C-type natriuretic peptide as a podocyte hormone and modulation of its cGMP production by glucose and mechanical stress.
BACKGROUND
High glucose and mechanical strain resulting from capillary hypertension are relevant risk factors affecting glomerular cells in diabetes. Altered activity of the natriuretic peptide (NP) system acting via vasorelaxing cyclic guanosine 5' monophosphate (cGMP) has been proposed to be one of the reasons for diabetes-dependent impairment of kidney function. Podocytes possess the NP receptors (NPRs) coupled to particular guanylyl cyclase. We investigated whether mechanical stress and high ambient glucose influence cGMP generation in podocytes stimulated with NPs. Additionally, the C-type natriuretic peptide (CNP) system has been characterized in these cells.


METHODS
Conditionally immortalized mouse podocytes were stimulated with NP for 15 minutes and cGMP was determined by enzymatic immunoassay. The mRNA expression for CNP and CNP-specific NPR-B was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR). In addition, cGMP synthesis was measured in cells exposed to mechanical stress and to 30 mmol/L glucose for 3 days.


RESULTS
Production of cGMP upon stimulation of the NPR-B receptor with CNP and inhibition by an antagonist HS-142-1 was dose-dependent. RT-PCR showed that podocytes express mRNA not only for NPR-B but also for CNP. Mechanical stress reduced the cGMP response by 50%, both to atrial natriuretic peptide (ANP) and to CNP. Conversely, upon high glucose, the CNP-induced production of cGMP was elevated twofold in stretched and in control cells. Furthermore, as compared to ANP, stimulation with CNP caused a larger increase in cGMP levels in stretched as well as in nonstretched cells.


CONCLUSIONS
Expression of CNP together with potent NPR-B receptors suggests that in podocytes, CNP may act in an autocrine and/or paracrine manner. Furthermore, in a diabetic kidney, high glucose and mechanical stress may modulate the CNP-dependent cGMP production in podocytes in an opposite manner.
Department of Immunopathology, Medical University of Gdansk, Gdansk, Poland. blew@amedec.amg.gda.pl
Barbara
B
Lewko
Nicole
N
Endlich
Wilhelm
W
Kriz
Jan
J
Stepinski
Karlhans
K
Endlich
D000818:Animals; D009320:Atrial Natriuretic Factor / Q000494:pharmacology; D002461:Cell Line, Transformed / Q000187:drug effects; D006152:Cyclic GMP / Q000096:biosynthesis / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006162:Guanylate Cyclase / Q000235:genetics; D007678:Kidney Glomerulus / Q000166:cytology*; D051379:Mice; D045283:Natriuretic Agents / Q000494:pharmacology*; D020098:Natriuretic Peptide, C-Type / Q000235:genetics / Q000494:pharmacology*; D009599:Nitroprusside / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D017461:Receptors, Atrial Natriuretic Factor / Q000235:genetics; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D013314:Stress, Mechanical; D014665:Vasodilator Agents / Q000494:pharmacology; D000099242:Atrial Natriuretic Factor Receptor B
D009320:Atrial Natriuretic Factor; D006152:Cyclic GMP; D005947:Glucose; D006162:Guanylate Cyclase; D045283:Natriuretic Agents; D020098:Natriuretic Peptide, C-Type; D009599:Nitroprusside; D012333:RNA, Messenger; D017461:Receptors, Atrial Natriuretic Factor; D043562:Receptors, G-Protein-Coupled; D014665:Vasodilator Agents; D000099242:Atrial Natriuretic Factor Receptor B