Interannual variations in abundance and distribution of Chattonella cysts, and the relationship to population dynamics of vegetative cells in the Yatsushiro Sea, Japan.

The fish-killing raphidophytes Chattonella spp. have a resting cyst stage. To investigate the abundance and distribution of Chattonella cysts and determine their relationship to the population dynamics of vegetative cells, we conducted field observations from 2002 to 2017 in the Yatsushiro Sea, a semi-enclosed embayment in Japan, and analyzed the data including environmental conditions. Analysis of sediment sampled in the spring (mid-April to early June), shows that cysts are relatively abundant in the northern to middle area, where initial vegetative cells and large blooms are frequently detected. The maximum density of cysts was 616 cysts cm-3 in the northern area in 2016. Mean cyst abundance in the spring varied interannually, ranging from 5 to 138 cysts cm-3. A significant positive correlation between mean cyst abundance in the spring and maximum density of vegetative cells the preceding summer was seen, but no significant correlation was observed the following summer. The first detected date of vegetative cells (FDD) each year, which is likely related to cyst abundance and environmental conditions influencing cyst germination and/or growth characteristics of vegetative cells, also varied interannually from mid-April to early June. Regression analyses showed that FDD tended to be early when cyst abundance and bottom-water temperature were high. However, no significant correlation was observed between mean cyst abundance and bloom timing (the period from FDD to the occurrence date of the bloom), and bloom duration the following summer, as was the maximum density of vegetative cells. Instead, the timing and duration of blooms were correlated significantly with meteorological factors (e.g., solar radiation) for a month after FDD. The results suggest that cyst abundance reflecting the bloom magnitude of the preceding summer contributes to the timing of the appearance of vegetative cells in the year, but that bloom occurrence is likely to be controlled by the growth dynamics of vegetative cells through environmental conditions rather than by cyst abundance. The three distinct peaks in Chattonella cysts and vegetative cells from 2002 to 2017 correspond to the timings just after the El Niño. Large-scale atmospheric variability and its global teleconnection are possibly linked to long-term population dynamics of Chattonella in the area through local meteorological conditions and their life cycle.

Hydrogen Peroxide-Induced Oxidative Stress Activates Proteasomal Trypsin-Like Activity in Human U373 Glioma Cells.

Degradation of oxidized or oxidatively modified proteins is an essential part of the cellular antioxidant defense system. 4-Hydroxy-2-nonenal, a major reactive aldehyde formed by lipid peroxidation, causes many types of cellular damage. The major proteolytic system for modified protein degradation is the ubiquitin-proteasome pathway. However, our previous studies using U937 human leukemic cells showed that 4-hydroxy-2-nonenal-modified glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is degraded by cathepsin G. In the present study, U373 human glioma cells were cultured in the presence of hydrogen peroxide (H2O2) to investigate the relationships of proteasome and/or cathepsin G activities and H2O2-induced GAPDH degradation. Treatment of cells with H2O2 for 5 h in culture decreased GAPDH activity as well as its protein concentration in a concentration-dependent manner. Two proteasomal activities (peptidylglutamyl-peptide hydrolase and chymotrypsin-like hydrolase activities) and cathepsin G activity were decreased by H2O2 treatment in a concentration-dependent manner, but proteasomal trypsin-like hydrolase activity increased with cell exposure to high H2O2 concentrations. Among the protease inhibitors examined here, H2O2-induced activation of trypsin-like activity and GAPDH degradation were inhibited by the proteasome inhibitor lactacystin. Furthermore, H2O2-induced activation of trypsin-like activity was also inhibited by another proteasome inhibitor MG-132. These results suggested that proteasomal trypsin-like activity played an important role in eliminating oxidatively modified GAPDH formed in these cells during H2O2 exposure.