Glucose stimulation of transforming growth factor-beta bioactivity in mesangial cells is mediated by thrombospondin-1

Ursodeoxycholic acid ameliorates erectile dysfunction and corporal fibrosis in diabetic rats by inhibiting the TGF-β1/Smad2 pathway

Corporal tissue fibrosis is critical in diabetes-associated erectile dysfunction. Transforming growth factor-β1/Small mothers against decapentaplegic-2 (TGF-β1/Smad2) contributes to the induction of fibrosis in corporal tissue. Smad7 is accepted as a general negative regulator of Smad signaling, although its role in corporal fibrosis is unknown. Ursodeoxycholic acid (UDCA) is a hydrophilic bile acid used for biliary and liver related disorders and has antifibrotic effects in the liver. This study investigated the effects of UDCA on diabetic erectile dysfunction. Forty-eight male Spraque Dawley rats were divided into six groups: nondiabetic (n = 6), nondiabetic+20 mg/kg UDCA (n = 6), nondiabetic+80 mg/kg UDCA (n = 6), diabetic (n = 10), diabetic+20 mg/kg UDCA (n = 10), diabetic+80 mg/kg UDCA (n = 10). Diabetes was induced by intraperitoneal injection of 60 mg/kg Streptozocin. UDCA (20 and 80 mg/kg/day) or saline was subsequently administered via oral gavage for 56 days. Erectile function was evaluated as measurement of maximum intracavernosal pressure (m-ICP)/mean arterial pressure (MAP) and total ICP/MAP. Corporal tissues were evaluated by Western blotting and Masson's trichrome staining. Electrical stimulation-induced m-ICP/MAP responses were higher in UDCA-treated diabetic rats compared to untreated diabetic rats, respectively (20 mg/kg; 4 V: 0.77 ± 0.11 vs 0.45 ± 0.09, p = 0.0001 and 80 mg/kg; 4 V: 0.78 ± 0.11 vs 0.45 ± 0.09, p = 0.0001) UDCA prevented the increase in phospho-Smad2 and fibronectin protein expressions in diabetic corporal tissue both at 20 mg/kg (p = 0.0002, p = 0.002 respectively) and 80 mg/kg doses (p < 0.0001 for both). Smad7 protein expressions were significantly increased in the UDCA-treated diabetic groups compared to the untreated diabetic group (20 mg/kg: p = 0.0079; 80 mg/kg: p = 0.004). Furthermore, UDCA significantly prevented diabetes-induced increase in collagen (20 mg/kg: p = 0.0172; 80 mg/kg: p = 0.0003) and smooth muscle loss (20 mg/kg: p = 0.044; 80 mg/kg: p = 0.039). In conclusion, UDCA has a potential protective effect on erectile function in diabetic rats by altering fibrotic pathways via inhibition of TGF-β1/Smad2 and activation of Smad7.

Cell surface GRP78 regulates TGFβ1-mediated profibrotic responses via TSP1 in diabetic kidney disease

Introduction: Diabetic kidney disease (DKD) is the leading cause of kidney failure in North America, characterized by glomerular accumulation of extracellular matrix (ECM) proteins. High glucose (HG) induction of glomerular mesangial cell (MC) profibrotic responses plays a central role in its pathogenesis. We previously showed that the endoplasmic reticulum resident GRP78 translocates to the cell surface in response to HG, where it mediates Akt activation and downstream profibrotic responses in MC. Transforming growth factor β1 (TGFβ1) is recognized as a central mediator of HG-induced profibrotic responses, but whether its activation is regulated by cell surface GRP78 (csGRP78) is unknown. TGFβ1 is stored in the ECM in a latent form, requiring release for biological activity. The matrix glycoprotein thrombospondin 1 (TSP1), known to be increased in DKD and by HG in MC, is an important factor in TGFβ1 activation. Here we determined whether csGRP78 regulates TSP1 expression and thereby TGFβ1 activation by HG. Methods: Primary mouse MC were used. TSP1 and TGFβ1 were assessed using standard molecular biology techniques. Inhibitors of csGRP78 were: 1) vaspin, 2) the C-terminal targeting antibody C38, 3) siRNA downregulation of its transport co-chaperone MTJ-1 to prevent GRP78 translocation to the cell surface, and 4) prevention of csGRP78 activation by its ligand, active α2-macroglobulin (α2M*), with the neutralizing antibody Fα2M or an inhibitory peptide. Results: TSP1 transcript and promoter activity were increased by HG, as were cellular and ECM TSP1, and these required PI3K/Akt activity. Inhibition of csGRP78 prevented HG-induced TSP1 upregulation and deposition into the ECM. The HG-induced increase in active TGFβ1 in the medium was also inhibited, which was associated with reduced intracellular Smad3 activation and signaling. Overexpression of csGRP78 increased TSP-1, and this was further augmented in HG. Discussion: These data support an important role for csGRP78 in regulating HG-induced TSP1 transcriptional induction via PI3K/Akt signaling. Functionally, this enables TGFβ1 activation in response to HG, with consequent increase in ECM proteins. Means of inhibiting csGRP78 signaling represent a novel approach to preventing fibrosis in DKD.

Spatially Resolved Transcriptomes of Mammalian Kidneys Illustrate the Molecular Complexity and Interactions of Functional Nephron Segments

Available transcriptomes of the mammalian kidney provide limited information on the spatial interplay between different functional nephron structures due to the required dissociation of tissue with traditional transcriptome-based methodologies. A deeper understanding of the complexity of functional nephron structures requires a non-dissociative transcriptomics approach, such as spatial transcriptomics sequencing (ST-seq). We hypothesize that the application of ST-seq in normal mammalian kidneys will give transcriptomic insights within and across species of physiology at the functional structure level and cellular communication at the cell level. Here, we applied ST-seq in six mice and four human kidneys that were histologically absent of any overt pathology. We defined the location of specific nephron structures in the captured ST-seq datasets using three lines of evidence: pathologist's annotation, marker gene expression, and integration with public single-cell and/or single-nucleus RNA-sequencing datasets. We compared the mouse and human cortical kidney regions. In the human ST-seq datasets, we further investigated the cellular communication within glomeruli and regions of proximal tubules–peritubular capillaries by screening for co-expression of ligand–receptor gene pairs. Gene expression signatures of distinct nephron structures and microvascular regions were spatially resolved within the mouse and human ST-seq datasets. We identified 7,370 differentially expressed genes (p_adj < 0.05) distinguishing species, suggesting changes in energy production and metabolism in mouse cortical regions relative to human kidneys. Hundreds of potential ligand–receptor interactions were identified within glomeruli and regions of proximal tubules–peritubular capillaries, including known and novel interactions relevant to kidney physiology. Our application of ST-seq to normal human and murine kidneys confirms current knowledge and localization of transcripts within the kidney. Furthermore, the generated ST-seq datasets provide a valuable resource for the kidney community that can be used to inform future research into this complex organ.

Sacubitril/Valsartan Improves Progression of Early Diabetic Nephropathy in Rats Through Inhibition of NLRP3 Inflammasome Pathway

PURPOSE

Diabetic nephropathy (DN), a global disease, is the leading cause of end-stage renal disease. There is a lack of specific treatment for this disease, and early intervention in disease progression is essential. In this paper, we used a rat model of early diabetic nephropathy to explore the therapeutic mechanism of sacubitril/valsartan in rats with early diabetic nephropathy.

MATERIALS AND METHODS

Rats were grouped into 1 normal group; 2. Model group (DN group): STZ (45 mg/kg/d) induced early diabetic nephropathy rats; 3. Sac group: DN rats + Sac group (orally, 60 mg/kg/d) for 6 weeks. After 6 weeks, the levels of serum albumin (ALB), glucose (GLU), creatinine (Cr), urea nitrogen (BUN) and 24-h urinary protein excretion were measured. In renal tissue homogenates, NLRP3 inflammasome, proinflammatory factors IL1-β and TNF-α, oxidative stress MDA and pro-fibrotic cytokine TGF-β1 were performed. Histological analysis of kidneys by hematoxylin and eosin (HE), PAS and Masson trichrome staining.

RESULTS

1. Sacubitril/valsartan (Sac) significantly improved renal hypertrophy, proteinuria and serum albumin levels in rats with early diabetic nephropathy (P < 0.001), and decreased GLU, Scr (P<0.001), and BUN levels (P < 0.01).2. Light microscopy of renal tissues showed glomerular hypertrophy and interstitial inflammatory cell infiltration, and mean glomerular area (MGA) and mean glomerular volume (MGV) were crucially increased in early diabetic nephropathy (P < 0.001), and the Sac group showed reduced renal pathology and improved MGA and MGV (P < 0.001).3. Kidney tissue homogenate levels of NLRP3, Caspase-1, IL1-β, TNF-α, MDA and TGF-β1 were critically, increased in DN rats (P < 0.001), and SOD was significantly decreased. All these indicators above were improved after treatment (P < 0.0001).

