Insights into Trx1, TRP14, and Prx1 homologs of Paralichthys olivaceus: molecular profiles and transcriptional responses to immune stimulations

Expression of antioxidant and stress-related genes in olive flounder, Paralichthys olivaceus exposed to high temperatures after pre-heating

The rising sea surface temperatures driven by climate change cause thermal stress, leading to oxidative stress, metabolic disorders, and increased disease susceptibility, thereby impairing the physiological functions of fish. Therefore, understanding the adaptation mechanisms of fish to high temperatures is essential for mitigating the negative impacts of thermal stress on aquaculture productivity and fish health. In this study, Paralichthys olivaceus were subjected to high temperatures following pre-heating to evaluate the advantages of pre-stimulation prior to exposure to the critical temperature. The P. olivaceus were exposed to four groups; Acute (subjected to acute heat shock at 32 °C), AH-S (exposed to acquired heat shock at 28 °C followed by short recovery of 2 h and subsequent heat shock at 32 °C), AH-L (exposed to acquired heat shock at 28 °C followed by long recovery of 2 days and subsequent heat shock at 32 °C) and AH-SL (combined of AH-S and AH-L protocols). In terms of antioxidant response, mRNA expression (caspase 10, thioredoxin (Trx), superoxide dismutase (SOD), peroxiredoxin (Prx), glutathione-S-transferase (GST), and transferrin (TF)) and enzyme activities (SOD, CAT, and GST) were significantly upregulated in P. olivaceus pre-heated prior to high-temperature exposure (AH-S, AH-L, and AH-SL groups). In addition, the stress gene expressions such as heat shock protein 70 (HSP70), HSP60, HSP90, warm-temperature-acclimation-associated 65-kDa protein (Wap65-1), and glucose-regulated protein 78 (GRP78) was significantly upregulated in AH-S, AH-L and AH-SL groups. Pre-heating has been found to be effective in mitigating thermal stress, with the efficacy varying according to the differences in pre-heating methods.

Exploring the immunological functions of thioredoxin domain-containing protein 17 (TXNDC17) in chub mackerel (Scomber japonicus): Immune response and cellular redox homeostasis

All organisms have evolved sophisticated antioxidant networks and enzymes to counteract reactive radicals, among which thioredoxin (Trx) systems are especially noteworthy. Thioredoxin domain-containing protein 17 (TXNDC17) is a ubiquitously expressed enzyme with oxidoreductase activity belonging to the Trx protein family. This study successfully uncovered and analyzed the TXNDC17 gene in Scomber japonicus (SjTXNDC17). The gene consists of a 372-base-pair coding sequence that encodes a protein of 123 amino acids, with an estimated molecular weight of 14.1 kDa. Structural analysis revealed that SjTXNDC17 contains a TRX-related protein 14 domain with two redox-responsive cysteine residues in the 42WCPDC46 motif. Spatial expression analysis indicated that SjTXNDC17 had the highest constitutive expression in the brain. Stimulation with polyinosinic-polycytidylic acid (poly I:C), Vibrio harveyi, and Streptococcus iniae, significantly upregulated the mRNA levels of SjTXNDC17 in the head kidney. The antioxidant activity of the recombinant SjTXNDC17 protein was evidenced by 2,2-Diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging, insulin reduction, and cupric ion-reducing antioxidant capacity assays. SjTXNDC17 overexpression in fathead minnow (FHM) cells significantly reduced reactive oxygen species (ROS) levels and decreased apoptosis. The anti-apoptotic effect was driven by the upregulation of the Bcl2 gene and the downregulation of the Bax gene, as well as the suppression of JNK signaling pathway genes. Moreover, overexpression of SjTXNDC17 facilitated M2 polarization and suppressed nitric oxide production in macrophages. Collectively, these results demonstrate that SjTXNDC17 plays a crucial role in both the immune response and cellular redox balance in Scomber japonicus.

