By S. Vak. Arkansas Tech University. 2019.
The major target organs for insulin are skeletal muscle and the liver purchase 40mg lasix with amex pulse pressure 19, as these are the sites where the major glucose uptake occurs generic lasix 100 mg overnight delivery blood pressure while pregnant. Adipose tissue only accounts for a small proportion of glucose clear- ance order 40mg lasix prehypertension prevalence, but is still important in maintaining normoglycemia as insulin resistance in fat cells results in increased hydrolysis of triglycerides, which may further increase insulin resistance. Reduced oxidative capacity of the mitochondria in skeletal muscle has been suggested to contribute to insulin resistance and type 2 diabetes . This provides an example of how genetic and epigenetic factors may interact to increase age-dependent susceptibility to insulin resistance . One potential explanation for this is that epigenetic mechanisms may drive a state that is benecial for the fetus, for example insulin resistance, which in adult life Epigenetics in Human Disease facilitates the development of type 2 diabetes and the metabolic syndrome when exposed to an obesogenic environment . Human studies in this area are still sparse, but recent animal studies show promising support of this idea. Dietary protein restriction of pregnant rats induces, and folic acid supplementation prevents, epigenetic modication of hepatic gene expression in the offspring. In humans, the Dutch Hunger Winter provides an example where the offspring to pregnant women exposed to famine show increases in insulin levels, suggesting an association with insulin resistance . Future studies need to be carried out in several organs under different environmental conditions, since there are multiple environmental risk factors for type 2 diabetes that target different organs. It is possible that these studies will generate information that can be used in the prediction and prevention of type 2 diabetes. Moreover, in the future it is possible that new drugs targeting epigenetic factors can be developed for patients with type 2 diabetes. Denition, diagnosis and classication of diabetes mellitus and its complications. Genetic and nutritional factors in the etiology and pathogenesis of diabetes mellitus. Genome-wide association analysis identies loci for type 2 diabetes and triglyceride levels. A genome-wide association study of type 2 diabetes in Finns detects multiple susceptibility variants. Meta-analysis of genome-wide association data and large-scale replication identies additional susceptibility loci for type 2 diabetes. Twelve type 2 diabetes susceptibility loci identied through large-scale association analysis. Environmental sensing by chromatin: an epigenetic contribution to evolutionary change. Predictors of and longitudinal changes in insulin sensitivity and secretion preceding onset of type 2 diabetes. Calpain-10 expression is elevated in pancreatic islets from patients with type 2 diabetes. The human insulin gene displays transcriptionally active epigenetic marks in islet-derived mesenchymal precursor cells in the absence of insulin expression. The human insulin gene is part of a large open chromatin domain specic for human islets. Regulation of insulin secretion: a matter of phase control and amplitude modulation. Decreased expression of genes involved in oxidative phosphorylation in human pancreatic islets from patients with type 2 diabetes. Global epigenomic analysis of primary human pancreatic islets provides insights into type 2 diabetes susceptibility loci. Early differential defects of insulin secretion and action in 19-year-old caucasian men who had low birth weight. Altered skeletal muscle ber composition and size precede whole-body insulin resistance in young men with low birth weight. Low birthweight is associated with specic changes in muscle insulin-signalling protein expression. Decreased protein levels of key insulin signalling molecules in adipose tissue from young men with a low birthweight: potential link to increased risk of diabetes? The intrauterine environment as reected by birth size and twin and zygosity status inuences insulin action and intracellular glucose metabolism in an age- or time-dependent manner. Persistent epigenetic differences asso- ciated with prenatal exposure to famine in humans. Dynamic epigenetic regulation by early-diet and aging of the type 2 diabetes susceptibility gene Hnf4a in pancreatic islets. Exendin-4 increases histone acetylase activity and reverses epigenetic modications that silence Pdx1 in the intrauterine growth retarded rat. Insulin-regulated mitochondrial gene expression is associated with glucose ux in human skeletal muscle. Gene expression prole in skeletal muscle of type 2 diabetes and the effect of insulin treatment. Mechanisms of disease: the developmental origins of disease and the role of the epigenotype. Diabetes is essentially a consequence of the bodys failure to regulate blood sugar caused primarily by having (a) too little insulin, (b) developing resistance to insulin, or (c) both. Complications associated with diabetes include kidney failure, non-traumatic lower-limb amputations, blindness and diabetes is a major cause of heart disease and stroke [1,2]. Globally, diabetes (and in particular type 2 diabetes) represents a major challenge to world health. For example it is estimated that in the period 2006e2015, China will lose $558 billion in foregone national income due to heart disease, stroke, and diabetes alone . Diabetes is a complex syndrome of dysregulation of carbohydrate and lipid metabolism due primarily to beta cell dysfunction associated with a variable degree of insulin resistance. It is clear that a complex interplay between environmental, nutritional, and genetic factors play a role in diabetes pathogenesis. Nevertheless, it is my contention that a common thread, that of histone and transcription factor/protein acetylation links many of the currently identied pathways known to be involved with diabetes pathogenesis. Four main mechanisms for epigenetic regulation of gene expression have been characterized. The enzymes and mechanisms for demethylation remain to be elucidated, with base excision repair emerging as the leading candidate . The importance of these non-epigenetic modications in the regulation of cellular processes can be exemplied by a recent study that found 3600 acety- lation sites on 1750 proteins. Nevertheless, if one considers all of the possible combinatorial possibilities for histone modications, the known modications on histone H3 alone could produce over one million distinct post-translational signatures . In this model mice which were heterozygous for the mutant displayed increased insulin sensitivity and glucose tolerance, even though they present with a marked lipidystrophy of white adipose tissue .
