Gene expression in diabetic nephropathy

Zerumbone, a tropical ginger sesquiterpene, ameliorates streptozotocin-induced diabetic nephropathy in rats by reducing the hyperglycemia-induced inflammatory response

Background

Zerumbone is one of the pungent constituents of Zingiber zerumbet (L) Smith (Zingiberaceae family). The aim of the present study was to examine the effects of zerumbone in rats with streptozotocin-induced diabetic nephropathy (DN).

Methods

Diabetic rats were treated orally with zerumbone (20 or 40 mg/kg/day) for 8 weeks. Changes in renal function-related parameters in plasma and urine were analyzed at the end of the study. Kidneys were isolated for pathology histology, immunohistochemistry, and Western blot analyses.

Results

Diabetic rats exhibited renal dysfunction, as evidenced by reduced creatinine clearance, increased blood glucose, blood urea nitrogen and proteinuria, along with marked elevation in the ratio of kidney weight to body weight, that were reversed by zerumbone. Zerumbone treatment was found to markedly improve histological architecture in the diabetic kidney. Hyperglycemia induced p38 mitogen-activated protein kinase activation, leading to increased infiltration of macrophages and increased levels of interleukin (IL)-1, IL-6 and tumor necrosis factor-α. All of the above abnormalities were reversed by zerumbone treatment, which also decreased the expression of intercellular adhesion molecule-1, monocyte chemoattractant protein-1, transforming growth factor-β1 and fibronectin in the diabetic kidneys.

Conclusions

The beneficial effect of zerumbone in rats with DN is at least in part through antihyperglycemia which was accompanied by inhibition of macrophage infiltration via reducing p38 mediated inflammatory response.

Isoangustone A suppresses mesangial fibrosis and inflammation in human renal mesangial cells

Development of diabetic nephropathy with fibrosis is associated with hypereglycemia-linked inflammation. Increased levels of proinflammatory factors have been found in diabetic patients with nephropathy. The present study was to test the hypothesis that isoangustone A, a novel compound present in licorice, can inhibit renal fibrosis and inflammation inflamed by high glucose (HG) in human mesangial cells through disturbing transforming growth factor β (TGF- β) and nuclear facor κB (NF- κB) pathways. Serum-starved mesangial cells were cultured in 33 mmol/L glucose media. Cells were treated with 1–20 μmol/L isoangustone A isolated from Glycyrrhiza uralensis licorice for three days. Exposure of cells to HG elevated connective tissue growth factor and collagen production, which was dose-dependently reversed by isoangustone A. Isoangustone A boosted HG-plummeted membrane type matrix metalloproteinase (MMP)-1 expression and diminished HG-elevated tissue inhibitor of MMP-2 expression. HG activated mesangial TGF- β1-SMAD-responsive signaling, which was repealed by ≥10 μmol/L isoangustone A. Furthermore, HG upregulated intracellular cell adhesion molecule-1 (ICAM-1) level and monocyte chemoattractant protein-1 (MCP-1) mRNA expression, and such increases were dose-dependently suppressed by isoangustone A most likely through hampering TGF- β signaling pathways. Blockade of NF- κB signaling appeared to be responsible for attenuating HG-triggered induction of ICAM-1 and MCP-1. Our findings provide the first evidence that isoangustone A dampens mesangial sclerosis associated with inflammation in response to HG through hindering TGF- β and NF- κB signaling.

Mislocalized scaffolding by the Na-H exchanger NHE1 dominantly inhibits fibronectin production and TGF-beta activation

Secretion and assembly of the extracellular matrix protein fibronectin regulates a number of normal cell and tissue functions and is dysregulated in disease states such as fibrosis, diabetes, and cancer. We found that mislocalized scaffolding by the plasma membrane Na-H exchanger NHE1 suppresses fibronectin expression, secretion, and assembly. In fibroblasts, wild-type NHE1 localizes to the distal margin of membrane protrusions or lamellipodia but a mutant NHE1-KRA2 lacking binding sites for PI(4,5)P2 and the ERM proteins ezrin, radixin, and moesin is mislocalized and found uniformly along the plasma membrane. Although NHE1 regulates intracellular pH homeostasis, fibronectin production is not regulated by changes in intracellular pH, nor is it attenuated in NHE1-deficient cells, indicating fibronectin expression is independent of NHE1 activity. However, fibronectin production is nearly absent in cells expressing NHE1-KRA2 because scaffolding by NHE1 is mislocalized. Additionally, secretion of active but not latent TGF-beta is reduced and exogenous TGF-beta restores fibronectin secretion and assembly. Our data indicate that scaffolding by NHE1-KRA2 dominantly suppresses fibronectin synthesis and TGF-beta activation, and they suggest that NHE1-KRA2 can be used for obtaining a mechanistic understanding of how fibronectin production is regulated and speculatively for therapeutic control of dysregulated production in pathological conditions.

