Functional role of sodium glucose transporter in high glucose-mediated angiotensin type 1 receptor downregulation in human proximal tubule cells

Am J Physiol Renal Physiol. 2012 Sep;303(5):F766-74. doi: 10.1152/ajprenal.00651.2011. Epub 2012 May 30.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Cells, Cultured
  • Down-Regulation
  • Glucose / administration & dosage
  • Glucose / metabolism
  • Glucose Transport Proteins, Facilitative / metabolism
  • Humans
  • Hyperglycemia / metabolism
  • Kidney Tubules, Proximal / drug effects
  • Kidney Tubules, Proximal / metabolism*
  • Phloretin / pharmacology
  • Phlorhizin / pharmacology
  • Receptor, Angiotensin, Type 1 / genetics
  • Receptor, Angiotensin, Type 1 / metabolism*
  • Sodium-Glucose Transport Proteins / physiology*

Substances

  • AGTR1 protein, human
  • Glucose Transport Proteins, Facilitative
  • Receptor, Angiotensin, Type 1
  • Sodium-Glucose Transport Proteins
  • Phlorhizin
  • Glucose
  • Phloretin