Angiogenesis and Expression of IGF2R, IGF2, uPAR, and TGFB in a Rat Obesity Model

Abstract

IntroductionOur group has previously shown that obesity decreases capillary density in skeletal muscle. Here, we tested the hypothesis that decreased capillary density in obesity is the result of increased activity of the insulin growth factor II receptor (IGF2R) in degrading urokinase‐plasminogen receptor (uPAR), activating transforming growth factor beta (TGFB), and degrading insulin growth factor II (IGF2) using an obese, diabetic rat model.MethodsAt four weeks of age, normophagic Long‐Evans Tokyushima Otsuka (LETO; n=20) and hyperphagic Otsuka Long‐Evans Tokushima Fatty (OLETF; n=20) rats were provided with either a normal, low‐fat diet (LFD, 10% kcal fat) or a high‐fat, high‐cholesterol diet (HFD, 45%kcal fat with 1% cholesterol). At 32 weeks of age, samples from rats were taken, including biceps brachii and vastus lateralis muscle, and arterial vessels. Whole tissue muscle samples were snapfrozen and cold sectioned. Slides were stained for IHC highlighting of capillaries, with manual counting of capillaries and muscle fibers in cross‐section. Vessels were homogenized in buffer and processed by way of Western blot procedure, with membranes probed for IGF2R, IGF2, TGFB, and uPAR.ResultsCapillary density in biceps brachii was reduced in OLETF LFD rats (p<0.07) compared to LETO LFD rats, but HFD increased capillary density significantly relative to LFD counterpart, especially in OLETF rats (19%, p<0.01). In addition, vastus lateralis IHC indicated a significant decrease in capillary density in OLETF LFD/HFD and LETO HFD relative to LETO LFD (p<0.05). Western blot analysis of arterial vessel samples did not indicate any significant difference in IGF2R, IGF2, TGFB, or uPAR between LETO LFD and other groups.DiscussionThese data demonstrate that capillary density is significantly downregulated in obese, type 2 diabetic OLETF rats. However, examination of arterial samples suggest that changes may not be related to changes in expression of IGF2R and associated proposed down‐regulators of vascular growth in the arterial vasculature. To complete the test of our hypothesis we will measure IGF2R, uPAR, IGF2, and TGFB expression in muscle tissue to determine whether changes in expression occur in the muscle that may mediate changes in capillarity in obesity/diabetes.Support or Funding InformationWe Acknowledge Support of this research: NIH HL36088(MHL), VHA CDA2 1BX001299 (RSR), Society of Phi Zeta, and the University of Missouri Department of Medical Pharmacology and Physiology.