17beta-Estradiol supplementation reduces tubulointerstitial fibrosis by increasing MMP activity in the diabetic kidney

We previously reported that supplementation with 17beta-estradiol (E2) attenuates albuminuria, glomerulosclerosis, and tubulointerstitial fibrosis in diabetic nephropathy. The present study examined the mechanisms by which E2 regulates extracellular matrix (ECM) metabolism, a process that contributes to the development of glomerulosclerosis and tubulointerstitial fibrosis. The study was performed in female nondiabetic (ND), streptozotocin-induced diabetic (D), and diabetic with E2 supplementation (D+E2) Sprague-Dawley rats for 12 wk. Diabetes was associated with an increase in the renal expression of collagen alpha type IV [ND, 0.22 +/- 0.02; D, 0.99 +/- 0.09 relative optical density (ROD); P < 0.05] and fibronectin protein (ND, 0.36 +/- 0.08; D, 1.47 +/- 0.08 ROD; P < 0.05), as measured by Western blot analysis. E2 supplementation partially attenuated this increase in collagen alpha type IV (D+E2, 0.47 +/- 0.10 ROD) and fibronectin (D+E2, 0.71 +/- 0.16 ROD) protein expression associated with D. Diabetes was also associated with a decrease in the expression of matrix metalloproteinase (MMP) isoform MMP-2 (ND, 0.79 +/- 0.01; D, 0.62 +/- 0.06 ROD; P < 0.05) and MMP-9 protein (ND, 0.49 +/- 0.02; D, 0.33 +/- 0.03 ROD; P < 0.05). E2 supplementation restored MMP-2 and MMP-9 protein to levels similar or even greater than in the ND kidneys (MMP-2, 0.75 +/- 0.06; MMP-9, 0.73 +/- 0.01 ROD). The activities of MMP-2 (ND, 7.88 +/- 0.44; D, 5.60 +/- 0.54 ROD; P < 0.05) and MMP-9 (ND, 29.9 +/- 1.8; D, 12.9 +/- 2.3 ROD; P < 0.05), as measured by zymography, were also decreased with D. E2 supplementation restored MMP-2 and MMP-9 activity to levels similar to that in ND kidneys (MMP-2, 7.66 +/- 0.35; MMP-9, 21.4 +/- 2.9 ROD). We conclude that E2 supplementation is renoprotective by attenuating glomerulosclerosis and tubulointerstitial fibrosis by reducing ECM synthesis and increasing ECM degradation.

SGK1-mediated Fibronectin Formation in Diabetic Nephropathy

The serum and glucocorticoid inducible kinase SGK1 has been shown to be up regulated in fibrosing tissue including diabetic nephropathy. The present study has been performed to determine the time course of SGK1 transcription in mouse kidneys following induction of diabetes by streptozotocin (STZ). Moreover, the study aimed to explore whether SGK1 may play an active role in the stimulation of matrix protein formation during hyperglycemia. The induction of diabetes in 8 weeks old male C57Bl/6 mice was indeed followed by a significant (p< 0.001) increase of SGK1 transcript levels (up to 2.5-fold) and protein abundance (up to 2.8-fold) both peaking 4 weeks after STZ treatment. The SGK1 transcript levels and protein abundance declined thereafter but remained significantly elevated up to 12 weeks (p<0.05). Exposure to high extracellular glucose concentration (25 mM) significantly increased SGK1 transcript levels in human mesangial cells (HMCs). At low extracellular glucose concentration (5.5 mM), transfection with constitutively active (S422D)SGK1 and transdominant inhibitory (K127N)SGK1 did not significantly modify fibronectin formation by HMCs. Exposure to high extracellular glucose concentration stimulated fibronectin formation (by 2.2 fold), an effect abrogated by transfection with inactive (K127N)SGK1 (1.2 fold) and markedly enhanced by transfection with (S422D)SGK1 (4.7 fold). In conclusion, hyperglycemia of diabetes mellitus leads to partially transient increase of SGK1 transcription and translation. SGK1 overexpression alone has little effect on fibronectin formation but potentiates the effect of hyperglycemia. Thus, SGK1 is upregulated in diabetic nephropathy and actively participates in the stimulation of matrix protein deposition in this common deleterious complication of diabetic hyperglycemia.

Carnosine as a protective factor in diabetic nephropathy: association with a leucine repeat of the carnosinase gene CNDP1

The risk of diabetic nephropathy is partially genetically determined. Diabetic nephropathy is linked to a gene locus on chromosome 18q22.3-q23. We aimed to identify the causative gene on chromosome 18 and to study the mechanism by which the product of this gene could be involved in the development of diabetic nephropathy. DNA polymorphisms were determined in 135 case (diabetic nephropathy) and 107 control (diabetes without nephropathy) subjects. The effect of carnosine on the production of extracellular matrix components and transforming growth factor-beta (TGF-beta) after exposure to 5 and 25 mmol/l d-glucose was studied in cultured human podocytes and mesangial cells, respectively. A trinucleotide repeat in exon 2 of the CNDP1 gene, coding for a leucine repeat in the leader peptide of the carnosinase-1 precursor, was associated with nephropathy. The shortest allelic form (CNDP1 Mannheim) was more common in the absence of nephropathy (P = 0.0028, odds ratio 2.56 [95% CI 1.36-4.84]) and was associated with lower serum carnosinase levels. Carnosine inhibited the increased production of fibronectin and collagen type VI in podocytes and the increased production of TGF-beta in mesangial cells induced by 25 mmol/l glucose. Diabetic patients with the CNDP1 Mannheim variant are less susceptible for nephropathy. Carnosine protects against the adverse effects of high glucose levels on renal cells.