CONCLUSION

Nlrp3-inflammasome promote progression of diabetic nephropathy through inflammation, fibrosis and oxidative stress; sacubitril/valsartan ameliorated early diabetes-induced renal damage by inhibiting NLRP3 pathway activation.

Comparative effects of incretin-based therapy on early-onset diabetic nephropathy in rats: Role of TNF-α, TGF-β and c-caspase-3

AIMS

Diabetic nephropathy, a major threat to diabetic patients, is considered as the main reason for end-stage renal disease. Fortunately, incretin-based therapy has been aroused as considerable source to attenuate diabetic renal damage. This study aimed to investigate whether superior protective effects on the progression of diabetic kidney are exerted by glucagon-like peptide-1 analog, exenatide, or dipeptidyl peptidase-4 inhibitor, sitagliptin.

MATERIALS AND METHODS

Male Wistar rats were fed high-fat diet for 2 weeks followed by injection of low dose streptozotocin to induce type 2 diabetes mellitus. Four weeks after induction of diabetes, diabetic rats were administered vehicle, exenatide (5 μg/kg/day, SC) or sitagliptin (10 mg/kg/day, orally) for 4 weeks.

KEY FINDINGS

Different incretin mimetic agents improved renal function as evident by significant decreases in serum creatinine and urea levels with decline in urinary microalbuminuria and marked improvement in histological alterations. Both treated diabetic rats also exhibited a significant improvement in metabolic intolerance with more pronounced effect of exenatide on glucose regulation. Ameliorated renal oxidative stress alongside significant downregulation in transforming growth factor-beta, tumor necrosis factor-alpha and cleaved-caspase-3 protein expressions in renal tissues were recorded in treated diabetic rats.

SIGNIFICANCE

Administration of either exenatide or sitagliptin showed ameliorative effects on early diabetic nephropathy without notable differences between their renal protective effects. However, further clinical studies are still required to ensure their comparative promising effects on the management of renal complication of diabetes.

Thrombospondin-1 CD47 Signalling: From Mechanisms to Medicine

Recent advances provide evidence that the cellular signalling pathway comprising the ligand-receptor duo of thrombospondin-1 (TSP1) and CD47 is involved in mediating a range of diseases affecting renal, vascular, and metabolic function, as well as cancer. In several instances, research has barely progressed past pre-clinical animal models of disease and early phase 1 clinical trials, while for cancers, anti-CD47 therapy has emerged from phase 2 clinical trials in humans as a crucial adjuvant therapeutic agent. This has important implications for interventions that seek to capitalize on targeting this pathway in diseases where TSP1 and/or CD47 play a role. Despite substantial progress made in our understanding of this pathway in malignant and cardiovascular disease, knowledge and translational gaps remain regarding the role of this pathway in kidney and metabolic diseases, limiting identification of putative drug targets and development of effective treatments. This review considers recent advances reported in the field of TSP1-CD47 signalling, focusing on several aspects including enzymatic production, receptor function, interacting partners, localization of signalling, matrix-cellular and cell-to-cell cross talk. The potential impact that these newly described mechanisms have on health, with a particular focus on renal and metabolic disease, is also discussed.

A Method to Isolate Pericytes From the Mouse Urinary Bladder for the Study of Diabetic Bladder Dysfunction

Purpose

Pericytes surround the endothelial cells in microvessels and play a distinct role in controlling vascular permeability and maturation. The loss of pericyte function is known to be associated with diabetic retinopathy and erectile dysfunction. This study aimed to establish a technique for the isolation of pericytes from the mouse urinary bladder and an in vitro model that mimics in vivo diabetic bladder dysfunction.

Methods

To avoid contamination with epithelial cells, the urothelial layer was meticulously removed from the underlying submucosa and detrusor muscle layer. The tissues were cut into multiple pieces, and the fragmented tissues were settled by gravity into collagen I-coated culture plates. The cells were cultured under normal-glucose (5 mmol/L) or high-glucose (30 mmol/L) conditions, and tube formation, cell proliferation, and TUNEL assays were performed. We also performed hydroethidine staining to measure superoxide anion production.

Results

We successfully isolated high-purity pericytes from the mouse urinary bladder. The cells were positively stained for platelet-derived growth factor receptor-β and NG2 and negatively stained for smooth muscle cell markers (desmin and myosin) and an endothelial cell marker (CD31). The number of tubes formed and the number of proliferating cells were significantly lower when the pericytes were exposed to high-glucose conditions compared with normal-glucose conditions. In addition, there were significant increases in superoxide anion production and the number of apoptotic cells when the pericytes were cultured under high-glucose conditions.

Conclusions

To the best of our knowledge, this is the first study to isolate and culture pericytes from the mouse urinary bladder. Our model would be a useful tool for screening the efficacy of therapeutic candidates targeting pericyte function in diabetic bladder dysfunction and exploring the functional role of specific targets at the cellular level.

Diabetic fibrosis

Diabetes-associated morbidity and mortality is predominantly due to complications of the disease that may cause debilitating conditions, such as heart and renal failure, hepatic insufficiency, retinopathy or peripheral neuropathy. Fibrosis, the excessive and inappropriate deposition of extracellular matrix in various tissues, is commonly found in patients with advanced type 1 or type 2 diabetes, and may contribute to organ dysfunction. Hyperglycemia, lipotoxic injury and insulin resistance activate a fibrotic response, not only through direct stimulation of matrix synthesis by fibroblasts, but also by promoting a fibrogenic phenotype in immune and vascular cells, and possibly also by triggering epithelial and endothelial cell conversion to a fibroblast-like phenotype. High glucose stimulates several fibrogenic pathways, triggering reactive oxygen species generation, stimulating neurohumoral responses, activating growth factor cascades (such as TGF-β/Smad3 and PDGFs), inducing pro-inflammatory cytokines and chemokines, generating advanced glycation end-products (AGEs) and stimulating the AGE-RAGE axis, and upregulating fibrogenic matricellular proteins. Although diabetes-activated fibrogenic signaling has common characteristics in various tissues, some organs, such as the heart, kidney and liver develop more pronounced and clinically significant fibrosis. This review manuscript summarizes current knowledge on the cellular and molecular pathways involved in diabetic fibrosis, discussing the fundamental links between metabolic perturbations and fibrogenic activation, the basis for organ-specific differences, and the promises and challenges of anti-fibrotic therapies for diabetic patients.

Transcriptional profiling of mouse cavernous pericytes under high-glucose conditions: Implications for diabetic angiopathy

Purpose

Penile erection requires integrative interactions between vascular endothelial cells, pericytes, smooth muscle cells, and autonomic nerves. Furthermore, the importance of the role played by pericytes in the pathogenesis of angiopathy has only recently been appreciated. However, global gene expression in pericytes in diabetes mellitus-induced erectile dysfunction (DMED) remains unclear. We aimed to identify potential target genes related to DMED in mouse cavernous pericytes (MCPs).

Materials and Methods

Mouse cavernous tissue was allowed to settle under gravity in collagen I-coated dishes, and sprouted cells were subcultivated for experiments. To imitate diabetic conditions, MCPs were treated with normal-glucose (NG, 5 mM) or high-glucose (HG, 30 mM) media for 3 days. Microarray technology was used to evaluate gene expression profiles, and RT-PCR was used to validate sequencing data. Histological examinations and Western blot were used to validate final selected target genes related to DMED.

Results

Decreased tube formation and increased apoptosis were detected in MCPs exposed to the HG condition. As shown by microarray analysis, the gene expression profiles of MCPs exposed to the NG or HG condition differed. A total of 2,523 genes with significantly altered expression were classified into 15 major gene categories. After further screening based on gene expression and RT-PCR and histologic results, we found that Hebp1 gene expression was significantly diminished under the HG condition and in DM mice.

Conclusions

This gene profiling study provides new potential targets responsible for diabetes in MCPs. Validation studies suggest that Hebp1 may be a suitable biomarker for DMED.

Blocking thrombospondin-1 signaling via CD47 mitigates renal interstitial fibrosis

Acute kidney injury triggers a complex cascade of molecular responses that can culminate in maladaptive repair and fibrosis. We have previously reported that the matrix protein thrombospondin-1 (TSP1), binding its high affinity its receptor CD47, promotes acute kidney injury. However, the role of this pathway in promoting fibrosis is less clear. Hypothesizing that limiting TSP1-CD47 signaling is protective against fibrosis, we interrogated this pathway in a mouse model of chronic ischemic kidney injury. Plasma and renal parenchymal expression of TSP1 in patients with chronic kidney disease was also assessed. We found that CD47^-/- mice or wild-type mice treated with a CD47 blocking antibody showed clear amelioration of fibrotic histological changes compared to control animals. Wild-type mice showed upregulated TSP1 and pro-fibrotic markers which were significantly abrogated in CD47^-/- and antibody-treated cohorts. Renal tubular epithelial cells isolated from WT mice showed robust upregulation of pro-fibrotic markers following hypoxic stress or exogenous TSP1, which was mitigated in CD47^-/- cells. Patient sera showed a proportionate correlation between TSP1 levels and worsening glomerular filtration rate. Immunohistochemistry of human kidney tissue demonstrated tubular and glomerular matrix localization of TSP1 expression in patients with CKD. These data suggest that renal tubular epithelial cells contribute to fibrosis by activating TSP1-CD47 signaling, and point to CD47 as a potential target to limit fibrosis following ischemic injury.

