Bilirubin-Induced Transcriptomic Imprinting in Neonatal Hyperbilirubinemia

Simple Summary Severe neonatal hyperbilirubinemia may damage the brain, leading to motor, cognitive, and auditory abnormalities. We recently discovered that bilirubin might act by controlling the genetic developmental program of the cerebellum, a region of the brain well known to be susceptible to bilirubin-induced damage. In this paper, we expand the study of the potential impact of bilirubin in the control of postnatal brain development to brain regions better correlating with human symptoms. The maximal abnormalities of structure and cell shape (histology) were detected 9 days after birth, fully recovering later on. Differently, the analysis of the gene expression revealed transient alterations (early after birth, then recovering) in the hippocampus (memory, learning, and cognition) and inferior colliculi (auditory functions), but permanent (until adulthood) changes in the areas of the brain involved in the control of movements, information confirmed by the abnormal results on the behavioral tests. These new findings are well in agreement with the clinic and open a way for better deciphering the neurotoxic features of bilirubin neurotoxicity and potential therapeutic approaches. Recent findings indicated aberrant epigenetic control of the central nervous system (CNS) development in hyperbilirubinemic Gunn rats as an additional cause of cerebellar hypoplasia, the landmark of bilirubin neurotoxicity in rodents. Because the symptoms in severely hyperbilirubinemic human neonates suggest other regions as privileged targets of bilirubin neurotoxicity, we expanded the study of the potential impact of bilirubin on the control of postnatal brain development to regions correlating with human symptoms. Histology, transcriptomic, gene correlation, and behavioral studies were performed. The histology revealed widespread perturbation 9 days after birth, restoring in adulthood. At the genetic level, regional differences were noticed. Bilirubin affected synaptogenesis, repair, differentiation, energy, extracellular matrix development, etc., with transient alterations in the hippocampus (memory, learning, and cognition) and inferior colliculi (auditory functions) but permanent changes in the parietal cortex. Behavioral tests confirmed the presence of a permanent motor disability. The data correlate well both with the clinic description of neonatal bilirubin-induced neurotoxicity, as well as with the neurologic syndromes reported in adults that suffered neonatal hyperbilirubinemia. The results pave the way for better deciphering the neurotoxic features of bilirubin and evaluating deeply the efficacy of new therapeutic approaches against the acute and long-lasting sequels of bilirubin neurotoxicity.