Urocortin (UCN), a newly identified, 40-amino-acid, corticotropin-releasing hormone (CRH) structurally related peptide, has been demonstrated to be expressed in the central nervous system and many peripheral tissues of rats and man. This study aimed to investigate the expression profile of UCN in rat lung and the effect of UCN on lung vascular permeability. The expression of UCN mRNA was detected by reverse transcriptase PCR (RT–PCR). UCN peptide was measured by immunohistochemistry and Western blot analysis. We found that both UCN mRNA and peptide were obviously expressed in rat lung. Immunohistochemistry results showed that UCN peptide is mainly expressed in bronchial epithelium mucosa and alveolar epithelium. We also found that rats receiving inhalation aerosol of UCN had a significant elevation of lung vascular permeability compared with rats receiving vehicle and ovalbumin (OVA) by the Evans blue (EB) technique. UCN aerosol inhalation resulted in obvious pulmonary congestion and edema observed under light microscope by hematoxylin and eosin (HE) staining. The nonselective peptide CRH receptor antagonist astressin markedly reduced lung vascular permeability triggered by UCN. Enhanced pulmonary vascular permeability induced by UCN was markedly inhibited by pretreatment with the mast-cell stabilizer cromolyn and histamine-1 (H₁) receptor antagonist azelastine respectively, but not by the leukotriene receptor antagonist montelukast. In summary, in the present study, we demonstrated for the first time that UCN is expressed in rat lung and contributes to an increase in lung vascular permeability through activation of CRH receptors. Mast cells and histamine may be involved in this effect of UCN. Peripherally produced UCN in lung may act as an autocrine and paracrine proinflammatory factor.

Glucocorticoids are steroid hormones, secreted by the adrenals to regulate a range of metabolic, immunologic, and homeostatic functions. Due to their potent anti-inflammatory effects, synthetic glucocorticoids are widely used to treat inflammatory disorders. However, their use especially at high doses and over the long-term is associated with several unwanted side effects that compromises their intended use (e.g. glucocorticoid-induced osteoporosis and/or diabetes, myopathy, and skin atrophy). Both endogenous and synthetic glucocorticoids exert their effects through the glucocorticoid receptor, a transcription factor present in nearly all nucleated cells. Glucocorticoid receptor knockout mouse models have proved to be valuable tools in understanding how glucocorticoids contribute to skeletal health and disease. These models, described in this review, have helped to establish that the effects of glucocorticoids on the skeleton are multifaceted, cell specific and concentration dependent. Intriguingly, while endogenous glucocorticoids are essential for bone formation, high-dose exogenous glucocorticoids may induce bone loss. Additionally, the actions of endogenous glucocorticoids vary greatly depending on the disease microenvironment. For example, endogenous glucocorticoids have predominately beneficial anti-inflammatory effects in rheumatoid arthritis, but detrimental actions in osteoarthritis by driving cartilage loss and abnormal bone formation. Studies in tissue-specific knockout models provide important insights that will aid the development of new glucocorticoid therapeutics that can specifically target certain cell types to minimise unwanted effects from current glucocorticoid therapy.

Nonalcoholic fatty liver disease and cirrhosis are strongly associated with insulin resistance and glucose intolerance. To date, the influence of metformin on glycogen synthesis in the liver is controversial. Limited studies have evaluated the effect of metformin on hepatic insulin signaling pathway in vivo. In this study, an insulin-resistant rat model of nonalcoholic steatohepatitis and cirrhosis was developed by high-fat and high-sucrose diet feeding in combination with subcutaneous injection of carbon tetrachloride. Liver tissues of the model rats were featured with severe steatosis and cirrhosis, accompanied by impaired liver function and antioxidant capacity. The glucose tolerance was impaired, and the index of insulin resistance was increased significantly compared with the control. The content of hepatic glycogen was dramatically decreased. The expression of insulin receptor β (IRβ); phosphorylations of IRβ, insulin receptor substrate 2 (IRS2), and Akt; and activities of phosphatidylinositol 3-kinase (PI3K) and glycogen synthase (GS) in the liver were significantly decreased, whereas the activities of glycogen synthase kinase 3α (GSK3α) and glycogen phosphorylase a (GPa) were increased. Metformin treatment remarkably improved liver function, alleviated lipid peroxidation and histological damages of the liver, and ameliorated glucose intolerance and insulin resistance. Metfromin also significantly upregulated the expression of IRβ; increased the phosphorylations of IRβ, IRS2, and Akt; increased the activities of PI3K and GS; and decreased GSK3α and GPa activities. In conclusion, our study suggests that metformin upregulates IRβ expression and the downstream IRS2/PI3K/Akt signaling transduction, therefore, to increase hepatic glycogen storage and improve insulin resistance. These actions may be attributed to the improved liver histological alterations by metformin.

