A circuit-dependent ROS feedback loop mediates glutamate excitotoxicity to sculpt the Drosophila motor system

Abstract

Overproduction of reactive oxygen species (ROS) is known to mediate glutamate excitotoxicity in neurological diseases. However, how ROS burdens can influence neural circuit integrity remains unclear. Here, we investigate the impact of excitotoxicity induced by depletion of Drosophila Eaat1, an astrocytic glutamate transporter, on locomotor central pattern generator (CPG) activity, neuromuscular junction architecture, and motor function. We show that glutamate excitotoxicity triggers a circuit-dependent ROS feedback loop to sculpt the motor system. Excitotoxicity initially elevates ROS, thereby inactivating cholinergic interneurons and consequently changing CPG output activity to overexcite motor neurons and muscles. Remarkably, tonic motor neuron stimulation boosts muscular ROS, gradually dampening muscle contractility to feedback-enhance ROS accumulation in the CPG circuit and subsequently exacerbate circuit dysfunction. Ultimately, excess premotor excitation of motor neurons promotes ROS-activated stress signaling that alters neuromuscular junction architecture. Collectively, our results reveal that excitotoxicity-induced ROS can perturb motor system integrity through a circuit-dependent mechanism.

Dynamin-2 Regulates Postsynaptic Cytoskeleton Organization and Neuromuscular Junction Development

“…Evoked excitatory junctional potential (EJP) was recorded as previously described (Peng et al, 2019). Briefly, third instar larvae were dissected in calcium-free HL3 buffer at room temperature, followed by incubation in 0.5 mM Ca 2+ HL3 solution for 5-10 min prior to recording.…”

JNK signalling regulates antioxidant responses in neurons

“…In addition to changes in ROS levels, we show that activation of the JNK-AP-1 pathway leads to overgrown synapses at the Drosophila NMJ suggesting that the status of JNK signalling has implications for structural synaptic plasticity. In mammalian cortical neurons we identified an 'adaptive' also been shown to mediate the effect of ROS generated during oxidative stress associated with excitotoxicity [14] and lysosomal storage disease [12]. Combined with reports that activation of the JNK pathway after neuronal injury coordinates a regenerative response [16] and that AP-1 signalling regulates dendrite growth during both development and during conditions of synaptic activity; JNK-AP-1 signalling has been demonstrated as a crucial regulator of neuronal homeostasis.…”

“…ROS have been shown to activate JNK-AP-1 signalling [9] which regulates neuronal growth and plasticity [10][11][12][13]. In Drosophila models, excessive ROS driving increases in synaptic growth are seen in both activity generated excitotoxicity and lysosomal storage disease [5,12,14]. Similar changes in synaptic structure can be induced directly by application of oxidants such as paraquat [12] or diethylmaleate (DEM) [5], or through genetic activation of JNK via manipulation of the JNKK hemipterous [15] (hep) or the JNKKK Wallenda [11] (wnd), upstream activators of JNK.…”

Dynamin-2 regulates synaptic podosome maturation to facilitate neuromuscular junction development

“…Evoked excitatory junctional potential (EJP) was recorded as previously described (Peng, Lin et al, 2019). Briefly, third instar larvae were dissected in calcium-free HL3 buffer at room temperature, followed by incubation in 0.5 mM Ca 2+ HL3 solution for 5-10 min prior to recording.…”