Macrophage migration inhibitory factor promotes renal injury induced by ischemic reperfusion.

Macrophage migration inhibitory factor (MIF) is pleiotropic cytokine that has multiple effects in many inflammatory and immune diseases. This study reveals a potential role of MIF in acute kidney injury (AKI) in patients and in kidney ischemic reperfusion injury (IRI) mouse model in MIF wild-type (WT) and MIF knockout (KO) mice. Clinically, plasma and urinary MIF levels were largely elevated at the onset of AKI, declined to normal levels when AKI was resolved and correlated tightly with serum creatinine independent of disease causes. Experimentally, MIF levels in plasma and urine were rapidly elevated after IRI-AKI and associated with the elevation of serum creatinine and the severity of tubular necrosis, which were suppressed in MIF KO mice. It was possible that MIF may mediate AKI via CD74/TLR4-NF-κB signalling as mice lacking MIF were protected from AKI by largely suppressing CD74/TLR-4-NF-κB associated renal inflammation, including the expression of MCP-1, TNF-α, IL-1ß, IL-6, iNOS, CXCL15(IL-8 in human) and infiltration of macrophages, neutrophil, and T cells. In conclusion, our study suggests that MIF may be pathogenic in AKI and levels of plasma and urinary MIF may correlate with the progression and regression of AKI.

Smad7 protects against acute kidney injury by rescuing tubular epithelial cells from the G1 cell cycle arrest.

Smad7 plays a protective role in chronic kidney disease; however, its role in acute kidney injury (AKI) remains unexplored. Here, we report that Smad7 protects against AKI by rescuing the G1 cell cycle arrest of tubular epithelial cells (TECs) in ischemia/reperfusion-induced AKI in mice in which Smad7 gene is disrupted or restored locally into the kidney. In Smad7 gene knockout (KO) mice, more severe renal impairment including higher levels of serum creatinine and massive tubular necrosis was developed at 48 h after AKI. In contrast, restored renal Smad7 gene locally into the kidney of Smad7 KO mice protected against AKI by promoting TEC proliferation identified by PCNA+ and BrdU+ cells. Mechanistic studies revealed that worsen AKI in Smad7 KO mice was associated with a marked activation of TGF-ß/Smad3-p21/p27 signaling and a loss of CDK2/cyclin E activities, thereby impairing TEC regeneration at the G1 cell cycle arrest. In contrast, restored Smad7 locally into the kidneys of Smad7 KO mice protected TECs from the G1 cell cycle arrest and promoted TEC G1/S transition via a CDK2/cyclin E-dependent mechanism. In conclusion, Smad7 plays a protective role in AKI. Blockade of TGF-ß/Smad3-p21/p27-induced G1 cell cycle arrest may be a key mechanism by which Smad7 treatment inhibits AKI. Thus, Smad7 may be a novel therapeutic agent for AKI.

C-reactive protein promotes acute kidney injury via Smad3-dependent inhibition of CDK2/cyclin E.

Acute kidney injury (AKI) is exacerbated in C-reactive protein transgenic mice but alleviated in Smad3 knockout mice. Here we used C-reactive protein transgenic/Smad3 wild-type and C-reactive protein transgenic/Smad3 knockout mice to investigate the signaling mechanisms by which C-reactive protein promotes AKI. Serum creatinine was elevated, and the extent of tubular epithelial cell necrosis following ischemia/reperfusion-induced AKI was greater in C-reactive protein transgenics but was blunted when Smad3 was deleted. Exacerbation of AKI in C-reactive protein transgenics was associated with increased TGF-ß/Smad3 signaling and expression of the cyclin kinase inhibitor p27, but decreased phosphorylated CDK2 and expression of cyclin E. Concomitantly, tubular epithelial cell proliferation was arrested at the G1 phase in C-reactive protein transgenics with fewer cells entering the S-phase cell cycle as evidenced by fewer bromodeoxyuridine-positive cells. In contrast, the protection from AKI in C-reactive protein transgenic/Smad3 knockout mice was associated with decreased expression of p27 and promotion of CDK2/cyclin E-dependent G1/S transition of tubular epithelial cells. In vitro studies using tubular epithelial cells showed that C-reactive protein activates Smad3 via both TGF-ß-dependent and ERK/MAPK cross talk mechanisms, Smad3 bound directly to p27, and blockade of Smad3 or the Fc receptor CD32 prevented C-reactive protein-induced p27-dependent G1 cell cycle arrest. In vivo, treatment of C-reactive protein transgenics with a Smad3 inhibitor largely improved AKI outcomes. Thus, C-reactive protein may promote AKI by impairing tubular epithelial cell regeneration via the CD32-Smad3-p27-driven inhibition of the CDK2/cyclin E complex. Targeting Smad3 may offer a new treatment approach for AKI.

