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      Inhibition of mTOR activity in diabetes mellitus reduces proteinuria but not renal accumulation of hyaluronan

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          Abstract

          Objectives. Accumulation of extracellular matrix (ECM) components is an early sign of diabetic nephropathy. Also the glycosaminoglycan hyaluronan (HA) is elevated in the renal interstitium during experimental diabetes. The mammalian target of rapamycin (mTOR) pathway participates in the signaling of hyperglycemia-induced ECM accumulation in the kidney, but this has not yet been investigated for HA. We hypothesized that interstitial HA accumulation during diabetes may involve mTOR activation.

          Methods. Diabetic rats (6 weeks post-streptozotocin (STZ)) were treated with rapamycin to inhibit mTOR or vehicle for 2 additional weeks. Kidney function (glomerular filtration rate, renal blood flow, urine output) and regional renal HA content were thereafter analyzed. The ability of the animals to respond to desmopressin was also tested.

          Results. Diabetic animals displayed hyperglycemia, proteinuria, hyperfiltration, renal hypertrophy, increased diuresis with reduced urine osmolality, and reduced weight gain. Cortical and outer medullary HA was elevated in diabetic rats. Urine hyaluronidase activity was almost doubled in diabetic rats compared with controls. The ability to respond to desmopressin was absent in diabetic rats. Renal blood flow and arterial blood pressure were unaffected by the diabetic state. In diabetic rats treated with rapamycin the proteinuria was reduced by 32%, while all other parameters were unaffected.

          Conclusion. Regional renal accumulation of the ECM component HA is not sensitive to mTOR inhibition by rapamycin, while proteinuria is reduced in established STZ-induced diabetes. Whether the diabetes-induced renal accumulation of HA occurs through different pathways than other ECM components, or is irreversible after being established, remains to be shown.

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          Most cited references38

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          Nephropathy in diabetes.

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            Extracellular matrix metabolism in diabetic nephropathy.

            Diabetic nephropathy is characterized by excessive deposition of extracellular matrix proteins in the mesangium and basement membrane of the glomerulus and in the renal tubulointerstitium. This review summarizes the main changes in protein composition of the glomerular mesangium and basement membrane and the evidence that, in the mesangium, these are initiated by changes in glucose metabolism and the formation of advanced glycation end products. Both processes generate reactive oxygen species (ROS). The review includes discussion of how ROS may activate intracellular signaling pathways leading to the activation of redox-sensitive transcription factors. This in turn leads to change in the expression of genes encoding extracellular matrix proteins and the protease systems responsible for their turnover.
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              Hyaluronan.

              Hyaluronan (hyaluronic acid) is a high-molecular-mass polysaccharide found in the extracellular matrix, especially of soft connective tissues. It is synthesized in the plasma membrane of fibroblasts and other cells by addition of sugars to the reducing end of the polymer, whereas the nonreducing end protrudes into the pericellular space. The polysaccharide is catabolized locally or carried by lymph to lymph nodes or the general circulation, from where it is cleared by the endothelial cells of the liver sinusoids. The overall turnover rate is surprisingly rapid for a connective tissue matrix component (t1/2 0.5 to a few days). Hyaluronan has been assigned various physiological functions in the intercellular matrix, e.g., in water and plasma protein homeostasis. Hyaluronan production increases in proliferating cells and the polymer may play a role in mitosis. Extensive hyaluronidase-sensitive coats have been identified around mesenchymal cells. They are either anchored firmly in the plasma membrane or bound via hyaluronan-specific binding proteins (receptors). Such receptors have now been identified on many different cells, e.g., the lymphocyte homing receptor CD 44. Interaction between a hyaluronan receptor and extracellular polysaccharide has been connected with locomotion and cell migration. Hyaluronan seems to play an important role during development and differentiation and has other cell regulatory activities. Hyaluronan has also been recognized in clinical medicine. A concentrated solution of hyaluronan (10 mg/ml) has, through its tissue protective and rheological properties, become a device in ophthalmic surgery. Analysis of serum hyaluronan is promising in the diagnosis of liver disease and various inflammatory conditions, e.g., rheumatoid arthritis. Interstitial edema caused by accumulation of hyaluronan may cause dysfunction in various organs.
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                Author and article information

                Journal
                Ups J Med Sci
                Ups. J. Med. Sci
                IUPS
                Upsala Journal of Medical Sciences
                Informa Healthcare
                0300-9734
                2000-1967
                November, 2015
                : 120
                : 4
                : 233-240
                Affiliations
                [1 ]Division of Integrative Physiology, Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden
                [2 ]Department of Medical and Health Sciences, Linköping University, Linköping, Sweden
                [3 ]Faculty of Pharmaceutical Sciences, Hoshi University, Tokyo, Japan
                Author notes
                Correspondence: Peter Hansell, Division of Integrative Physiology, Department of Medical Cell Biology, BMC, PO Box 571, SE-751 23 Uppsala, Sweden. peter.hansell@ 123456mcb.uu.se
                Article
                iups-120-233
                10.3109/03009734.2015.1062442
                4816883
                26175092
                7a36a453-03bc-4b8e-87b5-52eb4eb090ce
                © Informa Healthcare 2015

                This is an open-access article distributed under the terms of the CC-BY-NC-ND 3.0 License which permits users to download and share the article for non-commercial purposes, so long as the article is reproduced in the whole without changes, and provided the original source is credited.

                History
                : Received on April 07, 2015
                : Accepted on June 10, 2015
                Categories
                Original Articles

                Medicine
                diabetes mellitus,hyaluronan,hyaluronidase,mtor,nephropathy,rapamycin
                Medicine
                diabetes mellitus, hyaluronan, hyaluronidase, mtor, nephropathy, rapamycin

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