Caveolin-1 Deficiency Inhibits the Basolateral K+ Channels in the Distal Convoluted Tubule and Impairs Renal K+ and Mg2+ Transport

Kcnj10 encodes the inwardly rectifying K⁺ channel Kir4.1 in the basolateral membrane of the distal convoluted tubule (DCT) and is activated by c-Src. However, the regulation and function of this K⁺ channel are incompletely characterized. Here, patch-clamp experiments in Kcnj10-transfected HEK293 cells demonstrated that c-Src–induced stimulation of Kcnj10 requires coexpression of caveolin-1 (cav-1), and immunostaining showed expression of cav-1 in the basolateral membrane of parvalbumin-positive DCT. Patch-clamp experiments detected a 40-pS inwardly rectifying K⁺ channel, a heterotetramer of Kir4.1/Kir5.1, in the basolateral membrane of the early DCT (DCT1) in both wild-type (WT) and cav-1-knockout (KO) mice. However, the activity of this basolateral 40-pS K⁺ channel was lower in KO mice than in WT mice. Moreover, the K⁺ reversal potential (an indication of membrane potential) was less negative in the DCT1 of KO mice than in the DCT1 of WT mice. Western blot analysis demonstrated that cav-1 deficiency decreased the expression of the Na⁺/Cl^– cotransporter and Ste20-proline-alanine-rich kinase (SPAK) but increased the expression of epithelial Na⁺ channel-α. Furthermore, the urinary excretion of Mg²⁺ and K⁺ was significantly higher in KO mice than in WT mice, and KO mice developed hypomagnesemia, hypocalcemia, and hypokalemia. We conclude that disruption of cav-1 decreases basolateral K⁺ channel activity and depolarizes the cell membrane potential in the DCT1 at least in part by suppressing the stimulatory effect of c-Src on Kcnj10. Furthermore, the decrease in Kcnj10 and Na⁺/Cl^– cotransporter expression induced by cav-1 deficiency may underlie the compromised renal transport of Mg²⁺, Ca²⁺, and K⁺.     

Proline‐Serine–Threonine Phosphatase‐Interacting Protein 2 Alleviates Diabetes Mellitus‐Osteoarthritis in Rats through Attenuating Synovial Inflammation and Cartilage Injury

ObjectiveTo explore the possible way of proline‐serine–threonine phosphatase‐interacting protein 2 (PSTPIP2) influencing diabetes mellitus‐osteoarthritis (DM‐OA) progression.Methods In vivo, eight‐week‐old male Sprague Dawley rats were induced with DM‐OA by intraperitoneal injection of streptozotocin with high‐fat diet feeding and intra‐articular injection of monoiodoacetate. PSTPIP2 overexpression was achieved by intra‐articular injection of lentivirus vectors. PSTPIP2 expression was verified by real‐time polymerase chain reaction and Western blotting. Histological changes were examined by hematoxylin/eosin and safranin‐O/fast‐green staining. In vitro, rat synovial fibroblasts were induced DM‐OA by stimulation of high glucose (HG) and interleukin (IL)‐1β. PSTPIP2 overexpression was achieved by lentivirus infection. U0126 was added as an ERK inhibitor. Levels of tumor necrosis factor (TNF)‐α, IL‐6, and IL‐1β were detected using enzyme‐linked immunosorbent assay. Expression of matrix metalloproteinase (MMP)‐3, MMP‐13, aggrecanase‐2 (ADAMTS‐5), intercellular cell adhesion molecule (ICAM)‐1, extracellular regulated protein kinase (ERK) and phospho‐ERK (p‐ERK) was detected by Western blotting.ResultsIn DM‐OA rats, PSTPIP2 relative messenger RNA (mRNA) level was significantly decreased compared to control rats. The protein expression was also decreased obviously. Inflammation score in synovium was dramatically increased, accompanying with increased TNF‐α, IL‐6, and IL‐1β levels. Osteoarthritis research society international (OARSI) score in cartilage was markedly increased, along with increased MMP‐3, MMP‐13, ADAMTS‐5, ICAM‐1, ERK and p‐ERK expression. In PSTPIP2‐overexpressed DM‐OA rats, PSTPIP2 mRNA level and protein expression was increased compared to DM‐OA rats received negative‐control lentivirus vectors. The inflammation score, as well as TNF‐α, IL‐6, and IL‐1β levels were dramatically decreased. Also, the OARSI score and protein expression of MMP‐3, MMP‐13, ADAMTS‐5, ICAM‐1, ERK and p‐ERK were decreased. In HG+IL‐1β‐treated rat synovial fibroblasts, PSTPIP2 protein expression was decreased compared to normal glucose (NG)‐treated cells. Levels of TNF‐α, IL‐6, and IL‐1β, as well as expression of MMP‐3, MMP‐13, ADAMTS‐5, ICAM‐1, ERK and p‐ERK were increased. After cells were infected with PSTPIP2‐overexpressed lentivirus, levels of TNF‐α, IL‐6, and IL‐1β, and expression of MMP‐3, MMP‐13, ADAMTS‐5, ICAM‐1, ERK and p‐ERK were obviously decreased compared to cells infected with NC lentivirus. In addition, ERK inhibitor U0126 treatment also decreased the TNF‐α, IL‐6, and IL‐1βlevels and MMP‐3, MMP‐13, ADAMTS‐5, ICAM‐1, ERK and p‐ERK expression in HG + IL‐1β treated rat synovial fibroblasts.ConclusionOverexpression of PSTPIP2 alleviates synovial inflammation and cartilage injury during DM‐OA progression via inhibiting ERK phosphorylation.     

