JAK family members: Molecular cloning, expression profiles and their roles in leptin influencing lipid metabolism in Synechogobius hasta

Cloning and expression analysis of Janus activated kinase family genes from spotted seabass (Lateolabrax maculatus)

Janus kinases (JAKs) are important components of the JAK-STAT signaling pathway and play vital roles in innate immunity, autoimmune diseases, and inflammation. However, information about JAKs remains largely unknown in the spotted seabass, a fish species of Perciformes with great commercial value in the aquaculture industry. The aims of this study are to obtain the complete cDNA sequences of JAKs (JAK1, JAK2A, JAK2B, JAK3 and TYK2) from spotted seabass and to investigate their roles upon stimulation with lipopolysaccharides (LPS) and Edwardsiella tarda, using RT-PCR, PCR and qRT-PCR methods. All five JAK genes from the spotted seabass, each encode more than 1100 amino acids residues. JAK1 and JAK3 consist of 24 exons and 23 introns, whereas JAK2A, JAK2B and TYK2 consist of 23 exons and 22 introns. Furthermore, these five spotted seabass JAKs share high sequence identities with those of other fish species in protein domain analysis, synteny analysis, and phylogenetic analysis. Moreover, these five JAK genes were ubiquitously expressed in all tissues examined from healthy fish, and inducible expressions of JAKs were observed in the intestine, gill, head kidney, and spleen following LPS treatment or E. tarda infection. These findings indicate that all these JAK genes are involved in the antibacterial immunity of the spotted seabass and provide a basis for further understanding the mechanism of JAKs antibacterial response in the spotted sea bass.

Identifying transcriptomic indicators of tertiary treated municipal effluent in longnose dace (Rhinichthys cataractae) caged under semi-controlled conditions in experimental raceways

To evaluate effects of tertiary treated wastewater treatment plant effluent (MWWE) on transcriptomic responses in longnose dace (Rhinichthys cataractae; LND) we conducted a semi-controlled study in experimental raceways (Advancing Canadian Water Assets facility) imbedded in the Pine Creek treatment plant (Calgary, AB). LND collected from a reference site in the Bow River (REF) were caged in raceways containing either 5 % Pine Creek effluent (PC) or Bow River water (BR; control) over 28 d. Liver transcriptomes were analyzed in males and females sampled on days 7, 14 and 28 from BR and PC, and compared to REF fish on day 0. Concurrent with the caging, selected environmental substances of concern were analyzed in the BR and PC. Significantly different unigenes (SDUs) in females (vs males) within both BR and PC raceways increased over time and compared to REF fish. Moreover, SDUs in females and males within the same treatment (i.e., BR, PC) showed a temporal increase as well as compared to REF fish. Time was the dominant factor affecting SDUs, whereas sex and treatment had less of an impact on the transcriptome profiling. Gene Set Enrichment Analysis of BR vs PC over time revealed effects on genes involved in growth, metabolism of carbohydrates and lipids, and immune system on day 7; however, by day 28, 80-100 % of the transcripts localized to enriched biomarkers were associated with tissue immune responses in both sexes. Exposure to 5 % effluent had significant effects on female liver somatic index but no effects were observed on other phenotypic health indices in either sex. BR was used as the source of reference water, but analyses showed trace amounts of ESOCs. Analyses did not point towards definitive response patterns that could be used in field-based ecotoxicogenomic studies on the impacts of well-treated MWWE but suggested compromised adaptive immune responses.

Janus kinase 1 in Megalobrama amblycephala: Identification, phylogenetic analysis and expression profiling after Aeromonas hydrophila infection