This is partly supported by a study in twins that revealed that environmental factors contribute to the occurrence of autism [27 buy lasix 40 mg with visa arrhythmia uptodate,28] cheap lasix 100mg on line arteria thoracoacromialis. Furthermore epigenetic mechanisms are affected by environmental factors  discount lasix 40mg visa pulse pressure 61, and environment-induced epigenetics changed in early life can persist through adulthood and can be transmitted across generations resulting in abnormal behavior traits in the offspring . In this chapter, we show various examples of neurobiological disorders associated with epigenetics, environmental factors that affect epigenetic gene regulation, and discuss future directions in medicine for neurobiological disorders based on recent epigenetic understandings. Genomic imprinting is the epigenetic phenomenon initially discovered in human disorders. Therefore, mutations in the active allele or deletion of the active allele of the imprinted gene results in no expression. This has been found in autistic disorders, Angelman syndrome, and PradereWilli syndrome . To minimize this sex imbalance, one of the two X chromosomes in females is inactivated by an epigenetic mechanism . If X-inactivation does not properly occur in a female, such a female is believed to die in utero and abort. This hypothesis is supported by the recent ndings in cloned animals produced by somatic nuclear transfer in which failure of X-chromosome inactivation induces embryonic abortion [33,34]. Even if one of the X chromosomes is extremely small due to a large terminal deletion, making the overdosage effect of X-linked genes small, the female shows a severe congenital neuro- developmental delay , indicating that proper epigenetic control of gene expression is essential for normal brain development. However, a biological mechanism that links these two groups of factors has not been identied. Epigenetics may bridge these two groups of factors contributing to disease development . Gene expression in the dopaminergic and glutamatergic systems is mediated by an epigenetic mechanism, and cocaine and alcohol alter the epigenetic state. For example, cocaine induces either hyperacetylation or hypoacetylation of histones H3 and H4 in the nucleus accumbens of mice, and alcohol induces hyperacetylation of histones H3 and H4 in the frontal cortex and the nucleus accumbens of adolescent rats; such alterations may be associated with permanent 196 behavioral consequences [64,65]. The above studies were mainly performed in animals, and there is little evidence for such changes in humans. However, the fact that epigenomic differences are greater in older monozygotic twins than in younger twins suggests that epigenetic status may be altered during aging by environmental factors in humans . Therefore, we can rest easy, because this leads us to believe that the bad habits obtained during ones lifetime will not be inherited by our progeny. However, recent advances in epigenetics have revealed that such undesirable acquired traits might be transmitted into the next generation. A fundamental question in epigenetics is whether these marks can also be transmitted through the germline. If so, an aberrant epige- netic mark acquired in one generation could be inherited by the next generation. In general, 197 epigenetic marks should be erased by demethylating factors such as the cytidine deaminases (e. Transgenerational inheritance of epigenetic marks was rst demonstrated in a specic mouse strain. The methylation status at the Axin (Fu) locus in mature sperm reects the methylation state of the allele in the somatic tissue of the animal. This epigenetic status is linked to the shape of tail of the animals, and it does not undergo epigenetic reprogramming during gametogenesis . This observation was recently conrmed in Drosophila, in which an aberrant epigenetic mark (defective chromatin state) acquired in one generation induced by environmental stress (e. It has also been demonstrated that an aberrant epigenetic mark acquired in one generation by mental stress (maternal separation in early life) can be inherited by the next generation . These ndings may provide the biological evidence for the current social issue that traumatic experiences in early life are risk factors for the development of behavioral and emotional disorders. Based on the evidences described above, the readers of this chapter might be led to believe that epigenetics is a scientic eld that portends adverse news for society. However, if we could create an environment conducive to good human health, we will be able to sever the Epigenetics in Human Disease deleterious environment-induced epigenetic patterns across the generations. Even if epigenetic markings provide a "memory" of past experiences and the markings persist across the lifespan of an individual and then be transmitted to the offspring via epigenetic inheritance, future epigenetic research can possibly establish restorative methods taking advantage of the reversibility of stress-induced epigenetic modications. It can also show us the appropriate environment for keeping a healthy physical and mental condition [73,74]. Imipramine, a major antidepressant, was recently found to have the effect of restoring a depressive state by alteration of the epigenetic state (increasing histone H3 and H4 acetylation at the Bdnf P3 and P4 promoters and histone H3-K4 dimethylation at Bdnf P3 promoter), leading to up- regulation of Bdnf (brain-derived neurotrophic factor) in the hippocampus . Based on these ndings, chemicals that alter epigenetic gene expression are candidates of new drugs for a subset of the patients with mental and neuro- biological disorders . In Japan, the number of young women who do not take a sufcient amount of folic acid during pregnancy is increasing, and this increases the risk of having babies with neural tube defects . In rats, inappropriate supply of nutrients from the mother to the fetus also increases the susceptibility of the fetus to develop diabetes mellitus through epigenetic effects . These hypotheses are supported by obser- vation from a rat study in which protein restriction during pregnancy induced a state of malnutrition and hyperlipidemia in the fetus. However, supplementation of the maternal protein-restricted diet with folic acid during pregnancy relieved these abnormalities. These ndings indicate that specic nutrient intakes may alter the phenotype of the offspring through epigenetic changes. Protein restriction during pregnancy also reduced the expression of Mecp2 gene in the liver of the fetus . This observation implies that malnutrition during pregnancy may contribute to the development of neurobiological disorders, although the effect of malnutrition on Mecp2 has not been investigated in the brain. Royal jelly, known to change the phenotype from a genetically identical female honeybee to a fertile queen, also has epigenetic effects. Since the 1980s, folic acid is empirically used for the treatment of autistic patients, and these studies have shown that it is effective only for a subset of the patients [78e80]. However, it has not been completely proven that the effect of folic acid on autistic patients is based on epigenetic effects. Folic acid-based treatment may be safe, since it is a nutrient, and it is expected to have global effects, but not on individual genes. Besides these nutrition-based treatments, several alter- native epigenetic-based treatments are currently developed, which is gene-specic and able to restore the epigenetic status that has been changed by an environmental factor. Studies using a Rett syndrome mouse model (Mecp2 knockout mice) show that environmental enrichment (e. The reversibility of this epigenetic change is supported by a different study in which activation of Mecp2 expression after birth leads to relief of neurological symptoms in Mecp2 knockout mice . Note: This diagram depicts aberrant expression of normally suppressed gene by promoter hypermethylation; however, suppression of normally expressed genes by promoter hypermethylation is equally important for pathogenesis of human neurobiological disorders.