Evidence for a Direct Effect of the NAD+ Precursor Acipimox on Muscle Mitochondrial Function in Humans

Recent preclinical studies showed the potential of nicotinamide adenine dinucleotide (NAD⁺) precursors to increase oxidative phosphorylation and improve metabolic health, but human data are lacking. We hypothesize that the nicotinic acid derivative acipimox, an NAD⁺ precursor, would directly affect mitochondrial function independent of reductions in nonesterified fatty acid (NEFA) concentrations. In a multicenter randomized crossover trial, 21 patients with type 2 diabetes (age 57.7 ± 1.1 years, BMI 33.4 ± 0.8 kg/m²) received either placebo or acipimox 250 mg three times daily dosage for 2 weeks. Acipimox treatment increased plasma NEFA levels (759 ± 44 vs. 1,135 ± 97 μmol/L for placebo vs. acipimox, P < 0.01) owing to a previously described rebound effect. As a result, skeletal muscle lipid content increased and insulin sensitivity decreased. Despite the elevated plasma NEFA levels, ex vivo mitochondrial respiration in skeletal muscle increased. Subsequently, we showed that acipimox treatment resulted in a robust elevation in expression of nuclear-encoded mitochondrial gene sets and a mitonuclear protein imbalance, which may indicate activation of the mitochondrial unfolded protein response. Further studies in C2C12 myotubes confirmed a direct effect of acipimox on NAD⁺ levels, mitonuclear protein imbalance, and mitochondrial oxidative capacity. To the best of our knowledge, this study is the first to demonstrate that NAD⁺ boosters can also directly affect skeletal muscle mitochondrial function in humans.     

Propranolol suppresses bladder cancer by manipulating intracellular pH via NHE1

BackgroundIn recent years, a large number of clinical and epidemiological studies have revealed the anti-cancer activity of propranolol in solid tumors, though the underline mechanism is yet to be clarified.MethodsThe proliferation of bladder cancer cells treated with propranolol was detected by MTS assays. In vivo tumor xenograft experiments were used to observe the effect of propranolol on bladder cancer growth in mice. The expression levels of Na⁺/H⁺ exchanger (NHE1) was measured by western blot. The frequency of CD8⁺ T cells and CD4⁺ T cells were detected via flow cytometry.ResultsIn this study, propranolol inhibited the expression of NHE1 and sequentially led to a decrease of intracellular pH to 5.88 in MB49 cells and 6.85 in 5637 cells, thereafter, inhibited cell viability and induced apoptosis. Furthermore, propranolol inhibited the growth of bladder cancer in mice xenograft model. Flow cytometry found that the frequency of CD8⁺ T cells (34.58±2.11 vs. 32.34±0.6, P=0.35) and CD4⁺ T cells (57.80±2.45 vs. 51.44±0.79, P=0.06) in the spleen did not change compared with the control group, while the expression of IFN-γ, GZMB and T-bet secreted by CD8⁺ T cells increased respectively (IFN-γ 7.3±0.17 vs. 3.37±0.58, P=0.0017; GZMB 16.66±2.13 vs. 4.53±0.62, P=0.0034; T-bet 3.62±0.35 vs. 1.74±0.26, P=0.0027). Meantime, the expression of FoxP3 on CD4⁺ T cells decreased both in spleen and tumor tissue (1.53±0.11 vs. 0.91±0.1, P=0.004; 4.52±0.48 vs. 1.76±0.40, P=0.003).ConclusionsThese results suggested that propranolol exerted anti-proliferation and pro-apoptosis effects in bladder cancer cell by inhibiting Na⁺/H⁺ exchange and activated systemic anti-tumor immune response in vivo.     

