Increased sensitivity to kindling in mice lacking TSP1

Abstract

The development of a hyperexcitable neuronal network is thought to be a critical event in epilepsy. Thrombospondins (TSPs) regulate synaptogenesis by binding the neuronal α2δ subunit of the voltage-gated calcium channel. TSPs regulate synapse formation during development and in the mature brain following injury. It is unclear if TSPs are involved in hyperexcitability that contributes to the development of epilepsy. Here we explore the development of epilepsy using a pentylenetetrazole (PTZ) kindling model in mice lacking TSP1 and TSP2. Unexpectedly, we found increased sensitivity to PTZ kindling in mice lacking TSP1, while mice lacking TSP2 kindled similar to wild-type. We found that the increased seizure susceptibility in the TSP1 knockout (KO) mice was not due to a compensatory increase in TSP2 mRNA as TSP1/2 KO mice were sensitive to PTZ, similar to the TSP1 KO mice. Furthermore, there were similar levels of TGF-B signal activation during kindling in the TSP1 KO mice compared to wild-type. We observed decreased expression of voltage-dependent calcium channel subunit CACNA2D1 mRNA in TSP1, TSP2, and TSP1/2 KO mice. Decreased CACNA2D2 mRNA was only detected in mice that lacked TSP1 and α2δ-1/2 protein levels in the cortex were lower in the TSP 1/2 KO mice. CACNA2D2 knockout mice have spontaneous seizures and increased PTZ seizure susceptibility. Here we report similar findings, TSP1, and TSP1/2 KO mice have low levels of CACNA2D2 mRNA expression and α2δ-1/2 receptor level in the cortex, and are more susceptible to seizures. CACNA2D2 mutations in mice and humans can cause epilepsy. Our data suggest TSP1 in particular may control CACNA2D2 levels and could be a modifier of seizure susceptibility.

Alterations in the α2δ ligand, thrombospondin‐1, in a rat model of spontaneous absence epilepsy and in patients with idiopathic/genetic generalized epilepsies

“…34 Recent evidence suggests that thrombospondin-1, by promoting the formation of new excitatory synapses, contributes to the development of a hyperexcitable neuronal network, which is a critical event in epilepsy. As opposed to mice lacking thrombospondin-1, 35 we did not detect changes in a 2 d-1 mRNA and protein levels associated with the reduction of thrombospondin-1 in WAG/Rij rats. p < 0.05 vs. 2-month-old ACI rats (*) or vs. 6-month-old ACI and Wistar rats (#).…”

“…Several lines of evidence suggest that an abnormal synaptogenesis contributes to epileptogenesis, that is, to the process by which the brain develops epilepsy. Mendus et al 35 have found that mice lacking thrombospondin-1 or , two-way ANOVA shows a significant strain effect (F 2,30 = 7.15; p < 0.05) and age effect (F 1,30 = 4.18; p < 0.05), but no strain 9 age interaction effect (F 2,30 = 0.27; n.s.). 30 Other proteins that regulate synaptogenesis, such as synapsin II and synaptophysin, have been also implicated in the pathophysiology of epilepsy.…”

“…34 Recent evidence suggests that thrombospondin-1, by promoting the formation of new excitatory synapses, contributes to the development of a hyperexcitable neuronal network, which is a critical event in epilepsy. Mendus et al 35 have found that mice lacking thrombospondin-1 or Reduced VGLUT1 protein levels in the ventrobasal thalamus of WAG/Rij rats. Western blot analysis of a 2 d-1, Rab3A, and VGLUT1 in the ventrobasal thalamus of presymptomatic and symptomatic WAG/Rij rats and age-matched ACI or Wistar rats are shown in (A), (B), and (C), respectively.…”

“…Accordingly, temporal lobe epilepsy in patients and pilocarpine-induced epilepsy in rats are associated with an increased hippocampal and cortical expression of ephrinB3 and its receptor EphB3, which play a key role in synaptogenesis and mechanisms of synaptic reorganization and plasticity. 35 The importance of the thrombospondin/a 2 d axis in the pathophysiology of epilepsy is supported by the evidence that mice overexpressing a 2 d-1 show epileptiform activity and behavioral arrests associated with an increased number of excitatory synapses in the cortex. 31,32 Of interest, matrix metalloproteinases (MMPs), which cleave extracellular matrix (EM) proteins and regulate synaptogenesis, have an active role in epileptogenesis in different experimental animal models, 33 and the EM protein, SC1, translocates from neuronal cell bodies to excitatory nerve terminals following status epilepticus in the rat lithium-pilocarpine model.…”

“…These mice also showed a reduced expression of a 2 d-1/2 protein levels in the cortex, suggesting that the thrombospondin/a 2 d axis is a key regulator of susceptibility to seizures. 35 The importance of the thrombospondin/a 2 d axis in the pathophysiology of epilepsy is supported by the evidence that mice overexpressing a 2 d-1 show epileptiform activity and behavioral arrests associated with an increased number of excitatory synapses in the cortex. 36 Here, we showed for the first time that expression of the Thbs1 gene encoding for thrombospondin-1 was substantially reduced in the ventrobasal thalamus of WAG/Rij rats, which represent an established genetic animal model of spontaneous absence epilepsy.…”