Attenuation of intermittent hypoxia-induced apoptosis and fibrosis in pulmonary tissues via suppression of ER stress activation

Background

Obstructive sleep apnea (OSA) is associated with pulmonary fibrosis and endothelial apoptosis in pulmonary tissues. Chronic intermittent hypoxia (IH) is considered to be the primary player in OSA, but the mechanisms underlying its effect on pulmonary tissues are unknown. Endoplasmic reticulum (ER) stress induced by IH treatment plays an important role in accelerating the process of fibrosis and induction of apoptosis.

Methods

Mice were placed in IH chambers for 4 weeks with an oscillating oxygen (O₂) concentration between 5 and 21%, cycling every 90s for 8 h daily. Mice were randomly divided into four groups: control group (normal oxygen), tauroursodeoxycholic acid (TUDCA) group (normal oxygen intraperitoneally injected with TUDCA), IH group and IH + TUDCA group. After 4 weeks, the proteins in three branch signaling pathways of ER stress, including protein kinase RNA (PKR)-like/Pancreatic ER kinase (PERK), activating transcription factor 6 (ATF-6) and inositol-requiring enzyme 1 (IRE-1), were evaluated. The cleaved caspase-3, caspase-12 and TUNNEL staining was assessed. Furthermore, the expression of transforming growth factor-β1 (TGF-β1) and thrombospondin-1(TSP-1), two extracellular matrix proteins that play critical role in fibrosis, were examined. Finally, Masson’s trichrome staining was performed to detect the expression of collagen.

Results

After 4 weeks of IH treatment, the expressions of two ER stress markers, glucose regulated protein-78 (Grp78) and transcription factor C/EBP homologous protein (CHOP) were increased which was prevented by administration of the ER stress attenuator, TUDCA. The expressions of PERK, but not those of ATF-6 and IRE-1, were increased. The effects of IH were accompanied by an increased number of apoptotic cells and increased expressions of cleaved caspase-3 and caspase-12 in pulmonary tissues. In addition, histological examination suggested the presence of fibrosis after chronic IH treatment, indicated by increased expression of collagen, which was associated with the up-regulation of TGF-β1 and TSP-1 that are known to promote fibrosis. Similarly, TUDCA could reduce the extent of fibrotic area and the expression levels of these proteins.

Conclusions

It reveals the roles of ER stress, especially the PERK pathway, in IH induced apoptosis and fibrosis in pulmonary tissues that might underlie the pulmonary complications observed in OSA.

Long non-coding RNA RNF7 promotes the cardiac fibrosis in rat model via miR-543/THBS1 axis and TGFβ1 activation

Cardiac fibrosis (CF) is regulated by multiple factors, including transforming growth factor β1 (TGFβ1) and non-coding RNAs. Thrombospondin 1 (TSP1) is a physiologic regulator of TGFβ activation. Here, we performed microarray analyses on mRNAs and lncRNAs differentially-expressed in the CF and normal rat hearts. KEGG signaling annotation and GO enrichment analyses were performed to validate the roles of extracellular matrix (ECM) and TSP1-enhanced TGFβ activation in CF. The co-expression network between differentially-expressed lncRNAs and ECM-related factors was constructed to identify candidate lncRNAs and miRNAs. We found that lncRNA Homo sapiens ring finger protein 7 (lnc RNF7) was significantly correlated with TSP1 and ECM. Lnc RNF7 silence could attenuate isoproterenol (ISP)-induced CF in rat heart in vivo and in rat cardiac fibroblasts in vitro. Moreover, angiotensin II (Ang II) -induced CF in rat cardiac fibroblasts could also be attenuated by Lnc RNF7 silence. Furthermore, miR-543 could simultaneously target lnc RNF7 and 3' UTR of TSP1. Lnc RNF7 silence suppressed, while miR-543 inhibition promoted TSP1 protein and TGFβ activation, as well as ECM markers expression. The effects of lnc RNF7 silence was significantly reversed by miR-543 inhibition. In conclusion, CF progression might be regulated by lnc RNF7/miR-543 axis via TSP1-mediated TGFβ activation.

Thrombospondin 1 and Its Diverse Roles as a Regulator of Extracellular Matrix in Fibrotic Disease

Thrombospondin 1 (TSP1) is a matricellular extracellular matrix protein that has diverse roles in regulating cellular processes important for the pathogenesis of fibrotic diseases. We will present evidence for the importance of TSP1 control of latent transforming growth factor beta activation in renal fibrosis with an emphasis on diabetic nephropathy. Other functions of TSP1 that affect renal fibrosis, including regulation of inflammation and capillary density, will be addressed. Emerging roles for TSP1 N-terminal domain regulation of collagen matrix assembly, direct effects of TSP1-collagen binding, and intracellular functions of TSP1 in mediating endoplasmic reticulum stress responses in extracellular matrix remodeling and fibrosis, which could potentially affect renal fibrogenesis, will also be discussed. Finally, we will address possible strategies for targeting TSP1 functions to treat fibrotic renal disease.

The prognosis of trabeculectomy in primary angle-closure glaucoma patients

AIM

To evaluate whether the level of thrombospondin-1 (TSP-1) in aqueous humor can predict the prognosis of trabeculectomy in patients with primary angle-closure glaucoma (PACG).

METHODS

This case-control study involved 26 patients with PACG who experienced a failed trabeculectomy (case group) and 78 age- and sex-matched patients with PACG who underwent successful trabeculectomy (control group). Aqueous humor was collected at the time of trabeculectomy and tested for TSP-1 and TGF-β2 levels with an enzyme-linked immunosorbent assay method. Logistic regression modeling was used to assess the risk factors for failed trabeculectomy.

RESULTS

The mean TSP-1 aqueous concentrations were significantly higher in the case group (20.67±9.79 ng/mL) than the control group (5.17±2.29 ng/mL) (P<0.001). The transforming growth factor-β2 (TGF-β2) aqueous concentrations were significantly different between the case and control group, at 3633.25 and 1090.24 pg/mL, respectively (P<0.001). Logistic regression analysis revealed TSP-1 level as an independent risk factor for a failed trabeculectomy (OR=3.540; 95%CI=1.092-11.482).

CONCLUSION

The aqueous humor TSP-1 and TGF-β2 levels are higher in PACG eyes with failed trabeculectomy than with successful trabeculectomy at one year. The aqueous humor TSP-1 level is an independent risk factor associated with failed trabeculectomy.

Thrombospondin-1 regulation of latent TGF-β activation: A therapeutic target for fibrotic disease

Transforming growth factor-β (TGF-β) is a central player in fibrotic disease. Clinical trials with global inhibitors of TGF-β have been disappointing, suggesting that a more targeted approach is warranted. Conversion of the latent precursor to the biologically active form of TGF-β represents a novel approach to selectively modulating TGF-β in disease, as mechanisms employed to activate latent TGF-β are typically cell, tissue, and/or disease specific. In this review, we will discuss the role of the matricellular protein, thrombospondin 1 (TSP-1), in regulation of latent TGF-β activation and the use of an antagonist of TSP-1 mediated TGF-β activation in a number of diverse fibrotic diseases. In particular, we will discuss the TSP-1/TGF-β pathway in fibrotic complications of diabetes, liver fibrosis, and in multiple myeloma. We will also discuss emerging evidence for a role for TSP-1 in arterial remodeling, biomechanical modulation of TGF-β activity, and in immune dysfunction. As TSP-1 expression is upregulated by factors induced in fibrotic disease, targeting the TSP-1/TGF-β pathway potentially represents a more selective approach to controlling TGF-β activity in disease.

Transforming growth factor-β in stem cells and tissue homeostasis

TGF-β 1-3 are unique multi-functional growth factors that are only expressed in mammals, and mainly secreted and stored as a latent complex in the extracellular matrix (ECM). The biological functions of TGF-β in adults can only be delivered after ligand activation, mostly in response to environmental perturbations. Although involved in multiple biological and pathological processes of the human body, the exact roles of TGF-β in maintaining stem cells and tissue homeostasis have not been well-documented until recent advances, which delineate their functions in a given context. Our recent findings, along with data reported by others, have clearly shown that temporal and spatial activation of TGF-β is involved in the recruitment of stem/progenitor cell participation in tissue regeneration/remodeling process, whereas sustained abnormalities in TGF-β ligand activation, regardless of genetic or environmental origin, will inevitably disrupt the normal physiology and lead to pathobiology of major diseases. Modulation of TGF-β signaling with different approaches has proven effective pre-clinically in the treatment of multiple pathologies such as sclerosis/fibrosis, tumor metastasis, osteoarthritis, and immune disorders. Thus, further elucidation of the mechanisms by which TGF-β is activated in different tissues/organs and how targeted cells respond in a context-dependent way can likely be translated with clinical benefits in the management of a broad range of diseases with the involvement of TGF-β.

