Influence of diet on visceral adipose remodeling in NONcNZO10 mice with polygenic susceptibility for type 2 diabetes

The effect of chronic exposure to metformin in a new type-2 diabetic NONcNZO10/LtJ mouse model of stroke

BACKGROUND

Diabetes is an independent risk factor of stroke and previous studies have confirmed that diabetic patients and animals experience poorer clinical outcomes following stroke. In this study, we aim to determine the effect of chronic exposure of the first-line antidiabetic agent, metformin, to restore euglycemia and to impact brain cell death following stroke in a new type-2 diabetes, NONcNZO10/LtJ (RCS-10) mouse model of stroke.

METHODS

Male RCS-10 mice received a moderate (11%) fat diet post-weaning, at 4 weeks of age, and became diabetic by 12-14 weeks, thus resembling human maturity-onset diabetes. The mice received either metformin or vehicle for 4 weeks before undergoing a hypoxic/ischemic (HI) insult. Blood samples were collected pre-, post-treatment, and post HI for glucose and lipid measurements, and brains were analyzed for infarct size, glial activation, neuronal cell death, and metformin-mediated adenosine monophosphate-activated protein kinase (AMPK) signaling at 48 h post HI.

RESULTS

Pretreatment with metformin maintained euglycemia for 4 weeks but did not change body weight or lipid profile. Metformin treatment significantly enhanced the microglial Bfl-1 mRNA expression and showed a non-significant increase in GFAP mRNA, however, GFAP protein levels were reduced. Metformin treatment slightly increased neuronal NeuN and MAP-2 protein levels and significantly reduced overall mortality post HI but did not elicit any significant change in infarct size.

CONCLUSION

The study suggests that the prolonged effect of metformin-induced euglycemia promoted the microglial activation, reduced neuronal cell death, and improved the overall survival following stroke, without any change in infarct size.

A Comprehensive Review on Preclinical Diabetic Models

BACKGROUND

Preclinical experimental models historically play a critical role in the exploration and characterization of disease pathophysiology. Further, these in-vivo and in-vitro preclinical experiments help in target identification, evaluation of novel therapeutic agents and validation of treatments.

INTRODUCTION

Diabetes mellitus (DM) is a multifaceted metabolic disorder of multidimensional aetiologies with the cardinal feature of chronic hyperglycemia. To avoid or minimize late complications of diabetes and related costs, primary prevention and early treatment are therefore necessary. Due to its chronic manifestations, new treatment strategies need to be developed, because of the limited effectiveness of the current therapies.

METHODS

The study included electronic databases such as Pubmed, Web of Science and Scopus. The datasets were searched for entries of studies up to June, 2018.

RESULTS

A large number of in-vivo and in-vitro models have been presented for evaluating the mechanism of anti-hyperglycaemic effect of drugs in hormone-, chemically-, pathogen-induced animal models of diabetes mellitus. The advantages and limitations of each model have also been addressed in this review.

CONCLUSION

This review encompasses the wide pathophysiological and molecular mechanisms associated with diabetes, particularly focusing on the challenges associated with the evaluation and predictive validation of these models as ideal animal models for preclinical assessments and discovering new drugs and therapeutic agents for translational application in humans. This review may further contribute to discover a novel drug to treat diabetes more efficaciously with minimum or no side effects. Furthermore, it also highlights ongoing research and considers the future perspectives in the field of diabetes.

High protein/fish oil diet prevents hepatic steatosis in NONcNZO10 mice; association with diet/genetics-regulated micro-RNAs

OBJECTIVE

NONcNZO10 (NZ10) mice are predisposed to obesity and develop type 2 diabetes (T2D) and hepatic steatosis even when maintained on a control diet (CD) of 6% fat. Studies were designed to determine whether this extreme susceptibility phenotype could be alleviated by diet and if so the molecular targets of diet.

METHODS

NZ10 and SWR/J (SWR) control mice were fed a CD or a test diet of high protein and fish oil (HPO) for 19 weeks and then analyzed for steatosis, blood chemistry, hepatic gene and micro-RNA expression.

