Diabetes and pancreatic cancer risk in a multiracial cohort.

AIMS: To determine the relationship of diabetes with pancreatic cancer incidence among African American and Whites of similar socio-economic status. METHODS: Using the Southern Community Cohort Study, we conducted a follow-up during 2002-2015 of pancreatic cancer incidence of 73,378 mostly low-income participants aged 40-79 years; 15,913 reported diabetes at baseline. Multivariable Cox analysis controlling for sex, family history of pancreatic cancer, BMI, smoking status, alcohol consumption, education, income and other important covariates, and with age as the timescale was used. RESULTS: Totally, 265 incident pancreatic cancer cases were observed. Pancreatic cancer risk was increased among those with diabetes (HR 1.54, CI 1.16-2.05), with similar increases among African Americans (HR 1.51, CI 1.08-2.11) and Whites (HR 1.78, CI 1.00-3.16). No trend in risk was observed for diabetes duration among those with diabetes, with HRs of 1.39 (0.91-2.11), 2.31 (1.51-3.54) and 1.23 (0.80-1.89) for <5, 5-9 and 10+ years duration, respectively. African Americans were at increased risk of pancreatic cancer (HR = 1.40, 95% CI 1.05-1.87), which persisted after adjusting for diabetes (HR 1.36, CI 1.02-1.81). The effect sizes for other pancreatic cancer risk factors with pancreatic cancer were similar by diabetes status, although a stronger association with low BMI was evident among those with diabetes. CONCLUSIONS: Diabetes increases pancreatic cancer risk similarly among African Americans and Whites in this Southern U.S.

The Academic Learning Health System: A Framework for Integrating the Multiple Missions of Academic Medical Centers.

The learning health system (LHS) has emerged over the past 15 years as a concept for improving health care delivery. Core aspects of the LHS concept include: promoting improved patient care through organizational learning, innovation, and continuous quality improvement; identifying, critically assessing, and translating knowledge and evidence into improved practices; building new knowledge and evidence around how to improve health care and health outcomes; analyzing clinical data to support learning, knowledge generation, and improved patient care; and engaging clinicians, patients, and other stakeholders in processes of learning, knowledge generation, and translation. However, the literature has paid less attention to how these LHS aspects may integrate with the multiple missions of academic medical centers (AMCs). The authors define an academic learning health system (aLHS) as an LHS built around a robust academic community and central academic mission, and they propose 6 features that emphasize how an aLHS differs from an LHS. An aLHS capitalizes on embedded academic expertise in health system sciences; engages the full spectrum of translational investigation from mechanistic basic sciences to population health; builds pipelines of experts in LHS sciences and clinicians with fluency in practicing in an LHS; applies core LHS principles to the development of curricula and clinical rotations for medical students, housestaff, and other learners; disseminates knowledge more broadly to advance the evidence for clinical practice and health systems science methods; and addresses social determinants of health, creating community partnerships to mitigate disparities and improve health equity. As AMCs evolve, the authors expect that additional differentiating features and ways to operationalize the aLHS will be identified and hope this article stimulates further discussion around the intersection of the LHS concept and AMCs.

An early, reversible cholesterolgenic etiology of diet-induced insulin resistance.

OBJECTIVE: A buildup of skeletal muscle plasma membrane (PM) cholesterol content in mice occurs within 1 week of a Western-style high-fat diet and causes insulin resistance. The mechanism driving this cholesterol accumulation and insulin resistance is not known. Promising cell data implicate that the hexosamine biosynthesis pathway (HBP) triggers a cholesterolgenic response via increasing the transcriptional activity of Sp1. In this study we aimed to determine whether increased HBP/Sp1 activity represented a preventable cause of insulin resistance. METHODS: C57BL/6NJ mice were fed either a low-fat (LF, 10% kcal) or high-fat (HF, 45% kcal) diet for 1 week. During this 1-week diet the mice were treated daily with either saline or mithramycin-A (MTM), a specific Sp1/DNA-binding inhibitor. A series of metabolic and tissue analyses were then performed on these mice, as well as on mice with targeted skeletal muscle overexpression of the rate-limiting HBP enzyme glutamine-fructose-6-phosphate-amidotransferase (GFAT) that were maintained on a regular chow diet. RESULTS: Saline-treated mice fed this HF diet for 1 week did not have an increase in adiposity, lean mass, or body mass while displaying early insulin resistance. Consistent with an HBP/Sp1 cholesterolgenic response, Sp1 displayed increased O-GlcNAcylation and binding to the HMGCR promoter that increased HMGCR expression in skeletal muscle from saline-treated HF-fed mice. Skeletal muscle from these saline-treated HF-fed mice also showed a resultant elevation of PM cholesterol with an accompanying loss of cortical filamentous actin (F-actin) that is essential for insulin-stimulated glucose transport. Treating these mice daily with MTM during the 1-week HF diet fully prevented the diet-induced Sp1 cholesterolgenic response, loss of cortical F-actin, and development of insulin resistance. Similarly, increases in HMGCR expression and cholesterol were measured in muscle from GFAT transgenic mice compared to age- and weight-match wildtype littermate control mice. In the GFAT Tg mice we found that these increases were alleviated by MTM. CONCLUSIONS: These data identify increased HBP/Sp1 activity as an early mechanism of diet-induced insulin resistance. Therapies targeting this mechanism may decelerate T2D development.

