br Conclusion br Conflicts of Interest br Author Contributio

Conclusion
Conflicts of Interest
Author Contributions
Acknowledgments
Introduction Obesity is a typical lifestyle-related disease (Stein and Colditz, 2004). The disrupted balance between energy intake and energy expenditure causes obesity, which is defined as the excess accumulation of fat mass (Friedman, 2009). Diet-induced obesity is associated with inflammation not only in the peripheral tissues but also in the hypothalamus (De Souza et al., 2005), by which energy balance is primarily regulated (Morton et al., 2006). The consumption of a high-fat diet (HFD) increases the expression levels of tumor necrosis factor-alpha (TNFα) and interleukin-6 (IL-6) in the arcuate nucleus and lateral hypothalamus (Thaler et al., 2012; De Souza et al., 2005), leading to leptin resistance (De Souza et al., 2005; Zhang et al., 2008; De Git and Adan, 2015). The hypothalamic inflammation induced by a HFD is reported to occur prior to substantial body weight gain, suggesting that it might play a causal role in obesity (Valdearcos et al., 2014; Thaler et al., 2012; De Git and Adan, 2015). Recent studies suggest that glial cells, including microglia, are involved in the inflammatory processes in response to a HFD (De Git and Adan, 2015; Argente-Arizon et al., 2015), although the precise mechanisms by which glial cells regulate hypothalamic inflammation remain to be elucidated. Protein tyrosine phosphatase 1B (PTP1B) is a non-receptor tyrosine phosphatase that is widely expressed in the body, and negatively regulates leptin signaling by dephosphorylating Janus Activating Kinase 2 (JAK2) in the hypothalamus (Tsou and Bence, 2012; Myers et al., 2001; Zhang et al., 2015). Animals under HFD conditions show increased PTP1B expression in the hypothalamus (Zabolotny et al., 2008), and that increase facilitates the storage of body fat (Picardi et al., 2008; White et al., 2009; Zabolotny et al., 2008). Moreover, PTP1B–deficiency in the whole body, AZD 0530 cost or proopiomelanocortin (POMC) neurons leads to the increased phosphorylation of JAK2, and protects against obesity induced by a HFD (Klaman et al., 2000; Bence et al., 2006; Banno et al., 2010; Zabolotny et al., 2002; Cheng et al., 2002). PTP1B has also been implicated in the regulation of inflammatory responses in cells, including macrophages, myeloid cells and microglia (Zhang et al., 2013; Grant et al., 2014; Pike et al., 2014; Song et al., 2016). However, the role of PTP1B in hypothalamic inflammation induced by a HFD has yet to be clarified.
Materials and Methods
Results
Discussion It is reported that a HFD reduces leptin-induced STAT3 phosphorylation in the arcuate nucleus of WT mice (Munzberg et al., 2004), and that leptin sensitivity in hypothalamic neurons was increased in PTP1B KO compared to WT mice, which makes KO mice resistant to diet-induced obesity (Zabolotny et al., 2002; Bence et al., 2006). In the present study, hypothalamic inflammation, which could be related to obesity and leptin resistance (De Git and Adan, 2015), was examined in mice at the age of 7weeks when there were no significant differences in body weight between the WT and KO mice fed a HFD. Thus, the comparison between genotypes in the present study has provided us with an opportunity to elucidate the underlying mechanisms by which body weight is increased in WT compared to KO mice on a HFD. Consistent with previous studies (De Souza et al., 2005; Valdearcos et al., 2014), our data showed that TNFα immunoreactivity was increased in the arcuate nucleus in WT mice maintained on a HFD, but this was not the case in PTP1B KO mice. The analyses of Tnf and Il10 mRNA expression levels further support the conclusion that inflammation in the hypothalamus was not activated in KO mice at the age of 7weeks. Thus, it is indicated that hypothalamic inflammation preceded the relative increases in body weight in WT compared to KO mice fed a HFD. On the other hand, our data also showed that there were no significant differences in the activation of signaling pathways such as p65, p38, JNK and ERK between genotypes. This is probably because these signal transducers downstream from the TNFα receptor are not substrates for PTP1B (Tsou and Bence, 2012).