Blockade of endothelial-mesenchymal transition by a Smad3 inhibitor delays the early development of streptozotocin-induced diabetic nephropathy

Smads as therapeutic targets for chronic kidney disease

Renal fibrosis is a hallmark of chronic kidney disease (CKD). It is generally thought that transforming growth factor-β1 (TGF-β1) is a key mediator of fibrosis and mediates renal scarring positively by Smad2 and Smad3, but negatively by Smad7. Our recent studies found that in CKD, TGF-β1 is not a sole molecule to activate Smads. Many mediators such as angiotensin II and advanced glycation end products can also activate Smads via both TGF-β-dependent and independent mechanisms. In addition, Smads can interact with other signaling pathways, such as the mitogen-activated protein kinase and nuclear factor-kappaB (NF-κB) pathways, to regulate renal inflammation and fibrosis. In CKD, Smad2 and Smad3 are highly activated, while Smad7 is reduced or lost. In the context of fibrosis, Smad3 is pathogenic and mediates renal fibrosis by upregulating miR-21 and miR-192, but down-regulating miR-29 and miR-200 families. By contrast, Smad2 and Smad7 are protective. Overexpression of Smad7 inhibits both Smad3-mediated renal fibrosis and NF-κB-driven renal inflammation. Interestingly, Smad4 has diverse roles in renal fibrosis and inflammation. The complexity and distinct roles of individual Smads in CKD suggest that treatment of CKD should aim to correct the imbalance of Smad signaling or target the Smad3-dependent genes related to fibrosis, rather than to block the general effect of TGF-β1. Thus, treatment of CKD by overexpression of Smad7 or targeting Smad3-dependent miRNAs such as downregulation of miR-21 or overexpression of miR-29 may represent novel therapeutic strategies for CKD.

Regulation of endothelial cell plasticity by TGF-β

Recent evidence has demonstrated that endothelial cells can have a remarkable plasticity. By a process called Endothelial-to-Mesenchymal Transition (EndMT) endothelial cells convert to a more mesenchymal cell type that can give rise to cells such as fibroblasts, but also bone cells. EndMT is essential during embryonic development and tissue regeneration. Interestingly, it also plays a role in pathological conditions like fibrosis of organs such as the heart and kidney. In addition, EndMT contributes to the generation of cancer associated fibroblasts that are known to influence the tumor-microenvironment favorable for the tumor cells. EndMT is a form of the more widely known and studied Epithelial-to-Mesenchymal Transition (EMT). Like EMT, EndMT can be induced by transforming growth factor (TGF)-β. Indeed many studies have pointed to the important role of TGF-β receptor/Smad signaling and downstream targets, such as Snail transcriptional repressor in EndMT. By selective targeting of TGF-β receptor signaling pathological EndMT may be inhibited for the therapeutic benefit of patients with cancer and fibrosis.

Targeting the tumor stroma as a novel therapeutic approach for prostate cancer

Interactions between epithelium and the surrounding stroma are required to maintain organ function. These interactions provide proliferative and migratory restraints that define anatomical and positional information, mediated by growth factors and extracellular matrix components. When cancer develops, transformed cells lose these constraints while stroma adapts and coevolves to support the "function" of the tumor. The prostate is a good example of an organ that relies on its surrounding stroma during normal development and cancer progression. Carcinoma-associated fibroblasts (CAFs) constitute a substantial volume of the tumor stroma and play a pivotal role in tumor maintenance, dissemination, and even drug resistance. The origins of CAF and the exact mechanisms by which they promote tumor progression are still debated. CAF acquire an activated phenotype quite similar to the one seen during wound repair in sites of injury. Here, we describe the CAF ontogeny, the similarities with activated fibroblasts during physiological wound repair, and potential pathways that can be targeted to prevent their appearance in tumors and their protumorigenic functions in cancer progression. A strategy to identify aspects of stromal cell biology for therapeutic targeting is becoming increasingly plausible, driven by the increased understanding of the complex interplays between the cells and tissues of which tumors are comprised. Several preclinical and clinical studies show that targeting the stroma may be a promising and attractive therapeutic option for the treatment of cancer and has the potential to play an increasingly prominent role in future treatment strategies.

Diabetes alters subsets of endothelial progenitor cells that reside in blood, bone marrow, and spleen

