Impact de l’insuffisance rénale chronique sur les transporteurs de glucose et les effets subséquents sur la résistance à l’insuline

Parmi l’ensemble des désordres métaboliques retrouvés en insuffisance rénale chronique (IRC), la résistance à l’insuline demeure l’un des plus importantes à considérer en raison des risques de morbidité et de mortalité qu’elle engendre via les complications cardiovasculaires. Peu d’études ont considéré la modulation de transporteurs de glucose comme mécanisme sous-jacent à l’apparition et à la progression de la résistance à l’insuline en IRC. Nous avons exploré cette hypothèse en étudiant l’expression de transporteurs de glucose issus d’organes impliqués dans son homéostasie (muscles, tissus adipeux, foie et reins) via l’utilisation d’un modèle animal d’IRC (néphrectomie 5/6e). La sensibilité à l’insuline a été déterminée par un test de tolérance au glucose (GTT), où les résultats reflètent une intolérance au glucose et une hyperinsulinémie, et par les études de transport au niveau musculaire qui témoignent d’une diminution du métabolisme du glucose en IRC (~31%; p<0,05). La diminution significative du GLUT4 dans les tissus périphériques (~40%; p<0,001) peut être à l’origine de la résistance à l’insuline en IRC. De plus, l’augmentation de l’expression protéique de la majorité des transporteurs de glucose (SGLT1, SGLT2, GLUT1; p<0,05) au niveau rénal en IRC engendre une plus grande réabsorption de glucose dont l’hyperglycémie subséquente favorise une diminution du GLUT4 exacerbant ainsi la résistance à l’insuline. L’élévation des niveaux protéiques de GLUT1 et GLUT2 au niveau hépatique témoigne d’un défaut homéostatique du glucose en IRC. Les résultats jusqu’ici démontrent que la modulation de l’expression des transporteurs de glucose peut être à l’origine de la résistance à l’insuline en IRC. L’impact de la parathyroïdectomie (PTX) sur l’expression du GLUT4 a été étudié étant donné que la PTX pourrait corriger l’intolérance au glucose en IRC. Nos résultats démontrent une amélioration de l’intolérance au glucose pouvant être attribuable à la moins grande réduction de l’expression protéique du GLUT4 dans les tissus périphériques et ce malgré la présence d’IRC. L’excès de PTH, secondaire à l’hyperparathyroïdie, pourrait alors être à l’origine de la résistance à l’insuline en IRC en affectant l’expression du GLUT4. L’IRC partage de nombreuses similitudes avec le prédiabète quant aux défaillances du métabolisme du glucose tout comme l’hyperinsulinémie et l’intolérance au glucose. Aucune étude n’a tenté d’évaluer si l’IRC pouvait ultimement mener au diabète. Nos résultats ont par ailleurs démontré que l’induction d’une IRC sur un modèle animal prédisposé (rats Zucker) engendrait une accentuation de leur intolérance au glucose tel que constaté par les plus hautes glycémies atteintes lors du GTT. De plus, certains d’entre eux avaient des glycémies à jeun dont les valeurs surpassent les 25 mmol/L. Il est alors possible que l’IRC puisse mener au diabète via l’évolution de la résistance à l’insuline par l’aggravation de l’intolérance au glucose.Of all metabolic disorders found in chronic renal failure (CRF), insulin resistance remains one of the most important to consider because of the risk of morbidity and mortality it causes via cardiovascular complications. Few studies have considered the modulation of glucose transporters as the mechanism underlying the emergence and progression of insulin resistance in CRF. We explored this hypothesis by studying the expression of glucose transporters from organs involved in its homeostasis (muscle , fat , liver and kidneys) through the use of an animal model reflecting CRF (5/6th nephrectomy). The insulin sensitivity was determined by a glucose tolerance test (GTT), where the results reflect glucose intolerance and hyperinsulinemia , and transport studies in muscle show a decrease in glucose uptake in CRF ratss (~31% , p<0.05). The significant decrease in GLUT4 in peripheral tissues (~40%, p<0.001) may be the cause of insulin resistance in CRF. Furthermore, increased protein expression of the majority of glucose transporters (SGLT1, SGLT2, GLUT1, p<0.05) within the kidney in CRF causes greater glucose reabsorption in which consequential hyperglycemia promotes a decrease in GLUT4 thus exacerbating insulin resistance. Elevated protein levels of GLUT1 and GLUT2 in the liver reflects an impaired glucose homeostasis in CRF. The results show that the modulation of the expression of glucose transporters may be responsible for insulin resistance in CRF. The impact of parathyroidectomy (PTX) on the expression of GLUT4 was studied since PTX is known to correct glucose intolerance in CRF. Our results show an improvement in glucose intolerance which may be due to less reduction of GLUT4 protein expression in peripheral tissues despite the presence of CRF. The excess of PTH, linked to secondary hyperparathyroidism, could be held responsible to the presence of insulin resistance in CRF by affectant GLUT4 expression. CRF shares many similarities with prediabetes in regards to impaired glucose metabolism such as hyperinsulinemia and glucose intolerance. No studies have attempted to assess whether CRF could lead to diabetes. Our results demonstrated that the induction of CRF in a predisposed animal model (Zucker rats) provoked greater glucose intolerance as evidenced by the highest blood glucose levels reached in the GTT. In addition, some of them had fasting blood glucose levels whose values exceeded 25 mmol/L. It is therefore possible that CRF can lead to diabetes through the evolution of insulin resistance by the worsening of glucose intolerance

Mechanism of insulin resistance in a rat model of kidney disease and the risk of developing type 2 diabetes.

