Thrombospondin-2 therapy ameliorates experimental glomerulonephritis via inhibition of cell proliferation, inflammation, and TGF-beta activation

Transforming growth factor-β receptors: versatile mechanisms of ligand activation

Transforming growth factor-β (TGF-β) signaling is initiated by activation of transmembrane TGF-β receptors (TGFBR), which deploys Smad2/3 transcription factors to control cellular responses. Failure or dysregulation in the TGF-β signaling pathways leads to pathological conditions. TGF-β signaling is regulated at different levels along the pathways and begins with the liberation of TGF-β ligand from its latent form. The mechanisms of TGFBR activation display selectivity to cell types, agonists, and TGF-β isoforms, enabling precise control of TGF-β signals. In addition, the cell surface compartments used to release active TGF-β are surprisingly vibrant, using thrombospondins, integrins, matrix metalloproteinases and reactive oxygen species. The scope of TGFBR activation is further unfolded with the discovery of TGFBR activation initiated by other signaling pathways. The unique combination of mechanisms works in series to trigger TGFBR activation, which can be explored as therapeutic targets. This comprehensive review provides valuable insights into the diverse mechanisms underpinning TGFBR activation, shedding light on potential avenues for therapeutic exploration.

Thbs1 regulates skeletal muscle mass in a TGFβ-Smad2/3-ATF4-dependent manner

Loss of muscle mass is a feature of chronic illness and aging. Here, we report that skeletal muscle-specific thrombospondin-1 transgenic mice (Thbs1 Tg) have profound muscle atrophy with age-dependent decreases in exercise capacity and premature lethality. Mechanistically, Thbs1 activates transforming growth factor β (TGFβ)-Smad2/3 signaling, which also induces activating transcription factor 4 (ATF4) expression that together modulates the autophagy-lysosomal pathway (ALP) and ubiquitin-proteasome system (UPS) to facilitate muscle atrophy. Indeed, myofiber-specific inhibition of TGFβ-receptor signaling represses the induction of ATF4, normalizes ALP and UPS, and partially restores muscle mass in Thbs1 Tg mice. Similarly, myofiber-specific deletion of Smad2 and Smad3 or the Atf4 gene antagonizes Thbs1-induced muscle atrophy. More importantly, Thbs1-/- mice show significantly reduced levels of denervation- and caloric restriction-mediated muscle atrophy, along with blunted TGFβ-Smad3-ATF4 signaling. Thus, Thbs1-mediated TGFβ-Smad3-ATF4 signaling in skeletal muscle regulates tissue rarefaction, suggesting a target for atrophy-based muscle diseases and sarcopenia with aging.

Serum thrombospondin-2 level changes with liver stiffness improvement in patients with type 2 diabetes

OBJECTIVE

Baseline circulating thrombospondin-2 (TSP2) level was identified as a potential novel hepatic fibrosis biomarker that associates with development and progression of hepatic fibrosis in patients with nonalcoholic fatty liver disease and type 2 diabetes. Here, we investigated whether circulating TSP2 levels changed with improvement in liver stiffness (LS), which reflects liver fibrosis on transient elastography.

DESIGN

Serum TSP2 levels were measured in participants from a randomized, open-label intervention study, at baseline and after 24-weeks treatment of either dapagliflozin 10 mg (N = 30) or sitagliptin 100 mg daily (N = 30). Vibration-controlled transient elastography was performed to evaluate the severity of hepatic fibrosis and steatosis using LS and controlled attenuation parameter (CAP), respectively.

PATIENTS AND MEASUREMENTS

Among all 60 participants with similar clinical characteristics at baseline (mean HbA1c 8.9%, CAP 289 dB/m and LS 5.8 kPa), despite similar HbA1c lowering, treatment with dapagliflozin, but not sitagliptin, led to significant improvements in body weight (BW) (p = .012), CAP (p = .015) and LS (p = .011) after 24 weeks.

