Fructose diet ameliorate effects of macrophage migration inhibitory factor deficiency on prefrontal cortex inflammation, neural plasticity, and behavior in male mice.

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine that represents a link between diet-induced inflammation and insulin resistance. Our aim was to examine whether fructose diet affects inflammation and insulin signaling in the prefrontal cortex (PFC) of Mif knockout mice (MIF-KO), and their possible link to neural plasticity and behavior. We analyzed nuclear factor κB (NF-κB) and glucocorticoid signaling, expression of F4/80, IL-1ß, TNF-α, TLR-4, MyD88, arginase 1 (Arg-1), mannose receptor (Mrc-1), and leukemia inhibitory factor (Lif) to assess inflammation in the PFC of C57/BL6J and MIF-KO mice consuming 20% fructose solution for 9 weeks. Insulin receptor (IR), IRS-1 serine phosphorylations (307 and 1101) and activity of PKCα, Akt, GSK-3ß and AMPKα were used to analyze insulin signaling. Brain-derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1) mRNA levels, together with synapthophysin and PSD-95 protein level and calcium calmodulin-dependent kinase 2 (CaMKII) activity, were used as plasticity markers. Behavior was examined in elevated plus maze, light dark box and novel object recognition test. The results showed concomitant increase of Tnf-α, Tlr-4, MyD88 and M2 microglia markers (Arg-1, Mrc-1, Lif) in the PFC of MIF-KO, paralleled with unchanged glucocorticoid and insulin signaling. Increase of BDNF and IGF-1 was paralleled with increased CaMKII activity, decreased PSD-95 protein level, anxiogenic behavior, and impaired memory in MIF-KO mice. Fructose feeding restored these parameters in the PFC to the control level and mitigated behavioral changes, suggesting that ameliorating effects of fructose on neuroinflammation and behavior depend on the presence of MIF.

Effects of a fructose-rich diet and chronic stress on insulin signaling and regulation of glycogen synthase kinase-3 beta and the sodium-potassium pump in the hearts of male rats.

Both a diet rich in fructose and chronic stress exposure induce metabolic and cardiovascular disturbances. The aim of this study was to examine the effects of the fructose-rich diet and chronic stress, separately and in combination, on insulin signaling and molecules regulating glycogen synthesis and ion transport in the heart, and to reveal whether these effects coincide with changes in glucocorticoid receptor (GR) activation. Male Wistar rats were subjected to 10% fructose in drinking water and/or to chronic unpredictable stress for 9 weeks. Protein expression and/or phosphorylation of the insulin receptor (IR), protein tyrosine phosphatase 1B, insulin receptor substrate 1 (IRS1), protein kinase B (Akt), extracellular signal-regulated kinase 1/2 (ERK1/2), glycogen synthase kinase-3ß (GSK-3ß) and Na+/K+-ATPase α-subunits in cardiac tissue were analyzed by western blot. GR distribution between cytosolic and nuclear fractions was also analyzed. The fructose-rich diet decreased the level of pERK1/2 (Thr202/Tyr204) and pGSK-3ß (Ser9) independently of stress, while chronic stress increased the IRS1 content and prevented the fructose diet-induced decrease of the pAkt (Ser473) level. The fructose-rich diet in combination with chronic stress reduced the protein content of cardiac IR and attenuated IRS1 upregulation. Separate treatments increased the protein content of Na+/K+-ATPase α1- and α2-subunits, while after combined treatment the α2 content was at the control level and the α1 content was lower than the control level. The effect of combined treatment on cardiac IR and α2-subunit expression could be mediated by increased GR nuclear accumulation. Our study provides new insights into the effects of chronic stress and a combination of the fructose diet and chronic stress on the studied molecules in the heart.

Disturbances of systemic and hippocampal insulin sensitivity in macrophage migration inhibitory factor (MIF) knockout male mice lead to behavioral changes associated with decreased PSA-NCAM levels.

Macrophage migration inhibitory factor (MIF) is a multifunctional cytokine well known for its role in inflammation enhancement. However, a growing body of evidence is emerging on its role in energy metabolism in insulin sensitive tissues such as hippocampus, a brain region implicated in cognition, learning and memory. We hypothesized that genetic deletion of MIF may result in the specific behavioral changes, which may be linked tо impairments in brain or systemic insulin sensitivity by possible changes of the hippocampal synaptic plasticity. To assess memory, exploratory behavior and anxiety, three behavioral tests were applied on Mif gene-deficient (MIF-/-) and "wild type" C57BL/6J mice (WT). The parameters of systemic and hippocampal insulin sensitivity were also determined. The impact of MIF deficiency on hippocampal plasticity was evaluated by analyzing the level of synaptosomal polysialylated-neural cell adhesion molecule (PSA-NCAM) plasticity marker and mRNA levels of different neurotrophic factors. The results showed that MIF-/- mice exhibit emphasized anxiety-like behaviors, as well as impaired recognition memory, which may be hippocampus-dependent. This behavioral phenotype was associated with impaired systemic insulin sensitivity and attenuated hippocampal insulin sensitivity, characterized by increased inhibitory Ser307 phosphorylation of insulin receptor substrate 1 (IRS1). Finally, MIF-/- mice displayed a decreased hippocampal PSA-NCAM level and unchanged Bdnf, NT-3, NT-4 and Igf-1 mRNA levels. The results suggest that the lack of MIF leads to disturbances of systemic and hippocampal insulin sensitivity, which are possibly responsible for memory deficits and anxiety, most likely through decreased PSA-NCAM-mediated neuroplasticity rather than through neurotrophic factors.