Purpose Chronic kidney disease and progression to end-stage renal disease (ESRD) impose a significant burden on the health care system. Diabetic nephropathy (DN) accounts for a staggering 45% of all ESRD cases. As the number of individuals with diagnosed diabetes age ≥ 20 years is expected to reach 39 million in 2050, the number of diabetes-related ESRD cases is expected to dramatically rise. Unfortunately, current management can delay but not cure DN. Integrins and their corresponding matrix proteins are increased in DN. We used an Arg-Gly-Asp (RGD)-containing peptide to inhibit integrin function in vitro and examined its effect in diabetic db/db mice.
Method Using adhesion cell assays, we inhibited mesangial cell (MC) integrin attachment to fibronectin (FN) by blocking the α5β1-integrin receptor with an RGD hexapeptide in vitro. We customized the peptide by cyclization (cRGD; to enhance its bioavailability) and tested its effect in vivo in diabetic db/db mice by intraperitoneal administration 3MULT/week, since the db/db mouse is the best-accepted and characterized model of progressive human DN. Plasma glucose and systolic blood pressure were measured. Animals were placed in metabolic cages for 24 h urine collection. The right kidney was removed for periodic acid-Schiff staining, Western blot analysis, and immunostaining, and the left kidney was perfused, processed, and embedded for morphometric analysis of electron microscopy images. Primary rat mesangial cells were treated or pretreated with the RGD peptide or PD98059 and used in Western blot analysis for mitogen-activated protein kinase (MAPK) signal transduction.
Results Compared to untreated and cRGE-inactive peptide (which has a single amino acid change in the RGD recognition site)-treated diabetic mice and treated and untreated nondiabetic db/m mice, the cRGD peptide prevented the development of DN as determined by improved increased fractional volume of the mesangium, MC and mesangial matrix, as well as albuminuria. There was no effect on GBM widening. These findings were independent of alterations in plasma glucose or blood pressure and were accompanied by decreased expression of α5,β1 integrin, FN, collagen I and collagen IV matrix proteins. RGD peptide inhibited MC adhesion-induced MAPK signal transduction.
Conclusion These studies suggest that specifically targeting integrin function with a customized cRGD peptide is an innovative treatment of DN in db/db mice, which could potentially ameliorate or prevent DN in humans.