Carbon dioxide uptake in a eutrophic stratified reservoir: Freshwater carbon sequestration potential.

Carbon capture and storage due to photosynthesis activities has been proposed as a carbon sink to mitigate climate change. To enhance such mitigation, previous studies have shown that freshwater lakes should be included in the carbon sink, since they may capture as much carbon as coastal areas. In eutrophic freshwater lakes, there is uncertainty about whether the equilibrium equation can estimate the partial pressure of carbon dioxide (pCO2), owing to the presence of photosynthesis due to phytoplankton, and pH measurement error in freshwater fluid. Thus, this study investigated the applicability of the equilibrium equation and revealed the need to modify it. The modified equilibrium equation was successfully applied to reproduce pCO2 based on total alkalinity and pH through field observations. In addition, pCO2 at the water surface was lower than the atmospheric partial pressure of carbon dioxide due to photosynthesis by phytoplankton during strong stratification. The stratification effect on low pCO2 was verified by using the Net Ecosystem Production (NEP) model, and a submerged freshwater plants such as Potamogeton malaianus were found to have high potential for dissolved inorganic carbon (DIC) sequestration in a freshwater lake. These results should provide a starting point toward more sophisticated methods to investigate the effect of freshwater carbon on DIC uptake in freshwater stratified eutrophic lakes.

Palbociclib regulates intracellular lipids in mammary tumor cells by secreting lipoprotein lipase.

BACKGROUND: Lipoprotein metabolism is essential for the growth and proliferation of cancer cells, and is involved in the supply of energy and cellular components. Lipoprotein lipase (LPL) is a very important enzyme in lipoprotein metabolism; however, the details underlying the mechanism of LPL secretion are unclear. Palbociclib is an antitumor drug that inhibits cell cycle progression and suppresses the growth of cancer cells. The effects of palbociclib on energy metabolism, particularly on lipid metabolism, have not been fully elucidated. METHODS: We examined the regulation of LPL secretion, which is primarily involved in lipoprotein metabolism. FM3A mouse mammary tumor cells, which are hormone receptor-positive breast cancer cells, were treated with palbociclib, and the activity and protein levels of secreted LPL were measured. Moreover, the changes in intracellular lipid content were measured by fluorescence staining using Nile Red. RESULTS: FM3A cells were treated with palbociclib, the activity and protein content of secreted LPL were increased. The stimulatory secretion of LPL by palbociclib was suppressed by an intracellular Ca2+ chelator (BAPTA-AM) and a Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) inhibitor (STO-609). Furthermore, the palbociclib-stimulated secretion of LPL was not observed in AMP-activated protein kinase (AMPK)-knockdown cells. An increase in the fluorescence intensity of Nile Red was observed in palbociclib-treated cells; however, no increase was observed in LPL-knockdown cells. CONCLUSIONS: Our data suggest that palbociclib causes intracellular lipid accumulation in breast cancer cells by stimulating Ca2+/CaMKK/AMPK-mediated LPL secretion.

ß-Estradiol Enhanced Secretion of Lipoprotein Lipase from Mouse Mammary Tumor FM3A Cells.

The role of ß-estradiol (E2) in lipoprotein metabolism in mammary tumors is unclear, therefore, we investigated the effect of E2 on the secretion of lipoprotein lipase (LPL) from mouse mammary tumor FM3A cells. E2-treated cells increased the secretion of active LPL from FM3A cells in a time- and dose-dependent manner. Activity of mitogen-activated protein kinase (MAPK) was increased in the tumor cells treated with E2, and enhanced secretion of LPL was suppressed by MAPK kinase 1/2 inhibitor, PD98059, extracellular signal-regulated kinase (ERK) 1/2 inhibitor, FR180204, p38 MAPK inhibitor, SB202190, and phosphatidyl inositol 3-kinase (PI3K) inhibitor, LY294002. In addition, the effect of E2 on LPL secretion was markedly suppressed by an inhibitor of mammalian target of rapamycin complex (mTORC) 1 and 2, KU0063794, but were not by a mTORC1 inhibitor, rapamycin. Furthermore, a small interfering RNA (siRNA)-mediated decrease in the expression of rapamycin-insensitive companion of mTOR (Rictor), a pivotal component of mTORC2, suppressed secretion of LPL by E2. These results suggest that the stimulatory secretion of LPL by E2 from the tumor cells is closely associated with an activation of mTORC2 rather than mTORC1 possibly via the MAPK cascade.