RESULTS

HPO diet prevented steatosis, significantly increased serum adiponectin and reduced serum cholesterol and triglycerides only in NZ10 mice. The HPO diet repressed hepatic expression of fatty acid metabolic regulators including PPAR-γ, sterol regulatory element-binding protein-c1, peroxisome proliferator-activated receptor gamma co-activator-1, fatty acid synthase, fatty acid binding protein-4, and apolipoprotein A4 genes only in NZ10 mice. Also repressed by a HPO diet were adiponectinR2 receptor, leptin-R, PPAR-α, pyruvate dehydrogenase kinase isoforms 2 and 4, AKT2 and GSK3β. Micro-RNA (miR) arrays identified miRs that were diet and/or genetics regulated. QRTPCR confirmed increased expression of miR-205 and suppression of a series of miRs including miRs-411, 155, 335 and 21 in the NZ10-HPO group, each of which are implicated in the progression of diabetes and/or steatosis. Evidence is presented that miR-205 co-regulates with PPARγ and may regulate fibrosis and EMT during the progression of steatosis in the livers of NZ10-CD mice. The dietary responses of miR-205 are tissue-specific with opposite effects in adipose and liver.

CONCLUSION

The results confirm that a HPO diet overrides the genetic susceptibility of NZ10 mice and this correlates with the suppression of key genes and perhaps micro-RNAs involved in hyperglycemia, dyslipidemia and inflammation including master PPAR regulators, adiponectin and leptin receptors.

Role of Micro RNA-205 in Promoting Visceral Adiposity of NZ10 Mice with Polygenic Susceptibility for Type 2 Diabetes

SCOPE

To characterize diet-dependent miRNA profiles and their targets in the visceral adipose of mice with polygenic susceptibility to type 2 diabetes.

METHODS AND RESULTS

Six-week NONcNZO10/LtJ (NZ10) and control SWR/J mice were subjected to high protein-fish oil or control diets for 19 weeks and micro-RNA microarray analyses were implemented on visceral adipose RNA. We found that 27 miRNAs were significantly induced and 10 significantly repressed in the VA of obese NZ10 mice compared with controls. 12 selected regulated miRNAs were confirmed by RT-PCR based on the microarray data and we demonstrated that the expression of these miRNAs remained unaltered in the VA of control SWR mice. To assess the possible functional roles of miRNAs in adipogenesis, we also analyzed their expression in 3T3-L1 cells during growth and differentiation. This revealed that suppression of miRNA-205 alone correlated selectively with increased cell proliferation and lipid formation of adipocytes.

CONCLUSION

Diet and genetics control the expression of obesity-regulated miRNAs in the visceral adipose of NZ10 mice.

Comparison of Two New Mouse Models of Polygenic Type 2 Diabetes at the Jackson Laboratory, NONcNZO10Lt/J and TALLYHO/JngJ

This review compares two novel polygenic mouse models of type 2 diabetes (T2D), TALLYHO/JngJ and NONcNZO10/LtJ, and contrasts both with the well-known C57BLKS/J-Lepr(db) (db/db) monogenic diabesity model. We posit that the new polygenic models are more representative of the "garden variety" obesity underlying human T2D in terms of their polygenetic rather than monogenic etiology. Moreover, the clinical phenotypes in these new models are less extreme, for example, more moderated development of obesity coupled with less extreme endocrine disturbances. The more progressive development of obesity produces a maturity-onset development of hyperglycemia in contrast to the juvenile-onset diabetes observed in the morbidly obese db/db model. Unlike the leptin receptor-deficient db/db models with central leptin resistance, the new models develop a progressive peripheral leptin resistance and are able to maintain reproductive function. Although the T2D pathophysiology in both TALLYHO/JngJ and NONcNZO10/LtJ is remarkably similar, their genetic etiologies are clearly different, underscoring the genetic heterogeneity underlying T2D in humans.