Iron and the Pathophysiology of Diabetes.

High iron is a risk factor for type 2 diabetes mellitus (T2DM) and affects most of its cardinal features: decreased insulin secretion, insulin resistance, and increased hepatic gluconeogenesis. This is true across the normal range of tissue iron levels and in pathologic iron overload. Because of iron's central role in metabolic processes (e.g., fuel oxidation) and metabolic regulation (e.g., hypoxia sensing), iron levels participate in determining metabolic rates, gluconeogenesis, fuel choice, insulin action, and adipocyte phenotype. The risk of diabetes related to iron is evident in most or all tissues that determine diabetes phenotypes, with the adipocyte, beta cell, and liver playing central roles. Molecular mechanisms for these effects are diverse, although there may be integrative pathways at play. Elucidating these pathways has implications not only for diabetes prevention and treatment, but also for the pathogenesis of other diseases that are, like T2DM, associated with aging, nutrition, and iron.

Metformin Reduces Aging-Related Leaky Gut and Improves Cognitive Function by Beneficially Modulating Gut Microbiome/Goblet Cell/Mucin Axis.

Aging-related illnesses are increasing and effective strategies to prevent and/or treat them are lacking. This is because of a poor understanding of therapeutic targets. Low-grade inflammation is often higher in older adults and remains a key risk factor of aging-related morbidities and mortalities. Emerging evidence indicates that abnormal (dysbiotic) gut microbiome and dysfunctional gut permeability (leaky gut) are linked with increased inflammation in older adults. However, currently available drugs do not treat aging-related microbiome dysbiosis and leaky gut, and little is known about the cellular and molecular processes that can be targeted to reduce leaky gut in older adults. Here, we demonstrated that metformin, a safe Food and Drug Administration-approved antidiabetic drug, decreased leaky gut and inflammation in high-fat diet-fed older obese mice, by beneficially modulating the gut microbiota. In addition, metformin increased goblet cell mass and mucin production in the obese older gut, thereby decreasing leaky gut and inflammation. Mechanistically, metformin increased the goblet cell differentiation markers by suppressing Wnt signaling. Our results suggest that metformin can be used as a regimen to prevent and treat aging-related leaky gut and inflammation, especially in obese individuals and people with western-style high-fat dietary lifestyle, by beneficially modulating gut microbiome/goblet cell/mucin biology.

Transcriptional Regulation of Transforming Growth Factor ß1 by Glucose: Investigation into the Role of the Hexosamine Biosynthesis Pathway.

BACKGROUND: The hexosamine biosynthesis pathway (HBP) is hypothesized to mediate many of the adverse effects of hyperglycemia. We have shown previously that increased flux through this pathway leads to induction of the growth factor transforming growth factor-α (TGF-α) and to insulin resistance in cultured cells and transgenic mice. TGF-ß is regulated by glucose and is involved in the development of diabetic nephropathy. We therefore hypothesized that the HBP was involved in the regulation of TGF-ß by glucose in rat vascular and kidney cells. METHODS: A plasmid containing the promoter region of TGF-ß1 cloned upstream of the firefly luciferase gene was electroporated into rat aortic smooth muscle, mesangial, and proximal tubule cells. Luciferase activity was measured in cellular extracts from cells cultured in varying concentrations of glucose and glucosamine. RESULTS: Glucose treatment of all cultured cells led to a time- and dose-dependent stimulation in TGF-ß1 transcriptional activity, with high (20 mM) glucose causing a 1.4- to 2.0-fold increase. Glucose stimulation did not occur until after 12 hours and disappeared after 72 hours of treatment. Glucosamine was more potent than glucose, with 3 mM stimulating up to a 4-fold increase in TGFß1-transcriptional activity. The stimulatory effect of glucosamine was also dose-dependent but was slower to develop and longer lasting than that of glucose. CONCLUSIONS: The metabolism of glucose through the HBP mediates extracellular matrix production, possibly via the stimulation of TGF-ß in kidney cells. Hexosamine metabolism therefore, may play a role in the development of diabetic nephropathy.

