High glucose up-regulates ENaC and SGK1 expression in HCD-cells.
OBJECTIVE
Diabetic nephropathy is associated with progressive renal damage, leading to impaired function and end-stage renal failure. Secondary hypertension stems from a deranged ability of cells within the kidney to resolve and appropriately regulate sodium resorption in response to hyperglycaemia. However, the mechanisms by which glucose alters sodium re-uptake have not been fully characterised.


METHODS
Here we present RT-PCR, western blot and immunocytochemistry data confirming mRNA and protein expression of the serum and glucocorticoid inducible kinase (SGK1) and the alpha conducting subunit of the epithelial sodium channel (ENaC) in a model in vitro system of the human cortical collecting duct (HCD). We examined changes in expression of these elements in response to glucose challenge, designed to mimic hyperglycaemia associated with type 2 diabetes mellitus. Changes in Na+ concentration were assessed using single-cell microfluorimetry.


RESULTS
Incubation with glucose, the Ca2+-ionophore ionomycin and the cytokine TGF-beta1 were all found to evoke significant and time-dependent increases in both SGK1 and alphaENaC protein expression. These molecular changes were correlated to an increase in Na+-uptake at the single-cell level.


CONCLUSIONS
Together these data offer a potential explanation for glucose-evoked Na+-resorption and a potential contributory role of SGK1 and ENaCs in development of secondary hypertension, commonly linked to diabetic nephropathy.
Hills
Claire E
CE
Molecular Physiology, Biomedical Research Institute, Department of Biological Sciences, University of Warwick, Coventry, UK.
Bland
Rosemary
R
Bennett
Jeanette
J
Ronco
Pierre M
PM
Squires
Paul E
PE
D015153:Blotting, Western; D002478:Cells, Cultured; D003920:Diabetes Mellitus / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D006943:Hyperglycemia / Q000209:etiology / Q000378:metabolism; D006973:Hypertension / Q000209:etiology; D017874:Immediate-Early Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D007685:Kidney Tubules, Collecting / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D000099184:Serum-Glucocorticoid Regulated Kinases
D053503:Epithelial Sodium Channels; D005947:Glucose; D017874:Immediate-Early Proteins; D015759:Ionomycin; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D012964:Sodium; D053773:Transforming Growth Factor beta1; D000099184:Serum-Glucocorticoid Regulated Kinases