Adenosine kinase is a target for the prediction and prevention of epileptogenesis in mice

Abstract

Astrogliosis is a pathological hallmark of the epileptic brain. The identification of mechanisms that link astrogliosis to neuronal dysfunction in epilepsy may provide new avenues for therapeutic intervention. Here we show that astrocyte-expressed adenosine kinase (ADK), a key negative regulator of the brain inhibitory molecule adenosine, is a potential predictor and modulator of epileptogenesis. In a mouse model of focal epileptogenesis, in which astrogliosis is restricted to the CA3 region of the hippocampus, we demonstrate that upregulation of ADK and spontaneous focal electroencephalographic seizures were both restricted to the affected CA3. Furthermore, spontaneous seizures in CA3 were mimicked in transgenic mice by overexpression of ADK in this brain region, implying that overexpression of ADK without astrogliosis is sufficient to cause seizures. Conversely, after pharmacological induction of an otherwise epileptogenesis-precipitating acute brain injury, transgenic mice with reduced forebrain ADK were resistant to subsequent epileptogenesis. Likewise, ADK-deficient ES cell-derived brain implants suppressed astrogliosis, upregulation of ADK, and spontaneous seizures in WT mice when implanted after the epileptogenesis-precipitating brain injury. Our findings suggest that astrocyte-based ADK provides a critical link between astrogliosis and neuronal dysfunction in epilepsy.

Adenosine dysfunction in astrogliosis: cause for seizure generation?

“…This in turn causes adenosine deficiency, increased neuronal excitability and seizure generation. This hypothesis (Boison, 2008b) is based on previous work correlating astrogliosis and upregulation of ADK with the emergence of spontaneous seizures (Gouder et al, 2004;Fedele et al, 2005;Li et al, 2008). Here we expand these previous studies by providing a comprehensive analysis of the spatio-temporal requirements of ADK dysregulation in a new mouse model of focal CA3-selective epileptogenesis (Li et al, 2008).…”

“…This hypothesis (Boison, 2008b) is based on previous work correlating astrogliosis and upregulation of ADK with the emergence of spontaneous seizures (Gouder et al, 2004;Fedele et al, 2005;Li et al, 2008). Here we expand these previous studies by providing a comprehensive analysis of the spatio-temporal requirements of ADK dysregulation in a new mouse model of focal CA3-selective epileptogenesis (Li et al, 2008). To provide mechanistic insight of adenosine dysfunction in epileptogenesis, we will study astrogliosis and seizure generation in transgenic mice (1) with overexpressed ADK in brain (having an astrogliosis-independent adenosine deficiency), (2) with reduced levels of forebrain ADK (having increased levels of forebrain adenosine), and (3) lacking A 1 receptors to assess the role of this downstream effector of an altered brain adenosine tone.…”

“…Animals were kept in a 12-hour light/dark cycle with lights on from 7 am to 7 pm in individually ventilated isolator cages and food and water were supplied ad libitum. Four different genotypes of mice were used in this study, all maintained on a C57BL/6 background: (1) wild type; (2) homozygous Adk-tg mice with brain wide overexpression of a conditional Adk-transgene, but lack of the endogenous Adk gene; these animals are characterized by high ADK expression in CA3 neurons and have been characterized previously (Fedele et al, 2005;Pignataro et al, 2007;Wu and Boison, 2007;Yee et al, 2007;Li et al, 2008); (3) fb-Adk-def mice with reduced levels of forebrain ADK were created based on Emx1-Cre driven recombination of the loxP-flanked Adk-transgene in Adk-tg mice (Li et al, 2008); (4) homozygous and heterozygous A 1 receptor knockout mice (Johansson et al, 2001;Fedele et al, 2006).…”

“…Adult male mice weighing 25-30g underwent seizures induced by unilateral stereotaxic microinjection of KA into the basolateral amygdaloidal nucleus based on stereotactic coordinates relative to bregma: AP = -0.94 mm, L = -2.85 mm, V = -3.75 mm as described (Li et al, 2008). Briefly, under anesthesia with 68.5% N 2 O, 30% O 2 , and 1.5% isoflurane, mice were affixed with a 26-gauge steel guide cannula over the intact dura using dental cement, two cortical recording electrodes and a bipolar, coated, stainless steel electrode (0.2 mm in diameter, Plastics One, Roanoke, VA), which was implanted into the ipsilateral CA3 region and fixed with a pedestal of dental acrylate; this setup was used for chronic video-EEG monitoring (over up to three weeks, Fig.…”

“…Non-convulsive electrographic status epilepticus (SE) was triggered in six adult male C57BL/ 6 mice by intraamygdaloid injection of kainic acid (KA) as described previously (Li et al, 2008). Three weeks after KA-injection bipolar electrodes were implanted into the ipsilateral CA3 region.…”