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.

Neurochemical Profile of Dementia Pugilistica

“…In acute TBI, a-synuclein is present in axonal swellings 25,79 and detectable in CSF. 80 Similar to the results with tau (see below), a-synuclein may be decreased in DP subjects because it is converted to insoluble forms that evade ELISA detection. In addition, our assays were performed on frontal lobe samples which may have yielded artefactually low values.…”

Reducing synuclein accumulation improves neuronal survival after spinal cord injury

“…And, increased levels of α-, β- and γ-synuclein have been reported in cortical axons of mice and humans after TBI (Uryu et al, 2003; Uryu et al, 2007; Surgucheva et al, 2014). Furthermore, increased levels of α-synuclein have been observed in the brains and cerebral spinal fluid of TBI patients ranging from infants to adults (Uryu et al, 2007; Su et al, 2011; Mondello et al, 2013). Nonetheless, the fate of the neurons and the role of synuclein in injury-induced neurodegeneration have not been explored until now.…”

“…We therefore predict that increased synuclein immunoreactivity observed after injury in mammals is also due, at least in part, to synuclein aggregation and clearance deficiency within the degenerating neurons. As such, post-injury synuclein accumulation and related neurotoxicity may also be contributing to the poor outcomes after TBI (Su et al, 2011; Mondello et al, 2013). We propose that reducing synuclein accumulation could provide a potential means for improving neuronal survival and axon plasticity after injury in mammals, which should be explored in greater detail.…”

“…There is growing evidence that both SCI and traumatic brain injury (TBI) lead to increased immunoreactivity against α–, β–, and γ–synucleins in mammals, including humans (Uryu et al, 2003; Uryu et al, 2007; Sakurai et al, 2009; Mondello et al, 2013). Furthermore, α-synuclein is elevated in the cerebral spinal fluid of patients with severe TBI, and higher α-synuclein levels have been associated with worse post-injury outcomes, including a greater extent of injury and even death (Su et al, 2011; Mondello et al, 2013). However, previous studies have not determined the effects of increased synuclein levels on the neurons themselves and have not examined the aggregation state of the protein.…”

Increased CSF Concentrations of Myelin Basic Protein After TBI in Infants and Children: Absence of Significant Effect of Therapeutic Hypothermia

“…Because of the preponderance of animal data demonstrating that TH has a beneficial effect on axonal injury [3, 15, 16], as well as human pediatric data indicating TH after TBI leads to lower CSF concentrations of the cerebral biomarkers alpha synuclein [26], NSE, S100B, and CK-BB [27], it was surprising that patients treated with TH did not have lower mean CSF MBP concentrations compared with patients treated with NT. One possibility for the discontinuity between the experimental and clinical studies in the efficacy of TH on axonal injury is that rewarming in the clinical trial was too rapid.…”