The goal of this study is to investigate the functional implications of the sexual dimorphism in transporter patterns along the proximal tubule. To do so, we have developed sex-specific computational models of solute and water transport in the proximal convoluted tubule of the rat kidney. The models account for the sex differences in expression levels of the apical and basolateral transporters, in single-nephron glomerular filtration rate, and in tubular dimensions. Model simulations predict that 70.6 and 38.7% of the filtered volume is reabsorbed by the proximal tubule of the male and female rat kidneys, respectively. The lower fractional volume reabsorption in females can be attributed to their smaller transport area and lower aquaporin-1 expression level. The latter also results in a larger contribution of the paracellular pathway to water transport. Correspondingly similar fractions (70.9 and 39.2%) of the filtered Na are reabsorbed by the male and female proximal tubule models, respectively. The lower fractional Na reabsorption in females is due primarily to their smaller transport area and lower Na/H exchanger isoform 3 and claudin-2 expression levels. Notably, unlike most Na transporters, whose expression levels are lower in females, Na-glucose cotransporter 2 (SGLT2) expression levels are 2.5-fold higher in females. Model simulations suggest that the higher SGLT2 expression in females may compensate for their lower tubular transport area to achieve a hyperglycemic tolerance similar to that of males.

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Beclin-1, a well-known key regulator of autophagy, has been implicated in many disorders, including cancer, aging, and degenerative diseases. Previous studies demonstrated that Beclin-1 participated in tumorgenesis and was highly expressed in colorectal cancer cells, primary duodenal adenocarcinoma, and hepatocellular carcinoma cells, and overexpression of Beclin-1 could induce autophagic cell death in leukemia cells. However, the exact effects and molecular mechanisms of Beclin-1-mediated autophagy in osteosarcoma are still unknown up to now. Here, we evaluated the role of Beclin-1 in human osteosarcoma cell lines in vivo and in vitro. In order to characterize the endogenous expression of Beclin-1 in osteosarcoma cell lines, we performed real-time PCR and Western blot analysis. We further analyzed the level of Beclin-1 in osteosarcoma cells after chemotherapy and investigated the impact of autophagy inhibition on chemotherapy-induced cytotoxicity. We used the small interfering RNA (siRNA) directed against Beclin-1 to infect the osteosarcoma cell line with relatively high Belcin-1 expression. Furthermore, we determine the functional relevance of Beclin-1 knockdown to osteosarcoma cell growth, migration, and invasion, and investigate the expression levels of matrix metallopeptidase-2 (MMP-2), MMP-9, phosphoinositide 3-kinase p85α (PI3Kp85α), and phosphorylated AKT (p-AKT). As a result, HOS osteosarcoma cells exhibited higher Beclin-1 expression. Anticancer agents including doxorubicin, cisplatin, and methotrexate each induced Beclin-1 up-regulation in human osteosarcoma cells, and siRNA-mediated knockdown of Beclin-1 suppressed cell proliferation, migration, and invasion indicated by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenylthetrazolium bromide, would healing, and transwell assays. Cell apoptosis induced by anticancer agents was markedly increased. Knockdown of Beclin-1 or inhibition of autophagy by 3-methyladenine (an inhibitor of autophagy and PI3K) rendered them significantly more sensitive to chemotherapy. Addition of the pan-caspase inhibitor ZVAD-FMK partly reversed the cisplatin-induced cell death. When Beclin-1 expression was inhibited, the expression of PI3Kp85α, p-AKT, and MMP-9 was downregulated in HOS cells. In addition, the tumor volumes in subcutaneous nude mouse models in Beclin-1-deleted HOS cells were significantly smaller than those of control group. These results suggested that knockdown of Beclin-1 by siRNA exerts inhibitory effects on growth and migration of osteosarcoma cells possibly via blockade of the PI3K/AKT signaling. Beclin-1 knockdown rendered them significantly more sensitive to chemotherapy through activating apoptosis pathway. The results of this study suggest that Beclin-1 plays an important role in proliferation and tumor progression in osteosarcoma and inhibition autophagy can increase the efficacy of anticancer agent therapy.

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