BAMBI is expressed in endothelial cells and is regulated by lysosomal/autolysosomal degradation

The role of perirenal adipose tissue deposition in chronic kidney disease progression: Mechanisms and therapeutic implications

Chronic kidney disease (CKD) represents a significant and escalating global health challenge, with morbidity and mortality rates rising steadily. Evidence increasingly implicates perirenal adipose tissue (PRAT) deposition as a contributing factor in the pathogenesis of CKD. This review explores how PRAT deposition may exert deleterious effects on renal structure and function. The anatomical proximity of PRAT to the kidneys not only potentially causes mechanical compression but also leads to the dysregulated secretion of adipokines and inflammatory mediators, such as adiponectin, leptin, visfatin, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and exosomes. Additionally, PRAT deposition may contribute to renal lipotoxicity through elevated levels of free fatty acids (FFA), triglycerides (TAG), diacylglycerol (DAG), and ceramides (Cer). PRAT deposition is also linked to the hyperactivation of the renin-angiotensin-aldosterone system (RAAS), which further exacerbates CKD progression. Recognizing PRAT deposition as an independent risk factor for CKD underscores the potential of targeting PRAT as a novel strategy for the prevention and management of CKD. This review further discusses interventions that could include measuring PRAT thickness to establish a baseline, managing metabolic risk factors that promote its deposition, and inhibiting key PRAT-induced signaling pathways.

BMP and activin receptor membrane bound inhibitor: BAMBI has multiple roles in gene expression and diseases (Review)

BMP and activin membrane-bound inhibitor (BAMBI) is a transmembrane glycoprotein, known as a pseudo-receptor for TGFβ, as, while its extracellular domain is similar to that of type I TGFβ receptors, its intracellular structure is shorter and lacks a serine/threonine phosphokinase signaling motif. BAMBI can regulate numerous biological phenomena, including glucose and lipid metabolism, inflammatory responses, and cell proliferation and differentiation. Furthermore, abnormal expression of BAMBI at the mRNA and protein levels contributes to various human pathologies, including obesity and cancer. In the present review, the structure of BAMBI is briefly introduced and its associated signaling pathways and physiological functions are described. Understanding of BAMBI structure and function may contribute to knowledge regarding the occurrence of diseases, including obesity and diabetes, among others. The present review provides a theoretical foundation for the development of BAMBI as a potential biomarker or therapeutic target.

The study on role of endothelial cell autophagy in rats with sepsis-induced acute kidney injury

Sepsis often causes acute kidney injury (AKI). Autophagy of renal tubular epithelial cells is considered a cytoprotective mechanism in septic AKI; however, the role of autophagy of renal endothelial cells is uninvestigated. The current study examined whether autophagy was induced by sepsis in renal endothelial cells and whether induction of autophagy in these cells attenuated the degree of AKI. Cecal ligation and puncture (CLP) was used as a model of sepsis in rats. Four experimental groups included: sham, CLP alone, CLP + rapamycin (RAPA), and CLP + dimethyl sulfoxide (DMSO), where RAPA was used as an activator of autophagy. CLP increased renal LC3-II protein levels with an additional transient increase by RAPA at 18 h. In addition, CLP induced autophagosome formation in renal endothelial cells had an additional increase induced by RAPA. Interestingly, the levels of bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI), an endothelial cell-specific protein in the kidney, were also increased by CLP, albeit it was transiently downregulated by RAPA at 18 h. Serum thrombomodulin increased and renal vascular endothelial (VE)-cadherin decreased following CLP, and these changes were attenuated by RAPA. The renal cortex exhibited and inflammatory tissue damage after CLP, and RAPA alleviated these histopathological injuries. The current findings indicate that autophagy was induced by sepsis in renal endothelial cells, and upregulation of autophagy in these cells alleviated endothelial injury and AKI. In addition, BAMBI was induced by sepsis in the kidney, which may play a role in regulating endothelial stability in septic AKI.

AUTOPHAGY IN THE EYE: FROM PHYSIOLOGY TO PATHOPHYSOLOGY

Autophagy is a catabolic self-degradative pathway that promotes the degradation and recycling of intracellular material through the lysosomal compartment. Although first believed to function in conditions of nutritional stress, autophagy is emerging as a critical cellular pathway, involved in a variety of physiological and pathophysiological processes. Autophagy dysregulation is associated with an increasing number of diseases, including ocular diseases. On one hand, mutations in autophagy-related genes have been linked to cataracts, glaucoma, and corneal dystrophy; on the other hand, alterations in autophagy and lysosomal pathways are a common finding in essentially all diseases of the eye. Moreover, LC3-associated phagocytosis, a form of non-canonical autophagy, is critical in promoting visual cycle function. This review collects the latest understanding of autophagy in the context of the eye. We will review and discuss the respective roles of autophagy in the physiology and/or pathophysiology of each of the ocular tissues, its diurnal/circadian variation, as well as its involvement in diseases of the eye.

Expression and Function of BMP and Activin Membrane-Bound Inhibitor (BAMBI) in Chronic Liver Diseases and Hepatocellular Carcinoma

BAMBI (bone morphogenetic protein and activin membrane-bound inhibitor) is a transmembrane pseudoreceptor structurally related to transforming growth factor (TGF)-β type 1 receptors (TGF-β1Rs). BAMBI lacks a kinase domain and functions as a TGF-β1R antagonist. Essential processes such as cell differentiation and proliferation are regulated by TGF-β1R signaling. TGF-β is the best-studied ligand of TGF-βRs and has an eminent role in inflammation and fibrogenesis. Liver fibrosis is the end stage of almost all chronic liver diseases, such as non-alcoholic fatty liver disease, and at the moment, there is no effective anti-fibrotic therapy available. Hepatic BAMBI is downregulated in rodent models of liver injury and in the fibrotic liver of patients, suggesting that low BAMBI has a role in liver fibrosis. Experimental evidence convincingly demonstrated that BAMBI overexpression is able to protect against liver fibrosis. Chronic liver diseases have a high risk of hepatocellular carcinoma (HCC), and BAMBI was shown to exert tumor-promoting as well as tumor-protective functions. This review article aims to summarize relevant studies on hepatic BAMBI expression and its role in chronic liver diseases and HCC.