RESULTS

Serum TSP2 level decreased significantly from baseline in dapagliflozin-treated participants (p = .035), whereas no significant change was observed with sitagliptin. In correlation analysis, change in serum TSP2 levels only positively correlated with change in LS (r = .487, p = .006), but not with changes in BW, CAP or HbA1c after dapagliflozin treatment.

CONCLUSIONS

Serum TSP2 level decreased with LS after dapagliflozin treatment, and was independent of improvements in BW, glycemic control and hepatic steatosis, further supporting the potential of serum TSP2 level as a novel hepatic fibrosis biomarker in type 2 diabetes.

Dupuytren's Disease Is Mediated by Insufficient TGF-β1 Release and Degradation

Dupuytren's disease (DD) is a fibroproliferative disorder affecting the palmar fascia, causing functional restrictions of the hand and thereby limiting patients' daily lives. The disturbed and excessive myofibroblastogenesis, causing DD, is mainly induced by transforming growth factor (TGF)-β1. But, the extent to which impaired TGF-β1 release or TGF-β signal degradation is involved in pathologically altered myofibroblastogenesis in DD has been barely examined. Therefore, the complex in which TGF-β1 is secreted in the extracellular matrix to elicit its biological activity, and proteins such as plasmin, integrins, and matrix metalloproteinases (MMPs), which are involved in the TGF-β1 activation, were herein analyzed in DD-fibroblasts (DD-FBs). Additionally, TGF-β signal degradation via caveolin-1 was examined with 5-fluoruracil (5-FU) in detail. Gene expression analysis was performed via Western blot, PCR, and immunofluorescence analyses. As a surrogate parameter for disturbed myofibroblastogenesis, 𝛼-smooth-muscle-actin (𝛼-SMA) expression was evaluated. It was demonstrated that latency-associated peptide (LAP)-TGF-β and latent TGF-β-binding protein (LTBP)-1 involved in TGF-β-complex building were significantly upregulated in DD. Plasmin a serinprotease responsible for the TGF-β release was significantly downregulated. The application of exogenous plasmin was able to inhibit disturbed myofibroblastogenesis, as measured via 𝛼-SMA expression. Furthermore, a reduced TGF-β1 degradation was also involved in the pathological phenotype of DD, because caveolin-1 expression was significantly downregulated, and if rescued, myofibroblastogenesis was also inhibited. Therefore, our study demonstrates that a deficient release and degradation of TGF-β1 are important players in the pathological phenotype of DD and should be addressed in future research studies to improve DD therapy or other related fibrotic conditions.

Extracellular status of thrombospondin-2 in type 2 diabetes mellitus and utility as a biomarker in the determination of early diabetic kidney disease

OBJECTIVE

Thrombospondin-2 (TSP-2) is a multifunctional matricellular glycoprotein correlated with glucose homeostasis, insulin sensitivity, and estimated glomerular filtration rate. Investigation of the association of TSP-2 with type 2 diabetes mellitus (T2DM) and the potential diagnostic value of serum TSP-2 for detecting early diabetic kidney disease (DKD) is needed.

RESEARCH DESIGN AND METHODS

An enzyme-linked immunosorbent assay was used for detection serum TSP-2 levels in 494 Chinese T2DM subjects. The protein expression of TSP-2 in the kidney and other tissues were tested by western blotting.

RESULTS

Serum TSP-2 levels in T2DM subjects were significantly higher than in healthy individuals. Serum TSP-2 correlated positively with triglycerides, serum uric acid, creatinine, platelets, and urinary albumin-to-creatinine ratio (UACR), but negatively with estimated glomerular filtration rate, after adjusting for age, sex, and T2DM duration. Logistic regression analysis demonstrated an independent association between serum TSP-2 and early DKD. Furthermore, the high UACR identified at risk of early DKD increased significantly from 0.78 (95%CI 0.73-0.83) to 0.82 (95%CI 0.77-0.86, p < 0.001) when added to a clinical model consisting of TSP-2 and age. In db/db mice, serum TSP-2 levels were elevated. TSP-2 expression was markedly increased in the kidney tissue compared with that in db/m and m/m mice. Furthermore, serum TSP-2 expression correlated well with UACR in mice.