Circulating endothelial progenitor cells (EPCs) derived from the bone marrow (BM) participate in maintaining endothelial integrity and vascular homeostasis. Reduced EPC number and function result in vascular complications in diabetes. EPCs are a population of cells existing in various differentiation stages, and their cell surface marker profiles change during the process of mobilization and maturation. Hence, a generally accepted marker combination and a standardized protocol for the quantification of EPCs remain to be established. To determine the EPC subsets that are affected by diabetes, we comprehensively analyzed 32 surface marker combinations of mouse peripheral blood (PB), BM, and spleen cells by multicolor flow cytometry. Ten subsets equivalent to previously reported mouse EPCs significantly declined in number in the PB of streptozotocin-induced diabetic mice, and this reduction was reversed by insulin treatment. The PI(-)Lin(-)c-Kit(-)Sca-1(+)Flk-1(-)CD34(-)CD31(+) EPC cluster, which can differentiate into mature endothelial cells in vitro, was the highest population in the PB, BM, and spleen and occurred 61 times more in the spleen than in the PB. The cell number significantly decreased in the BM as well as in the PB but paradoxically increased in the spleen under diabetic conditions. Insulin treatment reversed the decrease of EPC subsets in the BM and PB and reversed their increase in spleen. A similar tendency was observed in some of the major cell populations in db/db mice. To the best of our knowledge, we are the first to report spatial population changes in mouse EPCs by diabetes in the blood and in the BM across the spleen. Diminished circulating EPC supply by diabetes may be ascribed to impaired EPC production in the BM and to decreased EPC mobilization from the spleen, which may contribute to vascular dysfunction in diabetic conditions.

Role of TGF-β in chronic kidney disease: an integration of tubular, glomerular and vascular effects

Transforming growth factor beta (TGF-β) has been recognized as an important mediator in the genesis of chronic kidney diseases (CKD), which are characterized by the accumulation of extracellular matrix (ECM) components in the glomeruli (glomerular fibrosis, glomerulosclerosis) and the tubular interstitium (tubulointerstitial fibrosis). Glomerulosclerosis is a major cause of glomerular filtration rate reduction in CKD and all three major glomerular cell types (podocytes or visceral epithelial cells, mesangial cells and endothelial cells) participate in the fibrotic process. TGF-β induces (1) podocytopenia caused by podocyte apoptosis and detachment from the glomerular basement membrane; (2) mesangial expansion caused by mesangial cell hypertrophy, proliferation (and eventually apoptosis) and ECM synthesis; (3) endothelial to mesenchymal transition giving rise to glomerular myofibroblasts, a major source of ECM. TGF-β has been shown to mediate several key tubular pathological events during CKD progression, namely fibroblast proliferation, epithelial to mesenchymal transition, tubular and fibroblast ECM production and epithelial cell death leading to tubular cell deletion and interstitial fibrosis. In this review, we re-examine the mechanisms involved in glomerulosclerosis and tubulointerstitial fibrosis and the way that TGF-β participates in renal fibrosis, renal parenchyma degeneration and loss of function associated with CKD.

Regulation of RAGE for attenuating progression of diabetic vascular complications

Diabetic angiopathy including micro- and macroangiopathy is concerned with high rate of morbidity and mortality in patients with long-standing diabetes. Receptor for advanced glycation end products (RAGE) and its ligands have been considered as important pathogenic triggers for the progression of the vascular injuries in diabetes. The deleterious link between RAGE and diabetic angiopathy has been demonstrated in animal studies. Preventive and therapeutic strategies focusing on RAGE and its ligand axis may be of great importance in relieving diabetic vascular complications and reducing the burden of disease.

Cellular and molecular mechanisms of renal fibrosis

Renal fibrosis, particularly tubulointerstitial fibrosis, is the common final outcome of almost all progressive chronic kidney diseases. Renal fibrosis is also a reliable predictor of prognosis and a major determinant of renal insufficiency. Irrespective of the initial causes, renal fibrogenesis is a dynamic and converging process that consists of four overlapping phases: priming, activation, execution and progression. Nonresolving inflammation after a sustained injury sets up the fibrogenic stage (priming) and triggers the activation and expansion of matrix-producing cells from multiple sources through diverse mechanisms, including activation of interstitial fibroblasts and pericytes, phenotypic conversion of tubular epithelial and endothelial cells and recruitment of circulating fibrocytes. Upon activation, matrix-producing cells assemble a multicomponent, integrin-associated protein complex that integrates input from various fibrogenic signals and orchestrates the production of matrix components and their extracellular assembly. Multiple cellular and molecular events, such as tubular atrophy, microvascular rarefaction and tissue hypoxia, promote scar formation and ensure a vicious progression to end-stage kidney failure. This Review outlines our current understanding of the cellular and molecular mechanisms of renal fibrosis, which could offer novel insights into the development of new therapeutic strategies.

Transforming growth factor beta signaling in adult cardiovascular diseases and repair

The majority of children with congenital heart disease now live into adulthood due to the remarkable surgical and medical advances that have taken place over the past half century. Because of this, adults now represent the largest age group with adult cardiovascular diseases. It includes patients with heart diseases that were not detected or not treated during childhood, those whose defects were surgically corrected but now need revision due to maladaptive responses to the procedure, those with exercise problems and those with age-related degenerative diseases. Because adult cardiovascular diseases in this population are relatively new, they are not well understood. It is therefore necessary to understand the molecular and physiological pathways involved if we are to improve treatments. Since there is a developmental basis to adult cardiovascular disease, transforming growth factor beta (TGFβ) signaling pathways that are essential for proper cardiovascular development may also play critical roles in the homeostatic, repair and stress response processes involved in adult cardiovascular diseases. Consequently, we have chosen to summarize the current information on a subset of TGFβ ligand and receptor genes and related effector genes that, when dysregulated, are known to lead to cardiovascular diseases and adult cardiovascular deficiencies and/or pathologies. A better understanding of the TGFβ signaling network in cardiovascular disease and repair will impact genetic and physiologic investigations of cardiovascular diseases in elderly patients and lead to an improvement in clinical interventions.

