Xenopus laevis Tail Regeneration: Investigating the Role of Aquaporins in NADPH oxidase Signalling

Abstract

Regeneration is a remarkable phenomenon involving the ability to replace lost or damaged body parts with fully functional replacements. Whilst vertebrates such as Xenopus, zebrafish and axolotls are able to regenerate several body parts, humans have a poor capacity to regenerate. Therefore, regenerative models provide invaluable insight in regenerative mechanisms that can be used to improve our own response to injury. Xenopus are a useful model for tail regeneration, which comprises of a variety of different tissue organised in a complex manner. Reactive oxygen species (ROS) have been previously identified as a signalling component during tail regeneration. NADPH oxidase was identified as a source of extracellular ROS, but other sources remain unexplored. Furthermore, aquaporins (AQPs) has been shown in other systems to facilitate the membrane influx of NADPH oxidase-derived hydrogen peroxide (H2O2), but this has not been demonstrated in Xenopus. In addition, current tools used to detect ROS are limited in Xenopus, providing a need to develop more methods in detecting ROS during tail regeneration. Here, a fluorescent based approach was used to detect different types of ROS during tail regeneration: superoxide (O2-) with DHE/mitoSOX; and H2O2 with cyto-/mito-HyPerYFP. Tail amputation caused an increase in O2- and H2O2 levels, whilst detection of both ROS in the mitochondria demonstrated its role as a major source of ROS. Further measurements of O2- and H2O2 at different time points provided a previously undefined spatiotemporal profile for both types of ROS. Building on the use of these ROS detection tools, the role of AQPs in tail regeneration was investigated. Through genetic and chemical based inhibition, AQP1 and AQP11 were found to facilitate an influx of NADPH oxidase-derived H2O2. Inflammatory cell recruitment and tail regeneration were also assessed, with the AQP inhibitor, AgNO3, impairing both processes. Further experiments demonstrated that NADPH oxidase-derived H2O2 is involved in positively regulating both mitochondrial and NADPH oxidase ROS production. Together, the findings of this thesis demonstrate the application of subcellular-targeted O2- and H2O2 detection in Xenopus tadpole tail regeneration. This has allowed the tracking of H2O2 in different subcellular compartments to uncover a redox-based crosstalk between two NADPH oxidase and mitochondria. Finally, this opens up the potential for different organelle-targeted ROS sensors to determine whether redox-based crosstalk occurs between other sources of ROS during tail regeneration.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Enrique Amaya (Supervisor) & Alistair Fielding (Supervisor)