α-Synuclein levels are elevated in cerebrospinal fluid following traumatic brain injury in infants and children: the effect of therapeutic hypothermia

Abstract

α-Synuclein is one of the most abundant proteins in presynaptic terminals. Normal expression of α-synuclein is essential for neuronal survival and it prevents the initiation of apoptosis in neurons through covalent cross-linking of cytochrome c released from mitochondria. Exocytosis of α-synuclein occurs with neuronal mitochondrial dysfunction, making its detection in cerebrospinal fluid (CSF) of children after severe traumatic brain injury (TBI) a potentially important marker of injury. Experimental therapeutic hypothermia (TH) improves mitochondrial function and attenuates cell death, and therefore may also affect CSF α-synuclein concentrations. We assessed α-synuclein levels in CSF of 47 infants and children with severe TBI using a commercial ELISA for detection of monomeric protein. 23 patients were randomized to TH based on published protocols where cooling (32-33°C) was initiated within 6-24 h, maintained for 48 h, and then followed by slow rewarming. CSF samples were obtained continuously via an intraventricular catheter for 6 days after TBI. Control CSF (n = 9) was sampled from children receiving lumbar puncture for CSF analysis of infection that was proven negative. Associations of initial Glasgow Coma Scale (GCS) score, age, gender, treatment, mechanism of injury and Glasgow Outcome Scale (GOS) score with CSF α-synuclein were compared by multivariate regression analysis. CSF α-synuclein levels were elevated in TBI patients compared to controls (p = 0.0093), with a temporal profile showing an early, approximately 5-fold increase on days 1-3 followed by a delayed, >10-fold increase on days 4-6 versus control. α-Synuclein levels were higher in patients treated with normothermia versus hypothermia (p = 0.0033), in patients aged <4 years versus ≥4 years (p < 0.0001), in females versus males (p = 0.0007), in nonaccidental TBI versus accidental TBI victims (p = 0.0003), and in patients with global versus focal injury on computed tomography of the brain (p = 0.046). Comparisons of CSF α-synuclein levels with initial GCS and GOS scores were not statistically significant. Further studies are needed to evaluate the conformational status of α-synuclein in CSF, and whether TH affects α-synuclein aggregation.

Fig. 1

α-Synuclein levels for all TBI patients, inclusive of both those receiving TH and normothermia, during the first 6 days (D1–6) of admission compared to controls and the mean peak level during the period of observation. Levels for D1–6 and peak levels for TBI patients were significantly higher than those for control. ∗ Levels for D4–6 were significantly higher than those for D1 or D2. ∗∗ Levels for D5 and D6 were also significantly higher than D3 levels. Bars: mean values for given day. Error bars: standard errors of the mean. D = Day.

Fig. 2

α-Synuclein levels for all TBI patients treated with TH versus normothermia. TBI patients randomized to TH demonstrated significantly lower levels of CSF α-synuclein overall. There was a differential time course in patients treated with hypothermia. ∗ Levels demonstrated a significant elevation in day 6 (D6) above D2. D = Day.

Fig. 3

α-Synuclein levels for all TBI patients <4 years old versus those 4 years or older. Patients <4 years of age demonstrated significantly higher α-synuclein levels. D = Day.

Fig. 4

α-Synuclein levels for all female versus male TBI patients. Females demonstrated significantly higher α-synuclein levels. D = Day.

Fig. 5

α-Synuclein levels for all trauma patients admitted with a diagnosis of accidental TBI versus nonaccidental head injury. Nonaccidental head injury victims demonstrated α-synuclein levels significantly elevated above those of accidental TBI patients. D = Day.

Fig. 6

α-Synuclein levels for all TBI patients who sustained global brain injury versus focal brain injury. ∗ Peak levels for patients with global injury were higher than levels for patients who had focal injury. D = Day.

Fig. 7

α-Synuclein levels for all TBI patients with 6-month GOS score of 2 or lower versus 3 or greater. There was no statistically significant association of GOS with synuclein levels. D = Day.