Diabetes and obesity pathophysiology as a teaching tool to emphasize physiology core concepts.

Diabetes mellitus and obesity are major public health issues that significantly impact the health care system. The next generation of health care providers will need a deep understanding of the pathophysiology of these diseases if we are to prevent, treat, and eventually cure these diseases and ease the burden on patients and the health care system. Physiology core concepts are a set of core principles, or "big ideas," identified by physiology educators that are thought to promote long-term retention, create a deeper understanding, and help with formation of critical thinking skills. Here we describe our scaffolded teaching approach in an upper year undergraduate pathophysiology course to educate students about these two diseases and discuss how learning about the basis of these highly integrative diseases from the biochemical to whole body level is a meaningful tool in the physiology educator toolbox to reinforce physiology core concepts. This teaching strategy is designed to engage students in the scientific process and hone their problem-solving skills such that they are hopefully equipped to treat and eventually cure these diseases as they move forward in their careers.NEW & NOTEWORTHY Students often struggle with integration of physiological systems. Type 2 diabetes mellitus and obesity are two related diseases that are useful to explore the interdependence of physiological systems and multiple physiology core concepts. Deep learning about these diseases has the potential to dramatically improve the health care system of the future.

MUREs: a new member of the URE-CURE family of research opportunities for undergrads.

Undergraduate research experiences are important for the development of scientific identity, appreciation of authentic research, and improvement of persistence toward science careers. We identified a gap in experiential research opportunities for undergraduate Biology students who were seeking a formal yet small-scale research experience that was unique to their own interests and career aspirations. These opportunities may be especially worthwhile for of science, technology, engineering, and mathematics (STEM) students aspiring to nonresearch scientific careers (i.e., medicine, dentistry, forensics, and communication) and underrepresented STEM students. Here, we reflect on the use of small-scale, individualized undergraduate research experiences that are based on established methods. These experiences have helped to fill this gap and create problem-centered learning opportunities for undergraduate students that are as unique as the students themselves.

Exercise in ZDF rats does not attenuate weight gain, but prevents hyperglycemia concurrent with modulation of amino acid metabolism and AKT/mTOR activation in skeletal muscle.

PURPOSE: Protein metabolism is altered in obesity, accompanied by elevated plasma amino acids (AA). Previously, we showed that exercise delayed progression to type 2 diabetes in obese ZDF rats with maintenance of ß cell function and reduction in hyperglucocorticoidemia. We hypothesized that exercise would correct the abnormalities we found in circulating AA and other indices of skeletal muscle protein metabolism. METHODS: Male obese prediabetic ZDF rats (7-10/group) were exercised (swimming) 1 h/day, 5 days/week from ages 6-19 weeks, and compared with age-matched obese sedentary and lean ZDF rats. RESULTS: Food intake and weight gain were unaffected. Protein metabolism was altered in obese rats as evidenced by increased plasma concentrations of essential AA, and increased muscle phosphorylation (ph) of Akt(ser473) (187%), mTOR(ser2448) (140%), eIF4E-binding protein 1 (4E-BP1) (111%), and decreased formation of 4E-BP1*eIF4E complex (75%, 0.01 ≤ p ≤ 0.05 for all measures) in obese relative to lean rats. Exercise attenuated the increase in plasma essential AA concentrations and muscle Akt and mTOR phosphorylation. Exercise did not modify phosphorylation of S6K1, S6, and 4E-BP1, nor the formation of 4E-BP1*eIF4E complex, mRNA levels of ubiquitin or the ubiquitin ligase MAFbx. Positive correlations were observed between ph-Akt and fed circulating branched-chain AA (r = 0.56, p = 0.008), postprandial glucose (r = 0.42, p = 0.04) and glucose AUC during an IPGTT (r = 0.44, p = 0.03). CONCLUSION: Swimming exercise-induced attenuation of hyperglycemia in ZDF rats is independent of changes in body weight and could result in part from modulation of muscle AKT activation acting via alterations of systemic AA metabolism.

Exercise maintains euglycemia in association with decreased activation of c-Jun NH2-terminal kinase and serine phosphorylation of IRS-1 in the liver of ZDF rats.