International audienceChronic kidney disease is associated with homeostatic imbalances such as insulin resistance. However, the underlying mechanisms leading to these imbalances and whether they promote the development of type 2 diabetes is unknown. The effect of chronic kidney disease on insulin resistance was studied on two different rat strains. First, in a 5/6th nephrectomised Sprague-Dawley rat model of chronic kidney disease, we observed a correlation between the severity of chronic kidney disease and hyperglycemia as evaluated by serum fructosamine levels (p<0.0001). Further, glucose tolerance tests indicated an increase of 25% in glycemia in chronic kidney disease rats (p<0.0001) as compared to controls whereas insulin levels remained unchanged. We also observed modulation of glucose transporters expression in several tissues such as the liver (decrease of ≈40%, p≤0.01) and muscles (decrease of ≈29%, p≤0.05). Despite a significant reduction of ≈37% in insulin-dependent glucose uptake in the muscles of chronic kidney disease rats (p<0.0001), the development of type 2 diabetes was never observed. Second, in a rat model of metabolic syndrome (Zucker Leprfa/fa), chronic kidney disease caused a 50% increased fasting hyperglycemia (p<0.0001) and an exacerbated glycemic response (p<0.0001) during glucose challenge. Similar modulations of glucose transporters expression and glucose uptake were observed in the two models. However, 30% (p<0.05) of chronic kidney disease Zucker rats developed characteristics of type 2 diabetes. Thus, our results suggest that downregulation of GLUT4 in skeletal muscle may be associated with insulin resistance in chronic kidney disease and could lead to type 2 diabetes in predisposed animals

Glucose and insulin responses to an intraperitoneal glucose tolerance test.

<p><b>(A)</b> Glucose and <b>(B)</b> Insulin responses to an intraperitoneal glucose tolerance test (2g/kg) performed on SD rats at Day 28 following a 16 hours fast. <b>(C)</b> Glucose and <b>(D)</b> Insulin responses to an intraperitoneal glucose tolerance test (1.5g/kg) performed on Zucker Lepr^fa/fa rats at Day 28 following a 16 hour fast. Values are mean ± S.D. n = 10 for each group. *, p<0.05; **, p<0.01; ***, p<0.001; ****, p<0.0001 as compared to CTL rats. Area under the curve is presented as percentage of controls, on the right corner of each graph.</p

Glucose transporters protein expression in selected organs of CKD rats.

<p>Protein levels are expressed in densitometry units. The densitometry units measured for glucose transporters were normalized to their respective loading control (β-actin: liver; GAPDH: muscles and adipose tissues; villin-1: kidneys) values. The normalized densitometry units of control rats were arbitrarily defined as 100%. The graph shows the mean expression in CKD rats expressed as percentage of CTL ± S.D of at least 5 rats in each group. *, p<0.05; **, p<0.01; ***, p<0.001; ****, p<0.0001 as compared to CTL rats. Protein levels of glucose transporters in the <b>(A)</b> Kidneys and liver of SD rats, <b>(B)</b> Skeletal muscle and white adipose tissue of SD rats. <b>(C)</b>. Skeletal muscle and white adipose tissue in Zucker Lepr^fa/fa rats. <b>(D)</b>. Representative Western blots for each glucose transporter. Each blot contains examples of three CKD (left) and three CTL (right) SD rats. Measurements at Day 42.</p

Time of glycosuria apparition in Zucker Lepr^fa/fa rats.

<p>The graph shows the proportion of rats with glycosuria as confirmed by a positive Diastix^™ (Bayer) test on two consecutive days for 15 Zucker Lepr^fa/fa rats per group.</p

Biochemical parameters and body weight of CTL and CKD SD rats at Day 21.

<p>Biochemical parameters and body weight of CTL and CKD SD rats at Day 21.</p

<i>Ex vivo</i> accumulation of radio-labeled 2-deoxyglucose in muscles.

<p>Uptake of radio-labeled 2-deoxyglucose in CTL and CKD rat muscles expressed as insulin response vs. basal condition. Basal condition of each muscle was arbitrarily defined as 1,0. Data are expressed as fold increase (mean) ± S.D for at least 5 rats per group. ***, p<0.001; ****, p<0.0001 as compared to CTL rats. <b>(A)</b> Sprague-Dawley rats and <b>(B)</b> Zucker Lepr^fa/fa rats. Measurements at Day 42.</p

Correlation between serum fructosamine and creatinine in CTL and CKD rats.

<p>Fructosamine concentration expressed as a ratio of fructosamine reported on total protein content in serum, versus creatininemia of <b>(A)</b> n = 26 SD rats and <b>(B)</b> n = 37 Zucker Lepr^fa/fa rats. Measurements at Day 21.</p

Glucose transporters mRNA expression in selected organs of CKD rats.

<p>mRNA encoding glucose transporters in CTL and CKD rats in the indicated tissues were measured by quantitative Real-Time PCR. mRNA levels are expressed in relative quantities and calculated using the ΔΔCT method [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0176650#pone.0176650.ref033" target="_blank">33</a>] with their respective housekeeping gene (Villin-1 for kidneys, β-actin for liver and GAPDH for muscles and adipose tissues). Data was normalized to the mean relative quantity of each gene in CTL rats. The graph shows the mean expression in CKD rats expressed as a percentage of controls ± S.D. of at least 10 rats in each group. *, p<0.05; **, p<0.01; ***, p<0.001; ****, p<0.0001 as compared to CTL rats. <b>(A)</b> Glucose transporters mRNA expression in the kidney and liver of SD rats. <b>(B)</b> GLUT1 and GLUT4 mRNA expression in skeletal muscle and white adipose tissue of SD rats. <b>(C)</b> GLUT1 and GLUT4 mRNA expression in skeletal muscle and white adipose tissue of Zucker Lepr^fa/fa rats. Measurements at Day 42.</p