Does reduced uptake contribute to dysregulation of adipose tissue and the development of obesity-related diseases?
Creators: name: Fell, Peter
Publisher: name: University of Lincoln
Year: 2023
Subjects: C741 - Medical biochemistry

description: Background: Adipocytes are derived from precursor cells, called preadipocytes, via a coordinated process of differentiation that involves substantial remodelling of molecular and cellular configuration and the extracellular matrix (ECM). Adipocytes function as energy stores and endocrine cells, secreting several biologically active cytokine-like proteins, termed adipokines, in a highly regulated manner to regulate essential aspects of metabolism, physiology and behaviour. Typically, adipocyte function and adipokine production become dysregulated in obesity contributing to the development of obesity-related diseases. Adiponectin is a key adipokine with anti-diabetic, anti-atherogenic and anti-inflammatory effects. It is secreted into the circulation in high concentrations in a variety of multimeric forms, the most biologically active being a high molecular weight (HMW) multimer, a form which is decreased in obesity. The efficient multimerisation and secretion of HMW adiponectin requires Vitamin C (VitC) to drive essential post-translational modifications (PTMs). The same PTMs are also required for collagen fibril formation, required for ECM remodelling. Surprisingly, the mechanism(s) of VitC uptake into preadipocytes and adipocytes is unknown, however recent papers suggest it’s transport may be mediated by the GLUT1 glucose transporter working in tandem with stomatin: an integral plasma membrane protein which facilitates plasma membrane ion transport and cytoskeletal anchoring. The aim of this project was to begin to define the pathway(s) that mediate VitC transport into (pre)adipocytes and determine whether this is compromised in obesity.Methods: (i) Twelve transcriptomic datasets from the gene expression omnibus (GEO) detailing changes in gene expression profiles during differentiation were analysed using GEO2R. (ii) The volume of regulatory sites (promoter and transcription factor binding) upstream of the stomatin gene (STOM) were analysed using genome analysis programmes ENCODE, BLAST and Ensemble. (iii) Six GSE (Genomic Spatial Event) datasets comparing gene expression profiles of tissues or cells from lean and obese subjects were analysed as above.Results: (i) Analysis of differentiating gene expression profiles showed characteristic induction of classic adipogenic markers (FABP4, C/EBP?, PPAR?, PLIN1, ADIPOQ and FASN) with evidence of differential induction of some genes in human and murine cells (eg FABP4: 1,000 vs 50-fold induction; ADIPOQ: 50 vs 1,000-fold induction). There were no major changes in expression of the VitC transporters responsible for transport of ascorbate (the reduced form of VitC), SVCT1/2, or the glucose transporters, GLUT1/4, capable of transporting dehydroascorbate (DHA - the oxidised form of VitC). However, the expression of stomatin, a protein that modulates the activity of GLUT1 such that it transports DHA preferentially over glucose, was significantly induced in differentiating human cells (?10-fold) but not rodent cells. (ii) The number of adipogenic transcription factor binding sites proximal to the stomatin gene was 50% higher in organisms such as humans that rely on dietary VitC, compared with others that can synthesise VitC. (iii) There were no significant differences between adipose tissues or cells from lean or obese subjects.Conclusions: Collectively these results raise the intriguing hypothesis that stomatin expression is differentially regulated during adipogenesis in those species incapable of VitC synthesis, compared to species that can. Increased stomatin expression may facilitate uptake of DHA, via modulation of GLUT1. Future investigations are required to test this hypothesis and, whilst stomatin gene expression does not appear to be compromised in obesity, whether stomatin protein and/or function is compromised remains to be investigated.