GP73 promotes invasion and metastasis of bladder cancer by regulating the epithelial-mesenchymal transition through the TGF-β1/Smad2 signalling pathway

This study investigated the effects of Golgi membrane protein 73 (GP73) on the epithelial-mesenchymal transition (EMT) and on bladder cancer cell invasion and metastasis through the TGF-β1/Smad2 signalling pathway. Paired bladder cancer and adjacent tissue samples (102) and normal bladder tissue samples (106) were obtained. Bladder cancer cell lines (T24, 5637, RT4, 253J and J82) were selected and assigned to blank, negative control (NC), TGF-β, thrombospondin-1 (TSP-1), TGF-β1+ TSP-1, GP73-siRNA-1, GP73-siRNA-2, GP73-siRNA-1+ TSP-1, GP73-siRNA-1+ pcDNA-GP73, WT1-siRNA and WT1-siRNA + GP73-siRNA-1 groups. Expressions of GP73, TGF-β1, Smad2, p-Smad2, E-cadherin and vimentin were detected using RT-qPCR and Western blotting. Cell proliferation, migration and invasion were determined using MTT assay, scratch testing and Transwell assay, respectively. Compared with the blank and NC groups, levels of GP73, TGF-β1, Smad2, p-Smad2, N-cadherin and vimentin decreased, and levels of WT1 and E-cadherin increased in the GP73-siRNA-1 and GP73-siRNA-2 groups, while the opposite results were observed in the WT1 siRNA, TGF-β, TSP-1 and TGF-β + TSP-1 groups. Cell proliferation, migration and invasion notably decreased in the GP73-siRNA-1 and GP73-siRNA-2 groups in comparison with the blank and NC groups, while in the WT1 siRNA, TGF-β, TSP-1 and TGF-β + TSP-1 groups, cell migration, invasion and proliferation showed the reduction after the EMT. These results suggest that GP73 promotes bladder cancer invasion and metastasis by inducing the EMT through down-regulating WT1 levels and activating the TGF-β1/Smad2 signalling pathway.

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

SIGNIFICANCE

In contrast to structural elements of the extracellular matrix, matricellular proteins appear transiently during development and injury responses, but their sustained expression can contribute to chronic disease. Through interactions with other matrix components and specific cell surface receptors, matricellular proteins regulate multiple signaling pathways, including those mediated by reactive oxygen and nitrogen species and H2S. Dysregulation of matricellular proteins contributes to the pathogenesis of vascular diseases and cancer. Defining the molecular mechanisms and receptors involved is revealing new therapeutic opportunities. Recent Advances: Thrombospondin-1 (TSP1) regulates NO, H2S, and superoxide production and signaling in several cell types. The TSP1 receptor CD47 plays a central role in inhibition of NO signaling, but other TSP1 receptors also modulate redox signaling. The matricellular protein CCN1 engages some of the same receptors to regulate redox signaling, and ADAMTS1 regulates NO signaling in Marfan syndrome. In addition to mediating matricellular protein signaling, redox signaling is emerging as an important pathway that controls the expression of several matricellular proteins.

CRITICAL ISSUES

Redox signaling remains unexplored for many matricellular proteins. Their interactions with multiple cellular receptors remains an obstacle to defining signaling mechanisms, but improved transgenic models could overcome this barrier.

FUTURE DIRECTIONS

Therapeutics targeting the TSP1 receptor CD47 may have beneficial effects for treating cardiovascular disease and cancer and have recently entered clinical trials. Biomarkers are needed to assess their effects on redox signaling in patients and to evaluate how these contribute to their therapeutic efficacy and potential side effects. Antioxid. Redox Signal. 27, 874-911.

Inhibition of angiogenesis by arsenic trioxide via TSP-1-TGF-β1-CTGF-VEGF functional module in rheumatoid arthritis

Angiogenesis is a critical factor for rheumatoid arthritis (RA). Although anti-TNF biologics work effectively on some RA patients, concerns have been raised about the possible increased development of malignancies alongside such treatments. Arsenic trioxide (As₂O₃) has attracted worldwide attention and has been reported to treat some cancers. However, the effects of As₂O₃ on angiogenesis in the RA synovium remain unclear. Here, we report a systematic increased expression of TSP-1, TGF-β1, CTGF and VEGF in supernatants of a RA fibroblast-like synoviocytes (RA-FLS) and human dermal microvascular endothelial cells (HDMECs) co-culture compared with those from a normal human fibroblast-like synoviocytes (NH-FLS) and HDMECs co-culture. This increased expression may up-regulate endothelial tube formation and transwell migration, as well as microvessel sprouting in ex vivo aortic ring assay. These networked angiogenic factors mainly form a functional module regulating angiogenesis in the RA synovium. We show that As₂O₃ inhibits angiogenesis in the collagen-induced arthritis (CIA) synovium and consequently arthritis severity via significant suppression of TSP-1, TGF-β1, CTGF and VEGF expression in the CIA synovium, plus in the RA-FLS and HDMECs co-culture as well as NH-FLS and HDMECs co-culture system along with the presence or absence of TNF-α treatment. Thus As₂O₃ has a significant anti-angiogenesis effect on the RA-FLS and CIA synovium via its inhibition of the RA angiogenic functional module of TSP-1, TGF-β1, CTGF and VEGF and may have a potential for treating RA beyond cancer therapy.

Establishment of in vitro model of erectile dysfunction for the study of high-glucose-induced angiopathy and neuropathy

Penile erection requires complex interaction between vascular endothelial cells, smooth muscle cells, pericytes, and autonomic nerves. Diabetes mellitus is one of the most common causes of erectile dysfunction (ED) and multiple pathogenic factors, such as cavernous angiopathy and autonomic neuropathy, are associated with diabetic ED. Although a variety of animal models of diabetic ED play an important role in understanding pathophysiologic mechanisms of diabetes-induced ED, these animal models have limitations for addressing the exact cellular or molecular mechanisms involved in ED. Therefore, we established an in vitro model of ED for the study of high-glucose-induced angiopathy and neuropathy. We successfully isolated and cultivated mouse cavernous endothelial cells (MCECs) and mouse cavernous pericytes (MCPs). The cells were exposed to the normal-glucose (5 mmoL) or high-glucose (30 mmoL) condition for 48 h. In vitro matrigel assay revealed impairments in tube formation in primary cultured MCECs or MCPs exposed to high-glucose condition. To study cellular interaction between MCECs and MCPs, co-culture systems including indirect contact, indirect non-contact, and direct mixed co-culture system, were established. We observed impaired tube formation and increased permeability in MCECs-MCPs co-culture exposed to high-glucose condition. To evaluate the effect of high-glucose on neurite sprouting, the mouse major pelvic ganglion (MPG) tissue was harvested and cultivated in matrigel. Neurite outgrowth and nNOS-positive nerve fibers were significantly lower in MPG tissues exposed to the high-glucose condition than in the tissues exposed to the normal-glucose condition. We believe that in vitro model of ED will aid us to understand the role of each cellular component in the pathogenesis of diabetic ED, and also be a useful tool for determining the efficacy of candidate therapeutics targeting vascular or neuronal function. This model would present a new avenue for drug discovery and development of novel therapeutic modalities for erectile dysfunction.

Thrombospondin 1 Deficiency Ameliorates the Development of Adriamycin-Induced Proteinuric Kidney Disease

Accumulating evidence suggests that thrombospondin 1 (TSP1) is an important player in diabetic nephropathy. However, the role of TSP1 in podocyte injury and the development of non-diabetic proteinuric kidney disease is largely unknown. In the current study, by using a well-established podocyte injury model (adriamycin-induced nephropathy mouse model), we examined the contribution of TSP1 to the development of proteinuric kidney disease. We found that TSP1 was up-regulated in the glomeruli, notably in podocytes, in adriamycin injected mice before the onset of proteinuria. ADR treatment also stimulated TSP1 expression in cultured human podocytes in vitro. Moreover, increased TSP1 mediated ADR-induced podocyte apoptosis and actin cytoskeleton disorganization. This TSP1's effect was through a CD36-dependent mechanism and involved in the stimulation of p38MAPK pathway. Importantly, in vivo data demonstrated that TSP1 deficiency protected mice from ADR induced podocyte loss and foot process effacement. ADR induced proteinuria, glomerulosclerosis, renal macrophage infiltration and inflammation was also attenuated in TSP1 deficient mice. Taken together, these studies provide new evidence that TSP1 contributes to the development of non-diabetic proteinuric kidney disease by stimulating podocyte injury and the progression of renal inflammation.