CONCLUSIONS

TSP-2 is a novel glycoprotein associated with early DKD in patients with T2DM. The paradoxical increase of serum TSP-2 in T2DM individuals may be due to a compensatory response to chronic inflammatory and renal vascular endothelial growth, warranting further investigation.

Transforming growth factor β latency: A mechanism of cytokine storage and signalling regulation in liver homeostasis and disease

Transforming growth factor-β (TGF-β) is a potent effector in the liver, which is involved in a plethora of processes initiated upon liver injury. TGF-β affects parenchymal, non-parenchymal, and inflammatory cells in a highly context-dependent manner. Its bioavailability is critical for a fast response to various insults. In the liver – and probably in other organs – this is made possible by the deposition of a large portion of TGF-β in the extracellular matrix as an inactivated precursor form termed latent TGF-β (L-TGF-β). Several matrisomal proteins participate in matrix deposition, latent complex stabilisation, and activation of L-TGF-β. Extracellular matrix protein 1 (ECM1) was recently identified as a critical factor in maintaining the latency of deposited L-TGF-β in the healthy liver. Indeed, its depletion causes spontaneous TGF-β signalling activation with deleterious effects on liver architecture and function. This review article presents the current knowledge on intracellular L-TGF-β complex formation, secretion, matrix deposition, and activation and describes the proteins and processes involved. Further, we emphasise the therapeutic potential of toning down L-TGF-β activation in liver fibrosis and liver cancer.

Thrombospondin 2 Promotes IL-6 Production in Osteoarthritis Synovial Fibroblasts via the PI3K/AKT/NF-κB Pathway

Background

It is known that osteoarthritis (OA) pathogenesis involves inflammation that drives pathologic changes and that the matricellular protein, thrombospondin-2 (TSP2), is involved in angiogenesis, carcinogenesis, and inflammation. However, how TSP2 contributes to OA inflammatory processes is unclear.

Objective

The aim of current study was to elucidate whether TSP2 could promote interleukin-6 (IL-6), a pro-inflammatory cytokine, expression in osteoarthritis synovial fibroblasts (OASFs).

Methods

The synovial fibroblasts isolated from osteoarthritis and healthy donors were incubated with recombinant TSP2 to evaluate its effect in OA pathogenesis. The SFs were incubated with recombinant TSP2, followed by determining the IL-6 expression by qPCR and Western blot. After SFs were incubated with TSP2 for different time interval, the Western blot was performed to investigate the activation of signal pathway. The different strategies including neutralizing antibodies, siRNAs, and chemical inhibitors were used to discover the signal transduction in response to TSP2 incubation in OASFs. To evaluate the therapeutic potential of TSP2 in osteoarthritis, the anterior cruciate ligament transection (ACLT) in SD rats was performed in the presence or absence of TSP neutralizing antibody treatment.

Results

Our investigations have revealed that TSP2 promoted IL-6 expression in OASFs in a dose-dependent manner, especially in 30 and 100 ng/mL concentration (p < 0.05). Using different strategies including neutralizing antibodies, siRNAs, and chemical inhibitors, all of which attenuated signal pathway components in OASFs, we found evidence for the involvement of integrin α_vβ₃, PI3K, Akt, and NF-κB in TSP2-mediated upregulation of IL-6 (p < 0.05). Finally, in the result of rat ACLT surgical model, we found that TSP2 neutralizing antibody had protective effects in cartilage destruction during OA progression.

Conclusion

Thrombospondin-2 palys an important role in osteoarthritis pathogenesis and provides an opportunity to deal with osteoarthritis.

Activated mesangial cells induce glomerular endothelial cells proliferation in rat anti-Thy-1 nephritis through VEGFA/VEGFR2 and Angpt2/Tie2 pathway

OBJECTIVES

We aimed to investigate the underlying mechanism of endothelial cells (ECs) proliferation in anti-Thy-1 nephritis.