Lipoteichoic acid from the cell wall of a heat killed Lactobacillus paracasei D3-5 ameliorates aging-related leaky gut, inflammation and improves physical and cognitive functions: from C. elegans to mice.

Increased inflammation associated with leaky gut is a major risk factor for morbidity and mortality in older adults; however, successful preventive and therapeutic strategies against these conditions are not available. In this study, we demonstrate that a human-origin Lactobacillus paracasei D3-5 strain (D3-5), even in the non-viable form, extends life span of Caenorhabditis elegans. In addition, feeding of heat-killed D3-5 to old mice (> 79 weeks) prevents high- fat diet-induced metabolic dysfunctions, decreases leaky gut and inflammation, and improves physical and cognitive functions. D3-5 feeding significantly increases mucin production, and proportionately, the abundance of mucin-degrading bacteria Akkermansia muciniphila also increases. Mechanistically, we show that the lipoteichoic acid (LTA), a cell wall component of D3-5, enhances mucin (Muc2) expression by modulating TLR-2/p38-MAPK/NF-kB pathway, which in turn reduces age-related leaky gut and inflammation. The findings indicate that the D3-5 and its LTA can prevent/treat age-related leaky gut and inflammation.

Type-2-Diabetes Alters CSF but Not Plasma Metabolomic and AD Risk Profiles in Vervet Monkeys.

Epidemiological studies suggest that individuals with type 2 diabetes (T2D) have a twofold to fourfold increased risk for developing Alzheimer's disease (AD), however, the exact mechanisms linking the two diseases are unknown. In both conditions, the majority of pathophysiological changes, including glucose and insulin dysregulation, insulin resistance, and AD-related changes in Aß and tau, occur decades before the onset of clinical symptoms and diagnosis. In this study, we investigated the relationship between metabolic biomarkers associated with T2D and amyloid pathology including Aß levels, from cerebrospinal fluid (CSF) and fasting plasma of healthy, pre-diabetic (PreD), and T2D vervet monkeys (Chlorocebus aethiops sabaeus). Consistent with the human disease, T2D monkeys have increased plasma and CSF glucose levels as they transition from normoglycemia to PreD and diabetic states. Although plasma levels of acylcarnitines and amino acids remained largely unchanged, peripheral hyperglycemia correlated with decreased CSF acylcarnitines and CSF amino acids, including branched chain amino acid (BCAA) concentrations, suggesting profound changes in cerebral metabolism coincident with systemic glucose dysregulation. Moreover, CSF Aß 40 and CSF Aß 42 levels decreased in T2D monkeys, a phenomenon observed in the human course of AD which coincides with increased amyloid deposition within the brain. In agreement with previous studies in mice, CSF Aß 40 and CSF Aß 42 were highly correlated with CSF glucose levels, suggesting that glucose levels in the brain are associated with changes in Aß metabolism. Interestingly, CSF Aß 40 and CSF Aß 42 levels were also highly correlated with plasma but not CSF lactate levels, suggesting that plasma lactate might serve as a potential biomarker of disease progression in AD. Moreover, CSF glucose and plasma lactate levels were correlated with CSF amino acid and acylcarnitine levels, demonstrating alterations in cerebral metabolism occurring with the onset of T2D. Together, these data suggest that peripheral metabolic changes associated with the development of T2D produce alterations in brain metabolism that lead to early changes in the amyloid cascade, similar to those observed in pre-symptomatic AD.

A Low Iron Diet Protects from Steatohepatitis in a Mouse Model.

