ER stress, mitochondrial dysfunction and calpain/JNK activation are involved in oligodendrocyte precursor cell death by unconjugated bilirubin.
Research on the mechanisms of bilirubin-induced neurological dysfunction focuses mainly on neuronal death, astrocyte-mediated events and microglia activation. Although myelin damage by unconjugated bilirubin (UCB) has been documented in neonatal kernicterus cases, the events leading to myelination impairment were never explored. This condition may occur by reduced oligodendrocyte precursor cells (OPC) number, or failure of OPC to differentiate in myelinating oligodendrocytes. We have shown that UCB elicits an inflammatory response, glutamate release and reactive oxygen species (ROS) generation in neurons and glial cells, biomolecules with toxic properties on OPC. Hence, we propose to examine whether UCB determines OPC demise and, if so, which signaling pathways are involved. Our results show that OPC display increased apoptosis and necrosis-like cell death upon UCB exposure, mediated by early signals of endoplasmic reticulum (ER) stress [e.g. upregulation of glucose-regulated protein (GRP)78, inositol-requiring enzyme (IRE)-1α and activation transcription factor (ATF)-6, as well as activation of caspase-2 and c-Jun N-terminal kinase (JNK)], followed by mitochondrial dysfunction (e.g. loss of mitochondria membrane potential and caspase-9 activation). The later calpain activation points to intracellular Ca(2+) overload and intervention of both ER and mitochondria. Downstream production of ROS may derive from mitochondria damage and secondary injuries, possibly determining the second cycle of GRP78, IRE-1α, caspase-2 and JNK activation. Moreover, inhibition of caspases, calpains and oxidative stress, by using specific inhibitors, prevented UCB-induced OPC death. UCB did not induce the release of cytokines or glutamate by OPC. These results indicate that UCB by reducing OPC survival, through a cascade of programmed intracellular events triggered by ER stress and mitochondria dysfunction, can compromise myelinogenesis.
Research Institute for Medicines and Pharmaceutical Sciences (iMed.UL), Faculty of Pharmacy, University of Lisbon, Avenida Professor Gama Pinto, 1649-003, Lisbon, Portugal.
Andreia
A
Barateiro
Ana Rita
AR
Vaz
Sandra Leitão
SL
Silva
Adelaide
A
Fernandes
Dora
D
Brites
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001663:Bilirubin / Q000737:chemistry / Q000633:toxicity*; D002154:Calpain / Q000502:physiology*; D020169:Caspases / Q000502:physiology; D002478:Cells, Cultured / Q000187:drug effects; D002540:Cerebral Cortex / Q000166:cytology; D016207:Cytokines / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress; D004789:Enzyme Activation; D018698:Glutamic Acid / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000502:physiology*; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000502:physiology*; D058953:Neural Stem Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D009836:Oligodendroglia / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D061251:Primary Cell Culture; D051381:Rats; D017208:Rats, Wistar; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D000590:Amino Acid Chloromethyl Ketones; D016207:Cytokines; D017382:Reactive Oxygen Species; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D018698:Glutamic Acid; D048031:JNK Mitogen-Activated Protein Kinases; D002154:Calpain; D020169:Caspases; D001663:Bilirubin