Glial Hsp70 Protects K+ Homeostasis in the Drosophila Brain during Repetitive Anoxic Depolarization

Abstract

Neural tissue is particularly vulnerable to metabolic stress and loss of ion homeostasis. Repetitive stress generally leads to more permanent dysfunction but the mechanisms underlying this progression are poorly understood. We investigated the effects of energetic compromise in Drosophila by targeting the Na+/K+-ATPase. Acute ouabain treatment of intact flies resulted in subsequent repetitive comas that led to death and were associated with transient loss of K+ homeostasis in the brain. Heat shock pre-conditioned flies were resistant to ouabain treatment. To control the timing of repeated loss of ion homeostasis we subjected flies to repetitive anoxia while recording extracellular [K+] in the brain. We show that targeted expression of the chaperone protein Hsp70 in glial cells delays a permanent loss of ion homeostasis associated with repetitive anoxic stress and suggest that this is a useful model for investigating molecular mechanisms of neuroprotection.

Cold hardening modulates K+ homeostasis in the brain of Drosophila melanogaster during chill coma

“…Flies were immobilized in a refrigerator (4°C) for 3 min and then secured on a 0.5 cm diameter bed of wax on either a cover slip or on top of a recessed porous platform (6 Â 12 cm, porous polyethylene) capable of delivering a laminar flow of N 2 gas over the entire fly (Armstrong et al, 2011). The brain was exposed by making a small ($200 lm sagittal slit in the cuticle along the dorsal midline of the fly head.…”

“…Surges of [K + ] o underlying nitrogen-induced comas can be measured precisely in the brain of D. melanogaster using K + -sensitive microelectrodes (Armstrong et al, 2011). In this study we were interested in testing the hypothesis that RCH modifies cellular processes of ion regulation in the CNS during chill-coma.…”

Protective effect of hypothermia on brain potassium homeostasis during repetitive anoxia in Drosophila melanogaster

“…So far, studies have mainly focused on the effects of constant hypoxia/anoxia (Krishnan et al, 1997;Le Corronc et al, 1999;Liu et al, 2006;Lighton, 2007;Schilman et al, 2011) and just a few have considered the fruit fly's response under a repetitive protocol (Lighton and Schilman, 2007;Armstrong et al, 2011). Furthermore, only Armstrong and colleagues They were chosen without using any selection criteria before every experiment.…”

Timing of Locomotor Recovery from Anoxia Modulated by the white Gene in Drosophila

“…Eye color and the timing of locomotor recovery in flies with w knockdown were examined. The pan-neuronal driver elav-Gal4 (Armstrong et al 2011;Dimitroff et al 2012) was used for targeting RNAi of w to the CNS. There was no visible difference in eye color between w + ; elav-Gal4/+; UAS-w-RNAi/+ flies and controls (w + ; elav-Gal4/+ and w + ;; UAS-w-RNAi/+) ( Figure 3C), indicating that w knockdown in the CNS had no visible effect on eye pigmentation.…”

“…On returning to normoxia, the timing of recovery varies depending on specific processes. Recovery of neural K + distribution after ,30 sec anoxia starts immediately and extracellular K + concentration is almost back to normal within 30 sec (Armstrong et al 2011). Propagation of action potentials recovers within 1 min whereas complex motor activity, such as continuous walking, takes longer (around 10 min) to recover (Krishnan et al 1997).…”