Minglan Li

Maternal Obesity and Developmental Programming of Metabolic Disorders in Offspring: Evidence from Animal Models

The incidence of obesity and overweight has reached epidemic proportions in the developed world as well as in those countries transitioning to first world economies, and this represents a major global health problem. Concern is rising over the rapid increases in childhood obesity and metabolic disease that will translate into later adult obesity. Although an obesogenic nutritional environment and increasingly sedentary lifestyle contribute to our risk of developing obesity, a growing body of evidence links early life nutritional adversity to the development of long-term metabolic disorders. In particular, the increasing prevalence of maternal obesity and excess maternal weight gain has been associated with a heightened risk of obesity development in offspring in addition to an increased risk of pregnancy-related complications. The mechanisms that link maternal obesity to obesity in offspring and the level of gene-environment interactions are not well understood, but the early life environment may represent a critical window for which intervention strategies could be developed to curb the current obesity epidemic. This paper will discuss the various animal models of maternal overnutrition and their importance in our understanding of the mechanisms underlying altered obesity risk in offspring.

Effects of taurine supplementation on hepatic markers of inflammation and lipid metabolism in mothers and offspring in the setting of maternal obesity.

Maternal obesity is associated with obesity and metabolic disorders in offspring. However, intervention strategies to reverse or ameliorate the effects of maternal obesity on offspring health are limited. Following maternal undernutrition, taurine supplementation can improve outcomes in offspring, possibly via effects on glucose homeostasis and insulin secretion. The effects of taurine in mediating inflammatory processes as a protective mechanism has not been investigated. Further, the efficacy of taurine supplementation in the setting of maternal obesity is not known. Using a model of maternal obesity, we examined the effects of maternal taurine supplementation on outcomes related to inflammation and lipid metabolism in mothers and neonates. Time-mated Wistar rats were randomised to either: 1) control : control diet during pregnancy and lactation (CON); 2) CON supplemented with 1.5% taurine in drinking water (CT); 3) maternal obesogenic diet (high fat, high fructose) during pregnancy and lactation (MO); or 4) MO supplemented with taurine (MOT). Maternal and neonatal weights, plasma cytokines and hepatic gene expression were analysed. A MO diet resulted in maternal hyperinsulinemia and hyperleptinemia and increased plasma glucose, glutamate and TNF-α concentrations. Taurine normalised maternal plasma TNF-α and glutamate concentrations in MOT animals. Both MO and MOT mothers displayed evidence of fatty liver accompanied by alterations in key markers of hepatic lipid metabolism. MO neonates displayed a pro-inflammatory hepatic profile which was partially rescued in MOT offspring. Conversely, a pro-inflammatory phenotype was observed in MOT mothers suggesting a possible maternal trade-off to protect the neonate. Despite protective effects of taurine in MOT offspring, neonatal mortality was increased in CT neonates, indicating possible adverse effects of taurine in the setting of normal pregnancy. These data suggest that maternal taurine supplementation may ameliorate the adverse effects observed in offspring following a maternal obesogenic diet but these effects are dependent upon prior maternal nutritional background.

Early Life Nutrition and Energy Balance Disorders in Offspring in Later Life

The global pandemic of obesity and type 2 diabetes is often causally linked to changes in diet and lifestyle; namely increased intake of calorically dense foods and concomitant reductions in physical activity. Epidemiological studies in humans and controlled animal intervention studies have now shown that nutritional programming in early periods of life is a phenomenon that affects metabolic and physiological functions throughout life. This link is conceptualised as the developmental programming hypothesis whereby environmental influences during critical periods of developmental plasticity can elicit lifelong effects on the health and well-being of the offspring. The mechanisms by which early environmental insults can have long-term effects on offspring remain poorly defined. However there is evidence from intervention studies which indicate altered wiring of the hypothalamic circuits that regulate energy balance and epigenetic effects including altered DNA methylation of key adipokines including leptin. Studies that elucidate the mechanisms behind these associations will have a positive impact on the health of future populations and adopting a life course perspective will allow identification of phenotype and markers of risk earlier, with the possibility of nutritional and other lifestyle interventions that have obvious implications for prevention of non-communicable diseases.

Pre-Weaning Growth Hormone Treatment Reverses Hypertension and Endothelial Dysfunction in Adult Male Offspring of Mothers Undernourished during Pregnancy

