Cyclosporine-A induced nephrotoxicity is associated with decreased renal bone morphogenetic protein-7 expression in rats

Imbalance in Bone Morphogenic Proteins 2 and 7 Is Associated with Renal and Cardiovascular Damage in Chronic Kidney Disease

Arterial stiffness is a major vascular complication of chronic kidney disease (CKD). The development of renal damage, hypertension, and increased pulse wave velocity (PWV) in CKD might be associated with an imbalance in bone morphogenetic proteins (BMP)-2 and BMP-7. Plasma BMP-2 and BMP-7 were determined by ELISA in CKD patients (stages I-III; n = 95) and Munich Wistar Frömter (MWF) rats. Age-matched Wistar rats were used as a control. The expression of BMP-2, BMP-7, and profibrotic and calcification factors was determined in kidney and perivascular adipose tissues (PVAT). BMP-2 was higher in stage III CKD patients compared to control subjects. BMP-7 was lower at any CKD stage compared to controls, with a significant further reduction in stage III patients. A similar imbalance was observed in MWF rats together with the increase in systolic (SBP) and diastolic blood pressure (DBP), or pulse wave velocity (PWV). MWF exhibited elevated urinary albumin excretion (UAE) and renal expression of BMP-2 or kidney damage markers, Kim-1 and Ngal, whereas renal BMP-7 was significantly lower than in Wistar rats. SBP, DBP, PWV, UAE, and plasma creatinine positively correlated with the plasma BMP-2/BMP-7 ratio. Periaortic and mesenteric PVAT from MWF rats showed an increased expression of BMP-2 and profibrotic and calcification markers compared to Wistar rats, together with a reduced BMP-7 expression. BMP-2 and BMP-7 imbalance in plasma, kidney, and PVATs is associated with vascular damage, suggesting a profibrotic/pro-calcifying propensity associated with progressive CKD. Thus, their combined analysis stratified by CKD stages might be of clinical interest to provide information about the degree of renal and vascular damage in CKD.

The blockade of the renin-angiotensin system reverses tacrolimus related cardiovascular toxicity at the histopathological level

Introduction. In this study, we investigate the toxic effects of tacrolimus (FK506) on the cardiovascular system at the histopathological level in a rat model and whether these effects can be reversed by the blockade of the renin-angiotensin system (RAS) by either an angiotensin-converting enzyme inhibitor (ACE-inhibitors) or an angiotensin receptor antagonist (ARB).

Methods and results. Thirty-one Wistar rats were divided into four groups. FK506 group was treated with FK506 intraperitoneally (i.p.), FK506+ACE-inhibitors and FK506+ARB groups were treated with either quinapril or valsartan orally in addition to FK506. Control group was treated with saline i.p. Histological and immunohistochemical staining of cardiovascular tissue in the FK506 group showed increased vacuolar degeneration (11.2 vs. 5.8, p=0.008), arterial hyalinosis (10.7 vs. 6. G 3, p=0.036), transforming growth factor-beta (TGF-β) (12.2 vs. 4.8, p=0.001) and vascular endothelial growth factor expression (VEGF) (10.7 vs. 6.3, p=0.036), elastic van Gieson (11.5 vs. 5.5, p=0.004), and periodic acid O Schiff stain scores (12.5 vs. 4.5, p<0.001) compared to the control group. Immunohistochemical scores showed that expression of TGF-β is up-regulated, and bone morphogenic protein (BMP-7) is down-regulated with FK506 toxicity. Adding RAS blockade with either an ACE-inhibitor or an ARB could reverse FK506 induced changes. Both FK506+ACE-inhibitors and FK506+ARB groups demonstrated decrease in arterial hyalinosis (22.1 vs. 14.4 (FK506+ACE-inhibitor) and 13.6 (FK506+ARB), p=0.09) and vacuolar degeneration (23.1 vs. 16.1 (FK506+ACE-inhibitor) and 12.4 (FK506+ARB), p=0.006) scores compared to the FK506 group.

Conclusion. Blockade of RAS could reverse the histopathological signs of FK506 induced cardiac toxicity in a rat model.