Regulation of Vascular Proteoglycan Synthesis by Metabolic Factors Associated with Diabetes

BACKGROUND

Diabetes is associated with accelerated atherosclerosis, but the mechanisms responsible for this are not known. Proteoglycans have been shown to play a critical role in the initiation of atherosclerosis owing to their ability to bind and retain atherogenic lipoproteins in the artery wall. Proteoglycan structure and composition are altered in atherosclerotic lesions compared with adjacent normal regions of the artery wall, and this is exaggerated in diabetes. The purpose of this study was to determine if metabolic factors associated with diabetes lead to altered proteoglycan structure and composition.

METHODS

Vascular smooth muscle cells, endothelial cells, and macrophages were exposed to normal (5.6 mmol/L) or high (25 mmol/L) glucose levels, various insulin and free fatty acid levels, and the cytokines transforming growth factor beta (TGF-beta1) and platelet-derived growth factor, alone or in combination, and proteoglycan synthesis was determined.

RESULTS

Glucose concentrations, insulin, and free fatty acids did not alter proteoglycan synthesis, size, or relative distribution. The effect of TGF-beta to increase biglycan and versican synthesis, increase sulfate incorporation, and increase the size of the secreted proteoglycans was not altered by the ambient glucose level in the culture medium, nor did high glucose increase levels of active TGF-beta.

CONCLUSION

Vascular proteoglycan synthesis is not affected by metabolic factors associated with diabetes. We suggest that elevated TGF-beta levels in diabetes are responsible for the altered proteoglycan synthesis observed in diabetes.

The Thrombospondin1-TGF-β Pathway and Glaucoma

Glaucoma is characterized by abnormal remodeling of the extracellular matrix (ECM) in the trabecular meshwork and in the connective tissue beams of the lamina cribrosa (LC) at the optic nerve head (ONH), which is associated with axonal damage. Mechanical strain can stimulate ECM remodeling and increased expression of matricellular proteins. Thrombospondins 1 and 2 are induced by cyclic mechanical strain in the eye in both the trabecular meshwork and in the LC region of the ONH. TGF-betas 1 and 2 are increased in glaucoma and play a role in the pathologic remodeling of the ECM in the eye in glaucoma. In this study, we address the role of thrombospondin1 as a regulator of latent TGF-beta activation and discuss the potential therapeutic use of antagonists of the thrombospondin1-TGF-beta pathway for treatment of glaucoma.

Effect of triptolide on expression of thrombospondin-1 and transforming growth factor-β1 in renal tubular cells

The objective of our study is to investigate the effect of triptolide on expression of thrombospondin-1 and transforming growth factor β1 in renal tubular cells. Human renal tubular epithelial cells were stimulated by different concentrations of triptolide (0.1, 1, and 10 μg/L) in the presence of angiotensin-II (10(-7)mol/L). Real Time PCR was used to detect the mRNA expression of thrombospondin-1 and transforming growth factor β1. Western blot analysis was used to detect the protein expression. ELISA was used to detect the level of total and active transforming growth factor β1. The mRNA expression of thrombospondin-1 (3.66 ± 0.48 vs. 1.33 ± 0.26, p < 0.05) and transforming growth factor β1 (3.58 ± 0.59 vs. 1.26 ± 0.28, p < 0.05) were up-regulated obviously when stimulated by angiotensin-II. And the protein expression of thrombospondin-1 (0.5126 ± 0.0936 vs. 0.1025 ± 0.0761, p < 0.01) and transforming growth factor β1 (0.5948 ± 0.0736 vs. 0.1318 ± 0.0614, p < 0.01) were also up-regulated simultaneously when stimulated by angiotensin-II. The expression of thrombospondin-1 and transforming growth factor β1 induced by angiotensin-II were down-regulated markedly with 1 μg/L and 10 μg/L of triptolide in mRNA and protein levels (p < 0.05, p <  0.01). And triptolide (1 and 10 μg/L) could reduce the expression of total and active transforming growth factor β1 (p < 0.05, p < 0.01). In conclusion, triptolide can inhibit the expression of thrombospondin-1 and transforming growth factor β1 in mRNA and protein levels and down-regulate the levels of total and active transforming growth factor β1.

The Function of Matricellular Proteins in the Lamina Cribrosa and Trabecular Meshwork in Glaucoma

PURPOSE

To review the current literature regarding the role of matricellular proteins in glaucoma, specifically in the lamina cribrosa (LC) region of the optic nerve head (ONH) and the trabecular meshwork (TM).

METHODS

A literature search was performed for published articles describing the expression and function of matricellular proteins such as thrombospondin (TSP), connective tissue growth factor (CTGF), secreted protein acidic and rich in cysteine (SPARC), and periostin in glaucoma.

RESULTS

In glaucoma, there are characteristic extracellular matrix (ECM) changes associated with optic disc cupping in the ONH and subsequent visual field defects. Matricellular proteins are a family of nonstructural secreted glycoproteins, which enable cells to communicate with their surrounding ECM, including CTGF, also known as CCN2, TSPs, SPARC, periostin, osteonectin, and tenascin-C and -X, and other ECM proteins. Such proteins appear to play a role in fibrosis and increased ECM deposition. Importantly, most are widely expressed in tissues particularly in the TM and ONH, and deficiency of TSP1 and SPARC has been shown to lower intraocular pressure in mouse models of glaucoma through enhanced outflow facility.

CONCLUSION

This article highlights the role of matricellular proteins in glaucoma pathology. The potential role of these proteins in glaucoma is emerging as some have an association with the pathophysiology of the TM and LC region and might therefore be potential targets for therapeutic intervention in glaucoma.

Thrombospondin1 deficiency attenuates obesity-associated microvascular complications in ApoE-/- mice

Obesity is associated with insulin resistance and the increased development of vascular complications. Previously, we have demonstrated that thrombospondin1 (TSP1) regulates macrophage function and contributes to obesity associated inflammation and insulin resistance. However, the role of TSP1 in the development of obesity associated vascular complications is not clear. Therefore, in the current study, we investigated whether TSP1 deficiency protects mice from obesity associated micro as well as macro-vascular complications in ApoE-/- mice. In this study, male ApoE-/- mice and ApoE-/-TSP1-/- mice were fed with a low-fat (LF) or a high-fat (HF) diet for 16 weeks. We found that body weight and fat mass increased similarly between the ApoE-/-TSP1-/- mice and ApoE-/- mice under HF feeding conditions. However, as compared to obese ApoE-/- mice, obese ApoE-/-TSP1-/- mice had improved glucose tolerance, increased insulin sensitivity, and reduced systemic inflammation. Aortic atherosclerotic lesion formation was similar in these two groups of mice. In contrast, albuminuria was attenuated and kidney fibrosis was reduced in obese ApoE-/-TSP1-/- mice compared to obese ApoE-/- mice. The improved kidney function in obese ApoE-/-TSP1-/- mice was associated with decreased renal lipid accumulation. Together, these data suggest that TSP1 deficiency did not affect the development of obesity associated macro-vascular complication, but attenuated obesity associated micro-vascular complications.

The role of matricellular proteins in glaucoma

Glaucoma is an optic neuropathy affecting approximately 60million people worldwide and is the second most common cause of irreversible blindness. Elevated intraocular pressure (IOP) is the main risk factor for developing glaucoma and is caused by impaired aqueous humor drainage through the trabecular meshwork (TM) and Schlemm's canal (SC). In primary open angle glaucoma (POAG), this elevation in IOP in turn leads to deformation at the optic nerve head (ONH) specifically at the lamina cribrosa (LC) region where there is also a deposition of extracellular matrix (ECM) molecules such as collagen and fibronectin. Matricellular proteins are non-structural secreted glycoproteins that help cells communicate with their surrounding ECM. This family of proteins includes connective tissue growth factor (CTGF), also known as CCN2, thrombospondins (TSPs), secreted protein acidic and rich in cysteine (SPARC), periostin, osteonectin, and Tenascin-C and -X and other ECM proteins. All members appear to play a role in fibrosis and increased ECM deposition. Most are widely expressed in tissues particularly in the TM and ONH and deficiency of TSP1 and SPARC have been shown to lower IOP in mouse models of glaucoma through enhanced outflow facility. The role of these proteins in glaucoma is emerging as some have an association with the pathophysiology of the TM and LC regions and might therefore be potential targets for therapeutic intervention in glaucoma.

