Calcium Channel Subunit α2δ4 Is Regulated by Early Growth Response 1 and Facilitates Epileptogenesis.

Transient brain insults, including status epilepticus (SE), can trigger a period of epileptogenesis during which functional and structural reorganization of neuronal networks occurs resulting in the onset of focal epileptic seizures. In recent years, mechanisms that regulate the dynamic transcription of individual genes during epileptogenesis and thereby contribute to the development of a hyperexcitable neuronal network have been elucidated. Our own results have shown early growth response 1 (Egr1) to transiently increase expression of the T-type voltage-dependent Ca2+ channel (VDCC) subunit CaV3.2, a key proepileptogenic protein. However, epileptogenesis involves complex and dynamic transcriptomic alterations; and so far, our understanding of the transcriptional control mechanism of gene regulatory networks that act in the same processes is limited. Here, we have analyzed whether Egr1 acts as a key transcriptional regulator for genes contributing to the development of hyperexcitability during epileptogenesis. We found Egr1 to drive the expression of the VDCC subunit α2δ4, which was augmented early and persistently after pilocarpine-induced SE. Furthermore, we show that increasing levels of α2δ4 in the CA1 region of the hippocampus elevate seizure susceptibility of mice by slightly decreasing local network activity. Interestingly, we also detected increased expression levels of Egr1 and α2δ4 in human hippocampal biopsies obtained from epilepsy surgery. In conclusion, Egr1 controls the abundance of the VDCC subunits CaV3.2 and α2δ4, which act synergistically in epileptogenesis, and thereby contributes to a seizure-induced "transcriptional Ca2+ channelopathy."SIGNIFICANCE STATEMENT The onset of focal recurrent seizures often occurs after an epileptogenic process induced by transient insults to the brain. Recently, transcriptional control mechanisms for individual genes involved in converting neurons hyperexcitable have been identified, including early growth response 1 (Egr1), which activates transcription of the T-type Ca2+ channel subunit CaV3.2. Here, we find Egr1 to regulate also the expression of the voltage-dependent Ca2+ channel subunit α2δ4, which was augmented after pilocarpine- and kainic acid-induced status epilepticus. In addition, we observed that α2δ4 affected spontaneous network activity and the susceptibility for seizure induction. Furthermore, we detected corresponding dynamics in human biopsies from epilepsy patients. In conclusion, Egr1 orchestrates a seizure-induced "transcriptional Ca2+ channelopathy" consisting of CaV3.2 and α2δ4, which act synergistically in epileptogenesis.

The zinc-finger transcription factor GLI3 is a regulator of precerebellar neuronal migration.

Hindbrain precerebellar neurons arise from progenitor pools at the dorsal edge of the embryonic hindbrain: the caudal rhombic lip. These neurons follow distinct migratory routes to establish nuclei that provide climbing or mossy fiber inputs to the cerebellum. Gli3, a zinc-finger transcription factor in the Sonic hedgehog signaling pathway, is an important regulator of dorsal brain development. We demonstrate that in Gli3-null mutant mice, disrupted neuronal migratory streams lead to a disorganization of precerebellar nuclei. Precerebellar progenitors are properly established in Gli3-null embryos and, using conditional gene inactivation, we provide evidence that Gli3 does not play a cell-autonomous role in migrating precerebellar neurons. Thus, GLI3 likely regulates the development of other hindbrain structures, such as non-precerebellar nuclei or cranial ganglia and their respective projections, which may in turn influence precerebellar migration. Although the organization of non-precerebellar hindbrain nuclei appears to be largely unaffected in absence of Gli3, trigeminal ganglia and their central descending tracts are disrupted. We show that rostrally migrating precerebellar neurons are normally in close contact with these tracts, but are detached in Gli3-null embryos.

Pyroglutamyl peptidase II inhibition enhances the analeptic effect of thyrotropin-releasing hormone in the rat medial septum.

Thyrotropin-releasing hormone (TRH; pGlu-His-Pro-NH(2)) has multiple, but transient, homeostatic functions in the brain. It is hydrolyzed in vitro by pyroglutamyl peptidase II (PPII), a narrow specificity ectoenzyme with a preferential localization in the brain, but evidence that PPII controls TRH communication in the brain in vivo is scarce. We therefore studied in male Wistar rats the distribution of PPII mRNA in the septum and the consequence of PPII inhibition on the analeptic effect of TRH injected into the medial septum. Twelve to 14% of cell profiles expressed PPII mRNA in the medial septum-diagonal band of Broca; in this region the specific activity of PPII was relatively high. Twenty to 35% of PPII mRNA-labeled profiles were positive for TRH-receptor 1 (TRH-R1) mRNA. The intramedial septum injection of TRH reduced, in a dose-dependent manner, the duration of ethanol-induced loss of righting reflex (LORR). Injection of the PPII inhibitor pGlu-Asn-Pro-7-amido-4-methylcoumarin into the medial septum enhanced the effect of TRH. The injection of a phosphinic TRH analog, a higher-affinity inhibitor of PPII, diminished the duration of LORR by itself. In contrast, the intraseptal injection of pGlu-Asp-Pro-NH(2), a peptide that did not inhibit PPII activity, or an inhibitor of prolyl oligopeptidase did not change the duration of LORR. We conclude that in the medial septum PPII activity may limit TRH action, presumably by reducing the concentration of TRH in the extracellular fluid around cells coexpressing PPII and TRH-R1.