BMP and activin membrane-bound inhibitor regulate connective tissue growth factor controlling mesothelioma cell proliferation

Background

Malignant mesothelioma (MM) is an aggressive mesothelial cell cancer type linked mainly to asbestos inhalation. MM characterizes by rapid progression and resistance to standard therapeutic modalities such as surgery, chemotherapy, and radiotherapy. Our previous studies have suggested that tumor cell-derived connective tissue growth factor (CTGF) regulates the proliferation of MM cells as well as the tumor growth in mouse xenograft models.

Methods

In this study, we knock downed the bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) and CTGF in MM cells and investigated the relationship between both and their impact on the cell cycle and cell proliferation.

Results

The knockdown of CTGF or BAMBI reduced MM cell proliferation. In contrast to CTGF knockdown which decreased BAMBI, knockdown of BAMBI increased CTGF levels. Knockdown of either BAMBI or CTGF reduced expression of the cell cycle regulators; cyclin D3, cyclin-dependent kinase (CDK)2, and CDK4. Further, in silico analysis revealed that higher BAMBI expression was associated with shorter overall survival rates among MM patients.

Conclusions

Our findings suggest that BAMBI is regulated by CTGF promoting mesothelioma growth by driving cell cycle progression. Therefore, the crosstalk between BAMBI and CTGF may be an effective therapeutic target for MM treatment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10080-x.

The physiological and pathophysiological roles of the autophagy lysosomal system in the conventional aqueous humor outflow pathway: More than cellular clean up

During the last few years, the autophagy lysosomal system is emerging as a central cellular pathway with roles in survival, acting as a housekeeper and stress response mechanism. Studies by our and other labs suggest that autophagy might play an essential role in maintaining aqueous humor outflow homeostasis, and that malfunction of autophagy in outflow pathway cells might predispose to ocular hypertension and glaucoma pathogenesis. In this review, we will collect the current knowledge and discuss the molecular mechanisms by which autophagy does or might regulate normal outflow pathway tissue function, and its response to different types of stressors (oxidative stress and mechanical stress). We will also discuss novel roles of autophagy and lysosomal enzymes in modulation of TGFβ signaling and ECM remodeling, and the link between dysregulated autophagy and cellular senescence. We will examine what we have learnt, using pre-clinical animal models about how dysregulated autophagy can contribute to disease and apply that to the current status of autophagy in human glaucoma. Finally, we will consider and discuss the challenges and the potential of autophagy as a therapeutic target for the treatment of ocular hypertension and glaucoma.

Mobile phone radiation might alter gene expression in the oral squamous epithelial cells

Background

Accumulating evidence has shown that radiofrequency radiation (RFR) emitted by mobile phones is a potential factor for DNA damage. Whether RFR affects the gene expression of human genes still requires further research. This may help in understanding the mechanisms of action of this radiation. On the assumption that expression of BAMBI and Survivin in the oral squamous epithelial cells might be modified in response to RF electromagnetic field (RF-EMF) exposure, the current study was conducted on a group of young university student volunteers.

Results

Statistical analysis of the RT-PCR data indicated that no significant association (P value ˃ 0.05) exists between the expression of either gene, and neither the length of history nor the frequency of the phone use.

Conclusions

Although no clear RF-EMF signature on gene expression could be detected in this in this preliminary study, it is one of the few studies indicating that molecular-level changes might take place in humans in response to chronic mobile phone EMR exposure. Further investigations in this field are warranted.

Development of Biomarkers and Molecular Therapy Based on Inflammatory Genes in Diabetic Nephropathy

Diabetic Nephropathy (DN) is a debilitating consequence of both Type 1 and Type 2 diabetes affecting the kidney and renal tubules leading to End Stage Renal Disease (ESRD). As diabetes is a world epidemic and almost half of diabetic patients develop DN in their lifetime, a large group of people is affected. Due to the complex nature of the disease, current diagnosis and treatment are not adequate to halt disease progression or provide an effective cure. DN is now considered a manifestation of inflammation where inflammatory molecules regulate most of the renal physiology. Recent advances in genetics and genomic technology have identified numerous susceptibility genes that are associated with DN, many of which have inflammatory functions. Based on their role in DN, we will discuss the current aspects of developing biomarkers and molecular therapy for advancing precision medicine.

Autophagy in kidney homeostasis and disease

Autophagy is a conserved lysosomal pathway for the degradation of cytoplasmic components. Basal autophagy in kidney cells is essential for the maintenance of kidney homeostasis, structure and function. Under stress conditions, autophagy is altered as part of the adaptive response of kidney cells, in a process that is tightly regulated by signalling pathways that can modulate the cellular autophagic flux - mammalian target of rapamycin, AMP-activated protein kinase and sirtuins are key regulators of autophagy. Dysregulated autophagy contributes to the pathogenesis of acute kidney injury, to incomplete kidney repair after acute kidney injury and to chronic kidney disease of varied aetiologies, including diabetic kidney disease, focal segmental glomerulosclerosis and polycystic kidney disease. Autophagy also has a role in kidney ageing. However, questions remain about whether autophagy has a protective or a pathological role in kidney fibrosis, and about the precise mechanisms and signalling pathways underlying the autophagy response in different types of kidney cells and across the spectrum of kidney diseases. Further research is needed to gain insights into the regulation of autophagy in the kidneys and to enable the discovery of pathway-specific and kidney-selective therapies for kidney diseases and anti-ageing strategies.