Long Noncoding RNA Arid2-IR Is a Novel Therapeutic Target for Renal Inflammation.

Increasing evidence shows that microRNAs play an important role in kidney disease. However, functions of long noncoding RNAs (lncRNAs) in kidney diseases remain undefined. We have previously shown that TGF-ß1 plays a diverse role in renal inflammation and fibrosis and Smad3 is a key mediator in this process. In this study, we used RNA-sequencing to identify lncRNAs related to renal inflammation and fibrosis in obstructive nephropathy induced in Smad3 wild-type and knockout mice. We found that Arid2-IR was a Smad3-associated lncRNA as a Smad3 binding site was found in the promoter region of Arid2-IR and deletion of Smad3 abolished upregulation of Arid2-IR in the diseased kidney. In vitro knockdown of Arid2-IR from tubular epithelial cells produced no effect on TGF-ß-induced Smad3 signaling and fibrosis but inhibited interleukin-1ß-stimulated NF-κB-dependent inflammatory response. In contrast, overexpression of Arid2-IR promoted interleukin-1ß-induced NF-κB signaling and inflammatory cytokine expression without alteration of TGF-ß1-induced fibrotic response. Furthermore, treatment of obstructed kidney with Arid2-IR shRNA blunted NF-κB-driven renal inflammation without effect on TGF-ß/Smad3-mediated renal fibrosis. Thus, Arid2-IR is a novel lncRNA that functions to promote NF-κB-dependent renal inflammation. Blockade of Arid2-IR may represent a novel and specific therapy for renal inflammatory disease.

Identification of novel long noncoding RNAs associated with TGF-ß/Smad3-mediated renal inflammation and fibrosis by RNA sequencing.

We have previously shown that transforming growth factor-ß/Smad3-dependent miRNAs play a critical role in renal inflammation and fibrosis. However, off-target effects of miRNAs limit their therapeutic application. Recently, emerging roles of long noncoding RNAs (lncRNAs) in diseases have been recognized. In this study, we used high-throughput RNA sequencing to identify the Smad3-dependent lncRNAs related to renal inflammation and fibrosis in Smad3 knockout mouse models of unilateral ureteral obstructive nephropathy and immunologically induced anti-glomerular basement membrane glomerulonephritis. Compared with wild-type mice, 151 lncRNAs in the unilateral ureteral obstructive nephropathy kidney and 413 lncRNAs in kidneys with anti-glomerular basement membrane glomerulonephritis were significantly altered in Smad3 knockout mice. Among them, 21 common lncRNAs were up-regulated in wild-type, but down-regulated in Smad3 knockout, kidneys in both disease models in which progressive renal inflammation and fibrosis were abolished when the Smad3 gene was deleted or suppressed. Real-time PCR confirmed these findings and revealed the functional link between Smad3-dependent lncRNAs np_5318/np_17856 and progressive kidney injury. Results demonstrate that the identification and characterization of functional lncRNAs associated with kidney disease may represent a promising research direction into renal disorder and may lead to the development of new lncRNA therapies for kidney diseases.

MicroRNA-29b inhibits diabetic nephropathy in db/db mice.

Inflammation and its consequent fibrosis are two main features of diabetic nephropathy (DN), but target therapy on these processes for DN remains yet ineffective. We report here that miR-29b is a novel therapeutic agent capable of inhibiting progressive renal inflammation and fibrosis in type 2 diabetes in db/db mice. Under diabetic conditions, miR-29b was largely downregulated in response to advanced glycation end (AGE) product, which was associated with upregulation of collagen matrix in mesangial cells via the transforming growth factor-ß (TGF-ß)/Smad3-dependent mechanism. These pathological changes were reversed by overexpressing miR-29b, but enhanced by knocking-down miR-29b. Similarly, loss of renal miR-29b was associated with progressive diabetic kidney injury, including microalbuminuria, renal fibrosis, and inflammation. Restored renal miR-29b by the ultrasound-based gene therapy was capable of attenuating diabetic kidney disease. Further studies revealed that inhibition of Sp1 expression, TGF-ß/Smad3-dependent renal fibrosis, NF-κB-driven renal inflammation, and T-bet/Th1-mediated immune response may be mechanisms associated with miR-29b treatment in db/db mice. In conclusion, miR-29b may play a protective role in diabetic kidney disease and may have therapeutic potential for diabetic kidney complication.