High tissue iron levels are a risk factor for multiple chronic diseases including type 2 diabetes mellitus (T2DM) and non-alcoholic fatty liver disease (NAFLD). To investigate causal relationships and underlying mechanisms, we used an established NAFLD model-mice fed a high fat diet with supplemental fructose in the water ("fast food", FF). Iron did not affect excess hepatic triglyceride accumulation in the mice on FF, and FF did not affect iron accumulation compared to normal chow. Mice on low iron are protected from worsening of markers for non-alcoholic steatohepatitis (NASH), including serum transaminases and fibrotic gene transcript levels. These occurred prior to the onset of significant insulin resistance or changes in adipokines. Transcriptome sequencing revealed the major effects of iron to be on signaling by the transforming growth factor beta (TGF-ß) pathway, a known mechanistic factor in NASH. High iron increased fibrotic gene expression in vitro, demonstrating that the effect of dietary iron on NASH is direct. Conclusion: A lower tissue iron level prevents accelerated progression of NAFLD to NASH, suggesting a possible therapeutic strategy in humans with the disease.

Low dose chloroquine decreases insulin resistance in human metabolic syndrome but does not reduce carotid intima-media thickness.

BACKGROUND: Metabolic syndrome, an obesity-related condition associated with insulin resistance and low-grade inflammation, leads to diabetes, cardiovascular diseases, cancer, osteoarthritis, and other disorders. Optimal therapy is unknown. The antimalarial drug chloroquine activates the kinase ataxia telangiectasia mutated (ATM), improves metabolic syndrome and reduces atherosclerosis in mice. To translate this observation to humans, we conducted two clinical trials of chloroquine in people with the metabolic syndrome. METHODS: Eligibility included adults with at least 3 criteria of metabolic syndrome but who did not have diabetes. Subjects were studied in the setting of a single academic health center. The specific hypothesis: chloroquine improves insulin sensitivity and decreases atherosclerosis. In Trial 1, the intervention was chloroquine dose escalations in 3-week intervals followed by hyperinsulinemic euglycemic clamps. Trial 2 was a parallel design randomized clinical trial, and the intervention was chloroquine, 80 mg/day, or placebo for 1 year. The primary outcomes were clamp determined-insulin sensitivity for Trial 1, and carotid intima-media thickness (CIMT) for Trial 2. For Trial 2, subjects were allocated based on a randomization sequence using a protocol in blocks of 8. Participants, care givers, and those assessing outcomes were blinded to group assignment. RESULTS: For Trial 1, 25 patients were studied. Chloroquine increased hepatic insulin sensitivity without affecting glucose disposal, and improved serum lipids. For Trial 2, 116 patients were randomized, 59 to chloroquine (56 analyzed) and 57 to placebo (51 analyzed). Chloroquine had no effect on CIMT or carotid contrast enhancement by MRI, a pre-specified secondary outcome. The pre-specified secondary outcomes of blood pressure, lipids, and activation of JNK (a stress kinase implicated in diabetes and atherosclerosis) were decreased by chloroquine. Adverse events were similar between groups. CONCLUSIONS: These findings suggest that low dose chloroquine, which improves the metabolic syndrome through ATM-dependent mechanisms in mice, modestly improves components of the metabolic syndrome in humans but is unlikely to be clinically useful in this setting.Trial registration ClinicalTrials.gov (NCT00455325, NCT00455403), both posted 03 April 2007.

Hypoglycemic symptoms in the absence of diabetes: Pilot evidence of clinical hypoglycemia in young women.

AIMS: Clinical visits of non-diabetic patients reporting hypoglycemic symptoms are common in endocrinology practices, but remain understudied and lack clinical definition and evidence-based recommendations for diagnosis or treatment. Our goal was to pilot test the concordance of hypoglycemic symptoms with low glucose values in young non-diabetic individuals. METHODS: We recruited eight individuals who reported regularly experiencing symptoms consistent with hypoglycemia to wear a blinded Dexcom continuous glucose monitor and report symptoms for seven days. We excluded individuals with diabetes or other known causes of hypoglycemia or similar symptoms. RESULTS: Participants were all women with an average age of 29 years. 25% were African American and 25% had obesity. All participants experienced glucose values ≤ 70 mg/dL and half (4/8) experienced glucose ≤ 54 mg/dL for at least 15 min or 3 consecutive readings. Average time between last meal and reported symptoms was 4.4 h. Lower glucose values were significantly associated with higher odds of experiencing hypoglycemic symptoms 1.15 (CI: 1.07-1.24) for every -5mg/dL, (p < 0.001) from mixed effects models for repeated measures adjusted for age, race, and body mass index. All participants also reported engaging in potentially obesogenic behaviors in order to avoid symptoms. CONCLUSIONS: Individuals with hypoglycemic symptoms in the absence of diabetes experience clinical hypoglycemia, indicating the need to understand the etiology, behavioral responses, and other health risks that might be associated with this understudied condition.

