Expression of apoptosis-related genes in liver-specific growth hormone receptor gene-disrupted mice is sex dependent

Zebrafish as an innovative model for exploring cardiovascular disease induction mechanisms and novel therapeutic interventions: a molecular insight

Cardiovascular disease (CVD) is a common cardiac disorder that leads to heart attacks, strokes, and heart failure. It is primarily characterized by conditions that impact the heart and blood arteries, including peripheral artery disease, arrhythmias, atherosclerosis, myocardial ischemia, congenital heart abnormalities, heart failure, rheumatic heart disease, hypertension, and cardiomyopathies. These conditions are mainly effect the heart and blood vessels, causing blockages or weakened pumping, due to severe hereditary and environmental factors. The frequency of CVD is rising significantly as life expectancy increases. Despite this, no effective treatment or management for its symptoms has been found. One of the most difficult obstacles to overcome, is finding a suitable animal model for drug screening and drug development. Although rodents, mice, swine, and mammals serve as the basis for most animal models of cardiovascular disease, no model accurately captures the epidemiology of the condition. Zebrafish (Danio rerio) have drawn the interest of the international scientific community due to certain shortcomings of the previously discussed animal models because they are smaller, less costly, and have an incredibly high rate of reproduction. This review article emphasizes the significance of using zebrafish as an animal model to investigate the possible facets of cardiovascular disease. Moreover, the ultimate purpose of this review article is to establish the advantages of employing zebrafish over other animal models and to investigate the boundaries of using zebrafish to study human disease. Furthermore, the mechanisms of cardiovascular diseases induction in zebrafish were covered to improve understanding for readers. Finally, the analysis of cardiotoxicity using Zebra fish model, is also explained. In order to stop the health index from deteriorating, the current study also covers some innovative, effective, and relatively safer treatments for treatment and management of cardiotoxicity.

Growth hormone receptor gene disruption

Much of our understanding of growth hormone's (GH)'s numerous activities stems from studies utilizing GH receptor (GHR) knockout mice. More recently, the role of GH action has been examined by creating mice with tissue-specific or temporal GHR disruption. To date, 37 distinct GHR knockout mouse lines have been created. Targeted tissues include fat, liver, muscle, heart, bone, brain, macrophage, intestine, hematopoietic stem cells, pancreatic β cells, and inducible multi-tissue "global" disruption at various ages. In this chapter, a summary of each mouse line is provided with background information on the generation of the mouse line as well as important physiological outcomes resulting from GHR gene disruption. Collectively, these mouse lines provide unique insights into GH action and have resulted in the development of new hypotheses about the functions ascribed to GH action in particular tissues.

Mice with gene alterations in the GH and IGF family

Much of our understanding of GH's action stems from animal models and the generation and characterization of genetically altered or modified mice. Manipulation of genes in the GH/IGF1 family in animals started in 1982 when the first GH transgenic mice were produced. Since then, multiple laboratories have altered mouse DNA to globally disrupt Gh, Ghr, and other genes upstream or downstream of GH or its receptor. The ability to stay current with the various genetically manipulated mouse lines within the realm of GH/IGF1 research has been daunting. As such, this review attempts to consolidate and summarize the literature related to the initial characterization of many of the known gene-manipulated mice relating to the actions of GH, PRL and IGF1. We have organized the mouse lines by modifications made to constituents of the GH/IGF1 family either upstream or downstream of GHR or to the GHR itself. Available data on the effect of altered gene expression on growth, GH/IGF1 levels, body composition, reproduction, diabetes, metabolism, cancer, and aging are summarized. For the ease of finding this information, key words are highlighted in bold throughout the main text for each mouse line and this information is summarized in Tables 1, 2, 3 and 4. Most importantly, the collective data derived from and reported for these mice have enhanced our understanding of GH action.