Podocyte and endothelial-specific elimination of BAMBI identifies differential transforming growth factor-β pathways contributing to diabetic glomerulopathy

Transforming growth factor-β (TGF-β) is a central mediator of diabetic nephropathy. The effect of TGF-β, mediated by the type I TGF-β receptor, ALK5, and subsequent Smad2/3 activation results in podocyte apoptosis and loss. Previously, we demonstrated that the genetic deletion of the BMP and Activin Membrane-Bound Inhibitor (BAMBI), a negative modulator TGF-β signaling, accelerates diabetic nephropathy in mice. This was associated with heightened ALK1-mediated activation of Smad1/5 in the glomerular endothelial cells (ECs). Therefore, to evaluate the glomerular cell-specific effects of TGF-β in diabetic nephropathy we examined the effects of the podocyte- or EC-specific loss of Bambi (Pod-Bambi-/- or EC-Bambi-/-) in streptozotocin-induced diabetic mice with endothelial nitric oxide synthase deficiency. Interestingly, although hyperglycemia and body weight loss were similar in all groups of diabetic mice, significant hypertension was present only in the diabetic EC-Bambi-/- mice. While the podocyte or EC-specific loss of BAMBI both accelerated the progression of diabetic nephropathy, the worsened podocyte injury and loss observed in the diabetic Pod-Bambi-/- mice were associated with enhanced Smad3 activation. Increased Smad1/5 activation and EC proliferation were apparent only in the glomeruli of diabetic EC-Bambi-/- mice. The enhanced Smad1/5 activation in diabetic EC-Bambi-/- mice was associated with increased glomerular expression of plasmalemma vesicle-associated protein, pointing to the involvement of immature or dedifferentiated glomerular ECs in diabetic nephropathy. Notably, diabetic EC-Bambi-/- mice displayed podocyte injury and loss that were comparable to diabetic Pod-Bambi-/- mice. Thus, our results highlight the glomerular cell-specific contribution of TGF-β signaling and the intricate cross-talk between injured glomerular cells in the progression of diabetic nephropathy.

Transcriptome analysis reveals autophagy as regulator of TGFβ/Smad-induced fibrogenesis in trabecular meshwork cells

The trabecular meshwork (TM) is a specialized ocular tissue, which is responsible, together with the Schlemm’s canal (SC), for maintaining appropriate levels of intraocular pressure. Dysfunction of these tissues leads to ocular hypertension and increases the risk for developing glaucoma. Previous work by our laboratory revealed dysregulated autophagy in aging and in glaucomatous TM cells. In order to gain more insight in the role of autophagy in the TM pathophysiology, we have conducted transcriptome and functional network analyses of TM primary cells with silenced expression of the autophagy genes Atg5 and Atg7. Atg5/7-deficient TM cells showed changes in transcript levels of several fibrotic genes, including TGFβ2, BAMBI, and SMA. Furthermore, genetic and pharmacological inhibition of autophagy was associated with a parallel reduction in TGFβ-induced fibrosis, caused by a BAMBI-mediated reduced activation of Smad2/3 signaling in autophagy-deficient cells. At the same time, TGFβ treatment led to Smad2/3-dependent dysregulation of autophagy in TM cells, characterized by increased LC3-II levels and autophagic vacuoles content. Together, our results indicate a cross-talk between autophagy and TGFβ signaling in TM cells.

Metformin inhibits TGF-beta 1-induced MCP-1 expression through BAMBI-mediated suppression of MEK/ERK1/2 signalling

AIMS

Metformin is a biguanide derivative widely used for the treatment of type 2 diabetes mellitus. Recent evidence demonstrates that this anti-hyperglycaemic drug exerts renal protective effects, yet the mechanisms remain poorly understood. monocyte chemoattractant protein 1 (MCP-1) has been recognized as a key mediator of renal fibrosis in chronic kidney diseases, including diabetic nephropathy. This study aimed to investigate the effects of metformin on transforming growth factor beta 1 (TGF-β1)-induced MCP-1 expression and the underlying mechanisms in rat renal tubular epithelial cells.

METHODS

Rat renal tubular epithelial cell line NRK-52E cells were stimulated with TGF-β1 and/or metformin. The messenger RNA (mRNA) of MCP-1 and bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) was evaluated by real-time quantitative polymerase chain reaction. MCP-1 protein was measured by enzyme linked immunosorbent assay (ELISA). Total and phosphorylated extracellular signal-regulated kinases 1/2 (ERK1/2) was evaluated by western blot. Down- and upregulation of BAMBI were achieved by RNA interference targeting BAMBI and lentiviral vector-mediated overexpression of the BAMBI gene, respectively. Cell viability was analysed using Cell Counting Kit 8 (CCK-8) reagents.

RESULTS

Stimulation with TGF-β1 resulted in the increased expression of MCP-1 and decreased expression of BAMBI in NRK-52E cells. Metformin inhibited the expression of MCP-1 in NRK-52E cells. Pretreatment with metformin suppressed upregulation of MCP-1 and downregulation of BAMBI, as well as phosphorylation of ERK1/2 induced by TGF-β1. U0126, a specific inhibitor for mitogen-activated and extracellular signal-regulated kinase kinases 1/2 (MEK-1/2), completely blocked TGF-β1-induced MCP-1 expression. Knockdown of the BAMBI gene promoted phosphorylation of ERK1/2 and TGF-β1-induced expression of MCP-1. Overexpression of BAMBI inhibited phosphorylation of ERK1/2 and TGF-β1-induced upregulation of MCP-1.

CONCLUSION

In rat renal tubular epithelial cells, metformin prevents TGF-β1-induced MCP-1 expression, in which BAMBI-mediated inhibition of MEK/ERK1/2 might be involved.

Functional Genomics for the Identification of Modulators of Platelet-Dependent Thrombus Formation

Despite the absence of the genome in platelets, transcription profiling provides important insights into platelet function and can help clarify abnormalities in platelet disorders. The Bloodomics Consortium performed whole-genome expression analysis comparing in vitro–differentiated megakaryocytes (MKs) with in vitro–differentiated erythroblasts and different blood cell types. This allowed the identification of genes with upregulated expression in MKs compared with all other cell lineages, among the receptors BAMBI, LRRC32, ESAM, and DCBLD2. In a later correlative analysis of genome-wide platelet RNA expression with interindividual human platelet reactivity, LLRFIP and COMMD7 were additionally identified. A functional genomics approach using morpholino-based silencing in zebrafish identified various roles for all of these selected genes in thrombus formation. In this review, we summarize the role of the six identified genes in zebrafish and discuss how they correlate with subsequently performed mouse experiments.

