Dysregulation of Inositol Synthesis Affects Obesity and Causes Developmental Birth Defects

Abstract

Myo‐inositol is a six‐carbon sugar alcohol that is a precursor of phosphatidylinositol (PI), a cell membrane phospholipid. Inositol is synthesized from glucose‐6‐phosphate by the product of the Drosophila melanogaster Inos gene, myo‐inositol‐3‐phosphate synthase (MIPSp). Abnormalities in myo‐inositol metabolism have been implicated in diseases and complications such as type 2 diabetes, polycystic ovary syndrome, and bipolar disorder. Obesity can be induced by a high sucrose diet in D. melanogaster third instar larvae. The hypothesis of this study was that obesity induced in D. melanogaster by high sucrose diet can be alleviated by inositol, either dietary or endogenously synthesized. A float buoyancy assay was used to assess obesity of larvae of three strains: a wild type strain (CS), a homozygous P‐element insertion strain with UASGAL4 5’ of the Inos gene (inosP‐UAS), and a heterozygous inosP‐UAS strain with GAL4 production driven by an actin promoter (inosP‐UAS ; Act5C‐Gal4). This last strain has up‐regulated inositol synthesis. Larval Inos transcript and MIPS protein expression levels in the three strains were confirmed by RT‐qPCR and Western blots. The inosP‐UAS larvae with GAL4 production driven by the actin promoter (inosP‐UAS ; Act5C‐Gal4) have the highest levels of Inos transcript and MIPS protein relative to the homozygous inosP‐UAS insertion larvae which have an intermediate level of expression, and the wild‐type CS with the lowest level of expression. In the float‐buoyancy assay, larvae with increased buoyancy are scored as ‘obese’. Provision of dietary inositol reduced the percentage of ‘obese’ wild‐type larvae from 74.75±1.94 to 63.95 ±1.70. Moreover, up‐regulation of inositol synthesis via inosP‐UAS ; Act5C‐Gal4 dramatically reduced the percentage of ‘obese’ larvae to 13.28±4.42. During these studies, it became apparent that dysregulation of inositol synthesis resulted in developmental abnormalities and birth defects. Attempts to grow inosP‐UAS ; Act5C‐Gal4 larvae to maturity (adult flies) resulted in a surprising outcome – nearly all flies died as pharate adults. Some structural alterations of wings, halteres, and legs were immediately apparent. The few flies that did eclose died within a few days. Scanning electron and light microscope imaging revealed that they all had malformed or missing proboscises. These data give us a better understanding of the importance of the regulation of inositol in obesity and development.Support or Funding InformationThis project is supported in part by the National Institute of General Medical Sciences of the National Institutes of Health under Award Number R25GM071638 and by the Frank Schatzlein Endowed Student Award.