ROS and cGMP signaling modulate persistent escape from hypoxia in Caenorhabditis elegans

Abstract

The ability to detect and respond to acute oxygen (O2) shortages is indispensable to aerobic life. The molecular mechanisms and circuits underlying this capacity are poorly understood. Here, we characterize the behavioral responses of feeding Caenorhabditis elegans to approximately 1% O2. Acute hypoxia triggers a bout of turning maneuvers followed by a persistent switch to rapid forward movement as animals seek to avoid and escape hypoxia. While the behavioral responses to 1% O2 closely resemble those evoked by 21% O2, they have distinct molecular and circuit underpinnings. Disrupting phosphodiesterases (PDEs), specific G proteins, or BBSome function inhibits escape from 1% O2 due to increased cGMP signaling. A primary source of cGMP is GCY-28, the ortholog of the atrial natriuretic peptide (ANP) receptor. cGMP activates the protein kinase G EGL-4 and enhances neuroendocrine secretion to inhibit acute responses to 1% O2. Triggering a rise in cGMP optogenetically in multiple neurons, including AIA interneurons, rapidly and reversibly inhibits escape from 1% O2. Ca2+ imaging reveals that a 7% to 1% O2 stimulus evokes a Ca2+ decrease in several neurons. Defects in mitochondrial complex I (MCI) and mitochondrial complex I (MCIII), which lead to persistently high reactive oxygen species (ROS), abrogate acute hypoxia responses. In particular, repressing the expression of isp-1, which encodes the iron sulfur protein of MCIII, inhibits escape from 1% O2 without affecting responses to 21% O2. Both genetic and pharmacological up-regulation of mitochondrial ROS increase cGMP levels, which contribute to the reduced hypoxia responses. Our results implicate ROS and precise regulation of intracellular cGMP in the modulation of acute responses to hypoxia by C. elegans.

Dissecting the genetic landscape of GPCR signaling through phenotypic profiling in C. elegans

“…C. elegans dramatically increases its locomotory speed when O 2 levels decrease rapidly from preferred (7%) to aversive hypoxia (1%) 22 . Double mutant animals for the G proteins gpa-3 and odr-3 are defective in locomotory response to acute drop of O 2 tension 22 , implicating GPCR-regulation of this response. To test this notion, we assessed all GPCR mutants for their responses to acute hypoxia (Supplementary Data 3 ).…”

GUCY2C signaling limits dopaminergic neuron vulnerability to toxic insults

“…Further complicating the directionality between GUCY2C, mitochondrial integrity, ROS production, and ROS scavenging is the apparent feedback loop between oxidative stress and cGMP signaling that is suggested from our data and may be conserved across species. Recent work exploring the relationship of ROS and cGMP in C. elegans revealed that mutated mitochondrial ETC complexes I or III or exposure to paraquat, a lipid membrane oxidation agent, increases cGMP accumulation and is prevented by pretreatment with antioxidants 74 . This finding parallels our mouse data; MPTP upregulates Gucy2c mRNA in the SNpc, but not in the VTA, which is comparitively resilient to mitochondrial toxins and has lower levels of oxidative stress at baseline 38 – 40 .…”

Reactive oxygen species drive foraging decisions in Caenorhabditis elegans

“…Recent work has shown that mitochondrial ROS alters C. elegans behavior [ 32 , 57 , [78] , [79] , [80] ]. Collectively, these reports have motivated questions regarding selectivity in ROS signaling cascades – in terms of origin and biological targets.…”