Childhood obesity: Implications on adipose tissue dynamics and metabolic health

Obesity is the leading risk factor for the development of type 2 diabetes and cardiovascular diseases. Childhood obesity represents an alarming health challenge because children with obesity are prone to remain with obesity throughout their life and have an increased morbidity and mortality risk. The ability of adipose tissue to store lipids and expand in size during excessive calorie intake is its most remarkable characteristic. Cellular and lipid turnovers determine adipose tissue size and are closely related with metabolic status. The mechanisms through which adipose tissue expands and how this affects systemic metabolic homeostasis are still poorly characterized. Furthermore, the mechanism through which increased adiposity extends from childhood to adulthood and its implications in metabolic health are in most part, still unknown. More studies on adipose tissue development in healthy and children with obesity are urgently needed. In the present review, we summarize the dynamics of white adipose tissue, from developmental origins to the mechanisms that allows it to grow and expand throughout lifetime and during obesity in children and in different mouse models used to address this largely unknown field. Specially, highlighting the role that excessive adiposity during the early life has on future's adipose tissue dynamics and individual's health.

The long-lasting shadow of litter size in rodents: litter size is an underreported variable that strongly determines adult physiology

BACKGROUND/PURPOSE

Litter size is a biological variable that strongly influences adult physiology in rodents. Despite evidence from previous decades and recent studies highlighting its major impact on metabolism, information about litter size is currently underreported in the scientific literature. Here, we urge that this important biological variable should be explicitly stated in research articles.

RESULTS/CONCLUSION

Below, we briefly describe the scientific evidence supporting the impact of litter size on adult physiology and outline a series of recommendations and guidelines to be implemented by investigators, funding agencies, editors in scientific journals, and animal suppliers to fill this important gap.

Increasing breast milk betaine modulates Akkermansia abundance in mammalian neonates and improves long-term metabolic health

Accelerated postnatal growth is a potentially modifiable risk factor for future obesity. To study how specific breast milk components contribute to early growth and obesity risk, we quantified one-carbon metabolism-related metabolites in human breast milk and found an inverse association between milk betaine content and infant growth. This association was replicated in an independent and geographically distinct cohort. To determine the potential role of milk betaine in modulating offspring obesity risk, we performed maternal betaine supplementation experiments in mice. Higher betaine intake during lactation increased milk betaine content in dams and led to lower adiposity and improved glucose homeostasis throughout adulthood in mouse offspring. These effects were accompanied by a transient increase in Akkermansia spp. abundance in the gut during early life and a long-lasting increase in intestinal goblet cell number. The link between breast milk betaine and Akkermansia abundance in the gut was also observed in humans, as infants exposed to higher milk betaine content during breastfeeding showed higher fecal Akkermansia muciniphila abundance. Furthermore, administration of A. muciniphila to mouse pups during the lactation period partially replicated the effects of maternal breast milk betaine, including increased intestinal goblet cell number, lower adiposity, and improved glucose homeostasis during adulthood. These data demonstrate a link between breast milk betaine content and long-term metabolic health of offspring.

Effects of Bifidobacterium animalis Subsp. lactis (BPL1) Supplementation in Children and Adolescents with Prader-Willi Syndrome: A Randomized Crossover Trial

Prader-Willi syndrome (PWS) is a rare genetic disorder characterized by a wide range of clinical manifestations, including obesity, hyperphagia, and behavioral problems. Bifidobacterium animalis subsp. lactis strain BPL1 has been shown to improve central adiposity in adults with simple obesity. To evaluate BPL1's effects in children with PWS, we performed a randomized crossover trial among 39 patients (mean age 10.4 years). Participants were randomized to placebo-BPL1 (n = 19) or BPL1-placebo (n = 20) sequences and underwent a 12-week period with placebo/BPL1 treatments, a 12-week washout period, and a 12-week period with the crossover treatment. Thirty-five subjects completed the study. The main outcome was changes in adiposity, measured by dual-energy X-ray absorptiometry. Secondary outcomes included lipid and glucose metabolism, hyperphagia, and mental health symptoms. Generalized linear modeling was applied to assess differences between treatments. While BPL1 did not modify total fat mass compared to placebo, BPL1 decreased abdominal adiposity in a subgroup of patients older than 4.5 years (n = 28). BPL1 improved fasting insulin concentration and insulin sensitivity. Furthermore, we observed modest improvements in some mental health symptoms. A follow-up trial with a longer treatment period is warranted to determine whether BPL1 supplementation can provide a long-term therapeutic approach for children with PWS (ClinicalTrials.gov NCT03548480).

