Dehydroepiandrosterone (DHEA) may be a promising agent for postmenopausal osteoporosis (PMO), but its mechanism to modulate osteoblasts (OBs) is yet to be explained. To elucidate the effects of DHEA treatment on the ovariectomized (OVX) mice and its mechanisms, we evaluated the morphology of mice bone tissue and expression of proliferating cell nuclear antigen (PCNA) in the vertebrae-derived OB after having treated the OVX animals with DHEA. The results showed that DHEA administration increased the expression of PCNA in OB and changed the bone tissue morphometry of the PMO model. To further investigate this mechanism, the OB was isolated from neonatal mice calvariae by the enzyme-digested assay, exposed to DHEA, and then analyzed for ultrastructure, DNA content, early apoptotic cells, and phosphorylation of extracellular signal-regulated kinase 1/2. It was found that DHEA promoted proliferation and inhibited apoptosis of OB significantly, via mitogen-activated protein kinase signaling pathway independent of either androgen receptor or estrogen receptor, suggesting that it may exert roles via a DHEA-specific receptor directly, not by way of conversion to androgens or estrogens.
Ling Wang, Yu-Dong Wang, Wen-Jun Wang, Ying Zhu and Da-Jin Li
Yu-Feng Zhao, Li Wang, Dingjun Zha, Li Qiao, Lianjun Lu, Jun Yu, Ping Qu, Qiang Sun, Jianhua Qiu and Chen Chen
GW9508 is an agonist of G protein-coupled receptor 40 (GPR40) that is expressed in pancreatic β-cells and is reported to regulate insulin secretion. However, the effects of GW9508 on pancreatic β-cells in primary culture have not been well investigated. This study measured the acute effects of GW9508 on insulin secretion from rat pancreatic islets in primary culture, and the insulin secretion-related events such as the changes in membrane potential, ATP-sensitive potassium currents (KATP currents), and intracellular Ca2+ concentrations ([Ca2+]i) of rat islet β-cells were also recorded. GW9508 (10–40 μM) did not influence basal insulin levels at 2 mM glucose, but it (above 20 μM) significantly inhibited 5 and 15 mM glucose-stimulated insulin secretion (GSIS). GW9508 did not inhibit insulin secretion stimulated by tolbutamide, the closer of KATP channels. GW9508 activated KATP channels and blocked the membrane depolarization and the increase in [Ca2+]i that were stimulated by glucose. GW9508 itself stimulated a transient increase in [Ca2+]i, which was fully blocked by depletion of intracellular Ca2+ stores with thapsigargin or by inhibition of phospholipase C (PLC) activity with U73122. GW9508-induced activation of KATP channels was only partly inhibited by U73122 treatment. In conclusion, although it stimulates a transient release of Ca2+ from intracellular Ca2+ stores via activation of PLC, GW9508 inhibits GSIS by activating KATP channels probably in a distal step to GPR40 activation in rat β-cells.
Yu-Guang Ma, Liang Liang, Yin-Bin Zhang, Bao-Feng Wang, Yun-Gang Bai, Zhi-Jun Dai, Man-Jiang Xie and Zhong-Wei Wang
Hyperglycemia and hypertension are considered to be the two leading risk factors for vascular disease in diabetic patients. However, few pharmacologic agents could provide a combinational therapy for controlling hyperglycemia and hypertension at the same time in diabetes. The objectives of this study are to investigate whether berberine treatment could directly reduce blood pressure and identify the molecular mechanism underlying the vascular protection of berberine in diabetic rats. Berberine was intragastrically administered with different dosages of 50, 100 and 200 mg/kg/day to diabetic rats for 8 weeks since the injection of streptozotocin. The endothelium-dependent/-independent relaxation in middle cerebral arteries was investigated. The activity of large-conductance Ca2+-activated K+ channel (BKCa) was investigated by recording whole-cell currents, analyzing single-channel activities and assessing the expressions of α- and β1-subunit at protein or mRNA levels. Results of the study suggest that chronic administration of 100 mg/kg/day berberine not only lowered blood glucose but also reduced blood pressure and improved vasodilation in diabetic rats. Furthermore, berberine markedly increased the function and expression of BKCa β1-subunit in cerebral vascular smooth muscle cells (VSMCs) isolated from diabetic rats or when exposed to hyperglycemia condition. The present study provided initial evidences that berberine reduced blood pressure and improved vasodilation in diabetic rats by activation of BKCa channel in VSMCs, which suggested that berberine might provide a combinational therapy for controlling hyperglycemia and blood pressure in diabetes. Furthermore, our work indicated that activation of BKCa channel might be the underlying mechanism responsible for the vascular protection of berberine in diabetes.
Chuan-Chou Tu, V Bharath Kumar, Cecilia Hsuan Day, Wei-Wen Kuo, Su-Peng Yeh, Ray-Jade Chen, Chen-Rong Liao, Hsiao-Yu Chen, Fuu-Jen Tsai, Wen-Jun Wu and Chih-Yang Huang
Previous studies have reported that estrogen receptors (ERs) are expressed in normal human liver, chronic hepatitis, and benign hepatic tumor tissues. However, decreased expression of ERs can be observed in hepatocellular carcinoma (HCC) and the role of ERs in HCC is not fully understood. Thus, the present study aimed to investigate the molecular mechanism induced by the overexpression of ERα (ERα (ESR1)) in Hep3B cells. We first detected the induction of apoptosis in ER-negative Hep3B cells using DNA fragmentation assay and flow cytometry. We found that ERα and ERα plus 17β-estradiol treatment increased apoptosis in Hep3B cells. Additionally, western blotting showed increased expression of active caspase 3 and tumor necrosis factor α (TNFα (TNF)) in ER α-transfected cells. To further understand the importance of SP1-binding sites in the TNF α promoter, ERα-negative Hep3B cells were co-transfected with ER α and a wild-type TNFα plasmid or TNF α with deleted SP1 regions. Deletion of both distant and primal SP1 sites abolished the activity of ERα, and similar results were observed by blocking the expression of SP1 protein using mithramycin (MA). This result indicates that SP1 protein is essential for ERα-activated TNF α promoter activity. Co-immunoprecipitation assay further confirmed the binding interaction between ERα and SP1 in a ligand-dependent manner. In general, we demonstrate that the overexpression of ERα mediates apoptosis in ERα-negative Hep3B cells by the binding of ERα to SP1 protein. Additionally, this ERα–SP1 complex binds to the proximal and distal sites of the TNF α gene promoter and further induces the expression of active caspase 3 in a ligand-dependent manner.