Stress-activated systems and oxidative stress are involved in insulin resistance, which, along with beta-cell failure, contribute to the development of type 2 diabetes mellitus (T2DM). Exercise improves insulin resistance and glucose tolerance, and these adaptations may, in part, be related to reductions in inflammation and oxidative stress. We investigated circulating and tissue-specific markers of inflammation and oxidative stress and insulin-signaling pathways in a rodent model of T2DM, the Zucker diabetic fatty rat, with and without voluntary exercise. At 5 wk of age, Zucker diabetic fatty rats (n = 8-9/group) were divided into basal (B), voluntary exercise (E), and sedentary control (S) groups. B rats were euthanized at 6 wk of age, and S and E rats were euthanized 10 wk later. E rats ran approximately 5 km/day, which improved insulin sensitivity and maintained fed and fasted glucose levels and glucose tolerance. Ten weeks of exercise also decreased whole body markers of inflammation and oxidative stress in plasma and liver, including lowered circulating IL-6, haptoglobin, and malondialdehyde levels, hepatic protein oxidation, and phosphorylated JNK, the latter indicating decreased JNK activity. Hepatic phosphoenolpyruvate carboxykinase levels and Ser(307)-phosphorylated insulin receptor substrate-1 were also reduced in E compared with S rats. In summary, we show that, in a rodent model of T2DM, voluntary exercise decreases circulating markers of inflammation and oxidative stress and lowers hepatic JNK activation and Ser(307)-phosphorylated insulin receptor substrate-1. These changes in oxidative stress markers and inflammation are associated with decreased hyperglycemia and insulin resistance and reduced expression of the main gluconeogenic enzyme phosphoenolpyruvate carboxykinase.

Physiological roles of the GIP receptor in murine brown adipose tissue.

OBJECTIVE: Glucose-dependent insulinotropic polypeptide (GIP) is secreted from the gut in response to nutrient ingestion and promotes meal-dependent insulin secretion and lipid metabolism. Loss or attenuation of GIP receptor (GIPR) action leads to resistance to diet-induced obesity through incompletely understood mechanisms. The GIPR is expressed in white adipose tissue; however, its putative role in brown adipose tissue (BAT) has not been explored. METHODS: We investigated the role of the GIPR in BAT cells in vitro and in BAT-specific (GiprBAT-/-) knockout mice with selective elimination of the Gipr within the Myf5+ expression domain. We analyzed body weight, adiposity, glucose homeostasis, insulin and lipid tolerance, energy expenditure, food intake, body temperature, and iBAT oxygen consumption ex vivo. High-fat diet (HFD)-fed GiprBAT-/- mice were studied at room temperature (21 °C), 4 °C, and 30 °C ambient temperatures. RESULTS: The mouse Gipr gene is expressed in BAT, and GIP directly increased Il6 mRNA and IL-6 secretion in BAT cells. Additionally, levels of thermogenic, lipid and inflammation mRNA transcripts were altered in BAT cells transfected with Gipr siRNA. Body weight gain, energy expenditure, and glucose and insulin tolerance were normal in HFD-fed GiprBAT-/- mice housed at room temperature. However, GiprBAT-/- mice exhibited higher body temperatures during an acute cold challenge and a lower respiratory exchange ratio and impaired lipid tolerance at 21 °C. In contrast, body weight was lower and iBAT oxygen consumption was higher in HFD-fed mice housed at 4 °C but not at 30 °C. CONCLUSIONS: The BAT GIPR is linked to the control of metabolic gene expression, fuel utilization, and oxygen consumption. However, the selective loss of the GIPR within BAT is insufficient to recapitulate the findings of decreased weight gain and resistance to obesity arising in experimental models with systemic disruption of GIP action.

Adaptation to mild, intermittent stress delays development of hyperglycemia in the Zucker diabetic Fatty rat independent of food intake: role of habituation of the hypothalamic-pituitary-adrenal axis.