Iron down-regulates leptin by suppressing protein O-GlcNAc modification in adipocytes, resulting in decreased levels of O-glycosylated CREB.

We previously reported that iron down-regulates transcription of the leptin gene by increasing occupancy of phosphorylated cAMP response element-binding protein (pCREB) at two sites in the leptin gene promoter. Several nutrient-sensing pathways including O-GlcNAcylation also regulate leptin. We therefore investigated whether O-glycosylation plays a role in iron- and CREB-mediated regulation of leptin. We found that high iron decreases protein O-GlcNAcylation both in cultured 3T3-L1 adipocytes and in mice fed high-iron diets and down-regulates leptin mRNA and protein levels. Glucosamine treatment, which bypasses the rate-limiting step in the synthesis of substrate for glycosylation, increased both O-GlcNAc and leptin, whereas inhibition of O-glycosyltransferase (OGT) decreased O-GlcNAc and leptin. The increased leptin levels induced by glucosamine were susceptible to the inhibition by iron, but in the case of OGT inhibition, iron did not further decrease leptin. Mice with deletion of the O-GlcNAcase gene, either via whole-body heterozygous deletion or through adipocyte-targeted homozygous deletion, exhibited increased O-GlcNAc levels in adipose tissue and increased leptin levels that were inhibited by iron. Of note, iron increased the occupancy of pCREB and decreased the occupancy of O-GlcNAcylated CREB on the leptin promoter. These patterns observed in our experimental models suggest that iron exerts its effects on leptin by decreasing O-glycosylation and not by increasing protein deglycosylation and that neither O-GlcNAcase nor OGT mRNA and protein levels are affected by iron. We conclude that iron down-regulates leptin by decreasing CREB glycosylation, resulting in increased CREB phosphorylation and leptin promoter occupancy by pCREB.

Comparative Microbiome Signatures and Short-Chain Fatty Acids in Mouse, Rat, Non-human Primate, and Human Feces.

Gut microbiome plays a fundamental role in several aspects of host health and diseases. There has been an exponential surge in the use of animal models that can mimic different phenotypes of the human intestinal ecosystem. However, data on host species-specific signatures of gut microbiome and its metabolites like short-chain fatty acids (SCFAs; i.e., acetate, propionate, and butyrate) and lactate in these models and their similarities/differences from humans remain limited, due to high variability in protocols and analyses. Here, we analyze the fecal microbiota composition and the fecal levels of SCFAs and lactate in three of the most-widely used animal models, i.e., mice, rats, and non-human primates (NHPs) and compare them with human subjects, using data generated on a single platform with same protocols. The data show several species-specific similarities and differences in the gut microbiota and fecal organic acids between these species groups. Based on ß-diversity, the gut microbiota in humans seems to be closer to NHPs than to mice and rats; however, among rodents, mice microbiota appears to be closer to humans than rats. The phylum-level analyses demonstrate higher Firmicutes-Bacteroidetes ratio in humans and NHPs vs. mice and rats. Human microbiota is dominated by Bacteroides followed by Ruminococcaceae and Clostridiales. Mouse gut is predominated by members of the family S24-7 followed by those from the order Clostridiales, whereas rats and NHPs have higher abundance of Prevotella compared with mice and humans. Also, fecal levels of lactate are higher in mice and rats vs. NHPs and humans, while acetate is highest in human feces. These data of host species-specific gut microbiota signatures in some of the most widely used animal models in context to the human microbiota might reflect disparities in host factors, e.g., diets, genetic origin, gender and age, and hence call for prospective studies investigating the features of gut microbiome in such animal models by controlling for these host elements.

Adipose Tissue Transferrin and Insulin Resistance.

