Tumor Necrosis Factor Alpha in Kainic Acid Induced Neurodegeneration

Abstract

Event Abstract Back to Event Tumor Necrosis Factor Alpha in Kainic Acid Induced Neurodegeneration Sara S. Sharkawi1* and Abdu Adem1 1 United Arab Emirates University, Pharmacology and Therapeutics, United Arab Emirates INTRODUCTION Excitotoxicity and oxidative stress are largely considered as common pathway of cellular injury in many human acute and chronic neurodegenerative diseases, including ischemia, Alzheimer’s disease and Parkinson disease [1, 2]. Tumor necrosis factor alpha (TNF-α) is a proinflammatory cytokine with homeostatic and pathophysiological roles in the central nervous system (CNS) [3]. It was shown that mice lacking TNF receptor-1 (TNFR1) exhibit greater neurodegeneration in kainic acid (KA)-induced neurotoxicity, suggesting that TNF-α exerts its protective role via TNFR1 [4]. The nerve growth factor (NGF) is involved primarily in the growth, maintenance, proliferation, and survival of neurons. Insulin-like growth factor-I (IGF-I) protects neurons against a wide range of injuries [5]. The objective of the present study is to investigate the role of TNF-α on KA-induced neurotoxicity at several time points in order to find out the possible mechanisms underlying its effects. METHODOLOGY TNF-α knockout (KO) and wild-type (WT) C57BL/6 male mice (6-8 weeks-old) were partially anesthetized with Isofluen and given KA dissolved in water (10 mg/1.3 ml) intranasally at a dose of 40mg/kg bodyweight [6]. Mice were sacrificed, hippocampi were dissected and kept in liquid nitrogen. Protein extraction is performed in T-PER tissue protein extraction reagent. Levels of glutathione (GSH), malondialdhyde (MDA), β-NGF, and IGF-I were assessed by ELISA using commercially available kits. For immunohistochemistry, mice were anesthetized, transcardially perfused, brains fixed and sectioned. Frozen hippocampal sections were exposed to rabbit anti-glial fibrillary acidic protein (GFAP) for astrocytes and rabbit antiionized calcium binding adaptor molecule-1 (Iba-1) [4]. RESULTS KA induces seizures in all the mice, however TNF-α KO mice showed more severe and long lasting seizures (Fig. 1). KA also produced oxidative stress in both strains represented by increased levels of MDA 30 min post KA administration. However, the MDA levels were significantly higher in TNF-α KO mice 1 day post KA treatment compared to Wt-mice (Fig. 2A). The Wt-mice showed a compensatory mechanism by increasing the levels of GSH 1 day and 3 days post KA treatment. However, the TNF-α KO mice failed to compensate and the GSH stores were depleted (Fig. 2B). Levels of IGF-I in hippocampal supernatants were significantly reduced in TNF-α KO mice 30 min and 4 hours post KA treatment, while it is reduced in Wt mice 4 hours post KA treatment then returned to its normal levels (Fig. 3A). Levels of β-NGF remained unchanged in Wt mice while it is significantly elevated in TNF-α KO mice (Fig 3B). KA resulted in increased expression of both GFAP and Iba-1 in the hippocampi of both groups; however, the expression was significantly higher in the TNF-α KO mice than in the Wt-mice (Fig. 4). Interestingly, astrogliosis and microglial activation were evident for up to 1 month after KA treatment especially in TNF-α KO mice with high seizure scores. CONCLUSION TNF-α deficiency worsens KA-induced neurotoxicity, as evident by more severe seizure activity, severe oxidative stress, depletion of GSH, reduced levels of IGF-I, induction of β-NGF as compensation to the severe damage, and prolonged astrogliosis and more activated microglia. Figure 1 Figure 2 Figure 3 Figure 4