Hypothalamic-pituitary-adrenal (HPA) axis hyperactivity occurs in type 2 diabetes, and stress is assumed to play a causal role. However, intermittent restraint stress, a model mimicking some mild stressors, delays development of hyperglycemia in Zucker diabetic fatty (ZDF) rats. We examine whether such stress delays hyperglycemia independent of stress-induced reductions in hyperphagia and is due to adaptations in gene expression of HPA-related peptides and receptors that ameliorate corticosteronemia and thus hyperglycemia. ZDF rats were intermittently restraint stressed (1 h/d, 5 d/wk) for 13 wk and compared with obese control, pair fed, and lean ZDF rats. After 13 wk, basal hormones were repeatedly measured over 24 h, and HPA-related gene expression was assessed by in situ hybridization. Although restraint initially induced hyperglycemia, this response habituated over time, and intermittent restraint delayed hyperglycemia. This delay was partly related to 5-15% decreased hyperphagia, which was not accompanied by decreased arcuate nucleus NPY or increased POMC mRNA expression, although expression was altered by obesity. Obese rats demonstrated basal hypercorticosteronemia and greater corticosterone responses to food/water removal. Basal hypercorticosteronemia was further exacerbated after 13 wk of pair feeding during the nadir. Importantly, intermittent restraint further delayed hyperglycemia independent of food intake, because glycemia was 30-40% lower than after 13 wk of pair feeding. This may be mediated by increased hippocampal MR mRNA, reduced anterior pituitary POMC mRNA levels, and lower adrenal sensitivity to ACTH, thus preventing basal and stress-induced hypercorticosteronemia. In contrast, 24-h catecholamines were unaltered. Thus, rather than playing a causal role, intermittent stress delayed deteriorations in glycemia and ameliorated HPA hyperactivity in the ZDF rat.

Inactivation of the Glucose-Dependent Insulinotropic Polypeptide Receptor Improves Outcomes following Experimental Myocardial Infarction.

Incretin hormones exert pleiotropic metabolic actions beyond the pancreas. Although the heart expresses both incretin receptors, the cardiac biology of GIP receptor (GIPR) action remains incompletely understood. Here we show that GIPR agonism did not impair the response to cardiac ischemia. In contrast, genetic elimination of the Gipr reduced myocardial infarction (MI)-induced ventricular injury and enhanced survival associated with reduced hormone sensitive lipase (HSL) phosphorylation; it also increased myocardial triacylglycerol (TAG) stores. Conversely, direct GIPR agonism in the isolated heart reduced myocardial TAG stores and increased fatty acid oxidation. The cardioprotective phenotype in Gipr-/- mice was partially reversed by pharmacological activation or genetic overexpression of HSL. Selective Gipr inactivation in cardiomyocytes phenocopied Gipr-/- mice, resulting in improved survival and reduced adverse remodeling following experimental MI. Hence, the cardiomyocyte GIPR regulates fatty acid metabolism and the adaptive response to ischemic cardiac injury. These findings have translational relevance for developing GIPR-based therapeutics.

Recurrent intermittent restraint delays fed and fasting hyperglycemia and improves glucose return to baseline levels during glucose tolerance tests in the Zucker diabetic fatty rat--role of food intake and corticosterone.

Short-term elevations of stress hormones cause an increase in glycemia. However, the effect of intermittent stress on development of type 2 diabetes mellitus is unclear. We hypothesized that recurrent intermittent restraint stress would deteriorate glycemia. Male, prediabetic Zucker diabetic fatty (ZDF) rats were restrained 1 hour per day, 5 days per week for 13 weeks and compared with unstressed, age-matched diabetic controls and lean nondiabetic rats. To differentiate the effects of recurrent restraint stress per se vs restraint-induced inhibition of food intake, a pair-fed group of rats was included. Surprisingly, recurrent restraint and pair feeding delayed fed and fasting hyperglycemia, such that they were lowered 50% by restraint and 30% by pair feeding after 13 weeks. Rats that were previously restrained or pair fed had lower glucose levels during a glucose tolerance test, but restraint further improved the return of glucose to baseline compared to pair feeding (P<.05). This was despite pair-fed rats having slightly lowered food intake and body weights compared with restrained rats. Restraint and pair feeding did not alter insulin responses to an intraperitoneal glucose tolerance test (IPGTT) or fasting insulin, and did not lower plasma lipids. Interestingly, restraint normalized basal corticosterone to one third that in control and pair-fed rats, prevented increases in pretreatment corticosterone seen with pair feeding, and led to habituation of restraint-induced corticosterone responses. After 13 weeks of treatment, multiple regression analysis showed that elevations in basal corticosterone could explain approximately 20% of the variance in fed glucose levels. In summary, intermittent restraint and its adaptations delayed hyperglycemia and improved glucose control in Zucker diabetic fatty rats. These benefits can be partially explained by restraint-induced lowering of food intake, but additional improvements compared to pair feeding may involve lower overall corticosterone exposure with repeated restraint. Paradoxically, these novel investigations suggest some types of occasional stress may limit development of diabetes.