Smad7 inhibits AngII-mediated hypertensive nephropathy in a mouse model of hypertension.

The TGFß (transforming growth factor ß)/SMAD and NF-κB (nuclear factor κB) signalling pathways play a key role in hypertensive nephropathy. The present study examined whether targeting these pathways by SMAD7, a downstream inhibitor of both pathways, blocks AngII (angiotensin II)-induced hypertensive kidney disease in mice. A doxycycline-inducible SMAD7-expressing plasmid was delivered into the kidney by a non-invasive ultrasound-microbubble technique before and after AngII infusion. Results showed that pre-treatment with SMAD7 prevented AngII-induced progressive renal injury by inhibiting an increase in proteinuria and serum creatinine while improving the glomerular filtration rate. Similarly, treatment with SMAD7 in the established hypertensive nephropathy at day 14 after AngII infusion halted the progressive renal injury. These preventive and therapeutic effects of SMAD7 on hypertensive kidney injury were associated with inhibition of AngII-induced up-regulation of SMURF2 (SMAD-specific E3 ubiquitin protein ligase 2) and Sp1 (specificity protein 1), blockade of TGFß/Smad3-mediated renal fibrosis and suppression of NF-κB-driven renal inflammation. Moreover, overexpression of SMAD7 also prevented AngII-induced loss of renal miR-29b, an miRNA with an inhibitory role in both TGFß/Smad3 and NF-κB pathways. In conclusion, SMAD7 may be a therapeutic agent for AngII-mediated hypertensive nephropathy. Inhibition of the Sp1/SMAD3/NF-κB/miR-29b regulatory network may be a mechanism by which SMAD7 inhibits hypertensive nephropathy.

A small-molecule macrophage migration inhibitory factor antagonist protects against glomerulonephritis in lupus-prone NZB/NZW F1 and MRL/lpr mice.

Autoimmunity leads to the activation of innate effector pathways, proinflammatory cytokine production, and end-organ injury. Macrophage migration inhibitory factor (MIF) is an upstream activator of the innate response that mediates the recruitment and retention of monocytes via CD74 and associated chemokine receptors, and it has a role in the maintenance of B lymphocytes. High-expression MIF alleles also are associated with end-organ damage in different autoimmune diseases. We assessed the therapeutic efficacy of (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1), an orally bioavailable MIF antagonist, in two distinct models of systemic lupus erythematosus: the NZB/NZW F1 and the MRL/lpr mouse strains. ISO-1, like anti-MIF, inhibited the interaction between MIF and its receptor, CD74, and in each model of disease, it reduced functional and histological indices of glomerulonephritis, CD74(+) and CXCR4(+) leukocyte recruitment, and proinflammatory cytokine and chemokine expression. Neither autoantibody production nor T and B cell activation were significantly affected, pointing to the specificity of MIF antagonism in reducing excessive proinflammatory responses. These data highlight the feasibility of targeting the MIF-MIF receptor interaction by small-molecule antagonism and support the therapeutic value of downregulating MIF-dependent pathways of tissue damage in systemic lupus erythematosus.

miR-29 inhibits bleomycin-induced pulmonary fibrosis in mice.

Loss of microRNA-29 (miR-29) is known to be a mechanism of transforming growth factor-ß (TGF-ß)-mediated pulmonary fibrosis, but the therapeutic implication of miR-29 for pulmonary fibrosis remains unexplored. The present study investigated whether miR-29 had therapeutic potential for lung disease induced by bleomycin in mice. In addition, the signaling mechanisms that regulated miR-29 expression were investigated in vivo and in vitro. We found that miR-29 was a downstream target gene of Smad3 and negatively regulated by TGF-ß/Smad signaling in fibrosis. This was evidenced by the findings that mice or pulmonary fibroblasts null for Smad3 were protected against bleomycin or TGF-ß1-induced loss of miR-29 along with fibrosis in vivo and in vitro. Interestingly, overexpression of miR-29 could in turn negatively regulated TGF-ß and connective tissue growth factor (CTGF) expression and Smad3 signaling. Therefore, Sleeping Beauty (SB)-mediated miR-29 gene transfer into normal and diseased lung tissues was capable of preventing and treating pulmonary fibrosis including inflammatory macrophage infiltration induced by bleomycin in mice. In conclusion, miR-29 is negatively regulated by TGF-ß/Smad3 and has a therapeutic potential for pulmonary fibrosis. SB-mediated miR-29 gene therapy is a non-invasive therapeutic strategy for lung disease associated with fibrosis.

