Zinc induces motor neuron death via a selective inhibition of brain-derived neurotrophic factor activity.
Amyotrophic lateral sclerosis is a debilitating disease that results from the deterioration and loss of motor neurons. The neurotoxic potential of Zn(2+), both in vitro and in vivo, has been well established; however, the mechanism(s) of zinc's toxicity remain unclear. Our laboratory has demonstrated that Zn(2+)-mediated inhibition of neurotrophins can induce cell death. The present study investigates the neurotoxic mechanism(s) of this metal ion by assessing zinc's selectivity in altering the neurotrophin BDNF, but not the neural cytokine CNTF, with respect to motor neuron survival. Embryonic day 15 rat spinal motor neuron cultures were maintained in either BDNF or CNTF. Terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL) staining showed that exposure to 100microM Zn(2+) significantly increased the number of pro-apoptotic neurons in cultures maintained with BDNF, while these conditions had no effect on cultures maintained with CNTF. We also demonstrate that BDNF protomer cross-linking efficiency and TrkB receptor cross-linking to BDNF are significantly inhibited by Zn(2+), suggesting that a Zn(2+)-induced change in BDNF conformation inhibits receptor-binding activity. This study reveals a mechanism by which zinc toxicity is mediated via a selective loss in neurotrophin activity resulting in motor neuron death.
Northern Ontario School of Medicine, Sudbury, Ontario, Canada. greg.ross@normed.ca
Joan Isabel
JI
Post
Joseph Karl
JK
Eibl
Gregory Michiel
GM
Ross
D000690:Amyotrophic Lateral Sclerosis / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000378:metabolism* / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects*; D002478:Cells, Cultured; D020934:Ciliary Neurotrophic Factor / Q000494:pharmacology; D003432:Cross-Linking Reagents / Q000378:metabolism; D009046:Motor Neurons / Q000166:cytology / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020813:Receptor, trkB / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013116:Spinal Cord / Q000166:cytology; D014131:Trace Elements / Q000633:toxicity*; D015032:Zinc / Q000633:toxicity*
D019208:Brain-Derived Neurotrophic Factor; D020934:Ciliary Neurotrophic Factor; D003432:Cross-Linking Reagents; D014131:Trace Elements; D020813:Receptor, trkB; D015032:Zinc