MATERIALS AND METHODS

We established anti-Thy-1 nephritis and co-culture system to explore the underlying mechanism of ECs proliferation in vivo and in vitro. EdU assay kit was used for measuring cell proliferation. Immunohistochemical staining and immunofluorescence staining were used to detect protein expression. ELISA was used to measure the concentration of protein in serum and medium. RT-qPCR and Western blot were used to qualify the mRNA and protein expression. siRNA was used to knock down specific protein expression.

RESULTS

In anti-Thy-1 nephritis, ECs proliferation was associated with mesangial cells (MCs)-derived vascular endothelial growth factor A (VEGFA) and ECs-derived angiopoietin2 (Angpt2). In vitro co-culture system activated MCs-expressed VEGFA to promote vascular endothelial growth factor receptor2 (VEGFR2) activation, Angpt2 expression and ECs proliferation, but inhibit TEK tyrosine kinase (Tie2) phosphorylation. MCs-derived VEGFA stimulated Angpt2 expression in ECs, which inhibited Tie2 phosphorylation and promoted ECs proliferation. And decline of Tie2 phosphorylation induced ECs proliferation. In anti-Thy-1 nephritis, promoting Tie2 phosphorylation could alleviate ECs proliferation.

CONCLUSIONS

Our study showed that activated MCs promoted ECs proliferation through VEGFA/VEGFR2 and Angpt2/Tie2 pathway in experimental mesangial proliferative glomerulonephritis (MPGN) and in vitro co-culture system. And enhancing Tie2 phosphorylation could alleviate ECs proliferation, which will provide a new idea for MPGN treatment.

TGF beta -1, -2 and -3 in the modulation of fibrosis in the cornea and other organs

The TGF beta-1, -2 and -3 isoforms are transcribed from different genes but bind to the same receptors and signal through the same canonical and non-canonical signal transduction pathways. There are numerous regulatory mechanisms controlling the action of each isoform that include the organ-specific cells producing latent TGF beta growth factors, multiple effectors that activate the isoforms, ECM-associated SLRPs and basement membrane components that modulate the activity and localization of the isoforms, other interactive cytokine-growth factor receptor systems, such as PDGF and CTGF, TGF beta receptor expression on target cells, including myofibroblast precursors, receptor binding competition, positive and negative signal transduction effectors, and transcription and translational regulatory mechanisms. While there has long been the view that TGF beta-1and TGF beta-2 are pro-fibrotic, while TGF beta-3 is anti-fibrotic, this review suggests that view is too simplistic, at least in adult tissues, since TGF beta-3 shares far more similarities in its modulation of fibrotic gene expression with TGF beta-1 and TGF beta-2, than it does differences, and often the differences are subtle. Rather, TGF beta-3 should be seen as a fibro-modulatory partner to the other two isoforms that modulates a nuanced and better controlled response to injury. The complex interplay between the three isoforms and numerous interactive proteins, in the context of the cellular milieu, controls regenerative non-fibrotic vs. fibrotic healing in a response to injury in a particular organ, as well as the resolution of fibrosis, when that occurs.

Contribution of Thrombospondin-1 and -2 to Lipopolysaccharide-Induced Acute Respiratory Distress Syndrome

Thrombospondin (TSP) proteins have been shown to impact T-cell adhesion, migration, differentiation, and apoptosis. Thrombospondin-1 (TSP-1) is specifically upregulated in several inflammatory diseases and can effectively promote lipopolysaccharide- (LPS-) induced inflammation. In contrast, thrombospondin-2 (TSP-2) has been associated with activation of "anti-inflammatory" T-regulatory cells (Tregs). In this study, we investigated the effects of both TSP-1 and TSP-2 overexpression on macrophage polarization and activation in vitro and in vivo. We analyzed the effects of TSP-1 and TSP-2 on inflammation, vascular endothelial permeability, edema, ultrastructural morphology, and apoptosis in lung tissues of an ARDS mouse model and cultured macrophages. Our results demonstrated that TSP-2 overexpression effectively attenuated LPS-induced ARDS in vivo and promoted M2 macrophage phenotype polarization in vitro. Furthermore, TSP-2 played a role in regulating pulmonary vascular barrier leakage by activating the PI3K/Akt pathway. Overall, our findings indicate that TSP-2 can modulate inflammation and could therefore be a potential therapeutic target against LPS-induced ARDS.

