Reduction of thalamic and cortical I h by deletion of TRIP8b produces a mouse model of human absence epilepsy

Abstract

Absence seizures occur in several types of human epilepsy and result from widespread, synchronous feedback between the cortex and thalamus that produces brief episodes of loss of consciousness. Genetic rodent models have been invaluable for investigating the pathophysiological basis of these seizures. Here, we identify tetratricopeptide-containing Rab8b-interacting protein (TRIP8b) knockout mice as a new model of absence epilepsy, featuring spontaneous spike-wave discharges on electroencephalography (EEG) that are the electrographic hallmark of absence seizures. TRIP8b is an auxiliary subunit of the hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels, which have previously been implicated in the pathogenesis of absence seizures. In contrast to mice lacking the pore-forming HCN channel subunit HCN2, TRIP8b knockout mice exhibited normal cardiac and motor function and a less severe seizure phenotype. Evaluating the circuit that underlies absence seizures, we found that TRIP8b knockout mice had significantly reduced HCN channel expression and function in thalamic-projecting cortical layer 5b neurons and thalamic relay neurons, but preserved function in inhibitory neurons of the reticular thalamic nucleus. Our results expand the known roles of TRIP8b and provide new insight into the region-specific functions of TRIP8b and HCN channels in constraining cortico-thalamo-cortical excitability.

Neuroinflammation Alters Integrative Properties of Rat Hippocampal Pyramidal Cells

“…A cohort of rats was injected with LPS (n=6) or vehicle (n=6) and killed after 24 h for immunohistochemical analysis of HCN1 and TRIP8b using custom guinea pig anti-HCN1 (1:1000) [34]) and mouse anti-TRIP8b (1:1000, N212/17, Neuromab, CA, USA) antibodies using a previously described protocol [35, 36]. Imaging analysis was performed using a Nikon A1 confocal microscope at the Northwestern University Center for Advanced Microscopy (generously supported by NCI CCSG P30 CA060553 awarded to the Robert H, Lurie Comprehensive Cancer Center).…”

“…For western blot analysis (n=18 LPS; n=9 LPS+CyP; n=19 Sham), we used antibodies against HCN1 (1:1000; Antibodies Inc, Davis, CA, USA [19, 38-40]), TRIP8b (1:1000, N212/17, Neuromab, CA, USA [35, 36]), total Kv4.2 and triply P-Kv4.2 (1:200 and 1:300, respectively; Chemicon, Labon [40]), ERK1/2 and P-ERK (1:10000 and 1:5000, respectively; Cell Signaling Technology, Beverly, MA, USA [40]), IL-1β (1:500; ABCAM, Cambridge, UK [41]), HMGB1 (1:1000; ABCAM, Cambridge, UK [33]), and actin (1:5000, Sigma-Aldrich, St. Louis, MO, USA) which was used to normalize the relevant protein bands.…”

Advances in Understanding of Structure, Function and Plasticity of HCN Channels

“…Recently, the role of HCN channels in depression is also coming to the fore 36,81 . Reduction of HCN channels in thalamus and cortex (through TRIP8b knockout) results in a model of absence epilepsy 82 and recent work has shown these channels to be a good drugable targets for epilepsy treatment 31,83,84 . Auditory roles of these channels are also becoming clearer with new information, with the latest study showing their crucial role in tinnitus too 85 .…”

Animal models suggest the TRIP8b-HCN interaction is a therapeutic target for major depressive disorder

“…To circumvent cardiac effects and take advantage of the potential for inhibiting HCN channel function as a novel antidepressant strategy, our lab recently proposed interfering with the function of a brain specific auxiliary subunit of HCN channels named tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b) 6,7 . As in HCN1 KO mice, TRIP8b KO mice also exhibit an antidepressant-like phenotype with less time immobile in the TST and FST tasks 3,8 (Table 1).…”

“…Targeting TRIP8b circumvents cardiac issues associated with directly antagonizing HCN channels 7 , but raises the question of off target effects associated with proteins structurally related to TRIP8b. TRIP8b was initially identified as Pex5l for Peroxin 5 like protein, based on its homology to Peroxin 5 (Pex5).…”