Brainstem Deficiency of the 14-3-3 Regulator of Serotonin Synthesis: A Proteomics Analysis in the Sudden Infant Death Syndrome

Abstract

Impaired brainstem responses to homeostatic challenges during sleep may result in the sudden infant death syndrome (SIDS). Previously we reported a deficiency of serotonin (5-HT) and its key biosynthetic enzyme, tryptophan hydroxylase (TPH2), in SIDS infants in the medullary 5-HT system that modulates homeostatic responses during sleep. Yet, the underlying basis of the TPH2 and 5-HT deficiency is unknown. In this study, we tested the hypothesis that proteomics would uncover previously unrecognized abnormal levels of proteins related to TPH2 and 5-HT regulation in SIDS cases compared with controls, which could provide novel insight into the basis of their deficiency. We first performed a discovery proteomic analysis of the gigantocellularis of the medullary 5-HT system in the same data set with deficiencies of TPH2 and 5-HT levels. Analysis in 6 SIDS cases and 4 controls revealed a 42-75% reduction in abundance in 5 of the 6 isoforms identified of the 14-3-3 signal transduction family, which is known to influence TPH2 activity (p < 0.07). These findings were corroborated in an additional SIDS and control sample using an orthogonal MS E -based quantitative proteomic strategy. To confirm these proteomics results in a larger data set (38 SIDS, 11 controls), we applied Western blot analysis in the gigantocellularis and found that 4/7 14-3-3 isoforms identified were significantly reduced in SIDS cases (p < 0.02), with a 43% reduction in all 14-3-3 isoforms combined (p < 0.001). Abnormalities in 5-HT and TPH2 levels and 5-HT 1A receptor binding were associated with the 14-3-3 deficits in the same SIDS cases. These data suggest a potential molecular defect in SIDS related to TPH2 regulation, as 14-3-3 is critical in this process. Molecular & Cellular Proteomics 11: 10.1074/mcp.M111.009530, 1-17, 2012. The sudden infant death syndrome (SIDS)1 is the sudden unexpected death of an infant less than 1 year of age, with onset of the fatal episode apparently occurring during sleep, that remains unexplained after a thorough investigation, including performance of a complete autopsy and review of the circumstances of death and clinical history (1). It is the leading cause of postneonatal infant mortality in the United States today; with an overall incidence of 0.53/1000 live birth(s) (2). Typically, a seemingly healthy infant is found dead after a sleep period, either in the early morning or after a day-time nap (1,3,4). Impaired brainstem responses to homeostatic challenges during sleep may result in the sleep-related sudden death characteristic of SIDS (4). We have reported various abnormalities in serotonergic (5-HT) receptors, 5-HT transporter, and 5-HT cellular maturation in the medullary 5-HT system in SIDS cases in three independent data sets over the last decade (5-7). This system within the medulla oblongata is a neural network comprised of 5-HT source neurons and their projection sites that help mediate homeostatic responses during the sleep-wake cycle (3). The medullary 5-HT system is defined by us as the regions of t...

Potential Asphyxia and Brainstem Abnormalities in Sudden and Unexpected Death in Infants

“…5,29 We hypothesize that at least a subset of SIDS is caused by an underlying brainstem abnormality in neural networks that mediate protective responses to asphyxia, resulting in sleep-related sudden death. [30][31][32][33][34][35] In support of this hypothesis, we have reported deficiencies in infants who died of SIDS in interrelated neurochemical parameters in the medullary serotonergic network that plays a key role in protective respiratory or autonomic responses to homeostatic stressors. [30][31][32][33][34][35] The parameters are related mainly to the neurotransmitters serotonin and g-aminobutyric acid (GABA) and the signal transduction family 14-3-3, involved in serotonin regulation.…”

“…[30][31][32][33][34][35] In support of this hypothesis, we have reported deficiencies in infants who died of SIDS in interrelated neurochemical parameters in the medullary serotonergic network that plays a key role in protective respiratory or autonomic responses to homeostatic stressors. [30][31][32][33][34][35] The parameters are related mainly to the neurotransmitters serotonin and g-aminobutyric acid (GABA) and the signal transduction family 14-3-3, involved in serotonin regulation. [30][31][32][33][34][35] Given a reduction in the overall SIDS rate associated with an increased rate of supine sleep, 5,[8][9][10] it is highly likely that prone sleep position plays a direct role in the chain of events leading to sudden death in some infants.…”

“…[30][31][32][33][34][35] The parameters are related mainly to the neurotransmitters serotonin and g-aminobutyric acid (GABA) and the signal transduction family 14-3-3, involved in serotonin regulation. [30][31][32][33][34][35] Given a reduction in the overall SIDS rate associated with an increased rate of supine sleep, 5,[8][9][10] it is highly likely that prone sleep position plays a direct role in the chain of events leading to sudden death in some infants. The hypothesized mechanisms include ineffective protective responses to airway obstruction or rebreathing of expired gases in the face-down position (compounded by soft bedding) 5,20 and thermal or cardiovascular stress.…”

“…[30][31][32][33][34][35] The brainstem samples were analyzed at Boston Children' s Hospital, resulting in publications in 2006 31 and 2010, 30 each concerned with a separate data set. In these publications, SIDS was defined as stated earlier; control infants also died suddenly, but a complete autopsy or death scene investigation demonstrated a pathologic explanation for the death.…”

“…In these publications, SIDS was defined as stated earlier; control infants also died suddenly, but a complete autopsy or death scene investigation demonstrated a pathologic explanation for the death. [30][31][32][33][34][35] Undetermined cases were equivocal cases in which a specific diagnosis could not be made, and they were not included in the published analyses. In the current study, however, we reclassified all unexplained cases, including the undetermined or equivocal cases, according to an asphyxial grading schema developed by us 36,37 (Tables 1-3).…”