Cell Apoptosis and Autophagy in Renal Fibrosis

Renal fibrosis is the final common pathway of all chronic kidney diseases progressing to end-stage renal diseases. Autophagy, a highly conserved lysosomal degradation pathway, plays important roles in maintaining cellular homeostasis in all major types of kidney cells including renal tubular cells as well as podocytes, mesangial cells and endothelial cells in glomeruli. Autophagy dysfunction is implicated in the pathogenesis of various renal pathologies. Here, we analyze the pathological role and regulation of autophagy in renal fibrosis and related kidney diseases in both glomeruli and tubulointerstitial compartments. Further research is expected to gain significant mechanistic insights and discover pathway-specific and kidney-selective therapies targeting autophagy to prevent renal fibrosis and related kidney diseases.

BAMBI shuttling between cytosol and membrane is required for skeletal muscle development and regeneration

Bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) gene encodes a transmembrane protein and is involved in multiple physiological and pathological processes, such as inflammatory response, tumor development and progression, cell proliferation and differentiation. A previous study suggested that BAMBI may interact with the Wnt/β-catenin signaling pathway via promoting β-catenin nuclear translocation associated with C2C12 myogenic myoblast differentiation. However, its biological function in skeletal muscle still remains unknown and requires further characterization. The present work sought to investigate its biological function in skeletal muscle, especially the physiological roles of BAMBI during skeletal muscle growth and regeneration. Our current work suggests that BAMBI protein is highly expressed in skeletal muscle and is only detected in cytosolic fraction in the resting muscle. Moreover, BAMBI protein is co-localized in fast-twitch (glycolytic) fibers, but not in slow-twitch (oxidative) fibers. Comparing with the cytosolic trapping in resting muscle, BAMBI protein is enriched on cellular membrane during the muscle growth and regeneration, suggesting that BAMBI-mediated a significant signaling pathway may be an essential part of muscle growth and regeneration.

Cytokine-induced alterations of BAMBI mediate the reciprocal regulation of human Th17/Treg cells in response to cigarette smoke extract

In CD4+ T helper (Th) cells, transforming growth factor β (TGF‑β) is indispensable for the induction of both regulatory T (Treg) and interleukin‑17‑producing effector T helper (Th17) cells. Although BMP and activin membrane‑bound inhibitor (BAMBI) is part of a rheostat‑like mechanism for the regulation of TGF‑β signalling and autoimmune arthritis in mouse models, the underlying activity of BAMBI on the human Th17/Treg cell axis, particularly during exposure to cigarette smoke, remains to be elucidated. The present study aimed to further characterize BAMBI expression in human CD4+ cells, as well as immune imbalance during activation and cigarette smoke exposure. Results from the present study indicated that exposure to cigarette smoke extract partially suppressed Treg differentiation and promoted Th17 cell generation under stimulation by anti‑CD3/28 antibodies and TGF‑β1. Additionally, exposure to cigarette smoke induced an inhibition of phosphorylated‑Smad2/Smad3, which may have arisen from a concomitant enhancement of BAMBI expression. In conclusion, human BAMBI may function as a molecular switch to control TGF‑β signalling strength and the Th17/Treg cell balance, which may be used not only as a biomarker but also as a target of new treatment strategies for maintaining immune tolerance and for the treatment of smoking‑induced immune disorders.

Serum level of the autophagy biomarker Beclin-1 in patients with diabetic kidney disease

Autophagy is a major cellular clearance mechanism that maintains cellular survival and homeostasis. Autophagy has a crucial role in the progression of diabetes and kidney diseases.

AIMS

To investigate serum concentrations of Beclin-1, a key regulator of autophagy, in patients with diabetic kidney disease (DKD).

METHODS

The study included 70 patients with type 2 diabetes and DKD (group 1; 35 patients with estimated glomerular filtration rate (eGFR) ≥ 30 ml/min/1.73 m² and group 2; 35 patients with eGFR < 30 ml/min/1.73 m²) and 20 age- and sex-matched healthy subjects (group 3). Laboratory work up included; glycated hemoglobin (HbA1c), serum creatinine, eGFR using modification of diet in renal disease (MDRD) formula, urine albumin to creatinine ratio (ACR), and serum Beclin-1 measurement.

RESULTS

Patients with DKD had significantly lower Beclin-1 levels (2.38 ± 1.46 ng/mL) compared to control group (6.03 ± 1.94 ng/mL; P < 0.001). Moreover, serum Beclin-1 significantly decreased in group 2 (1.43 ± 0.83 ng/mL) compared to group 1 (3.36 ± 1.30 ng/mL; P < 0.001). In univariate analysis, the concentration of Beclin-1 correlated well with eGFR (r = 0.64, P < 0.001), ACR (r = -0.63, P < 0.001), and duration of diabetes (r = -0.43, P < 0.001) but didn't correlate with HbA1c (r = -0.17, P = 0.15). However, ACR was the only significant predictor of Beclin-1 level on performing multiple regression analysis (β = -0.40, P = 0.01).

CONCLUSION

Serum level of Beclin-1 is reduced in patients with DKD. Furthermore, its level is related to the stage of DKD and correlates with the degree of albuminuria.

Integration of zebrafish fin regeneration genes with expression data of human tumors in silico uncovers potential novel melanoma markers

Tissue regeneration requires expression of a large, unknown number of genes to initiate and maintain cellular processes such as proliferation, extracellular matrix synthesis, differentiation and migration. A unique model to simulate this process in a controlled manner is the re-growth of the caudal fin of zebrafish after amputation. Within this tissue stem cells differentiate into fibroblasts, epithelial and endothelial cells as well as melanocytes. Many genes implicated in the regeneration process are deregulated in cancer. We therefore undertook a systematic gene expression study to identify genes upregulated during the re-growth of caudal fin tissue. By applying a high stringency cut-off value of 4-fold change, we identified 54 annotated genes significantly overexpressed in regenerating blastema. Further bioinformatics data mining studies showed that 22 out of the 54 regeneration genes where overexpressed in melanoma compared to normal skin or other cancers. Whereas the role of TNC (tenascin C) and FN1 (fibronectin 1) in melanoma development is well documented, implication of MARCKS, RCN3, BAMBI, PEA3/ETV4 and the FK506 family members FKBP7, FKBP10 and FKBP11 in melanoma progression is unclear. Corresponding proteins were detected in melanoma tissue but not in normal skin. High expression of FKBP7, DPYSL5 and MDK was significantly associated with poor survival. We discuss a potential role of these novel melanoma genes, which have promising potential as new therapeutic targets or diagnostic markers.

