PLASMINOGEN ACTIVATOR INHIBITOR-1 AND TISSUE-TYPE PLASMINOGEN ACTIVATOR ARE UP-REGULATED DURING UNILATERAL URETERAL OBSTRUCTION IN ADULT RATS

Early systemic microvascular damage in pigs with atherogenic diabetes mellitus coincides with renal angiopoietin dysbalance

Background

Diabetes mellitus (DM) is associated with a range of microvascular complications including diabetic nephropathy (DN). Microvascular abnormalities in the kidneys are common histopathologic findings in DN, which represent one manifestation of ongoing systemic microvascular damage. Recently, sidestream dark-field (SDF) imaging has emerged as a noninvasive tool that enables one to visualize the microcirculation. In this study, we investigated whether changes in the systemic microvasculature induced by DM and an atherogenic diet correlated spatiotemporally with renal damage.

Methods

Atherosclerotic lesion development was triggered in streptozotocin-induced DM pigs (140 mg/kg body weight) by administering an atherogenic diet for approximately 11 months. Fifteen months following induction of DM, microvascular morphology was visualized in control pigs (n = 7), non-diabetic pigs fed an atherogenic diet (ATH, n = 5), and DM pigs fed an atherogenic diet (DM+ATH, n = 5) using SDF imaging of oral mucosal tissue. Subsequently, kidneys were harvested from anethesized pigs and the expression levels of well-established markers for microvascular integrity, such as Angiopoietin-1 (Angpt1) and Angiopoietin-2 (Angpt2) were determined immunohistochemically, while endothelial cell (EC) abundance was determined by immunostaining for von Willebrand factor (vWF).

Results

Our study revealed an increase in the capillary tortuosity index in DM+ATH pigs (2.31±0.17) as compared to the control groups (Controls 0.89±0.08 and ATH 1.55±0.11; p<0.05). Kidney biopsies showed marked glomerular lesions consisting of mesangial expansion and podocyte lesions. Furthermore, we observed a disturbed Angpt2/ Angpt1balance in the cortex of the kidney, as evidenced by increased expression of Angpt2 in DM+ATH pigs as compared to Control pigs (p<0.05).

Conclusion

In the setting of DM, atherogenesis leads to the augmentation of mucosal capillary tortuosity, indicative of systemic microvascular damage. Concomitantly, a dysbalance in renal angiopoietins was correlated with the development of diabetic nephropathy. As such, our studies strongly suggest that defects in the systemic microvasculature mirror the accumulation of microvascular damage in the kidney.

Unilateral ureteral obstruction: beyond obstruction

Unilateral ureteral obstruction is a popular experimental model of renal injury. However, the study of the kidney response to urinary tract obstruction is only one of several advantages of this model. Unilateral ureteral obstruction causes subacute renal injury characterized by tubular cell injury, interstitial inflammation and fibrosis. For this reason, it serves as a model both of irreversible acute kidney injury and of events taking place during human chronic kidney disease. Being a unilateral disease, it is not useful to study changes in global kidney function, but has the advantage of a low mortality and the availability of an internal control (the non-obstructed kidney). Experimental unilateral ureteral obstruction has illustrated the molecular mechanisms of apoptosis, inflammation and fibrosis, all three key processes in kidney injury of any cause, thus providing information beyond obstruction. Recently this model has supported key concepts on the role in kidney fibrosis of epithelial-mesenchymal transition, tubular epithelial cell G2/M arrest, the anti-aging hormone Klotho and renal innervation. We now review the experimental model and its contribution to identifying novel therapeutic targets in kidney injury and fibrosis, independently of the noxa.