Janus kinase 1 (JAK1), a member of the JAK family, plays an essential and non-redundant role in the mammalian immune system. However, the potential role of JAK1 in fish immune response remains largely unclear. In the present study, the JAK1 gene of Megalobrama amblycephala (MamJAK1) was identified and characterized. The open reading frame (ORF) of MamJAK1 was 3462 bp, encoding 1153 amino acids. MamJAK1 consists of four common domains of the JAK family, including B41, SH2, STyrKc (a pseudo kinase domain), and TyrKc (a kinase domain). Phylogenetic analysis showed that JAK1s are divided into two evolutionary clades, one containing fish JAK1s, and the other containing JAK1s from other vertebrates. The results of quantitative real-time PCR (qPCR) showed that in healthy M. amblycephala, MamJAK1 mRNA was highest expressed in blood, followed by spleen, intestine and mid-kidney, and lowly expressed in other tissues including gill, liver, head kidney, muscle, brain and heart. After Aeromonas hydrophila infection, the expression of MamJAK1 mRNA was significantly induced in four selected tissues including spleen, mid-kidney, liver and intestine, reaching a peak at 24 hpi (hour post infection) in spleen and mid-kidney, at 12 hpi in liver and at 4 hpi in intestine, and then the expression level was restricted to control levels at 72 or 120 hpi. In addition, the results of Western blot showed that the phosphorylation level of MamJAK1 protein in spleen and mid-kidney increased significantly after A. hydrophila infection, although MamJAK1 protein did not change obviously. Further, the JAK1 phosphorylation in Ctenopharyngodon idellus kidney (CIK) cells was found to be significantly induced by LPS stimulation and IL-6R over-expression. The results above suggest that MamJAK1 may play an essential role in the immune response against bacterial infection through the IL-6R mediated JAK1/STAT signaling pathway, which further deepen our understanding of JAK1 and provides a potential target for the treatment and prevention of bacterial diseases in teleost.

PRL/PRLR Can Promote Insulin Resistance by Activating the JAK2/STAT5 Signaling Pathway

Objective

Although prolactin (PRL) is known to affect food intake, weight gain, and insulin resistance, its effects on lipid metabolism and underlying mechanisms remain underinvestigated. This study aimed to investigate the effects of PRL and its receptor (PRLR) on fat metabolism in regulating the JAK2/STAT5 signaling pathway.

Methods

SW872 adipocytes were incubated with oleic acid to establish an insulin resistance (IR) model. Western blot was used to detect the expression of PRLR, JAK2, p-JAK2, STAT5, and p-STAT5. Triglyceride (TG) mass was detected by chemical colorimetry methods.

Results

Fat droplets in the high-dose and medium-dose PRL groups were significantly higher than in the IR model group. TG mass in the cells was increased significantly compared with the model group. Compared with the control group, the expression of PRLR, p-JAK2, and p-STAT5 were significantly decreased in the IR model group when PRL was intervened for 24 h and 48 h. The expression of PRLR, p-JAK2, and p-STAT5 in the high-dose PRL intervention group increased significantly compared with the model group. The PRLR overexpressing group had significantly increased TG content and PRLR, and JAK2, p-JAK2, STAT5, and p-STAT5 levels compared with the IR model.

Conclusion

PRL and PRLR are related to fat metabolism, and the PRL/PRLR signaling pathway can promote insulin resistance by activating the JAK2/STAT5 signaling pathway and increasing the deposition of TGs.

Trajectory of leptin and leptin receptor in vertebrates: Structure, function and their regulation

The present review provides a comparative insight into structure, function and control of leptin system in fishes, herptiles, birds and mammals. In general, leptin acts as an anorexigenic hormone since its administration results in decrease of food intake in vertebrates. Nonetheless, functional paradox arises in fishes from contradictory observations on level of leptin during fasting and re-feeding. In addition, leptin is shown to modulate metabolic functions in fishes, reptiles, birds and mammals. Leptin also regulates reproductive and immune functions though more studies are warranted in non-mammalian vertebrates. The expression of leptin and its receptor is influenced by numerous factors including sex steroids, stress and stress-induced catecholamines and glucocorticoids though their effect in non-mammalian vertebrates is hard to be generalized due to limited studies.

Effects of sodium perchlorate and exogenous L-thyroxine on growth, development and leptin signaling pathway of Bufo gargarizans tadpoles during metamorphosis