The role of epigenetics in the fibrotic processes associated with glaucoma

Glaucoma is an optic neuropathy that affects 60 million people worldwide. The main risk factor for glaucoma is increased intraocular pressure (IOP), this is currently the only target for treatment of glaucoma. However, some patients show disease progression despite well-controlled IOP. Another possible therapeutic target is the extracellular matrix (ECM) changes in glaucoma. There is an accumulation of ECM in the lamina cribrosa (LC) and trabecular meshwork (TM) and upregulation of profibrotic factors such as transforming growth factor β (TGFβ), collagen1α1 (COL1A1), and α-smooth muscle actin (αSMA). One method of regulating fibrosis is through epigenetics; the study of heritable changes in gene function caused by mechanisms other than changes in the underlying DNA sequence. Epigenetic mechanisms have been shown to drive renal and pulmonary fibrosis by upregulating profibrotic factors. Hypoxia alters epigenetic mechanisms through regulating the cell's response and there is a hypoxic environment in the LC and TM in glaucoma. This review looks at the role that hypoxia plays in inducing aberrant epigenetic mechanisms and the role these mechanisms play in inducing fibrosis. Evidence suggests that a hypoxic environment in glaucoma may induce aberrant epigenetic mechanisms that contribute to disease fibrosis. These may prove to be relevant therapeutic targets in glaucoma.

Invoking the power of thrombospondins: regulation of thrombospondins expression

Increasing evidence suggests critical functions of thrombospondins (TSPs) in a variety of physiological and pathological processes. With the growing understanding of the importance of these matricellular proteins, the need to understand the mechanisms of regulation of their expression and potential approaches to modulate their levels is also increasing. The regulation of TSP expression is multi-leveled, cell- and tissue-specific, and very precise. However, the knowledge of mechanisms modulating the levels of TSPs is fragmented and incomplete. This review discusses the known mechanisms of regulation of TSP levels and the gaps in our knowledge that prevent us from developing strategies to modulate the expression of these physiologically important proteins.

Understanding the origin, activation and regulation of matrix-producing myofibroblasts for treatment of fibrotic disease

Fibrosis and scar formation results from chronic progressive injury in virtually every tissue and affects a growing number of people around the world. Myofibroblasts drive fibrosis, and recent work has demonstrated that mesenchymal cells, including pericytes and perivascular fibroblasts, are their main progenitors. Understanding the cellular mechanisms of pericyte/fibroblast-to-myofibroblast transition, myofibroblast proliferation and the key signalling pathways that regulate these processes is essential to develop novel targeted therapeutics for the growing patient population suffering from solid organ fibrosis. In this review, we summarize the current knowledge about different progenitor cells of myofibroblasts, discuss major pathways that regulate their transdifferentiation and discuss the current status of novel targeted anti-fibrotic therapeutics in development.

Thrombospondins: old players, new games

PURPOSE OF REVIEW

Thrombospondins (TSPs) are secreted extracellular matrix (ECM) proteins from TSP family, which consists of five homologous members. They share a complex domain structure and have numerous binding partners in ECM and multiple cell surface receptors. Information that has emerged over the past decade identifies TSPs as important mediators of cellular homeostasis, assigning new important roles in cardiovascular pathology to these proteins.

RECENT FINDINGS

Recent studies of the functions of TSP in the cardiovascular system, diabetes and aging, which placed several TSPs in a position of critical regulators, demonstrated the involvement of these proteins in practically every aspect of cardiovascular pathophysiology related to atherosclerosis: inflammation, immunity, leukocyte recruitment and function, function of vascular cells, angiogenesis, and responses to hypoxia, ischemia and hyperglycemia. TSPs are also critically important in the development and ultimate outcome of the complications associated with atherosclerosis--myocardial infarction, and heart hypertrophy and failure. Their expression and significance increase with age and with the progression of diabetes, two major contributors to the development of atherosclerosis and its complications.

SUMMARY

This overview of recent literature examines the latest information on the newfound functions of TSPs that emphasize the importance of ECM in cardiovascular homeostasis and pathology. The functions of TSPs in myocardium, vasculature, vascular complications of diabetes, aging and immunity are discussed.

Thrombospondin 1 mediates renal dysfunction in a mouse model of high-fat diet-induced obesity

Obesity is prevalent worldwide and is a major risk factor for many diseases including renal complications. Thrombospondin 1 (TSP1), a multifunctional extracellular matrix protein, plays an important role in diabetic kidney diseases. However, whether TSP1 plays a role in obesity-related kidney disease is unknown. In the present studies, the role of TSP1 in obesity-induced renal dysfunction was determined by using a diet-induced obese mouse model. The results demonstrated that TSP1 was significantly upregulated in the kidney from obese mice. The increased TSP1 was localized in the glomerular mesangium as well as in the tubular system from obese wild-type mice. Obese wild-type mice developed renal hypertrophy and albuminuria, which was associated with increased kidney macrophage infiltration, augmented kidney inflammation, and activated transforming growth factor (TGF)-β signaling and renal fibrosis. In contrast, obese TSP1-deficient mice did not develop these kidney damages. Furthermore, in vitro studies demonstrated that leptin treatment stimulated the expression of TSP1, TGF-β1, fibronectin, and collagen type IV in mesangial cells isolated from wild-type mice. These leptin-stimulated effects were abolished in TSP1-deficient mesangial cells. Taken together, these data suggest that TSP1 is an important mediator for obesity- or hyperleptinemia-induced kidney dysfunction.

Connective tissue growth factor (CTGF) expression modulates response to high glucose

Connective tissue growth factor (CTGF) is an important mediator of fibrosis; emerging evidence link changes in plasma and urinary CTGF levels to diabetic kidney disease. To further ascertain the role of CTGF in responses to high glucose, we assessed the consequence of 4 months of streptozotocin-induced diabetes in wild type (+/+) and CTGF heterozygous (+/−) mice. Subsequently, we studied the influence of glucose on gene expression and protein in mice embryonic fibroblasts (MEF) cells derived from wildtype and heterozygous mice. At study initiation, plasma glucose, creatinine, triglyceride and cholesterol levels were similar between non-diabetic CTGF+/+ and CTGF+/− mice. In the diabetic state, plasma glucose levels were increased in CTGF+/+ and CTGF+/− mice (28.2 3.3 mmol/L vs 27.0 3.1 mmol/L), plasma triglyceride levels were lower in CTGF+/− mice than in CTGF+/+ (0.7 0.2 mmol/L vs 0.5 0.1 mmol/L, p<0.05), but cholesterol was essentially unchanged in both groups. Plasma creatinine was higher in diabetic CTGF+/+ group (11.7±1.2 vs 7.9±0.6 µmol/L p<0.01), while urinary albumin excretion and mesangial expansion were reduced in diabetic CTGF+/− animals. Cortices from diabetic mice (both CTGF +/+ and CTGF +/−) manifested higher expression of CTGF and thrombospondin 1 (TSP1). Expression of nephrin was reduced in CTGF +/+ animals; this reduction was attenuated in CTGF+/− group. In cultured MEF from CTGF+/+ mice, glucose (25 mM) increased expression of pro-collagens 1, IV and XVIII as well as fibronectin and thrombospondin 1 (TSP1). In contrast, activation of these genes by high glucose was attenuated in CTGF+/− MEF. We conclude that induction of Ctgf mediates expression of extracellular matrix proteins in diabetic kidney. Thus, genetic variability in CTGF expression directly modulates the severity of diabetic nephropathy.

Partial restoration of macrophage alteration from diet-induced obesity in response to Porphyromonas gingivalis infection

Obesity is a chronic inflammatory disease that weakens macrophage innate immune response to infections. Since M1 polarization is crucial during acute infectious diseases, we hypothesized that diet-induced obesity inhibits M1 polarization of macrophages in the response to bacterial infections. Bone marrow macrophages (BMMΦ) from lean and obese mice were exposed to live Porphyromonas gingivalis (P. gingivalis) for three incubation times (1 h, 4 h and 24 h). Flow cytometry analysis revealed that the M1 polarization was inhibited after P. gingivalis exposure in BMMΦ from obese mice when compared with BMMΦ from lean counterparts. Using a computational approach in conjunction with microarray data, we identified switching genes that may differentially control the behavior of response pathways in macrophages from lean and obese mice. The two most prominent switching genes were thrombospondin 1 and arginase 1. Protein expression levels of both genes were higher in obese BMMΦ than in lean BMMΦ after exposure to P. gingivalis. Inhibition of either thrombospondin 1 or arginase 1 by specific inhibitors recovered the M1 polarization of BMMΦ from obese mice after P. gingivalis exposure. These data indicate that thrombospondin 1 and arginase 1 are important bacterial response genes, whose regulation is altered in macrophages from obese mice.

Molecular mechanisms in the pathogenesis of diabetic nephropathy: an update

Diabetes mellitus is known to trigger retinopathy, neuropathy and nephropathy. Diabetic nephropathy, a long-term major microvascular complication of uncontrolled hyperglycemia, affects a large population worldwide. Recent findings suggest that numerous pathways are activated during the course of diabetes mellitus and that these pathways individually or collectively play a role in the induction and progression of diabetic nephropathy. However, clinical strategies targeting these pathways to manage diabetic nephropathy remain unsatisfactory, as the number of diabetic patients with nephropathy is increasing yearly. To develop ground-breaking therapeutic options to prevent the development and progression of diabetic nephropathy, a comprehensive understanding of the molecular mechanisms involved in the pathogenesis of the disease is mandatory. Therefore, the purpose of this paper is to discuss the underlying mechanisms and downstream pathways involved in the pathogenesis of diabetic nephropathy.

