Crosstalk between BDNF and TNFα in brain versus serum of the cuprizone-induced multiple sclerosis in C57BL/6 mice

Introduction: Brain-derived neurotrophic factor (BDNF) and tumor necrosis factor-α (TNFα) are two critical factors in multiple sclerosis (MS). The aim of the present study is comparing the crosstalk between BDNF and TNFα in the brain versus serum and their effects on recovery of C57BL/6 mice demyelination in cuprizone model. Methods: Fifteen C57BL/6 mice 6-week-old in three different groups were used: control (standard rodent chow), cuprizone-exposed1 (CPZ1; 0.2% cuprizone feeding for 5 weeks) and cuprizone-exposed2 (CPZ2; 0.2% cuprizone feeding for 5 weeks followed by 2 weeks of cuprizone withdrawal). To prove MS induction and cognitive behavioral impairment, Y-maze test and histological studies with luxol fast blue staining were done. The levels of BDNF and TNFα in the brain and serum were measured by ELIZA kits. Results: In the present study, Y-maze test demonstrated that MS significantly impaired the cognitive behavior in both CPZ groups compared to control group. Demyelination in corpus callosum (CC) significantly was higher in the two CPZ groups relative to control group. The brain levels of BDNF significantly decreased while the brain levels of TNFα significantly increased in both CPZ groups compared to control group. Serum levels of BDNF and TNFα significantly increased in CPZ1 group compared to control group. Conclusion: According to the present results, cuprizone-induced MS caused to an extensive demyelination in CC, which led to impaired cognitive behavior. Moreover, brain and serum levels of BDNF and TNFα as well as their crosstalk were affected by cuprizone exposure. iD D ow nl oa de d fr om p pj . p hy ph a. ir at 1 0: 20 + 03 30 o n M on da y N ov em be r 4t h 20 19 175 | Physiol Pharmacol 23 (2019) 174-182 Rowhani-Rad et al. a specific role in MS (Patanella et al., 2010). Investigations showed that TNFα as a proinflammatory cytokine, is the principal mediator in immune defense as well as the development and maintenance of the immune system, and its level elevates in a variety of the CNS disorders such as MS by secretion from autoreactive T cells, microglia and astrocytes (Lim and Constantinescu, 2010). This factor can exhibit both neuroprotective and neurodegenerative properties (Saha et al., 2006). Moreover, it can significantly alter the levels of a brain neurotrophic factor (BDNF) (Patanella et al., 2010). One of the brain neurotrophin families that most widely distributed in the CNS is the BDNF. Multiple cell types including CNS neurons and glia, B and T lymphocytes and monocytes in blood can express it (Caggiula et al., 2005; Saha et al., 2006; Klein et al., 2011). This factor participates in neuronal growth and maintenance, as well as in different aspects of activity-dependent synaptic physiology (Saha et al., 2006). Some investigations showed that BDNF is mainly implicated in clinical recovery and it has neuroprotective effects during physiological and pathological conditions of the brain (Saha et al., 2006; Patanella et al., 2010). According to some evidence, BDNF can cross the blood–brain barrier in mice. However, it is uncertain whether blood BDNF levels can reflect brain BDNF levels across species (Klein et al., 2011). There are different results on the interaction and correlation between TNFα and BDNF in the brain and serum in various species of animals (Saha et al., 2006). In the present study, for MS induction determination, two procedures were used: 1Y-maze test, was used to investigate the impairment of spatial working memory and cognitive behavior in the MS model of C57BL/6 mice, 2luxol fast blue staining, is commonly used to observe myelin under light microscopy (Tsunoda et al., 2003). There are some investigations which used this staining for confirming the myelination (Boretius et al., 2012; Basoglu et al., 2013). On the other hand, the cuprizone mouse model allows the investigation of the complex molecular mechanisms behind nonautoimmune-mediated demyelination and spontaneous remyelination in animal MS model (Praet et al., 2014). At least in our search we have not found any direct report on the comparison between BDNF and TNF-α crosstalk in the brain versus serum of C57BL/6 mice cuprizone model of MS. The evaluation of BDNF and TNFα in other studies was not simultaneously in the brain and serum of cuprizone model of MS. Therefore, in the present study the main goal was to investigate the crosstalk between BDNF and TNF-α in the brain versus serum of the cuprizone-induced MS in C57BL/6 mice. Another goal of this study was to determine whether the spontaneous remyelination in the corpus callosum (CC) can be done in short time (two weeks) after cuprizone withdrawal or not. Materials and methods Animal Fifteen adult male C57BL/6 mice (6-weeks old, 18 to 21g) (Xu et al., 2010) were purchased from Pasteur Institute (Karaj, Iran). Research and animal care were approved by the review board for the care of animal subjects of the district government (Shiraz, Iran). The mice were housed in a temperature 20-24C, 12-hour light-dark cycle and humidity-controlled (Pfeifenbring et al., 2015).