Sodium perchlorate (NaClO₄) and exogenous L-thyroxine (T4), two kinds of endocrine-disrupting chemicals (EDCs), mainly affect the circulating thyroid hormones, which regulate the initiation and rate of metamorphosis in amphibian. The aim of this study is to evaluate the potential role of EDCs in regulating the development of tadpoles and leptin signaling pathway of liver during the metamorphosis of Bufo gargarizans. There was completely opposite result of average development stage of tadpoles and morphological parameters between the NaClO₄ and T4 exposure groups. Histological analysis revealed that NaClO₄ and T4 exposure both caused liver injury, such as the decreased size of hepatocytes, atrophy of nucleus, increased melanomacrophage centres and disappearance of hepatocyte membranes. In addition, the results of RT-qPCR revealed that NaClO₄ treatment significantly inhibited the transcript levels of genes related to thyroid hormone (D2, TRα and TRβ) and leptin signaling pathway (LepR, JAK1, JAK2, and TYK2), while there was an increase of mRNA expression of these genes in the liver of tadpoles administrated with T4 compared with control. This work lays an important foundation for assessing the risk of EDCs in relation to amphibian development during metamorphosis.

A cross-talk between leptin and 17β-estradiol in vitellogenin synthesis in rainbow trout Oncorhynchus mykiss liver

The existence of nutritional and energy reserves is fundamental for fish female fertility, so that the existence of a correlation between metabolic reserves and reproductive capacity is suggested. Leptin regulates body weight and energy homeostasis. Estradiol induces the synthesis of vitellogenin, a phospholipoglycoprotein produced by the liver and taken up by the growing oocytes. The objective of this study was to investigate the possible existence of a crosstalk between 17β-estradiol (E₂) and leptin in the modulation of E₂-induced vtg in the rainbow trout Oncorhynchus mykiss. Liver slices were incubated with recombinant trout leptin (rt-lep) at three different concentrations (1-10-100 ng/ml). rt-lep brought about the decrease of E₂-induced vtg secretion in the medium and the down-regulation of vtg mRNA expression. Moreover, rt-lep stimulated the lipase activity and diminished the liver fatty acid content. The combined employment of signal transduction inhibitors and the analysis of signal transduction phosphorylated factors revealed that rt-lep effect on E₂-induced vtg occurred through the activation of phosphodiesterase, protein kinase C, MAP kinases, and protein kinase A. In conclusion, our study suggests that leptin influences E₂-induced vtg synthesis in the rainbow trout Oncorhynchus mykiss by modifying both the protein and the lipid components.

Effects of di (2-ethylhexyl) phthalate and high-fat diet on lipid metabolism in rats by JAK2/STAT5

Exposure to di (2-ethylhexyl) phthalate (DEHP) induces lipid metabolism disorder and high-fat diet (HD) may have joint effects with DEHP. We aim to clarify the role of JAK2/STAT5 pathway in the process and reveal the effects of HD on the toxicity of DEHP. Wistar rats (160 animals) were fed with HD or normal diet (ND) respectively and exposed to DEHP 0, 5, 50, and 500 mg/kg/day for 8 weeks. Lipid levels, as well as the morphology of liver and adipose, mRNA levels, and protein levels of JAK2, STAT5A, STAT5B, FAS, ap2, and PDK4 were detected. The results showed that DEHP exposure leads to increased weight gain. The JAK2/STAT5 pathway was activated in adipose after DEHP exposure and promoted the expression of FAS, ap2, and PDK4 in ND rats. While in the liver, JAK2 was inhibited, and lipid synthesis and accumulation were increased. However, rats exposed to DEHP in combination with HD showed a complete disorder of lipid metabolism. Therefore, we conclude that DEHP affects lipid metabolism through regulating the JAK2/STAT5 pathway and promotes adipogenesis and lipid accumulation. High-fat diet may have a joint effect with DEHP on lipid metabolism disorder.

Assessing the Functional Role of Leptin in Energy Homeostasis and the Stress Response in Vertebrates

Leptin is a pleiotropic hormone that plays a critical role in regulating appetite, energy metabolism, growth, stress, and immune function across vertebrate groups. In mammals, it has been classically described as an adipostat, relaying information regarding energy status to the brain. While retaining poor sequence conservation with mammalian leptins, teleostean leptins elicit a number of similar regulatory properties, although current evidence suggests that it does not function as an adipostat in this group of vertebrates. Teleostean leptin also exhibits functionally divergent properties, however, possibly playing a role in glucoregulation similar to what is observed in lizards. Further, leptin has been recently implicated as a mediator of immune function and the endocrine stress response in teleosts. Here, we provide a review of leptin physiology in vertebrates, with a particular focus on its actions and regulatory properties in the context of stress and the regulation of energy homeostasis.