Molecular and functional explication of thioredoxin mitochondrial-like protein (Trx-2) from big-belly seahorse (Hippocampus abdominalis) and expression upon immune provocation

Thioredoxin (Trx) is a small ubiquitous multifunctional protein with a characteristic WCGPC thiol-disulfide active site that is conserved through evolution. Trx plays a crucial role in the antioxidant defense system. Further, it is involved in a variety of biological functions including gene expression, apoptosis, and growth regulation. Trx exists in several forms, with the cytosolic (Trx-1) and mitochondrial (Trx-2) forms being the most predominant. In this study, the mitochondrial Trx protein (HaTrx-2), from the big-belly seahorse (Hippocampus abdominalis) was characterized, and its molecular features and functional properties were investigated. The cDNA sequence of HaTrx-2 consists of a 519 bp ORF, and it encodes a polypeptide of 172 amino acids. This protein has a calculated molecular mass of 18.8 kDa and a calculated isoelectric point (pI) of 7.80. The highest values of identity (78.7%) and similarity (86.2%) were observed with Fundulus heteroclitus Trx-2 from the pairwise alignment results. The phylogenetic analysis revealed that HaTrx-2 is closely clustered with teleost fishes. The qPCR results showed that HaTrx-2 was prevalently expressed at various levels in all the tissues examined. The ovary showed the highest expression, followed by the brain and kidney. HaTrx-2 showed varying mRNA expression levels during the immune challenge experiment, depending on the type of tissue and the time interval. Our results confirmed the antioxidant property of HaTrx-2 by performing the MCO assay, DPPH radical scavenging activity, and cell viability assays. Further, an insulin disulfide reduction assay revealed the dithiol remove the enzymatic activity of HaTrx-2. Altogether these results indicate that HaTrx-2 plays indispensable roles in the regulation of oxidative stress and immune response in the seahorse.

Redox Equivalents and Mitochondrial Bioenergetics

Mitochondrial energy metabolism depends upon high-flux and low-flux electron transfer pathways. The former provide the energy to support chemiosmotic coupling for oxidative phosphorylation. The latter provide mechanisms for signaling and control of mitochondrial functions. Few practical methods are available to measure rates of individual mitochondrial electron transfer reactions; however, a number of approaches are available to measure steady-state redox potentials (E _h) of donor/acceptor couples, and these can be used to gain insight into rate controlling reactions as well as mitochondrial bioenergetics. Redox changes within the respiratory electron transfer pathway are quantified by optical spectroscopy and measurement of changes in autofluorescence. Low-flux pathways involving thiol/disulfide redox couples are measured by redox Western blot and mass spectrometry-based redox proteomics. Together, the approaches provide the opportunity to develop integrated systems biology descriptions of mitochondrial redox signaling and control mechanisms.

Effect of melatonin pre-intervention on expression of thioredoxin-2 in pancreatic tissue of rats with acute necrotizing pancreatitis: Implications for protective effects of melatonin

AIM: To assess the effect of melatonin pre-intervention on the expression of thioredoxin-2 (Trx-2) and to explore the relationship between the protective effects of melatonin on the pancreas and the expression of Trx-2 in rats with acute necrotizing pancreatitis (ANP).

METHODS: Male Spraque-Dawley rats (n = 72) were randomly divided into an ANP group (group A), a melatonin pre-intervention (group M), and a control group (group C), with 24 rats in each group. The rats in group A received three intraperitoneal injections of 6% L-arginine at 25 mL/kg body weight with an interval of 1 h to induce ANP. The rats in group M received intraperitoneal injections of 0.25% melatonin at 20 mL/kg body weight 30 min before ANP induction. The rats in groups A and C received intraperitoneal injections of the same amount of saline. Rats were sacrificed 6, 12 and 24 h after ANP induction. The pathological evaluation of pancreatic tissues was performed. The concentrations of malondialdehyde (MDA) and myeloperoxidase (MPO) were measured and the expression of Trx-2 mRNA in pancreatic tissues was determined by RT-PCR.

RESULTS: In group A, the pathologic score and the concentrations of MDA and MPO in pancreatic tissues were significantly higher, and the expression of Trx-2 mRNA was significantly lower than those in group C (P < 0.05). In group M, the pathologic score and the concentrations of MDA and MPO in pancreatic tissues were significantly lower, and the expression of Trx-2 mRNA was significantly higher than those in group A (P < 0.05).

CONCLUSION: The expression of Trx-2 mRNA in pancreatic tissues is significantly decreased in rats with ANP. Melatonin pre-intervention can promote pancreatic tissues to express Trx-2 mRNA and thus exert a protective effect against pancreatic tissue injury.