Autophagy in diabetic kidney disease: regulation, pathological role and therapeutic potential

Diabetic kidney disease, a leading cause of end-stage renal disease, has become a serious public health problem worldwide and lacks effective therapies. Autophagy is a highly conserved lysosomal degradation pathway that removes protein aggregates and damaged organelles to maintain cellular homeostasis. As important stress-responsive machinery, autophagy is involved in the pathogenesis of various diseases. Emerging evidence has suggested that dysregulated autophagy may contribute to both glomerular and tubulointerstitial pathologies in kidneys under diabetic conditions. This review summarizes the recent findings regarding the role of autophagy in the pathogenesis of diabetic kidney disease and highlights the regulation of autophagy by the nutrient-sensing pathways and intracellular stress signaling in this disease. The advances in our understanding of autophagy in diabetic kidney disease will facilitate the discovery of a new therapeutic target for the prevention and treatment of this life-threatening diabetes complication.

BAMBI promotes macrophage proliferation and differentiation in gliomas

The present study investigated the capacity of Bone morphogenic protein and activin membrane‑bound inhibitor homolog (BAMBI) to regulate the migration and differentiation of macrophages in gliomas. Using a migration assay, it was determined that BAMBI stimulated monocytes migration in a dose‑dependent effect. When induced by phorbol myristate acetate (PMA) the monocytes differentiated into macrophages, and BAMBI also increased the migration of PMA‑induced macrophages compared with control cells. The expression of CD68 and BAMBI protein and mRNA in glioma and normal specimens were detected using immunohistochemistry and reverse transcription‑quantitative polymerase chain reaction, respectively. The localization of BAMBI was primarily in macrophages, as demonstrated by staining for the macrophage marker CD68, and the mRNA expression of CD68 and BAMBI were higher in gliomas compared to normal tissues. In addition, the mRNA expression of CD68 and BAMBI were positively correlated (R2=0.64). After treatment with 50 nM PMA and 10 nM BAMBI for 48 h, RAW 264.7 macrophages were exhibited dendrite‑like morphology, indicating that the co‑treatment promoted the differentiation of monocytes to macrophages. The expression of specific markers of M1 [inducible nitric oxide synthase (iNOS) and interleukin (IL)-12] and M2 (IL-10 and arginase 1) type macrophages was determined following 10 nM BAMBI treatment. BAMBI promoted the expression of M1 markers, whereas the M2 markers were not affected, which indicated that BAMBI induced differentiation of M1 type macrophages. These results indicate that BAMBI may be involved in macrophage differentiation in gliomas.

Perpetual change: autophagy, the endothelium, and response to vascular injury

Current studies of vascular health, aging, and autophagy emphasize how the endothelium adapts to stress and contributes to disease. The endothelium is far from an inert barrier to blood-borne cells, pathogens, and chemical signals; rather, it actively translates circulating mediators into tissue responses, changing rapidly in response to physiologic stressors. Macroautophagy-the cellular ingestion of effete organelles and protein aggregates to provide anabolic substrates to fuel bioenergetics in times of stress-plays an important role in endothelial cell homeostasis, vascular remodeling, and disease. These roles include regulating vascular tone, sustaining or limiting cell survival, and contributing to the development of atherosclerosis secondary to infection, inflammation, and angiogenesis. Autophagy modulates these critical functions of the endothelium in a dynamic and perpetual response to tissue and intravascular cues.

Bone Morphogenetic Protein and Activin Membrane-Bound Inhibitor, a Transforming Growth Factor β Rheostat That Controls Murine Treg Cell/Th17 Cell Differentiation and the Development of Autoimmune Arthritis by Reducing Interleukin-2 Signaling

OBJECTIVE

Transforming growth factor β (TGFβ) plays a prominent role in the establishment of immunologic tolerance, and mice lacking TGFβ1 die of multiorgan inflammation early in life. TGFβ controls the differentiation of CD4+ lymphocytes into Treg cells or proinflammatory Th17 cells. Although this dual capacity is modulated by the presence of additional cytokines around the activated cells, TGFβ also dissociates Th17/Treg cell differentiation in a dose-dependent manner by mechanisms still unknown. The purpose of this study was to explore the contribution of bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) to the modulation of TGFβ activity during the differentiation of CD4+ cells and in the control of immunologic tolerance in mice with collagen-induced arthritis (CIA).

METHODS

The in vitro and in vivo Treg cell and Th17 cell differentiation and the development of CIA were compared in wild-type mice and BAMBI-deficient mice.

RESULTS

BAMBI was induced after activation by TGFβ and fixed the appropriate intensity level of TGFβ signaling in CD4+ cells. Its deficiency protected mice against the development of CIA by a Treg cell- and TGFβ-dependent mechanism. Mechanistically, BAMBI was found to regulate CD25 expression and interleukin-2 (IL-2) signaling in Treg cells and in IL-2- and/or TGFβ-activated CD4+ cells and modulated Treg cell and Th17 cell differentiation both in vitro and in vivo.

CONCLUSION

Taken together, the results indicate that BAMBI is a component of a rheostat-like mechanism that, through the control of TGFβ and IL-2 signaling strength, regulates the differentiation of CD4+ lymphocytes and the development of autoimmune arthritis.

Regulating Autophagy as a Therapeutic Target for Diabetic Nephropathy

PURPOSE OF REVIEW

Autophagy promotes cellular health in response to various cellular stresses and to changes in nutrient conditions. In this review, we focus on the role of autophagy in the pathogenesis of diabetic nephropathy and discuss the regulation of autophagy as a new therapeutic target for the suppression of diabetic nephropathy.

RECENT FINDINGS

Previous studies have indicated that autophagy deficiency or insufficiency in renal cells, including podocytes, mesangial cells, endothelial cells and tubular cells, contributes to the pathogenesis of diabetic nephropathy. Alterations in the nutrient-sensing pathways, including mammalian target of rapamycin complex1 (mTORC1), AMP-activated kinase (AMPK) and Sirt1, due to excess nutrition　in diabetes are implicated in the impairment of autophagy. Maintaining both basal and adaptive autophagy against cellular stress may protect the kidney from diabetes-induced cellular stresses. Therefore, the activation of autophagy through the modulation of nutrient-sensing pathways may be a new therapeutic option for the suppression of diabetic nephropathy.

