Signalling pathways for insulin-like growth factor type 1-mediated expression of uncoupling protein 3

TNF-α (G-308A) Polymorphism, Circulating Levels of TNF-α and IGF-1: Risk Factors for Ischemic Stroke—An Updated Meta-Analysis

Objective

Accumulated studies have explored gene polymorphisms and circulating levels of tumor necrosis factor (TNF)-α and insulin-like growth factor (IGF)-1 in the etiology of ischemic stroke (IS). Of the numerous etiopathological factors for IS, a single-nucleotide polymorphism (SNP) rs1800629 located in the TNF-α gene promoter region and increased levels of TNF-α were found to be associated with IS in different ethnic backgrounds. However, the published results are inconsistent and inconclusive. The primary objective of this meta-analysis was to investigate the concordance between rs1800629 polymorphism and IS. A secondary aim was to explore circulating levels of TNF-α and IGF-1 with IS in different ethnic backgrounds and different sourced specimens.

Methods

In this study, we examined whether rs1800629 genetic variant and levels of TNF-α and IGF-1 were related to the etiology of IS by performing a meta-analysis. Relevant case-control studies were retrieved by database searching and systematically selected according to established inclusion criteria.

Results

A total of 47 articles were identified that explored the relationship between the rs1800629 polymorphism and levels of TNF-α and IGF-1 with IS risk susceptibility. Statistical analyses revealed a significant association between the rs1800629 polymorphism and levels of TNF-α and IGF-1 with IS pathogenesis.

Conclusion

Our findings demonstrated that the TNF-α rs1800629 polymorphism, the increased levels of TNF-α, and decreased levels of IGF-1 were involved in the etiology of IS.

Insulin-like growth factor-1 directly mediates expression of mitochondrial uncoupling protein 3 via forkhead box O4

OBJECTIVE

The objective of our study was to examine the direct action of insulin-like growth factor-1(IGF-1) signaling on energy homeostasis in myocytes.

DESIGN

We studied the IGF-1 stimulation of mitochondrial uncoupling protein 3 (UCP3) expression in the HEK 293 derived cell line TSA201, murine C2C12 skeletal muscle myoblasts, and rat L6 skeletal myoblasts. We also investigated the direct effect of IGF-1 on the Insulin/IGF-1 receptor (IGF-1R)/phosphatidylinositol 3 (PI3)-Akt/forkhead box O4 (FOXO4) pathway using a combination of a reporter assay, semi-quantitative polymerase chain reaction, western blotting, and animal experiments.

RESULTS

We demonstrated that IGF-1 regulates UCP3 expression via phosphorylation of FOXO4, which is a downstream signal transducer of IGF-1. UCP3 expression increased with activated FOXO4 in a dose-dependent manner. We also examined the functional FOXO4 binding site consensus sequences and identified it as the -1922 bp site in the UCP3 promoter region. UCP3 was also found to be concomitantly expressed with IGF-1 during differentiation of C2C12 myoblasts. Our animal experiments showed that high fat diet induced IGF-1 levels which likely influenced UCP3 expression in the skeletal muscle.

CONCLUSION

Our findings demonstrate that that IGF-1 directly stimulates UCP3 expression via the IGF-1/IGF-1R/PI3-Akt/FOXO4 pathway.

Mitochondrial Function Is Compromised in Cortical Bone Osteocytes of Long-Lived Growth Hormone Receptor Null Mice

Despite increased longevity and resistance to multiple stressors, growth hormone receptor null (GHRKO) mice exhibit severe skeletal impairment. The role of GHR in maintaining osteocyte mitochondrial function is unknown. We found that GHR ablation was detrimental to osteocyte mitochondrial function. In vivo multiphoton microscopy revealed significant reductions of >10% in mitochondrial membrane potential (MMP) in GHRKO osteocytes and reduced mitochondrial volumetric density. Reductions in MMP were accompanied by reductions in glucose transporter-1 levels, steady state ATP, NADH redox index, oxygen consumption rate, and mitochondrial reserve capacity in GHRKO osteocytes. Glycolytic capacity did not differ between control and GHRKO males' osteocytes. However, osteocytes from aged female GHRKO mice exhibited reductions in glycolytic parameters, indicating impairments in glucose metabolism, which may be sex dependent. GHRKO osteocytes exhibited increased levels of cytoplasmic reactive oxygen species (ROS) (both basal and in response to high glucose), insulin-like growth factor-1 (IGF-1), and insulin. Mitochondrial ROS levels were increased and correlated with reduced glutathione in GHRKO osteocytes. Overall, the compromised osteocyte mitochondrial function and responses to metabolic insults strongly correlated with skeletal impairments, suggesting that despite increased life span of the GHRKO mice, skeletal health span is decreased. © 2018 American Society for Bone and Mineral Research.

