Abstract. Renal fibrosis is one of the major complications associated with the development of hypertension. The objective of the present study was to determine whether and by which mechanisms treatment with AT1 receptor antagonists makes possible the regression of renal vascular and glomerular fibrosis. Experiments were performed in the hypertensive model of nitric oxide (NO) deficiency in rats. After 4 wk of hypertension, mortality rates averaged 20%; the surviving animals displayed a decline of renal function (urine protein/ creatinine, 1.89 Ϯ 0.63 versus 0.24 Ϯ 0.03 mg/mmol; creatininemia, 110 Ϯ 14 versus 38 Ϯ 2 mmol/L in hypertensive animals and control, respectively; P Ͻ 0.01) and an exaggerated gene and protein expression of TGF-␤, collagen I, and collagen IV (P Ͻ 0.001) within the renal vasculature associated with the development of glomerulosclerosis (sclerotic index, 2.26 Ϯ 0.29 versus 0.12 Ϯ 0.04; P Ͻ 0.001). In addition, activities of matrix metalloproteinases 2 and 9 were increased twofold in renal vessels and glomeruli (P Ͻ 0.01).Afterwards, losartan, an antagonist of angiotensin receptor type I, or hydralazine were administered in subgroups of hypertensive animals. After 1 wk of angiotensin II antagonism, collagen I, collagen IV, and TGF-␤ gene and protein expressions were decreased and glomerulosclerosis was less marked (sclerotic index 1.04 Ϯ 0.45), whereas activities of metalloproteinases remained twofold higher than controls (P Ͻ 0.01). Hydralazine failed to improve renal function despite a similar degree of systolic pressure decrease. After 4 wk of losartan, the renal functional and histologic parameters were completely normalized, whereas they remained damaged in the hypertensive animals in which the mortality rate reached 85%. These data suggest that the progression of renal vascular fibrosis is a reversible process, at least in the NO deficiency model. The mechanism of the regression appears to be dual: inhibition of collagen synthesis due to AT1 receptor antagonism and activation of metalloproteinases that is probably associated with the degree of fibrosis independently of AT1 blockade.Development of renal sclerotic lesions is one of the most common complications of hypertension. This pathophysiologic process is associated with changes in the structure of renal vasculature due to abnormal accumulation of extracellular matrix (particularly collagen types I, III, and IV) in renal resistance vessels, glomeruli, and interstitium (1). Although recent data obtained in the cardiac tissue indicate that the development of cardiac fibrosis is a reversible process under certain circumstances and treatments (blockade of angiotensin-converting enzyme [ACE] or antagonism of AT1 receptor) (2), very little is known about the capability of the renal vasculature to recover after the development of fibrotic injury.In previous studies, we investigated the role of angiotensin II (AngII) in the mechanisms leading to the development of renal vascular and glomerular fibrosis using a strain of transgenic mice tha...

Chronic kidney disease, secondary to renal fibrogenesis, is a burden on public health. There is a need to explore new therapeutic pathways to reduce renal fibrogenesis. To study this, we used unilateral ureteral obstruction (UUO) in mice as an experimental model of renal fibrosis and microarray analysis to compare gene expression in fibrotic and normal kidneys. The cannabinoid receptor 1 (CB1) was among the most upregulated genes in mice, and the main endogenous CB1 ligand (2-arachidonoylglycerol) was significantly increased in the fibrotic kidney. Interestingly, CB1 expression was highly increased in kidney biopsies of patients with IgA nephropathy, diabetes, and acute interstitial nephritis. Both genetic and pharmacological knockout of CB1 induced a profound reduction in renal fibrosis during UUO. While CB2 is also involved in renal fibrogenesis, it did not potentiate the role of CB1. CB1 expression was significantly increased in myofibroblasts, the main effector cells in renal fibrogenesis, upon TGF-β1 stimulation. The decrease in renal fibrosis during CB1 blockade could be explained by a direct action on myofibroblasts. CB1 blockade reduced collagen expression in vitro. Rimonabant, a selective CB1 endocannabinoid receptor antagonist, modulated the macrophage infiltrate responsible for renal fibrosis in UUO through a decrease in monocyte chemoattractant protein-1 synthesis. Thus, CB1 has a major role in the activation of myofibroblasts and may be a new target for treating chronic kidney disease.