Higher plasma thrombospondin-1 levels in patients with coronary artery disease and diabetes mellitus

Background and Objectives

Thrombospondin-1 (TSP-1) is associated with atherosclerosis in animals with diabetes mellitus (DM). But, no study has investigated the role of TSP-1 in human atherosclerosis. This study investigated the relationship among plasma TSP-1 concentration, DM, and coronary artery disease (CAD).

Subjects and Methods

The study involved 374 consecutive subjects with suspected CAD, who had undergone coronary angiography to evaluate effort angina. Patients were divided into four groups as follows: DM(-) and CAD(-), DM(-) and CAD(+), DM(+) and CAD(-), and DM (+) and CAD(+).

Results

We found that plasma TSP-1 levels were higher in patients with DM(+) and CAD(+) (n=103) than those in other patients (n=271) (p<0.01). A multivariate analysis showed that male gender {odds ratio (OR), 2.728; 95% confidence interval (CI), 1.035-7.187}, high density lipoprotein-cholesterol (OR, 0.925; 95% CI, 0.874-0.980), glycated hemoglobin (OR, 1.373; 95% CI, 1.037-1.817), and plasma TSP-1 (OR, 1.004; 95% CI, 1.000-1.008) levels were independently associated with the presence of CAD in patients with DM.

Conclusion

Plasma TSP-1 levels were higher in patients with DM(+) and CAD(+) than those in other patients, and plasma TSP-1 levels were independently associated with the presence of CAD in patients with DM. These findings show a possible link between human plasma TSP-1 concentration and CAD in patients with DM.

Thrombospondin1 in tissue repair and fibrosis: TGF-β-dependent and independent mechanisms

Thrombospondin 1 (TSP1) plays major roles in both physiologic and pathologic tissue repair. TSP1 through its type 1 repeats is a known regulator of latent TGF-β activation and plays a role in wound healing and fibrosis. Binding of the TSP N-terminal domain to cell surface calreticulin in complex with LDL-receptor related protein 1 stimulates intermediate cell adhesion, cell migration, anoikis resistance, collagen expression and matrix deposition in an in vivo model of the foreign body response. There is also emerging evidence that TSP EGF-like repeats alter endothelial cell-cell interactions and stimulate epithelial migration through transactivation of EGF receptors. The mechanisms underlying these functions of TSP1 and the implications for physiologic and pathologic wound repair and fibrosis will be discussed.

BIM deficiency differentially impacts the function of kidney endothelial and epithelial cells through modulation of their local microenvironment

The extracellular matrix (ECM) acts as a scaffold for kidney cellular organization. Local secretion of the ECM allows kidney cells to readily adapt to changes occurring within the kidney. In addition to providing structural support for cells, the ECM also modulates cell survival, migration, proliferation, and differentiation. Although aberrant regulation of ECM proteins can play a causative role in many diseases, it is not known whether ECM production, cell adhesion, and migration are regulated in a similar manner in kidney epithelial and endothelial cells. Here, we demonstrate that lack of BIM expression differentially impacts kidney endothelial and epithelial cell ECM production, migration, and adhesion, further emphasizing the specialized role of these cell types in kidney function. Bim -/- kidney epithelial cells demonstrated decreased migration, increased adhesion, and sustained expression of osteopontin and thrombospondin-1 (TSP1). In contrast, bim -/- kidney endothelial cells demonstrated increased cell migration, and decreased expression of osteopontin and TSP1. We also observed a fivefold increase in VEGF expression in bim -/- kidney endothelial cells consistent with their increased migration and capillary morphogenesis. These cells also had decreased endothelial nitric oxide synthase activity and nitric oxide bioavailability. Thus kidney endothelial and epithelial cells make unique contributions to the regulation of their ECM composition, with specific impact on adhesive and migratory properties that are essential for their proper function.

Blockade of TSP1-dependent TGF-β activity reduces renal injury and proteinuria in a murine model of diabetic nephropathy

Transforming growth factor-β (TGF-β) is key in the pathogenesis of diabetic nephropathy. Thrombospondin 1 (TSP1) expression is increased in diabetes, and TSP1 regulates latent TGF-β activation in vitro and in diabetic animal models. Herein, we investigate the effect of blockade of TSP1-dependent TGF-β activation on progression of renal disease in a mouse model of type 1 diabetes (C57BL/6J-Ins2(Akita)) as a targeted treatment for diabetic nephropathy. Akita and control C57BL/6 mice who underwent uninephrectomy received 15 weeks of thrice-weekly i.p. treatment with 3 or 30 mg/kg LSKL peptide, control SLLK peptide, or saline. The effects of systemic LSKL peptide on dermal wound healing was assessed in type 2 diabetic mice (db/db). Proteinuria (urinary albumin level and albumin/creatinine ratio) was significantly improved in Akita mice treated with 30 mg/kg LSKL peptide. LSKL treatment reduced urinary TGF-β activity and renal phospho-Smad2/3 levels and improved markers of tubulointerstitial injury (fibronectin) and podocytes (nephrin). However, LSKL did not alter glomerulosclerosis or glomerular structure. LSKL did not increase tumor incidence or inflammation or impair diabetic wound healing. These data suggest that selective targeting of excessive TGF-β activity through blockade of TSP1-dependent TGF-β activation represents a therapeutic strategy for treating diabetic nephropathy that preserves the homeostatic functions of TGF-β.

The role of thrombospondin-1-mediated TGF-β1 on collagen type III synthesis induced by high glucose

Transforming growth factor-β1 (TGF-β1) has been thought to play a major role during cardiac fibrosis in the development of diabetic cardiomyopathy, and cardiac fibrosis mainly as a result of an increase of collagen type III occurs in the human hearts with diabetes. Thrombospondin-1 (TSP-1) has been reported to activate the latent complex of TGF-β1. We examined the effects of TSP-1 on the expression of TGF-β1 and collagen type III by rat cardiac fibroblasts in high ambient glucose. We demonstrated that high glucose induces the mRNA and protein expression of collagen type III, TGF-β1, and TSP-1. Furthermore, the mRNA and protein expression of collagen type III induced by high glucose was downregulated after treatment with TGF-β1 antibody, or TSP-1 siRNA. The expression of TGF-β1 increased by high glucose was also reversed after treatment with TSP-1 siRNA. Our findings suggest that the TSP-1 participates in the upregulation of TGF-β1, collagen type III by high glucose and may provide new therapeutic strategies for diabetic cardiomyopathy.

Glucose downregulation of PKG-I protein mediates increased thrombospondin1-dependent TGF-{beta} activity in vascular smooth muscle cells

Diabetes is a major predictor of in-stent restenosis, which is associated with fibroproliferative remodeling of the vascular wall due to increased transforming growth factor-beta (TGF-beta) action. It is well established that thrombospondin1 (TSP1) is a major regulator of TGF-beta activation in renal and cardiac complications of diabetes. However, the role of the TSP1-TGF-beta pathway in macrovascular diabetic complications, including restenosis, has not been addressed. In mesangial cells, high glucose concentrations depress protein kinase G (PKG) activity, but not PKG-I protein, thereby downregulating transcriptional repression of TSP1. Previously, we showed that high glucose downregulates PKG-I protein expression by vascular smooth muscle cells (VSMCs) through altered NADPH oxidase signaling. In the present study, we investigated whether high glucose regulation of PKG protein and activity in VSMCs similarly regulates TSP1 expression and downstream TGF-beta activity. These studies showed that high glucose stimulates both TSP1 expression and TGF-beta bioactivity in primary murine aortic smooth muscle cells (VSMCs). TSP1 is responsible for the increased TGF-beta bioactivity under high glucose conditions, because treatment with anti-TSP1 antibody, small interfering RNA-TSP1, or an inhibitory peptide blocked glucose-mediated increases in TGF-beta activity and extracellular matrix protein (fibronectin) expression. Overexpression of constitutively active PKG, but not the PKG-I protein, inhibited glucose-induced TSP1 expression and TGF-beta bioactivity, suggesting that PKG protein expression is insufficient to regulate TSP1 expression. Together, these data establish that glucose-mediated downregulation of PKG levels stimulates TSP1 expression and enhances TGF-beta activity and matrix protein expression, which can contribute to vascular remodeling in diabetes.

Adenosine mediates transforming growth factor-beta 1 release in kidney glomeruli of diabetic rats

Up regulation of the transforming growth factor-beta 1 (TGF-beta1) axis has been recognized as a pathogenic event for progression of glomerulosclerosis in diabetic nephropathy. We demonstrate that glomeruli isolated from diabetic rats accumulate up to sixfold more extracellular adenosine than normal rats. Both decreased nucleoside uptake activity by the equilibrative nucleoside transporter 1 and increased AMP hydrolysis contribute to raise extracellular adenosine. Ex vivo assays indicate that activation of the low affinity adenosine A2B receptor subtype (A2BAR) mediates TGF-beta1 release from glomeruli of diabetic rats, a pathogenic event that could support progression of glomerulopathy when the bioavailability of adenosine is increased.

