title: Atomic force microscopy, biochemical analysis of 3T3-L1 cells differentiated in the absence and presence of insulin.
abstract: BACKGROUND
  There are ample evidences to demonstrate that differentiation of preadipocytes is associated with deposition of fat in cells. Still, it is unclear whether the differentiation process also alters membrane topology as well as cholesterol levels and whether insulin contributes to it.
  
  
  METHODS
  Membrane scanning of differentiated cells, along with freshly plated and 11 day preadipocytes, was performed using Atomic Force Microscopy (AFM) to gain qualitative information about cell surface properties as well as roughness. Moreover, glucose uptake, lipid analysis, expression profiling of transcription factors and signaling molecules involved in the process of differentiation was also performed.
  
  
  RESULTS
  We report (i) differentiation in the presence of 500 microM isobutylmethylxanthine (IBMX), 0.25 microM dexamethasone (DEX) with or without 0.1 microM (0.57 microg/ml) insulin directly alters membrane topology. (ii) At nano-levels, addition of insulin maintains plasma membrane roughness during differentiation in comparison with IBMX and DEX only. (iii) At macro levels, decreased fat accumulation in preadipocytes exposed to insulin during the initial stages of differentiation is a result of reduced expression and nuclear localization of sterol regulatory element binding protein (SREBP)-1.
  
  
  CONCLUSIONS
  This study reports a significant reduction of membrane cholesterol and total cholesterol (p<0.01) in cells differentiated in the presence of insulin.
authors.affiliation: National Centre for Cell Science, Ganeshkhind, Pune-411007, India.
authors.forename: Vimal
authors.initials: V
authors.lastname: Pandey
authors.forename: Malepillil Vavachan
authors.initials: MV
authors.lastname: Vijayakumar
authors.forename: Ruchika
authors.initials: R
authors.lastname: Kaul-Ghanekar
authors.forename: Hitesh
authors.initials: H
authors.lastname: Mamgain
authors.forename: Kishore
authors.initials: K
authors.lastname: Paknikar
authors.forename: Manoj Kumar
authors.initials: MK
authors.lastname: Bhat
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D001692:Biological Transport; D002454:Cell Differentiation; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D002467:Cell Nucleus / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D020869:Gene Expression Profiling; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D018625:Microscopy, Atomic Force; D015398:Signal Transduction; D051780:Sterol Regulatory Element Binding Protein 1 / Q000378:metabolism; D014280:Triglycerides / Q000378:metabolism
chemical_list: D000943:Antigens, Differentiation; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D051780:Sterol Regulatory Element Binding Protein 1; D014280:Triglycerides; D002784:Cholesterol; D005947:Glucose