Abstract
Low levels of reactive oxygen species (ROS) are now recognized as essential players in cell signaling. Here, we studied the role of two conserved enzymes involved in redox regulation that play a critical role in the control of ROS in the digestive physiology of a blood-sucking insect, the kissing bug Rhodnius prolixus. RNAi-mediated silencing of RpNOX5 and RpXDH induced early mortality in adult females after a blood meal. Recently, a role for RpNOX5 in gut motility was reported, and here, we show that midgut peristalsis is also under the control of RpXDH. Together with impaired peristalsis, silencing either genes impaired egg production and hemoglobin digestion, and decreased hemolymph urate titers. Ultrastructurally, the silencing of RpNOX5 or RpXDH affected midgut cells, changing the cells of blood-fed insects to a phenotype resembling the cells of unfed insects, suggesting that these genes work together in the control of blood digestion. Injection of either allopurinol (an XDH inhibitor) or uricase recapitulated the gene silencing effects, suggesting that urate itself is involved in the control of blood digestion. The silencing of each of these genes influenced the expression of the other gene in a complex way both in the unfed state and after a blood meal, revealing signaling crosstalk between them that influences redox metabolism and nitrogen excretion and plays a central role in the control of digestive physiology.
Highlights
Reactive oxygen species (ROS) control many processes, from gene expression and protein translation to metabolism and cell signaling, and the NAD, NADP and thiol/disulfide systems are important for ROS signaling (Jones and Sies, 2015)
As ROS production has been implicated in the control of both pathogens and indigenous microbiota (Ha et al, 2005; Oliveira et al, 2011), we evaluated the effect of RpNOX5 or RpXDH silencing on the R. prolixus microbiota, which is known to be dominated by a mutualist symbiont, R. rhodnii (Baines, 1956)
Despite the increase in ROS levels with RpNOX5 silencing (Figure 4A), the results showed no statistically significant change in the bacterial population in RpNOX5silenced insects compared to the control insects, we did observe a trend toward an increase in the bacterial population, especially in the anterior midgut (AM) (Figure 4B)
Summary
Reactive oxygen species (ROS) control many processes, from gene expression and protein translation to metabolism and cell signaling, and the NAD, NADP and thiol/disulfide systems are important for ROS signaling (Jones and Sies, 2015). ROS are produced in different parts of the cell and modulate key target functions via the oxidative modification of redox-sensitive essential proteins and alterations in redox homeostasis that are associated with many different disease conditions (Holmström and Finkel, 2014; Sies, 2017; Bardaweel et al, 2018). Rhodnius prolixus only has calcium-activated DUOX and NOX5, which are involved in eggshell hardening and gut motility, respectively, in this insect (Dias et al, 2013; Montezano et al, 2018)
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