Combined toxicity of silica nanoparticles and cadmium chloride on the cardiovascular system of zebrafish (Danio rerio) larvae

Silica nanoparticles (SiNPs) and cadmium are major environmental pollutants that have severe detrimental effects on living organisms. Recent studies have demonstrated that the combined exposure of SiNPs and heavy metals is more toxic than individual exposure. However, studies on the effects of the combined exposure of SiNPs and cadmium, on the cardiovascular system are rare. In this study, zebrafish (Danio rerio) embryos were exposed to a combination of SiNPs and experimentally safe concentrations CdCl₂ for studying the alterations in heart morphology, heart rate, apoptosis, and vascular endothelial cells. The results demonstrated that the detrimental effects of SiNPs+CdCl₂ exposure on the heart rate and vascular endothelial cells were more severe than those following exposure to SiNPs or CdCl₂ alone. Gene expression analysis revealed that apoptosis and inflammation could be the major pathways underlying the toxicity caused by the combined exposure of SiNPs and CdCl₂.

Growth hormone receptor knockout: Relevance to xenotransplantation

Xenotransplantation research has made considerable progress in recent years, largely through the increasing availability of pigs with multiple genetic modifications, effective immunosuppressive therapy, and anti-inflammatory therapy to protect pig tissues from the primate immune and inflammatory responses and correct molecular incompatibilities. Further study is required regarding identification and investigation of physiological incompatibilities. Although the exact cause remains uncertain, we and others have observed relatively rapid growth of kidney xenografts after transplantation into nonhuman primates (NHPs). There has also been some evidence of growth, or at least ventricular hypertrophy, of the pig heart after orthotopic transplantation into NHPs. Rapid growth could be problematic, particularly with regard to the heart within the relatively restricted confines of the chest. It has been suggested that the problem of rapid growth of the pig organ after transplantation could be resolved by growth hormone receptor (GHR) gene knockout in the pig. The GHR, although most well-known for regulating growth, has many other biological functions, including regulating metabolism and controlling physiological processes. Genetically modified GHRKO pigs have recently become available. We provide data on their growth compared to comparable pigs that do not include GHRKO, and we have reviewed the literature regarding the effect of GHRKO, and its relevance to xenotransplantation.

Effects of tissue-specific GH receptor knockouts in mice

Growth hormone (GH) is pituitary derived hormone which acts on most tissues of the body either directly or indirectly and affects many metabolic processes throughout life. Genetically engineered mouse lines have become vital tools for uncovering the various in vivo activities of a GH. A particularly useful mouse line has been the GH receptor (GHR) gene disrupted or knockout (KO) mouse which has been used world-wide in many studies. Recent advances in biotechnology have allowed the development of tissue-specific knockout mouse lines which allows for more direct enquiries on the activities of a given protein in specific tissues or cell types. Accordingly, twenty-two novel tissue-specific GHRKO mouse lines have been developed in the last eleven years. In this paper we provide a detailed list and review the phenotypic changes that occur in each of these tissue-specific GHRKO mouse lines.

Identification of the cDNA Encoding the Growth Hormone Receptor (GHR) and the Regulation of GHR and IGF-I Gene Expression by Nutritional Status in Reeves' Turtle (Chinemys reevesii)

Chinemys reevesii (Reeves’ turtle) is a slow-growing reptile that is distributed widely across China. Prior to this study, the cDNA sequence of the growth hormone receptor (GHR) in the Reeve’s turtle, or how periods of starvation might influence the gene expression of GHR and insulin-like growth factor I (IGF-I) in this species, were unknown. Here, we identified the full-length sequence of the cDNA encoding GHR in Reeves’ turtle by using RT-PCR and RACE. The full-length GHR cDNA was identified to be 3936 base-pairs in length, with a 1848 base-pair open reading frame (ORF) that encodes a 615 amino acid protein. Analysis showed that GHR mRNA was detectable in a wide range of tissues; the highest and lowest levels of expression were detected in the liver and the gonad, respectively. IGF-I was also expressed in a range of tissues, but not in the gonad; the highest levels of IGF-I expression were detected in the liver. After 4 weeks of fasting, the expression levels of GHR and IGF-I in the liver had decreased significantly; however, these gradually returned to normal after refeeding. We report the first cloned cDNA sequence for the GHR gene in the Reeve’s turtle. Our findings provide a foundation from which to investigate the specific function of the GHR in Reeve’s turtle, and serve as a reference for studying the effects of different nutrient levels on GHR expression in this species.