Locally synthesized atrial natriuretic peptide (ANP) and its receptors have been found in reproductive tissues of various mammals, and play an important role in the acrosome reaction of human sperm. The objective of the present study was to examine the expression of ANP and its receptors in pig spermatozoa and oviduct, and the effect of ANP on pig spermatozoa function. The expression of ANP and its receptors was analyzed by RT-PCR. Only natriuretic peptide receptors-A (NPRA) mRNA was detected in fresh sperm. While the levels of natriuretic peptide receptors-C (NPRC) mRNA were low with no obvious change among different oviductal phases, the levels of ANP mRNA were high in oviduct(OT)1 , OT3 and OT5, but were very low in OT2. On the other hand, the levels of NPRA mRNA were low in OT1 and OT2, increased in OT3 and reached a maximum in OT4 and OT5. Western blot analysis revealed that the level of ANP was high in OT1, decreased in OT2 and OT3, and arrived at the nadir in OT4 and OT5. The effect of ANP on spermatozoa function was studied by the acrosome reaction and IVF. Incubation with ANP for 1 h significantly induced acrosome reaction of preincubated spermatozoa, and maximal response of acrosome reaction (34.1 ± 2.3%) was achieved at 1 nM ANP treatment. Both C-ANP-(4–23), a selective ligand of NPRC, and caffeine had no effect on the acrosome reaction. The stimulatory effect of ANP on acrosome reaction could be mimicked by the permeable cGMP analog, 8-Br-cGMP. ANP and caffeine had a similar effect on improving the oocytes penetration rate, polyspermy rate and the average number of sperm per penetrated oocyte. Also, ANP treatment had a similar effect on cleavage rate, blastocyst formation rate and the number of cells per blastocyst as that of caffeine treatment. The effects of ANP on the acrosome reaction and the parameters of oocyte penetration could be blocked by cGMP-dependent protein kinase (PKG) inhibitors KT5823 and/or Rp-8-pCPT-cGMPS. These results suggest that the expression of ANP in the oviduct may be involved in the regulation of the acrosome reaction and the fertilising ability of pig spermatozoa, and the PKG pathway possibly participates in the process.

Impaired glucose-stimulated insulin secretion (GSIS) and increasing β-cell death are two typical dysfunctions of pancreatic β-cells in individuals that are destined to develop type 2 diabetes, and improvement of β-cell function through GSIS enhancement and/or inhibition of β-cell death is a promising strategy for anti-diabetic therapy. In this study, we discovered that the small molecule, N-(2-benzoylphenyl)-5-bromo-2-thiophenecarboxamide (BBT), was effective in both potentiating GSIS and protecting β-cells from cytokine- or streptozotocin (STZ)-induced cell death. Results of further studies revealed that cAMP/PKA and long-lasting (L-type) voltage-dependent Ca^{2 +} channel/CaMK2 pathways were involved in the action of BBT against GSIS, and that the cAMP/PKA pathway was essential for the protective action of BBT on β-cells. An assay using the model of type 2 diabetic mice induced by high-fat diet combined with STZ (STZ/HFD) demonstrated that BBT administration efficiently restored β-cell functions as indicated by the increased plasma insulin level and decrease in the β-cell loss induced by STZ/HFD. Moreover, the results indicated that BBT treatment decreased fasting blood glucose and HbA1c and improved oral glucose tolerance further highlighting the potential of BBT in anti-hyperglycemia research.

