Study of biological phenomena implicated in neuromuscular ageing

Student thesis: Doctoral Thesis

Abstract

The neuromuscular junction (NMJ) defines the functional interface between nerve and muscle. Reactive oxygen species (ROS) are linked to pathological denervation in multiple neurodegenerative diseases, but whether and how ROS causes denervation is unclear. Our main hypothesis was that ROS recapitulates the signalling pathways of developmental denervation to cause pathological denervation in multiple diseases. To address our hypothesis, we made the local consequences of NMJ detectable as motor deficits by using disparate exogenous and endogenous models to induce synaptic inactivity in developing Xenopus laevis tadpoles. We resolved whether: (1) synaptic inactivity increases mitochondrial ROS; (2) chemically heterogeneous antioxidants rescue synaptic inactivity induced motor deficits; (3) ROS and mitochondrial calcium (mtCa2+) crosstalk exists; and (4) denervation is achieved by activating non apoptotic caspase 3. Regardless of whether it was achieved with muscle (α-Bungarotoxin), nerve (α-Latrotoxin) targeted neurotoxins or an endogenous pruning cue (SPARC), synaptic inactivity increased mitochondrial and cytosolic ROS in vivo. In addition, selectively inducing mitochondrial ROS—using mitochondria-targeted Paraquat (MitoPQ) - recapitulated synaptic inactivity induced motor deficits. In α—Bungarotoxin, α-Latrotoxin and SPARC, but not MitoPQ denervation models Ru360, specific mtCa2+ uptake inhibitor, blocked Ca2+ uptake in mitochondria and regulated ROS. In addition, Z-DEVD-FMK and AZ-10417808, specific caspase inhibitors, blocked caspase 3 activation, prevented denervation and mtCa2+ increase. Most importantly, the manganese porphyrins, MnTE-2-PyP5+ and MnTnBuOE-2-PyP5+ two novel antioxidants, blocked ROS and mtCa2+ increase, prevented caspase 3 activation and abolished nerve, muscle and environmental toxin-induced pathological denervation. We conclude that ROS are a shared biochemical feature of pathological denervation and recapitulate an endogenous redox-regulated developmental denervation pathway.
Date of Award20 Jan 2020
Original languageEnglish
Awarding Institution
  • Abertay University
SponsorsThe Carnegie Trust & The Royal Society
SupervisorKimberley Bennett (Supervisor), Sean Brown (Supervisor), Pete Moult (Supervisor) & James Cobley (Supervisor)

Keywords

  • ROS
  • Denervatiom
  • NMJ
  • Mitochondria
  • Signalling pathways

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