Critical Roles Of Calcium Signaling In Cadmium-induced Apoptosis In The Freshwater Crab Sinopptamon Henanense

Using the freshwater crab Sinopotamon henanense as a experimental model organism, I examined the effects of Cadmium (Cd) on intracellular Ca2+-Mg2+-ATPase and Na+-K+-ATPase activities as well as the histopathological alternations of hepatopancreas at different concentrations (0,14.5,29 and 58 mg·L-1) and exposure time(0,12,24, 48,72 and 96 h). Moreovcer, I investigated the intracellular calmodulin (CaM) level, Ca2+-ATPase activity and apoptosis, to analyze the role of calcium signaling in apoptosis triggered by Cd in the hepatopancreas of the frechwater crab Sinopotamon henanense.The results showed that:Firstly, after being exposed to different concentrations of Cd for 12 h and 24 h, the Ca2+-Mg2+-ATPase and Na+-K+-ATPase activities increased significantly, which dropped to the levels comparable to that in the controls after 24 h. This suggests that Cd can cause the membrane protein oxidative damage.Secondly, Cd caused progressive histopathological damages to the hepatopancreas after being treatment with Cd (58 mg·L-1) for 12 h,24 h, 48 h,72 h,96 h, which included extensive vacuolation, disappearance of glandular structure, and cell shedding from basement membrane. The levels of morphaological features of Cd toxicity in the hepatopancreas was depending on the time of treatment.Thirdly, compared to the controls, the Caspase-3 and Caspase-9 activities of hepatopancreatic cells in the experimental group (58 mg·L-1, 48h) increased significantly. Apoptotic DNA grementation which was evidenced by typidcal DNA ladders was noted after Cd treatment for 48 h and 72 hFinally, the CaM level and Ca2+-ATPase activity in the Cd-exposed crabs (12 h and 24 h respectively) were significantly increased compared to the controls. Pretreatment with Ca2+ inhibitor (EGTA and LaCl3 resepctively) for 4 h before Cd exposure effectively inhibited Caspases-3,9 activities.Conclusions:Firstly, the Ca2+ -ATPase activity, CaM protein concentration and morphology of hepatopancreas in S. henanense were significantly altered following Cd exposure in a time-dependent manner. This study provides mechanisms for exploring Cd toxicity and meantime provided effective index in water metal pollution monitoring.Secondly, compared to the controls, the Caspase-3 and Caspase-9 activities of hepatopancreatic cells treated with Cd (58 mg·L-1) was increased and the typical apoptotic DNA ladder was detected. Thus, Cd can induce apoptosis in hepatopancreas of freshwater crab S. henanense,Thirdly, Cd could increase the Ca2+-ATPase activity and protein concentration of CaM, which reflected indirectly a change in intracellular Ca concentration. The apoptotic features which included Caspase activation and DNA ladder formation were almost completely blocked by pretreatment with EGTA and LaCl3, indicating that Ca2+ signal is involved in Cd-induced cell apoptosis through Caspase pathway.