Diverse roles of TGF-β/Smads in renal fibrosis and inflammation

TGF-β1 has been long considered as a key mediator in renal fibrosis and induces renal scarring largely by activating its downstream Smad signaling pathway. Interestingly, while mice overexpressing active TGF-β1 develop progressive renal injury, latent TGF-β1 plays a protective role in renal fibrosis and inflammation. Under disease conditions, Smad2 and Smad3 are highly activated, while Smad7 is degraded through the ubiquitin proteasome degradation mechanism. In addition to TGF-β1, many pathogenic mediators such as angiotensin II and advanced glycation end products can also activate the Smad pathway via both TGF-β-dependent and independent mechanisms. Smads interact with other signaling pathways, such as the MAPK and NF-κB pathways, to positively or negatively regulate renal inflammation and fibrosis. Studies from gene knockout mice demonstrate that TGF-β1 acts by stimulating its downstream Smads to diversely regulate kidney injury. In the context of renal fibrosis and inflammation, Smad3 is pathogenic, while Smad2 and Smad7 are protective. Smad4 exerts its diverse roles by transcriptionally enhancing Smad3-mediated renal fibrosis while inhibiting NF-κB-driven renal inflammation via a Smad7-dependent mechanism. Furthermore, we also demonstrated that TGF-β1 acts by stimulating Smad3 to positively or negatively regulate microRNAs to exert its fibrotic role in kidney disease. In conclusion, TGF-β/Smad signaling is a major pathway leading to kidney disease. Smad3 is a key mediator in renal fibrosis and inflammation, whereas Smad2 and Smad7 are renoprotective. Smad4 exerts its diverse role in promoting renal fibrosis while inhibiting inflammation. Thus, targeting the downstream TGF-β/Smad3 signaling pathway by gene transfer of either Smad7 or Smad3-dependent microRNAs may represent a specific and effective therapeutic strategy for kidney disease.

Role of endothelial-mesenchymal transition (EndoMT) in the pathogenesis of fibrotic disorders

The accumulation of a large number of myofibroblasts is responsible for exaggerated and uncontrolled production of extracellular matrix during the development and progression of pathological fibrosis. Myofibroblasts in fibrotic tissues are derived from at least three sources: expansion and activation of resident tissue fibroblasts, transition of epithelial cells into mesenchymal cells (epithelial-mesenchymal transition, EMT), and tissue migration of bone marrow-derived circulating fibrocytes. Recently, endothelial to mesenchymal transition (EndoMT), a newly recognized type of cellular transdifferentiation, has emerged as another possible source of tissue myofibroblasts. EndoMT is a complex biological process in which endothelial cells lose their specific markers and acquire a mesenchymal or myofibroblastic phenotype and express mesenchymal cell products such as α smooth muscle actin (α-SMA) and type I collagen. Similar to EMT, EndoMT can be induced by transforming growth factor (TGF-β). Recent studies using cell-lineage analysis have demonstrated that EndoMT may be an important mechanism in the pathogenesis of pulmonary, cardiac, and kidney fibrosis, and may represent a novel therapeutic target for fibrotic disorders.

Knockout of toll-like receptor-2 attenuates both the proinflammatory state of diabetes and incipient diabetic nephropathy

OBJECTIVE

Type 1 diabetes (T1DM) is a proinflammatory state and confers an increased risk for vascular complications. Toll-like receptors (TLR) could participate in diabetic vasculopathies. Whether TLR activation contributes to the proinflammatory state of T1DM and the pathogenesis of diabetic nephropathy remains unknown.

METHODS AND RESULTS

We induced T1DM in TLR2 knockout mice (TLR2-/-) and wild-type littermates (C57BL/6J-WT) using streptozotocin (STZ). Fasting blood, peritoneal macrophages, and kidneys were obtained for flow cytometry, Western blot, microscopy, and cytokine assays at 6 and 14 weeks after induction of diabetes. Macrophage TLR2 expression and MyD88-dependent signaling were increased in diabetic mice (WT+STZ) compared with nondiabetic WT mice. These biomarkers were attenuated in diabetic TLR2-/- macrophages. WT+STZ mice showed increased kidney:body weight ratio due to cell hypertrophy, increased albuminuria, decreased kidney nephrin, podocin, and podocyte number and increased transforming growth factor-β and laminin compared with WT mice. Nephrin, podocin, and podocyte number and effacement were restored, and transforming growth factor-β and laminin levels were decreased in TLR2-/-+ STZ mice kidneys versus WT+STZ. Peritoneal and kidney macrophages were predominantly M1 phenotype in WT+STZ mice; this was attenuated in TLR2-/-+STZ mice.

CONCLUSIONS

These data support a role for TLR2 in promoting inflammation and early changes of incipient diabetic nephropathy, in addition to albuminuria and podocyte loss.