Promise(s) of mesenchymal stem cells as an in vitro model system to depict pre-diabetic/diabetic milieu in WNIN/GR-Ob mutant rats.

BACKGROUND:Development of model systems have helped to a large extent, in bridging gap to understand the mechanism(s) of disease including diabetes. Interestingly, WNIN/GR-Ob rats (Mutants), established at National Centre for Laboratory Animals (NCLAS) of National Institute of Nutrition (NIN), form a suitable model system to study obesity with Type 2 diabetes (T2D) demonstrating several secondary complications (cataract, cardiovascular complications, infertility, nephropathy etc). The present study has been carried out to explore the potent application(s) of multipotent stem cells such as bone marrow mesenchymal stem cells (BM-MSCs), to portray features of pre-diabetic/T2D vis-à-vis featuring obesity, with impaired glucose tolerance (IGT), hyperinsulinemia (HI) and insulin resistance (IR) seen with Mutant rats akin to human situation. METHODOLOGY/PRINCIPAL FINDINGS:Primary cultures of BM-MSCs (third passage) from Mutants, its lean littermate (Lean) and parental control (Control) were characterized for: proliferation markers, disease memory to mark obesity/T2D/HI/IR which included phased gene expression studies for adipogenic/pancreatic lineages, inflammatory markers and differentiation ability to form mature adipocytes/Insulin-like cellular aggregates (ILCAs). The data showed that BM-MSCs from Mutant demonstrated a state of disease memory, depicted by an upregulated expression of inflammatory markers (IL-6, TNFα); increased stem cell recruitment (Oct-4, Sox-2) and proliferation rates (CD90+/CD29+, PDA, 'S' phase of cell cycle by FACS and BrdU incorporation); accelerated preadipocyte induction (Dact-1, PPARγ2) with a quantitative increase in mature adipocyte formation (Leptin); ILCAs, which were non-responsive to high glucose did confer the Obese/T2D memory in Mutants. Further, these observations were in compliance with the anthropometric data. CONCLUSIONS:Given the ease of accessibility and availability of MSCs, the present study form the basis to report for the first time, application of BM-MSCs as a feasible in vitro model system to portray the disease memory of pre-clinical/T2D with IR - a major metabolic disorder of global concern

Population doubling assay and Cell cycle analysis of BM-MSCs.

<p>(A) MSCs from Mutant, Lean and Control, were measured for proliferation rate at 24, 48, 72 and 96 hrs. BM-MSCs from Mutants showed an increase in proliferation at all the time points and at 96 hours, the PDA was significantly higher compared to Lean and Control. Values represent the absolute cell count and have been computed from three independent experiments performed in duplicates (Mean ± SE, n = 6) (B) Cell cycle analysis of BM-MSCs from Mutants showing an increase in ‘S’ phase and G2-M as compared to Lean (C) and Control (D). Values have been represented as Mean ± SE (n = 6) from three individual experiments performed in duplicates. (E) Cell cycle analysis of BM-MSCs showing an increase in BrdU incorporation (‘S’ phase) (green) from Mutant compared to Lean and Control and proliferation index (F). Values have been represented as Mean ± SE (n = 6) from three individual experiments performed in duplicates. Asteric (*) indicates p<0.05 using ANOVA.</p

Assessment of Stress responses among BM-MSCs.

<p>(A) Increased expression of Interleukin-6 (IL-6) and Tumor necrosis factor alpha (TNFα) (inflammatory markers) was noted in MSCs from Mutant compared to Lean and Control. FACS analysis also showed an increase in TNFα in Mutant compared to Lean and Control (B). Immunolocalization data for TNFα (red) (C) and endoplasmic reticulum stress protein RL-77 (red) (E) showed an increase in Mutant compared to Lean and Control. Relative Fluorescence Units (RFU) for TNFα (D) and RL-77 (F) have also been represented. All images were captured at a magnification of 400x and quantified (as RFU) using Leica Advanced Fluorescence software in Leica Confocal Microscope (Leica SP5 series, Germany). Values have been represented as Mean ± SE (n = 6) from three independent experiments performed in duplicates.</p

Gene Sequences of Primers.

<p>Abbreviations:</p><p>Pref-1: Preadipocyte factor-1, PPARγ2: Peroxisome proliferator activator receptor gamma 2, C/EBPα: CCAAT/enhancer- binding protein alpha, TGFβ1: Transforming growth factor beta 1, AdipoQ: Adiponectin, GLUT-4: Glucose Transporter -4, IRS-1: Insulin receptor substrate -1, IL-6: Interleukin-6, TNFα: Tumor necrosis factor alpha, PDX-1: Pancreatic duodenum homeobox-1, GLUT-2: Glucose Transporter -2.</p

Differentiation of BM-MSCs to form ILCAs.

