👤 Lynne Levitsky

Youth-onset type 2 diabetes (T2D) is a growing public health concern. Its genetic basis and relationship to other forms of diabetes are largely unknown. To gain insight into the genetic architecture and biology of youth-onset T2D, we analyzed exome sequences of 3,005 youth-onset T2D cases and 9,777 ancestry matched adult controls. We identified (a) monogenic diabetes variants in 2.1% of individuals; (b) two exome-wide significant ( Show less

Homo sapiens evolved under conditions of intermittent food availability and prolonged fasting between meals. Periods of fasting are important for recovery from meal-induced oxidative and metabolic stress, and tissue repair. Constant high energy-density food availability in present-day society contributes to the pathogenesis of chronic diseases, including diabetes and its complications, with intermittent fasting (IF) and energy restriction shown to improve metabolic health. We have previously demonstrated that IF prevents the development of diabetic retinopathy in a mouse model of type 2 diabetes (db/db); however the mechanisms of fasting-induced health benefits and fasting-induced risks for individuals with diabetes remain largely unknown. Sirtuin 1 (SIRT1), a nutrient-sensing deacetylase, is downregulated in diabetes. In this study, the effect of SIRT1 stimulation by IF, fasting-mimicking cell culture conditions (FMC) or pharmacological treatment using SRT1720 was evaluated on systemic and retinal metabolism, systemic and retinal inflammation and vascular and bone marrow damage. The effects of IF were modelled in vivo using db/db mice and in vitro using bovine retinal endothelial cells or rat retinal neuroglial/precursor R28 cell line serum starved for 24 h. mRNA expression was analysed by quantitative PCR (qPCR). SIRT1 activity was measured via histone deacetylase activity assay. NR1H3 (also known as liver X receptor alpha [LXRα]) acetylation was measured via western blot analysis. IF increased Sirt1 mRNA expression in mouse liver and retina when compared with non-fasted animals. IF also increased SIRT1 activity eightfold in mouse retina while FMC increased SIRT1 activity and expression in retinal endothelial cells when compared with control. Sirt1 expression was also increased twofold in neuronal retina progenitor cells (R28) after FMC treatment. Moreover, FMC led to SIRT1-mediated LXRα deacetylation and subsequent 2.4-fold increase in activity, as measured by increased mRNA expression of the genes encoding ATP-binding cassette transporter (Abca1 and Abcg1). These changes were reduced when retinal endothelial cells expressing a constitutively acetylated LXRα mutant were tested. Increased SIRT1/LXR/ABC-mediated cholesterol export resulted in decreased retinal endothelial cell cholesterol levels. Direct activation of SIRT1 by SRT1720 in db/db mice led to a twofold reduction of diabetes-induced inflammation in the retina and improved diabetes-induced visual function impairment, as measured by electroretinogram and optokinetic response. In the bone marrow, there was prevention of diabetes-induced myeloidosis and decreased inflammatory cytokine expression. Taken together, activation of SIRT1 signalling by IF or through pharmacological activation represents an effective therapeutic strategy that provides a mechanistic link between the advantageous effects associated with fasting regimens and prevention of microvascular and bone marrow dysfunction in diabetes. Show less

Effective gene therapy requires regulated gene expression and vector safety. We developed a strategy to exponentially increase native promoter activity while retaining inherent regulation by inserting multi-copy response elements (REs) into non-adjacent locations. For the hepatocyte nuclear factor (HNF) 4α-dependent Hnf1a (MODY3) gene, HNF4α stimulation increased from 5- to 90-fold by inserting 3 additional HNF4α REs (H4REs). Constructing a promoter with two 4xH4REs 0.25kb apart by duplicating the 4xH4RE fragment increased stimulation to >1000-fold. HNF4α-induced protein expression by the duplicate 4xH4RE Hnf1a promoter was comparable to a viral promoter. Converting the two Apolipoprotein C3 (ApoC3) H4REs spaced 0.61kb apart to 4xH4REs achieved a similar result. Increasing spacing to 2.1kb with non-promoter DNA abolished the augmentation. Finally, converting the HNF1α RE of the HNF4A (MODY1) P2 promoter to 4xH1RE and adding a second 4xH1RE 0.84kb upstream increased HNF1α stimulation from 26- to >200-fold. Deleting intervening DNA to produce 0.23-kb spacing increased stimulation to >500-fold. Spaced multi-copy RE motifs is a novel strategy for engineering promoters that boosts activity far beyond other techniques. Augmentation of three promoters suggests that this approach is potentially applicable to other promoters for gene therapy and might obviate the need for viral promoters. Show less