BMP-7 Signaling and its Critical Roles in Kidney Development, the Responses to Renal Injury, and Chronic Kidney Disease

Chronic kidney disease (CKD) is a significant health problem that most commonly results from congenital abnormalities in children and chronic renal injury in adults. The therapeutic potential of BMP-7 was first recognized nearly two decades ago with studies demonstrating its requirement for kidney development and ability to inhibit the pathogenesis of renal injury in models of CKD. Since this time, our understanding of CKD has advanced considerably and treatment strategies have evolved with the identification of many additional signaling pathways, cell types, and pathologic processes that contribute to disease progression. The purpose of this review is to revisit the seminal studies that initially established the importance of BMP-7, highlight recent advances in BMP-7 research, and then integrate this knowledge with current research paradigms. We will provide an overview of the evolutionarily conserved roles of BMP proteins and the features that allow BMP signaling pathways to function as critical signaling nodes for controlling biological processes, including those related to CKD. We will discuss the multifaceted functions of BMP-7 during kidney development and the potential for alterations in BMP-7 signaling to result in congenital abnormalities and pediatric kidney disease. We will summarize the renal protective effects of recombinant BMP-7 in experimental models of CKD and then propose a model to describe the potential physiological role of endogenous BMP-7 in the innate repair mechanisms of the kidneys that respond to renal injury. Finally, we will highlight emerging clinical approaches for applying our knowledge of BMP-7 toward improving the treatment of patients with CKD.

Activin-like kinase 3 is important for kidney regeneration and reversal of fibrosis

Molecules associated with the transforming growth factor β (TGF-β) superfamily, such as bone morphogenic proteins (BMPs) and TGF-β, are key regulators of inflammation, apoptosis and cellular transitions. Here we show that the BMP receptor activin-like kinase 3 (Alk3) is elevated early in diseased kidneys after injury. We also found that its deletion in the tubular epithelium leads to enhanced TGF-β1-Smad family member 3 (Smad3) signaling, epithelial damage and fibrosis, suggesting a protective role for Alk3-mediated signaling in the kidney. A structure-function analysis of the BMP-Alk3-BMP receptor, type 2 (BMPR2) ligand-receptor complex, along with synthetic organic chemistry, led us to construct a library of small peptide agonists of BMP signaling that function through the Alk3 receptor. One such peptide agonist, THR-123, suppressed inflammation, apoptosis and the epithelial-to-mesenchymal transition program and reversed established fibrosis in five mouse models of acute and chronic renal injury. THR-123 acts specifically through Alk3 signaling, as mice with a targeted deletion for Alk3 in their tubular epithelium did not respond to therapy with THR-123. Combining THR-123 and the angiotensin-converting enzyme inhibitor captopril had an additive therapeutic benefit in controlling renal fibrosis. Our studies show that BMP signaling agonists constitute a new line of therapeutic agents with potential utility in the clinic to induce regeneration, repair and reverse established fibrosis.

Endogenous BMP-7 is a critical molecular determinant of the reversibility of obstruction-induced renal injuries

Although obstructive uropathies are frequently correctable through surgery, the potential for permanent renal injury remains even following the successful correction of obstructions. Little is known about the intrinsic mechanisms that determine the reversibility of renal injuries. We and others found that exogenous bone morphogenic protein 7 (BMP-7) inhibits the pathogenesis of renal injury. Here, we examine the role of endogenous BMP-7 in the outcome of renal recovery following the correction of obstructive uropathies using a reversible murine model of ureteral obstruction. The role of BMP-7 was determined by examining the regulation of BMP-7 during renal recovery and by treating with either BMP-7-neutralizing antibodies or exogenous BMP-7. While BMP-7 is upregulated following the correction of obstructions that lead to reversible renal injury, the upregulation of BMP-7 is diminished following the correction of prolonged obstructions that lead to irreversible renal injury. The activation of the BMP-7 pathway is required for several processes that contribute to renal recovery including the suppression of transforming growth factor-β-dependent profibrotic pathways, the restoration of renal architecture, and the resolution of fibrotic changes in the kidney. Importantly, the therapeutic restoration of BMP-7 enhances renal recovery following the correction of prolonged obstructions that typically lead to irreversible renal injury. Together, these findings show that, while BMP-7 plays a critical role in the repair of obstruction-induced renal injuries, the potential for renal recovery from prolonged obstruction is diminished, in part, due to the dysregulation of BMP-7. Accordingly, renal recovery from obstructive uropathies may be optimized through timely intervention and adjuvant approaches to restore BMP-7 activity.

