Lifelong prevention of mesangial enlargement by whole pancreas transplantation in rats with diabetes mellitus

Renal sympathetic nervous system hyperactivity in early streptozotocin-induced diabetic kidney disease

AIM

We assessed the role of renal sympathetic nervous system in the deterioration of renal hemodynamic and excretory functions in rats with streptozotocin (STZ)-induced diabetic kidney disease (DKD).

METHODS

Male Sprague-Dawley (SD) rats were induced with diabetes mellitus (DM) using STZ (55 mg/kg, i.p.). The acute studies were conducted on denervated anesthetized rats 7 days after STZ administration. Two sets of experiments were performed: clearance experiments in which six 20-min urine and plasma collections were carried out to measure kidney function parameters, and hemodynamic experiments in which the renal nerves were electrically stimulated and responses in renal vascular resistance (RVR) and renal blood flow (RBF) were recorded.

RESULTS

Renal denervation in STZ-induced diabetic rats produced higher fractional excretion of sodium (FE(Na) ) but lower plasma sodium (P(Na) ), glomerular filtration rate (GFR), and plasma creatinine (P(Cr) ) (all P<0.05 vs. innervated diabetic rats). In innervated diabetic rats, renal nerve stimulation (RNS) caused significant attenuation in the renal vasoconstrictor responses (all P<0.05 vs. innervated control). Renal denervation in diabetic rats significantly blunted these responses (all P<0.05 vs. innervated diabetic rats); however, they were significantly higher (all P<0.05) while compared to denervated control counterparts.

CONCLUSIONS

The data demonstrate an early role for the renal sympathetic innervation in the pathogenesis of DKD. If the kidney is prevented from renal sympathetic nerve action renal functional parameters are markedly improved. The data further suggest an early enhancement in renal sensitivity to intrarenal norepinephrine (NE) upon the removal of renal sympathetic tone in STZ-induced diabetic rats.

Initial characterization of a rat model of diabetic nephropathy

The lack of an appropriate animal model that spontaneously develops diabetic nephropathy has been a significant limitation in the search for genetic factors underlying this disease and the development of new therapeutic strategies to prevent progressive renal disease in diabetes. We introgressed the mitochondria and some passenger loci from the FHH/EurMcwi rat into the genetic background of diabetic GK rats, creating a new rat strain, T2DN (T2DN/Mcwi). Despite the high degree of genetic similarity between T2DN and GK rats (97% at 681 loci), diabetes ensues earlier and progresses more severely in T2DN rats. T2DN rats exhibit proteinuria by 6 months of age, accompanied by renal histologic abnormalities such as focal glomerulosclerosis, mesangial matrix expansion, and thickening of basement membranes. These characteristics progress over time, and nearly all T2DN rats exhibit diffuse global glomerulosclerosis with nodule formation and arteriolar hyalinosis by 18 months of age. The histologic changes in the kidney of T2DN rats closely mimic the changes seen in the kidney of patients with diabetes. These results indicate that the T2DN rat is a suitable model for investigating diabetic nephropathy. Here we report the initial genetic and physiological characterization of this new rat model of diabetic nephropathy.

Reversibility of established diabetic glomerulopathy by anti-TGF-beta antibodies in db/db mice

Treatment with a neutralizing anti-transforming growth factor-beta (TGF-beta) antibody can prevent the development of diabetic nephropathy in the db/db mouse, a model of type 2 diabetes. However, it is unknown whether anti-TGF-beta therapy can reverse the histological lesions of diabetic glomerulopathy once they are established. Diabetic db/db mice and their non-diabetic db/m littermates were allowed to grow until 16 weeks of age, by which time the db/db mice had developed glomerular basement membrane (GBM) thickening and mesangial matrix expansion. The mice were then treated with an irrelevant control IgG or a panselective, neutralizing anti-TGF-beta antibody for eight more weeks. Compared with control db/m mice, the db/db mice treated with IgG had developed increased GBM width (16.64+/-0.80 nm vs. 21.55+/-0.78 nm, P<0.05) and increased mesangial matrix fraction (4.01+/-0.81% of total glomerular area vs. 9.55+/-1.04%, P<0.05). However, the db/db mice treated with anti-TGF-beta antibody showed amelioration of GBM thickening (18.40+/-0.72 nm, P<0.05 vs. db/db-IgG) and mesangial matrix accumulation (6.32+/-1.79%, P<0.05 vs. db/db-IgG). Our results demonstrate that inhibiting renal TGF-beta activity can partially reverse the GBM thickening and mesangial matrix expansion in this mouse model of type 2 diabetes. Anti-TGF-beta regimens would be useful in the treatment of diabetic nephropathy.