Association analysis of common variants in FOXO3 with type 2 diabetes in a South Indian Dravidian population

Recent studies have identified common variants in forkhead box O3 gene (FOXO3) to be strongly associated with longevity in different populations. But studies have not been carried out to analyse the role of common variants in FOXO3 with type 2 diabetes. Since type 2 diabetes is an age related disorder and FOXO proteins play an important role in the regulation of metabolism, we studied the role of common variants in FOXO3 for association with type 2 diabetes. The study was carried out in 994 type 2 diabetic samples and 984 normoglycemic control samples from a South Indian Dravidian population. In our analysis, we found that there was no association between any of the selected SNPs in FOXO3 with type 2 diabetes. Analysis of these SNPs with diabetes related biochemical and clinical parameters also did not reveal any significant association. Haplotype association of SNPs in FOXO3 with type 2 diabetes was observed, but the frequency of the haplotypes was considerably lower and they do not remain significant after correction for multiple testing. In conclusion, we did not observe any association of SNPs in FOXO3 with type 2 diabetes and related parameters suggesting an entirely different mechanism by which these SNPs influence longevity. However additional studies in other populations are required to completely rule out the association of common variants in FOXO3 with type 2 diabetes.     

The Drosophila homolog of methionine sulfoxide reductase A extends lifespan and increases nuclear localization of FOXO

Methionine sulfoxide reductase A (msrA) was previously found to increase resistance to oxidative stress and longevity in animals. We identified Drosophila msrA (dmsrA), a Drosophila homolog of human msrA, as a downstream effector of forkhead box O (FOXO) signaling in Drosophila, which enhances resistance to oxidative stress and increases survival under stressed conditions. Additionally, overexpression of dmsrA in neurons extended the lifespan of flies. Moreover, overexpression of dmsrA in fat body cells caused FOXO to translocate to the nucleus, implying that this possible positive feedback loop between dmsrA and FOXO could potentiate the antioxidant activity of dmsrA and increase the lifespan in Drosophila.     

FOXO 1a and FOXO 3a gene polymorphisms in association with metabolic syndrome

The prevalence and magnitude of childhood and adult obesity and diabetes are increasing dramatically. FOXO 1a and FOXO 3a will be evaluated in this study, in an effort to identify genetic polymorphisms in potential candidate genes that may be associated with body mass index (BMI), and metabolic syndrome (MS). Also to assess whether there is a relation between insulin sensitivity, and genotype, we will test the relation between fasting insulin, glucose, insulin resistance, insulin secretion and genotype.A total number of 248 presenting normal, overweight and obese individuals were recruited; 100 children and 148 adults of both sexes. They were divided by body mass index as follows, normal, overweight and obese. Lipid profile, fasting glucose and insulin HOMA-IR and HOMA-β index and RT-PCR for FOXO 1a and FOXO 3a were performed.An association was found among the studied group (children and adults) as regards foxo3a gene polymorphism and HOMA IR, HOMA B index and T-cholesterol (P = 0.022, 0.011 and 0.028, respectively), while there was only an association between LDL-C and foxo1a gene polymorphism among the studied group of children and adults (P = 0.023).In this study we demonstrated that FOXO3a mutant is correlated with HOMA-IR (marker of insulin resistance), HOMA-B index (marker of insulin secretion) and total cholesterol while as regards FOXO1a there was only an association between LDL cholesterol and mutant type of FOXO1a.     

SIRT3, a Mitochondrial NAD+-Dependent Deacetylase,Is Involved in the Regulation of Myoblast Differentiation

Sirtuin 3 (SIRT3), one of the seven mammalian sirtuins, is a mitochondrial NAD⁺-dependent deacetylase known to control key metabolic pathways. SIRT3 deacetylases and activates a large number of mitochondrial enzymes involved in the respiratory chain, in ATP production, and in both the citric acid and urea cycles. We have previously shown that the regulation of myoblast differentiation is tightly linked to mitochondrial activity. Since SIRT3 modulates mitochondrial activity, we decide to address its role during myoblast differentiation. For this purpose, we first investigated the expression of endogenous SIRT3 during C2C12 myoblast differentiation. We further studied the impact of SIRT3 silencing on both the myogenic potential and the mitochondrial activity of C2C12 cells. We showed that SIRT3 protein expression peaked at the onset of myoblast differentiation. The inhibition of SIRT3 expression mediated by the stable integration of SIRT3 short inhibitory RNA (SIRT3shRNA) in C2C12 myoblasts, resulted in: 1) abrogation of terminal differentiation - as evidenced by a marked decrease in the myoblast fusion index and a significant reduction of Myogenin, MyoD, Sirtuin 1 and Troponin T protein expression - restored upon MyoD overexpression; 2) a decrease in peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and citrate synthase protein expression reflecting an alteration of mitochondrial density; and 3) an increased production of reactive oxygen species (ROS) mirrored by the decreased activity of manganese superoxide dismutase (MnSOD). Altogether our data demonstrate that SIRT3 mainly regulates myoblast differentiation via its influence on mitochondrial activity.     

Role of SEPALLATA3 (SEP3) as a downstream gene of miR156-SPL3-FT circuitry in ambient temperature-responsive flowering

SEPALLATA3 (SEP3) is important in determining flowering time as well as floral organ identity. Although much is known about the regulation of floral organ identity by SEP3, its role as a downstream gene of FLOWERING LOCUS T (FT) for the regulation of ambient temperature-responsive flowering is poorly understood. Here, we show that SEP3 as a downstream gene of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE3 (SPL3) and FT modulates the flowering time in response to different ambient temperatures. SEP3 overexpression showed temperature-insensitive flowering at 23°C and 16°C. This suggests that altered SEP3 activity affects ambient temperature-responsive flowering. However, a lesion in SEP3 did not obviously affect ambient temperature-responsive flowering. SEP3 expression was affected by altered SPL3 and FT activities in the leaf and shoot apical regions at different temperatures. These results suggest that the miR156-SPL3-FT circuitry directly or indirectly regulates SEP3 expression for the regulation of ambient temperature-responsive flowering in Arabidopsis.