Smad3 mediates ANG II-induced hypertensive kidney disease in mice.

Although Smad3 is a key mediator for fibrosis, its functional role and mechanisms in hypertensive nephropathy remain largely unclear. This was examined in the present study in a mouse model of hypertension induced in Smad3 knockout (KO) and wild-type (WT) mice by subcutaneous angiotensin II infusion and in vitro in mesangial cells lacking Smad3. After angiotensin II infusion, both Smad3 KO and WT mice developed equally high levels of blood pressure. However, disruption of Smad3 prevented angiotensin II-induced kidney injury by lowering albuminuria and serum creatinine (P < 0.01), inhibiting renal fibrosis such as collagen type I and IV, fibronectin, and α-SMA expression (all P < 0.01), and blocking renal inflammation including macrophage and T cell infiltration and upregulation of IL-1ß, TNF-α, and monocyte chemoattractant protein-1 in vivo and in vitro (all P < 0.001). Further studies revealed that blockade of angiotensin II-induced renal transforming growth factor (TGF)-ß1 expression and inhibition of Smurf2-mediated degradation of renal Smad7 are mechanisms by which Smad3 KO mice were protected from angiotensin II-induced renal fibrosis and NF-κB-driven renal inflammation in vivo and in vitro. In conclusion, Smad3 is a key mediator of hypertensive nephropathy. Smad3 promotes Smurf2-dependent ubiquitin degradation of renal Smad7, thereby enhancing angiotensin II-induced TGF-ß/Smad3-mediated renal fibrosis and NF-κB-driven renal inflammation. Results from this study suggest that inhibition of Smad3 or overexpression of Smad7 may be a novel therapeutic strategy for hypertensive nephropathy.

TGF-ß/Smad3 signaling promotes renal fibrosis by inhibiting miR-29.

TGF-ß/Smad3 signaling promotes fibrosis, but the development of therapeutic interventions involving this pathway will require the identification and ultimate targeting of downstream fibrosis-specific genes. In this study, using a microRNA microarray and real-time PCR, wild-type mice had reduced expression of miR-29 along with the development of progressive renal fibrosis in obstructive nephropathy. In contrast, Smad3 knockout mice had increased expression of miR-29 along with the absence of renal fibrosis in the same model of obstruction. In cultured fibroblasts and tubular epithelial cells, Smad3 mediated TGF-ß(1)-induced downregulation of miR-29 by binding to the promoter of miR-29. Furthermore, miR-29 acted as a downstream inhibitor and therapeutic microRNA for TGF-ß/Smad3-mediated fibrosis. In vitro, overexpression of miR-29b inhibited, but knockdown of miR-29 enhanced, TGF-ß(1)-induced expression of collagens I and III by renal tubular cells. Ultrasound-mediated gene delivery of miR-29b either before or after established obstructive nephropathy blocked progressive renal fibrosis. In conclusion, miR-29 is a downstream inhibitor of TGF-ß/Smad3-mediated fibrosis and may have therapeutic potential for diseases involving fibrosis.

SARS-CoV-2 N Protein Induces Acute Kidney Injury via Smad3-Dependent G1 Cell Cycle Arrest Mechanism.

COVID-19 is infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and can cause severe multiple organ injury and death. Kidney is one of major target organs of COVID-19 and acute kidney injury (AKI) is common in critically ill COVID-19 patients. However, mechanisms through which COVID-19 causes AKI remain largely unknown and treatment remains unspecific and ineffective. Here, the authors report that normal kidney-specifically overexpressing SARS-CoV-2 N develops AKI, which worsens in mice under ischemic condition. Mechanistically, it is uncovered that SARS-CoV-2 N-induced AKI is Smad3-dependent as SARS-CoV-2 N protein can interact with Smad3 and enhance TGF-ß/Smad3 signaling to cause tubular epithelial cell death and AKI via the G1 cell cycle arrest mechanism. This is further confirmed in Smad3 knockout mice and cells in which deletion of Smad3 protects against SARS-CoV-2 N protein-induced cell death and AKI in vivo and in vitro. Most significantly, it is also found that targeting Smad3 with a Smad3 pharmacological inhibitor is able to inhibit SARS-CoV-2 N-induced AKI. In conclusion, the authors identify that SARS-CoV-2 N protein is a key mediator for AKI and induces AKI via the Smad3-dependent G1 cell cycle arrest mechanism. Targeting Smad3 may represent as a novel therapy for COVID-19-asscoaited AKI.