New insights of growth hormone (GH) actions from tissue-specific GH receptor knockouts in mice

In order to provide new insights into the various activities of GH in specific tissues, recent advances have allowed for the generation of tissue-specific GHR knockout mice. To date, 21 distinct tissue-specific mouse lines have been created and reported in 28 publications. Targeted tissues include liver, muscle, fat, brain, bone, heart, intestine, macrophage, pancreatic beta cells, hematopoietic stem cells, and multi-tissue "global". In this review, we provide a brief history and description of the 21 tissue-specific GHR knockout mouse lines. Arch Endocrinol Metab. 2019;63(6):557-67.

MECHANISMS IN ENDOCRINOLOGY: Lessons from growth hormone receptor gene-disrupted mice: are there benefits of endocrine defects?

Growth hormone (GH) is produced primarily by anterior pituitary somatotroph cells. Numerous acute human (h) GH treatment and long-term follow-up studies and extensive use of animal models of GH action have shaped the body of GH research over the past 70 years. Work on the GH receptor (R)-knockout (GHRKO) mice and results of studies on GH-resistant Laron Syndrome (LS) patients have helped define many physiological actions of GH including those dealing with metabolism, obesity, cancer, diabetes, cognition and aging/longevity. In this review, we have discussed several issues dealing with these biological effects of GH and attempt to answer the question of whether decreased GH action may be beneficial.

The Growth Hormone Receptor: Mechanism of Receptor Activation, Cell Signaling, and Physiological Aspects

The growth hormone receptor (GHR), although most well known for regulating growth, has many other important biological functions including regulating metabolism and controlling physiological processes related to the hepatobiliary, cardiovascular, renal, gastrointestinal, and reproductive systems. In addition, growth hormone signaling is an important regulator of aging and plays a significant role in cancer development. Growth hormone activates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway, and recent studies have provided a new understanding of the mechanism of JAK2 activation by growth hormone binding to its receptor. JAK2 activation is required for growth hormone-mediated activation of STAT1, STAT3, and STAT5, and the negative regulation of JAK-STAT signaling comprises an important step in the control of this signaling pathway. The GHR also activates the Src family kinase signaling pathway independent of JAK2. This review covers the molecular mechanisms of GHR activation and signal transduction as well as the physiological consequences of growth hormone signaling.

Deconstructing the Growth Hormone Receptor(GHR): Physical and Metabolic Phenotypes of Tissue-Specific GHR Gene-Disrupted Mice

Growth hormone (GH)-induced signaling results in numerous effects in multiple tissues throughout the body. Elucidation of several of these effects has come from studies observing the various phenotypes of the GH receptor (GHR) gene-disrupted (GHR-/-) mouse. These mice are dwarf and obese with increased insulin sensitivity, are resistant to cancer and diabetes, and have an extended lifespan. While these mice have proven to be a valuable tool for understanding the pleiotropic effects of GH, we and others have generated novel tissue-specific GHR gene-disrupted mouse lines that are now helping to further dissect the actions of GH on specific cells/tissues. In this chapter, we summarize the various phenotypes observed in these mice.