ADMA elevation does not exacerbate development of diabetic nephropathy in mice with streptozotocin-induced diabetes mellitus

BACKGROUND AND AIMS

Cardiovascular disease is nowadays the major cause of mortality and morbidity worldwide. The risk of developing cardiovascular disease is significantly increased in patients with diabetic nephropathy. It has been suggested that asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthases (NOS), may play an important role in the pathogenesis of diabetic nephropathy. ADMA is mainly metabolized by dimethylarginine dimethylaminohydrolase 1 (DDAH1). The goal of this study was to test the hypothesis that elevation of systemic ADMA levels by knocking out DDAH1 would exacerbate functional and structural glomerular abnormalities in a murine model of diabetic nephropathy.

METHODS

Streptozotocin (STZ) was used to induce diabetes in adult DDAH1 knock-out and wild type mice. Healthy mice served as controls. Mice were sacrificed after 20 weeks of diabetes. Plasma ADMA levels were assessed by isotope-dilution tandem mass spectrometry and albumin by ELISA. Kidneys were used for FACS analysis and were also stained for markers of inflammation, cell proliferation, glomerular cells and cell matrix.

RESULTS

STZ led to development of diabetes mellitus in all injected animals. Deficiency of DDAH1 led to a significant increase in plasma ADMA levels in healthy and diabetic mice. The diabetic state itself did not influence systemic ADMA levels. Diabetic mice of both genotypes developed albuminuria and had increased glomerulosclerosis index. There were no changes in desmin expression, glomerular cell proliferation rate, matrix expansion and expression of Mac-2 antigen in the diabetic mice of both genotypes as compared to the healthy ones.

CONCLUSIONS

In summary, STZ-induced diabetes led to the development of early features of diabetic nephropathy. Deficiency of DDAH1 and subsequent increase in systemic ADMA levels did not exacerbate these changes, indicating that ADMA is not the major mediator of diabetic nephropathy in this experiment model.

Therapeutic Properties of Mesenchymal Stem Cell on Organ Ischemia-Reperfusion Injury

The shortage of donor organs is a major global concern. Organ failure requires the transplantation of functional organs. Donor’s organs are preserved for variable periods of warm and cold ischemia time, which requires placing them into a preservation device. Ischemia and reperfusion damage the organs, due to the lack of oxygen during the ischemia step, as well as the oxidative stress during the reperfusion step. Different methodologies are developed to prevent or to diminish the level of injuries. Preservation solutions were first developed to maximize cold static preservation, which includes the addition of several chemical compounds. The next chapter of organ preservation comes with the perfusion machine, where mechanical devices provide continuous flow and oxygenation ex vivo to the organs being preserved. In the addition of inhibitors of mitogen-activated protein kinase and inhibitors of the proteasome, mesenchymal stem cells began being used 13 years ago to prevent or diminish the organ’s injuries. Mesenchymal stem cells (e.g., bone marrow stem cells, adipose derived stem cells and umbilical cord stem cells) have proven to be powerful tools in repairing damaged organs. This review will focus upon the use of some bone marrow stem cells, adipose-derived stem cells and umbilical cord stem cells on preventing or decreasing the injuries due to ischemia-reperfusion.

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.

MicroRNA-20a regulates cell proliferation, apoptosis and autophagy by targeting thrombospondin 2 in cervical cancer