C-reactive protein promotes acute renal inflammation and fibrosis in unilateral ureteral obstructive nephropathy in mice.

Elevated blood level of C-reactive protein (CRP) is associated with increased risk of chronic kidney disease. However, whether this association reflects functional importance of CRP in the pathogenesis of kidney disease remains unclear. In this study, we examined the biological role of CRP in a well-characterized model of progressive kidney disease, unilateral ureteral obstruction (UUO), in mice that express the human CRP gene (CRPtg). Compared with wild-type (Wt) mice at 3 days after UUO, CRPtg mice developed more severe renal inflammation with a significant increase in tubulointerstitial T cells and macrophages, upregulation of proinflammatory cytokines (IL-1ß and TNF-α), chemokines (MCP-1), and adhesion molecules (ICAM-1). Renal fibrosis was also significantly enhanced in CRPtg mice as demonstrated by increased expression of tubulointerstitial α-smooth muscle actin and collagen types I and III compared with Wt mice. Interestingly, on days 7 and 14 after UUO, an equal severity of renal inflammation and fibrosis were observed in CRPtg and Wt mice. These findings suggested that CRP may have a role in the initiation of renal inflammation and fibrosis. Further study revealed that enhanced early renal inflammation and fibrosis on day 3 in CRPtg mice was associated with a significant upregulation of endogenous mouse CRP and FcγRI mRNA and increased activation of both NF-κB/p65 and TGF-ß/Smad2/3 signaling, while equal severity of progressive renal injury at day 7 and day 14 between CRPtg and Wt mice were attributed to equivalent levels of CRP, FcγRI, phospho-NF-κB/p65, and TGF-ß/Smad2/3 signaling. Based on these findings, we conclude that CRP may not only be a biomarker, but also a mediator in the early development of renal inflammation and fibrosis in a mouse model of UUO. Enhanced activation of both NF-κB and TGF-ß/Smad signaling pathways may be mechanisms by which CRP promotes early renal inflammation and fibrosis.

Amelioration of albuminuria in ROCK1 knockout mice with streptozotocin-induced diabetic kidney disease.

BACKGROUND: Although blockade of Rho kinase with pharmacologic inhibitors ameliorates renal fibrosis and diabetic kidney disease (DKD), the underlined mechanisms remain largely unclear. The present study tested the hypothesis that ROCK1 may regulate the early development of albuminuria via the megalin/cubilin-dependent mechanism. METHODS: A DKD model was induced in ROCK1 knockout and wild-type mice by streptozotocin (STZ). The effect of deleted ROCK1 on urinary albumin excretion and the expression of megalin/cubilin were examined. In addition, the effect of blocking ROCK activities with an inhibitor (Y-27632) on tubular albumin reabsorption was tested in a normal rat tubular epithelial cell line (NRK52E) under high-glucose conditions. Expression of transforming growth factor (TGF)-ß1, interleukin-1ß and collagen-1 was also been examined. RESULTS: Urinary albumin excretion was significantly increased in ROCK1 WT mice at 8 weeks after STZ injection. In contrast, mice lacking ROCK1 gene were protected against the development of albuminuria. This was associated with the protection against the loss of megalin/cubilin and an increase in TGF-ß(1), IL-1ß, and fibrosis in the kidney. In vitro, we also found that blockade of Rho kinase with inhibitor Y-27632 prevented high-glucose-induced loss of megalin expression and an increase of TGF-ß(1), thereby increasing the absorption rate of FITC-labeled albumin by tubular epithelial cells. CONCLUSION: ROCK1 may play a role in the development of albuminuria in DKD by downregulating the endocytosis receptors complex - megalin/cubilin.

miR-192 mediates TGF-beta/Smad3-driven renal fibrosis.

