In vivo changes in common carp (cyprinus carpio L.) liver during hypoxia at the molecular and cellular levels

Abstract

Fish survive low oxygen in the environment by switching on anaerobic metabolism, but the energy production of anaerobic metabolism is only one-tenth that of aerobic metabolism and so it will not allow survival for prolonged periods of hypoxia. Changes other than turning on anaerobic metabolism must occur and it was hypothesized that hypoxia induced apoptosis occurs in a hypoxia tolerant species, common carp, liver as one of the strategies for reducing energy utilization, sparing substrates for prolonged hypoxia survival. Human liver is an organ with high regenerative power. It is likely that fish liver also has this ability. If the size of the liver is reduced during hypoxia, it could regenerate quickly when oxygen levels return to normal. Common carp (Cyprinus carpio L.) were exposed to low oxygen in the water, at levels well below their critical oxygen limit, for a prolonged period of time. A series of measurements were made, including Terminal deoxynucleotidyl Transferase dUTP Nick End Labeling (TUNEL), anti-ssDNA antibody, DNA fragmentation, caspase 3 activity, flow cytometry and transmission electron microscopy (TEM) to determine if apoptosis had occurred in hypoxia exposed carp liver in vivo. All results indicate that apoptosis did not increase during hypoxia. Hepatosomatic index (HSI) and cell number of 42-day hypoxic liver was not significantly reduced compared with 0-day normoxic control liver and there was no up-regulation of a cell proliferation marker, Proliferating Cell Nuclear Antigen (PCNA) antibody, as measured by western hybridization in hypoxic liver samples compared to 0-day normoxic control. Therefore there was no reduction of liver size after prolonged hypoxia exposure and no apoptosis. Hypoxia appeared to induce cell cycle arrest as a protein, cyclin dependent kinase inhibitor p27, was up-regulated in hypoxic liver. There may be a potential role of p27 which halts the cell cycle and prolongs time for DNA damage repair, thus preventing cells from being forced to apoptosis. Anti-apoptotic HSP70 protein indicated differential gene expression between hepatic cells and appears to play a role in preventing cell death. Metabolic reduction occurs quickly within days but molecular, cellular and physiological adjustments carry on for days and/or weeks so as to reach a new homeostasis to adapt to prolonged hypoxia with a new energy utilization strategy.

Date of Award	3 Oct 2005
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	David John RANDALL (Supervisor)