GH directly stimulates UCP3 expression

OBJECTIVE

We evaluated the direct action of GH signaling in energy homeostasis in myocytes.

DESIGN

We investigated the GH-induced expression of UCP3 in human embryonic kidney 293 cells, human H-EMC-SS chondrosarcoma cells, murine C2C12 skeletal muscle myoblasts, and rat L6 skeletal muscle cells, as well as its direct effect on the GHR/JAK/STAT5 pathway using a combination of a reporter assay, real-time quantitative polymerase chain reaction, and western blotting.

RESULTS

We demonstrated that the regulation of energy metabolism by GH involves UCP3 via activated STAT5, a signal transducer downstream of GH. UCP3 expression increased with STAT5 in a dose-dependent manner and was higher than that of UCP2. We confirmed the functional STAT5 binding site consensus sequences at -861 and -507 bp in the UCP3 promoter region.

CONCLUSION

The results suggest that GH stimulates UCP3 directly and that UCP2 and that UCP3 participate in the signal transduction pathway that functions downstream of the GHR/JAK/STAT.

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

Insulin-like growth factor-1 receptor polymorphism and ischemic stroke: a case-control study in Chinese population

OBJECTIVES

Low levels of insulin-like growth factor 1 (IGF-1) are associated with atherosclerosis, and insulin-like growth factor-1 receptor (IGF-1R) polymorphisms can change plasma levels of IGF-1 and may alter the function of the receptor. Whether there is any association of genetic variation in IGF-1R gene with ischemic stroke (IS) is presently unknown.

MATERIALS AND METHOD

A 1:1 case-control study was conducted. The G --> A polymorphism of IGF-1R gene (rs2229765) were analyzed by TaqMan SNP genotyping technique in Chinese patients with IS (n = 309) and old subjects without IS (n = 309).

RESULTS

The frequency of A allele in the patients and controls was 45.79% and 39.64%, respectively. The AA genotype distribution of IGF-1R gene was significantly higher in the patients (27.51%) than controls (18.23%; P = 0.022). Conditional logistic regression revealed that the AA genotype of IGF-1R was associated with IS (OR = 1.641, P = 0.022). After adjustment for smoking, alcohol drinking, history of hypertension, and body mass index, IGF-1R AA genotype was still significantly associated with an increased risk of IS (OR = 1.787, P = 0.029), compared with IGF-1R GG.

CONCLUSIONS

The G --> A polymorphism in IGF-1R gene may affect the susceptibility to IS in Chinese population.

Mitochondrial uncoupling protein 3 and its role in cardiac- and skeletal muscle metabolism

Uncoupling protein 3 (UCP3), is primarily expressed in skeletal muscle mitochondria and has been suggested to be involved in mediating energy expenditure via uncoupling, hereby dissipating the mitochondrial proton gradient necessary for adenosine triphosphate (ATP) synthesis. Although some studies support a role for UCP3 in energy metabolism, other studies pointed towards a function in fatty acid metabolism. Thus, the protein is up regulated or high when fatty acid supply to the mitochondria exceeds the capacity to oxidize fatty acids and down regulated or low when oxidative capacity is high or improved. Irrespective of the exact operating mechanism, UCP3 seems to protect mitochondria against lipid-induced oxidative stress, which makes this protein a potential player in the development of type 2 diabetes mellitus. Next to skeletal muscle, UCP3 is also expressed in cardiac muscle where its role is relatively unexplored. Interestingly, energy deficiency in cardiac muscle is associated to heart failure and UCP3 might contribute to this energy deficiency. It has been suggested that UCP3 decreases energy status via uncoupling of mitochondrial respiration, but the available data does not provide a unified answer. In fact, the results obtained regarding cardiac UCP3 are very similar as in skeletal muscle, implying that its physiological function can be extrapolated. Therefore, cardiac UCP3 can just as well serve to protect the heart against lipid-induced oxidative stress, similar to the function described for skeletal muscle UCP3. The present review will deal with the available literature on both skeletal muscle- and cardiac UCP3 to elucidate its physiological function in these tissues.