Attenuation of type 2 diabetes mellitus in the male Zucker diabetic fatty rat: the effects of stress and non-volitional exercise.

To date, a limited number of studies have investigated the effects of exercise on the maintenance of endocrine pancreatic adaptations to worsening insulin resistance. In particular, the roles of stress hormones that are associated with commonly used forced-exercise paradigms are not fully explained. To examine the effects of exercise per se in ameliorating pancreatic decompensation over time, we investigated the role of forced swimming and sham exercise stress on the development of type 2 diabetes mellitus in the Zucker diabetic fatty (ZDF) rat. Thirty-two male ZDF rats were obtained at 5 weeks of age and all went through a 1-week acclimatization period. They were then divided into 4 groups: basal (euthanized at 6 weeks of age), exercise (1 h/d; 5 d/wk), sham exercise (sham), and non-treated controls (n = 8 per group). After 6 weeks of treatment, an intraperitoneal glucose tolerance test was performed and animals were euthanized for tissue analysis. By 5 weeks of treatment, controls had elevated fed and fasted glycemia (>11.1 and 7.1 mmol/L, respectively; both P < .05), whereas exercise and sham rats remained euglycemic. At euthanasia, there were elevations in fed insulin levels in exercise and sham rats compared with basal animals (both P < .05). Despite improvements in fed and fasting glucose levels in sham rats, glucose tolerance in sham-treated rats (intraperitoneal glucose tolerance test) was similar to controls, whereas glucose levels were similar in exercised trained and basal rats. After 6 weeks, gastrocnemius glycogen content was higher in exercised rats and sham rats when compared with age-matched controls, whereas muscle glucose transporter 4 levels were similar between groups. Compared with controls, the exercise group had increased beta cell proliferation, beta cell mass, and partial maintenance of normal islet morphology. Sham rats also displayed beta cell compensation, as evidenced by increased fasting insulin levels and partial preservation of normal islet morphology. Finally, at the time of euthanasia, plasma corticosterone was increased in sham and control rats but was at basal levels in the exercise group. In summary, both exercise and sham treatment delay the progression of type 2 diabetes mellitus in the male ZDF rat by distinct mechanisms related to pancreatic function and improvements in peripheral glucose disposal.

Gipr is essential for adrenocortical steroidogenesis; however, corticosterone deficiency does not mediate the favorable metabolic phenotype of Gipr(-/-) mice.

Glucose-dependent insulinotropic polypeptide (GIP) promotes glucose-dependent insulin secretion. However, GIP also enhances glucocorticoid secretion and promotes adiposity. Because obesity and diabetes are glucocorticoid dependent, we examined whether the effects of GIP on energy balance and glycemia are regulated by glucocorticoids using pharmacological activation of GIP receptor (GIPR) signaling with [d-Ala(2)]GIP in mice and in Y1 adrenocortical cells. Genetic elimination of GIPR activity was also studied in normal- and high-fat (HF)-fed Gipr-deficient (Gipr(-/-)) mice. [d-Ala(2)]GIP increased murine corticosterone levels in a GIPR-dependent manner. Conversely, basal corticosterone levels were reduced, whereas food deprivation resulted in significantly enhanced plasma corticosterone levels in Gipr(-/-) mice. [d-Ala(2)]GIP increased cAMP levels, activated extracellular signal\x{2013}related kinase (ERK)1/2, increased expression of steroidogenic genes, and increased neutral lipid storage in Y1GIPR cells. Gipr(-/-) adrenal glands demonstrated a twofold upregulation of the ACTH receptor mRNA and increased sensitivity to ACTH ex vivo. Although HF-fed Gipr(-/-) mice exhibited significantly lower plasma corticosterone, glucocorticoid-treated HF-fed Gipr(-/-) mice had similar energy balance and glycemia compared with Gipr(+)(/+) controls. Hence, although the Gipr is essential for adrenal steroidogenesis and links HF feeding to increased levels of corticosterone, reduced glucocorticoid levels do not significantly contribute to the enhanced metabolic phenotypes in HF-fed Gipr(-/-) mice.

