Differential regulation of the multiple insulin and insulin receptor mRNAs by somatostatin

Combined transcriptomics and metabolomics to reveal the effects of copper exposure on the liver of rainbow trout(Oncorhynchus mykiss)

Copper (Cu) is recognized as an essential trace elements for the body; However, excessive levels of Cu can lead to toxic effects. We investigated the effects of Cu2+(75 μg/L, 150 μg/L, and 300 μg/L) on the rainbow trout liver. Combination of transcriptome and metabolome analyses, the regulatory mechanisms of the liver under Cu stress were elucidated. The results showed that Cu affected the antioxidant levels, leading to disruptions in the normal tissue structure of the liver. Combined transcriptome and metabolome analyses revealed significant enrichment of the insulin signaling pathway and the adipocytokine signaling pathway. Additionally, Cu2+ stress altered the amino acid metabolism in rainbow trout by reducing serine and arginine levels while increasing proline content. Apoptosis is inhibited and autophagy and lipid metabolism are suppressed; In summary, Cu2+ stress affects energy and lipid metabolism, and the reduction of serine and arginine represents a decrease in the antioxidant capacity, whereas the increase in proline and the promotion of apoptosis potentially serving as crucial strategies for Cu2+ resistance in rainbow trout. These findings provided insights into the regulatory mechanisms of rainbow trout under Cu2+ stress and informed the prevention of heavy metal pollution and the selection of biomarkers under Cu pollution.

The mammalian insulin antagonist S961 does not exhibit insulin receptor antagonism in rainbow trout in vivo

Due to their reported 'glucose-intolerant' phenotype, rainbow trout have been the focus of comparative studies probing underlying endocrine mechanisms at the organismal, tissue and molecular level. A particular focus has been placed on the investigation of the comparative role of insulin, an important glucoregulatory hormone, and its interaction with macronutrients. A limiting factor in the comparative investigation of insulin is the current lack of reliable assays to quantify circulating mature and thus bioactive insulin. To circumvent this limitation, tissue-specific responsiveness to postprandial or exogenous insulin has been quantified at the level of post-translational modifications of cell signalling proteins. These studies revealed that the insulin responsiveness of these proteins and their post-translational modifications are evolutionarily highly conserved and thus provide useful and quantifiable proxy indices to investigate insulin function in rainbow trout. While the involvement of specific branches of the intracellular insulin signalling pathway (e.g., mTor) in rainbow trout glucoregulation have been successfully probed through pharmacological approaches, it would be useful to have a functionally validated insulin receptor antagonist to characterize the glucoregulatory role of the insulin receptor pathway in its entirety for this species. Here, we report two separate in vivo experiments to test the ability of the mammalian insulin receptor antagonist, S961, to efficiently block insulin signalling in liver and muscle in response to endogenously released insulin and to exogenously infused bovine insulin. We found that, irrespective of the experimental treatment or dose, activation of the insulin pathway in liver and muscle was not inhibited by S961, showing that its antagonistic effect does not extend to rainbow trout.

The insulin gene as an energy homeostasis biomarker in Yangtze sturgeon (Acipenser dabryanus)

Insulin plays an important role in maintaining energy homeostasis and has the potential to be an indicator of energy homeostasis in the Yangtze sturgeon, Acipenser dabryanus. In this study, the Yangtze sturgeon insulin (Adinsulin) was cloned and characterized. To evaluate the possibility of insulin as an energy state assessment indicator, quantification real-time PCR (qRT-PCR) was used to evaluate expression changes in different tissues (the whole brain, esophagus, cardiac stomach, pyloric stomach, pyloric caeca, duodenum, valvula intestine, rectum, liver, pancreas, spleen, kidney, heart, muscle, gill and eye) from 6 fish (average weight 325.7 ± 22.3 g) and in three experiments including postprandial, fasting and re-feeding, and glucose tolerance treatment in which fish were divided into two groups including a group that administered a glucose solution (1 ul/g body weight) and another group that administered sterile water as control. In these three experiments, 6 fish were sampled, respectively, then been used to evaluate expression changes of insulin. All fish in feeding groups were fed in tanks (60.0 cm × 50.0 cm × 40.0 cm) with a commercial diet (crude protein ≥ 40%, crude fat ≥ 12%, coarse fiber ≤ 6%, crude ash ≤ 18%; TONGWEI CO., LTD, China) once a day at 16:00. The result showed that Adinsulin was highly expressed in the pancreas, which was the basis for the next experiment to use the pancreas as the test target. Adinsulin expression significantly increased 1 h after feeding and decreased rapidly after 3 h of feeding, but it was still significantly higher than that of the group without feeding (P < 0.01). Compared to the feeding group, the expression of Adinsulin was significantly reduced in the fasting group of 3 days (P < 0.01), 6 days (P < 0.01), 10 days (P < 0.05), 11 days (P < 0.05) and 13 days (P < 0.01) and was no significant difference in re-feeding for 1st day, 2nd day and 4th day, but there was difference between re-feeding group and fasting group. After glucose tolerance treatment, serum glucose levels increased significantly (P < 0.05), accompanied by a significant increase (P < 0.001) in insulin expression. This study result shows that insulin has the capacity to measure the energy homeostasis of Yangtze sturgeon. Further development of detection methods for sturgeon plasma or serum insulin will avoid slaughtering animals and is more practical in energy homeostasis assessment.

