Irisin inhibits CCK-8-induced TNF-α production via integrin αVß5-NF-κB signaling pathways in Nile tilapia (Oreochromis niloticus).

Irisin, a secreted myokine generated by fibronectin type III domain-containing protein 5, has recently shown the potential to alleviate inflammation. Cholecystokinin-octapeptide (CCK-8) is closely associated with the inflammatory factor TNF-α, a central cytokine in inflammatory reactions. However, the interactions between irisin and CCK-8 in regulating TNF-α production and the underlying mechanism have not yet been elucidated. In the present study, irisin treatment inhibited the basal and the CCK-8-induced TNF-α production in vivo. Additionally, neutralizing circulating irisin using an irisin antiserum significantly augmented the CCK-8-induced stimulation of TNF-α levels. Moreover, the incubation of head kidney cells with irisin or CCK-8 has opposite effects on TNF-α secretion. Notably, irisin treatment inhibited basal and CCK-8-stimulated TNF-α release and gene transcription in head kidney cells. Mechanistically, the inhibitory actions of irisin on basal and CCK-8-induced TNF-α production could be negated by co-administered with the selective integrin αVß5 inhibitor cilengitide. In addition, the inhibitory effect of irisin on basal and CCK-8-triggered TNF-α production could be abolished by the inhibition of the nuclear factor-kappa B (NF-κB) signaling pathway. Furthermore, irisin impeded CCK-8-induced phosphorylation and degradation of IκBα, simultaneously inhibiting NF-κB phosphorylation, preventing its translocation into the nucleus, and suppressing its DNA-binding activity induced by CCK-8. Collectively, these results suggest that the inhibitory effect of irisin on TNF-α production caused by CCK-8 is mediated via the integrin αVß5-NF-κB signaling pathways in tilapia.

Molecular characterization and immune functions of lipasin in Nile tilapia (Oreochromis niloticus): Involvement in the regulation of tumor necrosis factor-α secretion.

Lipasin, the product of the angiopoietin-like 8 (angptl8) gene, is known as a critical regulator of plasma lipid metabolism. However, its immune function in vertebrates is currently poorly understood. By 5'/3'-rapid amplification of cDNA ends (RACE), we established the structural identity of Nile tilapia (Oreochromis niloticus) angptl8. The transcripts of tilapia angptl8 were widely expressed in various tissues, with the highest levels in the liver. Following lipopolysaccharide in vivo challenges, time-dependent angptl8 gene expression was observed in the head kidney and liver. On the basis of the sequence obtained, we produced recombinant lipasin that inhibited lipoprotein lipase activity. Treatment of head kidney leukocytes with lipasin stimulated tumor necrosis factor-α (TNF-α) secretion and gene expression. In addition, lipasin-induced TNF-α secretion could be prevented by inhibiting the nuclear factor-kappa B (NF-κB) signaling pathway. Furthermore, lipasin enhanced the phosphorylation and degradation of IκBα and promoted translocation of the p65 subunit of NF-κB to the nucleus. Collectively, the current findings suggested that lipasin was involved in the immune response of Nile tilapia and stimulated TNF-α secretion by activating the NF-κB pathway in tilapia head kidney leukocytes.

Interleukin-6 mediates lipopolysaccharide-inhibited irisin secretion in Nile tilapia (Oreochromis niloticus).

Irisin is a novel immunomodulatory adipomyokine released upon cleavage of the fibronectin type III domain-containing protein 5 (FNDC5). We aimed to examine interleukin-6 (IL-6) role in mediating irisin secretion in immunologically challenged animal and primary head kidney leukocytes cultured from tilapia. Intraperitoneal injection of lipopolysaccharide (LPS) increased plasma IL-6 levels and decreased irisin secretion, suggesting a causal relationship between the induction of IL-6 and irisin. To address this relationship, we further produced recombinant tilapia IL-6 and the anti-tilapia IL-6 polyclonal antiserum. Intraperitoneal injection of recombinant tilapia IL-6 inhibited plasma irisin levels. Consistent with this observation, LPS-induced inhibition of plasma irisin was significantly attenuated by neutralizing circulating IL-6 using an IL-6 antiserum. Besides, IL-6 treatment could inhibit irisin secretion and FNDC5 gene expression in primary cultures of tilapia head kidney leukocytes. In parallel experiments, both LPS and IL-6 blockade of irisin secretion could be reverted by IL-6 receptor antagonism. At the level of the leukocyte, IL-6 treatment also triggered rapid phosphorylation of Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3), whereas IL-6-reduced irisin secretion could be negated by inhibiting the JAK2 and STAT3 signaling pathways. These results, as a whole, provide the first evidence that IL-6 is the mediator of LPS-inhibited irisin secretion via activation of the JAK2/STAT3 signaling pathway.

Probiotics ameliorate polyethylene microplastics-induced liver injury by inhibition of oxidative stress in Nile tilapia (Oreochromis niloticus).