TGF-beta/Smad3 promotes renal fibrosis, but the mechanisms that regulate profibrotic genes remain unclear. We hypothesized that miR-192, a microRNA expressed in the kidney may mediate renal fibrosis in a Smad3-dependent manner. Microarray and real-time PCR demonstrated a tight association between upregulation of miR-192 in the fibrotic kidney and activation of TGF-beta/Smad signaling. Deletion of Smad7 promoted miR-192 expression and enhanced Smad signaling and fibrosis in obstructive kidney disease. In contrast, overexpression of Smad7 to block TGF-beta/Smad signaling inhibited miR-192 expression and renal fibrosis in the rat 5/6 nephrectomy model; in vitro, overexpression of Smad7 in tubular epithelial cells abolished TGF-beta1-induced miR-192 expression. Furthermore, Smad3 but not Smad2 mediated TGF-beta1-induced miR-192 expression by binding to the miR-192 promoter. Last, overexpression of a miR-192 mimic promoted and addition of a miR-192 inhibitor blocked TGF-beta1-induced collagen matrix expression. Taken together, miR-192 may be a critical downstream mediator of TGF-beta/Smad3 signaling in the development of renal fibrosis.

Activation of p53 promotes renal injury in acute aristolochic acid nephropathy.

Ingestion of aristolochic acid (AA) can cause AA nephropathy (AAN), in which excessive death of tubular epithelial cells (TECs) characterize the acute phase. AA forms adducts with DNA, which may lead to TEC apoptosis via p53-mediated signaling. We tested this hypothesis both by studying p53-deficient mice and by blocking p53 in TECs with its inhibitor pifithrin-alpha. AA induced acute AAN in wild-type mice, resulting in massive apoptotic and necrotic TEC death and acute renal failure; p53 deficiency or pharmacologic inhibition attenuated this injury. In vitro, AA induced apoptotic and necrotic death of TEC in a time- and dosage-dependent manner, with apoptosis marked by a 10-fold increase in cleaved caspase-3 and terminal deoxynucleotidyl transferase-mediated digoxigenin-deoxyuridine nick-end labeling-positive/Annexin V-positive propidium iodide-negative TECs (all P < 0.001). AA induced dephosphorylation of STAT3 and the subsequent activation of p53 and TEC apoptosis. In contrast, overexpression of STAT3, p53 inhibition, or p53 knockdown with small interfering RNA all attenuated AA-induced TEC apoptosis. Taken together, these results suggest that AA induces TEC death via apoptosis by dephosphorylation of STAT3 and posttranslational activation of p53, supporting the hypothesis that p53 promotes renal injury in acute AAN.

Advanced glycation end-products induce tubular CTGF via TGF-beta-independent Smad3 signaling.

Advanced glycation end-products (AGEs) can induce expression of connective tissue growth factor (CTGF), which seems to promote the development of diabetic nephropathy, but the exact signaling mechanisms that mediate this induction are unknown. Here, AGEs induced CTGF expression in tubular epithelial cells (TECs) that either lacked the TGF-beta1 gene or expressed dominant TGF-beta receptor II, demonstrating independence of TGF-beta. Furthermore, conditional knockout of the gene encoding TGF-beta receptor II from the kidney did not prevent AGE-induced renal expression of CTGF and collagen I. More specific, AGEs induced CTGF expression via the receptor for AGEs-extracellular signal-regulated kinase (RAGE-ERK)/p38 mitogen-activated protein kinase-Smad cross-talk pathway because inhibition of this pathway by several methods (anti-RAGE antibody, specific inhibitors, or dominant negative adenovirus to ERK1/2 and p38) blocked this induction. Overexpressing Smad7 abolished AGE-induced Smad3 phosphorylation and CTGF expression, demonstrating the necessity for activation of Smad signaling in this process. More important, knockdown of either Smad3 or Smad2 demonstrated that Smad3 but not Smad2 is essential for CTGF induction in response to AGEs. In conclusion, AGEs induce tubular CTGF expression via the TGF-beta-independent RAGE-ERK/p38-Smad3 cross-talk pathway. These data suggest that overexpression of Smad7 or targeting Smad3 may have therapeutic potential for diabetic nephropathy.

Latent TGF-ß1 protects against diabetic kidney disease via Arkadia/Smad7 signaling.