High glucose activates PKC-zeta and NADPH oxidase through autocrine TGF-beta1 signaling in mesangial cells

Conversion of normally quiescent mesangial cells into extracellular matrix-overproducing myofibroblasts in response to high ambient glucose and transforming growth factor (TGF)-beta(1) is central to the pathogenesis of diabetic nephropathy. Previously, we reported that mesangial cells respond to high glucose by generating reactive oxygen species (ROS) from NADPH oxidase dependent on protein kinase C (PKC) -zeta activation. We investigated the role of TGF-beta(1) in this action of high glucose on primary rat mesangial cells within 1-48 h. Both high glucose and exogenous TGF-beta(1) stimulated PKC-zeta kinase activity, as measured by an immune complex kinase assay and immunofluorescence confocal cellular imaging. In high glucose, Akt Ser473 phosphorylation appeared within 1 h and Smad2/3 nuclear translocation was prevented with neutralizing TGF-beta(1) antibodies. Neutralizing TGF-beta(1) antibodies, or a TGF-beta receptor kinase inhibitor (LY364947), or a phosphatidylinositol 3,4,5-trisphosphate (PI3) kinase inhibitor (wortmannin), prevented PKC-zeta activation by high glucose. TGF-beta(1) also stimulated cellular membrane translocation of PKC-alpha, -beta(1), -delta, and -epsilon, similar to high glucose. High glucose and TGF-beta(1) enhanced ROS generation by mesangial cell NADPH oxidase, as detected by 2,7-dichlorofluorescein immunofluorescence. This response was abrogated by neutralizing TGF-beta(1) antibodies, LY364947, or a specific PKC-zeta pseudosubstrate peptide inhibitor. Expression of constitutively active PKC-zeta in normal glucose caused upregulation of p22(phox), a likely mechanism of NADPH oxidase activation. We conclude that very early responses of mesangial cells to high glucose include autocrine TGF-beta(1) stimulation of PKC isozymes including PI3 kinase activation of PKC-zeta and consequent generation of ROS by NADPH oxidase.

Correlation of enhanced thrombospondin-1 expression, TGF-beta signalling and proteinuria in human type-2 diabetic nephropathy

Background. Activation of the thrombospondin-1 (TSP-1)-TGF-β pathway by glucose and the relevance of TSP-1-dependent activation of TGF-β for renal matrix expansion, renal fibrosis and sclerosis have previously been demonstrated by our group in in vivo and in vitro studies.

Design and methods. We investigated renal biopsies (n = 40) and clinical data (n = 30) of patients with diabetic nephropathy. Ten kidneys without evidence of renal disease served as controls. Glomerular and cortical expression of TSP-1, p-smad2/3, fibrosis and glomerular sclerosis (PAS) were assessed by immunhistochemical staining and related with clinical data.

Results. Glomerular (g) and cortical (c) TSP-1 were increased during diabetic nephropathy (g: 2.62 ± 2.65; c: 4.5 ± 4.2) compared to controls (g: 0.67 ± 0.7; c: 1.5 ± 1.2). P-smad2/3 was significantly increased (g: 16.7 ± 12.9; c: 148.7 ± 92.8) compared to controls (g: 7.1 ± 3.6; c: 55 ± 25; P < 0.05). TSP-1 was coexpressed with p-smad2/3 as an indicator of TGF-β activation. TSP-1 correlated with enhanced tubulointerstitial p-smad2/3 positivity (r = 0.39 and r = 0.4, P < 0.05) and glomerular p-smad2/3 correlated with proteinuria (r = 0.35, P < 0.05).

Conclusions. In summary, the present study suggests a functional activity of the TSP-1/TGF-β axis, especially in the tubulointerstitium of patients with diabetic nephropathy. The positive correlation of glomerular p-smad2/3 positivity with proteinuria further supports the importance of the TSP-1/TGF-β system as a relevant mechanism for progression of human type-2 diabetic nephropathy.

PDE-5 inhibition impedes TSP-1 expression, TGF-beta activation and matrix accumulation in experimental glomerulonephritis

BACKGROUND

Matrix expansion and mesangial proliferation are hallmarks of mesangial proliferative glomerulonephritis. Specific inhibition of PDE-5, an enzyme catalyzing the intracellular degradation of cyclic GMP, can be achieved by the inhibitor vardenafil. In this study, we investigated the effects of PDE-5 inhibition in the anti-Thy1 model in the rat in vivo.

METHODS

After disease induction, rats received 10 mg/kg bw vardenafil twice a day via gavage. On Days 2 and 6, renal biopsies, as well as glomerular isolates, urine and blood samples were taken to compare vardenafil- and placebo-treated groups during the course of disease.

RESULTS

Small amounts of PDE-5 were detected in healthy kidneys, but induced in a typical mesangial pattern during disease (by IHC and WB). Specific PDE-5 inhibition resulted in increased glomerular levels of cGMP. Treated animals demonstrated inhibition of MC proliferation and matrix accumulation while renal function and influx of inflammatory cells were not affected. Due to PDE-5 inhibition, the endogenous TGF-beta-activating protein TSP-1 and the TGF-beta-signalling protein p-smad-2/3 were decreased suggesting this as an antifibrotic mechanism of action of vardenafil in this model.

CONCLUSION

Considering the availability and safety profile of vardenafil, the beneficial antiproliferative and antifibrotic effect in experimental glomerulonephritis may potentially be applicable to the treatment of mesangial proliferative glomerulonephritis in man.

High glucose levels upregulate upstream stimulatory factor 2 gene transcription in mesangial cells

Previously, we demonstrated that upstream stimulatory factor 2 (USF2) mediates high glucose-induced thrombospondin1 (TSP1) gene expression and TGF-beta activity in glomerular mesangial cells and plays a role in diabetic renal complications. In the present studies, we further determined the molecular mechanisms by which high glucose levels regulate USF2 gene expression. In primary rat mesangial cells, we found that glucose treatment time and dose-dependently up-regulated USF2 expression (mRNA and protein). By using cycloheximide to block the de novo protein synthesis, similar rate of USF2 degradation was found under either normal glucose or high glucose conditions. USF2 mRNA stability was not altered by high glucose treatment. Furthermore, high glucose treatment stimulated USF2 gene promoter activity. By using the luciferase-promoter deletion assay, site-directed mutagenesis, and transactivation assay, we identified a glucose-responsive element in the USF2 gene promoter (-1,740 to -1,620, relative to the transcription start site) and demonstrated that glucose-induced USF2 expression is mediated through a cAMP-response element-binding protein (CREB)-dependent transactivation of the USF2 promoter. Furthermore, siRNA-mediated CREB knock down abolished glucose-induced USF2 expression. Taken together, these data indicate that high glucose levels up-regulate USF2 gene transcription in mesangial cells through CREB-dependent transactivation of the USF2 promoter.

Thrombospondin-1 is an adipokine associated with obesity, adipose inflammation, and insulin resistance

OBJECTIVE

We examined the relationship between the expression of thrombospondin (TSP)1, an antiangiogenic factor and regulator of transforming growth factor-beta activity, obesity, adipose inflammation, and insulin resistance.

RESEARCH DESIGN AND METHODS

TSP1 gene expression was quantified in subcutaneous adipose tissue (SAT) of 86 nondiabetic subjects covering a wide range of BMI and insulin sensitivity, from visceral adipose (VAT) and SAT from 14 surgical patients and from 38 subjects with impaired glucose tolerance randomized to receive either pioglitazone or metformin for 10 weeks. An adipocyte culture system was also used to assess the effects of pioglitazone and coculture with macrophages on TSP1 gene expression.

RESULTS

TSP1 mRNA was significantly associated with obesity (BMI) and insulin resistance (low insulin sensitivity index). Relatively strong positive associations were seen with markers of inflammation, including CD68, macrophage chemoattractant protein-1, and plasminogen activator inhibitor (PAI)-1 mRNA (r >/= 0.46, P = 0.001 for each), that remained significant after controlling for BMI and S(i). However, TSP1 mRNA was preferentially expressed in adipocyte fraction, whereas inflammatory markers predominated in stromal vascular fraction. Coculture of adipocytes and macrophages augmented TSP1 gene expression and secretion from both cell types. Pioglitazone (not metformin) treatment resulted in a 54% decrease (P < 0.04) in adipose TSP gene expression, as did in vitro pioglitazone treatment of adipocytes.

CONCLUSIONS

TSP1 is a true adipokine that is highly expressed in obese, insulin-resistant subjects; is highly correlated with adipose inflammation; and is decreased by pioglitazone. TSP1 is an important link between adipocytes and macrophage-driven adipose tissue inflammation and may mediate the elevation of PAI-1 that promotes a prothrombotic state.