Removal of growth hormone receptor (GHR) in muscle of male mice replicates some of the health benefits seen in global GHR-/- mice

Global disruption of the GH receptor in mice (GHR-/-) produces a large and reproducible extension in lifespan. Since lack of GH action in muscle resulting in improved glucose homeostasis is potentially a mechanism by which GHR-/- mice are long-lived, and since no information on muscle-specific GHR disruption in females is available, we generated and characterized a line of muscle-specific GHR disrupted (MuGHRKO) mice. As expected, male MuGHRKO mice had improved fasting blood glucose, insulin, c-peptide, and glucose tolerance. In contrast, female MuGHRKO mice exhibited normal glucose, insulin, and glucose tolerance. Body weight was mildly but significantly altered in opposite directions in males (decreased) and females (increased) compared to controls. Grip strength and treadmill endurance were unchanged with advanced age in both sexes, suggesting that the direct action of GH on muscle has minimal effect on age-related musculoskeletal frailty. Longevity was unchanged in both sexes at Ohio University and significantly increased for males at University of Michigan. These data suggest that removal of GHR in muscle of male MuGHRKO mice replicates some of the health benefits seen in global GHR-/- mice including improvements to glucose homeostasis and smaller body weight in males, which may explain the trends observed in lifespan.

Gene expression of key regulators of mitochondrial biogenesis is sex dependent in mice with growth hormone receptor deletion in liver

Mitochondrial biogenesis is an essential process for cell viability. Mice with disruption of the growth hormone receptor (GHR) gene (Ghr gene) in the liver (LiGHRKO), in contrast to long-lived mice with global deletion of the Ghr gene (GHRKO), are characterized by lack of improved insulin sensitivity and severe hepatic steatosis. Tissue-specific disruption of the GHR in liver results in a mouse model with dramatically altered GH/IGF1 axis. We have previously shown increased levels of key regulators of mitochondrial biogenesis in insulin-sensitive GHRKO mice. The aim of the present study is to assess, using real-time PCR, the gene expression of key regulators of mitochondrial biogenesis (Pgc1α, Ampk, Sirt1, Nrf2 and Mfn2) and a marker of mitochondrial activity (CoxIV) in brains, kidneys and livers of male and female LiGHRKO and wild-type (WT) mice. There were significant differences between males and females. In the brain, expression of Pgc1α, Ampk, Sirt1, Nrf2 and Mfn2 was lower in pooled females compared to pooled males. In the kidneys, expression of Ampk and Sirt1 was also lower in female mice. In the liver, no differences between males and females were observed. Sexual dimorphism may play an important role in regulating the biogenesis of mitochondria.

Regulation of mTOR activity in Snell dwarf and GH receptor gene-disrupted mice

The involvement of mammalian target of rapamycin (mTOR) in lifespan control in invertebrates, calorie-restricted rodents, and extension of mouse lifespan by rapamycin have prompted speculation that diminished mTOR function may contribute to mammalian longevity in several settings. We show here that mTOR complex-1 (mTORC1) activity is indeed lower in liver, muscle, heart, and kidney tissue of Snell dwarf and global GH receptor (GHR) gene-disrupted mice (GHR-/-), consistent with previous studies. Surprisingly, activity of mTORC2 is higher in fasted Snell and GHR-/- than in littermate controls in all 4 tissues tested. Resupply of food enhanced mTORC1 activity in both controls and long-lived mutant mice but diminished mTORC2 activity only in the long-lived mice. Mice in which GHR has been disrupted only in the liver do not show extended lifespan and also fail to show the decline in mTORC1 and increase in mTORC2 seen in mice with global loss of GHR. The data suggest that the antiaging effects in the Snell dwarf and GHR-/- mice are accompanied by both a decline in mTORC1 in multiple organs and an increase in fasting levels of mTORC2. Neither the lifespan nor mTOR effects appear to be mediated by direct GH effects on liver or by the decline in plasma IGF-I, a shared trait in both global and liver-specific GHR-/- mice. Our data suggest that a more complex pattern of hormonal effects and intertissue interactions may be responsible for regulating both lifespan and mTORC2 function in these mouse models of delayed aging.