Hypertension is often associated with the development of nephroangio- and glomerulo-sclerosis. This pathophysiological process is due to increased extracellular matrix protein, particularly type I collagen, accumulation. This study investigated whether nitric oxide (NO) synthesis is involved in the mechanism(s) regulating activation of the collagen I gene in afferent arterioles and glomeruli. Experiments were performed on transgenic mice harboring the luciferase gene under the control of the collagen I-alpha2 chain promoter [procolalpha2(I)]. Measurements of luciferase activity provide highly sensitive estimates of collagen I gene activation. NO synthesis was inhibited by NG-nitro-L-arginine methyl ester (L-NAME) (20 mg/kg per day) for a period of up to 14 wk. Systolic blood pressure was increased after 6 wk of treatment (117+/-2 versus 129+/-2 mmHg, P < 0.01) and reached a plateau after 10 wk (around 160 mmHg). Luciferase activity was increased in freshly isolated afferent arterioles and glomeruli as early as week 4 of L-NAME treatment (150 and 200% of baseline, P < 0.01, respectively). The activation of procolalpha2(I) became more pronounced with time, and at 14 wk increased four- and tenfold compared with controls in afferent arterioles and glomeruli, respectively (P < 0.001). In contrast, luciferase activity remained unchanged in aorta and heart up to 8 wk and was increased thereafter. Increased histochemical staining for extracellular matrix deposition, and particularly of collagen I, was detected in afferent arterioles and glomeruli after 10 wk of L-NAME treatment. This fibrogenic process was accompanied by an increased urinary excretion rate of endothelin. In separate experiments, the stimulatory effect of L-NAME on collagen I gene activation was abolished when animals were treated with bosentan, an endothelin receptor antagonist. Similarly, bosentan reduced the increased extracellular matrix deposition in afferent arterioles and glomeruli during NO inhibition. Interestingly, bosentan had no effect on the L-NAME- induced increase of systolic pressure. These data indicate that NO inhibition induces an early activation of the collagen I gene in afferent arterioles and glomeruli. This activation in the kidney precedes the increase in blood pressure and the procolalpha2(I) activation in heart and aorta, suggesting a specific renal effect of NO blockade on collagen I gene expression that is independent of increased blood pressure and, at least partly, mediated through stimulation of the endothelin receptor. Use of procolalpha2(I) transgenic mice provides a novel and efficient model to study the pathophysiological mechanism(s) regulating renal fibrosis.

A frequent complication of hypertension is the development of chronic renal failure. This pathology usually is initiated by inflammatory events and is characterized by the abnormal accumulation of collagens within the renal tissue. The purpose of this study was to investigate the role of discoidin domain receptor 1 (DDR1), a nonintegrin collagen receptor that displays tyrosine-kinase activity, in the development of renal fibrosis. To this end, hypertension was induced with angiotensin in mice that were genetically deficient of DDR1 and in wild-type controls. After 4 or 6 wk of angiotensin II administration, wild-type mice developed hypertension that was associated with perivascular inflammation, glomerular sclerosis, and proteinuria. Systolic pressure increase was similar in the DDR1-deficient mice, but the histologic lesions of glomerular fibrosis and inflammation were significantly blunted and proteinuria was markedly prevented. Immunostaining for lymphocytes, macrophages, and collagens I and IV was prominent in the renal cortex of wild-type mice but substantially reduced in DDR1 null mice. In separate experiments, renal cortical slices of DDR1 null mice showed a blunted response of chemokines to LPS that was accompanied by a considerable protection against the LPS-induced mortality. These results indicate the importance of DDR1 in mediating inflammation and fibrosis. Use of DDR1 inhibitors could provide a completely novel therapeutic approach against diseases that have these combined pathologies. H ypertension frequently is complicated by the development of chronic renal failure, a complex pathology that is initiated by inflammatory events that evolve to increased synthesis and accumulation of extracellular matrix (ECM; mainly collagens) within the renal tissue and lead over time to loss of function and ESRD. To date, no efficient treatment that can stop or, even more desirable, reverse the decline of renal function exists. Therefore, the understanding of the systems and/or mechanisms that are involved in the development of renal vascular inflammation and fibrosis will provide valuable information to design specific pharmacologic targets to treat this incurable disease.Important advancements have been made regarding the mechanisms that are involved in the development of chronic renal failure. These studies focused mainly in the systems or agents that promote ECM synthesis and progression of renal disease. We and other investigators, for instance, clearly identified and characterized the signaling pathways that vasoconstrictor peptides are using to activate collagen synthesis (1-4). Less is known about the mechanisms regarding the postsynthesis regulation of ECM, such as matrix anchoring and interactions with the cell membrane.Among the systems that interact with the ECM are the discoidin domain receptors (DDR). They are the first identified receptor tyrosine kinases that bind directly to the ECM (5). DDR1 binds all types of collagens and is widely expressed in a variety of tissues, including vascular smooth m...