TGF-β/BAMBI pathway dysfunction contributes to peripheral Th17/Treg imbalance in chronic obstructive pulmonary disease

BMP and activin membrane-bound inhibitor (BAMBI) is postulated to inhibit or modulate transforming growth factor β (TGF-β) signaling. Furthermore, strong upregulation of BAMBI expression following in vitro infection of chronic obstructive pulmonary disease (COPD) lung tissue has been demonstrated. In this study, we investigated whether TGF-β/BAMBI pathway is associated with COPD. Blood samples were obtained from 27 healthy controls (HC), 24 healthy smokers (HS) and 29 COPD patients. Elevated Th17/Treg ratios, and increased levels of BAMBI protein and mRNA (in plasma and CD4(+) T cells respectively), were observed in COPD compared with HC and HS. BAMBI expression was first observed on human CD4(+) T cells, with a typical membrane-bound pattern. The enhanced plasma BAMBI levels in COPD positively correlated with the increased plasma TGF-β1 levels and Th17/Treg ratio. Together, an impaired TGF-β/BAMBI pathway may promote the inflammation leading to Th17/Treg imbalance, which is a new mechanism in smokers who develop COPD.

Investigation of common and rare genetic variation in the BAMBI genomic region in light of human obesity

The aim of this study was to confirm the previously identified link between BAMBI and human obesity by means of a genetic and functional analysis. We performed both a mutation analysis, using high-resolution melting curve analysis, and a genetic association study, including 8 common tagSNPs in the BAMBI gene region. Three of the identified genetic variants (R151W, H201R, and C229R) were evaluated for their Wnt signaling enhancing capacity in a Wnt luciferase reporter assay. Mutation screening of the BAMBI coding region and exon-intron boundaries on our population of 677 obese children and adolescents and 529 lean control subjects resulted in the identification of 18 variants, 10 of which were not previously reported and 12 of which were exclusively found in obese individuals. The difference in variant frequency, not taking into account common polymorphisms, between obese (3.1 %) and lean (0.9 %) subjects was statistically significant (p = 0.004). Our Wnt luciferase assay, using WT and mutant BAMBI constructs, showed a significantly reduced activity for all of the investigated variants. Logistic and linear regression analysis on our Caucasian population of 1022 obese individuals and 606 lean controls, did not identify associations with obesity parameters (p values >0.05). We found several rare genetic variations, which represent the first naturally occurring missense variants of BAMBI in obese patients. Three variants (R151W, H201R, and C229R) were shown to reduce Wnt signaling enhancing capacity of BAMBI and we believe this result should encourage further study of this gene in other obese populations. In addition, we did not find evidence for the involvement of BAMBI common variation in human obesity in our population.

Autophagy in diabetic nephropathy

Diabetic nephropathy (DN) is the most common cause of end-stage kidney disease worldwide, and is associated with increased morbidity and mortality in patients with both type 1 and type 2 diabetes. Increasing prevalence of diabetes has made the need for effective treatment of DN critical and thereby identifying new therapeutic targets to improve clinical management. Autophagy is a highly conserved 'self-eating' pathway by which cells degrade and recycle macromolecules and organelles. Autophagy serves as an essential mechanism to maintain homeostasis of glomeruli and tubules, and plays important roles in human health and diseases. Impairment of autophagy is implicated in the pathogenesis of DN. Emerging body of evidence suggests that targeting the autophagic pathway to activate and restore autophagy activity may be renoprotective. In this review, we examine current advances in our understanding of the roles of autophagy in diabetic kidney injury, focusing on studies in renal cells in culture, human kidney tissues, and experimental animal models of diabetes. We discuss the major nutrient-sensing signal pathways and diabetes-induced altered intracellular metabolism and cellular events, including accumulation of advanced glycation end-products, increased oxidative stress, endoplasmic reticulum stress, hypoxia, and activation of the renin-angiotensin system, which modulate autophagic activity and contribute to the development of DN. We also highlight recent studies of autophagy and transforming growth factor-β in renal fibrosis, the final common response to injury that ultimately leads to end-stage kidney failure in both type 1 and type 2 diabetes. These findings suggest the possibility that autophagy can be a therapeutic target against DN.

Vessel wall BAMBI contributes to hemostasis and thrombus stability

Bone morphogenetic protein and activin membrane-bound inhibitor (BAMBI) is a transmembrane protein related to the transforming growth factor-β superfamily, and is highly expressed in platelets and endothelial cells. We previously demonstrated its positive role in thrombus formation using a zebrafish thrombosis model. In the present study, we used Bambi-deficient mice and radiation chimeras to evaluate the function of this receptor in the regulation of both hemostasis and thrombosis. We show that Bambi(-/-) and Bambi(+/-) mice exhibit mildly prolonged bleeding times compared with Bambi(+/+) littermates. In addition, using 2 in vivo thrombosis models in mesenterium or cremaster muscle arterioles, we demonstrate that Bambi-deficient mice form unstable thrombi compared with Bambi(+/+) mice. No defects in thrombin generation in Bambi(-/-) mouse plasma could be detected ex vivo. Moreover, the absence of BAMBI had no effect on platelet counts, platelet activation, aggregation, or platelet procoagulant function. Similar to Bambi(-/-) mice, Bambi(-/-) transplanted with Bambi(+/+) bone marrow formed unstable thrombi in the laser-induced thrombosis model that receded more rapidly than thrombi that formed in Bambi(+/+) mice receiving Bambi(-/-) bone marrow transplants. Taken together, these results provide strong evidence for an important role of endothelium rather than platelet BAMBI as a positive regulator of both thrombus formation and stability.

Fibrosis markers and CRIM1 increase in chronic heart failure of increasing severity

BACKGROUND

Fibrosis suppressors/activators in chronic heart failure (CHF) is a topic of investigation.

AIM

To quantify serum levels of fibrosis regulators in CHF.

METHODS

ELISA tests were used to quantify fibrosis regulators, procollagen type-(PIP)I, (PIP)III, collagen-I, III, BMP1,2,3,7, SDF1α, CXCR4, fibulin 1,2,3, BMPER, CRIM1 and BAMBI in 66 CHF (NYHA class I, n = 9; II, n = 34; III n = 23), and in 14 controls.