Genomic Structure and Regulation of Mitochondrial Uncoupling Protein Genes in Mammals and Plants

Uncoupling mitochondrial proteins (UCPs) belong to a discrete family within the mitochondrial anion carrier superfamily. Several uncoupling protein types have been found in mitochondria from mammals and plants, as well as in fishes, fungi, and protozoa. Mammalian UCPs and plant uncoupling proteins (PUMPs) form five distinct subfamilies. Only subfamily III contains both plant and animal uncoupling proteins, as well as UCPs from primitive eukaryotic organisms, which suggest that this group may represent an ancestral cluster from which other UCPs/PUMPs may have evolved. Genetic data indicate that UCPs/PUMPs are regulated at the transcriptional, post-transcriptional, and translational levels. Tissue/organ- and stress-specific gene expression suggests that UCPs/PUMPs are involved in the general balance of basic energy expenditure, protection against reactive oxygen species, and thermogenesis. Finally, the simultaneous occurrence of PUMP and alternative oxidase, another energy-dissipating system in plant mitochondria, raises the question of their response to biotic and abiotic stress at the transcriptional and functional levels.

Influence of size at birth on the endocrine profiles and expression of uncoupling proteins in subcutaneous adipose tissue, lung, and muscle of neonatal pigs

Epidemiological studies suggest that infants of low birth weight show poor neonatal growth and increased susceptibility to adult diseases such as diabetes and lung disease. Uncoupling protein 2 and 3 (UCP2 and UCP3) have been implicated in the development of such diseases; pigs provide an ideal model to examine the influence of birth weight due to the natural variance in piglet weight within a litter. This study examined whether birth weight influences the expression of UCP2 and UCP3 in adipose tissue, skeletal muscle, and lung. Piglets from 11 litters were ranked according to birth weight and three from each litter assigned to small (SFD), normal (NFD), or large for dates (LFD) groups. Blood samples and morphometric measurements were taken over the first 14 days of life, and tissue samples were taken on day 7 or 14. Plasma hormone and metabolite concentrations and the expression of UCP2 and UCP3 mRNA in adipose tissue, skeletal muscle, and lung were measured. UCP2 and UCP3 expression in adipose tissue was lower in the SFD compared with the LFD group on day 7. UCP3 expression in skeletal muscle was higher than that of adipose tissue. Lung UCP2 and skeletal muscle UCP3 mRNA expression were unaffected by size at birth. Regression analysis indicated that UCP3 expression was differentially associated with IGF-1, leptin, and insulin. In conclusion, low birth weight is associated with tissue-specific effects on UCP expression. It remains to be established whether these subsequently contribute to pathological conditions such as diabetes.

Diabetes Mellitus and the Sensory Neuron

Sensory neurons in diabetes may be primarily targeted by diabetes and their involvement may account for prominent sensory loss and pain in diabetic patients. Previous studies demonstrating evidence of excessive polyol flux, microangiopathy, and oxidative stress involving sensory axons and ganglia have been joined by more recent work demonstrating altered neuron phenotype, mitochondrial dysfunction, ion channel alterations, and abnormal growth factor signaling. As such, an interesting and unique panoply of molecular changes in primary sensory neurons has been identified in diabetic models. Insulin deficiency and subsequent changes in second messenger signaling may also play an important role in how sensory neurons respond to diabetes. Applying approaches to support sensory neurons in diabetes may be an important therapeutic direction in diabetic patients.

Insulin-like growth factor type 1 prevents hyperglycemia-induced uncoupling protein 3 down-regulation and oxidative stress

Uncoupling proteins (UCPs) have been reported to decrease the mitochondrial production of reactive oxygen species (ROS) by lowering the mitochondrial inner membrane potential (MMP). We have previously shown that UCP3 expression is positively regulated by insulin-like growth factor-1 (IGF-1). The aim of this study was to investigate the role of UCPs in IGF-1-mediated protection from hyperglycemia-induced oxidative stress and neurodegeneration. Human neuroblastoma SH-SY5Y cells were differentiated with retinoic acid for 6 days, after which exposure to 8, 30, or 60 mM glucose with or without 10 nM IGF-1 was started. After 48-72 hr, the number of neurites per cell, UCP3 protein expression, MMP, and intracellular levels of ROS and total glutathione were examined. These studies showed that glucose concentration-dependently reduced the number of neurites per cell, with a 50% reduction at 60 mM. In parallel, the UCP3 protein expression was down-regulated, and the MMP was raised 3.5-fold, compared with those in cells incubated with 8 mM glucose. Also, the ROS levels were increased, showing a twofold maximum at 60 mM glucose. This was accompanied by a twofold elevation of total glutathione levels, confirming an altered cellular redox state. IGF-1 treatment prevented the glucose-induced neurite degeneration and UCP3 down-regulation. Furthermore, the MMP and the intracellular levels of ROS and glutathione were normalized to those of control cells. These data indicate that IGF-1 may protect from hyperglycemia-induced oxidative stress and neuronal injuries by regulating MMP, possibly by the involvement of UCP3.