Transforming growth factor-beta1, vascular endothelial growth factor, and bone morphogenic protein-7 expression in tacrolimus-induced nephrotoxicity in rats

The aim of our study was to investigate transforming growth factor (TGF)-beta1, vascular endothelial growth factor (VEGF), and bone morphogenic protein-7 (BMP-7) expression in the rat model of chronic tacrolimus (TAC) toxicity compared to healthy controls. Seventeen male Wistar rats were divided into two groups: group 1 animals were healthy controls and Group 2 animals were treated with TAC (1 mg/kg per day intraperitoneally for 8 weeks). At the end of the study period the animals were sacrificed following renal function studies including blood urea nitrogen (BUN), serum creatinine, and creatinine clearance, and renal tissues were examined by light microscopy for the findings of tacrolimus toxicity, specifically for afferent arteriolopathy and interstitial fibrosis. TGF-beta1, VEGF, and BMP-7 expression were assessed by semiquantitative scoring of the immunohistochemically stained specimens. Mean TAC levels were 5.53 +/- 2.38 ng/mL in group 2. BUN, creatinine levels, and creatinine clearance were 57.99 +/- 11.13 vs 39.49 +/- 5.64 mg/dL; 0.60 +/- 0.16 vs 0.65 +/- 0.09 mg/dL; 0.97 +/- 0.39 vs 1.17 +/- 0.32 mL/min in group 2 versus group 1. Only the BUN level was significantly higher in group 2 compared to group 1. Afferent arteriolopathy and interstitial fibrosis were significantly increased in group 2 compared to group 1. TGF-beta1 and VEGF expression was significantly increased while BMP-7 expression was significantly decreased in group 2 versus group 1. In conclusion, our findings suggest that TAC-induced nephrotoxicity is associated with increased TGF-beta1 and VEGF and decreased BMP-7 expression.

Inhibition of the Renin Angiotensin System Decreases Fibrogenic Cytokine Expression in Tacrolimus Nephrotoxicity in Rats

The aim of our study was to investigate the influence of angiotensin-converting enzyme (ACE) inhibition and angiotensin II receptor blockage on the renal function by light microscopic and immunohistochemical findings in a rat model of tacrolimus nephrotoxicity. Thirty-two male Wistar rats were divided into four groups of eight: G1 = control group; G2-G3, G4 = Tacrolimus (Tac) 1 mg/kg/d intraperitoneally (ip); G3 (Tac + Q) = ip Tac and peroral quinapril 10 mg/kg; and G4 (Tac + V) = Tac and valsartan 40 mg/d. Serum blood urea nitrogen (BUN), creatinine, and creatinine clearance were measured before and at the end of the study period. Renal tissues were assessed for light microscopic findings of tacrolimus toxicity. Transforming growth factor-beta, VEGF, PDGF, BMP-7, and interleukin-6 (IL-6) expression were semiquantitatively scored after immunohistochemical staining. At the end of the study period serum BUN and creatinine levels were increased in all groups, but creatinine clearance was not significantly changed between the groups. Afferent arteriolopathy was significantly less pronounced in G3 versus G2 and G4. Interstial fibrosis was significantly less pronounced in G3 and G4 versus G2. TGF-beta, PDGF, and IL-6 expression were significantly increased in G2, G3, and G4 compared to G1, and in G2 compared to G3 and G4. BMP-7 expression was significantly decreased in G2, G3, and G4 compared to G1, whereas the differences between G2, G3, and G4 failed to reach statistical significance. In conclusion, the results of our study suggested that renin angiotensin inhibition down-regulates fibrogenic cytokine expression in rats displaying tacrolimus nephrotoxicity.