Rosuvastatin treatment prevents progressive kidney inflammation and fibrosis in stroke-prone rats

Salt-loaded, spontaneously hypertensive stroke-prone rats show progressive increases in blood pressure and proteinuria and accumulate acute-phase proteins in body fluids, modeling events during renal damage. The aim of this study was to assess the pathological events occurring in the kidney of spontaneously hypertensive stroke-prone rats over time and evaluate the effects of statin treatment, which is known to improve renal and cardiovascular outcomes. Kidneys of male spontaneously hypertensive stroke-prone rats euthanized at different stages of proteinuria showed progressive inflammatory cell infiltration, the accumulation of alpha-smooth muscle actin-positive cells, degenerative changes in podocytes, and severe fibrosis. These were accompanied by an imbalance in the plasminogen/plasmin and metalloprotease systems characterized by the increased renal expression of plasminogen activator inhibitor-1, tissue plasminogen activator, and urokinase plasminogen activator; the net result was an increase in plasmin and matrix metalloproteinase (MMP)-2 and a reduction in MMP-9 activity. Chronic treatment with the hydrophilic rosuvastatin had renoprotective effects in terms of morphology and inflammation and prevented the changes in plasmin, MMP-2, and MMP-9 activity. These effects were independent of the changes in blood pressure and plasma lipid levels. Treatment with the lipophilic simvastatin was not renoprotective. These data suggest that rosuvastatin may have potential utility as a therapeutic option in renal diseases that are characterized by inflammation and fibrosis.

Obstructive nephropathy: towards biomarker discovery and gene therapy

Obstructive nephropathy is a major cause of renal failure, particularly in infants and children. Cellular and molecular mechanisms responsible for the progression of the tubular atrophy and interstitial fibrosis-processes that lead to nephron loss-have been elucidated in the past 5 years. Following urinary tract obstruction and tubular dilatation, a cascade of events results in upregulation of the intrarenal renin-angiotensin system, tubular apoptosis and macrophage infiltration of the interstitium. This is followed by accumulation of interstitial fibroblasts through proliferation of resident fibroblasts and epithelial-mesenchymal transformation of renal tubular cells. Under the influence of cytokines, chemokines and other signaling molecules produced by tubular and interstitial cells, fibroblasts undergo transformation to myofibroblasts that induce expansion of the extracellular matrix. The cellular interactions that regulate development of interstitial inflammation, tubular apoptosis and interstitial fibrosis are complex. Changes in renal gene expression and protein production afford many potential biomarkers of disease progression and targets for therapeutic manipulation. These include signaling molecules and receptors involved in macrophage recruitment and proliferation, tubular death signals and survival factors, and modulators of epithelial-mesenchymal transformation. Targeted gene deletion and various forms of gene therapy have been used in experimental obstructive nephropathy, mostly rodent models of unilateral ureteral obstruction or cell culture techniques. Further refinement of these models is needed to develop a matrix of biomarkers with clinical predictive value, as well as molecular therapies that will prevent or reverse the renal structural and functional consequences of obstructive nephropathy.

Upregulated expression of transforming growth factor-beta, type IV collagen, and plasminogen activator inhibitor-1 mRNA are decreased after release of unilateral ureteral obstruction

Tubulointerstitial fibrosis is a major cause of irreversible renal damage in the obstructed kidney. The effects of release of obstruction on the obstructed kidney are not clearly understood. We investigated the effects of the release of ureteral obstruction on renal fibrosis and the expression of fibrogenic factors. Rats underwent 5 day of unilateral ureteral obstruction (UUO). After release of obstruction by removing an encased rubber tube, changes in interstitial volume were morphologically evaluated and the mRNA expression of transforming growth factor-beta (TGF-beta), type IV collagen (collagen IV), and plasminogen activator inhibitor-1 (PAI-1) were examined by reverse transcription-polymerase chain reaction (RT-PCR) up to 28 days. Renal interstitial volume, collagen IV and PAI-1 mRNA gradually decreased from 7 days to 28 days after release of obstruction. However, increased expression of TGF-beta mRNA persisted up to 14 days, and then declined 28 days after release. In conclusion, obstruction-induced renal fibrosis was recovered with diminished expression of TGF-beta and collagen IV. Decreased PAI-1 expression in the post-obstructed kidney may contribute to the degradation of extracellular matrix proteins and recovery of tubulointerstitial fibrosis, at least partly, after release of ureteral obstruction.