Deciphering the role of SGLT1 and SMIT1 in the pathophysiology of the heart

This thesis project aims to decipher the role of sodium-glucose co-transporter (SGLT)1 and SMIT1 in the heart. First, we showed that glucose uptake, glycogen content, facilitative glucose transporters (GLUTs) and cardiac hypertrophy were all unchanged in our SGLT1 Δex1KO model. We demonstrated that high concentrations of phlorizin exert aspecific effects on GLUT transporters independently of SGLT1. More importantly, we reported the expression of a SGLT1 truncated variant in mouse and human hearts. Ultimately, we examined the role of SMIT1 in a hyperglycemic chronic environment, via injection of streptozotocin (STZ). Our preliminary results on RNA-seq data showed dysregulated genes associated to heart failure and cardiac fibrosis in our SMIT1 KO mice. These data on SGLT1 and SMIT1 open new perspectives on their roles in cardiac pathophysiology.(BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 202

Gene Set Analysis for time-to-event outcome with the Generalized Berk–Jones statistic

Gene Set analysis allows to evaluate the impact of groups of genes on an outcome of interest, such as the occurrence of a disease. Through the definition of the gene sets, gene set analysis takes into account biological knowledge and makes it easier to interpret the results, while improving the statistical power compared to a gene-wise analysis. In the time-to-event context, few methods exist, but most of them do not take into account the correlation that occurs inside a gene set, which can be strong. As the Generalized Berk-Jones statistics showed great consistency and includes the correlation inside the test statistic, we adapted this method to the time-to-event context by using a Cox model. We compared our approach to other methods based on the Cox model, and showed that the Generalize Berk-Jones statistic offers great adaptability, meaning that it can be used in all kinds of data structures. We applied the different methods to two different contexts: Gliomas and Breast cancer. In terms of statistical power, we did offer similar results to the other Cox model methods, but with greater accuracy. In the breast cancer framework, we showed better statistical power than methods based on Kernel Machine score

Multiple roles of peroxiredoxins in inflammation.

Inflammation is a pathophysiological response to infection or tissue damage during which high levels of reactive oxygen and nitrogen species are produced by phagocytes to kill microorganisms. Reactive oxygen and nitrogen species serve also in the complex regulation of inflammatory processes. Recently, it has been proposed that peroxiredoxins may play key roles in innate immunity and inflammation. Indeed, peroxiredoxins are evolutionarily conserved peroxidases able to reduce, with high rate constants, hydrogen peroxide, alkyl hydroperoxides and peroxynitrite which are generated during inflammation. In this minireview, we point out different possible roles of peroxiredoxins during inflammatory processes such as cytoprotective enzymes against oxidative stress, modulators of redox signaling, and extracellular pathogen- or damage-associated molecular patterns. A better understanding of peroxiredoxin functions in inflammation could lead to the discovery of new therapeutic targets

New insight in understanding the contribution of SGLT1 in cardiac glucose uptake: evidence for a truncated form in mice and humans.

Although sodium-glucose co-transporter 1 (SGLT1) has been identified as one of the major SGLT isoforms expressed in the heart, its exact role remains elusive. Evidences using phlorizin, the most common inhibitor of SGLTs, suggested its role in glucose transport. However, phlorizin could also affect classical facilitated diffusion via glucose transporters (GLUTs), bringing into question the relevance of SGLT1 in overall cardiac glucose uptake. Accordingly, we assessed the contribution of SGLT1 in cardiac glucose uptake using the SGLT1 knock-out mouse model, which lacks exon 1. Glucose uptake was similar in cardiomyocytes isolated from SGLT1 knock-out (KO) and control littermate (WT) mice, either under basal state, insulin, or hyperglycemia. Similarly, in vivo basal and insulin-stimulated cardiac glucose transport measured by micro-PET scan technology did not differ between WT and KO mice. Micromolar concentrations of phlorizin had no impact on glucose uptake in either isolated WT or KO-derived cardiomyocytes. However, higher concentrations (1mM) completely inhibited insulin-stimulated glucose transport without affecting insulin signaling nor GLUT4 translocation, independently from cardiomyocyte genotype. Interestingly, we discover that mouse and human hearts expressed a shorter slc5a1 transcript, leading to SGLT1 protein lacking transmembrane domains and residues involved in glucose and sodium bindings. In conclusion, cardiac SGLT1 does not contribute to overall glucose uptake, probably due to the expression of slc5a1 transcript variant. The inhibitory effect of phlorizin on cardiac glucose uptake is SGLT1-independent and can be explained by GLUT transporter inhibition. These data open new perspectives in understanding the role of SGLT1 in the heart

Sodium-myoinositol cotransporter-1, SMIT1, mediates the production of reactive oxygen species induced by hyperglycemia in the heart

Hyperglycemia (HG) stimulates the production of reactive oxygen species in the heart through activation of NADPH oxidase 2 (NOX2). This production is independent of glucose metabolism but requires sodium/glucose cotransporters (SGLT). Seven SGLT isoforms (SGLT1 to 6 and sodium-myoinositol cotransporter-1, SMIT1) are known, although their expression and function in the heart remain elusive. We investigated these 7 isoforms and found that only SGLT1 and SMIT1 were expressed in mouse, rat and human hearts. In cardiomyocytes, galactose (transported through SGLT1) did not activate NOX2. Accordingly, SGLT1 deficiency did not prevent HG-induced NOX2 activation, ruling it out in the cellular response to HG. In contrast, myo-inositol (transported through SMIT1) reproduced the toxic effects of HG. SMIT1 overexpression exacerbated glucotoxicity and sensitized cardiomyocytes to HG, whereas its deletion prevented HG-induced NOX2 activation. In conclusion, our results show that heart SMIT1 senses HG and triggers NOX2 activation. This could participate in the redox signaling in hyperglycemic heart and contribute to the pathophysiology of diabetic cardiomyopathy