RESULTS

In CHF, TGFβR2, PIPIII, SDF1α and CRIM1 were increased. PIPIII correlated with CRIM1.

CONCLUSIONS

The BMPs inhibitor CRIM1 is increased and correlates with higher levels of serum PIPIII showing an imbalance in favor of pro-fibrotic mechanisms in CHF.

Transcriptional repression of the transforming growth factor β (TGF-β) Pseudoreceptor BMP and activin membrane-bound inhibitor (BAMBI) by Nuclear Factor κB (NF-κB) p50 enhances TGF-β signaling in hepatic stellate cells

TLR4 signaling induces down-regulation of the bone morphogenic protein (BMP) and activin membrane-bound inhibitor (BAMBI), which enhances TGF-β signaling during hepatic stellate cell (HSC) activation. We investigated the mechanism by which TLR4 signaling down-regulates BAMBI expression in HSCs and found that TLR4- and TNF-α-mediated BAMBI down-regulation is dependent on regulation of BAMBI promoter activity through the interaction with NF-κBp50 and HDAC1 in HSCs. Bambi was predominantly expressed in HSCs, at high levels in quiescent HSCs but at low levels in in vivo-activated and LPS-stimulated HSCs. In human HSCs, BAMBI expression was down-regulated in response to LPS and TNF-α. A BAMBI reporter assay demonstrated that the regulatory element to repress BAMBI transcription is located between 3384 and 1560 bp upstream from the transcription start site. LPS stimulation down-regulated BAMBI expression in cells with NF-κBp65 knockdown. However, it failed to down-regulate BAMBI in cells with inactivation of NF-κB or NF-κBp50 silencing, indicating that NF-κBp50 is a factor for BAMBI down-regulation. ChIP analysis revealed that LPS and TNF-α induced binding of the NF-κBp50/p50 homodimer to the BAMBI promoter region. We also found that HDAC1 is bound to this region as part of the NF-κBp50-HDAC1 complex, repressing transcriptional activity of the BAMBI promoter. Finally, we confirmed that LPS does not repress BAMBI reporter activity using a BAMBI reporter construct with a mutation at 3166 bp upstream of the coding region. In summary, our study demonstrates that LPS- and TNF-α-induced NF-κBp50-HDAC1 interaction represses BAMBI transcriptional activity, which contributes to TLR4-mediated enhancement of TGF-β signaling in HSCs during liver fibrosis.

Regulation of autophagy by TGF-β: emerging role in kidney fibrosis

Autophagy is a highly conserved homoeostatic mechanism for cell survival under conditions of stress, and is widely implicated as an important pathway in many biological processes and diseases. In progressive kidney diseases, fibrosis represents the common pathway to end-stage kidney failure. Transforming growth factor-β1 (TGF-β1) is a pleiotropic cytokine that has been established as a central mediator of kidney fibrosis. A recently emerging body of evidence from studies in renal cells in culture and experimental animal models suggests that TGF-β1 regulates autophagy and that autophagy regulates many critical aspects of normal and disease conditions associated with kidney fibrosis, such as tubulointerstitial fibrosis, glomerulosclerosis, and diabetic nephropathy. Here, we review the recent advances exploring the process of autophagy, its regulation by TGF-β1, and the implication in the pathogenesis of progressive kidney fibrosis and injury responses. Understanding the cellular and molecular bases of this process is crucial for identifying potential new diagnostic and therapeutic targets of kidney fibrosis.

RNase L triggers autophagy in response to viral infections

Autophagy is a programmed homeostatic response to diverse types of cellular stress that disposes of long-lived proteins, organelles, and invading microbes within double-membraned structures called autophagosomes. The 2',5'-oligoadenylate/RNase L system is a virus-activated host RNase pathway that disposes of or processes viral and cellular single-stranded RNAs. Here we report that activation of RNase L during viral infections induces autophagy. Accordingly, infections with encephalomyocarditis virus or vesicular stomatitis virus led to higher levels of autophagy in wild-type mouse embryonic fibroblasts (MEF) than in RNase L-null MEF. Similarly, direct activation of RNase L with a 2',5'-oligoadenylate resulted in p62(SQSTM1) degradation, LC3BI/LC3BII conversion, and appearance of autophagosomes. To determine the effect of RNase L-mediated autophagy on viral replication, we compared viral yields in wild-type and RNase L-null MEF in the absence or presence of either chemical inhibitors of autophagy (bafilomycin A1 or 3-methyladenine) or small interfering RNA (siRNA) against ATG5 or beclin-1. At a low multiplicity of infection, induction of autophagy by RNase L during the initial cycle of virus growth contributed to the suppression of virus replication. However, in subsequent rounds of infection, autophagy promoted viral replication, reducing the antiviral effect of RNase L. Our results indicate a novel function of RNase L as an inducer of autophagy that affects viral yields.

BAMBI regulates angiogenesis and endothelial homeostasis through modulation of alternative TGFβ signaling

BACKGROUND

BAMBI is a type I TGFβ receptor antagonist, whose in vivo function remains unclear, as BAMBI(-/-) mice lack an obvious phenotype.

METHODOLOGY/PRINCIPAL FINDINGS

Identifying BAMBI's functions requires identification of cell-specific expression of BAMBI. By immunohistology we found BAMBI expression restricted to endothelial cells and by electron microscopy BAMBI(-/-) mice showed prominent and swollen endothelial cells in myocardial and glomerular capillaries. In endothelial cells over-expression of BAMBI reduced, whereas knock-down enhanced capillary growth and migration in response to TGFβ. In vivo angiogenesis was enhanced in matrigel implants and in glomerular hypertrophy after unilateral nephrectomy in BAMBI(-/-) compared to BAMBI(+/+) mice consistent with an endothelial phenotype for BAMBI(-/-) mice. BAMBI's mechanism of action in endothelial cells was examined by canonical and alternative TGFβ signaling in HUVEC with over-expression or knock-down of BAMBI. BAMBI knockdown enhanced basal and TGFβ stimulated SMAD1/5 and ERK1/2 phosphorylation, while over-expression prevented both.