TGF-ß1 has long been considered as a key mediator in diabetic kidney disease (DKD) but anti-TGF-ß1 treatment fails clinically, suggesting a diverse role for TGF-ß1 in DKD. In the present study, we examined a novel hypothesis that latent TGF-ß1 may be protective in DKD mice overexpressing human latent TGF-ß1. Streptozotocin-induced Type 1 diabetes was induced in latent TGF-ß1 transgenic (Tg) and wild-type (WT) mice. Surprisingly, compared to WT diabetic mice, mice overexpressing latent TGF-ß1 were protected from the development of DKD as demonstrated by lowing microalbuminuria and inhibiting renal fibrosis and inflammation, although blood glucose levels were not altered. Mechanistically, the renal protective effects of latent TGF-ß1 on DKD were associated with inactivation of both TGF-ß/Smad and nuclear factor-κB (NF-κB) signaling pathways. These protective effects were associated with the prevention of renal Smad7 from the Arkadia-induced ubiquitin proteasomal degradation in the diabetic kidney, suggesting protection of renal Smad7 from Arkadia-mediated degradation may be a key mechanism through which latent TGF-ß1 inhibits DKD. This was further confirmed in vitro in mesangial cells that knockdown of Arkadia failed but overexpression of Arkadia reversed the protective effects of latent TGF-ß1 on high glucose-treated mesangial cells. Latent TGF-ß1 may protect kidneys from TGF-ß1/Smad3-mediated renal fibrosis and NF-κB-driven renal inflammation in diabetes through inhibiting Arkadia-mediated Smad7 ubiquitin degradation.

Essential role for macrophage migration inhibitory factor in gastritis induced by Helicobacter pylori.

Macrophage migration inhibitory factor (MIF) is an upstream regulator of immune and inflammatory responses; however, its role in Helicobacter pylori (HP)-associated gastritis remains unknown. We infected MIF knockout (KO) and wild-type mice with SS1 HP and found that 2 weeks after infection, MIF and its receptor CD74 were markedly up-regulated in wild-type mice. This up-regulation preceded the up-regulation of both tumor necrosis factor-alpha and intercellular adhesion molecule-1, as well as the development of moderate gastritis at 8 weeks, as determined by a significant infiltration of neutrophils, T cells, and macrophages. In contrast, KO mice were protected against HP-induced gastritis by preventing the up-regulation of CD74 and Th1-mediated immune injury, including a reduction in the Th1 transcriptional factor T-bet and the expression of interferon-gamma. Additionally, inhibition of skin delayed type hypersensitivity reactions to HP antigens in KO mice also suggested a critical role for MIF in cell-mediated injury. A regulatory role for MIF in Th1-immune responses was further demonstrated by the finding that antigen-primed CD4(+) T cells lacking MIF failed to differentiate into the Th1 phenotype; these cells were instead promoted to Th2 differentiation after challenge with HP antigen in vitro. Results from this study indicated that inhibition of HP-induced innate immune responses and Th1-mediated immune injury may be the key mechanisms by which KO mice failed to develop gastritis after HP infection.

Disruption of the Smad7 gene promotes renal fibrosis and inflammation in unilateral ureteral obstruction (UUO) in mice.

BACKGROUND: The present study tested the hypothesis that disruption of Smad7 function may accelerate renal fibrosis and inflammation. METHODS: This was investigated in a unilateral ureteral obstruction (UUO) model induced in wild-type (WT) and Smad7DeltaE1 mice in which functional Smad7 is disrupted by deleting exon I in the Smad7 gene. Renal fibrosis and inflammation after UUO were examined by histology, real-time PCR, western blot analyses and immunohistochemistry. RESULTS: Seven days after UUO, severe tubulointerstitial fibrosis developed in WT mice as evidenced by a marked increase in alpha-SMA, collagen I and III extracellular matrix. This was associated with a significant upregulation of renal TGF-beta1 and CTGF and activation of Smad2/3. Interestingly, compared to WT UUO mice, Smad7DeltaE1 mice with UUO exhibited a further increase in TGF-beta/Smad2/3-dependent renal fibrosis. Moreover, compared to WT UUO mice, deletion of the Smad7 gene also sustained NF-kappaB activation and thus enhanced further renal inflammation such as macrophage infiltration and upregulation of TNF-alpha, MCP-1, OPN and ICAM-1. CONCLUSION: Smad7 is a critical negative regulator of TGF-beta/Smad2/3 and NF-kappaB signalling and plays a negative regulating role in both renal fibrosis and inflammation after UUO. Results from this study further support the notion that Smad7 may be a therapeutic agent for kidney diseases.