Diabetic nephropathy is markedly enhanced in mice lacking the bradykinin B2 receptor

Abstract

Type I human diabetics and streptozotocin-induced diabetic mice with higher genetically determined levels of angiotensin-converting enzyme have an increased risk of developing nephropathy. However, previous experiments in mice and computer simulations indicate that modest increases in angiotensin-converting enzyme have minimal effects on blood pressure and angiotensin II levels, although bradykinin decreases significantly, inferring that bradykinin is critical for protecting the kidney in diabetics. Here, we confirm this inference by demonstrating that Akita diabetic mice lacking the bradykinin B2 receptor develop overt albuminuria, excreting the equivalent of >550 mg͞day albumin in humans, which contrasts with the microalbuminuria (equivalent to <150 mg͞day) seen in their simply diabetic littermates. The overt albuminuria is accompanied by a marked increase in glomerular mesangial sclerosis. The importance of bradykinin demonstrated here bears strongly on how current drugs reduce diabetic nephropathy and suggests that B2 receptor-specific agonists merit consideration in this context. maturity onset diabetes of the young ͉ albuminuria ͉ glomerulosclerosis D ifferences in expression of the gene coding for angiotensinconverting enzyme (ACE), such as are observed in humans in relation to the insertion͞deletion polymorphism in the ACE gene (1) and in mice with different numbers of the gene (2), have minimal effects on angiotensin II (ANGII) levels because the steady-state concentrations of the products of ACE are less sensitive to modest changes in the activity of the enzyme than the concentrations of its substrates. Thus, our recent computer simulations (3, 4) and accompanying experimental data indicate that a 50% increase in ACE causes a Ͻ5% increase in steadystate ANGII levels but close to a 20% decrease in bradykinin levels. Hence, our inference that the causative link between genetic differences in ACE expression and diabetic nephropathy (5, 6) is likely to be mediated by the ACE substrate bradykinin. To test this inference, we have combined the following two mutations: a dominant mutation that leads to maturity onset diabetes, Akita (7), resulting from an amino acid change in the insulin 2 gene (Ins2 C96Y ) (8), and a recessive knockout mutation (Bdkrb2 Ϫ ) (9) in the gene coding for the bradykinin B2 receptor, the receptor predominantly expressed in the normal kidney. Materials and MethodsAnimals. Animals were purchased from The Jackson Laboratory and bred in our mouse facility. The mice having the null allele for the bradykinin B2 receptor (9) were backcrossed to wild-type C57BL͞6J at least six times before mating to mice heterozygous for the Akita mutation (Ins2 ϩ/C96Y ) (7), which already have the C57BL͞6J genetic background. All experiments were conducted in accordance with the guidelines of the University of North Carolina Institutional Animal Care and Use Committee. Blood pressures were measured as described (2). Plasma glucose levels were determined with the glucose-oxidase method (Wako, Richmond, VA)....

ACE inhibitor reduces growth factor receptor expression and signaling but also albuminuria through B2-kinin glomerular receptor activation in diabetic rats

“…It has been demonstrated that DN is markedly enhanced in mice expressing high ACE activity, a situation associated with low levels of kinin and thereby low B2R activation (29). Similar observations have been reported in mice lacking the B2R (34). We also showed that renal fibrosis is increased in B2R null mice in response to unilateral obstruction (58).…”

“…Several other works from the same group put forward the hypothesis that increased renal production of kinins contributes to diabetes-induced glomerular hyperfiltration (32). More recently, the same group suggested that BK could promote glomerular injury in diabetes (63), an hypothesis which at first could appear opposite to our results but also to those observed in B2R knockout mice (34). However, the conclusion that BK can promote glomerular injury in diabetes was established on the fact that TGF-␤1 mRNA, TGF-␤ RII, CTGF, and B2R expression and levels in renal cortex of diabetic rats increased simultaneously.…”

“…Until now, only one study has suggested the involvement of BK in the antiproteinuric effect of ACEI in DN (65), whereas absence of B2R is associated with higher microalbuminuria in diabetes mice (34). It has been demonstrated that DN is markedly enhanced in mice expressing high ACE activity, a situation associated with low levels of kinin and thereby low B2R activation (29).…”

Bradykinine et néphroprotection

“…Les souris exprimant de multiples copies de l'ECA, c'est-à-dire capables de dégra-der de façon accrue la BK et d'aboutir ainsi à une très faible activation du RB2 [13], ainsi que les souris n'exprimant plus le RB2 [14], développent une néphropa-thie diabétique plus sévère que la souche sauvage. De même, la fibrose interstitielle se développant après une obstruction urétérale est aggravée chez la souris n'exprimant plus le RB2 [15].…”

“…Le polymorphisme du gène de RB2 apparaît comme un marqueur de susceptibilité de progression de la néphropathie diabé-tique ; le polymorphisme +/+ de l'exon 1 du RB2 serait associé à une faible excré-tion d'albumine, alors qu'une élévation du rapport albumine/créatinine est observée dans le polymorphisme +/- [17]. L'absence d'expression du RB2 est associée à une augmentation importante de l'expression de la néphrine et de la megsine lors de l'apparition du diabète [14]. L'expression de ces deux protéines est importante pour la stabilité du filtre glomérulaire.…”