CONCLUSIONS/SIGNIFICANCE

Thus we provide a first description of a vascular phenotype for BAMBI(-/-) mice, and provide in vitro and in vivo evidence that BAMBI contributes to endothelial and vascular homeostasis. Further, we demonstrate that in endothelial cells BAMBI interferes with alternative TGFβ signaling, most likely through the ALK 1 receptor, which may explain the phenotype observed in BAMBI(-/-) mice. This newly described role for BAMBI in regulating endothelial function has potential implications for understanding and treating vascular disease and tumor neo-angiogenesis.

Renal interstitial fibrosis: mechanisms and evaluation

PURPOSE OF REVIEW

Tubulointerstitial injury in the kidney is complex, involving a number of independent and overlapping cellular and molecular pathways, with renal interstitial fibrosis and tubular atrophy (IFTA) as the final common pathway. Furthermore, there are multiple ways to assess IFTA.

RECENT FINDINGS

Cells involved include tubular epithelial cells, fibroblasts, fibrocytes, myofibroblasts, monocyte/macrophages, and mast cells with complex and still incompletely characterized cell-molecular interactions. Molecular mediators involved are numerous and involve pathways such as transforming growth factor (TGF)-β, bone morphogenic protein (BMP), platelet-derived growth factor (PDGF), and hepatocyte growth factor (HGF). Recent genomic approaches have shed insight into some of these cellular and molecular pathways. Pathologic evaluation of IFTA is central in assessing the severity of chronic disease; however, there are a variety of methods used to assess IFTA. Most assessment of IFTA relies on pathologist assessment of special stains such as trichrome, Sirius Red, and collagen III immunohistochemistry. Visual pathologist assessment can be prone to intra and interobserver variability, but some methods employ computerized morphometery, without a clear consensus as to the best method.

SUMMARY

IFTA results from on orchestration of cell types and molecular pathways. Opinions vary on the optimal qualitative and quantitative assessment of IFTA.

Metformin-mediated Bambi expression in hepatic stellate cells induces prosurvival Wnt/β-catenin signaling

AMP-activated protein kinase (AMPK) regulates lipid, cholesterol, and glucose metabolism in specialized metabolic tissues, such as muscle, liver, and adipose tissue. Agents that activate AMPK, such as metformin and 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR), have beneficial effects on liver glucose and lipid metabolism. In addition, AMPK activation in proliferating hepatic stellate cells (HSC) induces growth arrest and inhibits hepatic fibrosis. As metformin and AICAR act in different ways to achieve their effects, our aim was to examine the effects of AMPK activation in quiescent HSCs with these two agents on HSC function. We found that phospho-AMPK levels were markedly upregulated by both AICAR and metformin in quiescent HSCs. However, although AICAR treatment induced cell death, cells treated with metformin did not differ from untreated controls. AICAR-mediated HSC cell death was paralleled by loss of expression of the TGF-β decoy receptor Bambi, whereas metformin increased Bambi expression. Transfection of siRNA-Bambi into HSCs also induced cell death, mimicking the effects of AICAR, whereas overexpression of Bambi partially rescued AICAR-treated cells. As Bambi has previously been shown to promote cell survival through Wnt/β-catenin signaling, a reporter incorporating binding sites for a downstream target of this pathway was transfected into HSCs and was induced. We conclude that although AICAR and metformin both activate AMPK in quiescent HSCs, AICAR rapidly induced cell death, whereas metformin-treated cells remained viable. The finding that metformin increases Bambi expression and activates Wnt/β-catenin signaling provides a possible mechanistic explanation for this observation. These results suggest that AICAR and metformin may confer disease-specific therapeutic benefits.

Homeodomain interacting protein kinase 2 regulates postnatal development of enteric dopaminergic neurons and glia via BMP signaling

Trophic factor signaling is important for the migration, differentiation, and survival of enteric neurons during development. The mechanisms that regulate the maturation of enteric neurons in postnatal life, however, are poorly understood. Here, we show that transcriptional cofactor HIPK2 (homeodomain interacting protein kinase 2) is required for the maturation of enteric neurons and for regulating gliogenesis during postnatal development. Mice lacking HIPK2 display a spectrum of gastrointestinal (GI) phenotypes, including distention of colon and slowed GI transit time. Although loss of HIPK2 does not affect the enteric neurons in prenatal development, a progressive loss of enteric neurons occurs during postnatal life in Hipk2(-/-) mutant mice that preferentially affects the dopaminergic population of neurons in the caudal region of the intestine. The mechanism by which HIPK2 regulates postnatal enteric neuron development appears to involve the response of enteric neurons to bone morphogenetic proteins (BMPs). Specifically, compared to wild type mice, a larger proportion of enteric neurons in Hipk2(-/-) mutants have an abnormally high level of phosphorylated Smad1/5/8. Consistent with the ability of BMP signaling to promote gliogenesis, Hipk2(-/-) mutants show a significant increase in glia in the enteric nervous system. In addition, numbers of autophagosomes are increased in enteric neurons in Hipk2(-/-) mutants, and synaptic maturation is arrested. These results reveal a new role for HIPK2 as an important transcriptional cofactor that regulates the BMP signaling pathway in the maintenance of enteric neurons and glia, and further suggest that HIPK2 and its associated signaling mechanisms may be therapeutically altered to promote postnatal neuronal maturation.

Adiponectin induces the transforming growth factor decoy receptor BAMBI in human hepatocytes

Transforming growth factor (TGF) β is the central cytokine in fibrotic liver diseases. We analyzed whether hepatoprotective adiponectin directly interferes with TGFβ1 signaling in primary human hepatocytes (PHH). Adiponectin induces the TGFβ decoy receptor BMP-and activin-membrane-bound inhibitor (BAMBI) in PHH. Overexpression of BAMBI in hepatoma cells impairs TGFβ-mediated phosphorylation of SMAD2 and induction of connective tissue growth factor. BAMBI is lower in human fatty liver with a higher susceptibility to liver fibrosis and negatively correlates with BMI of the donors. Hepatic BAMBI is reduced in rodent models of liver inflammation and fibrosis. In summary, the current data show that hepatoprotective effects of adiponectin include induction of BAMBI which is reduced in human fatty liver and rodent models of metabolic liver injury.