Context: Excessive body iron stores are a risk factor for decreased insulin sensitivity (SI) and diabetes. We hypothesized that transcriptional dysregulation of genes involved in iron metabolism in adipocytes causes insulin resistance. Objective and Design: To define the genetic regulation of iron metabolism and its role in SI, we used gene expression, genotype, and SI data from an African American cohort (N = 256). Replication studies were performed in independent European ancestry cohorts. In vitro studies in human adipocytes were performed to define the role of a selected gene in causing insulin resistance. Results: Among 62 transcripts representing iron homeostasis genes, expression of 30 in adipose tissue were correlated with SI. Transferrin (TF) and ferritin heavy polypeptide were most positively and negatively associated with SI, respectively. These observations were replicated in two independent European ancestry adipose data sets. The strongest cis-regulatory variant for TF expression (rs6785596; P = 7.84 × 10-18) was identified in adipose but not muscle or liver tissue. Variants significantly affected the normal relationship of serum ferritin to insulin resistance. Knockdown of TF in differentiated Simpson-Golabi-Behmel syndrome adipocytes by short hairpin RNA decreased intracellular iron, reduced maximal insulin-stimulated glucose uptake, and reduced Akt phosphorylation. Knockdown of TF caused differential expression of 465 genes, including genes involved in glucose transport, mitochondrial function, Wnt-pathway/ SI, chemokine activity, and obesity. Iron chelation recapitulated key changes in the expression profile induced by TF knockdown. Conclusion: Genetic regulation of TF expression in adipose tissue plays a novel role in regulating SI.

Synergistic Inhibitory Effects of Hypoxia and Iron Deficiency on Hepatic Glucose Response in Mouse Liver.

Hypoxia and iron both regulate metabolism through multiple mechanisms, including hypoxia-inducible transcription factors. The hypoxic effects on glucose disposal and glycolysis are well established, but less is known about the effects of hypoxia and iron deficiency on hepatic gluconeogenesis. We therefore assessed their effects on hepatic glucose production in mice. Weanling C57BL/6 male mice were fed an iron-deficient (4 ppm) or iron-adequate (35 ppm) diet for 14 weeks and were continued in normoxia or exposed to hypoxia (8% O2) for the last 4 weeks of that period. Hypoxic mice became hypoglycemic and displayed impaired hepatic glucose production after a pyruvate challenge, an effect accentuated by an iron-deficient diet. Stabilization of hypoxia-inducible factors under hypoxia resulted in most glucose being converted into lactate and not oxidized. Hepatic pyruvate concentrations were lower in hypoxic mice. The decreased hepatic pyruvate levels were not caused by increased utilization but rather were contributed to by decreased metabolism from gluconeogenic amino acids. Pyruvate carboxylase, which catalyzes the first step of gluconeogenesis, was also downregulated by hypoxia with iron deficiency. Hypoxia, and more so hypoxia with iron deficiency, results in hypoglycemia due to decreased levels of hepatic pyruvate and decreased pyruvate utilization for gluconeogenesis. These data highlight the role of iron levels as an important determinant of glucose metabolism in hypoxia.

Adipocyte iron regulates leptin and food intake.

Dietary iron supplementation is associated with increased appetite. Here, we investigated the effect of iron on the hormone leptin, which regulates food intake and energy homeostasis. Serum ferritin was negatively associated with serum leptin in a cohort of patients with metabolic syndrome. Moreover, the same inverse correlation was observed in mice fed a high-iron diet. Adipocyte-specific loss of the iron exporter ferroportin resulted in iron loading and decreased leptin, while decreased levels of hepcidin in a murine hereditary hemochromatosis (HH) model increased adipocyte ferroportin expression, decreased adipocyte iron, and increased leptin. Treatment of 3T3-L1 adipocytes with iron decreased leptin mRNA in a dose-dependent manner. We found that iron negatively regulates leptin transcription via cAMP-responsive element binding protein activation (CREB activation) and identified 2 potential CREB-binding sites in the mouse leptin promoter region. Mutation of both sites completely blocked the effect of iron on promoter activity. ChIP analysis revealed that binding of phosphorylated CREB is enriched at these two sites in iron-treated 3T3-L1 adipocytes compared with untreated cells. Consistent with the changes in leptin, dietary iron content was also directly related to food intake, independently of weight. These findings indicate that levels of dietary iron play an important role in regulation of appetite and metabolism through CREB-dependent modulation of leptin expression.

Metabolic aspects of high-altitude adaptation in Tibetans.