Pituitary adenylate cyclase activating peptides relax human pulmonary arteries by opening of KATP and KCa channels

BACKGROUND—Pituitaryadenylate cyclase activating peptides (PACAPs) are potent endotheliumindependent dilators of human coronary arteries; however, their effectson human pulmonary arteries are unknown.
Methods—Thevasorelaxant effects of PACAP27 on human pulmonary segmental arterieswere studied and the specific potassium (K⁺) channelregulatory mechanisms in the vasorelaxant effects were tested by meansof isometric contraction experiments.
RESULTS—PACAP27produced dose dependent relaxations of 10 µM rings preconstrictedwith prostaglandin F_2α (PGF_2α ) with half maximal relaxation (IC₅₀) at 17 nM. Pretreatment of thevessels with the ATP sensitive K⁺ (K_ATP)channel blocker glibenclamide (1 µM) or with the Ca²⁺activated K⁺ (K_Ca) channel blockeriberiotoxin (100 nM) inhibited the PACAP27 induced relaxation.
Conclusions—Theseresults provide evidence that PACAPs are potent vasodilators of humanpulmonary arteries and that this relaxation might be mediated byopening of K_ATP and K_Ca channels.

     

WNK4激酶通过溶酶体途径抑制BK通道表达

目的 研究WNK4激酶对BK通道的调节作用及机制.方法 将BK和WNK4野生型(WNK4-WT)或CD4(对照)质粒DNA共同转染进Cos-7细胞中,采用免疫染色-共聚焦激光显微镜、化学发光法、Western印迹法检测BK在细胞上的分布、细胞膜表面蛋白和总蛋白的表达;并使用质子泵抑制剂bafilomycin A1( Baf A1)阻断溶酶体降解检测BK蛋白表达水平的减少是否由于其蛋白降解增多所致.结果 免疫染色-共聚焦激光显微镜发现,与对照组相比,WNK4-WT组BK在细胞膜表面的分布明显减少.化学发光法检测结果显示,对照组BK的细胞膜表面蛋白表达水平为299.9±18.6,WNK4-WT组中其细胞膜表面蛋白表达水平为148.4±13.7,比对照组显著下降(P＜0.01).Western印迹结果提示,WNK4-WT组BK的总蛋白表达水平比对照组明显减少.和对照组(100％)相比,WNK4-WT显著减少BK的总蛋白水平(42.3％±15.2％,P＜0.01),而Baf A1则逆转WNK4-WT对BK蛋白的抑制作用(82.2％±12.1％,P＜0.05).结论 WNK4激酶能同时抑制BK在Cos-7细胞膜表面蛋白和总蛋白的表达水平;WNK4激酶抑制BK通道蛋白的表达是通过增加其在溶酶体内的降解所致的.     

Grg3/TLE3 and Grg1/TLE1 Induce Monohormonal Pancreatic β-Cells While Repressing α-Cell Functions

In the pancreas, α- and β-cells possess a degree of plasticity. In vitro differentiation of pluripotent cells yields mostly α- and polyhormonal β-like cells, indicating a gap in understanding of how functional monohormonal β-cells are formed and of the endogenous repressive mechanisms used to maintain β-cell identity. We show that the corepressor Grg3 is expressed in almost all β-cells throughout embryogenesis to adulthood. However, Grg3 is expressed in fewer nascent α-cells and is progressively lost from α-cells as endocrine cells mature into adulthood. We show that mouse Grg3^+/− β-cells have increased α-specific gene expression, and Grg3^+/− pancreata have more α-cells and more polyhormonal cells, indicating that Grg3 is required for the physiologic maintenance of monohormonal β-cell identity. Ectopic expression of Grg3 in α-cells represses glucagon and Arx, and the addition of Pdx1 induces Glut2 expression and glucose-responsive insulin secretion. Furthermore, we found that Grg1 is the predominant Groucho expressed in human β-cells but acts functionally similarly to Grg3. Overall, we find that Grg3 and Grg1 establish a monohormonal β-cell identity, and Groucho family members may be useful tools or markers for making functional β-cells.     

