Dafachronic acid and temperature regulate canonical dauer pathways during Nippostrongylus brasiliensis infectious larvae activation

Abstract

Background: While immune responses to the murine hookworm Nippostrongylus brasiliensis have been investigated, signaling pathways regulating development of infectious larvae (iL3) are not well understood. We hypothesized that N. brasiliensis would use pathways similar to those controlling dauer development in the free-living nematode Caenorhabditis elegans, which is formally known as the "dauer hypothesis. " Methods: To investigate whether dafachronic acid activates the N. brasiliensis DAF-12 homolog, we utilized an in vitro reporter assay. We then utilized RNA-Seq and subsequent bioinformatic analyses to identify N. brasiliensis dauer pathway homologs and examine regulation of these genes during iL3 activation. Results: In this study, we demonstrated that dafachronic acid activates the N. brasiliensis DAF-12 homolog. We then identified N. brasiliensis homologs for members in each of the four canonical dauer pathways and examined their regulation during iL3 activation by either temperature or dafachronic acid. Similar to C. elegans, we found that transcripts encoding antagonistic insulin-like peptides were significantly downregulated during iL3 activation, and that a transcript encoding a phylogenetic homolog of DAF-9 increased during iL3 activation, suggesting that both increased insulin-like and DAF-12 nuclear hormone receptor signaling accompanies iL3 activation. In contrast to C. elegans, we observed a significant decrease in transcripts encoding the dauer transforming growth factor beta ligand DAF-7 during iL3 activation, suggesting a different role for this pathway in parasitic nematode development. Conclusions: Our data suggest that canonical dauer pathways indeed regulate iL3 activation in the hookworm N. brasiliensis and that DAF-12 may be a therapeutic target in hookworm infections.

Characterization of the endogenous DAF-12 ligand and its use as an anthelmintic agent in Strongyloides stercoralis

“…The developmentally arrested L3i stage of S. stercoralis is analogous to the L3 dauer (d) stage of C. elegans . In C. elegans , L3d development is governed by DAF-12 ( Antebi et al, 1998 ; Antebi et al, 2000 ), a nematode-specific nuclear receptor that is conserved in parasitic species ( Ayoade et al, 2020 ; Long et al, 2020 ; Ma et al, 2019 ; Motola et al, 2006 ; Ogawa et al, 2009 ; Wang et al, 2017 ; Wang et al, 2009 ). In favorable environments, developing larvae synthesize the endogenous C. elegans ( Ce )-DAF-12 ligands called dafachronic acids ( Mahanti et al, 2014 ; Motola et al, 2006 ).…”

Identification of a nuclear receptor/coactivator developmental signaling pathway in the nematode parasite Strongyloides stercoralis

“…The dauer stage resembles the infective third stage (iL3) of parasitic nematodes, which is specialized to seek out and infect host organisms. Orthologs of DAF-12 have been identified in all parasitic species surveyed, including hookworms, threadworms, and filarial parasitic nematodes ( 9 – 14 ). One such parasite is Strongyloides stercoralis , which infects 200 to 300 million persons worldwide and under certain conditions can cause a disseminated hyperinfection that is frequently fatal if untreated ( 15 , 16 ).…”

The Two Faces of Nematode Infection: Virulence and Immunomodulatory Molecules From Nematode Parasites of Mammals, Insects and Plants

“…The steroidal hormone dafachronic acid (DA) modulates nematode lipid metabolism and development, and the ligand-binding domain for the steroid hormone nuclear receptor for DA (DAF-12) is highly conserved among nematode species, such as C. elegans, N. brasiliensis, Haemonchus contortus , and Strongyloides stercoralis , therefore targeting these receptors may have therapeutic potential to impair parasite fitness ( Ogawa et al, 2009 ; Patton et al, 2018 ; Ma et al, 2019a , b ; Ayoade et al, 2020 ). In C. elegans , the DAF-12 system acts to inhibit dauer formation, and in H. contortus , DA promoted transition from free-living to parasitism by modulating dauer-like signaling ( Ogawa et al, 2009 ; Ma et al, 2019a , b ).…”