Temporal lobe epilepsy (TLE) is the most common form of intractable epilepsy and is always accompanied with hippocampal sclerosis. The molecular mechanism of this pathological phenomenon has been extensively explored, yet remains unclear. Previous studies suggest that ion channels, especially calcium channels, might play important roles. Transient receptor potential canonical channel (TRPC) is a novel cation channel dominantly permeable to Ca(2+) and widely expressed in the human brain. We measured the expression of two subtypes of TRPC channels, TRPC3 and TRPC6, in temporal lobe epileptic foci excised from patients with intractable epilepsy and in hippocampus of mice with pilocarpine-induced status epilepticus (SE), an animal model of TLE. Cortical TRPC3 and TRPC6 protein expressions were significantly higher in TLE patients compared with those in controls. Expression of TRPC3 and TRPC6 protein also increased significantly in the CA3 region of the hippocampus of SE mice. Inhibition of TRPC3 by intracerebroventricular injection of anti-TRPC3 antibody prevented aberrant-sprouted mossy fiber collaterals in the CA3 region, while inhibition of TRPC6 by anti-TRPC6 antibody reduced dendritic arborization and spine density of CA3 pyramidal neurons. Our results indicate that TRPC3 and TRPC6 participate diversely in synaptic reorganization in the mossy fiber pathway in TLE.

Alterations in intracellular Ca(2+) concentration ([Ca(2+)]i) play a crucial role in fundamental cellular events from transcriptional regulation to migration and proliferation. The transient receptor potential (TRP) channels contribute to changes in [Ca(2+)]i by providing or modulating Ca(2+) entry pathways, as well as by releasing Ca(2+) from intracellular stores. On the basis of sequence homology, the TRP family can be divided into seven subfamilies: the TRPC ("canonical") family, the TRPV ("vanilloid") family, the TRPM ("melastatin") family, the TRPP ("polycystin") family, the TRPML ("mucolipin") family, the TRPA ("ankyrin") family, and the TRPN ("NOMPC") family. In this review, we focus on the physiology and pathophysiology of mammalian TRPC channels in the nervous system. Seven mammalian TRPC proteins (TRPC1-7) have been described and are widely distributed in the brain from early embryonic days till adulthood, with the exception of TRPC2. TRPC channels are nonselective Ca(2+)-permeable channels, which can be activated by G-protein-coupled receptors and receptor tyrosine kinases. These channels have been reported to act as essential cellular sensors in multiple processes during neuronal development, including neural stem cell proliferation and differentiation, neuronal survival, neurite outgrowth and axon path finding, and synaptogenesis. Not surprisingly, studies on these channels also provide new insights into underlying mechanisms of various neuropsychiatric disorders. The present review summarizes the expressions of all TRPC subtypes in different brain regions and different neural cell types, aiming to serve as a useful reference for future studies in this field. We also discuss the most updated evidence implicating involvement of TRPC channels in the generation of pathophysiological states in nervous system and their potentials as being promising targets for drug development.

Mossy fiber sprouting (MFS) is a unique feature of chronic epilepsy. However, the molecular signals underlying MFS are still unclear. The repulsive guidance molecule A (RGMa) appears to contribute to axon growth and axonal guidance, and may exert its biological effects by dephosphorylating focal adhesion kinase (FAK) at Tyr397, then regulating the activation of Ras. The objective of this study was to explore the expression patterns of RGMa, FAK (Tyr397) and Ras in epileptogenesis, and their correlation with MFS. The epileptic models were established by intraperitoneal pentylenetetrazole (PTZ) injection of Sprague-Dawley rats. At 3 days and at 1, 2, 4 and 6 weeks after the first PTZ injection, Timm staining was scored at different time points in the CA3 region of the hippocampus and dentate gyrus. The protein levels of RGMa, FAK (Tyr397) and Ras were analyzed at different time points in the CA3 region of the hippocampus using immunofluorescence, immunohistochemistry and western blot analysis. Compared with the control (saline-injected) group, the expression of RGMa in the CA3 area was significantly downregulated (P<0.05) from 3 days and still maintained the low expression at 6 weeks in the PTZ group. The expression of FAK (Tyr397) and Ras was upregulated (P<0.05) in the PTZ groups. The Timm score in the CA3 region was significantly higher than that in the control group at different time points and reached a peak at 4 weeks. In the CA3 region, no obvious distinction was observed at the different time points in the control group. To the best of our knowledge, these are the first results to indicate that the RGMa-FAK-Ras pathway may be involved in MFS and the development of temporal lobe epilepsy.

Epileptogenesis is a potential process. Mossy fibre sprouting (MFS) and synaptic plasticity promote epileptogenesis. Overexpression of repulsive guidance molecule a (RGMa) prevents epileptogenesis by inhibiting MFS. However, other aspects underlying the RGMa regulatory process of epileptogenesis have not been elucidated. We studied whether RGMa could be modulated by microRNAs and regulated RhoA in epileptogenesis. Using microRNA databases, we selected four miRNAs as potential candidates. We further experimentally confirmed miR‐20a‐5p as a RGMa upstream regulator. Then, in vitro, by manipulating miR‐20a‐5p and RGMa, we investigated the regulatory relationship between miR‐20a‐5p, RGMa and RhoA, and the effects of this pathway on neuronal morphology. Finally, in the epilepsy animal model, we determined whether the miR‐20a‐5p‐RGMa‐RhoA pathway influenced MFS and synaptic plasticity and then modified epileptogenesis. Our results showed that miR‐20a‐5p regulated RGMa and that RGMa regulated RhoA in vitro. Furthermore, in primary hippocampal neurons, the miR‐20a‐5p‐RGMa‐RhoA pathway regulated axonal growth and neuronal branching; in the PTZ‐induced epilepsy model, silencing miR‐20a‐5p prevented epileptogenesis through RGMa‐RhoA‐mediated synaptic plasticity but did not change MFS. Overall, we concluded that silencing miR‐20a‐5p inhibits axonal growth and neuronal branching and prevents epileptogenesis through RGMa‐RhoA‐mediated synaptic plasticity in the PTZ‐induced epilepsy model, thereby providing a possible strategy to prevent epileptogenesis.

Repulsive guidance molecule a (RGMa) is a membrane-associated glycoprotein that regulates axonal guidance and inhibits axon outgrowth. In our previous study, we hypothesized that RGMa may be involved in temporal lobe epilepsy (TLE) via the repulsive guidance molecule a (RGMa)-focal adhesion kinase (FAK)-Ras signaling pathway. To investigate the role of RGMa in epilepsy, recombinant RGMa protein and FAK inhibitor 14 was intracerebroventricularly injected into a pentylenetetrazol (PTZ) kindling model and Timm staining, co-immunoprecipitation and western blotting analyses were subsequently performed. The results of the present study revealed that intracerebroventricular injection of recombinant RGMa protein reduced the phosphorylation of FAK (Tyr397) and intracerebroventricular injection of FAK inhibitor 14 reduced the interaction between FAK and p120GAP, as wells as Ras expression. Recombinant RGMa protein and FAK inhibitor 14 exerted seizure-suppressant effects; however, recombinant RGMa protein but not FAK inhibitor 14 suppressed mossy fiber sprouting in the PTZ kindling model. Collectively, these results demonstrated that RGMa may be considered as a potential therapeutic agent for epilepsy, and that RGMa may exert the aforementioned biological effects partly via the FAK-p120GAP-Ras signaling pathway.