Cervical cancer (CC) is the fourth most frequent malignancy worldwide. MicroRNAs (miRNAs) can function as potential biomarkers or therapeutic targets in multiple cancers including CC. Our present study aimed to investigate the roles and downstream targets of microRNA-20a (miR-20a) in regulating CC proliferation, apoptosis and autophagy. Here, RT-qPCR assay revealed that miR-20a was highly expressed in CC tissues and cells. Functional analysis showed that the inhibition of miR-20a resulted in reduced proliferation, increased apoptosis and downregulated autophagic activity in CC cells. Bioinformatics analysis, luciferase reporter assay and RNA immunoprecipitation (RIP) assay manifested that thrombospondin 2 (THBS2) was a target of miR-20a. Also, THBS2 expression was notably reduced in CC tissues and cells, and inversely associated with miR-20a expression in CC tissues. Restoration experiments disclosed that THBS2 knockdown abrogated miR-20a inhibitor-mediated anti-proliferation, pro-apoptosis, and anti-autophagy effects in CC cells. In summary, these data showed that the depletion of miR-20a suppressed proliferation and autophagy and induced apoptosis by targeting THBS2 in CC cells, further elucidating the roles and molecular basis of miR-20a in the development of CC.

Towards frailty biomarkers: Candidates from genes and pathways regulated in aging and age-related diseases

OBJECTIVE

Use of the frailty index to measure an accumulation of deficits has been proven a valuable method for identifying elderly people at risk for increased vulnerability, disease, injury, and mortality. However, complementary molecular frailty biomarkers or ideally biomarker panels have not yet been identified. We conducted a systematic search to identify biomarker candidates for a frailty biomarker panel.

METHODS

Gene expression databases were searched (http://genomics.senescence.info/genes including GenAge, AnAge, LongevityMap, CellAge, DrugAge, Digital Aging Atlas) to identify genes regulated in aging, longevity, and age-related diseases with a focus on secreted factors or molecules detectable in body fluids as potential frailty biomarkers. Factors broadly expressed, related to several "hallmark of aging" pathways as well as used or predicted as biomarkers in other disease settings, particularly age-related pathologies, were identified. This set of biomarkers was further expanded according to the expertise and experience of the authors. In the next step, biomarkers were assigned to six "hallmark of aging" pathways, namely (1) inflammation, (2) mitochondria and apoptosis, (3) calcium homeostasis, (4) fibrosis, (5) NMJ (neuromuscular junction) and neurons, (6) cytoskeleton and hormones, or (7) other principles and an extensive literature search was performed for each candidate to explore their potential and priority as frailty biomarkers.

RESULTS

A total of 44 markers were evaluated in the seven categories listed above, and 19 were awarded a high priority score, 22 identified as medium priority and three were low priority. In each category high and medium priority markers were identified.

CONCLUSION

Biomarker panels for frailty would be of high value and better than single markers. Based on our search we would propose a core panel of frailty biomarkers consisting of (1) CXCL10 (C-X-C motif chemokine ligand 10), IL-6 (interleukin 6), CX3CL1 (C-X3-C motif chemokine ligand 1), (2) GDF15 (growth differentiation factor 15), FNDC5 (fibronectin type III domain containing 5), vimentin (VIM), (3) regucalcin (RGN/SMP30), calreticulin, (4) PLAU (plasminogen activator, urokinase), AGT (angiotensinogen), (5) BDNF (brain derived neurotrophic factor), progranulin (PGRN), (6) α-klotho (KL), FGF23 (fibroblast growth factor 23), FGF21, leptin (LEP), (7) miRNA (micro Ribonucleic acid) panel (to be further defined), AHCY (adenosylhomocysteinase) and KRT18 (keratin 18). An expanded panel would also include (1) pentraxin (PTX3), sVCAM/ICAM (soluble vascular cell adhesion molecule 1/Intercellular adhesion molecule 1), defensin α, (2) APP (amyloid beta precursor protein), LDH (lactate dehydrogenase), (3) S100B (S100 calcium binding protein B), (4) TGFβ (transforming growth factor beta), PAI-1 (plasminogen activator inhibitor 1), TGM2 (transglutaminase 2), (5) sRAGE (soluble receptor for advanced glycosylation end products), HMGB1 (high mobility group box 1), C3/C1Q (complement factor 3/1Q), ST2 (Interleukin 1 receptor like 1), agrin (AGRN), (6) IGF-1 (insulin-like growth factor 1), resistin (RETN), adiponectin (ADIPOQ), ghrelin (GHRL), growth hormone (GH), (7) microparticle panel (to be further defined), GpnmB (glycoprotein nonmetastatic melanoma protein B) and lactoferrin (LTF). We believe that these predicted panels need to be experimentally explored in animal models and frail cohorts in order to ascertain their diagnostic, prognostic and therapeutic potential.