Inhibition of Ca2+-Independent Phospholipase A2β (iPLA2β) Ameliorates Islet Infiltration and Incidence of Diabetes in NOD Mice

Autoimmune β-cell death leads to type 1 diabetes, and with findings that Ca²⁺-independent phospholipase A₂β (iPLA₂β) activation contributes to β-cell death, we assessed the effects of iPLA₂β inhibition on diabetes development. Administration of FKGK18, a reversible iPLA₂β inhibitor, to NOD female mice significantly reduced diabetes incidence in association with 1) reduced insulitis, reflected by reductions in CD4⁺ T cells and B cells; 2) improved glucose homeostasis; 3) higher circulating insulin; and 4) β-cell preservation. Furthermore, FKGK18 inhibited production of tumor necrosis factor-α (TNF-α) from CD4⁺ T cells and antibodies from B cells, suggesting modulation of immune cell responses by iPLA₂β-derived products. Consistent with this, 1) adoptive transfer of diabetes by CD4⁺ T cells to immunodeficient and diabetes-resistant NOD.scid mice was mitigated by FKGK18 pretreatment and 2) TNF-α production from CD4⁺ T cells was reduced by inhibitors of cyclooxygenase and 12-lipoxygenase, which metabolize arachidonic acid to generate bioactive inflammatory eicosanoids. However, adoptive transfer of diabetes was not prevented when mice were administered FKGK18-pretreated T cells or when FKGK18 administration was initiated with T-cell transfer. The present observations suggest that iPLA₂β-derived lipid signals modulate immune cell responses, raising the possibility that early inhibition of iPLA₂β may be beneficial in ameliorating autoimmune destruction of β-cells and mitigating type 1 diabetes development.     

Effects of WNK3 kinase on regulation of large-conductance calcium-activated potassium channels and its mechanisms

Objective To investigate the effects of WNK3 kinase on the regulation of large-conductance calcium-activated potassium channels (Maxi K channels) on African green monkey kidney fibroblast-like cells (Cos-7 cells) and its mechanisms. Methods (1) Cos-7 cells were transfected with 0, 0.6, 1.2, 1.8 μg WNK3 plasmid+0.5 μg Maxi K plasmid. The total protein expression of Maxi K channel and the phosphorylation of mitogen-activated protein kinase (MAPK) extracellular regulated kinase-1 and-2 (ERK1/2) were detected by Western blotting. (2) Cos-7 cells were divided into the control group (2.5 μg Maxi K plasmid) and the experimental group (2.5 μg WNK3 plasmid+2.5 μg Maxi K plasmid). Cell surface biotinylation was used to investigate the cell surface protein expression of Maxi K channel in Cos-7 cells. Immunoprecipitation and Western blotting were used to detect the ubiquitination of Maxi K channel protein. (3) WNK3 kinase was knocked down by WNK3 siRNA. The lysosomal degradation pathway was blocked by the proton pump inhibitor (Baf-A1). Cos-7 cells were divided into Maxi K+negative control siRNA group, Maxi K+WNK3 siRNA group and Maxi K+WNK3 siRNA+Baf-A1 group. The protein expression of Maxi K channel protein was detected by Western blotting. Results (1) Compared with those in 0 μg WNK3 plasmid groups, in 0.6, 1.2, 1.8 μg WNK3 plasmid groups the total protein expression of the Maxi K channel increased and the phosphorylation level of MAPK ERK1/2 reduced on a dose-dependent manner (all P＜0.01). (2) Compared with those in the control group, the total protein expression and cell surface membrane protein expression of the Maxi K channel increased in the experimental group (P＜0.01), while the ubiquitination of the Maxi K channel protein reduced (P＜0.01). (3) Compared with the Maxi K+negative control siRNA group, the expression of Maxi K protein reduced in the Maxi K+WNK3 siRNA group (P＜0.01), but did not change in the Maxi K+WNK3 siRNA+Baf-A1 group (P＞0.05). The expression of Maxi K protein in Maxi K+WNK3 siRNA+Baf-A1 group was higher than that in Maxi K+WNK3 siRNA group (P＜0.01). Conclusions WNK3 kinase inhibits the lysosomal degradation pathway of Maxi K channel protein by reducing the ubiquitination of Maxi K channel, and promotes the expression of Maxi K channel protein in cells and on cell membrane. These effects may be achieved by suppressing MAPK ERK1/2 signal transduction pathway.     