NEW FINDINGS: What is the topic of this review? The topic of this review is how Tibetans have adapted genetically to high altitude, particularly with reference to altitude-induced changes in metabolism. What advances does it highlight? It highlights recent work on metabolic phenotyping in Tibetans and demonstrates that selected genetic haplotypes influence their metabolism of fats and glucose. Recent studies have identified genes involved in high-altitude adaptation in Tibetans. Three of these genes (EPAS1, EGLN1 and PPARA) are associated with decreased haemoglobin levels compared with non-Tibetans living at altitude. Consistent with the phenotype, EGLN1 in Tibetans has a gain-of-function mutation that confers a higher affinity for oxygen, hence less sensitivity to hypoxia. Considering the demands imposed upon metabolism in meeting energy demands despite limitations on fuel oxidation, we hypothesized that other selected genes might alter metabolism to allow adaptation to altitude despite the desensitization of the upstream hypoxia sensing caused by the EGLN1 mutation that results in the failure to sense hypoxia. A shift in fuel preference to glucose oxidation and glycolysis at the expense of fatty acid oxidation would provide adaptation to decreased oxygen availability. Measurements of serum metabolites from Tibetans living at high altitude are consistent with this hypothesis; the EPAS1 haplotype is significantly associated with increased lactate levels (suggesting increased anaerobic metabolism), and the PPARA haplotype and serum free fatty acids are positively related (suggesting decreased fat oxidation). These data suggest that the high-altitude adaptations may offer protection from diabetes at high altitude but increase the risk of diabetes at lower elevations and/or with adoption of a non-traditional diet. It should also be considered in future work in the field that because iron is a cofactor for EGLN1, there may be significant associations of phenotypes with the significant degrees of variation seen in tissue iron among human populations.

Genetic polymorphism of APOB is associated with diabetes mellitus in sickle cell disease.

Environmental variations have strong influences in the etiology of type 2 diabetes mellitus. In this study, we investigated the genetic basis of diabetes in patients with sickle cell disease (SCD), a Mendelian disorder accompanied by distinct physiological conditions of hypoxia and hyperactive erythropoiesis. Compared to the general African American population, the prevalence of diabetes as assessed in two SCD cohorts of 856 adults was low, but it markedly increased with older age and overweight. Meta-analyses of over 5 million single-nucleotide polymorphisms (SNPs) in the two SCD cohorts identified a SNP, rs59014890, the C allele of which associated with diabetes risk at P = 3.2 × 10(-8) and, surprisingly, associated with decreased APOB expression in peripheral blood mononuclear cells (PBMCs). The risk allele of the APOB polymorphism was associated with overweight in 181 SCD adolescents, with diabetes risk in 592 overweight, non-SCD African Americans ≥ 45 years of age, and with elevated plasma lipid concentrations in general populations. In addition, lower expression level of APOB in PBMCs was associated with higher values for percent hemoglobin A1C and serum total cholesterol and triglyceride concentrations in patients with Chuvash polycythemia, a congenital disease with elevated hypoxic responses and increased erythropoiesis at normoxia. Our study reveals a novel, environment-specific genetic polymorphism that may affect key metabolic pathways contributing to diabetes in SCD.

MyD88 regulates physical inactivity-induced skeletal muscle inflammation, ceramide biosynthesis signaling, and glucose intolerance.

Physical inactivity in older adults is a risk factor for developing glucose intolerance and impaired skeletal muscle function. Elevated inflammation and ceramide biosynthesis have been implicated in metabolic disruption and are linked to Toll-like receptor (TLR)/myeloid differentiation primary response 88 (MyD88) signaling. We hypothesize that a physical inactivity stimulus, capable of inducing glucose intolerance, would increase skeletal muscle inflammation and ceramide biosynthesis signaling and that this response would be regulated by the TLR/MyD88 pathway. Therefore, we subjected wild-type (WT) and MyD88(-/-) mice to hindlimb unloading (HU) for 14 days or an ambulatory control period. We observed impaired glucose uptake, muscle insulin signaling (p-Akt), and increased markers of NF-κB signaling (p-IκBα), inflammation (p-JNK, IL-6), TLR4, and the rate-limiting enzyme of ceramide biosynthesis, SPT2, with HU WT (P < 0.05), but not in HU MyD88(-/-) mice. Concurrently, we found that 5 days of bed rest in older adults resulted in whole body glucose dysregulation, impaired skeletal muscle insulin signaling, and upregulation of muscle IL-6 and SPT2 (P < 0.05). Post-bed rest TLR4 abundance was tightly correlated with impaired postprandial insulin and glucose levels. In conclusion, MyD88 signaling is necessary for the increased inflammation, ceramide biosynthesis signaling, and compromised metabolic function that accompanies physical inactivity.