Adaptation to intermittent stress promotes maintenance of beta-cell compensation: comparison with food restriction.

Intermittent restraint stress delays hyperglycemia in ZDF rats better than pair feeding. We hypothesized that intermittent stress would preserve beta-cell mass through distinct mechanisms from food restriction. We studied temporal effects of intermittent stress on beta-cell compensation during pre-, early, and late diabetes. Six-week-old obese male ZDF rats were restraint-stressed 1 h/day, 5 days/wk for 0, 3, 6, or 13 wk and compared with age-matched obese ZDF rats that had been food restricted for 13 wk, and 19-wk-old lean ZDF rats. Thirteen weeks of stress and food restriction lowered cumulative food intake 10-15%. Obese islets were fibrotic and disorganized and not improved by stress or food restriction. Obese pancreata had islet hyperplasia and showed evidence of neogenesis, but by 19 wk old beta-cell mass was not increased, and islets had fewer beta-cells that were hypertrophic. Both stress and food restriction partially preserved beta-cell mass at 19 wk old via islet hypertrophy, whereas stress additionally lowered alpha-cell mass. Concomitant with maintenance of insulin responses to glucose, stress delayed the sixfold decline in beta-cell proliferation and reduced beta-cell hypertrophy, translating into 30% more beta-cells per islet after 13 wk. In contrast, food restriction did not improve insulin responses or beta-cell hyperplasia, exacerbated beta-cell hypertrophy, and resulted in fewer beta-cells and greater alpha-cell mass than with stress. Thus, preservation of beta-cell mass with adaptation to intermittent stress is related to beta-cell hyperplasia, maintenance of insulin responses to glucose, and reductions in alpha-cell mass that do not occur with food restriction.

Swim training prevents hyperglycemia in ZDF rats: mechanisms involved in the partial maintenance of beta-cell function.

Exercise improves glucose tolerance in obese rodent models and humans; however, effects with respect to mechanisms of beta-cell compensation remain unexplained. We examined exercise's effects during the progression of hyperglycemia in male Zucker diabetic fatty (ZDF) rats until 19 wk of age. At 6 wk old, rats were assigned to 1) basal--euthanized for baseline values; 2) exercise--swam individually for 1 h/day, 5 days/wk; and 3) controls (n = 8-10/group). Exercise (13 wk) resulted in maintenance of fasted hyperinsulinemia and prevented increases in fed and fasted glucose (P < 0.05) compared with sham-exercised and sedentary controls (P < 0.05). Beta-cell function calculations indicate prolonged beta-cell adaptation in exercised animals alone. During an intraperitoneal glucose tolerance test (IPGTT), exercised rats had lower 2-h glucose (P < 0.05) vs. controls. Area-under-the-curve analyses from baseline for IPGTT glucose and insulin indicate improved glucose tolerance with exercise was associated with increased insulin production and/or secretion. Beta-cell mass increased in exercised vs. basal animals; however, mass expansion was absent at 19 wk in controls (P < 0.05). Hypertrophy and replication contributed to expansion of beta-cell mass; exercised animals had increased beta-cell size and bromodeoxyuridine incorporation rates vs. controls (P < 0.05). The relative area of GLUT2 and protein kinase B was significantly elevated in exercised vs. sedentary controls (P < 0.05). Last, we show formation of ubiquitinated protein aggregates, a response to cellular/oxidative stress, occurred in nonexercised 19 wk-old ZDF rats but not in lean, 6 wk-old basal, or exercised rats. In conclusion, improved beta-cell compensation through increased beta-cell function and mass occurs in exercised but not sedentary ZDF rats and may be in part responsible for improved glucoregulation.