Insulin receptor substrate 1 (IRS1) is an essential molecule for the intracellular signaling of IGF1 and insulin, which are potent anabolic regulators of bone metabolism. Osteoblastic IRS1 is essential for maintaining bone turnover; however, the mechanism underlying this regulation remains unclear. To clarify the role of IRS1 in bone metabolism, we employed RNA interference to inhibit IRS1 gene expression and observed the effects of silencing this gene on the proliferation and differentiation of and the expression of matrix metallopeptidase (MMP) and tumor necrosis factor receptor superfamily, member 11b (TNFRSF11B) in MC3T3-E1 cells. Our results showed that IRS1 short hairpin RNAs can effectively suppress the expression of IRS1, and inhibit the phosphorylation of AKT in IRS1 pathway; reduce the expression of MMP2, MMP3, MMP13, and MMP14, decrease the expression of TNFRSF11B and RANKL (also known as tumor necrosis factor (ligand) superfamily, member 11), however increase the RANKL/TNFRSF11B ratio; decrease cell survival, proliferation, and mineralization, and impair the differentiation of MC3T3-E1 cells. The downregulation of IRS1 had no effect on the expression of MMP1. Our findings suggest that IRS1 not only promotes bone formation and mineralization but also might play roles in bone resorption partly via the regulation of MMPs and RANKL/TNFRSF11B ratio, thus regulates the bone turnover.

Overnutrition-induced endothelial inflammation plays a crucial role in high-fat diet (HFD)-induced insulin resistance in animals. Endothelial glycolysis plays a critical role in endothelial inflammation and proliferation, but its role in diet-induced endothelial inflammation and subsequent insulin resistance has not been elucidated. PFKFB3 is a critical glycolytic regulator, and its increased expression has been observed in adipose vascular endothelium of C57BL/6J mice fed with HFD in vivo, and in palmitate (PA)-treated primary human adipose microvascular endothelial cells (HAMECs) in vitro. We generated mice with Pfkfb3 deficiency selective for endothelial cells to examine the effect of endothelial Pfkfb3 in endothelial inflammation in metabolic organs and in the development of HFD-induced insulin resistance. EC Pfkfb3-deficientmice exhibited mitigated HFD-induced insulin resistance, including decreased body weight and fat mass, improved glucose clearance and insulin sensitivity, and alleviated adiposity and hepatic steatosis. Mechanistically, cultured PFKFB3 knockdown HAMECs showed decreased NF-κB activation induced by PA, and consequent suppressed adhesion molecule expression and monocyte adhesion. Taken together, these results demonstrate that increased endothelial PFKFB3 expression promotes diet-induced inflammatory responses and subsequent insulin resistance, suggesting that endothelial metabolic alteration plays an important role in the development of insulin resistance.

Insulin resistance-related disorders are associated with endothelial dysfunction. Accumulating evidence has suggested a role for adenosine signaling in the regulation of endothelial function. Here, we identified a crucial role of endothelial adenosine kinase (ADK) in the regulation of insulin resistance. Feeding mice with a high-fat diet (HFD) markedly enhanced the expression of endothelial Adk. Ablation of endothelial Adk in HFD-fed mice improved glucose tolerance and insulin sensitivity and decreased hepatic steatosis, adipose inflammation and adiposity, which were associated with improved arteriole vasodilation, decreased inflammation and increased adipose angiogenesis. Mechanistically, ADK inhibition or knockdown in human umbilical vein endothelial cells (HUVECs) elevated intracellular adenosine level and increased endothelial nitric oxide synthase (NOS3) activity, resulting in an increase in nitric oxide (NO) production. Antagonism of adenosine receptor A2b abolished ADK-knockdown-enhanced NOS3 expression in HUVECs. Additionally, increased phosphorylation of NOS3 in ADK-knockdown HUVECs was regulated by an adenosine receptor-independent mechanism. These data suggest that Adk-deficiency-elevated intracellular adenosine in endothelial cells ameliorates diet-induced insulin resistance and metabolic disorders, and this is associated with an enhancement of NO production caused by increased NOS3 expression and activation. Therefore, ADK is a potential target for the prevention and treatment of metabolic disorders associated with insulin resistance.