Maternal undernutrition results in elevated blood pressure (BP) and endothelial dysfunction in adult offspring. However, few studies have investigated interventions during early life to ameliorate the programming of hypertension and vascular disorders. We have utilised a model of maternal undernutrition to examine the effects of pre-weaning growth hormone (GH) treatment on BP and vascular function in adulthood. Female Sprague-Dawley rats were fed either a standard control diet (CON) or 50% of CON intake throughout pregnancy (UN). From neonatal day 3 until weaning (day 21), CON and UN pups received either saline (CON-S, UN-S) or GH (2.5 ug/g/day)(CON-GH, UN-GH). All dams were fed ad libitum throughout lactation. Male offspring were fed a standard diet until the end of the study. Systolic blood pressure (SBP) was measured at day 150 by tail cuff plethysmography. At day 160, intact mesenteric vessels mounted on a pressure myograph. Responses to pressure, agonist-induced constriction and endothelium-dependent vasodilators were investigated to determine vascular function. SBP was increased in UN-S groups and normalised in UN-GH groups (CON-S 121±2 mmHg, CON-GH 115±3, UN-S 146±3, UN-GH 127±2). Pressure mediated dilation was reduced in UN-S offspring and normalised in UN-GH groups. Vessels from UN-S offspring demonstrated a reduced constrictor response to phenylephrine and reduced vasodilator response to acetylcholine (ACh). Furthermore, UN-S offspring vessels displayed a reduced vasodilator response in the presence of L-NG-Nitroarginine Methyl Ester (L-NAME), carbenoxolone (CBX), L-NAME and CBX, Tram-34 and Apamin. UN-GH vessels showed little difference in responses when compared to CON and significantly increased vasodilator responses when compared to UN-S offspring. Pre-weaning GH treatment reverses the negative effects of maternal UN on SBP and vasomotor function in adult offspring. These data suggest that developmental cardiovascular programming is potentially reversible by early life GH treatment and that GH can reverse the vascular adaptations resulting from maternal undernutrition.

Early Life Exposure to Fructose and Offspring Phenotype: Implications for Long Term Metabolic Homeostasis

The consumption of artificially sweetened processed foods, particularly high in fructose or high fructose corn syrup, has increased significantly in the past few decades. As such, interest into the long term outcomes of consuming high levels of fructose has increased significantly, particularly when the exposure is early in life. Epidemiological and experimental evidence has linked fructose consumption to the metabolic syndrome and associated comorbidities—implicating fructose as a potential factor in the obesity epidemic. Yet, despite the widespread consumption of fructose-containing foods and beverages and the rising incidence of maternal obesity, little attention has been paid to the possible adverse effects of maternal fructose consumption on the developing fetus and long term effects on offspring. In this paper we review studies investigating the effects of fructose intake on metabolic outcomes in both mother and offspring using human and experimental studies.

Pre-weaning growth hormone treatment ameliorates bone marrow macrophage inflammation in adult male rat offspring following maternal undernutrition.

Maternal undernutrition (UN) is associated with the development of obesity and metabolic complications in adult offspring. While the role of inflammation in obesity and related comorbidities has been well established, there is little evidence regarding the effects of maternal UN-induced programming on immune function in male adult offspring. This study examines the effects growth hormone (GH), which is known to induce anti-inflammatory effects, on maternal UN-induced bone marrow macrophage (BMM) function in adult male offspring. Sprague-Dawley rats were assigned to chow (C) or UN (50% ad libitum; UN) diet throughout gestation. Male C and UN pups received saline (CS/UNS) or GH (2.5 µg/g/d; CGH/UNGH) from day 3–21. Bone marrow hematopoietic cells were differentiated to a macrophage phenotype in the presence of M-CSF (50 ng/ml). Differentiated bone marrow macrophages (BMM) were stimulated with LPS (100 ng/ml) for 6 h. UNS-derived BMM had significantly increased secretion and expression of IL-1β and IL-6 following LPS stimulation. This was accompanied by increased expression of IL-1R1, IL-6R and TLR4. Pre-weaning GH treatment reversed this pro-inflammatory phenotype. Furthermore UNGH displayed increased expression of markers of alternative (M2) macrophage activation, mannose receptor and PPARγ. This study demonstrates that fetal UN exposure primes hematopoietic immune cells to a more potent pro-inflammatory phenotype with heightened cytokine secretion and receptor expression. Furthermore these cells are pre-disposed to pro-inflammatory M1 macrophage phenotype which has wide-reaching and important effects in terms of obesity and metabolic disease.

Preweaning Growth Hormone Treatment Ameliorates Adipose Tissue Insulin Resistance and Inflammation in Adult Male Offspring Following Maternal Undernutrition

It is well established that early-life nutritional alterations lead to increased risk of obesity and metabolic disorders in adult life. Although it is clear that obesity gives rise to chronic low-grade inflammation, there is little evidence regarding the role of inflammation in the adipose tissue of undernourished (UN) offspring. GH reduces fat mass and has antiinflammatory properties. The present study examined the effect of maternal UN on adipose inflammation in adult offspring and whether GH treatment during a critical period of developmental plasticity could ameliorate metabolic dysfunction associated with a poor start to life. Sprague Dawley rats were assigned to chow (C) or UN (50% ad libitum; UN) diet throughout gestation. Male C and UN pups received saline (control saline [CS]/UN) or GH (2.5 μg/g/d; control growth hormone [CGH]/undernourished growth hormone [UNGH]) from days 3-21. Postweaning males were further randomized and fed either chow or high-fat diet until day 160. An ex vivo glucose uptake assay demonstrated adipose tissue from UN offspring displayed attenuated insulin-stimulated glucose uptake compared with CS, CGH, and UNGH. This was associated with increased insulin receptor, glucose transporter 4, and insulin receptor substrate 1 gene expression. Furthermore, UN demonstrated enhanced TNFα and IL-1β secretion from adipose explants and stromal vascular fraction cultures accompanied by increased adipose tissue gene expression of several key proinflammatory genes and markers of macrophage infiltration. Overall, UN offspring displayed a more potent immunophenotype, which correlated with decreased insulin sensitivity. Preweaning GH treatment negates these detrimental effects, indicating the potential for reversing metabolic dysfunction in UN adult offspring.

