OBJECTIVEWe have previously shown that serum insulin levels decrease threefold and blood glucose levels remain normal in mice fed a leucine-deficient diet, suggesting increased insulin sensitivity. The goal of the current study is to investigate this possibility and elucidate the underlying cellular mechanisms.RESEARCH DESIGN AND METHODSChanges in metabolic parameters and expression of genes and proteins involved in regulation of insulin sensitivity were analyzed in mice, human HepG2 cells, and mouse primary hepatocytes under leucine deprivation.RESULTSWe show that leucine deprivation improves hepatic insulin sensitivity by sequentially activating general control nonderepressible (GCN)2 and decreasing mammalian target of rapamycin/S6K1 signaling. In addition, we show that activation of AMP-activated protein kinase also contributes to leucine deprivation–increased hepatic insulin sensitivity. Finally, we show that leucine deprivation improves insulin sensitivity under insulin-resistant conditions.CONCLUSIONSThis study describes mechanisms underlying increased hepatic insulin sensitivity under leucine deprivation. Furthermore, we demonstrate a novel function for GCN2 in the regulation of insulin sensitivity. These observations provide a rationale for short-term dietary restriction of leucine for the treatment of insulin resistance and associated metabolic diseases.

Probiotics actively participate in neuropsychiatric disorders. However, the role of gut microbiota in brain disorders and vascular dementia (VaD) remains unclear. We used a mouse model of VaD induced by a permanent right unilateral common carotid arteries occlusion (rUCCAO) to investigate the neuroprotective effects and possible underlying mechanisms of Clostridium butyricum. Following rUCCAO, C. butyricum was intragastrically administered for 6 successive weeks. Cognitive function was estimated. Morphological examination was performed by electron microscopy and hematoxylin-eosin (H&E) staining. The BDNF-PI3K/Akt pathway-related proteins were assessed by western blot and immunohistochemistry. The diversity of gut microbiota and the levels of butyrate in the feces and the brains were determined. The results showed that C. butyricum significantly attenuated the cognitive dysfunction and histopathological changes in VaD mice. C. butyricum not only increased the levels of BDNF and Bcl-2 and decreased level of Bax but also induced Akt phosphorylation (p-Akt) and ultimately reduced neuronal apoptosis. Moreover, C. butyricum could regulate the gut microbiota and restore the butyrate content in the feces and the brains. These results suggest that C. butyricum might be effective in the treatment of VaD by regulating the gut-brain axis and that it can be considered a new therapeutic strategy against VaD.

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Chronic feeding of HCD (high-carbohydrate diet) is one of the major contributors to the prevailing of metabolic diseases. ATF4 (activating transcription factor 4) has been shown to play an important role in the regulation of glucose metabolism and obesity development; however, it is unclear how ATF4(-/-) mice respond to HCD. In the present study, we show that 8 weeks of HCD results in significant higher accumulation of TAGs (triacylglycerols) in livers and impairment in glucose tolerance in ATF4(+/+) mice, but not in ATF4(-/-) mice, compared with those on a normal diet. Meanwhile, energy expenditure is further enhanced by HCD in ATF4(-/-) mice. Moreover, we show that ATF4 deficiency suppresses HCD-induced SCD1 (stearoyl-CoA desaturase 1) expression, furthermore, oral supplementation of the main product of SCD1 oleate (18:1) increases TAG accumulation in livers of ATF4(-/-) mice. Taken together, these results suggest that ATF4 deficiency is protective for HCD-induced hepatic steatosis and impairment of glucose tolerance and insulin sensitivity. Furthermore, the resistance to hepatic steatosis is at least in part due to suppression of SCD1 expression under HCD.