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.

Thrombospondin immune regulation and the kidney

Most therapeutic attempts to prevent the progression of kidney diseases have been based on interventions to inhibit the production of transforming growth factor-β (TGF-β). Thrombospondins (TSPs) play an important role in activating TGF-β. In the healthy kidney, two TSPs are expressed, TSP1 and TSP2, which exert contrasting effects. While TSP1 is a major activator of TGF-β in renal cells and exerts pro-inflammatory effects both in vitro and in vivo, TSP2 lacks the ability for TGF-β activation but regulates matrix remodeling and inflammation in experimental kidney disease. The effects of TSPs in the kidney have been mostly investigated by using the murine model of unilateral ureteral obstruction. In this model, TSP1 expression is increased along with the development of interstitial fibrosis and TGF-β. Relief of the obstruction gradually improves renal function and decreases the expression in TSP1 and TGF-β1. Several inhibitors of TSP1 prevented progressive interstitial fibrosis in murine models of ureteral obstruction, suggesting that control of latent TGF-β activation by inhibiting TSP1 might represent a novel potential target for preventing renal interstitial fibrosis. However, further studies are needed to assess whether TSP1-mediated TGF-β activation can be safely used in humans. In fact, TSPs normally act to suppress tumors in vivo. Moreover, TGF-β can exert a pivotal function in the immune system, as it may induce the production of regulatory T cells and suppress B cell responses. Knowledge of the molecular mechanisms involved in TGF-β regulation may help in finding effective treatments of tissue fibrosis, cancer and autoimmune disease.

The role of transcriptional factor D-site-binding protein in circadian CCL2 gene expression in anti-Thy1 nephritis

Mesangial proliferative glomerulonephritis (MsPGN) is an inflammatory disease, but both the nature of disease progression and its regulation remain unclear. In the present study, we monitored the course of anti-Thy1 nephritis from days 1 to 5 and established gene expression profiles at each time point using microarrays to explore the development of inflammation. According to the gene expression profiles, macrophage infiltration (triggered by CCL2 activation) was evident on day 1 and enhanced inflammation over the next few days. We screened for genes with expression levels similar to CCL2 and found that the upregulation of the circadian gene albumin D-site-binding protein (DBP) was involved in CCL2 activation in mesangial cells. More importantly, CCL2 expression showed oscillatory changes similar to DBP, and DBP induced peak CCL2 expression at 16:00 a clock on day 1 in the anti-Thy1 nephritis model. We knocked down DBP through transfection with a small interfering RNA (siRNA) and used RNA sequencing to identify the DBP-regulated TNF-α-CCL2 pathway. We performed chromatin immunoprecipitation sequencing (ChIP-Seq) and the dual luciferase assay to show that DBP bound to the TRIM55 promoter, regulating gene expression and in turn controlling the TNF-α-CCL2 pathway. In conclusion, DBP-regulated circadian CCL2 expression by the TRIM55-TNF pathway in injured mesangial cells at an early stage, which promoted macrophage recruitment and in turn triggered infiltration and inflammation in a model of anti-Thy1 nephritis.

Revisiting the matricellular concept

The concept of a matricellular protein was first proposed by Paul Bornstein in the mid-1990s to account for the non-lethal phenotypes of mice with inactivated genes encoding thrombospondin-1, tenascin-C, or SPARC. It was also recognized that these extracellular matrix proteins were primarily counter or de-adhesive. This review reappraises the matricellular concept after nearly two decades of continuous investigation. The expanded matricellular family as well as the diverse and often unexpected functions, cellular location, and interacting partners/receptors of matricellular proteins are considered. Development of therapeutic strategies that target matricellular proteins are discussed in the context of pathology and regenerative medicine.