Microplastic particles (MPs) are environmental pollutants that can cause varying levels of aquatic toxicity. Probiotics have been shown to reduce the negative effects of toxic substances. However, the protective effect of probiotics against the adverse effects of MPs has yet to be reported. The current study sought to determine the effects of the commercial probiotic AquaStar® Growout on polystyrene (PS)-MPs-mediated hepatic oxidative stress in Nile tilapia (Oreochromis niloticus). Fishes were assigned into four groups: the first group was the control, the second group was exposed to 1 mg/L of 0.5 µm PS-MPs, and the third and fourth groups were exposed to 1 mg/L of 0.5 µm PS-MPs and pre-fed with probiotics at levels of 3 g/kg and 6 g/kg diet, respectively. At the end of the experiment, probiotics administration reversed liver damage caused by the PS-MPs, reducing serum levels of malondialdehyde, aspartate aminotransferase, and alanine aminotransferase, and increasing the total antioxidant capacity. Furthermore, probiotics alleviated PS-MPs-induced oxidative stress by restoring antioxidant enzyme activities (superoxide dismutase, catalase, glutathione S-transferase, and glutathione peroxidase) and reducing oxidized glutathione and enhancing the redox state. Besides, probiotics supplementation decreased the transcriptional level of C-reactive protein and tumor necrosis factor-α following PS-MPs exposure. Furthermore, probiotics counteracted PS-MPs-associated reactive oxygen species production and mitogen-activated protein kinases (MAPKs) phosphorylation status. These findings suggested that probiotics could decrease liver damage caused by PS-MPs through their antioxidant properties and modulation of MAPK signaling pathways.

Irisin promotes tilapia muscle cell growth and amino acid uptake via IGF-1 signaling.

Irisin is a recently discovered myokine that facilitates the browning of white adipose tissue, increases glucose uptake in skeletal muscle, and influences metabolic processes in the liver. However, its potential effects on amino acid absorption remained largely unexplored. This study aimed to elucidate the role of irisin in modulating amino acid uptake and delineate the underlying molecular mechanisms involved. To this end, juvenile tilapia were administered intraperitoneal irisin injections at 100 ng/g body weight over eight weeks. Evaluation of various physiological parameters revealed that irisin supplementation significantly improved the specific growth rate and feed conversion efficiency while reducing feed consumption. Muscle tissue analysis revealed that irisin significantly modified the proximate composition by increasing protein content and reducing lipid levels. It also significantly raised the levels of both essential and non-essential amino acids in the muscle. Histological analysis demonstrated that irisin stimulated muscle growth through hyperplasia rather than hypertrophy, corroborated by upregulated IGF-1 mRNA and downregulated myostatin mRNA expression. Mechanistic studies in cultured tilapia muscle cells elucidated that irisin activated integrin receptors on muscle cells, which subsequently engaged IGF-1/IGF-1R signaling. Downstream of IGF-1R activation, irisin simultaneously stimulates the ERK1/2 and PI3K/mTORC2/Akt pathways. The convergence of these pathways upregulates L-type amino acid transporter 1 expression, thereby augmenting amino acid uptake into muscle cells. In summary, irisin supplementation in tilapia leads to improved muscle growth, predominantly via hyperplasia and augmented amino acid assimilation, governed by intricate cellular signaling pathways. These findings provide valuable aquaculture applications and novel insights into muscle development.

Molecular cloning and characterization of the novel adropin from tilapia (Oreochromis niloticus): Involvement in the control of food intake.

Adropin has been shown to be involved in the regulation of food intake in mice. However, the mechanism of adropin in feeding regulation is still largely unknown. Using the tilapia, Oreochromis niloticus, we identified and characterized a novel form of adropin (designated adropin-b) encoding a 68-amino acid precursor. Although adropin-b shared low amino acid identities with its tilapia paralog (designated adropin-a), synteny analysis proved that tilapia adropin is orthologous to its human counterpart. The transcripts of adropin-b were ubiquitously expressed in various tissues with the highest levels in the olfactory bulb. A decrease in adropin-b mRNA levels was observed 1 h following a meal in the olfactory bulb, hypothalamus, and optic tectum, whereas fasting for 7 days induced an increase in adropin-b mRNA levels in the olfactory bulb, hypothalamus, and optic tectum of tilapia brain. However, no changes in adropin-a mRNA levels were observed in the postprandial and fasting state. Intraperitoneal injection of tilapia adropin-b was shown to increase food consumption, but adropin-a did not affect feeding. Co-treatment of the fish with adropin-b and neuropeptide Y (NPY) had no additive effects on appetite. The appetite stimulatory effects of adropin-b appeared to be mediated by upregulating the orexigenic Npy, Orexin, and Proapelin gene expression, paralleled by inhibition of the mRNA levels of anorexigenic proopiomelanocortin (Pomc) and cocaine-amphetamine-regulated transcript (Cart) in vivo and in vitro. These observations suggested that adropin-b participated in appetite control and gene regulation of central orexigenic and anorexigenic factors in a fish model.