect expression of neurotransmitters, regulate brain plasticity, improve neurological dysfunction, and thus achieve functional recovery. LncRNAs have been demonstrated to participated in multiple biological processes, including post-transcriptional and epigenetic regulation. It was reported that lncRNA inhibited the development of epilepsy by regulating miRNA to decrease neuronal apoptosis and neuroinflammation in vitro studies(Feng H et al., 2021;Feng H,Gui Q,Zhu W,Wu G,Dong X,Shen M,Luo H,Xue S and Cheng Q, 2020;Han CL et al., 2020). However, there was still a lack of global lncRNA-associated crosstalks in the treatment of LF-rTMS for epilepsy.
It is widely believed that miRNAs not only decrease mRNA reliability by linking with MRE but also block its translation. Owing to MRE, a single miRNA can target RNAs in “one to multiple”. On the contrary a single mRNA or LncRNA is modulated by miRNAs in “one to multiple” (Jeyapalan Z et al., 2011). Hereby, this ceRNA interaction may be a universal post-transcriptional modification. A miRNA is a noncoding RNA with the 5’ end that decreases gene expression by targeting mRNA with a complementary 3’-UTR. Accumulating evidence suggests that lncRNAs act as endogenous ceRNA through competitive inhibition of miRNA, thereby regulating other transcripts. CeRNA is involved in neuronal development, synaptic transmission and ion channels related to epileptogenesis. Additionally, it can also regulate neuronal inflammation, neuron apoptosis and autophagy to delay the progression of epilepsy. The detail functions and special expression pattern of miRNAs and lncRNAs in epilepsy remained largely unclear. However, the tricky ceRNA interplay mechanisms of lncRNA–miRNA–mRNA in LF-rTMS treatment for epilepsy remained to be investigated. In this study, we identified 1029 upregulated and 586 downregulated lncRNAs, 12 upregulated and 5 downregulated miRNAs, 383 upregulated and 127 downregulated mRNAs in the LF-rTMS-treated mice as compared to control mice. Although lncRNAs are considered to attract miRNAs competitively and then affect mRNAs expression, their biological characteristics and clinical relevance are still unclear. The constructed ceRNA regulatory network included five miRNAs (mmu-miR-7222-3p, mmu-miR-744-5p, mmu-miR-1934-3p, mmu-miR-19a-3p, and mmu-miR-8973b-5p).
Critical nodes identified in some studies and highly connected with other nodes of ceRNA network would be viewed as its topological properties to evaluate genes’ essentiality(Li Y et al., 2019;Ma N et al., 2019). As recently hypothesized, ceRNA is viewed as a new post-transcriptional regulation circuit. The lncRNAs, of this ceRNA network, connect with mRNAs that share MREs(Fan CN et al., 2018). After decade, hundreds of studies have seeked after the mechanisms of ceRNA in various neurological diseases, for instance, ischemic stroke and epilepsy(Brennan GP and Henshall DC, 2020;Homanics GE et al., 1997;Jiang H et al., 2017). To examine lncRNAs markedly linked with LF-rTMS treatment of epilepsy, in this paper, the mRNA and lncRNA expression alternation in mice after LF-rTMS, combined with miRNA-target interactions to establish ceRNA network, were utilized to seek for the deep significance of these lncRNAs in the molecular mechanisms of LF-rTMS treatment.
No definite signal pathway has been confirmed to be responsible for LF-rTMS treatment for epilepsy. In the present study, the differentially expressed genes appeared to take part in signaling pathways, involving GABA-A receptor activity, Th17 cell differentiation, T cell receptor signaling pathway, primary immunodeficiency and so on. GABA is a major neurotransmitter controling neuronal excitability. The suspected contacts in GABA and epilepsy as well as in GABA and brain development have been recognized(Homanics GE,DeLorey TM,Firestone LL,Quinlan JJ,Handforth A,Harrison NL,Krasowski MD,Rick CE,Korpi ER,Mäkelä R,Brilliant MH,Hagiwara N,Ferguson C,Snyder K and Olsen RW, 1997). Differential coassembly of α1-GABARs was associated with epileptic encephalopathy (Hannan S et al., 2020). Protrudin can modulate seizure activities by regulating GABA receptor(Lu X et al., 2019).HMGB1 / CXCL12-mediated immunity and Th17 cells are highly suggested as the core of autoimmune epilepsy (Han Y et al., 2020). Compared with antibody-mediated disease, T-cell-mediated disease has higher risk of epilepsy(Geis C et al., 2019). On the basis of our bioinformatics analysis, we speculated that GABA-A receptor activity, Th17 cell differentiation, T cell receptor signaling pathway are responsible pathways involved in the the molecular mechanisms of LF-rTMS treatment for epilepsy.Based on the role of LF-rTMS in regulating synaptic-associated protein level, glutamate concentration and GABA receptor, and even affecting GSK, TGF and other signaling pathways (Cacace AT et al., 2018;Dolgova N et al., 2021;Hou Y et al., 2021;Huang Z et al., 2017;Tan T et al., 2018),we explored the potential mechanisms of miRNA changes after LF-TMS treatment for epilepsy. Among the 12 up-regulated and 5 down-regulated miRNAs of rTMS treatment group, we seeked for several miRNAs that directly or indirectly affect epilepsy. According to previous reports, MiR-28 could up-regulate AQP4 (AQP4) by inhibiting aldehyde dehydrogenase 2 (ALDH2), and promote the recovery of water homeostasis after epilepsy(Hubbard JA et al., 2016;Li SP et al., 2015;Li Y et al., 2018). AQP4 was believed as the core of maintaining water and potassium homeostasis in brain, and AQP4 knockout mice showed spontaneous recurrent seizures with increased frequency and duration(Szu JI et al., 2020). In addition, mir-138 inhibited axon regeneration(Liu CM et al., 2013). Furthermore, mir-186 controls the surface expression of GluA2 (ionic glutamate receptor A2) in hippocampal neurons(Silva MM et al., 2019). Down-regulated miR-744 could downregulate Npas4 as an intrinsic regulator of seizures and epilepsy(Choy FC et al., 2017;Shan W et al., 2018). Together, these alterations represent an intrinsic therapeutic mechanism of LF-rTMS for epilepsy.
This study also has its limitation. First, the number of samples of LF-rTMS mice need to be further increased to clarify the differences. Second, in this study, the functions of dysregulated lncRNA were predicted as miRNA “sponge”. However, its association with LF-rTMS should be further investigated. Therefore, a careful interpretation of the above conclusions and results is needed.
In conclusion, a ceRNA based on lncRNA-miRNA-mRNA network was developed in the present study, providing a new strategy for investigating molecular mechanisms of LF-rTMS treatment for epilepsy. Furthermore, lncRNA-miRNA-mRNA pairs might view as valuable detectingbiomarkers or candidate curative targets for epilepsy.