The SGLT2 inhibitor empagliflozin ameliorates early features of diabetic nephropathy in BTBR ob/ob type 2 diabetic mice with and without hypertension

Diabetic nephropathy is the leading cause of end-stage renal disease in humans in the Western world. The recent development of Na+-glucose cotransporter 2 (SGLT2) inhibitors offers a new antidiabetic therapy via enhanced glucose excretion. Whether this strategy exerts beneficial effects on the development of type 2 diabetic nephropathy is still largely unclear. We investigated the effects of the specific SGLT2 inhibitor empagliflozin in BTBR.Cg-Lep<ob>/WiscJ (BTBR ob/ob) mice, which spontaneously develop type 2 diabetic nephropathy. In the first experiment, BTBR ob/ob mice received either a diet containing 300 ppm empagliflozin or equicaloric placebo chow for 12 wk. In the second experiment, BTBR ob/ob mice received 1 μg·kg body wt(-1)·day(-1) ANG II to induce arterial hypertension and were separated into the same two diet groups for 6 wk. In both experiments, empagliflozin treatment enhanced glucosuria, thereby lowering blood glucose. Independently of hypertension, empagliflozin reduced albuminuria in diabetic mice. However, empagliflozin treatment affected diabetes-related glomerular hypertrophy, markers of renal inflammation, and mesangial matrix expansion only in BTBR ob/ob mice without hypertension. In summary, empagliflozin demonstrated significant antihyperglycemic effects, differentially ameliorating early features of diabetic nephropathy in BTBR ob/ob mice with and without hypertension.

Long-term gene therapy with thrombospondin 2 inhibits TGF-β activation, inflammation and angiogenesis in chronic allograft nephropathy

We recently identified Thrombospondin-2 (TSP-2) as a regulator of matrix remodelling and inflammation in experimental kidney disease by using TSP-2 null mice and successfully proved TSP-2 overexpression as a therapeutic concept in a short term glomerulonephritis model in the rat. In this current study, we investigated if long-term TSP-2 overexpression is also capable to ameliorate the progression of chronic kidney disease in the setting of the chronic allograft nephropathy F344-Lewis model in the rat. Two weeks after renal transplantation, two rat thigh muscles were transfected once only with either a TSP-2 overexpressing plasmid (n = 8) or a luciferase-expressing plasmid as control (n = 8). Rats were monitored for renal function, histological changes and gene expression in the graft for up to 30 weeks after transplantation. Unexpectedly, only in the TSP-2 treated group 2 rats died before the end of the experiment and renal function tended to be worsened in the TSP-2 group compared to the luciferase-treated controls. In addition, glomerular sclerosis and tubular interstitial injury as well as cortical fibronectin deposition was significantly increased in the TSP-2 treated kidneys despite reduced TGF-β activation and marked anti-inflammatory (macrophages, T-cells and B-cells) effects in this group. Long-term TSP-2 therapy impaired repair of renal endothelium, as demonstrated by significant higher glomerular and peritubular endothelial rarefaction and reduced endothelial cell proliferation in the transplanted kidneys from TSP-2 treated rats compared to controls. This TSP-2 effect was associated with decreased levels of renal VEGF but not VEGF1 receptor. In conclusion, despite its anti-inflammatory and TGF-β activation blocking effects, TSP-2 gene therapy did not ameliorate but rather worsened experimental chronic allograft nephropathy most likely via its anti-angiogenic properties on the renal microvasculature.

RPE cell senescence: a key contributor to age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in industrialized countries. Although much progress has been made recently in the management of later stages of the disease, no agents have yet been developed for the early stages or for prophylactic use. Furthermore, even the treatments for the later stages have limited effectiveness. The process of developing improved treatments for AMD is complicated by the existence of several theories concerning the cause of the disorder, each suggesting a different strategy for finding effective therapeutics. One of the potential contributors to AMD pathology is retinal pigment epithelial (RPE) cell senescence. The present paper hypothesizes that RPE senescence plays a central role in the etiology of AMD. This hypothesis is supported by the ability of RPE cell senescence to account for the signs, risk factors, and successful treatment modalities of the disorder. This hypothesis also points to several new prophylactic and treatment strategies for AMD.