Structural insights into the redox regulation of Oncomelania hupensis TRP14 and its potential role in the snail host response to parasite invasion

The freshwater amphibious snail Oncomelania hupensis is the unique intermediate host of Schistosoma japonicum, but little attention has been paid to the interaction between the two. In snails, the production of reactive oxygen species (ROS) by hemocytes has been shown to be vital for snail immune defense against schistosome infection. However, excessive ROS accumulation could lead to oxidative damage, requiring the antioxidant system for maintaining the cellular redox homeostasis. Previously we identified a thioredoxin-related protein of 14 kDa from O. hupensis (OhTRP14), and showed that it was involved in the scavenging of ROS in circulating hemocytes. Here, we confirmed that OhTRP14 plays a potential role in the snail host response to parasite challenge and determined the crystal structures of OhTRP14 in two different states (oxidized and transition state). The overall structure revealed a typical Trx fold and is similar to that of human TRP14 (hTRP14), but there were significant structural differences between the two states. Noticeably, there was a different pair of thiol groups from Cys30 and Cys44 in the transition state of OhTRP14, were with the similar separation of 2.9 Å as that (2.6 Å) between Cys41 and Cys44, but in a different orientation, suggesting that the Cys30 is likely to function as an important molecular switch involved in the oxidoreductase activity of OhTRP14. Comparative studies between OhTRP14 and hTRP14 by analyzing the surface characteristics, charge distribution and oxidoreductase activity toward insulin demonstrated they might have similar substrates. The results are expected to provide structural insights into the redox regulation of OhTRP14 and contribute to better understanding of TRP14 family. DATA DEPOSITION: The atomic coordinates of the structure and the structure factors were deposited in Protein Data Bank with PDB ID codes 7XQ3 and 7XPW.

Molecular characterization and functional analysis of Trx and Trp14 in roughskin sculpin (Trachidermus fasciatus)

Thioredoxins (Trxs) are a family of small and highly conserved proteins which play crucial roles in the maintenance and regulation of the cellular redox homeostasis. In this study, the full-length cDNAs of thioredoxin 1 (TfTrx1) and thioredoxin-related protein of 14 kDa (TfTrp14) were isolated from roughskin sculpin (Trachidermus fasciatus). TfTrx1 is 662 bp in length with a 336-bp open reading frame (ORF) that encodes for a peptide with 111 amino acids, and TfTrp14 consists of 1066 bp with a 372-bp ORF that is translated to 123 amino acids. TfTrx1 and TfTrp14 contain highly conserved catalytic site motif CGPC and CPDC, respectively. Tissue distribution analysis indicated that both genes were broadly expressed in all examined tissues with the highest expression of TfTrx1 in the blood and TfTrp14 in the brain. In post-LPS and heavy metal challenge, the mRNA of both genes was significantly increased in the skin, liver, spleen, and brain at various times. The results of western blot detection displayed that the time of the induced maximum protein expression was 6-h post-LPS injection in the skin and liver, which were slightly delayed compared with that of 2 h at mRNA level. The recombinant TfTrp14 and TfTrx1 proteins were expressed in E. coli BL21 (DE3). The increase of the fluorescence intensity in rTfTrx1 and rTfTrp14 suggested the redox state changes in the microenvironment around tryptophan residues. Both of the recombinant proteins exhibited concentration-dependent disulfide reductase activity towards insulin, and the catalytic activity of rTfTrx1 was much higher than that of rTfTrp14.

Molecular characterization and immune regulatory, antioxidant, and antiapoptotic activities of thioredoxin domain-containing protein 17 (TXNDC17) in yellowtail clownfish (Amphiprion clarkii)