FGF1 Mediates Overnutrition-Induced Compensatory β-Cell Differentiation

Increased insulin demand resulting from insulin resistance and/or overnutrition induces a compensatory increase in β-cell mass. The physiological factors responsible for the compensation have not been fully characterized. In zebrafish, overnutrition rapidly induces compensatory β-cell differentiation through triggering the release of a paracrine signal from persistently activated β-cells. We identified Fgf1 signaling as a key component of the overnutrition-induced β-cell differentiation signal in a small molecule screen. Fgf1 was confirmed as the overnutrition-induced β-cell differentiation signal, as inactivation of fgf1 abolished the compensatory β-cell differentiation. Furthermore, expression of human FGF1 solely in β-cells in fgf1^−/− animals rescued the compensatory response, indicating that β-cells can be the source of FGF1. Additionally, constitutive secretion of FGF1 with an exogenous signal peptide increased β-cell number in the absence of overnutrition. These results demonstrate that fgf1 is necessary and FGF1 expression in β-cells is sufficient for the compensatory β-cell differentiation. We further show that FGF1 is secreted during prolonged activation of cultured mammalian β-cells and that endoplasmic reticulum stress acts upstream of FGF1 release. Thus, the recently discovered antidiabetes function of FGF1 may act partially through increasing β-cell differentiation.     

Antiaging Gene Klotho Attenuates Pancreatic β-Cell Apoptosis in Type 1 Diabetes

Apoptosis is the major cause of death of insulin-producing β-cells in type 1 diabetes mellitus (T1DM). Klotho is a recently discovered antiaging gene. We found that the Klotho gene is expressed in pancreatic β-cells. Interestingly, halplodeficiency of Klotho (KL^+/−) exacerbated streptozotocin (STZ)-induced diabetes (a model of T1DM), including hyperglycemia, glucose intolerance, diminished islet insulin storage, and increased apoptotic β-cells. Conversely, in vivo β-cell–specific expression of mouse Klotho gene (mKL) attenuated β-cell apoptosis and prevented STZ-induced diabetes. mKL promoted cell adhesion to collagen IV, increased FAK and Akt phosphorylation, and inhibited caspase 3 cleavage in cultured MIN6 β-cells. mKL abolished STZ- and TNFα-induced inhibition of FAK and Akt phosphorylation, caspase 3 cleavage, and β-cell apoptosis. These promoting effects of Klotho can be abolished by blocking integrin β1. Therefore, these cell-based studies indicated that Klotho protected β-cells by inhibiting β-cell apoptosis through activation of the integrin β1-FAK/Akt pathway, leading to inhibition of caspase 3 cleavage. In an autoimmune T1DM model (NOD), we showed that in vivo β-cell–specific expression of mKL improved glucose tolerance, attenuated β-cell apoptosis, enhanced insulin storage in β-cells, and increased plasma insulin levels. The beneficial effect of Klotho gene delivery is likely due to attenuation of T-cell infiltration in pancreatic islets in NOD mice. Overall, our results demonstrate for the first time that Klotho protected β-cells in T1DM via attenuating apoptosis.     

Curtailing Endothelial TGF-β Signaling Is Sufficient to Reduce Endothelial-Mesenchymal Transition and Fibrosis in CKD

Excessive TGF-β signaling in epithelial cells, pericytes, or fibroblasts has been implicated in CKD. This list has recently been joined by endothelial cells (ECs) undergoing mesenchymal transition. Although several studies focused on the effects of ablating epithelial or fibroblast TGF-β signaling on development of fibrosis, there is a lack of information on ablating TGF-β signaling in the endothelium because this ablation causes embryonic lethality. We generated endothelium-specific heterozygous TGF-β receptor knockout (TβRII^endo+/−) mice to explore whether curtailed TGF-β signaling significantly modifies nephrosclerosis. These mice developed normally, but showed enhanced angiogenic potential compared with TβRII^endo+/+ mice under basal conditions. After induction of folic acid nephropathy or unilateral ureteral obstruction, TβRII^endo+/− mice exhibited less tubulointerstitial fibrosis, enhanced preservation of renal microvasculature, improvement in renal blood flow, and less tissue hypoxia than TβRII^endo+/+ counterparts. In addition, partial deletion of TβRII in the endothelium reduced endothelial-to-mesenchymal transition (EndoMT). TGF-β–induced canonical Smad2 signaling was reduced in TβRII^+/− ECs; however, activin receptor-like kinase 1 (ALK1)–mediated Smad1/5 phosphorylation in TβRII^+/− ECs remained unaffected. Furthermore, the S-endoglin/L-endoglin mRNA expression ratio was significantly lower in TβRII^+/− ECs compared with TβRII^+/+ ECs. These observations support the hypothesis that EndoMT contributes to renal fibrosis and curtailing endothelial TGF-β signals favors Smad1/5 proangiogenic programs and dictates increased angiogenic responses. Our data implicate endothelial TGF-β signaling and EndoMT in regulating angiogenic and fibrotic responses to injury.     

