Functional role of sodium glucose transporter in high glucose-mediated angiotensin type 1 receptor downregulation in human proximal tubule cells.
Previously, we have demonstrated human angiotensin type 1 receptor (hAT(1)R) promoter architecture with regard to the effect of high glucose (25 mM)-mediated transcriptional repression in human proximal tubule epithelial cells (hPTEC; Thomas BE, Thekkumkara TJ. Mol Biol Cell 15: 4347-4355, 2004). In the present study, we investigated the role of glucose transporters in high glucose-mediated hAT(1)R repression in primary hPTEC. Cells were exposed to normal glucose (5.5 mM) and high glucose (25 mM), followed by determination of hyperglycemia-mediated changes in receptor expression and glucose transporter activity. Exposure of cells to high glucose resulted in downregulation of ANG II binding (4,034 ± 163.3 to 1,360 ± 154.3 dpm/mg protein) and hAT(1)R mRNA expression (reduced 60.6 ± 4.643%) at 48 h. Under similar conditions, we observed a significant increase in glucose uptake (influx) in cells exposed to hyperglycemia. Our data indicated that the magnitude of glucose influx is concentration and time dependent. In euglycemic cells, inhibiting sodium-glucose cotransporters (SGLTs) with phlorizin and facilitative glucose transporters (GLUTs) with phloretin decreased glucose influx by 28.57 ± 0.9123 and 54.33 ± 1.202%, respectively. However, inhibiting SGLTs in cells under hyperglycemic conditions decreased glucose influx by 53.67 ± 2.906%, while GLUT-mediated glucose uptake remained unaltered (57.67 ± 3.180%). Furthermore, pretreating cells with an SGLT inhibitor reversed high glucose-mediated downregulation of the hAT(1)R, suggesting an involvement of SGLT in high glucose-mediated hAT(1)R repression. Our results suggest that in hPTEC, hyperglycemia-induced hAT(1)R downregulation is largely mediated through SGLT-dependent glucose influx. As ANG II is an important modulator of hPTEC transcellular sodium reabsorption and function, glucose-mediated changes in hAT(1)R gene expression may participate in the pathogenesis of diabetic renal disease.
Department of Biomedical Sciences, Texas Tech University Health Sciences Center,1300 Coulter Dr., Amarillo, TX 79106, USA.
Rekha
R
Yesudas
Russell
R
Snyder
Thomas
T
Abbruscato
Thomas
T
Thekkumkara
D002478:Cells, Cultured; D015536:Down-Regulation; D005947:Glucose / Q000008:administration & dosage / Q000378:metabolism; D051246:Glucose Transport Proteins, Facilitative / Q000378:metabolism; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D010693:Phloretin / Q000494:pharmacology; D010695:Phlorhizin / Q000494:pharmacology; D044140:Receptor, Angiotensin, Type 1 / Q000235:genetics / Q000378:metabolism*; D051247:Sodium-Glucose Transport Proteins / Q000502:physiology*
C544065:AGTR1 protein, human; D051246:Glucose Transport Proteins, Facilitative; D044140:Receptor, Angiotensin, Type 1; D051247:Sodium-Glucose Transport Proteins; D010695:Phlorhizin; D005947:Glucose; D010693:Phloretin