Insulin treatment protects the brain against neuroinflammation by reducing cerebral cytokines and modulating mitochondrial function

In the central nervous system, glial cells protect the brain against neuronal stress by inducing inflammatory responses; namely, intracellular signaling and cytokine production. However, chronic inflammation is often associated with degenerative diseases that can damage hormone signaling and mitochondrial function. Lipopolysaccharide (LPS) induces neuroinflammation by stimulating the production of interleukin-1beta (IL-1β) and tumor necrosis factor-alpha (TNF-α); moreover, it generates oxidative stress and impairs cognitive functions. The aim of the present study was to assess the therapeutic efficacy of intracerebroventricular (i.c.v.) injections of insulin against neuroinflammation. Inflammation was first induced in male Wistar rats (60 days old, n = 12/group) through an intraperitoneal injection of 0.1 mg/kg LPS. The i.c.v. insulin treatment at a 0.5 mU dose was initiated 4 h later and administered once a day for 5 days. Thereafter, the spatial memory of the rats was assessed, and the hippocampus and cortex were later dissected for biochemical analyses. Our results showed that LPS induced cognitive function impairments, but the insulin treatment reversed these effects. Whereas the levels of brain-derived neurotrophic factor and beta-nerve growth factor in the hippocampus were not altered by LPS, they were decreased in the cortex by insulin. The IL-1β and TNF-α levels were increased in the cortex and hippocampus following exposure to LPS, but insulin reversed these effects. Evaluation of the H₂O₂levels and mitochondrial membrane potential revealed that LPS modulated mitochondrial function, an effect that was also reversed by insulin. Moreover, LPS induced oxidative stress by decreasing the superoxide dismutase and catalase activities and glutathione and sulfhydryl levels. Furthermore, the levels of oxidative stress probes/markers (i.e.,2',7'-dichlorodihydrofluoresceindiacetateand nitrite) were higher in the LPS-treated rats. These effects were all reversed in the cortex and hippocampus by insulin treatment. Our results suggest a potential role for insulin as a therapeutic drug against inflammatory diseases associated with mitochondrial dysfunction in the brain.

Duplication and diversification of insulin genes in ray-finned fish

Insulin is a key hormone for the regulation of metabolism in vertebrates. Insulin is produced by pancreatic islet cells in response to elevated glucose levels and leads to the uptake of glucose by tissues such as liver and adipose tissue to store energy. Insulin also has additional functions in regulating development. Previous work has shown that the proglucagon gene, which encodes hormones counter regulating insulin, is duplicated in teleost fish, and that the peptide hormones encoded by these genes have diversified in function. I sought to determine whether similar processes have occurred to insulin genes in these species. Searches of fish genomes revealed an unexpected diversity of insulin genes. A triplication of the insulin gene occurred at the origin of teleost fish, however one of these three genes, insc, has been lost in most teleost fish lineages. The two other insulin genes, insa and insb, have been retained but show differing levels of selective constraint suggesting that they might have diversified in function. Intriguingly, a duplicate copy of the insa gene, which I named insab, is found in many fish. The coding sequence encoded by insab genes is under weak selective constraint, with its predicted protein sequences losing their potential to be processed into a two-peptide hormone. However, these sequences have retained perfectly conserved cystine residues, suggesting that they maintain insulin's three-dimensional structure and therefore might modulate the processing and secretion of insulin produced by the other genes.

[Pharmacological approaches for correction of thyroid dysfunctions in diabetes mellitus]

Thyroid diseases are closely associated with the development of types 1 and 2 diabetes mellitus (DM), and as a consequence, the development of effective approaches for their treatment is one of the urgent problems of endocrinology. Traditionally, thyroid hormones (TH) are used to correct functions of the thyroid system. However, they are characterized by many side effects, such as their negative effect on the cardiovascular system as well as the ability of TH to enhance insulin resistance and to disturb insulin-producing function of pancreas, exacerbating thereby diabetic pathology. Therefore, the analogues of TH, selective for certain types of TH receptors, that do not have these side effects, are being developed. The peptide and low-molecular weight regulators of thyroid-stimulating hormone receptor, which regulate the activity of the thyroid axis at the stage of TH synthesis and secretion in thyrocytes, are being created. Systemic and intranasal administration of insulin, metformin therapy and drugs with antioxidant activity are effective for the treatment of thyroid pathology in types 1 and 2 DM. In the review, the literature data and the results of own investigations on pharmacological approaches for the treatment and prevention of thyroid diseases in patients with types 1 and 2 DM are summarized and analyzed.

Ancestral genomic duplication of the insulin gene in tilapia: An analysis of possible implications for clinical islet xenotransplantation using donor islets from transgenic tilapia expressing a humanized insulin gene

Tilapia, a teleost fish, have multiple large anatomically discrete islets which are easy to harvest, and when transplanted into diabetic murine recipients, provide normoglycemia and mammalian-like glucose tolerance profiles. Tilapia insulin differs structurally from human insulin which could preclude their use as islet donors for xenotransplantation. Therefore, we produced transgenic tilapia with islets expressing a humanized insulin gene. It is now known that fish genomes may possess an ancestral duplication and so tilapia may have a second insulin gene. Therefore, we cloned, sequenced, and characterized the tilapia insulin 2 transcript and found that its expression is negligible in islets, is not islet-specific, and would not likely need to be silenced in our transgenic fish.