Mesangial cells from diabetic NOD mice constitutively express increased density of atrial natriuretic peptide C receptors

Background. Experimental evidence shows that natriuretic peptides (NPs) pla y a pathophysiological role in the glomerular hemodynamic abnormalities tha t occur in diabetes mellitus. Methods. In this study, the cGMP response to NPs and the different subtypes of NP receptors were examined in mesangial cells derived from a genetic mo del of diabetes, the nonobese diabetic (NOD) mouse. Multiple mesangial cell lines were derived from diabetic (D-NOD) and nondiabetic (ND-NOD) adult mi ce and were studied at different passages. Results. cGMP accumulation after stimulation by atrial NP (ANP) or C-type N P (CNP) was markedly inhibited in D-NOD cells irrespective of the glucose c oncentration (6 or 20 mM) in the culture medium. In contrast, NP receptor d ensity measured from [I-125]-ANp saturation binding curves was 7.5 times gr eater in D-NOD than in ND-NOD cells. No change in K-D (200 pM in both cell lines) was observed. Competitive inhibition studies showed that 4-23 C-ANP, which is specific of clearance receptors (NPR-C), displaced 90% of the max imum fraction bound, suggesting the predominance of NPR-C in both cell line s. Further identification was obtained from RNase protection assay and reve rse transcription-polymerase chain reaction, which also demonstrated the hi gher expression of NPR-C mRNA in D-NOD cells. In contrast, NPR-A mRNA was n ot modified. Increased expression of NPR-C in D-NOD cells was associated wi th an increase of ANP internalization rate at 37 degrees C, indicating that these receptors were functional. Conclusions. These studies demonstrate that the constitutive overexpression of NPR-C in D-NOD mesangial cells is associated with a decreased response of cGMP to ANP or CNP treatment. This could be due to the lesser availabili ty of the peptides for binding to NPR-A or NPR-B or to an inhibitory effect on NP-dependent guanylate cyclase activity via the activation of NPR-C.