<p>BM-MSCs of Mutant, Lean and Control were subjected to a 10-day differentiation protocol to generate ILCAs. Monolayer of BM-MSCs exposed to serum free medium (SFM)-A (0.5 mM sodium butyrate, 4 nM Activin A and 50 µM β-mercaptoethanol) underwent aggregation by day 3 and when exposed to SFM-B (0.3 mM Taurine) formed clusters/ILCAs by day 5. These ILCAs mature with the addition of SFM-C (3 mM Taurine, 100 nM GLP-1 and 1 mM Nicotinamide) by day 10 and stain deep red/crimson red with dithizone (DTZ) (arrows). The data showed an increase in formation of ILCAs from Mutant compared to Lean and Control. All images were captured in phase contrast microscope (Nikon T2000, Japan) at magnifications, represented using scale bars within the images. Values have been represented as Mean ± SE (n = 6) from three independent experiments performed in duplicates.</p

Blood and Plasma measurements from WNIN/GR-Ob Rats.

<p>The Mutant rats demonstrated hyperinsulinemia which was significant compared to their Lean and Control. An increase in blood glucose levels was also evident among Mutants. IR was calculated based on three functions - a) FGIR <4.5 mg/10⁻⁴U; b) QUICKI – Lower among Obese; c) HOMA-IR >1 Asteric (*) indicates significance at p<0.05 by ANOVA compared to control. Values are represented as Mean ± SE (n = 6) from six animals per group.</p><p>Abbreviations:</p><p>FGIR: Fasting Glucose to Insulin Ratio, QUICKI: Quantitative Insulin Sensitivity Check Index, HOMA-IR: Homeostasis Model of Assessment for Insulin Resistance.</p

Gene expression analysis of BM-MSCs.

<p>BM-MSCs from Mutants demonstrated an upregulated expression of A) Embryonic (Oct-4/Sox-2 (Embryonic markers), (B) Mesenchymal/Preadipocyte markers (Dact-1/Pref-1) and (C) transcriptional factor (PPARγ2) compared to Lean and Control. However, TGFβ1 showed a decrease (C) and C/EBPα remained the same (C). Mature adipocyte markers Leptin and adiponectin (D) and GLUT-4 and IRS-1 (glucose homeostasis markers) (E) were decreased in Mutant. An upregulated expression of Insulin in Mutant, while PDX-1 and GLUT-2 levels were decreased in Mutant as compared to Lean and Control (F). Quantitative measurements of gene expression were carried out by densitometric analyses using QuantityOne software (BioRad, Italy) and represented graphically by plotting intensity/sq.mm vs gene/phenotype. Values represent Mean ± SE (n = 6) from three independent experiments performed in duplicates. Asteric (*) represents significance (p<0.05 by ANOVA) compared to Control.</p

Differentiation of BM-MSCs to form adipocytes.

<p>(A) Morphological changes in MSCs from Mutant, Lean and Control rats during adipogenic induction were visualized under phase contrast microscope (Nikon T2000, Japan) at day 1, 7 and 14 demonstrating the formation of lipid-droplet filled cells (arrows). Adipocyte formation was confirmed by staining with Oil Red O (arrows). Magnifications have been represented using scale bar. Panel B shows the quantification for increase in mature adipocytes formed from Mutant as compared to Lean and Control, using the ACT2U soft ware (Nikon, Japan). Values have been represented as Mean ± SE (n = 6), from three independent experiments performed in duplicates. Asteric (*) represents statistical significance (p<0.05) compared to Control as analyzed by ANOVA.</p

Characterization of the primary cultures of BM-MSCs.

<p>(A) Phase contrast photomicrographs showing primary cultures of BM-MSCs (day 7) from Mutant, Lean and Control. Spindle-like cell morphology with colony-formation units (CFU) were seen (insight), which have been captured using ACT2U software attached to Nikon Microscope at magnifications represented using scale bar. (B) MSCs characterized for mesenchymal-specific cytosolic protein STRO-1 (red) and cell nuclei were stained with 4′,6-diamidino-2-phenylindole (DAPI) (green - pseudo color). Images were captured in Confocal Microscope using Leica Advanced Fluorescence software (Leica SP5 series, Germany) at magnifications represented using scale bars.</p

Flow Cytometric analysis of BM-MSCs.

<p>Representative FACS analyses (FACS Diva software, FACS Aria II, BD, CA) of MSCs at passage 3 were positive for CD90-PE (A, B & C) and CD29-FITC (D, E & F) and negative for CD31-PE (G, H & I) demonstrating a mesenchymal phenotype from Mutant, Lean and Control respectively. Panels J, K & L and M, N & O represent the negative controls for PE (CD90/CD31) and FITC (CD29) fluorochromes respectively. Median Fluorescence Intensity (MFI) for CD90, CD29 and CD31 have been indicated in panel P and values have been represented as Mean ± SE (n = 6) from three independent experiments performed in duplicates for each phenotype. Values represented have been normalized against unstained controls for the fluorophore (PE/FITC).</p