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2016 Research Showcase
ST Abstracts
Abstract Title : Effects of Aldose Reductase Inhibition on Markers of Diabetic Neuropathy in Mice
Abstract : The polyol pathway is a key target for the prevention and reversal of diabetic neuropathy (1). The first step involves conversion of glucose into sorbitol by aldose reductase and can be inhibited by a variety of drugs termed aldose reductase inhibitors (ARI's). This study tested the effects of an ARI, sorbinil, on neuropathy in control and diabetic mice. Our goal was to determine whether this dose of sorbinil (200mg/kg/day by oral gavage) could prevent onset of a new and clinically relevant measures of peripheral neuropathy, namely paw skin intra-epidermal nerve fiber (IENF) density. Type 1 diabetes was induced by the pancreatic beta cell toxin streptozotocin (90 mg/kg IP on 2 consecutive days). The physiological endpoints studied were motor and sensory nerve conduction velocity (MNCV and SNCV) and behavioral responses to light touch and noxious heat. These endpoints were measured at weeks 4, 8, and 12. Foot skin was collected at the end of the study for histological analysis of IENF. Diabetes caused reduced body weight and increased blood glucose levels in mice. These indices of diabetes were not altered by ARI treatment indicating that the drug did not cure diabetes per se. Previous studies have established the efficacy of ARI treatment against NCV slowing in diabetic rats (2). These measurements served as positive drug efficacy controls and we confirmed the effectiveness of sorbinil treatment. A previous study also found that ARI treatment was not effective against tactile allodynia in diabetic rats (2) and we found a similar lack of efficacy in diabetic mice. We anticipated that ARI treatment would prevent loss of paw thermal sensation in diabetic mice, as this has been reported in diabetic rats (3). However, sorbinil was without effect on this thermal hypoalgesia in diabetic mice. This could reflect differences between the specific species or ARI drug used. Measurement of IENF density in the footskin, representing the small sensory fibers that detect heat, will be important for interpreting this finding, as prior studies have shown a decrease in IENF density in diabetic mice (4). The effects of ARI treatment on IENF density in diabetes are unknown and these measurements are in progress. We can conclude that sorbinil treatment of diabetic mice was effective on some aspects of peripheral neuropathy such as large fiber conduction slowing but not on a measure of large fiber mediated pain (tactile allodynia) or loss of small fiber mediated heat sensation. References: 1. Oates, Peter J. (2008). Aldose Reductase: Still a Compelling Target for Diabetic Neuropathy. Current Drug Targets, 9, 14-36. 2. Calcutt, N.A., Jorge, M.C., Yaksh, T.L. & Chaplan, S.R. (1996). Tactile allodynia and formalin hyperalgesia in streptozotocin-diabetic rats: effects of insulin, aldose reductase inhibition, and lidocaine. Pain, 68, 293-299. 3. Calcutt NA, Freshwater JD, Mizisin AP. (2004). Prevention of sensory disorders in diabetic Sprague Dawley rats by aldose reductase inhibition or treatment with ciliary neurotrophic factor. Diabetologia, 47, 718-724. 4. Beiswenger KK, Calcutt NA, Mizisin AP. (2008). Dissociation of thermal hypoalgesia and epidermal denervation in streptozotocin-diabetic mice. Neurosci Lett, 442, 267-272.
Abstract Title : The Role of mLST8 in mTOR Signal Transduction
Abstract : The mechanistic target of rapamycin (mTOR) is a protein kinase that regulates cellular growth and proliferation. In mammals, mTOR exists in two complexes: mTORC1 and mTORC2. Both complexes contain the protein LST8, but the function of LST8 in the mTOR complex is unknown. Previous studies have shown that the level of Hsp 70 associated to mTOR increases when bound LST8 levels decreases. Furthermore, attempts to use deuterium exchange mass spectrometry (DXMS) to analyze the structure mTOR without LST8 associated were unsuccessful. This suggested that LST8 is necessary for mTOR folding and kinase activity. By performing in vitro mTOR kinase reactions, we found that LST8 association increases mTOR phosphorylation activity. These results demonstrate that LST8 plays a positive role in modulating mTOR signaling. Perhaps, LST8 may be a possible cancer therapy drug target in attacking tumorigenesis.
Abstract Title : The Effect of PHLPP2 Removal on Cell Survival and Signaling in the Brain and in Astrocytes
Abstract : A newly found serine/threonine phosphatase PHLPP can directly dephosphorylate several members of the AGC family of kinases, including Akt. There are two isoforms of PHLPP: PHLPP1 and PHLPP2. Our lab has demonstrated that removal of PHLPP1 in astrocytes increases Akt activity leading to protection from ischemic damage. However the role of PHLPP2 is unknown. Astrocytes have been isolated from global PHLPP2 knockout (KO) mice and cell death and the activation of signaling pathways following different stressors have been analyzed. Remarkably, cellular viability was higher in KO than wild-type astrocytes following metabolic stress and simulated ischemia, however Akt activity was unaltered. Thus, deletion of PHLPP2 seems to increase cell survival following stress; however its target is unknown. We will continue to investigate the protective effect of PHLPP2 deletion and the inflammatory response following wound injury in wild-type and KO astrocytes. Findings will help identify new therapeutic targets for protection following brain injury.
Abstract Title : Protection of Leptin Resistance from Fertility-Altering Neuronal PPARγ
Abstract : Activation of the nuclear receptor peroxisome proliferator-activated receptor gamma attenuates susceptibility to diabetes. Thiazolidinediones (TZD) are a class of drugs that are used to activate PPARγ improving lipid synthesis and the metabolism of carbohydrates which benefits patients with diabetes mellitus type 2. Evidence suggests that PPARγ is involved in signaling within the central nervous system and partake in the process of energy intake and storage which are key components in energy homeostasis and glucose metabolism. Our investigation focuses on the neuronal PPARγ's affects on reproductive hormones and whether PPARγ is involved in obesity-induced reproductive defects. Our studies indicate that neuronal PPARγ induces weight gain by introducing a high-fat diet and causes diet-induced obesity by analyzing genes from the cytochrome P450 superfamily of enzymes, steroid hormone regulators, and genes responsible for the biosynthesis of hormonal steroids. Further evidence indicate that the deletion of PPARγ causes ovarian complications such as fertility and estrous cycle impairment due to longer estrous cycles with lower serum follicle stimulating hormones. To further supplement these findings, influential steroid hormone regulators and cholesterol, lipid, steroid enzymes were analyzed. Female PPARγ knockouts were recorded to have an elevated pituitary luteinizing hormone beta polypeptide mRNA expression and at the gonadal steroids level, estradiol was seen to be higher as testosterone is lower in PPARγ deleted mice when introduced with a luteinizing hormone surge. These findings present that neuronal PPARγ is crucial for normal female fertility but also detrimental for its effects from diet-induced obesity on estrous cycles because of leptin resistance.