Delayed innocent bystander cell death following hypoxia in Caenorhabditis elegans

Abstract

After hypoxia, cells may die immediately or have a protracted course, living or dying depending on an incompletely understood set of cell autonomous and nonautonomous factors. In stroke, for example, some neurons are thought to die from direct hypoxic injury by cell autonomous primary mechanisms, whereas other so called innocent bystander neurons die from factors released from the primarily injured cells. A major limitation in identifying these factors is the inability of current in vivo models to selectively target a set of cells for hypoxic injury so that the primarily injured cells and the innocent bystanders are clearly delineated. In order to develop such a model, we generated transgenic Caenorhabditis elegans strains where 2-3% of somatic cells were made selectively sensitive to hypoxia. This was accomplished by cell type-specific wild-type rescue in either pharyngeal myocytes or GABAergic neurons of a hypoxia resistance-producing translation factor mutation. Surprisingly, hypoxic targeting of these relatively small subsets of non-essential cells produced widespread innocent bystander cell injury, behavioral dysfunction and eventual organismal death. The hypoxic injury phenotypes of the myocyte or neuron sensitized strains were virtually identical. Using this model, we show that the C. elegans insulin receptor/FOXO transcription factor pathway improves survival when activated only after hypoxic injury and blocks innocent bystander death.

Mitochondrial Proteostatic Collapse Leads to Hypoxic Injury

“…As the previous experiments have all occurred under conditions of global hypoxia, we next tested to see if activation of the mtUPR is protective in a focal model of hypoxic injury [15]. The strains used for this model include two control strains where the whole worm is hypoxia resistant: rars-1(gc47) (control) and rars-1(gc47);gcSi2 (transformation control) along with two strains with selective tissue vulnerability to hypoxic injury: rars-1(gc47);gcIs3 (vulnerable pharyngeal myocytes) and rars-1(gc47);gcSi4 (vulnerable GABA neurons).…”

“…As hypoxia has been shown to disrupt ATP production and translation of nuclear encoded proteins [11], both shown to disrupt mitochondrial proteostasis in other contexts [3, 12], we hypothesized that failure to maintain mitochondrial proteostasis may play a role in hypoxic injury. Utilizing C. elegans models of global [13, 14], focal [15], and cell non-autonomous hypoxic injury we have found evidence of mitochondrial protein misfolding post-hypoxia, and that manipulation of the mitochondrial protein folding environment is an effective hypoxia protective strategy. …”

Neuronal responses to stress and injury in C. elegans

“…Necrosis triggered by neurotoxic stress can cause secondary cell death. In C. elegans , hypoxic injury to a small group of neurons can induce widespread delayed secondary cell death and eventual organismal death [66]. One study tested the effects of hypoxia on a hypoxia‐resistant rars‐1 mutant strain that only expresses the wild type copy of rars‐1 in GABAergic motor neurons.…”

Vascular ageing and endothelial cell senescence: Molecular mechanisms of physiology and diseases

“…HIFs directly impact on the control of tissue oxygen delivery, by regulating angiogenesis and vascular remodelling, and on the cellular homeostasis by regulating glucose metabolism and redox balance (Jeong et al, 2014;Luther et al, 2014;Semenza, 2014;Sun et al, 2014;Zhang et al, 2014). HIFs acts as transcriptional factors, activating gene transcription by binding to the core DNA sequence 5 -RCGTG-3 (R = A or G), included in a DNA binding consensus sequence defined hypoxia response element (HRE) (Semenza et al, 1996).…”