Very strong epitope-paratope binding prevents stimulation; weakly binding Bcells are outcompeted for stimulatory signals quality lasix 100 mg blood pressure chart stress. One of these epitopes stimulated the immunodominant IgG response; the other wasatthe opposite end of the peptide buy lasix 40mg mastercard from prehypertension to hypertension additional evidence. They began by constructing a peptide that had on one side a known B cell antigen of hepatitis B virus and on the other side a known T cell epitope from the malaria parasite Plasmodium falciparum lasix 100mg lowest price blood pressure chart pulse. The early IgM response had specicities that spanned the entire hepatitis B segment. Immunodominance depended on competition for antigen-specichelperTcells, which arelimiting during the initial stages of an immune response. In laterexperiments, Agarwal and Rao (1997) manipulated the size of the helper T cell pool. Reduced numbers of T cells allowed IgM response but prevented the switch from the IgMstagetothe IgG stage. This sup- ports the hypothesis that competition for T cell help is the rate-limiting step in the transition from the broad IgM response to the narrow IgG response. This led to the hypothesis that the Gibbs free-energy of binding between epitope and paratope determines antibody anity, and that the amino acid sequence of the epitope inuences the potential free-energy of the bond. They suggested that the relative ordering of anities for particular epitopes could be predicted by the amino acid sequence of the epitope. In particular, the amino acid side chains of an epitope sequence determine the potential free-energy of binding to an antibody paratope. Chemical determination of free-energy seems particularly important in the early phases of antibody response, when the antibodies have not yet been optimized for binding by anity maturation. Unoptimized antibodies do not have strong spatial complementarity of binding; thus there is less steric and greater chemicalconstraintonbinding at this stage. After optimization, it may be that greater steric complementarity of antibody-epitope binding places more emphasis on spatial t and reduces the predictability of binding energy based solely on chemical composition of amino acid side chains. During this stage, B cells congregate in germinal centers of the lymphoid tissue and mutate their antibody paratopes at a high rate. Aselection process favors those mutated paratopes that bind relatively strongly to antigen, driving anity maturation of antibodies for the par- ticular epitopes. They then compared binding of each of the two antibody types against the native and modi- ed antigen. Antibodies raised against the native antigen bound with approximate- ly equal equilibrium anity to native and modied antigen. Antibodies raised against the modied antigen also bound at equilibrium approxi- mately equally against the two antigens. By contrast, the kinetic on-rates of binding were 50-fold higher for native antibody to native antigen than for native antibody to modied antigen. Kinetic on-rates were 14- to 25- fold higher for modied antibody to modied antigen than for modied antibody to native antigen. Kinetic on-rates measure rates atwhichbonds form, whereas equi- librium anity measures the ratio of on-rates to o-rates. Selection during anity maturation apparently favors faster rates of interaction with increases in both on-rates and o-rates: the on-rates rise, but the equilibrium anity does not change. In this model system, it appears that B cells compete by rate of anti- gen acquisition during anity maturation. B cells with paratopes that bind more quickly to antigen receive stronger stimulatory signals to di- vide and to dominate the population in the germinal centers. Thus, the optimized antibodies bind more quickly to antigen than unoptimized precursors, but optimized antibodies do not necessarily increase their equilibrium binding anity. In summary, Rao proposed an integrated, dynamic view of how the specicity of an antibody response develops. The technical limitations for quantitative assay of specic T cells may soon be overcome with recently developed methods (Yewdell and Bennink 1999; Doherty and Christensen 2000). In this section, I focus on the relative abundance of T cell populations with dierent recognition specicities. Each host may have a relatively narrow response, but hosts may dier in their choice of epitopes. These pathogens tend to be ge- netically heterogeneous within a single host and may evolve by escape mutants in dominant epitopes. The timing of initial clonal expansion ap- pears to control immunodominance in this case. But if the infection is not intheblood or lymph compartments, the naive Tcells cannot reach the site of infection. One possible solution depends on the distinction between endoge- nous and exogenous antigen (Schumacher 1999; Sigal et al. When an infected cell dies, pathogen antigens become liberated and exist exogenously. Dendritic cells are known to take up exogenous antigen in periph- eral tissues and then to move to lymph nodes (Banchereau et al. Thus, dendritic cells may serve as scouts in the peripheral tissue, bringing exogenous antigen to lymph nodes when stimulated by signs of infection or tissue damage. For example, the capsid proteins of viruses may be moreabundant than replicase enzymes and therefore more likely to be taken up as exoge- nous antigen. On the whole, the evidence supports the second explanation, in which dominant clones suppress subdominant clones. Kinetic control suggests that immunodomination should be a quantitative phenomenon ordering epitopes into a hierarchy. Such changes in the hierarchy occur when the immune system has previously experienced an epitope. For example, if epitope A dominates epitope B in a naive host, then prior exposure only to B can reverse the dominance ranking and cause B to dominate A (Bennink and Doherty 1981; Jamieson and Ahmed 1989; Cole et al. It could simply be that the immunodominant epitopes are expressed more commonly on cell surfaces than subdominant epitopes. However, Yewdell and Bennink (1999) summarize various lines of evidence argu- ing against a simple correlation between the abundance of presented epitopes and immunodominance, for example, the study by Weidt et al. Both hu- mans and transgenic mice recognized the same immunodominant epi- topeswheninjected with viruses (Engelhard et al. This was shown in a study of human infection by Epstein-Barr virus (Burrows et al. Interference occurs even when the antagonist occurs in relatively low concentration and is presented on dierent cells from the partner epitope. Mutual interference suggests that hosts jointly infected with cp26 and cp29 will be less eective in clearing parasites than singly infected hosts or hosts with other combinations of strains.