Hypertrophy in the Distal Convoluted Tubule of an 11β-Hydroxysteroid Dehydrogenase Type 2 Knockout Model

Na⁺ transport in the renal distal convoluted tubule (DCT) by the thiazide-sensitive NaCl cotransporter (NCC) is a major determinant of total body Na⁺ and BP. NCC-mediated transport is stimulated by aldosterone, the dominant regulator of chronic Na⁺ homeostasis, but the mechanism is controversial. Transport may also be affected by epithelial remodeling, which occurs in the DCT in response to chronic perturbations in electrolyte homeostasis. Hsd11b2^−/− mice, which lack the enzyme 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) and thus exhibit the syndrome of apparent mineralocorticoid excess, provided an ideal model in which to investigate the potential for DCT hypertrophy to contribute to Na⁺ retention in a hypertensive condition. The DCTs of Hsd11b2^−/− mice exhibited hypertrophy and hyperplasia and the kidneys expressed higher levels of total and phosphorylated NCC compared with those of wild-type mice. However, the striking structural and molecular phenotypes were not associated with an increase in the natriuretic effect of thiazide. In wild-type mice, Hsd11b2 mRNA was detected in some tubule segments expressing Slc12a3, but 11βHSD2 and NCC did not colocalize at the protein level. Thus, the phosphorylation status of NCC may not necessarily equate to its activity in vivo, and the structural remodeling of the DCT in the knockout mouse may not be a direct consequence of aberrant corticosteroid signaling in DCT cells. These observations suggest that the conventional concept of mineralocorticoid signaling in the DCT should be revised to recognize the complexity of NCC regulation by corticosteroids.     

BAMBI Elimination Enhances Alternative TGF-β Signaling and Glomerular Dysfunction in Diabetic Mice

BMP, activin, membrane-bound inhibitor (BAMBI) acts as a pseudo-receptor for the transforming growth factor (TGF)-β type I receptor family and a negative modulator of TGF-β kinase signaling, and BAMBI^−/− mice show mild endothelial dysfunction. Because diabetic glomerular disease is associated with TGF-β overexpression and microvascular alterations, we examined the effect of diabetes on glomerular BAMBI mRNA levels. In isolated glomeruli from biopsies of patients with diabetic nephropathy and in glomeruli from mice with type 2 diabetes, BAMBI was downregulated. We then examined the effects of BAMBI deletion on streptozotocin-induced diabetic glomerulopathy in mice. BAMBI^−/− mice developed more albuminuria, with a widening of foot processes, than BAMBI^+/+ mice, along with increased activation of alternative TGF-β pathways such as extracellular signal–related kinase (ERK)1/2 and Smad1/5 in glomeruli and cortices of BAMBI^−/− mice. Vegfr2 and Angpt1, genes controlling glomerular endothelial stability, were downmodulated in glomeruli from BAMBI^−/− mice with diabetes. Incubation of glomeruli from nondiabetic BAMBI^+/+ or BAMBI^−/− mice with TGF-β resulted in the downregulation of Vegfr2 and Angpt1, effects that were more pronounced in BAMBI^−/− mice and were prevented by a MEK inhibitor. The downregulation of Vegfr2 in diabetes was localized to glomerular endothelial cells using a histone yellow reporter under the Vegfr2 promoter. Thus, BAMBI modulates the effects of diabetes on glomerular permselectivity in association with altered ERK1/2 and Smad1/5 signaling. Future therapeutic interventions with inhibitors of alternative TGF-β signaling may therefore be of interest in diabetic nephropathy.