Inhibition of p75 Neurotrophin Receptor Attenuates Isoflurane-mediated Neuronal Apoptosis in the Neonatal Central Nervous System

Abstract

Background Exposure to anesthetics during synaptogenesis results in apoptosis and subsequent cognitive dysfunction in adulthood. Probrain derived neurotrophic factor (proBDNF) is involved in synaptogenesis and can induce neuronal apoptosis via p75 neurotrophic receptors (p75NTR). proBDNF is cleaved into mature BDNF (mBDNF) by plasmin, a protease converted from plasminogen by tPA that is released with neuronal activity; mBDNF supports survival and stabilizes synapses through TrkB receptors. We hypothesized that anesthetics suppresses tPA release from neurons, enhances p75NTR signaling, reduces synapses resulting in apoptosis. Methods Primary neurons (DIV5) and postnatal day 5-7 (PND5-7) mice were exposed to isoflurane (1.4%, 4 h) in 5% CO2, 95% air. Apoptosis was assessed by cleaved caspase-3 (Cl-Csp3) immunoblot and immunofluorescence microscopy. Dendritic spine changes were evaluated with the neuronal spine marker, drebrin. Changes in synapses in PND5-7 mouse hippocampi were assessed by electron microscopy. Primary neurons were exposed to tPA, plasmin, or pharmacologic inhibitors of p75NTR (Fc-p75NTR or TAT-Pep5) 15 min prior to isoflurane. TAT-Pep5 was administered by intraperitoneal injection to PND5-7 mice 15 min prior to isoflurane. Results Exposure of neurons in vitro (DIV5) to isoflurane decreased tPA in the culture medium, reduced drebrin expression (marker of dendritic filopodial spines) and enhanced Cl-Csp3. tPA, plasmin or TAT-Pep5 stabilized dendritic filopodial spines and decreased Cl-Csp3 in neurons. TAT-Pep5 blocked isoflurane-mediated increase in Cl-Csp3 and reduced synapses in PND5-7 mouse hippocampi. Conclusion tPA, plasmin, or p75NTR inhibition blocked isoflurane-mediated reduction in dendritic filopodial spines and neuronal apoptosis in vitro. Isoflurane reduced synapses and enhanced Cl-Csp3 in the hippocampus of PND5-7 mice, the latter effect being mitigated by p75NTR inhibition in vivo. These data support the hypothesis that isoflurane neurotoxicity in the developing rodent brain is mediated by reduced synaptic tPA release and enhanced proBDNF/p75NTR-mediated apoptosis.

Long-Term Effects of Repetitive Transcranial Magnetic Stimulation on Markers for Neuroplasticity: Differential Outcomes in Anesthetized and Awake Animals

“…It is important to note that the reasons for the disparity between the two states in this study are likely multifaceted and may result from differences in stress levels, auditory arousal, and the effect of anesthetics. Indeed, volatile anesthesia (such as isoflurane) decreases excitatory and increases inhibitory transmission (Gomez and Guatimosim, 2003;Ouyang and Hemmings, 2005), affects neuroplasticity, and can alter BDNF expression (Lu et al, 2006;Head et al, 2009).…”

Anesthesia and Apoptosis in the Developing Brain: An Update

“…There are some data to support this mechanism. Active axons normally release tPA and proBDNF [21]. The tPA cleaves plasmin to plasminogen which in turn converts proBDNF to BDNF.…”

Anesthetic Neurotoxicity in Pediatric Patients

“…Activation of p75NTR receptor, also called the "death receptor," leads to actin depolymerization and apoptosis. Head et al [50] demonstrated that isolurane causes apoptosis in the neonatal mice brain through this pathway.…”