Background: Signaling events associated with diabetic nephropathy are not well understood. Triangulation of events triggered by unrelated bioactive peptides nephrilin and anephril, both of which inhibit albuminuria in diabetic mice, could reveal a common subset of events associated with albuminuria.
Methods: db/db mice received 20 microg/day anephril or nephrilin for 7 weeks. Streptozotocin (STZ)-treated DBA/2J mice received 2 mg/kg nephrilin for 26 days. In both studies, urine albumin and creatinine, plasma glucose, and tissue proteins were measured by enzyme-linked immunosorbent assay (ELISA). In a safety study, DBA/2J mice received 20 mg/kg nephrilin for 26 days, and tissues from these mice were fixed in formalin for histological analysis. HEK293 human kidney cells were treated with glycated hemoglobin plus 20 microg/mL nephrilin or anephril for 24 h.
Results: Both peptides reduced albuminuria in db/db mice compared to saline-treated animals without affecting plasma glucose or insulin. In kidney tissues, the immunoreactivities of insulin receptor substrate-2 (IRS2), phosphorylated protein kinase C (p-PKC), and serum- and glucocortocoid-inducible kinase (SGK1) were reduced. Nephrilin, but not anephril, lowered elevated SGK1 in spleens of db/db mice. In STZ-pretreated DBA/2J mice, nephrilin reduced albuminuria and the accumulation of nuclear Rictor, IRS2, and p-PKC in the kidney. In cultured kidney cells, nephrilin disrupted the association of Rictor with IRS2 and nuclear compartmentalization. Histopathological examination of tissues from mice treated with 20 mg/kg nephrilin daily for 26 days showed no significant pathology compared to saline-treated controls.
Conclusions: We define a subset of signaling markers closely associated with albuminuria. Mammalian target of rapamycin complex 2 (mTORC2)::IRS complexes may play a role in the nuclear accumulation, and possible downstream transcriptional effects, of p-PKC. The activity and apparent safety of nephrilin in rodents suggest a novel intervention strategy for diabetic kidney disease.