Integrity and wound healing of rainbow trout intestinal epithelial cell sheets at hypo-, normo-, and hyper-thermic temperatures.

How temperature influences fish physiological systems, such as the intestinal barrier, is important for understanding and alleviating the impact of global warming on fish and aquaculture. Monolayers of the rainbow trout cell line, RTgutGC, with or without linear 500 µm wide gaps (wounds) were the in vitro models used to study the integrity and healing of intestinal epithelial sheets at different temperatures. Cultures at hypothermic (4 °C) or hyperthermic (≥ 26 °C) temperatures were compared to normothermic control cultures (18-22 °C). Monolayers remained intact for at least a week at temperatures from 4 to 28 °C, but had lost their integrity after 3 h at 32 °C as the cells pulled away from one another and from the plastic surface. F-actin appeared as prominent stress fibers in cells at 28 °C and as blobs in cells at 32 °C. At normothermia and at 26 °C, cells migrated as sheets into the gaps and closed (healed) the gaps within 5-6 days. By contrast, wounds took 14 days to heal at 4 °C. At 28 °C some cells migrated into the gap in the first few days but mainly as single cells rather than collectively and wounds never healed. When monolayers with wounds were challenged at 32 °C for 3 h and returned to 18-22 °C, cells lost their shape and actin organization and over the next 6 days detached and died. When monolayers were subjected to 26 °C for 24 h and challenged at 32 °C for 3 h prior to being placed at 18-22 °C, cell shape and actin cytoskeleton were maintained, and wounds were healed over 6 days. Thus, intestinal epithelial cells become thermostabilized for shape, cytoskeleton and migration by a prior heat exposure.

Effect of selenomethionine on cell viability and heat shock protein 70 levels in rainbow trout intestinal epithelial cells at hypo-, normo-, and hyper-thermic temperatures.

As global warming and environmental pollution modify aquatic environments, the thermal biology of fish could be affected by interactions between temperature and pollutants, such as selenium (Se). Therefore, selenomethionine (SeMet) was studied for effects on cell viability and on heat shock protein 70 (HSP70) levels in the rainbow trout intestinal epithelial cell, RTgutGC, at hypothermic (4 °C), normothermic (14 and 18 °C) and hyperthermic (26 °C) temperatures. RTgutGC cultures remained viable for at least a week at all temperatures, although energy metabolism as measured with Alamar Blue (resazurin) was appreciably diminished at 4 °C. Over a 7-day incubation, HSP 70 levels in cultures remained steady at 4 °C, declined at 18 °C, and increased slightly at 26 °C. When 125 µM SeMet was present, cultures remained viable and HSP70 levels were neither increased nor decreased relative to control cultures, regardless of the temperature. With 500 and 1000 µM SeMet, cell viability was profoundly impaired after 7 days in cultures at 14, 18 and 26 °C but was unchanged at 4 °C. Overall the results suggest that only hypothermia modulated the response of rainbow trout cells to SeMet.

The characterization of γH2AX and p53 as biomarkers of genotoxic stress in a rainbow trout (Oncorhynchus mykiss) brain cell line.

Rainbow trout cell cultures were exposed to three genotoxicants and examined for effects on γH2AX and p53 levels by western blotting and on cell viability using the indicator dyes Alamar Blue (AB) for energy metabolism and 5'-carboxyfluorescein diacetate acetoxymethyl ester (CFDA-AM) for plasma membrane integrity. Bleomycin induced γH2AX and p53 in a dose- and time-dependent manner and had little cytotoxic effect. However, induction was first seen at 0.3 µM for γH2AX but not until 16.5 µM for p53. Methyl methanesulfonate (MMS) increased H2AX phosphorylation but diminished p53 levels as the dose was increased from 908 µM up to 2724 µM. Over this dose range cell viability was progressively lost. 4-nitroquinoline N-oxide (NQO) induced both γH2AX and p53, beginning at 62.5 nM, which was also the concentration at which cell viability began to decline. As the NQO concentration increased further, elevated γH2AX was detected at up to 2.0 µM, while p53 was elevated up to 1.0 µM. Therefore, H2AX phosphorylation was superior to p53 levels as a marker of DNA damage caused by genotoxicants that act by introducing double-stranded DNA breaks (bleomycin), alkyl groups (MMS), and quinoline adducts (NQO).