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This study was performed to understand whether P165 improves learning and memory by restoring insulin action using a diabetes mellitus (DM) rat model. A total of 34 male Sprague-Dawley rats were randomly divided into four groups: control group ( n = 8), DM group ( n = 8), DM group treated with a low dose of P165 ( n = 9), and DM group treated with a high dose of P165 ( n = 9). After 8 weeks of treatment, the animals were killed and the expression of insulin signaling-related proteins was examined in the hippocampus by Western blot and immunohistochemical staining. Administration of P165 in diabetic rats did not induce a significant effect on the fasting blood glucose level. The expression of IR, IRS-1, AKT, p-CREB, and Bcl-2 proteins was significantly enhanced in the hippocampus in diabetic rats. Treatment of diabetic rats with P165 at both low and high doses significantly attenuated the expression levels of these proteins. Moreover, immunohistochemistry staining showed that IR, IRS-1, AKT, p-CREB, and Bcl-2 were abundantly expressed in the CA1 region of the hippocampus. The number of cells positively stained for the above proteins was significantly higher in diabetic tissues compared to control tissues, whereas P165 treatments induced a significant reduction in the expression of these proteins. The expression of IR, IRS-1, AKT, p-CREB, and Bcl-2 was enhanced in DM rats, and administration of P165 normalized the expression of these molecules, suggesting that P165 can improve impaired insulin signal transduction. [ABSTRACT FROM AUTHOR]

Aim: Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) is known as a mammalian cell energy sensor, which could regulate cellular energy metabolism via sensing the alterations of energy balance, such as oversupply or lack of glucose and fatty acid. Recent studies have suggested that AMPK could also regulate many other biological processes, including cell cycling, inflammation, protein synthesis, and so on. In this study, AMPK signaling in high-glucose-induced dysfunction of mesangial cells (MCs) was investigated. Methods: Established rat glomerular MCs were treated under normal glucose (5.6 mM glucose) or high-glucose conditions (30 mM glucose). mRNA levels of AMPK subunits were detected by reverse transcriptase-polymerase chain reaction. Expressions of AMPK α, phosphorylated AMPK α (p-AMPK α), phosphorylated acetyl-CoA carboxylase (p-ACC), and collagen IV were measured by Western blot. Results: Under high-glucose conditions, AMPK α protein expression and mRNA levels were significantly decreased. High-glucose treatment also induced a notable decrease in p-AMPK α and p-ACC expression. AMPK α activation by 5-aminoimidazole-4-carboxamide-1- β-d-ribofuranoside (AICAR) effectively ameliorated high-glucose-induced dysfunction of MCs, including cell proliferation, cell-cycle progression, and collagen IV production. Conclusion: High glucose impaired AMPK α in its expression and activity; AICAR significantly ameliorated high-glucose-induced proliferation of MCs and collagen IV production, indicating a role of AMPK α in high-glucose-induced dysfunction of MCs. [ABSTRACT FROM AUTHOR]

Abstract: Fructose is a nutritional composition of fruits and honey. Its excess consumption induces insulin resistance-associated metabolic diseases. Hypothalamic insulin signaling plays a pivotal role in controlling whole-body insulin sensitivity and energy homeostasis. Quercetin, a natural flavonoid, has been reported to ameliorate high fructose-induced rat insulin resistance and hyperlipidemia. In this study, we investigated its regulatory effects on the hypothalamus of high fructose-fed rats. Rats were fed 10% fructose in drinking water for 10 weeks. After 4 weeks, these animals were orally treated with quercetin (50 and 100 mg/kg), allopurinol (5 mg/kg) and water daily for the next 6 weeks, respectively. Quercetin effectively restored high fructose-induced hypothalamic insulin signaling defect by up-regulating the phosphorylation of insulin receptor and protein kinase B. Furthermore, quercetin was found to reduce metabolic nutrient sensors adenosine monophosphate-activated protein kinase (AMPK) activation and thioredoxin-interacting protein (TXNIP) overexpression, as well as the glutamine–glutamate cycle dysfunction in the hypothalamus of high fructose-fed rats. Subsequently, it ameliorated high fructose-caused hypothalamic inflammatory lesions in rats by suppressing the activation of hypothalamic nuclear factor κB (NF-κB) pathway and NOD-like receptor 3 (NLRP3) inflammasome with interleukin 1β maturation. Allopurinol had similar effects. These results provide in vivo evidence that quercetin-mediated down-regulation of AMPK/TXNIP and subsequent inhibition of NF-κB pathway/NLRP3 inflammasome activation in the hypothalamus of rats may be associated with the reduction of hypothalamic inflammatory lesions, contributing to the improvement of hypothalamic insulin signaling defect in this model. Thus, quercetin with the central activity may be a therapeutic for high fructose-induced insulin resistance and hyperlipidemia in humans. [Copyright &y& Elsevier]

• GDF-15 expression was increased in response to high-glucose stimulation. • Overexpression of GDF-15 can inhibit activation of NF-κB. • GDF-15 mediates nuclear translocation of NF-κB through IKK and IκB. • GDF-15 mediates the expression of NEDD4L. • NEDD4L is involved in GDF-15 mediated inhibition of the NF-κB signaling pathway. Podocyte inflammatory injury has been indicated to play a pivotal role in the occurrence and development of diabetic nephropathy (DN). However, the pathogenesis of inflammation remains unclear. Recent researches have shown that GDF-15, a member of the transforming growth factor-β superfamily, were elevated under pathological conditions, such as myocardial ischemia, cancer, as well as inflammation. Here, we demonstrated that GDF-15 could alleviate podocyte inflammatory injury by modulating the NF-κB pathway. GDF-15 and other pro-inflammatory factors, such as TNF-α, IL-1β, and IL-6 were upregulated in the serum of HFD/STZ rat models. GDF-15 was also elevated in diabetic glomeruli and hyperglycemic stimuli treated-podocytes. The silence of GDF-15 in HG-stimulated podocytes further augmented inflammation and podocyte injury, while overexpression of GDF-15 significantly reduced the inflammatory response in podocytes. Mechanistically, we demonstrated that GDF-15 could inhibit the nuclear translocation of NF-κB through IKK and IκBα by interaction with ubiquitin ligase NEDD4L. Taken together, our data suggested a protective mechanism of elevated GDF-15 in DN through obstruction of ubiquitin degradation of IKK by inhibiting NEDD4L expression, thus decreasing the activation of NF-κB and relieving the inflammation. GDF-15 could serve as a potential therapeutic target for DN. [ABSTRACT FROM AUTHOR]