Developmental Programming of Nonalcoholic Fatty Liver Disease: The Effect of Early Life Nutrition on Susceptibility and Disease Severity in Later Life

Nonalcoholic fatty liver disease (NAFLD) is fast becoming the most common liver disease globally and parallels rising obesity rates. The developmental origins of health and disease hypothesis have linked alterations in the early life environment to an increased risk of metabolic disorders in later life. Altered early life nutrition, in addition to increasing risk for the development of obesity, type 2 diabetes, and cardiovascular disease in offspring, is now associated with an increased risk for the development of NAFLD. This review summarizes emerging research on the developmental programming of NAFLD by both maternal obesity and undernutrition with a particular focus on the possible mechanisms underlying the development of hepatic dysfunction and potential strategies for intervention.

Let-7 miRNA Profiles Are Associated With the Reversal of Left Ventricular Hypertrophy and Hypertension in Adult Male Offspring From Mothers Undernourished During Pregnancy After Preweaning Growth Hormone Treatment

Maternal undernutrition (UN) is known to cause cardiac hypertrophy, elevated blood pressure, and endothelial dysfunction in adult offspring. Maternal UN may also lead to disturbances in GH regulation in offspring. Because GH plays a key role in cardiac development, we used a model of maternal UN to examine the effects of neonatal GH treatment on cardiac hypertrophy, cardiac micro RNA (miRNA) profiles, and associated gene regulation in adult offspring. Female Sprague-Dawley rats were fed either a standard control diet (CON) or 50% of CON intake throughout pregnancy (UN). From neonatal day 3 until weaning (d 21), CON and UN pups received either saline (S) (CON-S, UN-S) or GH (2.5 μg/g·d) (CON-GH, UN-GH). Heart structure was determined by hematoxylin and eosin staining, and miRNA was isolated from cardiac tissue and miRNA expression analyzed using Cardiovascular miRNA gene Arrays (SABiosciences Ltd). Maternal UN caused marked increases in cardiac hypertrophy and left ventricular cardiomyocyte area, which were reversed by preweaning GH treatment. Systolic blood pressure was increased in UN-S groups and normalized in UN-GH groups (CON-S 121 ± 2 mmHg, CON-GH 115 ± 3 mm Hg, UN-S 146 ± 3 mmHg, and UN-GH 127 ± 2 mmHg). GH treatment during early development facilitated a reversal of pathological changes in offspring hearts caused by UN during pregnancy. Specific cardiac miRNA profiles were exhibited in response to maternal UN, accompanied by up-regulation of the lethal-7 (LET-7) miRNA family in GH-treated offspring. miRNA target analysis revealed a number of genes associated with inflammation and cardiovascular development, which may be involved in the altered cardiac function of these offspring. Up-regulation of the LET-7 family of miRNAs observed in GH groups may mediate the reversal of cardiac hypertrophy observed in adult offspring males of UN mothers.

Maternal taurine supplementation attenuates maternal fructose-induced metabolic and inflammatory dysregulation and partially reverses adverse metabolic programming in offspring

Excessive fructose consumption is associated with insulin resistance (IR) and nonalcoholic fatty liver disease (NAFLD), and high fructose intake during pregnancy can lead to compromised fetal development in the rat. Evidence suggests that the amino acid taurine can ameliorate fructose-induced IR and NAFLD in nonpregnant animals. This study investigated the efficacy of taurine supplementation on maternal fructose-induced metabolic dysfunction and neonatal health. Time-mated Wistar rats were randomized to four groups during pregnancy and lactation: (a) control diet (CON), (b) CON supplemented with 1.5% taurine in drinking water (CT), (c) CON supplemented with fructose solution (F) and (d) F supplemented with taurine (FT). Maternal and neonatal weights, plasma cytokines and hepatic gene expression were analyzed. Maternal hyperinsulinemia, increased homeostasis model assessment of IR indices and elevated proinflammatory cytokines were observed in F group and normalized in FT group. Maternal fructose-induced hepatic steatosis accompanied with increased liver weight was ameliorated with taurine supplementation. Maternal hepatic sterol regulatory element-binding protein-1c and fatty acid synthase expression was significantly increased in the F group compared to the CON, CT and FT groups. Neonatal hepatic phosphoenolpyruvate carboxykinase expression was increased in male F neonates compared to the CON, CT and FT groups and was increased in female F and FT neonates compared to CON and CT. Interleukin-1β expression was decreased in male CT and FT neonates compared to other male groups. Hepatic tumour necrosis factor receptor-1 was lower in the male FT group than the F group. These results demonstrate that maternal taurine supplementation can partially reverse fructose-induced maternal metabolic dysfunction and may ameliorate adverse developmental programming effects in offspring in a sex-specific manner.