Back to the future: transgenerational transmission of xenobiotic-induced epigenetic remodeling

Epigenetics, or regulation of gene expression independent of DNA sequence, is the missing link between genotype and phenotype. Epigenetic memory, mediated by histone and DNA modifications, is controlled by a set of specialized enzymes, metabolite availability, and signaling pathways. A mostly unstudied subject is how sub-toxic exposure to several xenobiotics during specific developmental stages can alter the epigenome and contribute to the development of disease phenotypes later in life. Furthermore, it has been shown that exposure to low-dose xenobiotics can also result in further epigenetic remodeling in the germ line and contribute to increase disease risk in the next generation (multigenerational and transgenerational effects). We here offer a perspective on current but still incomplete knowledge of xenobiotic-induced epigenetic alterations, and their possible transgenerational transmission. We also propose several molecular mechanisms by which the epigenetic landscape may be altered by environmental xenobiotics and hypothesize how diet and physical activity may counteract epigenetic alterations.

In utero undernutrition in male mice programs liver lipid metabolism in the second-generation offspring involving altered Lxra DNA methylation

Obesity and type 2 diabetes have a heritable component that is not attributable to genetic factors. Instead, epigenetic mechanisms may play a role. We have developed a mouse model of intrauterine growth restriction (IUGR) by in utero malnutrition. IUGR mice developed obesity and glucose intolerance with aging. Strikingly, offspring of IUGR male mice also developed glucose intolerance. Here, we show that in utero malnutrition of F1 males influenced the expression of lipogenic genes in livers of F2 mice, partly due to altered expression of Lxra. In turn, Lxra expression is attributed to altered DNA methylation of its 5' UTR region. We found the same epigenetic signature in the sperm of their progenitors, F1 males. Our data indicate that in utero malnutrition results in epigenetic modifications in germ cells (F1) that are subsequently transmitted and maintained in somatic cells of the F2, thereby influencing health and disease risk of the offspring.

Fatty acid transport protein 1 (FATP1) localizes in mitochondria in mouse skeletal muscle and regulates lipid and ketone body disposal

FATP1 mediates skeletal muscle cell fatty acid import, yet its intracellular localization and metabolic control role are not completely defined. Here, we examine FATP1 localization and metabolic effects of its overexpression in mouse skeletal muscle. The FATP1 protein was detected in mitochondrial and plasma membrane fractions, obtained by differential centrifugation, of mouse gastrocnemius muscle. FATP1 was most abundant in purified mitochondria, and in the outer membrane and soluble intermembrane, but not in the inner membrane plus matrix, enriched subfractions of purified mitochondria. Immunogold electron microscopy localized FATP1-GFP in mitochondria of transfected C2C12 myotubes. FATP1 was overexpressed in gastrocnemius mouse muscle, by adenovirus-mediated delivery of the gene into hindlimb muscles of newborn mice, fed after weaning a chow or high-fat diet. Compared to GFP delivery, FATP1 did not alter body weight, serum fed glucose, insulin and triglyceride levels, and whole-body glucose tolerance, in either diet. However, fatty acid levels were lower and β-hydroxybutyrate levels were higher in FATP1- than GFP-mice, irrespective of diet. Moreover, intramuscular triglyceride content was lower in FATP1- versus GFP-mice regardless of diet, and β-hydroxybutyrate content was unchanged in high-fat-fed mice. Electroporation-mediated FATP1 overexpression enhanced palmitate oxidation to CO2, but not to acid-soluble intermediate metabolites, while CO2 production from β-hydroxybutyrate was inhibited and that from glucose unchanged, in isolated mouse gastrocnemius strips. In summary, FATP1 was localized in mitochondria, in the outer membrane and intermembrane parts, of mouse skeletal muscle, what may be crucial for its metabolic effects. Overexpressed FATP1 enhanced disposal of both systemic fatty acids and intramuscular triglycerides. Consistently, it did not contribute to the high-fat diet-induced metabolic dysregulation. However, FATP1 lead to hyperketonemia, likely secondary to the sparing of ketone body oxidation by the enhanced oxidation of fatty acids.