Thioredoxin domain-containing protein 17 (TXNDC17) is an important, highly conserved oxidoreductase protein, ubiquitously expressed in all living organisms. It is a small (~14 kDa) protein mostly co-expressed with thioredoxin 1 (TRx1). In the present study, we obtained the TXNDC17 gene sequence from a previously constructed yellowtail clownfish (Amphiprion clarkii) (AcTXNDC17) database and studied its phylogeny as well as the protein's molecular characteristics, antioxidant, and antiapoptotic effects. The full length of the AcTXNDC17 cDNA sequence was 862 bp with a 372 bp region encoding a 123 amino acid (aa) protein. The predicted molecular mass and isoelectric point of AcTXNDC17 were 14.2 kDa and 5.75, respectively. AcTXNDC17 contained a TRX-related protein 14 domain and a highly conserved N-terminal Cys⁴³-Pro⁴⁴-Asp⁴⁵-Cys⁴⁶ motif. qPCR analysis revealed that AcTXNDC17 transcripts were ubiquitously and differently expressed in all the examined tissues. AcTXNDC17 expression in the spleen tissue was significantly upregulated in a time-dependent manner upon stimulation with lipopolysaccharide (LPS), polyinosinic-polycytidylic (poly I:C), and Vibrio harveyi. Besides, LPS-induced intrinsic apoptotic pathway (TNF-α, caspase-8, Bid, cytochrome C, caspase-9, and caspase-3) gene expression was significantly lower in AcTXNDC17-overexpressing RAW264.7 cells, as were NF-κB activation and nitric oxide (NO) production. Furthermore, the viability of H₂O₂-stimulated macrophages was significantly improved under AcTXNDC17 overexpression. Collectively, our findings indicate that AcTXNDC17 is involved in the innate immune response of the yellowtail clownfish.

Peptidylarginine deiminase and deiminated proteins are detected throughout early halibut ontogeny - Complement components C3 and C4 are post-translationally deiminated in halibut (Hippoglossus hippoglossus L.)

Post-translational protein deimination is mediated by peptidylarginine deiminases (PADs), which are calcium dependent enzymes conserved throughout phylogeny with physiological and pathophysiological roles. Protein deimination occurs via the conversion of protein arginine into citrulline, leading to structural and functional changes in target proteins. In a continuous series of early halibut development from 37 to 1050° d, PAD, total deiminated proteins and deiminated histone H3 showed variation in temporal and spatial detection in various organs including yolksac, muscle, skin, liver, brain, eye, spinal cord, chondrocytes, heart, intestines, kidney and pancreas throughout early ontogeny. For the first time in any species, deimination of complement components C3 and C4 is shown in halibut serum, indicating a novel mechanism of complement regulation in immune responses and homeostasis. Proteomic analysis of deiminated target proteins in halibut serum further identified complement components C5, C7, C8 C9 and C1 inhibitor, as well as various other immunogenic, metabolic, cytoskeletal and nuclear proteins. Post-translational deimination may facilitate protein moonlighting, an evolutionary conserved phenomenon, allowing one polypeptide chain to carry out various functions to meet functional requirements for diverse roles in immune defences and tissue remodelling.

Identification and functional characterization of thioredoxin-related protein of 14 kDa in Oncomelania hupensis, the intermediate host of Schistosoma japonicum

Oncomelania hupensis is the unique intermediate host of the blood fluke Schistosoma japonicum, which causes schistosomiasis. In snails, highly toxic reactive oxygen species (ROS) can be continually generated by hemocytes in response to foreign particles or pathogens, and may be involved in damaging and eliminating digenean larvae. Thioredoxin-related protein of 14 kDa (TRP14) is a member of the Trx superfamily, and plays an important role in the scavenging of ROS. This study was designed to identify and characterize TRP14 from O. hupensis (OhTRP14), and investigate the involvement of OhTRP14 in the scavenging of ROS in snail host immune response to the parasite S. japonicum. Here we expressed and purified the recombinant OhTRP14 and its mutant, and rOhTRP14 displayed oxidoreductase activity dependent on the CPDC motif. OhTRP14 protein was ubiquitously present in all the tested snail tissues, and especially immunolocalized in the cytoplasm of immune cell types (hemocytes). Both the expression of OhTRP14 and ROS level increased significantly in snails following challenge with S. japonicum. The dsRNA-mediated knockdown of OhTRP14 was successfully conducted by oral feeding, and ROS production was increased by OhTRP14 knockdown, implying that OhTRP14 was involved in the scavenging of ROS in O. hupensis circulating hemocytes. Therefore, we conclude that OhTRP14 may be involved in the scavenging of ROS in snail host immune response to the parasite S. japonicum. The results expand our understanding of the interaction between this parasite and host, and lay a foundation for the establishment of Oncomelania-schistosome infection models.