Molecular Mechanism Of Catabolic Changes Of Catecholamines In Bat Hibernation

During hibernation,hibernators experience periodic cycles of torpor and arousal,many biological processes undergo dramatic and frequent changes,with little or no physiological damages to themselves.Due to the fact that non-hibernated animals have no such abilities,the hibernation phenotype are wildly explored.Bats are a large group of mammals with more than 1,300 species and have long history of evolution.Most microbats are known to hibernate during winter,and therefore it would be valuable to use bats to learn molecular mechanism underlying mammalian hibernation.Our previous study showed that the phenylalanine and tyrosine metabolic pathway is adapted to bat hibernation.Activation of this pathway will remove the toxic metabolites and provides energy for bats during hibernation.Since catecholamines,including dopamine,norepinephrine,epinephrine are not only neurotransmitters but also important hormones,it is worthy to further investigate whether phenylalanine and tyrosine-catecholamines(CAs)metabolism is altered in bat during hibernation.In order to study catecholamines metabolism at different states of bat hibernation,we used quantitative real-time PCR and Western blotting to examine the relative level of six metabolic enzymes of CAs in brain,liver and kidney of Myotis ricketti.These enzymes include catechol-O-methyltransferase(COMT),monoamine oxidase A(MAOA),monoamine oxidase B(MAOB),aldehyde dehydrogenase 1 family member A1(ALDH1A1),aldehyde dehydrogenase 2 family(ALDH2)and aldo-keto reductase family 1 member A1(AKR1A1).We also apply targeted LC-MS to detect the level of dopamine,3,4-dihydroxyphenylacetaldehyde(DOPAL)and homovanillic acid(HVA).We found for the first time that:1.Six catabolic enzymes,COMT,MAOA,MAOB,ALDH1A1,ALDH2,and AKR1A1 were co-expressed in brain,liver and kidney of Myotis ricketti,implying that the metabolic function of this pathway is essential during hibernation of bats.2.In all tissues tested,the transcription level of most enzymes showed a trend of inhibition.However,the reciprocal expression pattern of the enzyme isoforms(e.g.,monoamine oxidase A and B)suggested an energy-saving strategy adopted by bats against cold winter.3.The relative expression levels of genes and proteins of some of these enzymes are not exactly identical in different hibernation states of bats.For example,some genes have lower amount in torpor than in summer active state,while some proteins have a higher(e.g.,MAOA,ALDH2,AKR1A1 in brain;COMT,MAOA,ALDH1A1 in liver)or a similar(e.g.,COMT,MAOA,ALDH1A1,ALDH2 in kidney)amount in torpor than in summer active state.Since protein abundance is directly corelated to the physiological function,these changes may support our hypothesis that the function of this metabolic pathway is important during bat hibernation.4.The dopamine and homovanillic acid concentration in the liver of torpor was higher than arousal,suggested that they may play an important role during hibernation;DOPAL was not detected,as some of these enzymes in CAs pathway have a high abundance in torpid bats(e.g.,ALDH1A1),suggesting that they catabolize DOPAL in the liver during hibernation,and thus this protects bats form toxicity of DOPAL.