Glucokinase gene transfer to skeletal muscle of diabetic Zucker fatty rats improves insulin-sensitive glucose uptake

Skeletal muscle has a prime role in glucose homeostasis. We have previously demonstrated that adenovirus-mediated glucokinase (GK) gene transfer to skeletal muscle of Wistar rats enhances muscle glucose uptake and whole body glucose disposal under conditions of hyperglycemia and hyperinsulinemia. In this study, we have tested whether GK gene transfer to the muscle of the Zucker Diabetic Fatty rat (ZDF), a genetic model of obesity and type 2 diabetes, could improve glycemic control and prevent the onset of hyperglycemia in obese males. We show that GK delivery results in a doubling of total gastrocnemius muscle glucose phosphorylating activity 9 weeks after gene transfer. GK-treated rats exhibited slightly reduced weight and normal insulin-sensitive glucose uptake, as assessed during an insulin tolerance test, whereas age-matched rats treated with a control virus were clearly insulin resistant. The improved glucose uptake in GK-expressing rats was associated with higher gastrocnemius lactate content, whereas glycogen and triacylglyceride (TAG) levels were unmodified. Remarkably, GK-treated rats showed increased expression of both hexokinase II (HKII) and GLUT4, in accordance with a glucose-dependent regulation of these proteins. Thus, our data show that delivery of GK, despite improving insulin-sensitive glucose disposal in muscle, is not sufficient to prevent or delay the appearance of elevated glucose and insulin levels associated with severe obesity in male ZDF animals.

Increased glucose disposal induced by adenovirus-mediated transfer of glucokinase to skeletal muscle in vivo

In non-insulin-dependent diabetes mellitus, insulin-stimulated glucose uptake is impaired in muscle, contributing in a major way to development of hyperglycemia. We previously showed that expression of the glucose phosphorylating enzyme glucokinase (GK) in cultured human myocytes improved glucose storage and disposal, suggesting that GK delivery to muscle in situ could potentially enhance glucose clearance. Here we have tested this idea directly by intramuscular delivery of an adenovirus containing the liver GK cDNA (AdCMV-GKL) into one hind limb. We injected an adenovirus containing the beta-galactosidase gene (AdCMV-lacZ) into the hind limb of newborn rats. beta-Galactosidase activity was localized in muscle for as long as 1 month after delivery, with a large percentage of fibers staining positive in the gastrocnemius. Using the same approach with AdCMV-GKL, GK protein content was increased from zero to 50-400% of the GK in normal liver sample, and total glucose phosphorylating activity was increased in GK-expressing muscles relative to the counterpart uninfected muscle. Expression of GK in muscle improved glucose tolerance rather than changing basal glycemic control. Glucose levels were reduced by approximately 35% 10 min after administration of a glucose bolus to fed animals treated with AdCMV-GKL relative to AdCMV-lacZ-treated controls. The enhanced rate of glucose clearance was reflected in increases in muscle 2-deoxy glucose uptake and blood lactate levels. We conclude that restricted expression of GK in muscle leads to an enhanced capacity for muscle glucose disposal and whole body glucose tolerance under conditions of maximal glucose-insulin stimulation, suggesting that under these conditions glucose phosphorylation becomes rate-limiting. Our findings also show that gene delivery to a fraction of the whole body is sufficient to improve glucose disposal, providing a rationale for the development of new therapeutic strategies for treatment of diabetes.-Jiménez-Chillarón, J. C., Newgard, C. B., Gómez-Foix, A. M. Increased glucose disposal induced by adenovirus-mediated transfer of glucokinase to skeletal muscle in vivo.

Reduction of islet amylin expression and basal secretion by adenovirus-mediated delivery of amylin antisense cDNA

Reduction of amylin content and secretion in rat islets was attempted by transduction with an adenovirus bearing a 0.2-kb fragment of rat amylin cDNA inserted in the antisense orientation (AdCMV-alpha amylin). Exposure of islets to AdCMV-alpha amylin at a multiplicity of infection (moi) of 200 (1.2 x 10(7) pfu/ml) reduced amylin mRNA levels by 37 +/- 5% (p < 0.005), whereas infection with an adenovirus expressing the reporter gene of beta-galactosidase (AdCMV-lacz) did not modify amylin expression. Transduction with the antisense construct was specifically associated with the decrease (30 +/- 6%; p < 0.001) in the amylin content. Insulin content was unaltered in AdCMV-alpha amylin islets compared to AdCMV-lacz-transduced or untransduced cells. Basal amylin secretion (2.8 mM glucose) was 36 +/- 3% (p < 0.005) lower in AdCMV-alpha amylin islets than in untransduced or AdCMV-lacz-transduced islets. In contrast, no difference in amylin secretion in response to high glucose concentrations (16.7 mM) was detected in AdCMV-alpha amylin-transduced islets. Thus, a reduction of amylin content and basal secretion in islet cells can be achieved by the adenovirus-mediated expression of antisense RNA.