Osmoregulation and salinity-induced oxidative stress: is oxidative adaptation determined by gill function?

Area of Science:

• Crustacean physiology
• Environmental adaptation
• Marine biology
• Oxidative stress

Background:

• Decapod crustaceans like the Mediterranean green crab (Carcinus aestuarii) have specialized gill regions for respiration and osmoregulation.
• Understanding differential tissue adaptation to environmental changes, such as salinity, is crucial for predicting species' responses.
• Free radical metabolism plays a key role in cellular responses to environmental stress.

Purpose of the Study:

• To investigate the differential adaptation of respiratory and osmoregulatory gills in Carcinus aestuarii under varying salinity conditions.
• To analyze the impact of salinity changes on free radical metabolism, mitochondrial activity, and apoptosis in distinct gill tissues.
• To determine the protective mechanisms employed by osmoregulatory gills against salinity-induced oxidative stress.

Main Methods:

• Crabs were exposed to three salinity levels: standard seawater (SW), diluted SW (dSW), and concentrated SW (cSW) for two weeks.
• Respiration rates of whole animals and isolated gills were measured.
• Free radical formation in hemolymph was assessed using C-H2DFFDA.
• Mitochondrial density (citrate synthase activity), reactive oxygen species (ROS) levels (electron paramagnetic resonance), and apoptosis marker (caspase 3/7 activity) were analyzed in anterior and posterior gills.
• Superoxide dismutase (SOD) activity was quantified in gill tissues.

Main Results:

• Diluted SW (dSW) posed the greatest challenge, increasing whole-animal respiration and hemolymph free radical formation.
• Posterior gills exhibited significantly higher respiration rates (3.2-fold) and increased mitochondrial density in dSW compared to anterior gills.
• Posterior gills showed elevated ROS production (1.4-fold) but maintained normal caspase 3/7 activity, indicating no apoptosis.
• SOD activity was over 6 times higher in posterior gills than in anterior gills, suggesting enhanced antioxidant capacity.

Conclusions:

• Posterior osmoregulatory gills are better adapted to diluted SW conditions than anterior respiratory gills.
• Increased mitochondrial activity and ROS production in posterior gills are associated with osmoregulatory demands under stress.
• High SOD levels in posterior gills effectively mitigate ROS-induced damage, allowing for successful osmoregulation despite salinity stress.